Cylindrical battery

Abstract

The present disclosure relates to a cylindrical battery, and the objective of the disclosure is to reduce the number of components of a sealing body that closes one end of an outer can, by providing a metal component, which is a constituent of the sealing body, with an electric current blocking function. A cylindrical battery (10) includes: an outer can (100) in the shape of a bottomed cylinder; a sealing body (11) which closes one end of the outer can; an electrode body (20) disposed inside the outer can; and an insulating resin component (18) disposed between the outer can and the sealing body. The sealing body includes a metal component (12) which is connected to a positive electrode lead (21a) that leads out from the electrode body. The metal component has an easily broken portion (16) radially inward of the connecting portion of the metal component and the positive electrode lead, and is crimp-secured by means of the outer can, with the resin component interposed therebetween. The resin component is crimp-secured by means of the metal component, on the radially inner side of the metal component relative to the easily broken portion.

Description

Cylindrical battery

[0001] The present disclosure relates to cylindrical batteries.

[0002] In recent years, the applications of secondary batteries have expanded to include power sources for electric vehicles and energy storage devices for utilizing natural energy, and further increases in capacity are desired. Electric vehicles and energy storage devices use battery modules formed by connecting multiple secondary batteries in series or parallel via external leads. As secondary batteries increase in capacity, higher safety is required for secondary batteries and battery modules. Conventionally, when the internal pressure of a secondary battery increases abnormally due to overcharging or other reasons, thermal runaway and explosion of the secondary battery have been prevented by interrupting the current path within the secondary battery.

[0003] Patent Document 1 describes a cylindrical battery incorporating a current interruption mechanism in a sealing body that seals one end of the outer can to ensure safety. This current interruption mechanism is composed of a metal valve body, an insulating member, and a metal body with a vent hole. The valve body and the metal body are connected at their centers, with an insulating member interposed between their outer peripheries. When the battery's internal pressure increases, the valve body pulls the connection with the metal body toward the outside of the battery, and this connection or a thin portion on the metal body breaks, interrupting the current path between the valve body and the metal body. Furthermore, when the battery's internal pressure increases, the valve body breaks, starting from the thin portion of the valve body, and gas inside the battery is released.

[0004] International Publication No. 2016 / 157748

[0005] In the configuration described in Patent Document 1, the sealing body that closes one end of the outer can includes three components: a valve body, an insulating member, and a metal body, in order to provide the sealing body with a current interruption function. These components are required to operate reliably in the event of a battery abnormality, and it is essential that they have a complex and highly precise processed shape. Therefore, having a large number of components for the sealing body, as in the configuration described in Patent Document 1, results in a significant burden, such as an increase in the number of processing steps, and therefore it is desirable to reduce the number of components for the sealing body.

[0006] An object of the present disclosure is to provide a cylindrical battery that can reduce the number of components of the sealing body by providing a current interruption function to the metal parts that make up the sealing body that closes one end of the outer can.

[0007] The cylindrical battery according to the present disclosure is a cylindrical battery comprising a bottomed cylindrical outer can, a sealing body that closes one end of the outer can, an electrode body disposed inside the outer can, and an insulating resin part disposed between the outer can and the sealing body, wherein the sealing body has a metal part electrically connected to an electrode lead extending from the electrode body, the metal part has an easily breakable part radially inward from the connection part between the metal part and the electrode lead, and is crimped to the outer can via the resin part, and the resin part is crimped to the metal part radially inward from the easily breakable part.

[0008] According to the cylindrical battery of the present disclosure, the metal parts that make up the sealing body can be given a current interruption function, so the number of components of the sealing body can be reduced.

[0009] Fig. 1 is a cross-sectional view of a cylindrical battery according to an example of the embodiment. Fig. 2 is a view corresponding to part A in Fig. 1 , showing a state in which the internal pressure of the battery has increased from the state in Fig. 1 and the current interrupt mechanism has been activated. Fig. 3 is a view corresponding to part A in Fig. 1 , showing a state in which the internal pressure of the battery has further increased from the state in Fig. 2 and the gas release mechanism has been activated. Fig. 4 is a cross-sectional view of a cylindrical battery according to a comparative example.

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, specific shapes, materials, directions, etc. are examples for facilitating understanding of the present disclosure and can be appropriately changed according to the use, purpose, specifications, etc. of the cylindrical battery. In the following, a case will be described in which the cylindrical battery is a non-aqueous electrolyte secondary battery, but the cylindrical battery is not limited to this.

[0011] FIG. 1 is a cross-sectional view of a cylindrical battery 10 according to an embodiment. For example, the cylindrical battery 10 may be a nonaqueous electrolyte secondary battery such as a lithium-ion battery. The cylindrical battery 10 includes a substantially cylindrical, bottomed, cylindrical outer can 100, which houses an electrode assembly 20 and a nonaqueous electrolyte (not shown). A sealing body 11 is fixed to an opening at one end (the upper end in FIG. 1 ) of the outer can 100 via an insulating resin part 18. This allows the opening at one end of the outer can 100 to be closed by the sealing body 11 via the resin part 18. The resin part 18 is an insulating member and functions as a gasket to seal the gap between the outer can 100 and the sealing body 11. It also functions to release gas when the internal pressure of the battery increases, as described below. The nonaqueous electrolyte includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. The nonaqueous electrolyte is not limited to a liquid electrolyte, but may also be a solid electrolyte using a gel polymer or the like.

[0012] The electrode assembly 20 is a wound type and includes a positive electrode plate 21, a negative electrode plate 22, and a separator 23, with the positive electrode plate 21 and the negative electrode plate 22 being spirally wound with the separator 23 interposed therebetween. Hereinafter, one side of the electrode assembly 20 in the direction of the winding axis may be referred to as the "top" and the other side of the winding axis may be referred to as the "bottom."

[0013] The sealing body 11 is composed only of a metal part 12. The metal part 12 functions as a positive terminal and as a current interruption mechanism that interrupts the current path when the battery's internal pressure increases. The metal part 12 has a disk-shaped outer end plate 13 located at the outer end of the battery, a disk-shaped inner end plate 15 located at the inner end of the battery, and a disk-shaped connecting part 17 that connects the outer end plate 13 and the inner end plate 15. The outer diameter of the outer end plate 13 is smaller than that of the inner end plate 15. The outer diameter of the connecting part 17 is smaller than that of the outer end plate 13 and the inner end plate 15. The outer end plate 13, the inner end plate 15, and the connecting part 17 are coaxial and have the same central axis. As a result, a circular groove 12a is formed between the outer end plate 13 and the inner end plate 15 of the metal component 12, and a flange 15a is formed on the inner end plate 15 radially outward from the connecting portion 17. The metal component 12 can be made of, for example, aluminum or an aluminum alloy. An external lead (not shown) is welded to the outer surface (top surface in Figure 1) of the external terminal formed by the outer end plate 13 for electrical connection to other cylindrical batteries in the battery module (not shown).

[0014] In the inner end plate portion 15, an end of a positive electrode lead 21a extending from the electrode body 20 is connected to a radially inner surface of a portion of the flange portion 15a. The positive electrode lead 21a corresponds to an electrode lead. Furthermore, the flange portion 15a has an easily breakable portion 16 located radially inward of a connection portion G between the metal component 12 and the positive electrode lead 21a. The easily breakable portion 16 is an annular thin-walled portion formed in a radially inner portion of the flange portion 15a, and is formed by forming an annular groove 15b in a radially inner portion of the inner surface (lower surface in FIG. 1 ) of the flange portion 15a. The easily breakable portion 16 can also be formed on the outer surface (upper surface in FIG. 1 ) of the flange portion 15a.

[0015] The resin part 18 is disposed between the inner peripheral surface of an opening formed at one end (the upper end in FIG. 1 ) of the outer can 100 and the outer peripheral surface of the sealing body 11. The resin part 18 has a generally J-shaped cross section in the circumferential direction, with the outer battery end (the upper end in FIG. 1 ) being longer than the inner battery end (the lower end in FIG. 1 ), and is generally annular in plan view. The flange portion 15a of the inner end plate 15 is crimped to the outer can 100 via the resin part 18. The resin part 18 is held in a compressed state between one end of the outer can 100 and the outer peripheral surface of the sealing body 11, and is crimped to the metal part 12 at a position radially inward of the metal part 12 relative to the frangible portion 16. For example, as shown in FIG. 1 , the tip of the resin part 18 extending from between the flange portion 15a and one end of the outer can 100 is crimped to the outer end plate 13 and the inner end plate 15. The entire periphery of the tip of the resin part 18 is crimped and fixed by the metal part 12, thereby forming a sealing structure between the tip of the resin part 18 and the sealing body 11. This ensures that the battery is sealed even if the internal pressure of the battery increases and the fragile part 16 breaks. The resin part 18 can be made of a material that can ensure insulation and does not affect the battery characteristics. A polymer resin is preferred as the material used for the resin part 18, and examples of such a material include polypropylene (PP) resin and polybutylene terephthalate (PBT) resin.

[0016] As described above, in the cylindrical battery 10, the internal sealing of the battery is maintained even after the frangible portion 16 breaks due to an increase in the battery's internal pressure. If the battery's internal pressure further increases, as shown in FIG. 2, the resin part 18 deforms toward the outside of the battery, and the portion including the outer end plate portion 13 is separated from the metal part 12 along the frangible portion 16. This constitutes a current interruption mechanism that interrupts the current path between the center of the metal part 12, to which the external lead is connected, and the positive electrode lead 21a. If the battery's internal pressure further increases, as shown in FIG. 3, a portion of the resin part 18 breaks. This constitutes a gas discharge mechanism that allows gas inside the battery to be discharged. The strength of the resin part 18 can be adjusted by the material and thickness, but the resin part 18 may also be provided with an frangible portion such as an annular groove.

[0017] The current interrupt mechanism and gas release mechanism will be described in more detail. Let P1 be the internal battery pressure when the fragile portion 16 ruptures, P2 be the internal battery pressure when the resin component 18 ruptures, and P3 be the internal battery pressure when the resin component 18 detaches from the metal component 12. The breaking strengths of the fragile portion 16 and the resin component 18, as well as the fixing strength of the resin component 18 by the metal component 12, are regulated so that the relationship P1 < P2 < P3 holds. When the internal battery pressure reaches P1, even if only a portion of the fragile portion 16 ruptures, the resin component 18 attempts to deform outward from the battery, allowing the portion connected to the external lead to be separated from the metal component 12 along the fragile portion 16. When the internal battery pressure increases after the fragile portion 16 ruptures and reaches P2, the resin component 18 ruptures, releasing the gas inside the battery. Furthermore, the breaking strength of the easily breakable portion 16 and the resin part 18, as well as the fixing strength of the resin part 18 by the metal part 12, may be regulated so as to satisfy the relationship P1 < P3 < P2. In this case, as in the case above, the portion to which the external lead is connected can be separated from the metal part 12 along the easily breakable portion 16. When the internal pressure of the battery increases after the easily breakable portion 16 breaks and reaches P3, the tip of the resin part 18 detaches from the metal part 12, and gas inside the battery is discharged. In the above relational formula, P2 and P3 may satisfy the relationship P2 = P3.

[0018] The easily breakable portion 16 is preferably formed in an annular shape. The annular easily breakable portion may be formed by a step portion whose thickness changes in the radial direction of the inner end plate portion 15. The easily breakable portion 16 may be partially discontinuous, such as in a C-shape, as long as a current-breaking mechanism can be realized. The breaking strength of the resin part 18 can be adjusted by its material and thickness, and an easily breakable portion may also be formed in the resin part 18. The easily breakable portion of the resin part 18 can be formed, for example, by an annular or C-shaped groove. The easily breakable portion may be formed by a step portion whose thickness changes in the radial direction of the resin part 18. The fixing strength of the resin part 18 by the metal part 12 can be adjusted by the pressure of the press process when compressing the resin part 18.

[0019] Next, the electrode body 20 will be described. The electrode body 20 is disposed inside the outer can 100. The positive electrode plate 21 constituting the electrode body 20 has a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. For example, a positive electrode active material layer is formed on both sides of the positive electrode current collector. For example, a foil of a metal such as aluminum, or a film with such a metal disposed on the surface layer, is used as the positive electrode current collector. A suitable positive electrode current collector is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode current collector is, for example, 10 μm to 30 μm.

[0020] The positive electrode active material layer preferably contains a positive electrode active material, a conductive agent, and a binder. The positive electrode plate 21 is produced by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, the binder, and a dispersion medium such as N-methyl-2-pyrrolidone (NMP) to both sides of a positive electrode current collector, followed by drying and rolling.

[0021] Examples of the positive electrode active material include lithium-containing transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. The lithium-containing transition metal composite oxides are not particularly limited, but include those represented by the general formula Li １＋ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0022] Examples of the conductive agent include carbon materials such as carbon black (CB), acetylene black (AB), ketjen black, and graphite. Examples of the binder include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0023] The positive electrode plate 21 is provided with a positive electrode current collector exposed portion (not shown) where the surface of the metal constituting the positive electrode current collector is exposed. The positive electrode current collector exposed portion is a portion to which a positive electrode lead 21a is connected, and is a portion of the positive electrode current collector surface that is not covered with the positive electrode active material layer. One end portion of the positive electrode lead 21a is joined to the positive electrode current collector exposed portion by, for example, ultrasonic welding. The other end portion of the positive electrode lead 21a extends upward through an opening (not shown) formed in a disk-shaped first insulating plate 30 arranged on the upper side of the electrode body 20 and is connected to the lower surface (inner surface) of the flange portion 15a of the metal component 12. The positive electrode lead 21a can be made of a material such as aluminum, an aluminum alloy, nickel, a nickel alloy, iron, or stainless steel.

[0024] The negative electrode plate 22 has a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. For example, the negative electrode active material layer is formed on both sides of the negative electrode current collector. Furthermore, the negative electrode plate 22 has a negative electrode current collector exposed portion (not shown) at the end of the winding. The negative electrode current collector exposed portion is a portion to which the negative electrode lead 22a is connected, and is a portion of the surface of the negative electrode current collector that is not covered with the negative electrode active material layer. One end portion of the negative electrode lead 22a is joined to the negative electrode current collector exposed portion by, for example, ultrasonic welding. The other end portion of the negative electrode lead 22a passes through the outer periphery of a disk-shaped second insulating plate 31 arranged below the electrode body 20 and is connected to the bottom of the outer can 100.

[0025] The negative electrode plate 22 is produced by, for example, applying a negative electrode mixture slurry containing the negative electrode active material, the binder, water, and the like to both sides of the negative electrode current collector, followed by drying and rolling.

[0026] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions. For example, carbon materials such as natural graphite and artificial graphite, metals that alloy with lithium such as Si and Sn, or alloys or composite oxides containing these, can be used. The binder contained in the negative electrode active material layer is, for example, the same resin as that used in the positive electrode plate 21. When preparing the negative electrode mixture slurry using an aqueous solvent, styrene-butadiene rubber (SBR), CMC or a salt thereof, polyacrylic acid or a salt thereof, polyvinyl alcohol, etc. can be used. These materials may be used alone or in combination of two or more.

[0027] The negative electrode plate 22 is used by being wound in a state in which it is stacked on the positive electrode plate 21 with the separator 23 interposed therebetween. Note that, in addition to using the negative electrode lead 22a, or omitting the negative electrode lead 22a, an exposed negative electrode current collector portion may be disposed around the entire outermost surface of the winding end of the negative electrode plate 22, and the exposed negative electrode current collector portion may be brought into contact with the inner circumferential surface of the cylindrical portion of the outer can 100, thereby electrically connecting the negative electrode plate 22 to the outer can 100. This ensures better current collection. In this case, one end portion of the negative electrode lead 22a may be joined to the exposed negative electrode current collector portion formed at the winding start end of the negative electrode plate 22.

[0028] A porous sheet having ion permeability and insulating properties is used for the separator 23. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Polyolefin resins such as polyethylene and polypropylene are preferred as the material for the separator 23. The thickness of the separator 23 is, for example, 10 μm to 50 μm. Separators 23 tend to be thinner as batteries become higher in capacity and power output. The separator 23 has a melting point of, for example, about 130°C to 180°C.

[0029] The cylindrical battery 10 is assembled, for example, as follows. The electrode assembly 20 is inserted into a cylindrical outer can 100, which is fabricated by drawing a steel plate, together with a disk-shaped second insulating plate 31 underneath. The negative electrode lead 22a connected to the negative electrode plate 22 is connected to the bottom of the outer can 100 by welding. Next, a disk-shaped first insulating plate 30 is inserted above the electrode assembly 20 inside the outer can 100. A U-shaped groove 101 ( FIG. 1 ) is formed around the entire circumference of the outer can 100 above the first insulating plate 30 on the opening side by plastic working. A predetermined amount of prepared nonaqueous electrolyte is then poured into the outer can 100 containing the electrode assembly 20. The positive electrode lead 21a connected to the positive electrode plate 21 is then connected to the flange 15a of the metal part 12 constituting the sealing body 11 by welding. At this time, a resin part 18 is previously crimped and fixed to the outer periphery of the metal part 12. For example, the resin part 18 is pressed by the inner end plate 15 and outer end plate 13 of the metal part 12, and the resin part 18 is then crimped to the metal part 12. Then, while folding the positive electrode lead 21a, the metal part 12 is placed inside the outer can 100 above the groove 101 with the resin part 18 interposed therebetween, and the open end of the outer can 100 is crimped to produce the sealed cylindrical battery 10. At this time, the outer end plate 13 is exposed at the top end of the sealing body 11, in the uppermost layer of the cylindrical battery 10.

[0030] Alternatively, the resin part 18 and the metal part 12 may be disposed inside one end of the outer can 100 without being crimped, and then the outer periphery of the metal part 12 may be crimped to one end of the outer can 100 via the resin part 18. Then, the resin part 18 may be pressed so that it is compressed by the inner end plate 15 and the outer end plate 13.

[0031] According to the cylindrical battery 10 described above, the metal component 12 that constitutes the sealing body 11 can be given a current interruption function, thereby reducing the number of components that make up the sealing body 11. This reduces the number of processing steps required for components that require high processing precision, thereby reducing manufacturing costs.

[0032] FIG. 4 is a cross-sectional view of a cylindrical battery 10a of the comparative example. Unlike the cylindrical battery 10 shown in FIGS. 1 to 3, the cylindrical battery 10a of the comparative example has a sealing structure at one end of the outer can 100a consisting of a gasket 34 as a resin part and a sealing body 11a. The sealing body 11a consists of three components: a metal valve body 36, an insulating member 38, and a metal body 40 with a vent hole. The valve body 36 and the metal body 40 are connected at their centers, with the insulating member 38 interposed between their outer peripheries. The end of the positive electrode lead 21a extending from the electrode body 20 is connected to the metal body 40 radially outward of the connection between the valve body 36 and the metal body 40. The metal body 40 has a thin-walled portion at the connection with the valve body 36. When the battery's internal pressure increases, the valve element 36 deforms upward due to the internal pressure, pulling the connection portion with the metal body 40 outward from the battery. This connection portion or a thin portion of the metal body 40 breaks, interrupting the current path between the valve element 36 and the positive electrode lead 21a. Furthermore, when the battery's internal pressure increases, the valve element 36 breaks, starting from the thin portion 36a of the valve element 36, and gas inside the battery is released. In this comparative cylindrical battery 10a, three components are required to provide the sealing body 11a with a current interrupt function, which increases the manufacturing process and creates a significant burden. The embodiment shown in Figures 1 to 3 can prevent this problem.

[0033] 10, 10a Cylindrical battery, 11, 11a Sealing body, 12 Metal part, 12a Groove portion, 13 Outer end plate portion, 15 Inner end plate portion, 15a Flange portion, 15b Groove, 17 Connecting portion, 18 Resin part, 20 Electrode body, 21 Positive electrode plate, 21a Positive electrode lead, 22 Negative electrode plate, 22a Negative electrode lead, 23 Separator, 30 First insulating plate, 31 Second insulating plate, 34 Gasket, 36 Valve body, 36a Thin portion, 38 Insulating member, 40 Metal body.

Claims

1. A cylindrical battery comprising: a bottomed cylindrical outer can; a sealing body closing one end of the outer can; an electrode assembly disposed inside the outer can; and an insulating resin part disposed between the outer can and the sealing body; the sealing body has a metal part electrically connected to an electrode lead extending from the electrode assembly; the metal part has an easily breakable part radially inward from a connection part between the metal part and the electrode lead, and is crimped to the outer can via the resin part; and the resin part is crimped to the metal part radially inward from the easily breakable part.

2. A cylindrical battery as described in claim 1, wherein the metal part has an inner end plate, an outer end plate, and a connecting part connecting the inner end plate and the outer end plate, a flange part on the radially outer side of the inner end plate is crimped and fixed to one end of the outer can via the resin part, and a tip part of the resin part extending from between the flange part and one end of the outer can is crimped and fixed to the inner end plate and the outer end plate.

3. A cylindrical battery according to claim 1 or 2, wherein the easily breakable portion is formed by an annular groove.

4. A cylindrical battery according to any one of claims 1 to 3, wherein the easily breakable portion breaks along the entire circumference when the internal pressure of the battery increases, cutting off the current path between the center of the metal part and the electrode lead, and when the internal pressure of the battery increases further, the outer portion of the easily breakable portion in the resin part breaks, allowing internal gas to be released.

5. A cylindrical battery according to any one of claims 1 to 3, wherein the easily breakable portion breaks along the entire circumference when the internal pressure of the battery increases, cutting off the current path between the center of the metal part and the electrode lead, and when the internal pressure of the battery increases further, the tip of the resin part comes off the metal part, thereby allowing internal gas to be discharged.

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