Power storage device and method for manufacturing power storage device

Abstract

In this power storage device, an end part of a metal foil (40) constituting an electrode and a bottom part of a metal collector plate (17) or a metal exterior can are welded by a plurality of linear welding parts (60a, 60b, 60c, 60d). The length of at least one linear welding part (60d) among the plurality of linear welding parts (60a, 60b, 60c, 60d) is shorter than the lengths of the other linear welding parts (60a, 60b, 60c).

Description

Power Storage Device and Method for Manufacturing Power Storage Device

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

[0002] Conventionally, as described in Patent Document 1, in a secondary battery which is a power storage device, it has been described that a metal foil constituting a negative electrode and a plate-shaped current collector terminal made of the same material as the metal foil are joined by resistance welding. Resistance welding is a welding method that uses Joule heat generated by sandwiching members to be joined between a pair of electrodes and passing current between the electrodes.

[0003] Japanese Patent No. 5949535

[0004] Incidentally, there are cases where an end portion of a metal foil constituting an electrode of a power storage device and a metal current collector plate are welded at a plurality of linear welds. For welding in this case, from the perspective of improving welding quality, it is conceivable to use laser welding in which an irradiation portion of a spot-shaped laser beam is scanned in a linear shape. In addition, from the perspective of improving welding quality and shortening welding time, it is also conceivable to perform line laser welding in which a linear laser beam is irradiated to weld the metal foil and the current collector plate.

[0005] However, when forming a plurality of linear welds by scanning the irradiation portion of a spot-shaped laser beam in a linear shape, scanning is performed while melting metal at the irradiation portion, so there is a limit to the reduction of scanning time because metal melting time is required. For this reason, since the laser process takes time, there is room for improvement in terms of reducing the manufacturing cost of the power storage device.

[0006] In addition, when forming a plurality of linear welds by line laser welding, the larger the total length of the linear welds is, the higher the original output of the laser beam output from the oscillator is, which may lead to an increase in the cost of the oscillator. This also leaves room for improvement in terms of reducing the manufacturing cost of the power storage device. In addition, it is conceivable that the end portion of the metal foil is directly welded to the bottom of an outer can through a plurality of welds without interposing a current collector plate, and the same inconvenience as described above occurs in this case as well.

[0007] The object of the present invention is to reduce the manufacturing cost of an energy storage device when welding a metal foil constituting an electrode to a current collector plate or the bottom of a metal outer casing using multiple linear welds, in an energy storage device and a method for manufacturing an energy storage device.

[0008] The energy storage device according to this disclosure is characterized in that the ends of the metal foil constituting the electrodes and the bottom of a metal current collector plate or a metal outer casing are welded together by a plurality of linear welds, and the length of at least one of the plurality of linear welds is shorter than the length of the other linear welds.

[0009] The method for manufacturing an energy storage device according to this disclosure includes the steps of: arranging the ends of metal foil constituting electrodes in an axial position; bending the tips of the ends; bringing the bottom of a current collector plate or a metal outer casing into contact with the bent metal foil; and welding the current collector plate or bottom and the metal foil by irradiating the surface of the current collector plate or bottom with a plurality of linear laser beams, wherein the welding step involves simultaneously irradiating the surface of the current collector plate or bottom with a plurality of laser beams, each with at least one linear laser beam shorter in length than the other linear laser beams, to weld the current collector plate or bottom and the metal foil.

[0010] According to the energy storage device and method for manufacturing the energy storage device described herein, the manufacturing cost of the energy storage device can be reduced when welding the metal foil constituting the electrodes to the current collector plate or the bottom of the outer casing with multiple linear welds.

[0011] This is an axial cross-sectional view of a power storage device according to an embodiment of this disclosure. This is a perspective view showing a portion of the electrode body of the power storage device of the embodiment unfolded before bending at both axial ends. This is an enlarged view corresponding to part A in Figure 1 before joining the negative electrode metal foil and the negative electrode current collector plate in the electrode body of the power storage device of the embodiment. This is a view from below, with the electrode body and negative electrode current collector plate removed from Figure 1. This is a schematic diagram from Figure 4 showing the arrangement relationship between the electrode body and a plurality of welded parts, with the shape of the negative electrode current collector plate omitted. This is a flowchart of a method for manufacturing the power storage device of the embodiment. This is a schematic diagram of a laser welding apparatus used in the method for manufacturing the power storage device of the embodiment, with the branched laser beam that branches along a part of the linear direction omitted. This is a schematic diagram showing a cross-section of the state in which the negative electrode current collector plate and the negative electrode metal foil are welded by a linear welding beam of the laser welding apparatus in the embodiment. This is a diagram corresponding to Figure 7 in another example of a power storage device of the embodiment. This is a diagram corresponding to Figure 7 in another example of a power storage device of the embodiment. This is a diagram corresponding to Figure 7 in another example of a power storage device of the embodiment. This figure corresponds to Figure 7 in another example of an energy storage device according to the embodiment.

[0012] Hereinafter, embodiments of the energy storage device and the method for manufacturing the energy storage device according to this disclosure will be described in detail with reference to the drawings. In this disclosure, a cylindrical non-aqueous electrolyte secondary battery will be described as the energy storage device, but the energy storage device according to this disclosure is not limited to this, and any device having a configuration in which metal foil constituting electrodes and a current collector plate are welded together may be used, and the energy storage device may be a capacitor.

[0013] In the following embodiments, the same components are denoted by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios such as length, width, and height of each component do not necessarily match between different drawings. In this specification, the axial opening side of the outer casing 15 of the cylindrical secondary battery 10, which is an energy storage device, is referred to as "upper," and the axial bottom 15a side is referred to as "lower." That is, the bottom 15a of the outer casing 15 is described as the lower end. The energy storage devices of this disclosure are not necessarily limited to those in which the bottom of the outer casing is located vertically below the opening in the operating state. For example, the bottom of the outer casing may be configured to be vertically above the opening of the outer casing in the operating state.

[0014] Figure 1 is an axial cross-sectional view of the secondary battery 10 of the embodiment. Figure 2 is a perspective view showing a portion of the electrode body 14 of the secondary battery 10 of the embodiment unfolded before bending at both axial ends.

[0015] As shown in Figures 1 to 3, the secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), and an outer casing 15 and a sealing body 16, which are metal cans. The wound electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, with the positive electrode 11 and the negative electrode 12 wound in a spiral shape via the separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all in the shape of a roughly rectangular, elongated strip. The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0016] In the electrode body 14, as shown in Figure 2, the positive electrode 11 protrudes above the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes below the positive electrode 11 and the separator 13.

[0017] As shown in Figure 2, the positive electrode 11 has an uncoated positive electrode portion 34 in which the positive electrode metal foil 30 is exposed without a positive electrode mixture layer 32. The uncoated positive electrode portion 34 is located at the upper end, which is one end in the winding axis direction (hereinafter sometimes referred to as the axis direction) from the winding start end to the winding end in the longitudinal direction of the electrode plate of the positive electrode 11. The longitudinal direction of the electrode plate is the direction corresponding to the winding direction in the wound state of the positive electrode 11 or negative electrode 12, and is the longitudinal direction of the elongated rectangle when the positive electrode 11 or negative electrode 12 is viewed in the thickness direction when the positive electrode 11 or negative electrode 12 is unfolded along a plane.

[0018] The negative electrode 12 has an uncoated negative electrode portion 44 in which the negative electrode metal foil 40 (Figure 2) is exposed without a negative electrode mixture layer 42 (Figure 2). The uncoated negative electrode portion 44 is located at the lower end, which is the other end in the axial direction, from the beginning end to the end end in the longitudinal direction of the electrode plate of the negative electrode 12. Therefore, the upper end in the axial direction of the electrode body 14 is composed of the uncoated positive electrode portion 34, and the lower end in the axial direction of the electrode body 14 is composed of the uncoated negative electrode portion 44.

[0019] The non-aqueous electrolyte has ionic conductivity (e.g., lithium ion conductivity). The non-aqueous electrolyte comprises 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 (non-aqueous electrolyte solution), but may also be a solid electrolyte using a gel-like polymer or the like. The secondary battery 10 is preferably a lithium-ion battery. The electrolyte salt may be, for example, LiBF ４ LiPF ６ Lithium salts such as the above are used. Non-aqueous solvents include, for example, esters such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and methyl propionate (MP), as well as ethers, nitriles, amides, and mixed solvents of two or more of these. The non-aqueous solvent may contain halogen-substituted products in which at least some of the hydrogen atoms of these solvents are replaced with halogen atoms such as fluorine.

[0020] Examples of halogen-substituted compounds include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated linear carbonates, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP). In terms of suppressing the deterioration of the charge-discharge cycle characteristics of non-aqueous electrolyte secondary batteries or improving the input characteristics, the non-aqueous electrolyte preferably contains 5% by mass or more of FEC relative to the mass of the non-aqueous electrolyte, and more preferably contains 5% to 15% by mass of FEC.

[0021] As solid electrolytes, for example, solid or gel-like polymer electrolytes, inorganic solid electrolytes, etc., are used. Polymer electrolytes include, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As matrix polymers, for example, polymer materials that absorb non-aqueous solvents and gel are used. As polymer materials, for example, fluororesins, acrylic resins, polyether resins, etc., are used. As inorganic solid electrolytes, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.) are used.

[0022] The positive electrode 11 has a positive electrode metal foil 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode metal foil 30. The positive electrode metal foil 30 is a metal foil that is stable in the potential range of the positive electrode 11, such as aluminum or an aluminum alloy, but a film with the metal arranged on its surface may be used instead of the positive electrode metal foil 30. The thickness of the positive electrode metal foil 30 is, for example, 10 μm or more and 30 μm or less. The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode metal foil 30, drying the coating film, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode metal foil 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode metal foil 30. The thickness of the positive electrode mixture layer 32 is, for example, 10 μm to 150 μm on one side of the positive electrode metal foil 30.

[0023] 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. A preferred example of a lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0024] Examples of conductive agents included in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binders included 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 carboxymethylcellulose (CMC) or its salts, polyethylene oxide (PEO), etc.

[0025] The negative electrode 12 has a negative electrode metal foil 40 and a negative electrode mixture layer 42 formed on both sides of the negative electrode metal foil 40. The negative electrode metal foil 40 is made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy. The thickness of the negative electrode metal foil 40 is, for example, 5 μm to 30 μm. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be manufactured, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode metal foil 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode metal foil 40. The negative electrode mixture layer 42 may also be formed on only one side of the negative electrode metal foil 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm to 150 μm on one side of the negative electrode metal foil 40.

[0026] Generally, carbon materials that reversibly intercalate and release lithium ions are used as the negative electrode active material. Preferred carbon materials are graphite such as natural graphite such as flake graphite, lump graphite, and earthy graphite, and artificial graphite such as lump graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer 42 may contain a silicon (Si) material as the negative electrode active material. In addition, metals other than Si that alloy with lithium, alloys containing such metals, compounds containing such metals, etc., may be used as the negative electrode active material.

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

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

[0029] As shown in Figure 1, the secondary battery 10 has a metal negative electrode current collector plate 17 on the axially lower side of the electrode body 14. The negative electrode current collector plate 17 is made of, for example, nickel-plated iron, nickel, or a nickel alloy. In this example, the melting point of the negative electrode current collector plate 17 is higher than the melting point of the negative electrode metal foil 40.

[0030] The negative electrode current collector plate 17 can be radial, such as in a cross shape, or disc shape, but the following description will explain the case where it is radial with multiple arms extending in the radial direction. The unpainted negative electrode portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector plate 17, and the negative electrode current collector plate 17 is joined to the inner surface of the bottom plate of the outer casing 15. The outer casing 15 to which the unpainted negative electrode portion 44 is electrically connected via the negative electrode current collector plate 17 becomes the negative electrode terminal.

[0031] The secondary battery 10 has a positive electrode current collector plate 18 located inside the outer casing 15. The positive electrode current collector plate 18 is a metal disc made of aluminum or an aluminum alloy, etc., located above the electrode body 14 in the axial direction. When the positive electrode current collector plate 18 is disc-shaped, a through hole is formed to allow gas generated in the electrode body 14 to escape upward. The unpainted positive electrode portion 34 protruding from the electrode body 14 is joined to the positive electrode current collector plate 18 in a state where it is bent inward in at least a part of its circumferential direction. As a result, the positive electrode current collector plate 18 is fixed to the upper end of the electrode body 14 in the axial direction and electrically connected. Alternatively, it may be joined to multiple unpainted positive electrode portions provided at multiple locations on the upper part of the positive electrode 11, and the electrode body 14 may be connected to the positive electrode current collector plate via multiple positive electrode leads protruding from the upper end of the positive electrode 11. The secondary battery 10 has an annular insulating plate 19 on the above the positive electrode current collector plate 18 in the axial direction.

[0032] One end of the positive electrode connection lead 20 is joined to the upper surface of the positive electrode current collector plate 18 by welding or the like. The positive electrode connection lead 20 extends through a through-hole in the insulating plate 19 towards the sealing body 16, and the other end of the positive electrode connection lead 20 is connected to the lower surface of the internal terminal plate 22 of the sealing body 16 by welding or the like. The cap 26 that forms the top plate of the sealing body 16 is electrically connected to the internal terminal plate 22. As a result, the positive electrode current collector plate 18 is electrically connected to the cap 26, and the cap 26 becomes the positive electrode terminal. The positive electrode connection lead 20 is a conductive member made of a metal mainly composed of aluminum.

[0033] The secondary battery 10 further includes a resin gasket 27 positioned between the outer casing 15 and the sealing body 16. The gasket 27 is sandwiched between the outer casing 15 and the sealing body 16, insulating the sealing body 16 from the outer casing 15. The gasket 27 serves as a sealing material to maintain airtightness inside the battery and as an insulating material to insulate the outer casing 15 from the sealing body 16. The outer casing 15 has an annular groove 21 in a part of its axial direction.

[0034] The grooved portion 21 can be formed, for example, by spinning a part of the side surface radially inward to create a recess in the radial direction. The outer casing 15 has a bottomed cylindrical portion including the grooved portion 21 and an annular shoulder portion. The bottomed cylindrical portion houses the electrode body 14 and the non-aqueous electrolyte, and the shoulder portion is bent radially inward from the opening end of the bottomed cylindrical portion and extends inward. The shoulder portion is formed when the upper end of the outer casing 15 is bent inward and crimped to the periphery of the sealing body 16. The sealing body 16 is crimped and fixed to the outer casing 15 via a gasket 27 between the shoulder portion and the grooved portion 21. In this way, the internal space of the secondary battery 10 is sealed.

[0035] The sealing body 16 has a structure in which an internal terminal plate 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 16 has, for example, a disc shape or a ring shape, and each component except the insulating member 24 is electrically connected to one another. The internal terminal plate 22 has at least one through hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, and the insulating member 24 is interposed between their respective peripheral edges.

[0036] When the secondary battery 10 overheats abnormally and its internal pressure rises to a predetermined value, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 upward towards the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further and reaches a predetermined value, the upper valve body 25 ruptures, and gas is discharged from the through-hole 26a of the cap 26. This gas discharge prevents the secondary battery 10 from deforming or rupturing due to an excessive rise in internal pressure, thereby improving the safety of the secondary battery 10. It also suppresses the impact on adjacent components (not shown) due to deformation or rupture of the secondary battery 10. Such a gas discharge mechanism may be provided at the bottom 15a of the outer casing 15, which is on the negative electrode side.

[0037] Next, referring to Figures 1 to 5, the surrounding configuration of the joint between the negative electrode metal foil 40 and the negative electrode current collector plate 17 at the bottom of the secondary battery 10 will be explained. Figure 3 is an enlarged view corresponding to part A in Figure 1, before joining the negative electrode metal foil 40 and the negative electrode current collector plate 17 in the electrode body 14. Figure 4 is a view from below, with the electrode body 14 and the negative electrode current collector plate 17 removed from Figure 1. Figure 5 is a schematic diagram showing the arrangement relationship between the electrode body 14 and the multiple welded parts 60a, 60b, 60c, and 60d, with the shape of the negative electrode current collector plate 17 omitted from Figure 4.

[0038] As shown in Figure 3, the negative electrode 12 has a laminated portion 45 in which a negative electrode mixture layer 42 is laminated on both sides of the negative electrode metal foil 40, and an uncoated negative electrode portion 44 provided at the end located on the lower side (one axial side) of the laminated portion 45, on the negative electrode current collector plate 17 side. The uncoated negative electrode portion 44 has an axial extension portion 47 extending substantially parallel to the axial direction of the electrode body 14, and a bent portion 48 bent inward from the lower end of the axial extension portion 47. The bent portion 48 is welded to the upper surface of the negative electrode current collector plate 17. As a result, the uncoated negative electrode portion 44 is provided at the lower axial end of the negative electrode 12 on the negative electrode current collector plate 17 side, and the negative electrode mixture layer is not laminated thereon. In this case, the bent portion 48 may be a portion in which only a part is bent inward, such as a cross-shaped portion that overlaps with the negative electrode current collector plate 17 when the uncoated negative electrode portion 44 is viewed from the axial outside. Furthermore, the bent portion 48 may be a portion that is continuously bent inward along its entire circumference when viewed from one axial side of the tip side of the uncoated negative electrode portion 44, or a portion that is continuously bent inward along its entire circumference so as to be arranged in a spiral from the outer end to the inner end.

[0039] In this example, the bent portion 48 of the uncoated negative electrode portion 44 is welded to the negative electrode current collector plate 17 by multiple linear welds 60a, 60b, 60c, and 60d. Furthermore, of the multiple linear welds 60a, 60b, 60c, and 60d, at least one linear weld 60d is shorter in length than the other linear welds 60a, 60b, and 60c. This reduces the manufacturing cost of the secondary battery 10 when the negative electrode metal foil 40 and the negative electrode current collector plate 17 are welded by multiple linear welds 60a, 60b, 60c, and 60d, as described later.

[0040] More specifically, among the lower end portion of the negative electrode metal foil 40, a plurality of different portions extending from a plurality of positions differing in the winding direction of the electrode body 14 are welded to the negative electrode current collector plate 17. The negative electrode current collector plate 17 may be made of the same metal as the negative electrode metal foil 40, but is preferably made of a metal different from that of the negative electrode metal foil 40. Hereinafter, a case where the negative electrode metal foil 40 is a copper foil and the negative electrode current collector plate 17 is formed of a nickel-plated iron plate will be described, but the negative electrode current collector plate 17 and the negative electrode metal foil 40 may be made of different metals in another combination other than the combination of a copper foil and a nickel-plated iron plate.

[0041] The negative electrode metal foil 40, in a wound state, constitutes a cylindrical electrode body 14, and a wound end portion of the negative electrode metal foil 40 is provided at an axial end portion of the electrode body 14.

[0042] As shown in Fig. 4, the negative electrode current collector plate 17 has a plate shape having a plurality of arm portions 17a extending outward from the center along the radial direction when viewed from below. Hereinafter, the description will focus on a case where the negative electrode current collector plate 17 is formed in a cross shape having four arm portions 17a, but the number of arm portions 17a may be three, or five or more. The plurality of arm portions 17a are connected by a flat plate-shaped central plate portion 17b provided at the center. The plurality of arm portions 17a radially extend from four positions on the outer circumference of the central plate portion 17b that differ in phase by 90 degrees. Further, in each arm portion 17a, a protruding portion 17c that protrudes toward the electrode body 14 side and extends in the radial direction is formed from the root end to the tip end of the arm portion 17a.

[0043] For example, the protruding portion 17c has a rectangular cross-sectional shape orthogonal to the longitudinal direction. The protruding portion 17c is joined to the uncoated negative electrode portion 44 in a state of being pressed against the uncoated negative electrode portion 44 bent toward the inner peripheral side of the electrode body 14. For example, in a state where the protruding portion 17c is pressed against the uncoated negative electrode portion 44, a laser beam, which is laser light, is irradiated toward the bottom of the groove forming the protruding portion 17c from the side of the arm portion 17a opposite to the uncoated negative electrode portion 44. Thereby, the uncoated negative electrode portion 44 and the protruding portion 17c are joined by laser welding.

[0044] A distal end plate portion 17d having a larger circumferential width than the intermediate portion of the arm portion 17a is provided at the radially outer end of each arm portion 17a. In the illustrated example, the distal end plate portion 17d is formed in a trapezoidal shape in which the circumferential length of the distal end is larger than the circumferential length of the root side end, but the shape is not limited thereto, and various shapes can be employed. The central plate portion 17b is joined to the bottom portion 15a of the outer can 15.

[0045] When joining the central plate portion 17b and the bottom portion 15b, for example, laser welding is performed to join the central plate portion 17b and the bottom portion 15b by irradiating a laser beam from the outer side of the bottom portion 15b in a state where the lower surface of the central plate portion 17b is brought into contact with the inner surface of the bottom portion 15b.

[0046] Thereby, as shown in the schematic diagram of FIG. 5, the negative electrode current collector plate 17 and the negative electrode metal foil 40 are welded at four linear welded portions 60a, 60b, 60c, and 60d. Hereinafter, the plurality of welded portions 60a, 60b, 60c, and 60d may be collectively referred to as the welded portion 60. The four linear welded portions 60 are divided in the circumferential direction of the electrode body 14 on the outer surface of the negative electrode current collector plate 17 overlapping the axial end portion of the electrode body 14, and are respectively arranged along the substantially radial direction of the electrode body 14. Therefore, the linear welded portion 60 is substantially along the longitudinal direction of the arm portion 17a. Further, the plurality of welded portions 60 are arranged substantially uniformly in the circumferential direction of the electrode body 14.

[0047] The welded portion 60 has a current collector plate melted and solidified portion formed by melting and solidifying a part of the negative electrode current collector plate 17, and an intermediate melted and solidified portion formed in a single layer along the longitudinal direction of the welded portion 60 so as to be located between the current collector plate melted and solidified portion and the negative electrode metal foil 40. Here, "single-layered" means a state in which two portions overlap without a gap and are continuous without being divided.

[0048] The intermediate melted and solidified portion has a composition different from that of the negative electrode current collector plate 17. For example, in this example, the negative electrode current collector plate 17 is a nickel-plated iron plate, and the intermediate melted and solidified portion is an alloy containing 80% or more of copper.

[0049] It is preferable that the thickness in the vertical direction of the intermediate melted and solidified portion is substantially constant over at least a predetermined range in the longitudinal direction of the welded portion 60.

[0050] Furthermore, as shown in Figures 4 and 5, the length L2 of one of the four linear welds 60d is shorter than the length L1 of the other three linear welds 60a, 60b, and 60c (L2 < L1). The lengths L1 of the other three linear welds 60a, 60b, and 60c are the same. It is also possible to make the length of a portion of the weld of the other three linear welds 60a, 60b, and 60c different from the length of the other welds of the other three linear welds 60a, 60b, and 60c, for example, by making a portion of the weld of the other three linear welds 60a, 60b, and 60c shorter than the other two linear welds.

[0051] In the examples shown in Figures 4 and 5, the radial inner end of the weld 60d is positioned radially at the same location as the radial inner ends of the other welds 60a, 60b, and 60c. In this specification, the radial direction of a weld refers to the radial direction of the electrode body 14 in the weld. On the other hand, the radial outer end of the weld 60d is positioned radially inward from the radial outer ends of the other welds 60a, 60b, and 60c.

[0052] In the secondary battery 10 described above, the length L2 of at least one of the multiple linear welds 60a, 60b, 60c, and 60d is shorter than the length L1 of the other welds 60a, 60b, and 60c. This reduces the manufacturing cost of the secondary battery 10 when the negative electrode metal foil 40 and the negative electrode current collector plate 17 are welded together by multiple linear welds 60. For example, when multiple linear welds 60 are formed by line laser welding, the total length of the linear welds 60 can be shortened, which reduces the original output of the laser beam output from the laser oscillator. This reduces the increase in the cost of the laser oscillator, and therefore reduces the manufacturing cost of the secondary battery 10.

[0053] Next, a method for manufacturing the secondary battery 10 will be described. Figure 6 is a flowchart showing the manufacturing method of the secondary battery 10 according to an embodiment. As shown in Figure 6, this manufacturing method includes a negative electrode end placement step (S10), a bending step (S12), a negative electrode current collector contact step (S14), and a welding step (S16).

[0054] The negative electrode end placement step involves aligning the end of the negative electrode metal foil 40, which will be the lower end when in use, in the axial direction so that the lower end when in use coincides with the axial position. For example, with the positive electrode 11 and the negative electrode 12 wound around a separator 13 to form an electrode body 14, the end of the wound negative electrode metal foil 40 is placed at one axial end of the electrode body 14 so as to extend in the axial direction, and its axial end is aligned.

[0055] Next, in the bending process, as shown in Figure 3, the leading edge of the negative electrode metal foil 40 is bent in a regular manner. For example, as an example of regularity, the leading edge of the negative electrode metal foil 40 is bent from the outer circumference to the inner circumference only in the cross-shaped portion that overlaps with the negative electrode current collector plate 17 when the unpainted negative electrode portion 44 is viewed from the axial outer side. Alternatively, the bent portion 48 of the negative electrode metal foil 40 may be bent continuously towards the inner circumference over the entire circumference when the leading edge of the unpainted negative electrode portion 44 is viewed from one axial side, or the leading edge of the unpainted negative electrode portion 44 may be bent towards the inner circumference so that it is arranged in a continuous spiral shape from the outer circumference end to the inner circumference end.

[0056] Next, in the negative electrode current collector contact process, as shown in Figure 4, the negative electrode current collector 17 is brought into contact with the negative electrode metal foil 40 that was bent in the bending process. At this time, the electrode body shown in Figure 3 is reversed in its vertical direction, with the bent portion 48 (Figure 3) of the negative electrode metal foil 40 facing upwards, and the negative electrode current collector 17 is brought into contact with the upper side of the negative electrode metal foil 40.

[0057] Next, in the welding process, with the negative electrode current collector plate 17 positioned above the bent portion 48 of the negative electrode metal foil 40, multiple linear laser beams are irradiated onto the surface of each arm portion 17a of the negative electrode current collector plate 17. Then, after the negative electrode current collector plate 17 is melted to the back surface by heat conduction, the heat from the molten negative electrode current collector plate 17 melts the negative electrode metal foil 40. After melting, a single-layer, linear intermediate molten solidification portion, mainly composed of copper, is formed on the entire surface of the linear molten solidification portion of the current collector plate on the negative electrode metal foil 40 side of the solidified portion of the negative electrode current collector plate 17. This welds the negative electrode current collector plate 17 and the negative electrode metal foil 40. In this specification, a component that accounts for 80% or more of the total is referred to as the main component.

[0058] Furthermore, the welding process involves simultaneously irradiating the surface of the negative electrode current collector plate 17 with multiple laser beams, each with at least one linear laser beam shorter in length than the other linear laser beams, to weld the negative electrode current collector plate 17 to the negative electrode metal foil 40. Specifically, in the example shown in Figures 4 and 5, four linear laser beams, each with a linear laser beam forming one linear weld 60d shorter in length than the linear laser beams forming the other three linear welds 60a, 60b, and 60c, are simultaneously irradiated radially onto the surface of each arm 17a of the negative electrode current collector plate 17 shown in Figure 4, substantially along the radial direction of the electrode body 14, to weld the negative electrode current collector plate 17 to the negative electrode metal foil 40.

[0059] In this example, in the welding described above, a branched DOE is preferably used to form a line-shaped laser beam, and the negative electrode current collector plate 17 and the negative electrode metal foil 40 are welded by irradiation with this laser beam. As shown in Figure 7, which will be described later, the pre-branched laser beam 90 output from a laser oscillator (not shown) is branched by the branched DOE 81, thereby irradiating the surface of the negative electrode current collector plate 17 with multiple line-shaped laser beams. The branched DOE 81 forms a line-shaped laser beam 93 at the processing position, where each beam profile is uniform in the longitudinal direction, as shown in Figure 8, which will be described later. Furthermore, the length of one line of the laser beam 93 at the processing position is preferably 7 mm or more, more preferably 10 mm or more, and even more preferably 15 mm or more. At this time, it is preferable that the number of branches forming one line beam of the branched DOE is 31 or more.

[0060] Figure 7 is a schematic diagram showing a laser welding apparatus 80 used in the manufacturing method of a secondary battery 10, with the branched laser beams that branch along a certain straight direction omitted.

[0061] As shown in Figure 7, the laser welding apparatus 80 is composed of a laser oscillator (not shown), a branched DOE 81, and a focusing lens 82. The laser oscillator outputs a laser beam 90. The pre-branched laser beam 90 output from the laser oscillator is irradiated onto the branched DOE 81 in a parallel state via an optical fiber, collimator, etc.

[0062] The branching DOE 81 is a diffractive optical component that has the function of splitting a single incident pre-branching laser beam 90 into multiple laser beams 91. After the laser beam 90 is split into multiple laser beams 91 by the branching DOE 81, it is incident on the focusing lens 82.

[0063] Note that in Figure 7, for the sake of clarity, only two laser beam groups 91a and 91b are shown as the laser beam 91 branched by the branching DOE 81, which are arranged linearly at the processing position and form two linear laser beams that are radially opposite to each other. In reality, the branching DOE 81 also branches multiple laser beams in a direction perpendicular to the branching direction of the laser beam shown in Figure 7, forming two more laser beam groups perpendicular to the two laser beam groups 91a and 91b.

[0064] In the focusing lens 82, the laser beams 92 are irradiated onto the negative electrode current collector plate 17 (Figure 4) in a linear arrangement for each laser beam 92 corresponding to each laser beam group 91a and 91b at the processing point, which is the processing position. At this time, the spacing between the laser beams 92 at the processing point is reduced for each laser beam 92 corresponding to each laser beam group 91a and 91b by bringing the focusing lens 82 closer to the branched DOE 81, etc. As a result, as shown in Figure 8, linear laser beams 93 can be irradiated onto the surface of the negative electrode current collector plate 17. Therefore, the negative electrode current collector plate 17 and the negative electrode metal foil 40 are irradiated with four linear laser beams 93 and welded together at four linear welding points 60. At this time, the diffraction pattern of the branched DOE 81 is pre-formed such that the length of one of the four linear laser beams 93 is shorter than the lengths of the other laser beams 93.

[0065] As described above, when the laser welding apparatus 80 uses a configuration that forms a line-shaped laser beam using a branched DOE 81, it becomes easier to ensure the uniformity of the laser beam and to easily perform optical adjustments. In this case, variations in the penetration depth at multiple positions in the longitudinal direction of the welded area 60 can be suppressed to a small extent.

[0066] Furthermore, in the welding process, at least one linear laser beam is used to irradiate the surface of the negative electrode current collector plate 17 with multiple laser beams, each shorter than the other linear laser beams, to weld the negative electrode current collector plate 17 to the negative electrode metal foil 40. This reduces the total length of the multiple linear laser beams, thereby reducing the original output of the laser beam emitted from the laser oscillator. This reduces the increase in the cost of the laser oscillator, and thus reduces the manufacturing cost of the secondary battery 10.

[0067] In the secondary battery manufacturing method described in this example, instead of a branched DOE, a beam shaper DOE or a laser welding device that forms a line-shaped laser beam using a homogenizer optical system can also be used. In a configuration using a beam shaper DOE, the incident beam is divided into multiple blocks provided in the beam shaper DOE, and the incident beam is rearranged at the processing position. Therefore, if the incident position of the laser beam in the beam shaper DOE shifts from the initial position when the laser beam profile is adjusted, the laser beam profile will tilt at the processing position, which may necessitate optical adjustment. For this reason, using a branched DOE 81 is more advantageous.

[0068] Furthermore, using a homogenizer optical system requires a microlens array, making it expensive and less tolerant of misalignment. Additionally, changing the laser beam profile length is difficult. From this perspective, using a branched DOE 81 is more advantageous.

[0069] The above describes a case in which multiple linear welds 60 are formed by line laser welding, and the negative electrode metal foil 40 and the negative electrode current collector plate 17 are welded together by these multiple welds 60. However, the configuration of this example is not limited to this, and when welding the negative electrode metal foil 40 and the negative electrode current collector plate 17 with multiple linear welds 60, it is also possible to form multiple linear welds 60 by scanning the irradiation area of ​​a spot-shaped laser beam in a linear manner. Even in this case, in the secondary battery 10 of this example, at least one of the multiple linear welds 60, specifically 60d, is shorter in length than the other linear welds 60a, 60b, and 60c. This allows for a shorter operating time of the irradiation area when forming the shorter weld 60d, thus reducing the time required for the laser process. For this reason, the manufacturing cost of the secondary battery 10 can be reduced, similar to the case in which multiple linear welds 60 are formed by line laser welding.

[0070] Figure 9 is a diagram corresponding to Figure 7, showing another example of a secondary battery in the embodiment. In this example, the four welds 60, which are multiple welds, are arranged such that the center of each weld 60 in the width direction is the position that is shifted parallel to one side in the circumferential direction of the electrode body 14 from a position along the radial direction of the electrode body 14. As a result, the multiple welds 60 are arranged on the outer surface of the negative electrode current collector plate 57, which overlaps with the axial end of the electrode body 14, divided in the circumferential direction of the electrode body 14, and along directions A1, A2, A3, and A4 parallel to the radial direction of the electrode body 14. The distance between the center of each weld 60 in the width direction and a radial line adjacent to the weld 60 is constant for all multiple welds 60.

[0071] In this example, for instance, the width of the arm portion 57a ​​of the negative electrode current collector plate 57 is increased, and the welded portion 60 formed on the surface of the arm portion 57a ​​is formed only on one side of the arm portion 57a ​​in the circumferential direction of the electrode body 14. Furthermore, in this example as well, the length of one of the four linear welded portions 60, 60d, is shorter than the lengths of the other three linear welded portions 60a, 60b, and 60c. In this example configuration as well, similar to the configurations in Figures 1 to 8, the manufacturing cost of the secondary battery can be reduced when welding the negative electrode metal foil 40 and the negative electrode current collector plate 57 with multiple linear welded portions 60. In this example, the other configurations and operations are the same as those in Figures 1 to 8.

[0072] Figure 10 is a diagram corresponding to Figure 7 in a secondary battery of another embodiment. In this example, unlike the configurations in Figures 1 to 8, the radial outer end of the weld 60d is positioned radially at the same position as the radial outer ends of the other welds 60a, 60b, and 60c. On the other hand, the radial inner end of the weld 60d is positioned radially outward than the radial inner ends of the other welds 60a, 60b, and 60c. As a result, the length of one of the four linear welds 60d is shorter than the lengths of the other three linear welds 60a, 60b, and 60c.

[0073] According to the configuration of this example, even if some welds 60d are shorter than other welds 60a, 60b, and 60c, it is possible to suppress a decrease in the welding strength between the negative electrode metal foil 40 and the negative electrode current collector plate 17 (see Figure 4) due to the multiple welds 60, and to suppress an increase in electrical resistance between the negative electrode metal foil 40 and the negative electrode current collector plate 17 in some areas. When welding the negative electrode metal foil 40 and the negative electrode current collector plate 17 of the electrode body 14, it is preferable to form the welds between the negative electrode metal foil 40 and the negative electrode current collector plate 17 at the narrowest possible intervals in the winding direction of the negative electrode metal foil 40, in order to increase the welding strength and keep the electrical resistance low.

[0074] On the other hand, in the configuration shown in Figures 4 and 5 above, in order to shorten the length of some of the welds 60d, the radial outer ends of some of the welds 60d are positioned radially inward from the radial outer ends of the other welds 60a, 60b, and 60c. In this case, no welds are placed in the area near the outer circumference of the axial end of the negative electrode metal foil 40 that coincides circumferentially with the short welds 60d (near point P in Figure 5). As a result, in the configurations of Figures 4 and 5, the spacing between adjacent welds 60 in the circumferential direction near the outer circumference of the axial end of the negative electrode metal foil 40 becomes longer in some areas. Therefore, there is room for improvement in terms of suppressing a decrease in welding strength between the negative electrode metal foil 40 and the negative electrode current collector plate 17, and in suppressing the overall electrical resistance between the negative electrode metal foil 40 and the negative electrode current collector plate 17.

[0075] On the other hand, in the configuration of this example shown in Figure 10, in order to shorten the length of some of the welds 60d, the radial inner ends of some of the welds 60d are positioned radially outward from the radial inner ends of the other welds 60a, 60b, and 60c. As a result, near the outer circumference of the axial end of the negative electrode metal foil 40, welds 60d are positioned in the same way as the other longer welds 60a, 60b, and 60c in the portion that coincides circumferentially with the short welds 60d. Instead, in the configuration of this example, no welds are positioned near the inner circumference of the axial end of the negative electrode metal foil 40 in the portion that coincides circumferentially with the short welds 60d (near point Q in Figure 9). However, the length per turn is shorter near the inner circumference of the axial end of the negative electrode metal foil 40 compared to the outer circumference of the negative electrode metal foil 40. Therefore, even if the welds are not evenly distributed near the inner circumference of the negative electrode metal foil 40, the distance between adjacent welds 60 in the circumferential direction near the inner circumference will not become excessively long. Consequently, regardless of the configuration in which some welds 60d are shorter than other welds 60a, 60b, and 60c, it is possible to suppress a decrease in the welding strength between the negative electrode metal foil 40 and the negative electrode current collector plate 17, and to suppress an increase in electrical resistance between the negative electrode metal foil 40 and the negative electrode current collector plate 17 in some areas. In this example, the other configurations and operations are the same as those in Figures 1 to 8.

[0076] Figure 11 is a diagram corresponding to Figure 7, showing another example of a secondary battery in the embodiment. In this example, unlike the configuration in Figure 10, a pair of welds 60b and 60d, which are some of the multiple linear welds 60, are shorter than the other welds 60a and 60c. Furthermore, the pair of welds 60b and 60d are arranged radially at point-symmetrical positions with respect to the center O of the electrode body 14 when viewed from one axial side of the electrode body 14. In addition, the radial inner ends of the pair of welds 60b and 60d are positioned radially outward from the radial inner ends of the other welds 60a and 60c.

[0077] According to the configuration of this example, the number of short welds 60b and 60d is increased, which further reduces the manufacturing cost of the secondary battery when welding the negative electrode metal foil 40 and the negative electrode current collector plate 17 (see Figure 4) with multiple linear welds 60. In addition, in this example, no welds are placed in the area near the inner circumference of the axial end of the negative electrode metal foil 40 that coincides with the circumferential direction of the short welds 60b and 60d (near points Q1 and Q2 in Figure 11). Therefore, the distance between the welds 60 near the inner circumference of the axial end of the negative electrode metal foil 40 is equal on both the side of one short weld 60b and the side of the other short weld 60d. Therefore, unlike the configuration in Figure 11, the two long welds and the two short welds are adjacent to each other in the circumferential direction near the inner circumference of the axial end of the negative electrode metal foil 40, and the configuration in this example prevents the length between adjacent welds near the inner circumference of the axial end from becoming excessively long in some areas, compared to a configuration in which the short welds are not arranged point-symmetrically. This effectively suppresses a decrease in the welding strength between the negative electrode metal foil 40 and the negative electrode current collector plate 17, and also effectively suppresses an increase in the electrical resistance between the negative electrode metal foil 40 and the negative electrode current collector plate 17 in some areas. In this example, the other configurations and operations are the same as those in Figures 1 to 8.

[0078] In addition, in the configuration shown in Figure 11, the radial inner ends of the pair of short welds may coincide radially with the radial inner ends of the other longer welds of the multiple welds, and the radial outer ends of the pair of short welds may be positioned radially inward from the radial outer ends of the other longer welds. In this case, although the effect is less than that of the configuration shown in Figure 11, it is possible to suppress the excessive length between the two welds in some areas near the outer circumference of the axial end of the negative electrode metal foil. Therefore, it is possible to suppress a decrease in the welding strength between the negative electrode metal foil and the negative electrode current collector, and also suppress an increase in the electrical resistance between the negative electrode metal foil and the negative electrode current collector in some areas.

[0079] Figure 12 is a diagram corresponding to Figure 7 in a secondary battery of another embodiment. The configuration of this example has a configuration that combines the configuration shown in Figure 9 and the configuration shown in Figure 11. Specifically, unlike the configuration shown in Figure 9, among the multiple welds 60, the short welds 60b and 60d are a pair of welds 60b and 60d, and the radial outer ends of the pair of welds 60b and 60d coincide radially with the radial outer ends of the other welds 60a and 60c. Furthermore, the radial inner ends of the pair of welds 60b and 60d are positioned radially outward from the radial inner ends of the other welds 60a and 60c. The pair of welds 60b and 60d are positioned point-symmetric with respect to the center O of the electrode body when viewed from one side in the axial direction of the electrode body 14. The multiple welded joints 60 are arranged on the outer surface of the negative electrode current collector plate 57 (see Figure 9), which overlaps with the axial end of the electrode body 14, in the same configuration as in Figure 9. They are separated in the circumferential direction of the electrode body 14 and are arranged along directions A1, A2, A3, and A4, which are parallel to the radial direction of the electrode body 14.

[0080] With the configuration in this example, similar to the configuration shown in Figure 11, it is possible to effectively suppress a decrease in the welding strength between the negative electrode metal foil 40 and the negative electrode current collector plate 57, and to effectively suppress an increase in electrical resistance in some areas between the negative electrode metal foil and the negative electrode current collector plate. In this example, the other configurations and operations are the same as those shown in Figures 1 to 8, or Figure 9, or Figure 11.

[0081] Although not shown in the diagrams, the number of welds may be changed or the welds may be unevenly arranged in the circumferential direction in each of the above examples. Furthermore, the multiple linear welds are not limited to being formed linearly along the radial direction or a direction parallel to the radial direction via the negative electrode current collector plate at the axial end of the negative electrode metal foil 40, but may also be curved shapes such as arcs or S-shapes that extend radially outward. On the other hand, from the viewpoint of suppressing a decrease in welding strength between the negative electrode metal foil and the negative electrode current collector plate and suppressing the overall electrical resistance between the negative electrode metal foil and the negative electrode current collector plate to a low level, it is preferable that the multiple welds are arranged substantially evenly in the circumferential direction of the electrode body, as in each of the above examples.

[0082] Furthermore, although the bonding of the negative electrode metal foil 40 and the negative electrode current collector plate 17 has been described in the above embodiment, the negative electrode current collector plate 17 may be omitted and the negative electrode metal foil 40 and the bottom portion 15b may be directly welded by laser welding.

[0083] For example, in this case, the ends of the metal foil constituting the electrode and the bottom of the metal current collector plate or metal outer casing are welded together by multiple linear welds. In this case as well, the length of at least one of the multiple linear welds is shorter than the length of the other linear welds.

[0084] In this case, the multiple linear welds may be arranged on the outer surface of the bottom of the outer casing, overlapping the axial ends of the electrode body, and separated in the circumferential direction of the electrode body. Alternatively, the metal foil may be copper foil, and the bottom of the outer casing may be made of iron plate. Furthermore, the manufacturing method of an energy storage device such as a secondary battery may include, after the bending step (S12) in Figure 6, a step of bringing the bottom of a metal outer casing into contact with the bent metal foil, and a welding step of irradiating the surface of the bottom with multiple linear laser beams to weld the bottom and the metal foil. In this case, the welding step involves irradiating the surface of the bottom with multiple laser beams, at least one of which is shorter than the other linear laser beams, simultaneously to weld the bottom and the metal foil. Alternatively, the laser beam before branching may be branched at DOE to irradiate the surface of the bottom with multiple linear laser beams.

[0085] This disclosure is further illustrated by the following embodiments. Configuration 1: A power storage device characterized in that the ends of a metal foil constituting an electrode and the bottom of a metal current collector plate or a metal outer casing are welded together by a plurality of linear welds, wherein the length of at least one of the plurality of linear welds is shorter than the length of the other linear welds. Configuration 2: The power storage device according to Configuration 1, wherein the metal foil, in a wound state, constitutes a cylindrical electrode body, and the ends of the metal foil are provided at the axial ends of the electrode body, the plurality of linear welds are arranged separately in the circumferential direction of the electrode body on the outer surface of the current collector plate or the bottom that overlaps with the axial ends of the electrode body, and the radial inner end of at least one linear weld is arranged radially outward from the radial inner end of the other linear welds. Configuration 3: The metal foil, in a wound state, constitutes a cylindrical electrode body, and the end of the metal foil is provided at the axial end of the electrode body; the plurality of linear welds are arranged separately in the circumferential direction of the electrode body on the outer surface of the current collector plate or the bottom that overlaps with the axial end of the electrode body; and at least one of the linear welds is a pair of linear welds arranged in point-symmetric positions when viewed from one side in the axial direction of the electrode body; the energy storage device according to Configuration 1. Configuration 4: The radial inner ends of the pair of linear welds are arranged radially outward from the radial inner end of the other linear weld; the energy storage device according to Configuration 3. Configuration 5: The energy storage device according to any one of Configurations 1 to 4, wherein the metal foil is copper foil and the current collector plate or the bottom is an iron plate.Configuration 6: A method for manufacturing an energy storage device, comprising the steps of: aligning the ends of metal foil constituting an electrode in the axial position; bending the tips of the ends; contacting the bent metal foil with a metal current collector plate or the bottom of a metal outer casing; and welding the current collector plate or the bottom and the metal foil by irradiating the surface of the current collector plate or the bottom with a plurality of linear laser beams, wherein the welding step involves irradiating the surface of the current collector plate or the bottom with a plurality of laser beams, at least one of which has a length shorter than the other linear laser beams, in a single operation to weld the current collector plate or the bottom and the metal foil. Configuration 7: The method for manufacturing an energy storage device according to Configuration 6, wherein the laser beam before branching is branched by a DOE to irradiate the surface of the current collector plate or the bottom with the plurality of linear laser beams.

[0086] 10 Secondary battery (energy storage device), 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Outer can, 16 Sealing body, 17 Negative electrode current collector plate, 18 Positive electrode current collector plate, 19 Insulating plate, 20 Positive electrode connection lead, 21 Grooved section, 22 Internal terminal plate, 23 Lower valve body, 24 Insulating member, 25 Insulating member, 25 Upper valve body, 26 Cap, 27 Gasket, 30 Positive electrode metal foil, 32 Positive electrode mixture layer, 34 Positive electrode uncoated section, 40 Negative electrode metal foil, 42 Negative electrode mixture layer, 44 Negative electrode uncoated section, 45 Laminated section, 47 Axial extension section, 48 Bent section, 57 Negative electrode current collector plate, 60, 60a, 60b, 60c, 60d Welded section, 80 Laser welding device, 81 Branched DOE, 82 focusing lens, 90 pre-branching laser beam, 91, 92, 93 laser beams.

Claims

1. An energy storage device characterized in that the ends of the metal foil constituting the electrodes and the bottom of a metal current collector plate or a metal outer casing are welded together by a plurality of linear welds, wherein the length of at least one of the plurality of linear welds is shorter than the length of the other linear welds.

2. The energy storage device according to claim 1, wherein the metal foil, when wound, constitutes a cylindrical electrode body, and the end of the metal foil is provided at the axial end of the electrode body, and the plurality of linear welds are arranged separately in the circumferential direction of the electrode body on the outer surface of the current collector plate or the bottom portion that overlaps with the axial end of the electrode body, and the radial inner end of at least one linear weld is arranged radially outward from the radial inner end of the other linear welds.

3. The energy storage device according to claim 1, wherein the metal foil, in a wound state, constitutes a cylindrical electrode body, and the end of the metal foil is provided at the axial end of the electrode body, the plurality of linear welds are arranged separately in the circumferential direction of the electrode body on the outer surface of the current collector plate or the bottom portion that overlaps with the axial end of the electrode body, and at least one of the linear welds is a pair of linear welds arranged in point-symmetric positions when viewed from one side in the axial direction of the electrode body.

4. The radial inner ends of the pair of linear welds are positioned radially outward from the radial inner end of the other linear weld, as described in claim 3.

5. The energy storage device according to claim 1, wherein the metal foil is copper foil and the current collector plate or the bottom is an iron plate.

6. A method for manufacturing an energy storage device, comprising the steps of: arranging the ends of metal foil constituting an electrode in an axial position; bending the tips of the ends; bringing a metal current collector plate or the bottom of a metal outer casing into contact with the bent metal foil; and welding the current collector plate or the bottom and the metal foil by irradiating the surface of the current collector plate or the bottom with a plurality of linear laser beams, wherein the welding step involves irradiating the surface of the current collector plate or the bottom with a plurality of laser beams, at least one of which has a length shorter than the other linear laser beams, in a single operation to weld the current collector plate or the bottom and the metal foil.

7. A method for manufacturing an energy storage device according to claim 6, wherein the laser beam before branching is branched by a DOE, thereby irradiating the surface of the current collector plate or the bottom with the plurality of line-shaped laser beams.

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