Power storage device

Abstract

A battery (10) comprises: an electrode body (14) in which a belt-shaped positive electrode (11) and a belt-shaped negative electrode (12) are wound with a belt-shaped separator (13) in between; an outer can (16) that accommodates the electrode body (14) and includes a cylindrical part (30); and a sealing body (17) that closes an opening part of the outer can (16). In the axial direction of the electrode body (14), the negative electrode (12) has a first end and a second end. Power is collected from the negative electrode (12) through the first end side. At the second end, there is formed a second exposed part (shock-absorbing part) (46) where a region on the outer peripheral side of the electrode body (14) protrudes outward in the axial direction more than a region on the inner peripheral side. The second exposed part (46) constitutes a shock-absorbing part.

Description

Power storage device

[0001] The present disclosure relates to an electricity storage device, for example, a battery or a capacitor.

[0002] A conventional energy storage device is a cylindrical battery described in Patent Document 1. This cylindrical battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The outer can has a cylindrical portion and a bottom, and the cylindrical portion includes an annular groove and an annular shoulder. The groove is formed by recessing a portion of the cylindrical portion radially inward. The shoulder extends radially inward at the upper end of the cylindrical portion. The sealing body is fixed to the outer can by being sandwiched between the groove and the shoulder via a gasket.

[0003] The axial end of the electrode body facing the sealing body is constituted by a positive electrode substrate exposed portion, and the axial end of the electrode body facing the bottom plate of the outer casing is constituted by a negative electrode substrate exposed portion. The positive electrode substrate exposed portions are bundled from the outer periphery to the inner periphery and welded to the upper current collector plate, and the upper current collector plate is electrically connected to the sealing body. Furthermore, the negative electrode substrate exposed portions are bundled from the outer periphery to the inner periphery and welded to the lower current collector plate, and the lower current collector plate is welded to the bottom plate of the outer casing. The terminal cap of the sealing body electrically connected to the positive electrode substrate exposed portions via the upper current collector plate constitutes a positive electrode terminal, and the outer casing electrically connected to the negative electrode substrate exposed portions via the lower current collector plate constitutes a negative electrode terminal.

[0004] Japanese Patent Application Laid-Open No. 2018-056091

[0005] In recent years, in the field of power storage devices including the cylindrical batteries, there has been a demand for highly reliable power storage devices that can be used in more severe environments and have improved capacity and output.

[0006] In order to solve the above problems, the energy storage device of the present disclosure comprises an electrode body in which a strip-shaped first electrode and a strip-shaped second electrode are wound with a strip-shaped separator interposed therebetween, an outer can that houses the electrode body and includes a tubular portion, and a sealing body that closes the opening of the outer can, wherein in the axial direction of the electrode body, the first electrode has a first end and a second end, current is collected from the first end side, and at the second end, a buffer portion is formed in which the area on the outer periphery of the electrode body protrudes outward in the axial direction from the area on the inner periphery side.

[0007] According to the power storage device according to the present disclosure, reliability can be improved.

[0008] 1A is a cross-sectional view in the axial direction of a cylindrical battery according to a first embodiment of the energy storage device of the present disclosure; FIG. 2B is a schematic plan view of the negative electrode when unfolded into a long strip; FIG. 3A is a view illustrating an example of a method for joining a groove portion, a second upper current collector plate, and an upper negative electrode substrate exposed portion; FIG. 3B is a view illustrating the structure of the second upper current collector plate, FIG. 3C is a view illustrating the structure of the second upper current collector plate of a first modified example; and FIG. 3C is a cross-sectional view of the cylindrical battery according to the first modified example, corresponding to FIG. 1; FIG. 4A is a schematic plan view of the negative electrode of the second modified example, corresponding to FIG. 2; FIG. 4B is a schematic plan view of the negative electrode of the third modified example, corresponding to FIG. 2; FIG. 4C is a schematic plan view of the negative electrode of the fourth modified example, corresponding to FIG. 2; and FIG. 4D is a schematic plan view of the negative electrode of the fifth modified example, corresponding to FIG. 2. A cross-sectional view of the cylindrical battery according to the second embodiment, corresponding to FIG. 1; and FIG. 4E is a schematic plan view of the positive electrode of the cylindrical battery according to the second embodiment when unfolded into a long strip. A cross-sectional view of the cylindrical battery according to the sixth modified example, corresponding to FIG. 1. 10 is a cross-sectional view of a cylindrical battery according to a third embodiment, corresponding to FIG. 1. FIG. 11 is a cross-sectional view of a cylindrical battery according to a seventh modified example, corresponding to FIG.

[0009] Hereinafter, with reference to the drawings, an embodiment of the power storage device according to the present disclosure will be described in detail. The power storage device according to the present disclosure may be a primary battery or a secondary battery. Alternatively, the power storage device according to the present disclosure may be a capacitor. In all of the following embodiments and modifications, the power storage device is described as a cylindrical secondary battery (lithium ion battery) including a non-aqueous electrolyte and a wound electrode body. However, the power storage device according to the present disclosure may include an aqueous electrolyte and is not limited to a cylindrical secondary battery using a non-aqueous electrolyte.

[0010] It is anticipated from the beginning that new embodiments can be constructed by appropriately combining the features of the following multiple embodiments and modified examples. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, the multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component do not necessarily match between different drawings. In this specification, the sealing body side (protruding terminal side (convex portion side)) in the axial direction (height direction) of a cylindrical battery is referred to as "upper," and the bottom plate side of the outer can in the axial direction is referred to as "lower." In the following description, when an axial direction is mentioned, it refers to the axial direction of the cylindrical battery. The axial direction of a cylindrical battery coincides with the height direction of the electrode assembly, the positive electrode width direction of a long positive electrode, and the negative electrode width direction of a long negative electrode.

[0011] In all of the schematic plan views of the negative electrode when it is expanded, which will be described below, the white area indicates the area where the first core (metal foil of the negative electrode) is exposed, the light gray area indicates the area where the resin is disposed on the first core, and the dark gray area indicates the area where the first mixture layer is disposed on the first core. Also, in the schematic plan views of the positive electrode when it is expanded, the white area indicates the area where the second core (metal foil of the positive electrode) is exposed, the light gray area indicates the area where the resin is disposed on the second core, and the dark gray area indicates the area where the second mixture layer is disposed on the second core.

[0012] Among the components described below, those not recited in the independent claims showing the highest concepts are optional components and are not essential components. Furthermore, the present disclosure is not limited to the following embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of this application and their equivalents.

[0013] First Embodiment Fig. 1 is an axial cross-sectional view of a cylindrical battery 10 according to a first embodiment of the energy storage device of the present disclosure. As shown in Fig. 1, the cylindrical battery (hereinafter simply referred to as battery) 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a bottomed cylindrical outer can 16 that accommodates the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17. The electrode assembly 14 includes a strip-shaped positive electrode 11, a strip-shaped negative electrode 12, and two strip-shaped separators 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. In this embodiment, the negative electrode 12 constitutes a first electrode, and the positive electrode 11 constitutes a second electrode.

[0014] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte may be a liquid electrolyte (electrolytic solution) or a solid electrolyte. The liquid electrolyte (electrolytic solution) includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous 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. The electrolyte salt may include, for example, LiPF ６ Lithium salts such as

[0015] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. 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. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0016] One or more positive electrode leads 20 are joined and electrically connected to the positive electrode 11, and preferably, a plurality of positive electrode leads 20 are joined and electrically connected at intervals from each other in the longitudinal direction of the positive electrode. For example, eight positive electrode leads 20 are joined to the positive electrode 11 in a state where they are spaced apart. The negative electrode 12 is formed to have dimensions slightly larger than the positive electrode 11 to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. In addition, two separators 13 are formed to have dimensions slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11.

[0017] The positive electrode 11 has a long second core (positive electrode core) and second mixture layers (positive electrode mixture layers) formed on both sides of the second core. The second core can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The second mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the second core, drying the coating, and then compressing it to form second mixture layers on both sides of the second core.

[0018] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0019] Examples of the conductive agent contained in the second mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the second mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO).

[0020] The positive electrode 11 has third exposed portions spaced apart in the longitudinal direction and the same number as the positive electrode leads 20. The positive electrode leads 20 are joined to the third exposed portions. By joining the multiple positive electrode leads 20 at intervals in the longitudinal direction of the second core, preferably at approximately equal intervals in the longitudinal direction, the current path in the longitudinal direction of the positive electrode 11 can be shortened, and the electrical resistance (internal resistance) of the battery 10 can be reduced. The positive electrode leads 20 are preferably covered with insulating tape (not shown), which preferably suppresses short circuits between the positive electrode 11 and the negative electrode 12. The insulating tape preferably covers all of the third exposed portions.

[0021] FIG. 2 is a schematic plan view of the negative electrode 12 when unfolded. As shown in FIG. 2, the negative electrode 12 has a strip-shaped first core (negative electrode core) 40 and a first mixture layer (negative electrode mixture layer) 42 formed on both sides of the first core 40. The negative electrode 12 has a strip-shaped first exposed portion 41 at a first end in the width direction (axial direction) of the first core 40. The first exposed portion 41 is provided from the inner peripheral end to the outer peripheral end in the winding direction. The lower axial end of the electrode body 14 is constituted by the first exposed portion 41.

[0022] The first mixture layer 42 is strip-shaped (rectangular). A second axial end on the outer circumferential side of the negative electrode 12 is formed by a strip-shaped second exposed portion (negative electrode core exposed portion) 46 where the first mixture layer 42 is not provided. The second exposed portion 46 protrudes upward in the axial direction beyond the separator 13. A buffer portion is formed in this second exposed portion 46. A strip-shaped resin layer 47 is formed on the second exposed portion 46 on the first end side.

[0023] In the present embodiment, the strip-shaped resin layer 47 is provided on both sides of the second exposed portion 46. In the axial direction, the resin layer 47 is located between the second exposed portion 46 and the first mixture layer 42. The resin layer 47 and the second exposed portion 46 protrude upward from the first mixture layer 42. The resin layer 47 is made of a resin material having spring properties (elasticity), such as polyvinylidene fluoride (PVdF).

[0024] At the outer peripheral end of the negative electrode 12 in the winding direction, a peripheral edge exposed portion 48 is provided at a location adjacent to the first mixture layer 42 in the longitudinal direction of the negative electrode 12. The resin layer 47 and the second exposed portion 46 are also present above the peripheral edge exposed portion 48, and the first exposed portion 41 is also present below the peripheral edge exposed portion 48. At least a portion of the peripheral edge exposed portion 48 is present on the outermost peripheral surface of the electrode assembly 14 and is in contact with the inner peripheral surface of the outer can 16. This reduces the electrical resistance of the battery 10. The negative electrode 12 may form the inner peripheral edge of the electrode assembly 14. However, typically, the separator 13 extends beyond the inner peripheral edge of the negative electrode 12, and the inner peripheral edge of the separator 13 becomes the inner peripheral edge of the electrode assembly 14.

[0025] The first core 40 can be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film having such a metal disposed on its surface. The first mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the binder to the first core 40, drying the coating, and then compressing it to form the first mixture layer 42 on both sides of the first core 40.

[0026] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Examples of the carbon material include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The first mixture layer 42 may contain, as the negative electrode active material, a silicon (Si) material in addition to the carbon material. The negative electrode active material may also include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0027] The binder contained in the first mixture layer 42 may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, as in the case of the positive electrode 11. Alternatively, styrene-butadiene rubber (SBR) or a modified product thereof may be used. The negative electrode mixture layer may contain, in addition to SBR or the like, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0028] The separator 13 is strip-shaped, and a porous sheet having ion permeability and insulating properties is used as the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Examples of materials used for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0029] As shown in FIG. 1 , the sealing body 17 has a first upper current collecting plate 50 and a terminal cap 27. The first upper current collecting plate 50 is a metal, annular plate member having an insertion hole 50a in its radial center. The terminal cap 27 is a metal, plate-like member located axially above the sealing body 17. The center of the terminal cap 27 is exposed to the outside. The center of the terminal cap 27 has a terminal portion 27b that protrudes outward in the axial direction, and this terminal portion 27b constitutes a positive electrode terminal. The sealing body 17 further has an auxiliary current collecting plate 51. The auxiliary current collecting plate 51 is a metal, annular plate member. The auxiliary current collecting plate 51 has a through-hole 51a that is a cylindrical hole.

[0030] Each positive electrode lead 20 is bent at the second end side of the negative electrode 12 from the positive electrode 11 through the insertion hole 50a of the first upper current collector plate 50 so as to fit along the upper surface of the first upper current collector plate 50. The tip of each positive electrode lead 20 is sandwiched between the upper surface of the first upper current collector plate 50 and the lower surface of the auxiliary current collector plate 51. Each positive electrode lead 20 is joined to the upper surface of the first upper current collector plate 50. The first upper current collector plate 50 and the auxiliary current collector plate 51 are also joined, and each positive electrode lead 20 and the auxiliary current collector plate 51 are also joined.

[0031] These joining steps can be achieved, for example, by sandwiching the tip end of each positive electrode lead 20 between the first upper current collector 50 and the auxiliary current collector 51 and irradiating the auxiliary current collector 51 with a laser beam from above to perform laser welding. By laser welding the tip end of the positive electrode lead 20 between the first upper current collector 50 and the auxiliary current collector 51, the positive electrode lead 20 can be reliably and easily joined to the first upper current collector 50. The electricity storage device of the present disclosure does not need to use an auxiliary current collector. Furthermore, the positive electrode lead 20 may be directly joined to the terminal cap 27 without using the first upper current collector 50. When the first upper current collector 50 is not used, only the terminal cap 27 may be interposed between the shoulder 38 and the groove 35 of the sealing body 17. Furthermore, when the first upper current collecting plate 50 is used, the only part of the sealing body 17 that is interposed between the shoulder portion 38 and the groove portion 35 may be the first upper current collecting plate 50, and the outer peripheral edge portion of the terminal cap 27 does not have to be positioned between the shoulder portion 38 and the groove portion 35.

[0032] The first upper current collecting plate 50 has an annular outer peripheral portion 60 located radially outward and extending radially, an annular step portion 62 extending downward from the radially inner end of the outer peripheral portion 60, and an annular inner peripheral portion 63 extending radially inward from the lower end of the annular step portion 62. The lower surface of the terminal cap 27, the inner peripheral surface of the annular step portion 62, and the upper surface of the annular inner peripheral portion 63 define an annular space that opens radially inward. At least a portion of the auxiliary current collecting plate 51 is accommodated in this annular space. The positive electrode lead 20 is joined to the upper surface of the inner peripheral portion 63. By extending the positive electrode lead 20 axially inward from the buffer portion, current can be efficiently collected from the positive electrode 11.

[0033] The battery 10 includes a lower current collector plate 18 made of a metal such as copper, iron, nickel, or a nickel alloy, located axially below the electrode assembly 14. In this embodiment, the lower current collector plate 18 includes a base 18a and a protruding portion 18b, with the protruding portion 18b protruding downward from the base 18a at its radial center. While the upper surface of the base 18a is pressed against a first exposed portion 41 that constitutes the axial lower end of the electrode assembly 14, a laser beam is irradiated from below onto the lower surface of the base 18a. This laser welding joins the first exposed portion 41 to the upper surface of the base 18a. Furthermore, after the bottom plate portion 18c of the protruding portion 18b is placed on the upper surface of the bottom plate portion 68 of the outer can 16, a laser beam is irradiated onto the bottom plate portion 68 from below. This laser welding joins the lower current collector plate 18 to the bottom plate portion 68 and electrically connects it to the outer can 16. This forms a first current collection path between the first end of the negative electrode 12 and the outer can 16. By joining the first exposed portion 41 to the lower current collector plate 18 over a wide area in the longitudinal direction of the negative electrode 12, the current collection path in the longitudinal direction of the negative electrode 12 is shortened, thereby reducing the electrical resistance of the battery 10. The lower current collector plate 18 may not be provided. The first exposed portion 41 may be joined directly to the bottom plate portion 68.

[0034] The outer can 16 has a cylindrical portion 30 and a bottom plate portion 68. The cylindrical portion 30 includes a shoulder portion 38 and a groove portion 35. The groove portion 35 can be formed, for example, by spinning a portion of the outer peripheral surface of the cylindrical portion 30 of the outer can 16 radially inward to form an annular recess radially inward, and then protruding the corresponding inner peripheral surface of the cylindrical portion 30 radially. The sealing body 17 closes the opening of the outer can 16 via a gasket 28. More specifically, the sealing body 17 is placed on the groove portion 35 and is fixed to the opening of the outer can 16 by crimping via the resin gasket 28. The shoulder portion 38 is formed when the upper end of the cylindrical portion 30 is bent radially inward and crimped to the flange portion 61 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 30.

[0035] The space between the outer can 16 and the sealing body 17 is sealed with an annular gasket 28, thereby sealing the internal space of the battery 10. The gasket 28 is made of, for example, polyolefin. The gasket 28 is sandwiched between the outer can 16 and the sealing body 17, and insulates the sealing body 17 from the outer can 16. The gasket 28 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer can 16 and the sealing body 17.

[0036] The battery 10 has a thin-walled portion 69 on the bottom plate portion 68 of the outer can 16. The thin-walled portion 69 can be formed by providing a circular, C-shaped, or other marking on the bottom plate portion 68. By providing the thin-walled portion 69 on the bottom plate portion 68, the bottom plate portion 68 can be smoothly broken starting from the thin-walled portion 69 when the battery 10 generates abnormal heat. Therefore, when the battery 10 generates abnormal heat, high-temperature gas and molten material inside the battery can be smoothly discharged to the outside, thereby improving the safety of the battery 10.

[0037] The battery 10 further includes an annular metal plate 80 and an annular insulating plate 81 made of an insulating material. The metal plate 80 extends in a substantially radial direction. The metal plate 80 is joined to the upper surface of the shoulder portion 38. The metal plate 80, whose first exposed portion 41 is electrically connected to the lower current collector plate 18 via the outer casing 16, serves as a negative terminal. The metal plate 80 is electrically connected to a current collector plate (not shown) that connects multiple batteries 10 together in series or parallel, for example, using a tongue portion (lead) of the current collector plate. This configuration allows multiple batteries 10 to be easily electrically connected to the current collector plate.

[0038] The insulating plate 81 is interposed between the metal plate 80 and the sealing body 17 to insulate the metal plate 80 from the sealing body 17. The outer peripheral edge 81a on the radially outer side of the insulating plate 81 may be located above the protruding portion 28a of the gasket 28 and contact the gasket 28. In this manner, the gasket 28 and the insulating plate 81 reliably insulate the metal plate 80 from the sealing body 17. The insulating plate 81 includes a base 82 and a cylindrical portion 83 that covers the outer peripheral surface of the terminal portion 27b of the terminal cap 27. The cylindrical portion 83 is connected to the radially inner side of the base 82. The battery does not need to have a metal plate and an insulating plate.

[0039] The battery 10 further includes a metal, annular second upper current collector plate 19. The upper surface of the second upper current collector plate 19 is bonded to the lower surface of the groove portion 35, and the second exposed portion 46 is bonded to the lower surface of the second upper current collector plate 19. This bonding can be achieved, for example, by the following method. As shown in FIG. 3( a), a second upper current collector plate 19 with a V-shaped cross section is prepared. With the tip of the second exposed portion 46 pressed against the lower surface of the second upper current collector plate 19, a laser beam is irradiated onto the second upper current collector plate 19 from above. This laser beam irradiation laser-bonds the second exposed portion 46 to the second upper current collector plate 19, thereby integrating the electrode body 14 and the second upper current collector plate 19. This bonding forms a second current collection path between the second end and the outer can 16.

[0040] Next, the electrode body 14 is housed in the outer can 16 so that the second upper current collector plate 19 is located on the upper side. Subsequently, as shown in Fig. 3(b), spinning is performed until the lower surface of the groove 35 is aligned with the upper surface of the second upper current collector plate 19. Thereafter, a laser beam is irradiated onto the lower surface of the groove 35 from outside the outer can 16. This irradiation joins the lower surface of the groove 35 and the upper surface of the second upper current collector plate 19 by laser welding.

[0041] Thereafter, spinning is performed until the upper surface of the groove 35 expands in the approximately radial direction. As the spinning is performed, the inclination angle θ of the second upper current collector 19, which has a V-shaped cross section, decreases. The second upper current collector 19 is then subjected to an axial load by crimping the upper end of the tubular portion 30, and is bent until the inclination angle θ becomes approximately 0°. The groove 35, the second upper current collector 19, and the second exposed portion 46 are joined in this manner. At least a portion of the second exposed portion 46 overlaps the groove 35 in the axial direction. In this embodiment, the entire second exposed portion 46 overlaps the groove 35 in the axial direction. To easily achieve a joining structure among the groove 35, the second upper current collector 19, and the second exposed portion 46 and to prevent contact between the second exposed portion 46 and the positive electrode lead 20, it is preferable that the entire second exposed portion 46 overlaps the groove 35 in the axial direction.

[0042] 4( a) is a plan view of the second upper current collecting plate 19 before processing as seen from above, an axial cross-sectional view of the second upper current collecting plate 19 after welding the second upper current collecting plate, and an axial cross-sectional view of the second upper current collecting plate 19 after the battery is compressed. Also, FIG. 4( b) is a plan view of the second upper current collecting plate 89 of the first modified example before processing as seen from above, an axial cross-sectional view of the second upper current collecting plate 89 of the first modified example after welding the second upper current collecting plate of the first modified example, and an axial cross-sectional view of the second upper current collecting plate 89 of the first modified example after the battery is compressed. Also, FIG. 4( c) is a plan view of the second upper current collecting plate 99 of the second modified example before processing as seen from above, an axial cross-sectional view of the second upper current collecting plate 99 of the second modified example after welding the second upper current collecting plate of the second modified example, and an axial cross-sectional view of the second upper current collecting plate 99 of the second modified example after the battery is compressed.

[0043] As shown in FIG. 4( a), the bent upper plate portion 19a of the second upper current collecting plate 19 preferably has multiple notches 19b spaced apart in the circumferential direction (e.g., equally spaced in the circumferential direction). The leading end of the upper plate portion 19a is displaced radially inward as the upper plate portion 19a bends, increasing internal stress in the upper plate portion 19a. Providing multiple notches 19b in the upper plate portion 19a can alleviate this stress and prevent damage to the upper plate portion 19a, for example, preventing wrinkles from forming in the upper plate portion 19a. The second upper current collecting plate 19 has been described as having a V-shaped cross section before processing. However, as shown in FIG. 4( b), the second upper current collecting plate 89 before processing may have an annular plate shape, and as shown in FIG. 4( c), the second upper current collecting plate 99 before processing may have an S-shaped cross section.

[0044] Next, we will explain the effects and advantages that can be achieved by providing the second exposed portion 46, which is an example of a buffer portion that is an outer peripheral region protruding from the inner peripheral region of the negative electrode 12, as well as other effects and advantages. To improve the productivity of electric vehicles (EVs) and large-scale energy storage systems (ESSs), cylindrical batteries are becoming larger in diameter and size. As a result, the weight of cylindrical batteries and the weight of the electrode body are increasing, which increases the inertial force acting on the electrode body due to vibration and impact, making cylindrical battery components and welds more susceptible to damage.

[0045] In light of this background, the battery 10 of the present disclosure is provided with a buffer portion at the second end of the negative electrode 12. Therefore, the second exposed portion 46, which has springiness (elasticity), can absorb axial vibrations and impacts, thereby suppressing damage to components and welds of the battery 10. This makes the battery 10 less susceptible to damage, and improves the reliability of the battery 10.

[0046] Furthermore, when the battery 10 is a secondary battery as in this embodiment, it has been found that repeated charge and discharge cycles cause the positive electrode 11 and the negative electrode 12 to elongate in the axial direction. In light of this background, even if the positive electrode 11 and the negative electrode 12 elongate in the axial direction due to repeated charge and discharge cycles, the spring-like buffer section can absorb this elongation. Therefore, even if the positive electrode 11 and the negative electrode 12 elongate in the axial direction, buckling in the first mixture layer 42 and the second mixture layer can be effectively suppressed, thereby significantly improving the reliability of the battery 10. Furthermore, by previously bending the buffer section formed at the second end of the negative electrode 12 so that it collapses in the radial direction of the electrode body 14, the cushioning properties of the buffer section can be further improved. Furthermore, the buffer section can function as a buffer section even if it is not composed solely of a core body, as in the case of the second exposed section 46. The buffer section may be configured in the region where the first mixture layer is formed.

[0047] Furthermore, since the second exposed portion 46, which is a buffer portion, has the same potential as the outer can 16, it can be brought into contact with the outer can 16, eliminating the need for an upper insulating plate that is placed above the electrode body in a typical cylindrical battery. This reduces the number of parts in the battery 10 and reduces the manufacturing cost of the cylindrical battery. However, a spacer or the like may be provided to insulate the buffer portion from the positive electrode lead 20.

[0048] The outer can 16 has a groove portion 35 recessed radially inward around the entire circumference, and the second exposed portion 46 (buffer portion) overlaps the groove portion 35 in the axial direction. Therefore, the second exposed portion 46 does not become excessively long, so that the second exposed portion 46 can easily effectively absorb vibrations and shocks and quickly attenuate the vibrations and shocks. Furthermore, because the second exposed portion 46 does not become excessively long, contact between the second exposed portion 46 and the positive electrode lead 20 can also be suppressed.

[0049] Furthermore, at least a portion of the outer peripheral region at the second end of the negative electrode 12 is formed by the peripheral edge exposed portion 48. By bringing the peripheral edge exposed portion 48 into contact with the inner peripheral surface of the outer can 16, the current collection path can be shortened, and the electrical resistance of the battery 10 can be reduced.

[0050] The negative electrode 12 also has a resin layer 47 disposed on the second exposed portion 46. Therefore, the resin layer 47, which has a high spring property (elasticity), is present on the first mixture layer 42 side of the second exposed portion 46 as a buffer portion, and therefore the spring property (elasticity) of the portion of the negative electrode 12 located above the first mixture layer 42 can be increased. Therefore, vibrations and shocks can be more effectively absorbed by the second exposed portion 46 and the resin layer 47, and the reliability of the battery 10 can be further improved.

[0051] In recent years, electric vehicles (EVs) have become increasingly popular, but their adoption is still insufficient. One of the challenges in the widespread adoption of EVs is the longer charging time compared to the time it takes to refuel with gasoline. Therefore, to improve user convenience and avoid occupying charging stations for long periods of time, there is a demand for batteries that can be quickly charged.

[0052] In light of this background, the battery 10 of the present disclosure includes a second upper current collecting plate 19 located axially above the second exposed portion 46, which is a buffer portion, and the second exposed portion 46 is joined to the second upper current collecting plate 19, which is also joined to the lower side of the groove portion 35. Therefore, on the lower side of the electrode body 14, the first exposed portion 41 can be electrically connected to the bottom plate portion 68 of the outer can 16 via the lower current collecting plate 18 (first current collecting path), and on the upper side of the electrode body 14, the second exposed portion 46 can be electrically connected to the groove portion 35 of the outer can 16 via the second upper current collecting plate 19 (second current collecting path).

[0053] That is, with respect to the negative electrode 12, the first and second current collection paths are two systems, and the negative electrode 12 can be electrically connected to two locations, top and bottom, of the outer can 16, so that the current collection path on the negative electrode 12 side can be significantly shortened, and accordingly, the electrical resistance of the battery 10 can be significantly reduced. Therefore, the Joule heat generated in the battery 10 during charging can be significantly reduced, and the temperature rise of the battery 10 during charging can be significantly suppressed, making it easier to achieve rapid charging.

[0054] Radially adjacent portions of the second exposed portion 46 constituting the second end may include dispersed portions that are directly joined or in contact with each other, or may include dispersed portions that are indirectly joined or in contact with each other via the conductive second upper current collecting plate 19. For example, in this embodiment, radially adjacent portions of the second exposed portion 46 are electrically connected via the second upper current collecting plate 19, thereby suppressing bias in the current collection path on the negative electrode side. This further reduces the electrical resistance of the battery 10, making it easier to achieve rapid charging. The second upper current collecting plate 19 constitutes a connecting member, and radially adjacent portions of the second exposed portion 46 constitute dispersed portions.

[0055] (Variation of First Embodiment) In the battery 10 of the first embodiment, the second upper current collector plate 19 was disposed between the second exposed portion 46 located above the first mixture layer 42 and the groove 35. However, as shown in FIG. 5 , i.e., a cross-sectional view corresponding to FIG. 1 of a cylindrical battery 110 of the first variation (hereinafter simply referred to as battery), the second upper current collector plate does not have to be disposed between the second exposed portion (negative electrode core exposed portion) 146 located above the negative electrode mixture layer and the groove 35. The second exposed portion 146 may face the lower surface of the groove 35 in the axial direction while either contacting or not contacting the lower surface. It is preferable that the length of the second exposed portion 146 of the negative electrode 112 be longer than the second exposed portion 46 of the negative electrode 12 so as to prevent an axial gap from occurring between the groove 35 and the electrode body 114. Even if the second exposed portion 146 faces the axial direction without contacting the underside of the groove portion 35, when the battery 110 is subjected to axial vibration or impact, the second exposed portion 146, which has spring properties (elasticity), can be brought into contact with the groove portion 35, thereby allowing the second exposed portion 146 to absorb the vibration or impact, thereby suppressing damage to the battery 110.

[0056] Alternatively, the second exposed portion 146 may be joined to the lower surface of the groove portion 35. When the second exposed portion 146 is welded to the groove portion 35, not only can the second exposed portion 146 absorb vibrations and shocks, but also the negative electrode 112 can be electrically connected to two locations, upper and lower, of the outer can 16 in two systems, so that the electrical resistance of the battery 110 can be significantly reduced and rapid charging can be easily achieved.

[0057] Furthermore, regardless of whether the second exposed portion 146 is electrically connected to the groove portion 35, radially adjacent portions of the second exposed portion 146 may be joined using laser welding, resistance welding, or the like before the electrode body 114 is housed in the outer can 16. When radially adjacent portions of the second exposed portion 146 are joined, the strength of the second exposed portion 146 can be increased, thereby increasing the springiness (elasticity) of the second exposed portion 146 and improving the vibration and shock absorption performance of the second exposed portion 146. Furthermore, when radially adjacent portions of the second exposed portion 146 are joined, the electrical resistance of the battery 110 can be reduced, making it easier to achieve rapid charging.

[0058] Also, the case where the resin layer 47 is provided between the second exposed portion 46 and the first mixture layer 42 in the axial direction (negative electrode width direction) has been described. However, as shown in FIG. 6 , that is, a schematic plan view of the negative electrode 212 of the second modified example corresponding to FIG. 2 , the negative electrode 212 does not need to have a resin layer. The second exposed portion 246 may protrude upward from the first mixture layer 42 and the peripheral end exposed portion 48 provided at the outer end of the winding. Furthermore, the negative electrode 212 may have a peripheral end exposed portion 245 at the inner peripheral end.

[0059] As shown in Figure 7, that is, a schematic plan view corresponding to Figure 2 of the negative electrode 312 of the third modified example, the negative electrode 312 may not have a peripheral end exposed portion adjacent to the first mixture layer 42 in the negative electrode longitudinal direction on the outer periphery in the longitudinal direction, and may not have a negative electrode core exposed portion adjacent to the first mixture layer 42 in the negative electrode longitudinal direction on the inner periphery.

[0060] 8 , that is, as shown in a schematic plan view of a negative electrode 412 of a fourth modified example corresponding to FIG. 2 , the outer peripheral region at the upper end (second end) in the axial direction of the negative electrode 412 may be formed by a second exposed portion 446. The axial length of the second exposed portion 446 may become gradually smaller in a stepped manner toward the inner side of the winding in the longitudinal direction of the negative electrode.

[0061] The positive electrode lead 20 extending in the axial direction is present on the inner peripheral side of the second exposed portion 446. Therefore, if the length of the radially inner portion (inner winding portion) 446a of the second exposed portion 446 is longer than necessary, there is a risk that the inner peripheral portion 446a will come into contact with the positive electrode lead 20. According to this configuration, the axial length of the inner peripheral portion 446a is short, so that contact between the second exposed portion 446 and the positive electrode lead 20 can be reliably prevented.

[0062] As shown in Figure 9, that is, a schematic plan view of a negative electrode 512 of the fifth modification corresponding to Figure 2, the outer periphery of the second end of the negative electrode 512 may be formed by a second exposed portion 546. The axial length of the second exposed portion 546 may continuously decrease from the outer periphery toward the inner periphery. Even in this case, contact between the second exposed portion 546 and the positive electrode lead 20 can be reliably prevented, as in the case where the negative electrode 412 of the fourth modification is used.

[0063] Second Embodiment In the following embodiments including the second embodiment, the same effects and modifications as those of the first embodiment will not be described.

[0064] In the first embodiment, the case has been described in which the positive electrode 11 and the sealing body 17 are electrically connected using one or more positive electrode leads 20. However, as shown in Figure 10, that is, a cross-sectional view of a cylindrical battery (hereinafter simply referred to as battery) 610 of the second embodiment, which corresponds to Figure 1, a positive electrode lead does not have to be used, and a third exposed portion (positive electrode core exposed portion) 636 of the positive electrode 611 may be electrically connected to the sealing body 617.

[0065] Specifically, as shown in FIG. 11 , i.e., a schematic plan view of the expanded positive electrode 611, the positive electrode 611 includes a strip-shaped second core (positive electrode core) 630 and a second mixture layer 632 formed on both sides of the second core 630. The second mixture layer 632 has an elongated (rectangular) shape. The axial end (end on the second end side) on the inner circumferential side of the positive electrode 611 in the longitudinal direction is formed by a strip-shaped third exposed portion 636. The third exposed portion 636 is located axially above the separator 13. At least one surface of the positive electrode 11 in the thickness direction of the positive electrode includes a strip-shaped resin layer 637 adjacent to the third exposed portion 636 in the axial direction (positive electrode width direction) and disposed on the second core 630. The resin layer 637 is provided primarily to prevent electrical connection between the positive electrode 611 and the negative electrode 612.

[0066] In the present embodiment, the strip-shaped resin layer 637 is provided on both surfaces of the positive electrode 11 in the thickness direction of the positive electrode. In the axial direction, the resin layer 637 is located between the third exposed portion 636 and the second mixture layer 632. The resin layer 637 and the third exposed portion 636 protrude upward from the second mixture layer 632. The resin layer 637 is made of, for example, polyvinylidene fluoride (PVdF).

[0067] 10 , sealing body 617 is clamped by crimping between shoulder portion 38 and groove portion 35 with gasket 28 interposed therebetween, and is fixed to outer can 16. Sealing body 617 is composed of a metal upper current collecting plate 622 and terminal cap 27. Upper current collecting plate 622 is composed of a flat base portion 622a having a through hole 622b formed therein.

[0068] With the lower surface of the base 622a pressed against the third exposed portion 636 of the electrode body 614, a laser beam is irradiated from above onto the upper surface of the base 622a. By this laser welding, the third exposed portion 636 is joined to the lower surface of the base 622a.

[0069] Terminal cap 27 has base 27a and terminal 27b, which includes a circular cylindrical surface and a flat top surface surrounded by the cylindrical surface. Terminal 27b may have a sloped surface instead of the circular cylindrical surface. Base 27a of terminal cap 27 is electrically connected to upper current collecting plate 622 via conductive lead 643.

[0070] In battery 610, not only the second exposed portion 46 having spring properties but also the third exposed portion 636 having spring properties on the upper side of electrode body 614 can absorb axial vibrations and impacts. This can more effectively prevent damage to the components and welds of battery 610, further improving the reliability of battery 10. Note that, as shown in FIG. 12 , even in battery 710 in which the third exposed portion 638 of the positive electrode is electrically connected to sealing body 617, the second upper current collector plate does not have to be disposed between second exposed portion 146, which is located above the first mixture layer on the upper side of negative electrode 112, and groove portion 35.

[0071] Third Embodiment In the first and second embodiments, the case has been described in which the second exposed portion 46 that protrudes upward in the negative electrode 12 faces the groove portion 35 in the axial direction. However, as shown in Figure 13 , that is, the cross-sectional view of a cylindrical battery (hereinafter simply referred to as battery) 810 of the third embodiment, which corresponds to Figure 1 , the second exposed portion (negative electrode core exposed portion) 846 that protrudes upward in the negative electrode 812 does not have to face the groove portion in the axial direction.

[0072] More specifically, the sealing body 817 of the battery 810 has a terminal cap 827 having an annular recess 860 on its outer peripheral surface, and a disk-shaped upper current collecting plate 861 joined to the underside of the terminal cap 827. The radially inner end of an annular flat plate portion 862 constituting the upper end of the outer can 816 is fitted and fixed to an annular recess 880 provided on the outer peripheral surface of an annular upper gasket 828 that is fitted and fixed to the annular recess 860.

[0073] The outer can 816 has an S-shaped cross-section portion on its lower side and a U-shaped cross-section portion at its lower end that opens radially inward. A lower gasket 868, also having a U-shaped cross-section, is fixed within the U-shaped cross-section portion. The outer edge of a disk-shaped bottom plate 888 is fitted and fixed within a recess in the lower gasket 868. The electrode body 814 has a structure similar to that of the electrode body 614 shown in FIG. 10. A first exposed portion 841 constituting the lower end of the electrode body 814 is joined to the upper surface of a disk-shaped lower current collecting plate 898. The lower current collecting plate 898 is connected to the bottom plate 888 via a conductive lead 833.

[0074] On the upper and outer periphery of the electrode body 814, a second exposed portion 846 protruding upward is joined to the lower surface of a circular second upper current collector plate 819 joined to the lower surface of the flat plate portion 862. On the upper and radially inward side of the electrode body 814, a third exposed portion (positive electrode substrate exposed portion) 838 protruding upward is joined to the lower surface of an upper current collector plate 861 joined to the lower surface of the sealing body 817. In a battery 810 having this structure, the second exposed portion 846 and the third exposed portion 838 can also absorb vibrations and shocks. In addition, in a battery 810 having this structure, the negative electrode 812 can be electrically connected to upper and lower locations of the outer can 816 in two systems, upper and lower, and therefore electrical resistance can also be significantly reduced.

[0075] 14 , in a battery with this structure, the second upper current collecting plate 819 may be omitted, and the second exposed portion (negative electrode core exposed portion) 946 that protrudes upward on the upper and radially outer side of the electrode body 814 may be opposed in the axial direction in a state of contact or non-contact with the lower surface of the flat portion 862. Alternatively, the second upper current collecting plate 819 may be omitted, and the second exposed portion 946 that protrudes upward on the upper and radially outer side of the electrode body 914 may be joined to the lower surface of the flat portion 862.

[0076] (Other Modifications) An energy storage device according to an embodiment of the present disclosure includes an electrode assembly in which a strip-shaped first electrode and a long, strip-shaped second electrode are wound with an insulating portion interposed therebetween, an outer can that houses the electrode assembly and includes a tubular portion, and a sealing body that closes an opening of the outer can. In addition, a first side end portion in the height direction of the electrode assembly on the outer side of the winding in the longitudinal direction of the first electrode is formed by a first electrode core, and the first side end portion is located on a first side in the height direction of the electrode assembly relative to the insulating portion.

[0077] In the present invention, the case where the first electrode is a negative electrode and the first axial end is the upper axial end (the end on the protruding terminal side (the end on the convex portion side)) has been described. However, the first electrode may be a negative electrode and the first axial end may be the lower axial end (the end on the opposite side from the protruding terminal side). Alternatively, the third exposed portion protruding in the axial direction can absorb axial vibrations and impacts in the same way as the second exposed portion protruding in the axial direction as a buffer portion. Therefore, the first electrode may be a positive electrode and the first axial end may be the upper axial end (the end on the protruding terminal side). Alternatively, the first electrode may be a positive electrode and the first axial end may be the lower axial end (the end on the opposite side from the protruding terminal side). In the positive electrode or negative electrode, the mixture layer molded into a sheet shape and the electrode core (electrode foil) may be bonded via a conductive adhesive layer.

[0078] The power storage device of the present disclosure may have the following configurations. Configuration 1: A power storage device including an electrode assembly in which a strip-shaped first electrode and a strip-shaped second electrode are wound with a strip-shaped separator interposed therebetween, an outer can housing the electrode assembly and including a cylindrical portion, and a sealing body closing an opening of the outer can, wherein the first electrode has a first end and a second end in the axial direction of the electrode assembly, current is collected from the first end, and a buffer portion is formed at the second end, where a region on the outer periphery of the electrode assembly is protruding outward in the axial direction from a region on the inner periphery of the electrode assembly. Configuration 2: The power storage device according to Configuration 1, wherein an outer periphery of the cylindrical portion of the outer can has a groove portion recessed such that an inner periphery of the cylindrical portion protrudes inward, and the buffer portion overlaps with the groove portion in the axial direction. Configuration 3: The power storage device according to Configuration 1 or 2, wherein the first electrode has a strip-shaped core and a first mixture layer formed on the core. Configuration 4: The electricity storage device according to Configuration 3, wherein the first mixture layer is not formed at a first end of the core body, and a first exposed portion is formed, exposing the core body.Configuration 5: The electricity storage device according to Configuration 3, wherein the first mixture layer is not formed at a second end of the core body, and a second exposed portion is formed, exposing the core body, and the buffer portion is formed at the second exposed portion.Configuration 6: The electricity storage device according to any one of Configurations 1 to 5, wherein the buffer portion is bent in the radial direction.Configuration 7: The electricity storage device according to Configuration 5, wherein a resin layer is formed on the second exposed portion.Configuration 8: The electricity storage device according to any one of Configurations 1 to 7, wherein parts of the second ends adjacent in the radial direction include dispersed portions that are directly joined or in contact with each other, or include dispersed portions that are indirectly joined or in contact with each other via a conductive connecting member.Configuration 9: The electricity storage device according to any one of Configurations 1 to 8, comprising a current collector plate that is electrically connected to the second end. The present invention relates to an electric storage device and an electric storage apparatus, and more particularly ...

[0079] 10,110,610,710,810,910 Battery, 11,611 Positive electrode (second electrode), 12,112,212,312,412,512,612,812 Negative electrode (first electrode), 13 Separator, 14,114,614,814,914 Electrode body, 16,816 Outer can, 17,617,817 Sealing body, 18 Lower current collector plate (current collector plate), 18a Base, 18b Protruding portion, 18c Bottom plate portion, 19,89,99,819 Second upper current collector plate, 19a Upper plate portion, 19b Notch, 20 Positive electrode lead, 27,827 Terminal cap, 27a Annular portion, 27b Terminal portion, 28 Gasket, 28a Protruding portion, 30 Cylindrical portion, 35 Groove portion, 38 Shoulder portion, 40 First core body, 41, 841 First exposed portion, 42 First mixture layer, 46, 146, 246, 446, 546, 846, 946 Second exposed portion (buffer portion), 47, 637 Resin layer, 48, 245 Peripheral end exposed portion, 50, 622 Upper current collecting plate, 50a Insertion hole, 51 Auxiliary current collecting plate, 51a Through hole, 60 Outer periphery portion, 61 Base portion, 62 Step portion, 63 Inner periphery portion, 68 Bottom plate portion, 69 Thin portion, 80 Metal plate, 81 Insulating plate, 81a Outer periphery edge portion, 82 Flange portion, 83 cylindrical portion, 446a inner peripheral portion, 622a base portion, 622b through hole, 630 second core body, 632 second mixture layer, 636, 638, 838 third exposed portion, 828 upper gasket, 860 recessed portion, 861 upper current collecting plate, 862 flat portion, 868 lower gasket, 880 recessed portion, 888 bottom plate, 898 lower current collecting plate.

Claims

1. An energy storage device comprising: an electrode body in which a band-shaped first electrode and a band-shaped second electrode are wound with a band-shaped separator interposed between them; an outer can containing the electrode body and including a cylindrical portion; and a sealing body closing an opening of the outer can, wherein the first electrode has a first end and a second end in the axial direction of the electrode body, current is collected from the first end side, and a buffer portion is formed at the second end such that an area on the outer periphery of the electrode body protrudes outward in the axial direction relative to an area on the inner periphery of the electrode body.

2. The energy storage device according to claim 1, wherein an outer peripheral surface of the cylindrical portion of the outer can has a groove portion recessed so that an inner peripheral portion of the cylindrical portion protrudes inward, and the buffer portion overlaps with the groove portion in the axial direction.

3. The power storage device according to claim 1, wherein the first electrode has a strip-shaped core body and a first mixture layer formed on the core body.

4. The electricity storage device according to claim 3, wherein the core body has a first exposed portion at a first end thereof where the first mixture layer is not formed and the core body is exposed.

5. The energy storage device according to claim 3, further comprising a second exposed portion at a second end of the core body where the first mixture layer is not formed and the core body is exposed, and the buffer portion is formed in the second exposed portion.

6. The power storage device according to claim 1, wherein the buffer portion is bent in a radial direction.

7. The energy storage device according to claim 5, wherein a resin layer is formed on the second exposed portion.

8. An energy storage device as described in claim 1 or 2, wherein parts of the second ends adjacent to each other in the radial direction include dispersed portions that are directly joined or in contact with each other, or include dispersed portions that are indirectly joined or in contact with each other via a conductive connecting member.

9. The electricity storage device according to claim 1 or 2, further comprising a current collector plate electrically connected to the second end.

10. The energy storage device according to claim 1 or 2, wherein the length of the second end in the axial direction decreases stepwise or continuously from the outer periphery side to the inner periphery side of the first electrode.

11. The energy storage device according to claim 1, wherein, in the axial direction, current is collected from the second electrode from the side of the second end of the first electrode, and current is collected from the second electrode on the inner circumferential side of the buffer portion.

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