Secondary battery

Abstract

This secondary battery comprises: an electrode body including a positive electrode, a negative electrode, and a separator, the electrode body being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween; a bottomed cylindrical outer can housing the electrode body; a sealing body closing an opening of the outer can; and a current collector plate (30) electrically connected to the outer can. The secondary battery includes an exhaust mechanism provided at least at a bottom of the outer can. The negative electrode is connected to the bottom of the outer can via the current collector plate (30). The current collector plate (30) has a plurality of extending portions (32) extending in radial directions of the outer can from a base portion (31) joined to an inner bottom of the outer can. Each extending portion (32) is provided with an easily deformable portion (50). The easily deformable portion (50) is more easily deformable in the thickness direction of the current collector plate (30) than portions of the current collector plate (30) other than the easily deformable portion (50).

Description

secondary battery

[0001] The present disclosure relates to a secondary battery and to a current collection structure of the secondary battery.

[0002] A cylindrical battery generally has a structure comprising a wound electrode body in which a positive electrode and a negative electrode are spirally wound with a separator interposed therebetween, a cylindrical outer can with a bottom that houses the electrode body, and a sealing body that closes the opening of the outer can, with leads extending from the electrode body connected to the sealing body.

[0003] Patent Document 1 discloses a cylindrical battery in which an uncoated portion where no negative electrode mixture layer is provided is provided on one axial side of the negative electrode of an electrode body, the uncoated portion is welded to a disk-shaped current collector plate, and the current collector plate is welded to the inside bottom of an outer can, the negative electrode is electrically connected to the outer can, and the outer can serves as the negative electrode terminal.

[0004] Japanese Patent Application Publication No. 9-161837

[0005] In cylindrical batteries, when abnormal combustion occurs, gas generated inside the outer can may be vented from the bottom of the outer can. Specifically, a portion of the bottom of the outer can is broken to create an opening and allow the gas to be vented. However, if the current collector plate blocks the opening, the gas venting is hindered, resulting in a problem that the temperature of the battery after combustion remains high. Note that even the cylindrical battery described in Patent Document 1 cannot solve this problem.

[0006] The secondary battery according to the present disclosure is a secondary battery comprising: an electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween; a cylindrical outer can with a bottom that houses the electrode assembly; a sealing body that closes the opening of the outer can; and a current collector plate electrically connected to the outer can, the secondary battery having an exhaust mechanism at least at the bottom of the outer can, wherein the negative electrode is connected to the bottom of the outer can via the current collector plate, the current collector plate has a plurality of extension portions that extend radially in a radial direction of the outer can from a base that is joined to the bottom of the inner side of the outer can, the extension portions having easily deformable portions that are more easily deformed in the thickness direction of the current collector plate than portions of the current collector plate other than the easily deformable portions.

[0007] According to the secondary battery according to the present disclosure, it is possible to suppress obstruction of exhaust gas caused by the current collector plate.

[0008] Fig. 3 is an axial cross-sectional view of a secondary battery that is an example of an embodiment; Fig. 4 is a diagram showing a valve portion and a groove portion provided on an outer can; Fig. 5 is a perspective view of a current collector plate that is an example of an embodiment; Fig. 6 is a plan view of a current collector plate that is an example of an embodiment; Fig. 7 is a cross-sectional view taken along line A-A in Fig. 3; Fig. 4 is an enlarged perspective view showing a portion surrounded by a dashed line in Fig. 3; Fig. 5 is a diagram showing another example of an easily deformable portion;

[0009] Hereinafter, an example of an embodiment of a secondary battery according to the present disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure also includes configurations obtained by selectively combining the components of the embodiments described below. The secondary battery according to the present disclosure may be a battery using an aqueous electrolyte or a battery using a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery (lithium ion battery) using a nonaqueous electrolyte will be exemplified as a secondary battery 10 according to one embodiment, but the secondary battery according to the present disclosure is not limited thereto.

[0010] In the following, a cylindrical battery including a wound electrode assembly 14 and a bottomed cylindrical outer can 15 that houses the electrode assembly 14 is exemplified, but the secondary battery according to the present disclosure is not limited to a cylindrical battery. The secondary battery according to the present disclosure may be, for example, a prismatic battery including a bottomed rectangular tubular outer can 15 as the bottomed cylindrical outer can that houses the electrode assembly 14.

[0011] FIG. 1 is a cross-sectional view of a secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, a cylindrical outer can 15 with a bottom that accommodates the electrode assembly 14 and the nonaqueous electrolyte, and a sealing member 16 that closes the opening of the outer can 15. The secondary battery 10 also includes an exhaust mechanism at least at the bottom of the outer can 15. The exhaust mechanism exhausts gases and other substances generated within the outer can 15 during abnormal heat generation. The exhaust mechanism may also exhaust not only gases but also combustible materials generated during abnormal heat generation, such as a current collector plate 30 (described later). The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13. The electrode assembly 14 has a spirally wound structure in which the positive electrode 11 and the negative electrode 12 are wound around the separator 13. Hereinafter, for convenience of explanation, the sealing member 16 side of the battery is referred to as the top, and the bottom side of the outer can 15 is referred to as the bottom.

[0012] The electrolyte may be an aqueous electrolyte, but in this embodiment, a nonaqueous electrolyte is used. The nonaqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent. Examples of nonaqueous solvents include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of nonaqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The nonaqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0013] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0014] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the length direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11. The secondary battery 10 includes an insulating plate 17 arranged on the electrode assembly 14.

[0015] The electrode assembly 14 has a positive electrode current collector tab 20 connected to the positive electrode 11 by welding or the like. In this embodiment, the positive electrode current collector tab 20 is connected to the longitudinal center of the positive electrode 11. The positive electrode current collector tab 20 is connected to the underside of an internal terminal plate 22, which is the bottom plate of the sealing body 16. Therefore, the sealing body 16 serves as a positive electrode external terminal. The current collection structure of the positive electrode 11 is not particularly limited, and multiple positive electrode current collector tabs 20 may be connected to the positive electrode 11. The positive electrode 11 may also have an uncoated portion like the negative electrode 12 described below, or may similarly have a current collection structure like the current collector plate 30 described below. As will be described in detail later, the negative electrode 12 has an uncoated portion 12A on one axial side of the electrode assembly 14 where no negative electrode mixture layer is formed on the negative electrode core, and the uncoated portion 12A is connected to the outer can 15 via the current collector plate 30. Therefore, the outer can 15 serves as a negative electrode external terminal.

[0016] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core. The positive electrode core can be a foil of a metal stable within the potential range of the positive electrode 11, such as aluminum, an aluminum alloy, stainless steel, or titanium, or a film having a surface layer made of such a metal. The thickness of the positive electrode core is preferably 5 μm to 25 μm, more preferably 10 μm to 20 μm. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder, and is preferably provided on both sides of the positive electrode core. The thickness of the positive electrode mixture layer is greater than the thickness of the positive electrode core, and is, for example, 60 μm to 120 μm on one side of the positive electrode core.

[0017] The positive electrode active material uses a lithium transition metal composite oxide containing transition metal elements such as Ni, Co, and Mn. Examples of metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, and Bi. Among these, it is preferable to contain at least one of Ni, Co, and Mn. One type of lithium transition metal composite oxide may be used alone, or multiple types may be used in combination.

[0018] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powder, and conductive whiskers. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, and acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like.

[0019] The positive electrode 11 can be produced by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto a positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core. The positive electrode 11, which has a core exposed portion at the center in the longitudinal direction to which the positive electrode current collector tab 20 is connected, is produced by intermittently applying the positive electrode mixture slurry and pausing the application of the slurry midway, with the portion not coated becoming the core exposed portion. For example, N-methyl-2-pyrrolidone (NMP) is used as the dispersion medium for the positive electrode mixture slurry.

[0020] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer disposed on the negative electrode core. The negative electrode core can be a foil of a metal stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film having a surface layer made of such a metal. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably provided on both sides of the negative electrode core. The negative electrode 12 can be fabricated, as in the case of the positive electrode 11, by applying a negative electrode mixture slurry to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core. The thickness of the negative electrode 12 is, for example, 90 μm or more and 210 μm or less. The thickness of the negative electrode core is, for example, 5 μm or more and 15 μm or less. The thickness of the negative electrode mixture layer is, for example, 40 μm or more and 110 μm or less on one side of the negative electrode core.

[0021] The negative electrode active material is not particularly limited as long as it reversibly absorbs and releases lithium ions, and generally, carbon materials such as graphite are used. Furthermore, elements that alloy with Li, such as Si and Sn, or materials containing such elements may also be used as the negative electrode active material. Among these, silicon-containing materials containing Si are preferred. Furthermore, lithium titanate, which has a higher charge / discharge potential relative to metallic lithium than carbon materials, may also be used as the negative electrode active material. One type of negative electrode active material may be used alone, or multiple types may be used in combination.

[0022] As in the case of the positive electrode 11, the binder contained in the negative electrode mixture layer can be a fluororesin, an olefin resin, PAN, a polyimide, a polyamide, an acrylic resin, or the like. However, polyvinyl acetate, styrene-butadiene rubber (SBR), or the like may also be used. Among these, SBR is preferably used. One type of binder may be used alone, or multiple types may be used in combination. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. The negative electrode mixture layer may also contain a conductive agent such as CNT.

[0023] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0024] As described above, the outer can 15 is a cylindrical metal container with a bottom and an opening on one axial side. A gasket 27 is provided between the outer can 15 and the sealing body 16 to ensure sealing of the battery interior and insulation between the outer can 15 and the sealing body 16. The outer can 15 has a groove 21 formed by a portion of the side surface protruding inward. The groove 21 is preferably formed in an annular shape along the circumferential direction of the outer can 15, and supports the sealing body 16 on its top surface. The sealing body 16 is fixed to the top of the outer can 15 by the groove 21 and the open end of the outer can 15, which is crimped to the sealing body 16.

[0025] The sealing body 16 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges. If an abnormality occurs in the battery and the internal pressure increases, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure further increases, the upper valve body 25 ruptures, and gas is discharged from the opening of the cap 26.

[0026] The outer can 15 according to this embodiment will be described in detail with further reference to Fig. 2. Fig. 2 is a bottom view of the bottom of the outer can 15 as viewed from the outside, illustrating the valve portion 40 and the groove portion 41 provided on the outer can 15. In the following, a case where the groove portion 41 is formed on the outer bottom portion of the outer can 15 will be described as an example, but the groove portion 41 may also be provided on the inner bottom portion of the outer can 15.

[0027] As shown in Fig. 2, the outer can 15 has a valve portion 40 on the outer bottom and a groove portion 41 that continuously or discontinuously surrounds the periphery of the valve portion 40. The thickness of the groove portion 41 is smaller than the thickness of the bottom of the outer can 15. That is, the groove portion 41 is formed to be thinner than the outer can 15. The cross-sectional shape of the groove portion 41 is not particularly limited, and may be, for example, a triangular shape as shown in Fig. 1. The depth of the groove portion 41 is preferably 50% to 85% of the thickness of the bottom of the outer can 15, taking into consideration durability during normal use and the operability of the safety valve when the internal pressure increases.

[0028] The valve portion 40 is a portion located radially inside the groove portion 41. The valve portion 40 opens to form a gas exhaust port when the internal pressure in the outer can 15 reaches a predetermined pressure. Therefore, the valve portion 40 is a portion that is scheduled to open when the internal pressure rises, and functions as a lower safety valve.

[0029] 2A, the outer can 15 has a valve portion 40 provided on the outer bottom of the outer can 15, and a groove portion 41 having a circular ring shape in bottom view, centered on a center point O of the bottom of the outer can 15, surrounding the valve portion 40. The groove portion 41 breaks when the pressure inside the outer can 15 reaches or exceeds a predetermined pressure, thereby opening the valve portion 40. Note that the shape of the groove portion 41 in bottom view is not limited to a circular ring shape, and other shapes such as a polygonal shape may be used.

[0030] The groove 41 shown in FIG. 2B forms part of a circular ring centered on the center point O of the bottom. That is, the groove 41 is formed in a C-shape, which is an arc. The inside of the groove 41 forms the valve portion 40. Therefore, each end of the groove 41 is connected by a connecting portion 42 that is thicker than the groove 41. The connecting portion 42 has a thickness similar to that of the bottom of the outer can 15, for example. As a result, the groove 41 discontinuously surrounds the disk-shaped valve portion 40. Similar to the groove 41 in FIG. 2A, the groove 41 in FIG. 2B also ruptures when the pressure inside the outer can 15 exceeds a predetermined pressure, opening the valve portion 40 and discharging gas. Note that the bottom view shape of the groove 41 is not limited to a C-shape and can be different, such as a shape consisting of multiple arcs.

[0031] 3 to 7, the current collecting plate 30, which is an example of an embodiment, will be described in detail. FIG. 3 is a perspective view of the current collecting plate 30, which is an example of an embodiment. FIG. 4 is a plan view of the current collecting plate 30, which is an example of an embodiment. FIG. 5 is a cross-sectional view taken along line A-A in FIG. 3. FIG. 6 is an enlarged perspective view of the portion surrounded by the dashed line in FIG. 3. FIG. 7 is a diagram showing another example of the easily deformable portion 50.

[0032] 1, the current collector 30 is disposed between the electrode body 14 and the bottom of the outer can 15. It also electrically connects the negative electrode 12 and the outer can 15. The current collector 30 can improve current collection, enabling highly efficient charging and discharging.

[0033] 3 and 4 , the current collecting plate 30 has a base 31 and a plurality of extensions 32 extending radially from the base 31 in the radial direction of the outer can 15. The base 31 is located in the center of the current collecting plate 30, and the extensions 32 extend radially from the base 31. The base 31 is also located in the center of the bottom of the outer can 15 and is joined to the inner bottom of the outer can 15 by welding or the like. It is preferable that the base 31 is smaller in the radial direction of the outer can 15 than the valve portion 40 defined by the groove portion 41.

[0034] As described above, the base 31 is joined to the inner bottom of the outer can 15, and is therefore formed so as to be recessed relative to the extending portions 32 when viewed in cross section as in Fig. 1. The shape of the base 31 in a plan view is not particularly limited, and may be, for example, a quadrilateral shape with chamfered corners as shown in Fig. 4. The shape of the base 31 in a plan view is set appropriately depending on the number of extending portions 32, etc.

[0035] In this embodiment, the current collector plate 30 is formed so as to have a cross shape in a plan view by having four extension portions 32 extending from a base portion 31. The number of extension portions 32 is not particularly limited, but is preferably two to four. The length of the extension portions 32 is preferably such that they extend from the base portion 31 close to the inner side surface of the outer can 15.

[0036] 5 , the extension portion 32 has a flat portion 33, a curved portion 34A that is curved so as to be convex mainly in the upward direction, a curved portion 34B that is curved so as to be convex mainly in the downward direction, and a bottom contact portion 35 that comes into contact with the inside bottom surface of the outer can 15. In detail, the flat portion 33 is provided in the center of the extension portion 32 in the width direction, the curved portion 34A is formed from the flat portion 33 toward both ends in the width direction, the curved portion 34B is formed from the curved portion 34A toward both ends in the width direction, and the bottom contact portion 35 is formed from the curved portion 34B toward both ends in the width direction.

[0037] In this embodiment, the uncoated portion 12A of the negative electrode 12, where no negative electrode mixture layer is formed, is joined to the flat portion 33 of the extending portion 32 by laser welding or the like. As a result, the outer can 15 functions as the negative electrode. The uncoated portion 12A of the negative electrode 12 may be joined to a part of the flat portion 33 of the extending portion 32, or may be joined to the entire surface of the flat portion 33. Furthermore, the uncoated portion 12A may be joined to a location other than the flat portion 33, or may be joined to the curved portions 34A, 34B, etc. The joining location between the uncoated portion 12A of the negative electrode 12 and the current collector plate 30 is selected as appropriate depending on the design purpose, etc.

[0038] The extension 32 may have a tip 36 that is distant from the base 31 and has a generally arrow-shaped configuration in plan view. The tip 36 may have a shape in which one vertex of the arrow shape is chamfered, as shown in Figures 3 and 4, for example. The tip 36 prevents the current collecting plate 30 from being ejected to the outside of the exterior can 15 in a low-pressure state when abnormal heat is generated in the exterior can 15, and keeps the current collecting plate 30 in the exterior can 15 until the pressure inside the exterior can 15 reaches a predetermined pressure.

[0039] 3 and 4 , the extension 32 includes an easily deformable portion 50. The easily deformable portion 50 is configured to be more easily deformed in the thickness direction of the current collector plate 30 than portions of the current collector plate 30 other than the easily deformable portion 50. In particular, the easily deformable portion 50 is configured to bend more easily in the thickness direction of the current collector plate 30.

[0040] The easily deformable portions 50 are preferably provided radially inward of the grooves 41 of the outer can 15. In other words, the easily deformable portions 50 are preferably provided closer to the center point O than the grooves 41. As a result, when the grooves 41 are broken and the valve portion 40 is opened due to internal pressure in the outer can 15 during abnormal heat generation, the easily deformable portions 50 bend, making it easier to discharge the current collecting plate 30 to the outside of the outer can 15. As a result, gas exhaust can be promoted. Note that it is not necessary for all the easily deformable portions 50 to be provided radially inward of the grooves 41 of the outer can 15; some easily deformable portions 50 are provided radially inward of the grooves 41, and some easily deformable portions 50 are provided radially outward of the grooves 41.

[0041] The number of easily deformable portions 50 to be provided is not particularly limited, but it is preferable that the easily deformable portions 50 be provided at one to five locations per extending portion 32, and it is more preferable that the easily deformable portions 50 be provided at two locations per extending portion 32. Furthermore, the easily deformable portions 50 may be formed at equal intervals between the tip end 36 and the base 31 of the extending portion 32. It is preferable that the number of easily deformable portions 50 provided be the same for each of the multiple extending portions 32.

[0042] The easily deformable portion 50 may have cutout portions 51 provided at both widthwise ends of the extension portion 32 so as to face each other. In this case, the easily deformable portion 50 refers to the cutout portions 51 facing each other at both widthwise ends and the region of the extension portion 32 sandwiched between the two cutout portions 51. In other words, it refers to the region spanning the entire width of the extension portion 32, including the cutout portions 51. As shown in FIG. 4 , the cutout portions 51 may have a shape in a plan view that is a substantially front-rear circular shape that combines a circle and a square. Note that the shape of the cutout portions 51 in a plan view is not particularly limited. Examples of the shape of the cutout portions 51 include a semicircular shape such as a perfect circle or an ellipse, a polygonal shape such as a triangle, and combinations thereof.

[0043] 6, the notch 51 may be formed in an area other than the flat portion 33 of the extension 32. This makes it possible to ensure a sufficient welding area between the flat portion 33 and the uncoated portion 12A of the negative electrode 12.

[0044] The cutout portion 51 preferably has a dimension in the width direction of the extending portion 32 that is 10% to 40% of the width length of the extending portion 32, and more preferably has a dimension in the range of 15% to 35%. The cutout portion 51 particularly preferably has a dimension in the range of 20% to 30% of the width length of the extending portion 32. The cutout portion 51 has a dimension that is, for example, 25% of the width length of the extending portion 32.

[0045] The cutout 51 preferably has a dimension in the length direction of the extension 32 that is 3% to 15% of the length from the base 31 to the tip 36 of the extension 32, and more preferably has a dimension in the length direction of the extension 32 that is 4% to 10% of the length from the base 31 to the tip 36 of the extension 32. For example, the cutout 51 has a dimension that is 5% of the length from the base 31 to the tip 36 of the extension 32.

[0046] The easily deformable portion 50 may have thin-walled portions 52 provided opposite each other at both widthwise ends of the extension portion 32. In this case, the easily deformable portion 50 refers to the cutout portions 51 that are opposite each other at both widthwise ends and the region of the extension portion 32 sandwiched between the two cutout portions 51. In other words, it refers to the region across the entire width of the extension portion 32, including the cutout portions 51.

[0047] As shown in FIG. 7 , the thin-walled portion 52 is a region of the extension portion 32 that is thinner than the remaining portions of the extension portion 32. The planar shape of the thin-walled portion 52, the widthwise dimension of the extension portion 32, and the lengthwise dimension of the extension portion 32 are similar to those of the cutout portion 51, and therefore description thereof will be omitted. The thickness of the thin-walled portion 52 is preferably 10% to 70% of the thickness of the extension portion 32, and more preferably 15% to 60%. The thickness of the thin-walled portion 52 is, for example, 30% of the thickness of the extension portion 32. The thin-walled portion 52 may be formed across the entire width of the extension portion 32. In this case, it is preferable that cutout portions 51 be formed at both widthwise ends of the extension portion 32. That is, in this case, the easily deformable portion 50 is preferably formed from both the cutout portion 51 and the thin-walled portion 52.

[0048] The extension portion 32 may have both the cutout portion 51 and the thin-walled portion 52 as the easily deformable portion 50. For example, the extension portion 32 may employ the cutout portion 51 on a radially inner side of the outer can 15 relative to the groove portion 41, and employ the thin-walled portion 52 on a radially outer side of the outer can 15 relative to the groove portion 41. As a result, the cutout portion 51 is more likely to break, making it easier to eject the current collecting plate 30 to the outside of the outer can 15. By adjusting the arrangement of the cutout portion 51 and the thin-walled portion 52, the easily deformable portion 50 can control the deformation of the current collecting plate 30 in response to the internal pressure of the outer can 15.

[0049] The dimensions of the cutout portions 51 and the thin-walled portions 52 may be the same for all of the multiple extending portions 32 or may be different for each. Furthermore, within one extending portion 32, the dimensions of the cutout portions 51 and the thin-walled portions 52 may be the same for all of the extending portions 32 or may be different for each. For example, the dimensions of the cutout portions 51 radially inward from the groove portions 41 may be different from the dimensions of the cutout portions 51 radially outward from the groove portions 41. The easily deformable portions 50 can control the deformation of the current collecting plate 30 in response to the internal pressure of the outer casing 15 by adjusting the shapes and dimensions of the cutout portions 51 and the thin-walled portions 52.

[0050] As described above, with the secondary battery 10 having the current collector 30 configured as described above, in the event of abnormal heat generation, the current collector 30 can be easily expelled from the exhaust mechanism of the outer can 15, thereby suppressing the current collector 30 from interfering with the exhaust of gas inside the outer can 15.

[0051] The present disclosure will be further described by the following embodiments. Configuration 1: A secondary battery comprising: an electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween; a cylindrical outer can with a bottom that houses the electrode assembly; a sealing body that closes an opening of the outer can; and a current collector plate electrically connected to the outer can, the secondary battery having an exhaust mechanism at least at the bottom of the outer can, wherein the negative electrode is connected to the bottom of the outer can via the current collector plate, the current collector plate has a base that is joined to the bottom of the outer can inside, a plurality of extension portions that extend radially in a radial direction of the outer can, and the extension portions are provided with easily deformable portions that are more easily deformed in the thickness direction of the current collector plate than portions of the current collector plate other than the easily deformable portions. Configuration 2: The secondary battery according to Configuration 1, wherein the bottom of the outer can has a valve portion and a groove portion that continuously or discontinuously surrounds the periphery of the valve portion, and the easily deformable portion is provided so as to be located radially inward of the groove portion.Configuration 3: The secondary battery according to Configuration 1 or 2, wherein the easily deformable portion has notches provided opposite both widthwise ends of the extension portion.Configuration 4: The secondary battery according to Configuration 3, wherein the notches have a dimension in the width direction of the extension portion that is 10% to 40% of the widthwise length of the extension portion.Configuration 5: The secondary battery according to Configuration 3, wherein the notches have a dimension in the lengthwise direction of the extension portion that is 3% to 15% of the length from the base to the tip of the extension portion.Configuration 6: The secondary battery according to any one of Configurations 1 to 5, wherein the easily deformable portion has thin-walled portions provided opposite both widthwise ends of the extension portion. Configuration 7: The secondary battery according to any one of configurations 1 to 6, wherein the easily deformable portions are formed at equal intervals between the tip end of the extension and the base.

[0052] REFERENCE SIGNS LIST 10 secondary battery 11 positive electrode 12 negative electrode 13 separator 14 electrode body 15 outer can 16 sealing body 17 insulating plate 20 positive electrode current collecting tab 21 grooved portion 22 internal terminal plate 23 lower valve body 24 insulating member 25 upper valve body 26 cap 27 gasket 30 current collecting plate 31 base portion 32 extension portion 33 flat portion 34A, 34B curved portion 35 bottom contact portion 40 valve portion 41 groove portion 50 easily deformable portion 51 notched portion 52 thin portion

Claims

1. A secondary battery comprising: an electrode assembly having a positive electrode, a negative electrode, and a separator, the electrode assembly being formed by winding the positive electrode and the negative electrode with the separator interposed therebetween; a cylindrical outer can with a bottom that houses the electrode assembly; a sealing body that closes the opening of the outer can; and a current collector plate electrically connected to the outer can, the secondary battery having an exhaust mechanism at least at the bottom of the outer can, wherein the negative electrode is connected to the bottom of the outer can via the current collector plate, the current collector plate has a plurality of extension portions that extend radially in the radial direction of the outer can from a base portion joined to the bottom of the inner side of the outer can, and the extension portions are provided with easily deformable portions that are more easily deformed in the thickness direction of the current collector plate than portions of the current collector plate other than the easily deformable portions.

2. A secondary battery as described in claim 1, wherein the bottom of the outer can has a valve portion and a groove portion that continuously or discontinuously surrounds the periphery of the valve portion, and the easily deformable portion is provided so as to be located radially inward of the groove portion of the outer can.

3. The secondary battery according to claim 1, wherein the easily deformable portion has notches provided at both widthwise ends of the extension portion so as to face each other.

4. The secondary battery according to claim 3, wherein the notch has a dimension in the width direction of the extension that is 10% to 40% of the width direction length of the extension.

5. The secondary battery according to claim 3, wherein the notch has a dimension in the longitudinal direction of the extension that is 3% to 15% of the length of the extension from the base to the tip.

6. The secondary battery according to claim 1, wherein the easily deformable portion has thin-walled portions provided opposite both widthwise ends of the extension portion.

7. The secondary battery according to any one of claims 1 to 6, wherein the easily deformable portions are formed at equal intervals between the tip end of the extension and the base.

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