Nonaqueous electrolyte secondary battery and method for manufacturing separator for nonaqueous electrolyte secondary battery

Abstract

A separator (13) is characterized by having a base material layer (50) and a filler layer (52). The filler layer (52) includes an inorganic particle layer (54) containing inorganic particles and resin particles (56). When a surface of the filler layer (52) is observed with a scanning electron microscope, 40 or more and 150 or less of the resin particles (56) are detected in a region of 100 μm × 100 μm, when the average particle diameter of the resin particles (56) is X [μm], the average thickness of the inorganic particle layer (54) is Y [μm], and the average length between the end part on the base material layer (50) side of the resin particles (56) and the surface of the base material layer (50) in the thickness direction of the separator (13) is Z [μm], X, Y, and Z satisfy Z > Y-X.

Description

Nonaqueous electrolyte secondary battery and method for manufacturing separator for nonaqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery and a method for manufacturing a separator for 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. These batteries include an electrode assembly having a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, a non-aqueous electrolyte, and an exterior housing that houses these components. The separator not only retains the non-aqueous electrolyte but also isolates the positive and negative electrodes to prevent internal short circuits. Patent Document 1 discloses a separator in which a filler layer containing inorganic particles and resin particles is disposed on the surface of a substrate layer made of a porous membrane. By incorporating resin particles into the filler layer, it is possible to prevent the positive and negative electrodes from elongating when the electrode assembly expands.

[0003] Japanese Patent Application Laid-Open No. 2023-152737

[0004] However, as a result of investigations by the present inventors, it has become clear that when the filler layer contains resin particles, the rate characteristics of the battery may be deteriorated. The technology disclosed in Patent Document 1 does not consider the rate characteristics of the battery, and there is still room for improvement.

[0005] A nonaqueous electrolyte secondary battery according to one embodiment of the present disclosure is a nonaqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a nonaqueous electrolyte, wherein the separator has a base layer and a filler layer disposed on at least one surface of the base layer, and the filler layer includes an inorganic particle layer containing inorganic particles and resin particles at least a portion of which is disposed in the inorganic particle layer, and when the surface of the filler layer is observed with a scanning electron microscope, 40 to 150 resin particles are detected in an area of ​​100 μm × 100 μm, and where X [μm] is the average particle size of the resin particles, Y [μm] is the average thickness of the inorganic particle layer, and Z [μm] is the average length from the surface of the base layer to the end of the resin particle on the base layer side in the thickness direction of the separator, X, Y, and Z satisfy the relationships represented by the following formulas (I) and (II): Formula (I): Z>Y-X Formula (II): 0.25≦Z≦1.0

[0006] Furthermore, a method for manufacturing a separator for a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is characterized by comprising: a first coating step of applying a first coating liquid containing inorganic particles to at least one surface of a substrate layer to form a first coating film; and a second coating step of applying a second coating liquid containing inorganic particles and resin particles onto the first coating film to form a second coating film.

[0007] According to the nonaqueous electrolyte secondary battery of one aspect of the present disclosure, it is possible to improve the rate characteristics of the battery while suppressing the expansion of the electrode plates.

[0008] 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a separator constituting the non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[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. Note that configurations obtained by selectively combining the components of the multiple embodiments and modifications described below are included within the scope of the present disclosure.

[0010] In the following, a cylindrical battery in which a wound electrode assembly 14 is housed in a cylindrical exterior body 16 with a bottom is exemplified as a nonaqueous electrolyte secondary battery, but the exterior body of the battery is not limited to a cylindrical exterior body. The nonaqueous electrolyte secondary battery according to the present disclosure may be, for example, a prismatic battery having a prismatic exterior body, a coin battery having a coin-shaped exterior body, or a pouch-type battery having an exterior body composed of a laminate sheet including a metal layer and a resin layer. Furthermore, the design of the nonaqueous electrolyte secondary battery according to the present disclosure is not limited to the design of the exemplified nonaqueous electrolyte secondary battery, and known nonaqueous electrolyte secondary battery designs may also be applied.

[0011] FIG. 1 is an axial cross-sectional view of a nonaqueous electrolyte secondary battery 10 according to an embodiment. As shown in FIG. 1 , the nonaqueous electrolyte secondary battery 10 includes a wound electrode assembly 14, a nonaqueous electrolyte, and an exterior body 16 that accommodates the electrode assembly 14 and the nonaqueous electrolyte. The electrode assembly 14 includes 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 exterior body 16 is a cylindrical metal container with a bottom that is open on one axial side, and the opening of the exterior body 16 is closed by a sealing body 17. Hereinafter, for convenience of explanation, the sealing body 17 side of the nonaqueous electrolyte secondary battery 10 will be referred to as the "top" and the bottom side of the exterior body 16 will be referred to as the "bottom."

[0012] The positive electrode 11, negative electrode 12, and separator 13 that make up the electrode assembly 14 are all rectangular, elongated bodies that are spirally wound in the longitudinal direction and stacked alternately in the radial direction of the electrode assembly 14. The separator 13 isolates the positive electrode 11 and the negative electrode 12 from each other. Two separators 13 are arranged, for example, to sandwich the positive electrode 11. The electrode assembly 14 includes 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. In the electrode assembly 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the lateral direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the lateral end faces of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode assembly 14.

[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] 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 through a through-hole in the center of the insulating plate 19 and extends toward the bottom side of the exterior body 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 surface of the bottom of the exterior body 16 by welding or the like, and the exterior body 16 serves as the negative electrode terminal.

[0017] A gasket 28 is provided between the exterior body 16 and the sealing body 17 to ensure airtightness inside the battery. The exterior body 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 body 16, and supports the sealing body 17 on its upper surface. The sealing body 17 is fixed to the top of the exterior body 16 by the grooved portion 22 and the open end of the exterior body 16 that is crimped to the sealing body 17.

[0018] 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 the internal pressure of the battery increases due to abnormal heat generation, 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 through a vent hole in the cap 27.

[0019] Next, the positive electrode 11 and the negative electrode 12 that constitute the electrode body 14 will be described.

[0020] [Positive Electrode] As shown in FIG. 1 , the positive electrode 11 has a positive electrode current collector 30 and a positive electrode mixture layer 32 formed on the positive electrode current collector 30. The positive electrode current collector 30 can be 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 its surface. The positive electrode mixture layer 32 contains a positive electrode active material, a conductive agent, and a binder. The positive electrode 11 can be produced, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, a binder, etc., onto the positive electrode current collector 30, drying the coating, and then compressing it to form the positive electrode mixture layer 32 on both sides of the positive electrode current collector 30.

[0021] The positive electrode mixture layer 32 contains particulate lithium metal composite oxide as a positive electrode active material. The lithium metal 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 metal 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 lithium metal composite oxides containing Ni, Co, and Mn, and lithium metal composite oxides containing Ni, Co, and Al.

[0022] Examples of the conductive agent contained in the positive electrode mixture layer 32 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 32 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.

[0023] [Negative Electrode] As shown in FIG. 1 , the negative electrode 12 has a negative electrode current collector 40 and a negative electrode mixture layer 42 formed on the negative electrode current collector 40. The negative electrode current collector 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 its surface. The negative electrode mixture layer 42 contains a negative electrode active material, a binder, and, if necessary, a conductive agent. The negative electrode 12 can be produced by applying a negative electrode mixture slurry containing the negative electrode active material and the binder to the surface of the negative electrode current collector 40, drying the coating, and then compressing it to form the negative electrode mixture layer 42 on both sides of the negative electrode current collector 40.

[0024] The negative electrode mixture layer 42 preferably contains a carbon material and a silicon-containing material as negative electrode active materials. The inclusion of a silicon-containing material facilitates achieving a high capacity of the nonaqueous electrolyte secondary battery 10. Furthermore, silicon-containing materials undergo greater volumetric expansion and contraction than carbon materials during charge and discharge. Therefore, when the negative electrode mixture layer 42 contains a silicon-containing material, the electrode plate is more likely to elongate during charge and discharge. As will be described in more detail below, the separator 13 of the present disclosure suppresses elongation of the electrode plate during charge and discharge. Therefore, when the negative electrode mixture layer 42 contains a silicon-containing material, the effects of the present disclosure are more pronounced.

[0025] 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 average particle size (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.

[0026] The silicon-containing material may be any material containing Si, and examples thereof include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The D50 of the composite material is generally smaller than the D50 of graphite. The volume-based 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.

[0027] 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 42.

[0028] 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.

[0029] As with the positive electrode mixture layer 32, the binder contained in the negative electrode mixture layer 42 can be a fluorine-containing resin, PAN, polyimide, acrylic resin, polyolefin, or the like, but styrene butadiene rubber (SBR) is preferably used. The negative electrode mixture layer 42 preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), or the like. Among these, it is preferable to use a combination of SBR with CMC or a salt thereof, PAA or a salt thereof, or the like. The negative electrode mixture layer 42 may also contain a conductive agent such as carbon nanotubes (CNT).

[0030] Next, the separator 13 constituting the electrode assembly 14 will be described with further reference to Fig. 2. Fig. 2 is a diagram schematically showing a cross section of the separator 13.

[0031] [Separator] As shown in Fig. 2 , the separator 13 has a substrate layer 50 and a filler layer 52 disposed on the surface of the substrate layer 50 facing the positive electrode 11. In this embodiment, the filler layer 52 is disposed on only one side of the substrate layer 50, with the filler layer 52 facing the positive electrode 11 and the substrate layer 50 facing the negative electrode 12. Note that the form of the separator 13 is not limited to the example shown in Fig. 2 , and the filler layer 52 may be disposed on both sides of the substrate layer 50. By disposing the filler layer 52, the shape of the separator 13 is maintained when the battery abnormally heats up, and the occurrence of an internal short circuit can be suppressed.

[0032] The substrate layer 50 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. 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.

[0033] The thickness of the base 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.

[0034] From the viewpoint of ensuring the movement of lithium ions during charge and discharge of the battery, the porosity of the substrate layer 50 is preferably, for example, 30% or more and 70% or less. The porosity of the substrate layer 50 is measured by the following method. (1) Ten circular pieces with a diameter of 2 cm are punched out of the substrate layer 50, and the thickness h and mass w of the center of each of the punched pieces of the substrate layer 50 are measured. (2) The volume V and mass W of the 10 pieces are determined 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 substrate.

[0035] The filler layer 52 includes an inorganic particle layer 54 containing inorganic particles and a binder, and resin particles 56, at least a portion of which is disposed in the inorganic particle layer 54. By disposing the resin particles 56 on the surface of the separator 13 (filler layer 52), it is possible to suppress elongation of the positive electrode 11 and the negative electrode 12. This is because by disposing the resin particles 56 on the surface of the separator 13, an uneven structure is formed on the surface of the separator 13, which can alleviate internal stress caused by expansion and contraction of the positive electrode 11 and the negative electrode 12 when the nonaqueous electrolyte secondary battery 10 is charged and discharged. Furthermore, by adhering the resin particles 56 to the positive electrode 11, movement of the positive electrode 11 due to charge and discharge is suppressed, and elongation of the positive electrode 11 can be suppressed.

[0036] Meanwhile, as a result of investigations by the present inventors, it has become clear that the rate characteristics of the battery deteriorate as the content of resin particles 56 contained in separator 13 (filler layer 52) increases. This is presumably because resin particles 56 inhibit the movement of lithium ions in separator 13. Therefore, in order to improve the rate characteristics of the battery while suppressing the elongation of the electrode plate, it is necessary to limit the content of resin particles 56 contained in filler layer 52 and to arrange an appropriate amount of resin particles 56 on the surface of filler layer 52.

[0037] In the separator 13 of this embodiment, when the average particle size of the resin particles 56 is X [μm], the average thickness of the inorganic particle layer 54 is Y [μm], and the average length from the surface of the base material layer 50 to the end of the resin particles 56 on the base material layer 50 side in the thickness direction of the separator 13 is Z [μm], X, Y, and Z satisfy the relationship Z>Y-X. This allows the resin particles 56 to protrude from the inorganic particle layer 54, and a large amount of the resin particles 56 can be arranged on the surface of the filler layer 52. As a result, even when the content of the resin particles 56 is reduced, an appropriate amount of the resin particles 56 is arranged on the surface of the filler layer 52, which can suppress elongation of the electrode plate and improve the rate characteristics of the battery.

[0038] The average particle diameter X [μm] of the resin particles 56 is preferably 2.0 or more, and more preferably 2.5 or more. In this case, more resin particles 56 protrude from the inorganic particle layer 54, making it easier to suppress elongation of the electrode plate. Furthermore, the average particle diameter X [μm] of the resin particles 56 is preferably 8.0 or less, and more preferably 7.5 or less. If the average particle diameter X [μm] of the resin particles 56 exceeds 8.0, the thickness of the separator 13 may increase excessively, the radial length of the electrode body 14 may increase, and the battery may become larger. Therefore, the average particle diameter X [μm] of the resin particles 56 is preferably 2.0 or more and 8.0 or less, and more preferably 2.5 or more and 7.5 or less. Furthermore, the average particle diameter X [μm] of the resin particles 56 may be 2.0 or more and 7.5 or less, or 2.5 or more and 8.0 or less. The average particle size of the resin particles 56 refers to the particle size at which the cumulative frequency of the smallest particle size in a volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the resin particles 56 can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by Microtrac-Bell) with water as the dispersion medium.

[0039] The average thickness Y [μm] of the inorganic particle layer 54 is preferably 2.0 or more, and more preferably 2.5 or more. By setting the average thickness Y [μm] of the inorganic particle layer 54 to 2.0 or more, the shape of the separator 13 is maintained during abnormal heat generation of the battery, making it easier to suppress the occurrence of internal short circuits. Furthermore, the average thickness Y [μm] of the inorganic particle layer 54 is preferably 4.0 or less, and more preferably 3.5 or less. If the average thickness Y [μm] of the inorganic particle layer 54 exceeds 4.0, the thickness of the separator 13 may increase excessively, increasing the radial length of the electrode body 14 and resulting in an increased battery size. Therefore, the average thickness Y [μm] of the inorganic particle layer 54 is preferably 2.0 or more and 4.0 or less, and more preferably 2.5 or more. Furthermore, the average thickness Y [μm] of the inorganic particle layer 54 may be 2.0 or more and 3.5 or less, or 2.5 or more and 4.0 or less. The average thickness Y [μm] can be determined by photographing a cross section of the separator 13 using a scanning electron microscope (SEM, for example, SU8220 manufactured by Hitachi High-Technologies Corporation).

[0040] The average length Z [μm] from the surface of the substrate layer 50 to the end of the resin particle 56 on the substrate layer 50 side in the thickness direction of the separator 13 is 0.25 or more, and preferably 0.30 or more. In this case, more resin particles 56 protrude from the inorganic particle layer 54, thereby suppressing elongation of the electrode plate. Furthermore, the average length Z [μm] is 1.0 or less, and preferably 0.70 or less. If the average length Z [μm] exceeds 1.0, the thickness of the separator 13 may increase excessively, increasing the radial length of the electrode body 14 and resulting in an increased battery size. Furthermore, if the average length Z [μm] exceeds 1.0, the resin particles 56 may detach from the surface of the filler layer 52. Therefore, the average length Z [μm] from the surface of the substrate layer 50 to the end of the resin particle 56 on the substrate layer 50 side in the thickness direction of the separator 13 is 0.25 or more and 1.0 or less, and preferably 0.30 or more and 0.70 or less. The average length Z [μm] may be 0.25 or more and 0.70 or less, or 0.30 or more and 1.0 or less. The average length Z [μm] can be determined by photographing a cross section of the separator 13 with a scanning electron microscope (for example, SU8220 manufactured by Hitachi High-Technologies Corporation), randomly selecting 50 resin particles 56, measuring the lengths from the surface of the base material layer 50 to the end of the resin particle 56 on the base material layer 50 side, and then calculating the arithmetic average of the measured values.

[0041] Furthermore, when the surface of the filler layer 52 is observed with a scanning electron microscope (e.g., SU8220 manufactured by Hitachi High-Technologies Corporation), 40 to 150 resin particles 56 are detected in an area of ​​100 μm × 100 μm. By setting the number of detected resin particles 56 within the above range, it is possible to improve the rate characteristics of the battery while suppressing the elongation of the electrode plate. In other words, if the number of detected resin particles 56 is less than 40, the electrode plate may elongate. Furthermore, if the number of detected resin particles 56 is more than 150, the movement of lithium ions in the separator 13 may be hindered, which may result in a decrease in the rate characteristics of the battery.

[0042] When the surface of the filler layer 52 is observed with a scanning electron microscope, the number of resin particles 56 detected in a 100 μm × 100 μm area is preferably 125 or less, and more preferably 100 or less. In this case, it becomes easier to ensure the movement of lithium ions in the separator 13, and the rate characteristics of the battery are further improved. Therefore, when the surface of the filler layer 52 is observed with a scanning electron microscope, the number of resin particles 56 detected in a 100 μm × 100 μm area is preferably 40 or more and 125 or less, and more preferably 40 or more and 100 or less.

[0043] 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. 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.

[0044] The average particle size of the inorganic particles is, for example, 0.05 μm or more and 2 μm or less. The average particle size of the inorganic particles, like the average particle size of the resin particles 56, refers to the particle size at which the cumulative frequency of the smallest particle size in a volume-based particle size distribution is 50%, and is also called the median diameter. The particle size distribution of the inorganic particles can be measured using a laser diffraction particle size distribution analyzer (e.g., MT3000II manufactured by Microtrac-Bell) with water as the dispersion medium.

[0045] The content of inorganic particles in the filler layer 52 is, for example, 70% by mass or more and 99% by mass or less, preferably 80% by mass or more and 99% by mass or less, and more preferably 85% by mass or more and 99% by mass or less, relative to the total mass of the filler layer 52.

[0046] Examples of the material of the resin particles 56 contained in the filler layer 52 include acrylic resins made of ethylenically unsaturated carboxylic acid alkyl esters such as methyl acrylate, butyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate; resins made of cyano group-containing ethylenically unsaturated monomers such as acrylonitrile; and resins made of ethylenically unsaturated carboxylic acids and salts thereof such as acrylic acid, methacrylic acid, and maleic acid.

[0047] The resin particles 56 have adhesive properties with the positive electrode 11, and in the non-aqueous electrolyte secondary battery 10, the resin particles 56 are preferably adhered to the positive electrode 11. By adhering the resin particles 56 to the positive electrode 11, movement of the positive electrode 11 due to charge and discharge is suppressed, and the effect of suppressing peeling of the positive electrode mixture layer 32 becomes more pronounced. The resin particles 56 may exhibit adhesive properties with respect to the positive electrode 11, for example, when a non-aqueous electrolyte is held therein. Here, having adhesive properties means that when the separator 13 and the positive electrode 11 are laminated and pressed together, the surfaces of the positive electrode 11 and the separator 13 can be in contact with each other and cannot be separated.

[0048] The binder contained in the filler layer 52 functions to bond the inorganic particles serving as fillers together and to bond the fillers to the base material layer 50. The binder is preferably a polymer material, and 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 a salt thereof, polyacrylic acid (PAA) or a salt thereof, and polyvinyl alcohol (PVA). These may be used alone or in combination of two or more.

[0049] Next, an example of a method for manufacturing the separator 13 of this embodiment will be described. However, the method for manufacturing the separator 13 is not limited to this.

[0050] The manufacturing method of the separator 13 of this embodiment includes a preparation process of preparing a first coating liquid in which inorganic particles are dispersed and a second coating liquid in which inorganic particles and resin particles 56 are dispersed, and a coating process of applying the first coating liquid and the second coating liquid in that order to at least one surface of the substrate layer 50.

[0051] In the preparation step, the first coating liquid is prepared, for example, by mixing inorganic particles and a binder and then adding an appropriate amount of water. The second coating liquid is prepared, for example, by mixing inorganic particles, resin particles 56, and a binder and then adding an appropriate amount of water. The solid content concentrations in the first coating liquid and the second coating liquid are, for example, 3% by mass or more and 50% by mass or less, and may be 5% by mass or more and 40% by mass or less. In the second coating liquid, the ratio of the mass of the resin particles 56 to the mass of the inorganic particles is, for example, 1% by mass or more and 20% by mass or less, and may be 2% by mass or more and 10% by mass or less.

[0052] The coating process includes a first coating process in which a first coating liquid is applied to at least one surface of the substrate layer 50 to form a first coating film, and a second coating process in which a second coating liquid containing inorganic particles and resin particles is applied to the first coating film to form a second coating film. Examples of methods for applying the first and second coating liquids include gravure coating, spraying, die coating, roll coating, reverse roll coating, screen printing, and inkjet printing, with gravure coating being preferred. Adjusting the thickness of the first coating film allows for adjustment of the average length Z [μm] from the surface of the substrate layer 50 to the end of the resin particles 56 on the substrate layer 50 side. Furthermore, the basis weight of the first coating liquid is preferably smaller than the basis weight of the second coating liquid. That is, the thickness of the first coating film is preferably smaller than the thickness of the second coating film.

[0053] In the method for producing the separator 13, the coating film produced in the coating step may be subjected to a drying treatment to remove the solvent. The drying method is not particularly limited, and may be, for example, natural drying, ventilation drying using hot air or the like, heat drying, reduced pressure / vacuum drying, or a combination of these. The drying temperature is generally 10°C or higher and 150°C or lower, and may be 25°C or higher and 125°C or lower. The drying treatment may be performed only after the second coating step, or may be performed after the second coating step and between the first and second coating steps.

[0054] The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0055] Example 1 [Fabrication of Positive Electrode] As a positive electrode active material, LiNi ０．８８ Co ０．０９ Al ０．０３ O ２An 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 current collector 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 current collector. Then, a positive electrode current collector exposed portion was provided in a part of the positive electrode where the positive electrode mixture layer was not present and the positive electrode current collector surface was exposed, and an aluminum positive electrode lead was welded to the positive electrode current collector exposed portion.

[0056] [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 88:12:1:1, 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 current collector 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 current collector. A negative electrode current collector exposed portion in which the negative electrode mixture layer was not present and the current collector 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 current collector exposed portion.

[0057] [Preparation of separator] Alumina (α-Al) was used as inorganic particles having an average particle size of 0.7 μm. ２ O ３ The first coating liquid was prepared by mixing the acrylic ester-based binder emulsion with an acrylic ester-based binder emulsion at a solid content mass ratio of 100:3, and then adding an appropriate amount of water to adjust the solid content concentration to 10 mass %. ２ O ３ ) particles, acrylic resin particles as resin particles having a D50(X) of 3.0 μm, and an acrylic acid ester-based binder emulsion were mixed in a solids mass ratio of 100:5:3, and then an appropriate amount of water was added to adjust the solids concentration to 10% by mass to prepare a second coating liquid.

[0058] A 10 μm-thick porous polyethylene substrate was used as the substrate layer. The first coating liquid and the second coating liquid were applied in this order to the surface of the porous substrate serving as the substrate layer, facing the positive electrode. At this time, the basis weight of the first coating liquid was 0.4 g / m. ２ The coating weight of the second coating liquid was 3.4 g / m ２ Thereafter, the coating film was dried by heating in an oven at 50°C for 4 hours to prepare a filler layer.

[0059] When the cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), a structure in which acrylic resin particles protruded from the surface of the inorganic particle layer was confirmed. The average thickness (Y) of the inorganic particle layer was 2.5 μm, and the average length (Z) in the thickness direction of the separator from the surface of the substrate layer to the end of the acrylic resin particle on the substrate layer side was 0.25 μm. When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 130 acrylic resin particles were detected in an area of ​​100 μm × 100 μm.

[0060] [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.

[0061] [Fabrication of Non-Aqueous Electrolyte Secondary Battery] A wound electrode assembly was fabricated by spirally winding the positive electrode and negative electrode with a separator interposed therebetween. At this time, the filler layer of the separator faced the positive electrode. Insulating plates were placed on the top and bottom of the electrode assembly, respectively, and the electrode assembly was housed in an outer can. The negative electrode lead was welded to the bottom of the cylindrical outer can with a bottom, and the positive electrode lead was welded to a sealing member. After injecting a non-aqueous electrolyte into the outer can, the opening of the outer can was sealed with a sealing member via a gasket, thereby fabricating a non-aqueous electrolyte secondary battery.

[0062] [Evaluation of the elongation rate of electrode plates (positive electrodes)] The fabricated nonaqueous electrolyte secondary batteries were charged to 4.2 V at a constant current of 0.3 C in a temperature environment of 25°C, and then charged at a constant voltage of 4.2 V until the current value reached 0.01 C. After a one-hour rest, the batteries were discharged to 2.5 V at a constant current of 0.3 C. This constituted one cycle, and 100 cycles were performed. Then, X-ray CT images of the nonaqueous electrolyte secondary batteries after cycling and the nonaqueous electrolyte secondary batteries without cycling were taken using an inspeXio SMX-255CT FPD HR manufactured by Shimadzu Corporation. The elongation rate of the electrode plates was evaluated from the X-ray CT images of each battery using the following formula: Elongation rate of electrode plates [%] = (average axial length of positive electrodes after cycling - average axial length of positive electrodes before cycling) / (average axial length of positive electrodes before cycling) × 100

[0063] [Evaluation of Rate Characteristics] The fabricated nonaqueous electrolyte secondary battery was subjected to constant current charging at a constant current of 0.2 C in a temperature environment of 25° C. until the cell voltage reached 4.2 V, and constant voltage charging at 4.2 V until the current value reached 0.02 C. Subsequently, constant current discharging was performed at a constant current of 1 C until the cell voltage reached 2.5 V, and the discharge capacity at 1 C was measured. Next, constant current charging was performed at a constant current of 0.5 C until the cell voltage reached 4.2 V, and constant voltage charging was performed at 4.2 V until the current value reached 0.02 C. Subsequently, constant current discharging was performed at a constant current of 3 C until the cell voltage reached 2.5 V, and the discharge capacity at 3 C was measured. The rate characteristics were evaluated using the following formula: Rate characteristic [%] = (discharge capacity at 3 C) / (discharge capacity at 1 C) × 100

[0064] Example 2 In the production of a separator, alumina (α-Al) was used as inorganic particles having an average particle size of 0.7 μm. ２ O ３ A nonaqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 1, except that the second coating liquid was prepared by mixing the acrylic resin particles having a D50(X) of 3.0 μm, the acrylic resin particles as resin particles, and the acrylic acid ester-based binder emulsion in a solid content mass ratio of 100:3:3, and then adding an appropriate amount of water so that the solid content concentration was 10 mass%.

[0065] When the cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), a structure in which acrylic resin particles protruded from the surface of the inorganic particle layer was confirmed. The average thickness (Y) of the inorganic particle layer was 2.5 μm, and the average length (Z) in the thickness direction of the separator from the surface of the substrate layer to the end of the acrylic resin particle on the substrate layer side was 0.25 μm. When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 70 acrylic resin particles were detected in an area of ​​100 μm × 100 μm.

[0066] Example 3 In the production of a separator, the coating weight of the first coating liquid was 1.5 g / m ２ The coating weight of the second coating liquid was 2.3 g / m ２ A non-aqueous electrolyte secondary battery was fabricated and evaluated in the same manner as in Example 2, except that the above-mentioned conditions were met.

[0067] When the cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), a structure in which acrylic resin particles protruded from the surface of the inorganic particle layer was confirmed. The average thickness (Y) of the inorganic particle layer was 2.5 μm, and the average length (Z) in the thickness direction of the separator from the surface of the substrate layer to the end of the acrylic resin particle on the substrate layer side was 1.0 μm. When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 100 acrylic resin particles were detected in an area of ​​100 μm × 100 μm.

[0068] <Comparative Example 1> A nonaqueous electrolyte secondary battery was produced and evaluated in the same manner as in Example 1, except that in the production of the separator, only the second coating liquid was applied to the surface of the porous substrate as the substrate layer that faced the positive electrode.

[0069] When the cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), a structure in which acrylic resin particles protruded from the surface of the inorganic particle layer was confirmed. The average thickness (Y) of the inorganic particle layer was 2.5 μm, and the average length (Z) in the thickness direction of the separator from the surface of the substrate layer to the end of the acrylic resin particle on the substrate layer side was 0.1 μm. When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 90 acrylic resin particles were detected in an area of ​​100 μm × 100 μm.

[0070] <Comparative Example 2> A nonaqueous electrolyte secondary battery was produced and evaluated in the same manner as in Example 2, except that in the production of the separator, only the second coating liquid was applied to the surface of the porous substrate as the substrate layer, which surface faced the positive electrode.

[0071] When the cross section of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), a structure in which acrylic resin particles protruded from the surface of the inorganic particle layer was confirmed. The average thickness (Y) of the inorganic particle layer was 2.5 μm, and the average length (Z) in the thickness direction of the separator from the surface of the substrate layer to the end of the acrylic resin particle on the substrate layer side was 0.1 μm. When the surface of the filler layer was observed with a scanning electron microscope (SU8220 manufactured by Hitachi High-Technologies Corporation), 35 acrylic resin particles were detected in an area of ​​100 μm × 100 μm.

[0072] The elongation percentages and rate characteristics of the electrode plates of the nonaqueous electrolyte secondary batteries of the Examples and Comparative Examples are shown in Table 1. Table 1 also shows the average particle size X [μm] of the resin particles, the average thickness Y [μm] of the inorganic particle layer, the average length Z [μm], and the number of acrylic resin particles (resin particles) detected in a 100 μm × 100 μm area of ​​each separator.

[0073]

[0074] As shown in Table 1, the nonaqueous electrolyte secondary batteries of the Examples achieve a good balance between suppressing the elongation rate of the electrode plates and improving the rate characteristics. On the other hand, the nonaqueous electrolyte secondary battery of Comparative Example 1 suppresses the elongation rate of the electrode plates, but its rate characteristics deteriorate. This is presumably because the high content of resin particles in the filler layer suppresses the elongation of the electrode plates, but the excess resin particles inhibit the migration of lithium ions, resulting in a deterioration in the rate characteristics. Furthermore, the nonaqueous electrolyte secondary battery of Comparative Example 2 improves the rate characteristics, but its elongation deteriorates. This is presumably because the low content of resin particles in the filler layer prevents the migration of lithium ions, improving the rate characteristics, but the low amount of resin particles present on the surface of the separator causes the electrode plates to elongate.

[0075] From the above results, when X, Y, and Z satisfy the relationships Z > Y - X and 0.25 ≦ Z ≦ 1.0, and 40 to 150 resin particles are detected in a 100 μm × 100 μm area, the resin particles can be protruded from the inorganic particle layer and a large amount of resin particles can be arranged on the surface of the filler layer. As a result, even when the resin particle content is reduced, an appropriate amount of resin particles can be arranged on the surface of the filler layer, suppressing electrode plate elongation and improving the rate characteristics of the battery.

[0076] The present disclosure will be further described by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery including an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, the separator having a base layer and a filler layer disposed on at least one surface of the base layer, the filler layer including an inorganic particle layer containing inorganic particles and resin particles at least a portion of which is disposed in the inorganic particle layer, when the surface of the filler layer is observed with a scanning electron microscope, 40 to 150 of the resin particles are detected in an area of ​​100 μm × 100 μm, and when the average particle diameter of the resin particles is X [μm], the average thickness of the inorganic particle layer is Y [μm], and the average length in the thickness direction of the separator from the surface of the base layer to the end of the resin particle on the base layer side is Z [μm], X, Y, and Z satisfy the relationships represented by the following formulas (I) and (II): Formula (I): Z>Y-X Formula (II): 0.25≦Z≦1.0 Configuration 2: The nonaqueous electrolyte secondary battery according to Configuration 1, wherein Z is 0.25 or more and 0.70 or less. Configuration 3: The nonaqueous electrolyte secondary battery according to Configuration 1 or 2, wherein X is 2.0 or more and 8.0 or less. Configuration 4: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein Y is 2.0 or more and 4.0 or less. Configuration 5: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein, when the surface of the filler layer is observed with a scanning electron microscope, 40 to 100 resin particles are detected in an area of ​​100 μm × 100 μm. Configuration 6: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the resin particles have adhesive properties. Configuration 7: The nonaqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein the resin particles include an acrylic resin. Configuration 8: The nonaqueous electrolyte secondary battery of any one of Configurations 1 to 7, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and the negative electrode mixture layer includes a silicon-containing material as a negative electrode active material.and a second coating step of applying a second coating solution containing inorganic particles and resin particles onto the first coating film to form a second coating film. The method for producing a separator for a non-aqueous electrolyte secondary battery according to the present invention is characterized in that, when the surface of the second coating film is observed with a scanning electron microscope, 40 to 150 of the resin particles are detected in an area of ​​100 μm × 100 μm, and when X [μm] is the average particle diameter of the resin particles, Y [μm] is the average thickness of the inorganic particle layer containing the inorganic particles, and Z [μm] is the average length from the surface of the substrate layer to the end of the resin particle on the substrate layer side in the thickness direction of the separator, X, Y, and Z satisfy the relationships represented by the following formulas (I) and (II): Formula (I): Z>Y-X Formula (II): 0.25≦Z≦1.0 Configuration 11: The method for producing a separator for a non-aqueous electrolyte secondary battery according to Configuration 9 or 10, wherein the resin particles have adhesive properties. Configuration 12: The method for producing a separator for a non-aqueous electrolyte secondary battery according to any one of Configurations 9 to 11, wherein the resin particles contain an acrylic resin.

[0077] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Exterior body, 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, 30 Positive electrode current collector, 32 Positive electrode mixture layer, 40 Negative electrode current collector, 42 Negative electrode mixture layer, 50 Base layer, 52 Filler layer, 54 Inorganic particle layer, 56 Resin particles

Claims

1. A non-aqueous electrolyte secondary battery comprising an electrode assembly in which a positive electrode and a negative electrode are wound with a separator interposed therebetween, and a non-aqueous electrolyte, wherein the separator has a base layer and a filler layer disposed on at least one surface of the base layer, and the filler layer comprises an inorganic particle layer containing inorganic particles and resin particles at least a portion of which is disposed in the inorganic particle layer, and when the surface of the filler layer is observed with a scanning electron microscope, 40 to 150 of the resin particles are detected in an area of ​​100 μm × 100 μm, and when the average particle size of the resin particles is X [μm], the average thickness of the inorganic particle layer is Y [μm], and the average length in the thickness direction of the separator from the surface of the base layer to the end of the resin particle on the base layer side is Z [μm], X, Y, and Z satisfy the relationships represented by the following formulas (I) and (II): Formula (I): Z>YX Formula (II): 0.25≦Z≦1.0 2. The nonaqueous electrolyte secondary battery according to claim 1, wherein Z is 0.25 or more and 0.70 or less.

3. The nonaqueous electrolyte secondary battery according to claim 1, wherein X is 2.0 or more and 8.0 or less.

4. The nonaqueous electrolyte secondary battery according to claim 1, wherein Y is 2.0 or more and 4.0 or less.

5. The nonaqueous electrolyte secondary battery according to claim 1, wherein when the surface of said filler layer is observed with a scanning electron microscope, 40 to 100 of said resin particles are detected in an area of ​​100 μm×100 μm.

6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the resin particles have adhesive properties.

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

8. The nonaqueous electrolyte secondary battery according to claim 1, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and the negative electrode mixture layer includes a silicon-containing material as a negative electrode active material.

9. A method for manufacturing a separator for a non-aqueous electrolyte secondary battery, comprising: a first coating step of applying a first coating liquid containing inorganic particles to at least one surface of a substrate layer to form a first coating film; and a second coating step of applying a second coating liquid containing inorganic particles and resin particles onto the first coating film to form a second coating film.

10. The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 9, wherein, when the surface of the second coating film is observed with a scanning electron microscope, 40 to 150 of the resin particles are detected in an area of ​​100 μm × 100 μm, and when the average particle size of the resin particles is X [μm], the average thickness of the inorganic particle layer containing inorganic particles is Y [μm], and the average length in the thickness direction of the separator from the surface of the base layer to the end of the resin particle on the base layer side is Z [μm], X, Y, and Z satisfy the relationships represented by the following formulas (I) and (II): Formula (I): Z>Y-X Formula (II): 0.25≦Z≦1.0 11. The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 9, wherein the resin particles have adhesive properties.

12. The method for producing a separator for a non-aqueous electrolyte secondary battery according to claim 9, wherein the resin particles contain an acrylic resin.

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