Non-aqueous electrolyte secondary battery

Abstract

This non-aqueous electrolyte secondary battery comprises a wound electrode body in which a strip-form positive electrode and a strip-form negative electrode are wound with a separator (13) interposed therebetween, a non-aqueous electrolyte, and an outer can that accommodates the electrode body and the non-aqueous electrolyte, the non-aqueous electrolyte secondary battery being characterized in that: particles including at least one of inorganic particles or resin particles are present on at least one surface of the separator (13); and in a surface view of the separator (13), the proportion of the area occupied by the particles in first regions (54) is greater than the proportion of the area occupied by the particles in a second region (56), where the first regions (54) are regions within a range of 20% of the total width of the separator (13) along the width direction of the separator (13) from the two width-direction ends of the separator (13), and the second region (56) is a region sandwiched by the first regions (54).

Description

Nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

[0002] In recent years, non-aqueous electrolyte secondary batteries have been widely used as high-power, high-energy density secondary batteries. The battery includes an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, a non-aqueous electrolyte, and an outer can housing these. The separator separates the positive electrode and the negative electrode while retaining the non-aqueous electrolyte. Patent Document 1 discloses a non-aqueous electrolyte secondary battery using a separator in which a functional layer containing inorganic particles and resin particles is provided on the surface of a substrate layer made of a porous film in order to improve adhesion at low temperatures.

[0003] International Publication No. 2021 / 161842

[0004] In a non-aqueous electrolyte secondary battery using an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, repeated charging and discharging of the battery tends to increase the pressure inside the battery due to expansion and contraction of the negative electrode mixture layer. This may result in damage such as elongation and breakage of the electrode plate. In particular, with the recent increase in capacity of non-aqueous electrolyte secondary batteries, the expansion and contraction of the negative electrode mixture layer during charging and discharging has become greater, making the above-mentioned damage to the electrode plate more pronounced.

[0005] An object of the present disclosure is to provide a highly reliable non-aqueous electrolyte secondary battery that suppresses damage to electrode plates during charging and discharging.

[0006] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including a wound electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode 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 particles including at least one of inorganic particles and resin particles are present on at least one surface of the separator, and when regions extending from both widthwise ends of the separator along the widthwise direction of the separator and covering 20% ​​of the entire width of the separator are defined as first regions and regions sandwiched between the first regions are defined as second regions, the area occupied by the particles in the first regions is greater than the area occupied by the particles in the second regions when viewed from the surface of the separator.

[0007] According to the nonaqueous electrolyte secondary battery according to the present disclosure, damage to the electrode plates caused by charging and discharging can be suppressed, and a highly reliable nonaqueous electrolyte secondary battery can be provided.

[0008] FIG. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery that is an example of an embodiment; FIG. 2 is a perspective view of a wound electrode body included in the nonaqueous electrolyte secondary battery that is an example of an embodiment; FIG. 3 is a view showing a positive electrode included in the nonaqueous electrolyte secondary battery that is an example of an embodiment in an expanded state; FIG. 4 is a cross-sectional view of a separator included in the nonaqueous electrolyte secondary battery that is an example of an embodiment; FIG. 5 is a view showing a separator included in the nonaqueous electrolyte secondary battery that is an example of an embodiment in an expanded state; FIG. 6 is a cross-sectional view of a separator included in the nonaqueous electrolyte secondary battery that is another example of an embodiment; FIG. 7 is a cross-sectional view of a separator included in the nonaqueous electrolyte secondary battery that is another example of an embodiment.

[0009] 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.

[0010] In the following, a cylindrical battery in which a wound electrode body is housed in a cylindrical outer can with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the outer can of the battery is not limited to a cylindrical outer can. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery having a prismatic outer can, a coin battery having a coin-shaped outer can, or a pouch battery having an outer can made of a laminate sheet including a metal layer and a resin layer.

[0011] 1 is a cross-sectional view of an example of a nonaqueous electrolyte secondary battery 10. As shown in FIG. 1, the nonaqueous electrolyte secondary battery 10 includes an electrode assembly 14, a nonaqueous electrolyte (not shown), and an outer can 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte.

[0012] As will be described in detail later, the electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and 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 electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0013] The non-aqueous electrolyte has lithium ion conductivity and may be a liquid electrolyte (electrolytic solution) or a solid electrolyte.

[0014] 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

[0015] 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.

[0016] The outer can 16 is a cylindrical metal container with a bottom and an opening at one axial end, and the opening of the outer can 16 is closed by a sealing body 17. For ease of explanation, the sealing body 17 side of the battery will be referred to as the "top" and the bottom side of the outer can 16 will be referred to as the "bottom" below.

[0017] Insulating plates 18 and 19 are disposed above and below the electrode body 14. In the example shown in Fig. 1 , the positive electrode lead 20 passes through a through hole in the insulating plate 18 and extends toward the sealing body 17, and the negative electrode lead 21 passes outside the insulating plate 19 and extends toward the bottom side of the outer can 16. The positive electrode lead 20 is connected to the underside of an internal terminal plate 23 of the sealing body 17 by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 serves as the negative electrode terminal.

[0018] A gasket 28 is provided between the exterior can 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior can 16 has a grooved portion 22 formed on its side surface that protrudes inward and supports the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the exterior can 16, and supports the sealing body 17 on its top surface. The sealing body 17 is fixed to the top of the exterior can 16 by the grooved portion 22 and the open end of the exterior can 16 that is crimped to the sealing body 17.

[0019] The sealing body 17 has a structure in which, in order from the electrode body 14 side, an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When abnormal heat generation causes an increase in the internal pressure of the battery, the lower valve body 24 deforms and breaks, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0020] Next, the electrode assembly 14 will be described in detail with further reference to Figures 2 to 5. Figure 2 is a perspective view of the electrode assembly 14.

[0021] 1 and 2, 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. In other words, the separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other, and prevents the positive electrode 11 and the negative electrode 12 from coming into contact with each other, thereby preventing a short circuit from occurring.

[0022] The positive electrode 11, negative electrode 12, and separator 13 are all formed in a strip shape and spirally wound around a winding core disposed along a winding axis 29, resulting in an alternately stacked state in the radial direction of the electrode assembly 14. In the electrode assembly 14, the longitudinal direction of the positive electrode 11, negative electrode 12, and separator 13 is the winding direction, and the width direction of the positive electrode 11, negative electrode 12, and separator 13 is the axial direction. At the upper end of the electrode assembly 14, the positive electrode lead 20 extends axially upward from approximately the center in the radial direction between the center and the outermost periphery. At the lower end of the electrode assembly 14, the negative electrode lead 21 extends axially downward from near the winding axis 29. Note that the negative electrode lead 21 may also extend axially downward from the lower end of the outermost periphery of the electrode assembly 14.

[0023] In a nonaqueous electrolyte secondary battery including a wound electrode assembly 14, repeated charge and discharge cycles cause the negative electrode mixture layer 41 (see FIG. 1 ) constituting the negative electrode 12 to expand, increasing the pressure inside the battery. In this case, the central portion of the positive electrode 11 in the width direction tends to experience a greater pressure load than the ends of the positive electrode 11 in the width direction. As a result, the positive electrode 11 tends to stretch toward both ends in the width direction. As will be described in detail later, in this embodiment, particles 52 (see FIG. 4 ) containing at least one of inorganic particles and resin particles are disposed on the surface of the separator 13 facing the positive electrode 11. The particles 52 are disposed in greater numbers at the ends of the separator 13 in the width direction than at the central portion in the width direction. As a result, when the negative electrode mixture layer 41 expands during charge and discharge, pressure is applied to the positive electrode 11 from the particles 52, further increasing the pressure load at the ends of the positive electrode 11 in the width direction. As a result, the difference between the pressure load applied to the center of the positive electrode 11 in the width direction and the pressure load applied to the ends of the positive electrode 11 in the width direction is reduced, and the positive electrode 11 is prevented from stretching toward both ends in the width direction.

[0024] FIG. 3 is a diagram showing the positive electrode 11 in an expanded state. As shown in FIGS. 1 and 3 , the positive electrode 11 includes a positive electrode core 30 and a positive electrode mixture layer 31 provided on the positive electrode core 30. The positive electrode core 30 can be made of a foil of a metal, such as aluminum or an aluminum alloy, that is stable within the potential range of the positive electrode 11, or a film with such a metal disposed on the surface. The thickness of the positive electrode core 30 is, for example, 10 μm or more and 30 μm or less. The positive electrode mixture layer 31 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 31 on both sides of the positive electrode core 30.

[0025] A positive electrode core exposed portion 32, where the positive electrode core 30 is exposed, is provided on the surface of the positive electrode 11. A positive electrode lead 20 is connected to the positive electrode core exposed portion 32. The positive electrode core exposed portion 32 contacts only the upper end portion 11A in the width direction of the positive electrode 11. In other words, the positive electrode core exposed portion 32 does not extend to the lower end portion 11B in the width direction of the positive electrode 11. This increases the area of ​​the positive electrode mixture layer 31, thereby improving the battery capacity of the nonaqueous electrolyte secondary battery 10. Note that, although there is one positive electrode core exposed portion 32 in this embodiment, there may be multiple positive electrode core exposed portions 32. In other words, the electrode body 14 may have multiple positive electrode leads 20.

[0026] The positive electrode mixture layer 31 is divided into a first positive electrode mixture layer 33 aligned with the positive electrode substrate exposed portion 32 in the longitudinal direction of the positive electrode 11 and a second positive electrode mixture layer 34 adjacent to the positive electrode substrate exposed portion 32 and the first positive electrode mixture layer 33 in the width direction of the positive electrode 11. The widthwise length of the first positive electrode mixture layer 33 is designated t1, and the widthwise length of the second positive electrode mixture layer 34 is designated t2. In this case, the ratio of t1 to t2 (t1 / t2) is preferably 0.1 or greater, and more preferably 0.15 or greater. By setting (t1 / t2) to 0.1 or greater, an area for connecting the positive electrode lead 20 is ensured, and the positive electrode lead 20 can be easily connected to the positive electrode substrate exposed portion 32. Furthermore, the ratio of t1 to t2 (t1 / t2) is preferably 1.0 or less, and more preferably 0.5 or less. Setting (t1 / t2) to 1.0 or less increases the area of ​​the positive electrode mixture layer 31, thereby further improving the battery capacity of the nonaqueous electrolyte secondary battery 10. Therefore, the ratio of t1 to t2 (t1 / t2) is preferably 0.1 or more and 1.0 or less, and more preferably 0.15 or more and 0.5 or less.

[0027] Furthermore, in the case where the positive electrode substrate exposed portion 32 contacts only one of both widthwise end portions of the positive electrode 11 as in the present embodiment, when the negative electrode mixture layer 41 expands due to charge and discharge, the positive electrode 11 is likely to elongate near the positive electrode substrate exposed portion 32. This is presumably because there is a large difference between the pressure load applied near the positive electrode substrate exposed portion 32 and the pressure load applied to the central portion of the positive electrode 11 in the widthwise direction. Therefore, the effects of the present disclosure are more pronounced in a nonaqueous electrolyte secondary battery 10 in which the positive electrode substrate exposed portion 32 contacts only one of both widthwise end portions of the positive electrode 11.

[0028] The positive electrode mixture layer 31 contains a particulate lithium-containing composite oxide as a positive electrode active material. The lithium-containing composite oxide is a composite oxide containing metal elements such as Co, Mn, Ni, and Al in addition to Li. The metal element constituting the lithium-containing composite oxide is, for example, at least one selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Sn, Sb, W, Pb, and Bi. Among these, it is preferable to contain at least one selected from Co, Ni, Al, and Mn. Examples of suitable composite oxides include a lithium-containing composite oxide containing Ni, Co, and Mn, and a lithium-containing composite oxide containing Ni, Co, and Al.

[0029] The lithium-containing composite oxide is, for example, a secondary particle formed by the aggregation of a plurality of primary particles. The volume-based median diameter (D50) of the composite oxide is not particularly limited, but is, for example, 3 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less. When the composite oxide is a secondary particle formed by the aggregation of primary particles, the D50 of the composite oxide refers to the D50 of the secondary particles. D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the median diameter. The particle size distribution of the composite oxide (as well as that of the negative electrode active material) can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II, manufactured by Microtrac-Bell Corporation) using water as a dispersion medium.

[0030] The average particle size of the primary particles constituting the lithium-containing composite oxide is, for example, 0.05 μm or more and 1 μm or less, and is calculated by averaging the diameters of the circumscribed circles of the primary particles extracted by analyzing a scanning electron microscope (SEM) image of the cross section of the secondary particles.

[0031] Examples of the conductive agent contained in the positive electrode mixture layer 31 include carbon black such as acetylene black and ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, and other carbon materials. Examples of the binder contained in the positive electrode mixture layer 31 include fluorine-containing resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, and the like. Furthermore, these resins may be used in combination with carboxymethyl cellulose (CMC) or a salt thereof, polyethylene oxide (PEO), and the like.

[0032] The negative electrode 12 includes a negative electrode core 40 and a negative electrode mixture layer 41 formed on the surface of the negative electrode core 40. The negative electrode core 40 can be a foil of a metal, such as copper or a copper alloy, that is stable within the potential range of the negative electrode 12, or a film with such a metal disposed on the surface. An example of the negative electrode core 40 is a copper or copper alloy foil having a thickness of 5 μm or more and 15 μm or less. The negative electrode mixture layer 41 preferably contains a negative electrode active material and a binder and is formed on both sides of the negative electrode core 40. The thickness of the negative electrode mixture layer 41 is, for example, 30 μm or more and 200 μm or less on one side of the negative electrode core 40. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc. to the negative electrode core 40, drying the coating, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40.

[0033] The negative electrode mixture layer 41 preferably contains a carbon material and a silicon-containing material as the negative electrode active material. The inclusion of the silicon-containing material can improve the battery capacity of the nonaqueous electrolyte secondary battery 10. For example, the negative electrode mixture layer 41 may use, as the negative electrode active material, a material containing at least one of an element that alloys with Li, such as Sn, and a material containing the element.

[0034] The carbon material functioning as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Among them, it is preferable to use at least artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, and amorphous graphite, or a mixture thereof. The volume-based median diameter (D50) of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0035] The silicon-containing material may be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The volume-based median diameter (D50) of the composite material is generally smaller than the volume-based median diameter (D50) of graphite. The volume-based median diameter (D50) of the composite material is, for example, 1 μm or more and 15 μm or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0036] From the viewpoint of achieving high capacity, the content of the silicon-containing material is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, of the total mass of the negative electrode active material. Generally, silicon-containing materials exhibit a larger volume change during charge and discharge than carbon materials. Therefore, when a silicon-containing material is included as the negative electrode active material, repeated charge and discharge cycles result in a greater increase in stress within the battery, leading to more pronounced deformation of the electrode plate. Therefore, the effects of the present disclosure are more pronounced in nonaqueous electrolyte secondary batteries 10 in which the content of the silicon-containing material is 5% by mass or more of the total mass of the negative electrode active material. The upper limit of the content of the silicon-containing material is, for example, 80% by mass of the total mass of the negative electrode active material.

[0037] A suitable silicon-containing material (composite material) is a composite particle including an ion-conducting phase, a Si phase dispersed in the ion-conducting phase, and a conductive layer covering the surface of the ion-conducting phase. The ion-conducting phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ion-conducting phase is a continuous phase composed of a collection of particles finer than the Si phase. The conductive layer is composed of a material with higher conductivity than the ion-conducting phase and forms a good conductive path in the negative electrode mixture layer 41.

[0038] An example of a suitable Si-containing composite material has a sea-island structure in which fine Si is dispersed almost uniformly in an amorphous silicon oxide phase, and the overall structure is represented by the general formula SiO ｘ The silicon oxide may be mainly composed of silicon dioxide. The oxygen to silicon content (x) is, for example, 0.5≦x<2.0, preferably 0.8≦x≦1.5.

[0039] The binder contained in the negative electrode mixture layer 41 can be, as in the case of the positive electrode mixture layer 31, fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, etc., but styrene butadiene rubber (SBR) is preferably used. The negative electrode mixture layer 41 also preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, it is preferable to use a combination of SBR with CMC or a salt thereof, PAA or a salt thereof, etc. The negative electrode mixture layer 41 may also contain a conductive agent such as carbon nanotubes (CNT).

[0040] Next, the separator 13 constituting the electrode assembly 14 will be described in detail with further reference to Figures 4 and 5. Figure 4 is a schematic cross-sectional view of the separator 13, and Figure 5 is a view showing the separator 13 in an expanded state.

[0041] As shown in Fig. 4, the separator 13 has a substrate layer 50 and particles 52 including at least one of inorganic particles and resin particles provided on at least one surface of the substrate layer 50. The presence of the particles 52 on the surface of the substrate layer 50 makes it possible to create an uneven shape on the surface of the separator 13. In the example shown in Fig. 4, the particles 52 are directly attached to the surface of the substrate layer 50, but at least a portion of the particles 52 may be attached to the surface of the particles 52.

[0042] In this embodiment, the particles 52 are provided only on the surface of the base material layer 50 that faces the positive electrode 11. Therefore, when the separator 13 is incorporated into the nonaqueous electrolyte secondary battery 10, at least a portion of the particles 52 comes into contact with the surface of the positive electrode 11. This makes the coefficient of friction of the surface of the separator 13 that faces the positive electrode 11 greater than the coefficient of friction of the surface of the separator 13 that faces the negative electrode 12. As a result, when the negative electrode mixture layer 41 expands during charge and discharge, the frictional force applied to the positive electrode 11 increases, and displacement of the positive electrode 11 toward both end sides in the width direction is suppressed.

[0043] 5 , when a region extending from both widthwise ends of the separator 13 along the widthwise direction of the separator 13 and covering 20% ​​of the total width of the separator 13 is defined as a first region 54, and a region sandwiched between the first regions 54 is defined as a second region 56, the occupied area ratio of the particles 52 in the first region 54 is larger than the occupied area ratio of the particles 52 in the second region 56 when viewed from the surface of the separator 13. In other words, a high-density region in which the occupied area ratio of the particles 52 is larger than in other regions is provided on the widthwise end side of the separator 13, and as a result, more particles 52 are arranged at the widthwise end portion of the separator 13 than at the widthwise central portion.

[0044] As described above, in the wound electrode body 14, the central portion of the positive electrode 11 in the width direction tends to be subjected to a greater pressure load than the ends of the positive electrode 11 in the width direction. By increasing the area ratio occupied by the particles 52 at both ends of the separator 13 in the width direction, the pressure load applied by the particles 52 at the ends of the positive electrode 11 in the width direction increases. This reduces the difference between the pressure load applied to the central portion of the positive electrode 11 in the width direction and the pressure load applied to the ends of the positive electrode 11 in the width direction. As a result, the positive electrode 11 is prevented from stretching toward both ends in the width direction. Note that if the area ratio occupied by the particles 52 is increased over the entire width of the separator 13, the pressure load applied to the ends of the positive electrode 11 in the width direction increases, and the pressure load applied to the central portion of the positive electrode 11 in the width direction also increases. Therefore, it is not possible to reduce the difference between the pressure load applied to the central part of the positive electrode 11 in the width direction and the pressure load applied to the ends of the positive electrode 11 in the width direction, and the positive electrode 11 may stretch toward both ends in the width direction.

[0045] When viewed from the surface of the separator 13, if the occupied area ratio of the particles 52 in the first region 54 is S1 and the occupied area ratio of the particles 52 in the second region 56 is S2, the ratio of S1 to S2 (S1 / S2) is preferably 1.25 or greater, more preferably 2.5 or greater, and even more preferably 5.0 or greater. When (S1 / S2) is 1.25 or greater, the pressure load applied to the widthwise end of the positive electrode 11 can be further increased when the negative electrode mixture layer 41 expands during charge and discharge. The upper limit of (S1 / S2) is, for example, 20.0. S1 and S2 can be calculated using a laser microscope (e.g., a VK-X3000 manufactured by Keyence Corporation).

[0046] The occupied area ratio (S1) of the particles 52 in the first region 54 is preferably 70% or more, more preferably 80% or more, and even more preferably 90% or more. By setting the occupied area ratio (S1) of the particles 52 in the first region 54 to 70% or more, it is possible to further increase the pressure load applied to the widthwise end of the positive electrode 11 when the negative electrode mixture layer 41 expands during charge and discharge. The upper limit of the occupied area ratio (S1) of the particles 52 in the first region 54 is, for example, 99%. Furthermore, by setting the occupied area ratio (S1) of the particles 52 in the first region 54 to 70% or more, it becomes easy to increase the coefficient of friction of the surface of the separator 13 facing the positive electrode 11.

[0047] The high-density region in which the occupied area ratio of the particles 52 is larger than that of other regions may be provided over the entire first region 54, or may be provided in a partial region of the first region 54. In other words, the high-density region may be provided in a range of 20% or less of the total width of the separator 13 along the width direction of the separator 13 from both ends in the width direction of the separator 13, or may be provided in a range of 15% or less of the total width of the separator 13, or may be provided in a range of 10% or less of the total width of the separator 13. Furthermore, as long as the occupied area ratio of the particles 52 in the first region 54 is larger than the occupied area ratio of the particles 52 in the second region 56, the high-density region may be provided in a partial region of the second region 56.

[0048] The substrate layer 50 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. The material of the substrate layer 50 is not particularly limited, but examples include polyolefins such as polyethylene, polypropylene, and copolymers of polyethylene and α-olefins, acrylic resins, polystyrene, polyesters, cellulose, polyimides, polyphenylene sulfide, polyether ether ketones, and fluororesins. The substrate layer 50 may have a single-layer structure or a multi-layer structure. The thickness of the substrate 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.

[0049] The porosity of the base layer 50 is, for example, 30% or more and 70% or less. The porosity of the base layer 50 is measured by the following method. (1) The base layer 50 is punched out into a circle having a diameter of 2 cm, and the thickness h and mass w of the center of the punched piece of the base layer 50 are measured. (2) The volume V and mass W of the piece are found from the thickness h and mass w, and the porosity ε is calculated using the following formula: Porosity ε (%) = ((ρV - W) / (ρV)) × 100, where ρ is the density of the material constituting the base layer 50.

[0050] As described above, the particles 52 include at least one of inorganic particles and resin particles. Examples of inorganic particles include metal oxide particles, metal nitride particles, metal fluoride particles, and metal carbide particles. Examples of metal oxide particles include aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, nickel oxide, silicon oxide, and manganese oxide, with aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide being preferred. Examples of metal nitride particles include titanium nitride, boron nitride, aluminum nitride, magnesium nitride, and silicon nitride. Examples of metal fluoride particles include aluminum fluoride, lithium fluoride, sodium fluoride, magnesium fluoride, calcium fluoride, and barium fluoride. Examples of metal carbide particles include silicon carbide, boron carbide, titanium carbide, and tungsten carbide. Furthermore, inorganic particles include zeolite (M ２／ｎ O.Al ２ O ３ xSiO ２ ・yH ２ O, M is a metal element, n is the valence of M, x≧2, y≧0), porous aluminosilicates such as talc (Mg ３ Si ４ O １０ (OH) ２ ), layered silicates such as barium titanate (BaTiO ３ ), strontium titanate (SrTiO ３ These may be used alone or in combination of two or more kinds.

[0051] Examples of resin particles include acrylic resins, polyester resins, polyimide resins, polyamide resins, polyurethane resins, polyethylene glycol, polyvinyl alcohol, and polyvinylpyrrolidone, among which acrylic resins are preferred. Examples of acrylic resin particles include resin particles of polyacrylate, polymethacrylate, or copolymers thereof. These may be used alone or in combination of two or more.

[0052] The particles 52 may be a combination of the inorganic particles and the resin particles. The particles 52 present in the first region 54 and the particles 52 present in the second region 56 may be the same type or different types. For example, inorganic particles made of aluminum oxide may be disposed as the particles 52 in the first region 54, and resin particles made of an acrylic resin may be disposed as the particles 52 in the second region 56.

[0053] The volumetric median diameter (D1) of the particles 52 in the first region 54 is preferably larger than the volumetric median diameter (D2) of the particles 52 in the second region 56. In this case, the pressure load applied to the widthwise ends of the positive electrode 11 increases. Furthermore, the ratio (D1 / D2) of the volumetric median diameter (D1) of the particles 52 in the first region 54 to the volumetric median diameter (D2) of the particles 52 in the second region 56 is preferably 1.5 or more, more preferably 2.0 or more. In this case, the pressure load applied to the widthwise ends of the positive electrode 11 further increases, and the difference between the pressure load applied to the center of the widthwise direction of the positive electrode 11 and the pressure load applied to the widthwise ends of the positive electrode 11 becomes smaller. Furthermore, the upper limit of (D1 / D2) is, for example, 5.0. The volume-based median diameter of the particles 52 means the particle size at which the cumulative frequency of the particles in the volume-based particle size distribution is 50% from the smallest particle size, and is also called the middle diameter. The particle size distribution of the particles 52 can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac Bell Co., Ltd.) using water as a dispersion medium.

[0054] The volume-based median diameter (D1) of the particles 52 in the first region 54 is preferably 0.5 μm or more, more preferably 1.0 μm or more, and even more preferably 1.5 μm or more. If the volume-based median diameter (D1) of the particles 52 in the first region 54 is 0.5 μm or more, when the negative electrode mixture layer 41 expands during charge and discharge, the particles 52 can apply an appropriate amount of pressure to the positive electrode 11. As a result, the positive electrode 11 is prevented from extending toward both ends in the width direction. Furthermore, if the volume-based median diameter (D1) of the particles 52 in the first region 54 is 0.5 μm or more, appropriate unevenness can be created on the surface of the separator 13, thereby increasing the coefficient of friction of the surface of the separator 13. As a result, when the negative electrode mixture layer 41 expands during charge and discharge, the frictional force applied to the positive electrode 11 increases, preventing the positive electrode 11 from shifting toward both ends in the width direction. Furthermore, the volume-based median diameter (D1) of the particles 52 in the first region 54 is preferably 10.0 μm or less, more preferably 9.0 μm or less, and even more preferably 8.0 μm or less. If the volume-based median diameter (D1) of the particles 52 in the first region 54 exceeds 10.0 μm, the thickness of the separator 13 may increase excessively, the diameter of the electrode body 14 may increase, and the battery size may become large. If the volume-based median diameter (D1) of the particles 52 in the first region 54 exceeds 10.0 μm, when the negative electrode mixture layer 41 expands during charge and discharge, the pressure applied from the particles 52 to the positive electrode 11 may increase excessively, which may result in deformation of the positive electrode 11. Therefore, the volume-based median diameter (D1) of the particles 52 in the first region 54 is preferably 0.5 μm or more and 10.0 μm or less, more preferably 1.0 μm or more and 9.0 μm or less, and even more preferably 1.5 μm or more and 8.0 μm or less.

[0055] The Young's modulus (E1) of the separator 13 in the first region 54 is preferably greater than the Young's modulus (E2) of the separator 13 in the second region 56. In this case, the pressure load applied to the widthwise end of the positive electrode 11 is further increased. Furthermore, the ratio (E1 / E2) of the Young's modulus (E1) of the separator 13 in the first region 54 to the Young's modulus (E2) of the separator 13 in the second region 56 is preferably 1.5 or more, more preferably 2.0 or more. In this case, the pressure load applied to the widthwise end of the positive electrode 11 is further increased, and the difference between the pressure load applied to the center of the widthwise direction of the positive electrode 11 and the pressure load applied to the widthwise end of the positive electrode 11 can be further reduced. The upper limit of (E1 / E2) is, for example, 5.0. E1 and E2 can be calculated by the method described in the Examples below. Furthermore, E1 and E2 can be adjusted by changing the compressive strength of the particles 52 or the occupied area ratio of the particles 52.

[0056] The Young's modulus (E1) of the separator 13 in the first region 54 is preferably 100 MPa or more, more preferably 150 MPa or more, and even more preferably 200 MPa or more. In this case, the pressure load applied to the widthwise end of the positive electrode 11 increases. The upper limit of the Young's modulus (E1) of the separator 13 in the first region 54 is, for example, 500 MPa.

[0057] A method for causing the particles 52 to be present on the surface of the separator 13 includes preparing a dispersion liquid in which the particles 52 are dispersed, applying the dispersion liquid to the surface of the base layer 50, and drying the dispersion liquid. At this time, by making the amount of the dispersion liquid applied to the first region 54 larger than the amount of the dispersion liquid applied to the second region 56, a larger number of the particles 52 can be present in the first region 54. Alternatively, two types of dispersion liquid with different particle 52 contents may be prepared, and the dispersion liquid with the larger particle 52 content may be applied to the first region 54, thereby causing a larger number of the particles 52 to be present in the first region 54. Examples of methods for applying the dispersion liquid to the surface of the base layer 50 include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing, with gravure coating being preferred among them.

[0058] As described above, by increasing the area ratio occupied by the particles 52 at both widthwise ends of the separator 13, the pressure load applied to the widthwise ends of the positive electrode 11 increases. This reduces the difference between the pressure load applied to the center of the widthwise direction of the positive electrode 11 and the pressure load applied to the widthwise ends of the positive electrode 11. As a result, the positive electrode 11 is prevented from stretching toward both widthwise ends. Furthermore, by having the particles 52 present on the surface of the separator 13 facing the positive electrode 11, the coefficient of friction of the surface of the separator 13 facing the positive electrode 11 is greater than the coefficient of friction of the surface of the separator 13 facing the negative electrode 12. This increases the frictional force applied to the positive electrode 11 when the negative electrode mixture layer 41 expands during charge and discharge, thereby preventing the positive electrode 11 from shifting toward both widthwise ends.

[0059] The above embodiment can be modified as appropriate without impairing the objectives of the present disclosure. For example, in this embodiment, the particles 52 are present only on the surface of the separator 13 facing the positive electrode 11, but they may also be present on the surface of the separator 13 facing the negative electrode 12. Furthermore, the particles 52 may also be present only on the surface of the separator 13 facing the negative electrode 12. Even if the particles 52 are present only on the surface of the separator 13 facing the negative electrode 12, the pressure load applied from the separator 13 to the positive electrode 11 can be increased. From the viewpoint of increasing the coefficient of friction of the surface of the separator 13 facing the positive electrode 11, the particles 52 are preferably disposed on the surface of the separator 13 facing the positive electrode 11.

[0060] Furthermore, in the above embodiment, the occupied area ratio of the particles 52 in the first region 54 located on the upper side of the separator 13 in the width direction and the occupied area ratio of the particles 52 in the first region 54 located on the lower side of the separator 13 in the width direction are substantially the same, but are not limited to this. For example, the occupied area ratio of the particles 52 in a region ranging from the end (upper end) on the side where the positive electrode lead 20 (see FIG. 2 ) is provided along the width direction of the separator 13 to 20% of the entire width of the separator 13 may be larger than the occupied area ratio of the particles 52 in a region ranging from the end (lower end) on the side where the positive electrode lead 20 is not provided along the width direction of the separator 13 to 20% of the entire width of the separator 13. That is, the particles 52 may be present in greater numbers on the upper side of the separator 13 in the width direction than on the lower side of the separator 13 in the width direction. As described above, the positive electrode 11 is prone to elongation in the vicinity of the positive electrode substrate exposed portion 32 to which the positive electrode lead 20 is connected. Therefore, by having more particles 52 present on the upper side of the separator 13 in the width direction, the positive electrode 11 is further prevented from extending toward both end sides in the width direction.

[0061] Furthermore, in the above embodiment, the occupied area ratio of the particles 52 is substantially uniform across the longitudinal direction of the separator 13, but this is not limiting. For example, the occupied area ratio of the particles 52 on the inner side of the separator 13 may be greater than the occupied area ratio of the particles 52 on the outer side of the separator 13. When the negative electrode mixture layer 41 expands during charge and discharge, the positive electrode 11 is more likely to stretch toward both ends in the width direction on the inner side of the electrode assembly 14 than on the outer side of the electrode assembly 14. This is presumably because the difference between the pressure load applied to the central portion of the positive electrode 11 in the width direction and the pressure load applied to the ends in the width direction of the positive electrode 11 is greater on the inner side of the electrode assembly 14 than on the outer side of the electrode assembly 14. Therefore, by making the occupied area ratio of the particles 52 on the inner side of the separator 13 greater than the occupied area ratio of the particles 52 on the outer side of the separator 13, the positive electrode 11 is more likely to stretch toward both ends in the width direction even on the inner side of the electrode assembly 14.

[0062] In the above embodiment, the particles 52 are disposed directly on the surface of the substrate layer 50, but this is not limiting. For example, as shown in FIG. 6 , the separator 13 may include a substrate layer 50 and a heat-resistant layer 58 disposed on one side of the substrate layer 50, with the particles 52 disposed on the surface of the heat-resistant layer 58. The heat-resistant layer 58 may be made of a highly heat-resistant resin material such as polyimide, polyamideimide, aramid, polyethersulfone, or polyetherimide. Furthermore, as shown in FIG. 7 , at least a portion of the particles 52 may be present inside the heat-resistant layer 58, with the tops of the particles 52 protruding from the heat-resistant layer 58. The heat-resistant layer 58 may be disposed on both sides of the substrate layer 50.

[0063] The present disclosure will be explained in more detail below with reference to examples, but the present disclosure is not limited to these examples.

[0064] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２ An aluminum-containing lithium nickel cobalt oxide represented by the formula (I) was used. The above positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) were mixed in a solids mass ratio of 100:1:0.9, and N-methyl-2-pyrrolidone (NMP) was used as a dispersion medium to prepare a positive electrode mixture slurry. Next, the positive electrode mixture slurry was applied to both sides of a strip-shaped positive electrode core made of aluminum foil with a thickness of 15 μm, dried, rolled, and cut to a predetermined electrode plate size to produce a positive electrode in which a positive electrode mixture layer was formed on both sides of the positive electrode core. Then, as shown in FIG. 3, a positive electrode core exposed portion in which the positive electrode mixture layer was not present and the positive electrode core surface was exposed was provided at one end of the approximately central portion in the longitudinal direction of the positive electrode. At this time, (t1 / t2) calculated from the width direction length t1 of the first positive electrode mixture layer and the width direction length t2 of the second positive electrode mixture layer was 0.2. In addition, an aluminum positive electrode lead was welded to the exposed portion of the positive electrode substrate.

[0065] [Preparation of Negative Electrode] Graphite, silicon oxide (SiO), sodium carboxymethyl cellulose (CMC-Na), and styrene butadiene rubber (SBR) were mixed in a solids mass ratio of 92:8:1:1, and an appropriate amount of water was added to prepare a negative electrode mixture slurry. Next, the negative electrode mixture slurry was applied to both sides of a strip-shaped negative electrode core made of copper foil with a thickness of 8 μm, dried, rolled, and cut to a predetermined electrode plate size to prepare a negative electrode in which a negative electrode mixture layer was formed on both sides of the negative electrode core. A negative electrode exposed portion in which the negative electrode mixture layer was not present and the core surface was exposed was provided at the inner end of the winding of the negative electrode, and a nickel negative electrode lead was welded to the negative electrode exposed portion.

[0066] [Preparation of separator] A porous polyethylene substrate having a thickness of 12 μm was used as the substrate layer. Alumina (α-Al ２ O ３ ) particles, an acrylic acid ester binder emulsion, and carboxymethyl cellulose as a thickener were mixed in a solid content mass ratio of 100:3:1.5, and then an appropriate amount of water was added to prepare a dispersion so that the solid content concentration was 40% by mass. This dispersion was applied to the entire surface of one side of a porous substrate serving as a substrate layer using a gravure coater set at a conveying speed of 1.5 m / min and a drying oven temperature of 60 °C, and alumina particles were placed on one side of the substrate layer. In this case, the coating amount in the range (first region) from both ends of the separator in the width direction to 20% of the separator's total width was 10 times the coating amount in the other range (second region). In other words, a high-density region of inorganic particles was formed in the range from both ends of the separator in the width direction to 20% of the separator's total width. When the surface of the separator was observed using a laser microscope (VK-X3000 manufactured by Keyence Corporation), the area ratio occupied by the alumina particles in the first region was 90%, and the area ratio occupied by the alumina particles in the second region was 9%.

[0067] Additionally, sample pieces measuring 10 mm in length and 10 mm in width were cut out from each of the first and second regions of the separator. Each sample piece was subjected to a compression test using a universal testing machine (Tensilon Universal Testing Machine RTG-1310, manufactured by A&D Corporation). The Young's modulus was calculated from the slope of the strain and stress of the sample in accordance with JIS K 7161-1. As a result, the Young's modulus of the separator in the first region was 250 MPa, and the Young's modulus of the separator in the second region was 120 MPa.

[0068] [Preparation of non-aqueous electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 3:7, and lithium hexafluorophosphate (LiPF ６ A non-aqueous electrolyte was prepared by dissolving 1.5 mol / L of ammonium hydroxide in water.

[0069] [Fabrication of Test Cell (Non-Aqueous Electrolyte Secondary Battery)] A wound electrode assembly was fabricated by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween. The separator was positioned so that the surface containing the alumina particles faced the positive electrode. Insulating plates were then placed above and below the electrode assembly, and the electrode assembly was housed in an outer can. The negative electrode lead was welded to the bottom of a cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. After pouring the electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket to fabricate a test cell.

[0070] [Reliability Evaluation] Five test cells were fabricated using the above fabrication method. Each test cell was charged at a constant current of 0.5 C until the battery voltage reached 4.2 V, and then constant-voltage charged at a constant voltage of 4.2 V until the charging current reached 0.05 C. Next, the test cell was discharged at a constant current of 0.5 C until the battery voltage reached 2.5 V. This cycle of charge and discharge was counted as one cycle, and 1000 charge and discharge cycles were performed. If a voltage drop of 0.1 V / sec or more was confirmed during charging of each test cell during the 1000 charge and discharge cycles, it was determined that a voltage abnormality had occurred in that test cell.

[0071] Example 2 A test cell was fabricated and evaluated in the same manner as in Example 1, except that the coating amount in a range of 10% of the separator's total width from both widthwise ends was 10 times the coating amount in other areas. That is, a high-density region of inorganic particles was formed in a range of 10% of the separator's total width from both widthwise ends. When the surface of the separator was observed using a laser microscope (Keyence Corporation, VK-X3000), the area ratio of the alumina particles in the first region was 49.5%, and the area ratio of the alumina particles in the second region was 9%. Furthermore, the Young's modulus of the separator in the first region was 200 MPa, and the Young's modulus of the separator in the second region was 120 MPa.

[0072] Comparative Example 1 A test cell was fabricated and evaluated in the same manner as in Example 1, except that a heat-resistant layer made of aramid resin was provided instead of alumina particles on the surface of the substrate layer. The heat-resistant layer was provided only on the surface of the separator facing the positive electrode. The thickness of the heat-resistant layer was approximately uniform across the surface of the separator, measuring 2.5 μm. The Young's modulus of the separator in both the first and second regions was 100 MPa.

[0073] Comparative Example 2 A test cell was prepared and evaluated in the same manner as in Example 1, except that in preparing the separator, a dispersion containing alumina particles was uniformly applied over the entire surface of the substrate layer. When the surface of the separator was observed using a laser microscope (VK-X3000 manufactured by Keyence Corporation), the area ratio of the alumina particles in both the first region and the second region was 9%. Furthermore, the Young's modulus of the separator in both the first region and the second region was 120 MPa.

[0074] Table 1 shows the number of voltage abnormalities occurring versus the number of test cells in the reliability evaluation described above for the test cells of Examples 1 and 2 and Comparative Examples 1 and 2. Table 1 also shows the occupied area ratios and Young's moduli of the particles (alumina particles) in the first and second regions.

[0075]

[0076] As shown in Table 1, the test cell of Example 1 experienced fewer voltage abnormalities than the test cells of Comparative Examples 1 and 2. X-ray CT images were then taken of each test cell of Example 1 and Comparative Examples 1 and 2 after 1000 cycles using an inspeXio SMX-255CT FPD HR (Shimadzu Corporation) to confirm the elongation of the positive electrode. As a result, the test cells in which voltage abnormalities occurred had positive electrodes elongated toward both ends in the width direction compared to test cells in which voltage abnormalities did not occur. In other words, it can be said that the elongation of the positive electrode can be suppressed by disposing alumina particles on the surface of the separator and disposing more alumina particles at the width ends of the separator than at the center in the width direction.

[0077] Example 3 A test cell was fabricated and evaluated in the same manner as in Example 1, except that in fabricating the positive electrode, the positive electrode substrate exposed portion was formed across the width direction of the positive electrode. When the surface of the separator was observed using a laser microscope (VK-X3000 manufactured by Keyence Corporation), the area ratio occupied by the alumina particles in the first region was 90%, and the area ratio occupied by the alumina particles in the second region was 9%. In addition, the Young's modulus of the separator in the first region was 250 MPa, and the Young's modulus of the separator in the second region was 120 MPa.

[0078] <Comparative Example 3> A test cell was produced and evaluated in the same manner as in Comparative Example 1, except that in the production of the positive electrode, the positive electrode substrate exposed portion was formed across the width direction of the positive electrode. In addition, the Young's modulus of the separator in both the first region and the second region was 100 MPa.

[0079] Comparative Example 4 A test cell was fabricated and evaluated in the same manner as in Comparative Example 2, except that in fabricating the positive electrode, the positive electrode substrate exposed portion was formed across the width direction of the positive electrode. When the surface of the separator was observed using a laser microscope (VK-X3000 manufactured by Keyence Corporation), the area ratio occupied by alumina particles in both the first region and the second region was 9%. In addition, the Young's modulus of the separator in both the first region and the second region was 120 MPa.

[0080] Table 2 shows the number of voltage abnormalities occurring versus the number of test cells in the reliability evaluation described above for the test cells of Example 3 and Comparative Examples 3 and 4. Table 1 also shows the occupied area ratios and Young's moduli of the particles (alumina particles) in the first and second regions.

[0081]

[0082] As shown in Table 2, the test cell of Example 3 had a reduced number of voltage abnormalities compared to the test cells of Comparative Examples 3 and 4. In other words, even when the positive electrode substrate exposed portion is formed across the width direction of the positive electrode, it can be said that elongation of the positive electrode can be suppressed by arranging alumina particles on the surface of the separator and arranging more alumina particles at the width direction ends of the separator than at the width direction center.

[0083] The present disclosure is further described by the following embodiments. Aspect 1: A nonaqueous electrolyte secondary battery including a wound electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween, a nonaqueous electrolyte, and an outer can accommodating the electrode assembly and the nonaqueous electrolyte, wherein particles including at least one of inorganic particles and resin particles are present on at least one surface of the separator, and where regions extending from both widthwise ends of the separator along the widthwise direction of the separator and spanning 20% ​​of the entire width of the separator are defined as first regions and regions sandwiched between the first regions are defined as second regions, the area occupied by the particles in the first regions is greater than the area occupied by the particles in the second regions when viewed from the surface of the separator. Aspect 2: The nonaqueous electrolyte secondary battery according to Aspect 1, wherein a ratio of the area occupied by the particles in the first regions to the area occupied by the particles in the second regions is 1.25 or greater. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the ratio of the area occupied by the particles in the first region to the area occupied by the particles in the second region is 5.0 or more. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the area occupied by the particles in the first region is 70% or more. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein the area occupied by the particles in the first region is 90% or more. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the inorganic particles are at least one selected from the group consisting of aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the resin particles are acrylic resin particles. Configuration 8: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the volume-based median diameter of the particles in the first region is larger than the volume-based median diameter of the particles in the second region. Configuration 9: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 8, wherein the ratio of the volume-based median diameter of the particles in the first region to the volume-based median diameter of the particles in the second region is 1.5 or greater.Configuration 10: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 9, wherein the volume-based median diameter of the particles in the first region is 0.5 μm or more and 10.0 μm or less. Configuration 11: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 10, wherein the Young's modulus of the separator in the first region is 100 MPa or more. Configuration 12: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 11, wherein the Young's modulus of the separator in the first region is 200 MPa or more. Configuration 13: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 12, wherein the Young's modulus of the separator in the first region is greater than the Young's modulus of the separator in the second region. Configuration 14: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 13, wherein the ratio of the Young's modulus of the separator in the first region to the Young's modulus of the separator in the second region is 1.5 or more. a positive electrode lead is connected to one of both widthwise end portions of the positive electrode, and an area ratio of the particles in a region ranging from the end of the separator in the widthwise direction on the side where the positive electrode lead is provided to 20% of the total width of the separator along the widthwise direction of the separator is greater than an area ratio of the particles in a region ranging from the end of the separator in the widthwise direction on the side where the positive electrode lead is not provided to 20% of the total width of the separator along the widthwise direction of the separator. a positive electrode core exposed portion on a surface of the positive electrode, the positive electrode core exposed portion being in contact with only one of both widthwise ends of the positive electrode, and a positive electrode lead being connected to the positive electrode core exposed portion.

[0023] A nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 16, wherein the particles are provided only on a surface of the separator facing the positive electrode.Aspect 19: The nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 18, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, the negative electrode mixture layer containing a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5 mass% or more of the total mass of the negative electrode active material. Aspect 20: The nonaqueous electrolyte secondary battery according to any one of Aspects 1 to 19, wherein the separator has a high-density region in which the area ratio of the particles is larger than that of other regions when viewed from the surface of the separator, and the high-density region is provided in a range from both widthwise end portions of the separator to 20% or less of the total width of the separator along the width direction of the separator. Aspect 21: The nonaqueous electrolyte secondary battery according to Aspect 20, wherein the high-density region is provided in a range from both widthwise end portions of the separator to 10% or less of the total width of the separator along the width direction of the separator.

[0084] REFERENCE SIGNS LIST 10 non-aqueous electrolyte secondary battery, 11 positive electrode, 11A upper end, 11B lower end, 12 negative electrode, 13 separator, 14 electrode body, 16 outer can, 17 sealing body, 18, 19 insulating plate, 20 positive electrode lead, 21 negative electrode lead, 22 grooved portion, 23 internal terminal plate, 24 lower valve body, 25 insulating member, 26 upper valve body, 27 cap, 28 gasket, 29 winding shaft, 30 positive electrode core, 31 positive electrode mixture layer, 32 positive electrode core exposed portion, 33 first positive electrode mixture layer, 34 second positive electrode mixture layer, 40 negative electrode core, 41 negative electrode mixture layer, 50 substrate layer, 52 particles, 54 first region, 56 second region, 58 heat-resistant layer

Claims

1. A non-aqueous electrolyte secondary battery comprising: a wound-type electrode assembly in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound with a separator interposed therebetween; a non-aqueous electrolyte; and an exterior can accommodating the electrode assembly and the non-aqueous electrolyte, wherein particles including at least one of inorganic particles and resin particles are present on at least one surface of the separator, and when a region ranging from both ends in the width direction of the separator to 20% of the entire width of the separator along the width direction of the separator is defined as a first region, and a region sandwiched between the first regions is defined as a second region, when viewed from the surface of the separator, the area occupied by the particles in the first region is greater than the area occupied by the particles in the second region.

2. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the area occupied by said particles in said first region to the area occupied by said particles in said second region is 1.25 or more.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the area occupied by said particles in said first region to the area occupied by said particles in said second region is 5.0 or more.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein the area ratio of the particles in the first region is 70% or more.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein the area ratio of said particles in said first region is 90% or more.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the inorganic particles are at least one type selected from the group consisting of aluminum oxide, titanium oxide, magnesium oxide, and zirconium oxide.

7. The nonaqueous electrolyte secondary battery according to claim 1, wherein the resin particles are acrylic resin particles.

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein a volumetric median diameter of said particles in said first region is larger than a volumetric median diameter of said particles in said second region.

9. The nonaqueous electrolyte secondary battery according to claim 1, wherein the ratio of the volume-based median diameter of the particles in the first region to the volume-based median diameter of the particles in the second region is 1.5 or greater.

10. The nonaqueous electrolyte secondary battery according to claim 1, wherein the volume-based median diameter of the particles in the first region is 0.5 μm or more and 10.0 μm or less.

11. The nonaqueous electrolyte secondary battery according to claim 1, wherein the Young's modulus of the separator in the first region is 100 MPa or more.

12. The nonaqueous electrolyte secondary battery according to claim 1, wherein the Young's modulus of the separator in the first region is 200 MPa or more.

13. The nonaqueous electrolyte secondary battery according to claim 1, wherein the Young's modulus of the separator in the first region is greater than the Young's modulus of the separator in the second region.

14. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the Young's modulus of the separator in the first region to the Young's modulus of the separator in the second region is 1.5 or greater.

15. The nonaqueous electrolyte secondary battery according to claim 1, wherein a ratio of the Young's modulus of the separator in the first region to the Young's modulus of the separator in the second region is 2.0 or greater.

16. The nonaqueous electrolyte secondary battery according to claim 1, wherein a positive electrode lead is connected to either one of both ends in the width direction of the positive electrode, and an area ratio of the particles in a region ranging from the end on the side where the positive electrode lead is provided, along the width direction of the separator, of both ends in the width direction of the separator, to 20% of the total width of the separator is greater than an area ratio of the particles in a region ranging from the end on the side where the positive electrode lead is not provided, along the width direction of the separator, of both ends in the width direction of the separator.

17. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode has a positive electrode core and a positive electrode mixture layer provided on the positive electrode core, a positive electrode core exposed portion where the positive electrode core is exposed is provided on a surface of the positive electrode, the positive electrode core exposed portion contacts only one of both ends in the width direction of the positive electrode, and a positive electrode lead is connected to the positive electrode core exposed portion.

18. The nonaqueous electrolyte secondary battery according to claim 1, wherein the particles are provided only on the surface of the separator that faces the positive electrode.

19. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode has a negative electrode core and a negative electrode mixture layer provided on the negative electrode core, the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5 mass% or more of the total mass of the negative electrode active material.

20. The nonaqueous electrolyte secondary battery according to claim 1, wherein the separator has a high density region in which the area ratio of the particles is larger than other regions when viewed from the surface of the separator, and the high density region is provided in a range of 20% or less of the total width of the separator along the width direction of the separator from both ends in the width direction of the separator.

21. The nonaqueous electrolyte secondary battery according to claim 20, wherein the high density regions are provided in a range of 10% or less of the total width of the separator from both widthwise ends of the separator along the widthwise direction of the separator.

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