Secondary battery, battery module, battery pack, and electric device

This application is a continuation of international application PCT/CN2022/084874, filed Apr. 1, 2022 and entitled “SECONDARY BATTERY, BATTERY MODULE, BATTERY PACK, AND ELECTRIC DEVICE”, the entire content of which is hereby incorporated by reference in its entirety.

The present application relates to the technical field of lithium batteries, and more particularly to a secondary battery, a battery module, a battery pack, and an electric device.

In recent years, as the application range of lithium-ion batteries has become more and more extensive, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. Due to the great development of lithium-ion batteries, higher requirements have been exerted on energy density, cycle performance, and safety performance.

Compared with other cathode active materials, lithium manganese phosphate cathode active materials have higher safety and cycle life, but is disadvantageous in its poor rate performance, which is usually solved by means of coating or doping. However, it is still desired to further improve the rate performance, cycle performance, and high temperature stability of lithium manganese phosphate cathode active materials.

The present application is made in view of the above problems, and it is an objective of the present application to provide a secondary battery, a battery module, a battery pack, and an electric device, so as to solve the problem that the lithium manganese phosphate secondary battery has poor rate performance and cycle performance.

In order to achieve the above object, a first aspect of the present application provides a secondary battery, comprising a cathode piece and a non-aqueous electrolyte, in which, the cathode piece comprises a cathode active material, and the cathode active material comprises a core and a shell covering the core; the core comprises Li 1+x Mn 1-y A y P 1-z R z O 4 , in which, x=−0.100 to 0.100, y=0.001 to 0.500, z=0.001 to 0.100, and A is one or more selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, optionally one or more selected from the group consisting of Fe, Ti, V, Ni, Co, and Mg, and R is one or more selected from the group consisting of B, Si, N and S; the shell comprises: a first cladding layer covering the core, and a second cladding layer covering the first cladding layer, in which, the first cladding layer comprises pyrophosphate MP 2 O 7 and phosphate XPO 4 , in which, M and X are each independently one or more selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; and the second cladding layer comprises carbon;

the non-aqueous electrolyte includes a first lithium salt and a first additive, and the first lithium salt is one or more selected from the group consisting of LiN(C m F 2m+1 SO 2 )(C n F 2n+1 SO 2 ) and Li(FSO 2 ) 2 N, m and n represent positive integers; the first additive includes one or more of the compounds represented by Formula 1,

O═C═N—R 1 —N═C═O  Formula 1

in which, R 1 represents any one of a C 2 -C 10 alkylene, a C 2 -C 10 heteroalkylene, a C 6 -C 18 arylene, a C 2 -C 18 heteroarylene, a C 3 -C 18 alicyclylene, a C 3 -C 18 heteroalicyclylene, which are substituted by one or more R a or are unsubstituted, and R a comprises one or more selected from a halogen atom, —CN, —NCO, —OH, —COOH, —SOOH, a —COOR b , a C 2 -C 10 alkyl, a C 2 -C 10 alkenyl, a C 2 -C 10 alkynyl, a C 2 -C 10 oxaalkyl, and R b is any one selected from C 1 -C 10 alkyls.

Unless otherwise stated, in the above chemical formula, when A is two or more elements, the limitation on the numerical range of y is not only a limitation on a stoichiometric number of each element as A, but also a limitation on a sum of stoichiometric numbers of all elements as A. For example, when A is two or more elements A1, A2 . . . An, the stoichiometric numbers y1, y2 . . . yn of A1, A2 . . . An each need to fall within the numerical range defined by the application for y, and the sum of y1, y2 . . . yn also needs to fall within this value range. Similarly, for the case where R is two or more elements, the limitation of the numerical range of the stoichiometric number of R in the present application also has the above meaning.

The lithium manganese phosphate cathode active material of the present application has a core-shell structure with two cladding layer s, in which, the core includes Li 1+X Mn 1-y A y P 1-z R z O 4 . The element A doped at the manganese position of lithium manganese phosphate in the core helps to reduce the lattice change rate of lithium manganese phosphate during lithium deintercalation, improves the structural stability of lithium manganese phosphate cathode material, and greatly reduces the dissolution of manganese and the oxygen activity on the particle surface. The element R doped at the phosphorus site helps to change the difficulty of the change of the Mn—O bond length, thereby reducing the migration barrier of lithium ions, promoting the migration of lithium ions, and improving the rate performance of the secondary battery.

The first cladding layer of the cathode active material of the present application includes pyrophosphate and phosphate. Due to the high migration barrier (>1 eV) of transition metals in pyrophosphate, the dissolution of transition metals can be effectively inhibited. Phosphate has an excellent ability to conduct lithium ions, and can reduce the content of lithium impurities on the surface. In addition, since the second cladding layer is a carbon-containing layer, the electrical conductivity and desolvation ability of LiMnPO 4 can be effectively improved. In addition, the “barrier” effect of the second cladding layer can further hinder the migration of manganese ions into the electrolyte and reduce the corrosion of the active materials by the electrolyte.

Therefore, the present application can effectively suppress the dissolution of manganese ions during lithium deintercalation by performing specific element doping and surface coating on lithium manganese phosphate, and at the same time promote the migration of lithium ions, thereby improving the rate performance of the battery cell and improving the cycle performance and high temperature performance of the secondary battery.

It should be noted that, as shown in FIG. 1 , in the present application, by comparing the XRD spectra before and after LiMnPO 4 doping, it can be seen that the cathode active material of the present application is basically consistent with the positions of the main characteristic peaks before LiMnPO 4 doping, indicating that the doped lithium manganese phosphate cathode active material has no impurity phase, and the improvement of secondary battery performance mainly comes from element doping rather than impurity phase. In the present application, the cathode active material is obtained by doping the Mn site and the P site of the compound LiMnPO 4 with a specific amount of specific elements at the same time and coating the compound surface with two layers, which can greatly reduce the dissolution of transition metals and reduce the oxygen activity on the particle surface, promote the migration of lithium ions, improve the conductivity and desolvation performance of the material, improve the rate performance of the battery, improve the cycle performance and high temperature performance of the secondary battery, and reduce the corrosion of the active material by the electrolyte.

In addition, the non-aqueous electrolyte includes the first lithium salt as the main lithium salt, due to its excellent thermal stability and hydrolysis resistance, the first lithium salt can effectively reduce the acidity of the electrolyte, reduce the dissolution of manganese ions, and improve high-temperature cycle, and storage performance. The isocyanate-based compound represented by Formula 1 is introduced into the electrolyte, and can react with trace water in the battery to form —NHCOOH, prevent trace water from interacting with non-aqueous electrolyte to produce HF, further reduce the acidity of the electrolyte and reduce the dissolution of manganese ions, thereby improving high-temperature cycle and storage performance. Moreover, the isocyanate-based compound represented by Formula 1 can also form a uniform SEI film on the anode, reduce the reduction of dissolved Mn at the anode, and further improve the high-temperature cycle and storage performance.

In some embodiments, R 1 represents any one of a C 2 -C 10 alkylene, a C 2 -C 10 oxaalkylene, a C 2 -C 10 azaalkylene, phenylene, naphthylene, anthrylene, cyclobutylene, cyclopentylene, cyclohexylene, biphenylene, methylenediphenylene, which are substituted by one or more R a or are unsubstituted; optionally, the R 1 represents any one of a C 2 -C 6 alkylene, phenylene, naphthylene, anthracene, cyclobutylene, cyclopentylene, cyclohexylene, biphenylene, and methylenediphenylene, which are substituted by one or more R a or are unsubstituted; and/or, the R a comprises one or more selected from halogen atoms, —CN, C 2 -C 3 alkyl; and/or, a number of R a in the compound represented by the Formula 1 is 0, 1, 2, 3, or 4.

Optionally, the first additive includes one or more of the following compounds:

LiN(C m F 2m+1 SO 2 )(C n F 2m+1 SO 2 ) in the first lithium salt may be selected from any corresponding specific substance in the existing technology, and in some embodiments, m and n each independently represent 0, 1, 2, 3 or 4, so as to provide more excellent thermal stability.

In some embodiments of the present application, when the first lithium salt is any one selected from LiN(CF 3 SO 2 )(FSO 2 ), Li(CF 3 SO 2 ) 2 N, and LiN(C 4 F 9 SO 2 )(FSO 2 ), the first additive is any one selected from the following compounds:

In this way, the advantages of the first lithium salt and the first additive are fully utilized and the acidity of the electrolyte and the dissolution of manganese ions are significantly reduced, and the high-temperature cycle and storage performance of the lithium-ion battery are significantly improved.

In some embodiments, based on a total weight of the non-aqueous electrolyte, a content of the first lithium salt is W1 wt. %, W1 is between 0.1 and 48 (such as 0.1, 0.5, 1, 2, 3, 4, 5, 7, 10, 12, 14, 15, 16, 18, 20, 22, 25, 28, 30, 40, 45, or 48), optionally between 5 and 20, such that the problem of aluminum foil corrosion caused by the first lithium salt at high operating voltage is alleviated.

In some embodiments, a content of the first additive is W2 wt. %, W2 is between 0.01 and 20 (such as 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2, 3, 4, 5, 8, 10, 12, 15, 18 or 20), optionally between 0.1 and 10 or between 0.3 and 5, when a weight ratio of the first additive in the electrolyte is within the above range, not only is the acidity of the electrolyte lowered and the manganese ion dissolution reduced, but also the deterioration of the impedance of the anode is avoided, thereby improving the high-temperature cycle and storage performance of the lithium-ion battery, while not affecting the capacity and rate performance of the lithium-ion battery.

In some embodiments, the W2/W1 is defined as M, and M is between 0.001 and 3 (such as 0.001, 0.002, 0.005, 0.007, 0.1, 0.2, 0.3, 0.4, 0.5, 1, 2 or 3), optionally between 0.005 and 0.5. When W2/W1 is within the above range, the first lithium salt and the first additives can play a better synergistic effect to ensure that the acidity of the system is low, the dissolution of manganese ions is reduced, and the high-temperature cycle and storage performance of lithium ions are excellent.

On the basis of controlling the content of the first lithium salt, in some embodiments, the lithium salt in the non-aqueous electrolyte can be supplemented by adding a second lithium salt, that is, the non-aqueous electrolyte further includes a second lithium salt, and the second lithium salt includes one or more selected from lithium difluorophosphate, lithium difluorodioxalate phosphate, lithium difluorooxalate borate, lithium bisoxalate borate, LiPF 6 , and LiBF 4 . The second lithium salt is added to the non-aqueous electrolyte as a lithium salt-type additive, which will be preferentially decomposed on a surface of an aluminum foil, and the insoluble precipitate formed by the combination of a decomposition product and the aluminum ion adheres to the surface of the aluminum foil, thereby forming a passivation film, which prevents the direct contact between the aluminum foil and the electrolyte, protects the aluminum foil, and in turn cooperates with the first lithium salt to improve high-temperature cycle and storage performance.

In some embodiments, based on the total weight of the non-aqueous electrolyte, the content of the second lithium salt is W3 wt. %, W3 is between 0.01 and 20, optionally between 0.1 and 5 or between 0.3 and 5. When a weight ratio of the second lithium salt in the electrolyte is within the above range, not only is the corrosion of the aluminum foil inhibited, but also the high-temperature cycle and storage performance of the lithium-ion battery are improved, while not deteriorating the capacity and rate performance of the lithium-ion battery.

In some embodiments, (W2+W3)/W1 is defined as N, and N is between 0.01 and 5 (such as 0.01, 0.02, 0.05, 0.08, 0.1, 0.5, 0.8, 1.0, 2, 3, 4 or 5), optionally between 0.02 and 1. When W2/W1 and (W2+W3)/W1 are within the above ranges, the three can play a better synergistic effect, ensuring that the acidity of the system is low, the dissolution of manganese ions is reduced, and the high-temperature cycle and storage performance of lithium ions are excellent; in addition, the corrosion of aluminum foil is effectively inhibited, the high-temperature cycle and storage performance of lithium-ion batteries are improved, while not deteriorating the capacity and rate performance of the lithium-ion battery.

In some embodiments, the non-aqueous electrolyte further includes a second additive, and the second additive includes one or more selected from the group consisting of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted saturated cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphorous acid ester compound, a phosphate ester compound, a borate ester compound. Those skilled in the art can select the corresponding second additive from the above substances according to actual needs, and the amount of the second additive in the non-aqueous electrolyte can also refer to the existing technology, which will not be repeated in the present application.

In some embodiments, the non-aqueous electrolyte further includes an organic solvent. The type of the organic solvent is not particularly limited and can be selected according to actual needs. Specifically, the organic solvent includes one or more of a cyclic carbonate compound, a chain carbonate compound, and a carboxylate compound. Operationally, the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, tetrahydrofuran.

In some embodiments, based on a weight of the core, the coating amount of the first cladding layer is C1 wt. %, where C1 is greater than 0 and less than or equal to 7, optionally 4 to 5.6; and/or, based on the weight of the core, the coating amount of the second cladding layer is C2 wt. %, C2 is greater than 0 and less than or equal to 6, and can be 3 to 5. When the coating amount of the first cladding layer is within the above range, the dissolution of manganese ions can be further suppressed, and meanwhile the transport of lithium ions can be further promoted, in addition, the following situations can be effectively avoided: if the coating amount of the first cladding layer is too small, pyrophosphate may have insufficient inhibitory effect on the dissolution of manganese ions, and the improvement of lithium ion transport performance may also not significant; and if the coating amount of the first cladding layer is too large, the cladding layer may be too thick, which may increase the battery impedance and affect the kinetic performance of the battery.

In some embodiments, the ratio of (W1+W2)/(C1+C2) is defined as Q, Q is between 0.1 and 10, optionally between 0.5 and 5, when C is less than the above range, the lithium salt and the additive are insufficient to reduce the acidity of the electrolyte, inhibitory effect on the dissolution of manganese ions are limited, and the high-temperature cycle and storage performance cannot be significantly improved; and when C is greater than the above range, the film-forming impedance is too large, and the capacity and rate performance of the lithium-ion battery will be affected and are difficult to be effectively improved.

In some embodiments, in the cathode active material, a weight ratio of pyrophosphate to phosphate in the first cladding layer is between 1:3 and 3:1, optionally between 1:3 and 1:1. The proper weight ratio of pyrophosphate to phosphate is helpful for the two to fully play the synergistic effect, and can effectively avoid the following situations: in case of too much pyrophosphate and too little phosphate, an increase in battery impedance may be resulted; and in case of too much phosphate and too little pyrophosphate, the effect of inhibiting the dissolution of manganese ions is not significant.

In any embodiment, an interplanar spacing of phosphate in the first cladding layer is 0.345-0.358 nm, and an included angle of a crystal direction (111) is 24.25°-26.45°; and an interplanar spacing of pyrophosphate in the first cladding layer is 0.293-0.326 nm, and the included angle of the crystal direction (111) is 26.41°-32.57°. When the interplanar spacing and the included angle of the crystal direction (111) of phosphate and pyrophosphate in the first cladding layer are within the above range, the impurity phase in the cladding layer can be more effectively avoided, thereby further improving the gram capacity of the material, further improving the cycle performance and rate performance of the secondary battery.

In any embodiment of the first aspect to the third aspect, y is selected from any value within a range of 0.1-0.4. By selecting the value of y within this range, the gram capacity and rate performance of the first cathode active material can be further improved.

In any embodiment of the first aspect to the third aspect, M and X are independently selected from one or more elements of Li and Fe.

In any embodiment, a ratio of y to 1−y is selected from between 1:10 and 10:1, optionally between 1:4 and 1:1. Here y represents the sum of stoichiometric numbers of Mn-site doping elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made of the cathode piece can be further improved.

In any embodiment, a ratio of z to 1−z is selected from between 1:999 and 1:9, optionally between 1:499 and 1:249. Here z represents the sum of the stoichiometric numbers of the P-site doping elements. When the above conditions are met, the energy density and cycle performance of the secondary battery made of the cathode piece can be further improved.

In any embodiment, in the first cathode active material, the crystallinities of pyrophosphate and phosphate are independently between 10% and 100%, optionally between 50% and 100%. In the first cladding layer of the lithium manganese phosphate cathode active material in this embodiment, pyrophosphate and phosphate with a certain degree of crystallinity are beneficial to keep the structure of the first cladding layer stable and reduce lattice defects. On the one hand, this is beneficial for pyrophosphate to fully play the effect of hindering the dissolution of manganese ions. On the other hand, it is also beneficial to phosphate to reduce the content of lithium impurities on the surface and the valence state of oxygen on the surface, thereby reducing the interface side reaction between the cathode material and the electrolyte, reducing the consumption of electrolyte, and improving the cycle performance and the safety performance of the secondary battery.

In any embodiment, A is at least two elements selected from Fe, Ti, V, Ni, Co, and Mg. By selecting the doping elements within the above range, it is beneficial to enhance the doping effect. On the one hand, the lattice change rate is further reduced, thereby inhibiting the dissolution of manganese and reducing the consumption of electrolyte and active lithium. On the other hand, it is also beneficial to further reduce the surface oxygen activity and reduce the interface side reaction between the cathode active material and the electrolyte, thereby improving the cycle performance and high temperature storage performance of the battery.

In any embodiment, the concentration of Li/Mn antisite defect in the first cathode active material is less than 4%, optionally less than 2%. In the cathode active material of the present application, the Li/Mn antisite defect refers to the exchange of Li + and Mn 2+ positions in the LiMnPO 4 lattice. Since the Li + transport channel is a one-dimensional channel, it is difficult for Mn 2+ to migrate in the Li + transport channel. Therefore, the Mn 2+ of the antisite defect will hinder the transport of Li + . The gram capacity and rate performance of LiMnPO 4 can be improved by controlling the concentration of Li/Mn antisite defect at a low level.

In any embodiment, the lattice change rate of the cathode active material is less than 6%, optionally less than 4%. The lithium deintercalation process of LiMnPO 4 is a two-phase reaction. The interfacial stress of the two phases is determined by the lattice change rate. The smaller the lattice change rate, the smaller the interfacial stress and the easier Li + transport. Therefore, the reduction of the lattice change rate of the core will be beneficial to enhance the Li + transport ability, thereby improving the rate performance of the secondary battery.

In any embodiment, a surface oxygen valence state of the first cathode active material is below −1.88, optionally between −1.98 and −1.88. This is because the higher the valence state of oxygen in the compound is, the stronger the ability thereof to obtain electrons is, that is, the stronger the oxidation is. However, in the first cathode active material of the present application, by controlling the surface valence state of oxygen at a lower level, the reactivity of the surface of the cathode material can be reduced, and the interface side reaction between the cathode material and the electrolyte can be further reduced, thereby further improving the cycle performance and high temperature storage performance of the secondary battery.

In any embodiment, the cathode active material has a compacted density at 3 tons (T) of higher than 2.0 g/cm 3 , optionally higher than 2.2 g/cm 3 . The higher the compacted density of the first cathode active material is, that is, the greater the weight of the active material per unit volume is, it is more conducive to increasing the volumetric energy density of the secondary battery.

A second aspect of the present application further provides a battery module, the battery module includes a secondary battery, and the secondary battery is any one of the above-mentioned secondary batteries of the present application.

A third aspect of the present application further provides a battery pack, the battery pack includes a battery module, and the battery module is the above-mentioned battery module of the present application.

A fourth aspect of the present application also provides an electric device, which includes at least one of a secondary battery, a battery module, or a battery pack; and the secondary battery, battery module, and battery pack are the secondary battery, the battery module, the battery pack provided by the present application.

As a result, the battery module and the battery pack of the present application have higher cycle performance and rate characteristics, especially the high temperature stability has also been significantly improved, thereby providing an electric device having the secondary battery, the battery module, or the battery pack of the present application with high power cycle stability and high temperature running stability.

FIG. 1 is an XRD spectrum of a cathode active material according to an embodiment of the present application;

FIG. 2 is a schematic diagram of a secondary battery according to an embodiment of the present application;

FIG. 3 is an exploded view of the secondary battery according to an embodiment of the present application shown in FIG. 2 ;

FIG. 4 is a schematic diagram of a battery module according to an embodiment of the present application;

FIG. 5 is a schematic diagram of a battery pack according to an embodiment of the present application;

FIG. 6 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG. 5 ; and

FIG. 7 is a schematic diagram of an electric device in which a secondary battery is used as a power source according to an embodiment of the present application.

Explanations of reference numerals are as follows:

1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 housing; 52 electrode assembly; and 53 top cover assembly

Hereinafter, embodiments of the secondary battery, battery module, battery pack, and power consumption device of the present application will be specifically disclosed in detail with reference to the accompanying drawings. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known items and repeated descriptions of substantially the same configurations may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

A “range” disclosed herein is defined in terms of a lower limit and an upper limit, and a given range is defined by selecting the lower limit and the upper limit that define a boundary of the particular range. The range defined in this manner may be inclusive or exclusive and may be combined arbitrarily, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are contemplated. Additionally, if minimum range values of 1 and 2 and maximum range values of 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range “0-5” indicates that all real numbers between “0-5” have been listed in the present application, and “0-5” is only an abbreviated representation of the combination of these values. In addition, when expressing that a certain parameter is an integer ≥2, it is equivalent to the disclosure that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and so on.

Unless otherwise specified, all the implementation modes and optional implementation modes of the present application can be combined with each other to form new technical solutions.

Unless otherwise specified, all the technical features and optional technical features of the present application can be combined with each other to form a new technical solution.

Unless otherwise specified, all steps in the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed in sequence, and may further include steps (b) and (a) performed in sequence. For example, when mentioning that the method may further include step (c), it means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b), and (c), may also include steps (a), (c), and (b), may also include steps (c), (a), and (b), and so on.

Unless otherwise specified, the “comprising” and “including” mentioned in the present application mean open or closed. For example, the “comprising” and “including” may mean that other components not listed may be included or included, or only listed components may be included or included.

In the present application, the term “or” is inclusive unless otherwise specified. For example, the phrase “A or B” means “A, B, or both A and B”. More specifically, any one of the following condition satisfy “A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

In the present application, the term “cladding layer” refers to a material layer coated on the core. The material layer can completely or partially cover the core. The use of “cladding layer” is only for the convenience of description and is not intended to limit the present invention. Likewise, the term “thickness of the cladding layer” refers to the thickness of the material layer coated on the core in a radial direction of the core.

As used herein, the term “source” refers to a compound that is the source of a certain element. As an example, the types of the “source” include but are not limited to carbonates, sulfates, nitrates, elemental substances, halides, oxides, and hydroxide, and so on.

The inventors of the present application have found in practical work that serious dissolution of the manganese ions occurs during the deep charge and discharge process of the lithium manganese phosphate cathode active material. Although it is attempted in the existing technology to coat lithium manganese phosphate with lithium iron phosphate to reduce interface side reactions, such coating cannot prevent the migration of dissolved manganese into the electrolyte. The dissolved manganese is reduced to metal manganese after migrating to the anode. The generated metal manganese is equivalent to a “catalyst”, which can catalyze the decomposition of the SEI film (solid electrolyte interphase film) on the surface of the anode, and a part of the generated by-products is gas, which can easily cause the battery to expand affect the safety of the secondary battery. The other part of the by-products is deposited on the surface of the anode, hindering the passage of lithium ions into and out of the anode, causing the increase in the impedance of the secondary battery and affecting the kinetic performance of the battery. In addition, in order to supplement the lost SEI film, the electrolyte and the active lithium inside the battery are continuously consumed, which has an irreversible impact on the capacity retention of the secondary battery.

After a lot of research, the inventors found that for lithium manganese phosphate cathode active materials, the serious dissolution of manganese ions and high surface reactivity may be caused by the Jahn-Teller effect of Mn 3+ and the change of Li + channel size after delithiation. For this reason, the inventors modified lithium manganese phosphate to obtain a cathode active material that can significantly reduce the dissolution of manganese ions and the lattice change rate, and then have excellent cycle performance, high-temperature storage performance, and safety performance.

[Secondary Battery]

Secondary batteries, also known as rechargeable batteries or accumulators, refer to batteries that can be activated by charging the active materials and continue to be used after the battery is discharged.

Typically, a secondary battery includes a cathode piece, an anode piece, a separator, and an electrolyte. During the charging and discharging process of the battery, active ions (such as lithium ions) are repeatedly intercalated and deintercalated between the cathode and the anode. The separator is arranged between the cathode piece and the anode piece, which mainly plays a role in preventing the short circuit of the cathode and the anode, as well as preventing the active ions from passing therethrough. The electrolyte is between the cathode piece and the anode piece, and mainly plays the role of conducting active ions.

An embodiment of the present application provides a secondary battery, comprising a cathode piece and a non-aqueous electrolyte, in which, the cathode piece comprises a cathode active material, and the cathode active material comprises a core and a shell covering the core; the core comprises Li 1+x Mn 1-y A y P 1-z R z O 4 , in which, x=−0.100 to 0.100, y=0.001 to 0.500, z=0.001 to 0.100, and A is one or more selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, optionally one or more selected from the group consisting of Fe, Ti, V, Ni, Co, and Mg, and R is one or more selected from the group consisting of B, Si, N and S; the shell comprises: a first cladding layer covering the core, and a second cladding layer covering the first cladding layer, in which, the first cladding layer comprises pyrophosphate MP 2 O 7 and phosphate XPO 4 , in which, M and X are each independently one or more selected from the group consisting of Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al; and the second cladding layer comprises carbon;

the non-aqueous electrolyte includes a first lithium salt and a first additive, and the first lithium salt includes one or more selected from the group consisting of LiN(C m F 2m+1 SO 2 )(C n F 2m+1 SO 2 ) and Li(FSO 2 ) 2 N, m and n represent positive integers; the first additive includes one or more of the compounds represented by Formula 1,

O═C═N—R 1 —N═C═O  Formula 1

in which, R 1 represents any one of a C 2 -C 10 alkylene, a C 2 -C 10 heteroalkylene, a C 6 -C 18 arylene, a C 2 -C 18 heteroarylene, a C 3 -C 18 alicyclylene, a C 3 -C 18 heteroalicyclylene, which are substituted by one or more R a or are unsubstituted, and R a comprises one or more selected from a halogen atom, —CN, —NCO, —OH, —COOH, —SOOH, a —COOR b , a C 2 -C 10 alkyl, a C 2 -C 10 alkenyl, a C 2 -C 10 alkynyl, a C 2 -C 10 oxaalkyl, and R b is any one selected from C 1 -C 10 alkyls.

The cathode piece generally includes a cathode current collector and a cathode film layer arranged on at least one surface of the cathode current collector, and the cathode film layer includes a cathode active material.

As an example, the cathode current collector has two opposing surfaces in its own thickness direction, and the cathode film layer is disposed on any one or both of the two opposing surfaces of the cathode current collector.

In some embodiments, a metal foil or a composite current collector can be used as the cathode current collector. For example, an aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and so on) on the polymer material substrate (such as polypropylene (PP), poly(ethylene terephthalate) (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and other substrates).

The cathode active material of the present application is obtained by element doping in the compound LiMnPO 4 , in which, A, B, C, and D represent elements doped at the Li site, the Mn site, the P site, and O site of the compound LiMnPO 4 , respectively. Without wishing to be bound by theory, it is believed that the performance improvement of lithium manganese phosphate is related to reducing the lattice change rate of lithium manganese phosphate and reducing surface activity during lithium deintercalation. Reducing the lattice change rate can reduce the lattice constant difference between the two phases at the grain boundary, reduce the interfacial stress, and enhance the Li + transport capacity at the interface, thereby improving the rate performance of the cathode active material. However, high surface activity can easily lead to serious interface side reactions, and aggravate gas production, electrolyte consumption, and interface damage, thereby affecting battery cycle performance. In the present application, the lattice change rate is reduced by Li-site and Mn-site doping. Mn-site doping can also effectively reduce surface activity, thereby inhibiting the dissolution of manganese ions and the interface side reaction between the cathode active material and the electrolyte. P-site doping makes the change rate of the Mn—O bond length faster, lowers the small polaron migration barrier of the material, and thus being beneficial to the electronic conductivity. O-site doping has good effect on reducing the side reactions at the interface. The doping of P site and O site also affects the dissolution of manganese ions and kinetic performance of antisite defects. Therefore, doping reduces the concentration of antisite defects in the material, improves the kinetic performance and gram capacity of the material, and can also change the morphology of the particles, thereby increasing the compaction density. The applicant unexpectedly found that by doping the Li site, Mn site, P site, and O site of the compound LiMnPO 4 with a specific element at a specific amount of the application at the same time, a significantly improved rate performance can be obtained, while significantly reducing dissolution of Mn and Mn-site doping elements results in significantly improved cycle performance and/or high-temperature stability, and the gram capacity and compacted density of the material can also be improved.

In addition, the non-aqueous electrolyte includes the first lithium salt as the main lithium salt, due to its excellent thermal stability and hydrolysis resistance, the first lithium salt can effectively reduce the acidity of the electrolyte, reduce the dissolution of manganese ions, and improve high-temperature cycle, and storage performance. The isocyanate-based compound represented by Formula 1 is introduced into the electrolyte, and can react with trace water in the battery to form —NHCOOH, prevent trace water from interacting with non-aqueous electrolyte to produce HF, further reduce the acidity of the electrolyte and reduce the dissolution of manganese ions, thereby improving high-temperature cycle and storage performance. Moreover, the isocyanate-based compound represented by Formula 1 can also form a uniform SEI film on the anode, reduce the reduction of dissolved Mn at the anode, and further improve the high-temperature cycle and storage performance.

In some embodiments, the non-aqueous electrolyte includes a first lithium salt and a first additive, and the first lithium salt exists as a main lithium salt. LiN(C m F 2m+1 SO 2 )(C n F 2m+1 SO 2 ) in the first lithium salt may be selected from any corresponding specific substance in the existing technology. In some embodiments, m and n each independently represent 1, 2, or 3, to provide better thermal stability. For example, the first lithium salt is any one or more selected from the group consisting of LiN(C m F 2m+1 SO 2 )(C n F 2n+1 SO 2 ) and Li(FSO 2 ) 2 N, for example, the first lithium salt may be selected from the following substances: (fluorosulfonimide) (trifluoromethanesulfonimide) lithium Li(FSO 2 )(CF 3 SO 2 )N, bis(trifluoromethanesulfonimide) lithium (LiN(CF 3 SO 2 ) 2 ), bis(pentafluoroethanesulfonimide) lithium (LiN(C 2 F 5 SO 2 ) 2 ), (trifluoromethanesulfonimide) (pentafluoroethanesulfonimide) lithium (LiN(CF 3 SO 2 )(C 2 F 5 SO 2 )), (trifluoromethanesulfonimide) (heptafluoropropanesulfonimide) lithium (LiN(CF 3 SO 2 )(C 3 F 7 SO 2 )), (trifluoromethanesulfonimide) (nonafluorobutanesulfonimide) lithium (LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )), (pentafluoroethanesulfonimide) (heptafluoropropanesulfonimide) lithium LiN(C 2 F 5 SO 2 )(C 3 F 7 SO 2 ), and Li(FSO 2 ) 2 N.

The isocyanate compound shown in Formula 1 in the present application may be selected from the isocyanate compounds commonly used in electrolytes in the existing technology. In some embodiments, R 1 represents any one of a C 2 -C 10 alkylene, a C 2 -C 10 oxaalkylene, a C 2 -C 10 azaalkylene, phenylene, naphthylene, anthrylene, cyclobutylene, cyclopentylene, cyclohexylene, biphenylene, methylenediphenylene, which are substituted by one or more R a or are unsubstituted; optionally, the R 1 represents any one of a C 2 -C 6 alkylene, phenylene, naphthylene, anthracene, cyclobutylene, cyclopentylene, cyclohexylene, biphenylene, and methylenediphenylene, which are substituted by one or more R a or are unsubstituted; and/or, the R a comprises one or more selected from halogen atoms, —CN, C 2 -C 3 alkyl; and/or, a number of R a in the compound represented by the Formula 1 is 0, 1, 2, 3, or 4.

Optionally, the first additive includes one or more of the following compounds:

The compounds have good dispersion and solubility properties in the solvent of the non-aqueous electrolyte, and can fully react with trace water in the battery to form —NHCOOH, prevent trace water from interacting with non-aqueous electrolyte to produce HF, further reduce the acidity of the electrolyte and reduce the dissolution of manganese ions, thereby improving high-temperature cycle and storage performance. In addition, the isocyanate-based compounds are more likely to form a uniform SEI film on the anode, which is more conducive to reducing the reduction of dissolved Mn on the anode, and further improving high-temperature cycle and storage performance.

In some embodiments of the present application, when the first lithium salt is any one selected from LiN(CF 3 SO 2 )(FSO 2 ), Li(CF 3 SO 2 ) 2 N, and LiN(C 4 F 9 SO 2 )(FSO 2 ), the first additive is any one selected from the following compounds:

In this way, the advantages of the first lithium salt and the first additive are fully utilized and the acidity of the electrolyte and the dissolution of manganese ions are significantly reduced, and the high-temperature cycle and storage performance of the lithium-ion battery are significantly improved.

Although adopting the first lithium salt as the main lithium salt of the non-aqueous electrolyte can effectively improve the high-temperature cycle and storage performance of the secondary battery, the substance will corrode the lithium salt under certain conditions, such as when the operating voltage of the lithium-ion battery is >4.2V, the problem of aluminum foil corrosion occurs. A possible mechanism is that after the original oxide film on the surface of the aluminum foil is destroyed in the electrolyte, aluminum having higher activity is exposed, and the aluminum is oxidized to produce Al 3+ ions, then FSI- or TFSI- in the 1 electrolyte combines with Al 3+ to form soluble Al(FSI) 3 or Al(TFSI) 3 , and the dissolution of Al(FSI) 3 or Al(TFSI) 3 causes aluminum corrosion. Therefore, in order to alleviate the aluminum foil corrosion problem caused by the first lithium salt under high operating voltage, in some embodiments, based on the total weight of the non-aqueous electrolyte, the content of the first lithium salt is W1 wt. %, and W1 is between 0.1 and 48, which can be The selection range is between 5 and 20.

On the basis of controlling the content of the first lithium salt, in some embodiments, the lithium salt in the non-aqueous electrolyte can be supplemented by adding a second lithium salt, that is, the non-aqueous electrolyte further includes a second lithium salt, and the second lithium salt includes one or more selected from lithium difluorophosphate, lithium difluorodioxalate phosphate, lithium difluorooxalate borate, lithium bisoxalate borate, LiPF 6 , and LiBF 4 . The second lithium salt is added to the non-aqueous electrolyte as a lithium salt-type additive, which will be preferentially decomposed on a surface of an aluminum foil, and the insoluble precipitate formed by the combination of a decomposition product and the aluminum ion adheres to the surface of the aluminum foil, thereby forming a passivation film, which prevents the direct contact between the aluminum foil and the electrolyte, protects the aluminum foil, and in turn cooperates with the first lithium salt to improve high-temperature cycle and storage performance.

However, too much lithium salt-type additive will increase the impedance of the cathode and the anode, resulting in abnormal lithium-ion battery capacity and poor rate performance. In some embodiments, based on a total weight of the non-aqueous electrolyte, a content of the second lithium salt is W3 wt. %, W3 is between 0.01 and 20, optionally between 0.1 and 10 or between 0.3 and 5. When a weight ratio of the second lithium salt in the electrolyte is within the above range, not only is the corrosion of the aluminum foil inhibited, but also the high-temperature cycle and storage performance of the lithium-ion battery are improved, while not deteriorating the capacity and rate performance of the lithium-ion battery.

Although the first additive can form a uniform SEI film on the anode, reduce the reduction of dissolved Mn at the anode, and further improve the high-temperature cycle and storage performance; too much isocyanate-based compounds will increase the impedance of the anode, resulting in abnormal lithium-ion battery capacity and poor rate performance. Optionally, a content of the first additive is W2 wt. %, W2 is between 0.01 and 20, optionally between 0.1 and 10 or between 0.3 and 5, when a weight ratio of the first additive in the electrolyte is within the above range, not only is the acidity of the electrolyte lowered and the manganese ion dissolution reduced, but also the deterioration of the impedance of the anode is avoided, thereby improving the high-temperature cycle and storage performance of the lithium-ion battery, while not affecting the capacity and rate performance of the lithium-ion battery.

In some embodiments, the W2/W1 is defined as M, and M is between 0.001 and 3, optionally between 0.005 and 0.5. (W2+W3)/W1 is defined as N, and N is 0.01 to 2, optionally between 0.02 and 1.

When W2/W1 and (W2+W3)/W1 are within the above ranges, the three can play a better synergistic effect, ensuring that the acidity of the system is low, the dissolution of manganese ions is reduced, and the high-temperature cycle and storage performance of lithium ions are excellent; in addition, the corrosion of aluminum foil is effectively inhibited, the high-temperature cycle and storage performance of lithium-ion batteries are improved, while not deteriorating the capacity and rate performance of the lithium-ion battery.

In some embodiments, the non-aqueous electrolyte further includes a second additive, and the second additive includes one or more selected from the group consisting of a cyclic carbonate compound containing an unsaturated bond, a halogen-substituted saturated cyclic carbonate compound, a sulfate compound, a sulfite compound, a sultone compound, a disulfonic acid compound, a nitrile compound, an aromatic compound, an isocyanate compound, a phosphazene compound, a cyclic anhydride compound, a phosphorous acid ester compound, a phosphate ester compound, a borate ester compound. Those skilled in the art can select the corresponding second additive from the above substances according to actual needs, and the amount of the second additive in the non-aqueous electrolyte can also refer to the existing technology, which will not be repeated in the present application.

In some embodiments, the non-aqueous electrolyte further includes an organic solvent. The type of the organic solvent is not particularly limited and can be selected according to actual needs. Specifically, the organic solvent includes one or more of a cyclic carbonate compound, a chain carbonate compound, and a carboxylate compound. Operationally, the organic solvent includes one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene propyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, butyl propionate, tetrahydrofuran.

In some embodiments, A, C, and D of the cathode active material are each independently any element within the above respective ranges, and the B is at least two elements. This makes it possible to more easily and accurately control the composition of the cathode active material.

In some embodiments, based on a weight of the core, the coating amount of the first cladding layer is C1 wt. %, where C1 is greater than 0 and less than or equal to 7, optionally 4 to 5.6. When the coating amount of the first cladding layer is within the above range, the dissolution of manganese ions can be further suppressed, and meanwhile the transport of lithium ions can be further promoted, in addition, the following situations can be effectively avoided: if the coating amount of the first cladding layer is too small, pyrophosphate may have insufficient inhibitory effect on the dissolution of manganese ions, and the improvement of lithium ion transport performance may also not significant; and if the coating amount of the first cladding layer is too large, the cladding layer may be too thick, which may increase the battery impedance and affect the kinetic performance of the battery.

In some embodiments, based on the weight of the core, the coating amount of the second cladding layer is C2 wt. %, and C2 is greater than 0 and less than or equal to 6, optionally 3 to 5. On the one hand, the carbon-containing layer as the second cladding layer can play a “barrier” function to avoid direct contact between the cathode active material and the electrolyte, thereby reducing the corrosion of the active material by the electrolyte and improving the safety performance of the battery at high temperatures. On the other hand, the second cladding layer has strong electrical conductivity, which can reduce the internal resistance of the battery, thereby improving the kinetic performance of the battery. However, since the gram capacity of the carbon material is low, when the amount of the second cladding layer is too large, the gram capacity of the entire cathode active material may be reduced. Therefore, when the coating amount of the second cladding layer is within the above range, the kinetic performance and safety performance of the battery can be further improved without sacrificing the gram capacity of the cathode active material.

In some embodiments, the ratio of (W1+W2)/(C1+C2) is defined as Q, and Q is between 0.1 and 10 (such as 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10), and may be optionally between 0.5 and 5, when C is less than the above range, the lithium salt and the additive are insufficient to reduce the acidity of the electrolyte, inhibitory effect on the dissolution of manganese ions are limited, and the high-temperature cycle and storage performance cannot be significantly improved; and when C is greater than the above range, the film-forming impedance is too large, and the capacity and rate performance of the lithium-ion battery will be affected and are difficult to be effectively improved.

In some embodiments, optionally, a weight ratio of pyrophosphate to phosphate in the first cladding layer is between 1:3 and 3:1, optionally between 1:3 and 1:1.

The proper weight ratio of pyrophosphate to phosphate is helpful for the two to fully play the synergistic effect, and can effectively avoid the following situations: in case of too much pyrophosphate and too little phosphate, an increase in battery impedance may be resulted; and in case of too much phosphate and too little pyrophosphate, the effect of inhibiting the dissolution of manganese ions is not significant.

In some embodiments, optionally, an interplanar spacing of phosphate in the first cladding layer is 0.345-0.358 nm, and an included angle of a crystal direction (111) is 24.25°-26.45°; and an interplanar spacing of pyrophosphate in the first cladding layer is 0.293-0.326 nm, and the included angle of the crystal direction (111) is 26.41°-32.57°.

When the interplanar spacing and the included angle of the crystal direction (111) of phosphate and pyrophosphate in the first cladding layer are within the above range, the impurity phase in the cladding layer can be more effectively avoided, thereby further improving the gram capacity of the material, further improving the cycle performance and rate performance of the secondary battery.

In some embodiments, optionally, a ratio of y to 1−y in the core is between 1:10 and 10:1, optionally between 1:4 and 1:1. Here y represents a sum of stoichiometric numbers of Mn-site doping elements. When the above conditions are met, the energy density and cycle performance of the cathode active material can be further improved.

In some embodiments, optionally, a ratio of z to 1−z in the core is between 1:9 and 1:999, optionally between 1:499 and 1:249. Here y represents a sum of the stoichiometric numbers of the P-site doping elements. When the above conditions are met, the energy density and cycle performance of the cathode active material can be further improved.

In some embodiments, optionally, crystallinities of pyrophosphate and phosphate are independently between 10% and 100%, optionally between 50% and 100%.

In the first cladding layer of the lithium manganese phosphate cathode active material in the present application, pyrophosphate and phosphate with a certain degree of crystallinity are beneficial to keep the structure of the first cladding layer stable and reduce lattice defects. On the one hand, this is beneficial for pyrophosphate to fully play the effect of hindering the dissolution of manganese ions. On the other hand, it is also beneficial to phosphate to reduce the content of lithium impurities on the surface and the valence state of oxygen on the surface, thereby reducing the interface side reaction between the cathode material and the electrolyte, reducing the consumption of electrolyte, and improving the cycle performance and the safety performance of the secondary battery.

It should be noted that, in the present application, the crystallinities of pyrophosphate and phosphate can be adjusted, for example, by adjusting the process conditions of the sintering process, such as sintering temperature, sintering time, and the like. The crystallinities of pyrophosphate and phosphate salts can be measured by methods known in the art, such as by X-ray diffraction, densitometry, infrared spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance absorption.

In some embodiments, optionally, the A is at least two selected from Fe, Ti, V, Ni, Co, and Mg.

Simultaneously doping two or more of the above elements on the manganese site of the lithium manganese phosphate cathode active material is beneficial to enhance the doping effect, on the one hand, the lattice change rate is further reduced, thereby inhibiting the dissolution of manganese and reducing the electrolyte and active lithium; and on the other hand, it is also beneficial to further reduce the surface oxygen activity and reduce the interface side reaction between the cathode active material and the electrolyte, thereby improving the cycle performance and high temperature storage performance of the battery.

In some embodiments, optionally, the concentration of Li/Mn antisite defect in the cathode active material is less than 4%, optionally less than 2%.

In the cathode active material of the present application, the Li/Mn antisite defect refers to the exchange of Li + and Mn 2+ positions in the LiMnPO 4 lattice. Since the Li + transport channel is a one-dimensional channel, it is difficult for Mn 2+ to migrate in the Li + transport channel. Therefore, the Mn 2+ of the antisite defect will hinder the transport of Li + . The gram capacity and rate performance of LiMnPO 4 can be improved by controlling the concentration of Li/Mn antisite defect at a low level. In the present application, the concentration of the antisite defect can be measured, for example, according to JIS K 0131-1996.

In some embodiments, optionally, the lattice change rate of the cathode active material is less than 6%, optionally less than 4%.

The lithium deintercalation process of LiMnPO 4 is a two-phase reaction. The interfacial stress of the two phases is determined by the lattice change rate. The smaller the lattice change rate, the smaller the interfacial stress and the easier Li + transport. Therefore, the reduction of the lattice change rate of the core will be beneficial to enhance the Li + transport ability, thereby improving the rate performance of the secondary battery.

In some embodiments, optionally, a button battery average discharge voltage of the cathode active material is above 3.5 V, and the discharge gram capacity is above 140 mAh/g; optionally, the average discharge voltage is above 3.6 V, and the discharge gram capacity is above 145 mAh/g.

Although the average discharge voltage of undoped LiMnPO 4 is above 4.0V, the discharge gram capacity thereof is low, usually less than 120 mAh/g, so the energy density is low. By doping to adjust the lattice change rate, the discharge gram capacity can be greatly increased, and the overall energy density increases significantly in the case of a slight drop in the average discharge voltage.

In some embodiments, optionally, the surface oxygen valence state of the cathode active material is below −1.88, optionally between −1.98 and −1.88.

This is because the higher the valence state of oxygen in the compound is, the stronger the ability thereof to obtain electrons is, that is, the stronger the oxidation is. However, in the first cathode active material of the present application, by controlling the surface valence state of oxygen at a lower level, the reactivity of the surface of the cathode material can be reduced, and the interface side reaction between the cathode material and the electrolyte can be further reduced, thereby further improving the cycle performance and high temperature storage performance of the secondary battery.

In some embodiments, optionally, the cathode active material has a compacted density at 3 tons (T) of higher than 2.0 g/cm 3 , optionally higher than 2.2 g/cm 3 .

The higher the compacted density of the first cathode active material is, that is, the greater the weight of the active material per unit volume is, it is more conducive to increasing the volumetric energy density of the secondary battery. In the present application, the compacted density can be measured, for example, according to GB/T 24533-2009.

The cathode active material used in the secondary battery of the present application is prepared by the following preparation method, and the preparation method includes the following steps:

providing a core material comprising Li 1+x Mn 1-y A y P 1-z R z O 4 ; providing a MP 2 O 7 powder and a XPO 4 suspension containing a source of carbon; adding the core material, the MP 2 O 7 powder to the XPO 4 suspension containing the source of carbon for mixing, and sintering a resulting mixture to obtain the cathode active material.

In some embodiments, the step of providing the core material includes the following steps: step (1): mixing and stirring a source of manganese, a source of element A, and an acid in a container to obtain manganese salt particles doped with the element A; step (2): mixing the manganese salt particles doped with the element A with a source of lithium, a source of phosphorus, and a source of element R in a solvent to obtain a slurry, sintering the slurry under the protection of an inert gas atmosphere to obtain a lithium manganese phosphate doped with the element A and the element R, in which, the lithium manganese phosphate doped with the element A and the element R is Li 1+x Mn 1-y A y P 1-z R z O 4 , where x=−0.100-0.100, y=0.001-0.500, z=0.001-0.100, A is one or more selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge, and optionally one or more selected from Fe, Ti, V, Ni, Co, and Mg, and R is one or more selected from B, Si, N, and S.

Preferably, the above step (1) is carried out at a temperature of 20-120° C., optionally 25-80° C.; and/or, the stirring in step (1) is carried out at 500-700 rpm for 60-420 mins, which can be preferably 120-360 mins.

In some embodiments, the source of the element A is one or more selected from an elemental substance, a sulfate, a halide, nitrate, an organic acid salt, an oxide, or a hydroxide of the element A; and/or, the source of the element R is one or more selected from a elemental substance, a sulfate, a halide, a nitrate, an organic acid salt, an oxide, or a hydroxide, and an inorganic acid of the element R.

In some embodiments, the MP 2 O 7 powder is prepared by the following method: adding the source of the element M and the source of phosphorus to a solvent to obtain a mixture, adjusting a pH value of the mixture to 4-6, stirring the mixture for complete reaction, and then drying and sintering resulting mixture to obtain the MP 2 O 7 powder, in which, M is one or more selected from Li, Fe, Ni, Mg, Co, Cu, Zn, Ti, Ag, Zr, Nb, and Al. Preferably, the drying step includes drying at 100-300° C., optionally 150-200° C. for 4-8 hrs; the sintering step includes sintering under an inert gas atmosphere at 500-800° C., optionally 650-800° C., for 4-10 hrs.

In some embodiments, a sintering temperature in the coating step is 500-800° C., and the sintering time is 4-10 hrs.

In some embodiments, the cathode film layer may further include other cathode active materials known in the art for secondary batteries. As an example, the cathode active material may include at least one of the following materials: olivine-structured lithium-containing phosphate, lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials suitable for cathode active materials of the secondary batteries can also be used. These cathode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, at least one of lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and modified compounds thereof. Examples of the olivine-structured lithium-containing phosphate may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 , which may also be abbreviated as LFP), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

In some embodiments, the cathode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

In some embodiments, the cathode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of a superconducting carbon, an acetylene black, a carbon black, a Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the cathode piece can be prepared as follows: dispersing the components for preparing the cathode piece, such as the cathode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a cathode slurry; coating the cathode slurry on the cathode current collector; and performing drying, cold pressing, and other processes, to obtain the cathode piece.

[Anode Piece]

The anode piece includes an anode current collector and an anode film layer arranged on at least one surface of the anode current collector, and the anode film layer includes an anode active material.

As an example, the anode current collector has two opposing surfaces in its own thickness direction, and the anode film layer is arranged on any one or both of the two opposing surfaces of the anode current collector.

In some embodiments, a metal foil or a composite current collector can be used as the anode current collector. For example, a copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of polymer material substrate. The composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, and so on) on the polymer material substrate (such as polypropylene (PP), poly(ethylene terephthalate) (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and other substrates).

In some embodiments, the anode active material can be an anode active material known in the art of batteries. As an example, the anode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and the like. The silicon-based material may be at least one selected from elemental silicon, a silicon-oxygen compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The tin-based material can be at least one selected from of elemental tin, a tin oxide, and a tin alloy. However, the present application is not limited to these materials, and other conventional materials suitable for the anode active materials of the batteries can also be used. These anode active materials may be used alone or in combination of two or more.

In some embodiments, the anode film layer may further optionally include a binder. As an example, the binder may be at least one selected from a styrene-butadiene rubber (SBR), a polyacrylic acid (PAA), a sodium polyacrylate (PAAS), a polyacrylamide (PAM), a polyvinyl alcohol (PVA), a sodium alginate (SA), a polymethacrylic acid (PMAA), and a carboxymethyl chitosan (CMCS).

In some embodiments, the anode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of a superconducting carbon, an acetylene black, a carbon black, a Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the anode film layer may optionally include other additives, such as a thickener (such as, a sodium carboxymethylcellulose (CMC-Na)) and the like.

In some embodiments, the anode piece can be prepared as follows: dispersing the components for preparing the anode piece, such as the anode active material, the conductive agent, the binder, and any other components, in a solvent (such as a deionized water) to form an anode slurry; coating the anode slurry on the anode current collector, and performing drying, cold pressing, and other processes, to obtain the anode piece.

[Separator]

In some embodiments, a separator is further included in the secondary battery. The present application has no particular limitation on the type of the separator, and any known separator in a porous structure having good chemical stability and mechanical stability can be selected.

In some embodiments, the material for the separator can be at least one selected from a glass fiber, a non-woven fabric, a polyethylene, a polypropylene, and a polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, which is not particularly limited herein. When the separator is a multilayer composite film, the materials of each layer may be the same or different, which is not particularly limited herein.

In some embodiments, the cathode piece, the anode piece, and the separator can be made into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package. The outer package can be used to package the electrode assembly and THE electrolyte.

In some embodiments, the outer packaging of the secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like. The outer packaging of the secondary battery may also be a soft case, such as a bag-type soft case. The material of the soft case may be plastic, and examples of the plastic include a polypropylene, a polybutylene terephthalate, a polybutylene succinate, and the like.

The present application has no special limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG. 2 shows a square-shaped secondary battery 5 as an example.

In some embodiments, referring to FIG. 3 , the outer package may include a housing 51 and a cover 53 . The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating cavity, and the cover 53 can cover the opening to enclose the accommodating cavity. The cathode piece, the anode piece, and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 . The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which may be selected by those skilled in the art according to specific actual needs.

In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

FIG. 4 is a battery module 4 as an example. Referring to FIG. 4 , in the battery module 4 , a plurality of secondary batteries 5 may be arranged in sequence along a length direction of the battery module 4 . It can be understood any other arrangement manners can also be adopted. Furthermore, the plurality of secondary batteries 5 may be fixed by fasteners.

Optionally, the battery module 4 may further include a case having an accommodation space, in which a plurality of secondary batteries 5 are accommodated.

In some embodiments, the battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

FIGS. 5 - 6 show a battery pack 1 as an example. Referring to FIGS. 5 - 6 , the battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery case includes an upper case 2 and a lower case 3 , the upper case 2 can cover the lower case 3 and form an enclosed space for accommodating the battery modules 4 . The plurality of battery modules 4 can be arranged in the battery case in any manner.

In addition, the present application also provides an electric device, which includes at least one of the secondary battery, the battery module, or the battery pack provided in the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the electric device, and can also be used as an energy storage unit of the electric device. The electric devices may include mobile devices (such as mobile phones, laptops, and the like), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, and the like), electric trucks, and the like), electric trains, ships and satellites, energy storage systems, and the like, but not limited thereto.

The secondary battery, the battery module, or the battery pack can be selected as the electric device according to the use requirements.

FIG. 7 is an example of an electric device. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the electric device for the secondary battery, a battery pack, or a battery module may be used.

Hereinafter, examples of the present application will be described. The embodiments described below are exemplary and are only used for explaining the present application, and should not be construed as limiting the present application. If no specific technique or condition is indicated in the examples, it shall be carried out according to the technique or condition described in the literature in this field or according to the product specification. The reagents or instruments used, if not indicated by the manufacturer, are all commercially available conventional products.

The first additive is selected from the following compounds: