Nonaqueous electrolyte secondary battery

Abstract

The present invention provides a highly reliable nonaqueous electrolyte secondary battery in which the occurrence of an internal short circuit is suppressed. A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure includes: a wound electrode body which is obtained by winding a belt-shaped positive electrode and a belt-shaped negative electrode, with a separator being interposed therebetween; and an outer package which houses the electrode body. The positive electrode has a positive electrode current collector and a positive electrode mixture layer that is formed on the surface of the positive electrode current collector. The positive electrode mixture layer has, in the central part of the winding termination end in the short-side direction of the positive electrode, a recess that is recessed toward the winding start end side relative to the both edges of the winding termination end in the short-side direction of the positive electrode.

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, nonaqueous 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 an outer casing. In secondary batteries in which a wound electrode assembly is housed in an outer casing, expansion of the negative electrode during charging can cause a large stress near the end of the winding of the positive electrode mixture layer, which can damage the separator facing the end of the winding of the positive electrode mixture layer and cause an internal short circuit. Patent Document 1 discloses a technique for covering the periphery of the end of the winding of the positive electrode mixture layer with heat-resistant insulating tape to prevent damage to the separator.

[0003] JP 2013-73794 A

[0004] The electrode assembly expands with repeated charge / discharge cycles, with the central portion of the electrode assembly in the axial direction expanding more than the opposite ends. Therefore, at the winding end of the positive electrode mixture layer, the stress applied to the central portion in the width direction of the positive electrode is greater than the stress applied to the opposite ends in the width direction of the positive electrode. The technology disclosed in Patent Document 1 does not take into consideration the large stress applied to the central portion of the winding end of the positive electrode mixture layer. Furthermore, the technology disclosed in Patent Document 1 covers the winding end of the positive electrode mixture layer with heat-resistant insulating tape, which may increase the stress applied to the winding end of the positive electrode mixture layer, and therefore there is still room for improvement.

[0005] An object of the present disclosure is to provide a highly reliable non-aqueous electrolyte secondary battery that suppresses the occurrence of internal short circuits.

[0006] A nonaqueous electrolyte secondary battery according to one aspect of the present disclosure includes a wound electrode assembly in which strip-shaped positive and negative electrodes are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, and the positive electrode mixture layer has a recess in the center of the winding end in the short direction of the positive electrode, which is recessed closer to the winding start end than both ends of the winding end in the short direction of the positive electrode.

[0007] The nonaqueous electrolyte secondary battery according to the present disclosure can suppress internal short circuits caused by breakage of the separator facing the winding end of the positive electrode mixture layer.

[0008] Fig. 3 is an axial cross-sectional view of a cylindrical secondary battery that is an example of an embodiment. Fig. 4 is a perspective view of a wound electrode body provided in the secondary battery shown in Fig. 1. Fig. 5 is a front view showing a positive electrode and a negative electrode that constitute an electrode body according to an example of an embodiment in a developed state. Fig. 6 is an enlarged view of the vicinity of the winding end of the positive electrode shown in Fig. 3. Fig. 7 is a view corresponding to Fig. 4 in another example of an embodiment.

[0009] Hereinafter, an example of an embodiment of a cylindrical 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 cylindrical secondary battery. Furthermore, when the following description includes multiple embodiments and modified examples, it is assumed from the beginning that the characteristic portions of those embodiments and modified examples can be appropriately combined and used.

[0010] FIG. 1 is an axial cross-sectional view of a cylindrical secondary battery 10 according to an embodiment. The secondary battery 10 shown in FIG. 1 includes an electrode assembly 14 and a nonaqueous electrolyte (not shown) housed in an outer casing 15. The electrode assembly 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound with a separator 13 interposed therebetween. Examples of nonaqueous solvents (organic solvents) for the nonaqueous electrolyte include carbonates, lactones, ethers, ketones, esters, and the like. Two or more of these solvents can be mixed together. When two or more solvents are mixed together, a mixed solvent containing a cyclic carbonate and a chain carbonate is preferably used. For example, ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC) can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) can be used as the chain carbonate. The electrolyte salt of the non-aqueous electrolyte is LiPF ６ , LiBF ４ , LiCF ３ SO ３etc., and mixtures thereof can be used. The amount of electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 mol / L or more and 2.0 mol / L or less. For convenience of explanation, the following description will be given with the sealing body 16 side as the "upper" and the bottom side of the exterior body 15 as the "lower".

[0011] The opening of the exterior body 15 is closed with the sealing body 16, thereby sealing the interior of the secondary battery 10. Insulating plates 17 and 18 are provided above and below the electrode body 14. The positive electrode tab 19 extends upward through a through-hole in the insulating plate 17 and is welded to the underside of the filter 22, which is the bottom plate of the sealing body 16. In the secondary battery 10, the cap 26, which is the top plate of the sealing body 16 and is electrically connected to the filter 22, serves as the positive electrode terminal. On the other hand, the negative electrode tab 20 extends through a through-hole in the insulating plate 18 toward the bottom of the exterior body 15 and is welded to the inner bottom surface of the exterior body 15. In addition, the negative electrode 12 is located on the outermost peripheral surface of the electrode body 14 and is in contact with the exterior body 15. In the secondary battery 10, the exterior body 15 serves as the negative electrode terminal.

[0012] The exterior body 15 is, for example, a cylindrical metal exterior can with a bottom. A gasket 27 is provided between the exterior body 15 and the sealing body 16 to ensure the airtightness of the interior of the secondary battery 10. The exterior body 15 has a grooved portion 21 that supports the sealing body 16, formed, for example, by pressing the side surface from the outside. The grooved portion 21 is preferably formed in an annular shape along the circumferential direction of the exterior body 15, and supports the sealing body 16 on its upper surface.

[0013] The sealing body 16 includes a filter 22, a lower valve body 23, an insulating member 24, an upper valve body 25, and a cap 26, which are stacked in this order from the electrode body 14 side. Each component of the sealing body 16 has, for example, a disk or ring shape, and all components except for the insulating member 24 are electrically connected to each other. The lower valve body 23 and the upper valve body 25 are connected to each other at their respective centers, with the insulating member 24 interposed between their respective peripheral edges. If the internal pressure of the battery increases due to abnormal heat generation, for example, the lower valve body 23 may rupture, causing the upper valve body 25 to bulge toward the cap 26 and separate from the lower valve body 25, thereby cutting off the electrical connection between them. If the internal pressure continues to increase, the upper valve body 25 may rupture, allowing gas to be released from the opening 26a of the cap 26.

[0014] Next, the electrode assembly 14 will be described with reference to Fig. 2. Fig. 2 is a perspective view of the electrode assembly 14. As described above, the electrode assembly 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are spirally wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all formed in a strip shape, and are spirally wound around a winding axis, thereby being alternately stacked in the radial direction of the electrode assembly 14. The separator 13 is formed to be at least one size larger than the positive electrode 11, and, for example, two separators 13 are arranged to sandwich the positive electrode 11.

[0015] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and the surface of the separator 13 may be coated with a material such as an aramid-based resin or ceramic.

[0016] In the radial direction β, the side of the winding axis is referred to as the inner winding side, and the opposite side is referred to as the outer winding side. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction γ, and the short direction of the positive electrode 11 and the negative electrode 12 is the axial direction α. ​​In the winding direction γ, the ends of the positive electrode 11 and the negative electrode 12 on the winding axis side are referred to as the winding start end, and the opposite end is referred to as the winding end. Similarly, both ends of the winding direction γ of the current collector and the mixture layer described below are also referred to as the winding start end and the winding end end. The positive electrode tab 19 extends in the axial direction α from approximately the center in the radial direction from the center to the outermost periphery at the upper end of the electrode body 14. The negative electrode tab 20 extends in the axial direction α from near the winding axis at the lower end of the electrode body 14.

[0017] The electrode body 14 may be housed in the exterior body 15 with fixing tape attached so as to cover at least a portion of the winding end of the negative electrode 12 exposed on the outermost peripheral surface. The fixing tape is attached, for example, to both ends in the axial direction α on the outermost peripheral surface of the electrode body 14. In this case, the central portion in the axial direction of the electrode body 14 is more likely to expand due to charging and discharging, and the effects of the present disclosure described below become more pronounced.

[0018] Next, the positive electrode 11 and the negative electrode 12 will be described in detail with reference to Figures 3 to 5. Figure 3 is a front view showing the positive electrode 11 and the negative electrode 12 constituting the electrode body 14 according to one example of the embodiment in a developed state. 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 than the positive electrode 11 in the lateral and longitudinal directions.

[0019] The positive electrode 11 has a strip-shaped positive electrode current collector 30 and a positive electrode mixture layer 32 formed on the surface of the positive electrode current collector 30. The positive electrode current collector 30 may be, for example, a foil of a metal such as aluminum, or a film having such a metal disposed on its surface. A suitable positive electrode current collector 30 is a foil of a metal whose main component is aluminum or an aluminum alloy. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 30 μm or less.

[0020] The positive electrode mixture layer 32 contains, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 is produced by applying a positive electrode mixture slurry containing the positive electrode active material, the conductive agent, the binder, and a solvent such as N-methyl-2-pyrrolidone (NMP) to both sides of the positive electrode current collector 30, followed by drying and rolling.

[0021] As the positive electrode active material, a lithium-containing transition metal oxide containing a transition metal element such as Co, Mn, or Ni can be used. The lithium-containing transition metal oxide is not particularly limited, but may be any of the following oxides represented by the general formula: Li １＋ｘ MO ２ (wherein, −0.2<x≦0.2, and M contains at least one of Ni, Co, Mn, and Al) is preferred.

[0022] Examples of the conductive agent contained in the positive electrode mixture layer 32 include carbon black (CB) such as acetylene black (AB) and Ketjen black, and carbon materials such as graphite. Examples of the binder contained in the positive electrode mixture layer 32 include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide (PI), acrylic resins, and polyolefin resins. These resins may also be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), or the like. These may be used alone or in combination of two or more.

[0023] A positive electrode current collector exposed portion 34, where the positive electrode current collector 30 is exposed, is formed on the surface of the positive electrode 11, and a positive electrode tab 19 is connected to the positive electrode current collector exposed portion 34. The positive electrode current collector exposed portion 34 is a portion of the surface of the positive electrode current collector 30 that is not covered with the positive electrode mixture layer 32, and is provided, for example, by intermittent application of the positive electrode mixture slurry to a portion of the positive electrode current collector 30. The positive electrode current collector exposed portion 34 is preferably provided on both sides of the positive electrode 11 so as to overlap in the thickness direction of the positive electrode 11. The positive electrode tab 19 is joined to the positive electrode current collector exposed portion 34 by, for example, ultrasonic welding.

[0024] In this embodiment, a positive electrode current collector exposed portion 34 is provided at approximately the center in the longitudinal direction of the positive electrode 11, over the entire length in the lateral direction. The position of the positive electrode current collector exposed portion 34 is not limited to this example, but from the viewpoint of current collection performance, the positive electrode current collector exposed portion 34 is preferably provided at a position approximately equidistant from the winding start end and the winding end end of the positive electrode. Alternatively, multiple positive electrode current collector exposed portions 34 may be formed on the surface of the positive electrode 11, and a positive electrode tab 19 may be connected to each of the positive electrode current collector exposed portions 34.

[0025] As will be described in detail later, the positive electrode mixture layer 32 has a recess 37 in the center of the winding end 32a of the positive electrode mixture layer 32 in the short direction of the positive electrode 11, which is recessed closer to the winding start end than both end portions 35 of the winding end 32a in the short direction of the positive electrode 11. The provision of the recess 37 relieves stress applied to the center of the winding end 32a of the positive electrode mixture layer 32, and can suppress internal short circuits due to damage to the separator 13 facing the winding end 32a of the positive electrode mixture layer 32.

[0026] In this embodiment, the winding end 30a of the positive electrode current collector 30 overlaps with the winding end 32a of the positive electrode mixture layer 32 in the thickness direction of the positive electrode 11. That is, the positive electrode current collector 30 has a recess in the winding end 30a that is in the same position as the recess 37 and has the same shape as the recess 37, and the positive electrode mixture layer 32 is formed on the entire surface of the positive electrode current collector 30 in the vicinity of the winding end 30a.

[0027] The negative electrode 12 has a strip-shaped negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the surface of the negative electrode current collector 40. The negative electrode current collector 40 may be, for example, a foil of a metal such as copper, or a film having such a metal disposed on its surface. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less.

[0028] The negative electrode mixture layer 42 contains, for example, a negative electrode active material and a binder. The negative electrode mixture layer 42 is produced, for example, by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, and a solvent such as water to both surfaces of the negative electrode current collector 40, followed by drying and rolling.

[0029] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release Li ions, and generally, a carbon material such as graphite is used. The graphite may be any of natural graphite such as flake graphite, lump graphite, and amorphous graphite, or artificial graphite such as lump artificial graphite and graphitized mesophase carbon microbeads. Furthermore, metals that alloy with Li, such as Si and Sn, metal compounds containing Si and Sn, and lithium-titanium composite oxides may also be used as the negative electrode active material. For example, SiO ｘ (x is 0.5 to 1.6), silicon oxide represented by the formula Li ２ｙ SiO （２＋ｙ）A silicon-containing material in which fine particles of Si are dispersed in a lithium silicate phase represented by (0<y<2), a silicon-containing material in which fine particles of Si are dispersed in a carbon phase, or the like may be used in combination with graphite.

[0030] The negative electrode mixture layer 42 contains, for example, graphite as a negative electrode active material and a silicon-containing material. By including the silicon-containing material in the negative electrode 12 together with graphite, the battery capacity can be increased. The content of the silicon-containing material in the negative electrode active material may be 3% by mass or more. In this case, the rate at which the negative electrode 12 expands upon charge and discharge increases, making the effects of the present disclosure more pronounced. The upper limit of the content of the silicon-containing material in the negative electrode active material is, for example, 30% by mass.

[0031] Examples of the binder contained in the negative electrode mixture layer 42 include styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), carboxymethyl cellulose (CMC) or its salts (CMC-Na, CMC-K, CMC-NH ４ and the like, which may be a partially neutralized salt), polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, and the like, which may be a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0032] In this embodiment, a negative electrode current collector exposed portion 44, where the negative electrode current collector 40 is exposed, is formed near the winding start end and the winding end end on the surface of the negative electrode 12. The negative electrode current collector exposed portion 44 is a portion of the surface of the negative electrode current collector 40 that is not covered with the negative electrode mixture layer 42. For example, the negative electrode current collector exposed portion 44 is formed by intermittent application of the negative electrode mixture slurry to a portion of the negative electrode current collector 40. A negative electrode tab 20 is connected to the negative electrode current collector exposed portion 44 near the winding start end. The negative electrode current collector exposed portion 44 near the winding end is in direct contact with the outer casing 15. The negative electrode current collector exposed portion 44 is preferably provided on both sides of the negative electrode 12 so as to overlap in the thickness direction of the negative electrode 12. The negative electrode tab 20 is joined to the negative electrode current collector exposed portion 44 by, for example, ultrasonic welding.

[0033] Next, the recess 37 provided at the winding end 32a of the positive electrode mixture layer 32 will be described with reference to Fig. 4. Fig. 4 is an enlarged view of the vicinity of the winding end of the positive electrode 11 shown in Fig. 3.

[0034] The shape of the recess 37 is not particularly limited and may be a triangle, a rectangle, or the like, but is preferably a curved shape. The curved recess 37 has no corners and can alleviate stress concentration, thereby further reducing the risk of breakage of the separator 13. In this embodiment, the recess 37 is arc-shaped. The arc-shaped recess 37 is easier to fabricate than recesses 37 formed by other curves, and therefore the productivity of the positive electrode 11 is improved.

[0035] The shape of the corners 39 connecting the end portions 35 and the recesses 37 is not particularly limited, but is preferably chamfered. The chamfered corners 39 have no sharp edges and can alleviate stress concentration, further reducing the risk of breakage of the separator 13. In this embodiment, the corners 39 are rounded.

[0036] In the longitudinal direction of the positive electrode 11, the distance D between the position of the recess 37 closest to the winding start end and the positions of both end portions 35 of the winding end 32a is, for example, 1 mm or more and 5 mm or less. By making the distance D 1 mm or more, it is possible to further reduce the stress applied to the central portion of the winding end 32a of the positive electrode mixture layer 32. Furthermore, by making the distance D 5 mm or less, it is possible to suppress a significant decrease in battery capacity.

[0037] In the short direction of the positive electrode 11, the length L1 of one end 35a, the length L2 of the recess 37, and the length L3 of the other end 35b satisfy the relationship 50%≦(L1+L3) / (L1+L2+L3)≦75%, for example. Here, the boundary between L1 and L2 and the boundary between L2 and L3 are the midpoints of the corner portions 39.

[0038] Next, another embodiment of the positive electrode 11 will be described with reference to Fig. 5. Fig. 5 is a view corresponding to Fig. 4 in another example of the embodiment.

[0039] The winding end 30a of the positive electrode current collector 30 is substantially parallel to the short direction of the positive electrode 11 and overlaps both end portions 35 of the winding end 32a of the positive electrode mixture layer 32 in the thickness direction of the positive electrode 11. The positive electrode 11 also has a positive electrode current collector exposed portion 34 where the positive electrode current collector 30 is exposed in an area surrounded by the winding end 30a of the positive electrode current collector 30 and a recess 37. In other words, in this embodiment, the winding end 30a of the positive electrode current collector 30 does not have a recess, but the winding end 32a of the positive electrode mixture layer 32 has a recess 37, so that the positive electrode current collector 30 is exposed in an area surrounded by the winding end 30a of the positive electrode current collector 30 and the recess 37. Even in this case, as in the embodiment shown in FIG. 4 , stress applied to the center portion of the winding end of the positive electrode 11 can be alleviated, and an internal short circuit due to damage to the separator 13 can be suppressed. The positive electrode current collector exposed portion 34 may be extended so that the winding end 30 a of the positive electrode current collector 30 is located closer to the winding end than both end portions 35 of the positive electrode mixture layer 32. In other words, the positive electrode current collector exposed portion 34 may be formed in an area surrounded by the winding end of the positive electrode 11 and the winding end 30 a of the positive electrode mixture layer 32.

[0040] As described above, according to the nonaqueous electrolyte secondary battery of the present disclosure, the stress applied to the central portion of the winding end of the positive electrode mixture layer can be reduced, and therefore, an internal short circuit due to breakage of the separator facing the winding end of the positive electrode mixture layer can be suppressed.

[0041] The present disclosure is further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including a wound electrode assembly in which strip-shaped positive and negative electrodes are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on the surface of the positive electrode current collector, and the positive electrode mixture layer has a recess in a center of an end of winding in the short direction of the positive electrode, the recess being recessed closer to the start of winding than both ends of the end of winding in the short direction of the positive electrode. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the recess is arc-shaped. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the distance between the position of the recess closest to the start of winding and the positions of both ends in the longitudinal direction of the positive electrode is 1 mm or more and 5 mm or less. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein a winding end of the positive electrode current collector overlaps with a winding end of the positive electrode mixture layer in the thickness direction of the positive electrode.Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein a winding end of the positive electrode current collector overlaps with both ends of the winding end of the positive electrode mixture layer in the thickness direction of the positive electrode, and the positive electrode has a positive electrode current collector exposed portion where the positive electrode current collector is exposed in an area surrounded by the winding end of the positive electrode current collector and the recess.Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the negative electrode includes graphite as a negative electrode active material and a silicon-containing material, and a content of the silicon-containing material in the negative electrode active material is 3 mass% or more.

[0042] REFERENCE SIGNS LIST 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Exterior body, 16 Sealing body, 17, 18 Insulating plate, 19 Positive electrode tab, 20 Negative electrode tab, 21 Grooved portion, 22 Filter, 23 Lower valve body, 24 Insulating member, 25 Upper valve body, 26 Cap, 26a Opening, 27 Gasket, 30 Positive electrode current collector, 30a Winding end, 32 Positive electrode mixture layer, 32a Winding end, 34 Positive electrode current collector exposed portion, 35 Both ends, 35a One end, 35b Other end, 37 Recessed portion, 39 Corner portion

Claims

1. A non-aqueous electrolyte secondary battery comprising a wound electrode assembly in which strip-shaped positive and negative electrodes are wound with a separator interposed therebetween, and an exterior housing that houses the electrode assembly, wherein the positive electrode has a positive electrode current collector and a positive electrode mixture layer formed on a surface of the positive electrode current collector, and the positive electrode mixture layer has a recess in the center of the winding end in the short side direction of the positive electrode, which is recessed closer to the winding start end than both ends of the winding end in the short side direction of the positive electrode.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the recess is in the shape of a circular arc.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the distance in the longitudinal direction of the positive electrode between the position of the recess closest to the winding start end and the positions of both ends is 1 mm or more and 5 mm or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein a winding end of the positive electrode current collector overlaps with a winding end of the positive electrode mixture layer in a thickness direction of the positive electrode.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein a winding end of the positive electrode current collector overlaps with both ends of the winding end of the positive electrode mixture layer in a thickness direction of the positive electrode, and the positive electrode has a positive electrode current collector exposed portion where the positive electrode current collector is exposed in an area surrounded by the winding end of the positive electrode current collector and the recess.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode contains graphite as a negative electrode active material and a silicon-containing material, and the content of the silicon-containing material in the negative electrode active material is 3 mass % or more.

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