Cylindrical battery, and manufacturing method of cylindrical battery

Abstract

To provide a cylindrical battery and the like with high reliability capable of improving the durability of the outer can.SOLUTION: A battery 10 includes: an electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween; and an outer can 20 that includes a cylindrical portion 20B having a shoulder 29 extending radially inward at one end in the axial direction, and accommodates the electrode body 14. The shoulder portion 29 includes a melting mark 37. The melting mark 37 may contain Ni that has diffused throughout the melting mark 37. The maximum depth of the melting mark 37 may be 0.7 or less of the thickness of the outer can 20 at the maximum depth position of the melting mark 37.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to cylindrical batteries and methods for manufacturing cylindrical batteries. [Background technology]

[0002] A conventional cylindrical battery is described in Patent Document 1. This cylindrical battery includes an electrode assembly, a cylindrical outer can with a bottom that houses the electrode assembly, a sealing body that closes the opening of the outer can, and a gasket that is sandwiched between the outer can and the sealing body. The cylindrical portion of the outer can has a grooved portion and an annular shoulder portion. The grooved portion is formed by recessing a portion of the cylindrical portion radially inward. The shoulder portion is formed when the tip of the opening side of the cylindrical portion is bent inward and crimped onto the peripheral edge of the sealing body, and extends radially inward. The sealing body is clamped between the shoulder portion and the grooved portion via the gasket by crimping, and is fixed to the outer can. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 09-274923 Summary of the Invention [Problem to be solved by the invention]

[0004] When forming the shoulder of the outer can, the tip of the opening side of the tubular portion is bent to cause plastic deformation, which generates residual stress in the shoulder due to the bending process, and this residual stress may reduce the durability of the outer can. Therefore, an object of the present disclosure is to provide a cylindrical battery that can improve the durability of the outer can and is highly reliable, and an object of the present disclosure is to provide a method for manufacturing a cylindrical battery that can improve the durability of the outer can and is highly reliable. [Means for solving the problem]

[0005] In order to solve the above problems, the cylindrical battery of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and an outer can that houses the electrode body and includes a tubular portion having a shoulder portion at one axial end portion that extends radially inward, and the shoulder portion includes a melting mark.

[0006] In addition, the manufacturing method of the cylindrical battery according to the present disclosure includes a step of forming an annular shoulder portion by bending the tip portion on the opening side of a bottomed cylindrical outer can radially inward around the entire circumference, and a step of irradiating the shoulder portion with laser light. [Effects of the Invention]

[0007] According to the cylindrical battery of the present disclosure, the durability of the outer can can be improved, resulting in higher reliability. Furthermore, according to the manufacturing method of the cylindrical battery of the present disclosure, the durability of the outer can can be improved, resulting in the manufacturing of a highly reliable cylindrical battery. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is an axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged half cross-sectional view of the shoulder portion and its surroundings in FIG. 1. [Figure 3] FIG. 2 is a schematic diagram illustrating the Ni concentration around the melting mark on the shoulder of the outer can. [Figure 4] FIG. 2 is a schematic diagram illustrating the particle size of Fe crystals around the melting mark in the shoulder of the outer can. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of a cylindrical battery according to the present disclosure will be described in detail with reference to the drawings. The cylindrical battery according to the present disclosure may be a primary battery or a secondary battery. It may also be a battery using an aqueous electrolyte or a battery using a non-aqueous electrolyte. Hereinafter, a lithium ion secondary battery will be exemplified as a cylindrical battery 10 according to one embodiment, but the cylindrical battery according to the present disclosure is not limited thereto.

[0010] It is anticipated from the beginning that new embodiments may be constructed by appropriately combining the features of the embodiments and variations described below. In the following embodiments, the same components are designated by the same reference numerals in the drawings, and redundant explanations are omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, and other dimensions of each component between different drawings do not necessarily match. In this specification, the axial (height) side of the sealing body 19 of the cylindrical battery 10 is referred to as "top," and the axial side of the bottom 20A of the outer can 20 is referred to as "bottom." Among the components described below, components not recited in the independent claims representing the highest concepts are optional and not essential. The present disclosure is not limited to the following embodiments and variations thereof, and various improvements and modifications are possible within the scope of the claims and their equivalents.

[0011] Fig. 1 is an axial cross-sectional view of a cylindrical battery 10 according to one embodiment of the present disclosure. As shown in Fig. 1, the cylindrical battery (hereinafter simply referred to as battery) 10 includes an electrode assembly 14, a non-aqueous electrolyte, a cylindrical outer can 20 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 19 that closes the opening of the outer can 20 via an annular gasket 24.

[0012] The electrode assembly 14 includes a long positive electrode 11, a long negative electrode 12, and two long separators 13 interposed between the positive electrode 11 and the negative electrode 12, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separators 13 interposed therebetween. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. The negative electrode 12 is formed to be longer than the positive electrode 11 in the winding direction and the axial direction. The two separators 13 are formed to be slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11. The separators 13 protrude above and below the positive electrode 11 and the negative electrode 12.

[0013] 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 solvent (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 be, for example, a lithium salt such as LiPF6.

[0014] 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.).

[0015] The positive electrode 11 has a positive electrode core and positive electrode mixture layers formed on both sides of the positive electrode core. The positive electrode core can be made of a metal foil, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder. The positive electrode is produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode core, drying the coating, and then compressing it to form positive electrode mixture layers on both sides of the positive electrode core.

[0016] 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.

[0017] Examples of conductive agents contained in the positive electrode mixture layer include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of binders contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO).

[0018] The negative electrode 12 has a negative electrode core and negative electrode mixture layers formed on both sides of the negative electrode core. The negative electrode core 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 layer. The negative electrode mixture layer contains a negative electrode active material and a binder. The negative electrode 12 is produced, for example, by applying a negative electrode mixture slurry containing the negative electrode active material and the binder onto the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

[0019] The negative electrode active material generally uses a carbon material that reversibly absorbs and releases lithium ions. Preferred carbon materials include natural graphite, such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite, such as lump artificial graphite and graphitized mesophase carbon microbeads. The negative electrode mixture layer may contain a silicon (Si) material as the negative electrode active material. Furthermore, the negative electrode active material may include a metal other than Si that alloys with lithium, an alloy containing such a metal, or a compound containing such a metal.

[0020] The binder contained in the negative electrode mixture layer may be a fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like, as in the case of the positive electrode 11. Preferably, styrene-butadiene rubber (SBR) or a modified product thereof is used. In addition to SBR, the negative electrode mixture layer may contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0021] 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.

[0022] An upper insulating plate 15 is disposed above the electrode body 14, and a lower insulating plate 16 is disposed below the electrode body 14. In the example shown in FIG. 1 , a positive electrode lead 17 attached to the positive electrode 11 passes through a through-hole in the upper insulating plate 15, extends toward the sealing body 19, and is connected to the underside of the sealing body 19 by welding or the like. On the other hand, a negative electrode lead 18 attached to the negative electrode 12 passes outside the lower insulating plate 16, extends toward the bottom 20A of the outer can 20, and is connected to the inner surface of the bottom 20A by welding or the like. The sealing body 19 to which the positive electrode lead 17 is connected serves as a positive electrode terminal, and the outer can 20 to which the negative electrode lead 18 is connected serves as a negative electrode terminal.

[0023] A gasket 24 is provided between the outer can 20 and the sealing body 19 to ensure sealing of the battery interior and insulation between the outer can 20 and the sealing body 19. The outer can 20 has a cylindrical portion 20B and a bottom portion 20A. The cylindrical portion 20B includes an annular grooved portion 28 and an annular shoulder portion 29. The grooved portion 28 is formed by spinning a portion of the cylindrical portion 20B to recess it radially inward. The shoulder portion 29, on the other hand, is formed when the upper end of the cylindrical portion 20B is bent radially inward and crimped to the flange portion (peripheral edge) 31 of the sealing body 19, and extends radially inward. The crimping causes the sealing body 19 to be sandwiched between the shoulder portion 29 and the grooved portion 28 via the gasket 24, and the sealing body 19 is fixed to the outer can 20.

[0024] Sealing body 19 is a disc-shaped member equipped with a current interruption mechanism. Sealing body 19 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 21, an insulating plate 23, and a rupture plate 22 are stacked. Rupture plate 22 forms a valve body and is disposed opposite internal terminal plate 21 with insulating plate 23 sandwiched therebetween. Insulating plate 23 has opening 23A formed in its radial center, and air vent 23B formed in a portion overlapping with air vent 21C of internal terminal plate 21.

[0025] Rupture plate 22 has valve portion 22A at its radial center that ruptures when the battery internal pressure exceeds a predetermined threshold, and valve portion 22A is connected by welding or the like to central portion 21B of internal terminal plate 21 through opening 23A of insulating plate 23. Valve portion 22A includes a lower convex portion that protrudes toward the inside of the battery and is provided in the radial center, and a thin-walled portion formed around the lower convex portion. The thickness of the thin-walled portion becomes thinner as it goes radially outward.

[0026] The internal terminal plate 21 is a metal plate and includes a thick annular portion 21A to which the positive electrode lead 17 is connected, and a disk-shaped central portion 21B that is connected to the radially inner end of the annular portion 21A and is thinner than the annular portion 21A. An air vent 21C is formed in the annular portion 21A. The positive electrode lead 17 is connected to the underside of the annular portion 21A. The internal terminal plate 21 to which the positive electrode lead 17 is connected is electrically connected to the rupture plate 22, thereby forming a current path that connects the electrode body 14 to the rupture plate 22.

[0027] When the internal pressure of the battery 10 increases, the valve portion 22A inverts so as to become convex axially upward, using the annular end portion 22B, which is the thin-walled portion on the radially outer side and has low rigidity, as a fulcrum. Simultaneously with this inversion, the center portion 21B is separated from the annular portion 21A or disengages from the valve portion 22A. Because the valve portion 22A is insulated from the annular portion 21A by the insulating plate 23, this inversion interrupts the current path. When the internal pressure of the battery further increases, the annular end portion 22B of the thin-walled portion breaks, forming a gas outlet.

[0028] The structure of sealing body 19 is not limited to the structure shown in Fig. 1. For example, sealing body 19 may be composed of only a rupture plate. Alternatively, sealing body 19 may have a laminated structure including two rupture plates, and the laminated structure may have a convex portion that protrudes upward in the radial center and a terminal cap that covers the rupture plate.

[0029] The structure of the shoulder portion 29 of the outer can 20 will be described in detail below with reference to Figures 2 to 4. Figure 2 is an enlarged half-sectional view of the area around the shoulder portion in Figure 1. In the present disclosure, the shoulder portion 29 is defined as the upper end portion of the tubular portion 20B that has been plastically deformed by being bent radially inward by bending.

[0030] Corner portion 29a located on the radially outer side of shoulder portion 29 includes melting trace 37. Corner portion 29a of shoulder portion 29 is a portion that has been plastically deformed by bending in outer can 20, and is a portion of outer can 20 that is located between a first location K1 that overlaps with the radial outer peripheral edge 45 of sealing body 19 on the upper side in the axial direction, and a second location K2 that overlaps with an upper end face 46 of the peripheral edge portion of sealing body 19 in the radial direction. The presence or absence of melting trace 37 can be easily determined, for example, by a planar image taken with an optical microscope (microscope).

[0031] As will be explained in detail later, by forming the melt marks 37 in the shoulder portion 29, it is possible to reduce the residual stress in the shoulder portion 29 caused by the bending process, thereby improving the durability and reliability of the outer can 20. Furthermore, by forming the melt marks 37 in the corner portion 29a of the shoulder portion 29, which is particularly prone to high residual stress due to the bending process, the residual stress can be reduced, thereby improving the durability and reliability of the outer can 20.

[0032] The melting marks 37 are formed by irradiating the entire circumference of the curved, annular corner 29a with laser light. In this embodiment, the melting marks 37 are formed by irradiating the entire circumference of the outer surface of the corner 29a with laser light focused on the outer surface of the corner 29a and having an irradiation energy of 60 W from a direction tilted 45° radially outward with respect to the axial direction.

[0033] To effectively reduce residual stress in the corner 29a, it is preferable to irradiate the entire outer surface of the corner 29a with a laser beam focused on the outer surface of the corner 29a from a direction tilted radially outward by an angle θ of 35° to 55° relative to the axial direction, thereby forming a melt mark 37. It is even more preferable to irradiate the entire outer surface of the corner 29a from a direction tilted radially outward by an angle θ of 40° to 50° relative to the axial direction, thereby forming a melt mark 37. The irradiation energy of the irradiated laser beam can be, for example, 30 W to 80 W, and preferably 45 W to 70 W. Setting the irradiation angle range of the laser beam within the above-mentioned preferred range facilitates uniform heat transfer to the material and minimizes reflection on non-irradiated surfaces. Furthermore, setting the irradiation angle range of the laser beam within the above-mentioned preferred range allows for efficient laser energy transmission, thereby concentrating more energy on the target object.

[0034] In the battery 10 of this embodiment, in order to improve the corrosion resistance, conductivity, and connectivity of the outer can 20, the outer can 20 is manufactured by forming a Ni plating film on the entire inner and outer surfaces of the original steel material of the outer can using electrolytic Ni plating or electroless Ni plating. More specifically, forming a Ni plating film on the entire inner and outer surfaces of the original steel material of the outer can allows for efficient conduction of electricity to the plated steel sheet, thereby improving battery performance. Furthermore, forming a Ni plating film on the entire inner and outer surfaces of the original steel material of the outer can facilitates connections to bus bars for modularization and connections to internal electrode leads (positive or negative electrode leads), thereby achieving highly reliable connections. Therefore, an outer film 33 and an inner film 34 containing Ni are provided on the outer and inner surfaces of the outer can 20 in the thickness direction, respectively. Laser irradiation melts a portion of the shoulder 29, leaving a melting mark 37, and in the melting mark 37, Ni from the outer film 33 diffuses throughout the melting mark. Therefore, the melting mark 37 contains Ni that has diffused throughout the melting mark.

[0035] 3 is a schematic diagram illustrating the Ni concentration around the melting mark 37 in the shoulder portion 29. In FIG. 3, the region 41 shown with diagonal hatching indicates a region with a high Ni concentration, the region 42 shown with dotted hatching indicates a region with a medium Ni concentration, and the region 43 shown with cross hatching indicates a region with a low Ni concentration. The outer film 33 is provided on the outer side in the thickness direction of the outer can 20 at a portion where the melting mark 37 does not exist over the entire thickness direction, and has a high Ni concentration. Furthermore, the Ni concentration in most regions other than the inner edge of the melting mark 37 is medium. Furthermore, the Ni concentration at the inner edge of the melting mark 37 is low.

[0036] The Ni concentration in the fusion mark 37 is preferably 30% or more of the Ni concentration in the outer film 33, as this effectively reduces the residual stress in the shoulder portion 29 and tends to improve the durability of the outer can 20. Furthermore, the Ni concentration in the fusion mark 37 is preferably 80% or less of the Ni concentration in the outer film 33, as this tends to facilitate melting that achieves good sealing properties for the outer can 20.

[0037] It is preferable that the maximum depth of the fusion mark 37 be ⅛ or more of the thickness of the outer can 20 at the position of the maximum depth of the fusion mark 37, because this effectively reduces the residual stress in the shoulder portion 29 and tends to improve the durability of the outer can 20. Furthermore, it is preferable that the maximum depth of the fusion mark 37 be 0.7 or less of the thickness of the outer can 20 at the position of the maximum depth of the fusion mark 37, because this tends to facilitate realizing a melting that easily achieves good sealing of the outer can 20.

[0038] The thickness of the outer can 20 is defined as the dimension of the outer can 20 in an orthogonal direction perpendicular to the tangent to the outer surface of the outer can 20 in the axial cross section of the outer can 20. The thickness of the outer can 20 at the maximum depth position of the melt mark 37 is defined as the dimension of the outer can 20 in the orthogonal direction at a point where the orthogonal direction passes through the maximum depth position.

[0039] Fig. 4 is a schematic diagram illustrating the particle size of Fe crystals around the melting mark 37 in the shoulder 29. In Fig. 4, the area 51 indicated by diagonal hatching has the smallest particle size of Fe crystals, the area 52 indicated by dot hatching has medium particle size of Fe crystals, and the area 53 indicated by cross hatching has the largest particle size of Fe crystals.

[0040] The region where melting mark 37 exists corresponds to the region formed by region 51 and region 52. The average particle size of Fe crystals in melting mark 37 is smaller than the average particle size of Fe crystals in the portion of outer can 20 where melting mark 37 does not exist. The particle size of Fe crystals tends to become smaller as the melting temperature increases. This shows that the outer portion of melting mark 37 has a higher melting temperature than the inner portion of melting mark 37.

[0041] Example 1 In the laser irradiation process, a laser beam with an irradiation energy of 60 W was focused on the outer surface of the corner of the shoulder, and was irradiated from a direction tilted 45° radially outward from the axial direction around the entire outer surface of the corner, thereby forming a melted mark around the corner.

[0042] <Example 2> A battery was fabricated that was different from the battery of Example 1 in that the irradiation energy of the laser light irradiated on the corner of the shoulder was changed from 60W to 30W.

[0043] <Comparative Example> In comparison with the battery of Example 1, a battery was fabricated by omitting the step of irradiating the shoulder with laser light.

[0044] [Residual stress measurement] For each battery, the residual stress on the material surface was measured non-destructively by X-ray diffraction (XRD), that is, by analyzing the diffraction pattern obtained as a result of scattering and interference of X-rays by electrons around the atoms when X-rays are irradiated onto a crystalline sample. 2 The residual stress on the material surface was measured using the Ψ method.

[0045] When the measured stress was smaller than the stress threshold by a predetermined value or more, it was evaluated as "good." When the measured stress was smaller than the stress threshold by less than the predetermined value, it was evaluated as "fair." When the measured stress was larger than the stress threshold, it was evaluated as "bad." The stress measurement results for one test example are shown in Table 1. [Table 1]

[0046] Although not shown in Table 1, it has been confirmed that residual stress in the shoulder area can be effectively reduced when the laser beam irradiation output is 45 W or higher, compared to when no laser beam is irradiated. Therefore, when the laser beam irradiation output for the shoulder area is 45 W or higher, the durability of the outer can is significantly improved, making it possible to manufacture cylindrical batteries with extremely high reliability.

[0047] The above description deals with the case where a Ni plating film is formed on the entire inner and outer surfaces of the original material of the outer can. However, a Ni plating film may be formed on at least one of at least a portion of the inner surface of the original material of the outer can and at least a portion of the outer surface of the original material of the outer can. Alternatively, a plating film other than a Ni plating film may be formed on at least one of at least a portion of the inner surface of the original material of the outer can and at least a portion of the outer surface of the original material of the outer can. Alternatively, no plating film may be present on the surfaces (outer and inner surfaces) of the outer can.

[0048] The cylindrical battery of the present disclosure may also have the following configuration. Configuration 1: A cylindrical battery comprising: an electrode body in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; and an outer can containing the electrode body, the outer can including a tubular portion having a shoulder portion at one axial end portion that extends radially inward, the shoulder portion including a melting mark. Configuration 2: The cylindrical battery of Configuration 1, wherein the melt mark includes Ni diffused throughout the melt mark. Configuration 3: The cylindrical battery according to Configuration 2, wherein a film containing Ni is provided on the outer side of a portion of the outer can where the melting mark does not exist across the entire thickness direction, and the Ni concentration in the melting mark is 30% or more and 80% or less of the Ni concentration in the film. Configuration 4: The cylindrical battery according to any one of Configurations 1 to 3, wherein the maximum depth of the melting mark is 0.7 or less of the thickness of the outer can at the position of the maximum depth of the melting mark. Configuration 5: The cylindrical battery according to any one of Configurations 1 to 4, wherein the average particle size of the Fe crystals in the melting mark is smaller than the average particle size of the Fe crystals in a portion of the outer can where the melting mark is not present. [Explanation of symbols]

[0049] 10 battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 upper insulating plate, 16 lower insulating plate, 17 positive electrode lead, 18 negative electrode lead, 19 sealing body, 20 outer can, 20A bottom, 20B cylindrical portion, 21 internal terminal plate, 21A annular portion, 21B center portion, 21C vent hole, 22 rupture plate, 22A valve portion, 22B annular end portion, 23 insulating plate, 23A opening, 23B vent hole, 24 gasket, 28 grooved portion, 29 shoulder portion, 29a corner portion, 33 outer film, 34 inner film, 37 melting mark.

Claims

1. an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; an outer can that includes a cylindrical portion having a shoulder portion that extends radially inward at one axial end thereof, and that houses the electrode assembly; The cylindrical battery, wherein the shoulder portion includes a fusion mark.

2. The cylindrical battery according to claim 1 , wherein the melt mark contains Ni diffused throughout the melt mark.

3. a film containing Ni is provided on the outer side in the thickness direction of a portion of the outer can where no melting trace exists across the entire thickness direction, 3. The cylindrical battery according to claim 2, wherein the Ni concentration in the melting mark is 30% or more and 80% or less of the Ni concentration in the film.

4. 4. The cylindrical battery according to claim 1, wherein the maximum depth of the melting mark is 0.7 or less of the thickness of the outer can at the position of the maximum depth of the melting mark.

5. 4. The cylindrical battery according to claim 1, wherein an average particle size of the Fe crystals in the melting mark is smaller than an average particle size of the Fe crystals in a portion of the outer can where the melting mark is not present.

6. forming an annular shoulder portion by bending the entire periphery of a tip portion on the opening side of the bottomed cylindrical outer can inward in the radial direction; irradiating the shoulder with laser light; A method for manufacturing a cylindrical battery, comprising:

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