Cylindrical battery and method for producing the same

The present invention relates to a cylindrical battery including a sealing body having a current interrupting mechanism and to a method for producing the cylindrical battery.

Sealed batteries are roughly classified into cylindrical batteries, prismatic batteries, and pouch batteries according to the shape and the material of housings that contain an electrode body which is a power-generating element. In particular, cylindrical batteries are used in a wide range of applications pertaining to, for example, power tools, electric power-assisted bicycles, and electric vehicles. In these applications, cylindrical batteries are used as assembled batteries in which batteries are connected in series or in parallel.

In the related art, sealing bodies in cylindrical batteries include a mechanism for ensuring safety. For example, Patent Literature 1 discloses a sealing body including a current interrupting mechanism and an explosion-proof valve as illustrated in FIG. 8 .

The sealing body 81 illustrated in FIG. 8 is famed by stacking a terminal cap 82 , a valve body 83 , an insulating member 84 , and a metal plate 85 serving as a terminal plate. The valve body 83 has, in its center portion, an annular projection part 83 a that projects toward the metal plate 85 . The metal plate 85 is connected to the projection part 83 a . The insulating member 84 is annularly provided in the vicinity of this connection part so that an outer circumferential portion of the valve body 83 is insulated from an outer circumferential portion of the metal plate 85 . Since the valve body 83 receives a battery inner pressure increased by generation of gas inside a battery due to, for example, misuse of the battery, the valve body 83 works so as to pull the connection part in a direction away from the battery. When the battery inner pressure further increases to reach a predetermined value, the connection part fractures to interrupt a current path between the valve body 83 and the metal plate 85 . When the battery inner pressure further increases, the valve body 83 fractures so that gas inside the battery is released through a gas port provided in the terminal cap 82 .

In the sealing body 81 disclosed in Patent Literature 1, the valve body 83 has a protrusion part 83 b that inclines toward the center, and the insulating member 84 has a Z shape in cross section. The insulating member 84 is fitted to the protrusion part 83 b , and the metal plate 85 is fitted to the insulating member 84 , such that these members are fixed to each other. This structure prevents a fracture of the connection part between the valve body 83 and the metal plate 85 even if the sealing body 81 receives external shock.

Patent Literature

PTL 1: International Publication No. WO 2014/097586

PTL 2: Japanese Published Unexamined Patent Application No. 2010-287567

Technical Problem

In connecting cylindrical batteries to each other to produce an assembled battery, resistance welding has been commonly employed as a method for connecting respective lead plates to a sealing body serving as a positive electrode terminal and an outer can serving as a negative electrode terminal. As described in Patent Literature 2, wire bonding for attaching an aluminum wire by ultrasonic welding has been recently employed as a method for connecting batteries to provide an assembled battery with a function for interrupting connection between batteries in case of malfunctions of batteries in the assembled battery.

When an aluminum wire is connected to sealing bodies by ultrasonic welding, ultrasonic vibration is applied to sealing bodies through the aluminum wire. Such application of ultrasonic vibration to a sealing body causes vibrations to be transmitted to the inside of the sealing body, which may result in a fracture of the connection part between the valve body and the metal plate and/or misalignment of the metal plate relative to the insulating member.

The sealing body disclosed in Patent Literature 1 is less likely to have the above-described issues because the valve body, the insulating member, and the terminal plate are fixed to each other. However, Patent Literature 1 does not consider the case where ultrasonic vibration is applied to the sealing body.

In light of the above-mentioned circumstances, the present invention is directed to a cylindrical battery having a current interrupting mechanism that is unlikely to fracture even if ultrasonic vibration is applied to a sealing body.

Solution to Problem

To solve the above-mentioned issues, a cylindrical battery according to an aspect of the present invention includes an electrode body famed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween, an electrolyte, a bottomed cylindrical outer can, and a sealing body crimped to an opening of the outer can via a gasket.

The sealing body includes a valve body having an annular protrusion part, an insulating member disposed on an inner circumference of the protrusion part of the valve body and having a skirt portion, and a metal plate disposed on an inner circumference of the skirt portion of the insulating member and connected to a center portion of the valve body.

The metal plate is crimped with the protrusion part of the valve body via the insulating member.

The present invention is further directed to a method for producing the cylindrical battery according to an aspect including steps (1) to (4) described below.

Step (1) of preparing a valve body having an annular protrusion part, a metal plate, and an insulating member having a skirt portion.

Step (2) of fitting the metal plate to the inner side of the skirt portion of the insulating member.

Step (3) of fitting the insulating member to the inner side of the protrusion part of the valve body.

Step (4) of pressing the protrusion part of the valve body such that the protrusion part of the valve body secures the metal plate via the insulating member.

Advantageous Effects of Invention

Since three members, which are the valve body, the insulating member, and the metal plate, are fixed to each other to form a current interrupting mechanism according to the present invention, the current interrupting mechanism retains its function even if ultrasonic vibration is applied to the sealing body. The present invention can provide a cylindrical battery having high quality because, for example, the current interrupting mechanism operates properly even if external shock or vibration is applied to the battery.

FIG. 1 is a cross-sectional perspective view of a cylindrical non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is a sectional view of a sealing body according to an embodiment of the present invention.

FIG. 3 is a plan view of a valve body according to an embodiment of the present invention as viewed from inside the battery.

FIG. 4 is a plan view of a modified valve body according to an embodiment of the present invention as viewed from inside the battery.

FIG. 5 is a sectional view of a modified sealing body according to an embodiment of the present invention.

FIG. 6 is a sectional view of a modified sealing body according to an embodiment of the present invention.

FIG. 7 is a sectional view of a modified sealing body according to an embodiment of the present invention.

FIG. 8 is a sectional view of a sealing body according to an example of the prior art.

Embodiments of the present invention will be described below by using a non-aqueous electrolyte secondary battery which is an example cylindrical battery. The present invention is not limited to the following embodiments. Changes and modifications can be appropriately carried out without departing from the scope of the present invention.

A non-aqueous electrolyte secondary battery 10 illustrated in FIG. 1 includes an electrode body 19 and an electrolyte (not shown) in a bottomed cylindrical outer can 23 . A sealing body 11 is crimped to an opening of the outer can 23 via a gasket 22 . This configuration seals the battery.

As illustrated in FIG. 2 , the sealing body 11 includes a terminal cap 12 , a valve body 13 , an insulating member 14 , and a metal plate 15 . The valve body 13 and the metal plate 15 are connected at their center portions. The insulating member 14 is interposed between the outer circumferential portion of the valve body 13 and the outer circumferential portion of the metal plate 15 . The terminal cap 12 on the battery outer side of the valve body 13 functions as an external terminal, whereas the metal plate 15 connected to a positive electrode lead 16 a extending from the electrode body 19 functions as an inner terminal.

The current interrupting mechanism operates in the following manner. The metal plate 15 has a gas port. When the battery inner pressure increases, the valve body 13 receives an increased battery inner pressure. As the battery inner pressure increases, the valve body 13 works so as to pull the connection part between the valve body 13 and the metal plate 15 in a direction away from the battery. When the battery inner pressure reaches a predetermined value, a thin part 15 a located in a part of the metal plate connected to the valve body 13 or in the metal plate 15 fractures to interrupt a current path between the valve body 13 and the metal plate 15 . The sealing body 11 including three members, the valve body 13 , the insulating member 14 , and the metal plate 15 , forms a current interrupting mechanism. When the battery inner pressure further increases after operation of the current interrupting mechanism, the valve body 13 fractures with a thin part 13 c in the valve body 13 as a starting point so that gas inside the battery is released through a gas port provided in the terminal cap 12 .

The valve body 13 can be produced by performing press processing on a plate material made of aluminum or an aluminum alloy. Since aluminum and aluminum alloys have good flexibility, they are suitable for materials of the valve body 13 . The valve body 13 has a protrusion part 13 a in the center portion and a protrusion part 13 b in the outer circumferential portion on the battery inner side-surface. The protrusion part 13 a in the center portion facilitates connection between the valve body 13 and the metal plate 15 and provides a space for interposing the insulating member 14 between the outer circumferential portion of the valve body 13 and the outer circumferential portion of the metal plate 15 . As illustrated in FIG. 3 , the protrusion part 13 b in the outer circumferential portion is formed so as to have an annular shape in plan view. The protrusion part 13 b secures the metal plate 15 via the insulating member 14 .

In the present invention, the modifications illustrated in FIGS. 4 to 6 can be used instead of having the protrusion part 13 b illustrated in FIG. 2 and FIG. 3 .

FIG. 4 illustrates a protrusion part 43 b in which plural protrusions are arranged into a broken annular shape. Such a protrusion part including plural protrusions makes it easy to press the protrusion part so as to bend the protrusion part toward the center. The size and the number of the protrusions can be freely set as long as the metal plate can be crimped with the protrusion part.

FIG. 5 illustrates a protrusion part 53 b that is tapered from the bottom toward the end. Such a tapered cross section of the protrusion part can increase the mechanical strength of the protrusion part.

FIG. 6 illustrates a protrusion part 63 b famed to have a curved cross section. Such a curved cross section of the protrusion part allows the end of the protrusion part to locally press the insulating member. The protrusion part having a curved cross section can thus increase a force with which the metal plate is secured. Since the above-described effect is obtained as long as the inner side of the cross section of the protrusion part is curved, the outer side of the cross section of the protrusion part may be linear.

The insulating member 14 ensures electrical insulation and can be made of a material that does not affect battery characteristics. The material used for the insulating member 14 is preferably a polymer resin. Examples of the polymer resin include a polypropylene (PP) resin and a polybutylene terephthalate (PBT) resin.

The insulating member 14 has, on its outer circumference, a skirt portion 14 a extending inward in the battery so that the protrusion part 13 b of the valve body 13 can secure the metal plate 15 via the insulating member 14 . As illustrated in FIG. 2 , the metal plate 15 is disposed on the inner circumference of the skirt portion 14 a , which allows the metal plate 15 to be secured with the protrusion part 13 b of the valve body 13 via the insulating member 14 . The cross section of the insulating member 14 may be Z-shaped as a result of bending the end of the skirt portion 14 a toward the protrusion part 13 b of the valve body 13 . However, the end of the skirt portion 14 a is preferably bent toward the metal plate 15 in order to avoid misalignment of the metal plate 15 relative to the insulating member 14 .

In order that the metal plate 15 be secured with the protrusion part 13 b of the valve body 13 via the insulating member 14 , the method for producing the sealing body 11 preferably includes the following processes. First, the valve body 13 , the insulating member 14 , and the metal plate 15 for forming the sealing body 11 are prepared. Next, the metal plate 15 is fitted to the inner side of the skirt portion 14 a of the insulating member 14 , and the insulating member 14 is fitted to the inner side of the protrusion part 13 b of the valve body 13 . The protrusion part 13 b is then pressed toward the center such that the protrusion part 13 b of the valve body 13 secures the metal plate 15 via the insulating member 14 . The order of these two processes for fitting the above-described members may be changed.

The valve body 13 and the metal plate 15 are preferably connected to each other after completion of the above-mentioned processes. Since the valve body 13 and the metal plate 15 can be connected to each other with these members fixed to each other, there is a small variation in connection strength. The metal plate 15 is preferably made of aluminum or an aluminum alloy like the valve body 13 . This configuration facilitates connection between the valve body 13 and the metal plate 15 . The valve body 13 and the metal plate 15 are preferably connected by laser welding.

The sealing body having the terminal cap 12 is described as an embodiment of the present invention. However, the terminal cap 12 can be omitted as shown in FIG. 7 because the current interrupting mechanism can be famed by the valve body, the insulating member, and the metal plate. The use of the valve body 73 as an external terminal in this way can sufficiently ensure the path through with gas inside the battery is released when the valve body 73 fractures due to an increased battery inner pressure.

Next, the electrode body 19 will be described. In this embodiment, the electrode body 19 formed by winding a positive electrode plate 16 and a negative electrode plate 17 with a separator 18 interposed therebetween as illustrated in FIG. 1 is used.

The positive electrode plate 16 can be produced, for example, in the following manner. First, a positive electrode mixture slurry is prepared by uniformly kneading a positive electrode active material and a binder in a dispersion medium. The binder is preferably polyvinylidene difluoride and the dispersion medium is preferably N-methylpyrrolidone. A conducting agent, such as graphite or carbon black, is preferably added to the positive electrode mixture slurry. This positive electrode mixture slurry is applied onto a positive electrode current collector and dried to form a positive electrode mixture layer. At this time, a positive electrode current collector-exposed portion without the positive electrode mixture layer is formed on part of the positive electrode current collector. Next, the positive electrode mixture layer is compressed to a predetermined thickness with a roller, and the electrode plate after compression is cut in a predetermined size. Finally, the positive electrode lead 16 a is connected to the positive electrode current collector-exposed portion to obtain the positive electrode plate 16 .

As a positive electrode active material, any lithium-transition metal composite oxide that can intercalate and deintercalate lithium ions can be used. Examples of lithium-transition metal composite oxides include general formula LiMO 2 (M represents at least one of Co, Ni, and Mn), LiMn 2 O 4 , and LiFePO 4 . These lithium-transition metal composite oxides may be used alone or as a mixture of two or more. These lithium-transition metal composite oxides may be used with the addition of at least one selected from the group consisting of Al, Ti, Mg, and Zr or the substitution with a transition metal element.

The negative electrode plate 17 can be produced, for example, in the following manner. First, a negative electrode mixture slurry is prepared by uniformly kneading a negative electrode active material and a binder in a dispersion medium. The binder is preferably a styrene-butadiene (SBR) copolymer, and the dispersion medium is preferably water. A thickener, such as carboxymethyl cellulose, is preferably added to the negative electrode mixture slurry. This negative electrode mixture slurry is applied onto a negative electrode current collector and dried to form a negative electrode mixture layer. In this process, a negative electrode current collector-exposed portion without the negative electrode mixture layer is famed on part of the negative electrode current collector. Next, the negative electrode mixture layer is compressed to a predetermined thickness with a roller, and the electrode plate after compression is cut in a predetermined size. Finally, a negative electrode lead 17 a is connected to the negative electrode current collector-exposed portion to obtain the positive electrode plate 17 .

As the negative electrode active material, a carbon material or metal material that can intercalate and deintercalate lithium ions can be used. Examples of carbon materials include graphite, such as natural graphite and artificial graphite. Examples of metal materials include silicon, tin, and oxides thereof. These carbon materials or metal materials may be used alone or as a mixture of two or more.

As a separator 18 , a microporous membrane containing, as a main component, a polyolefin, such as polyethylene (PE) or polypropylene (PP), can be used. A single layer of microporous membrane may be used or two or more layers of microporous membranes may be used. A multilayer separator composed of two or more layers preferably includes an intermediate layer famed of a layer mainly composed of polyethylene (PE) having a low melting point and a surface layer composed of polypropylene (PP) having high oxidation resistance. Furthermore, inorganic particles made of, for example, aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), or silicon oxide (SiO 2 ) may be added to the separator 18 . These inorganic particles may be contained in the separator or may be applied to the surface of the separator together with a binder.

A non-aqueous electrolyte containing a lithium salt, or an electrolyte salt, dissolved in a non-aqueous solvent can be used.

Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, cyclic carboxylates, and chain carboxylates. These non-aqueous solvents are preferably used as a mixture of two or more. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Cyclic carbonates, such as fluoroethylene carbonate (FEC), in which some of hydrogen atoms are substituted with fluorine atoms can also be used. Examples of chain carbonates include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propyl carbonate (MPC). Examples of cyclic carboxylates include γ-butyrolactone (γ-BL) and γ-valerolactone (γ-VL). Examples of chain carboxylates include methyl pivalate, ethyl pivalate, methyl isobutyrate, and methyl propionate.

Examples of lithium salts include LiPF 6 , LiBF 4 , LiCF 3 SO 3 , LiN(CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ), LiC(CF 3 SO 2 ) 3 , LiC(C 2 F 5 SO 2 ) 3 , LiAsF 6 , LiClO 4 , Li 2 B 10 Cl 10 , and Li 2 B 12 CL 12 . Among these lithium salts, LiPF 6 is particularly preferred, and the concentration of LiPF 6 in the non-aqueous electrolyte is preferably 0.5 to 2.0 mol/L. LiPF 6 may be mixed with another lithium salt, such as LiBF 4 .

Embodiments of the present invention will be described below in detail on the basis of Examples of the cylindrical non-aqueous electrolyte secondary battery.

As described above, the present invention can provide a cylindrical battery having a sealing body that retains its function even if external vibration such ultrasonic vibration is applied to the sealing body. Therefore, the present invention can greatly contribute to an improvement in the quality of the cylindrical battery. Since cylindrical batteries can be connected to each other by wire bonding according to the present invention, the present invention can improve the degree of freedom in design of assembled batteries.

10 Non-aqueous electrolyte secondary battery

11 Sealing body

12 Terminal cap

13 Valve body

13 b Protrusion part

13 c Thin part

14 Insulating member

14 a Skirt portion

15 Metal plate

15 a Thin part

16 Positive electrode plate

17 Negative electrode plate

18 Separator

19 Electrode body

23 Outer can