Power storage device

Abstract

Provided is a highly reliable power storage device. The present invention comprises an electrode body (14) in which a first electrode and a second electrode are laminated in a first direction with a separator (13) interposed therebetween, an exterior body (16) that accommodates the electrode body (14), and a first current collector plate that is connected to the first electrode. The first electrode has a distal-end portion that extends from an end portion of the second electrode in a second direction orthogonal to the first direction. The distal-end portion is bent in the first direction and is connected to the first current collector plate.

Description

Power storage device

[0001] The present disclosure relates to an electrical storage device, such as a battery or a capacitor.

[0002] A conventional energy storage device is a cylindrical secondary battery described in Patent Document 1. This cylindrical secondary battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a bottomed cylindrical outer can that houses the electrode assembly, and a sealing body that closes the opening of the outer can. The positive electrode of the electrode assembly is electrically connected to the bottom surface of the sealing body via a positive electrode lead, and the negative electrode of the electrode assembly is electrically connected to the bottom of the outer can via a negative electrode lead.

[0003] Japanese Patent Application Laid-Open No. 2000-048825

[0004] In order to further improve the capacity and output of power storage devices and to enable stable charging and discharging in more severe environments, there is a need for further improving reliability. Therefore, an object of the present disclosure is to provide a highly reliable power storage device.

[0005] The energy storage device of the present disclosure comprises an electrode body in which a first electrode and a second electrode are stacked in a first direction with a separator interposed therebetween, an outer casing that houses the electrode body, and a first current collector plate that connects to the first electrode, wherein the first electrode has a tip portion that extends from an end of the second electrode in a second direction that is perpendicular to the first direction, and the tip portion is bent in the first direction and connected to the first current collector plate.

[0006] According to the power storage device of the present disclosure, a highly reliable power storage device can be provided.

[0007] FIG. 1 is an axial cross-sectional view of a battery according to an embodiment of the present disclosure. FIG. 2 is an enlarged cross-sectional view of a joint between a positive electrode and an upper current collector plate. FIG. 3 is an axial cross-sectional view of a battery according to an embodiment of the present disclosure. FIG. 4 is an enlarged cross-sectional view of a joint between a positive electrode and an upper current collector plate. FIG. 5 is a schematic view showing a state of a joint between a tip portion of an exposed portion of a positive electrode substrate and a positive current collector plate. FIG. 6 is a cross-sectional view showing a state of bending. FIG. 7 is a plan view illustrating a bending direction. FIG. 8 is a plan view showing a state in which a positive current collector plate is connected to a groove portion of an electrode body. FIG. 9 is a cross-sectional view showing a modified example of an extended portion of a protective layer. FIG. 10 is a cross-sectional view showing another modified example of an extended portion of a protective layer. FIG. 11 is an enlarged cross-sectional view of a joint between a positive electrode and an upper current collector plate. FIG. 12 is a schematic view showing a bent state of a joint between a tip portion of an exposed portion of a positive electrode substrate and a positive current collector plate. FIG. 13 is a plan view showing a bending direction of bending. FIG. 14 is a plan view showing a state in which a positive current collector plate is connected to a groove portion of an electrode body. FIG. 15 is an enlarged cross-sectional view of a joint between a positive electrode and an upper current collector plate in an embodiment having an extended portion of a protective layer. FIG. 16 is an axial cross-sectional view of a battery according to an embodiment having an extended portion of a protective layer.

[0008] Hereinafter, an embodiment of an energy storage device according to the present disclosure will be described in detail with reference to the drawings. The energy storage device according to the present disclosure may be a secondary battery using an aqueous electrolyte or a secondary battery using a nonaqueous electrolyte. The energy storage device according to the present disclosure may be a cylindrical battery having a cylindrical (e.g., bottomed cylindrical) outer can, a prismatic battery having a prismatic outer can, or a pouch-type battery having an outer body made of a laminate sheet. In these batteries, the cylindrical outer can, the prismatic outer can, and the laminate sheet form the outer body. Alternatively, the energy storage device according to the present disclosure may be a capacitor that is repeatedly charged and discharged. Below, a cylindrical secondary battery (lithium ion battery) using a nonaqueous electrolyte is illustrated as an example of an energy storage device according to one embodiment, but the energy storage device according to the present disclosure is not limited thereto.

[0009] When the following description includes multiple embodiments and variations, it is anticipated from the beginning that new embodiments can be constructed by appropriately combining their characteristic features. In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant description is omitted. Furthermore, the drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc., of each component do not necessarily match between different drawings. In this specification, the sealing body 17 side in the axial direction (height direction) of the cylindrical battery 10 is referred to as "upper," and the bottom plate portion 68 side of the outer can 16 in the axial direction is referred to as "lower." The axial direction of the battery 10 coincides with the height direction of the electrode assembly. Among the components described below, components not recited in the independent claims representing the highest concept are optional components and are not required components. The upward axial direction is referred to as the first direction.

[0010] 1 is an axial cross-sectional view of a battery 10 according to an embodiment of the energy storage device of the present disclosure. The battery 10 includes a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17.

[0011] The electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are stacked in a first direction with two strip-shaped separators 13 interposed therebetween and wound. Note that the electrode assembly of the present disclosure may be a stacked electrode assembly in which a plurality of sheet-type positive electrodes and negative electrodes are alternately stacked in the first direction with separators interposed therebetween. The positive electrode constitutes the first electrode, and the negative electrode 12 constitutes the second electrode. Note that in the energy storage device of the present disclosure, the first electrode may be the negative electrode, and the second electrode may be the positive electrode. In this case, a tip portion is formed on the negative electrode.

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

[0013] 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.).

[0014] The positive electrode 11 has a 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 constitutes a first core, and the positive electrode mixture layer 32 constitutes a first mixture layer. In the positive electrode 11, a positive electrode exposed portion 31 where the positive electrode mixture layer 32 is not formed is formed at one end in the width direction of the positive electrode core 30. In this embodiment, the positive electrode exposed portion 31 constitutes the tip portion of the present disclosure. For the positive electrode core 30, a metal foil such as aluminum or an aluminum alloy that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface layer, can be used. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, and the like onto the positive electrode core 30, drying the coating, and then compressing it to form a positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer may be formed on only one side of the positive electrode core. Alternatively, the positive electrode mixture layer may be formed by laminating a layered sheet to the positive electrode core. When laminating them, a conductive adhesive containing conductive particles may be interposed between the positive electrode mixture layer and the positive electrode core.

[0015] 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.

[0016] 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 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, or polyethylene oxide (PEO).

[0017] The negative electrode 12 includes a 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 constitutes a second core, and the negative electrode mixture layer 42 constitutes a second mixture layer. The negative electrode 12 has a negative electrode exposed portion 41, where the negative electrode mixture layer 42 is not formed, at the other end in the width direction of the negative electrode core 40. The negative electrode core 40 can be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing 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 may be formed on only one surface of the negative electrode core. Alternatively, a layered negative electrode mixture layer may be attached to the negative electrode core. When attaching them, a conductive adhesive containing conductive particles may be interposed between the negative electrode core and the negative electrode mixture layer.

[0018] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials are graphites such as 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 may contain a silicon (Si) material as the negative electrode active material. In addition, the negative electrode active material may be a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0019] As in the case of the positive electrode 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 may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0020] 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.

[0021] The battery 10 includes a metal lower current collector plate (negative electrode current collector plate) 18 made of copper, iron, nickel, nickel alloy, or alloy of these metals, located below the electrode assembly 14 in the axial direction (a second direction perpendicular to the first direction). In this embodiment, the lower current collector plate 18 has a disk-shaped base 18a and a bottomed, cylindrical protrusion 18b located at the center of the base 18a and protruding downward in the axial direction. The electrode assembly 14 is wound with the positive electrode 11 and the negative electrode 12 offset from each other in the axial direction. This winding results in a positive electrode exposed portion 31 and a negative electrode exposed portion 41 protruding on opposite sides of each other in the axial direction. While the upper surface of the base 18a is pressed against the negative electrode exposed portion 41, which constitutes the lower axial end of the electrode assembly 14, a laser beam is irradiated from below onto the lower surface of the base 18a. This laser welding bonds the negative electrode exposed portion 41 to the upper surface of the base 18a. Furthermore, the bottom plate portion 18c located at the tip of the protrusion 18b is placed on the upper surface of the bottom plate portion 68 of the outer can 16, and then a laser beam is irradiated from below onto the bottom plate portion 68. By this laser welding, the lower current collecting plate 18 is joined to the bottom plate portion 68 and electrically joined to the outer can 16.

[0022] In addition, in Figures 1 and 2, the negative electrode exposed portion 41 has a shape that is bent radially inward, but as shown in Figures 3 and 4, it may be bent radially from the outside to the inside, similar to the positive electrode exposed portion 31.

[0023] The case where the negative electrode exposed portion 41 is electrically connected to the outer can 16 via the lower current collector plate 18 has been described. However, the negative electrode may be electrically connected to the outer can via one or more negative electrode leads protruding from the lower end of the electrode assembly. Alternatively, in addition to or instead of being electrically connected to the outer can via one or more negative electrode leads, the negative electrode may be electrically connected to the outer can by contacting a negative electrode exposed portion provided on the outermost periphery of the electrode assembly with the inner circumferential surface of the outer can. The negative electrode exposed portion 41 may also be directly bonded to the bottom plate of the outer can using a laser or the like. The negative electrode exposed portion 41 may also be bonded to the lower current collector plate 18 in a radially bent state. Furthermore, the negative electrode exposed portions 41 aligned radially may be bonded to the lower current collector plate 18 in a state where they overlap each other.

[0024] The battery 10 includes a positive electrode current collector 19 (positive electrode current collector) made of a metal such as aluminum or an aluminum alloy, located axially above the electrode assembly 14. The positive electrode current collector 19 has a base 19a electrically connected to the positive electrode 11 and a through-hole 19b provided in the center of the base 19a. A spacer 37 made of an insulating material that prevents connection between the positive electrode current collector 19 and the outer can 16 is provided between the base 19a and the outer can 16. While the lower surface of the base 19a is pressed against a positive electrode exposed portion 31 that constitutes the upper end of the electrode assembly 14, a laser beam is irradiated from above onto the upper surface of the base 19a. This laser welding bonds the positive electrode exposed portion 31 to the lower surface of the base 19a. The positive electrode exposed portion 31 constitutes a first exposed portion.

[0025] Here, the tip side of the positive electrode exposed portion 31 is bent in the radial direction (first direction) by bending, and is joined to the positive electrode current collector plate 19 in a bent state in the radial direction. Here, the bent surface of the positive electrode exposed portion 31 is the first surface of the present disclosure, and the surface opposite the first surface is the second surface of the present disclosure. Furthermore, the positive electrode exposed portions aligned in the radial direction may be joined to the positive electrode current collector plate 19 in a state where they overlap each other.

[0026] Furthermore, a protective layer 33 is formed around the end of the positive electrode mixture layer 32 on the first and second surfaces of the positive electrode exposed portion 31 to prevent short-circuiting with the adjacent negative electrode 12. Here, the protective layer 33 formed on the first surface is the first protective layer, and the protective layer 33 formed on the second surface is the second protective layer. Furthermore, in this embodiment, an extension 33a formed by extending a portion of the protective layer 33 is formed on the first surface of the positive electrode exposed portion 31. This extension 33a can more reliably prevent short-circuiting with the adjacent negative electrode 12.

[0027] In particular, in a lithium-ion battery, the negative electrode 12 may elongate as the charge / discharge cycle progresses. For example, an elongated portion 12a indicated by the two-dot chain line in Fig. 2 may occur. In this embodiment, the presence of the extension portion 33a prevents direct contact with the elongated portion 12a even if the positive electrode exposed portion 31 falls over significantly, thereby effectively preventing the occurrence of a short circuit.

[0028] The details of the structure of the joint between the positive electrode exposed portion 31 and the positive electrode current collector plate 19 will be described later.

[0029] The sealing body 17 is composed of a gasket 28 and a terminal cap 27. The terminal cap 27 is made of metal. The terminal cap 27 has a disk-shaped base 27a and a protrusion 27b, and the protrusion 27b includes, for example, a cylindrical protrusion. The base 27a of the terminal cap 27 may be connected to the upper surface of the base 19a of the positive current collector plate 19 via a strip-shaped lead 55. Welding can be used as a method for joining the lead 55 to the base 27a and the base 19a. For example, the terminal cap 27 and the positive current collector plate 19 are electrically connected by laser welding.

[0030] The outer can 16 is generally made of a metal primarily composed of iron, such as nickel-plated iron. The outer can 16 may also be made of a metal primarily composed of aluminum or the like. The outer can 16 has a cylindrical portion 65 and a bottom plate portion 68. The cylindrical portion 65 includes an annular groove portion 35 and an annular shoulder portion 38. The groove portion 35 is formed by spinning a portion of the cylindrical portion 65 to recess it radially inward around the entire circumferential direction. The shoulder portion 38 is formed when the upper end of the cylindrical portion 65 is bent radially inward and crimped onto the peripheral edge portion 48 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 65.

[0031] The sealing body 17 is fixed to the outer can 16 by crimping the peripheral edge 48 of the terminal cap 27 between the shoulder 38 and the groove 35 via the gasket 28. The gasket 28 serves as a sealant to maintain airtightness inside the battery and as an insulator to insulate the outer can 16 from the sealing body 17. The gasket 28 is made of, for example, polyolefin. The groove 35 is formed at a position a predetermined distance from the upper end of the outer can 16. The predetermined length is, for example, a length equivalent to 1 to 20% of the axial length of the outer can 16. The gasket 28 is compressed by the shoulder 38 and the groove 35. The gasket 28 has a protrusion 28a that protrudes radially inward from between the shoulder 38 and the sealing body 17.

[0032] A thin, easily breakable portion 69 is provided on the bottom plate portion 68. The easily breakable portion 69 is provided, for example, by stamping a circle or a C-shape on the underside of the bottom plate portion 68. When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises to a predetermined pressure, the easily breakable portion 69 breaks and gas is released from the bottom plate portion 68. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby increasing the safety of the battery 10.

[0033] The battery 10 further includes an annular metal plate 80 and an annular insulating plate 82 made of an insulating material. The metal plate 80 extends in a generally radial direction. The metal plate 80 is joined to the upper surface of the shoulder portion 38. The terminal cap 27, to which the positive electrode exposed portion 31 is electrically connected via the positive electrode current collector plate 19, serves as a positive electrode terminal, and the metal plate 80, to which the negative electrode exposed portion 41 is electrically connected via the lower current collector plate 18 and the outer can 16, serves as a negative electrode terminal. The metal plate 80 is electrically connected to a current collector plate (not shown) that connects multiple batteries 10 in series or parallel, for example, using a tongue portion (lead) of the current collector plate. This increases the area that can be joined to the current collector plate, making it easier to electrically connect multiple batteries 10 to the current collector plate.

[0034] The insulating plate 82 is interposed between the metal plate 80 and the sealing body 17 to insulate the metal plate 80 from the sealing body 17. The outer peripheral edge of the insulating plate 82 on the radially outer side may be located above the protruding portion 28a of the gasket 28 and may be in contact with the gasket 28. In this manner, the metal plate 80 is insulated from the sealing body 17 by the gasket 28 and the insulating plate 82. The periphery of the hollow portion of the insulating plate 82 includes a cylindrical portion 83 that covers the outer peripheral surface of the protruding portion 27b of the terminal cap 27. The cylindrical portion 83 is connected to the radially inner end of the plate-shaped base of the insulating plate 82. Note that the battery does not necessarily have to have a metal plate and an insulating plate.

[0035] "Configuration of Joint Portion Between Positive Electrode and Upper Current Collector Plate (Positive Current Collector Plate)" FIG. 2 is an enlarged cross-sectional view of the joint portion between the positive electrode 11 and a positive current collector plate 19 (positive current collector plate).

[0036] The positive electrode 11 is composed of a positive electrode core 30 and a positive electrode mixture layer 32 coated on both side surfaces thereof. The positive electrode mixture layer 32 is not formed on the upper end portion in the width direction of the positive electrode 11, and the positive electrode core 30 is exposed to form a positive electrode exposed portion 31 that constitutes the tip portion. The tip portion of the positive electrode exposed portion 31 of this positive electrode core 30 has a bent portion that bends radially from the inside (center side) to the outside, and the upper side of the tip portion is joined to the positive electrode current collector plate 19.

[0037] Furthermore, a protective layer 33 is provided on the first and second surfaces of the positive electrode exposed portion 31 from the upper end of the positive electrode mixture layer 32 upward. This protective layer 33 is made of an insulating material having a higher melting point than the positive electrode core 30. The protective layer 33 is made of, for example, alumina (aluminum oxide (Al ２ O ３ )) or the like can be used. Inorganic oxides such as silica, zirconia, and titania can also be used. The protective layer 33 on the second surface may be omitted. The protective layer 33 on the first surface side does not necessarily have to extend continuously from the boundary between the positive electrode mixture layer 32 and the positive electrode exposed portion 31 to the extension portion 33a. The protective layer 33 on the first surface may extend discontinuously.

[0038] In particular, at the portion of the positive electrode exposed portion 31 that is joined to the positive electrode current collector plate 19, the extension portion 33 a of the protective layer 33 provided on the first surface side branches off from the positive electrode exposed portion 31, separating them. The branched extension portion 33 a extends while remaining bent, independently of the positive electrode exposed portion 31. By forming the protective layer 33 on the first surface as close as possible (as long as possible) to the tip that extends from the positive electrode mixture layer on the first surface, after the positive electrode exposed portion 31 is joined to the positive electrode current collector plate 19, the branched extension portion 33 a can cover the joint (solidified portion) between the positive electrode exposed portion 31 and the positive electrode current collector plate 19 and the underside of the positive electrode current collector plate 19.

[0039] The protective layer 33 may be formed by applying a paste of particles such as alumina with a binder such as a water-insoluble polymer. In this embodiment, a relatively small amount of binder is used. For example, the mass ratio of the binder to the mass of the particles may be 20%, 10%, 5% or less.

[0040] 5 is a schematic diagram showing the state of the joint between the tip portion of the positive electrode exposed portion 31 of the positive electrode core 30 and the positive electrode current collector plate 19. In this way, the tip portion of the positive electrode exposed portion 31 is integrated with the positive electrode current collector plate 19. That is, by irradiating the positive electrode current collector plate 19 with a laser, the positive electrode current collector plate 19 and the positive electrode exposed portion 31 in contact therewith are melted and integrated.

[0041] "Bending" A bending process is performed on the wound electrode body 14. For example, as shown in Fig. 6, a jig with a curved lower surface 95a is moved while being pressed against the tip of the positive electrode exposed portion 31. As a result, the portion of the positive electrode exposed portion 31 on which the protective layer 33 is formed that is pressed by the jig 95 is bent.

[0042] Furthermore, after such bending processing has been performed, the positive current collector plate 19 is pressed against the tip of the bent positive electrode exposed portion 31, and a laser is irradiated onto the positive current collector plate 19. In this example, the laser is in a line shape corresponding to the width of the positive current collector plate 19, and this is moved in the length direction of the positive current collector plate 19, i.e., in the radial direction of the electrode body 14.

[0043] As a result, the portion of the positive current collector plate 19 irradiated with the laser heats up and melts. The positive electrode exposed portion 31 in contact with the positive current collector plate 19 also melts, and the two melt together and become one. At this time, the molten material of the positive electrode exposed portion 31 is attracted to the molten material of the positive current collector plate 19, and the direction of extension from the extension portion 33a of the protective layer 33 changes, and a part of the positive electrode exposed portion 31 branches off from the extension portion 33a.

[0044] Here, the protective layer 33 is made of a high-melting-point material such as alumina. Therefore, although the binder may be partially burned away, the protective layer 33 does not melt. Therefore, the protective layer 33 remains as it is, separated from the positive electrode exposed portion 31.

[0045] Therefore, the presence of the protective layer 33 between the positive electrode substrate 30 and the negative electrode can effectively prevent short circuits between the positive electrode and the negative electrode.

[0046] "Bending Direction" The bending of the upper end of the positive electrode exposed portion 31 can be performed by moving a jig 95 from the center of winding toward the outer periphery, as shown in FIG. 6, for example. This causes the positive electrode exposed portion 31 and the extension portion 33a to be bent and shaped to a width corresponding to the width of the jig 95 (the length perpendicular to the direction of movement). At this time, the outer peripheral surface of the positive electrode exposed portion 31 becomes the first surface. In other words, recessed grooves 97 are formed in the electrode body 14 by four radial barrel-shaped bending processes. Note that the positive electrode exposed portion of the present disclosure may be bent toward the inner periphery of the wound electrode body by moving the jig from the outer periphery toward the inner periphery. At this time, the inner peripheral surface of the positive electrode exposed portion becomes the first surface.

[0047] After the bending is completed, the positive current collector plates 19 are pressed into the grooves 97 from above and laser-welded. Fig. 8 is a schematic diagram showing the state after the upper current collector plates 19 have been laser-welded, as viewed from above. Four upper current collector plates 19 are attached to the grooves 97.

[0048] When the exposed positive electrode portion 31 of the positive electrode core 30 of the wound electrode body 14 is bent from the outer periphery toward the center, the outer periphery, which has a lower curvature, is prone to collapse, and as the curvature increases toward the inside, it becomes more tense, resulting in a difference in the degree of collapse. If a load is applied during laser welding to the current collector plate in a state in which there is a difference in the degree of collapse between the inside and outside, the foil on the outer periphery is prone to buckling from the base, and the distance to the stretched negative electrode becomes closer, posing a risk of short circuit.

[0049] By bending the inner periphery first (applying a load with a jig that can cause the inner periphery to bend), the positive electrode core 30 can be bent uniformly toward the outer periphery. By maintaining a uniformly bent shape on both the inner and outer peripheries, when welding the positive electrode core 30 to the positive current collector plate 19, even if a load is applied to the positive electrode core 30, it will not buckle from its base, and the distance from the extended negative electrode 12 can be maintained, thereby reducing the risk of short circuit.

[0050] "Arrangement of Protective Layer" FIGS. 9(a), 9(b), and 10 are diagrams showing modified examples of the protective layer 33. In FIG. 9(a), the protective layer 33 is provided only on one side of the positive electrode core 30, which is the inner side in the bending direction. In FIG. 9(b), the protective layer 33 on the inner side of the bending direction of the positive electrode core 30 is made slightly shorter than the positive electrode core 30, and a region of the positive electrode exposed portion is formed on the tip side of the positive electrode exposed portion relative to the region where the protective layer is formed on the second surface. This configuration allows the second surface of the positive electrode exposed portion to be efficiently insulated from the surroundings while leaving a bonding region with the positive electrode current collector plate on the second surface. In FIG. 10, the protective layer 33 on the inner side of the bending direction of the positive electrode core 30 is striped in the vertical direction (width direction, axial direction). In this way, by providing regions with a protective layer and regions without a protective layer (or regions where the protective layer is thinner) on the first surface or second surface of the positive electrode exposed portion, it is possible to bias the rigidity within the positive electrode exposed portion. By biasing the rigidity, it becomes possible to control the starting point at which the exposed positive electrode portion bends.

[0051] These configurations also effectively prevent short circuits, similar to the above-described embodiment.

[0052] Here, as described above, the electrode body 14 is housed in the outer can 16 in a cylindrically wound state, but the protective layer 33 may be formed before or after winding. In this embodiment, the protective layer 33 is formed before winding. For example, the protective layer 33 can be formed in parallel with the formation of the positive electrode mixture layer 32 on the positive electrode core 30 by coating. Similarly, for the negative electrode 12, the negative electrode mixture layer 42 is coated on the negative electrode core 40. Then, the separator 13 is sandwiched between the positive electrode 11 and the negative electrode 12, and they are wound.

[0053] "Configuration of Joint Portion Between Positive Electrode and Upper Current Collector Plate (Positive Current Collector Plate)" FIG. 11 is an enlarged cross-sectional view of the joint portion between the positive electrode 11 and the upper current collector plate 19 (positive current collector plate).

[0054] The positive electrode 11 is composed of a positive electrode core 30 and a positive electrode mixture layer 32 coated on both side surfaces thereof. The upper end portion in the width direction (axial direction) of the positive electrode 11 is free of the positive electrode mixture layer 32, forming a positive electrode exposed portion 31 where the positive electrode core 30 is exposed. The tip portion of this positive electrode exposed portion 31 has a bent portion (first bent portion) that bends from the inside (center side) to the outside, i.e., toward the outside in the radial direction, and the upper side of this tip portion is joined to the upper current collector plate 19.

[0055] Furthermore, a protective layer 33 is provided on the first and second surfaces of the positive electrode exposed portion 31 at a predetermined distance (approximately half the distance from the upper current collector plate 19) from the upper end of the positive electrode mixture layer 32. This protective layer 33 is made of an insulating material that is a water-insoluble polymer mixed with a filler. The inorganic filler is alumina (aluminum oxide (Al ２ O ３ )), inorganic oxides such as silica, zirconia, titania, etc. In addition, to prevent the protective layer 33 from melting during laser welding of the positive electrode substrate 30 and the upper current collector plate 19, it is preferable that the protective layer 33 has a melting point higher than that of the positive electrode substrate 30.

[0056] "Bending" A bending process is performed on the wound electrode body 14. For example, as shown in Fig. 12, a jig 95 with a curved lower surface 95a is moved while being pressed against the tip of the positive electrode exposed portion 31. As a result, the portion of the positive electrode exposed portion 31 on which the protective layer 33 is formed that is pressed by the jig 95 is bent.

[0057] Furthermore, after such bending processing has been performed, a laser is irradiated onto the upper current collector 19 while the upper current collector 19 is pressed against the tip of the bent positive electrode exposed portion 31. In this example, the laser is in a line shape corresponding to the width of the upper current collector 19, and this is moved in the length direction of the upper current collector 19, i.e., in the radial direction of the electrode body 14.

[0058] As a result, the portion of the upper current collecting plate 19 irradiated with the laser becomes hot and melts. The positive electrode exposed portion 31 in contact with the upper current collecting plate 19 also melts, and the two fuse together and become one body.

[0059] The upper end of the positive electrode exposed portion 31 can be bent in this manner by moving a jig 95 from the center of winding toward the outer periphery, as shown in FIG. 13, for example.

[0060] As a result, the positive electrode exposed portion 31 is bent and formed to a size corresponding to the width (length in the direction perpendicular to the direction of movement) of the jig 95. In other words, the electrode body 14 is bent in four radial directions to form grooves 97 that are recessed compared to the surrounding area.

[0061] After the bending is completed, the upper current collecting plates 19 are pressed against the grooves 97 from above and laser-welded. Fig. 14 is a schematic diagram showing the state after the upper current collecting plates 19 have been laser-welded, as viewed from above. Four upper current collecting plates 19 are attached to the grooves 97.

[0062] "Bending direction" Here, when the exposed portion 31 of the positive electrode substrate 30 of the wound electrode body 14 is bent from the outer periphery toward the center, the outer periphery, which has a low curvature, is prone to collapse, and as the curvature increases toward the inside, it becomes more tense, resulting in a difference in the direction of collapse. If a load is applied when laser welding to the current collector plate in a state where there is a difference in the way the inner and outer sides collapse, the foil on the outer periphery is prone to buckling from the base, and the distance to the stretched negative electrode becomes closer, which poses a risk of short circuit.

[0063] In this embodiment, by bending the inner periphery with the highest curvature first, the positive electrode core 30 can be uniformly bent toward the outer periphery. Maintaining a uniformly bent shape on both the inner and outer peripheries of the positive electrode core 30 prevents buckling at its base when welding it to the upper current collector plate 19, even when a load is applied to the positive electrode core 30. This maintains a distance from the extended negative electrode 12, thereby reducing the risk of short-circuiting. Furthermore, having a second bent portion bent inward toward the mixture layer in the direction in which the positive electrode exposed portion extends from the first bent portion bent outward allows for more uniform contact with the current collector plate. Furthermore, a protective layer is formed on the mixture layer side in the direction in which the positive electrode exposed portion extends from the second bent portion, thereby increasing the rigidity of the region in the positive electrode exposed portion where the protective layer is formed. This increased rigidity makes it easier to position the starting point of the second bent portion further upward (outside the electrode body) in the portion of the positive electrode exposed portion where the protective layer is not formed. Therefore, it is preferable that the protective layer extend axially outward beyond the end of the negative electrode. Furthermore, if the plurality of first bent portions aligned in the radial direction in the cross section overlap each other, the reliability of the welding is improved.

[0064] "Extension of Protective Layer" FIG. 15 shows the state during laser welding in another embodiment, and FIG. 16 is a diagram showing the overall structure of a battery when this structure is adopted.

[0065] An extension 33 a is formed below the bent portion on the tip side of the positive electrode exposed portion 31 , where a part of the protective layer 33 extends.

[0066] In this way, at the portion of the positive electrode exposed portion 31 joined to the upper current collecting plate 19, the extension portion 33a of the protective layer 33 branches off from the first surface of the positive electrode exposed portion 31, and the two are spaced apart. This is because the extension portion 33a does not melt during laser welding, for example.

[0067] In this way, the presence of the extension 33a can more reliably prevent short circuits between adjacent negative electrodes 12. In this example, the protective layer 33 has a higher melting point than the positive electrode substrate 30.

[0068] REFERENCE SIGNS LIST 10 battery, 11 positive electrode, 12 negative electrode, 12a extension portion, 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18 lower current collector plate, 19 positive electrode current collector plate (upper current collector), 27 terminal cap, 28 gasket, 30 positive electrode core, 31 positive electrode exposed portion (tip portion), 32 positive electrode mixture layer, 33 protective layer (first protective layer, second protective layer), 33a extension portion, 35 groove portion, 37 spacer, 38 shoulder portion, 40 negative electrode core, 41 negative electrode exposed portion, 42 negative electrode mixture layer, 48 peripheral portion, 55 lead, 65 cylindrical portion, 68 bottom plate portion, 69 easily breakable portion, 80 metal plate, 82 insulating plate, 83 cylindrical portion, 95 Jig, 95a underside, 97 groove portion.

Claims

1. An energy storage device comprising: an electrode assembly in which a first electrode and a second electrode are stacked in a first direction with a separator between them; an exterior body that houses the electrode assembly; and a first current collecting plate connected to the first electrode, wherein the first electrode has a tip portion that extends from an end of the second electrode in a second direction perpendicular to the first direction, the tip portion being bent in the first direction and connected to the first current collecting plate.

2. An electric storage device as claimed in claim 1, wherein an insulating first protective layer is formed on a first surface on the bent side of the tip of the first electrode, and a part of the first protective layer extends away from the tip at a portion where the tip is connected to the first current collecting plate.

3. The power storage device according to claim 2, wherein the first electrode, the second electrode and the separator are each in the form of a strip, and the first electrode and the second electrode are wound with the separator interposed therebetween.

4. The energy storage device according to claim 2 or 3, wherein the first electrode has a strip-shaped first core and a first mixture layer arranged on the first core, and the second electrode has a strip-shaped second core and a second mixture layer arranged on the second core.

5. The electricity storage device according to claim 4, wherein the first mixture layer is not formed on the tip portion, a first exposed portion is formed where the first core body is exposed, and the first current collecting plate and the first exposed portion are joined.

6. The electricity storage device according to claim 5, wherein an insulating second protective layer is formed on a second surface of the tip portion that is located opposite to the first surface.

7. The energy storage device according to claim 6, wherein in the tip portion, a region in which the second protective layer is formed and a region in which the second protective layer is not formed are arranged side by side in a direction in which the tip portion extends.

8. The energy storage device according to claim 5, wherein the first surface has an area on the first mixture layer side, the area being thinner than the area where the first protective layer is formed, or where the first protective layer is not formed.

9. The electricity storage device according to claim 2, wherein the first protective layer covers a joint between the first current collecting plate and the tip portion.

10. The electricity storage device according to claim 1, wherein the tip portion has a first bent portion bent radially outward, the first bent portion being connected to the first current collecting plate.

11. The energy storage device according to claim 10, wherein the first electrode has a strip-shaped first core and a first mixture layer disposed on the first core, and the second electrode has a strip-shaped second core and a second mixture layer disposed on the second core.

12. The energy storage device as described in claim 11, wherein the first mixture layer is not formed on the tip portion of the first electrode, a first exposed portion is formed where the first core is exposed, and the first current collecting plate and the first exposed portion are joined.

13. The energy storage device according to claim 10 or 11, further comprising a second current collecting plate electrically connected to the second electrode, the second electrode having a tip portion extending beyond an end of the second electrode in the second direction, the tip portion of the second electrode being connected to the second current collecting plate.

14. The energy storage device according to claim 13, wherein the tip portion has a second bent portion bent toward the inner periphery of the electrode body at a position farther from the first current collector plate than the first bent portion in the direction in which the tip portion extends.

15. The electricity storage device according to claim 13, wherein an insulating protective layer is formed on the surface of the tip portion on the side of the first mixture layer in the extending direction of the tip portion.

16. The energy storage device described in claim 15, wherein the tip portion has a second bent portion bent toward the inner circumference of the electrode body at a position farther from the first current collector plate than the first bent portion in the direction in which the tip portion extends, and the second bent portion is formed between the first bent portion and the area in which the protective layer is formed in the direction in which the tip portion extends.

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