Secondary battery

Abstract

A first core body exposed portion (41a) to which a positive electrode lead (20) is joined is provided on a first surface of a positive electrode (11), and a second core body exposed portion (41b), which at least partially overlaps the first core body exposed portion (41a) in the thickness direction of the positive electrode (11), is provided on a second surface thereof. The leading end of a second non-tail portion (58) provided on the second surface is disposed so as to oppose, in the thickness direction of the positive electrode (11), a first flat portion (42c) of a first mixture layer (42a) adjacent to a first tail portion (57) provided on the first surface. The leading end of a first non-tail portion (48) provided on the first surface is disposed so as to oppose, in the thickness direction of the positive electrode (11), a second flat portion (42d) of a second mixture layer (42b) adjacent to a second tail portion (57) provided on the second surface.

Description

secondary battery

[0001] The present disclosure relates to secondary batteries.

[0002] Conventional secondary batteries include a cylindrical battery described in Patent Document 1. This cylindrical battery includes an electrode assembly in which a positive electrode and a negative electrode are wound longitudinally with a separator interposed therebetween, a bottomed cylindrical outer can housing the electrode assembly, and a sealing body crimped to the opening of the outer can via a gasket. A positive electrode core exposed portion is provided in the longitudinal middle of the positive electrode so as to be sandwiched between positive electrode mixture layers in the longitudinal direction. One end of a positive electrode lead is joined to the positive electrode core exposed portion, and the other end of the positive electrode lead is joined to the inner surface of the sealing body. Furthermore, one end of a negative electrode lead is joined to the end of the winding of the negative electrode, and the other end of the negative electrode lead is joined to the inner bottom surface of the outer can.

[0003] Re-table No. 2019-044770

[0004] In a secondary battery electrode, the material mixture layer expands and contracts with charge and discharge, but the core exposed portion does not. Therefore, when a core exposed portion is provided in the longitudinal middle of the electrode, deformation such as wrinkles is likely to occur in the core at the boundary between the material mixture layer forming region and the core exposed portion. Therefore, an object of the present disclosure is to provide a cylindrical battery in which deformation of the core is less likely to occur at the boundary between the material mixture layer forming region and the core exposed portion.

[0005] In order to solve the above problems, the cylindrical battery according to the present disclosure is a secondary battery including an electrode assembly in which two electrodes of opposite polarity are wound in the longitudinal direction with a separator interposed therebetween, wherein a first surface of one of the two electrodes is arranged so as to be sandwiched in the longitudinal direction by a first mixture layer provided on the first surface and has a first core exposed portion to which an electrode lead is joined, and a second surface of one of the electrodes is arranged so as to be sandwiched in the longitudinal direction by a second mixture layer provided on the second surface and has a second core exposed portion, at least a portion of which is arranged to face the first core exposed portion in the thickness direction, and the first mixture layer is adjacent to an end portion on a first side in the longitudinal direction of the first core exposed portion and is joined to the longitudinal direction of the first core exposed portion. The tape has a first tailing portion having a plurality of first tails extending in the longitudinal direction, and a first non-tailing portion adjacent to the end of the first core exposed portion on the second longitudinal side and having a tip extending approximately in the width direction, and the second mixture layer has a second non-tailing portion adjacent to the end of the second core exposed portion on the first longitudinal side and having a tip extending approximately in the width direction, and a second tailing portion adjacent to the end of the second core exposed portion on the second longitudinal side and having a plurality of second tails extending in the longitudinal direction, the tip of the second non-tailing portion being arranged opposite in the thickness direction to a first flat portion of the first mixture layer adjacent to the first tailing portion, and the tip of the first non-tailing portion being arranged opposite in the thickness direction to a second flat portion of the second mixture layer adjacent to the second tailing portion.

[0006] In the secondary battery according to the present disclosure, the core is less likely to deform at the boundary between the mixture layer forming region and the core exposed portion.

[0007] Fig. 2 is an axial cross-sectional view of a cylindrical battery according to an embodiment of the present disclosure; Fig. 3 is a plan view of the periphery of a first substrate exposed portion to which a positive electrode lead is joined on the outer winding surface that constitutes the first surface of the positive electrode; Fig. 4 is a cross-sectional view taken along line A-A in Fig. 2; Fig. 5 is a cross-sectional view corresponding to Fig. 3 of a battery of a reference example; Fig. 6 is a plan view corresponding to Fig. 2 of a battery of a modified example.

[0008] Hereinafter, with reference to the drawings, an embodiment of a secondary battery according to the present disclosure will be described in detail. The secondary battery according to the present disclosure may be any secondary battery including a wound electrode assembly, and may be a secondary battery using an aqueous electrolyte or a secondary battery using a nonaqueous electrolyte. The secondary battery according to the present disclosure may be a cylindrical battery including a bottomed cylindrical outer can, a prismatic battery including a prismatic outer can, or a pouch-type battery including an outer body formed of a laminate sheet including a metal layer and a resin layer. Below, a cylindrical battery (lithium ion battery) using a nonaqueous electrolyte will be exemplified as one embodiment of the secondary battery, but the secondary battery according to the present disclosure is not limited thereto.

[0009] It is anticipated from the beginning that new embodiments will 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 will be omitted. Furthermore, multiple drawings include schematic diagrams, and the dimensional ratios of the length, width, height, etc. of each component between different drawings do not necessarily match. In this specification, the side of the sealing body 17 in the axial direction (height direction) of the cylindrical battery 10 is referred to as "upper," and the side of the bottom 68 of the outer can 16 in the axial direction is referred to as "lower." Among the components described below, those not recited in the independent claims representing the highest concepts are optional and not required.

[0010] 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 a wound electrode assembly 14, a non-aqueous electrolyte (not shown), a cylindrical metal outer can 16 with a bottom that houses the electrode assembly 14 and the non-aqueous electrolyte, and a sealing body 17 that closes the opening of the outer can 16. The electrode assembly 14 has a wound structure in which an elongated positive electrode 11 and an elongated negative electrode 12 are wound longitudinally with two elongated separators 13 interposed therebetween.

[0011] The negative electrode 12 is formed to be slightly larger than the positive electrode 11 in order to prevent lithium precipitation. The negative electrode 12 is formed to be longer than the positive electrode 11 in the longitudinal direction and width direction (short direction). The two separators 13 are formed to be at least slightly larger than the positive electrode 11 and are arranged to sandwich the positive electrode 11, for example. The negative electrode 12 may form the winding start end of the electrode assembly 14. However, in general, the separator 13 extends beyond the winding start end of the negative electrode 12, and the winding start end of the separator 13 becomes the winding start end of the electrode assembly 14.

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

[0013] Examples of the solid electrolyte include solid or gel polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt, and a matrix polymer. Examples of the matrix polymer include a polymer material that absorbs the non-aqueous solvent and gels. Examples of the polymer material include fluororesin, acrylic resin, and polyether resin. Examples of the inorganic solid electrolyte include materials known in all-solid-state lithium ion secondary batteries (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halide-based solid electrolytes, etc.).

[0014] The positive electrode 11 has a positive electrode core 41 (see FIG. 3 ) and positive electrode mixture layers 42 (see FIG. 3 ) formed on both sides of the positive electrode core 41. The positive electrode core 41 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 layer. The positive electrode mixture layer 42 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc. to the positive electrode core 41, drying the coating, and then compressing it to form the positive electrode mixture layers 42 on both sides of the positive electrode core 41.

[0015] The positive electrode active material is mainly composed of a lithium-containing metal composite oxide. Examples of metal elements contained in the lithium-containing metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. An example of a preferred lithium-containing metal composite oxide is a composite oxide containing at least one of Ni, Co, Mn, and Al.

[0016] Examples of the conductive agent contained in the positive electrode mixture layer 42 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, or polyethylene oxide (PEO).

[0017] The negative electrode 12 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 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core, drying the coating, and then compressing it to form a negative electrode mixture layer on both sides of the negative electrode core.

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

[0019] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. In addition to SBR or the like, the negative electrode mixture layer may also contain, for example, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0020] A porous sheet having ion permeability and insulating properties is used for the separator 13. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a nonwoven fabric. Preferred materials for the separator 13 include polyolefin resins such as polyethylene and polypropylene, and cellulose. The separator 13 may have either a single-layer structure or a laminated structure. A heat-resistant layer or the like may be formed on the surface of the separator 13.

[0021] As shown in FIG. 1 , the positive electrode lead 20 is electrically connected to an intermediate portion, such as the center portion, of the positive electrode core 41 (see FIG. 3 ) in the winding direction, and the negative electrode lead 21 is electrically connected to the end portion of the negative electrode core at the winding end. The battery 10 has an insulating plate 18 above the electrode body 14 and an insulating plate 19 below the electrode body 14. The positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, while the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom 68 of the outer can 16. The positive electrode lead 20 is connected to the underside of a terminal plate 23 of the sealing body 17 by welding or the like. A terminal cap 27 constituting the top plate of the sealing body 17 is electrically connected to the terminal plate 23, and the terminal cap 27 serves as a positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom 68 of the metal outer can 16 by welding or the like, and the outer can 16 serves as a negative electrode terminal.

[0022] The battery 10 includes a resin gasket 28 disposed between the exterior can 16 and the sealing body 17. The sealing body 17 is fixed to the opening of the exterior can 16 by crimping via the gasket 28. This seals the internal space of the battery 10. The gasket 28 is sandwiched between the exterior can 16 and the sealing body 17, and insulates the sealing body 17 from the exterior can 16. The gasket 28 serves as a sealant to maintain airtightness inside the battery and as an insulating material to insulate the exterior can 16 and the sealing body 17.

[0023] The outer can 16 has a cylindrical portion 30 and a bottom portion 68. The cylindrical portion 30 includes an annular grooved portion 34 and an annular shoulder portion 38. The grooved portion 34 is formed by subjecting a portion of the cylindrical portion 30 to a spinning process to form a recess radially inward. The shoulder portion 38 is formed when the upper end of the cylindrical portion 30 is bent radially inward and crimped onto the peripheral edge portion 35 of the sealing body 17, and extends radially inward at the upper end of the cylindrical portion 30.

[0024] The sealing body 17 has a structure in which, in order from the electrode body 14 side, a terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a terminal cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to each other. The terminal plate 23 has at least one through-hole 23a. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. The terminal cap 27 has a convex shape with its radial center portion protruding outward.

[0025] When the battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the terminal cap 27, cutting off the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 breaks and gas is released from the through-hole 27a of the terminal cap 27. This gas release prevents the internal pressure of the battery 10 from rising excessively, which could cause the battery 10 to explode, thereby improving the safety of the battery 10.

[0026] In the above description, the sealing body 17 has a laminated structure including two rupture plates (lower valve body 24 and upper valve body 26) and a convex terminal cap 27 that covers the rupture plate. However, the sealing body may be composed of only a rupture plate, or may have a structure in which an internal terminal plate, an insulating plate, and a rupture plate are laminated in this order from the electrode body side. Alternatively, the sealing body may not have a rupture plate, and the bottom of the outer can may have a thin, easily breakable portion that breaks when the battery generates abnormal heat.

[0027] The configuration of the positive electrode 11 will be described in further detail below with reference to Figures 2 to 4. Figure 2 is a plan view of the periphery of the first core exposed portion 41a to which the positive electrode lead 20 is joined on the outer winding surface 51 that constitutes the first surface of the positive electrode 11. Figure 3 is a cross-sectional view taken along line A-A in Figure 2, showing the battery 10 cut along a cutting plane that includes the longitudinal direction and thickness direction and passes through the positive electrode lead 20. In Figure 2, the outer edge of the insulating tape 61a is shown by a virtual line.

[0028] 2, the first core exposed portion 41a to which the positive electrode lead 20, which is an example of an electrode lead, is joined is configured to be sandwiched in the longitudinal direction by a first mixture layer 42a of the positive electrode mixture layer 42 formed on the outer winding surface 51. In addition, a part of the first mixture layer 42a is disposed adjacent to the first core exposed portion 41a in the width direction.

[0029] The first mixture layer 42a is produced, for example, as follows. The hoop-shaped positive electrode core 41 is unwound by a drive roll (not shown), transporting the positive electrode core 41 at a constant speed to one side in the longitudinal direction and running at a constant speed in the longitudinal direction below first and second discharge sections (not shown) that discharge positive electrode mixture slurry. At this time, the positive electrode mixture slurry is intermittently discharged from the second discharge section into a range in the width direction of the positive electrode core 41 where the first core exposed portion 41a is formed, and the positive electrode mixture slurry is continuously discharged from the first discharge section into a range in the width direction adjacent to the first core exposed portion 41a where the first mixture layer 42a is formed. The positive electrode mixture slurry is not discharged from the second discharge section into a range in the longitudinal direction where the first core exposed portion 41a is formed. By discharging the positive electrode mixture slurry in this manner, the first mixture layer 42a shown in FIG. 2 is formed.

[0030] 2 and 3 , in the first mixture layer 42a formed in association with the discharge of such positive electrode mixture slurry, no tail is formed at the start end of the discharge of the positive electrode mixture slurry, but a comb-shaped tail portion 47 is formed near the end end of the discharge of the positive electrode mixture slurry in a plan view of the positive electrode 11. More specifically, the first mixture layer 42a has a first tail portion 47 having a plurality of first tails 47a that are adjacent to an end of the first core exposed portion 41a on a first side in the longitudinal direction of the positive electrode 11 and extend in the longitudinal direction of the positive electrode 11, and a first non-tail portion 48 that is adjacent to an end of the first core exposed portion 41a on a second side in the longitudinal direction of the positive electrode 11 and has a tip that extends substantially in the width direction.

[0031] A first side in the longitudinal direction of the positive electrode 11 coincides with the winding start side of the positive electrode 11, and a second side in the longitudinal direction of the positive electrode 11 coincides with the winding end side of the positive electrode 11. By discharging the positive electrode mixture slurry onto the positive electrode core 41 in the same manner as described above, a second mixture layer 42b is formed on the inner winding surface 52 that constitutes the second surface of the positive electrode 11, and a second core exposed portion 41b is formed that is sandwiched between the second mixture layers 42b and at least a portion of which faces the first core exposed portion 41a in the thickness direction.

[0032] Although not shown, a second mixture layer 42b having a planar shape similar to that of the first mixture layer 42a is also formed on the inner winding surface 52 of the positive electrode 11, and a portion of the second mixture layer 42b is disposed adjacent to the second core exposed portion 41b in the width direction. As shown in Fig. 3, the second mixture layer 42b has a second non-tailing portion 58 that is adjacent to an end of the second core exposed portion 41b on a first side in the longitudinal direction of the positive electrode 11 and has a tip that extends substantially in the width direction, and a second tailing portion 57 that is adjacent to an end of the second core exposed portion 41b on a second side in the longitudinal direction of the positive electrode 11 and has a plurality of second tails 57a that extend in the longitudinal direction of the positive electrode 11.

[0033] The tip of the second non-tailing portion 58 is disposed opposite, in the thickness direction of the positive electrode 11, a first flat portion 42c of the first mixture layer 42a that is adjacent to the first tailing portion 47 in the longitudinal direction of the positive electrode 11, and the tip of the first non-tailing portion 48 is disposed opposite, in the thickness direction of the positive electrode 11, a second flat portion 42d of the second mixture layer 42b that is adjacent to the second tailing portion 57 in the longitudinal direction of the positive electrode 11. Insulating tapes 61a, 61b that cover the positive electrode lead 20 and the core exposed portions 41a, 41b are attached to the front and back of the positive electrode 11.

[0034] 4 is a cross-sectional view of a battery 210 of the reference example corresponding to FIG. 3. In the positive electrode 211 of the battery 210 of the reference example, the tip of the second non-tailing portion 258 is arranged opposite the first tailing portion 247 in the thickness direction of the positive electrode 211, and the tip of the first non-tailing portion 248 is arranged opposite the second tailing portion 257 in the thickness direction of the positive electrode 211.

[0035] When the mixture layer expands and contracts during charge and discharge, the exposed core portion formed in the longitudinal middle of the electrode is susceptible to stress similar to that of the mixture layer-forming portion. When the difference in rigidity between the mixture layer-forming portion and the exposed core portion increases, deformation such as wrinkles is more likely to occur in the core at the boundary between the mixture layer-forming portion and the exposed core portion. Therefore, deformation such as wrinkles is more likely to occur in the core at the boundary between the non-tailing portion and the exposed core portion than at the boundary between the tailing portion and the exposed core portion. In the battery 10 of the above embodiment, the tips of the non-tailing portions 48, 58 are positioned opposite the flat portions 42c, 42d of the positive electrode mixture layer 42 adjacent to the tailing portions 47, 57 in the thickness direction of the positive electrode 11. This reduces the change in rigidity from the non-tailing portions 48, 58 to the exposed core portions 41a, 41b, thereby suppressing deformation of the positive electrode core 41 at the boundary between the non-tailing portions 48, 58 and the exposed core portions 41a, 41b. On the other hand, in the battery 210 of the reference example, the tips of the non-tailing portions 248, 258 of the positive electrode mixture layer 242 are arranged opposite the tailing portions 247, 257, which have lower rigidity than the flat portion, so the effect of mitigating the difference in rigidity from the non-tailing portions 248, 258 to the core exposed portions 241a, 241b is insufficient, and deformation of the positive electrode core 241 cannot be sufficiently suppressed.

[0036] Furthermore, since the tips of the non-tailing portions 48, 58 are disposed opposite the flat portions 42c, 42d of the positive electrode mixture layer 42 adjacent to the tailing portions 47, 57 in the thickness direction of the positive electrode 11, when the coating film is compressed by the roller after the positive electrode mixture slurry coating film has dried, the length in the thickness direction over which the roller descends at the boundary portion is reduced. Therefore, the impact that the positive electrode 11 receives when the roller descends is reduced, and for this reason as well, deformation of the boundary portion of the positive electrode core 41 is suppressed.

[0037] When a portion of the positive electrode mixture layer 42 is disposed adjacent to the substrate exposed portions 41 a, 41 b in the width direction, the range in which a difference in rigidity occurs from the non-tailing portions 48, 58 to the substrate exposed portions 41 a, 41 b is reduced. Therefore, the effect of suppressing deformation at the boundary between the positive electrode substrate 41 and the positive electrode mixture layer 42 according to the present disclosure becomes significant.

[0038] Furthermore, when a portion of the positive electrode mixture layer 42 is disposed adjacent to the core exposed portions 41 a, 41 b in the width direction, the length of descent of the roller at the boundary portion in the width direction of the positive electrode 11 is further reduced. Therefore, the impact that the positive electrode 11 receives when the roller is lowered is further reduced, and deformation at the boundary portion of the positive electrode core 41 is further suppressed.

[0039] In order to prevent the positive electrode mixture layer 42 from peeling off from the positive electrode substrate 41, it is preferable to arrange a trailing portion 57 adjacent to the end portion on the winding start side of the substrate exposed portion 41 a on the outer winding surface 51 of the positive electrode 11. This is because the trailing portion 57 is less likely to peel off from the positive electrode substrate 41 than the non-trailing portion 58.

[0040] The present disclosure is not limited to the above-described embodiments and their modifications, and various improvements and modifications are possible within the scope of the claims of the present application and their equivalents.

[0041] FIG. 5 is a plan view of a modified battery 110 corresponding to FIG. 2 . As shown in FIG. 5 , a first core exposed portion 141a may be provided on the outer winding surface 151, which is the first surface of the positive electrode 111, from one end to the other end in the width direction of the positive electrode 111. In this case, a tail portion 147 and a non-tail portion 148 are also provided on the first core exposed portion 141a from one end to the other end in the width direction of the positive electrode 111. A positive electrode lead 120 is joined to the first core exposed portion 141a. In this case, a second core exposed portion (not shown), at least a portion of which is disposed opposite the first core exposed portion 141a in the thickness direction of the positive electrode 111, may also be provided on the second surface of the positive electrode 111 from one end to the other end in the width direction of the positive electrode 111. Note that in FIG. 5 , the outer edges of the insulating tape 161a covering the positive electrode lead 120 and the first core exposed portion 141a are shown by imaginary lines. The cross section taken along line A'-A' in FIG. 5 corresponds to the cross section shown in FIG. 3 .

[0042] The first core exposed portion to which the positive electrode lead is joined may be provided on the inner winding surface of the positive electrode. In this case, too, in order to prevent peeling of the positive electrode mixture layer, it is preferable that the non-tailing portion be located on the winding start side of the first core exposed portion on the inner winding surface of the positive electrode.

[0043] In the negative electrode, a tip of the second non-tailing portion may be disposed opposite a first flat portion of the first mixture layer adjacent to the first tailing portion in the thickness direction of the negative electrode, and a tip of the first non-tailing portion may be disposed opposite a second flat portion of the second mixture layer adjacent to the second tailing portion in the thickness direction of the negative electrode. In this case, a negative electrode lead, which is an example of an electrode lead, is joined to the first core exposed portion.

[0044] The electrodes of the present disclosure may be applied to both positive and negative electrodes.

[0045] The secondary battery of the present disclosure may also have the following configuration: Configuration 1: A secondary battery including an electrode assembly in which two electrodes having opposite polarities are wound longitudinally with a separator interposed therebetween, wherein a first surface of one of the two electrodes is arranged so as to be sandwiched in the longitudinal direction by a first mixture layer provided on the first surface and has a first core exposed portion to which an electrode lead is joined, a second surface of the one electrode is arranged so as to be sandwiched in the longitudinal direction by a second mixture layer provided on the second surface and has a second core exposed portion, at least a portion of which is arranged to face the first core exposed portion in the thickness direction, and the first mixture layer is adjacent to an end on a first side in the longitudinal direction of the first core exposed portion and has a plurality of first tails extending in the longitudinal direction. and a first non-tailing portion adjacent to the end of the second core exposed portion on the second side in the longitudinal direction and having a tip extending substantially in the width direction, the second mixture layer having a second non-tailing portion adjacent to the end of the second core exposed portion on the first side in the longitudinal direction and having a tip extending substantially in the width direction, and a second tailing portion adjacent to the end of the second core exposed portion on the second side in the longitudinal direction and having a plurality of second tails extending in the longitudinal direction, the tip of the second non-tailing portion being disposed opposite in the thickness direction to a first flat portion of the first mixture layer adjacent to the first tailing portion, and the tip of the first non-tailing portion being disposed opposite in the thickness direction to a second flat portion of the second mixture layer adjacent to the second tailing portion. Configuration 4: The secondary battery according to any one of configurations 1 to 3, wherein a portion of the first mixture layer is disposed adjacent to the first substrate exposed portion in the width direction, and a portion of the second mixture layer is disposed adjacent to the second substrate exposed portion in the width direction.Configuration 5: The secondary battery according to any one of configurations 1 to 4, wherein the first surface is an outer winding surface, and the first side in the longitudinal direction is a winding start side of the one electrode.Configuration 6: The secondary battery according to any one of configurations 1 to 4, wherein the first surface is an inner winding surface, and the first side in the longitudinal direction is a winding end side of the one electrode.

[0046] REFERENCE SIGNS LIST 10,110 Battery, 11,111 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18,19 Insulating plate, 20,120 Positive electrode lead, 21 Negative electrode lead, 23 Terminal plate, 23a Through hole, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Terminal cap, 27a Through hole, 28 Gasket, 30 Cylindrical portion, 34 Grooved portion, 35 Peripheral portion, 38 Shoulder portion, 41 Positive electrode core, 41a, 141a First core exposed portion, 41b Second core exposed portion, 42 Positive electrode mixture layer, 42a First mixture layer, 42b Second mixture layer 42c First flat portion, 42d Second flat portion, 47 First tailing portion, 47a First tailing portion, 48 First non-tailing portion, 51, 151 Outer surface of winding, 52 Inner surface of winding, 57 Second tailing portion, 57a Second tailing portion, 58 Second non-tailing portion, 61a, 61b, 161a Insulating tape, 68 Bottom portion, 74 Boundary portion, 147 Tail portion, 148 Non-tailing portion.

Claims

1. A secondary battery comprising an electrode assembly in which two electrodes of opposite polarity are wound in the longitudinal direction with a separator interposed therebetween, wherein a first surface of one of the two electrodes is arranged so as to be sandwiched in the longitudinal direction by a first mixture layer provided on the first surface and has a first core exposed portion to which an electrode lead is joined, and a second surface of the one electrode is arranged so as to be sandwiched in the longitudinal direction by a second mixture layer provided on the second surface and has a second core exposed portion, at least a portion of which is arranged facing the first core exposed portion in the thickness direction, and the first mixture layer has a first tail portion adjacent to an end portion on a first side in the longitudinal direction of the first core exposed portion and having a plurality of first tails extending in the longitudinal direction, and a first non-tail portion adjacent to an end portion on a second side in the longitudinal direction of the first core exposed portion and having a tip extending in approximately the width direction, a second mixture layer having a second non-tailing portion adjacent to an end portion on the first side in the longitudinal direction of the second core exposed portion and having a tip extending approximately in the width direction, and a second tailing portion having a plurality of second tails adjacent to an end portion on the second side in the longitudinal direction of the second core exposed portion and extending in the longitudinal direction, wherein the tip of the second non-tailing portion is arranged to face a first flat portion of the first mixture layer adjacent to the first tailing portion in the thickness direction, and the tip of the first non-tailing portion is arranged to face a second flat portion of the second mixture layer adjacent to the second tailing portion in the thickness direction.

2. The secondary battery according to claim 1, wherein said one electrode is a positive electrode.

3. The secondary battery according to claim 1, wherein said one electrode is a negative electrode.

4. A secondary battery described in any one of claims 1 to 3, wherein a portion of the first mixture layer is arranged adjacent to the first core exposed portion in the width direction, and a portion of the second mixture layer is arranged adjacent to the second core exposed portion in the width direction.

5. A secondary battery according to any one of claims 1 to 3, wherein the first surface is an outer winding surface, and the first side in the longitudinal direction is the winding start side of the one electrode.

6. A secondary battery according to any one of claims 1 to 3, wherein the first surface is an inner surface of the winding, and the first side in the longitudinal direction is a winding end side of the one electrode.

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