Electricity storage device

Abstract

This electricity storage device is provided with: an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; and a negative electrode collector plate that is disposed at one end in the axial direction of the electrode body and that is joined to the negative electrode, the negative electrode collector plate having: a core material joining section that extends in the radial direction of the electrode body and that is joined to the negative electrode on a surface that faces the negative electrode in the axial direction; and eave portions formed at both end portions in the circumferential direction of the core material joining portion and extending in the axial direction toward the negative electrode.

Description

Technical Field

[0001] The present invention relates to an electric storage device. Background Art

[0002] A cylindrical battery, one of the power storage devices, has a wound electrode body formed by winding a positive electrode plate and a negative electrode plate with a separator interposed therebetween. In addition, a large-diameter cylindrical battery sometimes has a structure in which a negative electrode collector plate is joined to an exposed portion of a negative electrode core material protruding from the wound electrode body (hereinafter referred to as an end face collector structure) (e.g., Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2008-103309 Summary of the invention

[0006] In the above-mentioned end face current collection structure, a long strip of negative electrode collector plate is welded to the exposed portion of the negative electrode core material protruding downward from the wound electrode body along the radial direction of the wound electrode body. In the joining process of the end face current collection structure, the negative electrode collector plate and the exposed portion of the negative electrode core material that is in close contact with the upper surface of the negative electrode collector plate are melted and joined by irradiating a laser or the like from the lower side of the negative electrode collector plate. At this time, spatters caused by welding may be generated on the upper surface side of the negative electrode collector plate. When the spatters fly between the negative electrode collector plate and the electrode body and adhere to the composite material of the wound electrode body, it may cause poor voltage of the cylindrical battery.

[0007] Therefore, an object of the present invention is to provide a power storage device capable of improving reliability.

[0008] The storage device of the present invention comprises: an electrode body, which is formed by winding a first electrode plate and a second electrode plate with a separator therebetween; and a collector plate, which is arranged at one axial end of the electrode body and is joined to the first electrode plate, and is characterized in that the collector plate has: a joining portion, which extends along the radial direction of the electrode body and is joined to the first electrode plate on the surface of the joining portion facing the first electrode plate in the axial direction; and an eaves portion, which is formed at both circumferential end portions of the joining portion and extends axially toward the first electrode plate.

[0009] According to the power storage device of the present invention, voltage failure can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a cross-sectional view showing a power storage device as an example of an embodiment.

[0011] Figure 2 It is a perspective view showing a current collector plate as an example of the embodiment.

[0012] Figure 3is a cross-sectional view perpendicular to the radial direction of the negative electrode collector ( Figure 2 AA section view).

[0013] Figure 4 It is a cross-sectional view perpendicular to the radial direction, showing a negative electrode current collector plate as another example of the embodiment.

[0014] Figure 5 It is a cross-sectional view perpendicular to the radial direction showing the joint between the negative electrode collector plate and the negative electrode core member.

[0015] Figure 6 It is a cross-sectional view perpendicular to the circumferential direction showing the junction between the negative electrode collector plate and the negative electrode core member.

[0016] Figure 7 This is a flow chart showing the flow of the process of joining the negative electrode current collector plate and the negative electrode core member. DETAILED DESCRIPTION

[0017] In the following description, specific shapes, materials, directions, numerical values, etc. are illustrative for easy understanding of the present invention and can be appropriately changed according to the application, purpose, specification, etc.

[0018] <Electricity storage device>

[0019] use Figure 1 A battery 10 as an example of an embodiment will be described. The power storage device of the present invention is not limited to a battery, and may be a capacitor or the like including an electrode body in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween.

[0020] The battery 10 as an example of an electric storage device includes an electrode body 14 formed by winding a strip-shaped positive electrode plate 11 as a strip-shaped first electrode plate and a negative electrode plate 12 as a second electrode plate via a strip-shaped separator 13, and a negative electrode collector plate 20 joined to a negative electrode core material exposed portion 29 (negative electrode plate 12) protruding from the electrode body 14. The battery 10 can improve reliability, which will be described in detail later.

[0021] In addition, the battery 10 includes the electrode body 14, an electrolyte (not shown), an outer can 30 for storing the electrode body 14 and the electrolyte, and a sealing body 35 for sealing the opening of the outer can 30. Hereinafter, each component will be described according to the axial direction P, radial direction D, and circumferential direction R of the battery 10 (electrode body 14). In addition, in the axial direction P, the side where the sealing body 35 described later is provided is sometimes set as the upper side, and the bottom 30B side of the outer can 30 is set as the lower side for description.

[0022] The positive electrode plate 11 has a strip-shaped positive electrode core material and a positive electrode mixture layer formed on at least one surface of the positive electrode core material. For the positive electrode core material, a foil of a metal such as aluminum or aluminum alloy that is stable within the potential range of the positive electrode, a film that arranges the metal on the surface, etc. can be used. The positive electrode mixture layer contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride, and the positive electrode mixture layer is preferably formed on both surfaces of the positive electrode core material. For the positive electrode active material, for example, a lithium transition metal composite oxide is used.

[0023] On the upper side of the electrode body 14, there are provided a positive electrode collector plate 37 constituting the sealing body 35 and an upper insulating plate 34 disposed between the electrode body 14 and the sealing body 35. The positive electrode collector plate 37 is connected to the positive electrode core material of the positive electrode plate 11 through the positive electrode lead 16. The upper insulating plate 34 prevents the positive electrode plate 11 and the positive electrode lead 16 from contacting the outer can 30, and prevents the positive electrode lead 16 from contacting the negative electrode of the electrode body 14.

[0024] The negative electrode plate 12 has a strip-shaped negative electrode core material and a negative electrode mixture layer formed on at least one surface of the negative electrode core material. For the negative electrode core material, foils of metals such as copper, copper alloy, nickel, nickel alloy, etc. that are stable within the potential range of the negative electrode, and films that arrange the metal on the surface layer, etc. can be used. The negative electrode mixture layer contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR), and the negative electrode mixture layer is preferably formed on both surfaces of the negative electrode core material. For the negative electrode active material, for example, graphite, silicon-containing compounds, etc. are used.

[0025] On the lower side of the negative electrode plate 12 (one end in the width direction of the negative electrode plate 12), there is a negative electrode core material exposed portion 29 protruding from the negative electrode core material where no negative electrode mixture layer is provided. The negative electrode core material exposed portion 29 is formed from the end of the winding start side in the length direction (circumferential direction R) of the long strip of negative electrode plate 12 to the end of the winding end side. A negative electrode collector plate 20, which will be described in detail later, is provided on the lower side of the electrode body 14, and the negative electrode core material exposed portion 29 is joined to the negative electrode collector plate 20. Thus, the negative electrode plate 12 and the negative electrode collector plate 20 are electrically connected. In addition, the negative electrode collector plate 20 is joined to the inner surface of the bottom 30B of the outer can 30, and the negative electrode collector plate 20 is electrically connected to the outer can 30. Through this connection, the outer can 30 functions as a negative external terminal.

[0026] The electrolyte is a non-aqueous electrolyte, comprising a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. For the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and mixed solvents of two or more thereof are used. The non-aqueous solvent may contain a halogen substituted substance formed by replacing at least a portion of the hydrogen of these solvents with a halogen atom such as fluorine. As an example of a non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and mixed solvents thereof, etc. can be cited. For the electrolyte salt, for example, a lithium salt such as LiPF6 is used.

[0027] The outer can 30 is a metal container with a bottomed cylindrical shape and an opening on the upper end side, and has a cylindrical barrel 30A formed in a cylindrical shape and a bottom 30B that is circular when viewed from above. The outer can 30 is usually made of a metal with iron as the main component. However, in particular, when the outer can 30 is electrically connected to the positive electrode plate 11, the outer can 30 may also be made of a metal with aluminum or the like as the main component. In the case where the outer can 30 is made of iron as the main component, a plating layer of nickel or the like may also be formed on the surface made of the iron. In addition, the barrel 30A of the outer can 30 has a groove 30C formed along the circumferential direction R of the barrel 30A. The groove 30C is formed near the opening of the outer can 30 and at a position of a predetermined length from the opening edge (the upper end of the outer can 30). The predetermined length is, for example, a length equivalent to 1% to 20% of the length of the axial direction P of the outer can 30.

[0028] In the present embodiment, a safety valve mechanism that operates when an abnormality occurs in the battery 10 is provided at the bottom 30B of the outer can 30. On the other hand, the safety valve mechanism is not provided at the sealing body 35. However, the safety valve mechanism may also be provided at the sealing body 35. A groove-shaped thin-walled portion is formed at the bottom 30B, for example. When the bottom 30B is pushed out of the outer can 30 when an abnormality occurs in the battery 10 and the internal pressure rises, the thin-walled portion is preferentially broken to form a gas discharge port at the bottom 30B.

[0029] The groove portion 30C is a portion of the barrel portion 30A that extends toward the inner side of the outer can 30. For example, the barrel portion 30A is spun from the outside to form the groove portion 30C. In addition, the outer can 30 is reduced in diameter at the position where the groove portion 30C is formed, and a fine line-shaped groove is formed on the outer peripheral surface of the barrel portion 30A. Preferably, the cross section of the groove portion 30C has a substantially U-shaped shape, and is formed in an annular shape over the entire length of the circumferential direction R of the barrel portion 30A. The groove portion 30C is formed by processing the barrel portion 30A after the electrode body 14 is housed in the outer can 30.

[0030] The sealing body 35 has a cover 36, a positive electrode collector plate 37 and a gasket 38, and is formed in a disc shape as a whole. The sealing body 35 is arranged on the groove portion 30C of the outer can 30 and is fixed to the opening of the outer can 30. The upper end of the opening is bent inward and is clamped relative to the sealing body 35 through the gasket 38. In other words, the sealing body 35 is fixed to the upper end of the outer can 30 through the groove portion 30C of the outer can 30 and the clamping portion, and the opening of the outer can 30 is blocked. The clamping portion is formed in an annular shape along the circumferential direction R of the outer can 30, and clamps the sealing body 35 together with the groove portion 30C.

[0031] The cover 36 is a disc-shaped metal member, which is exposed to the outside of the outer can 30 and forms the top surface of the battery 10. The cover 36 has a shape (raised portion) in which the central portion of the radial direction D protrudes to the outside of the battery 10. When a plurality of batteries 10 are modularized to form a battery pack, a wiring material is connected to the cover 36. Therefore, the cover 36 functions as an external terminal of the battery 10. In the present embodiment, the positive electrode lead 16 is electrically connected to the positive electrode collector plate 37, and the cover 36 functions as a positive electrode external terminal.

[0032] The positive electrode collector plate 37 is a metal member having a diameter approximately equal to that of the cover 36, and is disposed at a position closer to the electrode body 14 than the cover 36. The positive electrode collector plate 37 is formed into a ring shape having an opening at the center of the radial direction D. The cover 36 and the positive electrode collector plate 37 are welded together, and the positive electrode collector plate 37 is welded, for example, at a position of the cover 36 where the distance from the center of the radial direction D is greater than the distance from the outer peripheral edge. In addition, the annular collector member may be brought into contact with the back surface (the surface facing the cover 36 side) of the surface of the positive lead 16 that is opposite to the positive electrode collector plate 37, and the positive electrode lead 16 may be clamped and fixed from the top and bottom by the positive electrode collector plate 37 and the collector member.

[0033] The gasket 38 is provided on the outer periphery of the stack of the cover 36 and the positive electrode collector plate 37. The gasket 38 is an annular resin or rubber member for preventing the cover 36 and the positive electrode collector plate 37 from contacting the outer can 30 and ensuring insulation between the outer can 30 and the sealing body 35.

[0034] <Negative electrode collector plate>

[0035] use Figure 2 to Figure 4 The negative electrode current collector plate 20 as an example of the embodiment will be described.

[0036] The negative electrode current collector plate 20 as a current collector is joined to the negative electrode core material exposed portion 29 protruding from the lower side of the axial direction P of the electrode body 14. In addition, the negative electrode current collector plate 20 is joined to the bottom 30B of the outer can 30, so that the outer can 30 functions as a negative electrode external terminal (see Figure 1 ). According to the negative electrode current collector plate 20, reliability can be improved, which will be described in detail later.

[0037] The negative electrode collector plate 20 is made of metal, for example, preferably copper, copper alloy, nickel or nickel alloy, or a material obtained by plating nickel on the surface of an iron material. The negative electrode collector plate 20 is provided on the lower side of the electrode body 14 in the axial direction P, and is housed in the outer can 30 together with the electrode body 14. In other words, the negative electrode collector plate 20 is arranged between the electrode body 14 and the bottom 30B of the outer can 30 (see Figure 1 ).

[0038] like Figure 2As shown, the negative electrode current collector plate 20 has a central portion 21 provided at the center when viewed from the axial direction P and an extension portion 23 extending from the central portion 21 along the radial direction D, which will be described in detail later. The central portion 21 has a tank bottom joint portion 22 surrounded by a circular groove. The tank bottom joint portion 22 is joined to the bottom 30B of the outer tank 30 by welding.

[0039] The extension portions 23 include a plurality of extension portions 23 extending from the central portion 21 along the radial direction D. The plurality of extension portions 23 are arranged at intervals in the circumferential direction R. Figure 3 In the example shown, four extensions 23 are arranged radially every 90 degrees from the central portion 21. In this embodiment, the extensions 23 extend in four directions, but may extend in one, two, three, or five or more directions.

[0040] The extension portion 23 includes a flat plate-shaped core material joint portion 24 extending along the radial direction D, which will be described in detail later, and an overhang portion 25 formed at both ends of the core material joint portion 24 in the circumferential direction R. The negative electrode core material exposed portion 29 is welded to the upper surface of the core material joint portion 24 in the axial direction. In addition, the overhang portion 25 can be provided at both ends of a core material joint portion 24, or can be formed only at one end in the circumferential direction.

[0041] like Figure 3 As shown, the eaves 25 are formed at both ends of the core material joint 24 in the circumferential direction R as described above. Each eaves 25 is formed in a substantially V-shaped or substantially U-shaped manner (see FIG. 1 ) so as to extend in a direction away from the joint and then bend back and extend toward the electrode body 14 when viewed from the radial direction D. Figure 3 ). The outer end of the circumferential direction R of the eaves portion 25 is formed to face the upper side (electrode body side) in the axial direction P. In addition, the outer end of the circumferential direction R of the eaves portion 25 is formed to be located above the core material joint portion 24 in the axial direction P. In other words, at least a portion of the eaves portion 25 is formed to be located above the core material joint portion 24 in the axial direction P, and each outer end of the circumferential direction R of the extension portion 23 is formed to be located at the uppermost part in the axial direction P.

[0042] According to the eaves portion 25, when the negative electrode collector plate 20 and the negative electrode core material exposed portion 29 are welded, it is possible to prevent the spatter from scattering in the circumferential direction R, which will be described in detail later. As a result, it is possible to prevent the spatter from scattering on the upper side of the negative electrode collector plate 20 and adhering to the composite material of the electrode body 14, and the voltage failure of the battery 10 can be reduced. In addition, according to the eaves portion 25, since only the axial end surface of the electrode body 14 is partially covered, when the gas is exhausted in the case of abnormality of the battery 10 and the internal pressure rises, the exhaust area will not be reduced, and the exhaust can be performed stably. In addition, the movement of the electrolyte in the outer tank 30 becomes easy. In addition, according to the eaves portion 25, the strength of the extension portion 23 can be improved.

[0043] Furthermore, in the present embodiment, the outer end of the circumferential direction R of the eaves portion 25 is formed to be located above the core material joint 24 in the axial direction P, but is not limited thereto. The outer end of the circumferential direction R of the eaves portion 25 may also be located at the same position as the core material joint 24 in the axial direction P, and from the viewpoint of suppressing damage to the negative electrode core material, may also be formed to be located below the core material joint 24. In addition, the end of the outer end of the eaves portion 25 on the radial side of the central portion 21 may not be connected to the central portion 21, but may protrude away from the central portion 21. According to this structure, the processing of the eaves portion 25 becomes easy, the adverse effects of sputtering can be easily prevented by using the eaves portion 25 up to the vicinity of the central portion 21, exhaust becomes easy, and the electrolyte becomes easy to move.

[0044] like Figure 4 As shown, the outer edge of the circumferential direction R of the eaves portion 25 may be bent. In this structure, when the outer end of the eaves portion 25 is embedded in the negative electrode core material exposed portion 29 and is closely fitted thereto, the R portion formed by the bending is embedded in the negative electrode core material exposed portion 29, so that the foil breakage of the negative electrode core material exposed portion 29 can be reduced, which will be described in detail later. In addition, in the present embodiment, the outer end of the circumferential direction R of the eaves portion 25 is bent toward the outside of the circumferential direction R, but it is not limited to this. It may also be a structure in which the outer end of the circumferential direction R of the eaves portion 25 is bent toward the inside of the circumferential direction R. In addition, when the outer end is bent toward the outside or inside of the circumferential direction R, it may be folded back away from the electrode body 14 in the axial direction P, or the outer end may extend along the circumferential direction R. In addition, the collector plate used in the power storage device of the present invention is described as a negative electrode collector plate, but the power storage device of the present invention is not limited to this structure. Alternatively, the core material exposed portion may be provided on the positive electrode plate, and the current collector plate of the positive electrode may be the structure of the negative electrode current collector plate. Alternatively, the core material exposed portion may be formed on the positive electrode plate and the negative electrode plate, respectively, and a current collector plate of the same structure as the negative electrode current collector plate may be joined to each core material exposed portion.

[0045] <Joining of the negative electrode current collector plate and the exposed portion of the negative electrode core material>

[0046] use Figure 5 and Figure 6 The joining between the negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 will be described.

[0047] At the lower end of the electrode body 14, as described above, in order to electrically connect the negative electrode plate 12 to the negative electrode collector plate 20, the negative electrode core material exposed portion 29 protruding from the bottom of the electrode body 14 is joined to the core material joint portion 24 of the extension portion 23 of the negative electrode collector plate 20. The negative electrode core material exposed portion 29 and the core material joint portion 24 are joined by welding, which will be described in detail later.

[0048] The negative electrode core material exposed portion 29 is bent inwardly in the radial direction D and joined to the core material joint portion 24. As a result, when the negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 are welded, it is possible to prevent the sputtering from scattering in the radial direction D, which will be described in detail later. As a result, it is possible to prevent the sputtering from scattering on the upper side of the negative electrode current collector plate 20 and adhering to the composite material of the electrode body 14, and it is possible to reduce the voltage failure of the battery 10 caused by the scattering of the sputtering.

[0049] In this embodiment, the negative electrode core exposed portion 29 is bent inward in the radial direction D over the entire circumferential direction R, but the present invention is not limited thereto. Alternatively, only the portion of the negative electrode core exposed portion 29 that is joined to the negative electrode current collector plate 20 in the circumferential direction R may be bent.

[0050] On the other hand, the extension portion 23 of the negative electrode current collector plate 20 is joined to the negative electrode core material exposed portion 29 while being embedded in the negative electrode core material exposed portion 29 bent inwardly in the radial direction D. More specifically, the outer ends of the core material joint portion 24 and the eaves portion 25 are embedded in the negative electrode core material exposed portion 29 in a manner that deforms the negative electrode core material exposed portion 29 bent inwardly in the radial direction D. Thus, the close fit between the negative electrode plate 12 and the negative electrode current collector plate 20 can be improved, and welding defects can be reduced.

[0051] <Step of joining the negative electrode current collector plate to the exposed portion of the negative electrode core material>

[0052] use Figure 7 The bonding step S10 as an example of the embodiment will be described.

[0053] The joining step S10 is a step of joining the negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 by welding. The joining step S10 is one of the steps in the manufacturing process of the battery 10, and the description of other steps in the manufacturing process of the battery 10 is omitted. The joining step S10 includes a bending step S11, a sealing step S12, and a welding step S13, which are described in detail later.

[0054] In the bending step S11, the negative electrode core material exposed portion 29 protruding from the bottom of the electrode body 14 is bent inwardly in the radial direction D. In the present embodiment, the negative electrode core material exposed portion 29 is bent inwardly in the radial direction D over the entire circumferential direction R, but the present invention is not limited thereto. Alternatively, only the portion of the negative electrode core material exposed portion 29 in the circumferential direction R that is joined to the negative electrode current collector plate 20 may be bent.

[0055] In the sealing step S12, the core material joint portion 24 of the extension portion 23 of the negative electrode current collector plate 20 and the outer end portions of the overhang portion 25 are crimped so that the outer end portions of the core material joint portion 24 and the overhang portion 25 are embedded in the negative electrode core material exposed portion 29 in a manner that deforms the negative electrode core material exposed portion 29 bent inwardly in the radial direction D. Thus, the negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 are sealed.

[0056] In the welding step S13, the negative electrode current collector plate 20 that has been in close contact with the negative electrode core material exposed portion 29 is joined to the negative electrode core material exposed portion 29 by welding. More specifically, the core material joint portion 24 of the extension portion 23 of the negative electrode current collector plate 20 is joined to the negative electrode core material exposed portion 29 by laser welding. At this time, the laser is irradiated from the lower side of the axial direction P of the negative electrode current collector plate 20. In addition, the laser is irradiated in order from the outer side to the inner side of the radial direction D of the core material joint portion 24 of the negative electrode current collector plate 20.

[0057] In the welding step S13, although spatter is generated on the upper side of the negative electrode current collector plate 20 joined to the negative electrode core material exposed portion 29, since the negative electrode core material exposed portion 29 is bent, the spatter can be prevented from scattering in the radial direction D. In addition, since the shielding portions 25 are formed at both ends of the core material joint portion 24 of the negative electrode current collector plate 20 in the circumferential direction R, the spatter can be prevented from scattering in the circumferential direction R. Thus, the spatter can be prevented from scattering on the upper side of the negative electrode current collector plate 20 and adhering to the composite material of the electrode body 14, and the voltage failure of the battery 10 can be reduced.

[0058] In this embodiment, the negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 are joined by laser welding, but the present invention is not limited thereto. The negative electrode current collector plate 20 and the negative electrode core material exposed portion 29 may also be joined by electron beam welding, brazing, resistance welding, friction stir welding, ultrasonic welding, or the like.

[0059] In addition, the present invention is not limited to the above-mentioned embodiment and its modified example, and it is needless to say that various changes and improvements can be made within the scope of the matters described in the claims of the present application.

[0060] Description of Reference Numerals

[0061] 10. Battery (electricity storage device); 11. Positive plate; 12. Negative plate; 13. Spacer; 14. Electrode body; 16. Positive lead; 20. Negative collector plate (collector plate); 21. Central portion; 22. Tank bottom joint; 23. Extension portion; 24. Core material joint (joint portion); 25. Eaves portion; 29. ​​Negative core material exposed portion; 30. Outer tank; 30A. Cylinder; 30B. Bottom; 30C. Groove; 34. Upper insulating plate; 35. Sealing body; 36. Cover; 37. Positive collector plate; 37A. Opening; 38. Gasket.

Claims

1. A power storage device comprising: an electrode body formed by winding a first electrode plate and a second electrode plate with a separator interposed therebetween; and a current collector plate disposed at one end of the electrode body in the axial direction and joined to the first electrode plate, wherein: The collector plate has: a joining portion extending in a radial direction of the electrode body, wherein a surface of the joining portion facing the first electrode plate in the axial direction is joined to the first electrode plate; as well as The eaves are formed at both ends of the joint in the circumferential direction and extend toward the first electrode plate in the axial direction.

2. The power storage device according to claim 1, wherein The eaves portion is formed in a V-shape when viewed from the radial direction.

3. The power storage device according to claim 1 or 2, wherein: The outer end portion of the overhang portion in the circumferential direction is located on one side of the joint portion in the axial direction.

4. The power storage device according to any one of claims 1 to 3, wherein: The outer end portion of the overhang portion in the circumferential direction is folded back in a direction away from the first electrode plate.

5. The power storage device according to any one of claims 1 to 4, wherein: In the circumferential direction, a connection portion of the portion of the overhang portion on the joining portion side connected to the joining portion extends in a direction away from the first electrode plate.

6. The power storage device according to any one of claims 1 to 5, wherein: The collector plate is provided with a plurality of the joining portions. The first electrode plate is exposed between adjacent joining portions in the circumferential direction.

7. The power storage device according to any one of claims 1 to 6, wherein: The collector plate has a central portion in the center, In the radial direction, one end of the engagement portion is connected to the central portion, The outer end portion of the overhang portion in the circumferential direction is not connected to the central portion but protrudes away from the central portion.

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