Non-aqueous electrolyte secondary battery

Abstract

Provided is a non-aqueous electrolyte secondary battery provided with an electrode body in which the flatness of an end face is improved. This non-aqueous electrolyte secondary battery comprises: an electrode body in which a first electrode and a second electrode having different polarities from each other are wound via a separator; a non-aqueous electrolyte; and an exterior can that accommodates the electrode body and the non-aqueous electrolyte. The first electrode has a first core body and a first mixture layer formed on the surface of the first core body. A first core body exposed part in which the first core body is exposed is disposed at one end part of the electrode body in a winding axis direction. The first core body exposed part has a recessed part thinner than the first core body in a region where the first mixture layer is formed. The position of the recessed part changes from the end part side of the first mixture layer to the end part side of the first core body from the winding outer side to the winding inner side along the winding direction of the electrode body.

Description

Non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery including a wound electrode assembly.

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been widely used, in which a wound electrode assembly, in which strip-shaped positive and negative electrodes are stacked and wound, is housed in a bottomed cylindrical outer can. In non-aqueous electrolyte secondary batteries, in order to improve current collection efficiency, an end of the electrode core is protruded from the electrode assembly, and the tip of the end is pressed to form a flat portion, which is then joined to a current collector plate. Patent Document 1 discloses a technique in which a core protruding from the electrode assembly is provided with a deformable portion parallel to the winding direction of the electrode assembly, and the core is bent at the deformable portion. Patent Document 1 describes that this configuration reduces the gap between the cores at the flat portion, preventing laser light from reaching the interior of the electrode assembly, thereby suppressing damage to the electrode assembly during laser welding.

[0003] International Publication No. 2023 / 002798

[0004] In order to increase the current collection efficiency and obtain a high-power battery, it is necessary to improve the flatness of the end surface of the electrode assembly that contacts the current collector plate. However, in recent years, electrode assemblies have become larger due to increases in capacity, etc., making it increasingly difficult to improve the flatness of the end surface of the electrode assembly. The technology described in Patent Document 1 still has room for improvement in terms of improving the flatness of the end surface of the electrode assembly.

[0005] An object of the present disclosure is to provide a nonaqueous electrolyte secondary battery including an electrode assembly with improved end surface flatness.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure comprises an electrode body in which a first electrode and a second electrode of opposite polarity are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can accommodating the electrode body and the non-aqueous electrolyte, wherein the first electrode has a first core and a first mixture layer formed on the surface of the first core, and a first core exposed portion where the first core is exposed is disposed at one end of the electrode body in the winding axis direction, and the first core exposed portion has a recessed portion that is thinner than the first core at the location where the first mixture layer is formed, and the position of the recessed portion varies from the end side of the first mixture layer to the end side of the first core from the outer side of the winding to the inner side of the winding along the winding direction of the electrode body.

[0007] According to the nonaqueous electrolyte secondary battery according to the present disclosure, the output characteristics of the battery can be improved.

[0008] 5 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery that is an example of an embodiment. FIG. 6 is a perspective view of a wound electrode body provided in the nonaqueous electrolyte secondary battery shown in FIG. 1. FIG. 7 is a front view showing a positive electrode included in an electrode body according to an example of an embodiment in a developed state. FIG. 8 is a cross-sectional view taken along line A-A in FIG. 3. FIG. 9 is a plan view showing an end face of an electrode body provided in a nonaqueous electrolyte secondary battery that is another example of an embodiment. FIG. 10 is an enlarged view of a portion of a positive electrode substrate exposed portion, and is a plan view showing the state of a recessed portion when producing the electrode body shown in FIG.

[0009]

[0003] Non-aqueous electrolyte secondary batteries have been known in which a positive electrode core and a negative electrode core protrude from the upper and lower ends of the electrode assembly in the winding axis direction, respectively, and these cores are joined to two current collector plates arranged above and below the electrode assembly. Generally, the exposed portion of the positive electrode core is bent from the outer side of the winding to the inner side of the winding along the radial direction of the electrode assembly, with the outer side being bent more. After extensive research, the inventors discovered that if the recessed portion is parallel to the winding direction of the electrode assembly, portions that are not recessed may be bent, resulting in a decrease in the flatness of the end face of the electrode assembly.

[0010] The inventors have found that the flatness of the end face of the electrode body can be improved by varying the position of a thin recess provided in an exposed portion of the substrate located at one end of the electrode body in the winding axis direction, from the end side of the mixture layer to the end side of the substrate, from the outer side to the inner side along the winding direction of the electrode body, thereby increasing the adhesion between the electrode body and the current collector plate and improving the output characteristics of the battery.

[0011] Hereinafter, an example of an embodiment of a nonaqueous electrolyte secondary battery according to the present disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc. are examples for facilitating understanding of the present invention and can be appropriately changed according to the specifications of the nonaqueous electrolyte secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is initially assumed that the characteristic portions thereof will be used in appropriate combination.

[0012] Fig. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment of the present disclosure, and Fig. 2 is a perspective view illustrating the structure of an electrode assembly 14. As shown in Fig. 1, the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte (not shown), a cylindrical metal outer can 15 with a bottom that houses the electrode assembly 14 and the nonaqueous electrolyte, and a sealing body 16 that closes the opening of the outer can 15. For ease of explanation, the sealing body 16 side will be referred to as "top" and the bottom side of the outer can 15 will be referred to as "bottom."

[0013] As shown in FIG. 2 , the electrode assembly 14 has a wound structure in which a strip-shaped positive electrode 11 and a strip-shaped negative electrode 12 are wound with two strip-shaped separators 13 interposed therebetween. The positive electrode 11 protrudes upward relative to the negative electrode 12 and the separator 13, and the negative electrode 12 protrudes downward relative to the positive electrode 11 and the separator 13. The positive electrode 11 has a positive electrode core exposed portion 34 in which the positive electrode core 30 is exposed and no positive electrode mixture layer 32 is provided, at an upper end in the winding axial direction (hereinafter sometimes referred to as the axial direction) from the inner end to the outer end in the winding direction of the strip-shaped positive electrode 11. The negative electrode 12 has a negative electrode core exposed portion 44 in which the negative electrode core 40 is exposed and no negative electrode mixture layer 42 is provided, at a lower end in the axial direction from the inner end to the outer end in the winding direction of the strip-shaped negative electrode 12. For this reason, the upper axial end of the electrode body 14 is constituted by the positive electrode substrate exposed portion 34, and the lower axial end of the electrode body 14 is constituted by the negative electrode substrate exposed portion 44. The width (length in the winding axis direction) of the positive electrode substrate exposed portion 34 is, for example, 2 mm or more and 20 mm or less, and the width (length in the winding axis direction) of the negative electrode substrate exposed portion 44 is, for example, 2 mm or more and 20 mm or less. In this embodiment, a case will be described in which the first electrode is the positive electrode 11 and the second electrode is the negative electrode 12, but the first electrode may be the negative electrode 12 and the second electrode may be the positive electrode 11. Furthermore, both the positive electrode 11 and the negative electrode 12 may have the configuration of the first electrode.

[0014] The non-aqueous 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 includes a positive electrode core 30 and a positive electrode mixture layer 32 formed on both sides of the positive electrode core 30. The positive electrode mixture layer 32 is preferably formed on both sides of the positive electrode core 30. The positive electrode core 30 may 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 thickness of the positive electrode core 30 is, for example, 10 μm to 30 μm. The positive electrode mixture layer 32 includes a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., to the positive electrode core 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode core 30. The positive electrode mixture layer 32 may be formed on only one side of the positive electrode core 30. The thickness of the positive electrode mixture layer 32 on one side of the positive electrode substrate 30 is, for example, 10 μm or more and 150 μm or less.

[0018] 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.

[0019] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon materials such as carbon black, acetylene black, ketjen black, and graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide resin, acrylic resin, and polyolefin resin. These resins may be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0020] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode core 40. The negative electrode mixture layer 42 is preferably formed on both sides of the negative electrode core 40. The negative electrode core 40 may be made of a metal foil, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. The thickness of the negative electrode core 40 is, for example, 5 μm to 30 μm. The negative electrode mixture layer 42 contains a negative electrode active material and a binder. The negative electrode 12 can be produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material and a binder to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode core 40. The negative electrode mixture layer 42 may be formed on only one side of the negative electrode core 40. The thickness of the negative electrode mixture layer 42 is, for example, 10 μm or more and 150 μm or less on one side of the negative electrode substrate 40 .

[0021] 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 42 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.

[0022] As in the case of the positive electrode 11, fluororesin, PAN, polyimide resin, acrylic resin, polyolefin resin, or the like may be used as the binder contained in the negative electrode mixture layer 42, but styrene-butadiene rubber (SBR) or a modified product thereof is preferably used. The negative electrode mixture layer 42 may contain, in addition to SBR or the like, CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, or the like.

[0023] 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.

[0024] 1 , the nonaqueous electrolyte secondary battery 10 has a metallic negative electrode current collector 17 made of nickel, a nickel alloy, or the like, on the axially lower side of the electrode body 14. An exposed negative electrode substrate portion 44 protruding from the electrode body 14 is joined to the negative electrode current collector 17, which is joined to the inner surface of the bottom plate of an outer can 15. The outer can 15 to which the exposed negative electrode substrate portion 44 is electrically connected via the negative electrode current collector 17 serves as the negative electrode terminal.

[0025] The nonaqueous electrolyte secondary battery 10 has a metallic positive electrode current collector 18 made of aluminum, aluminum alloy, or the like, on the axially upper side of the electrode body 14. A positive electrode core exposed portion 34 protruding from the electrode body 14 is joined to the positive electrode current collector 18. The nonaqueous electrolyte secondary battery 10 has a circular insulating plate 19 on the axially upper side of the positive electrode current collector 18.

[0026] The nonaqueous electrolyte secondary battery 10 further includes a sealing body 16 and a connection lead 20 made of a metal such as aluminum or an aluminum alloy. The lower end of the connection lead 20 is joined by welding or the like to the upper surface of the positive electrode current collector plate 18. The connection lead 20 passes through a through hole in the insulating plate 19 and extends toward the sealing body 16, and the upper end of the connection lead 20 is connected by welding or the like to the lower surface of a filter 22 of the sealing body 16. A cap 26 constituting the top plate of the sealing body 16 is electrically connected to the filter 22, and the cap 26 serves as a positive electrode terminal.

[0027] The nonaqueous electrolyte secondary battery 10 further includes a resin gasket 27 disposed between the exterior can 15 and the sealing body 16. The gasket 27 is sandwiched between the exterior can 15 and the sealing body 16, and insulates the sealing body 16 from the exterior can 15. The gasket 27 serves as a sealant to maintain airtightness inside the battery and as an insulating material to insulate the exterior can 15 from the sealing body 16. The exterior can 15 has an annular grooved portion 21 along part of its axial direction.

[0028] The grooved portion 21 can be formed, for example, by spinning a portion of the side surface radially inward to create a recess radially inward. The outer can 15 has a bottomed tubular portion including the grooved portion 21 and an annular shoulder portion. The bottomed tubular portion accommodates the electrode assembly 14 and the nonaqueous electrolyte, and the shoulder portion is bent radially inward from the end of the open side of the bottomed tubular portion and extends inward. The shoulder portion is formed when the upper end of the outer can 15 is bent inward and crimped onto the peripheral edge of the sealing body 16. The sealing body 16 is crimped and fixed to the outer can 15 with a gasket 27 interposed between the shoulder portion and the grooved portion 21. In this manner, the internal space of the nonaqueous electrolyte secondary battery 10 is sealed.

[0029] The sealing body 16 has a structure in which a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 16 has, for example, a disk or ring shape, and each member except for the insulating member 24 is electrically connected to one another. The filter 22 has at least one through-hole. The lower valve body 23 and the upper valve body 25 are connected at their respective centers, with the insulating member 24 interposed between their respective peripheral edges.

[0030] When the nonaqueous electrolyte secondary battery 10 generates abnormal heat and the internal pressure of the battery 10 rises, the lower valve body 23 deforms and ruptures, pushing the upper valve body 25 toward the cap 26, thereby interrupting the current path between the lower valve body 23 and the upper valve body 25. If the internal pressure rises further, the upper valve body 25 ruptures, and gas is discharged from the through-hole 26a of the cap 26. This gas discharge 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.

[0031] Next, the configuration of the positive electrode 11 will be described with reference to Figures 3 and 4. Figure 3 is a front view showing the positive electrode 11 included in the electrode assembly 14 according to an example embodiment in a developed state. Figure 4 is a cross-sectional view taken along line A-A in Figure 3. Line A-A is parallel to the winding axis of the electrode assembly 14.

[0032] 3, a positive electrode core exposed portion 34 where the positive electrode core 30 is exposed is disposed at one end of the electrode body 14 in the winding axis direction. A positive electrode mixture layer 32 is formed on the surface of the positive electrode core 30 in an area other than the positive electrode core exposed portion 34.

[0033] The positive electrode core exposed portion 34 has a recessed portion 50 that is thinner than the positive electrode core 30 at the location where the positive electrode mixture layer 32 is formed. When pressure is applied to the end face of the electrode body 14, the positive electrode core exposed portion 34 bends at the recessed portion 50, and the end face of the electrode body 14 is flattened.

[0034] The position of the recessed portion 50 varies from the end 32a of the positive electrode mixture layer 32 to the end 30a of the positive electrode core 30 along the winding direction of the electrode body 14, from the outer side of the winding to the inner side of the winding. In other words, the position of the recessed portion 50 varies obliquely toward the outside of the electrode body 14, from the outer side of the winding to the inner side of the winding, along the winding direction of the electrode body 14. As a result, when the positive electrode core exposed portion 34 is bent from the outer side of the winding to the inner side of the winding along the radial direction of the electrode body 14, the positive electrode core 30 bends at the position of the recessed portion 50, thereby improving the flatness of the end surface of the electrode body 14.

[0035] In Fig. 3, the recessed portion 50 is provided continuously. That is, the recessed portion 50 is connected from the outer end of the winding to the inner end of the winding. In Fig. 3, the recessed portion 50 is linear, but this is not limiting and the recessed portion 50 may be curved. The recessed portion 50 may also be provided intermittently. That is, the recessed portion 50 does not need to be continuous from the outer end of the winding to the inner end of the winding, and may be composed of multiple straight or curved lines.

[0036] In FIG. 4 , the thickness T1 of the positive electrode core 30 at the portion where the positive electrode mixture layer 32 is formed and the thickness T2 of the recessed portion 50 satisfy the relationship T2 / T1<0.95, for example. This makes it easier to bend the positive electrode core 30 at the recessed portion 50. The lower limit of T2 / T1 is, for example, 0.3, from the viewpoint of ensuring the rigidity of the positive electrode core 30. In FIG. 4 , the positive electrode core 30 has a substantially uniform thickness T1 except for the portion where the recessed portion 50 is formed. If the thickness of the positive electrode core 30 is not uniform, T1 is measured at the end 32a of the positive electrode mixture layer 32. T2 is measured at the deepest position of the recessed portion 50. In FIG. 4 , the cross section of the recessed portion 50 is rectangular, but this is not limited to this example and may be arc-shaped, for example. The width W of the recessed portion 50 is, for example, 0.1 mm or more and 1 mm or less.

[0037] Next, another example of the embodiment will be described with reference to Figures 5 and 6. Only the parts that are different from the embodiment shown in Figures 3 and 4 will be described below, and parts that are not described can have the same configuration as the embodiment shown in Figures 3 and 4.

[0038] Fig. 5 is a plan view showing an end face of an electrode assembly 14 included in a nonaqueous electrolyte secondary battery 10 according to another embodiment. Fig. 6 is an enlarged view of a portion of a positive electrode substrate exposed portion 34, and is a plan view showing the state of a recessed portion 50 when the electrode assembly 14 shown in Fig. 5 is produced.

[0039] In FIG. 5 , the end face of the electrode assembly 14 has a welded region 60 and a non-welded region 62. The welded region 60 is a region for welding to the positive current collector plate 18, and the non-welded region 62 is a region that is not welded to the positive current collector plate 18. The welded region 60 and the non-welded region 62 are formed by bending the positive electrode core 30 protruding from the end face of the electrode assembly 14 in the winding axis direction radially inward of the electrode assembly 14. The positive electrode core 30 in the welded region 60 protrudes relative to the positive electrode core 30 in the non-welded region 62. For example, the welded region 60 can be formed by bending the positive electrode core 30 radially inward of the electrode assembly 14 from four directions to form the non-welded region 62, and then bending the positive electrode core 30 radially inward of the electrode assembly 14 in four regions where the positive electrode core 30 remains standing between the non-welded regions 62.

[0040] 6, the recesses 50 are provided intermittently, and each of the recesses 50a to 50h is located in a welding region 60. The recesses 50a to 50d and the recesses 50e to 50h each correspond to one turn in the winding direction. Along the winding direction of the electrode body 14, the recesses 50a to 50d located on the inner side of the winding are located closer to the end 30a of the positive electrode substrate 30 than the recesses 50e to 50h located on the outer side of the winding.

[0041] As described above, according to the electrode assembly of the present disclosure, the adhesion between the electrode assembly and the current collector plate is increased, and the output characteristics of the battery can be improved.

[0042] The present disclosure will be further described by the following embodiments. Configuration: 1 A non-aqueous electrolyte secondary battery including an electrode assembly in which a first electrode and a second electrode having opposite polarities are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the first electrode has a first core and a first mixture layer formed on the surface of the first core, a first core exposed portion in which the first core is exposed is disposed at one end of the electrode assembly in the winding axis direction, the first core exposed portion has a recessed portion that is thinner than the first core at a portion where the first mixture layer is formed, and the position of the recessed portion changes from the end side of the first mixture layer to the end side of the first core from the outer side to the inner side along the winding direction of the electrode assembly. Configuration 2: The nonaqueous electrolyte secondary battery according to claim 1, wherein a thickness T1 of the first substrate at a portion where the first mixture layer is formed and a thickness T2 of the recessed portion satisfy the relationship T2 / T1<0.95. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the recessed portion is provided continuously. Configuration 4: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the recessed portion is provided intermittently. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the length of the first substrate exposed portion in the winding axis direction is 2 mm or more and 20 mm or less. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the width of the recessed portion is 0.1 mm or more and 1 mm or less. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the outer can is cylindrical with a bottom.

[0043] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 12 negative electrode, 13 separator, 14 electrode body, 15 outer can, 16 sealing body, 17 negative electrode current collector plate, 18 positive electrode current collector plate, 19 insulating plate, 20 connection lead, 21 grooved portion, 22 filter, 23 lower valve body, 24 insulating member, 25 upper valve body, 26 cap, 26a through hole, 27 gasket, 30 positive electrode core, 32 positive electrode mixture layer, 34 positive electrode core exposed portion, 40 negative electrode core, 42 negative electrode mixture layer, 44 negative electrode core exposed portion, 50 recessed portion, 60 welded region, 62 non-welded region

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a first electrode and a second electrode of opposite polarity are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can accommodating the electrode assembly and the non-aqueous electrolyte, wherein the first electrode has a first core and a first mixture layer formed on the surface of the first core, a first core exposed portion where the first core is exposed is disposed at one end of the electrode assembly in the winding axis direction, the first core exposed portion has a recessed portion that is thinner than the first core at the portion where the first mixture layer is formed, and the position of the recessed portion changes from the end side of the first mixture layer to the end side of the first core from the outer side of the winding to the inner side of the winding along the winding direction of the electrode assembly.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein a thickness T1 of the first substrate at the portion where the first mixture layer is formed and a thickness T2 of the recessed portion satisfy the relationship T2 / T1<0.

95.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the recessed portion is provided continuously.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the recesses are provided intermittently.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the length of the first substrate exposed portion in the winding axis direction is 2 mm or more and 20 mm or less.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the width of the recess is 0.1 mm or more and 1 mm or less.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the outer can has a cylindrical shape with a bottom.

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