A lithium secondary battery comprising: a positive electrode and a negative electrode which each has a specific composition and specific properties; and a nonaqueous electrolyte which contains a cyclic siloxane compound represented by general formula (1), fluorosilane compound represented by general formula (2), compound represented by general formula (3), compound having an S—F bond in the molecule, nitric acid salt, nitrous acid salt, monofluorophosphoric acid salt, difluorophosphoric acid salt, acetic acid salt, or propionic acid salt in an amount of 10 ppm or more of the whole nonaqueous electrolyte. This lithium secondary battery has a high capacity, long life, and high output. [structure] [In general formula (1), R 1 and R 2 are an organic group having 1-12 carbon atoms and n is an integer of 3-10. In general formula (2), R 3 to R 5 are an organic group having 1-12 carbon atoms; x is an integer of 1-3; and p, q, and r each are an integer of 0-3, provided that 1≤p+q+r≤3. In general formula (3), R 6 to R 8 are an organic group having 1-12 carbon atoms and symbol A is a group constituted of H, C, N, O, F, S, Si, and/or P.]

Description

82 parts

›CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 16/394,100 filed Apr. 25, 2019, which is a continuation of U.S. patent application Ser. No. 15/291,314, filed Oct. 12, 2016, which is a continuation of U.S. patent application Ser. No. 14/660,517, filed Mar. 17, 2015, which is a continuation of U.S. application Ser. No. 13/614,215, filed Sep. 13, 2012, which is a continuation application of U.S. patent application Ser. No. 12/090,655, filed Jun. 5, 2009, which is the U.S. National Stage of International Patent Application No. PCT/JP06/320882, filed Oct. 19, 2006, the disclosures of which are incorporated herein by reference in their entireties. This application claims priority to each of the following Japanese patent application, listed with their filing dates, the disclosures of which are incorporated herein by reference in their entireties.

›TECHNICAL FIELD

The present invention relates to lithium secondary batteries and a nonaqueous electrolyte for use therein. More particularly, the invention relates to: lithium secondary batteries which comprise a nonaqueous electrolyte for lithium secondary batteries which contains a specific ingredient and a positive electrode and a negative electrode each having a specific composition and specific properties and capable of occluding/releasing lithium, and which are excellent especially in low-temperature discharge characteristics and have a high capacity, long life, and high output; and the nonaqueous electrolyte for use in these batteries.

›BACKGROUND ART

With the recent trend toward size reduction in electronic appliances, secondary batteries are increasingly required to have a higher capacity. Attention is hence focused on lithium secondary batteries, which have a higher energy density than nickel-cadmium batteries and nickel-hydrogen batteries.

Lithium secondary batteries are used in various applications because they are high-capacity secondary batteries. In these applications, however, the lithium secondary batteries are mainly used as batteries of relatively small sizes as in, e.g., portable telephones. In the future, the batteries are expected to be used in a wider range of applications as large batteries for motor vehicles, etc. Although output is especially required of large batteries, mere enlargement of conventional small batteries results in insufficient performances. Various improvements in battery materials for an output improvement have been proposed (see, for example, patent documents 1 to 25 and non-patent document 1). However, a sufficient output has not been obtained so far, and a further improvement is desired.

Patent Document 1: JP-A-2005-071749 Patent Document 2: JP-A-2005-123180 Patent Document 3: JP-A-2001-206722 Patent Document 4: JP-A-2003-267732 Patent Document 5: JP-A-2001-015108 Patent Document 6: WO 2003/34518 Patent Document 7: JP-A-11-067270 Patent Document 8: JP-A-61-168512 Patent Document 9: JP-A-6-275263 Patent Document 10: JP-A-2000-340232 Patent Document 11: JP-A-2005-235397 Patent Document 12: JP-A-11-031509 Patent Document 13: JP-A-3-055770 Patent Document 14: JP-A-2004-071458 Patent Document 15: JP-A-2004-087459 Patent Document 16: JP-A-10-270074 Patent Document 17: JP-A-2002-075440 Patent Document 18: JP-A-10-270075 Patent Document 19: JP-A-8-045545 Patent Document 20: JP-A-2001-006729 Patent Document 21: JP-A-10-050342 Patent Document 22: JP-A-9-106835 Patent Document 23: JP-A-2000-058116 Patent Document 24: JP-A-2001-015158 Patent Document 25: JP-A-2005-306619 Non-Patent Document 1 : J. Electrochem. Soc., 145, L1 (1998)

›DISCLOSURE OF THE INVENTION · 1 of 3

Problems that the Invention is to Solve

The invention has been achieved in view of such background-art techniques. An object of the invention is to provide lithium secondary batteries which, even when fabricated so as to have a larger size, have a high capacity, long life, and high output.

Means for Solving the Problems

The present inventors made intensive investigations in view of the problems described above. As a result, they have found that a lithium secondary battery having a high capacity, long life, and high output is obtained by using a positive electrode and a negative electrode each having a specific composition and specific properties and further using a nonaqueous electrolyte containing a compound selected from a specific group. The invention has been thus completed.

The invention provides a lithium secondary battery at least comprising: an electrode group comprising a positive electrode, a negative electrode, and a microporous separator interposed between the electrodes; and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer containing an active material capable of occluding/releasing a lithium ion,

[wherein R 1 and R 2 may be the same or different and represent an organic group which has 1-12 carbon atoms and n represents an integer of 3-10],

fluorosilane compounds represented by the following general formula (2):

[Ka-2]

SiF x R 3 p R 4 q R 5 r (2)

[wherein R 3 to R 5 may be the same or different and represent an organic group which has 1-12 carbon atoms; x represents an integer of 1-3; and p, q, and r each represents an integer of 0-3, provided that 1≤p+q+r≤3],

compounds represented by the following general formula (3):

[wherein R 6 to R 8 may be the same or different and represent an organic group which has 1-12 carbon atoms and symbol A represents a group constituted of H, C, N, O, F, S, Si, and/or P],

compounds having an S—F bond in the molecule, nitric acid salts, nitrous acid salts, monofluorophosphoric acid salts, difluorophosphoric acid salts, acetic acid salts, and propionic acid salts in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and

the positive electrode is any positive electrode selected from the group consisting of the following positive electrode [1] to positive electrode [5]:

positive electrode [1]: a positive electrode containing a positive-electrode active material containing manganese;

positive electrode [2]: a positive electrode containing a positive-electrode active material having a composition represented by the following composition formula (4):

Li x Ni (1-y-z) Co y M z O 2 composition formula (4)

[wherein M represents at least one element selected from the group consisting of Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; y represents a number satisfying 0.05≤y≤0.5; and z represents a number satisfying 0.01≤z≤0.5];

positive electrode [3]: a positive electrode containing a positive-electrode active material selected from the group consisting of the following (a) to (d):

(a) a positive-electrode active material having a BET specific surface area of from 0.4 m 2 /g to 2 m 2 /g, (b) a positive-electrode active material having an average primary-particle diameter of from 0.1 μm to 2 μm, (c) a positive-electrode active material having a median diameter d 50 of from 1 μm to 20 μm, (d) a positive-electrode active material having a tap density of from 1.3 g/cm 3 to 2.7 g/cm 3 ;

positive electrode [4]: a positive electrode satisfying any requirement selected from the group consisting of the following (e) to (f):

(e) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material, a conductive material, and a binder on a current collector, wherein the content of the conductive material in the positive-electrode active-material layer is in the range of from 6% by mass to 20% by mass, (f) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the positive-electrode active-material layer has a density in the range of from 1.7 g/cm 3 to 3.5 g/cm 3 , (g) is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the ratio of the thickness of the positive-electrode active-material layer to the thickness of the current collector, i.e., the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector), is in the range of from 1.6 to 20; and

positive electrode [5]: a positive electrode containing two or more positive-electrode active materials differing in composition.

The invention further provides a lithium secondary battery at least comprising: an electrode group comprising a positive electrode, a negative electrode, and a microporous separator interposed between the electrodes; and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, and the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer containing an active material capable of occluding/releasing a lithium ion,

wherein the nonaqueous electrolyte is a nonaqueous electrolyte which contains at least one compound selected from the group consisting of cyclic siloxane compounds represented by general formula (1) given above, fluorosilane compounds represented by general formula (2) given above, compounds represented by general formula (3) given above, compounds having an S—F bond in the molecule, nitric acid salts, nitrous acid salts, monofluorophosphoric acid salts, difluorophosphoric acid salts, acetic acid salts, and propionic acid salts in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and

›DISCLOSURE OF THE INVENTION · 2 of 3

the negative electrode is any negative electrode selected from the group consisting of the following negative electrode [1] to negative electrode [10]:

negative electrode [1]: a negative electrode containing as a negative-electrode active material two or more carbonaceous substances differing in crystallinity;

negative electrode [2]: a negative electrode containing as a negative-electrode active material an amorphous carbonaceous substance which, when examined by wide-angle X-ray diffractometry, has an interplanar spacing (d002) for the (002) planes of 0.337 nm or larger and a crystallite size (Lc) of 80 nm or smaller and which, in an examination by argon ion laser Raman spectroscopy, has a Raman R value of 0.2 or higher defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 ;

negative electrode [3]: a negative electrode containing as a negative-electrode active material a titanium-containing metal oxide capable of occluding and releasing lithium;

negative electrode [4]: a negative electrode containing as a negative-electrode active material a carbonaceous substance having a roundness of 0.85 or higher and a surface functional-group amount O/C value of from 0 to 0.01;

negative electrode [5]: a negative electrode containing as a negative-electrode active material an orientation-differing-carbon composite comprising two or more carbonaceous substances differing in orientation;

negative electrode [6]: a negative electrode containing, as a negative-electrode active material, graphitic carbon particles which have a roundness of 0.85 or higher and an interplanar spacing (d002) for the (002) planes of smaller than 0.337 nm as determined by wide-angle X-ray diffractometry and which, in an examination by argon ion laser Raman spectroscopy, have a Raman R value of from 0.12 to 0.8 defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 ;

negative electrode [7]: a negative electrode containing as a negative-electrode active material a multielement-containing negative-electrode active material (C) which contains at least one of a lithium-occluding metal (A) selected from the group consisting of Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb and/or a lithium-occluding alloy (B) and further contains C and/or N as element Z;

negative electrode [8]: a negative electrode containing as a negative-electrode active material two or more negative-electrode active materials differing in property;

negative electrode [9]: a negative electrode containing a negative-electrode active material which has a tap density of 0.1 g/cm 3 or higher and has a pore volume, in terms of the volume of particle pores corresponding to the diameter range of from 0.01 μm to 1 μm as determined by mercury porosimetry, of 0.01 mL/g or larger; and

negative electrode [10]: a negative electrode which, when charged to 60% of a nominal capacity, has a reaction resistance in a negative-electrode opposing cell of 500Ω or lower.

The invention furthermore provides a lithium secondary battery at least comprising: an electrode group comprising a positive electrode, a negative electrode, and a microporous separator interposed between the electrodes; and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, and the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer containing an active material capable of occluding/releasing a lithium ion,

the nonaqueous electrolyte satisfies any requirement selected from the group consisting of the following electrolyte [1] to electrolyte [9]:

electrolyte [2]: the nonaqueous solvent as a component of the electrolyte contains at least one asymmetric chain carbonate and the proportion of the asymmetric chain carbonate to the whole nonaqueous solvent is from 5% by volume to 90% by volume;

electrolyte [3]: the nonaqueous solvent as a component of the electrolyte contains at least one chain carboxylic acid ester;

electrolyte [4]: the nonaqueous solvent as a component of the electrolyte contains at least one solvent having a flash point of 70° C. or higher in an amount of 60% by volume or larger based on the whole nonaqueous solvent;

electrolyte [5]: the lithium salt as a component of the electrolyte comprise LiN(C n F 2n+1 SO 2 ) 2 (wherein n is an integer of 1-4) and/or lithium bis(oxalato)borate;

electrolyte [6]: the lithium salt as a component of the electrolyte comprise a fluorine-containing lithium salt and the nonaqueous electrolyte contains hydrogen fluoride (HF) in an amount of from 10 ppm to 300 ppm of the whole electrolyte;

electrolyte [7]: the electrolyte contains vinylene carbonate and the content of the vinylene carbonate is in the range of from 0.001% by mass to 3% by mass based on the whole electrolyte;

electrolyte [8]: the electrolyte further contains at least one compound selected from the group consisting of compounds represented by general formula (4), heterocyclic compounds containing nitrogen and/or sulfur, cyclic carboxylic acid esters, and fluorine-containing cyclic carbonates in an amount of from 0.001% by mass to 5% by mass based on the whole nonaqueous electrolyte:

›DISCLOSURE OF THE INVENTION · 3 of 3

[wherein R 9 to R 12 may be the same or different and each represent a group constituted of one or more elements selected from the group consisting of H, C, N, O, F, S, and P]; and

electrolyte [9]: the electrolyte further contains an overcharge inhibitor.

The secondary batteries described above each especially preferably are one which has any property selected from the group consisting of the following (1) to (3):

(1) the overall electrode area of the positive electrode is at least 20 times the surface area of the case of the secondary battery; (2) the secondary battery has a direct-current resistance component of 20 milliohms (mΩ) or less; and (3) the battery elements held in each battery case of the secondary battery have an electric capacity of 3 ampere-hours (Ah) or higher.

The invention still further provides a lithium secondary battery at least comprising: an electrode group comprising a positive electrode, a negative electrode, and a microporous separator interposed between the electrodes; and a nonaqueous electrolyte comprising a nonaqueous solvent and a lithium salt contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, and the positive electrode and the negative electrode each comprising a current collector and, formed thereon, an active-material layer containing an active material capable of occluding/releasing a lithium ion,

wherein the secondary battery has any property selected from the group consisting of the following structure [1] to structure [6]:

structure [1]: the overall electrode area of the positive electrode is at least 20 times the surface area of the case of the secondary battery; structure [2]: the secondary battery has a direct-current resistance component of 20 milliohms (mΩ) or less; structure [3]: the battery elements held in each battery case of the secondary battery have an electric capacity of 3 ampere-hours (Ah) or higher; structure [4]: the current collectors of the positive electrode and negative electrode of the secondary battery each are made of a metallic material, and the metallic material of each current collector has been bonded to a conductor for outwardly discharging current by any of spot welding, high-frequency welding, and ultrasonic welding; structure [5]: the case of the secondary battery is made of aluminum or an aluminum alloy; and structure [6]: the battery case of the secondary battery is made of a casing material in which at least part of the battery inner side comprises a sheet formed from a thermoplastic resin and with which the electrode group can be enclosed by placing the electrode group in the casing material and heat sealing layers of the thermoplastic resin to each other.

The invention still further provides a nonaqueous electrolyte for secondary battery which at least comprises a nonaqueous solvent and a lithium salt, wherein

the nonaqueous electrolyte contains at least one compound selected from the group consisting of cyclic siloxane compounds represented by general formula (1) given above, fluorosilane compounds represented by general formula (2) given above, compounds represented by general formula (3) given above, compounds having an S—F bond in the molecule, nitric acid salts, nitrous acid salts, monofluorophosphoric acid salts, difluorophosphoric acid salts, acetic acid salts, and propionic acid salts in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and

the nonaqueous electrolyte satisfies any requirement selected from the group consisting of the following electrolyte [1] to electrolyte [9]:

electrolyte [1]: the nonaqueous solvent as a component of the electrolyte is a mixed solvent at least containing ethylene carbonate and the proportion of the ethylene carbonate to the whole nonaqueous solvent is from 1% by volume to 25% by volume; electrolyte [2]: the nonaqueous solvent as a component of the electrolyte contains at least one asymmetric chain carbonate and the proportion of the asymmetric chain carbonate to the whole nonaqueous solvent is from 5% by volume to 90% by volume; electrolyte [3]: the nonaqueous solvent as a component of the electrolyte contains at least one chain carboxylic acid ester; electrolyte [4]: the nonaqueous solvent as a component of the electrolyte contains at least one solvent having a flash point of 70° C. or higher in an amount of 60% by volume or larger based on the whole nonaqueous solvent; electrolyte [5]: the lithium salt as a component of the electrolyte comprise LiN(C n F 2n+1 SO 2 ) 2 (wherein n is an integer of 1-4) and/or lithium bis(oxalato)borate; electrolyte [6]: the lithium salt as a component of the electrolyte comprise a fluorine-containing lithium salt and the nonaqueous electrolyte contains hydrogen fluoride (HF) in an amount of from 10 ppm to 300 ppm of the whole electrolyte; electrolyte [7]: the electrolyte contains vinylene carbonate and the content of the vinylene carbonate is in the range of from 0.001% by mass to 3% by mass based on the whole electrolyte; electrolyte [8]: the electrolyte further contains at least one compound selected from the group consisting of compounds represented by general formula (4) given above, heterocyclic compounds containing nitrogen and/or sulfur, cyclic carboxylic acid esters, and fluorine-containing cyclic carbonates in an amount of from 0.001% by mass to 5% by mass based on the whole nonaqueous electrolyte; and electrolyte [9]: the electrolyte further contains an overcharge inhibitor.

›Advantages of the Invention · 1 of 2

According to the invention, lithium secondary batteries especially having excellent low-temperature discharge characteristics can be provided. The embodiments of the invention which will be described later produce, for example, the following effects.

Positive Electrode [1]:

According to the invention, a lithium secondary battery especially suitable for use as a large battery in, e.g., applications such as motor vehicles can be provided because a long life and a high output are obtained with less expensive materials.

Positive Electrode [2]:

According to the invention, a lithium secondary battery having a high capacity, long life, and high output can be provided, and a lithium secondary battery especially suitable for use as a large battery in, e.g., applications such as motor vehicles can be provided.

Positive Electrode [3]:

According to the invention, a lithium secondary battery having a long life and a high output is obtained and, hence, a lithium secondary battery especially suitable for use as a large battery in, e.g., applications such as motor vehicles can be provided.

Positive Electrode [4]:

According to the invention, a lithium secondary battery having a high output is obtained and, hence, a lithium secondary battery especially suitable for use as a large battery in, e.g., applications such as motor vehicles can be provided.

Positive Electrode [5]:

According to the invention, a lithium secondary battery which has a high capacity, long life, and high output and is inhibited from decreasing in battery capacity or output with repetitions of charge/discharge (has excellent suitability for repetitions of charge/discharge (cycle characteristics)) is obtained. Consequently, a lithium secondary battery especially suitable for use as a large battery in, e.g., applications such as motor vehicles can be provided.

Negative Electrode [1]:

According to the invention, a lithium secondary battery can be provided which can realize high-output characteristics from an initial to a final stage in a cycle while retaining improved suitability for cycling and which, even after having deteriorated through charge/discharge cycling, retains high-output characteristics. This battery is suitable especially for use as a large battery.

Negative Electrode [2]:

According to the invention, a lithium secondary battery having satisfactory suitability for short-time high-current-density charge/discharge can be provided.

Negative Electrode [3]:

According to the invention, a lithium secondary battery having a low output resistance and enabling the effective utilization of energy can be provided.

Negative Electrode [4]:

According to the invention, a lithium secondary battery improved in high-temperature storability at a low state of charge can be provided.

Negative Electrode [5]:

According to the invention, a lithium secondary battery can be provided which can retain satisfactory suitability for long-term repetitions of charge/discharge at a low state of charge.

Negative Electrode [6]:

According to the invention, a lithium secondary battery showing a quick output recovery from a low-output state at low temperatures can be provided.

Negative Electrode [7]:

According to the invention, a lithium secondary battery can be provided which, even when fabricated so as to have a larger size, has a high capacity and is satisfactorily chargeable.

Negative Electrode [8]:

According to the invention, a lithium secondary battery having both satisfactory cycle characteristics and a satisfactory low-temperature output can be provided.

Negative Electrodes [9] and [10]:

According to the invention, a lithium secondary battery can be provided which, even when fabricated so as to have a larger size, has a high capacity retention through cycling and can attain a satisfactory battery life, and which can attain a high output even after a charge/discharge cycle test. This battery has both of these properties.

Electrolytic Solution [1]:

According to the invention, the low-temperature characteristics of a nonaqueous-electrolyte secondary battery can be greatly improved. More specifically, the low-temperature characteristics can be improved without impairing cycle characteristics and storability.

Electrolytic Solution [2]:

According to the invention, a nonaqueous electrolyte for secondary battery greatly improved in both cycle characteristics and low-temperature characteristics and a secondary battery which employs this nonaqueous electrolyte and is excellent in these performances can be provided.

Electrolytic Solution [3]:

According to the invention, a nonaqueous electrolyte for secondary battery greatly improved in low-temperature output characteristics and a secondary battery having such performances can be provided.

Electrolytic Solution [4]:

According to the invention, a nonaqueous electrolyte for secondary battery can be provided which has an electrolyte composition less apt to pose problems associated with the incorporation of a large amount of a low-viscosity solvent, such as the problem that salt precipitation, a decrease in flash point, and an increase in internal pressure at high temperatures are apt to occur due to solvent vaporization, and which, despite this, enables high low-temperature characteristics and high output characteristics to be retained. A secondary battery having such performances can also be provided.

Electrolytic Solution [5]:

According to the invention, a nonaqueous electrolyte for secondary battery which greatly improves output characteristics and brings about excellent high-temperature storability and excellent cycle characteristics and a secondary battery having such performances can be provided.

Electrolytic Solution [6]:

According to the invention, a nonaqueous electrolyte for secondary battery excellent in high-temperature storability and cycle characteristics and greatly improved in output characteristics can be provided.

Electrolytic Solution [7]:

According to the invention, a secondary battery greatly improved in both cycle characteristics and low-temperature characteristics can be provided.

›Advantages of the Invention · 2 of 2

Electrolytic Solution [8]:

According to the invention, a nonaqueous electrolyte for secondary battery greatly improved in low-temperature discharge characteristics and excellent in high-temperature storability and cycle characteristics and a secondary battery having such performances can be provide.

Electrolytic Solution [9]:

According to the invention, a secondary battery satisfying both of high rate characteristics and safety in overcharge can be provided.

Structures [1] to [5]:

According to the invention, a lithium secondary battery which has a high capacity, long life, and high output and is highly safe in overcharge is obtained. Consequently, a lithium secondary battery especially suitable for use as a large battery in applications such as, e.g., motor vehicles can be provided.

Structure [6]

According to the invention, a lithium secondary battery which has a high capacity, long life, and high output, is reduced in gas evolution, and is highly safe in overcharge is obtained. Consequently, a lithium secondary battery especially suitable for use as a large battery in applications such as, e.g., motor vehicles can be provided.

›BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) shows a SEM of the thin film negative electrode produced in Negative Electrode Production 1.

FIG. 1 (B) shows the Si distribution of thin film negative electrode produced in Negative Electrode Production 1.

FIG. 1 (C) shows the C distribution of thin film negative electrode produced in Negative Electrode Production 1.

›BEST MODE FOR CARRYING OUT THE INVENTION · 1 of 73

Embodiments of the invention will be explained below in detail. The following explanations on constituent elements are for embodiments (typical embodiments) of the invention, and should not be construed as limiting the invention unless they depart from the spirit of the invention.

The lithium secondary batteries of the invention each are a lithium secondary battery which comprises an electrode group constituted at least of a positive electrode, a negative electrode, and a microporous separator interposed between the electrodes and a nonaqueous electrolyte comprising a nonaqueous solvent and one or more lithium salts contained therein, the electrode group and the nonaqueous electrolyte being held in a battery case, and in which

the positive electrode and the negative electrode each comprise a current collector and, formed thereon, an active-material layer containing an active material capable of occluding/releasing lithium ions,

the nonaqueous electrolyte is a nonaqueous electrolyte which contains at least one compound selected from the group consisting of cyclic siloxane compounds represented by general formula (1) given above, fluorosilane compounds represented by general formula (2) given above, compounds represented by general formula (3) given above, compounds having an S—F bond in the molecule, nitric acid salts, nitrous acid salts, monofluorophosphoric acid salts, difluorophosphoric acid salts, acetic acid salts, and propionic acid salts (hereinafter, these compounds are often abbreviated to “specific compounds”) in an amount of 10 ppm or more of the whole nonaqueous electrolyte, and

the positive electrode, negative electrode, electrolyte, or battery constitution satisfies a specific requirement.

The lithium secondary batteries of the invention will be explained below in detail.

The positive electrode for use in the lithium secondary batteries of the invention is explained below.

The positive electrode for use in the invention is not particularly limited as long as it has an active-material layer containing an active material capable of occluding and releasing lithium ions. However, it preferably is any positive electrode selected from the group consisting of the following positive electrode [1] to positive electrode [5]: positive electrode [1]: a positive electrode containing a positive-electrode active material containing manganese; positive electrode [2]: a positive electrode containing a positive-electrode active material having a composition represented by the following composition formula (4):

Li x Ni (1-y-z) Co y M z O 2 composition formula (4)

positive electrode [3]: a positive electrode containing a positive-electrode active material selected from the group consisting of the following (a) to (d):

positive electrode [4]: a positive electrode satisfying any requirement selected from the group consisting of the following (e) to (f):

(e) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material, a conductive material, and a binder on a current collector, wherein the content of the conductive material in the positive-electrode active-material layer is in the range of from 6% by mass to 20% by mass, (f) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the positive-electrode active-material layer has a density in the range of from 1.7 g/cm 3 to 3.5 g/cm 3 , (g) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the ratio of the thickness of the positive-electrode active-material layer to the thickness of the current collector, i.e., the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector), is in the range of from 1.6 to 20; and positive electrode [5]: a positive electrode containing two or more positive-electrode active materials differing in composition.

Positive electrodes which are usually employed in the lithium secondary batteries of the invention will be first explained below.

[Positive-Electrode Active Material]

The positive-electrode active material for general use in the positive electrodes will be described below.

[[Composition]]

The positive-electrode active material is not particularly limited as long as it is capable of electrochemically occluding/releasing lithium ions. It preferably is a substance containing lithium and at least one transition metal. Examples thereof include lithium-transition metal composite oxides and lithium-containing transition metal/phosphoric acid compounds.

The transition metal in the lithium-transition metal composite oxides preferably is V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like. Specific examples of the composite oxides include lithium-cobalt composite oxides such as LiCoO 2 , lithium-nickel composite oxides such as LiNiO 2 , lithium-manganese composite oxides such as LiMnO 2 , LiMn 2 O 4 , and Li 2 MnO 3 , and ones formed by partly replacing the transition metal atom(s) as a main component of these lithium-transition metal composite oxides by one or more other metals, e.g., Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, etc. Examples of such compounds formed by replacement include LiNi 0.5 Mn 0.5 O 2 , LiNi 0.85 Co 0.10 Al 0.05 O 2 , LiNi 0.33 Co 0.33 Mn 0.33 O 2 , LiMn 1.8 Al 0.2 O 4 , and LiMn 1.5 Ni 0.5 O 4 .

›BEST MODE FOR CARRYING OUT THE INVENTION · 2 of 73

The transition metal in the lithium-containing transition metal/phosphoric acid compounds preferably is V, Ti, Cr, Mn, Fe, Co, Ni, Cu, or the like. Specific examples of the compounds include iron phosphate compounds such as LiFePO 4 , Li 3 Fe 2 (PO 4 ) 3 , and LiFeP 2 O 7 , cobalt phosphate compounds such as LiCoPO 4 , and ones formed by partly replacing the transition metal atom(s) as a main component of these lithium-transition metal/phosphoric acid compounds by one or more other metals, e.g., Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[[Surface Coating]]

It is preferred to use a material comprising any of those positive-electrode active materials and, adherent to the surface thereof, a substance having a composition different from that of the core positive-electrode active material. Examples of the substance to be adhered to the surface (hereinafter abbreviated to “surface-adherent substance”) include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate, and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

Those surface-adherent substances each can be adhered to the surface of a positive-electrode active material, for example, by: a method in which the substance is dissolved or suspended in a solvent and this solution or suspension is infiltrated into a positive-electrode active material and dried; a method in which a precursor for the surface-adherent substance is dissolved or suspended in a solvent and this solution or suspension is infiltrated into a positive-electrode active material and then heated or otherwise treated to react the precursor; or a method in which the substance is added to a precursor for a positive-electrode active material and heat-treated together with the precursor.

The amount of the surface-adherent substance to be used may be as follows. The lower limit thereof is preferably 0.1 ppm or larger, more preferably 1 ppm or larger, even more preferably 10 ppm or larger, in terms of mass ppm of the positive-electrode active material. The upper limit thereof is preferably 20% or smaller, more preferably 10% or smaller, even more preferably 5% or smaller, in terms of % by mass based on the positive-electrode active material. The surface-adherent substance serves to inhibit the nonaqueous electrolyte from undergoing an oxidation reaction on the surface of the positive-electrode active material, whereby the battery life can be improved. However, in case where the amount of the substance adhered is too small, that effect is not sufficiently produced. On the other hand, too large amounts thereof may result in an increase in resistance because the surface-adherent substance inhibits the occlusion/release of lithium ions.

[[Shape]]

The particle shape of the positive-electrode active material to be used in the invention may be any of massive, polyhedral, spherical, ellipsoidal, platy, acicular, columnar, and other shapes such as those in common use. Preferred of these is one in which the primary particles have aggregated to form secondary particles and these secondary particles have a spherical or ellipsoidal shape. In electrochemical elements, the active material in each electrode usually expands/contracts with the charge/discharge of the element and, hence, deterioration is apt to occur, such as active-material breakage and conduction path breakage, due to the stress caused by the expansion/contraction. Because of this, a positive-electrode active material in which the primary particles have aggregated to form secondary particles is preferable to an active material composed of primary particles only since the particles in the former active material relieve the stress caused by expansion/contraction to prevent deterioration. Furthermore, particles of a spherical or ellipsoidal shape are preferable to particles showing axial orientation, e.g., platy ones, because the former particles are less apt to orient during electrode molding and hence this electrode is reduced in expansion/contraction during charge/discharge, and because these particles are apt to be evenly mixed with a conductive material in electrode production.

[[Tap Density]]

The tap density of the positive-electrode active material is generally 1.3 g/cm 3 or higher, preferably 1.5 g/cm 3 or higher, more preferably 1.6 g/cm 3 or higher, most preferably 1.7 g/cm 3 or higher. When the tap density of the positive-electrode active material is lower than the lower limit, there are cases where it is necessary to use a larger amount of a dispersion medium and larger amounts of a conductive material and a binder in forming a positive-electrode active-material layer and this results in a limited loading of the positive-electrode active material in the positive-electrode active-material layer and a limited battery capacity. By employing a composite oxide powder having a high tap density, a positive-electrode active-material layer having a high density can be formed. The higher the tap density, the more the positive-electrode active material is generally preferred. Although there is no particular upper limit thereon, too high tap densities may result in cases where the diffusion of lithium ions in the positive-electrode active-material layer through the nonaqueous electrolyte as a medium becomes a rate-determining stage and this is apt to reduce load characteristics. Consequently, the tap density of the positive-electrode active material is generally 2.9 g/cm 3 or lower, preferably 2.7 g/cm 3 or lower, more preferably 2.5 g/cm 3 or lower.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the capacity of the cell with the sample, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining a density from the resultant volume of the sample and the weight thereof. This density is defined as the tap density.

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[[Median Diameter d 50 ]]

The median diameter d 50 (secondary-particle diameter in the case where the primary particles have aggregated to form secondary particles) of the particles of the positive-electrode active material is generally 0.1 μm or larger, preferably 0.5 μm or larger, more preferably 1 μm or larger, most preferably 3 μm or larger. The upper limit thereof is generally 20 μm or smaller, preferably 18 μm or smaller, more preferably 16 μm or smaller, most preferably 15 μm or smaller. When the median diameter thereof is smaller than the lower limit, there are cases where a product having a high tap density cannot be obtained. When the median diameter thereof exceeds the upper limit, lithium diffusion in the individual particles requires a longer time and this results in a decrease in battery performance. In addition, there are cases where such positive-electrode active-material particles, when used in producing a positive electrode for batteries, i.e., when the active material and other ingredients including a conductive material and a binder are slurried with a solvent and this slurry is applied in a thin-film form, pose a problem, for example, that streak lines generate. It is possible to further improve loading in positive-electrode production by mixing two or more positive-electrode active materials differing in median diameter d 50 .

Median diameter d 50 in the invention is determined with a known laser diffraction/scattering type particle size distribution analyzer. In the case where LA-920, manufactured by HORIBA, Ltd., is used as a particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as a dispersion medium for the examination and a five-minute ultrasonic dispersing treatment is conducted before the particles are examined at a measuring refractive index set at 1.24.

[[Average Primary-Particle Diameter]]

In the case where the primary particles have aggregated to form secondary particles, the average primary-particle diameter of this positive-electrode active material is generally 0.01 μm or larger, preferably 0.05 μm or larger, more preferably 0.08 μm or larger, most preferably 0.1 μm or larger, and is generally 3 μm or smaller, preferably 2 μm or smaller, more preferably 1 μm or smaller, most preferably 0.6 μm or smaller. In case where the average primary-particle diameter thereof exceeds the upper limit, spherical secondary particles are difficult to form and this adversely influences powder loading or results in a considerably reduced specific surface area. There may hence be a high possibility that battery performances such as output characteristics might decrease. Conversely, when the average primary-particle diameter thereof is smaller than the lower limit, crystal growth is usually insufficient and, hence, there are cases where this positive-electrode active material poses a problem, for example, that charge/discharge reversibility is poor.

Primary-particle diameter is determined through an examination with a scanning electron microscope (SEM). Specifically, arbitrarily selected 50 primary-particle images in a photograph having a magnification of 10,000 diameters each are examined for the length of the longest segment of a horizontal line which extends across the primary-particle image from one side to the other side of the boundary. These measured lengths are averaged, whereby the average value can be determined.

[[BET Specific Surface Area]]

The BET specific surface area of the positive-electrode active material to be used in the lithium secondary batteries of the invention is generally 0.2 m 2 /g or larger, preferably 0.3 m 2 /g or larger, more preferably 0.4 m 2 /g or larger. The upper limit thereof is generally 4.0 m 2 /g or smaller, preferably 2.5 m 2 /g or smaller, more preferably 1.5 m 2 /g or smaller. In case where the BET specific surface area thereof is smaller than the lower limit of that range, battery performances are apt to decrease. In case where the BET specific surface area thereof exceeds the upper limit, a high tap density is difficult to obtain and this may pose a problem concerning applicability in forming a positive-electrode active material.

BET specific surface area is measured with a surface area meter (e.g., a fully automatic surface area measuring apparatus manufactured by Ohukura Riken Co., Ltd.). The specific surface area is defined as a value obtained by preliminarily drying a sample at 150° C. for 30 minutes in a nitrogen stream and then measuring the specific surface area thereof by the gas-flowing nitrogen adsorption BET one-point method using a nitrogen/helium mixture gas precisely regulated so as to have a nitrogen pressure of 0.3 relative to atmosphere pressure.

[[Production Processes]]

For producing the positive-electrode active material, processes in general use for producing inorganic compounds may be employed. Especially for producing spherical or ellipsoidal active materials, various techniques are usable. Examples thereof include: a method which comprises dissolving or pulverizing/dispersing a transition metal source, e.g., a transition metal nitrate or transition metal sulfate, optionally together with a source of other element(s) in a solvent, e.g., water, regulating the pH of the solution or dispersion with stirring to produce a spherical precursor, recovering and optionally drying the precursor, subsequently adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; a method which comprises dissolving or pulverizing/dispersing a transition metal source, e.g., a transition metal nitrate, transition metal sulfate, transition metal hydroxide, or transition metal oxide, optionally together with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; and a method which comprises dissolving or pulverizing/dispersing a transition metal source, e.g., a transition metal nitrate, transition metal sulfate, transition metal hydroxide, or transition metal oxide, together with an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and optionally with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, and heat-treating the precursor at a high temperature to obtain the active material.

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[Constitution of Positive Electrode]

The constitution of the positive electrode to be used in the invention will be described below.

[[Electrode Structure and Production Process]]

The positive electrode to be used in the lithium secondary batteries of the invention is produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector. The production of the positive electrode with a positive-electrode active material can be conducted in an ordinary manner. Namely, a positive-electrode active material and a binder are mixed together by a dry process optionally together with a conductive material, thickener, etc. and this mixture is formed into a sheet and press-bonded to a positive-electrode current collector. Alternatively, those materials are dissolved or dispersed in a liquid medium to obtain a slurry and this slurry is applied to a positive-electrode current collector and dried. Thus, a positive-electrode active-material layer is formed on the current collector, whereby the positive electrode can be obtained.

The content of the positive-electrode active material in the positive-electrode active-material layer in the invention is generally 10% by mass or higher, preferably 30% by mass or higher, especially preferably 50% by mass or higher. The upper limit thereof is generally 99.9% by mass or lower, preferably 99% by mass or lower. When the content of the positive-electrode active-material particles in the positive-electrode active-material layer is too low, there are cases where an insufficient electrical capacity results. Conversely, when the content thereof is too high, there are cases where the positive electrode has an insufficient strength. One positive-electrode active material may be used alone, or any desired combination of two or more positive-electrode active materials differing in composition or powder properties may be used in any desired proportion.

[[Compaction]]

It is preferred that the positive-electrode active-material layer obtained by coating fluid application and drying should be compacted with a handpress, roller press, or the like in order to heighten the loading density of the positive-electrode active material. The lower limit of the density of the positive-electrode active-material layer is preferably 1 g/cm 3 or higher, more preferably 1.5 g/cm 3 or higher, even more preferably 2 g/cm 3 or higher. The upper limit thereof is preferably 4 g/cm 3 or lower, more preferably 3.5 g/cm 3 or lower, even more preferably 3 g/cm 3 or lower. When the density thereof exceeds the upper limit of that range, the infiltration of a nonaqueous electrolyte into around the current collector/active material interface becomes insufficient and there are cases where charge/discharge characteristics especially at a high current density decrease. When the density thereof is lower than the lower limit, there are cases where electrical conductivity among the active-material particles decreases to increase battery resistance.

[[Conductive Material]]

As the conductive material, a known conductive material can be used at will. Examples thereof include metallic materials such as copper and nickel; graphites such as natural graphites and artificial graphites; carbon blacks such as acetylene black; and carbon materials such as amorphous carbon, e.g., needle coke. One of these materials may be used alone, or any desired combination of two or more thereof in any desired proportion may be used.

The conductive material may be used so that it is incorporated in the positive-electrode active-material layer in an amount of generally 0.01% by mass or larger, preferably 0.1% by mass or larger, more preferably 1% by mass or larger, and that the upper limit of the content thereof is generally 50% by mass or lower, preferably 30% by mass or lower, more preferably 15% by mass or lower. When the content thereof is lower than the lower limit of that range, there are cases where electrical conductivity becomes insufficient. Conversely, when the content thereof exceeds the upper limit of that range, there are cases where battery capacity decreases.

[[Binder]]

The binder to be used for producing the positive-electrode active-material layer is not particularly limited. In the case where the layer is to be formed through coating fluid application, any binder may be used as long as it is a material which is soluble or dispersible in the liquid medium for use in electrode production. Examples thereof include resinous polymers such as polyethylene, polypropylene, poly(ethylene terephthalate), poly(methyl methacrylate), aromatic polyamides, cellulose, and nitrocellulose; rubbery polymers such as SBR (styrene/butadiene rubbers), NBR (acrylonitrile/butadiene rubbers), fluororubbers, isoprene rubbers, butadiene rubbers, and ethylene/propylene rubbers; thermoplastic elastomeric polymers such as styrene/butadiene/styrene block copolymers or products of hydrogenation thereof, EPDM (ethylene/propylene/diene terpolymers), styrene/ethylene/butadiene/ethylenecopolymers, and styrene/isoprene/styrene block copolymers or products of hydrogenation thereof; flexible resinous polymers such as syndiotactic 1,2-polybutadiene, poly(vinyl acetate), ethylene/vinyl acetate copolymers, and propylene/α-olefin copolymers; fluorochemical polymers such as poly(vinylidene fluoride) (PVdF), polytetrafluoroethylene, fluorinated poly(vinylidene fluoride), and polytetrafluoroethylene/ethylene copolymers; and polymer compositions having the property of conducting alkali metal ions (especially lithium ions). One of these substances may be used alone, or any desired combination of two or more thereof in any desired proportion may be used.

The proportion of the binder in the positive-electrode active-material layer is generally 0.1% by mass or higher, preferably 1% by mass or higher, more preferably 3% by mass or higher. The upper limit thereof is generally 80% by mass or lower, preferably 60% by mass or lower, more preferably 40% by mass or lower, most preferably 10% by mass or lower. When the proportion of the binder is too low, there are cases where the positive-electrode active material cannot be sufficiently held and the positive electrode has an insufficient mechanical strength to impair battery performances such as cycle characteristics. On the other hand, too high proportions thereof may lead to a decrease in battery capacity or conductivity.

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[[Liquid Medium]]

Examples of the aqueous medium include water and mixed solvents comprising an alcohol and water. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; and aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide.

Especially when an aqueous medium is used, it is preferred to use a thickener and a latex of, e.g., a styrene/butadiene rubber (SBR) to prepare a slurry. A thickener is used generally for the purpose of regulating the slurry viscosity. The thickener is not particularly limited. Examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, poly(vinyl alcohol), oxidized starch, phosphorylated starch, casein, and salts of these. One of these thickeners may be used alone, or any desired combination of two or more thereof in any desired proportion may be used. In the case where such a thickener is further added, the proportion of the thickener to the active material is generally 0.1% by mass or higher, preferably 0.5% by mass or higher, more preferably 0.6% by mass or higher. The upper limit thereof is generally 5% by mass or lower, preferably 3% by mass or lower, more preferably 2% by mass or lower. When the proportion thereof is lower than the lower limit of that range, there are cases where applicability decreases considerably. Proportions thereof exceeding the upper limit result in a reduced proportion of the active material in the positive-electrode active-material layer, and this may pose a problem that battery capacity decreases and a problem that resistance among the particles of the positive-electrode active material increases.

[[Current Collector]]

The material of the positive-electrode current collector is not particularly limited, and a known one can be used at will. Examples thereof include metallic materials such as aluminum, stainless steel, nickel-plated materials, titanium, and tantalum; and carbon materials such as carbon cloths and carbon papers. Of these, metallic materials are preferred. Especially preferred is aluminum.

In the case of a metallic material, examples of the shape of the current collector include metal foils, metal cylinders, metal coils, metal plates, thin metal films, expanded metals, punching metals, and metal foams. In the case of a carbon material, examples of the collector shape include carbon plates, thin carbon films, and carbon cylinders. Of these, a thin metal film is preferred. The thin film may be in a suitable mesh form. Although the thin film may have any desired thickness, the thickness thereof is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, and is generally 1 mm or smaller, preferably 100 μm or smaller, more preferably 50 μm or smaller. When the thin film is thinner than the lower limit of that range, there are cases where this film is deficient in strength required of a current collector. Conversely, when the thin film is thicker than the upper limit of that range, there are cases where this film has impaired handleability.

The thickness ratio between the current collector and the positive-electrode active-material layer is not particularly limited. However, the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector) is preferably 150 or smaller, more preferably 20 or smaller, most preferably 10 or smaller. The lower limit thereof is preferably 0.1 or larger, more preferably 0.4 or larger, most preferably 1 or larger. When that ratio exceeds the upper limit of that range, there are cases where this current collector heats up due to Joule's heat during high-current-density charge/discharge. When that ratio decreases beyond the lower limit of that range, the proportion by volume of the current collector to the positive-electrode active material increases and this may reduce the capacity of the battery.

[[Electrode Area]]

When the nonaqueous electrolyte of the invention is used, it is preferred that the area of the positive-electrode active-material layer relative to the outer surface area of the battery case should be large from the standpoint of attaining a high output and enhanced high-temperature stability. Specifically, the overall electrode area of the positive electrode is preferably at least 15 times, more preferably at least 40 times, the surface area of the case of the secondary battery. When the battery has a bottomed polygonal shape, the term “outer surface area of the case” means a total area calculated from the length, width, and thickness dimensions of that case part packed with power-generating elements which excludes the terminal projections. When the battery has a bottomed cylindrical shape, that term means a geometric surface area obtained through the approximation to a cylinder of that case part packed with power-generating elements which excludes the terminal projections. The term “overall electrode area of the positive electrode” means the geometric surface area of the positive-electrode mix layer facing the mix layer containing a negative-electrode active material. In a structure in which a positive-electrode mix layer has been formed on each side of a current collector foil, that term means the sum of the areas separately calculated respectively for both sides.

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[[Discharge Capacity]]

When the nonaqueous electrolyte for secondary battery of the invention is used, it is preferred that the battery elements held in each battery case of the secondary battery should have an electric capacity (electric capacity measured when the battery in a fully charged state is discharged to a discharged state) of 3 ampere-hours (Ah) or higher. This is because such electric capacity is highly effective in improving low-temperature discharge characteristics.

For attaining that, a positive-electrode plate is designed to have a discharge capacity as measured in discharge from a fully charged state of preferably from 3 ampere-hours (Ah) to less than 20 Ah, more preferably from 4 Ah to less than 10 Ah. When the discharge capacity thereof is lower than 3 Ah, there are cases where high-current discharge results in a large decrease in voltage due to electrode reaction resistance and hence in a poor power efficiency. When the discharge capacity thereof is 20 Ah or higher, electrode reaction resistance is low and a satisfactory power efficiency is obtained. In this case, however, the battery has a wide temperature distribution during pulse charge/discharge due to internal heat generation and has poor durability in repetitions of charge/discharge. In addition, the efficiency of heat dissipation in the case of abrupt heat generation in an abnormality, such as overcharge or internal short-circuiting, is also poor. There are hence cases where the probability that the poor heat dissipation efficiency leads to a phenomenon in which the internal pressure increases and the gas release valve works (valve working) or a phenomenon in which the battery contents are vigorously ejected outside (rupture) increases.

[[Thickness of Positive-Electrode Plate]]

The thickness of the positive-electrode plate is not particularly limited. However, from the standpoints of high capacity and high output, the thickness of the mix layer, excluding the thickness of the core metal foil, on one side of the current collector is such that the lower limit thereof is preferably 10 μm or larger, more preferably 20 μm or larger, and the upper limit thereof is preferably 200 μm or smaller, more preferably 100 μm or smaller.

Positive electrode [1], i.e., “a positive electrode containing a positive-electrode active material containing manganese”, for use in a lithium secondary battery of the invention will be explained below.

[Positive Electrode [1]: Positive-Electrode Active Material]

The positive-electrode active material for use in positive electrode [1] is described below.

[[Composition]]

The positive-electrode active material is a substance which contains one or more transition metals and is capable of electrochemically occluding/releasing lithium ions. One containing manganese as at least part of the transition metals is used in this invention. It is preferred that lithium should be further contained. More preferred is a composite oxide containing lithium and manganese.

The manganese-containing positive-electrode active material is not particularly limited. However, it preferably is one having a composition represented by the following composition formula (5):

Li x Mn (1-y) M 1 y O 2 composition formula (5)

[wherein M 1 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8].

In composition formula (5), M 1 especially preferably is Ni, Co, or Fe; x especially preferably satisfies 0.2≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.7. Examples of the positive-electrode active material having a composition represented by composition formula (5) include LiMn 0.5 Ni 0.5 O 2 .

Especially preferred is one in which M 1 is Ni and which has a composition represented by the following composition formula (6):

Li x Mn (1-y-z) Ni y M 2 z O 2 composition formula (6)

[wherein M 2 represents at least one element selected from the group consisting of Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; y represents a number satisfying 0.05≤y≤0.8; and z represents a number satisfying 0.01≤z≤0.5].

In composition formula (6), M 2 especially preferably is Co, Al, Fe, or Mg; x especially preferably satisfies 0.2≤x≤1.15; y especially preferably satisfies 0.1≤y≤0.7; z especially preferably satisfies 0.1≤z≤0.7; and y+z especially preferably satisfies 0.2≤y+z≤0.7. Examples of the positive-electrode active material having a composition represented by composition formula (6) include LiMn 0.33 Ni 0.33 Co 0.33 O 2 .

Also preferred as the manganese-containing positive-electrode active material is one having a composition represented by the following composition formula (7):

Li x Mn (2-y) M 3 y O 4 composition formula (7)

[wherein M 3 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8].

In composition formula (7), M 3 especially preferably is Ni, Co, Al, or Mg; x especially preferably satisfies 0.05≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.7. Examples of the positive-electrode active material having a composition represented by composition formula (7) include LiMn 1.8 Al 0.2 O 4 and LiMn 1.5 Ni 0.5 O 4 .

[[Surface Coating]]

It is preferred to use an active material which comprises the manganese-containing positive-electrode active material and, adherent to the surface thereof, a substance having a composition different from that of the positive-electrode active material. The kind of the surface-adherent substance, method of adhesion, amount of the substance to be adherends, etc. are the same as those described above.

[[Shape]]

The shape of the particles of this positive-electrode active material is the same as described above.

[[Tap Density]]

The tap density of this positive-electrode active material is the same as described above.

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[[Median Diameter d 50 ]]

The median diameter d 50 (secondary-particle diameter in the case where the primary particles have aggregated to form secondary particles) of the particles of this positive-electrode active material is the same as described above.

[[Average Primary-Particle Diameter]]

In the case where the primary particles have aggregated to form secondary particles, the average primary-particle diameter of this positive-electrode active material is the same as described above.

[[BET Specific Surface Area]]

The BET specific surface area of this positive-electrode active material is the same as described above.

[[Production Processes]]

For producing this positive-electrode active material, processes in general use for producing inorganic compounds may be employed. Especially for producing the active material which is spherical or ellipsoidal, various techniques are usable. Examples thereof include: a method which comprises dissolving or pulverizing/dispersing a manganese source, e.g., manganese nitrate or manganese sulfate, optionally together with a source of other element(s) in a solvent, e.g., water, regulating the pH of the solution or dispersion with stirring to produce a spherical precursor, recovering and optionally drying the precursor, subsequently adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; a method which comprises dissolving or pulverizing/dispersing a manganese source, e.g., manganese nitrate, manganese sulfate, manganese oxide, or manganese oxyhydroxide, optionally together with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; and a method which comprises dissolving or pulverizing/dispersing a manganese source, e.g., manganese nitrate, manganese sulfate, manganese oxide, or manganese oxyhydroxide, together with an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and optionally with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, and heat-treating the precursor at a high temperature to obtain the active material.

In the invention, the manganese-containing positive-electrode active material may be used alone as the only positive-electrode active material, or a combination of the manganese-containing positive-electrode active material with any desired one or more positive-electrode active materials differing in composition or powder properties from the manganese-containing positive-electrode active material may be used in any desired proportion. In this case, preferred examples of the combination include: a combination of the manganese-containing positive-electrode active material with LiNiO 2 or an active material formed by replacing part of the Ni by another transition metal; and a combination of the manganese-containing positive-electrode active material with LiCoO 2 or an active material formed by replacing part of the Co by another transition metal. Especially preferred examples of the combination include: a combination of the positive-electrode active material represented by any of composition formulae (5) to (7) with LiNiO 2 or an active material formed by replacing part of the Ni by another transition metal; and a combination of the positive-electrode active material represented by any of composition formulae (5) to (7) with LiCoO 2 or an active material formed by replacing part of the Co by another transition metal. The content of the manganese-containing positive-electrode active material, in particular the positive-electrode active material represented by any of composition formulae (5) to (7), is preferably 30% by mass or higher, more preferably 50% by mass or higher, based on all positive-electrode active materials. When the positive-electrode active material represented by any of composition formulae (5) to (7) is used in too small a proportion, there are cases where the cost of the positive electrode is not reduced.

[Positive Electrode [1]: Constitution of Positive Electrode]

The constitution of the positive electrode to be used as positive electrode [1] is described below.

Positive electrode [2], i.e., “a positive electrode containing a positive-electrode active material having a specific composition represented by composition formula (4)”, for use in a lithium secondary battery of the invention will be explained below.

[Positive Electrode [2]: Positive-Electrode Active Material]

The positive-electrode active material for use in positive electrode [2] is described below.

[[Composition]]

As the positive-electrode active material is used a substance which contains one or more transition metals and is capable of electrochemically occluding/releasing lithium ions and which has a composition represented by the following composition formula (4) (hereinafter abbreviated to “this positive-electrode active material”):

Li x Ni (1-y-z) Co y M z O 2 composition formula (4)

In composition formula (4), M preferably is Mn, Al, or Mg, and x preferably satisfies 0.2≤x≤1.15. Symbol y preferably satisfies 0.08≤y≤0.4 and especially preferably satisfies 0.1≤y≤0.3. Furthermore, z preferably satisfies 0.02≤z≤0.4 and especially preferably satisfies 0.03≤z<0.3.

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[[Surface Coating]]

It is preferred to use an active material which comprises this positive-electrode active material and, adherent to the surface thereof, a substance having a composition different from that of the positive-electrode active material. The kind of the surface-adherent substance, method of adhesion, amount of the substance to be adherend, etc. are the same as those described above.

[[Shape]]

The shape of the particles of this positive-electrode active material is the same as described above.

[[Tap Density]]

The tap density of this positive-electrode active material is the same as described above.

[[Median Diameter d 50 ]]

[[Average Primary-Particle Diameter]]

In the case where the primary particles have aggregated to form secondary particles, the average primary-particle diameter of this positive-electrode active material is the same as described above.

[[BET Specific Surface Area]]

The BET specific surface area of this positive-electrode active material is the same as described above.

[[Production Processes]]

For producing this positive-electrode active material, processes in general use for producing inorganic compounds may be employed. Especially for producing the active material which is spherical or ellipsoidal, various techniques are usable. Examples thereof include: a method which comprises dissolving or pulverizing/dispersing a nickel source, e.g., nickel nitrate or nickel sulfate, a cobalt source, e.g., cobalt nitrate or cobalt sulfate, and a source of M in composition formula (4) in a solvent, e.g., water, regulating the pH of the solution or dispersion with stirring to produce a spherical precursor, recovering and optionally drying the precursor, subsequently adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; a method which comprises dissolving or pulverizing/dispersing a nickel source, e.g., nickel nitrate, nickel sulfate, nickel oxide, nickel hydroxide, or nickel oxyhydroxide, a cobalt source, e.g., cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, or cobalt oxyhydroxide, and a source of M in composition formula (4) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; and a method which comprises dissolving or pulverizing/dispersing a nickel source, e.g., nickel nitrate, nickel sulfate, nickel oxide, nickel hydroxide, or nickel oxyhydroxide, a cobalt source, e.g., cobalt nitrate, cobalt sulfate, cobalt oxide, cobalt hydroxide, or cobalt oxyhydroxide, a source of M in composition formula (4), and an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, and heat-treating the precursor at a high temperature to obtain the active material.

For producing the positive electrode in this invention, this positive-electrode active material (the positive-electrode active material represented by composition formula (4) and/or the positive-electrode active material represented by composition formula (4) covered with the surface-adherent substance) may be used alone, or a combination of this positive-electrode active material with any desired one or more positive-electrode active materials differing in composition from that positive-electrode active material may be used in any desired proportion. In this case, preferred examples of the combination include: a combination of this positive-electrode active material with LiMn 2 O 4 or an active material formed by replacing part of the Mn by another transition metal, etc.; and a combination of this positive-electrode active material with LiCoO 2 or an active material formed by replacing part of the Co with another transition metal, etc.

Here, the content of this positive-electrode active material is preferably 30% by mass or higher, more preferably 50% by mass or higher, based on all positive-electrode active materials. When this positive-electrode active material is used in too small a proportion, there are cases where the battery capacity decreases. Incidentally, “this positive-electrode active material” and “positive-electrode active materials other than this positive-electrode active material” are inclusively referred to as “positive-electrode active materials”.

[Positive Electrode [2]: Constitution of Positive Electrode]

The constitution of the positive electrode to be used as positive electrode [2] is described below.

An explanation will be given below on positive electrode [3] for use in a lithium secondary battery of the invention, i.e., “a positive electrode containing a positive-electrode active material selected from the group consisting of the following (a) to (d):

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[Positive Electrode [3]: Positive-Electrode Active Material]

The positive-electrode active material for use in positive electrode [3] is described below.

[[Composition]]

The positive-electrode active material is not particularly limited as long as it is a substance capable of electrochemically occluding/releasing lithium ions. It preferably is a substance containing lithium and at least one transition metal. Examples thereof include lithium-transition metal composite oxides and lithium-containing transition metal/phosphoric acid compounds. Specifically, such a compound having the same composition as described above may be used.

[[Surface Coating]]

It is also preferred that the positive-electrode active material should comprise a core positive-electrode active material and, adherent to the surface thereof, a substance having a composition different from that of the core positive-electrode active material. The kind of the surface-adherent substance, method of adhesion, amount of the substance to be adhered, etc. are the same as those described above.

[[Shape]]

The shape of the particles of this positive-electrode active material is the same as described above.

[[BET Specific Surface Area]]

The BET specific surface area of this positive-electrode active material is preferably 0.4 m 2 /g or larger, more preferably 0.5 m 2 /g or larger, even more preferably 0.6 m 2 /g or larger. The upper limit thereof is preferably 2 m 2 /g or smaller, more preferably 1.8 m 2 /g or smaller, even more preferably 1.5 m 2 /g or smaller. In case where the BET specific surface area thereof is smaller than the lower limit of that range, battery performances are apt to decrease. In case where the BET specific surface area thereof exceeds the upper limit, a high tap density is difficult to obtain and this may pose a problem concerning applicability in forming a positive-electrode active material.

[[Average Primary-Particle Diameter]]

In the case where the primary particles have aggregated to form secondary particles, the average primary-particle diameter of this positive-electrode active material is preferably 0.1 μm or larger, more preferably 0.2 μm or larger, even more preferably 0.3 μm or larger, most preferably 0.4 μm or larger. The upper limit thereof is preferably 2 μm or smaller, more preferably 1.6 μm or smaller, even more preferably 1.3 μm or smaller, most preferably 1 μm or smaller. In case where the average primary-particle diameter thereof exceeds the upper limit, spherical secondary particles are difficult to form and this adversely influences powder loading or results in a considerably reduced specific surface area. There may hence be a high possibility that battery performances such as output characteristics might decrease. Conversely, when the average primary-particle diameter thereof is smaller than the lower limit, crystal growth is usually insufficient and, hence, there are cases where this positive-electrode active material poses a problem, for example, that charge/discharge reversibility is poor.

[[Median Diameter d 50 ]]

The median diameter d 50 (secondary-particle diameter in the case where the primary particles have aggregated to form secondary particles) of the particles of the positive-electrode active material is preferably 1 μm or larger, more preferably 1.2 μm or larger, even more preferably 1.5 μm or larger, most preferably 2 μm or larger. The upper limit thereof is preferably 20 μm or smaller, more preferably 18 μm or smaller, even more preferably 16 μm or smaller, most preferably 15 μm or smaller. When the median diameter thereof is smaller than the lower limit, there are cases where a product having a high tap density cannot be obtained. When the median diameter thereof exceeds the upper limit, lithium diffusion in the individual particles requires a longer time and this results in a decrease in battery performance. In addition, there are cases where such positive-electrode active-material particles, when used in producing a positive electrode for batteries, i.e., when the active material and other ingredients including a conductive material and a binder are slurried with a solvent and this slurry is applied in a thin-film form, pose a problem, for example, that streak lines generate. The positive-electrode active material for use in this invention preferably is a mixture of two or more positive-electrode active materials differing in median diameter, because this mixture of positive-electrode active materials is effective in further improving loading in positive-electrode production.

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[[Tap Density]]

The tap density of this positive-electrode active material is preferably 1.3 g/cm 3 or higher, more preferably 1.5 g/cm 3 or higher, even more preferably 1.6 g/cm 3 or higher, most preferably 1.7 g/cm 3 or higher. When the tap density of the positive-electrode active material is lower than the lower limit, there are cases where it is necessary to use a larger amount of a dispersion medium and larger amounts of a conductive material and a binder in forming a positive-electrode active-material layer and this results in a limited loading of the positive-electrode active material in the positive-electrode active-material layer and a limited battery capacity. By employing a composite oxide powder having a high tap density, a positive-electrode active-material layer having a high density can be formed. The higher the tap density, the more the positive-electrode active material is generally preferred. Although there is no particular upper limit thereon, too high tap densities may result in cases where the diffusion of lithium ions in the positive-electrode active-material layer through the electrolyte as a medium becomes a rate-determining stage and this is apt to reduce load characteristics. Consequently, the upper limit of the tap density thereof is preferably 2.7 g/cm 3 or lower, more preferably 2.5 g/cm 3 or lower.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the capacity of the cell with the sample, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining the resultant bulk density. This bulk density is defined as the tap density.

From the standpoints of long life and high output, this positive-electrode active material for use in a lithium secondary battery of the invention especially preferably is one which simultaneously satisfies two or more of the properties described above, i.e., BET specific surface area, average primary-particle diameter, median diameter d 50 , and tap density.

[[Production Processes]]

Processes usable for producing this positive-electrode active material are the same as described above.

This positive-electrode active material for use in a lithium secondary battery of the invention may be a single positive-electrode active material alone, or any desired combination of two or more positive-electrode active materials differing in composition or powder properties may be used in any desired proportion as that positive-electrode active material. Furthermore, from the standpoint of life improvement, this positive electrode in the invention preferably contains a positive-electrode active material having any one of the properties described above (this positive-electrode active material) and a positive-electrode active material differing in composition from that positive-electrode active material.

[Positive Electrode [3]: Constitution of Positive Electrode]

The constitution of the positive electrode to be used as positive electrode [3] is described below.

An explanation will be given below on positive electrode [4] for use in a lithium secondary battery of the invention, i.e., “a positive electrode satisfying any requirement selected from the group consisting of the following (e) to (f):

(e) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material, a conductive material, and a binder on a current collector, wherein the content of the conductive material in the positive-electrode active-material layer is in the range of from 6% by mass to 20% by mass (embodiment 1), (f) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the positive-electrode active-material layer has a density in the range of from 1.7 g/cm 3 to 3.5 g/cm 3 (embodiment 2), (g) it is a positive electrode produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector, wherein the ratio of the thickness of the positive-electrode active-material layer to the thickness of the current collector, i.e., the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector), is in the range of from 1.6 to 20 (embodiment 3)”.

[Positive Electrode [4]: Positive-Electrode Active Material]

The positive-electrode active material for use in positive electrode [4] is described below.

This positive-electrode active material is not particularly limited as long as it is a substance capable of electrochemically occluding/releasing lithium ions. It preferably is a substance containing lithium and at least one transition metal. Examples thereof include lithium-transition metal composite oxides and lithium-containing transition metal/phosphoric acid compounds. Specifically, such a compound having the same composition as described above may be used.

The surface coating, shape, tap density, median diameter d 50 , average primary-particle diameter, and BET specific surface area of this positive-electrode active material, processes for producing the active material, etc. are the same as described above.

[Positive Electrode [4]: Constitution of Positive Electrode]

The constitution of the positive electrode to be used as positive electrode [4] is described below.

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[[Electrode Structure and Production Process]]

Positive electrode [4] in a lithium secondary battery of the invention is produced by forming a positive-electrode active-material layer comprising a positive-electrode active material and a binder on a current collector. The production of this positive electrode with a positive-electrode active material can be conducted in an ordinary manner. Namely, at least a positive-electrode active material and a binder are mixed together by a dry process optionally together with a conductive material (essential ingredient in embodiment 1) and optionally further with a thickener, etc. and this mixture is formed into a sheet and press-bonded to a positive-electrode current collector. Alternatively, those materials are dissolved or dispersed in a liquid medium to obtain a slurry and this slurry is applied to a positive-electrode current collector and dried. Thus, a positive-electrode active-material layer is formed on the current collector, whereby the positive electrode can be obtained.

The content of the positive-electrode active material in the positive-electrode active-material layer is preferably 80% by mass or higher, more preferably 82% by mass or higher, especially preferably 84% by mass or higher. The upper limit thereof is preferably 95% by mass or lower, more preferably 93% by mass or lower. When the content of the positive-electrode active material in the positive-electrode active-material layer is too low, there are cases where an insufficient electric capacity results. Conversely, when the content thereof is too high, there are cases where the positive electrode has an insufficient strength.

[[Conductive Material]]

As the conductive material, a known conductive material can be used at will. Examples thereof include the same conductive materials as shown above.

In this positive electrode for use in a lithium secondary battery of the invention, the content of the conductive material in the positive-electrode active-material layer in embodiment 1 should be 6% by mass or higher and is preferably 7% by mass or higher, especially preferably 8% by mass or higher, more preferably 9% by mass or higher. In embodiment 2 and embodiment 3, there are no particular limitations thereon. However, the content of the conductive material in embodiments 2 and 3 is preferably 6% by mass or higher, especially preferably 7% by mass or higher, more preferably 8% by mass or higher. When the content of the conductive material in the positive-electrode active-material layer is too low, there are cases where this positive-electrode active-material layer has insufficient electrical conductivity and a high output cannot be obtained.

The upper limit of the content of the conductive material in the positive-electrode active-material layer is as follows. In embodiment 1, the content thereof should be 20% by mass or lower and is preferably 18% by mass or lower, especially preferably 15% by mass or lower. In embodiment 2 and embodiment 3, the upper limit thereof is not particularly limited. However, the content of the conductive material in embodiments 2 and 3 is preferably 20% by mass or lower, especially preferably 18% by mass or lower, more preferably 15% by mass or lower. When the content thereof is too high, there are cases where battery capacity decreases and a high output cannot be obtained.

[[Binder]]

The proportion of the binder in the positive-electrode active-material layer is generally 0.1% by mass or higher, preferably 1% by mass or higher, especially preferably 3% by mass or higher. The upper limit thereof is generally 80% by mass or lower, preferably 60% by mass or lower, especially preferably 40% by mass or lower, more preferably 10% by mass or lower. When the proportion of the binder is too low, there are cases where the positive-electrode active material cannot be sufficiently held and the positive electrode has an insufficient mechanical strength to impair battery performances such as cycle characteristics. On the other hand, too high proportions thereof may lead to a decrease in battery capacity or conductivity.

[[Liquid Medium for Slurry Formation]]

The kind of the liquid medium to be used for forming a slurry is not particularly limited as long as it is a solvent in which the positive-electrode active material, conductive material, and binder and a thickener, which is used according to need, can be dissolved or dispersed. Either an aqueous solvent or an organic solvent may be used. Examples thereof include the same liquid media as shown above. The kind and addition amount of the thickener also are the same as described above.

[[Compaction]]

It is preferred that the positive-electrode active-material layer obtained by coating fluid application and drying should be compacted with a handpress, roller press, or the like in order to heighten the loading density of the positive-electrode active material. The density of the positive-electrode active-material layer is as follows. In embodiment 2, the lower limit thereof should be 1.7 g/cm 3 or higher and is preferably 2.0 g/cm 3 or higher, especially preferably 2.2 g/cm 3 or higher. In embodiment land embodiment 3, there are no particular limitations. However, the lower limit thereof in embodiments 1 and 3 is preferably 1.7 g/cm 3 or higher, especially preferably 2.0 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher. When the density of the layer is lower than the lower limit, there are cases where conductivity among the active-material particles decreases to increase battery resistance and a high output cannot be obtained.

The upper limit of the density of the positive-electrode active-material layer, in embodiment 2, should be 3.5 g/cm 3 or lower and is preferably 3.0 g/cm 3 or lower, especially preferably 2.8 g/cm 3 or lower. In embodiment 1 and embodiment 3, the upper limit thereof is not particularly limited. However, the upper limit thereof in embodiments 1 and 3 is preferably 3.5 g/cm 3 or lower, especially preferably 3.0 g/cm 3 or lower, more preferably 2.8 g/cm 3 or lower. When the density of the positive-electrode active-material layer exceeds the upper limit of that range, the infiltration of a nonaqueous electrolyte into around the current collector/active material interface decreases and there are cases where charge/discharge characteristics especially at a high current density decrease and a high output cannot be obtained.

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[[Current Collector]]

The material of the positive-electrode current collector is not particularly limited and is the same as described above. The shape of the current collector and the thickness of the thin film thereof also are the same as described above.

With respect to the ratio of the thickness of the positive-electrode active-material layer to that of the current collector, the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector) in embodiment 3 should be 20 or smaller and is preferably 15 or smaller, especially preferably 10 or smaller. In embodiment 1 and embodiment 2, that value is preferably 20 or smaller, especially preferably 15 or smaller, more preferably 10 or smaller, although there are no particular limitations thereon. When that ratio exceeds the upper limit of that range, there are cases where the current collector heats up due to Joule's heat during high-current-density charge/discharge to damage the positive electrode.

The lower limit of the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector) in embodiment 1 should be 1.6 or larger and is preferably 1.8 or larger, especially preferably 2 or larger. In embodiment 1 and embodiment 2, the lower limit thereof is preferably 1.6 or larger, especially preferably 1.8 or larger, more preferably 2 or larger, although there are no particular limitations thereon. When that ratio decreases beyond the lower limit, the proportion by volume of the current collector to the positive-electrode active material increases and there are hence cases where battery capacity decreases and a high output cannot be obtained.

When the preferred ranges of “the content of the conductive material in the positive-electrode active-material layer”, “the density of the positive-electrode active-material layer”, and “the ratio of the thickness of the positive-electrode active-material layer to that of the current collector, i.e., the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector)” are combined, then a more preferred high-output lithium secondary battery is obtained.

[[Electrode Area]]

[[Discharge Capacity]]

The design of a positive-electrode plate, etc. for attaining that electric capacity are the same as described above.

[[Thickness of Positive-Electrode Plate]]

The thickness of the positive-electrode plate is not particularly limited, and is the same as described above.

Positive electrode [5] for use in a lithium secondary battery of the invention will be explained below. [Positive Electrode [5]: Positive-Electrode Active Materials]

The positive-electrode active materials for use in positive electrode [5] are described below.

[[Composition]]

The positive-electrode active materials are not particularly limited as long as these are substances capable of electrochemically occluding/releasing lithium ions. They preferably are substances containing lithium and at least one transition metal. Examples thereof include lithium-transition metal composite oxides and lithium-containing transition metal/phosphoric acid compounds.

The lithium-cobalt composite oxides are not particularly limited. However, one having a composition represented by the following composition formula (8) is preferred.

Li x Co (1-y) M 1 y O 2 composition formula (8)

[In composition formula (8), M 1 represents at least one element selected from the group consisting of Ni, Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying]

In composition formula (8), M 1 especially preferably is Ni, Mn, Al, or Fe; x especially preferably satisfies 0.2≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.5.

The lithium-nickel composite oxides are not particularly limited. However, one having a composition represented by the following composition formula (9) is preferred.

Li x Ni (1-y) M 2 y O 2 composition formula (9)

[In composition formula (9), M 2 represents at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8.]

In composition formula (9), M 2 especially preferably is Co, Mn, Al, or Fe; x especially preferably satisfies 0.2≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.5.

The lithium-manganese composite oxides are not particularly limited. However, one having a composition represented by the following composition formula (10) is preferred.

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Li x Mn (1-y) M 3 y O 2 composition formula (10)

[In composition formula (10), M 3 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8.]

In composition formula (10), M 3 especially preferably is Ni, Co, or Fe; x especially preferably satisfies 0.2≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.7.

Another preferred example of the lithium-manganese composite oxides is one having a composition represented by the following composition formula (11).

Li x Mn (2-y) M 4 y O 4 composition formula (11)

[In composition formula (11), M 4 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8.]

In composition formula (11), M 4 especially preferably is Ni, Co, Al, or Mg; x especially preferably satisfies 0.05≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.7.

Still another preferred example of the lithium-manganese composite oxides is one having a composition represented by the following composition formula (12).

Li x Mn (1-y) M 5 y O 3 composition formula (12)

[In composition formula (12), M 5 represents at least one element selected from the group consisting of Ni, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤2.4; and y represents a number satisfying 0.05≤y≤0.8.]

In composition formula (12), M 5 especially preferably is Ni, Co, Al, or Mg; x especially preferably satisfies 0.1≤x≤2.3; and y especially preferably satisfies 0.1≤y≤0.5.

The iron phosphate compounds are not particularly limited. However, one having a composition represented by the following composition formula (13) is preferred.

Li x Fe (1-y) M y 6 PO 4 composition formula (13)

[In composition formula (13), M 6 represents at least one element selected from the group consisting of Ni, Co, Mn, Al, Ti, Mg, Cr, Ga, Cu, Zn, and Nb; x represents a number satisfying 0<x≤1.2; and y represents a number satisfying 0.05≤y≤0.8.]

In composition formula (13), M 6 especially preferably is Ni, Co, Mn, or Al; x especially preferably satisfies 0.2≤x≤1.15; and y especially preferably satisfies 0.1≤y≤0.5.

It is preferred in this invention that any desired combination of two or more positive-electrode active materials differing in composition selected from the positive-electrode active materials described above should be used in any desired proportion. Those positive-electrode active materials differ from each other in merit performance and, hence, it is preferred to combine necessary performances according to the intended use of the battery. It is generally thought that a combination results in arithmetic-mean performances. With respect to life, however, there are cases where effects of the positive-electrode active material having a longer life are more produced unexpectedly. By using a positive-electrode active material attaining a relatively satisfactory life in combination with a positive-electrode active material which is relatively poor in life but is satisfactory in other performances, the lithium secondary battery of the invention having a high output, high capacity, and long life could be achieved.

Examples of such preferred combinations include:

a positive-electrode active material represented by composition formula (8) and a positive-electrode active material represented by composition formula (10); a positive-electrode active material represented by composition formula (8) and a positive-electrode active material represented by composition formula (11); a positive-electrode active material represented by composition formula (8) and a positive-electrode active material represented by composition formula (12); a positive-electrode active material represented by composition formula (8) and a positive-electrode active material represented by composition formula (13); a positive-electrode active material represented by composition formula (9) and a positive-electrode active material represented by composition formula (10); a positive-electrode active material represented by composition formula (9) and a positive-electrode active material represented by composition formula (11); a positive-electrode active material represented by composition formula (9) and a positive-electrode active material represented by composition formula (12); a positive-electrode active material represented by composition formula (9) and a positive-electrode active material represented by composition formula (13); a positive-electrode active material represented by composition formula (10) and a positive-electrode active material represented by composition formula (11); a positive-electrode active material represented by composition formula (10) and a positive-electrode active material represented by composition formula (12); and a positive-electrode active material represented by composition formula (10) and a positive-electrode active material represented by composition formula (13).

Especially preferred are:

a positive-electrode active material represented by composition formula (9) and a positive-electrode active material represented by composition formula (11); and a positive-electrode active material represented by composition formula (10) and a positive-electrode active material represented by composition formula (11).

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The proportion in each combination is not particularly limited. However, it is preferably from 10:90 to 90:10, more preferably from 20:80 to 80:20.

Although two or more positive-electrode active materials differing in composition are contained in the positive electrode for use in the lithium secondary battery of this invention, it is preferred that at least one of these positive-electrode active materials should be one whose BET specific surface area, average primary-particle diameter, median diameter d 50 , and/or tap density (hereinafter abbreviated to “following properties”) is within the following specific range. The two or more positive-electrode active materials differing in composition may include a positive-electrode active material in which any property is not within the range shown below. It is, however, preferred that all of the two or more positive-electrode active materials should be ones in each of which any property is within the range shown below. The proportion of “all positive-electrode active materials in each of which any of the following properties is within the specific range shown below” to “all positive-electrode active materials contained in the positive electrode” depends on that property and is not particularly limited. However, that proportion is preferably 30% by mass or higher, more preferably 50% by mass or higher. Especially preferably, the former positive-electrode active materials account for the whole of the latter. It is preferred that each of the two or more positive-electrode active materials contained in the positive electrode should be one in which any one or more of the following properties are within the specific range (s) shown below. However, more preferably any two or more of, especially preferably any three or more of, most preferably all of the following properties of each positive-electrode active material are within the specific ranges shown below.

[[BET Specific Surface Area]]

The BET specific surface area of at least one of the positive-electrode active materials is preferably 0.4 m 2 /g or larger, more preferably 0.5 m 2 /g or larger, even more preferably 0.6 m 2 /g or larger. The upper limit thereof is 2 m 2 /g or smaller, preferably 1.8 m 2 /g or smaller, more preferably 1.5 m 2 /g or smaller. In case where the BET specific surface area thereof is smaller than the lower limit of that range, battery performances are apt to decrease. In case where the BET specific surface area thereof exceeds the upper limit, a high tap density is difficult to obtain and this may pose a problem concerning applicability in forming a positive-electrode active material.

[[Average Primary-Particle Diameter]]

The average primary-particle diameter of at least one of the positive-electrode active materials is preferably 0.1 μm or larger, more preferably 0.2 μm or larger, even more preferably 0.3 μm or larger, most preferably 0.4 μm or larger. The upper limit thereof is preferably 2 μm or smaller, more preferably 1.6 μm or smaller, even more preferably 1.3 μm or smaller, most preferably 1 μm or smaller. In case where the average primary-particle diameter thereof exceeds the upper limit, spherical secondary particles are difficult to form and this adversely influences powder loading or results in a considerably reduced specific surface area. There may hence be a high possibility that battery performances such as output characteristics might decrease. Conversely, when the average primary-particle diameter thereof is smaller than the lower limit, crystal growth is usually insufficient and, hence, there are cases where this positive-electrode active material poses a problem, for example, that charge/discharge reversibility is poor.

[[Median Diameter d 50 ]]

The median diameter d 50 (secondary-particle diameter in the case where the primary particles have aggregated to form secondary particles) of the particles of at least one of the positive-electrode active materials is preferably 1 μm or larger, more preferably 1.2 μm or larger, even more preferably 1.5 μm or larger, most preferably 2 μm or larger. The upper limit thereof is preferably 20 μm or smaller, more preferably 18 μm or smaller, even more preferably 16 μm or smaller, most preferably 15 μm or smaller. When the median diameter thereof is smaller than the lower limit, there are cases where a product having a high tap density cannot be obtained. When the median diameter thereof exceeds the upper limit, lithium diffusion in the individual particles requires a longer time and this results in a decrease in battery performance. In addition, there are cases where such positive-electrode active-material particles, when used in producing a positive electrode for batteries, i.e., when the active material and other ingredients including a conductive material and a binder are slurried with a solvent and this slurry is applied in a thin-film form, pose a problem, for example, that streak lines generate. It is possible to further improve loading in positive-electrode production by mixing two or more positive-electrode active materials differing in median diameter d 50 .

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[[[Tap Density]]]

The tap density of at least one of the positive-electrode active materials is preferably 1.3 g/cm 3 or higher, more preferably 1.5 g/cm 3 or higher, even more preferably 1.6 g/cm 3 or higher, most preferably 1.7 g/cm 3 or higher. When the tap density of the positive-electrode active material is lower than the lower limit, there are cases where it is necessary to use a larger amount of a dispersion medium and larger amounts of a conductive material and a binder in forming a positive-electrode active-material layer and this results in a limited loading of the positive-electrode active material in the positive-electrode active-material layer and a limited battery capacity. By employing a composite oxide powder having a high tap density, a positive-electrode active-material layer having a high density can be formed. The higher the tap density, the more the positive-electrode active material is generally preferred. Although there is no particular upper limit thereon, too high tap densities may result in cases where the diffusion of lithium ions in the positive-electrode active-material layer through the nonaqueous electrolyte as a medium becomes a rate-determining stage and this is apt to reduce load characteristics. Consequently, the upper limit of the tap density thereof is preferably 2.7 g/cm 3 or lower, more preferably 2.5 g/cm 3 or lower.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the capacity of the cell with the sample, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining the resultant bulk density. This bulk density is defined as the tap density.

[[Surface Coating]]

It is preferred that at least one of the positive-electrode active materials should be one which has, adherent to the surface thereof, a substance having a composition different from that of the main positive-electrode active material or core positive-electrode active material (hereinafter, the substance adherent to the surface is abbreviated to “surface-adherent substance”). The kind of the surface-adherent substance, method of adhesion, amount of the substance to be adhered, etc. are the same as those described above.

[[Shape]]

The shape of the particles of at least one of the positive-electrode active materials is the same as any of those of positive-electrode active-material particles heretofore in use.

[[Production Processes]]

For producing the positive-electrode active materials, the same general processes for producing inorganic compounds as described above may be used.

[Positive Electrode [5]: Constitution of Positive Electrode]

The constitution of positive electrode [5] for use in this invention is described below.

The electrode structure, process for electrode production, compaction of a positive-electrode active-material layer, conductive material, binder for use in producing a positive-electrode active-material layer, liquid medium for slurry formation, current collector, electrode area, discharge capacity, thickness of the positive-electrode plate, etc. in this invention are the same as described above. In producing the positive electrode, the two or more positive-electrode active materials may be mixed beforehand or may be mixed by simultaneously adding these during positive-electrode production.

The negative electrode for use in the lithium secondary batteries of the invention is not particularly limited as long as it comprises a current collector and formed thereon an active-material layer containing an active material capable of occluding/releasing lithium ions. However, the negative electrode preferably is any negative electrode selected from the group consisting of the following negative electrode [1] to negative electrode [10]:

negative electrode [1]: a negative electrode containing as a negative-electrode active material two or more carbonaceous substances differing in crystallinity; negative electrode [2]: a negative electrode containing as a negative-electrode active material at least one amorphous carbonaceous substance which, when examined by wide-angle X-ray diffractometry, has an interplanar spacing (d002) for the (002) planes of 0.337 nm or larger and a crystallite size (Lc) of 80 nm or smaller and which, in an examination by argon ion laser Raman spectroscopy, has a Raman R value defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 of 0.2 or higher; negative electrode [3]: a negative electrode containing as a negative-electrode active material a titanium-containing metal oxide capable of occluding and releasing lithium; negative electrode [4]: a negative electrode containing as a negative-electrode active material a carbonaceous substance having a roundness of 0.85 or higher and a surface functional-group amount O/C value of from 0 to 0.01; negative electrode [5]: a negative electrode containing as a negative-electrode active material an orientation-differing-carbon composite comprising two or more carbonaceous substances differing in orientation; negative electrode [6]: a negative electrode containing, as a negative-electrode active material, graphitic carbon particles which have a roundness of 0.85 or higher and an interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry of smaller than 0.337 nm and which, in an examination by argon ion laser Raman spectroscopy, have a Raman R value defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 of from 0.12 to 0.8; negative electrode [7]: a negative electrode containing as a negative-electrode active material a multielement-containing negative-electrode active material (C) which contains at least one of a lithium-occluding metal (A) selected from the group consisting of Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb and/or a lithium-occluding alloy (B) and further contains C and/or N as element Z; negative electrode [8]: a negative electrode containing as a negative-electrode active material two or more negative-electrode active materials differing in property; negative electrode [9]: a negative electrode containing a negative-electrode active material which has a tap density of 0.1 g/cm 3 or higher and has a pore volume, in terms of the volume of particle pores corresponding to the diameter range of from 0.01 μm to 1 μm as determined by mercury porosimetry, of 0.01 mL/g or larger; and negative electrode [10]: a negative electrode which, when charged to 60% of a nominal capacity, has a reaction resistance in a negative-electrode opposing cell of 500Ω or lower.

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Negative electrodes which are usually employed in the lithium secondary batteries of the invention will be first explained below.

[Negative-Electrode Active Material]

The negative-electrode active material for general use in the negative electrodes will be explained below.

[[Composition]]

The negative-electrode active material is not particularly limited as long as it is capable of electrochemically occluding/releasing lithium ions. Examples thereof include a carbonaceous material, a metal oxide such as tin oxide or silicon oxide, a metal composite oxide, elemental lithium, a lithium alloy such as a lithium-aluminum alloy, and a metal capable of alloying with lithium, such as Sn or Si. One of these may be used alone, or any desired two or more thereof may be used in combination in any desired proportion. From the standpoint of safety, it is preferred to use a carbonaceous material or a lithium composite oxide among those.

The metal composite oxide is not particularly limited as long as it is capable of occluding/releasing lithium. However, from the standpoint of high-current-density charge/discharge characteristics, it is preferred that the composite oxide should contain titanium and/or lithium as a component.

The carbonaceous material preferably is one selected from:

(1) natural graphites; (2) artificial carbonaceous substances and artificial graphitic substances; and carbon materials obtained by subjecting carbonaceous substances [e.g., natural graphites, coal coke, petroleum coke, coal pitch, petroleum pitch, carbonaceous substances obtained by oxidizing these pitches, needle coke, pitch coke, carbon materials obtained by partly graphitizing these cokes, products of the pyrolysis of organic substances, such as furnace black, acetylene black, and pitch-derived carbon fibers, organic substances capable of carbonization (e.g., coal tar pitches ranging from soft pitch to hard pitch, coal-derived heavy oil such as dry distillation/liquefaction oil, straight-run heavy oil such as topping residues and vacuum distillation residues, heavy oils resulting from petroleum cracking, such as ethylene tar as a by-product of the thermal cracking of crude oil, naphtha, etc., aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene, nitrogen-ring compounds such as phenazine and acridine, sulfur-ring compounds such as thiophene and bithiophene, polyphenylenes such as biphenyl and terphenyl, poly(vinylchloride), poly(vinylalcohol), poly(vinylbutyral), substances obtained by insolubilizing these compounds, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophene, organic polymers such as polystyrene, natural polymers such as polysaccharides represented by cellulose, lignin, mannan, poly(galacturonic acid), chitosan, and saccharose, thermoplastic resins such as poly(phenylene sulfide) and poly(phenylene oxide), and thermosetting resins such as furfuryl alcohol resins, phenol-formaldehyde resins, and imide resins) and products of the carbonization thereof, or solutions obtained by dissolving any of such organic substances capable of carbonization in a low-molecular organic solvent, e.g., benzene, toluene, xylene, quinoline, or n-hexane, and products of the carbonization of these solutions] to a heat treatment at a temperature in the range of from 400° C. to 3,200° C. one or more times; (3) carbon materials constituting a negative-electrode active-material layer which comprise at least two carbonaceous substances differing in crystallinity and/or have an interface where at least two carbonaceous substances differing in crystallinity are in contact with each other; and (4) carbon materials constituting a negative-electrode active-material layer which comprise at least two carbonaceous substances differing in orientation and/or have an interface where at least two carbonaceous substances differing in orientation are in contact with each other. This is because this carbonaceous material brings about a satisfactory balance between initial irreversible capacity and high-current-density charge/discharge characteristics.

[Constitution of Negative Electrode, Properties, and Method of Preparation]

With respect to the properties of the carbonaceous material, negative electrode containing the carbonaceous material, method of electrode formation, current collector, and lithium secondary battery, it is desirable that any one of the following (1) to (19) should be satisfied or two or more thereof be simultaneously satisfied.

(1) X-Ray Parameter

The carbonaceous material preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. It is desirable that the upper limit of the value of d should be generally 0.36 nm or smaller, preferably 0.35 nm or smaller, more preferably 0.345 nm or smaller. The crystallite size (Lc) of the carbonaceous material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is preferably 1 nm or larger, more preferably 1.5 nm or larger.

(2) Ash Content

The ash content of the carbonaceous material may be 1% by mass or lower and is especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole carbonaceous material. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous material. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous material necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

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(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the carbonaceous material, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 100 μm or smaller, preferably 50 μm or smaller, more preferably 40 μm or smaller, even more preferably 30 μm or smaller, especially preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a carbonaceous material is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode is produced through coating fluid application.

Volume-average particle diameter in the invention is defined as the median diameter determined by dispersing the carbon powder in a 0.2% by mass aqueous solution (about 10 mL) of poly(oxyethylene (20)) sorbitan monolaurate as a surfactant and examining the dispersion with a laser diffraction/scattering type particle size distribution analyzer (e.g., LA-700, manufactured by HORIBA, Ltd.).

(4) Raman R Value, Raman Half-Value Width

The R value of the carbonaceous material as determined by the argon ion laser Raman spectroscopy is generally 0.01 or higher, preferably 0.03 or higher, more preferably 0.1 or higher. The upper limit thereof may be 1.5 or lower and is preferably 1.2 or lower, more preferably 1.0 or lower, even more preferably 0.5 or lower. When the R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the carbonaceous material is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 100 cm −1 or smaller, preferably 80 cm −1 or smaller, more preferably 60 cm −1 or smaller, even more preferably 40 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A around 1,580 cm −1 and the intensity I B of a peak P B around 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the carbonaceous material. Furthermore, the half-value width of the peak P A around 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the carbonaceous material.

Conditions for this Raman spectroscopy are as follows.

Wavelength of argon ion laser: 514.5 nm Laser power on sample: 15-25 mW Resolution: 10-20 cm −1 Examination range: 1,100 cm −1 to 1,730 cm −1 Analysis for R value and half-value width: background processing Smoothing: simple average; convolution, 5 points

(5) BET Specific Surface Area

The specific surface area of the carbonaceous material for use in the invention, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1.0 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this carbonaceous material as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this carbonaceous material as a negative-electrode material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

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The specific surface area as determined by the BET method is a value measured with a surface area meter (e.g., a fully automatic surface area measuring apparatus manufactured by Ohukura Riken Co., Ltd.) by preliminarily drying a sample at 350° C. for 15 minutes in a nitrogen stream and then measuring the specific surface area thereof by the gas-flowing nitrogen adsorption BET one-point method using a nitrogen/helium mixture gas precisely regulated so as to have a nitrogen pressure of 0.3 relative to atmosphere pressure.

(6) Pore Diameter Distribution

With respect to the pore diameter distribution of the carbonaceous material for use in the invention, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles, particle surface irregularities formed by steps, and contact surfaces among the particles, as determined by mercury porosiometry (mercury intrusion method), may be 0.01 mL/g or larger and is preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof may be 0.6 mL/g or smaller and is preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the amount thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The total volume of pores corresponding to the pore diameter range of from 0.01 μm to 100 μm is preferably 0.1 mL/g or larger, more preferably 0.25 mL/g or larger, even more preferably 0.4 mL/g or larger. The upper limit thereof may be 10 mL/g or smaller and is preferably 5 mL/g or smaller, more preferably 2 mL/g or smaller. When the total volume thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the total volume thereof is smaller than the lower limit, there are cases where the dispersing effect of a thickener or binder in electrode plate formation is not obtained.

The average pore diameter of the carbonaceous material is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof may be 50 μm or smaller and is preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. When the average pore diameter thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease.

As an apparatus for the mercury porosimetry is used a mercury porosimeter (Autopore 9520, manufactured by Micromeritics Corp.). About 0.2 g of a sample is placed in a powder cell and this cell is closed. The sample in the cell is pretreated by degassing it at room temperature under vacuum (50 μmHg or lower) for 10 minutes. Subsequently, the pressure in the cell is reduced to 4 psia (about 28 kPa) and mercury is introduced thereinto. The internal pressure is stepwise elevated from 4 psia (about 28 kPa) to 40,000 psia (about 280 MPa) and then lowered to 25 psia (about 170 kPa). The number of steps in the pressure elevation is 80 or larger. In each step, the amount of mercury intruded is measured after an equilibrium time of 10 seconds. A pore diameter distribution is calculated from the mercury intrusion curve thus obtained, using the Washburn equation. Incidentally, the surface tension (γ) and contact angle (ψ) of mercury are taken as 485 dyne/cm and 140°, respectively. The average pore diameter used is the pore diameter corresponding to a cumulative pore volume of 50%.

(7) Roundness

Roundness is used as an index to the degree of sphericity of the carbonaceous material. The roundness of the particles having a particle diameter in the range of 3-40 μm is preferably 0.1 or higher, especially preferably 0.5 or higher, more preferably 0.8 or higher, even more preferably 0.85 or higher, most preferably 0.9 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics.

Roundness is defined by the following equation. When a particle has a roundness of 1, this particle theoretically is a true sphere.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

The value of roundness is determined, for example, with a flow type particle image analyzer (e.g., FPIA, manufactured by Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample in a 0.2% by mass aqueous solution (about 50 mL) of poly(oxyethylene(20)) sorbitan monolaurate as a surfactant, propagating an ultrasonic wave of 28 kHz to the dispersion for 1 minute at an output of 60 W, and then examining particles having a particle diameter in the range of 3-40 μm with the analyzer having a detection range set at 0.6-400 μm.

Methods for improving roundness are not particularly limited. However, a carbonaceous material in which the particles have been rounded by a rounding treatment (mechanical energy treatment) is preferred because it gives an electrode in which the interstices among particles are uniform in shape. Examples of the rounding treatment include: a method in which a shear force or compressive force is applied to thereby mechanically make the shape of the particles close to sphere; and a method of mechanical/physical treatment in which fine particles are aggregated into particles by means of the bonding force of a binder or of the fine particles themselves.

(8) True Density

The true density of the carbonaceous material is generally 1.4 g/cm 3 or higher, preferably 1.6 g/cm 3 or higher, more preferably 1.8 g/cm 3 or higher, even more preferably 2.0 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the carbonaceous material is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

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(9) Tap Density

The tap density of the carbonaceous material desirably is generally 0.1 g/cm 3 or higher, preferably 0.5 g/cm 3 or higher, more preferably 0.7 g/cm 3 or higher, especially preferably 1.0 g/cm 3 or higher. The upper limit thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where this carbonaceous material, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain. Tap density is determined by the same method as described above with regard to the positive electrode and is defined as described therein.

(10) Orientation Ratio

The orientation ratio of the carbonaceous material is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

Orientation ratio is determined by X-ray diffractometry after a sample is molded by compaction. A molding obtained by packing 0.47 g of a sample into a molding machine having a diameter of 17 mm and compacting the sample at 600 kgf/cm 2 is set with clay on a sample holder for examination so as to be flush with the holder. This sample molding is examined for X-ray diffraction. From the intensities of the resultant (110) diffraction peak and (004) diffraction peak for the carbon, the ratio represented by (110) diffraction peak intensity/(004) diffraction peak intensity is calculated. This ratio is defined as the orientation ratio of the active material.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=0.5 degrees Receiving slit=0.15 mm Scattering slit=0.5 degrees

Examination range and step angle/measuring time:

(110) plane: 75°≤2θ≤80° 1°/60 sec (004) plane: 52°≤2θ≤57° 1°/60 sec

(11) Aspect Ratio (Powder)

The aspect ratio is theoretically 1 or higher. The upper limit thereof may be 10 or lower and is preferably 8 or lower, more preferably 5 or lower. When the aspect ratio exceeds the upper limit, there are cases where this carbonaceous material causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

The aspect ratio of a carbonaceous-material particle is represented by A/B, wherein A is the length of the longest axis of the particle in a three-dimensional examination and B is the length of the shortest axis perpendicular to that axis. The examination of carbon particles is made with a scanning electron microscope capable of enlargement examination. Fifty are arbitrarily selected from graphite particles fixed to an edge face of a metal sheet having a thickness of 50 μm or smaller, and each particle is examined for A and B while rotating or inclining the stage to which the sample is fixed. The average of the A/B values is determined.

(12) Minor-Material Mixing

“Minor-material mixing” means that the negative electrode and/or the negative-electrode active material contains two or more carbonaceous materials differing in property. The term “property” herein means one or more properties selected from X-ray diffraction parameter, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, roundness, and ash content.

Especially preferred embodiments include: one in which the volume-based particle size distribution is not symmetrical about the median diameter; one in which two or more carbonaceous materials differing in Raman R value are contained; and one in which carbonaceous materials differing in X-ray parameter are contained.

One example of the effects thereof is that the incorporation of a carbonaceous material, such as a graphite, e.g., a natural graphite or artificial graphite, or an amorphous carbon, e.g., a carbon black such as acetylene black or needle coke, as a conductive material serves to reduce electrical resistance. One of these carbonaceous materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion. In the case where such a carbonaceous material is added as a conductive material, the amount thereof may be 0.1% by mass or larger and is preferably 0.5% by mass or larger, more preferably 0.6% by mass or larger. The upper limit thereof may be 45% by mass or smaller and is preferably 40% by mass. Amounts thereof smaller than the lower limit of that range may result in difficulties in obtaining the effect of improving conductivity. Amounts thereof exceeding the upper limit may lead to an increase in initial irreversible capacity.

(13) Electrode Production

Electrode production may be conducted by an ordinary method. For example, a binder and a solvent are added to a negative-electrode active material optionally together with a thickener, conductive material, filler, etc. to obtain a slurry and this slurry is applied to a current collector and dried. Thereafter, the coated current collector is pressed, whereby an electrode can be formed. The thickness of the negative-electrode active-material layer per one side in the stage just before the step of injecting a nonaqueous electrolyte in battery fabrication is generally 15 μm or larger, preferably 20 μm or larger, more preferably 30 μm or larger. The upper limit thereof may be 150 μm or smaller and is preferably 120 μm or smaller, more preferably 100 μm or smaller. When the thickness thereof is larger than the upper limit of that range, a nonaqueous electrolyte is less apt to infiltrate into around the interface of the current collector and, hence, there are cases where high-current-density charge/discharge characteristics decrease. When the thickness thereof is smaller than the lower limit of that range, the proportion by volume of the current collector to the negative-electrode active material increases and there are cases where battery capacity decreases. The negative-electrode active material may be roller pressed to obtain a sheet electrode. It is also possible to subject the negative-electrode active material to compression molding to obtain a pellet electrode.

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(14) Current Collector

As the current collector, a known one can be used at will. Examples of the current collector for the negative electrode include metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. Copper is especially preferred of these from the standpoints of processability and cost. In the case where the current collector is a metallic material, examples of the shape of the current collector include metal foils, metal cylinders, metal coils, metal plates, thin metal films, expanded metals, punching metals, and metal foams. Preferred of these are thin metal films. More preferred are copper foils. Even more preferred are a rolled copper foil, which is produced by the rolling process, and an electrolytic copper foil, which is produced by the electrolytic process. Either of these can be used as a current collector. In the case of a copper foil having a thickness smaller than 25 μm, use can be made of a copper alloy (e.g., phosphor bronze, titanium-copper, Corson alloy, or Cu—Cr—Zr alloy) having a higher strength than pure copper. Furthermore, an aluminum foil can be advantageously used because it has a low specific gravity and, hence, use of the foil as a current collector can reduce the weight of the battery.

The current collector comprising a copper foil produced by the rolling process is less apt to crack even when the negative electrode is rolled tightly or rolled at an acute angle, because the copper crystals are oriented in the rolling direction. This current collector can be advantageously used in small cylindrical batteries. The electrolytic copper foil is obtained by immersing a metallic drum in a nonaqueous electrolyte containing copper ions dissolved therein, causing current to flow through the system while rotating the drum to thereby deposit copper on the drum surface, and peeling the copper deposit from the drum. Copper may be deposited on a surface of the rolled copper foil by the electrolytic process. One or each side of such a copper foil may have undergone a surface-roughening treatment or a surface treatment (e.g., a chromate treatment in a thickness of from several nanometers to about 1 μm or a priming treatment with titanium).

The current collector base is desired to further have the following properties.

(1) Average Surface Roughness (Ra)

The average surface roughness (Ra) of that side of the current collector base on which a thin active-material film is to be formed, as determined by the method provided for in JIS B 0601-1994, is not particularly limited. However, the average surface roughness thereof is generally 0.05 μm or higher, preferably 0.1 μm or higher, especially preferably 0.15 μm or higher. The upper limit thereof is generally 1.5 μm or lower, preferably 1.3 μm or lower, especially preferably 1.0 μm or lower. By regulating the average surface roughness (Ra) of the current collector base so as to be in the range of from the lower limit to upper limit, satisfactory charge/discharge cycle characteristics can be expected. By regulating the average surface roughness thereof to a value not lower than the lower limit, the area of the interface between the base and a thin active-material film is increased and adhesion to the thin active-material film is improved. The upper limit of the average surface roughness (Ra) thereof is not particularly limited. However, it is preferably 1.5 μm or lower because a foil having a practical thickness for batteries and having an average surface roughness (Ra) exceeding 1.5 μm is generally difficult to procure.

(2) Tensile Strength

The tensile strength of the current collector base is not particularly limited. However, it is generally 100 N/mm 2 or higher, preferably 250 N/mm 2 or higher, more preferably 400 N/mm 2 or higher, especially preferably 500 N/mm 2 or higher. Tensile strength is a quotient obtained by dividing the maximum tensile force required before test piece breakage by the sectional area of the test piece. In the invention, the tensile strength is determined through a measurement conducted with the same apparatus and by the same method as for elongation. A current collector base having a high tensile strength can be inhibited from cracking with the expansion/contraction of the thin active-material film which occur upon charge/discharge. With this current collector base, satisfactory cycle characteristics can be obtained.

(3) 0.2% Proof Stress

The 0.2% proof stress of the current collector base is not particularly limited. However, it is generally 30 N/mm 2 or higher, preferably 150 N/mm 2 or higher, especially preferably 300 N/mm 2 or higher. The term 0.2% proof stress means the degree of load necessary for imparting a plastic (permanent) deformation of 0.2%. Namely, it means that application of that degree of load and subsequent removal thereof result in a 0.2% deformation. In the invention, the 0.2% proof stress is determined through a measurement conducted with the same apparatus and by the same method as for elongation. A current collector base having a high 0.2% proof stress can be inhibited from plastically deforming with the expansion/contraction of the thin active-material film which occur upon charge/discharge. With this current collector base, satisfactory cycle characteristics can be obtained.

The thin metal film may have any desired thickness. However, the thickness thereof is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger. The upper limit thereof is generally 1 mm or smaller, preferably 100 μm or smaller, more preferably 30 μm or smaller. In case where the thin metal film is thinner than 1 μm, this film has a reduced strength and there are hence cases where coating is difficult. When the thin metal film is thicker than 100 μm, there are cases where this film deforms an electrode shape, e.g., a rolled form. The thin metal film may be in a mesh form.

(15) Thickness Ratio between Current Collector and Active-Material Layer

The thickness ratio between the current collector and the active-material layer is not particularly limited. However, the value of (thickness of the active-material layer on one side just before impregnation with the nonaqueous electrolyte)/(thickness of the current collector) is preferably 150 or smaller, especially preferably 20 or smaller, more preferably 10 or smaller. The lower limit thereof is preferably 0.1 or larger, especially preferably 0.4 or larger, more preferably 1 or larger. When that ratio exceeds the upper limit of that range, there are cases where this current collector heats up due to Joule's heat during high-current-density charge/discharge. When that ratio decreases beyond the lower limit of that range, the proportion by volume of the current collector to the negative-electrode active material increases and this may reduce the capacity of the battery.

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(16) Electrode Density

When the negative-electrode active material is used to form an electrode, the electrode structure is not particularly limited. However, the density of the active material present on the current collector is preferably 1.0 g/cm 3 or higher, more preferably 1.2 g/cm 3 or higher, even more preferably 1.3 g/cm 3 or higher. The upper limit thereof is generally 2.0 g/cm 3 or lower, preferably 1.9 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, even more preferably 1.7 g/cm 3 or lower. When the density thereof exceeds the upper limit of that range, there are cases where the active-material particles are broken and this increases the initial irreversible capacity and reduces the infiltration of a nonaqueous electrolyte into around the current collector/active material interface. As a result, high-current-density charge/discharge characteristics may decrease. When the density thereof is lower than the lower limit, there are cases where electrical conductivity among the active-material particles decreases and this increases battery resistance, resulting in a reduced capacity per unit volume.

(17) Binder

The binder for binding the active material is not particularly limited as long as it is stable to the nonaqueous electrolyte and the solvent to be used for electrode production. Examples thereof include resinous polymers such as polyethylene, polypropylene, poly(ethylene terephthalate), poly(methyl methacrylate), aromatic polyamides, cellulose, and nitrocellulose; rubbery polymers such as SBR (styrene/butadiene rubbers), isoprene rubbers, butadiene rubbers, fluororubbers, NBR (acrylonitrile/butadiene rubbers), and ethylene/propylene rubbers; styrene/butadiene/styrene block copolymers or products of hydrogenation thereof; thermoplastic elastomeric polymers such as EPDM (ethylene/propylene/diene terpolymers), styrene/ethylene/butadiene/styrene copolymers, and styrene/isoprene/styrene block copolymers or products of hydrogenation thereof; flexible resinous polymers such as syndiotactic 1,2-polybutadiene, poly(vinyl acetate), ethylene/vinyl acetate copolymers, and propylene/α-olefin copolymers; fluorochemical polymers such as poly(vinylidene fluoride), polytetrafluoroethylene, fluorinated poly(vinylidene fluoride), and polytetrafluoroethylene/ethylene copolymers; and polymer compositions having the property of conducting alkali metal ions (especially lithium ions). One of these may be used alone, or any desired combination of two or more thereof in any desired proportion may be used.

The kind of the solvent to be used for forming a slurry is not particularly limited as long as it is a solvent in which the active material and binder and the thickener and conductive material which are optionally used according to need can be dissolved or dispersed. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water and alcohols. Examples of the organic solvent include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, propylene oxide, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane. Especially when an aqueous solvent is used, it is preferred to add a dispersant or the like in combination with the thickener described above and prepare a slurry using a latex of, e.g., SBR. One of such ingredients may be used alone, or any desired combination of two or more thereof in any desired proportion may be used.

The proportion of the binder to the active material is preferably 0.1% by mass or higher, especially preferably 0.5% by mass or higher, more preferably 0.6% by mass or higher. The upper limit thereof is generally 20% by mass or lower, preferably 15% by mass or lower, more preferably 10% by mass or lower, even more preferably 8% by mass or lower. In case where the binder amount exceeds the upper limit of that range, the proportion of the binder which does not contribute to battery capacity increases and this may lead to a decrease in battery capacity. When the binder amount is small than the lower limit, there are cases where the negative electrode has a reduced strength. Especially when the binder comprises a rubbery polymer represented by SBR as the main component, the proportion of this binder to the active material is generally 0.1% by mass or higher, preferably 0.5% by mass or higher, more preferably 0.6% by mass or higher. The upper limit thereof is generally 5% by mass or lower, preferably 3% by mass or lower, more preferably 2% by mass or lower. In the case where the binder comprises a fluorochemical polymer represented by poly(vinylidene fluoride) as the main component, the proportion of this binder to the active material is generally 1% by mass or higher, preferably 2% by mass or higher, more preferably 3% by mass or higher. The upper limit thereof is generally 15% by mass or lower, preferably 10% by mass or lower, more preferably 8% by mass or lower.

A thickener is used generally for the purpose of regulating the slurry viscosity. The thickener is not particularly limited. Examples thereof include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, poly(vinyl alcohol), oxidized starch, phosphorylated starch, casein, and salts of these. One of these thickeners may be used alone, or any desired combination of two or more thereof in any desired proportion may be used. In the case where such a thickener is further added, the proportion of the thickener to the active material is generally 0.1% by mass or higher, preferably 0.5% by mass or higher, more preferably 0.6% by mass or higher. The upper limit thereof is generally 5% by mass or lower, preferably 3% by mass or lower, more preferably 2% by mass or lower. When the proportion thereof is lower than the lower limit of that range, there are cases where applicability decreases considerably. Proportions thereof exceeding the upper limit result in a reduced proportion of the active material in the negative-electrode active-material layer, and this may pose a problem that battery capacity decreases and a problem that resistance among the particles of the negative-electrode active material increases.

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(18) Orientation Ratio in Electrode Plate

The orientation ratio in the electrode plate is preferably 0.001 or higher, more preferably 0.005 or higher, especially preferably 0.01 or higher. The upper limit thereof is up to 0.67, which is a theoretical value. When the orientation ratio therein is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

An examination for determining the orientation ratio in the electrode plate is as follows. The negative electrode which has been pressed to a target density is examined by X-ray diffractometry to determine the orientation ratio of the active material in this electrode. Although specific techniques therefor are not particularly limited, a standard method is as follows. The peaks attributable to the (110) diffraction and (004) diffraction of the carbon obtained by X-ray diffractometry are subjected to peak separation by fitting with asymmetric Pearson VII as a profile function. Thus, the integrated intensities of the (110) diffraction and (004) diffraction peaks are calculated. From the integrated intensities obtained, the ratio represented by (integrated intensity of (110) diffraction)/(integrated intensity of (004) diffraction) is calculated. The active-material orientation ratio for the electrode thus calculated is defined as the orientation ratio in the electrode plate.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

Sample preparation:

The electrode is fixed to a glass plate with a double-faced pressure-sensitive adhesive tape having a thickness of 0.1 mm.

(19) Impedance

At the time when the battery in a discharged state has been charged to 60% of its nominal capacity, the resistance of the negative electrode is preferably 100Ω or lower, more preferably 50Ω or lower, especially preferably 20Ω or lower and/or the double-layer capacity of the negative electrode is preferably 1×10 −6 F or higher, more preferably 1×10 −5 F, especially preferably 1×10 −4 F. This range is preferred because satisfactory output characteristics are obtained.

The resistance and double-layer capacity of the negative electrode are determined by the following procedure. The lithium secondary battery to be examined is one which, when charged at a current at which the nominal capacity can be charged over 5 hours, subsequently kept for 20 minutes in the state of being neither charged nor discharged, and then discharged at a current at which the nominal capacity can be discharged over 1 hour, has a capacity of at least 80% of the nominal capacity. This lithium secondary battery in a discharged state is charged to 60% of the nominal capacity at a current at which the nominal capacity can be charged over 5 hours. Immediately thereafter, the lithium secondary battery is transferred to a gloved box filled with an argon atmosphere. In this gloved box, the lithium secondary battery is rapidly disassembled and taken out while preventing the negative electrode from suffering discharge or short-circuiting. In the case where this negative electrode is a double-sided electrode, the electrode active material on one side is stripped off without marring the electrode active material on the other side. Two disks of 12.5 mmϕ are punched out of this negative electrode, and are superposed through a separator so that the active-material sides rightly face each other. Sixty microliters of the nonaqueous electrolyte which has been used in the battery is dropped onto the separator and between the two negative electrodes, and the negative electrodes and separator are brought into tight contact with each other. While keeping this assemblage isolated from the surrounding air, the current collectors of the respective negative electrodes are electrically connected to each other and the assemblage is examined by the alternating-current impedance method. In the examination, the complex impedance is measured at a temperature of 25° C. in a frequency region of 10 −2 -10 3 Hz to determine a Cole-Cole plot. The circular arc for the negative-electrode resistance component in the plot is approximated to a semicircle to determine the surface resistance (R) and the double-layer capacity (Cdl).

(20) Area and Thickness of Negative-Electrode Plate

The area of the negative-electrode plate is not particularly limited. However, the negative-electrode plate is designed to be slightly larger than the positive-electrode plate facing it so that the positive-electrode plate does not protrude outward from the negative-electrode plate. From the standpoints of cycle life in repetitions of charge/discharge and inhibition of deterioration caused by high-temperature storage, it is preferred to regulate the area of the negative electrode so as to be as close as possible to the area of the positive electrode. This is because such negative-electrode area heightens the proportion of electrodes which function more evenly and effectively and thereby improves properties. Especially when the battery is to be used at a high current, this electrode area design is important.

The thickness of the negative-electrode plate is designed so as to be suitable for the positive-electrode plate to be used, and is not particularly limited. However, the thickness of the mix layer, excluding the thickness of the core metal foil, is generally 15 μm or larger, preferably 20 μm or larger, more preferably 30 μm or larger. The upper limit thereof is generally 150 μm or smaller, preferably 120 μm or smaller, more preferably 100 μm or smaller.

Negative electrode [1], i.e., “a negative electrode containing as a negative-electrode active material two or more carbonaceous substances differing in crystallinity”, for use in a lithium secondary battery of the invention will be explained below.

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[Negative Electrode [1]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [1] is described below.

[[Constitution]]

The negative-electrode active material for use in negative electrode [1] in a lithium secondary battery of the invention is characterized by comprising two or more carbonaceous substances differing in crystallinity. The term “comprising two or more carbonaceous substances differing in crystallinity” herein means that carbonaceous substances differing in crystallinity coexist in the negative electrode. The state in which these carbonaceous substances coexist is not limited. Namely, particles of one carbonaceous substance and particles of another may be present as a mixture of these, or the carbonaceous substances may be contained in one secondary particle. Furthermore, a mixture of both is possible. The negative-electrode active material preferably is one which comprises a composite carbonaceous material comprising two or more carbonaceous substances differing in crystallinity. Also preferred is one which comprises the composite carbonaceous material and, as a minor ingredient, one or more carbonaceous substances (carbonaceous materials) differing in property from the carbonaceous substances constituting the composite carbonaceous material.

The term “contained in one secondary particle” means, for example, the state in which the carbonaceous substances differing in crystallinity are restrained by bonding, the state in which the substances are physically restrained, or the state in which the substances retain a shape by means of electrostatic restraint. The term “physically restrained” herein means a state such as that in which one of the carbonaceous substances differing in crystallinity is surrounded by the other or the state in which one is caught by the other. The term “electrostatic restraint” means the state in which one of the carbonaceous substances differing in crystallinity is adherent to the other by means of electrostatic energy. Furthermore, the term “the state in which the substances are restrained by bonding” means chemical bonding by hydrogen bonds, covalent bonds, ionic bonds, etc.

Of those, the state in which the surface of a core carbonaceous substance at least partly has an interface where a coating layer differing in crystallinity is bonded to the core carbonaceous substance is advantageous because resistance in lithium movement between the carbonaceous substances differing in crystallinity is low. The coating layer is not limited as to whether it is one formed by the bonding of an externally supplied material and/or of a product of alteration thereof or one formed by the alteration of a surface-part material of a carbonaceous substance. The term “coating” herein means that the interface between the coating layer and the surface of the carbonaceous substance at least partly has chemical bonds and the coating layer is (1) in the state of covering the whole surface, (2) in the state of locally covering the carbonaceous particles, (3) in the state of selectively covering part of the surface, or (4) in the state of being present in ultrafine regions including chemical bonds. At the interface, crystallinity may change continuously or discontinuously.

It is preferred that the composite carbonaceous material should be one which includes a particulate carbonaceous substance and has an interface where the particulate carbonaceous substance is covered with and/or bonded to a carbonaceous substance differing in crystallinity from the particulate carbonaceous substance, the interface changing in crystallinity discontinuously and/or continuously. There are no limitations on which of the “particulate carbonaceous substance” and the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” has higher crystallinity. However, from the standpoint of producing the effects of the invention, it is preferred that the particulate carbonaceous substance should have higher crystallinity.

A difference in crystallinity herein is judged based on a difference in interplanar spacing (d002) for the (002) planes, difference in Lc, or difference in La, each determined by wide-angle X-ray diffractometry. From the standpoint of producing the effects of the invention, the difference in crystallinity is preferably 0.0002 nm or larger in terms of (d002), or 1 nm or larger in terms of La, or 1 nm or larger in terms of Lc. The difference in (d002), among those ranges, is preferably 0.0005 nm or larger, more preferably 0.001 nm or larger, even more preferably 0.003 nm or larger. The upper limit thereof is generally 0.03 nm or smaller, preferably 0.02 nm or smaller. When the difference therein is smaller than the lower limit of that range, there are cases where the effect of the difference in crystallinity becomes low. On the other hand, in case where the difference therein exceeds the upper limit of that range, the part having lower crystallinity tends to be too low in crystallinity and there is a possibility that the reduced crystallinity might increase irreversible capacity. The difference in La or Lc, among those ranges, is preferably 2 nm or larger, more preferably 5 nm or larger, even more preferably 10 nm or larger. In graphites, values larger than 100 nm cannot be specified because definition is generally impossible. When the difference in La or Lc is smaller than the lower limit of that range, there are cases where the effect of the difference in crystallinity becomes low.

As stated above, the composite carbonaceous material may comprise a particulate carbonaceous substance and a carbonaceous substance which differs in crystallinity from the particulate carbonaceous substance and which covers and/or is bonded to the particulate carbonaceous substance. In this material, either of the “particulate carbonaceous substance” and the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” may be a graphitic carbonaceous substance and the other may be a lowly crystalline carbonaceous substance. It is preferred that the “particulate carbonaceous substance” should be a graphitic carbonaceous substance and the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” be a lowly crystalline carbonaceous substance.

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[[[Particulate Carbonaceous Substance]]]

The particulate carbonaceous substance preferably is a graphitic carbonaceous substance comprising a natural graphite and/or an artificial graphite or is one comprising at least one member selected from the group consisting of the following (a), (b), and (c), which have slightly lower crystallinity than those graphites:

(a) a product of organic-substance pyrolysis selected from the group consisting of coal coke, petroleum coke, furnace black, acetylene black, and pitch-derived carbon fibers; (b) a product of the carbonization of the gas of an organic substance; and (c) a carbonaceous substance obtained by partly or wholly graphitizing (a) or (b).

[[[[Graphitic Carbonaceous Substance]]]]

The particulate carbonaceous substance preferably is a graphitic carbonaceous substance comprising a natural graphite and/or an artificial graphite. The term graphitic carbonaceous substance means any of various carbonaceous substances which have such high crystallinity that the interplanar spacing (d002) for the (002) planes thereof as determined by wide-angle X-ray diffractometry is smaller than 0.340 nm.

Preferred examples of the graphitic carbonaceous substance include powders selected from natural graphites, artificial graphites, products obtained by the mechanical pulverization or re-heat treatment of these graphites, products of the re-heat treatment of an expanded graphite, and highly purified products obtained from those graphites. Preferred examples of the artificial graphites are ones obtained by graphitizing one or more organic substances selected from coal tar pitch, coal-derived heavy oil, topping residues, petroleum-derived heavy oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylenes, poly(vinyl chloride), poly(vinyl alcohol), polyacrylonitrile, poly(vinyl butyral), natural polymers, poly(phenylene sulfide), poly(phenylene oxide), furfuryl alcohol resins, phenol-formaldehyde resins, imide resins, and the like at a heat-treating temperature of generally about from 2,500° C. to 3,200° C. and powdering the graphitized substances by an appropriate pulverizer.

(Properties of Graphitic Carbonaceous Substance)

It is desirable that the graphitic carbonaceous substance should satisfy any one of the following properties (1) to (11) or simultaneously satisfy two or more thereof.

(1) X-Ray Parameter

The graphitic carbonaceous substance preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The lower limit of the value of d is smaller than 0.340 nm according to the definition, and is preferably 0.337 nm or smaller. When the value of d is too large, there are cases where crystallinity decreases to increase initial irreversible capacity. On the other hand, 0.335 is a theoretical value for graphites. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 100 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to increase initial irreversible capacity.

(2) Ash Content

The ash content of the graphitic carbonaceous substance is preferably 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole graphitic carbonaceous substance. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous substance. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous material necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the graphitic carbonaceous substance, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 100 μm or smaller, preferably 50 μm or smaller, more preferably 40 μm or smaller, even more preferably 30 μm or smaller, especially preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a carbonaceous substance is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

(4) Raman R Value, Raman Half-Value Width

The R value of the graphitic carbonaceous substance as determined by the argon ion laser Raman spectroscopy is generally 0.01 or higher, preferably 0.03 or higher, more preferably 0.10 or higher. The upper limit thereof is generally 0.60 or lower, preferably 0.40 or lower. When the R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

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The Raman half-value width around 1,580 cm −1 of the graphitic carbonaceous substance is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 60 cm −1 or smaller, preferably 45 cm −1 or smaller, more preferably 40 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A around 1,580 cm −1 and the intensity I B of a peak P B around 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the carbon material. Furthermore, the half-value width of the peak P A around 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the carbon material.

Conditions for this Raman spectroscopy are as follows.

Wavelength of argon ion laser: 514.5 nm Laser power on sample: 15-25 mW Resolution: 10-20 cm −1 Examination range: 1,100-1,730 cm −1 Analysis for R value and half-value width: background processing Smoothing: simple average; convolution, 5 points

(5) BET Specific Surface Area

The specific surface area of the graphitic carbonaceous substance, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this graphitic carbonaceous substance as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this graphitic carbonaceous substance as a negative-electrode material is apt to result in enhanced reactivity with the electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

BET specific surface area is defined as a value measured with a surface area meter (e.g., a fully automatic surface area measuring apparatus manufactured by Ohukura Riken Co., Ltd.) by preliminarily drying a sample at 350° C. for 15 minutes in a nitrogen stream and then measuring the specific surface area thereof by the gas-flowing nitrogen adsorption BET one-point method using a nitrogen/helium mixture gas precisely regulated so as to have a nitrogen pressure of 0.3 relative to atmosphere pressure.

(6) Pore Distribution

In the graphitic carbonaceous substance, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. On the other hand, when the amount thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The total pore volume is preferably 0.1 mL/g or larger, more preferably 0.25 mL/g or larger. The upper limit thereof is generally 10 mL/g or smaller, preferably 5 mL/g or smaller, more preferably 2 mL/g or smaller. When the total pore volume exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the total pore volume is smaller than the lower limit, there are cases where the dispersing effect of a thickener or binder in electrode plate formation is not obtained.

The average pore diameter of the graphitic carbonaceous substance is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. On the other hand, when the average pore diameter thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease.

As an apparatus for the mercury porosimetry is used a mercury porosimeter (Autopore 9520, manufactured by Micromeritics Corp.). About 0.2 g of a sample (negative-electrode material) is weighed out and placed in a powder cell and this cell is closed. The sample in the cell is pretreated by degassing it at room temperature under vacuum (50 μmHg or lower) for 10 minutes. Subsequently, the pressure in the cell is reduced to 4 psia (about 28 kPa) and mercury is introduced thereinto. The internal pressure is stepwise elevated from 4 psia (about 28 kPa) to 40,000 psia (about 280 MPa) and then lowered to 25 psia (about 170 kPa). The number of steps in the pressure elevation is 80 or larger. In each step, the amount of mercury intruded is measured after an equilibrium time of 10 seconds. A pore distribution is calculated from the mercury intrusion curve thus obtained, using the Washburn equation. For the calculation, the surface tension (γ) and contact angle (ψ) of mercury are taken as 485 dyne/cm and 140°, respectively. The average pore diameter used is the pore diameter corresponding to a cumulative pore volume of 50%.

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(7) Roundness

With respect to the degree of sphericity of the graphitic carbonaceous substance, the roundness of the particles having a particle diameter in the range of 3-40 μm is preferably 0.1 or higher, especially preferably 0.5 or higher, more preferably 0.8 or higher, even more preferably 0.85 or higher, most preferably 0.9 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics. Roundness is defined by the following equation. When a particle has a roundness of 1, this particle theoretically is a true sphere.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

The value of roundness is determined, for example, with a flow type particle image analyzer (e.g., FPIA, manufactured by Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample in a 0.2% by mass aqueous solution (about 50 mL) of poly(oxyethylene (20)) sorbitan monolaurate as a surfactant, propagating an ultrasonic wave of 28 kHz to the dispersion for 1 minute at an output of 60 W, and then examining particles having a particle diameter in the range of 3-40 μm with the analyzer having a detection range set at 0.6-400 μm.

Methods for improving roundness are not particularly limited. However, a graphitic carbonaceous substance in which the particles have been rounded by a rounding treatment is preferred because it gives an electrode in which the interstices among particles are uniform in shape. Examples of the rounding treatment include: a method in which a shear force or compressive force is applied to thereby mechanically make the shape of the particles close to sphere; and a method of mechanical/physical treatment in which fine particles are aggregated into particles by means of the bonding force of a binder or of the fine particles themselves.

(8) True Density

The true density of the graphitic carbonaceous substance is generally 2 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the graphitic carbonaceous substance is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

(9) Tap Density

The tap density of the graphitic carbonaceous substance desirably is generally 0.1 g/cm 3 or higher, preferably 0.5 g/cm 3 or higher, more preferably 0.7 g/cm 3 or higher, especially preferably 0.9 g/cm 3 or higher. The upper limit thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where this graphitic carbonaceous substance, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining the resultant bulk density. This bulk density is defined as the tap density.

(10) Orientation Ratio (Powder)

The orientation ratio of the graphitic carbonaceous substance is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

Orientation ratio is determined by X-ray diffractometry. The peaks attributable to the (110) diffraction and (004) diffraction of the carbon obtained by X-ray diffractometry are subjected to peak separation by fitting with asymmetric Pearson VII as a profile function. Thus, the integrated intensities of the (110) diffraction and (004) diffraction peaks are calculated. From the integrated intensities obtained, the ratio represented by (integrated intensity of (110) diffraction)/(integrated intensity of (004) diffraction) is calculated. This ratio is defined as the active-material orientation ratio.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

(11) Aspect Ratio (Powder)

The aspect ratio of the graphitic carbonaceous substance is theoretically 1 or higher. The upper limit thereof is generally 10 or lower, preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this graphitic carbonaceous substance causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

The aspect ratio of a carbon material particle is represented by A/B, wherein A is the length of the longest axis of the particle in a three-dimensional examination and B is the length of the shortest axis perpendicular to that axis. The examination of carbon particles is made with a scanning electron microscope capable of enlargement examination. Fifty are arbitrarily selected from graphite particles fixed to an edge face of a metal having a thickness of 50 μm or smaller, and each particle is examined for A and B while rotating or inclining the stage to which the sample is fixed. The average of the A/B values is determined.

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[[[[Lowly Crystalline Carbonaceous Substance]]]]

The term lowly crystalline carbonaceous substance means a carbonaceous substance which has such low crystallinity that the interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry is 0.340 nm or larger.

(Composition of Lowly Crystalline Carbonaceous Substance)

The “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” preferably is a carbonaceous substance having lower crystallinity than the particulate carbonaceous substance. It preferably is a product of the carbonization of the following (d) or (e) (d) an organic substance capable of carbonization which is selected from the group consisting of coal-derived heavy oil, straight-run heavy oil, petroleum-derived cracked heavy oil, aromatic hydrocarbons, nitrogen-ring compounds, sulfur-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins; and (e) a solution obtained by dissolving any of these organic substances capable of carbonization in a low-molecular organic solvent.

The coal-derived heavy oil preferably is any of coal tar pitches ranging from soft pitch to hard pitch, dry distillation/liquefaction oil, and the like. The straight-run heavy oil preferably is any of topping residues, vacuum distillation residues, and the like. The petroleum-derived cracked heavy oil preferably is, for example, ethylene tar as a by-product of the thermal cracking of crude oil, naphtha, etc. The aromatic hydrocarbons preferably are acenaphthylene, decacyclene, anthracene, phenanthrene, and the like. The nitrogen-ring compounds preferably are phenazine, acridine, and the like. The sulfur-ring compounds preferably are thiophene, bithiophene, and the like. The polyphenylenes preferably are biphenyl, terphenyl, and the like. The organic synthetic polymers preferably are poly(vinyl chloride), poly(vinyl alcohol), poly(vinyl butyral), substances obtained by insolubilizing these compounds, polyacrylonitrile, polypyrrole, polythiophene, polystyrene, and the like. The natural polymers preferably are, for example, polysaccharides such as cellulose, lignin, mannan, poly(galacturonic acid), chitosan, saccharose, and the like. The thermoplastic resins preferably are poly(phenylene sulfide), poly(phenylene oxide), and the like. The thermosetting resins preferably are furfuryl alcohol resins, phenol-formaldehyde resins, imide resins, and the like.

Although the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” preferably is a product of the carbonization of the “organic substance capable of carbonization” described above, it also preferably is a product of the carbonization of a solution obtained by dissolving the “organic substance capable of carbonization” in a low-molecular organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane. It is furthermore preferred that the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” should be a product of the carbonization of coal coke or petroleum coke.

It is especially preferred that the (d) or (e) should be liquid. Namely, to cause carbonization to proceed in a liquid phase is preferred from the standpoint of forming an interface between the lowly crystalline carbonaceous substance and a graphitic carbonaceous substance part.

(Properties of Lowly Crystalline Carbonaceous Substance)

It is desirable that the lowly crystalline carbonaceous substance should satisfy any one of the following properties (1) to (5) or simultaneously satisfy two or more thereof. Furthermore, one lowly crystalline carbonaceous substance having such properties may be used alone, or any two or more such carbonaceous substances may be used in combination in any desired proportion.

(1) X-Ray Parameter

With respect to the lowly crystalline carbonaceous substance part, the value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is 0.340 nm or larger according to the definition. However, the value of d thereof is preferably 0.340 nm or larger, especially preferably 0.341 nm or larger. The upper limit thereof is preferably 0.380 nm or smaller, especially preferably 0.355 nm or smaller, more preferably 0.350 nm or smaller. When the value of d is too large, there are cases where the surface of this carbonaceous substance has considerably low crystallinity to increase irreversible capacity. When the value of d is too small, there are cases where the effect of improving suitability for charge which is obtained by disposing a lowly crystalline carbonaceous substance on the surface is lessened to reduce the effects of the invention. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 1 nm or larger, preferably 1.5 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there are cases where crystallinity decreases to increase initial irreversible capacity.

(2) Ash Content

The ash content of the lowly crystalline carbonaceous substance part may be 1% by mass or lower and is especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole composite carbonaceous material. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous material. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

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(4) Raman R Value, Raman Half-Value Width

The R value of the lowly crystalline carbonaceous substance part as determined by the argon ion laser Raman spectroscopy is generally 0.5 or higher, preferably 0.7 or higher, more preferably 0.9 or higher. The upper limit thereof is generally 1.5 or lower, preferably 1.2 or lower. When the R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a composite carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the lowly crystalline carbonaceous substance part is not particularly limited. However, the half-value width thereof is generally 40 cm −1 or larger, preferably 50 cm −1 or larger. The upper limit thereof is generally 100 cm −1 or smaller, preferably 90 cm −1 or smaller, more preferably 80 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a composite carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

(4) True Density

The true density of the lowly crystalline carbonaceous substance part is generally 1.4 g/cm 3 or higher, preferably 1.5 g/cm 3 or higher, more preferably 1.6 g/cm 3 or higher, even more preferably 1.7 g/cm 3 or higher. The upper limit thereof is generally 2.1 g/cm 3 or lower, preferably 2 g/cm 3 or lower. In case where the true density thereof exceeds the upper limit of that range, there is a possibility that suitability for charge might be impaired. When the true density thereof is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

(5) Orientation Ratio

The orientation ratio of the lowly crystalline carbonaceous substance part is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower.

Orientation ratios thereof lower than the lower limit of that range are undesirable because high-density charge/discharge characteristics decrease. Orientation ratio is determined by X-ray diffractometry. The peaks attributable to the (110) diffraction and (004) diffraction of the carbon obtained by X-ray diffractometry are subjected to peak separation by fitting with asymmetric Pearson VII as a profile function. Thus, the integrated intensities of the (110) diffraction and (004) diffraction peaks are calculated. From the integrated intensities obtained, the ratio represented by (integrated intensity of (110) diffraction)/(integrated intensity of (004) diffraction) is calculated. This ratio is defined as the electrode active-material orientation ratio.

[[[Composite Carbonaceous Material]]]

The composite carbonaceous material for use in negative electrode [1] in a lithium secondary battery of the invention preferably comprises a “particulate carbonaceous substance” and a “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” as stated above. In this case, either of these substances may be a graphitic carbonaceous substance and the other may be a lowly crystalline carbonaceous substance. Preferably, the “particulate carbonaceous substance” is a graphitic carbonaceous substance and the “carbonaceous substance differing in crystallinity from the particulate carbonaceous substance” is a lowly crystalline carbonaceous substance.

In the composite carbonaceous material, the proportion of the graphitic carbonaceous substance to the lowly crystalline carbonaceous substance by mass is preferably 50/50 or higher, more preferably 80/20 or higher, especially preferably 90/10 or higher, and is preferably 99.9/0.1 or lower, more preferably 99/1 or lower, especially preferably 98/2 or lower. When the proportion thereof exceeds the upper limit of that range, there are cases where the possession of the two kinds of crystalline carbonaceous substances does not produce its effect. In case where the proportion thereof is lower than the lower limit of that range, initial irreversible capacity tends to increase and this may pose a problem concerning battery design. It is preferred that the graphitic carbonaceous substance should account for 50% by mass or more of the whole composite carbonaceous material.

(Properties of Composite Carbonaceous Material)

It is desirable that the composite carbonaceous material should satisfy any one of the following properties (1) to (11) or simultaneously satisfy two or more thereof. Furthermore, one composite carbonaceous material having such properties may be used alone, or any two or more such composite carbonaceous materials may be used in combination in any desired proportion.

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(1) X-Ray Parameter

The composite carbonaceous material preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The value of d desirably is generally 0.350 nm or smaller, preferably 0.345 nm or smaller, more preferably 0.340 nm or smaller. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 1.5 nm or larger, preferably 3.0 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to increase initial irreversible capacity.

(2) Ash Content

The ash content of the composite carbonaceous material is generally 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole composite carbonaceous material. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole composite carbonaceous material. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this composite carbonaceous material necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the composite carbonaceous material, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 100 μm or smaller, preferably 50 μm or smaller, more preferably 40 μm or smaller, even more preferably 30 μm or smaller, especially preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a composite carbonaceous material is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

(4) Raman R Value, Raman Half-Value Width

The R value of the composite carbonaceous material as determined by the argon ion laser Raman spectroscopy is generally 0.03 or higher, preferably 0.10 or higher, more preferably 0.15 or higher. The upper limit thereof may be 0.60 or lower and is preferably 0.50 or lower. When the R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a composite carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the composite carbonaceous material is not particularly limited. However, the half-value width thereof is generally 15 cm −1 or larger, preferably 20 cm −1 or larger. The upper limit thereof is generally 70 cm −1 or smaller, preferably 60 cm −1 or smaller, more preferably 50 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. In addition, when a coating fluid containing such a composite carbonaceous material is applied to a current collector and the resultant coating is pressed to heighten the density of the negative electrode, then the crystals are apt to orient in directions parallel to the electrode plate and this may lead to a decrease in load characteristics. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

(5) BET Specific Surface Area

The specific surface area of the composite carbonaceous material, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this composite carbonaceous material as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this composite carbonaceous material as a negative-electrode material is apt to result in enhanced reactivity with the electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

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(6) Pore Distribution

In the composite carbonaceous material, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the amount thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The average pore diameter of the composite carbonaceous material is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 80 μm or smaller, preferably 50 μm or smaller, more preferably 20 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. When the average pore diameter thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease.

(7) Roundness

With respect to the degree of sphericity of the composite carbonaceous material, the roundness of the particles having a particle diameter in the range of 3-40 μm is preferably 0.85 or higher, more preferably 0.87 or higher, even more preferably 0.9 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics.

(8) True Density

The true density of the composite carbonaceous material is generally 1.9 g/cm 3 or higher, preferably 2 g/cm 3 or higher, more preferably 2.1 g/cm 3 or higher, even more preferably 2.2 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the composite carbonaceous material is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

(9) Tap Density

The tap density of the composite carbonaceous material desirably is generally 0.1 g/cm 3 or higher, preferably 0.5 g/cm 3 or higher, more preferably 0.7 g/cm 3 or higher, especially preferably 1 g/cm 3 or higher. The tap density thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where this composite carbonaceous material, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain. Tap density is determined by the same method as described above and is defined as described therein.

(10) Orientation Ratio (Powder)

The orientation ratio of the composite carbonaceous material is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

(11) Aspect Ratio (Powder)

The aspect ratio of the composite carbonaceous material is theoretically 1 or higher. The upper limit thereof may be 10 or lower and is preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this composite carbonaceous material causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

(Processes for Producing Composite Carbonaceous Material)

Processes for producing the composite carbonaceous material are not particularly limited. Examples thereof include the following methods.

Methods usable for combining a graphitic carbonaceous substance with a lowly crystalline carbonaceous substance include: a method in which a carbon precursor for obtaining a lowly crystalline carbonaceous substance is used as it is and a mixture of the carbon precursor and a powder of a graphitic carbonaceous substance is heat-treated to obtain the composite powder; a method which comprises partly carbonizing the carbon precursor to produce a powder of a lowly crystalline carbonaceous substance beforehand, mixing this powder with a powder of a graphitic carbonaceous substance, and heat-treating the mixture to combine the two substances; and a method which comprises producing the powder of a lowly crystalline carbonaceous substance beforehand, mixing a powder of a graphitic carbonaceous substance, the powder of a lowly crystalline carbonaceous substance, and a carbon precursor, and heat-treating the mixture to combine these substances. In the latter two methods, in which a powder of a lowly crystalline carbonaceous substance is prepared beforehand, it is preferred that the particles of the lowly crystalline carbonaceous substance to be used should have an average particle diameter not larger than one-tenth the average particle diameter of the particles of the graphitic carbonaceous substance. Also usable is a method in which the lowly crystalline carbonaceous substance produced beforehand is mixed with a graphitic carbonaceous substance while applying mechanical energy thereto by, e.g., pulverization to thereby impart thereto a structure in which one is surrounded by the other or a structure in which one is electrostatically adherent to the other.

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In a preferred process, a mixture of particles of a graphitic carbonaceous substance and a carbon precursor is heated to obtain an intermediate, or a mixture of particles of a graphitic carbonaceous substance and particles of a lowly crystalline carbonaceous substance is mixed with a carbon precursor and this mixture is heated to obtain an intermediate. Thereafter, the intermediate is carbonized/heat-treated and pulverized to finally obtain a composite carbonaceous material comprising the particles of a graphitic carbonaceous substance and a lowly crystalline carbonaceous substance combined therewith.

This process for obtaining a composite carbonaceous material is divided into the following four steps.

First step: Either particles of a graphitic carbonaceous substance or a mixture of particles of a graphitic carbonaceous substance and particles of a lowly crystalline carbonaceous substance is mixed with a carbon precursor for particles of a lowly crystalline carbonaceous substance and optionally with a solvent by means of any of various commercial mixers, kneaders, etc. to obtain a mixture.

Second step: The mixture is heated to obtain an intermediate from which the solvent and any volatile ingredient generating from the carbon precursor have been removed. According to need, this heating may be conducted while stirring the mixture. Even when a volatile ingredient remains, this poses no problem because it will be removed in the subsequent step, i.e., the third step.

Third step: The mixture or intermediate is heated to a temperature of from 400° C. to 3,200° C. in an inert gas atmosphere such as nitrogen gas, carbon dioxide gas, or argon gas to obtain a graphite/lowly crystalline carbonaceous substance composite.

Fourth step: The composite is subjected to powder processing such as pulverization, disaggregation, classification, etc. according to need.

Of those steps, the second step and the fourth step can be omitted in some cases, and the fourth step may be conducted before the third step. However, in the case where the fourth step was conducted before the third step, powder processing such as pulverization, disaggregation, classification, etc. is conducted again according to need to obtain a composite carbonaceous material.

With respect to conditions for the heat treatment in the third step, heat hysteresis temperature conditions are important. The lower limit of the temperature is generally 400° C. or higher, preferably 900° C. or higher, although it changes slightly depending on the kind of the carbon precursor and the heat hysteresis thereof. On the other hand, with respect to upper-limit temperature, the mixture or intermediate can be heated basically to a temperature at which the carbon precursor does not come to have a structural order higher than the crystal structure of the graphitic carbonaceous substance particles as cores. Consequently, the upper-limit temperature in the heat treatment is generally 3,200° C. or lower, preferably 2,000° C. or lower, more preferably 1,500° C. or lower. Heating rate, cooling rate, heat treatment period, and the like, among conditions of such heat treatment, can be determined at will according to purposes. It is also possible to conduct a heat treatment in a relatively low-temperature region and then heat the work to a given temperature. The reactor to be used in the steps may be of the batch type or continuous type, and one reactor or two or more reactors may be used.

[[Minor-Material Mixing]]

Besides the composite carbonaceous material, one or more carbonaceous substances (carbonaceous materials) differing in carbonaceous-substance property from the composite carbonaceous material may be incorporated into the negative-electrode active material for use in a lithium secondary battery of the invention. Thus, battery performances can be further improved. The term “carbonaceous-substance property” herein means one or more properties selected from X-ray diffraction parameter, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, roundness, and ash content. Preferred embodiments include: one in which the volume-based particle size distribution is not symmetrical about the median diameter; one in which two or more carbon materials differing in Raman R value are contained; and one in which carbon materials differing in X-ray parameter are contained. One example of the effects thereof is that the incorporation of a carbon material, such as a graphite, e.g., a natural graphite or artificial graphite, or an amorphous carbon, e.g., a carbon black such as acetylene black or needle coke, as a sub material serves to reduce electrical resistance. One of these carbon materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion. In the case where such a carbon material is added as a sub material, the amount thereof may be 0.1% by mass or larger and is preferably 0.5% by mass or larger, more preferably 0.6% by mass or larger. The upper limit thereof may be 80% by mass or smaller and is preferably 50% by mass or smaller, more preferably 40% by mass or smaller, even more preferably 30% by mass or smaller. Amounts thereof smaller than the lower limit of that range are undesirable because they result in difficulties in obtaining the effect of improving conductivity. Amounts thereof exceeding the upper limit are undesirable because they lead to an increase in initial irreversible capacity.

[Negative Electrode [1]: Electrode Production]

Negative electrode [1] may be produced by an ordinary method. It can be formed in the same manner as described above. The current collector, thickness ratio between the current collector and the active-material layer, electrode density, binder, electrode-plate orientation ratio, impedance, etc. also are the same as described above.

An explanation will be given below on negative electrode [2] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing as a negative-electrode active material at least one amorphous carbonaceous substance which, when examined by wide-angle X-ray diffractometry, has an interplanar spacing (d002) for the (002) planes of 0.337 nm or larger and a crystallite size (Lc) of 80 nm or smaller and which, in an examination by argon ion laser Raman spectroscopy, has a Raman R value defined as the ratio of the peak intensity at 1, 360 cm −1 to the peak intensity at 1, 580 cm −1 of 0.2 or higher”.

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[Negative Electrode [2]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [2] is described below.

The negative-electrode active material for use in negative electrode [2] in a lithium secondary battery of the invention comprises an amorphous carbonaceous substance satisfying at least the following (a), (b), and (c).

(a) The interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry is 0.337 nm or larger. (b) The crystallite size (Lc) of the (002) planes as determined by wide-angle X-ray diffractometry is 80 nm or smaller. (c) The Raman R value defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 in an examination by argon ion laser Raman spectroscopy (hereinafter often referred to simply as “Raman R value”) is 0.2 or higher.

Although the negative-electrode active material for use in this invention comprises an amorphous carbonaceous substance satisfying at least (a), (b), and (c), the content of this amorphous carbonaceous substance in the whole negative-electrode active material is preferably 10% by mass or higher, especially preferably 50% by mass or higher. More preferably, the content thereof is 100%, i.e., this amorphous carbonaceous substance accounts for the whole negative-electrode active material. Negative-electrode active materials usable with this amorphous carbonaceous substance are not particularly limited, and known negative-electrode active materials such as artificial graphites and natural graphites may be used.

[[Interplanar Spacing (d002) and Lc]]

The interplanar spacing (d002) for the (002) planes of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention, as determined by wide-angle X-ray diffractometry, is 0.337 nm or larger, preferably 0.34 nm or larger. The upper limit thereof is generally 0.39 nm or smaller, preferably 0.38 nm or smaller, more preferably 0.37 nm or smaller, even more preferably 0.36 or smaller, especially preferably 0.35 or smaller. In case where the interplanar spacing (d002) thereof exceeds the upper limit of that range, crystallinity decreases considerably and the resultant decrease in conductivity among the particles becomes not negligible. There are hence cases where the effect of improving short-time high-current-density charge/discharge characteristics is difficult to obtain. On the other hand, when the interplanar spacing (d002) thereof is smaller than the lower limit of that range, there are cases where crystallinity is too high and the effect of improving short-time high-current-density charge/discharge characteristics is difficult to obtain.

The term “interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry” in the invention means the value of d (interplanar spacing) of the lattice planes ((002) planes) as determined by X-ray diffractometry by the method of the Japan Society for Promotion of Scientific Research.

On the other hand, the crystallite size (Lc) for the (002) planes of the amorphous carbonaceous substance as determined by X-ray diffractometry by the method of the Japan Society for Promotion of Scientific Research is 80 nm or smaller, preferably 35 nm or smaller, more preferably 20 nm or smaller, even more preferably 10 nm or smaller. The lower limit thereof is generally 0.1 nm or larger, preferably 1 nm or larger. When the Lc thereof is smaller than the lower limit of that range, there are cases where crystallinity decreases considerably and the resultant decrease in conductivity among the particles becomes not negligible and where the effect of improving suitability for short-time high-current-density charge/discharge is difficult to obtain. On the other hand, when the Lc thereof exceeds the upper limit of that range, there are cases where crystallinity is too high and the effect of improving suitability for short-time high-current-density charge/discharge is difficult to obtain.

[[Raman R Value]]

The Raman R value of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention should be 0.2 or higher, and is preferably 0.5 or higher, especially preferably 0.7 or higher, more preferably 0.8 or higher. The upper limit thereof is preferably 1.5 or lower, more preferably 1.2 or lower. In case where the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and suitability for charge decreases. There are hence cases where the effect of improving suitability for short-time high-current-density charge/discharge is difficult to obtain. On the other hand, in case where the Raman R value thereof exceeds the upper limit of that range, the surface of such particles has considerably reduced crystallinity, resulting in increased contact resistance among the particles. There are hence cases where the effect of improving suitability for short-time high-current-density charge/discharge is difficult to obtain.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A at 1,580 cm −1 and the intensity I B of a peak P B at 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the amorphous carbonaceous substance. Furthermore, the half-value width of the peak P A at 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the amorphous carbonaceous substance.

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Conditions for this Raman spectroscopy are as follows.

Wavelength of argon ion laser: 514.5 nm Laser power on sample: 15-25 mW Resolution: 10-20 cm −1 Examination range: 1,100 cm −1 to 1,730 cm −1 Analysis for Raman R value and Raman half-value width: background processing Smoothing: simple average; convolution, 5 points

The Raman half-value width at 1,580 cm −1 of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is not particularly limited. However, the half-value width thereof is generally 20 cm −1 or larger, preferably 25 cm −1 or larger. The upper limit thereof is generally 150 cm −1 or smaller, preferably 140 cm −1 or smaller. In case where the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and suitability for charge decreases. There is hence a possibility that the effect of improving suitability for short-time high-current-density charge/discharge might be difficult to obtain. On the other hand, in case where the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has considerably reduced crystallinity, resulting in increased contact resistance among the particles. There is hence a possibility that the effect of improving suitability for short-time high-current-density charge/discharge might be difficult to obtain. It is, however, noted that there are cases where the Raman half-value widths of some peaks cannot be judged because of the shapes of the peaks.

Although the amorphous carbonaceous substance for use in this invention satisfies the requirements concerning interplanar spacing (d002), crystallite size (Lc), and Raman R value described above, it is preferred from the standpoint of battery performance balance that the carbonaceous substance should further satisfy any one of the following requirements or simultaneously satisfy two or more thereof. It is especially preferred that any one of or two or more of true density, H/C value, O/C value, tap density, BET specific surface area, pore volume in the range of 0.01 μm to 1 μm, ash content, and volume-average particle diameter, among those requirements, should be simultaneously satisfied.

[[True Density]]

The true density of the amorphous carbonaceous substance is generally 2.22 g/cm 3 or lower, preferably 2.2 g/cm 3 or lower, more preferably 2.1 g/cm 3 or lower, even more preferably 2.0 g/cm 3 or lower. The lower limit thereof is generally 1.4 g/cm 3 or higher, preferably 1.5 g/cm 3 or higher, more preferably 1.6 g/cm 3 or higher, even more preferably 1.7 g/cm 3 or higher, especially preferably 1.8 g/cm 3 or higher. When the true density thereof is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. When the true density thereof exceeds the upper limit of that range, there are cases where this carbon has too high crystallinity and the effect of improving suitability for short-time high-current-density charge/discharge is difficult to obtain.

In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

[[O/C Value]]

The upper limit of the atomic amount ratio O/C value of the amorphous carbonaceous substance is generally 0.15 or lower, preferably 0.1 or lower, more preferably 0.05 or lower, even more preferably 0.03 or lower. The lower limit thereof is generally 0 or higher, preferably 0.01 or higher.

The term O/C value means the ratio of the molar concentration of oxygen atoms in the amorphous carbonaceous substance to the molar concentration of carbon atoms therein. It is an index to the amount of functional groups, such as carboxyl, phenolic hydroxyl, and carbonyl groups, present in the substance. An amorphous carbonaceous substance having a high O/C value frequently has an oxygen-containing functional group bonded to, e.g., an edge face of the carbon crystallite. When the O/C value of the amorphous carbonaceous substance exceeds the upper limit of that range, there are cases where irreversible capacity increases.

[[H/C Value]]

The upper limit of the atomic amount ratio H/C value of the amorphous carbonaceous substance is generally 0.3 or lower, preferably 0.15 or lower, more preferably 0.1 or lower, even more preferably 0.08 or lower. The lower limit thereof is generally 0 or higher, preferably 0.01 or higher.

The term H/C value means the ratio of the molar concentration of hydrogen atoms in the amorphous carbonaceous substance to the molar concentration of carbon atoms therein. It is an index to the amount of hydrogen present in an edge face of the crystallite of the amorphous carbonaceous substance. An amorphous carbonaceous material having a high H/C value frequently has a large hydrogen amount relative to carbon amount in, e.g., edge faces of the carbon crystallites in the particle surface. When the H/C value of the amorphous carbonaceous substance exceeds the upper limit of that range, there are cases where irreversible capacity increases.

The terms “O/C value” and “H/C value” in the invention are values determined by the following CHN elemental analysis.

[[CHN Elemental Analysis]]

An amorphous carbonaceous substance to be examined was vacuum-dried at 120° C. for about 15 hours and then dried at 100° C. for 1 hour on a hot plate in a dry box. Subsequently, a sample was taken out of the dried carbonaceous substance and placed in an aluminum cup in an argon atmosphere, and this sample was heat-treated. The carbon content, hydrogen content, and nitrogen content were determined respectively from the weights of the CO2 gas, H2O, and NO2 generated by the combustion. The inorganic content was determined from the weight of the residue which remained after the combustion. The oxygen amount was determined by subtracting the carbon content, hydrogen content, nitrogen content, and inorganic content from the whole weight. From these values, the number of moles of each element was calculated. The O/C value and H/C value were determined from the numbers of moles of the elements contained, using the following equations.

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O/C value=(number of moles of oxygen contained)/(number of moles of carbon contained)

H/C value(number of moles of hydrogen contained)/(number of moles of carbon contained)

[[Tap Density]]

The tap density of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is preferably 0.1 g/cm 3 or higher, more preferably 0.2 g/cm 3 or higher, even more preferably 0.5 g/cm 3 or higher, especially preferably 0.7 g/cm 3 or higher. The upper limit thereof is preferably 1.4 g/cm 3 or lower, more preferably 1.2 g/cm 3 or lower, especially preferably 1.1 g/cm 3 or lower. In case where the tap density thereof is lower than the lower limit of that range, this amorphous carbonaceous substance, when used in a negative electrode, is less apt to have a high loading density and has a reduced interparticle contact area. There are hence cases where interparticle resistance increases and short-time high-current-density chare/discharge characteristics decrease. On the other hand, in case where the tap density thereof exceeds the upper limit of that range, the electrode has too small an amount of interparticle interstices and a reduced amount of channels for the nonaqueous electrolyte. There are hence cases where short-time high-current-density chare/discharge characteristics decrease.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining a density from the resultant volume of the sample and the weight thereof. This density is defined as the tap density.

[[BET Specific Surface Area]]

The specific surface area of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention, as determined by the BET method, is preferably 0.1 m 2 /g or larger, especially preferably 0.5 m 2 /g or larger, more preferably 0.7 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is preferably 100 m 2 /g or smaller, especially preferably 50 m 2 /g or smaller, more preferably 25 m 2 /g or smaller, even more preferably 15 m 2 /g or smaller. When the BET specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this amorphous carbonaceous substance as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this amorphous carbonaceous substance as a negative-electrode material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

[[Volume-Average Particle Diameter]]

The volume-average particle diameter of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention, which is defined as the volume-average particle diameter (median diameter) determined by the laser diffraction/scattering method, is preferably 1 μm or larger, especially preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, even more preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such an amorphous carbonaceous substance is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

[[Pore Volume]]

With respect to the pore volume of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), may be 0.01 mL/g or larger and is preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof may be 0.6 mL/g or smaller and is preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the amount thereof is smaller than the lower limit, there are cases where short-time high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

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The average pore diameter of the amorphous carbonaceous substance is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. When the average pore diameter thereof is smaller than the lower limit, there are cases where short-time high-current-density charge/discharge characteristics decrease.

[[Ash Content]]

The ash content of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is preferably 1% by mass or lower, especially preferably 0.5% by mass or lower, more preferably 0.1% by mass or lower, based on the whole amorphous carbonaceous substance. The lower limit thereof is preferably 1 ppm by mass or higher. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. On the other hand, when the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

[[Roundness]]

The roundness of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is generally 0.1 or higher, preferably 0.8 or higher, more preferably 0.85 or higher, especially preferably 0.9 or higher. With respect to the upper limit thereof, a particle having a roundness of 1 theoretically is a true sphere. In case where the roundness thereof is lower than the lower limit of that range, use of this negative-electrode active material results in a reduced loading and interparticle resistance increases. There are hence cases where short-time high-current-density charge/discharge characteristics decrease.

In the invention, roundness is defined by the following equation.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

The value of roundness is determined, for example, with a flow type particle image analyzer (e.g., FPIA, manufactured by Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample in a 0.2% by mass aqueous solution (about 50 mL) of poly(oxyethylene(20)) sorbitan monolaurate as a surfactant, propagating an ultrasonic wave of 28 kHz to the dispersion for 1 minute at an output of 60 W, subsequently examining particles having a particle diameter in the range of 3-40 μm with the analyzer having a detection range set at 0.6-400 μm, and averaging the measured values.

[[Orientation Ratio]]

The orientation ratio of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where short-time high-density charge/discharge characteristics decrease.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

[[Aspect Ratio]]

The aspect ratio of the amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is theoretically 1 or higher. The upper limit thereof is generally 10 or lower, preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this amorphous carbonaceous material causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in short-time high-current-density charge/discharge characteristics.

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The aspect ratio of a particle is represented by A/B, wherein A is the length of the longest axis of the particle in a three-dimensional examination and B is the length of the shortest axis perpendicular to that axis. The examination of particles is made with a scanning electron microscope capable of enlargement examination. Fifty are arbitrarily selected from particles fixed to an edge face of a metal having a thickness of 50 μm or smaller, and each particle is examined for A and B while rotating or inclining the stage to which the sample is fixed. The average of the A/B values is determined.

The amorphous carbonaceous substance contained as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention preferably is an amorphous carbonaceous substance selected from the following (1) to (4):

(1) one obtained by further heat-treating a carbonization product selected from the group consisting of coal coke, petroleum coke, furnace black, acetylene black, and pitch-derived carbon fibers; (2) an organic substance selected from the group consisting of pitch materials, aromatic hydrocarbons, nitrogen-ring compounds, sulfur-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins and/or a product of the pyrolysis of the organic substance and/or a substance obtained by further heat-treating the pyrolysis product; (3) a product of the pyrolysis of a solution obtained by dissolving the organic substance (2) in a low-molecular organic solvent and/or a substance obtained by further heat-treating the pyrolysis product; and (4) a product of the carbonization of a gas containing an organic substance.

The substance in (2) is not particularly limited as long as it is capable of carbonization. Examples thereof include the following organic substances: pitch materials; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; nitrogen-ring compounds such as phenazine and acridine; sulfur-ring compounds such as thiophene and bithiophene; polyphenylenes such as biphenyl and terphenyl; poly(vinylchloride), poly(vinylalcohol), poly(vinylbutyral), substances obtained by crosslinking or insolubilizing these compounds; nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole; sulfur-containing organic polymers such as polythiophene; organic polymers such as polystyrene; natural polymers such as polysaccharides represented by cellulose, lignin, mannan, poly(galacturonic acid), chitosan, and saccharose; thermoplastic resins such as poly(phenylene sulfide) and poly(phenylene oxide); thermosetting resins such as furfuryl alcohol resins, phenol-formaldehyde resins, and imide resins; and solutions obtained by dissolving any of such organic substances in a low-molecular organic solvent, e.g., benzene, toluene, xylene, quinoline, or n-hexane. Examples thereof further include gases capable of carbonization and containing any of those organic substances.

Preferred of these are pitch materials. This is because pitch materials have a high actual carbon ratio and, hence, can give a material in high yield. The term “pitch material” in this description means a substance which is a pitch or a similar material and can be carbonized or graphitized by an appropriate treatment. Examples of the pitch materials which can be used include tars, heavy oils, and pitches. Examples of the tars include coal tar and petroleum tar. Examples of the heavy oils include petroleum-derived heavy oils such as catalytically cracked oil, thermally cracked oil, topping residues, and vacuum distillation residues. Examples of the pitches include coal tar pitch, petroleum pitch, and synthetic pitch. Of these, coal tar pitch is preferred because it has high aromaticity. Anyone of these pitch materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion.

With respect to (3), preferred examples thereof include a carbonization product obtained from a precursor which is a product of the pyrolysis of a solution of the organic substance (2) in a low-molecular organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane.

With respect to (4), examples include hydrocarbon compounds such as methane, ethane, propane, benzene, acetylene, and ethylene; and carbon monoxide.

To conduct a crosslinking treatment is also preferred. A crosslinking treatment is conducted for the purpose of giving a crosslinked pitch material or the like which, when heat-treated, gives a carbonaceous material which is less apt to be graphitized. By conducting this treatment, charge capacity per unit mass can be increased.

Examples of the crosslinking treatment include: a crosslinking treatment in which a vinyl monomer such as divinylbenzene, trivinylbenzene, diallyl phthalate, ethylene glycol dimethacrylate, or N,N-methylenebisacrylamide is used in combination with a radical polymerization initiator such as α,α′-azobisisobutyronitrile (AIBN), benzoyl peroxide (BPO), lauryl peroxide, cumene hydroperoxide, t-butyl hydroperoxide, or hydrogen peroxide; and an oxidizing agent treatment in which an oxidizing gas such as oxygen, ozone, or nitrogen dioxide or an oxidizing liquid such as sulfuric acid, nitric acid, or an aqueous hydrogen peroxide solution is used. One example of methods for such crosslinking treatments comprises mixing a pitch material kept at 50° C.-400° C. with a crosslinking agent, oxidizing agent, etc. to treat the material.

[[Li-NMR Shift]]

When an amorphous carbonaceous substance for use as the negative-electrode active material of negative electrode [2] in a lithium secondary battery of the invention is charged to a fully charged state and subjected, in this state, to 7Li-NMR analysis, then there are cases where a main resonance peak is observed in a position shifted by 80-200 ppm to the low-magnetic-field side from the resonance line for LiCl as a reference. This amorphous carbonaceous substance has an increased capacity per unit mass. It is therefore preferred to use an amorphous carbonaceous substance which has undergone a crosslinking treatment.

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[[Processes for Producing Amorphous Carbonaceous Substance]]

Processes for producing the amorphous carbonaceous substance described above are not particularly limited unless they depart from the spirit of the invention. Examples thereof include several processes. For producing the amorphous carbonaceous substance, it is necessary to conduct a heat treatment one or more times. However, a heat treatment may be conducted in two or more portions. It is also preferred to conduct any of various treatments before or after a heat treatment and/or during the heat treatment. Examples of the various treatments include pulverization, classification, and the crosslinking treatment described above. The pulverization and classification treatments can be conducted in any stage, i.e., before, after, or during the heat treatment, as long as the carbonaceous substance is solid. In the case of the crosslinking treatment, it preferably is conducted before or during the heat treatment. By conducting these treatments, the specific surface area of the negative-electrode active material can be regulated and the capacity thereof per unit mass can be increased.

Apparatus usable for the pulverization before the heat treatment are not particularly limited. Examples of coarse pulverizers include shearing mills, jaw crushers, impact crushers, and cone crushers. Examples of intermediate pulverizers include roll crushers and hammer mills. Examples of fine pulverizers include ball mills, oscillating mills, pin mills, stirring mills, and jet mills.

Apparatus usable for the heat treatment of a raw material are not particularly limited. For example, use can be made of a reaction vessel such as a shuttle furnace, tunnel kiln, electric furnace, Riedhammer furnace, rotary kiln, or autoclave, a coker (heat-treatment vessel for coke production), a direct voltage application type electric furnace, or the like. During the treatment of a raw material, stirring may be conducted according to need.

Temperature conditions in the case of conducting the heat treatment are not particularly limited. However, the temperature is generally 600° C. or higher, preferably 900° C. or higher. The upper limit thereof is generally 2,500° C. or lower, preferably 1,300° C. or lower. In case where the temperature conditions are lower than the lower limit of that range, there is a possibility that crystallinity might become too low, resulting in an increase in irreversible capacity. On the other hand, in case where the temperature exceeds the upper limit of that range, there is a possibility that crystallinity might become too high, resulting in reduced short-time high-current-density charge/discharge characteristics.

The amorphous carbonaceous substance which has undergone the heat treatment may be subjected to pulverization and classification according to the size of the aggregates or particles. Apparatus usable for the pulverization are not particularly limited. Examples of crushers include shearing mills, jaw crushers, impact crushers, and cone crushers. Examples of intermediate pulverizers include roll crushers and hammer mills. Examples of pulverizers include ball mills, oscillating mills, pin mills, stirring mills, and jet mills. Apparatus usable for the classification are not particularly limited. However, in the case of dry sieving, use can be made of a rotary sieve, swing sieve, revolving sieve, vibrating sieve, or the like. In the case of dry air classification, use can be made of a gravitational classifier, inertial classifier, or centrifugal classifier (e.g., classifier or cyclone). Furthermore, for wet sieving, use can be made of a mechanical wet classifier, hydraulic classifier, sedimentation classifier, centrifugal wet classifier, or the like.

[Negative Electrode [2]: Electrode Production]

Negative electrode [2] may be produced by an ordinary method. It can be formed in the same manner as described above. The current collector, thickness ratio between the current collector and the active-material layer, electrode density, binder, electrode-plate orientation ratio, impedance, etc. also are the same as described above.

An explanation will be given below on negative electrode [3] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing as a negative-electrode active material a titanium-containing metal oxide capable of occluding and releasing lithium”.

[Negative Electrode [3]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [3] is described below.

[[Constitution of Negative-Electrode Active Material]]

The negative-electrode active material for use in negative electrode [3] in a lithium secondary battery of the invention contains a titanium-containing metal oxide capable of occluding and releasing lithium. Preferred of such metal oxides is a composite oxide of lithium and titanium (hereinafter abbreviated to “lithium-titanium composite oxide”). Furthermore, the metal oxide preferably is a titanium-containing metal oxide having a spinel structure. A metal oxide simultaneously satisfying these, i.e., a lithium-titanium composite oxide having a spinel structure, is especially preferred because use of this composite oxide in the negative-electrode active material for a lithium secondary battery is effective in considerably reducing output resistance.

Also preferred are lithium-titanium composite oxides in which the lithium or titanium has been replaced by one or more other metallic elements, e.g., at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.

The metal oxide preferably is a lithium-titanium composite oxide represented by general formula (1) wherein 0.7≤x≤1.5, 1.5≤y≤2.3, and 0≤z≤1.6, because the structure thereof is stable during lithium ion doping/undoping.

Li x Ti y M z O 4 (1)

[In general formula (1), M represents at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.]

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Of the compositions represented by general formula (1), the following structures are especially preferred because they bring about a satisfactory balance among battery performances.

Structures represented by general formula (1), i.e., Li x Ti y M 2 O 4 , wherein

(a) 1.2≤x≤1.4, 1.5≤y≤1.7, and z=0; (b) 0.9≤x≤1.1, 1.9≤y≤2.1, and z=0; or (c) 0.7≤x≤0.9, 2.1≤y≤2.3, and z=0.

Especially preferred typical compositions of those compounds are: Li 4/3 Ti 5/3 O 4 for (a), Li 1 Ti 2 O 4 for (b), and Li 4/5 Ti 11/5 O 4 for (c).

Preferred examples of the structure wherein z≠0 include Li 4/3 Ti 4/3 Al 1/3 O 4 .

[[Properties, Shape, etc. of Negative-Electrode Active Material]]

It is preferred that the negative-electrode active material for use in negative electrode [3] in a lithium secondary battery of the invention should satisfy at least one of the following properties besides the requirements described above. Especially preferably, the negative-electrode active material simultaneously satisfies two or more of the following properties besides the requirements described above.

[[[BET Specific Surface Area]]]

The specific surface area of the titanium-containing metal oxide for use as the negative-electrode active material in negative electrode [3] in a lithium secondary battery of the invention, as determined by the BET method, is preferably 0.5 m 2 /g or larger, more preferably 0.7 m 2 /g or larger, especially preferably 1.0 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is preferably 200 m 2 /g or smaller, more preferably 100 m 2 /g or smaller, especially preferably 50 m 2 /g or smaller, even more preferably 25 m 2 /g or smaller. When the BET specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this metal oxide as a negative-electrode material results in a reduced reaction area available for contact with the nonaqueous electrolyte and in an increase in output resistance. On the other hand, in case where the BET specific surface area thereof exceeds the upper limit of that range, the proportion of surfaces and edge faces of crystals of the titanium-containing metal oxide increases and this causes crystal deformation. There are hence cases where irreversible capacity becomes not negligible and a preferred battery is difficult to obtain.

[[[Volume-Average Particle Diameter]]]

The volume-average particle diameter (secondary-particle diameter in the case where the primary particles have aggregated to form secondary particles) of the titanium-containing metal oxide for use as the negative-electrode active material in negative electrode [3] in a lithium secondary battery of the invention, which is defined as the volume-average particle diameter (median diameter) determined by the laser diffraction/scattering method, is preferably 0.1 μm or larger, more preferably 0.5 μm or larger, even more preferably 0.7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, even more preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where a large amount of a binder is necessary in electrode production and this results in a decrease in battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a metal oxide is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

[[[Average Primary-Particle Diameter]]]

In the case where the primary particles have aggregated to form secondary particles, the average primary-particle diameter of the titanium-containing metal oxide for use as the negative-electrode active material in a lithium secondary battery of the invention is preferably 0.01 μm or larger, more preferably 0.05 μm or larger, even more preferably 0.1 μm or larger, most preferably 0.2 μm or larger. The upper limit thereof is preferably 2 μm or smaller, more preferably 1.6 μm or smaller, even more preferably 1.3 μm or smaller, most preferably 1 μm or smaller. In case where the average primary-particle diameter thereof exceeds the upper limit, spherical secondary particles are difficult to form and this adversely influences powder loading or results in a considerably reduced specific surface area. There may hence be a high possibility that battery performances such as output characteristics might decrease. Conversely, when the average primary-particle diameter thereof is smaller than the lower limit, crystal growth is usually insufficient and, hence, there are cases where this positive-electrode active material poses a problem, for example, that charge/discharge reversibility is poor.

Primary-particle diameter is determined through an examination with a scanning electron microscope (SEM). Specifically, arbitrarily selected 50 primary-particle images in a photograph having a magnification capable of particle observation, e.g., 10,000-100,000 diameters, each are examined for the length of the longest segment of a horizontal line which extends across the primary-particle image from one side to the other side of the boundary. These measured lengths are averaged, whereby the average value can be determined.

[[[Shape]]]

The particle shape of the titanium-containing metal oxide for use in negative electrode [3] in a lithium secondary battery of the invention may be any of massive, polyhedral, spherical, ellipsoidal, platy, acicular, columnar, and other shapes such as those in common use. Preferred of these is one in which the primary particles have aggregated to form secondary particles and these secondary particles have a spherical or ellipsoidal shape. In electrochemical elements, the active material in each electrode usually expands/contracts with the charge/discharge of the element and, hence, deterioration is apt to occur, such as active-material breakage and conduction path breakage, due to the stress caused by the expansion/contraction. Because of this, a positive-electrode active material in which the primary particles have aggregated to form secondary particles is preferable to an active material composed of primary particles only since the particles in the former active material relieve the stress caused by expansion/contraction to prevent deterioration. Furthermore, particles of a spherical or ellipsoidal shape are preferable to particles showing axial orientation, e.g., platy ones, because the former particles are less apt to orient during electrode molding and hence this electrode is reduced in expansion/contraction during charge/discharge, and because these particles are apt to be evenly mixed with a conductive material in electrode production.

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[[[Tap Density]]]

The tap density of the titanium-containing metal oxide for use as the negative-electrode active material in negative electrode [3] in a lithium secondary battery of the invention is preferably 0.05 g/cm 3 or higher, more preferably 0.1 g/cm 3 or higher, even more preferably 0.2 g/cm 3 or higher, especially preferably 0.4 g/cm 3 or higher. The upper limit thereof is preferably 2.8 g/cm 3 or lower, more preferably 2.4 g/cm 3 or lower, especially preferably 2 g/cm 3 or lower. In case where the tap density thereof is lower than the lower limit of that range, this metal oxide, when used in a negative electrode, is less apt to have a high loading density and has a reduced interparticle contact area. There are hence cases where interparticle resistance increases and output resistance increases. On the other hand, in case where the tap density thereof exceeds the upper limit of that range, the electrode has too small an amount of interparticle interstices and a reduced amount of channels for the nonaqueous electrolyte. There are hence cases where output resistance increases.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining a density from the resultant volume of the sample and the weight thereof. This density is defined as the tap density.

[[[Roundness]]]

The roundness of the titanium-containing metal oxide for use as the negative-electrode active material of negative electrode [3] in a lithium secondary battery of the invention is generally 0.10 or higher, preferably 0.80 or higher, more preferably 0.85 or higher, especially preferably 0.90 or higher. With respect to the upper limit thereof, a particle having a roundness of 1 theoretically is a true sphere. In case where the roundness thereof is lower than the lower limit of that range, use of this negative-electrode active material results in a reduced loading and interparticle resistance increases. There are hence cases where short-time high-current-density charge/discharge characteristics decrease.

In the invention, roundness is defined by the following equation.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

The value of roundness is determined with a flow type particle image analyzer (e.g., FPIA, manufactured by Sysmex Industrial Corp.) by dispersing about 0.2 g of a sample in a 0.2% by mass aqueous solution (about 50 mL) of poly(oxyethylene(20)) sorbitan monolaurate as a surfactant, propagating an ultrasonic wave of 28 kHz to the dispersion for 1 minute at an output of 60 W, and then examining particles having a particle diameter in the range of 3-40 μm with the analyzer having a detection range set at 0.6-400 μm.

[[[Aspect Ratio]]]

The aspect ratio of the titanium-containing metal oxide for use as the negative-electrode active material of negative electrode [3] in a lithium secondary battery of the invention is theoretically 1 or higher. The upper limit thereof may be 5 or lower and is preferably 4 or lower, more preferably 3 or lower, even more preferably 2 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this metal oxide causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in short-time high-current-density charge/discharge characteristics.

[[Processes for Producing Negative-Electrode Active Material]]

Processes for producing the negative-electrode active material of negative electrode [3] in a lithium secondary battery of the invention are not particularly limited unless they depart from the spirit of the invention. Examples thereof include several processes, and processes in general use for producing inorganic compounds may be employed. For example, use may be made of a method in which a titanium source, e.g., titanium oxide, is evenly mixed with an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and optionally with a source of other element (s) and this mixture is heat-treated at a high temperature to obtain the active material. Especially for producing spherical or ellipsoidal active materials, various techniques are usable. Examples thereof include: a method which comprises dissolving or pulverizing/dispersing a titanium source, e.g., titanium oxide, optionally together with a source of other element(s) in a solvent, e.g., water, regulating the pH of the solution or dispersion with stirring to produce a spherical precursor, recovering and optionally drying the precursor, subsequently adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; a method which comprises dissolving or pulverizing/dispersing a titanium source, e.g., titanium oxide, optionally together with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, adding thereto an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and heat-treating the mixture at a high temperature to obtain the active material; and a method which comprises dissolving or pulverizing/dispersing a titanium source, e.g., titanium oxide, together with an Li source, e.g., LiOH, Li 2 CO 3 , or LiNO 3 , and optionally with a source of other element(s) in a solvent, e.g., water, drying and forming the solution or dispersion with a spray dryer or the like to obtain a spherical or ellipsoidal precursor, and heat-treating the precursor at a high temperature to obtain the active material.

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In those steps, one or more of elements other than Ti, such as, e.g., Al, Mn, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, C, Si, Sn, and Ag, can be caused to be present in the titanium-containing metal oxide structure and/or present so as be in contact with the titanium-containing oxide. The incorporation of such elements can be used for regulating the operating voltage and capacity of the battery.

[Negative Electrode [3]: Electrode Production]

Negative electrode [3] may be produced by an ordinary method. It can be formed in the same manner as described above. The current collector, thickness ratio between the current collector and the active-material layer, electrode density, binder, electrode-plate orientation ratio, impedance, etc. also are the same as described above.

An explanation will be given below on negative electrode [4] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing as a negative-electrode active material a carbonaceous substance having a roundness of 0.85 or higher and a surface functional-group amount O/C value of from 0 to 0.01”.

[Negative Electrode [4]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [4] is described below.

The negative-electrode active material for use in negative electrode [4] in a lithium secondary battery of the invention comprises a carbonaceous substance satisfying at least the following requirements (a) and (b).

(a) The roundness is 0.85 or higher. (b) The surface functional-group amount O/C value is from 0 to 0.01.

Details of the carbonaceous substance for use in this invention are explained below.

[[ Roundness]]

The roundness of the carbonaceous substance is generally 0.85 or higher, preferably 0.87 or higher, more preferably 0.89 or higher, especially preferably 0.92 or higher. With respect to the upper limit thereof, a particle having a roundness of 1 theoretically is a true sphere. In case where the roundness thereof is lower than the lower limit of that range, use of this negative-electrode active material results in a reduced loading and compaction in negative-electrode formation is difficult and leads to particle breakage. There is hence a possibility that those inner parts of the particles which have poor high-temperature storability at a low state of charge are apt to be exposed.

In the invention, roundness is defined by the following equation.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

[[O/C Value]]

The surface functional-group amount O/C value of the carbonaceous substance should be from 0 to 0.01. The upper limit of the O/C value thereof is preferably 0.005 or lower. The closer the O/C value to 0, the more the carbonaceous substance is preferred.

The term O/C value in the invention indicates the proportion of the amount of surface functional groups determined by X-ray photoelectron spectroscopy (XPS). Incase where the surface functional-group amount O/C value exceeds the upper limit of that range, the particle surface has an increased amount of a functional group and the SEI film which is formed on the surface during charge in the presence of a specific compound does not have sufficient stability. There are hence cases where high-temperature storability at a low state of charge decreases.

Surface functional-group amount O/C value means the ratio of the concentration of oxygen atoms present on the surface of, e.g., a graphite material, to the concentration of carbon atoms present thereon. It is an index to the amount of functional groups, such as carboxyl, phenolic hydroxyl, and carbonyl groups, present on the surface. When a carbon material has a high surface functional-group amount O/C value, this frequently means that an oxygen-containing surface functional group is bonded to, e.g., edge faces of the carbon crystallites in the particle surface. Incidentally, the surface functional-group amount O/C value of a graphite material is determined by determining the areas of C1s and O1s spectral peaks in X-ray photoelectron spectroscopy and calculating the carbon-oxygen atomic concentration ratio O/C (O atom concentration/C atom concentration) from the peak areas. Although specific procedures of the determination are not particularly limited, an example is as follows.

An X-ray photoelectron spectrometer (e.g., ESCA, manufactured by ULVAC-PHI, INC.) is used for the X-ray photoelectron spectroscopy. A sample to be examined (here, a graphite material) is placed on a sample table so as to form a flat surface. An aluminum Kα line is used as an X-ray source to obtain a spectrum having C1s (280-300 eV) and O1s (525-545 eV) peaks in the multiplex mode. Charge correction is made, with the top of the C1s peak being at 284.3 eV, and the areas of the C1s and O1s spectral peaks are determined. Furthermore, these areas are multiplied by the apparatus sensitivity coefficient to calculate the concentrations of surface C atoms and surface O atoms. From the O and C atom concentrations obtained, the atomic concentration ratio O/C (O atom concentration/C atom concentration) is calculated. This ratio is defined as the surface functional-group amount O/C value of the graphite material.

Although the carbonaceous substance for use in this invention satisfies the requirements concerning “roundness” and “surface functional-group amount O/C value” described above, it is preferred from the standpoint of battery performance balance that the carbonaceous substance should further satisfy anyone of the following requirements or simultaneously satisfy two or more thereof. It is preferred that any one of or two or more of tap density, Raman R value, and volume-average particle diameter, among those requirements, should be simultaneously satisfied.

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[[Tap Density]]

The tap density of the carbonaceous substance is generally 0.55 g/cm 3 or higher, preferably 0.7 g/cm 3 or higher, more preferably 0.8 g/cm 3 or higher, especially preferably 0.9 g/cm 3 or higher. The upper limit thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. In case where the tap density thereof is lower than the lower limit of that range, this carbonaceous substance, when used in a negative electrode, is less apt to have a high loading density. There are hence cases where a high-capacity battery cannot be obtained. On the other hand, in case where the tap density thereof exceeds the upper limit of that range, the electrode has too small an amount of interparticle interstices and electrical conductivity among the particles is difficult to secure. There are hence cases where preferred battery characteristics are difficult to obtain.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and calculating a density from the resultant volume of the sample and the weight thereof. This value is defined as the tap density.

[[Raman R Value, Half-Value Width]]

The R value of the carbonaceous substance, as determined by argon ion laser Raman spectroscopy, is generally 0.001 or higher, preferably 0.01 or higher. The upper limit thereof is generally 0.2 or lower, preferably 0.18 or lower, more preferably 0.15 or lower. When the R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, in case where the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and the SEI film which is formed on the surface during charge in the presence of a specific compound is not sufficiently stable. There are hence cases where high-temperature storability at a low state of charge decreases.

The Raman half-value width around 1,580 cm −1 of the carbonaceous substance is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 35 cm −1 or smaller, preferably 30 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and the SEI film which is formed on the surface during charge in the presence of a specific compound is not sufficiently stable. There are hence cases where high-temperature storability at a low state of charge decreases.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A around 1,580 cm −1 and the intensity I B of a peak P B around 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the carbon material. Furthermore, the half-value width of the peak P A around 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the carbonaceous substance.

Conditions for this Raman spectroscopy are as follows.

[[Volume-Average Particle Diameter]]

With respect to the volume-average particle diameter of the carbonaceous substance, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, even more preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a carbonaceous substance is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

Furthermore, in the volume-based particle diameter distribution thereof, the ratio of the 90% particle diameter to the 10% particle diameter (d 90 /d 10 ) may be 1.2 or higher and is preferably 1.5 or higher, more preferably 1.7 or higher. The upper limit thereof may be 8 or lower and is preferably 5 or lower, more preferably 4 or lower, even more preferably 3 or lower.

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Volume-average particle diameter in the invention is defined as the median diameter determined by dispersing the carbon powder in a 0.2% by mass aqueous solution (about 1 mL) of polyoxyethylene (20) sorbitan monolaurate as a surfactant and examining the dispersion with a laser diffraction type particle size distribution analyzer (e.g., LA-700, manufactured by HORIBA, Ltd.). With respect to the 90% particle diameter/10% particle diameter ratio (d 90 /d 10 ), the volume-based 90% particle diameter and 10% particle diameter are determined in the same manner and the ratio (d 90 /d 10 ) can be calculated therefrom.

[[X-Ray Parameter]]

The carbonaceous substance preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The upper limit of the value of d is 0.340 nm or smaller and is preferably 0.337 nm or smaller. When the value of d is too large, there are cases where such particles have reduced crystallinity to increase initial irreversible capacity. On the other hand, 0.335 is a theoretical value for graphites. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 80 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that such particles might have reduced crystallinity to increase initial irreversible capacity.

[[Ash Content]]

The ash content of the carbonaceous substance is preferably 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole carbonaceous substance. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous substance. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

[[BET Specific Surface Area]]

The specific surface area of the carbonaceous substance, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this carbonaceous substance as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this carbonaceous substance as a negative-electrode material is apt to result in enhanced reactivity with the electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

[[Pore Distribution]]

In the carbonaceous substance, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. On the other hand, when the amount thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The average pore diameter of the carbonaceous substance is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. On the other hand, when the average pore diameter thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease.

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[[True Density]]

The true density of the carbonaceous substance is generally 2 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the carbonaceous substance is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

[[Orientation Ratio]]

The orientation ratio of the carbonaceous substance is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

[[Aspect Ratio]]

The aspect ratio of the carbonaceous substance is theoretically 1 or higher. The upper limit thereof may be 10 or lower and is preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this carbonaceous substance causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

The aspect ratio of a particle is represented by A/B, wherein A is the length of the longest axis of the particle in a three-dimensional examination and B is the length of the shortest axis perpendicular to that axis. The examination of particles is made with a scanning electron microscope capable of enlargement examination. Fifty are arbitrarily selected from graphite particles fixed to an edge face of a metal having a thickness of 50 μm or smaller, and each particle is examined for A and B while rotating or inclining the stage to which the sample is fixed. The average of the A/B values is determined.

[[Processes for Producing Carbonaceous Substance and Raw Materials Therefor]]

The carbonaceous substance for use in this invention may be one which occurs naturally or one produced artificially. However, one derived from a natural graphite is preferred. The carbonaceous substance may be one obtained by subjecting a naturally occurring one or artificially produced one to a specific treatment. Processes for producing the carbonaceous substance (including classification methods) also are not particularly limited. For example, a carbonaceous substance obtained by a classification technique such as, e.g., sieving or air classification so as to have the properties described above may be employed.

Of these, a carbonaceous substance obtained by heat-treating a naturally occurring carbon material (raw natural graphite material) is preferred from the standpoints of availability and processability in a preceding step. Furthermore, a carbonaceous substance obtained by subjecting a naturally occurring carbon material (raw natural graphite material) or an artificially produced carbon material to a mechanical energy treatment to modify/round the material and heat-treating the rounded carbonaceous substance is preferred from the standpoints of loading improvement, etc. Moreover, a carbonaceous substance prepared by subjecting a raw natural graphite material to a mechanical energy treatment and heat-treating the resultant rounded natural graphite is especially preferred from the standpoints of balance among lithium secondary battery performances, etc. Hereinafter, the carbon material (raw material) which has not undergone a heat treatment, e.g., a raw natural graphite material, is often referred to simply as “raw material before heat treatment”.

[[[Raw Natural Graphite Material]]]

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Natural graphites are especially preferred raw materials for the carbonaceous substance as stated above.

Natural graphites are classified into flake graphite, crystalline (vein) graphite, and amorphous graphite according to properties (see “Graphite” in Funrūtai Purosesu Gijutsu Shūsei , published by Industrial Technology Center in 1974; and HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES , published by Noyes Publications). With respect to the degree of graphitization, crystalline graphite has a highest graphitization degree of 100% and flake graphite is second, which has a graphitization degree of 99.9%. The graphitization degree of amorphous graphite is as low as 28%. The quality of the natural graphites is governed mainly by locality and vein. Flake graphite occurs in Madagascar, China, Brazil, Ukraine, Canada, etc. Crystalline graphite occurs mainly in Sri Lanka. Amorphous graphite occurs mainly in the Korean Peninsula, China, Mexico, etc. Of these natural graphites, flake graphite and crystalline graphite are preferred raw materials for the carbonaceous substance because of their advantages including a high degree of graphitization and a low impurity content.

[[[Mechanical Energy Treatment/Rounding Treatment]]]

The mechanical energy treatment is conducted so that the ratio between the volume-average particle diameters before and after the treatment becomes 1 or less. The term “ratio between the volume-average particle diameters before and after the treatment” means a value obtained by dividing the volume-average particle diameter as measured after the treatment by the volume-average particle diameter as measured before the treatment. In the mechanical energy treatment in the invention for producing a raw material before heat treatment, it is preferred to conduct the mechanical energy treatment so that the ratio between the average particle diameters before and after this treatment becomes 1 or less.

The mechanical energy treatment is performed for the purposes of reducing the size of the powder particles to 1 or less in terms of the ratio between the average particle diameters before and after the treatment and simultaneously regulating the particle shape. This mechanical energy treatment belongs to the pulverization treatment among engineering unit operations utilizable for particle design, such as pulverization, classification, mixing, granulation, surface modification, and reaction.

Pulverization means an operation in which a force is applied to a substance to thereby reduce the size thereof and regulate the particle diameter, particle size distribution, and loading of the substance. Pulverization treatments are classified according to the kind of force to be applied to the substance and the method of treatment. Forces to be applied to the substance are roughly divided into the following four: (1) breaking force (impact force), (2) crushing force (compressive force), (3) milling force (grinding force), and (4) scraping force (shear force). On the other hand, treatment methods are roughly divided into the following two: volume pulverization in which cracks are generated and propagated in inner parts of the particles; and surface pulverization in which surface parts of the particles are scraped off. Volume pulverization proceeds by means of impact force, compressive force, and shear force, while surface pulverization proceeds by means of grinding force and shear force. Pulverization is a treatment based on any of various combinations of such kinds of forces to be applied to a substance and such treatment methods. A suitable combination can be determined according to the purpose of the treatment.

There are cases where pulverization is conducted by a chemical reaction, e.g., explosion, or by volume expansion. However, pulverization is generally conducted with a mechanical apparatus such as a pulverizer. It is preferred that the pulverization treatment to be used for producing a rounded carbonaceous substance as a raw material in the invention should be a treatment which finally involves a high proportion of surface treatment, regardless of whether volume pulverization occurs or not. This is because surface pulverization is important for eliminating angles of the surface-pulverized particles and thereby imparting roundness to the particle shape. Specifically, use may be made of a method in which surface treatment is conducted after volume pulverization has proceeded to some degree or a method in which surface treatment only is conducted almost without conducting volume pulverization. Furthermore, volume pulverization and surface treatment may be simultaneously conducted. It is preferred to conduct a pulverization treatment in which surface pulverization proceeds finally and angles are eliminated from the surface of the particles.

The apparatus to be used for conducting the mechanical energy treatment is selected from ones usable for conducting the preferred treatment described above. The mechanical energy treatment may be accomplished with one or more of the four kinds of forces applicable to a substance. However, it is preferred and effective to repeatedly apply impact force as a main force and other mechanical actions such as compressive, frictional, shear, and other forces, including those caused by particle interaction, to the particles. Consequently, a preferred apparatus specifically is one which comprises a casing and disposed therein a rotor having many blades and in which the rotor is rotated at a high speed to thereby apply mechanical actions such as impact, compressive, frictional, and shear forces to a carbon material introduced therein and conduct surface treatment while allowing volume pulverization to proceed. More preferred is one which has a mechanism in which a carbonaceous substance is circulated to thereby repeatedly apply mechanical actions thereto.

Examples of the preferred apparatus include Hybridization System (manufactured by Nara Machinery Co., Ltd.), Kryptron (Earth Technica Co., Ltd.), CF Mill (manufactured by Ube Industries, Ltd.), and Mechanofusion System (manufactured by Hosokawa Micron Corp.). Preferred of these is Hybridization System, manufactured by Nara Machinery Co., Ltd. In the case where the treatment is conducted with this apparatus, the rotor is rotated at a peripheral speed of preferably 30-100 m/sec, more preferably 40-100 m/sec, even more preferably 50-100 m/sec. Although a carbonaceous substance can be treated by merely passing it through the apparatus, it is preferred to treat the carbonaceous substance while causing it to circulate or reside in the apparatus for 30 seconds or longer. More preferably, the carbonaceous substance is treated while circulating or residing in the apparatus for 1 minute or longer.

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Through such mechanical energy treatment, the carbon particles become particles in which only parts near the surface are rough and which have exposed strains and edge faces, while retaining high crystallinity as a whole. Thus, the carbon particles come to have an increased amount of surfaces where lithium ions can come in and out, and hence have a high capacity even at a high current density.

In general, flaky, crystalline, and platy carbon materials tend to become poorer in suitability for loading as the particle diameter decreases. It is thought that as a result of pulverization, the particles come to have more irregular shapes, have a larger amount of surface projections such as “fine splits”, “half-peeled parts”, and “bent parts”, and have finer particles of irregular shapes adherent to the particle surface at some degree of strength. The impaired suitability for loading is thought to be attributable to increased resistance between adjacent particles due to such causes.

As long as such shape irregularity is reduced and the particle shape becomes close to sphere, a decrease in particle diameter should result in a limited decrease in loading and large-diameter carbon particles and small-diameter carbon particles should have almost the same tap density.

[[[Properties of Raw Material before Heat Treatment]]]

It is desirable that the raw material before heat treatment should have properties which satisfy any one of the following items (1) to (11) or simultaneously satisfy two or more thereof. The methods of determining the following properties and the definitions thereof are the same as in the carbonaceous substances described above.

(1) X-Ray Parameter

The raw material before heat treatment preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The lower limit of the value of d is smaller than 0.340 nm, and is preferably 0.337 nm or smaller. When the value of d is too large, there are cases where crystallinity decreases to increase initial irreversible capacity. On the other hand, 0.335 is a theoretical value for graphites. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 80 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to increase initial irreversible capacity.

(2) Ash Content

The ash content of the raw material before heat treatment is generally 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole raw material before heat treatment. The lower limit of the ash content thereof is generally preferably at least 1 ppm by mass of the whole raw material. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this raw material necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the raw material before heat treatment, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, even more preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a raw material is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

(4) Raman R Value, Raman Half-Value Width

The R value of the raw material before heat treatment as determined by the argon ion laser Raman spectroscopy is generally 0.10 or higher, preferably 0.15 or higher, more preferably 0.17 or higher, even more preferably 0.2 or higher. The upper limit thereof is generally 0.8 or lower, preferably 0.6 or lower, more preferably 0.4 or lower. When the R value thereof is lower than the lower limit of that range, there is a possibility that the particles might have not been sufficiently rounded and the effect of improving suitability for loading cannot be obtained. On the other hand, when the R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the raw material before heat treatment is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 80 cm −1 or smaller, preferably 60 cm −1 or smaller, more preferably 45 cm −1 or smaller, even more preferably 40 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, there is a possibility that the particles might have not been sufficiently rounded and the effect of improving suitability for loading cannot be obtained. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

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(5) BET Specific Surface Area

The specific surface area of the raw material before heat treatment, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 50 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of the carbonaceous substance obtained from this raw material as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where the carbonaceous substance obtained therefrom through a heat treatment is apt to excessively react with the electrolyte and evolve a larger amount of a gas, although it has a reduced specific surface area, making it difficult to obtain a preferred battery.

(6) Pore Distribution

In the raw material before heat treatment, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. On the other hand, when the amount thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The average pore diameter of the raw material before heat treatment is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. On the other hand, when the average pore diameter thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease.

(7) Roundness

With respect to the degree of sphericity of the raw material before heat treatment, the roundness of the particles having a particle diameter in the range of 3-40 μm is generally preferably 0.85 or higher, more preferably 0.87 or higher, especially preferably 0.90 or higher, even more preferably 0.92 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics and suitability for loading.

Methods for improving roundness are not particularly limited. However, a raw material before heat treatment in which the particles have been rounded by a rounding treatment with the mechanical energy described above is preferred because it gives an electrode in which the interstices among particles are uniform in shape.

(8) True Density

The true density of the raw material before heat treatment is generally 2 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the raw material is lower than the lower limit of that range, there are cases where the carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

(9) Tap Density

The tap density of the raw material before heat treatment is generally 0.55 g/cm 3 or higher, preferably 0.7 g/cm 3 or higher, more preferably 0.8 g/cm 3 or higher, especially preferably 0.9 g/cm 3 or higher. The upper limit thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where the carbonaceous substance obtained from this raw material, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain.

(10) Orientation Ratio

The orientation ratio of the raw material before heat treatment is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

(11) Aspect Ratio

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The aspect ratio of the raw material before heat treatment is theoretically 1 or higher. The upper limit thereof is generally 10 or lower, preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where the carbonaceous substance obtained from this raw material causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

[[[Heat Treatment Temperature]]]

The temperature in the heat treatment of the raw material before heat treatment is generally 600° C. or higher, preferably 1,200° C. or higher, more preferably 2,000° C. or higher, even more preferably 2,500° C. or higher, especially preferably 2,800° C. or higher. The upper limit thereof is generally 3,200° C. or lower, preferably 3,100° C. or lower. When the temperature conditions are lower than the lower limit of that range, there are cases where the surface of the graphite particles which has been disordered by the rounding treatment, etc. does not undergo a sufficient crystal repair and the graphite particles come to have neither a reduced Raman R value nor a reduced BET specific surface area. On the other hand, when the temperature exceeds the upper limit of that range, there are cases where graphite sublimation is apt to occur in an increased amount.

[[[Method of Heat Treatment]]]

The heat treatment is accomplished by heating the raw material once to a temperature in that range. Although the holding time period in which the temperature conditions are kept in that range is not particularly limited, it generally is longer than 10 seconds and is not longer than 168 hours.

In general, the heat treatment is conducted in an inert gas atmosphere, e.g., nitrogen gas, or in a non-oxidizing atmosphere formed by the gas generated from the raw graphite. It is, however, noted that in a furnace of the type in which the raw material is buried in a breeze (fine carbon powder obtained by pitch heat-treating), there are cases where the atmosphere in an initial stage is a mixture with the air. In such cases, it is not always necessary to use a completely inert gas atmosphere.

Apparatus usable for the heat treatment are not particularly limited. For example, use can be made of a shuttle furnace, tunnel kiln, electric furnace, Riedhammer furnace, rotary kiln, direct voltage application type electric furnace, Acheson furnace, resistance heating furnace, induction heating furnace, or the like.

Besides the treatments described above, various treatments including classification can be conducted. Classification is a treatment for removing coarse particles and fine particles in order to obtain a target particle diameter. Apparatus usable for the classification are not particularly limited. However, in the case of dry sieving, use can be made of a rotary sieve, swing sieve, revolving sieve, vibrating sieve, or the like. In the case of dry air classification, use can be made of a gravitational classifier, inertial classifier, or centrifugal classifier (e.g., classifier or cyclone). In the case of wet sieving, use can be made of a mechanical wet classifier, hydraulic classifier, sedimentation classifier, centrifugal wet classifier, or the like. Classification may be conducted before the heat treatment or may be conducted in another timing, e.g., after the heat treatment. It is also possible to omit the classification treatment itself. However, from the standpoint of productivity of the graphite powder as a negative-electrode material, it is preferred to conduct a classification treatment immediately after the rounding treatment and prior to the heat treatment.

[[Minor-Material Mixing]]

Besides the carbonaceous substance described above, one or more carbonaceous substances (carbonaceous materials) differing in carbonaceous-substance property from that carbonaceous substance may be incorporated into the negative-electrode active material for use in this invention. Thus, battery performances can be further improved. The term “carbonaceous-substance property” herein means one or more properties selected from X-ray diffraction parameter, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, roundness, and ash content. Preferred embodiments include: one in which the volume-based particle size distribution is not symmetrical about the median diameter; one in which two or more carbon materials differing in Raman R value are contained; and one in which carbon materials differing in X-ray parameter are contained. One example of the effects thereof is that the incorporation of a carbon material, such as a graphite, e.g., a natural graphite or artificial graphite, or an amorphous carbon, e.g., a carbon black such as acetylene black or needle coke, as a sub material serves to reduce electrical resistance. One of these carbon materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion. In the case where such a carbon material is added as a sub material, the amount thereof is generally 0.1% by mass or larger, preferably 0.5% by mass or larger, more preferably 0.6% by mass or larger. The upper limit thereof is generally 80% by mass or smaller, preferably 50% by mass or smaller, more preferably 40% by mass or smaller, especially preferably 30% by mass or smaller. Amounts thereof smaller than the lower limit of that range are undesirable because they result in difficulties in obtaining the effect of improving conductivity. When the amount thereof exceeds the upper limit, there are cases where this leads to an increase in initial irreversible capacity.

[Negative Electrode [4]: Electrode Production]

The negative electrode may be produced by an ordinary method. It can be formed in the same manner as described above. The current collector, thickness ratio between the current collector and the active-material layer, electrode density, binder, electrode-plate orientation ratio, impedance, etc. also are the same as described above.

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An explanation will be given below on negative electrode [5] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing as a negative-electrode active material an orientation-differing-carbon composite comprising two or more carbonaceous substances differing in orientation”.

[Negative Electrode [5]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [5] is described below.

[[Constitution of Orientation-Differing-Carbon Composite]]

The negative-electrode active material to be used in negative electrode [5] in a lithium secondary battery of the invention comprises an orientation-differing-carbon composite comprising two or more carbonaceous substances differing in orientation.

The term “differing in orientation” herein means that when the powder is examined with a polarizing microscope and the optically anisotropic structures are visually compared in the pattern of anisotropic units, i.e., the size, direction, number, etc. of the anisotropic units, then the structures differ in at least any of the size, direction, number, etc. of the anisotropic units. Examples thereof include: the case where one of carbonaceous substance 1 and carbonaceous substance 2 has crystal orientation in one direction and the other has random crystal orientation; and the case where both of carbonaceous substance 1 and carbonaceous substance 2 have crystal orientation in respective certain directions and these directions are different. In the case where one or each of carbonaceous substance 1 and carbonaceous substance 2 is not composed of single-crystal particles but composed of aggregates of crystals, each unit aggregate is taken as one region and the optically anisotropic structures are compared in the aggregation pattern of the anisotropic units.

With respect to the state in which carbonaceous substance and carbonaceous substance 2 coexist in the orientation-differing-carbon composite, it is preferred that the two carbonaceous substances should be contained in one secondary particle. The term “contained in one secondary particle” herein means, for example, the state in which the carbonaceous substances differing in orientation are physically restrained or adhered, the state in which the carbonaceous substances retain a shape by means of electrostatic restraint or adhesion, or the state in which the carbonaceous substances are restrained by bonding. The term “physically restrained or adhered” herein means a state such as that in which one of the carbonaceous substances is surrounded by the other or the state in which one is caught by the other. The term “electrostatic restraint or adhesion” means the state in which one of the carbonaceous substances is adherent to the other by means of electrostatic energy. As long as the carbonaceous substances in this restrained or adhered state are different from each other in orientation as described above, the original carbonaceous substances may be equal. Furthermore, the term “the state in which the carbonaceous substances are restrained by bonding” means chemical bonding by hydrogen bonds, covalent bonds, ionic bonds, etc.

Preferred of those is the state in which the surface of one of the carbonaceous substances at least partly has an interface where another carbonaceous substance, which differs in orientation from that carbonaceous substance, is adhered and/or bonded to that carbonaceous substance. Such composite having an interface is preferred because this composite, as compared with negative-electrode active materials having no interface and having the same particle shape as the composite, is effective in dispersing in many directions the expansion caused by lithium intercalation during charge to thereby prevent battery deterioration.

The part differing in orientation is not limited as to whether it is one formed by the bonding of an externally supplied material and/or of a product of alteration thereof or one formed by the alteration of a surface-part material of a carbonaceous substance. The term “coating” herein means that the interface between one carbonaceous substance and the surface of the other carbonaceous substance at least partly has chemical bonds and the former carbonaceous substance is (1) in the state of covering the whole surface, (2) in the state of locally covering the carbonaceous particles, (3) in the state of selectively covering part of the surface, or (4) in the state of being present in ultrafine regions including chemical bonds.

Around the interface, the orientation of the carbonaceous substances may change continuously or discontinuously. Namely, it is preferred that the orientation-differing-carbon composite should be one which has an interface where carbonaceous substances differing in orientation are adhered and/or bonded to each other, and in which the orientation of the carbonaceous substances at the interface changes discontinuously and/or continuously.

The components of the orientation-differing-carbon composite (A) are not particularly limited as long as they have crystallinity. However, it is preferred that one or more of the carbonaceous substances differing in orientation should be a graphitic carbonaceous substance (B) derived from a natural graphite (D) (hereinafter, this substance (B) is abbreviated to “natural-graphite-derived carbonaceous substance (B)), because use of this carbonaceous substance (B) increases charge capacity per unit mass.

The proportion of the natural-graphite-derived carbonaceous substance (B) contained in the orientation-differing-carbon composite is generally 5% by mass or higher, preferably 20% by mass or higher, more preferably 30% by mass or higher, even more preferably 40% by mass or higher, especially preferably 50% by mass or higher, based on the orientation-differing-carbon composite. The upper limit thereof is generally 99.9% by mass or lower, preferably 99% by mass or lower, more preferably 95% by mass or lower, even more preferably 90% by mass or lower. When the proportion of the carbonaceous substance (B) is lower than the lower limit of that range, there are cases where electrode rolling results in a considerably increased load and this causes electrode peeling, etc. On the other hand, when the proportion thereof exceeds the upper limit of that range, there are cases where the composite comprising particles differing in orientation has weak interfacial bonding.

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With respect to other components of the orientation-differing-carbon composite, it is also preferred, from the standpoints of interface formation during the preparation of the orientation-differing-carbon composite and interfacial-bonding improvement, that one or more of the carbonaceous substances differing in orientation should be a carbonaceous substance (C) selected from the following (1) to (5):

(1) a carbonization product selected from the group consisting of coal coke, petroleum coke, furnace black, acetylene black, and pitch-derived carbon fibers; (2) a carbonization product obtained from a precursor which is an organic substance selected from the group consisting of pitch materials, aromatic hydrocarbons, nitrogen-ring compounds, sulfur-ring compounds, polyphenylenes, organic synthetic polymers, natural polymers, thermoplastic resins, and thermosetting resins and/or a product of the pyrolysis of the organic substance; (3) a carbonization product obtained from a precursor which is a product of the pyrolysis of a solution obtained by dissolving the organic substance (2) in a low-molecular organic solvent; (4) a product of the carbonization of a gas containing an organic substance; and (5) a product of the graphitization of any of (1) to (4) above.

The substance in (2) is not particularly limited as long as it is capable of carbonization. Examples thereof include the following organic substances: pitch materials; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; nitrogen-ring compounds such as phenazine and acridine; sulfur-ring compounds such as thiophene and bithiophene; polyphenylenes such as biphenyl and terphenyl; poly(vinylchloride), poly(vinylalcohol), poly(vinylbutyral), and substances obtained by insolubilizing these compounds; nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole; sulfur-containing organic polymers such as polythiophene; organic polymers such as polystyrene; natural polymers such as polysaccharides represented by cellulose, lignin, mannan, poly(galacturonic acid), chitosan, and saccharose; thermoplastic resins such as poly(phenylene sulfide) and poly(phenylene oxide); thermosetting resins such as furfuryl alcohol resins, phenol-formaldehyde resins, and imide resins; and solutions obtained by dissolving any of such organic substances in a low-molecular organic solvent, e.g., benzene, toluene, xylene, quinoline, or n-hexane. Examples thereof further include gases capable of carbonization.

Preferred of these are pitch materials. This is because pitch materials have a high actual carbon ratio and, hence, can give a material in high yield. The term “pitch material” in this description means a substance which is a pitch or a similar material and can be carbonized or graphitized by an appropriate treatment. Examples of the pitch materials which can be used include tars, heavy oils, and pitches. Examples of the tars include coal tar and petroleum tar. Examples of the heavy oils include petroleum-derived heavy oils such as catalytically cracked oil, thermally cracked oil, topping residues, and vacuum distillation residues. Examples of the pitches include coal tar pitch, petroleum pitch, and synthetic pitch. Of these, coal tar pitch is preferred because it has high aromaticity. Any one of these pitch materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion.

With respect to (4), examples include hydrocarbon compounds such as methane, ethane, propane, benzene, acetylene, and ethylene and carbon monoxide.

The proportion of the carbonaceous substance (C) contained in the orientation-differing-carbon composite is generally 0.1% by mass or higher, preferably 1% by mass or higher, more preferably 5% by mass or higher, even more preferably 10% by mass or higher. There is no particular upper limit on the proportion thereof, as long as the composite has an interface where orientation changes. When the proportion of the carbonaceous substance (C) is lower than the lower limit of that range, there are cases where interfacial bonding in the orientation-differing-carbon composite becomes weak. Furthermore, proportions thereof lower than the lower limit of that range may lessen the effect of inhibiting particle deformation during pressing which is produced by the carbonaceous substance (C) contained, resulting in reduced cycle characteristics.

From the standpoints of pressing load during electrode rolling and of balance of interfacial bonding in the composite, a more preferred constitution of this negative-electrode active material for use in a lithium secondary battery of the invention is one in which the orientation-differing-carbon composite comprises both of one or more natural-graphite-derived carbonaceous substances (B) and one or more carbonaceous substances (C).

For the same reasons as described above, the proportion by mass of the natural-graphite-derived carbonaceous substance (B) to the carbonaceous substance (C) (natural-graphite-derived carbonaceous substance (B)/carbonaceous substance (C)) in the orientation-differing-carbon composite is generally 20/80 or higher, preferably 40/60 or higher, more preferably 60/40 or higher, even more preferably 70/30 or higher. The upper limit thereof may be 99.9/0.1 or lower and is preferably 99/1 or lower, more preferably 95/5 or lower. When the proportion thereof is higher than the higher limit of that range (when the proportion of the natural-graphite-derived carbonaceous substance (B) is too high), there is a possibility that the interfacial bonding brought about by the carbonaceous substance (C) might decrease. On the other hand, when the proportion thereof is lower than the lower limit of that range (when the proportion of the natural-graphite-derived carbonaceous substance (B) is too low), there are cases where electrode rolling results in a considerably increased pressing load to cause peeling during the rolling.

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The orientation-differing-carbon composite comprising the natural-graphite-derived carbonaceous substance (B) and the carbonaceous substance (C) may be in any desired form unless this is counter to the spirit of the invention. Examples thereof are shown below.

(i) The form in which the surface of the natural-graphite-derived carbonaceous substance (B) is wholly or partly adhered to and/or covered with and/or bonded to the carbonaceous substance (C). (ii) The form in which the carbonaceous substance (C) is bonded to the whole or part of the surface of the natural-graphite-derived carbonaceous substance (B) to combine two or more particles of the natural-graphite-derived carbonaceous substance (B) and/or carbonaceous substance (C). (iii) The form which comprises a mixture of (i) and (ii) above in any proportion.

The natural-graphite-derived carbonaceous substance (B) and the carbonaceous substance (C) may be replaced by each other. Specific examples of the state of combination in the orientation-differing-carbon composite include: the state in which the surface of the particle serving as a core is adhered to and/or covered with and/or bonded to a carbonaceous substance differing in orientation; the state in which the surface of the core particle is adhered to and/or covered with and/or bonded to two or more such carbonaceous substances; and the state in which particles serving as cores have been aggregated in non-parallel arrangement. The term “the state in which particles have been aggregated in non-parallel arrangement” herein means that particles having a certain degree of crystallinity have been fixed, in the state of being randomly oriented, with another carbonaceous substance and have bonds which cause the two substances to differ in orientation.

[[Preparation of Orientation-Differing-Carbon Composite]]

The preparation of the orientation-differing-carbon composite will be described later under “Production Process 1 and Production Process 2 for Producing Orientation-Differing-Carbon Composite”. In preparing the orientation-differing-carbon composite, crystallinity can be improved by conducting a heat treatment and capacity per unit weight can hence be increased. The temperature for the heat treatment is generally 400° C. or higher, preferably 1,000° C. or higher, more preferably 2,000° C. or higher, even more preferably 2, 400° C. or higher, especially preferably 2, 800° C. or higher. The upper limit thereof is generally 3,400° C. or lower, preferably 3,200° C. or lower. In case where the temperature is lower than the lower limit of that range, there is a possibility that crystallinity improvement might be insufficient and the effect of increasing capacity per unit weight cannot be obtained. On the other hand, in case where the temperature exceeds the upper limit of that range, there is a possibility that the loss caused by carbon sublimation becomes not negligible, resulting in a decrease in yield.

[[Properties of Orientation-Differing-Carbon Composite]]

It is preferred that the orientation-differing-carbon composite should have properties which satisfy any one of the following items (1) to (5) or simultaneously satisfy two or more thereof.

(1) Roundness

With respect to the degree of sphericity of the orientation-differing-carbon composite, the roundness of the particles having a particle diameter in the range of 3-40 μm is generally 0.1 or higher, preferably 0.5 or higher, more preferably 0.8 or higher, even more preferably 0.85 or higher, most preferably 0.9 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics. Roundness is defined by the following equation. When a particle has a roundness of 1, this particle theoretically is a true sphere.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

Methods for improving roundness are not particularly limited. However, an orientation-differing-carbon composite in which the particles have been rounded by a rounding treatment is preferred because it gives an electrode in which the interstices among particles are uniform in shape. Examples of the rounding treatment include: a method in which a shear force or compressive force is applied to thereby mechanically make the shape of the particles close to sphere; and a method of mechanical/physical treatment in which fine particles are aggregated into particles by means of the bonding force of a binder or of the fine particles themselves.

(2) Raman R Value, Raman Half-Value Width

The Raman R value of the orientation-differing-carbon composite as determined by the argon ion laser Raman spectroscopy is generally 0.01 or higher, preferably 0.02 or higher, more preferably 0.04 or higher. The upper limit thereof is generally 0.35 or lower, preferably 0.30 or lower, more preferably 0.25 or lower. When the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

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The Raman half-value width around 1,580 cm −1 of the carbon material in this invention is not particularly limited. However, the half-value width thereof is generally 5 cm −1 or larger, preferably 10 cm −1 or larger. The upper limit thereof is generally 40 cm −1 or smaller, preferably 35 cm −1 or smaller, more preferably 30 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A around 1,580 cm −1 and the intensity I B of a peak P B around 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the carbon material. Furthermore, the half-value width of the peak P A around 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the carbon material.

Conditions for this Raman spectroscopy are as follows.

(3) Tap Density

The tap density of the orientation-differing-carbon composite desirably is generally 0.55 g/cm 3 or higher, preferably 0.70/cm 3 or higher, more preferably 0.9 g/cm 3 or higher, especially preferably 1 g/cm 3 or higher. The tap density thereof is preferably 2.0 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, even more preferably 1.7 g/cm 3 or lower, especially preferably 1.5 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where this orientation-differing-carbon composite, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining a density from the resultant volume of the sample and weight thereof. This density is defined as the tap density.

(4) BET Specific Surface Area

The specific surface area of the orientation-differing-carbon composite as a carbon material for use in this invention, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1.0 m 2 /g or larger, even more preferably 1.2 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this orientation-differing-carbon composite as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this orientation-differing-carbon composite as a negative-electrode material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

(5) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the orientation-differing-carbon composite, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 100 μm or smaller, preferably 50 μm or smaller, more preferably 40 μm or smaller, even more preferably 30 μm or smaller, especially preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a carbon composite is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

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From the standpoint of balance among battery characteristics, the orientation-differing-carbon composite preferably satisfies one or more of the following items (6) to (11) besides items (1) to (5) given above.

(6) X-Ray Parameter

The orientation-differing-carbon composite preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The lower limit of the value of d desirably is generally 0.340 nm or smaller, preferably 0.337 nm or smaller. When the value of d exceeds the upper limit of that range, there is a possibility that crystallinity might decrease to increase initial irreversible capacity. The value of 0.335 nm as the lower limit is a theoretical value for graphites. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 80 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to increase initial irreversible capacity.

(7) Ash Content

The ash content of the orientation-differing-carbon composite is generally 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole orientation-differing-carbon composite. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbon composite. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbon composite necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(8) Pore Distribution

In the orientation-differing-carbon composite, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), may be 0.001 mL/g or larger and is preferably 0.002 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. On the other hand, when the amount thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

The average pore diameter of the orientation-differing-carbon composite is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. On the other hand, when the average pore diameter thereof is smaller than the lower limit of that range, there are cases where high-current-density charge/discharge characteristics decrease.

(9) True Density

The true density of the orientation-differing-carbon composite is generally 2.0 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the orientation-differing-carbon composite is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

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(10) Orientation Ratio (Powder)

The orientation ratio of the orientation-differing-carbon composite is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

(11) Aspect Ratio (Powder)

The aspect ratio of the orientation-differing-carbon composite is theoretically 1 or higher. The upper limit thereof may be 10 or lower and is preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this orientation-differing-carbon composite causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

[[Raw Materials for Natural-Graphite-Derived Carbonaceous Substance (B)]]

Examples of raw materials for the natural-graphite-derived carbonaceous substance (B) to be contained in the orientation-differing-carbon composite include ones obtained from a natural graphite having such high crystallinity that the interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry is generally 0.340 nm or smaller. Specifically, it is preferred to use a powder selected from natural graphites, materials obtained by mechanically pulverizing natural graphites to improve their roundness and/or by heat-treating natural graphites at 1,000° C. or higher, materials obtained by heat-treating expanded graphites, and high-purity products obtained from those graphites.

The natural graphites (D) usable as precursors for the natural-graphite-derived carbonaceous substance (B) are classified into flake graphite, crystalline (vein) graphite, and amorphous graphite according to properties (see “Graphite” in Funrūtai Purosesu Gijutsu Shūsei (published by Industrial Technology Center in 1974); and HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES (published by Noyes Publications)). With respect to the degree of graphitization, crystalline graphite has a highest graphitization degree of 100% and flake graphite is second, which has a graphitization degree as high as 99.9%. However, the graphitization degree of amorphous graphite is as low as 28%. Flake graphite, among such natural graphites, occurs in Madagascar, China, Brazil, Ukraine, Canada, etc. Crystalline graphite occurs mainly in Sri Lanka. Amorphous graphite occurs mainly in the Korean Peninsula, China, Mexico, etc. Of these natural graphites, amorphous graphite generally has a small particle diameter and a low purity. In contrast, flake graphite and crystalline graphite have advantages such as the degree of graphitization and a low impurity content, and can hence be advantageously used in the invention.

[[Preparation of Natural-Graphite-Derived Carbonaceous Substance (B)]]

The preparation of the natural-graphite-derived carbonaceous substance (B) will be described later under “Production Process 1 and Production Process 2 for Producing Orientation-Differing-Carbon Composite”.

[[Properties of Natural-Graphite-Derived Carbonaceous Substance (B)]]

It is desirable that the natural-graphite-derived carbonaceous substance (B) should satisfy any one of the following items (1) to (11) or simultaneously satisfy two or more thereof. The definition of each of the following properties, method of determining the same, etc. are the same as those described above with regard to the orientation-differing-carbon composite.

(1) X-Ray Parameter

The natural-graphite-derived carbonaceous substance preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The value of d thereof desirably is generally 0.340 nm or smaller, preferably 0.337 nm or smaller. When the value of d exceeds the upper limit of that range, there is a possibility that crystallinity might decrease to enhance the increase in initial irreversible capacity. The value of 0.335 nm is a theoretical value for graphites. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 90 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to enhance the increase in initial irreversible capacity.

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(2) Ash Content

The ash content of the natural-graphite-derived carbonaceous substance is generally 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole natural-graphite-derived carbonaceous substance. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous substance. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the natural-graphite-derived carbonaceous substance, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, even more preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such a carbonaceous substance is undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

(4) Raman R Value, Raman Half-Value Width

The Raman R value of the natural-graphite-derived carbonaceous substance as determined by the argon ion laser Raman spectroscopy is generally 0.01 or higher, preferably 0.02 or higher, more preferably 0.04 or higher. The upper limit thereof may be 0.35 or lower and is preferably 0.30 or lower, more preferably 0.25 or lower. When the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the carbon material in the invention is not particularly limited. However, the half-value width thereof is generally 5 cm −1 or larger, preferably 10 cm −1 or larger. The upper limit thereof is generally 40 cm −1 or smaller, preferably 35 cm −1 or smaller, more preferably 30 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

(5) BET Specific Surface Area

The specific surface area of the natural-graphite-derived carbonaceous substance, as determined by the BET method, is generally 0.1 m 2 /g or larger, preferably 0.7 m 2 /g or larger, more preferably 1.0 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is generally 100 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, even more preferably 10 m 2 /g or smaller. When the specific surface area thereof is smaller than the lower limit of that range, there are cases where use of the carbon composite containing this carbonaceous substance as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of the carbon composite containing this carbonaceous substance as a negative-electrode material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

(6) Pore Distribution

In the natural-graphite-derived carbonaceous substance, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the amount thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is difficult to obtain.

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The average pore diameter of the natural-graphite-derived carbonaceous substance is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, especially preferably 0.5 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. When the average pore diameter thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease.

(7) Roundness

With respect to the degree of sphericity of the natural-graphite-derived carbonaceous substance, the roundness of the particles having a particle diameter in the range of 3-40 μm is preferably 0.1 or higher, especially preferably 0.5 or higher, more preferably 0.8 or higher, even more preferably 0.85 or higher, most preferably 0.9 or higher. High roundness values are preferred because they are effective in improving high-current-density charge/discharge characteristics.

(8) True Density

The true density of the natural-graphite-derived carbonaceous substance is generally 2.0 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the carbonaceous substance is lower than the lower limit of that range, there are cases where the carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

(9) Tap Density

The tap density of the natural-graphite-derived carbonaceous substance desirably is generally 0.1 g/cm 3 or higher, preferably 0.5 g/cm 3 or higher, more preferably 0.7 g/cm 3 or higher, especially preferably 0.9 g/cm 3 or higher. The upper limit thereof is preferably 2.0 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where the carbon composite containing this carbonaceous substance, when used in a negative electrode, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, the amount of interparticle interstices in the electrode is too small and it is difficult to secure electrical conductivity among the particles. There are hence cases where preferred battery performances are difficult to obtain.

(10) Orientation Ratio (Powder)

The orientation ratio of the natural-graphite-derived carbonaceous substance is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

(11) Aspect Ratio (Powder)

The aspect ratio of the natural-graphite-derived carbonaceous substance is theoretically 1 or higher. The upper limit thereof is generally 10 or lower, preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where the carbon composite containing this carbonaceous substance causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

[[Raw Materials for Carbonaceous Substance (C)]]

Raw materials for the carbonaceous substance (C) to be contained in the orientation-differing-carbon composite in this invention are not particularly limited as long as they are capable of carbonization. Examples thereof include the following organic substances: pitch materials; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; nitrogen-ring compounds such as phenazine and acridine; sulfur-ring compounds such as thiophene and bithiophene; polyphenylenes such as biphenyl and terphenyl; poly(vinylchloride), poly(vinylalcohol), poly(vinylbutyral), and substances obtained by insolubilizing these compounds; nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole; sulfur-containing organic polymers such as polythiophene; organic polymers such as polystyrene; natural polymers such as polysaccharides represented by cellulose, lignin, mannan, poly(galacturonic acid), chitosan, and saccharose; thermoplastic resins such as poly(phenylene sulfide) and poly(phenylene oxide); thermosetting resins such as furfuryl alcohol resins, phenol-formaldehyde resins, and imide resins; and solutions obtained by dissolving any of such organic substances in a low-molecular organic solvent, e.g., benzene, toluene, xylene, quinoline, or n-hexane. Examples thereof further include gases capable of carbonization.

In the pitch materials described above, the quinoline insoluble content is not particularly limited. However, pitch materials having a quinoline insoluble content of 30 or lower are generally used. Quinoline insolubles are, for example, submicron carbon particles, a fine sludge, etc. which are contained in a slight amount in coal tar. In case where such ingredients are contained in too large an amount, they considerably inhibit crystallinity from improving in a graphitization step and this leads to a considerable decrease in discharge capacity after graphitization. For determining the content of quinoline insolubles, use can be made of, e.g., the method as provided for in JIS K2425.

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The pitch materials described above may be used as a raw material in combination with any of various thermosetting resins, thermoplastic resins, and the like unless this lessens the effects of the invention.

[[Preparation of Carbonaceous Substance (C)]]

The preparation of the carbonaceous substance (C) will be described later under “Production Process 1 and Production Process 2 for Producing Orientation-Differing-Carbon Composite”.

[[Properties of Carbonaceous Substance (C)]]

It is preferred that the carbonaceous substance (C) should satisfy any one of the following items (1) to (4) or simultaneously satisfy two or more thereof. The definition of each of the following properties, method of determining the same, etc. are the same as those described above with regard to the orientation-differing-carbon composite.

(1) X-Ray Parameter

The carbonaceous substance (C) preferably has a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The value of d thereof desirably is generally 0.345 nm or smaller, preferably 0.340 nm or smaller, more preferably 0.337 nm or smaller. Furthermore, the crystallite size (Lc) of this carbon material, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 5 nm or larger, preferably 10 nm or larger, more preferably 50 nm or larger, even more preferably 80 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to enhance the increase in initial irreversible capacity.

(2) Ash Content

The ash content of the carbonaceous substance (C) is generally 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole orientation-differing-carbon composite. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbon composite. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Raman R Value, Raman Half-Value Width

The Raman R value of the carbonaceous substance (C) as determined by the argon ion laser Raman spectroscopy is generally 0.01 or higher, preferably 0.03 or higher, more preferably 0.05 or higher. The upper limit thereof is generally 0.60 or lower, preferably 0.30 or lower. When the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

The Raman half-value width around 1,580 cm −1 of the carbonaceous substance (C) in the invention is not particularly limited. However, the half-value width thereof is generally 5 cm −1 or larger, preferably 10 cm −1 or larger. The upper limit thereof is generally 60 cm −1 or smaller, preferably 45 cm −1 or smaller, more preferably 30 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and there are cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity and enhanced reactivity with the nonaqueous electrolyte and this may lead to a decrease in efficiency and enhanced gas evolution.

(4) True Density

The true density of the carbonaceous substance (C) is generally 2.0 g/cm 3 or higher, preferably 2.2 g/cm 3 or higher, more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be up to 2.26 g/cm 3 , which is a theoretical value for graphites. When the true density of the carbonaceous substance (C) is lower than the lower limit of that range, there are cases where the carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

[Negative Electrode [5]: Processes for Producing Orientation-Differing-Carbon Composite]

Production processes are not particularly limited, and any technique may be used unless it departs from the spirit of the invention. However, a preferred example thereof roughly comprises the following (1) and (2).

(1) A starting material for the carbonaceous substance (C) is wholly or partly brought into a liquid state in any step, and the material in this liquid state is mixed and/or kneaded with a natural graphite (D).

(2) The composite obtained in that step is subjected to volatile removal/heat-treating, graphitized, and then pulverized and classified to regulate the particle size. Between these steps, a pulverization/classification step may be conducted one or more times.

Specific examples of the process roughly explained above are shown below.

[[Production Process 1 for Producing Orientation-Differing-Carbon Composite]]

The orientation-differing-carbon composite in the invention preferably comprises a natural-graphite-derived carbonaceous substance (B) and, combined therewith, a carbonaceous substance (C) differing in orientation from the natural-graphite-derived carbonaceous substance (B). Examples of processes for producing it include a process which comprises mixing the natural graphite (D) with a precursor for the carbonaceous substance (C), i.e., a pitch material or a material obtained by heat-treating a pitch material or another material and pulverizing the heat-treated material (hereinafter abbreviated to “heat-treated graphite crystal precursor”), and with a natural polymer or the like in a given proportion, subjecting the mixture to heat treatment A, subsequently pulverizing the heat-treated mixture, and then subjecting the resultant powder to heat treatment B (heat-treating and graphitization). The pulverization may be omitted when the heat-treated mixture has a sufficiently small median diameter and does not necessitate pulverization.

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[[[Production of Heat-Treated Graphite Crystal Precursor]]]

A pitch material is subjected beforehand to a heat treatment to obtain a heat-treated graphite crystal precursor. This heat treatment conducted beforehand is called pitch heat treatment. This heat-treated graphite crystal precursor is pulverized and subsequently mixed with a natural graphite (D), and this mixture is subjected to heat treatment A, during which the precursor melts partly or wholly. By regulating the content of volatiles through the heat treatment conducted beforehand (pitch heat treatment), the molten state can be properly controlled. Examples of the volatiles contained in the heat-treated graphite crystal precursor generally include hydrogen, benzene, naphthalene, anthracene, and pyrene.

Temperature conditions for the pitch heat treatment are not particularly limited. However, the temperature is generally in the range of from 300° C. to 550° C. When the heat treatment temperature is lower than the lower limit of that range, there are cases where volatiles remain in an increased amount and, hence, safe pulverization in the air is difficult to conduct. On the other hand, when the temperature exceeds the upper limit, there are cases where the heat-treated graphite crystal precursor does not melt partly or wholly during the heat treatment A and particles comprising a natural-graphite-derived carbonaceous substance (B) and the heat-treated graphite crystal precursor combined therewith (orientation-differing-carbon composite) are difficult to obtain. The pitch heat treatment is conducted in an inert gas atmosphere such as, e.g., nitrogen gas or in the atmosphere of volatiles generated from the pitch material.

Apparatus usable for the pitch heat treatment are not particularly limited. For example, use can be made of a reaction vessel such as a shuttle furnace, tunnel kiln, electric furnace, or autoclave, a coker (heat-treatment vessel for coke production), or the like. During the pitch heat treatment, stirring may be conducted according to need.

It is preferred that the heat-treated graphite crystal precursor to be used should be one having a volatile content of generally 5% by mass or higher. When the graphite crystal precursor having a volatile content in that range is used, the carbonaceous substance (C) is combined with a natural-graphite-derived carbonaceous substance (B) by the heat treatment A, whereby an orientation-differing-carbon composite having the properties specified above can be obtained.

First, a process for producing the bulk mesophase which is the precursor for graphite crystals obtained beforehand by heat-treating a pitch material (bulk mesophase is a graphite crystal precursor which has been heat-treated; hereinafter it is abbreviated to “heat-treated graphite crystal precursor) will be explained.

(Volatile Content of Heat-Treated Graphite Crystal Precursor)

The volatile content of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited. However, the volatile content thereof is generally 5% by mass or higher, preferably 6% by mass or higher, and is generally 20% by mass or lower, preferably 15% by mass or lower. When the volatile content thereof is lower than the lower limit of that range, there are cases where safe pulverization in the air is difficult to conduct because of the volatiles contained in a large amount. On the other hand, when the volatile content thereof is higher than the upper limit, there are cases where the graphite crystal precursor does not melt partly or wholly during the heat treatment A and particles comprising a natural-graphite-derived carbonaceous substance (B) and the heat-treated graphite crystal precursor combined therewith (orientation-differing-carbon composite) are difficult to obtain. For determining the content of volatiles, use is made of, e.g., the method as provided for in JIS M8812.

(Softening Point of Heat-Treated Graphite Crystal Precursor)

The softening point of the graphite crystal precursor obtained by the pitch heat treatment is not particularly limited. However, the softening point thereof is generally 250° C. or higher, preferably 300° C. or higher, more preferably 370° C. or higher, and is generally 470° C. or lower, preferably 450° C. or lower, more preferably 430° C. or lower. When the softening point thereof is lower than the lower limit, there are cases where a heat treatment of this graphite crystal precursor results in a low carbonization yield and a homogeneous mixture with a natural-graphite-derived carbonaceous substance (B) is difficult to obtain. When the softening point thereof exceeds the upper limit, there are cases where the graphite crystal precursor does not melt partly or wholly during the heat treatment A and particles comprising a natural-graphite-derived carbonaceous substance (B) and the heat-treated graphite crystal precursor combined therewith (orientation-differing-carbon composite) are difficult to obtain.

The values of softening point used are ones measured by examining a sample molded in a thickness of 1 mm with a tableting press, by the penetration method using an apparatus for thermomechanical analysis (e.g., TMA4000, manufactured by Bruker AXS K.K.) in a nitrogen stream under the conditions of a heating rate of 10° C./min, needle tip shape of 1 mmϕ, and load of 20 gf.

(Pulverization of Heat-Treated Graphite Crystal Precursor)

Subsequently, the heat-treated graphite crystal precursor obtained by the pitch heat treatment is pulverized. This pulverization is conducted for the purpose of pulverizing the heat-treated graphite crystal precursor crystals which have come into a half-oriented state in each of large units due to the heat treatment and/or of evenly mixing and combining the heat-treated graphite crystal precursor with a natural graphite (D).

The pulverization of the heat-treated graphite crystal precursor obtained by the pitch heat treatment is not particularly limited. However, it is conducted so that the particle size of the heat-treated graphite crystal precursor is reduced by the pulverization to a value which is generally 1 μm or larger, preferably 5 μm or larger, and is generally 10 mm or smaller, preferably 5 mm or smaller, more preferably 500 μm or smaller, especially preferably 200 μm or smaller, even more preferably 50 μm or smaller. When the particle size thereof is smaller than 1 μm, there are cases where the heat-treated graphite crystal precursor is oxidized during or after the pulverization when the surface of the precursor comes into contact with air. This oxidation may inhibit crystallinity from improving in the step of graphitization, leading to a decrease in discharge capacity after the graphitization. On the other hand, when the particle size thereof exceeds 10 mm, the size-reducing effect of the pulverization is lessened and this tends to result in crystal orientation and the orientation of the carbonaceous substance (C). There are hence cases where the electrode employing this orientation-differing carbonaceous composite (A) has a reduced active-material orientation ratio and the electrode expansion which occurs upon battery charge is difficult to inhibit. Furthermore and/or alternatively, there are cases where the increased difference in particle diameter between the natural graphite (D) and the heat-treated graphite crystal precursor makes it difficult to conduct even mixing and this tends to result in a composite which is not homogeneous.

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Apparatus usable for the pulverization are not particularly limited. Examples of crushers include shearing mills, jaw crushers, impact crushers, and cone crushers. Examples of intermediate pulverizers include roll crushers and hammer mills. Examples of pulverizers include ball mills, oscillating mills, pin mills, stirring mills, jet mills, and turbo mills.

[[[Heat Treatment of Natural Graphite (D) and Heat-Treated Graphite Crystal Precursor]]]

A natural graphite (D) is mixed with the heat-treated graphite crystal precursor (raw material for a carbonaceous substance (C)) in a given proportion. This mixture is subjected to heat treatment A, pulverization, and heat treatment B (heat-treating and graphitization) to thereby produce an orientation-differing-carbon composite.

(Mixing of Natural Graphite (D) and Heat-Treated Graphite Crystal Precursor)

The mixing of the natural graphite (D) with the heat-treated graphite crystal precursor, which is conducted before heat treatment A, is not particularly limited in mixing ratio. However, the two ingredients are mixed together so that the proportion of the natural graphite (D) to the mixture is generally 20% by mass or higher, preferably 30% by mass or higher, more preferably 40% by mass or higher, and is generally 95% by mass or lower, preferably 90% by mass or lower. When the proportion thereof is lower than the lower limit, the proportion of the carbonaceous substance (C) in the orientation-differing carbonaceous composite (A) increases. There are hence cases where use of this carbon composite (A) in electrode formation is less apt to result in a high loading density and necessitates an excessively high pressing load. Namely, the effect to be produced by combining the natural-graphite-derived carbonaceous substance (B) is difficult to obtain. When the proportion of the natural graphite (D) exceeds the upper limit, the natural-graphite-derived carbonaceous substance (B) in the orientation-differing carbonaceous composite (A) comes to have an increased amount of exposed surfaces and this may result in an increase in the specific surface area of the orientation-differing carbonaceous composite (A). Namely, there are cases where such carbon composite (A) is undesirable from the standpoint of powder properties.

Apparatus usable for mixing the natural graphite (D) with the heat-treated graphite crystal precursor regulated so as to have a given particle size are not particularly limited. Examples thereof include V-shaped mixers, W-shaped mixers, change-can mixers, kneaders, drum mixers, and shearing mixers.

(Heat Treatment A)

Subsequently, the mixture of the natural graphite (D) and the heat-treated graphite crystal precursor is subjected to heat treatment A. This heat treatment is conducted for the purpose of re-melting or fusing the pulverized heat-treated graphite crystal precursor to thereby fix the natural graphite (D) and the fine particles of the heat-treated graphite crystal precursor while keeping the two ingredients in contact with each other in an unoriented state. Thus, the mixture of the natural graphite (D) and the heat-treated graphite crystal precursor can be converted to not a mere mixture of particles but a more homogeneous composite mixture (hereinafter suitably referred to as “graphite composite mixture”).

Temperature conditions for the heat treatment A are not particularly limited. However, the temperature is generally 300° C. or higher, preferably 400° C. or higher, more preferably 450° C. or higher, and is generally 650° C. or lower, preferably 600° C. or lower. When the temperature in heat treatment A is lower than the lower limit of that range, a large amount of volatiles remain in the material after heat treatment A and, hence, there is a possibility that the powder particles might be fused to each other during the step of heat-treating or graphitization. Namely, there are cases where re-pulverization becomes necessary. On the other hand, when the temperature exceeds the upper limit of that range, there are cases where the ingredient which was re-melted is broken into an acicular shape during pulverization, resulting in a decrease in tap density. Heat treatment A is conducted in an inert gas atmosphere, e.g., nitrogen gas, or in the atmosphere of volatiles generated from the heat-treated graphite crystal precursor which has been reduced into fine particles by pulverization.

Apparatus usable for heat treatment A are not particularly limited. For example, a shuttle furnace, tunnel kiln, electric furnace, or the like can be used.

(Treatment as Substitute for Pulverization of Heat-Treated Graphite Crystal Precursor and for Heat Treatment A)

Incidentally, a treatment as a substitute for the pulverization and heat treatment A described above can be conducted. Namely, it is possible to mix the heat-treated graphite crystal precursor with a natural graphite (D) and heat-treat the mixture while conducting a treatment in which the structure of the graphite crystal precursor can be reduced into fine particles in an unoriented state, e.g., a treatment in which mechanical energy is applied at a temperature in a range where the heat-treated graphite crystal precursor melts or softens.

This heat treatment as a substitute is not particularly limited. However, it is conducted at a temperature which is generally 200° C. or higher, preferably 250° C. or higher, and is generally 450° C. or lower, preferably 400° C. or lower. When the temperature conditions are lower than the lower limit of that range, there are cases where the melting or softening of the graphite crystal precursor during this substitute treatment is insufficient and this precursor is difficult to combine with the natural graphite (D). When the temperature exceeds the upper limit, the heat treatment is apt to proceed rapidly and there are hence cases where the particles of the carbonaceous heat-treated graphite crystal precursor, etc. are broken into an acicular shape during pulverization, resulting in a decrease in tap density.

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This substitute treatment is generally conducted in an inert atmosphere, e.g., nitrogen gas, or in an oxidizing atmosphere, e.g., air. It should, however, be noted that when the treatment is conducted in an oxidizing atmosphere, there are cases where high crystallinity is difficult to obtain after graphitization. It is therefore necessary to prevent oxygen from excessively making the precursor infusible. Specifically, the substitute treatment is conducted so that the graphite crystal precursor after the treatment has an oxygen content of generally 8% by mass or lower, preferably 5% by mass or lower.

Apparatus usable for the substitute treatment are not particularly limited. However, a mixer, kneader, or the like can be used.

(Pulverization)

Subsequently, the graphite composite mixture which has undergone heat treatment A is pulverized. This graphite composite mixture is in the form of aggregates formed through heat treatment A by combining the finely powdered structure in an unoriented state with the natural graphite (D) through melting or fusion. This pulverization is conducted for the purpose of pulverizing the aggregates to a target particle diameter.

The particle size of the graphite composite mixture after the pulverization is not particularly limited. However, it is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger, and is generally 50 μm or smaller, preferably 35 μm or smaller, more preferably 30 μm or smaller. In case where the particle size thereof is smaller than the lower limit of that range, the resultant orientation-differing carbonaceous composite (A) has a reduced tap density and gives an electrode less apt to have an increased active-material loading density. Namely, a high-capacity battery is difficult to obtain. On the other hand, when the particle size thereof exceeds the upper limit of that range, there are cases where the resultant orientation-differing carbonaceous composite (A) is apt to cause coating unevenness when used in producing an electrode through coating fluid application.

Apparatus usable for the pulverization are not particularly limited. Examples of crushers include jaw crushers, impact crushers, and cone crushers. Examples of intermediate pulverizers include roll crushers and hammer mills. Examples of pulverizers include ball mills, oscillating mills, pin mills, stirring mills, and jet mills.

(Heat Treatment B: Burning)

Heat treatment B means heat-treating and graphitization. The heat-treating is first explained. However, this heat-treating may be omitted. The graphite composite mixture which has been reduced into fine particles by the pulverization is heat-treated. This heat-treating is conducted for the purpose of removing volatiles from the graphite composite mixture in order to control the fusion of the graphite composite mixture in graphitization.

Temperature conditions in the heat-treating are not particularly limited. However, the temperature is generally 600° C. or higher, preferably 1,000° C. or higher. The upper limit thereof is generally 2,400° C. or lower, preferably 1,300° C. or lower. When the temperature conditions are lower than the lower limit of that range, there are cases where the powder of the graphite composite mixture is apt to fuse during graphitization. On the other hand, in case where the temperature exceeds the upper limit of that range, the heat-treating apparatus becomes costly. Consequently, the heat-treating is conducted usually under temperature conditions within that range.

The heat-treating is conducted in an inert gas atmosphere, e.g., nitrogen gas, or in a non-oxidizing atmosphere comprising gases generated from the graphite composite mixture which has been re-pulverized. For the purpose of simplifying production steps, graphitization may be directly conducted without via a heat-treating step.

Apparatus usable for the heat-treating are not particularly limited. For example, use can be made of a shuttle furnace, tunnel kiln, electric furnace, Riedhammer furnace, rotary kiln, or the like.

(Heat Treatment B: Graphitization)

Subsequently, the graphite composite mixture which has been heat-treated is graphitized. This graphitization is conducted for the purpose of improving crystallinity in order to increase discharge capacity in battery evaluation. Through the graphitization, an orientation-differing carbonaceous composite (A) can be obtained.

Temperature conditions in the graphitization are not particularly limited. However, the temperature is generally 2, 800° C. or higher, preferably 2, 900° C. or higher, more preferably 3,000° C. or higher, and is generally 3,400° C. or lower, preferably 3,200° C. or lower. When the temperature exceeds the upper limit of that range, there are cases where a battery having a reduced reversible capacity results. Namely, there are cases where a high-capacity battery is difficult to produce. In addition, temperatures higher than the upper limit of that range may apt to result in enhanced graphite sublimation.

The graphitization is conducted in an inert gas atmosphere, e.g., argon gas, or in a non-oxidizing atmosphere comprising gases generated from the graphite composite mixture which has been heat-treated. Apparatus usable for the graphitization are not particularly limited. Examples thereof include direct voltage application type electric furnaces, Acheson furnaces, and indirect voltage application type furnaces such as resistance heating furnaces and induction heating furnaces.

Incidentally, a graphitization catalyst such as, e.g., Si or B may be added to inner parts or the surface of a material (the natural graphite (D), pitch material, or graphite crystal precursor) during the graphitization or in any of the steps before the graphitization, i.e., the steps ranging from the heat treatment to the heat-treating.

(Other Treatments)

Besides the treatments described above, other various treatments including classification can be conducted unless such treatments lessen the effects of the invention. Classification is a treatment for removing coarse particles and fine particles in order to regulate the particle size after the graphitization treatment to a target particle diameter.

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Apparatus usable for the classification are not particularly limited. However, in the case of dry sieving, use can be made of a rotary sieve, swing sieve, revolving sieve, vibrating sieve, or the like. In the case of dry air classification, use can be made of a gravitational classifier, inertial classifier, or centrifugal classifier (e.g., classifier or cyclone). Furthermore, for wet sieving, use can be made of a mechanical wet classifier, hydraulic classifier, sedimentation classifier, centrifugal wet classifier, or the like.

Classification may be conducted immediately after the pulverization after heat treatment A, or may be conducted in another timing. For example, it may be conducted after the heat-treating after the pulverization or conducted after the graphitization. It is also possible to omit the classification treatment itself. However, from the standpoints of reducing the BET specific surface area of the orientation-differing carbonaceous composite (A) and of productivity, it is preferred to conduct a classification treatment immediately after the pulverization after heat treatment A.

(Treatment after Production of Orientation-Differing Carbonaceous Composite (A))

An artificial-graphite powder separately produced or a natural-graphite powder may be further mixed with the orientation-differing carbonaceous composite (A) produced by the procedure described above, for the purposes of regulating the BET specific surface area of the negative-electrode material, improving suitability for electrode pressing, improving discharge capacity, cost reduction, etc.

[Negative Electrode [5]: Production Process 2 for Orientation-Differing-Carbon Composite]

The orientation-differing-carbon composite may be produced also by the following process. The orientation-differing-carbon composite in the invention preferably comprises a natural-graphite-derived carbonaceous substance (B) and, combined therewith, a carbonaceous substance (C) differing in orientation from the natural-graphite-derived carbonaceous substance (B). Examples of processes for producing it include a process in which the natural graphite (D) and a pitch material as a precursor for the carbonaceous substance (C) are subjected to the steps of “kneading (mixing)”, “molding”, “heat-treating”, “graphitization”, and “pulverization”. Of these steps, “molding”, “heat-treating”, and “pulverization” may be omitted and/or conducted simultaneously with another step. Specifically, the carbon composite can be obtained, for example, by the following production process.

[[Kneading (Mixing)]]

Raw materials comprising a natural graphite (D), a pitch material, and optional ingredients, e.g., a graphitization catalyst, are mixed together. In this operation, it is preferred to conduct heating for even mixing. Thus, a mixture is obtained in which the liquid pitch material is adherent to the natural graphite (D) and the raw material which does not melt at the kneading temperature. In this case, use may be made of a method in which all raw materials are charged into a kneading machine and are kneaded and heated simultaneously. Alternatively, use may be made of a method in which the ingredients other than the pitch material are charged into a kneading machine and heated with stirring and the pitch material having ordinary temperature or in a vulcanized and molten state is charged after the contents have been heated to a kneading temperature.

The heating temperature for the kneading is generally a temperature not lower than the softening point of the pitch material, preferably a temperature higher than the softening point by 10° C. or more, more preferably a temperature higher than the softening point by 20° C. or more. The upper limit thereof is generally 300° C. or lower, preferably 250° C. or lower. When the temperature is lower than the lower limit of that range, there are cases where the pitch material has an increased viscosity to make the mixing difficult. On the other hand, when the temperature exceeds the upper limit of that range, there are cases where the system being mixed comes to have too high a viscosity due to volatilization and polycondensation.

A mixing machine of the kind having stirring blades is preferred. As the stirring blades, general ones can be used, such as the Z type or the matiscator type. The amount of the raw materials to be charged into the mixing machine generally is 10% by volume or larger, preferably 15% by volume or larger, and is 50% by volume or smaller, preferably 30% by volume or smaller, based on the capacity of the mixing machine. A mixing period of 5 minutes or longer is necessary. The mixing period is up to the time when the volatilization of volatile ingredients results in a large viscosity change. Usually, the mixing period is 30-120 minutes. It is preferred that the mixing machine be preheated to the kneading temperature before the mixing.

[[Molding]]

The mixture obtained may be subjected as it is to the step of volatile removal/heat-treating, which is conducted for the removal of volatile ingredients and carbonization. It is, however, preferred to mold the mixture in order to facilitate handling before it is subjected to the step of volatile removal/heat-treating.

Molding methods are not particularly limited as long as the resultant shape can be maintained. Use can be made of extrusion molding, molding with a mold, hydraulic molding, or the like. Of these molding techniques, extrusion molding is apt to give molded objects in which the particles are oriented, while hydraulic molding is inferior in productivity although the particles are in a randomly oriented state. Molding with a mold is preferable to these two techniques because it has advantages that the operation is relatively easy and a molded object can be obtained without breaking the structure in which the particles are in a randomly oriented state due to the mixing.

The molding may be conducted either at room temperature (cold molding) or with heating (hot molding; temperature not lower than the softening point of the pitch material). In the case of cold molding, it is desirable that the mixture which has been cooled after the kneading should be crushed beforehand to a maximum size of 1 mm or smaller in order to improve moldability and obtain molded-object evenness. The shape and size of the molded object are not particularly limited. In the case of hot molding, however, formation of too large a molding necessitates much time in conducting even preheating prior to the molding. Consequently, the size thereof is generally preferably up to about 150 cm in terms of maximum dimension.

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With respect to molding pressure, too high a pressure makes it difficult to remove volatile ingredients through pores of the resultant molded object and orients particles of the natural graphite (D) which are not completely round, making it difficult to conduct pulverization in a later step. Consequently, the upper limit of the molding pressure is generally 3,000 kgf/cm 2 (294 MPa) or lower, preferably 500 kgf/cm 2 (49 MPa) or lower, more preferably 10 kgf/cm 2 (0.98 MPa) or lower. Although the lower limit of the pressure is not particularly limited, it is preferably regulated to a value which enables the molded object to retain its shape in the step of volatile removal/heat-treating.

[[Volatile Removal/Burning]]

The molded object obtained is subjected to the step of volatile removal/heat-treating for the purpose of removing volatile ingredients from the natural graphite (D) and pitch material to thereby prevent the volatile ingredients from fouling a packing and the molded object from adhering to the packing during graphitization. The volatile removal/heat-treating is conducted at a temperature which is generally 600° C. or higher, preferably 650° C. or higher, and is generally 1,300° C. or lower, preferably 1,100° C. or lower, for a period of generally 0.1-10 hours. For the purpose of preventing oxidation, the heating is conducted generally in the stream of an inert gas, e.g., nitrogen or argon, or in a non-oxidizing atmosphere formed by packing a particulate carbon material such as, e.g., a breeze or packing coke in spaces.

Apparatus usable for the volatile removal/heat-treating are not particularly limited as long as they can be used for heat-treating in a non-oxidizing atmosphere, like electric furnaces, gas furnaces, Riedhammer furnaces for electrode materials, and the like. The heating rate in the heating desirably is low from the standpoint of removing volatile ingredients. In general, heating from about 200° C., at which low-boiling ingredients begin to volatilize, to about 700° C., at which hydrogen becomes the only substance which generates, is conducted at 3-100° C./hr.

[[Graphitization]]

The carbonized molding obtained by the volatile removal/heat-treating is subsequently graphitized by high-temperature heating. Conditions for this graphitization are the same as described above under Production Process 1.

With respect to atmospheres for the graphitization, it is conducted in the stream of an inert gas, e.g., nitrogen or argon, or in a non-oxidizing atmosphere formed by packing a particulate carbon material such as, e.g., a breeze or packing coke in spaces, in order to prevent oxidation. Apparatus usable for the graphitization are not particularly limited as long as they meet the purpose. For example, an electric furnace, gas furnace, Acheson furnace, or the like can be used. Conditions including heating rate, cooling rate, and heat treatment period can be determined at will within the ranges allowable for the apparatus.

[[Pulverization]]

The graphitization product thus obtained is usually in the form of aggregates. This product, without any treatment, is usually difficult to use as a negative-electrode active material. Consequently, pulverization and/or removal of large particles and small particles is conducted. Methods for pulverizing the graphitization product are not particularly limited. Examples of pulverization devices include devices for mechanical grinding, such as, e.g., ball mills, hammer mills, CF mills, atomizer mills, and pulverizers, and pulverization devices utilizing wind force, such as, e.g., jet mills. For crushing and intermediate pulverization, use may be made of an impact type crushing device, such as a jaw crusher, hammer mill, or roller mill. The timing of pulverization may be before the graphitization or after the graphitization.

[Negative Electrode [5]: Minor-Material Mixing]

Besides the orientation-differing-carbon composite, one or more carbonaceous substances (carbonaceous materials) differing in carbonaceous-substance property from the carbon composite may be incorporated into the negative-electrode active material for use in a lithium secondary battery of the invention. Thus, battery performances can be further improved. The term “carbonaceous-substance property” herein means one or more properties selected from X-ray diffraction parameter, median diameter, aspect ratio, BET specific surface area, orientation ratio, Raman R value, tap density, true density, pore distribution, roundness, and ash content. Preferred embodiments include: one in which the volume-based particle size distribution is not symmetrical about the median diameter; one in which two or more carbon materials differing in Raman R value are contained; and one in which carbon materials differing in X-ray parameter are contained. One example of the effects thereof is that the incorporation of a carbon material, such as a graphite, e.g., a natural graphite or artificial graphite, or an amorphous carbon, e.g., a carbon black such as acetylene black or needle coke, as a sub material serves to reduce electrical resistance. One of these carbon materials may be used alone, or any desired two or more thereof may be used in combination in any desired proportion. In the case where such a carbon material is added as a sub material, the amount thereof may be 0.1% by mass or larger and is preferably 0.5% by mass or larger, more preferably 0.6% by mass or larger. The upper limit thereof may be 80% by mass or smaller and is preferably 50% by mass or smaller, more preferably 40% by mass or smaller, even more preferably 30% by mass or smaller. When the amount thereof is smaller than the lower limit of that range, there are cases where the effect of improving conductivity is difficult to obtain. When the amount thereof exceeds the upper limit, there are cases where this leads to an increase in initial irreversible capacity.

[Negative Electrode [5]: Electrode Production]

This negative electrode may be produced by an ordinary method. It can be formed in the same manner as described above. The current collector, thickness ratio between the current collector and the active-material layer, electrode density, binder, electrode-plate orientation ratio, impedance, etc. also are the same as described above.

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An explanation will be given below on negative electrode [6] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing, as a negative-electrode active material, graphitic carbon particles which have a roundness of 0.85 or higher and an interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry of smaller than 0.337 nm and which, in an examination by argon ion laser Raman spectroscopy, have a Raman R value defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 of from 0.12 to 0.8”.

[Negative Electrode [6]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [6] is described below.

The negative-electrode active material for use in negative electrode [6] in a lithium secondary battery of the invention comprises graphitic carbon particles satisfying at least the following (a), (b), and (c).

(a) The roundness is 0.85 or higher. (b) The interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry is smaller than 0.337 nm. (c) The Raman R value defined as the ratio of the peak intensity at 1,360 cm −1 to the peak intensity at 1,580 cm −1 in an examination by argon ion laser Raman spectroscopy (hereinafter often referred to simply as “Raman R value”) is from 0.12 to 0.8.

[[Roundness]]

The roundness of the graphitic carbon particles for use as a negative-electrode active material in a lithium secondary battery of the invention is generally 0.85 or higher, preferably 0.87 or higher, more preferably 0.89 or higher, especially preferably 0.92 or higher. With respect to the upper limit thereof, a particle having a roundness of 1 theoretically is a true sphere. In case where the roundness thereof is lower than the lower limit of that range, use of this negative-electrode active material results in a reduced loading and thermal conductivity decreases. There are hence cases where a quick output recovery is inhibited. In particular, there are cases where an output recovery from a low-output state at low temperatures is slow.

In the invention, roundness is defined by the following equation.

Roundness=(length of periphery of equivalent circle having the same area as projected particle shape)/(actual length of periphery of projected particle shape)

[[Interplanar Spacing (d002)]]

The interplanar spacing (d002) for the (002) planes of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention, as determined by wide-angle X-ray diffractometry, is smaller than 0.337 nm, and is preferably 0.336 nm or smaller. The lower limit thereof is 0.335, which is a theoretical value for graphites. In case where the interplanar spacing (d002) thereof exceeds the upper limit of that range, crystallinity decreases and heat conduction by electrons decreases. There are hence cases where the property of quickly recovering output decreases. In particular, there are cases where an output recovery from a low-output state at low temperatures is slow.

The term “interplanar spacing (d002) for the (002) planes as determined by wide-angle X-ray diffractometry” in the invention means the value of d (interplanar spacing) for the lattice planes ((002) planes) as determined by X-ray diffractometry by the method of the Japan Society for Promotion of Scientific Research.

The crystallite size (Lc) of the graphitic carbon particles as determined by X-ray diffractometry by the method of the Japan Society for Promotion of Scientific Research is not particularly limited. However, the Lc thereof is generally 10 nm or larger, preferably 30 nm or larger, more preferably 80 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, crystallinity decreases and heat conduction by electrons decreases. There are hence cases where the property of quickly recovering output decreases.

[[Raman R Value]]

The Raman R value of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention should be 0.12 or higher, and is preferably 0.15 or higher, more preferably 0.17 or higher, especially preferably 0.2 or higher. The upper limit thereof is preferably 0.8 or lower, more preferably 0.6 or lower, especially preferably 0.45 or lower. In case where the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity and the number of charge/discharge sites decreases. There are hence cases where output itself decreases accordingly. On the other hand, in case where the Raman R value thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity. There are hence cases where heat conduction by electrons decreases and the property of recovering output decreases.

The examination for a Raman spectrum is made with a Raman spectrometer (e.g., a Raman spectrometer manufactured by Japan Spectroscopic Co., Ltd.). In the examination, a sample is charged into a measuring cell by causing the sample to fall naturally into the cell and the surface of the sample in the cell is irradiated with argon ion laser light while rotating the cell in a plane perpendicular to the laser light. The Raman spectrum obtained is examined for the intensity I A of a peak P A at 1,580 cm −1 and the intensity I B of a peak P B at 1,360 cm −1 . The ratio between these intensities R (R=I B /I A ) is calculated and this ratio is defined as the Raman R value of the graphitic carbon particles. Furthermore, the half-value width of the peak P A at 1,580 cm −1 in the Raman spectrum obtained is measured, and this value is defined as the Raman half-value width of the graphitic carbon particles.

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Conditions for this Raman spectroscopy are as follows.

The Raman half-value width at 1,580 cm −1 of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 60 cm −1 or smaller, preferably 50 cm −1 or smaller, more preferably 45 cm −1 or smaller. In case where the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity and the number of charge/discharge sites decreases. There are hence cases where output itself decreases accordingly. On the other hand, in case where the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles has reduced crystallinity. There are hence cases where heat conduction by electrons decreases and the property of recovering output decreases.

[[Tap Density]]

The tap density of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention is preferably 0.55 g/cm 3 or higher, more preferably 0.7 g/cm 3 or higher, even more preferably 0.8 g/cm 3 or higher, especially preferably 1 g/cm 3 or higher. The upper limit thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. In case where the tap density thereof is lower than the lower limit of that range, this graphitic carbon, when used in a negative electrode, is less apt to have a high loading density and has a reduced interparticle contact area. There are hence cases where thermal conductivity decreases. On the other hand, in case where the tap density thereof exceeds the upper limit of that range, the electrode has too small an amount of interparticle interstices and a reduced amount of channels for the nonaqueous electrolyte. There are hence cases where output itself decreases.

In the invention, the tap density of a sample is determined by dropping the sample through a sieve having an opening size of 300 μm into a 20-cm 3 tapping cell to fill the cell with the sample up to the brim, subsequently conducting tapping operations 1,000 times over a stroke length of 10 mm using a powder densimeter (e.g., Tap Denser, manufactured by Seishin Enterprise Co., Ltd.), and determining a density from the resultant volume of the sample and the weight thereof. This density is defined as the tap density.

[[BET Specific Surface Area]]

The specific surface area of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention, as determined by the BET method, is preferably 0.1 m 2 /g or larger, more preferably 0.7 m 2 /g or larger, especially preferably 1 m 2 /g or larger, even more preferably 1.5 m 2 /g or larger. The upper limit thereof is preferably 100 m 2 /g or smaller, more preferably 50 m 2 /g or smaller, especially preferably 25 m 2 /g or smaller, even more preferably 15 m 2 /g or smaller. When the BET specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this graphitic carbon as a negative-electrode material is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, there are cases where use of this graphitic carbon as a negative-electrode material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

[[Volume-Average Particle Diameter]]

The volume-average particle diameter of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention, which is defined as the volume-average particle diameter (median diameter) determined by the laser diffraction/scattering method, is preferably 1 μm or larger, more preferably 3 μm or larger, especially preferably 5 μm or larger, even more preferably 7 μm or larger. The upper limit thereof is generally 50 μm or smaller, preferably 40 μm or smaller, more preferably 30 μm or smaller, especially preferably 25 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where irreversible capacity increases, leading to a loss in initial battery capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where such graphitic carbon particles are undesirable from the standpoint of battery production because an uneven coating surface is apt to result when an electrode plate is produced.

[[Pore Volume]]

With respect to the pore volume of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention, the amount of interstices corresponding to a pore diameter of from 0.01 μm to 1 μm which include pores in the particles and particle surface irregularities formed by steps, as determined by mercury porosimetry (mercury intrusion method), is generally 0.01 mL/g or larger, preferably 0.05 mL/g or larger, more preferably 0.1 mL/g or larger. The upper limit thereof is generally 0.6 mL/g or smaller, preferably 0.4 mL/g or smaller, more preferably 0.3 mL/g or smaller. When the amount of interstices therein is larger than the upper limit of that range, there are cases where a large amount of a binder is necessary in electrode plate formation. When the amount thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease and the effect of diminishing electrode expansion/contraction during charge/discharge is not obtained.

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The average pore diameter of the graphitic carbon particles is preferably 0.05 μm or larger, more preferably 0.1 μm or larger, even more preferably 0.5 μm or larger. The upper limit thereof may be 50 μm or smaller and is preferably 20 μm or smaller, more preferably 10 μm or smaller. When the average pore diameter thereof exceeds the upper limit of that range, there are cases where a large amount of a binder is necessary. When the average pore diameter thereof is smaller than the lower limit, there are cases where high-current-density charge/discharge characteristics decrease.

As an apparatus for the mercury porosimetry was used a mercury porosimeter (Autopore 9520, manufactured by Micromeritics Corp.). About 0.2 g of a sample (negative-electrode material) was weighed out and placed in a powder cell and this cell was closed. The sample in the cell was pretreated by degassing it at room temperature under vacuum (50 μmHg or lower) for 10 minutes. Subsequently, the pressure in the cell was reduced to 4 psia (about 28 kPa) and mercury was introduced thereinto. The internal pressure was stepwise elevated from 4 psia (about 28 kPa) to 40,000 psia (about 280 MPa) and then lowered to 25 psia (about 170 kPa). The number of steps in the pressure elevation was 80 or larger. In each step, the amount of mercury intruded was measured after an equilibrium time of 10 seconds. A pore distribution was calculated from the mercury intrusion curve thus obtained, using the Washburn equation. For the calculation, the surface tension (γ) and contact angle (ψ) of mercury were taken as 485 dyne/cm and 140°, respectively. The average pore diameter used was the pore diameter corresponding to a cumulative pore volume of 50%.

[[Ash Content]]

The ash content of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention is preferably 1% by mass or lower, especially preferably 0.5% by mass or lower, more preferably 0.1% by mass or lower, based on the whole graphitic carbon particles. The lower limit thereof is preferably 1 ppm or higher. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. On the other hand, when the ash content thereof is lower than the lower limit of that range, there are cases where the production of this graphitic carbon necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

The true density of the graphitic carbon particles is generally 2.0 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, even more preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density thereof is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity. In the invention, true density is defined as one determined by the liquid-phase displacement method (pycnometer method) using butanol.

[[Orientation Ratio]]

The orientation ratio of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention is generally 0.005 or higher, preferably 0.01 or higher, more preferably 0.015 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where high-density charge/discharge characteristics decrease.

Conditions for this X-ray diffractometry are as follows. Incidentally, “2θ” represents diffraction angle.

Target: Cu(Kα line) graphite monochromator Slit:

Divergence slit=1 degree Receiving slit=0.1 mm Scattering slit=1 degree

Examination range and step angle/measuring time:

(110) plane: 76.5°≤2θ≤78.5° 0.01°/3 sec (004) plane: 53.5°≤2θ≤56.0° 0.01°/3 sec

[[Aspect Ratio]]

The aspect ratio of the graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention is theoretically 1 or higher. The upper limit thereof may be 10 or lower and is preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where this graphitic carbon causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

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The graphitic carbon particles for use as the negative-electrode active material of negative electrode [6] in a lithium secondary battery of the invention may be ones which occur naturally or ones produced artificially. However, the graphitic carbon particles preferably are ones comprising a natural graphite. The graphitic carbon particles may be ones obtained by subjecting naturally occurring ones or artificially produced ones to a specific treatment. Processes for producing the graphitic carbon particles (including classification methods) also are not particularly limited. For example, graphitic carbon particles obtained by a classification technique such as, e.g., sieving or air classification so as to have the properties described above may be employed.

Especially preferred graphitic carbon particles, among those, are ones produced by modifying naturally occurring carbonaceous particles or artificially produced carbonaceous particles by subjecting them to a mechanical energy treatment. More preferred are ones produced by this modification in which the carbonaceous particles to be subjected as a raw material to the mechanical energy treatment comprise a natural graphite.

[[Mechanical Energy Treatment]]

This mechanical energy treatment is explained below. The carbonaceous particles to be subjected as a raw material to the mechanical energy treatment are not particularly limited. Examples thereof include carbonaceous particles derived from a natural or artificial graphite and carbonaceous particles which are a graphite precursor. Properties of these raw materials will be shown below.

[[[Graphite-Derived Carbonaceous Particles as Raw Material for Mechanical Energy Treatment]]]

It is desirable that the graphite-derived carbonaceous particles to be used as a raw material should have properties which satisfy any one of the following items (1) to (11) or simultaneously satisfy two or more thereof. The methods of determining the following properties and the definitions thereof are the same as in the graphitic carbon particles described above.

(1) X-Ray Parameter

The graphite-derived carbonaceous particles as a raw material preferably have a value of d (interplanar spacing) for the lattice planes (002), as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, of 0.335 nm or larger. The upper limit of the value of d desirably is generally 0.340 nm or smaller, preferably 0.337 nm or smaller. Furthermore, the crystallite size (Lc) of the graphite-derived carbonaceous particles, as determined by X-ray diffractometry in accordance with the method of the Japan Society for Promotion of Scientific Research, is generally 30 nm or larger, preferably 50 nm or larger, more preferably 100 nm or larger. In case where the Lc thereof is smaller than the lower limit of that range, there is a possibility that crystallinity might decrease to enhance the increase in initial irreversible capacity.

(2) Ash Content

The ash content of the graphite-derived carbonaceous particles as a raw material is preferably 1% by mass or lower, especially 0.5% by mass or lower, in particular 0.1% by mass or lower, based on the whole graphite-derived carbonaceous substance. The lower limit of the ash content thereof is preferably at least 1 ppm by mass of the whole carbonaceous substance. When the ash content thereof exceeds the upper limit of that range, there are cases where battery performance deterioration caused by reaction with the nonaqueous electrolyte during charge/discharge becomes not negligible. When the ash content thereof is lower than the lower limit of that range, there are cases where the production of this carbonaceous substance necessitates much time and energy and an apparatus for pollution prevention, resulting in an increase in cost.

(3) Volume-Average Particle Diameter

With respect to the volume-average particle diameter of the graphite-derived carbonaceous particles as a raw material, the volume-average particle diameter (median diameter) thereof as determined by the laser diffraction/scattering method is generally 1 μm or larger, preferably 3 μm or larger, more preferably 5 μm or larger, even more preferably 7 μm or larger. Although the upper limit thereof is not particularly limited, it is generally 10 mm or smaller, preferably 1 mm or smaller, more preferably 500 μm or smaller, even more preferably 100 μm or smaller, especially preferably 50 μm or smaller. When the volume-average particle diameter thereof is smaller than the lower limit of that range, there are cases where application of mechanical energy results in too small a particle diameter and this leads to an increase in irreversible capacity. When the volume-average particle diameter thereof exceeds the upper limit of that range, there are cases where the apparatus to be used for the application of mechanical energy is difficult to operate efficiently and this leads to a time loss.

(4) Raman R Value, Raman Half-Value Width

The Raman R value of the graphite-derived carbonaceous particles as a raw material, as determined by the argon ion laser Raman spectroscopy, is generally 0.01 or higher, preferably 0.03 or higher, more preferably 0.1 or higher. The upper limit thereof may be 0.6 or lower and is preferably 0.4 or lower. When the Raman R value thereof is lower than the lower limit of that range, the surface of such particles has too high crystallinity. Even after the Raman R value thereof is increased by applying mechanical energy, crystallinity remains low. There are hence cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman R value thereof exceeds the upper limit of that range, the surface of such particles comes to have further reduced crystallinity upon reception of mechanical energy. There are hence cases where the particles have enhanced reactivity with the nonaqueous electrolyte, leading to a decrease in efficiency and enhanced gas evolution.

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The Raman half-value width around 1,580 cm −1 of the graphite-derived carbonaceous particles is not particularly limited. However, the half-value width thereof is generally 10 cm −1 or larger, preferably 15 cm −1 or larger. The upper limit thereof is generally 50 cm −1 or smaller, preferably 45 cm −1 or smaller, more preferably 40 cm −1 or smaller. When the Raman half-value width thereof is smaller than the lower limit of that range, the surface of such particles has too high crystallinity. Even after the Raman half-value width thereof is increased by applying mechanical energy, crystallinity remains low. There are hence cases where the number of intercalation sites into which lithium comes with charge/discharge decreases. Namely, there are cases where suitability for charge decreases. On the other hand, when the Raman half-value width thereof exceeds the upper limit of that range, the surface of such particles comes to have further reduced crystallinity upon reception of mechanical energy. There are hence cases where the particles have enhanced reactivity with the nonaqueous electrolyte, leading to a decrease in efficiency and enhanced gas evolution.

(5) BET Specific Surface Area

The specific surface area of the graphite-derived carbonaceous particles as a raw material, as determined by the BET method, is generally 0.05 m 2 /g or larger, preferably 0.2 m 2 /g or larger, more preferably 0.5 m 2 /g or larger, especially preferably 1 m 2 /g or larger. The upper limit thereof is generally 50 m 2 /g or smaller, preferably 25 m 2 /g or smaller, more preferably 15 m 2 /g or smaller, especially preferably 10 m 2 /g or smaller. When the BET specific surface area thereof is smaller than the lower limit of that range, there are cases where use of this carbonaceous substance is apt to result in poor lithium acceptance during charge and in lithium deposition on the electrode surface even after the BET specific surface area thereof is increased by applying mechanical energy. On the other hand, when the specific surface area thereof exceeds the upper limit of that range, this carbonaceous substance comes to have a further increased BET specific area upon reception of mechanical energy. There are hence cases where use of this carbonaceous substance as a negative-electrode active material is apt to result in enhanced reactivity with the nonaqueous electrolyte and enhanced gas evolution and a preferred battery is difficult to obtain.

(7) Roundness

With respect to the degree of sphericity of the graphite-derived carbonaceous particles as a raw material, the roundness of the particles having a particle diameter in the range of 3-40 μm is preferably 0.1 or higher, more preferably 0.2 or higher, especially preferably 0.4 or higher, even more preferably 0.5 or higher, most preferably 0.6 or higher. When the roundness thereof is lower than the lower limit of that range, there are cases where rounding does not proceed sufficiently even with application of mechanical energy, resulting in a decrease in high-current-density charge/discharge characteristics.

(8) True Density

The true density of the graphite-derived carbonaceous particles as a raw material is generally 2 g/cm 3 or higher, preferably 2.1 g/cm 3 or higher, more preferably 2.2 g/cm 3 or higher, especially preferably 2.22 g/cm 3 or higher. The upper limit thereof may be 2.26 g/cm 3 or lower. This upper limit is a theoretical value for graphites. When the true density of the carbonaceous substance is lower than the lower limit of that range, there are cases where this carbon has too low crystallinity, resulting in an increase in initial irreversible capacity.

(9) Tap Density

The tap density of the graphite-derived carbonaceous particles as a raw material desirably is generally 0.05 g/cm 3 or higher, preferably 0.1 g/cm 3 or higher, more preferably 0.2 g/cm 3 or higher, especially preferably 0.5 g/cm 3 or higher. The tap density thereof is preferably 2 g/cm 3 or lower, more preferably 1.8 g/cm 3 or lower, especially preferably 1.6 g/cm 3 or lower. When the tap density thereof is lower than the lower limit of that range, there are cases where application of mechanical energy does not result in a sufficiently improved tap density. Namely, there are cases where the treated carbonaceous substance, when used as a negative-electrode active material, is less apt to have a high loading density and cannot give a battery having a high capacity. On the other hand, when the tap density thereof exceeds the upper limit of that range, application of mechanical energy results in a further increased tap density. There is hence a possibility that use of the treated carbonaceous substance in electrode formation might give an electrode which has too small an amount of interparticle interstices and has a deficiency in passages for the nonaqueous electrolyte, resulting in a decrease in high-current-density charge/discharge characteristics. The tap density of the graphite-derived carbonaceous particles also is measured and defined by the same method as described above.

(10) Orientation Ratio (Powder)

The orientation ratio of the graphite-derived carbonaceous particles as a raw material is generally 0.001 or higher, preferably 0.005 or higher. The upper limit thereof is theoretically 0.67 or lower. When the orientation ratio thereof is lower than the lower limit of that range, there are cases where application of mechanical energy does not result in a sufficiently improved orientation ratio, resulting in a decrease in high-density charge/discharge characteristics.

(11) Aspect Ratio (Powder)

The aspect ratio of the graphite-derived carbonaceous particles as a raw material is theoretically 1 or higher. The upper limit thereof is generally 10 or lower, preferably 8 or lower, more preferably 5 or lower. When the aspect ratio thereof exceeds the upper limit, there are cases where application of mechanical energy does not result in a sufficiently reduced aspect ratio and where the treated carbonaceous substance causes streak lines in electrode plate formation and an even coating surface cannot be obtained, resulting in a decrease in high-current-density charge/discharge characteristics.

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The graphite-derived carbonaceous particles as a raw material described above may be ones made of a highly crystalline carbon material in which carbon-hexagonal planar structures have grown. Examples of this carbon material include a highly oriented graphite in which the hexagonal planes have been grown so as to enhance planar orientation and an isotropic high-density graphite in which highly oriented graphite particles have been aggregated in isotropic directions. Preferred examples of the highly oriented graphite include natural graphites occurring in Sri Lanka and Madagascar, the so-called Kish graphite obtained by precipitating carbon from supersaturated molten iron, and some artificial graphites having a high degree of graphitization.

Natural graphites are classified into flake graphite, crystalline (vein) graphite, and amorphous graphite according to properties (see “Graphite” in Funrūtai Purosesu Gijutsu Shūsei (published by Industrial Technology Center in 1974); and HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES (published by Noyes Publications)). With respect to the degree of graphitization, crystalline graphite has a highest graphitization degree of 100% and flake graphite is second, which has a graphitization degree as high as 99.9%. However, the graphitization degree of amorphous graphite is as low as 28%. Flake graphite, among such natural graphites, occurs in Madagascar, China, Brazil, Ukraine, Canada, etc. Crystalline graphite occurs mainly in Sri Lanka. Amorphous graphite occurs mainly in the Korean Peninsula, China, Mexico, etc. Of these natural graphites, amorphous graphite generally has a small particle diameter and a low purity. In contrast, flake graphite and crystalline graphite have advantages such as a high degree of graphitization and a low impurity content, and can hence be advantageously used in the invention.

Artificial graphites can be produced by heating a petroleum-derived heavy oil, coal-derived heavy oil, petroleum coke, or coal coke at a temperature of 1,500-3,000° C. or higher in a non-oxidizing atmosphere.

In the invention, any artificial graphite can be used as a raw material as long as it comes to have high orientation and high capacity through the mechanical energy treatment and a heat treatment. Furthermore, even an incompletely graphitized material such as, e.g., a graphite precursor, among those artificial graphites, can be used as a raw material for the mechanical energy treatment in the invention as long as it can become graphitic carbon particles satisfying the properties described above through the mechanical energy treatment.

[[[Details of Mechanical Energy Treatment]]]

The mechanical energy treatment of such graphite-derived carbonaceous particles as a raw material is a treatment for reducing the particle diameter thereof so that the ratio between the volume-average particle diameters before and after the treatment becomes 1 or lower and for heightening the tap density thereof and increasing the Raman R value thereof 1.1 time or more.

Through such mechanical energy treatment, the carbonaceous particles such as graphite-derived carbonaceous particles as a raw material become particles in which only parts near the surface are rough and which have exposed strains and edge faces, while maintaining high crystallinity as a whole. Thus, the particles come to have an increased amount of surfaces where lithium ions can come in and out, and hence have a high capacity even at a high current density.

The “mechanical energy treatment” in the invention belongs to a “pulverization treatment” among engineering unit operations utilizable for particle design, such as pulverization, classification, mixing, granulation, surface modification, and reaction. However, it simultaneously includes a surface treatment which causes fine structural defects in the surface structure by impacts, friction, compression, etc.

In general, a pulverization treatment means an operation in which a force is applied to a substance to thereby reduce the size thereof and regulate the particle diameter, particle size distribution, and loading of the substance. Pulverization treatments are classified according to the kind of force to be applied to the substance and the method of treatment. Forces to be applied to the substance are roughly divided into the following four: breaking force (impact force), crushing force (compressive force), milling force (grinding force), and scraping force (shear force). On the other hand, treatment methods are roughly divided into the following two: volume pulverization in which cracks are generated and propagated in inner parts of the particles; and surface pulverization in which surface parts of the particles are scraped off. Volume pulverization proceeds by means of impact force, compressive force, and shear force, while surface pulverization proceeds by means of grinding force and shear force. Pulverization is a treatment based on any of various combinations of such kinds of forces to be applied to a substance and such treatment methods. A suitable combination can be determined according to the purpose of the treatment. There are cases where a pulverization treatment is conducted by a chemical reaction, e.g., explosion, or by volume expansion. However, pulverization is generally conducted with a mechanical apparatus such as a pulverizer.

The mechanical energy treatment use of which is preferred for producing the graphitic carbon particles in the invention preferably is a treatment which finally involves surface treatment and involves a high proportion of the pulverization of particle surface parts (surface pulverization) regardless of whether volume pulverization occurs or not. This is because particle surface pulverization is important for eliminating angles of the carbonaceous particles, e.g., graphitic carbon particles, and thereby imparting roundness to the particle shape. Specifically, a mechanical energy treatment may be conducted in such a manner that surface pulverization is conducted after volume pulverization has proceeded to some degree, or may be conducted in such a manner that surface pulverization only is conducted almost without conducting volume pulverization. Furthermore, a mechanical energy treatment may be conducted in such a manner that volume pulverization and surface pulverization are simultaneously conducted. Preferred is a mechanical energy treatment in which surface pulverization proceeds finally and angles are eliminated from the surface of the particles.

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The mechanical energy treatment in the invention is a treatment for reducing the particle diameter thereof so that the ratio between the volume-average particle diameters before and after the treatment becomes 1 or lower and for heightening the tap density thereof and increasing the Raman R value thereof 1.1 time or more.

The term “ratio between the volume-average particle diameters before and after the treatment” means a value obtained by dividing the volume-average particle diameter as measured after the treatment by the volume-average particle diameter as measured before the treatment. Although the value of (volume-average particle diameter after the treatment)/(volume-average particle diameter before the treatment) is 1 or smaller, it is preferably 0.95 or smaller. When the value thereof is substantially 1, there are cases where the loading-improving effect of the mechanical energy treatment through roundness improvement is low. Incidentally, the treatment in which the particle size is reduced so that the ratio between the average particle diameters before and after the treatment becomes 1 or lower is effective also in regulating the particle shape.

The mechanical energy treatment in the invention is one which increases tap density. To increase tap density means an improvement in the degree of sphericity represented by roundness as will be described later. The mechanical energy treatment hence should be one which produces such an effect. Although the value of (tap density after the treatment)/(tap density before the treatment) is 1 or larger, it is preferably 1.1 or larger. When the value thereof is smaller than 1, there are cases where the effect of improving loading through a roundness improvement is low.

The mechanical energy treatment in the invention is one which increases Raman R value 1.1 time or more. To increase Raman R value means that crystallinity around the particle surface decreases as will be described later. The mechanical energy treatment hence should be one which produces such an effect. Although the value of (Raman R value after the treatment)/(Raman R value before the treatment) is 1.1 or larger, it is preferably 1.4 or larger. When the value thereof is smaller than 1.1, there are cases where the effect of improving suitability for charge through a change in Raman R value is low.

The mechanical energy treatment in the invention imparts roundness to particles and increases the tap density of the particles. It is known that for heightening the tap density of powder particles, it is effective to fill interstices among the particles with smaller particles capable of coming into the interstices. Although it may be thought that the tap density of carbonaceous particles, e.g., graphite-derived carbonaceous particles, can be increased by subjecting the particles to a treatment such as pulverization to reduce the particle diameter thereof, the particle diameter reduction by such a technique generally reduces rather than increases the tap density. The reason for this is thought to be that the pulverization makes the particle shape more irregular.

On the other hand, the proportion of interstices in a layer packed with powder particles decreases as the number of particles in contact with one particle (any particle selected) increases (i.e., as the coordination number n increases). Namely, important factors influencing tap density include the proportions of particle sizes, i.e., particle diameter distribution. It should, however, be noted that this investigation was made on a model powder composed of spherical particles. The carbonaceous particles to be handled in the invention, e.g., graphite-derived carbonaceous particles before treatment, are flaky, crystalline, or platy. Because of this, even when it is attempted to heighten a tap density by regulating the particle diameter distribution by merely conducting general pulverization, classification, etc. only, such a highly packed state cannot be attained.

Flaky, crystalline, and platy carbonaceous particles such as, e.g., graphite-derived carbonaceous particles, generally tend to decrease in tap density as the particle diameter decreases. The reasons for this are thought to be as follows. As a result of pulverization, the particles come to have more irregular shapes, have a larger amount of surface projections such as “fine splits”, “half-peeled parts”, and “bent parts”, and have finer particles of irregular shapes adherent to the particle surface at some degree of strength. These are causative of increased resistance between adjacent particles and impaired suitability for loading, resulting in a decrease in tap density.

As a result of investigations made by the inventors on carbonaceous or graphitic particulate materials which are almost equal in true density and in average particle diameter, it has been ascertained that the materials having a more spherical shape have a higher tap density. Namely, it is important to impart roundness to the particle shape and make the shape close to sphere. As the particle shape becomes close to sphere, the suitability for loading of the powder simultaneously improves greatly. For the reasons shown above, powder tap density is employed as an index to the application of mechanical energy. In the case where the suitability for loading of a powdery or particulate material was improved through a treatment, it can be thought that this improvement is a result of the rounding of the particles due to the treatment used. Furthermore, when particles are treated by the method according to the invention while considerably reducing the particle diameter and the carbon material thus obtained has a tap density which is higher than the tap densities of carbon materials obtained by general pulverization and having almost the same particle diameter, then this can be thought to be a result of rounding.

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As indexes to the crystallinity of particles and the roughness of the particle surface, i.e., to the amount of crystal edge faces present, use can be made of interplanar spacing (d002) for the (002) planes and crystallite size (Lc) both determined by wide-angle X-ray diffractometry and Raman R value. In general, carbon materials having a smaller interplanar spacing (d002) for the (002) planes and a larger crystallite size (Lc) have lower Raman R value. Namely, carbonaceous particles such as graphite-derived carbonaceous particles as a whole have almost the same crystalline state. In contrast, the graphitic carbon particles according to this invention have a small interplanar spacing (d002) for the (002) planes and a large crystallite size (Lc) and, despite this, have a high Raman R value. This means that in these graphitic carbon particles, a surface layer (to a depth of about 100 Å from the particle surface) has disordered crystallinity and a large amount of exposed edge faces although the particles have high bulk crystallinity.

From the standpoint of improving suitability for loading, the mechanical energy treatment in the invention preferably is one which further increases roundness 1.02 times, especially preferably 1.04 times.

[[[Apparatus for Mechanical Energy Treatment]]]

The apparatus to be used for conducting the mechanical energy treatment is selected from ones usable for conducting the preferred treatment described above. An investigation made by the inventors revealed the following. The mechanical energy treatment may be accomplished with one or more of the four kinds of forces. However, it is effective to employ an apparatus which repeatedly applies impact force as a main force and other mechanical actions such as compressive force, frictional force, shear force, etc., including those caused by particle interaction, to the particles. Specifically, a preferred apparatus is one which comprises a casing and disposed therein a rotor having blades and in which the rotor is rotated at a high speed to thereby apply mechanical actions such as impact, compressive, frictional, and shear forces to carbonaceous particles introduced therein and conduct surface pulverization while allowing volume pulverization to proceed. More preferred is one which has a mechanism in which carbonaceous particles are circulated to thereby repeatedly apply mechanical actions thereto. The number of blades in the casing is preferably 3 or more, especially preferably 5 or more.

One example of preferred apparatus which satisfy such requirements is Hybridization System, manufactured by Nara Machinery Co., Ltd. In the case where the treatment is conducted with this apparatus, the rotor is rotated at a peripheral speed of preferably 30-100 m/sec, more preferably 40-100 m/sec, even more preferably 50-100 m/sec. Although carbonaceous particles can be treated by merely passing these through the apparatus, it is preferred to treat the carbonaceous particles while causing these to circulate or reside in the apparatus for 30 seconds or longer. More preferably, the carbonaceous particles are treated while circulating or residing in the apparatus for 1 minute or longer.

In the case where the graphite-derived carbonaceous particles as a raw material have a true density lower than 2.25 and the crystallinity thereof is not so high, it is preferred that a heat treatment for enhancing crystallinity should be further conducted after the mechanical energy treatment. This heat treatment is conducted at a temperature of preferably 2,000° C. or higher, more preferably 2,500° C. or higher, even more preferably 2,800° C. or higher.

[Negative Electrode [6]: Electrode Production]

An explanation will be given below on negative electrode [7] for use in a lithium secondary battery of the invention, i.e., “a negative electrode containing as a negative-electrode active material a multielement-containing negative-electrode active material (C) which contains at least one of a lithium-occluding metal (A) selected from the group consisting of Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb and/or a lithium-occluding alloy (B) and further contains C and/or N as element Z.”

[Negative Electrode [7]: Negative-Electrode Active Material]

The negative-electrode active material for use in negative electrode [7] is described below.

[[Composition]]

The negative-electrode active material to be used in negative electrode [7] in a lithium secondary battery of the invention is characterized by containing at least a metal capable of occluding lithium (lithium-occluding metal (A)) and/or an alloy capable of occluding lithium (lithium-occluding alloy (B)) and containing C and/or N as element Z.

The lithium-occluding metal (A) means at least one member selected from the group consisting of Al, Pb, Zn, Sn, Bi, In, Mg, Ga, Cd, Ag, Si, B, Au, Pt, Pd, and Sb. Preferred of these is Al, Si, Sn, or Pb. More preferred is Si or Sn. Even more preferred is Si. The reasons for the preference of Si include that it brings about a high capacity per unit mass.

The lithium-occluding alloy (B) means one comprising two or more of those lithium-occluding metals (A) or one comprising a lithium-occluding metal (A) and at least one element other than the lithium-occluding metal (A), C, and N. This element other than the lithium-occluding metal (A), C, and N preferably is one or more elements selected from Groups 4, 5, 6, 8, 9, 10, 11, 13, and 16 of the periodic table. More preferred are one or more of the elements Ti, Zr, V, Cr, W, B, O, and Co. Even more preferred are one or more of the elements Ti, Zr, W, O, and Co. These elements are apt to form high-melting compounds and, hence, can be advantageously used from the standpoint of reactivity control. The content of the alloy-forming element, i.e., the element other than the lithium-occluding metal (A), C, and N, is preferably 50% by mole or lower based on the whole lithium-occluding alloy (B) from the standpoint of capacity.

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Examples of the state in which the C and/or N as element Z is present in the multielement-containing negative-electrode active material (C) include:

1. the state in which element Z is contained in the lithium-occluding metal (A) and/or lithium-occluding alloy (B) (element-Z-internally-possessing lithium-occluding substance (D)); 2. the state in which element Z is present around the lithium-occluding metal (A) and/or lithium-occluding alloy (B) (element-Z-externally-possessing lithium-occluding substance (F)); and 3. the state in which element Z is present in both the states 1. and 2. above.

In a preferred embodiment of the element-Z-internally-possessing lithium-occluding substance (D), element Z (C and/or N) is present in a non-equilibrium state in the lithium-occluding metal (A) and/or lithium-occluding alloy (B). Especially preferably, the lithium-occluding metal (A) is Si.

A preferred embodiment of the element-Z-externally-possessing lithium-occluding substance (F) is one in which element Z is C. This is because C can impart electrical conductivity.

Although the multielement-containing negative-electrode active material (C) for use as a negative-electrode active material in this invention contains a lithium-occluding metal (A) and/or a lithium-occluding alloy (B) and further contains C and/or N as an essential component, it preferably further contains one or more elements selected from Groups 4, 5, 6, 8, 9, 10, 11, 13, and 16 of the periodic table. More preferred are one or more of the elements Ti, Zr, V, Cr, W, B, O, and Co. Even more preferred are one or more of the elements Ti, Zr, W, O, and Co.

1. Element-Z-Internally-Possessing Lithium-Occluding Substance (D)

Of the lithium-occluding metals (A) usable in the invention, Si is apt to produce the effect. Because of this, the element-Z-internally-posses sing lithium-occluding substance (D) preferably is one which comprises as a main component a compound represented by the general formula SiZ x M y (wherein Z, M, x, and y are as defined under the following (1) to (4)) and constituting a phase in which element Z is present in a non-equilibrium state in Si:

(1) element Z is C and/or N; (2) element M is one or more elements selected from elements other than Si and element Z; (3) x is such a value that, with respect to the Z concentration (p/(a+p)) in the compound Si a Z p (wherein a and p are integers) present in an equilibrium state so as to have a composition closest to Si, the value of Z concentration ratio Q(Z) calculated with the equation Q(Z)=[x/(1+x)]/[p/(a+p)] is 0.10-0.95; and (4) y is a number in the range of 0≤y≤0.50.

(With Respect to SiZ x M y )

((Element Z))

Element Z in SiZ x M y is at least one element which is C and/or N. The reasons why C and/or N is preferred as the element Z to be internally possessed include the following:

(1) C and N each are capable of forming a compound having a higher melting point than Si; (2) C and N each have a smaller covalent radius than Si; (3) C and N each have a low coefficient of diffusion in Si; and (4) C and N each change little in volume even when reacted with lithium.

Specifically, the elements C and N can form compounds which have a higher melting point than Si and are present in an equilibrium state, such as, e.g., SiC and Si 3 N 4 . High-melting compounds generally are stable compounds having a large negative value of free energy regarding formation and, hence, can effectively reduce the activity of Si. From the standpoint of controlling reactivity with the nonaqueous electrolyte, element Z preferably is C and/or N.

Furthermore, since the elements C and N each have a smaller covalent radius than Si, they are less apt to form a compound present in an equilibrium state in the compound SiZ x M y although details of this tendency are unclear. This is thought to be effective in more evenly distributing element Z in a high concentration. The elements C and N can hence more effectively reduce the activity of Si and are preferred also from the standpoint of controlling reactivity with the nonaqueous electrolyte.

Moreover, since the elements C and N each have a low coefficient of diffusion in Si, the elements C and N, when present in the state of being dispersed in the Si, inhibit the Si from aggregating or crystallizing with charge/discharge. The elements C and N are preferred also from the standpoint of inhibiting the Si from becoming fine particles or reacting with the nonaqueous electrolyte. In addition, since the elements C and N change little in volume even when reacted with lithium, they are less apt to influence Si conduction path breakage and are hence preferred.

Incidentally, when a compound capable of being present in an equilibrium state has a lower melting point than Si, such as, e.g., Cu 3 Si or Ni 2 Si, as in the case of elements such as Cu and Ni, there are cases where the activity of Si is not effectively reduced and reactivity with nonaqueous electrolyte is difficult to control. Moreover, since the elements Cu and Ni have a high coefficient of diffusion in Si, the aggregation and crystallization of Si proceed with charge/discharge. There are hence cases where the Si is apt to become fine particles and cycle characteristics are not improved. When such a compound present in an equilibrium state in the compound SiZ x M y is a main component, there are cases where the activity of Si does not decrease and reactivity with the nonaqueous electrolyte cannot be controlled, resulting in impaired cycle characteristics, etc.

((Element M))

Element Min SiZ x M y is one or more elements selected from elements other than Si and element Z. Preferably, element M is one or more elements selected from Groups 4, 5, 6, 8, 9, 10, 11, 13, and 16 of the periodic table. From the standpoint of reaction inhibition, the elements Ti, Zr, V, Cr, W, B, and O are preferred because these elements are apt to form a high-melting compound. More preferred are the elements Ti, Zr, W, and O.

With respect to the composition of SiZ x M y , x in the SiZ x M y is such a value that, with respect to the Z concentration (p/(a+p)) in the compound Si a Z p (wherein a and p are integers) present in an equilibrium state so as to have a composition closest to Si, the value of Z concentration ratio Q(Z) calculated with the equation Q(Z)=[x/(1+x)]/[p/(a+p)] is generally 0.10 or larger, preferably 0.15 or larger, more preferably 0.30 or larger, especially preferably 0.40 or larger. The upper limit of the value of Q(Z) is generally 0.95 or smaller, preferably 0.85 or smaller, more preferably 0.75 or smaller, especially preferably 0.65 or smaller. The “compound present in an equilibrium state so as to have a composition closest to Si” means the compound Si a Z p in which the value of p/(a+p) is minimum and which is present in an equilibrium state.

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Incidentally, the compound Si a Z p present in an equilibrium state so as to have a composition closest to Si, in this invention, is described in phase diagrams for Si and element Z (e.g., Desk Handbooks Phase Diagrams for Binary Alloys , ASM International). In this invention, the Z concentration ratio Q(Z) described above is used for the Z concentration (p/(a+p)) of this Si a Z p , and the range of x is specified in terms of the numerical-value range of the Z concentration ratio Q(Z).

The term “compound present in an equilibrium state” herein means a constant-proportion compound, such as the compound Si a Z p (wherein a and p are integers), indicated by a vertex in a diagram, e.g., the phase diagram given above. For example, when Z is C, SiC is known as a stable compound and this compound is regarded as the compound present in an equilibrium state in the invention. Consequently, when Z is C, then SiC corresponds to the Si a Z p according to the invention. Furthermore, when Z is, for example, N, then Si 3 N 4 is known as the most stable compound. However, Si 2 N 3 and SiN also are known to be present as constant-proportion compounds. In this invention, all these compounds are regarded as compounds present in an equilibrium state. Consequently, when Z is N, then SiN corresponds to the Si a Z p according to the invention.

On the other hand, the term “compound constituting a phase present in a non-equilibrium state” means any compound other than the compounds present in an equilibrium state. In the case of the compound present in a non-equilibrium state, no specific constant-proportion compound is formed and Si atoms and Z atoms are evenly dispersed when viewed macroscopically.

When the Z concentration ratio Q (Z) is lower than the lower limit of that range, the effect of reducing the activity of Si is low. There are hence cases where reactivity with the nonaqueous electrolyte cannot be controlled and electrode expansion is enhanced, making it impossible to obtain preferred cycle characteristics. On the other hand, when the ratio Q (Z) exceeds the upper limit of that range, a stable compound Si a Z p or the like present in an equilibrium state is formed and the activity of Si is not reduced even when the amount of element Z is increased. There are hence cases where reactivity with the nonaqueous electrolyte cannot be controlled. Furthermore, Si a Z p or the like has low electrical conductivity. There are hence cases where formation of such a compound results in impaired electrical conductivity of the active material and difficulties in lithium doping/undoping, making it impossible to conduct charge/discharge.

When the Z concentration ratio Q(Z) is 1, this means that the Si is present as a stable compound Si a Z p ; this state is undesirable. When the ratio Q(Z) is far higher than the upper limit of that range, the effect of increasing capacity which is produced by the Si contained is difficult to obtain and there are cases where preferred battery characteristics are not obtained.

Incidentally, when the elements C and N are simultaneously used as element Z, the values of the Z concentration ratio Q(Z) are determined respectively for the two elements from the element Z concentrations based on Si a Z p , and the sum of these is taken as the Z concentration ratio Q(Z).

Symbol y in SiZ x M y is a real number satisfying 0≤y≤0.5. In the case where the compound SiZ x M y contains element M and y≠0, the proportion y of element M in this compound SiZ x M y is generally 0.08 or higher, preferably 0.10. The upper limit thereof is generally 0.50 or lower, preferably 0.40 or lower, more preferably 0.30 or lower. When y exceeds the upper limit of that range, the content of Si is low and there are cases where high capacity is difficult to obtain. In the case where the compound contains substantially no element M, the proportion y of element M is such that y=0 or y≈0. In this invention, y≈0 indicates the case where the element M unavoidably came into the compound during, e.g., steps for producing the negative-electrode active material according to the invention (i.e., the case where substantially no element M is contained) and the y is, e.g., less than 0.08.

The composition of the multielement-containing negative-electrode active material (C) can be determined in an ordinary manner, for example, with an X-ray photoelectron spectroscope (e.g., “ESCA” manufactured by ULVAC-PHI, INC.) by placing the negative-electrode active material on a sample table so that the side containing the negative-electrode compound faces upward and forms a flat surface, making a depth profile examination while conducting Ar sputtering using an aluminum Kα line as an X-ray source, and calculating the concentrations of the atoms of Si, element Z, element M, etc.

(Composition of SiC x O y )

In the case where element Z is C and element M is O, then x in the general formula SiC x O y is generally 0.053 or larger, preferably 0.08 or larger, more preferably 0.15 or larger, especially preferably 0.25 or larger. The upper limit of x is generally 0.90 or smaller, preferably 0.75 or smaller, more preferably 0.60 or smaller, especially preferably 0.45 or smaller. Furthermore, y is generally 0 or larger, preferably a value larger than 0, especially preferably 0.08 or larger, more preferably 0.10 or larger. The upper limit of y is generally 0.50 or smaller, preferably 0.40 or smaller, especially preferably 0.30 or smaller.

(State of Element Z Present in Si in Element-Z-Internally-Possessing Lithium-Occluding Substance (D))

With respect to the state in which element Z is present in Si in the negative-electrode compound SiZ x M y in the invention, the value of XIsz in X-ray diffractometry is not particularly limited. However, in the case where element Z is C, the value of XIsz is preferably 1.2 or smaller, more preferably 0.7 or smaller. In the case where element Z is N, the value of XIsz is preferably 1.1 or smaller, more preferably 1.0 or smaller. When the value of XIsz is not larger than the upper limit of that range, this means that a phase in which element Z is present in a non-equilibrium state in the Si constitutes a main component and any compound present in an equilibrium state, e.g., Si a Z p , is not a main component. Such values of XIsz are preferred because of freedom from the following problems associated with too large values of XIsz. When the value of XIsz exceeds the upper limit of that range, i.e., when the phase of a compound present in an equilibrium state, such as, e.g., Si a Z p (silicon carbide or silicon nitride when element Z is C or N, respectively), is a main component, then the activity of Si is not reduced. There are hence cases where reactivity with the nonaqueous electrolyte cannot be controlled, resulting in impaired cycle characteristics. Furthermore, since the Si a Z p or the like has poor electrical conductivity, there are cases where the active-material thin film has impaired electrical conductivity and lithium doping/undoping becomes difficult, making it impossible to conduct charge/discharge. There also are cases where this active material has a reduced capacity per unit mass. Such values of XIsz are hence undesirable. The lower limit of the value of XIsz is generally 0.00 or larger.

›BEST MODE FOR CARRYING OUT THE INVENTION · 72 of 73

((Method of X-Ray Diffractometry))

In X-ray diffractometry, the value of XIsz can be determined, for example, by setting the negative-electrode active material according to the invention on a surface to be irradiated and examining the active material with an X-ray diffractometer (e.g., “X-Ray Diffractometer” manufactured by Rigaku Corp.). Examination conditions are the same as those shown in Examples which will be given later.

The definitions of the value of XIsz are as follows.

(((Value of XIsz when Element Z is C)))

The peak intensity Isz at a 2θ of 35.7° and the peak intensity Is at a 2θ of 28.4° are measured, and the intensity ratio XIsz (XIsz=Isz/Is) is calculated and defined as the XIsz of the active-material thin film. The peak at a 2θ of 35.7° and the peak at a 2θ of 28.4° are thought to be a peak attributable to SiC and a peak attributable to silicon, respectively. When the value of XIsz is 1.2 or smaller, this means that almost no SiC is detected.

(((Value of XIsz when Element Z is N)))

The peak intensity Isz at a 2θ of 70.2° and the peak intensity Is at a 2θ of 28.4° are measured, and the intensity ratio XIsz (XIsz=Isz/Is) is calculated and defined as the XIsz of the active-material thin film. The peak at a 2θ of 27.1° and the peak at a 2θ of 28.4° are thought to be a peak attributable to Si 3 N 4 and a peak attributable to silicon, respectively. When the value of XIsz is 1.1 or smaller, this means that almost no Si 3 N 4 is detected.

(State of Element Z Distributed in Element-Z-Internally-Possessing Lithium-Occluding Substance (D))

In the SiZ x M y in the invention, element Z is present, for example, as atoms, molecules, clusters, etc. of the size of 1 μm or smaller. With respect to the state in which element Z is distributed, it is preferably distributed evenly in the SiZ x M y , more preferably distributed so as to have a concentration gradient in which the concentration thereof increases from a central part of the SiZ x M y toward the surface thereof (in the case of the negative-electrode material in a thin film form described later, the concentration has a gradient so that it increases from the part in contact with the current collector toward the surface of the thin film; in the case of the negative-electrode material in a powder form, the concentration has a gradient so that it increases from a central part of each particle toward the particle surface). When element Z is unevenly distributed and locally present in the negative-electrode active material, the expansion/contraction of Si with charge/discharge localizes in Si parts where element Z is absent. There are hence cases where electrical conductivity becomes poor with the progress of cycling. The state in which element Z is dispersed can be ascertained, for example, by EPMA as will be shown later.

(State of Element M Distribution)

The state in which element M is distributed in the SiZ x M y in the invention is not particularly limited. Element M may be distributed either evenly or unevenly.

(Raman RC Value, Raman RSC Value, and Raman RS Value)

In the invention, the element-Z-internally-possessing lithium-occluding substance (D) in analysis by Raman spectroscopy has a Raman RC value of generally 0.0 or higher. The upper limit of the Raman RC value thereof is preferably 2.0 or lower. In case where the Raman RC value thereof exceeds the upper limit of that range, the effect of increasing capacity which is produced by the Si contained is difficult to obtain, making it difficult to obtain preferred battery characteristics. Especially when element Z comprises C, the Raman RC value of the negative-electrode active material SiZ x M y according to the invention is preferably 2.0 or lower, more preferably 1.0 or lower, especially preferably 0.5 or lower. The lower limit of the Raman RC value thereof is generally 0.0 or higher because of limitations in measurement.

In the invention, the element-Z-internally-possessing lithium-occluding substance (D) in analysis by Raman spectroscopy has a Raman RSC value of generally 0.0 or higher. The upper limit of the Raman RSC value thereof is preferably 0.25 or lower. When the Raman RSC value thereof exceeds the upper limit of that range, there are cases where electrical conductivity becomes poor and lithium doping/undoping becomes difficult, making it impossible to conduct charge/discharge. Furthermore, especially when element Z comprises C, the RSC value of the substance (D) is preferably 0.25 or lower, more preferably 0.20 or lower. The lower limit of the Raman RSC value thereof is generally 0.0 or higher because of limitations in measurement.

In the invention, the element-Z-internally-possessing lithium-occluding substance (D) in analysis by Raman spectroscopy has a Raman RS value of preferably 0.40 or higher, more preferably 0.50 or higher. The upper limit of the Raman RS value thereof is preferably 1.00 or lower, more preferably 0.90 or lower. In case where the Raman RS value thereof is lower than the lower limit of that range, there is a possibility that cycle characteristics might be impaired. On the other hand, Raman RS values thereof exceeding the upper limit of that range are undesirable because there is a possibility that charge/discharge might be impossible. Especially when element Z comprises C, the Raman RS value of the substance (D) is preferably 0.40 or higher, more preferably 0.50 or higher. The upper limit thereof is preferably 0.75 or lower, more preferably 0.65 or lower. Furthermore, especially when element Z comprises N, the Raman RS value of the substance (D) is preferably 0.40 or higher, more preferably 0.50 or higher. The upper limit thereof is preferably 1.00 or lower, more preferably 0.90 or lower.

Raman RC value, Raman RSC value, and Raman RS value in analysis by Raman spectroscopy in the invention are determined by Raman spectroscopy conducted by the following method of Raman spectroscopy, and the definitions thereof are as follows.

((Method of Raman Spectroscopy))

A Raman spectrometer (e.g., “Raman Spectrometer” manufactured by Japan Spectroscopic Co., Ltd.) is used. A negative electrode of the invention for nonaqueous-electrolyte secondary batteries is set in a measuring cell, and is examined while irradiating the surface of the sample in the cell with argon ion laser light. The Raman spectrum obtained is subjected to background correction to thereby determine the Raman RC value, RSC value, and RS value. The background correction is conducted by connecting the initiation and termination points for a peak with a straight line to determine a background and subtracting this value from the peak intensity.

›BEST MODE FOR CARRYING OUT THE INVENTION · 73 of 73

Conditions for this Raman spectroscopy are as follows. Smoothing is conducted by determining a simple average for 15 convolution points.

Wavelength of argon ion laser: 514.5 nm Laser power on sample: 15-40 mW Resolution: 10-20 cm −1 Examination range: 200 cm −1 to 1,900 cm −1

(((Raman RC Value)))

The peak intensity Ic of a peak “c” appearing at around 1,300 cm −1 to 1,600 cm −1 and the peak intensity Ias of a peak “as” appearing at around 300 cm −1 to 500 cm −1 are measured, and the intensity ratio RC between these (RC=Ic/Ias) is calculated. This ratio is defined as the Raman RC value of the negative electrode. The peak “c” and the peak “as” are thought to be peaks attributable to carbon and silicon, respectively. Consequently, Raman RC value reflects the amount of carbon. When the Raman RC value is 2.0 or lower, this means that almost no carbon is detected.

(((Raman RSC Value)))

The peak intensity Isc of a peak “sc” appearing at around 650 cm −1 to 850 cm −1 and the peak intensity Ias of a peak “as” appearing at around 300 cm −1 to 500 cm −1 are measured, and the intensity ratio RSC between these (RSC=Isc/Ias) is calculated. This ratio is defined as the Raman RSC value of the negative electrode.

The peak “sc” and the peak “as” are thought to be peaks attributable to SiC and silicon, respectively. Consequently, Raman RSC value reflects the amount of SiC. When the Raman RSC value is 0.25 or lower, this means that almost no SiC is detected.

(((Raman RS Value)))

The intensity Is at 520 cm −1 and the peak intensity Ias of a peak “as” appearing at around 300 cm −1 to 500 cm −1 are measured, and the intensity ratio RS between these (RS=Is/Ias) is calculated. This ratio is defined as the Raman RS value of the negative electrode. Raman RS value reflects the state of Si.

(IRsc Value)

When a negative electrode having the negative-electrode active material for use in the invention, which has undergone charge/discharge, is examined by infrared reflection spectroscopy, it gives an IRsc value of preferably 0.9 or higher, more preferably 1.1 or higher, especially preferably 1.2 or higher. When the IRsc value thereof is lower than the lower limit of that range, there are cases where the negative electrode containing Si reacts with the nonaqueous electrolyte during cycling and the amount of the active material substantially capable of charge/discharge decreases gradually, making it difficult to obtain preferred cycle characteristics. The upper limit of the IRsc value thereof is about 3.0. The IRsc value of a negative electrode in infrared reflection spectroscopy in the invention is determined by the following infrared reflection spectroscopy with an infrared spectrophotometer and is defined as shown below.

((Method of Infrared Reflection Spectroscopy with Infrared Spectrophotometer))

An infrared spectrophotometer (e.g., “ Magna 560” manufactured by Thermo Electron Corp.) is used. The active-material side of the negative electrode of a lithium secondary battery which has undergone charge/discharge is set in a measuring cell and examined by the reflection method. The examination is made in an inert atmosphere using a sample holder for reflection examination having a window made of diamond. The infrared absorption spectrum obtained is subjected to background correction to thereby determine the IRsc value. The background correction is conducted by prolonging a straight line connecting minimum values in the range of 2,000-4,000 cm −1 to determine a background and subtracting this value from each intensity. The reflection intensity Isc at 1,600 cm −1 and the reflection intensity Iaco at 1,650 cm −1 are measured, and the intensity ratio IRsc between these (IRsc=Isc/Iaco) is calculated. This ratio is defined as the IRsc value after charge/discharge.

Isc is thought to indicate a film derived from Si, while Iaco is thought to indicate a film derived from a lithium alkyl carbonate, although details thereof are unclear. Consequently, the IRsc reflects the state and amount of the negative-electrode film (solid electrolyte interface: SEI). When the IRsc value is 0.9 or higher, this means that the negative-electrode film is constituted of a film derived from a lithium alkyl carbonate and a film derived from Si.

Activity is explained first. In general, activity is a kind of thermodynamic concentration. In a multicomponent system comprising substance amounts n 1 , n 2 . . . n i . . . , when the chemical potential of component i and the chemical potential of the pure substance are expressed by μ i and μ i 0 , respectively, then a i defined by

μ i −μ i 0 =RT log a i

is called activity.

Furthermore, the ratio γ i of the activity a i to the concentration c i

a i /c i =γ i

is called activity coefficient.

For example, when a system comprising a solvent and a solute is considered to be a thermodynamic solution, the activity coefficient is an amount corresponding to a difference between the chemical potential of a certain component of the system regarded as an ideal solution and the true chemical potential of the certain component of the system regarded as a real solution. In the case of (1) the real solution in which a certain component i is the solute, as the solute concentration decreases, the system approaches an ideal solution in which the component i is the solute and the activity coefficient approaches 1. Conversely, in the case of (2) the real solution in which a certain component i is the solvent, as the solvent concentration increases, the system approaches an ideal solution in which the component i is the solvent and the activity coefficient approaches 1. Furthermore, when the chemical potential of the component i is more stable in the real solution than in the ideal solution, then γ i <1.

An example of Si which showed satisfactory properties in the invention is an element-Z-containing Si compound (solid solution; regarded as a real solution) in which component i is Si and element Z regarded as a solute is contained in the Si regarded as a solvent. Because of the solute contained, the solvent Si has a reduced activity a i and γ i <1. This Si compound is more stable than Si (regarded as an ideal solution). It is thought that this Si compound was hence inhi

›Tables in the description — 57

2005-305368	Japan	Oct. 20, 2005
2005-305300	Japan	Oct. 20, 2005
2005-314043	Japan	Oct. 28, 2005
2005-314260	Japan	Oct. 28, 2005
2005-331255	Japan	Nov. 16, 2005
2005-331362	Japan	Nov. 16, 2005
2005-331391	Japan	Nov. 16, 2005
2005-331477	Japan	Nov. 16, 2005
2005-331513	Japan	Nov. 16, 2005
2005-331585	Japan	Nov. 16, 2005
2005-332173	Japan	Nov. 16, 2005
2005-339794	Japan	Nov. 25, 2005
2005-344732	Japan	Nov. 29, 2005
2005-343629	Japan	Nov. 29, 2005
2005-349052	Japan	Dec. 2, 2005
2005-353005	Japan	Dec. 7, 2005
2005-359061	Japan	Dec. 13, 2005
2005-367747	Japan	Dec. 21, 2005
2005-369824	Japan	Dec. 22, 2005
2005-370024	Japan	Dec. 22, 2005
2005-377366	Japan	Dec. 28, 2005
2006-005622	Japan	Jan. 13, 2006
2006-013664	Japan	Jan. 23, 2006
2006-019863	Japan	Jan. 27, 2006
2006-019879	Japan	Jan. 27, 2006

TABLE 1

	BET	Average
Positive-	specific	primary-	Median
electrode	surface	particle	diameter	Tap
active	area	diameter	d 50	density
material	m 2 /g	μm	μm	g/cm 3
A	1.2	0.8	4.4	1.6
B	3.0	0.2	0.9	1.0
C	1.2	0.8	4.4	1.6
D	1.0	0.5	8.0	2.3
E	0.4	9.0	9.0	2.6

TABLE 2 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 1	hexamethylcyclo-	6.4	605	5.4	401
	trisiloxane
Example 2	trimethylsilyl	6.4	608	5.5	407
	methanesulfonate
Example 3	phenyldimethyl-	6.4	600	5.4	398
	fluorosilane
Example 4	LiPO 2 F 2	6.4	618	5.5	415
Comparative	none	6.4	525	5.1	325
Example 1

TABLE 3 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 5	hexamethylcyclo-	6.4	641	5.2	406
	trisiloxane
Example 6	trimethylsilyl	6.4	648	5.2	409
	methanesulfonate
Example 7	phenyldimethyl-	6.4	637	5.1	403
	fluorosilane
Example 8	LiPO 2 F 2	6.4	657	5.2	419
Comparative	none	6.4	558	4.9	328
Example 2

TABLE 4 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 9	hexamethylcyclo-	6.4	604	5.6	412
	trisiloxane
Example 10	trimethylsilyl	6.4	609	5.6	419
	methanesulfonate
Example 11	phenyldimethyl-	6.4	599	5.6	409
	fluorosilane
Example 12	LiPO 2 F 2	6.4	618	5.6	427
Comparative	none	6.4	525	5.3	337
Example 3

TABLE 5 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 13	hexamethylcyclo-	5.6	792	3.5	392
	trisiloxane
Example 14	trimethylsilyl	5.6	800	3.6	398
	methanesulfonate
Example 15	phenyldimethyl-	5.6	788	3.5	388
	fluorosilane
Example 16	LiPO 2 F 2	5.6	811	3.6	407
Comparative	none	5.6	689	3.2	304
Example 4

TABLE 6 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 17	hexamethylcyclo-	5.8	694	4.2	397
	trisiloxane
Example 18	trimethylsilyl	5.8	700	4.2	401
	methanesulfonate
Example 19	phenyldimethyl-	5.8	690	4.2	393
	fluorosilane
Example 20	LiPO 2 F 2	5.8	711	4.3	411
Comparative	none	5.8	604	3.9	313
Example 5

TABLE 7 — Average

Positive-	BET specific	primary particle	Median	Tap
electrode	surface area	diameter	diameter d 50	density
active material	m 2 /g	μm	μm	g/cm 3
A	0.6	0.7	9.0	2.1
B	3.1	0.2	0.8	1.2
C	0.6	0.7	9.0	2.1
D	0.5	0.6	10.9	2.1
E	1.0	0.5	8.0	2.3

TABLE 8 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 1	hexamethylcyclo	6.1	551	5.4	377
	trisiloxane
Example 2	trimethylsilyl	6.1	556	5.4	381
	methanesulfonate
Example 3	phenyldimethyl	6.1	545	5.3	371
	fluorosilane
Example 4	LiPO 2 F 2	6.1	563	5.4	387
Comparative	none	6.1	478	5.0	303
Example 1

TABLE 9 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 5	hexamethylcyclo	6.1	590	5.0	375
	trisiloxane
Example 6	trimethylsilyl	6.1	596	5.0	378
	methanesulfonate
Example 7	phenyldimethyl	6.1	585	4.9	369
	fluorosilane
Example 8	LiPO 2 F 2	6.1	604	5.0	385
Comparative	none	6.1	514	4.8	310
Example 2

TABLE 10 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 9	hexamethylcyclo-	6.1	548	5.3	374
	trisiloxane
Example 10	trimethylsilyl	6.1	555	5.4	379
	methanesulfonate
Example 11	phenyldimethyl-	6.1	546	5.3	371
	fluorosilane
Example 12	LiPO 2 F 2	6.1	563	5.4	386
Comparative	none	6.1	478	5.1	311
Example 3

TABLE 11 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 13	hexamethylcyclo-	6.1	580	5.0	369
	trisiloxane
Example 14	trimethylsilyl	6.1	586	5.0	374
	methanesulfonate
Example 15	phenyldimethyl-	6.1	578	5.0	366
	fluorosilane
Example 16	LiPO 2 F 2	6.1	594	5.0	380
Comparative	none	6.1	505	4.7	300
Example 4

TABLE 12 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 17	hexamethylcyclo-	6.0	617	4.7	381
	trisiloxane
Example 18	trimethylsilyl	6.0	623	4.7	384
	methanesulfonate
Example 19	phenyldimethyl-	6.0	615	4.7	378
	fluorosilane
Example 20	LiPO 2 F 2	6.0	632	4.8	392
Comparative	none	6.0	538	4.6	316
Example 5

TABLE 13

Positive-		Average
electrode	BET specific	primary-particle	Median diameter
active	surface	diameter	d 50	Tap density
material	aream 2 /g	μm	μm	g/cm 3
A	1.3	0.7	6.0	2.0
B	2.9	0.2	0.9	1.1
C	1.3	0.7	6.0	2.0
D	1.0	0.5	8.0	2.3

TABLE 14 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 1	hexamethylcyclo-	6.5	505	4.8	290
	trisiloxane
Example 2	trimethylsilyl	6.5	509	4.8	293
	methanesulfonate
Example 3	phenyldimethyl-	6.5	500	4.8	286
	fluorosilane
Example 4	LiPO 2 F 2	6.5	516	4.8	297
Comparative	none	6.5	438	4.7	244
Example 1

TABLE 15 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 5	hexamethylcyclo-	6.5	524	4.6	288
	trisiloxane
Example 6	trimethylsilyl	6.5	529	4.6	290
	methanesulfonate
Example 7	phenyldimethyl-	6.5	519	4.6	284
	fluorosilane
Example 8	LiPO 2 F 2	6.5	536	4.6	294
Comparative	none	6.5	456	4.6	247
Example 2

TABLE 16 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 9	hexamethylcyclo-	6.5	503	4.2	252
	trisiloxane
Example 10	trimethylsilyl	6.5	509	4.2	255
	methanesulfonate
Example 11	phenyldimethyl-	6.5	500	4.2	251
	fluorosilane
Example 12	LiPO 2 F 2	6.5	516	4.2	259
Comparative	none	6.5	438	4.2	217
Example 3

TABLE 17 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 13	hexamethylcyclo-	6.1	631	4.3	346
	trisiloxane
Example 14	trimethylsilyl	6.1	637	4.3	350
	methanesulfonate
Example 15	phenyldimethyl-	6.1	628	4.3	344
	fluorosilane
Example 16	LiPO 2 F 2	6.1	645	4.3	354
Comparative	none	6.1	549	4.3	297
Example 4

TABLE 18

Positive-		Average	Median
electrode	BET specific	primary-particle	diameter
active	surface area	diameter	d 50	Tap density
material	m 2 /g	μm	μm	g/cm 3
A	1.1	0.9	7.0	2.1
B	3.2	0.2	0.8	1.0
C	1.1	0.9	7.0	2.1
D	1.0	0.5	8.0	2.3

TABLE 19 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 1	hexamethylcyclo-	5.9	530	4.2	296
	trisiloxane
Example 2	trimethylsilyl	5.9	535	4.2	299
	methanesulfonate
Example 3	phenyldimethyl-	5.9	524	4.2	292
	fluorosilane
Example 4	LiPO 2 F 2	5.9	541	4.3	303
Comparative	none	5.9	460	4.2	249
Example 1

TABLE 20 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 5	hexamethylcyclo-	5.9	584	3.6	276
	trisiloxane
Example 6	trimethylsilyl	5.9	590	3.6	277
	methanesulfonate
Example 7	phenyldimethyl-	5.9	579	3.6	272
	fluorosilane
Example 8	LiPO 2 F 2	5.9	598	3.6	281
Comparative	none	5.9	509	3.6	236
Example 2

TABLE 21 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 9	hexamethylcyclo-	5.9	546	4.0	291
	trisiloxane
Example 10	trimethylsilyl	5.9	553	4.0	295
	methanesulfonate
Example 11	phenyldimethyl-	5.9	544	4.0	289
	fluorosilane
Example 12	LiPO 2 F 2	5.9	560	4.0	299
Comparative	none	5.9	476	4.0	250
Example 3

TABLE 22 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 13	hexamethylcyclo-	5.9	529	4.3	303
	trisiloxane
Example 14	trimethylsilyl	5.9	535	4.3	306
	methanesulfonate
Example 15	phenyldimethyl-	5.9	527	4.3	301
	fluorosilane
Example 16	LiPO 2 F 2	5.9	541	4.3	310
Comparative	none	5.9	460	4.3	260
Example 4

TABLE 23 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 17	hexamethylcyclo-	5.7	624	3.9	333
	trisiloxane
Example 18	trimethylsilyl	5.7	629	3.9	335
	methanesulfonate
Example 19	phenyldimethyl-	5.7	621	3.9	330
	fluorosilane
Example 20	LiPO 2 F 2	5.7	639	3.9	341
Comparative	none	5.7	543	3.9	285
Example 5

TABLE 24

Positive-	BET	Average	Median
electrode	specific	primary-particle	diameter	Tap
active	surface area	diameter	d 50	density
material	m 2 /g	μm	μm	g/cm 3
A	1.1	0.9	7.0	2.1
B	1.3	0.7	6.0	2.0
C	0.6	0.7	9.0	2.1
D	0.6	0.7	9.0	2.1
E	1.2	0.8	4.4	1.6
F	1.0	0.5	8.0	2.3

TABLE 25 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 1	hexamethylcyclo-	6.3	539	4.6	309
	trisiloxane
Example 2	trimethylsilyl	6.3	544	4.6	311
	methanesulfonate
Example 3	phenyldimethyl-	6.3	534	4.6	305
	fluorosilane
Example 4	LiPO 2 F 2	6.3	551	4.6	315
Comparative	none	6.3	468	4.6	264
Example 1

TABLE 26 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 5	hexamethylcyclo-	6.1	589	5.0	377
	trisiloxane
Example 6	trimethylsilyl	6.1	595	5.0	379
	methanesulfonate
Example 7	phenyldimethyl-	6.1	584	5.0	370
	fluorosilane
Example 8	LiPO 2 F 2	6.1	604	5.0	387
Comparative	none	6.1	513	4.7	305
Example 2

TABLE 27 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 9	hexamethylcyclo-	5.7	679	4.2	390
	trisiloxane
Example 10	trimethylsilyl	5.7	687	4.2	397
	methanesulfonate
Example 11	phenyldimethyl-	5.7	675	4.2	387
	fluorosilane
Example 12	LiPO 2 F 2	5.7	696	4.3	404
Comparative	none	5.7	592	3.9	313
Example 3

TABLE 28 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 13	hexamethylcyclo-	6.3	578	5.5	397
	trisiloxane
Example 14	trimethylsilyl	6.3	584	5.6	402
	methanesulfonate
Example 15	phenyldimethyl-	6.3	576	5.5	393
	fluorosilane
Example 16	LiPO 2 F 2	6.3	591	5.6	410
Comparative	none	6.3	503	5.1	315
Example 4

TABLE 29 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 17	hexamethylcyclo-	6.1	723	5.0	457
	trisiloxane
Example 18	trimethylsilyl	6.1	732	5.0	469
	methanesulfonate
Example 19	phenyldimethyl-	6.1	719	5.0	455
	fluorosilane
Example 20	LiPO 2 F 2	6.1	741	5.0	477
Comparative	none	6.1	630	4.6	363
Example 5

TABLE 30 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 21	hexamethylcyclo-	6.3	578	5.6	402
	trisiloxane
Example 22	trimethylsilyl	6.3	584	5.6	406
	methanesulfonate
Example 23	phenyldimethyl-	6.3	576	5.6	397
	fluorosilane
Example 24	LiPO 2 F 2	6.3	591	5.7	415
Comparative	none	6.3	503	5.2	319
Example 6

TABLE 31 — Battery

				capacity	Output
				after	after
		Battery	Initial	durability	durability
	Specific	capacity	output	test	test
	compound	Ah	W	Ah	W
Example 25	hexamethylcyclo-	5.9	744	4.8	474
	trisiloxane
Example 26	trimethylsilyl	5.9	755	4.9	484
	methanesulfonate
Example 27	phenyldimethyl-	5.9	739	4.8	469
	fluorosilane
Example 28	LiPO 2 F 2	5.9	763	4.9	493
Comparative	none	5.9	648	4.4	368
Example 7

TABLE 33

	Negative-				Direct	Capacity		Output
	electrode	Impedance	Impedance	Initial	current	retention	Initial	after	Output
	active	Rct	Cdl	capacity	resistance	through	output	cycling	retention
No.	material	Ω	×10 −4 F	mAh	mΩ	cycling %	W	W	%
Ex. 1	Binary	22	1.1	6001	5.2	80	574	420	73
	crystalline
	carbonaceous
	mixture (C)
Ex. 2	Composite	25	0.9	6010	4.9	84	595	450	76
	carbonaceous
	substance (D)
Ex. 3	Composite	11	1.9	6005	5.2	82	602	432	72
	carbonaceous
	substance (E)
Ex. 4	Composite	28	1.2	6000	5.2	83	581	420	72
	carbonaceous
	substance (F)
Ex. 5	Composite	30	0.8	5890	5.6	81	567	396	70
	carbonaceous
	substance (G)
Ex. 6	Composite	24	1.2	5987	5.1	82	588	414	70
	carbonaceous
	substance (J)
Ex. 7	Composite	35	1.0	6010	5.3	84	574	414	72
	carbonaceous
	substance (I)
Ex. 8	Composite	75	0.7	5609	5.4	79	560	390	70
	carbonaceous
	substance (M)
Ex. 9	Composite	25	0.9	6007	4.9	78	574	408	71
	carbonaceous
	substance (R)
Ex. 10	Composite	60	0.7	5045	5.5	76	532	342	64
	carbonaceous
	substance (L)
Ex. 11	Composite	22	1.0	6002	5.8	81	574	402	70
	carbonaceous
	substance (S)
Ex. 12	Composite	150	0.1	5928	5.4	80	539	366	68
	carbonaceous
	substance (O)
Ex. 13	Composite	42	0.7	5920	5.4	82	539	366	68
	carbonaceous
	substance (P)
Ex. 14	Composite	45	0.9	5902	5.2	79	553	372	67
	carbonaceous
	substance (Q)
Ex. 15	Composite	14	0.8	5989	5.1	76	560	366	65
	carbonaceous
	substance (D)
Ex. 16	Composite	15	1.0	5989	4.8	79	588	396	67
	carbonaceous
	substance (D)
Ex. 17	Composite	50	0.4	5982	5.5	78	602	390	65
	carbonaceous
	substance (D)

TABLE 34

	Negative-				Direct	Capacity		Output
	electrode	Impedance	Impedance	Initial	current	retention	Initial	after	Output
	active	Rct	Cdl	capacity	resistance	through	output	cycling	retention
No.	material	Ω	×10 −4 F	mAh	mΩ	cycling %	W	W	%
Ex. 18	Binary	23	1.1	5821	5.3	78	557	400	72
	crystalline
	carbonaceous
	mixture (C)
Ex. 19	Composite	27	0.9	5830	5.6	82	577	426	74
	carbonaceous
	substance (D)
Ex. 20	Composite	12	1.8	5825	4.9	80	584	415	71
	carbonaceous
	substance (E)
Ex. 21	Composite	30	1.2	5820	4.6	81	564	391	69
	carbonaceous
	substance (F)
Ex. 22	Composite	32	0.7	5713	5.5	79	550	375	68
	carbonaceous
	substance (G)
Ex. 23	Composite	25	1.2	5807	5.2	80	570	396	69
	carbonaceous
	substance (J)
Ex. 24	Composite	37	0.9	5830	5.3	82	557	394	71
	carbonaceous
	substance (I)
Ex. 25	Composite	80	0.7	5441	5.1	77	543	368	68
	carbonaceous
	substance (M)
Ex. 26	Composite	27	0.9	5827	5.3	76	557	389	70
	carbonaceous
	substance (R)
Ex. 27	Composite	64	0.7	4894	4.8	74	516	318	62
	carbonaceous
	substance (L)
Ex. 28	Composite	23	0.9	5822	4.7	79	557	382	69
	carbonaceous
	substance (S)
Ex. 29	Composite	159	0.1	5750	4.8	78	523	348	67
	carbonaceous
	substance (O)
Ex. 30	Composite	45	0.6	5742	5.2	80	523	336	64
	carbonaceous
	substance (P)
Ex. 31	Composite	48	0.8	5725	5.2	77	536	345	64
	carbonaceous
	substance (Q)
Ex. 32	Composite	15	0.8	5809	5.0	74	543	335	62
	carbonaceous
	substance (D)
Ex. 33	Composite	16	1.0	5809	4.7	77	570	372	65
	carbonaceous
	substance (D)
Ex. 34	Composite	53	0.4	5803	4.9	76	584	365	63
	carbonaceous
	substance (D)

TABLE 35

	Negative-				Direct	Capacity		Output
	electrode	Impedance	Impedance	Initial	current	retention	Initial	after	Output
	active	Rct	Cdl	capacity	resistance	through	output	cycling	retention
No.	material	Ω	×10 −4 F	mAh	mΩ	cycling %	W	W	%
Ex. 35	Binary	26	1.3	6061	4.8	78	557	391	70
	crystalline
	carbonaceous
	mixture (C)
Ex. 36	Composite	30	1.0	6070	5.2	81	577	419	73
	carbonaceous
	substance (D)
Ex. 37	Composite	13	2.0	6065	5.1	80	584	402	69
	carbonaceous
	substance (E)
Ex. 38	Composite	34	1.3	6060	5.0	81	564	391	69
	carbonaceous
	substance (F)
Ex. 39	Composite	36	0.8	5949	5.2	79	550	369	67
	carbonaceous
	substance (G)
Ex. 40	Composite	29	1.3	6047	4.9	80	570	386	68
	carbonaceous
	substance (J)
Ex. 41	Composite	42	1.1	6070	4.7	81	557	386	69
	carbonaceous
	substance (I)
Ex. 42	Composite	90	0.8	5665	5.1	77	543	363	67
	carbonaceous
	substance (M)
Ex. 43	Composite	30	1.0	6067	5.0	76	557	377	68
	carbonaceous
	substance (R)
Ex. 44	Composite	72	0.8	5095	4.8	74	516	314	61
	carbonaceous
	substance (L)
Ex. 45	Composite	26	1.1	6062	5.3	79	557	358	64
	carbonaceous
	substance (S)
Ex. 46	Composite	180	0.1	5987	5.1	78	523	341	65
	carbonaceous
	substance (O)
Ex. 47	Composite	50	0.7	5979	4.9	80	523	341	65
	carbonaceous
	substance (P)
Ex. 48	Composite	54	1.0	5961	5.1	77	536	354	66
	carbonaceous
	substance (Q)
Ex. 49	Composite	17	0.9	6049	5.0	74	543	345	63
	carbonaceous
	substance (D)
Ex. 50	Composite	18	1.1	6049	4.6	77	570	352	62
	carbonaceous
	substance (D)
Ex. 51	Composite	60	0.4	6042	5.4	76	584	350	60
	carbonaceous
	substance (D)

TABLE 36

				Direct	Capacity		Output
		Additive for	Initial	current	retention	Initial	after	Output
	Electrolytic	electrolyte	capacity	resistance	through	output	cycling	retention
No.	solution	solution	mAh	mΩ	cycling %	W	W	%
Ex. 52	Electrolytic-	lithium	5780	4.6	88	634	465	73
	Solution	difluorophosphate
	Production 1
Ex. 53	Electrolytic-	trimethylsilyl	5830	5.5	88	632	457	72
	Solution	methanesulfonate
	Production 2
Ex. 54	Electrolytic-	hexamethylcyclo-	5760	4.9	88	619	452	73
	Solution	trisiloxane
	Production 3
Comp.	Electrolytic-	none	5810	4.7	82	543	364	67
Ex. 15	Solution
	Production 4

TABLE 38 — Short-time high-current- density charge/

	Negative-		Initial	discharge
	electrode	Specific	capacity	characteristics
No.	active material	compound	mAh	%
Ex. 1	Amorphous	lithium	6020	93
	carbonaceous
	substance (A)	difluorophosphate
Ex. 2	Amorphous	lithium	6035	94
	carbonaceous
	substance (B)	difluorophosphate
Ex. 3	Amorphous	lithium	6001	90
	carbonaceous
	substance (C)	difluorophosphate
Ex. 4	Amorphous	trimethylsilyl	6021	91
	carbonaceous
	substance (A)	methanesulfonate
Ex. 5	Amorphous	trimethylsilyl	6023	92
	carbonaceous
	substance (B)	methanesulfonate
Ex. 6	Amorphous	trimethylsilyl	6015	88
	carbonaceous
	substance (C)	methanesulfonate
Ex. 7	Amorphous	hexamethylcyclo-	6004	91
	carbonaceous
	substance (A)	trisiloxane
Ex. 8	Amorphous	hexamethylcyclo-	5997	90
	carbonaceous
	substance (B)	trisiloxane
Ex. 9	Amorphous	hexamethylcyclo-	5987	92
	carbonaceous
	substance (C)	trisiloxane
Comp.	Amorphous	—	6012	88
Ex. 1	carbonaceous
	substance (A)
Comp.	Amorphous	—	6029	89
Ex. 2	carbonaceous
	substance (B)
Comp.	Amorphous	—	6009	85
Ex. 3	carbonaceous
	substance (C)
Comp.	Graphitic	lithium	5998	87
Ex. 4	carbonaceous	difluorophosphate
	substance (D)
Comp.	Graphitic	lithium	6012	78
Ex. 5	carbonaceous	difluorophosphate
	substance (E)
Comp.	Graphitic	trimethylsilyl	6001	86
Ex. 6	carbonaceous	methanesulfonate
	substance (D)
Comp.	Graphitic	trimethylsilyl	6003	79
Ex. 7	carbonaceous	methanesulfonate
	substance (E)
Comp.	Graphitic	hexamethylcyclo-	6032	87
Ex. 8	carbonaceous	trisiloxane
	substance (D)
Comp.	Graphitic	hexamethylcyclo-	6002	78
Ex. 9	carbonaceous	trisiloxane
	substance (E)
Comp.	Graphitic	—	6004	85
Ex. 10	carbonaceous
	substance (D)
Comp.	Graphitic	—	5990	77
Ex. 11	carbonaceous
	substance (E)

TABLE 40

			Output	Output
	Negative-electrode	Specific	resistance	resistance
No.	active material	compound	Ω	reduction %
Ex. 1	Lithium-titanium	lithium	75	34
	composite oxide (A)	difluorophosphate
Ex. 2	Lithium-titanium	lithium	69	31
	composite oxide (B)	difluorophosphate
Ex. 3	Lithium-titanium	lithium	65	28
	composite oxide (C)	difluorophosphate
Ex. 4	Lithium-titanium	trimethylsilyl	68	40
	composite oxide (A)	methanesulfonate
Ex. 5	Lithium-titanium	trimethylsilyl	71	29
	composite oxide (B)	methanesulfonate
Ex. 6	Lithium-titanium	trimethylsilyl	64	29
	composite oxide (C)	methanesulfonate
Ex. 7	Lithium-titanium	hexamethylcyclo-	71	38
	composite oxide (A)	trisiloxane
Ex. 8	Lithium-titanium	hexamethylcyclo-	66	34
	composite oxide (B)	trisiloxane
Ex. 9	Lithium-titanium	hexamethylcyclo-	63	30
	composite oxide (C)	trisiloxane
Comp.	Lithium-titanium	—	114	—
Ex. 1	composite oxide (A)
Comp.	Lithium-titanium	—	100	—
Ex. 2	composite oxide (B)
Comp.	Lithium-titanium	—	90	—
Ex. 3	composite oxide (C)
Comp.	Graphitic	lithium	130	17
Ex. 4	carbonaceous	difluorophosphate
	substance (D)
Comp.	Graphitic	trimethylsilyl	137	13
Ex. 5	carbonaceous	methanesulfonate
	substance (D)
Comp.	Graphitic	hexamethylcyclo-	135	14
Ex. 6	carbonaceous	trisiloxane
	substance (D)
Comp.	Graphitic	—	157	—
Ex. 7	carbonaceous
	substance (D)

TABLE 47

	Negative-				Percentage
	electrode		Initial	Output	improvement in		Double-layer
	active material		low-temperature	during	temperature	Impedance	capacity
	Carbonaceous		output	heating up	adaptation output	Rct	Cdl
No.	substance	Specific compound	W	W	%	Ω	×10 −4 F
Example 1	(D)	lithium difluorophosphate	21.7	29.0	33	6	0.8
Example 2	(E)	lithium difluorophosphate	22.2	31.0	40	8	0.6
Example 3	(G)	lithium difluorophosphate	20.0	24.9	24	13	0.5
Example 4	(J)	lithium difluorophosphate	21.5	27.6	28	100	0
Example 5	(L)	lithium difluorophosphate	21.9	29.6	35	8	0.5
Example 6	(D)	trimethylsilyl methanesulfonate	21.6	27.7	28	9	1
Example 7	(E)	trimethylsilyl methanesulfonate	21.9	29.1	33	11	0.9
Example 8	(G)	trimethylsilyl methanesulfonate	20.2	24.5	21	22	0.6
Example 9	(J)	trimethylsilyl methanesulfonate	21.2	25.9	22	135	0
Example 10	(L)	trimethylsilyl methanesulfonate	21.9	28.7	31	10	1
Example 11	(D)	hexamethylcyclotrisiloxane	22.0	27.9	27	9	0.9
Example 12	(E)	hexamethylcyclotrisiloxane	22.1	30.2	37	9	0.6
Example 13	(G)	hexamethylcyclotrisiloxane	20.1	24.1	20	20	0.5
Example 14	(J)	hexamethylcyclotrisiloxane	21.3	25.8	21	121	0
Example 15	(L)	hexamethylcyclotrisiloxane	21.5	29.2	36	9	0.7
Comparative Example 1	(B)	lithium difluorophosphate	21.1	24.7	17	7	1
Comparative Example 2	(B)	—	20.0	21.1	5	13	1.2
Comparative Example 3	(E)	—	20.5	22.7	11	10	0.9
Comparative Example 4	(D)	—	21.5	23.4	9	10	1
Comparative Example 5	(H)	lithium difluorophosphate	21.3	23.0	8	36	0.2
Comparative Example 6	(H)	—	20.7	21.2	2	50	0.3
Comparative Example 7	(N)	lithium difluorophosphate	19.4	21.4	10	11	0.8
Comparative Example 8	(N)	—	19.0	20.1	6	16	0.7
Comparative Example 9	(I)	lithium difluorophosphate	17.5	19.5	11	125	0
Comparative Example 10	(I)	—	17.1	18.3	7	160	0
Comparative Example 11	(B)	trimethylsilyl methanesulfonate	21.1	24.7	14	7	1.1
Comparative Example 12	(H)	trimethylsilyl methanesulfonate	21.3	23.0	5	44	0.3
Comparative Example 13	(N)	trimethylsilyl methanesulfonate	19.4	21.4	7	13	0.7
Comparative Example 14	(I)	trimethylsilyl methanesulfonate	17.5	19.4	9	131	0
Comparative Example 15	(B)	hexamethylcyclotrisiloxane	21.1	24.7	15	9	1.4
Comparative Example 16	(H)	hexamethylcyclotrisiloxane	21.3	23.0	6	42	0.4
Comparative Example 17	(N)	hexamethylcyclotrisiloxane	19.4	21.4	9	13	0.4
Comparative Example 18	(I)	hexamethylcyclotrisiloxane	17.5	19.4	10	142	0

TABLE 48

Negative-		Z	Composition of SiZ x M y
electrode	Kind of	concentration	Atomic concentration		XIsz of SiZ x M y
active	element	ratio	ratio	Raman values of SiZ x M y	by X-ray
material	Z	Q(Z)	Si	Z	O	RC	RSC	RS	diffractometry
Thin-film	C	0.49	1.00	0.33	0.04	0.05	nopeak	0.55	0.38
negative
electrode
(1)
Thin-film	(Si)	(0.00)	1.00	(0.00)	0.02	nopeak	nopeak	0.30	—
negative
electrode
(2)

TABLE 49 — Battery characteristics

	Nonaqueous		Discharge	0.2-C charge	1-C charge	Suitability
	electrolyte	Negative-electrode	capacity	capacity	capacity	for charge
No.	Specific compound	active material	(mAh/g)	(mAh/g)	(mAh/g)	(%)	Remarks
Example 1	lithium	Thin-film negative	2614	2680	2567	95.8	within the invention
	difluorophosphate	electrode (1)
Example 2	trimethylsilyl	Thin-film negative	2598	2690	2566	95.4	within the invention
	methanesulfonate	electrode (1)
Example 3	hexamethylcyclo-	Thin-film negative	2621	2670	2488	93.2	within the invention
	trisiloxane	electrode (1)
Comparative	—	Thin-film negative	2614	2690	2405	89.4	no specific compound
Example 1		electrode (1)
Comparative	lithium	Thin-film negative	3920	4012	3406	84.9	no element Z
Example 2	difluorophosphate	electrode (2)
Comparative	trimethylsilyl	Thin-film negative	3896	4002	3458	86.4	no element Z
Example 3	methanesulfonate	electrode (2)
Comparative	hexamethylcyclo-	Thin-film negative	3945	3989	3486	87.4	no element Z
Example 4	trisiloxane	electrode (2)
Comparative	—	Thin-film negative	3930	3998	3406	85.2	no element Z
Example 5		electrode (2)

TABLE 51

			Low-	Capacity
			tempera-	retention
			ture	through
	Negative-electrode	Specific	output	cycling
No.	active material	compound	W	%
Ex. 1	Carbonaceous-	lithium	26.2	81
	substance	difluorophosphate
	mixture (E)
Ex. 2	Carbonaceous-	lithium	27.4	80
	substance	difluorophosphate
	mixture (F)
Ex. 3	Carbonaceous-	lithium	29.4	85
	substance	difluorophosphate
	mixture (G)
Ex. 4	Carbonaceous-	trimethylsilyl	24.7	80
	substance	methanesulfonate
	mixture (E)
Ex. 5	Carbonaceous-	trimethylsilyl	28.2	78
	substance	methanesulfonate
	mixture (F)
Ex. 6	Carbonaceous-	trimethylsilyl	29.7	84
	substance	methanesulfonate
	mixture (G)
Ex. 7	Carbonaceous-	hexamethylcyclo-	26.1	80
	substance	trisiloxane
	mixture (E)
Ex. 8	Carbonaceous-	hexamethylcyclo-	29.1	77
	substance	trisiloxane
	mixture (F)
Ex. 9	Carbonaceous-	hexamethylcyclo-	28.8	84
	substance	trisiloxane
	mixture (G)
Comp.	Carbonaceous-	—	21.1	78
Ex. 1	substance
	mixture (E)
Comp.	Carbonaceous-	—	23.2	75
Ex. 2	substance
	mixture (F)
Comp.	Carbonaceous	—	20.5	77
Ex. 3	substance (A)
Comp.	Carbonaceous	—	24.5	71
Ex. 4	substance (B)
Comp.	Carbonaceous	—	27.5	69
Ex. 5	substance (C)
Comp.	Carbonaceous	lithium	22.2	79
Ex. 6	substance (A)	difluorophosphate
Comp.	Carbonaceous	lithium	25.8	72
Ex. 7	substance (B)	difluorophosphate
Comp.	Carbonaceous	lithium	29.4	70
Ex. 8	substance (C)	difluorophosphate
Comp.	Carbonaceous	trimethylsilyl	21.7	80
Ex. 9	substance (A)	methanesulfonate
Comp.	Carbonaceous	trimethylsilyl	25.2	72
Ex. 10	substance (B)	methanesulfonate
Comp.	Carbonaceous	trimethylsilyl	28.8	70
Ex. 11	substance (C)	methanesulfonate
Comp.	Carbonaceous	hexamethylcyclo-	21.7	78
Ex. 12	substance (A)	trisiloxane
Comp.	Carbonaceous	hexamethylcyclo-	24.5	72
Ex. 13	substance (B)	trisiloxane
Comp.	Carbonaceous	hexamethylcyclo-	28.2	69
Ex. 14	substance (C)	trisiloxane

TABLE 53

						Capacity		Impedance	Double of negative-
					Output	retention	Impedance Rct	Cdl Double-	electrode active-
	Negative-		Initial	Initial	after	through	Reacion	layer	material
	electrode		capacity	output	cycling	cycling	resistance	capacity	layer
No.	active material	Specific compound	mAh	W	W	%	Ω	×10 −4 F	g/cm 3
Ex. 1	Carbonaceous	lithium	6021	558	398	82	9.0	1.5	1.36
	substance (A)	difluorophosphate
Ex. 2	Carbonaceous	trimethylsilyl	6022	545	384	82	9.5	1.4	1.36
	substance (A)	methanesulfonate
Ex. 3	Carbonaceous	hexamethylcyclo-	6020	531	375	81	10.8	1.4	1.36
	substance (A)	trisiloxane
Comp.	Carbonaceous	—	6099	486	290	78	12.1	1.3	1.36
Ex. 1	substance (A)
Ex. 4	Carbonaceous	lithium	6032	551	350	81	10.4	1.5	1.35
	substance (B)	difluorophosphate
Ex. 5	Carbonaceous	trimethylsilyl	6021	525	332	79	10.8	1.4	1.35
	substance (B)	methanesulfonate
Ex. 6	Carbonaceous	hexamethylcyclo-	6112	524	315	78	10.8	1.4	1.35
	substance (B)	trisiloxane
Comp.	Carbonaceous	—	6099	469	275	71	12.3	1.5	1.35
Ex. 2	substance (B)
Ex. 7	Carbonaceous	lithium	5998	570	445	85	16.4	1.2	1.36
	substance (C)	difluorophosphate
Ex. 8	Carbonaceous	trimethylsilyl	6021	564	423	83	17.8	1.1	1.36
	substance (C)	methanesulfonate
Ex. 9	Carbonaceous	hexamethylcyclo-	6070	554	418	82	15.6	1.2	1.36
	substance (C)	trisiloxane
Comp.	Carbonaceous	—	5989	507	340	79	19.4	1.1	1.36
Ex. 3	substance (C)
Ex. 10	Carbonaceous	lithium	5991	546	346	77	32.0	0.9	1.33
	substance (D)	difluorophosphate
Ex. 11	Carbonaceous	trimethylsilyl	5987	557	337	76	41.0	0.8	1.33
	substance (D)	methanesulfonate
Ex. 12	Carbonaceous	hexamethylcyclo-	5982	541	335	76	34.2	0.9	1.33
	substance (D)	trisiloxane
Comp.	Carbonaceous	—	5889	521	287	73	48.0	0.7	1.33
Ex. 4	substance (D)

TABLE 54 — Low-

		Propor-		temper-
		tion		ature
		of EC	Compound	output
	Solvent	(vol %)	contained	(W)	Remarks
Example	EC:EMC	15	hexamethyl-	20.1	26.4%
1			cyclo-		increase
			trisiloxane		based on
					Comparative
					Example 1
Example	EC:EMC	20	hexamethyl-	19.9	25.9%
2			cyclo-		increase
			trisiloxane		based on
					Comparative
					Example 2
Example	EC:DMC:	15	hexamethyl-	20.5	27.3%
3	EMC		cyclo-		increase
			trisiloxane		based on
					Comparative
					Example 3
Example	EC:EMC	15	phenyl-	19.8	24.5%
4			dimethyl-		increase
			fluorosilane		based on
					Comparative
					Example 1
Example	EC:EMC	15	hexamethyl-	20.2	27.0%
5			disiloxane		increase
					based on
					Comparative
					Example 1
Example	EC:EMC	15	trimethylsilyl	20.4	28.3%
6			methane-		increase
			sulfonate		based on
					Comparative
					Example 1
Example	EC:EMC	15	methyl	19.8	24.5%
7			fluoro-		increase
			sulfonate		based on
					Comparative
					Example 1
Example	EC:EMC	15	lithium	20.0	25.8%
8			nitrate		increase
					based on
					Comparative
					Example 1
Example	EC:EMC	15	lithium	20.8	30.8%
9			difluoro-		increase
			phosphate		based on
			(0.3%)		Comparative
					Example 1
Example	EC:EMC	15	lithium	19.0	19.5%
10			difluoro-		increase
			phosphate		based on
			(0.08%)		Comparative
					Example 1
Example	EC:EMC	15	lithium	19.9	25.2%
11			acetate		increase
					based on
					Comparative
					Example 1
Example	EC:EMC	15	hexamethyl-	1.86	20.8%
12			cyclo-		increase
			trisiloxane		based on
					Comparative
					Example 13
Comparative	EC:EMC	15	none	15.9
Example
1
Comparative	EC:EMC	20	none	15.8
Example
2
Comparative	EC:DMC:	15	none	16.1
Example	EMC
3
Comparative	EC:EMC	40	hexamethyl-	17.6	15.0%
Example			cyclo-		increase
4			trisiloxane		based on
					Comparative
					Example 12
Comparative	EC:EMC	40	phenyl-	17.5	14.4%
Example			dimethyl-		increase
5			fluorosilane		based on
					Comparative
					Example 12
Comparative	EC:EMC	40	hexamethyl-	17.6	15.0%
Example			disiloxane		increase
6					based on
					Comparative
					Example 12
Comparative	EC:EMC	40	trimethylsilyl	17.8	16.3%
Example			methane-		increase
7			sulfonate		based on
					Comparative
					Example 12
Comparative	EC:EMC	40	methyl	17.5	14.4%
Example			fluoro-		increase
8			sulfonate		based on
					Comparative
					Example 12
Comparative	EC:EMC	40	lithium	17.7	15.7%
Example			nitrate		increase
9					based on
					Comparative
					Example 12
Comparative	EC:EMC	40	lithium	17.9	17.0%
Example			difluoro-		increase
10			phosphate		based on
					Comparative
					Example 12
Comparative	EC:EMC	40	lithium	17.6	15.0%
Example			acetate		increase
11					based on
					Comparative
					Example 12
Comparative	EC:EMC	40	none	15.3
Example
12
Comparative	EC:EMC	15	none	1.54
Example
13

TABLE 55

		Capacity	Proportion of	Proportion of
		retention	initial low-	low-temperature
		through	temperature	discharge after
		cycling	discharge	cycling
No.	Battery	(%)	(%)	(%)
Example 1	cylindrical	64	68	64
Comparative	cylindrical	58	59	50
Example 1
Comparative	cylindrical	60	60	50
Example 2
Example 2	cylindrical	63	65	63
Comparative	cylindrical	55	57	45
Example 3
Example 3	prismatic	73	74	71
Comparative	prismatic	68	62	53
Example 4
Comparative	prismatic	68	63	59
Example 5

TABLE 57

No.	Specific compound	Output (W)
Example 1	hexamethylcyclotrisiloxane	500
Example 2	phenyldimethylfluorosilane	510
Example 3	methyl fluorosulfonate	510
Example 4	lithium difluorophosphate	525
Example 5	hexamethylcyclotrisiloxane	45
Comparative Example 1	—	390
Comparative Example 2	—	37

TABLE 58

				Output	Output
	Specific		Initial	after	after
	lithium		output	cycling	storage
No.	salt	Specific compound	(W)	(W)	(W)
Example 1	LiN(CF 3 SO 2 ) 2	hexamethyltrisiloxane	535	350	410
Example 2	LiN(CF 3 SO 2 ) 2	phenyldimethylfluorosilane	520	320	405
Example 3	LiN(CF 3 SO 2 ) 2	methyl fluorosulfonate	515	330	400
Example 4	LiN(CF 3 SO 2 ) 2	lithium difluorophosphate	545	360	435
Example 5	LiBOB	hexamethyltrisiloxane	515	325	400
Example 6	LiBOB	lithium difluorophosphate	520	355	420
Comparative	—	hexamethyltrisiloxane	800	285	345
Example 1
Comparative	LiN(CF 3 SO 2 ) 2	—	450	240	340
Example 2
Comparative	—	—	440	225	330
Example 3
Example 7	LiN(CF 3 SO 2 ) 2	hexamethyltrisiloxane	48	29	35
Example 8	LiN(CF 3 SO 2 ) 2	phenyldimethylfluorosilane	47	28	34
Example 9	LiN(CF 3 SO 2 ) 2	methyl fluorosulfonate	47	28	34
Example 10	LiN(CF 3 SO 2 ) 2	lithium difluorophosphate	49	31	36
Example 11	LiBOB	hexamethyltrisiloxane	48	29	33
Example 12	LiBOB	lithium difluorophosphate	48	31	34
Comparative	—	hexamethyltrisiloxane	45	25	32
Example 4
Comparative	LiN(CF 3 SO 2 ) 2	—	41	23	30
Example 5
Comparative	—	—	40	21	29
Example 6

TABLE 59

		Amount			Capacity
		of HF		Output	retention
	Alcohol	(ppm)	Compound contained	(W)	(%)
Example 1	methanol 10 ppm	14	hexamethylcyclotrisiloxane	481	71.0
Example 2	methanol 20 ppm	19	hexamethylcyclotrisiloxane	489	71.0
Example 3	methanol 35 ppm	27	hexamethylcyclotrisiloxane	498	70.9
Example 4	EG 15 ppm	16	hexamethylcyclotrisiloxane	483	71.0
Example 5	EG 35 ppm	27	hexamethylcyclotrisiloxane	498	70.9
Example 6	methanol 25 ppm	36	hexamethylcyclotrisiloxane	507	70.9
	EG 25 ppm
Example 7	methanol 10 ppm	14	lithium difluorophosphate	492	71.3
Example 8	methanol 35 ppm	27	lithium difluorophosphate	506	71.1
Example 9	EG 15 ppm	16	lithium difluorophosphate	494	71.3
Example 10	methanol 25 ppm	36	lithium difluorophosphate	519	71.0
	EG 25 ppm
Example 11	methanol 25 ppm	36	trimethylsilyl methanesulfonate	509	70.9
	EG 25 ppm
Example 12	methanol 25 ppm	36	hexamethylcyclotrisiloxane	45.7	70.4
	EG 25 ppm
Comparative	methanol 35 ppm	27	none	395	69.5
Example 1
Comparative	EG 35 ppm	27	none	395	69.6
Example 2
Comparative	methanol 25 ppm	36	none	393	68.8
Example 3	EG 25 ppm
Comparative	none	9	hexamethylcyclotrisiloxane	462	71.0
Example 4
Comparative	none	9	lithium difluorophosphate	472	71.3
Example 5
Comparative	none	9	trimethylsilyl methanesulfonate	467	71.0
Example 6
Comparative	methanol 700 ppm	403	hexamethylcyclotrisiloxane	458	59.6
Example 7
Comparative	none	9	none	401	70.7
Example 8
Comparative	methanol 25 ppm	36	none	38.4	68.5
Example 9	EG 25 ppm

TABLE 60

							Proportion of	Proportion of low-
					Direct-	Capacity	initial low-	temperature
				Initial	current	retention	temperature	discharge after
				capacity	resistance	through cycling	discharge	cycling
No.	Battery	VC	LiPO 2 F 2	(mAh)	(mΩ)	(%)	(%)	(%)
Example 1	cylindrical	1%	present	702	35	79	68	69
Comparative	cylindrical	Nil	absent	700	35	64	61	54
Example 1
Comparative	cylindrical	1%	absent	701	35	74	59	56
Example 2
Comparative	cylindrical	Nil	present	700	35	65	68	64
Example
Comparative	cylindrical	5%	present	699	35	84	37	29
Example 4
Example 2	prismatic	1%	present	6010	5	85	73	75
Comparative	prismatic	Nil	absent	6005	5	70	63	57
Example 5
Comparative	prismatic	1%	absent	6003	5	78	60	57
Example 6
Comparative	prismatic	Nil	present	6006	5	72	72	69
Example 7

TABLE 61 — Proportion

				Proportion	of low-
			Capacity	of initial	temperature
			retention	low-	discharge
			through	temperature	after
	Specific		cycling	discharge	cycling
No.	compound A	Specific compound B	(%)	(%)	(%)
Example 1	hexamethylcyclo	vinylethylene carbonate	83	74	73
	trisiloxane
Example 2	phenyldilmethyl	vinylethylene carbonate	81	71	69
	fluorosilane
Example 3	methylfluorosulfonate	vinylethylene carbonate	80	70	69
Example 4	lithium di	vinylethylene carbonate	84	76	75
	fluorophosphate
Example 5	hexamethylcyclo	1,3-propanesultone	82	72	69
	trisiloxane
Example 6	hexamethylcyclo	γ-butyrolactone	79	73	66
	trisiloxane
Example 7	hexamethylcyclo	fluoroethylene	83	73	70
	trisiloxane	carbonate
Example 8	lithium di	1,3-propanesultone	83	73	72
	fluorophosphate
Example 9	lithium di	γ-butyrolactone	80	73	69
	fluorophosphate
Example 10	lithium di	fluoroethylene	84	74	73
	fluorophosphate	carbonate
Comparative	—	vinylethylene carbonate	76	58	51
Example 1
Comparative	hexamethylcyclo	—	72	73	66
Example 2	trisiloxane
Comparative	—	—	68	65	54
Example 3
Example 11	hexamethylcyclo	vinylethylene carbonate	69	67	65
	trisiloxane
Example 12	lithium di	vinylethylene carbonate	70	69	67
	fluorophosphate
Comparative	—	vinylethylene carbonate	65	54	49
Example 4
Comparative	hexamethylcyclo	—	60	66	60
Example 5	trisiloxane
Comparative	—	—	58	60	52
Example 6

TABLE 62 — 5-C discharge capacity after

			storage	Over-charge
No.	Overcharge inhibitor	Specific compound	(mAh)	test
Example 1	cyclohexylbenzene	hexamethylcyclotri-siloxane	4016	valve working
Example 2	cyclohexylbenzene	phenyldimethylfluoro-silane	3967	valve working
Example 3	cyclohexylbenzene	trimethylsilylmethanesulfonate	4023	valve working
Example 4	cyclohexylbenzene	lithiumdifluorophosphate	4062	valve working
Example 5	biphenyl	hexamethylcyclotri-siloxane	3810	valve working
Example 6	biphenyl	phenyldimethylfluoro-silane	3772	valve working
Example 7	biphenyl	trimethylsilylmethanesulfonate	3806	valve working
Example 8	biphenyl	lithiumdifluorophosphate	3855	valve working
Example 9	t-amylbenzene	hexamethylcyclotri-siloxane	4004	valve working
Example 10	product of partial	hexamethylcyclotri-siloxane	3959	valve working
	hydrogenation of
	m-terphenyl
Comparative	cyclohexylbenzene	none	3522	valve working
Example 1
Comparative	biphenyl	none	3217	valve working
Example 2
Comparative	t-amylbenzene	none	3511	valve working
Example 3
Comparative	product of partial	none	3403	valve working
Example 4	hydrogenation of
	m-terphenyl
Comparative	none	none	4091	rupture
Example 5

TABLE 63 — Specific

Particle

surface

Raman R

Raman half-

Ash

Micro-pore

Total pore

True

Aspect

diameter

Roundness

area

value

value width

d 002

content

distribution

density

Roundness

ratio

μm

—

m 2 /g

—

cm −1

mass %

mL/g

g/cm 3

—

Negative-

15.2

0.93

3.0

0.35

0.336

0.07

0.101

0.692

2.25

0.93

1.4

electrode

active material

TABLE 64 — Direct-current

			Direct-		Battery	resistance	Output after
		Battery	current	Initial	capacity after	after	durability
		capacity	resistance	output	durability test	durability test	test	Over-charge
	Specific compound	Ah	mΩ	W	Ah	mΩ	W	test
Example 1	hexamethylcyclotrisiloxane	6.1	4.8	577	5.4	5.0	395	valve opening
Example 2	trimethylsilyl methanesulfonate	6.1	4.9	579	5.4	5.1	403	valve opening
Example 3	phenyldimethylfluorosilane	6.1	4.9	572	5.4	5.1	393	valve opening
Example 4	lithium difluorophosphate	6.1	4.8	588	5.5	5.0	410	valve opening
Comparative	None	6.1	5.0	500	5.1	5.5	321	rupture
Example 1

TABLE 65 — Direct-current

			Direct-		Battery	resistance	Output after
		Battery	current	Initial	capacity after	after	durability
		capacity	resistance	output	durability test	durability test	test	Over-charge
	Specific compound	Ah	mΩ	W	Ah	mΩ	W	test
Example 5	hexamethylcyclotrisiloxane	6.1	5.7	569	5.3	5.9	386	valve opening
Example 6	trimethylsilyl methanesulfonate	6.1	5.6	572	5.3	5.8	389	valve opening
Example 7	phenyldimethylfluorosilane	6.1	5.7	564	5.3	5.9	379	valve opening
Example 8	lithium difluorophosphate	6.1	5.6	582	5.3	5.8	399	valve opening
Comparative	None	6.1	5.9	493	5.0	6.3	303	rupture
Example 2

TABLE 66

Particle

Specific

Raman R

Raman half-

Ash

Micro-pore

Total pore

True

Aspect

diameter

Roundness

surface area

value

value width

d 002

content

distribution

density

Roundness

ratio

μm

—

M 2 /g

—

cm −1

mass %

mL/g

g/cm 3

—

Negative-

15.2

0.93

3.0

0.35

0.336

0.07

0.101

0.692

2.25

0.93

1.4

electrode

active

material

TABLE 67 — Specific compound in nonaqueous

No.	electrolyte
Example 1	hexamethylcyclotrisiloxane
Example 2	trimethylsilyl methanesulfonate
Example 3	phenyldimethylfluorosilane
Example 4	lithium difluorophosphate
Comparative Example 1	none

TABLE 68 — Direct-current

		Direct-current		Battery capacity	resistance component	Output after
	Battery	resistance		after durability	after durability	durability
	capacity	component	Initial output	test	test	test		Volume
No.	Ah	mΩ	W	W	mΩ	W	Over-charge test	change
Example 1	6.1	4.3	583	5.3	4.2	394	valveworking	1.01
Example 2	6.1	4.2	585	5.3	4.4	398	valveworking	1.01
Example 3	6.1	4.3	579	5.3	4.5	388	valveworking	1.01
Example 4	6.1	4.3	595	5.3	4.5	407	valveworking	1.01
Comparative	6.1	4.5	508	5.0	4.9	318	rupture	1.03
Example 1

description truncated at 500,000 characters

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Claims as granted

23 claims

Classifications

31 codes

IPC · International Patent Classification

Section B — Performing operations; transporting

B60L50/64

Section H — Electricity

H01M50/46
H01M4/02
H01M4/04
H01M4/131
H01M4/133
H01M4/1391
H01M4/1393
H01M4/36
H01M4/485
H01M4/505
H01M4/525
H01M4/583
H01M4/587
H01M10/052
H01M10/0525
H01M10/0567
H01M10/0568
H01M10/0569
H01M10/0587
H01M10/613
H01M10/625
H01M50/119
H01M50/121
H01M50/124
H01M4/134
H01M4/50
H01M4/52
H01M10/0566
H01M10/058
H01M10/36

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