Electricity storage device and method for manufacturing electricity storage device

Abstract

This electricity storage device comprises: an electrode body (14) in which a first electrode plate and a second electrode plate are wound with a separator interposed therebetween; and an exterior body (15) that accommodates the electrode body. The first electrode plate has a first core body and a first mixture layer formed on the surface of a first core body. First exposed portions where the first core body is exposed are disposed at one side end portion of the electrode body in the winding axis direction. Each first exposed portion has a folded portion obtained by folding back one or more times and folding so as to overlap. The folded portions are tilted in a first direction, and the folded portions of the adjacent circumferential portions of the first electrode plate overlap. A current collecting portion is formed at the one side end portion in the winding axis direction.

Description

Electricity storage device and method for manufacturing the same

[0001] The present disclosure relates to an electricity storage device and a method for manufacturing an electricity storage device.

[0002] BACKGROUND ART Conventionally, there has been known an electric storage device such as a cylindrical secondary battery that includes an electrode assembly in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly.

[0003] Patent Document 1 describes a cylindrical battery in which the upper end of an internal current collector on the positive electrode side forms a side end that does not have an active material, the side end is bent inward at the top end, and the bent portion is primarily welded to a disk-shaped current collector. The current collector is secondarily welded to the disk portion of a positive electrode terminal, thereby welding the positive electrode terminal to the internal current collector.

[0004] Japanese Patent Application Publication No. 11-185725

[0005] The configuration described in Patent Document 1 leaves room for improvement in terms of improving the reliability of the power storage device.

[0006] An object of the present disclosure is to improve the reliability of a power storage device.

[0007] The energy storage device according to the present disclosure includes an electrode body in which a first electrode plate and a second electrode plate are stacked in a first direction with a separator interposed therebetween, and an outer casing that houses the electrode body, wherein the first electrode plate includes a first core and a first mixture layer formed on the surface of the first core, a first exposed portion where the first core is exposed is arranged at one end of the electrode body in the winding axis direction, the first exposed portion has a folded portion that is folded back one or more times and folded so as to overlap, and the folded portion is tilted in the first direction so that the folded portions in adjacent winding portions of the first electrode plate overlap, thereby forming a current collecting portion at one end of the electrode body in the winding axis direction.

[0008] According to the power storage device according to the present disclosure, reliability can be improved.

[0009] 6A is a cross-sectional view taken along the axial direction of a cylindrical secondary battery that is an example of an electric storage device according to an embodiment; FIG. 7B is a perspective view showing a state before a positive electrode current collector and a negative electrode current collector are formed, showing a partially developed view of an electrode body of the cylindrical secondary battery shown in FIG. 1; FIG. 8A is an enlarged view of part A of FIG. 1, with some parts omitted; FIG. 9B is a top view of the electrode body and upper insulating plate removed from FIG. 1; FIG. 10B is a view showing the upper insulating plate removed from FIG. 4; FIG. 11A is an expanded view of a positive electrode plate before the formation of a positive electrode folded portion; FIG. 9B is a cross-sectional view taken along the line B-B of FIG. 6A, and FIG. 9B is an enlarged view of part C of FIG. 9A, showing a state in which a positive electrode folded portion is formed on a positive electrode exposed portion in a folding step; and FIG. 9C is a cross-sectional view showing that the positive electrode folded portion overlaps with adjacent winding portions of the positive electrode plate in the winding step. 10 is a cross-sectional view showing, in a tilting step, the positive electrode folded portions of the multiple winding portions of the positive electrode plate are tilted toward the inner periphery at one end of the electrode body in the winding axis direction, so that the positive electrode folded portions of adjacent winding portions of the positive electrode plate overlap. 11 is a cross-sectional view showing a state in which, in a welding step, the positive electrode folded portions of the multiple winding portions of the positive electrode plate are welded together. 12 is a schematic view showing a state in which, in a tilting step, the positive electrode folded portions of the multiple winding portions of the positive electrode plate are tilted further toward the inner periphery of the electrode body than in FIG.

[0010] Conventionally, in a storage battery device having a wound electrode assembly, an exposed portion of the electrode plate protrudes from one end in the winding axis direction and is joined to a current collector. This configuration has the potential to reduce resistance, unlike a configuration in which a connection lead joined to a portion of the electrode plate in the winding direction is led out and joined to a current collector. However, each circumferential portion of the exposed portion of the electrode plate is connected only in the winding direction. This may result in a lower rigidity of the portion formed by the exposed portion located at the end in the winding axis direction of the electrode plate. This results in an unstable shape and position of the portion formed by the exposed portion, leaving room for improvement in terms of reliability.

[0011] As a result of extensive research, the inventors have found that reliability can be improved by arranging a first exposed portion where the first core is exposed at one end of the electrode body in the winding axis direction, the first exposed portion having a folded portion that is folded back one or more times to overlap, and the folded portion being tilted in a first direction that is the stacking direction of the electrode body so that the folded portions of adjacent winding portions of the electrode body overlap to form a current collecting portion at one end of the winding axis direction. Specifically, by increasing the rigidity of the current collecting portion formed by the exposed portion, the shape and position of the current collecting portion can be stabilized, thereby achieving the above-mentioned effects.

[0012] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are merely examples for ease of understanding the present invention and can be appropriately changed according to the specifications of the energy storage device. The term "substantially" is used below to mean, for example, "exactly the same" as well as "substantially the same." Furthermore, when multiple embodiments and variations are included below, it is initially assumed that their characteristic features will be appropriately combined. While a cylindrical secondary battery will be described below as the energy storage device of the embodiment, the energy storage device of the present disclosure is not limited to a cylindrical secondary battery. Various configurations can be adopted as long as the energy storage device includes a wound electrode assembly and an exterior housing that houses the electrode assembly. For example, the energy storage device may be an alkaline storage battery or a capacitor.

[0013] Fig. 1 is a cross-sectional view along the axial direction of a battery 10, which is an electricity storage device of an embodiment. Fig. 2 is a perspective view showing a partially developed electrode body 14 of the battery 10, illustrating a state before a positive electrode current collector and a negative electrode current collector are formed. Fig. 3 is an enlarged view of part A in Fig. 1, with some parts omitted. Fig. 4 is a view from above with the electrode body 14 and upper insulating plate 19 removed from Fig. 1. Fig. 5 is a view showing the battery 10 with the upper insulating plate 19 removed from Fig. 4.

[0014] As shown in Figures 1 and 2, battery 10 is a non-aqueous electrolyte secondary battery and includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a metal can-shaped exterior body 15, and a sealing member 16 fixed to the open end of the exterior body 15. The wound electrode assembly 14 includes a positive electrode plate 11, a negative electrode plate 12, and two separators 13a and 13b, with the positive electrode plate 11 and the negative electrode plate 12 being spirally wound with the separators 13a and 13b interposed between them. In the following description, the sealing member 16 side will be referred to as the "top" and the bottom side of the exterior body 15 as the "bottom." The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0015] As shown in FIG. 2 , the electrode assembly 14 has a wound structure in which a long positive electrode plate 11 and a long negative electrode plate 12 are stacked in a first direction via two long separators 13a, 13b and then wound. The electrode assembly of the present disclosure may also be configured by alternately stacking multiple sheet-shaped positive electrode plates and multiple negative electrode plates via multiple separators. In this case, the folded portions formed on the exposed portions of each electrode plate (described later) lean in the stacking direction. Furthermore, the exposed positive electrode portion of the positive electrode plate 11 protrudes upward relative to the negative electrode plate 12 and the separators 13a, 13b, while the exposed negative electrode portion of the negative electrode plate 12 protrudes downward relative to the positive electrode plate 11 and the separators 13a, 13b. One separator 13a of the two separators 13a, 13b protrudes upward relative to the other separator 13b, and the other separator 13b protrudes downward relative to the one separator 13a. Hereinafter, the two separators 13 a and 13 b may be collectively referred to as separator 13 .

[0016] The positive electrode plate 11 has a positive electrode exposed portion 34 where the positive electrode core 30 is exposed without the positive electrode mixture layer 32 at an upper end portion, which is one end portion in the winding axis direction (hereinafter sometimes referred to as the axial direction), from the winding start end to the winding end end in the longitudinal direction of the long positive electrode plate 11. At the upper end portion of the positive electrode plate 11, a positive electrode protective layer 36 is provided between the positive electrode mixture layer 32 and the positive electrode exposed portion 34 to prevent short circuits of the positive electrode core 30. However, the positive electrode protective layer 36 may not be provided in the energy storage device of the present disclosure. In this embodiment, a case where one side in the winding axis direction is the upper side will be described, but one side in the winding axis direction may also be the lower side.

[0017] The negative electrode plate 12 has a negative electrode exposed portion 44, where the negative electrode core 40 is exposed and no negative electrode mixture layer 42 is provided, at the lower end, which is the other end in the axial direction, from the winding start end to the winding end end in the longitudinal direction of the long negative electrode plate 12. Therefore, the upper end of the electrode body 14 in the axial direction (the width direction of the positive electrode plate) is constituted by the positive electrode exposed portion 34, and the lower end of the electrode body 14 in the axial direction is constituted by the negative electrode exposed portion 44. Furthermore, at the lower end of the negative electrode plate 12, a negative electrode protective layer 46 is provided between the negative electrode mixture layer 42 and the negative electrode exposed portion 44 to prevent short-circuiting of the negative electrode core 40. However, the negative electrode protective layer 46 may be omitted in the energy storage device of the present disclosure.

[0018] In this embodiment, the positive electrode plate 11 corresponds to the first electrode plate, and the negative electrode plate 12 corresponds to the second electrode plate. The positive electrode core 30 corresponds to the first core, and the positive electrode mixture layer 32 corresponds to the first mixture layer. The negative electrode core 40 corresponds to the second core, and the negative electrode mixture layer 42 corresponds to the second mixture layer. Note that the first electrode plate may be the negative electrode plate 12, and the second electrode plate may be the positive electrode plate 11.

[0019] As described below, the positive electrode exposed portion 34 has a positive electrode folded portion that has been folded back one or more times to overlap, the positive electrode folded portion is tilted toward the inner periphery of the electrode body 14, and the positive electrode folded portions of adjacent winding portions of the positive electrode plate 11 overlap to form a positive electrode current collecting portion 37 at its upper axial end. As described below, the negative electrode exposed portion 44 has a negative electrode folded portion that has been folded back one or more times to overlap, and the negative electrode folded portion is tilted toward the inner periphery of the electrode body 14, and the negative electrode folded portions of adjacent winding portions of the negative electrode plate 12 overlap to form a negative electrode current collecting portion 47 at its lower axial end.

[0020] The non-aqueous electrolyte has ion conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous electrolyte is not limited to a liquid electrolyte (nonaqueous electrolytic solution), and may be a solid electrolyte using a gel polymer or the like. The battery 10 is preferably a lithium ion battery. The electrolyte salt may be, for example, LiBF ４ , LiPF ６Examples of the non-aqueous solvent include esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain a halogen-substituted product in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0021] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP). From the viewpoint of suppressing a decrease in the charge-discharge cycle characteristics of a nonaqueous electrolyte secondary battery or improving input characteristics, the nonaqueous electrolyte preferably contains 5% by mass or more of FEC, and more preferably 5% by mass to 15% by mass of FEC, relative to the mass of the nonaqueous electrolyte.

[0022] 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.).

[0023] The positive electrode plate 11 includes a strip-shaped positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode core 30 may be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode plate 11, or a film with such a metal disposed on the surface. The thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode plate 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 positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 on one side of the positive electrode substrate 30 is, for example, 10 μm or more and 150 μm or less.

[0024] 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.

[0025] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0026] A positive electrode protective layer 36 is provided on both sides of the upper end of the positive electrode core 30, between the positive electrode mixture layer 32 and the positive electrode exposed portion 34. The positive electrode protective layer 36 is composed of, for example, an inorganic material such as alumina, a resin such as polyvinylidene fluoride (PVdF), and a conductive additive such as acetylene black (AB) or carbon black (CB) in a predetermined ratio. For example, the positive electrode protective layer 36 may be configured to contain the inorganic material and the conductive additive in a mass ratio of 100:0.5. The conductive additive may be omitted from the positive electrode protective layer 36. The positive electrode protective layer 36 can be provided on the surface of the positive electrode core 30, and various materials may be used as long as they have the function of suppressing short circuits in the positive electrode core 30.

[0027] The negative electrode plate 12 includes a strip-shaped negative electrode core 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode core 40. The negative electrode core 40 may be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode plate 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. The negative electrode mixture layer 42 includes a negative electrode active material and a binder. The negative electrode plate 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0028] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials 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 negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0029] As in the case of the positive electrode plate 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 42, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer 42 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0030] A negative electrode protective layer 46 is provided between the negative electrode mixture layer 42 and the negative electrode exposed portion 44 on both sides of the lower end (in the width direction) of the negative electrode core 40. The negative electrode protective layer 46 can have a configuration similar to that of the positive electrode protective layer 36. The negative electrode protective layer 46 can be provided on the surface of the negative electrode core 40, and various types can be used as long as they have the function of suppressing short circuits in the negative electrode core 40.

[0031] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials 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.

[0032] As shown in FIG. 1 , a positive electrode current collecting portion 37 and a negative electrode current collecting portion 47 are provided at the upper and lower axial ends of the electrode body 14, respectively. As described below, the positive electrode current collecting portion 37 is formed by folding the positive electrode folded portion formed in the positive electrode exposed portion 34 inward, and by overlapping the positive electrode folded portions in adjacent circumferential portions of the positive electrode plate 11 from the outermost to the innermost circumference of the positive electrode plate 11 and integrating them by welding. Note that the positive electrode folded portion may be folded outward. Alternatively, some of the positive electrode folded portions aligned in the radial direction of the electrode body may be folded inward and some may be folded outward.

[0033] As described below, the negative electrode current collecting portion 47 is formed by folding the negative electrode folded portion formed in the negative electrode exposed portion 44 toward the inner periphery, and overlapping the negative electrode folded portions in adjacent circumferential portions of the negative electrode plate 12 from the outermost to the innermost periphery of the negative electrode plate 12, and integrating them by welding.

[0034] The battery 10 also includes an upper insulating plate 19 axially above the positive current collector 37, the upper insulating plate 19 having a circular cross-shaped through hole 19a. This insulating plate 19 may be omitted. One end of a positive electrode lead 20 is joined to the upper surface of the positive current collector 37 by welding or the like. The positive electrode lead 20 passes through the through hole 19a of the insulating plate 19 and extends toward the sealing body 16, and the other end of the positive electrode lead 20 is connected to the underside of the filter 22 of the sealing body 16 by welding or the like. A cap 26 constituting the top plate of the sealing body 16 is electrically connected to the filter 22. This electrically connects the positive current collector 37 to the cap 26, and the cap 26 serves as a positive terminal. The positive electrode lead 20 is a conductive member made of a metal primarily composed of aluminum. The positive current collector in the present disclosure may be joined to a metal positive current collector plate, and the positive current collector plate and the positive electrode lead may be connected. In this case, the insulating plate is placed on the positive electrode current collector plate. Alternatively, the positive electrode current collector may be joined to the filter without the positive electrode lead.

[0035] Furthermore, the battery 10 includes a circular insulating plate 17 with a cross-shaped through hole 17a formed therein, axially below the negative current collector 47. Note that this insulating plate 17 is optional. One end of a negative electrode lead 28 is joined to the underside of the negative current collector 47 by welding or the like. The negative electrode lead 28 is folded back into a U-shape inside the through hole 17a of the insulating plate 17. The other end of the negative electrode lead 28 is connected to the inner surface of the bottom of the exterior body 15 by welding or the like. This electrically connects the negative electrode current collector 47 to the exterior body 15, which serves as a negative terminal. The negative electrode lead 28 is a conductive member made of a metal such as copper. Note that the negative electrode current collector in the present disclosure may be joined to a negative electrode current collector, which is a metal plate, and the negative electrode current collector and the positive electrode lead may be connected. In this case, the insulating plate is disposed on the positive electrode current collector. Alternatively, the negative electrode current collector may be joined to the exterior body without a negative electrode lead.

[0036] Battery 10 further includes a resin gasket 27 disposed between exterior body 15 and sealing body 16. Gasket 27 is sandwiched between exterior body 15 and sealing body 16 to insulate sealing body 16 from exterior body 15. Gasket 27 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate exterior body 15 from sealing body 16. Exterior body 15 has an annular grooved portion 21 in part of its axial direction.

[0037] The grooved portion 21 can be formed, for example, by spinning a portion of the side surface radially inward to create a recess radially inward. The exterior body 15 has a bottomed tubular portion including the grooved portion 21 and an annular shoulder portion. The bottomed tubular portion houses the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion is bent radially inward from the end of the open side of the bottomed tubular portion and extends inward. The shoulder portion is formed when the upper end of the exterior body 15 is bent inward and crimped to the peripheral edge of the sealing body 16. The sealing body 16 is crimped and fixed to the exterior body 15 with a gasket 27 between the shoulder portion and the grooved portion 21. In this manner, the internal space of the battery 10 is sealed.

[0038] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0039] When battery 10 generates abnormal heat and the internal pressure of battery 10 rises, lower valve body 23 deforms and ruptures, pushing upper valve body 25 toward cap 26, cutting off the current path between lower valve body 23 and upper valve body 25. If the internal pressure rises further, upper valve body 25 ruptures and gas is discharged from through-hole 26a of cap 26. This gas discharge prevents the internal pressure of battery 10 from rising excessively, which could cause battery 10 to explode, thereby improving the safety of battery 10.

[0040] The configuration and manufacturing method of the positive electrode current collecting portion 37 will be described in detail using Figures 3 to 10. Figure 3 is an enlarged view of part A in Figure 1, with some parts omitted. Figure 4 is a view from above, with the electrode body 14 and upper insulating plate 19 removed from Figure 1. Figure 5 is a view from Figure 4, with the upper insulating plate 19 removed. Figure 6 is a development view of the positive electrode plate 11 before the positive electrode folded portion is formed.

[0041] As shown in FIGS. 3 to 5 , a positive electrode current collector 37 having a generally annular upper end is formed at the upper end of the positive electrode exposed portion 34. The positive electrode current collector 37 is formed by the positive electrode exposed portion 34 and is provided at the upper end of the electrode assembly 14. Specifically, the positive electrode exposed portion 34 has a positive electrode folded portion 38 that is folded twice and overlapped as described below, and the positive electrode folded portion 38 is folded toward the inner periphery of the electrode assembly 14. By providing the positive electrode folded portion in this manner, the density of the positive electrode exposed portion in the positive electrode current collector of the electrode assembly can be increased, which tends to improve the welding reliability of the positive electrode current collector. The bent portion of the folded positive electrode folded portion 38 may be located closer to the mixture layer in the positive electrode exposed portion than the positive electrode folded portion before being folded. By arranging the bent portion in this manner, the positive electrode folded portion can be easily folded. The positive electrode folded portions 38 in each winding portion of the positive electrode plate 11 are overlapped with adjacent winding portions abutting each other in the radial direction (first direction), and the upper ends are melted and integrated by welding to form the positive electrode current collecting portion 37. The positive electrode folded portion may have at least one notch aligned in the winding direction of the electrode body. This notch makes the positive electrode folded portion prone to collapse. When the exposed portion of the folded portion is folded two or more times, it may be folded in a spiral or zigzag pattern.

[0042] At this time, the above-mentioned positive electrode protective layer 36 is provided between the positive electrode mixture layer 32 and the positive electrode exposed portion 34 on both sides of the upper end of the positive electrode plate 11. Fig. 6 shows one side surface in the thickness direction of the positive electrode plate 11. In Fig. 6, the positive electrode mixture layer 32 is indicated by a sandy portion, and the positive electrode protective layer 36 is indicated by a diagonal grid portion. As shown in Fig. 6, the positive electrode protective layer 36 is provided in the longitudinal direction of the positive electrode plate 11 from one end to the other end in the longitudinal direction of the electrode plate.

[0043] By providing the positive electrode protective layer 36 as described above, a difference in rigidity can be created at the upper end of the positive electrode plate 11, making it easier to stably bend the positive electrode exposed portion 34 toward the inner periphery of the electrode body 14 near the base of the portion that protrudes from the upper end of the positive electrode protective layer 36.

[0044] Furthermore, an upper insulating plate 19 is disposed above the positive electrode current collector 37. As shown in Fig. 4, a cross-shaped through-hole 19a is formed in the insulating plate 19. The two linear portions that form the through-hole 19a intersect at the center of the insulating plate 19. When the insulating plate 19 is viewed from above, the positive electrode current collector 37 is exposed in a cross shape through the through-hole 19a of the insulating plate 19.

[0045] Welding such as laser welding is performed by, for example, irradiating a laser beam from the upper side of the insulating plate 19 through the through holes 19a at radially extending positions on the upper surface of the positive current collector 37. Then, the overlapping positive folded portions 38 of the positive current collector 37 are welded at a plurality of welds 39 (four in FIG. 4 ) shown as sandy areas inside the dashed line frame in FIG. 4 , thereby integrating the positive current collector 37. The welds are not shown in FIG. 5 .

[0046] One end of the positive electrode lead 20 is connected by welding or the like to one or more of the four straight line portions on the upper surface of the positive electrode current collector 37 that are exposed above the insulating plate 19 through the through hole 19a. The other end of the positive electrode lead 20 is connected by welding or the like to the filter 22 that constitutes the sealing body 16. As a result, the positive electrode current collector 37 is connected to the sealing body 16 by the long plate-shaped positive electrode lead 20 without via a positive electrode current collector separate from the positive electrode plate 11. This allows the space required for arranging the positive electrode current collector within the exterior body 15 to be reduced, thereby increasing the capacity of the battery 10 and, due to the elimination of component resistance in the positive electrode current collector, reducing resistance.

[0047] A method for manufacturing the battery 10 will be described with reference to Figure 6 and Figures 7 to 10. The method for manufacturing the battery 10 includes a positive electrode plate base forming step, a folded portion forming step, a winding step, a laying step, and a welding step.

[0048] FIG. 7( a) is a cross-sectional view taken along the line B-B in FIG. 6 . FIG. 7( b) is an enlarged view of portion C in FIG. 7( a), showing the state in which the positive electrode folded portion 38 has been formed in the positive electrode exposed portion 34 in the folding step. As shown in FIGS. 6 and 7( a), in the positive electrode plate base formation step, the positive electrode mixture layer 32 and the positive electrode protective layer 36 are formed on both sides of the positive electrode core 30, and the positive electrode exposed portion 34 is formed on both sides of the upper end of the positive electrode core 30, thereby forming the positive electrode plate 11 before the formation of the positive electrode folded portion 38. At this time, the positive electrode exposed portion 34 is bent at the upper end of the positive electrode plate 11 in advance at a predetermined position in the short-side direction of the electrode plate, indicated by the dashed line B1 in FIG. 6 , and at the intended bending position when the positive electrode folded portion 38 is folded in the folding step described below, and then can be bent back. This allows the positive electrode exposed portion 34 to be bent at the predetermined position. In this case, in the bending step described below, the positive electrode exposed portion 34 can be easily bent inward from the predetermined position where the bending was performed as a starting point.

[0049] In the folding step described below, folding is performed along the broken lines B2 and B3 in Fig. 6. Therefore, to make the folding easier, the folded portion can be bent at the broken lines B2 and B3 and then unbent to form a bent shape.

[0050] As shown in FIG. 7( b), in the folded portion forming step, the positions indicated by dashed lines B2 and B3 in FIG. 6 are used as bending positions, and the positive electrode exposed portion 34 is folded twice toward the electrode plate end so as to overlap, thereby forming a positive electrode folded portion 38. At this time, as shown in FIG. 7( b), it is preferable to fold the positive electrode exposed portion 34 in a rolling manner, as this makes it less likely to bend back. The positive electrode exposed portion 34 is folded so as to minimize gaps on the inside. In this example, the positive electrode folded portion 38 is formed by folding it twice, but it may also be formed by folding it only once or three or more times. The more times the positive electrode folded portion is folded, the higher the rigidity of the positive electrode folded portion.

[0051] Fig. 8 is a cross-sectional view showing that in the winding step, the positive electrode folded portion 38 overlaps adjacent winding portions of the positive electrode plate 11. As shown in Fig. 8, in the winding step, the positive electrode plate 11 is wound together with the negative electrode plate 12 and the separator 13. In Fig. 8 and Figs. 9 to 11 described below, the negative electrode plate 12 and the separator 13 are not shown, and the spacing between adjacent winding portions of the positive electrode plate 11 is shown as being extremely smaller than it actually is.

[0052] As shown in FIG. 8, by winding the positive electrode plate 11 in the winding step, the positive electrode folded portions 38 of adjacent winding portions of the positive electrode plate 11 are brought into contact with each other or are closely opposed to each other.

[0053] FIG. 9 is a cross-sectional view showing that, in the tilting step, the positive electrode folded portions 38 of the multiple windings of the positive electrode plate 11 are tilted inward at the upper end of the positive electrode plate 11, and the positive electrode folded portions 38 of adjacent windings of the positive electrode plate 11 overlap. As shown in FIG. 9 , in the tilting step, the rolled electrode assembly 14 obtained in the winding step is inserted into the exterior body 15 ( FIG. 1 ). Then, an insulating plate 19 ( FIG. 1 ) is placed above the positive electrode exposed portion 34, and the insulating plate 19 presses the positive electrode exposed portion 34 downward from above. Then, the positive electrode folded portion 38 is tilted inward of the electrode assembly 14 by bending the positive electrode exposed portion 34 near the base of the portion that protrudes upward from the positive electrode protective layer 36. Then, the positive electrode folded portions 38 of the adjacent windings of the positive electrode plate 11 overlap, forming a positive electrode current collecting portion 37 at the upper end of the electrode assembly 14. At this time, the positive electrode folded portions 38 in adjacent winding portions are overlapped so that no gaps are generated between the positive electrode folded portions 38 .

[0054] Furthermore, if the positive electrode plate 11 is bent in advance at a predetermined position in the short side direction of the plate (position indicated by dashed line B1 in Figure 6) before being wound, the positive electrode plate 11 will be bent at the above-mentioned predetermined position, making the positive electrode folding portion 38 more likely to collapse toward the inner periphery of the electrode body 14.

[0055] In the above-described tilting step, two separators 13a, 13b and one negative electrode plate 12 are actually arranged between the respective winding portions of the positive electrode plate 11, as shown in Fig. 3. At this time, as shown in Figs. 2 and 3, the upper end of one separator 13a of the two separators 13a, 13b protrudes upward relative to the other separator 13b, and therefore the upper end of one separator 13a, together with the positive electrode exposed portion 34, is also tilted toward the inner periphery of the electrode body 14, covering the upper side of the negative electrode plate 12. This more reliably prevents short circuits even when the positive electrode exposed portion 34 is tilted toward the upper side of the negative electrode plate 12.

[0056] FIG. 10 is a cross-sectional view showing the state in which the positive electrode folded portions 38 in multiple winding portions of the positive electrode plate 11 are welded and integrated in the welding step. In FIG. 10, the welded portions 39 are schematically indicated by filled black squares. As shown in FIG. 10, in the welding step, as described above, welding such as laser welding is performed on the portion of the upper surface of the positive electrode current collector 37 that is exposed through the through hole 19a of the insulating plate 19 when viewed from above the insulating plate 19. As a result, the positive electrode folded portions 38 in adjacent winding portions of the positive electrode plate 11 in the positive electrode exposed portion 34 are joined by welding, and the positive electrode current collector 37 is integrated with the positive electrode folded portions 38 closely overlapping each other.

[0057] 11 is a schematic diagram showing a state in which, in the tilting step, the positive electrode folded portions 38 in the multiple winding portions of the positive electrode plate 11 are tilted further toward the inner periphery of the electrode body 14 than in FIG. 9 . As shown in FIG. 11 , in the tilting step, the positive electrode folded portions 38 in the multiple winding portions of the positive electrode plate 11 are tilted further toward the inner periphery of the electrode body 14 than in the case shown in FIG. 9 so that they are closer to extending in the radial direction. In this state, the positive electrode current collecting portion 37 may be integrated by welding with the positive electrode folded portions 38 closely overlapping each other. FIG. 11 shows that the positive electrode folded portions 38 are welded at the area surrounded by the dashed dotted line D.

[0058] In the above embodiment, a configuration has been described in which welding of the positive current collecting portion 37 is performed with the insulating plate 19 placed above the electrode body 14 after the laying down step, but after the laying down step using the insulating plate 19, the insulating plate 19 may be removed from above the electrode body 14, and welding such as laser welding may be performed from above the positive current collecting portion 37. After welding, the insulating plate 19 is placed again above the electrode body 14.

[0059] Meanwhile, as shown in FIG. 1 , a negative electrode current collecting portion 47 having a circular lower end is formed at the lower end of the negative electrode exposed portion 44. The negative electrode current collecting portion 47 is formed by the negative electrode exposed portion 44 and is provided at the lower end of the electrode body 14. Specifically, like the positive electrode exposed portion 34, the negative electrode exposed portion 44 has a negative electrode folded portion that is folded twice and overlapped, and the negative electrode folded portion is tilted toward the inner periphery of the electrode body 14. The negative electrode folded portions in each winding portion of the negative electrode plate 12 overlap with adjacent winding portions, and further, the lower ends are melted and integrated by welding. In this way, the above-mentioned negative electrode current collecting portion 47 is formed.

[0060] At this time, the above-described anode protective layer 46 ( FIG. 2 ) is provided between the anode mixture layer 42 ( FIG. 2 ) and the anode exposed portion 44 on both sides of the lower end of the anode plate 12. By providing the anode protective layer 46, a difference in rigidity can be created at the lower end of the anode plate 12, making it easier to stably bend the anode exposed portion 44 toward the inner periphery of the electrode body 14 near the base of the portion that protrudes from the lower end of the anode protective layer 46. Note that the anode protective layer 46 of the anode plate 12 may be omitted.

[0061] Furthermore, when the negative electrode folded portion is folded toward the inner periphery of the electrode assembly 14, two separators 13a, 13b and one positive electrode plate 11 are actually disposed between each winding portion of the negative electrode plate 12. At this time, as shown in FIG. 2 , the other separator 13b of the two separators 13a, 13b protrudes downward more than the other separator 13a, so that the other separator 13b is also folded toward the inner periphery of the electrode assembly 14 together with the negative electrode exposed portion 44, and can cover the underside of the positive electrode plate 11. This more reliably prevents short circuits even when the negative electrode exposed portion 44 is folded toward the underside of the positive electrode plate 11.

[0062] Furthermore, the lower insulating plate 17 is disposed above the negative electrode current collector 47. A cross-shaped through-hole 17a is formed in the lower insulating plate 17, similar to the upper insulating plate 19. The negative electrode current collector 47 is exposed below the insulating plate 17 from the through-hole 17a of the insulating plate 17 in a cross shape.

[0063] Welding, such as laser welding, is performed by irradiating a laser beam from the underside of the insulating plate 17 through the through-hole 17a at radially extending positions on the underside of the negative electrode current collector 47. The overlapping negative electrode folded portions of the negative electrode current collector 47 are welded at multiple welds, and the negative electrode current collector 47 is integrated with the negative electrode folded portions tightly overlapping each other. Furthermore, when viewed from below the insulating plate 17, one end of the negative electrode lead 28 is connected by welding or the like to one or more of the four straight portions on the underside of the negative electrode current collector 47 exposed through the through-hole 17a. The negative electrode lead 28 is folded back into a substantially U-shape within the through-hole 17a. The other end of the negative electrode lead 28 is connected to the bottom of the exterior body 15 by welding, such as laser welding. As a result, the negative electrode current collector 47 is connected to the exterior body 15 by the negative electrode lead 28 without a negative electrode current collector separate from the negative electrode plate 12. This reduces the space required for arranging the negative electrode current collector within the exterior body 15, thereby increasing the capacity of the battery 10, and also reducing the resistance due to the elimination of the component resistance of the negative electrode current collector.

[0064] For example, welding to the negative electrode current collecting portion 47 can be performed by turning the electrode body 14 upside down before inserting it into the outer casing 15, placing the insulating plate 17 on top of the negative electrode current collecting portion 47, and then using laser welding or the like from above the insulating plate 17.

[0065] Alternatively, the lower insulating plate 17 and negative electrode lead 28 may be omitted, and after inserting the electrode assembly 14 into the exterior housing 15, the negative electrode exposed portion 44 may be pressed against the bottom of the exterior housing 15 to tilt the folded portion of the negative electrode exposed portion 44 inward, thereby forming the negative electrode current collecting portion 47. Laser light may then be applied from the outside of the bottom of the exterior housing 15 to laser-weld the negative electrode current collecting portion 47 to the bottom of the exterior housing 15, while welding the lower end of the overlapping negative electrode folded portion of the negative electrode current collecting portion, thereby integrating the negative electrode current collecting portion 47 with the negative electrode folded portion tightly overlapping. This configuration also reduces the space required for the insulating plate 17 and negative electrode lead 28 within the exterior housing 15, thereby further increasing the capacity of the battery 10.

[0066] In the battery 10 described above, a positive electrode exposed portion 34, in which the positive electrode core 30 is exposed, is disposed at one axial end of the electrode body 14. The positive electrode exposed portion 34 has a positive electrode folded portion 38 that is folded back one or more times to overlap. The positive electrode folded portion 38 is also tilted toward the inner periphery of the electrode body 14, and the positive electrode folded portions 38 in adjacent turns of the electrode body 14 overlap, forming a positive electrode current collector 37 at one axial end. This increases the rigidity of the positive electrode current collector 37 formed by the positive electrode exposed portion 34, thereby stabilizing the shape and position of the positive electrode current collector 37. This allows the connection between the positive electrode current collector 37 and the positive electrode connection lead to be maintained in a stable and favorable state, thereby improving the reliability of the battery 10.

[0067] Similarly, the rigidity of the negative electrode current collecting portion 47 formed by the negative electrode exposed portion 44 can be increased, which stabilizes the shape and position of the negative electrode current collecting portion 47. This further improves the reliability of the battery 10.

[0068] Furthermore, unlike a configuration in which a positive electrode lead connected only partially in the winding direction of the positive electrode plate is connected to a sealing body, current can flow through the positive electrode folded portion 38, where adjacent winding portions overlap, in the positive electrode current collector 37, not only in the winding direction of the positive electrode plate 11 but also in directions other than the winding direction, such as the radial direction of the wound positive electrode plate, thereby achieving low resistance. Similarly, low resistance can be achieved in the negative electrode current collector 47. Furthermore, the positive electrode current collector 37 and the negative electrode current collector 47 are integrated by welding, with their respective folded portions closely overlapping, thereby further reducing resistance. This improves the performance of the battery 10. Note that the positive electrode current collector 37 and the negative electrode current collector 47 may not be integrated by welding.

[0069] In the above embodiment, both a positive electrode current collector and a negative electrode current collector are provided on the electrode body, but only one of the positive electrode current collector and the negative electrode current collector may be provided on the electrode body. In addition, in the above embodiment, a configuration is described in which the positive electrode current collector to which the positive electrode exposed portion is joined and the negative electrode current collector to which the negative electrode exposed portion is joined are not provided, but one or both of the positive electrode current collector and the negative electrode current collector may be provided. Even in this case, the rigidity of the cylindrical secondary battery can be increased by providing one or both of the positive electrode current collector and the negative electrode current collector, thereby improving the reliability of the cylindrical secondary battery.

[0070] Furthermore, in the above embodiment, a cross-shaped through hole is formed in the insulating plate, but the through hole formed in the insulating plate is not limited to this, and may be, for example, a through hole extending in a single straight line in the radial direction, or a through hole having a shape in which three or more straight lines extending radially intersect at the center.

[0071] In the above embodiment, the folded portion of the exposed portion of each of the positive and negative current collectors is tilted toward the inner periphery of the electrode body, and the folded portions of adjacent windings of the positive or negative electrode plate overlap to form a current collector at the end of the winding axis. However, the folded portion of the exposed portion of either or both of the positive and negative current collectors may be tilted toward the outer periphery of the electrode body, and the folded portions of adjacent windings of the positive or negative electrode plate overlap to form a current collector at the end of the winding axis.

[0072] The present disclosure is further described by the following embodiments. Aspect 1: An energy storage device comprising: an electrode assembly in which a first electrode plate and a second electrode plate are stacked in a first direction with a separator interposed therebetween; and an exterior housing that houses the electrode assembly, wherein the first electrode plate includes a first core and a first mixture layer formed on a surface of the first core, a first exposed portion in which the first core is exposed is disposed at one end of the electrode assembly in the winding axis direction, the first exposed portion having a folded portion that is folded back one or more times to overlap, the folded portion being tilted in the first direction so that the folded portions of adjacent winding portions of the first electrode plate overlap each other to form a current collecting portion at one end of the electrode assembly in the winding axis direction. Aspect 2: The energy storage device according to Aspect 1, wherein the first electrode plate and the second electrode plate are stacked and wound with the separator interposed therebetween, and the first direction is a direction perpendicular to the winding axis of the electrode assembly. Configuration 3: The electricity storage device according to Configuration 1, wherein the current collecting portion is connected to a sealing body fixed to the exterior body by a long, plate-shaped connection lead, without interposing a current collector separate from the first electrode plate.Configuration 4: The electricity storage device according to any one of Configurations 1 to 3, wherein the current collecting portion is joined to a current collector.Configuration 5: The electricity storage device according to any one of Configurations 1 to 4, wherein a protective layer for suppressing short circuits is provided between the first mixture layer and the first exposed portion.Configuration 6: The electricity storage device according to any one of Configurations 1 to 5, wherein adjacent winding portions of the current collecting portion in the first exposed portion are joined by welding.Configuration 7: The electricity storage device according to any one of Configurations 1 to 6, wherein the folded portion is folded back two or more times so as to overlap. Configuration 8: The power storage device according to any one of configurations 1 to 7, wherein the bending point at which the folding portion falls is provided in a region of the first exposed portion that does not overlap with the folding portion before bending.Aspect 9: The method for manufacturing an electricity storage device according to Aspect 1, wherein the first exposed portion is formed on one end of the first electrode plate in a short side direction of the electrode plate corresponding to the winding axis direction, and the first exposed portion is folded back one or more times in the short side direction of the electrode plate to overlap to form the folded portion, and then the folded portion is tilted toward the inner periphery or the outer periphery of the electrode body to overlap the folded portions of adjacent winding portions of the first electrode plate, thereby forming the current collecting portion at one end of the first electrode plate in the winding axis direction. Aspect 10: The method for manufacturing an electricity storage device according to Aspect 9, wherein the folded portion is tilted toward the inner periphery or the outer periphery of the electrode body to overlap the folded portions of adjacent winding portions of the first electrode plate, and then adjacent winding portions of the first exposed portion are joined by welding to form the integrated current collecting portion. Configuration 11: The method for manufacturing an energy storage device according to Configuration 9 or 10, wherein, before winding the first electrode plate, the first electrode plate is bent at a predetermined position in the short side direction of the electrode plate, which is a position where the folding portion is to be bent when the folding portion is folded down, and then the first electrode plate is bent back to form a bend at the predetermined position.

[0073] REFERENCE SIGNS LIST 10 battery, 11 positive electrode plate, 12 negative electrode plate, 13a, 13b separator, 14 electrode body, 15 outer can, 16 sealing body, 17 insulating plate, 19 insulating plate, 20 positive electrode lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a through hole, 27 gasket, 28 negative electrode lead, 30 positive electrode core, 32 positive electrode mixture layer, 34 positive electrode exposed portion, 36 positive electrode protective layer, 37 positive electrode current collecting portion, 38 positive electrode folded portion, 39 welded portion, 40 negative electrode core, 42 negative electrode mixture layer, 44 negative electrode exposed portion, 46 negative electrode protective layer.

Claims

1. A power storage device comprising: an electrode body in which a first electrode plate and a second electrode plate are laminated in a first direction with a separator interposed therebetween; and an exterior body that houses the electrode body, wherein the first electrode plate includes a first core body and a first mixture layer formed on the surface of the first core body, a first exposed portion where the first core body is exposed is disposed at one end portion of the electrode body in the winding axis direction, the first exposed portion has a folded portion that is folded back one or more times and folded so as to overlap, the folded portion is laid down in the first direction, and the folded portions in the circumferential portions adjacent to each other in the first direction of the first electrode plate overlap, and a current collecting portion is formed at one end portion in the winding axis direction.

2. The power storage device according to claim 1, wherein in the electrode body, the first electrode plate and the second electrode plate are laminated and wound with the separator interposed therebetween, and the first direction is a direction perpendicular to the winding axis of the electrode body.

3. The power storage device according to claim 1, wherein the current collecting portion is connected to a sealing body fixed to the exterior body by a long plate-shaped connection lead without passing through a current collector different from the first electrode plate.

4. The power storage device according to claim 1, wherein the current collecting portion is joined to a current collector.

5. The power storage device according to claim 1, wherein a protective layer for suppressing a short circuit is provided between the first mixture layer and the first exposed portion.

6. The power storage device according to claim 1, wherein adjacent circumferential portions in the current collecting portion of the first exposed portion are joined by welding.

7. The power storage device according to claim 1, wherein the folded portion is folded back two or more times and folded so as to overlap.

8. The power storage device according to claim 1, wherein a bending point at which the folded portion is laid down is provided in a region of the first exposed portion that does not overlap the folded portion before bending.

9. A method for manufacturing the power storage device according to claim 1, wherein the first exposed portion is formed at one end portion in the short side direction of the electrode plate corresponding to the winding axis direction in the first electrode plate, after forming the folded portion by folding back the first exposed portion one or more times in the short side direction of the electrode plate and folding so as to overlap, the folded portion is laid down on the inner circumferential side or the outer circumferential side of the electrode body, and the folded portions in the adjacent circumferential portions of the first electrode plate are overlapped to form the current collecting portion at one end portion in the winding axis direction.

10. The manufacturing method of the power storage device according to claim 9, wherein the folding portion is tilted to the inner peripheral side or the outer peripheral side of the electrode body, and after overlapping the folding portions at the adjacent circumferential portions of the first electrode plate, among the first exposed portions, the adjacent circumferential portions are joined by welding to form the integrated current collecting portion.

11. The manufacturing method of the power storage device according to claim 9, wherein before winding the first electrode plate, at a predetermined position in the short side direction of the electrode plate, which is the bending planned position when tilting the folding portion, after bending and then bending back, the bending is set at the predetermined position.

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