Secondary battery

Abstract

A secondary battery according to the present invention comprises: an electrode body in which a positive electrode and a negative electrode are wound with a separator (13) interposed therebetween; and an exterior can that accommodates the electrode body. The secondary battery is characterized in that the separator (13) is disposed on the outermost periphery of the electrode body and includes a base material layer (50) and a surface layer (52) disposed on the base material layer (50), the surface layer (52) includes a resin material that forms protrusions (58) on a surface of the surface layer (52), and in the separator (13), if a region located on the outermost periphery of the electrode body is a first region (54), and a region located on the inner peripheral side of the electrode body with respect to the first region (54) and at a position facing the positive electrode and the negative electrode is a second region (56), on the surface on the surface layer (52) side of the separator (13), the area ratio occupied by the area of the protrusions (58) in the first region (54) is larger than the area ratio occupied by the area of the protrusions (58) in the second region (56).

Description

secondary battery

[0001] This disclosure relates to secondary batteries.

[0002] As a secondary battery, a battery is known in which an electrode body, in which a positive electrode and a negative electrode are wound with a separator in between, is housed in an outer casing.

[0003] For example, Patent Document 1 discloses a separator in which discrete polymer particles having at least two different weight-average particle sizes are arranged on a separator substrate to form an irregular surface. Patent Document 1 states that the irregular surface of the separator provides a gap between the separator and the electrode, allowing the battery components to expand during charge-discharge cycles without significantly changing the external dimensions of the battery, thereby promoting good battery performance.

[0004] Special Publication No. 2021-501453

[0005] Incidentally, when a secondary battery is subjected to impact, the electrode body inside the outer casing vibrates and collides with the inner wall of the casing. This impact can damage the electrode body. Therefore, improving the impact resistance of secondary batteries is an important issue. It is also conceivable to improve the impact resistance of secondary batteries by using a separator as described in Patent Document 1, but on the other hand, there are concerns about a decrease in battery capacity.

[0006] The purpose of this disclosure is to provide a secondary battery that can improve shock resistance while suppressing a decrease in battery capacity.

[0007] A secondary battery according to one aspect of the present disclosure comprises an electrode body in which a positive electrode and a negative electrode are wound via a separator, and an outer casing for housing the electrode body, wherein the outermost periphery of the electrode body is on which the separator is disposed, the separator has a base layer and a surface layer disposed on the base layer, the surface layer has a resin material that forms protrusions on the surface of the surface layer, and in the separator, if the region located on the outermost periphery of the electrode body is defined as a first region, and the region located on the inner periphery of the electrode body from the first region and facing the positive electrode and the negative electrode is defined as a second region, then on the surface of the separator on the surface layer side, the area ratio occupied by the protrusions in the first region is greater than the area ratio occupied by the protrusions in the second region.

[0008] The secondary battery described herein makes it possible to improve shock resistance while suppressing a decrease in battery capacity.

[0009] This is a cross-sectional view of a secondary battery, which is an example of an embodiment. This is a front view showing the separator constituting the electrode body in an unfolded state. This is a side view showing the separator constituting the electrode body in an unfolded state.

[0010] In the following, an example of an embodiment of the secondary battery according to this disclosure will be described with reference to the drawings. In the following description, the specific shapes, materials, numerical values, directions, etc. are illustrative and can be appropriately changed according to the specifications of the secondary battery. Furthermore, if the following description includes multiple embodiments and modifications, it is intended from the outset that their characteristic parts may be used in appropriate combinations.

[0011] Figure 1 is a cross-sectional view of a secondary battery, which is an example of an embodiment. The secondary battery 10 shown in Figure 1 comprises a wound electrode body 14 in which a positive electrode 11 and a negative electrode 12 are wound around a separator 13, an electrolyte, insulating plates 18 and 19 arranged above and below the electrode body 14, and a battery case 15. The battery case 15 is composed of an outer casing 16 that houses the electrode body 14, etc., and a sealing body 17 that closes the opening of the outer casing 16. The battery case 15 is, for example, a cylindrical or rectangular metal case.

[0012] The electrolyte may, for example, be ionic conductive (e.g., lithium ion conductive). The electrolyte may be a liquid electrolyte (electrolyte solution) or a solid electrolyte.

[0013] A liquid electrolyte (electrolyte solution) includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0014] Furthermore, as the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic 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 can be used. Examples of polymer materials include fluororesins, acrylic resins, and polyether resins. As the inorganic solid electrolyte, for example, materials known for all-solid-state lithium-ion secondary batteries, etc. (e.g., oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. Although the electrolytes exemplified above are non-aqueous electrolytes, the electrolyte is not limited to non-aqueous electrolytes and may also be an aqueous electrolyte.

[0015] The outer casing 16 is, for example, a metal container with a bottomed cylindrical shape. A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has, for example, a protruding portion 22 that supports the sealing body 17, where a part of the side surface protrudes inward. The protruding portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17.

[0016] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in this order from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected to each other at their central portions, and the insulating member 25 is interposed between their peripheral portions. When the internal pressure of the secondary battery 10 rises due to heat generation caused by internal short circuit or the like, for example, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, and the current path between the lower valve body 24 and the upper valve body 26 is interrupted. When the internal pressure further rises, the upper valve body 26 is broken, and gas is discharged from the opening of the cap 27.

[0017] In the secondary battery 10 shown in FIG. 1, the positive electrode lead 20 attached to the positive electrode 11 extends toward the sealing body 17 side through the through hole of the insulating plate 18, and the negative electrode lead 21 attached to the negative electrode 12 extends outside the insulating plate 19 and toward the bottom side of the exterior can 16. The positive electrode lead 20 is connected to the lower surface of the filter 23 which is the bottom plate of the sealing body 17 by welding or the like, and the cap 27 which is the top plate of the sealing body 17 electrically connected to the filter 23 serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the exterior can 16 by welding or the like, and the exterior can 16 serves as the negative electrode terminal.

[0018] The electrode body 14 has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound with the separator 13 interposed therebetween. The positive electrode 11, the negative electrode 12, and the separator 13 are all strip-shaped elongated bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape.

[0019] As shown in Figure 1, a separator 13 is placed on the outermost circumference of the electrode body 14. The separator 13 may be placed on a part of the outermost circumference of the electrode body 14, but it is preferable that the separator 13 is placed over the entire outermost circumference of the electrode body 14. For example, the separator 13 is placed on the outermost circumference of the electrode body 14 for a length of more than half a turn but less than one full turn from the end of the winding of the separator 13. When the separator 13 is placed on a part of the outermost circumference of the electrode body 14, the area on the outermost circumference of the electrode body 14 where the separator 13 is not placed is where the positive electrode 11 or negative electrode 12 is placed. In this embodiment, however, since the outer casing 16 becomes the negative electrode terminal, it is desirable that the negative electrode 12 is placed there.

[0020] Figure 2 is a front view of the separator 13 constituting the electrode body in an unfolded state, showing the outer peripheral surface of the separator 13. Figure 3 is a side view of the separator 13 constituting the electrode body 14 in an unfolded state. As shown in Figure 3, the separator 13 has a base layer 50 and a surface layer 52 disposed on the base layer 50. In the separator 13 of Figure 3, the left side of the figure is the outer peripheral surface, and the right side of the figure is the inner peripheral surface. The outer peripheral surface of the separator 13 is the surface located on the outside in the radial direction (i.e., the radial direction of the electrode body 14) of the separator 13 wound around the electrode body 14. The inner peripheral surface of the separator 13 is the surface located on the inside in the radial direction of the separator 13 wound around the electrode body 14.

[0021] In the separators 13 of FIGS. 2 and 3, the upper end in the drawing is the starting end of winding, and the lower end in the drawing is the ending end of winding. Therefore, when forming the electrode body 14, the separator 13 in FIG. 3 is wound from the upper end in the drawing with the right side surface in the drawing as the inner peripheral side surface. And in the separators 13 of FIGS. 2 and 3, a region having a predetermined length in the longitudinal direction from the lower end in the drawing becomes a first region 54 located on the outermost periphery of the electrode body 14. Also, in the separators 13 of FIGS. 2 and 3, a region having a predetermined length in the longitudinal direction on the starting side of winding from the first region 54 becomes a second region 56 located at a position facing the positive electrode 11 and the negative electrode 12. Note that there is a predetermined interval between the first region 54 and the second region 56, but the region between the first region 54 and the second region 56 is, for example, a region of the separator 13 that does not face both the positive electrode 11 and the negative electrode 12 on the inner peripheral side of the electrode body 14, or a region of the separator 13 that faces only one of the positive electrode 11 and the negative electrode 12. This region is due to the general design of the electrode body 14, and the present embodiment is not limited to the above. That is, the electrode body 14 may be designed such that the second region 56 that faces the positive electrode 11 and the negative electrode 12 is arranged without an interval from the first region 54 located on the outermost periphery of the electrode body 14.

[0022] As the base material layer 50, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, and the like. The material of the base material layer 50 is not particularly limited, and examples thereof include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefin, acrylic resins, polystyrene, polyester, cellulose, polyimide, polyphenylene sulfide, polyether ether ketone, and fluororesins. The base material layer 50 may have a single-layer structure or a multilayer structure. The thickness of the base material layer 50 is preferably 3 μm or more and 20 μm or less, and more preferably 5 μm or more and 15 μm or less.

[0023] The surface layer 52 includes, for example, a resin material and a binder. The surface layer 52 may also contain inorganic particles. On the surface of the surface layer 52, which forms the surface of the separator 13, there are protrusions 58 formed by the resin material. In the separator 13 shown in Figures 2 and 3, the surface layer 52 is located on the outer peripheral surface of the base layer 50, but is not limited to this, and may be located on the inner peripheral surface of the base layer 50, or on both the inner and outer peripheral surfaces of the base layer 50. Furthermore, the surface layer 52 may be located on the entire surface of the base layer 50, or on a part of the surface of the base layer 50.

[0024] The protrusions 58 are formed, for example, by applying and drying a slurry containing resin particles, a binder, and inorganic particles, which are resin materials, onto the base layer 50, thereby exposing at least a portion of the resin particles dispersed in the coating film from the surface. Alternatively, for example, the protrusions 58 may be formed by applying a slurry containing a binder and inorganic particles onto the base layer 50, and then scattering resin particles, which are resin materials, onto the surface of the coating film. Alternatively, for example, the protrusions 58 may be formed by intermittently applying a resin solution, which is a resin material, onto the coating film containing a binder and inorganic particles applied on the base layer 50.

[0025] In this embodiment, on the surface of the separator 13 on the surface layer 52 side, the area ratio (S1) of the area occupied by the protrusions 58 in the first region 54 is greater than the area ratio (S2) of the area occupied by the protrusions 58 in the second region 56. By setting S1 > S2, there are many protrusions 58 derived from the resin material on the outermost periphery of the electrode body 14. These resin material-derived protrusions 58 act as shock-absorbing cushions, mitigating the impact caused by the collision between the electrode body 14 and the inner wall of the outer casing 16 when the secondary battery 10 is subjected to impact. As a result, damage to the electrode body 14 is suppressed, and the shock resistance of the secondary battery 10 is improved. On the other hand, since there are fewer resin material-derived protrusions 58 inside the electrode body 14, the increase in the gap between electrodes is suppressed, and the decrease in battery capacity is suppressed. The area ratio (S3) of the area occupied by the protrusions 58 in areas other than the first region 54 and the second region 56 (for example, the area between the first region 54 and the second region 56) is not particularly limited, but for example, S3 = S1, S3 = S2, S1 > S3 > S2, or S1 > S2 > S3.

[0026] The area ratio (S1) occupied by the area of ​​the protrusions 58 in the first region 54 is preferably 5% to 30%, and more preferably 10% to 30%, in order to further improve the shock resistance of the secondary battery 10. The area ratio (S2) occupied by the area of ​​the protrusions 58 in the second region 56 is preferably 0% to 5%, and more preferably 0% to 3%, in order to further suppress the decrease in battery capacity.

[0027] The measurement methods for S1 and S2 are described below. Using a scanning electron microscope (for example, SU8220 manufactured by Hitachi High-Tech Corporation), the surface of the separator 13 on the surface layer 52 side is observed from above. Then, in each of the first region 54 and the second region 56, the sum of the areas of the observed protrusions 58 derived from the resin material is divided by the sum of the predetermined areas at multiple randomly selected locations (total area) to calculate S1 and S2. If the surface layer 52 is formed on both sides of the separator, S1 and S2 are calculated for each surface.

[0028] Since the separator 13 only needs to satisfy S1 > S2, the protrusions 58 derived from the resin material formed on the surface layer 52 only need to be present in the first region 54. For example, the surface layer 52 having the resin material protrusions 58 may be placed on the base layer 50 of the first region 54, but the surface layer 52 having the resin material protrusions 58 may not be placed on the other base layers 50. For example, another surface layer composed of inorganic particles and a binder may be placed on the base layers 50 other than the first region 54.

[0029] When the protrusions 58 derived from the resin material formed on the surface layer 52 are formed in both the first region 54 and the second region 56, for example, S1 > S2 can be achieved by making the average particle size and number of resin particles, which are the resin material contained in the first region 54, larger than the average particle size and number of resin particles contained in the second region 56. The average particle size of the resin particles is, for example, 1 μm or more and 10 μm or less. The average particle size (D50) refers to the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution, and is called the median diameter. The particle size distribution of the resin particles is measured by dispersing them in a dispersion medium using a laser diffraction particle size distribution analyzer (for example, Microtrac-Bell MT3000II).

[0030] In the first region 54, it is preferable to arrange a surface layer 52 having protrusions 58 derived from the resin material on the outer peripheral surface of the base layer 50, so that the protrusions 58 derived from the resin material are present on the outer peripheral surface of the separator 13. As a result, the protrusions 58 derived from the resin material are present on the outermost surface of the electrode body 14 that faces the inner wall of the outer casing 16, so that the impact caused by the collision between the electrode body 14 and the inner wall of the outer casing 16 when the secondary battery 10 is subjected to impact is further mitigated, and the impact resistance of the secondary battery 10 is further improved.

[0031] Examples of the resin material for forming the convex portion 58 include acrylic resins composed of alkyl esters of ethylenically unsaturated carboxylic acids such as methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate; resins composed of cyano group-containing ethylenically unsaturated monomers such as acrylonitrile; resins composed of ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and maleic acid and their salts, and the like.

[0032] The binder is preferably a polymer material. Examples thereof include fluorine-based resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); polyimide-based resins; polyamide-based resins; acrylic resins; polyolefin-based resins; styrene-butadiene rubber (SBR); nitrile-butadiene rubber (NBR); carboxymethyl cellulose (CMC) or its salts; polyacrylic acid (PAA) or its salts; polyvinyl alcohol (PVA), and the like. These may be used alone or in combination of two or more. Examples of the inorganic particles include metal oxide particles, metal nitride particles, metal fluoride particles, metal carbide particles, and the like. Examples of the metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, manganese oxide, and the like. Examples of the metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, silicon nitride, and the like. Examples of the metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, barium fluoride, and the like. Examples of the metal carbide particles include silicon carbide, boron carbide, titanium carbide, tungsten carbide, and the like. Further, the inorganic particles include zeolites (M ２／ｎ O·Al ２ O ３ ·xSiO ２ ·yH ２ O, where M is a metal element, n is the valence of M, x≥2, y≥0), etc., porous aluminosilicates, talc (Mg ３ Si ４ O １０ (OH) ２ ), etc., layered silicates, barium titanate (BaTiO３ ), strontium titanate (SrTiO ３ Minerals such as those listed above may also be used. These may be used individually or in combination of two or more types.

[0033] The positive electrode 11 comprises a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode current collector can be made of a metal foil that is stable in the positive electrode potential range, such as aluminum, or a film with the metal disposed on its surface. The thickness of the positive electrode current collector is, for example, 10 μm to 30 μm.

[0034] The positive electrode mixture layer may be provided on one side of the positive electrode current collector or on both sides. The thickness of the positive electrode mixture layer is, for example, 10 μm to 150 μm on one side of the positive electrode current collector. The positive electrode mixture layer includes, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode can be manufactured, for example, by applying a positive electrode mixture slurry containing the positive electrode active material, conductive agent, binder, etc., onto the positive electrode current collector, drying the coating film, and then rolling the coating film using a roller or the like.

[0035] Examples of positive electrode active materials included in the positive electrode mixture layer include lithium transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. ｘ CoO ２ Li ｘ NiO ２ Li ｘ MnO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Co ｙ M １－ｙ O ｚ Li ｘ Ni １－ｙ M ｙ O ｚ Li ｘ Mn ２ O ４ Li ｘ Mn ２－ｙ M ｙ O ４ LiMPO ４ Li ２ MPO ４F (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, or B, with 0 < x ≤ 1.2, 0 < y ≤ 0.9, and 2.0 ≤ z ≤ 2.3). These may be used individually or in combination of multiple elements.

[0036] In order to increase the capacity of the secondary battery 10, it is preferable that the positive electrode active material contains a lithium nickel composite oxide. As for the lithium nickel composite oxide, Li ｘ NiO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ Examples include (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, with 0 < x ≤ 1.2, 0 < y ≤ 0.9, and 2.0 ≤ z ≤ 2.3).

[0037] Examples of conductive agents included in the positive electrode mixture layer include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphene, and other carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0038] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used individually or in combination of two or more types.

[0039] The negative electrode 12 comprises a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. The negative electrode current collector can be made of a metal foil that is stable in the negative electrode potential range, such as copper, or a film with the metal disposed on its surface. The thickness of the negative electrode current collector is, for example, 5 μm to 30 μm.

[0040] The negative electrode mixture layer may be provided on one side of the negative electrode current collector or on both sides. The thickness of the negative electrode mixture layer is, for example, 10 μm to 150 μm on one side of the negative electrode current collector. The negative electrode mixture layer includes, for example, a negative electrode active material and a binder. The negative electrode can be manufactured, for example, by applying a negative electrode mixture slurry containing the negative electrode active material, binder, etc., onto the negative electrode current collector, drying the coating, and then rolling the coating using a roller or the like.

[0041] The negative electrode active material contained in the negative electrode mixture layer is not particularly limited as long as it can reversibly intercept and release lithium ions, and generally carbon materials such as graphite are used. The graphite may be any of the following: natural graphite such as flake graphite, lump graphite, or clay-like graphite; lump artificial graphite; or artificial graphite such as graphitized mesophase carbon microbeads.

[0042] As the negative electrode active material, metals that alloy with Li, such as Si and Sn, metal compounds containing Si and Sn, lithium titanium composite oxides, etc., may be used. For example, SiO ｘ Si-containing compounds represented by (0.5 ≤ x ≤ 1.6), or Li ２ｙ SiO （２＋ｙ） A Si-containing compound in which fine Si particles are dispersed in a lithium silicate phase represented by (0 < y < 2) may be used in combination with graphite.

[0043] Examples of binders included in the negative electrode mixture layer include styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethylcellulose (CMC) or its salts, polyacrylic acid (PAA) or its salts (PAA-Na, PAA-K, etc., or partially neutralized salts), and polyvinyl alcohol (PVA). These may be used individually or in combination of two or more types.

[0044] This disclosure will be further described by the following embodiments. Configuration 1: A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound via a separator, and an outer casing for housing the electrode body, wherein the outermost periphery of the electrode body is on which the separator is disposed, the separator has a base layer and a surface layer disposed on the base layer, the surface layer has a resin material that forms protrusions on the surface of the surface layer, and in the separator, if the region located on the outermost periphery of the electrode body is defined as a first region, and the region located on the inner periphery of the electrode body from the first region and facing the positive electrode and the negative electrode is defined as a second region, the area ratio of the area of ​​the protrusions in the first region on the surface layer side of the separator is greater than the area ratio of the area of ​​the protrusions in the second region. Configuration 2: The secondary battery according to Configuration 1, wherein the area ratio occupied by the protrusions in the first region is 5% or more and 30% or less, and the area ratio occupied by the protrusions in the second region is 0% or more and 5% or less. Configuration 3: The secondary battery according to Configuration 1 or 2, wherein in the first region, the protrusions are located on the outer surface of the separator. Configuration 4: The secondary battery according to any one of Configurations 1 to 3, wherein the resin material is resin particles, and the resin particles are dispersed in the surface layer.

[0045] 10 Secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Outer can, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding part, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 50 Base layer, 52 Surface layer, 54 First region, 56 Second region, 58 Protrusion.

Claims

1. A secondary battery comprising an electrode body in which a positive electrode and a negative electrode are wound via a separator, and an outer casing for housing the electrode body, wherein the outermost periphery of the electrode body is on which the separator is disposed, the separator has a base layer and a surface layer disposed on the base layer, the surface layer has a resin material that forms protrusions on the surface of the surface layer, and in the separator, the region located on the outermost periphery of the electrode body is defined as a first region, and the region located on the inner periphery of the electrode body from the first region and facing the positive electrode and the negative electrode is defined as a second region, the area ratio of the area of ​​the protrusions in the first region on the surface layer side of the separator is greater than the area ratio of the area of ​​the protrusions in the second region.

2. The secondary battery according to claim 1, wherein the area ratio occupied by the protrusions in the first region is 5% or more and 30% or less, and the area ratio occupied by the protrusions in the second region is 0% or more and 5% or less.

3. The secondary battery according to claim 1 or 2, wherein in the first region, the protrusion is located on the outer surface of the separator.

4. The secondary battery according to claim 1 or 2, wherein the resin material is resin particles, and the resin particles are dispersed in the surface layer.

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