Secondary battery and method for manufacturing secondary battery

Abstract

This secondary battery comprises: an electrode body that is obtained by winding a positive electrode and a negative electrode with a separator interposed therebetween; a cylindrical outer can (20) that has a bottom part and that houses the electrode body; a sealing body (30) that closes an opening (24) of the outer can (20); and an annular gasket (40) that is interposed between the outer can and the sealing body (30), the sealing body (30) being fixed by crimping to the opening (24) of the outer can (20) with the gasket (40) interposed therebetween. The secondary battery is characterized in that: the gasket includes a first gasket (41) and a second gasket (42) disposed on the bottom side of the first gasket (41); the sealing body (30) is sandwiched between the first gasket (41) and the second gasket (42) from both sides in the axial direction of the outer can (20); and at least a portion of the first gasket (41) is adjacent to the second gasket (42) in the radial direction of the outer can (20).

Description

Secondary battery and method of manufacturing the same

[0001] The present disclosure relates to a secondary battery and a method for manufacturing a secondary battery.

[0002] Generally, in a secondary battery, a sealing body that closes the opening of an outer can is fixed to the opening of the outer can by crimping via a resin gasket (see, for example, Patent Document 1). The provision of the gasket ensures airtightness inside the battery and insulation between the outer can and the sealing body.

[0003] International Publication No. 2016 / 157749

[0004] However, when the gasket is made of a single member, as in the secondary battery disclosed in Patent Document 1, warping or wrinkling may occur near the radially inner end of the gasket when the opening of the outer can is crimped. If warping or wrinkling occurs in the gasket, the gasket may undesirably interfere with other components.

[0005] It was also found that if the gasket is made of a single material, the sealing ability inside the battery may be reduced when the opening of the outer can is crimped. This is presumably because the resin material constituting the gasket is pushed radially inward when the opening of the outer can is crimped, reducing the thickness of the gasket on the radially outer side.

[0006] Therefore, an object of the present disclosure is to prevent the occurrence of warping or wrinkling of the gasket when the opening of the outer can is crimped while ensuring the sealing of the inside of the battery.

[0007] A secondary battery according to one aspect of the present disclosure comprises an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a cylindrical outer can having a bottom and housing the electrode assembly, a sealing body that closes the opening of the outer can, and an annular gasket that is interposed between the outer can and the sealing body, wherein the sealing body is crimped and fixed to the opening of the outer can via the gasket, and the gasket includes a first gasket and a second gasket that is positioned closer to the bottom than the first gasket, the sealing body is sandwiched between the first gasket and the second gasket from both axial sides of the outer can, and at least a portion of the first gasket is adjacent to the second gasket in the radial direction of the outer can.

[0008] Furthermore, a method for manufacturing a secondary battery according to one aspect of the present disclosure is a method for manufacturing a secondary battery including a cylindrical outer can having a bottom and accommodating an electrode assembly, a disk-shaped sealing body that closes an opening of the outer can, and an annular gasket that is interposed between the outer can and the sealing body, wherein the gasket includes a first gasket and a second gasket that abuts against the first gasket and is positioned closer to the bottom than the first gasket, and is characterized by including the steps of: before crimping the opening of the outer can, sandwiching the sealing body between the first gasket and the second gasket from both axial sides with at least a portion of the first gasket adjacent to the second gasket in the radial direction of the outer can; and bending the opening of the outer can radially inward and crimping and fixing the sealing body to the opening of the outer can via the gasket.

[0009] Furthermore, another aspect of the present disclosure is a method for manufacturing a secondary battery including a cylindrical outer can having a bottom and accommodating an electrode assembly, a disk-shaped sealing body that closes the opening of the outer can, and an annular gasket made of a resin material that is interposed between the outer can and the sealing body, wherein the gasket includes a first gasket and a second gasket that abuts against the first gasket and is positioned closer to the bottom than the first gasket, and the method includes the steps of: sandwiching the sealing body between the first gasket and the second gasket from both axial sides before crimping the opening of the outer can; heating the first gasket and the second gasket from the radial outside at a temperature equal to or higher than the softening temperature of the resin material; and bending the opening of the outer can radially inward, and crimping and fixing the sealing body to the opening of the outer can via the gasket.

[0010] According to the secondary battery of one aspect of the present disclosure, it is possible to ensure the airtightness of the interior of the battery while suppressing the occurrence of warping or wrinkling of the gasket when the opening of the outer can is crimped.

[0011] Fig. 1 is a cross-sectional view of a secondary battery that is one example of an embodiment; Fig. 2 is a cross-sectional view of a gasket that constitutes a secondary battery that is one example of an embodiment, in a state before an outer can is crimped; Fig. 3 is a cross-sectional view of a gasket that constitutes a secondary battery that is one example of an embodiment, in a state after an outer can is crimped; Fig. 4 is a cross-sectional view of a gasket that constitutes a secondary battery that is another example of an embodiment, in a state before an outer can is crimped; Fig. 5 is a cross-sectional view of a gasket that constitutes a secondary battery that is another example of an embodiment, in a state before an outer can is crimped;

[0012] Hereinafter, an example of an embodiment of a secondary battery according to the present disclosure will be described in detail with reference to the drawings. The embodiment described below is merely an example, and the present disclosure is not limited to the following embodiment. Furthermore, the present disclosure also includes embodiments obtained by selectively combining the components of the embodiments described below.

[0013] FIG. 1 is a schematic diagram illustrating a cross section of a secondary battery 10 according to an embodiment. As shown in FIG. 1 , the secondary battery 10 includes an electrode assembly 14, an electrolyte (not shown), and an outer can 20 that accommodates the electrode assembly 14 and the electrolyte. The electrode assembly 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and is configured such that the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The outer can 20 is a cylindrical metal container with a bottom that is open on one axial side, and the opening of the outer can 20 is closed by a sealing member 30. Hereinafter, the side of the sealing member 30 in the axial direction (height direction) of the secondary battery 10 is referred to as "upper," and the side of the bottom 21 of the outer can 20 in the axial direction is referred to as "lower."

[0014] The electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0015] The liquid electrolyte (electrolytic solution) contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent include esters, ethers, nitriles, amides, and mixed solvents of two or more of these. Examples of the non-aqueous solvent include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixed solvents of these. The non-aqueous solvent may contain a halogen-substituted compound (e.g., fluoroethylene carbonate) in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine. Examples of the electrolyte salt include LiPF ６ Lithium salts such as

[0016] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc. can be used. As the inorganic solid electrolyte, a material known in all-solid-state lithium ion secondary batteries, etc. (for example, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, a halogen-based solid electrolyte, etc.) can be used. 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. As the matrix polymer, for example, a polymer material that absorbs the non-aqueous solvent and gels is used. As the polymer material, for example, a fluororesin, an acrylic resin, a polyether resin, etc. can be used.

[0017] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all long, strip-like bodies that are spirally wound and alternately stacked in the radial direction of the electrode assembly 14. The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal direction and width direction (short direction) than the positive electrode 11. The separator 13 is formed to be at least slightly larger than the positive electrode 11, and two separators 13 are arranged to sandwich the positive electrode 11. The secondary battery 10 includes insulating plates 16 and 17 arranged above and below the electrode assembly 14, respectively.

[0018] The positive electrode 11 has a positive electrode core and a positive electrode mixture layer formed on the positive electrode core. The positive electrode core can be a foil of a metal, 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, and is preferably formed on both sides of the positive electrode core, excluding the exposed portion of the positive electrode core (not shown) to which the positive electrode lead 18 is welded. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core, drying the coating, and then compressing it to form a positive electrode mixture layer on both sides of the positive electrode core.

[0019] The positive electrode mixture layer contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium metal composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among them, it is preferable to contain at least one selected from Co, Ni, and Mn. Examples of suitable composite oxides include lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0020] Examples of conductive agents contained in the positive electrode mixture layer include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of binders contained in the positive electrode mixture layer include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0021] The negative electrode 12 has a negative electrode core and a negative electrode mixture layer formed on the negative electrode core. The negative electrode core can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The negative electrode mixture layer contains a negative electrode active material, a binder, and, if necessary, a conductive agent, and is preferably formed on both sides of the negative electrode core, excluding the exposed portion of the negative electrode core (not shown) to which the negative electrode lead 19 is welded. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the surface of 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.

[0022] The negative electrode mixture layer generally contains, as the negative electrode active material, a carbon material that reversibly absorbs and releases lithium ions. Suitable examples of the carbon material include natural graphite such as flake graphite, lump graphite, and amorphous graphite, and artificial graphite such as lump artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB). Furthermore, as the negative electrode active material, a material containing at least one of an element that alloys with Li, such as Si or Sn, and a material containing such an element may be used. Among these, a composite material containing Si is preferred.

[0023] A suitable example of a composite material containing Si is SiO ２ Examples of the composite material include a material in which Si fine particles are dispersed in a silicate phase such as lithium silicate, or a material in which Si fine particles are dispersed in an amorphous carbon phase. A conductive layer such as a carbon coating is formed on the particle surface of the composite material. The combined use of a carbon material and a Si-containing composite material as the negative electrode active material is preferred from the viewpoint of achieving both high capacity and high durability of the battery.

[0024] As in the case of the positive electrode mixture layer, the binder contained in the negative electrode mixture layer can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene-butadiene rubber (SBR) is preferably used. The negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use SBR in combination with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer may contain a conductive agent such as CNT.

[0025] The separator 13 is a porous sheet having ion permeability and insulating properties. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include polyolefins such as polyethylene and polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. A highly heat-resistant resin layer such as an aramid resin may be formed on the surface of the separator 13. A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12.

[0026] A positive electrode lead 18 is connected to the positive electrode 11, and a negative electrode lead 19 is connected to the winding end side of the negative electrode 12. The positive electrode lead 18 passes through a through hole in the insulating plate 16 and extends toward the sealing body 30, and the negative electrode lead 19 passes outside the insulating plate 17 and extends toward the bottom 21 of the outer can 20. The positive electrode lead 18 is connected to the underside of an internal terminal plate 31 of the sealing body 30 by welding or the like, and the sealing body 30 serves as a positive electrode terminal. The negative electrode lead 19 is connected to the inner surface of the bottom 21 of the metal outer can 20 by welding or the like, and the outer can 20 serves as a negative electrode terminal.

[0027] The exterior can 20 is a cylindrical metal container with a bottom that is open on one axial side. The exterior can 20 has a bottom 21 and a side surface 22 that forms the side surface of the secondary battery 10. The side surface 22 is the portion of the exterior can 20 excluding the bottom 21, and includes a groove 23 and an opening 24, which will be described later.

[0028] Groove portion 23 is a portion of side surface portion 22 that protrudes radially inward, and its upper surface supports sealing body 30. Groove portion 23 is formed in an annular shape along the circumferential direction of outer can 20. Groove portion 23 can be formed, for example, by spinning a portion of side surface portion 22 radially inward to form an annular recess radially inward.

[0029] The opening 24 is a region of the side surface portion 22 above the groove portion 23 and forms an opening in the outer can 20. The opening 24 is bent radially inward toward the peripheral edge of the sealing body 30 when the sealing body 30 is crimped to the outer can 20. As a result, the opening 24 is formed with an opening side surface portion 25 that forms part of the side surface of the secondary battery 10 and covers the outer peripheral surface of the gasket 40, and an opening top surface portion 26 that forms part of the top surface of the secondary battery 10 and covers part of the top surface of the gasket 40. In this embodiment, the radial inner end of the opening top surface portion 26 is located radially outward of the radial inner end of the gasket 40. In other words, the top surface of the radial inner end of the gasket 40 is not covered by the opening top surface portion 26.

[0030] The sealing body 30 is a disc-shaped member equipped with a safety valve. The sealing body 30 has a structure in which an internal terminal plate 31, an insulating member 32, and an external terminal plate 33 are stacked in this order from the electrode body 14 side.

[0031] The internal terminal plate 31 is a metal plate including a thick portion 31A to which the positive electrode lead 18 is connected and a thin central portion 31B that is separated from the thick portion 31A when the internal pressure of the battery exceeds a predetermined threshold. A plurality of vent holes 31C are formed in the thick portion 31A.

[0032] The insulating member 32 insulates the portions other than the connection portion between the internal terminal plate 31 and the external terminal plate 33. The insulating member 32 has an opening 32A formed in the radial center thereof, and an air vent 32B formed in a portion overlapping with the air vent 31C of the internal terminal plate 31.

[0033] The external terminal plate 33 forms a part of the upper surface of the secondary battery 10 and is disposed opposite the internal terminal plate 31 with the insulating member 32 sandwiched therebetween. The external terminal plate 33 has a thin-walled portion 33A that breaks when the internal pressure of the secondary battery 10 exceeds a predetermined threshold. The external terminal plate 33 is connected at its radial center to a central portion 31B of the internal terminal plate 31 by welding or the like. Furthermore, as will be described in detail later, the radial outer side of the external terminal plate 33 is held between the groove 23 and the opening 24 formed by bending the opening of the outer can 20 inward, via a gasket 40.

[0034] When an abnormality occurs in the secondary battery 10 and the internal pressure rises, the generated high-temperature gas pushes the internal terminal plate 31 upward, causing the internal terminal plate 31 to break, separating the central portion 31B from the thick portion 31A, and deforming the external terminal plate 33 so that it protrudes toward the outside of the battery, thereby interrupting the current path in the sealing body 30. Then, if the internal pressure of the secondary battery 10 rises further after the current path is interrupted, the thin portion 33A of the external terminal plate 33 breaks, forming a gas outlet in the external terminal plate 33.

[0035] The structure of sealing body 30 is not limited to the structure shown in Fig. 1. Sealing body 30 may have, for example, a convex cap that covers external terminal board 33.

[0036] The gasket 40 is a sealing material interposed between the outer can 20 and the external terminal plate 33 that constitutes the sealing body 30. By providing the gasket 40, the gap between the outer can 20 and the external terminal plate 33 is sealed, thereby ensuring the airtightness of the interior of the secondary battery 10. In other words, the gasket 40 is required to seal the gap between the outer can 20 and the external terminal plate 33.

[0037] Next, the gasket 40 will be described in detail with further reference to Figures 2 and 3. Figure 2 is a cross-sectional view of the gasket 40 before the outer can 20 is crimped, and Figure 3 is a cross-sectional view of the gasket 40 after the outer can 20 has been crimped. For ease of explanation, Figures 2 and 3 show a gap at the boundary between the first gasket 41 and the second gasket 42.

[0038] 2 and 3 , the gasket 40 includes a first gasket 41 and a second gasket 42 that is disposed closer to the bottom portion 21 than the first gasket 41. The thicknesses of the first gasket 41 and the second gasket 42 may be different from each other, but are preferably approximately the same from the viewpoint of ensuring the airtightness of the interior of the secondary battery 10. Hereinafter, the first gasket 41 and the second gasket 42 may be collectively referred to as the gasket 40.

[0039] The first gasket 41 and the second gasket 42 are both formed in an annular shape before and after the outer can 20 is crimped, and are generally L-shaped in axial cross section. The first gasket 41 and the second gasket 42 are arranged to sandwich the external terminal board 33 from both axial sides before and after the outer can 20 is crimped. More specifically, the first gasket 41 covers the radially outer side of the upper surface 33B of the external terminal board 33 and the upper side of the outer peripheral surface 33D of the external terminal board 33 before and after the outer can 20 is crimped. The second gasket 42 covers the radially outer side of the lower surface 33C of the external terminal board 33 and the lower side of the outer peripheral surface 33D of the external terminal board 33 before and after the outer can 20 is crimped. As will be described in more detail later, even before the outer can 20 is crimped, by arranging the first gasket 41 and the second gasket 42 so as to sandwich the external terminal board 33 from both axial sides, it is possible to reduce the amount of deformation of the first gasket 41 and the second gasket 42 when the outer can 20 is crimped.

[0040] Both the first gasket 41 and the second gasket 42 are made of a resin material. Examples of resin materials that can be used to make the first gasket 41 and the second gasket 42 include polyolefin resins such as polypropylene (PP), fluorinated resins such as tetrafluoroethylene-perfluoroalkoxyethylene copolymers (PFA), and polyphenylene sulfide (PPS). Making the first gasket 41 and the second gasket 42 out of a resin material makes it easier to seal the gap between the outer can 20 and the sealing body 30 while ensuring insulation between the outer can 20 and the sealing body 30. While the first gasket 41 and the second gasket 42 may be made of different resin materials, it is preferable that they be made of the same resin material from the viewpoint of productivity.

[0041] At least a portion of the first gasket 41 is adjacent to the second gasket 42 in the radial direction. In the present embodiment, a convex portion 44 is provided on the radially inner side of the second gasket 42, and a concave portion 43 into which the convex portion 44 fits is provided on the radially inner side of the first gasket 41. This forms an area where the first gasket 41 and the second gasket 42 are adjacent to each other in the radial direction.

[0042] When the opening 24 of the exterior can 20 is crimped, the first gasket 41 in particular is pressed radially inward. At this time, by providing an area where the first gasket 41 and the second gasket 42 are adjacent to each other in the radial direction, the first gasket 41 is prevented from coming off the second gasket 42. As a result, it is possible to ensure the airtightness of the interior of the secondary battery 10. In other words, if there is no area where the first gasket 41 and the second gasket 42 are adjacent to each other in the radial direction, the first gasket 41 may come off the second gasket 42 when the opening 24 of the exterior can 20 is crimped, which may reduce the airtightness of the interior of the secondary battery 10.

[0043] Furthermore, by providing a region where the first gasket 41 and the second gasket 42 are adjacent in the radial direction, a step is formed at the boundary between the first gasket 41 and the second gasket 42. This allows the distance between the boundary between the first gasket 41 and the second gasket 42 to be increased. As a result, even if foreign matter such as an electrolyte solution is present on the inner surface of the opening 24, the foreign matter can be prevented from penetrating into the sealing body 30. In other words, if the first gasket 41 and the second gasket 42 are not provided in a region where they are adjacent in the radial direction and no step is formed at the boundary between the first gasket 41 and the second gasket 42, the foreign matter present on the inner surface of the opening 24 may penetrate into the sealing body 30. If the foreign matter is conductive, the insulation between the outer can 20 and the sealing body 30 may not be sufficiently ensured, which may result in a decrease in battery performance.

[0044] The depth of the recessed portion 43 is the same as the height of the protruding portion 44. This makes it difficult for a gap to form between the first gasket 41 and the second gasket 42, thereby ensuring the airtightness of the interior of the secondary battery 10.

[0045] The depth of the recess 43 (the height of the protrusion 44) is preferably 20% or more, and more preferably 25% or more, of the thickness of the sealing body 30 (in this embodiment, the external terminal plate 33) sandwiched between the first gasket 41 and the second gasket 42. By making the depth of the recess 43 (the height of the protrusion 44) 20% or more of the thickness of the sealing body 30 sandwiched between the first gasket 41 and the second gasket 42, the first gasket 41 is less likely to come off the second gasket 42 when they are crimped and fixed. Furthermore, by making the depth of the recess 43 (the height of the protrusion 44) 20% or more of the thickness of the sealing body 30 sandwiched between the first gasket 41 and the second gasket 42, a step of a reasonable size can be formed at the boundary between the first gasket 41 and the second gasket 42. The upper limit of the depth of the recess 43 (the height of the protrusion 44 ) is, for example, 90% of the thickness of the sealing body 30 sandwiched between the first gasket 41 and the second gasket 42 .

[0046] The recessed portion 43 and the protruding portion 44 are preferably provided over the entire periphery of the first gasket 41 and the second gasket 42. In this case, the first gasket 41 is less likely to come off the second gasket 42 when the gaskets are fixed by crimping.

[0047] In the present embodiment, the first gasket 41 is provided with the recessed portion 43 and the second gasket 42 is provided with the protruding portion 44, but this is not limited thereto, and the first gasket 41 may be provided with the protruding portion and the second gasket 42 may be provided with the recessed portion. Furthermore, the position where the protruding portion 44 is formed is not limited to the radially inner side of the second gasket 42, and the protruding portion 44 may be provided in the radial center of the second gasket 42 or on the radially outer side of the second gasket 42.

[0048] Here, the structure of a conventional gasket made of one member will be described, and the effects of the gasket 40 made of two members according to this embodiment will be explained. Generally, when a gasket is made of one member, a gasket that is generally L-shaped in axial cross section is used before the outer can 20 is crimped. Before the outer can 20 is crimped, the gasket is disposed in contact with the lower surface 33C and the outer peripheral surface 33D of the external terminal board 33, but is not disposed in contact with the upper surface 33B of the external terminal board 33, with the upper region of the gasket abutting the opening 24. In other words, when a gasket is formed of one member, before the outer can 20 is crimped, the gasket is disposed in a state where it does not sandwich the external terminal board 33 from both sides in the axial direction. When the outer can 20 is crimped, the upper region of the gasket is pressed against the opening 24 and bent radially inward toward the peripheral edge of the external terminal board 33. As a result, the gaskets sandwich the external terminal board 33 from both sides in the axial direction.

[0049] When the upper region of the gasket is folded radially inward, the volume of the gasket near the folded region may decrease. This may increase the volume of the gasket toward the radially inner end, which may result in warping or wrinkles near the radially inner end of the gasket. Furthermore, when the upper region of the gasket is folded radially inward, the outer periphery of the gasket may be stretched toward the radially inner end of the gasket. This may reduce the volume of the outer periphery of the gasket, which may result in a decrease in the sealing ability of the interior of the secondary battery 10.

[0050] On the other hand, by configuring the gasket 40 with two members, the first gasket 41 and the second gasket 42, as in the present embodiment, the gasket 40 can sandwich the external terminal board 33 from both sides in the axial direction even before the outer can 20 is crimped. As a result, the gasket 40 is not bent radially inward when the outer can 20 is crimped, and therefore the volume of the gasket 40 is less likely to change. As a result, the gasket 40 can be prevented from warping or wrinkling while ensuring the airtightness of the interior of the secondary battery 10.

[0051] Next, a manufacturing process of the secondary battery 10 of this embodiment will be described with reference to FIGS.

[0052] The manufacturing process of the secondary battery 10 includes, for example, an attachment step of attaching the gasket 40 to the sealing body 30, an insertion step of inserting the electrode body 14 into the outer can 20 and connecting the sealing body 30 to the electrode body 14, and a crimping step of crimping and fixing the opening 24 of the outer can 20. The order of the attachment step and the insertion step is not particularly limited, and the attachment step may be performed after the insertion step.

[0053] In the attachment process, the first gasket 41 and the second gasket 42 are attached to the radial outside of the sealing body 30 (in this embodiment, the external terminal plate 33). More specifically, first, the second gasket 42 is placed from below the external terminal plate 33 so that the second gasket 42 covers the radial outside of the lower surface 33C of the external terminal plate 33 and the lower side of the outer peripheral surface 33D. Then, the first gasket 41 is placed from above the external terminal plate 33 so that the first gasket 41 covers the radial outside of the upper surface 33B of the external terminal plate 33 and the upper side of the outer peripheral surface 33D. At this time, the first gasket 41 is placed so that the protrusions 44 provided on the second gasket 42 fit into the recesses 43 provided on the first gasket 41. This allows the external terminal board 33 to be sandwiched between the first gasket 41 and the second gasket 42 from both axial sides with the first gasket 41 and the second gasket 42 adjacent to each other in the radial direction.

[0054] In the insertion step, the sealing body 30 prepared in the attachment step is connected to the electrode body 14 via the positive electrode lead 18. Then, the electrode body 14 is inserted into the outer can 20. Then, a groove 23 that supports the sealing body 30 is formed on the opening side of the side surface portion 22 of the outer can 20 by spinning from the radial outside.

[0055] In the crimping process, as shown in Fig. 2, the sealing body 30 is inserted into the outer can 20, and the external terminal plate 33 is placed on the upper surface of the groove 23. Then, as shown in Fig. 3, the opening 24 is bent radially inward toward the peripheral edge of the external terminal plate 33. This causes the sealing body 30 to be crimped and fixed to the opening 24 of the outer can 20 via the gasket 40.

[0056] Next, modified shapes of the gasket 40 will be shown with reference to Figures 4 to 6. Figures 4 to 6 are cross-sectional views of the gasket 40 in a state before it is crimped to the outer can 20. For ease of explanation, Figures 4 to 6 show a gap at the boundary between the first gasket 41 and the second gasket 42.

[0057] As shown in FIG. 4 , claws 46 may be provided on the outer peripheral surface of the protrusion 44 of the second gasket 42, and grooves 45 that fit into the claws 46 may be provided on the inner peripheral surface of the recess 43 of the first gasket 41. By providing the claws 46 and the grooves 45, the first gasket 41 and the second gasket 42 can be firmly fixed together. As a result, the first gasket 41 is more likely to be prevented from coming off the second gasket 42 when the outer can 20 is crimped, thereby further ensuring the sealing of the interior of the secondary battery 10. Note that the claws 46 and the grooves 45 may be provided around the entire circumference of the first gasket 41 and the second gasket 42, or may be provided only in a partial region in the circumferential direction.

[0058] 5 , a male thread 48 may be provided on the outer peripheral surface of a protrusion 44 provided on the second gasket 42, and a female thread 47 that fits into the male thread 48 may be provided on the inner peripheral surface of a recess 43 provided on the first gasket 41. By providing the male thread 48 and the female thread 47, the first gasket 41 and the second gasket 42 can be firmly fixed together. As a result, the first gasket 41 is more likely to be detached from the second gasket 42 when the outer can 20 is crimped, and the internal sealing of the secondary battery 10 can be more reliably ensured.

[0059] 6 , the boundary line between the first gasket 41 and the second gasket 42 may be wavy in an axial cross-sectional view. By making the boundary line between the first gasket 41 and the second gasket 42 wavy, a region where the first gasket 41 and the second gasket 42 are adjacent to each other in the radial direction can be provided. As a result, when the outer can 20 is crimped, the first gasket 41 is prevented from coming off the second gasket 42, and the internal sealing of the secondary battery 10 can be ensured.

[0060] Here, one method for forming the boundary line between the first gasket 41 and the second gasket 42 into a corrugated shape is to heat the first gasket 41 and the second gasket 42 from the radial outside at a temperature equal to or higher than the softening temperature of the resin material. More specifically, before crimping the opening of the outer can 20, the sealing body 30 (in this embodiment, the external terminal plate 33) is sandwiched between the first gasket 41 and the second gasket 42 from both axial sides. In this case, the boundary line between the first gasket 41 and the second gasket 42 may be a straight line, and further, the boundary line between the first gasket 41 and the second gasket 42 may not have a step. In other words, the first gasket 41 and the second gasket 42 may not have a recessed portion 43 or a protruding portion 44, and the contact surface between the first gasket 41 and the second gasket 42 may be flat.

[0061] Then, with the external terminal board 33 sandwiched between the first gasket 41 and the second gasket 42 from both axial sides, the first gasket 41 and the second gasket 42 are heated from the radial outside at a temperature equal to or higher than the softening temperature of the resin material (e.g., 150°C or higher). This softens the resin material constituting the first gasket 41 and the second gasket 42, causing the boundary line between the first gasket 41 and the second gasket 42 to become wavy. Note that the boundary line between the first gasket 41 and the second gasket 42 after the heat treatment is not limited to being wavy, and may be straight or have an uneven shape.

[0062] The present disclosure is further described by the following embodiments. Configuration 1: A secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a cylindrical outer can having a bottom and accommodating the electrode assembly; a disc-shaped sealing body that closes an opening of the outer can; and an annular gasket interposed between the outer can and the sealing body, wherein the sealing body is crimped and fixed to the opening of the outer can via the gasket, the gasket including a first gasket and a second gasket that is disposed closer to the bottom than the first gasket, the sealing body being sandwiched between the first gasket and the second gasket from both axial sides of the outer can, and at least a portion of the first gasket being adjacent to the second gasket in the radial direction of the outer can. Configuration 2: The secondary battery according to claim 1, wherein one of the first gasket and the second gasket has a convex portion, and the other of the first gasket and the second gasket has a concave portion in which the convex portion is disposed. Configuration 3: The secondary battery of claim 2, wherein the convex portion and the concave portion are provided around the entire circumference of the gasket.Configuration 4: The secondary battery of claim 2 or 3, wherein the convex portion is provided with a claw portion, and the concave portion is provided with a groove portion that fits into the claw portion.Configuration 5: The secondary battery of claim 2, wherein the convex portion is provided with a male thread portion, and the concave portion is provided with a female thread portion that fits into the male thread portion.Configuration 6: The secondary battery of claim 1, wherein, in an axial cross-sectional view of the outer can, a boundary line between the first gasket and the second gasket is wavy.Configuration 7: A method for manufacturing a secondary battery including a cylindrical outer can having a bottom and accommodating an electrode assembly, a disk-shaped sealing body that closes an opening of the outer can, and an annular gasket that is interposed between the outer can and the sealing body, wherein the gasket includes a first gasket and a second gasket that abuts against the first gasket and is positioned closer to the bottom than the first gasket, the method including: before crimping the opening of the outer can, sandwiching the sealing body between the first gasket and the second gasket from both axial sides with at least a portion of the first gasket adjacent to the second gasket in the radial direction; and bending the opening of the outer can radially inward, and crimping and fixing the sealing body to the opening of the outer can via the gasket. Configuration 8: A method for manufacturing a secondary battery including: a cylindrical outer can having a bottom and accommodating an electrode assembly; a disk-shaped sealing body that closes an opening of the outer can; and an annular gasket made of a resin material that is interposed between the outer can and the sealing body, wherein the gasket includes a first gasket and a second gasket that abuts against the first gasket and is positioned closer to the bottom than the first gasket, the method including the steps of: before crimping the opening of the outer can, sandwiching the sealing body between the first gasket and the second gasket from both axial sides; heating the first gasket and the second gasket from the radial outside at a temperature that is equal to or higher than the softening temperature of the resin material; and bending the opening of the outer can radially inward, and crimping and fixing the sealing body to the opening of the outer can via the gasket.

[0063] REFERENCE SIGNS LIST 10 secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 16, 17 insulating plate, 18 positive electrode lead, 19 negative electrode lead, 20 outer can, 21 bottom, 22 side surface, 23 groove, 24 opening, 25 opening side surface, 26 opening top surface, 30 sealing body, 31 internal terminal plate, 31A thick portion, 31B center, 31C ventilation hole, 32 insulating member, 32A opening, 32B ventilation hole, 33 external terminal plate, 33A thin portion, 33B top surface, 33C bottom surface, 33D outer peripheral surface, 40 gasket, 41 first gasket, 42 second gasket 42, 43 recess, 44 convex portion, 45 groove, 46 claw portion, 47 female screw portion, 48 Male threaded part.

Claims

1. A secondary battery comprising: an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween; a cylindrical outer can having a bottom and housing the electrode assembly; a disk-shaped sealing body that closes an opening of the outer can; and an annular gasket that is interposed between the outer can and the sealing body, wherein the sealing body is crimped and fixed to the opening of the outer can via the gasket, wherein the gasket includes a first gasket and a second gasket that is positioned closer to the bottom than the first gasket, the sealing body is sandwiched between the first gasket and the second gasket from both axial sides of the outer can, and at least a portion of the first gasket is adjacent to the second gasket in the radial direction of the outer can.

2. The secondary battery according to claim 1, wherein one of the first gasket and the second gasket has a convex portion, and the other of the first gasket and the second gasket has a concave portion in which the convex portion is disposed.

3. The secondary battery according to claim 2, wherein the protrusions and the recesses are provided around the entire circumference of the gasket.

4. The secondary battery according to claim 2, wherein the protrusion is provided with a claw portion, and the recess is provided with a groove portion that fits into the claw portion.

5. The secondary battery according to claim 2, wherein the convex portion is provided with a male thread portion, and the concave portion is provided with a female thread portion that fits into the male thread portion.

6. The secondary battery according to claim 1, wherein, in a cross-sectional view in the axial direction of the exterior can, the boundary lines of the first gasket and the second gasket are wavy.

7. A method for manufacturing a secondary battery comprising: a cylindrical outer can having a bottom and accommodating an electrode assembly; a disk-shaped sealing body closing an opening of the outer can; and an annular gasket interposed between the outer can and the sealing body, wherein the gasket comprises a first gasket and a second gasket abutting the first gasket and positioned closer to the bottom than the first gasket, the method comprising: before crimping the opening of the outer can, sandwiching the sealing body from both axial sides between the first gasket and the second gasket with at least a portion of the first gasket adjacent to the second gasket in the radial direction of the outer can; and bending the opening of the outer can radially inward and crimping and fixing the sealing body to the opening of the outer can via the gasket.

8. A method for manufacturing a secondary battery comprising: a cylindrical outer can having a bottom and accommodating an electrode assembly; a disk-shaped sealing body closing an opening of the outer can; and an annular gasket made of a resin material interposed between the outer can and the sealing body, wherein the gasket includes a first gasket and a second gasket abutting the first gasket and positioned closer to the bottom than the first gasket, the method comprising the steps of: sandwiching the sealing body between the first gasket and the second gasket from both axial sides before crimping the opening of the outer can; heating the first gasket and the second gasket from the radial outside at a temperature equal to or higher than the softening temperature of the resin material; and bending the opening of the outer can radially inward, and crimping and fixing the sealing body to the opening of the outer can via the gasket.

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