Separator for electricity storage device and electricity storage device including the same

Abstract

To provide a separator for electricity storage device which has a high adhesive force to an electrode, small thermal shrinkage, and is capable of improving cycle characteristic and output characteristic of the electricity storage device.SOLUTION: A separator includes: a base material to be a polyolefin microporous film containing polyolefin as a main component; and a coating layer disposed on at least one surface of the base material. Film thickness of the base material ranges from 1 μm to 30 μm, and gas permeability is 500 sec / 100 cm3 or below. The coating layer includes the inorganic filler and particulate polymer of thermoplastic polymer. The particulate polymer contains a particulate polymer projecting from the coating layer having 0.1 or more multiple of thickness of the inorganic filler part of the coating layer. Then, porosity after compression that is measured after the base material is compressed under the condition of the temperature of 70°C, pressure of 8 MPa, and 3 minutes compression time is 30% or higher, and / or a crystal long period measured by small-angle X-ray scattering of the polyolefin microporous film is 37.0 nm or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a separator for an electricity storage device and an electricity storage device including the same. [Background technology]

[0002] Development of energy storage devices, typified by lithium-ion secondary batteries, is currently underway. Energy storage devices generally include a positive electrode, a negative electrode, and a microporous membrane separator between them. The separator functions to prevent direct contact between the positive and negative electrodes and to allow ions to pass through the electrolyte solution held within the micropores. Separators are required to have safety features, such as the ability to quickly stop the battery reaction in the event of abnormal heating (fuse characteristics) and the ability to maintain their shape even at high temperatures and prevent dangerous situations in which the positive and negative electrodes would directly react with each other (short-circuit resistance).

[0003] On the other hand, nonaqueous secondary batteries such as lithium ion secondary batteries are available in a variety of shapes depending on their applications, including cylindrical, prismatic, and pouch shapes. The manufacturing method for a battery varies depending on the shape of the battery. For example, the manufacture of a prismatic battery includes a step of pressing a wound or laminate of an electrode and a polyolefin microporous membrane and inserting the wound or laminate into a rectangular outer can.

[0004] In particular, in recent years, with the aim of increasing the capacity of electricity storage devices, the volume of electricity storage devices has been reduced by hot pressing a laminate of electrodes and a separator or by hot pressing a wound body obtained by winding a laminate of electrodes and a separator. In this case, in order to fix the electrodes and the separator after hot pressing and maintain the volume at the time of pressing, a technique is known in which a coating layer containing a thermoplastic polymer that exhibits adhesive properties under specified conditions is disposed on the separator substrate, thereby improving the adhesion between the entire separator and the electrodes.

[0005] Furthermore, with improvements in electrode materials and high-density modularization of multiple nonaqueous secondary batteries (single cells) (increasing module volume energy density), there is a need to ensure the ion permeability of the microporous membrane serving as a separator, and the output characteristics or cycle characteristics of the battery including the membrane, even when external pressure is applied to the cell and separator.

[0006] For example, Patent Document 1 describes a separator with a porous coating layer containing organic polymer particles, which aims to enhance safety by strengthening the integration of the separator and electrodes by increasing the bonding strength between the separator and electrodes without performing a humidification phase separation process for an organic binder polymer or a secondary coating with an adhesive layer. In this separator, the organic polymer particles protrude to a height of 0.1 μm to 3 μm from the surface of the porous coating layer.

[0007] Patent Document 2 describes a separator with a surface coating containing polymer binder particles of different particle sizes, with the aim of suppressing deformation of the electricity storage device due to volume expansion of the electrodes during charging. The polymer binder particles of different particle sizes form voids between the separator and the electrodes that allow for internal expansion of the electricity storage device.

[0008] Patent Document 3 describes a separator having a composite coating containing inorganic particles, polymer particles, and a binder, with the aim of further improving existing separators and their manufacturing methods, providing good thermal stability and good adhesion to electrodes, thereby ensuring the safety and flatness of the power storage device. The polymer particles are dispersed among the inorganic particles and protrude from the surfaces of the inorganic particles.

[0009] Patent Document 4 describes a separator with a functional layer containing inorganic particles and a particulate polymer, with the aim of achieving excellent adhesion, heat resistance, and improved electrolyte injection properties. In this functional layer, when viewed from above, the inorganic particles account for more than 90% of the surface area per unit area of ​​the functional layer, and the volume average particle diameter of the particulate polymer is within a specific range and is greater than the thickness of the inorganic particle layer.

[0010] Patent Document 5 describes a separator having a functional layer containing inorganic particles and a particulate polymer, with the aim of providing a functional layer for electrochemical devices that has excellent process adhesion and can enable electrochemical devices to exhibit excellent cycle characteristics. The functional layer has particle-shedding portions, and when the surface of the functional layer for electrochemical devices is viewed from above, the ratio of the area of ​​the particle-shedding portions to the total area of ​​the particulate polymer and the particle-shedding portions is 0.1% to 40.0%, and the volume-average particle diameter of the particulate polymer is larger than the thickness of the inorganic particle layer containing the inorganic particles.

[0011] Furthermore, from the viewpoint of the heat resistance or rigidity of the separator substrate and the cycle characteristics of lithium-ion secondary batteries, the crystallinity of the polyolefin contained in the separator or the press test characteristics of the polyolefin microporous film used as the separator have been investigated (Patent Documents 6 to 9).

[0012] Patent Document 6 describes the long period of the lamellar crystal portion of a polyolefin microporous film that has been dry-stretched and porous, as measured by small-angle X-ray scattering (SAXS), from the viewpoint of achieving both excellent lithium ion permeability and heat resistance.

[0013] Patent Document 7 describes the long period of polymer crystals measured by the SAXS method in a stretched polypropylene film from the viewpoint of achieving both low heat shrinkage and high rigidity.

[0014] Patent Documents 8 and 9 describe, for example, the rate of change in membrane thickness of a polyolefin microporous membrane before and after a heat-compression test at a temperature of 80°C and a pressure of 1 MPa for 60 minutes (Patent Document 8), from the viewpoint of the compression resistance of a separator for a lithium ion secondary battery and the cycle characteristics of a lithium ion secondary battery, or describe the rate of change in air permeability and rate of change in membrane thickness of a polyolefin microporous membrane before and after a heat-compression test at a temperature of 90°C and a pressure of 5.0 MPa for 5 minutes (Patent Document 9). [Prior art documents] [Patent documents]

[0015] [Patent Document 1] Korean Patent Publication No. 10-2016-0118979 [Patent Document 2] International Publication No. 2019 / 089492 [Patent Document 3] Chinese Patent No. 105958000 [Patent Document 4] International Publication No. 2020 / 175079 [Patent Document 5] International Publication No. 2021 / 085144 [Patent Document 6] International Publication No. 2014 / 175252 [Patent Document 7] International Publication No. 2015 / 012324 [Patent Document 8] International Publication No. 2018 / 164056 [Patent Document 9] International Publication No. 2015 / 194504 Summary of the Invention [Problem to be solved by the invention]

[0016] However, these conventional separators for lithium ion secondary batteries and separators having a substrate made of a polyolefin microporous film have the following problems.

[0017] For example, Patent Documents 1 and 3 use a secondary particle adhesive polymer, which causes the problem of uneven separator thickness distribution. Furthermore, because the adhesive polymer has poor dispersibility in the coating state, the adhesive polymer aggregates in areas on the separator, causing uneven adhesion to the electrode, resulting in a decrease in overall adhesion and a deterioration in heat resistance. Patent Document 2 does not include a heat-resistant layer containing an inorganic filler, which means the separator cannot be provided with sufficient heat resistance. Patent Documents 4 and 5 have insufficient adhesive strength of the coating layer, leaving room for improvement in preventing powder shedding during the manufacturing process and in adhesion to the electrode.

[0018] On the other hand, the pressing process used in the fabrication of batteries using conventional polyolefin microporous membranes, as described in Patent Documents 6 to 9, can sometimes result in a phenomenon in which the cycle characteristics and output characteristics of the battery are reduced. Furthermore, a similar phenomenon occurs significantly when a high-capacity electrode that is prone to expansion is used.

[0019] In view of the above circumstances, the present disclosure aims to provide a separator for an electricity storage device that has high adhesive strength with electrodes, a small thermal shrinkage rate, and can improve the cycle characteristics and output characteristics of the electricity storage device, and an electricity storage device having the separator. [Means for solving the problem]

[0020] Examples of embodiments of the present disclosure are listed below. [1] A separator for an electricity storage device, comprising: a substrate that is a polyolefin microporous film containing a polyolefin as a main component; and a coating layer disposed on at least one surface of the substrate, The film thickness of the substrate is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm 3 and the porosity after compression measured after compressing the substrate under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer. [2] A separator for an electricity storage device, comprising: a substrate that is a polyolefin microporous film containing a polyolefin as a main component; and a coating layer disposed on at least one surface of the substrate, the polyolefin microporous membrane has a crystalline long period measured by small-angle X-ray scattering (SAXS) of 37.0 nm or more; the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer. [3] The film thickness of the substrate is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm 3 or less, and the porosity after compression measured after compressing the substrate under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more. [4] In the coating layer, the amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less relative to 100 parts by mass of the inorganic filler contained in the coating layer, The separator for an electricity storage device according to any one of items [1] to [3], wherein the coating layer is formed in a gradient shape so that the thickness increases toward the protruding particulate polymer. [5] Item [4]. The separator for an electricity storage device according to Item [4], wherein the average value of the slope ratio L2 / L1 of the coating layer is 1.2 or more, where L1 is the thickness of the inorganic filler portion of the coating layer and L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler in the coating layer formed in the sloped shape. [6] The separator for an electricity storage device according to item [4] or [5], wherein an average value of a coverage rate (L2-L1) / (L3-L1) of the protruding portions of the protruding particulate polymer is 0.4 or more, where L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the boundary between the substrate and the coating layer to the outer surface of the inorganic filler in the coating layer formed in the inclined shape, and L3 is the maximum distance from the boundary between the substrate and the coating layer to the outline of the protruding particulate polymer. [7] The separator for an electricity storage device according to any one of items [1] to [6], wherein the particulate polymer comprises at least one selected from the group consisting of a (meth)acrylic polymer, a styrene-butadiene copolymer, and a copolymer containing a fluorine atom. [8] The separator for an electricity storage device according to any one of items [1] to [6], wherein the particulate polymer comprises a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers. [9] The separator for an electricity storage device according to any one of items [1] to [6], wherein the particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

[10] An electricity storage device comprising the separator for an electricity storage device according to any one of items [1] to [9].

[0021] Examples of other embodiments of the present disclosure are listed below.

[11] A separator for an electricity storage device, comprising: a substrate that is a polyolefin microporous film containing a polyolefin as a main component; and a coating layer disposed on at least one surface of the substrate, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer.

[12] The film thickness of the substrate is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm 3 or less, and has a post-compression porosity of 30% or more as measured in a compression test under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes.

[13] Item

[11] or

[12] , wherein the polyolefin microporous membrane has a crystalline long period of 37.0 nm or more as measured by small-angle X-ray scattering (SAXS).

[14] The separator for an electricity storage device according to any one of items

[11] to

[13] , wherein the amount of the particulate polymer in the coating layer is 1 part by mass or more and 50 parts by mass or less per 100 parts by mass of the inorganic filler contained in the coating layer.

[15] The separator for an electricity storage device according to any one of items

[11] to

[14] , wherein the coating layer is formed in a gradient shape so that the thickness increases toward the protruding particulate polymer.

[16] The separator for an electricity storage device according to any one of items

[11] to

[15] , wherein 20% or more of the protruding particulate polymer is in contact with the surface of the substrate.

[17] The separator for a power storage device according to any one of items

[11] to

[16] , wherein the coating layer has a 180° peel strength from the substrate of 200 gf / cm or more.

[18] The separator for an electricity storage device according to any one of items

[11] to

[17] , wherein the average number of the protruding particulate polymers adjacent to any one of the protruding particulate polymers is less than two.

[19] The separator for a power storage device according to any one of items

[11] to

[18] , wherein the ratio of the average particle size of the protruding particulate polymer to the average particle size of the inorganic filler is greater than 10.

[20] The separator for an electricity storage device according to any one of items

[11] to

[19] , wherein the average value of the slope ratio L2 / L1 of the coating layer is 1.2 or more, where L1 is the thickness of the inorganic filler portion of the coating layer and L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler in the coating layer formed on the slope. [twenty one] The separator for an electricity storage device according to any one of items

[11] to

[20] , wherein an average value of a coverage rate (L2-L1) / (L3-L1) of the protruding portions of the protruding particulate polymer is 0.4 or more, where L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler of the coating layer formed on the inclined surface, and L3 is the maximum distance from the boundary line between the substrate and the coating layer to the outline of the protruding particulate polymer. [twenty two] The separator for an electricity storage device according to any one of items

[11] to

[21] , wherein the number of the protruding particulate polymers is 50% or more of the total number of the particulate polymers contained in the coating layer. [twenty three] The separator for an electricity storage device according to any one of items

[11] to

[22] , wherein the number of other protruding particulate polymers present within a radius of 10 μm from any one of the protruding particulate polymers is less than 60. [twenty four] The separator for a storage battery device according to any one of items

[11] to

[23] , wherein the separator for a storage battery device has a methylene chloride soluble content of 0.05% by mass or more and 0.80% by mass or less, relative to the total mass of the separator for a storage battery device. [twenty five] The separator for a power storage device according to any one of items

[11] to

[24] , wherein the total amount of metal cations contained in the coating layer is 0.1 ppm or more and 100 ppm or less based on the total mass of the coating layer.

[26] The separator for an electricity storage device according to any one of items

[11] to

[25] , wherein the coating layer contains a water-soluble polymer.

[27] Item

[26] . The separator for a storage battery device according to item

[26] , wherein the content of the water-soluble polymer is 0.04 parts by mass or more and less than 2 parts by mass per 100 parts by mass of the inorganic filler.

[28] The separator for an electricity storage device according to any one of items

[11] to

[27] , wherein the thickness of one of the coating layers disposed on at least one of the substrates is 0.3 μm or more and 1.3 μm or less.

[29] The separator for an electricity storage device according to any one of items

[11] to

[28] , wherein the particulate polymer comprises at least one selected from the group consisting of a (meth)acrylic polymer, a styrene-butadiene copolymer, and a copolymer containing a fluorine atom.

[30] The separator for an electricity storage device according to any one of items

[11] to

[28] , wherein the particulate polymer comprises a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers.

[31] The separator for an electricity storage device according to any one of items

[11] to

[28] , wherein the particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

[32] The separator for an electricity storage device according to any one of items

[11] to

[31] , wherein the particulate polymer is a primary particle.

[33] Item

[32] . The separator for an electricity storage device according to item

[32] , wherein the primary particles have an average particle size of 1 μm or more and 10 μm or less.

[34] The separator for an electricity storage device according to any one of items

[11] to

[33] , which has a thermal shrinkage rate in the TD direction at 130°C for 1 hour of 5% or less.

[35] The separator for an electricity storage device according to any one of items

[11] to

[34] , which has a thermal shrinkage rate in the TD direction at 150°C for 1 hour of 5% or less.

[36] An electricity storage device comprising the separator for an electricity storage device according to any one of

[11] to

[35] . [Effects of the Invention]

[0022] According to the present disclosure, there are provided a separator for an electricity storage device that has high adhesive strength with electrodes, a small thermal shrinkage rate, and can improve the cycle characteristics and output characteristics of an electricity storage device, and an electricity storage device including the separator. [Brief explanation of the drawings]

[0023] [Figure 1] 2 is a schematic diagram of the surface of a coating layer of the separator for an electricity storage device according to the present embodiment. FIG. [Figure 2] FIG. 2 is a schematic diagram of a cross section taken along line AA in FIG. [Figure 3] 10 is an example of a power approximation curve relating to the porosity after compression and the air permeability after compression. DETAILED DESCRIPTION OF THE INVENTION

[0024] Hereinafter, exemplary embodiments of the present disclosure (hereinafter abbreviated as "present embodiments") will be described in detail, but the present disclosure is not limited to these embodiments.

[0025] As used herein, longitudinal direction (MD) means the machine direction of the continuous microporous membrane molding, and transverse direction (TD) means the direction crossing the MD of the microporous membrane at a 90° angle.

[0026] In this specification, the upper and lower limits of each numerical range can be arbitrarily combined. Furthermore, when a certain component contains a specific component as a main component, it means that the content of the specific component is the largest in the mass of the component. Unless otherwise specified, the physical properties or numerical values ​​described in this specification are measured or calculated by the methods described in the examples.

[0027] <Separator for power storage device> The separator for an electricity storage device of this embodiment includes a substrate that is a microporous polyolefin film containing a polyolefin as a main component, and a coating layer disposed on at least one surface of the substrate. The coating layer includes an inorganic filler and a particulate polymer of a thermoplastic polymer.

[0028] <Amount of Particulate Polymer> The amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less, preferably 3 parts by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 30 parts by mass or less, and even more preferably 10 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the inorganic filler. By using the particulate polymer in an amount of 1 part by mass or more and 50 parts by mass or less, it is possible to increase the adhesive strength with the electrode while maintaining ion permeability. Furthermore, from the viewpoint of improving heat shrinkage resistance, an amount of 10 parts by mass or less is preferable.

[0029] <Protrusion amount of particulate polymer> The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer.

[0030] In this specification, the "thickness of the inorganic filler portion of the coating layer" refers to the distance (L1) between the surface of the polyolefin microporous membrane and the outermost surface of the layer of inorganic filler stacked thereon (layer of inorganic filler), and is measured from an SEM image of the cross section of the coating layer. The "inorganic filler portion" refers to a portion that does not contain particulate polymer and is 1.5D or more away from the center of each protruding particulate polymer in the horizontal direction (toward the surface of the coating layer), where D is the diameter of each protruding particulate polymer. The measurement conditions are explained in the Examples section.

[0031] By having the protrusion of the particulate polymer be at least 0.1 times the thickness of the inorganic filler portion of the coating layer, the adhesive strength with the electrode can be enhanced. Furthermore, by having the protrusion of the particulate polymer be at least 0.1 times the thickness of the inorganic filler portion of the coating layer, a gap is formed between the separator and the electrode. This gap can mitigate the effects of internal expansion associated with charging and discharging of the energy storage device, suppress distortion of the wound body, and improve cycle characteristics. In particular, it has been found that by combining a particulate polymer with a large particle size that protrudes at least 0.1 times the thickness of the coating layer with a substrate having characteristics (6) and / or (7) described below, not only can the air permeability of the substrate portion not in contact with the particulate polymer when bonded to the electrode be maintained at a good level, but also the air permeability of the substrate portion that contacts the electrode via the particulate polymer (the portion that bears the load) can be maintained at a good level, resulting in excellent cycle characteristics and output characteristics. From this perspective, the protrusion of the particulate polymer is preferably at least 0.2 times or at least 0.3 times the thickness of the particulate polymer. From the viewpoint of preventing the particulate polymer from falling off the separator, the protrusion of the particulate polymer is preferably 5 times or less, more preferably 4 times or less, 3 times or less, 2 times or less, 1 time or less, or 0.4 times or less.

[0032] In this specification, "protruding" means that the particulate polymer protrudes toward the surface side of the coating layer beyond the "thickness of the inorganic filler portion of the coating layer." In the protruding portion of the particulate polymer (hereinafter referred to as "protruding portion"), the particulate polymer does not need to be exposed on the surface of the coating layer, and at least a part or all of the protruding portion may be covered with an inorganic filler. From the viewpoint of preventing the particulate polymer from slipping off the coating layer and obtaining a higher adhesive strength, it is preferable that at least a part of the periphery of the protruding portion is covered with an inorganic filler. Furthermore, from the viewpoint of ensuring a contact area between the particulate polymer and the electrode and obtaining a higher adhesive strength, it is preferable that the center of the protruding portion is exposed on the surface of the coating layer.

[0033] In this specification, "a state in which the particulate polymer protrudes from the coating layer by 0.1 times or more the thickness of the inorganic filler portion of the coating layer" means that, when the thickness of the inorganic filler portion of the coating layer measured from an SEM image of the cross section of the coating layer is L1 and the maximum distance from the boundary line between the substrate and coating layer to the outline of the protruding particulate polymer is L3, the average value of the ratio (L3-L1) / L1 is 0.1 or more. In this specification, "the maximum distance from the boundary line between the substrate and coating layer to the outline of the protruding particulate polymer" means the distance to the point on the outline of the protruding particulate polymer that is farthest from the boundary line between the substrate and coating layer.

[0034] In this specification, "a state in which the particulate polymer protrudes from the coating layer by 0.1 times or more the thickness of the inorganic filler portion of the coating layer" means, in other words, that the maximum distance (L3) from the substrate-coating layer boundary to the outline of the protruding particulate polymer measured from an SEM image of the coating layer cross section is 1.1 times or more the thickness (L1) of the inorganic filler portion of the coating layer.

[0035] <Gradient morphology of the coating layer, contact ratio between the particulate polymer and the substrate, 180° peel strength, average number of adjacent particulate polymer particles, and average particle size ratio> The separator for an electricity storage device of this embodiment preferably has one or more of the following characteristics (1) to (5): (1) the coating layer is formed in a gradient such that it becomes thicker toward the protruding particulate polymer; (2) 20% or more of the protruding particulate polymers are in contact with the surface of the substrate; (3) the 180° peel strength of the coating layer from the substrate (hereinafter simply referred to as "180° peel strength") is 200 gf / cm (196 N / m) or more; (4) the average number of protruding particulate polymers adjacent to any one protruding particulate polymer (hereinafter simply referred to as "average number of adjacent particulate polymers") is less than two; and (5) the ratio of the average particle size of the protruding particulate polymers to the average particle size of the inorganic filler, i.e., the ratio calculated as the average particle size of the particulate polymers / the average particle size of the inorganic filler (hereinafter simply referred to as "average particle size ratio"), is greater than 10. By having at least one of the above characteristics (1) to (5), it is possible to provide a separator for an electricity storage device that has a higher adhesive strength to electrodes and a smaller thermal shrinkage rate.

[0036] Feature(1): In a separator for an electric storage device, the coating layer is preferably formed in a gradient so that it thickens toward the protruding particulate polymer. This prevents the particulate polymer from sliding off the coating layer and enhances adhesion to the electrode. In this specification, "graded" means that, when L1 is the thickness of the inorganic filler portion of the coating layer and L2 is the maximum distance from the substrate-coating layer boundary to the outer surface of the inorganic filler in the gradient-formed coating layer, the average gradient ratio L2 / L1 of the coating layer is 1.1 or greater. For an example of the relationship between L1 and L2, see the schematic diagram in Figure 2. The gradient is preferably such that the thickness of the coating layer changes continuously so that it gradually thickens toward the protruding particulate polymer, and preferably does not include discontinuous changes due to missing portions of the coating layer. The absence of missing portions of the coating layer tends to improve heat resistance and cycle characteristics. The gradient may be gentler as it moves away from the protruding particulate polymer and steeper as it approaches the protruding portion of the protruding particulate polymer. Also, when the inorganic filler covers at least a part or all of the protruding portion, the slope on the protruding portion may become gentler again toward the center of the protruding portion. The average value of the slope ratio L2 / L1 of the coating layer is preferably 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, or 1.7 or more.

[0037] The coating layer may be formed in a gradient such that it thickens toward the protruding particulate polymer, allowing the inorganic filler to cover at least a portion or all of the protruding portion by following the contour of the particulate polymer. The inorganic filler preferably covers a portion of the periphery of the protruding portion by following the contour of the particulate polymer. Furthermore, the vicinity of the center of the protruding portion is preferably exposed on the surface of the coating layer. If the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer (the distance from the substrate-coating layer boundary to the point on the contour of the protruding particulate polymer that is farthest from the substrate-coating layer boundary) is L3, the average value of the coverage ratio of the protruding portion (L2-L1) / (L3-L1) is preferably 0.4 or greater. For an example of the relationship between L1, L2, and L3, see the schematic diagram in Figure 2. By setting the average value of the gradient ratio L2 / L1 to 1.1 or the average value of the coverage ratio (L2-L1) / (L3-L1) to 0.4 or greater, the particulate polymer is prevented from slipping off the coating layer and its adhesion to the electrode is enhanced. The upper limit of the average value of the slope ratio L2 / L1 is not particularly limited, but may be 5.0 or less, 4.0 or less, 3.0 or less, 2.8 or less, 2.5 or less, 2.3 or less, 2.0 or less, or 1.8 or less, from the viewpoint of ensuring the adhesion area between the particulate polymer and the electrode and increasing the adhesive strength with the electrode. The upper limit of the coverage ratio (L2-L1) / (L3-L1) is preferably less than 1.0, 0.9 or less, 0.8 or less, or 0.7 or less. A coverage ratio of 1.0 or more means that the inorganic filler on the protruding portion of the particulate polymer reaches the top of the outline of the protruding particulate polymer (the point farthest from the boundary line between the substrate and the coating layer). A coverage ratio of less than 1.0 ensures the contact area between the particulate polymer and the electrode, thereby increasing the adhesive strength with the electrode. A coverage ratio of 0.8 or less increases the contact area between the particulate polymer and the electrode, thereby increasing the adhesive strength with the electrode.

[0038] Feature (2): In the separator for an electric storage device, the contact rate between the particulate polymer protruding from the coating layer and the surface of the substrate is preferably 20% or more, more preferably 50% or more, and even more preferably 70% or more. The "contact rate" is calculated from an image of the cross section of the coating layer of the separator for an electric storage device observed with an SEM. Increasing the amount of particulate polymer protruding from the coating layer and in contact with the substrate further increases the binding strength between the substrate and the particulate polymer, improving the 180° peel strength and the adhesive strength with the electrode. The upper limit of the contact rate between the particulate polymer protruding from the coating layer and the surface of the substrate is not particularly limited, but may be less than 100% or 100%.

[0039] Feature(3): The separator for an electricity storage device preferably has a 180° peel strength of 200 gf / cm or more, more preferably 230 gf / cm or more, and even more preferably 250 gf / cm or more. The "180° peel strength" refers to the strength when the coating layer is peeled off so that the surface of the coating layer facing the substrate forms an angle of 180° with the substrate. A 180° peel strength of 200 gf / cm or more increases the adhesive strength with the electrode and suppresses thermal shrinkage. The upper limit of the 180° peel strength is not particularly limited, but may be 500 gf / cm or less.

[0040] Feature(4): In the separator for an electric storage device, the average number of adjacent particulate polymers is preferably less than two, more preferably less than one. "Adjacent" means that, in an image of the surface of the coating layer of the separator for an electric storage device observed with an SEM, the shortest distance between the outer edge of one particulate polymer and the outer edge of another particulate polymer is 0.2 μm or less. Having an average number of adjacent particulate polymers of less than two means that the particulate polymers are uniformly dispersed in the coating layer, which improves 180° peel strength, enhances adhesion to the electrode, suppresses thermal shrinkage, and ensures uniformity in the thickness of the coating layer. The lower limit of the average number of adjacent particulate polymers is not particularly limited, but may be greater than 0 or even 0.

[0041] Feature(5): In the separator for an electric storage device, the ratio of the average particle size of the protruding particulate polymer to the average particle size of the inorganic filler is preferably greater than 10. Each "average particle size" is measured from an image of the coating layer surface of the separator for an electric storage device observed with an SEM. The measurement conditions are explained in the Examples section. When the average particle size ratio is greater than 10, the particulate polymer is likely to form a structure in which it protrudes from the surface of the coating layer, thereby increasing the adhesive strength with the electrode and suppressing thermal shrinkage. From the viewpoint of achieving both the permeability and adhesive strength of the separator, the upper limit of the average particle size ratio is preferably 50 or less, more preferably 35 or less, even more preferably 25 or less, 22 or less, or 20 or less.

[0042] The separator for an electricity storage device of this embodiment may have any combination of the above features (1) to (5), i.e., (1) and (2); (1) and (3); (1) and (4); (1) and (5); (2) and (3); (2) and (4); (2) and (5); (3) and (4); (3) and (5); (4) and (5); (1), (2) and (3); (1), (2) and (4); (1), (2) and (5); (1), (3) and (4); (1), ( (1), (4) and (5); (2), (3) and (4); (2), (3) and (5); (2), (4) and (5); (3), (4) and (5); (1), (2), (3) and (4); (1), (2), (3) and (5); (1), (2), (4) and (5); (1), (3), (4) and (5); (2), (3), (4) and (5); or combinations of (1), (2), (3), (4) and (5). Among these, from the viewpoint of higher adhesive strength and smaller thermal shrinkage, the combination of (1), (2) and (3) is preferred, i.e., the coating layer is formed in a gradient shape so that it becomes thicker toward the protruding particulate polymer, the contact rate between the particulate polymer protruding from the coating layer and the substrate surface is 20% or more, and the 180° peel strength is 200 gf / cm or more.

[0043] <Number of polymer particles within a radius of 10 μm> In the separator for an electricity storage device of this embodiment, the number of other protruding particulate polymers present within a radius of 10 μm from any one protruding particulate polymer is preferably less than 60, more preferably less than 40, even more preferably less than 15, and even more preferably less than 5. This makes it possible to suppress variations in adhesive strength. The lower limit of the number of particulate polymers within a radius of 10 μm is not particularly limited and may be 0, but may be 1 or more in order to appropriately dense the particulate polymers and improve adhesive strength.

[0044] <Methylene chloride solubles> The separator for an electric storage device according to this embodiment preferably has a methylene chloride soluble content of 0.05% by mass or more and 0.80% by mass or less, more preferably 0.10% by mass or more and 0.60% by mass or less, and even more preferably 0.15% by mass or more and 0.50% by mass or less, based on the total mass of the separator for an electric storage device. The "methylene chloride soluble content" refers to components extracted into methylene chloride when the separator is immersed in methylene chloride. The methylene chloride soluble content mainly consists of plasticizers mixed during the production of the substrate. By including a methylene chloride soluble content of 0.10% by mass or more, the bonding strength between the substrate and the coating layer is further enhanced, making it easier to adjust the 180° peel strength to 200 gf / cm or more. By including a methylene chloride soluble content of 0.60% by mass or less, the internal resistance of the battery can be reduced. Methods for adjusting the methylene chloride soluble content to 0.05% by mass or more and 0.80% by mass or less include adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, number of extractions, etc. in the plasticizer extraction process during base material production if the process is batchwise, or adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, amount of extraction solvent supplied, etc. if the process is continuous.

[0045] <Metal cations> In the separator for an electricity storage device of this embodiment, the total amount of metal cations contained in the coating layer is preferably 0.1 ppm or more and 100 ppm or less, more preferably 0.1 ppm or more and 70 ppm or less, and even more preferably 0.1 ppm or more and 50 ppm or less, based on the total mass of the coating layer. When the total amount of metal cations is adjusted to a low amount, the inorganic filler and the particulate polymer are easily dispersed and applied uniformly in the formation of the coating layer. As the metal cation, sodium ions (Na + ), calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ ) and the like. One method for adjusting the total amount of metal cations to 0.1 ppm or more and 100 ppm or less is to wash the filler, which is the raw material for the coating layer, with water before use. The number of washings may be one or more, but the more washings are performed, the lower the total amount of metal cations contained in the filler.

[0046] <Heat shrinkage rate> The separator for an electric storage device according to this embodiment preferably has a TD heat shrinkage of 5% or less, more preferably 0% to 3% and even more preferably 0% to 1% at 130°C for 1 hour. The TD heat shrinkage of 150°C for 1 hour is preferably 5% or less, more preferably 0% to 3% and even more preferably 0% to 1%. A TD heat shrinkage of 5% or less can more effectively prevent short circuits from occurring in locations other than those to which external force is applied when heat is generated due to a short circuit during a crash test. This more reliably prevents temperature increases throughout the battery and the associated smoke and fire. The separator heat shrinkage can be adjusted by appropriately combining the stretching operation and heat treatment of the substrate described above. While suppressing the TD heat shrinkage, the MD heat shrinkage is also preferably 5% or less, more preferably 0% to 3% and even more preferably 0% to 1%.

[0047] <Air permeability of separator> The separator for an electricity storage device preferably has an air permeability of 10 seconds / 100 cm 3More than 10000 seconds / 100cm 3 Less than 10 seconds / 100cm, preferably less than 10 seconds / 100cm 3 More than 1000 seconds / 100cm 3 Less than 50 seconds / 100cm, more preferably 3 More than 500 seconds / 100cm 3 Below 80 seconds / 100cm, particularly preferably 3 More than 250 seconds / 100cm 3 This results in high ion permeability. The air permeability is the air resistance measured in accordance with JIS P-8117.

[0048] <Base material> The substrate is a polyolefin microporous membrane containing polyolefin as a main component, and preferably has the following characteristics (6), (7), or a combination thereof: (6) A membrane thickness of 1 μm to 30 μm and an air permeability of 500 sec / 100 cm 3 (7) The polyolefin microporous membrane has a crystal long period of 37.0 nm or more as measured by small-angle X-ray scattering (SAXS).

[0049] Feature(6): Without being bound by theory, it is believed that the polyolefin microporous membrane can be stretched at a rate of 500 sec / 100 cm within a thickness range of 1 μm to 30 μm. 3 By having an air permeability below 100°C and a post-compression porosity of 30% or more, it is believed that, for example, in the fabrication of a nonaqueous secondary battery using a polyolefin microporous membrane as a separator, the electrical resistance of the polyolefin microporous membrane can be reduced or an increase in electrical resistance can be suppressed after the pressing step, thereby achieving high output and high cycle characteristics of the nonaqueous secondary battery. The suppression of resistance increase by the polyolefin microporous membrane is remarkable when an electrode that easily expands and contracts within the cell of the nonaqueous secondary battery is used, and is even more remarkable when a high-capacity electrode used in an automotive battery or a silicon (Si)-containing negative electrode is used. The method for conducting a compression test under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is described in detail in the Examples.

[0050] The porosity after compression is thought to be related to the structure of the main component of the polyolefin microporous membrane, which reduces resistance and / or suppresses resistance increase in nonaqueous secondary batteries. From the viewpoints explained above, the porosity of the polyolefin microporous membrane after compression is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the porosity of the polyolefin microporous membrane after compression can be determined depending on the porosity before compression, and may be, for example, preferably 60% or less, more preferably 50% or less.

[0051] The post-compression porosity of the polyolefin microporous membrane can be adjusted within the above-described numerical ranges, for example, in the production process of the polyolefin microporous membrane by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching process, the preheating coefficient in the biaxial stretching process, the stretch coefficient in the biaxial stretching process, the MD / TD stretching temperature in the biaxial stretching process, the heat setting temperature, etc. Alternatively, the post-compression porosity of the polyolefin microporous membrane can be adjusted within the above-described numerical ranges by controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching process, the preheating coefficient in the biaxial stretching process, the stretch coefficient in the biaxial stretching process, the ratio of the preheating coefficient to the stretch coefficient, etc.

[0052] Comparing the porosity of a polyolefin microporous membrane before and after a compression test is preferable from the viewpoint of identifying the structure of the main component of the membrane that can reduce resistance and / or suppress resistance increase in a nonaqueous secondary battery and achieve high output and high cycle characteristics. The porosity of a polyolefin microporous membrane before or before a compression test (hereinafter simply referred to as "porosity") is measured by the method described in the Examples, and the preferred numerical range is described below.

[0053] The thickness of the polyolefin microporous membrane is preferably 3 μm to 20 μm, more preferably 5 μm to 16 μm, and even more preferably 6 μm to 13 μm, from the viewpoint of reducing electrical resistance and suppressing resistance increase as described above, as well as achieving a smaller size. The thickness of the microporous membrane can be optimized, for example, by the distance between the cast rolls, the stretching ratio in the stretching step, etc.

[0054] The air permeability of the polyolefin microporous membrane before compression is shown in the item "Air permeability before compression (sec / 100 cm)" in the Examples. 3 The air permeability of the polyolefin microporous membrane is preferably 400 sec / 100 cm from the viewpoints of the reduction in electrical resistance and the suppression of resistance increase as described above, as well as the ion permeability of the microporous membrane and the high output of the nonaqueous secondary battery. 3 Less than 300sec / 100cm, preferably less than 300sec / 100cm 3 Less than 200 sec / 100 cm is more preferable. 3 Below 160 sec / 100 cm, particularly preferred 3 From the viewpoint of the mechanical strength of the microporous membrane, it is preferably 40 sec / 100 cm or less. 3 The air permeability of the microporous membrane can be optimized in the same manner as the above-described means for controlling the post-compression porosity.

[0055] Feature(7): Without being bound by theory, it has been found that a polyolefin microporous membrane with a long crystal period of 37.0 nm or more surprisingly improves the structural uniformity and compression resistance of the polyolefin microporous membrane, thereby improving the reaction uniformity within a nonaqueous secondary battery. This is believed to enable the nonaqueous secondary battery to achieve high power output and high cycle performance, even after a pressing process during fabrication of the nonaqueous secondary battery using the polyolefin microporous membrane as a separator. The improved structural uniformity and compression resistance of the polyolefin microporous membrane are particularly pronounced when electrodes that easily expand and contract within the cell of a nonaqueous secondary battery are used, and are even more pronounced when high-capacity electrodes or silicon (Si)-containing negative electrodes used in automotive batteries, etc., are used.

[0056] SAXS measurement of polyolefin microporous membranes is described in detail in the Examples. Without being bound by theory, it is believed that the crystalline long period obtained by SAXS measurement is related to the polyethylene structure that improves the membrane's structural uniformity and compression resistance, and reaction uniformity in nonaqueous secondary batteries. It is also believed that the crystalline long period of polyolefin microporous membranes correlates with the membrane's porosity after compression. From the viewpoints explained above, the crystalline long period of polyolefin microporous membranes is preferably 37.0 nm to 60.0 nm, 38.0 nm to 55.0 nm, 40.0 nm to 50.0 nm, or 42.0 nm to 50.0 nm.

[0057] The crystal long period of the polyolefin microporous membrane can be adjusted to within the above-described numerical ranges by, for example, controlling the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretch ratio in the biaxial stretching step, the preheating coefficient in the biaxial stretching step, the stretch coefficient in the biaxial stretching step, the MD / TD stretching temperature in the biaxial stretching step, the heat setting temperature, etc. in the production process of the polyolefin microporous membrane.

[0058] The lower limit of the thickness of the polyolefin microporous membrane is 1 μm or more to ensure mechanical strength and insulation. To improve battery safety by ensuring the amount of resin per unit area, the membrane thickness is preferably 2 μm or more, more preferably 3 μm or more. To ensure insulation when lithium dendrites grow, the membrane thickness is preferably 6 μm or more, more preferably 10 μm or more. From the viewpoint of increasing the capacity of nonaqueous secondary batteries, the membrane thickness of the polyolefin microporous membrane is preferably 16 μm or less. The membrane thickness of the microporous membrane can be adjusted by controlling the distance between the cast rolls, the stretch ratio in the stretching step, etc.

[0059] The air permeability of the polyolefin microporous membrane before compression is preferably 30 sec / 100 cm 3 More than 250sec / 100cm 3 Less than 40sec / 100cm, preferably less than 40sec / 100cm 3 More than 200sec / 100cm 3Less than 50 sec / 100 cm, more preferably 3 More than 180sec / 100cm 3 More preferably, 60 sec / 100 cm or less 3 More than 150sec / 100cm 3 The air permeability of the microporous membrane before compression is preferably 40 sec / 100 cm from the viewpoint of ensuring puncture strength. 3 From the viewpoint of output characteristics, it is preferable that the output is 200 sec / 100 cm. 3 The following is the result.

[0060] Common features of features (6) and (7): Examples of polyolefin microporous membranes include porous membranes containing polyolefin resins; porous membranes containing, in addition to polyolefin resins, resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene; woven polyolefin fibers (woven fabrics); and nonwoven polyolefin fiber fabrics. Among these, from the viewpoints of reducing or suppressing an increase in the electrical resistance of the membrane, and the compression resistance and structural uniformity of the membrane, microporous membranes containing polyolefin resins (hereinafter referred to as polyolefin resin porous membranes) are preferred, and microporous membranes containing polyethylene as a main component are more preferred.

[0061] From the viewpoint of improving shutdown performance and the like when a polyolefin microporous membrane for a non-aqueous secondary battery is formed, the polyolefin resin porous membrane is preferably a porous membrane formed from a polyolefin resin composition in which polyolefin resin accounts for 50% by mass or more and 100% by mass or less of the resin components constituting the porous membrane.

[0062] Polyolefins have excellent coatability when a coating liquid is applied onto the film, which is advantageous for making the separator thinner, thereby increasing the ratio of active material in the electricity storage device and increasing the capacity per volume. The polyolefin microporous film can be one that has been used as a substrate for conventional separators, and is preferably a porous film with fine pores that is non-electronically conductive, ionic conductive, highly resistant to organic solvents, and has a high pore size.

[0063] (Base material) The substrate is a polyolefin microporous membrane containing polyolefin as a main component. "Containing as a main component" means that the mass of the target component (polyolefin) constitutes the largest mass in the entire substrate. The polyolefin content in the polyolefin microporous membrane is, for example, more than 50 parts by mass, preferably 75 parts by mass or more, more preferably 85 parts by mass or more, even more preferably 90 parts by mass or more, still more preferably 95 parts by mass or more, particularly preferably 98 parts by mass or more, and may even be 100 parts by mass, based on the total mass of the substrate.

[0064] The polyolefin is not particularly limited, but may be a polyolefin that can be used in ordinary extrusion, injection, inflation, blow molding, etc. Examples of polyolefins include homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. as monomers, as well as copolymers and multistage polymers of two or more of these monomers. These homopolymers, copolymers, and multistage polymers may be used alone or in combination of two or more.

[0065] Examples of polyolefins include polyethylene, polypropylene, and polybutene, among others, from the viewpoints of reducing or suppressing an increase in the electrical resistance of the membrane, compressibility and structural uniformity of the membrane, and more specifically, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene-propylene rubber.

[0066] These may be used alone or in combination of two or more. Among these, the polyolefin is preferably at least one selected from the group consisting of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene, from the viewpoint of shutdown characteristics in which pores are closed by thermal melting. In particular, high-density polyethylene is preferred because of its low melting point and high strength, and high-density polyethylene having a density of 0.93 g / cm as measured in accordance with JIS K 7112 is preferred. 3 Polyethylenes having a molecular weight of 100 or more are more preferred. The polymerization catalyst used in the production of these polyethylenes is not particularly limited, but examples include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts. It is preferred that the main component of the polyolefin is polyethylene, and the content of polyethylene relative to the total mass of the polyolefins in the substrate is preferably 50 parts by mass or more.

[0067] To improve the heat resistance of the substrate, the polyolefin microporous membrane preferably contains polypropylene and a polyolefin other than polypropylene. Examples of the polyolefin resin other than polypropylene include homopolymers containing ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. as monomers, copolymers of two or more of these monomers, and multi-stage polymers.

[0068] The amount of polypropylene relative to the total mass of polyolefin in the substrate (polypropylene / polyolefin) is not particularly limited, but from the viewpoint of achieving both heat resistance and good shutdown function, it is preferably 1 to 35 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 4 to 10 parts by mass. From the same viewpoint, the content ratio of olefin resin other than polypropylene, such as polyethylene, relative to the total mass of polyolefin in the polyolefin microporous membrane (olefin resin other than polypropylene / polyolefin) is preferably 65 to 99 parts by mass, more preferably 80 to 97 parts by mass, and even more preferably 90 to 96 parts by mass.

[0069] From the viewpoints of crystallinity, high strength, compression resistance, etc. when a polyolefin microporous membrane for a nonaqueous secondary battery is formed, the polyolefin resin porous membrane is preferably a porous membrane formed from a polyethylene composition in which polyethylene accounts for 50 to 100% by mass of the resin components constituting the microporous membrane. The proportion of polyethylene in the resin components constituting the porous membrane is more preferably 60 to 100% by mass, even more preferably 70 to 100% by mass, and still more preferably 90 to 100% by mass.

[0070] When the microporous membrane is a polyolefin resin porous membrane, the viscosity-average molecular weight (Mv) of the polyolefin resin used as the raw material is preferably 30,000 to 6,000,000, more preferably 80,000 to 3,000,000, and even more preferably 150,000 to 2,000,000. A viscosity-average molecular weight of 30,000 or more is preferred because the entanglement of polymer molecules tends to result in high strength. On the other hand, a viscosity-average molecular weight of 6,000,000 or less is preferred from the viewpoint of improving moldability in the extrusion and stretching steps.

[0071] When the polyolefin resin porous membrane contains polyethylene as a main component, the lower limit of the Mv of at least one polyethylene is preferably 600,000 or more, more preferably 700,000 or more, from the viewpoint of membrane orientation and rigidity, and the upper limit of the Mv of the polyethylene may be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the polyolefin resin porous membrane is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 100% by mass. From the viewpoint of reduced fluidity of the membrane when melted and short-circuit resistance in a nail penetration test, the proportion of polyethylene with an Mv of 600,000 or more in the polyolefin resin constituting the polyolefin resin porous membrane is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, still more preferably 70% by mass or more, and may be 100% by mass.

[0072] The viscosity average molecular weight (Mv) is calculated from the intrinsic viscosity [η] measured at a measurement temperature of 135° C. using decalin as a solvent according to ASTM-D4020, using the following formula: Polyethylene: [η] = 6.77 × 10 -4 Mv 0.67 (Chiang's formula) Polypropylene: [η] = 1.10 × 10 -4 Mv 0.80

[0073] For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight of which is less than 1 million, may be used.

[0074] The substrate may contain other resins in addition to polyolefin, such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene.

[0075] The substrate may contain any additives. Such additives are not particularly limited and include, for example, plasticizers, polymers other than polyolefins; inorganic particles; phenolic, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polyolefin resin in the polyolefin microporous membrane.

[0076] The substrate preferably contains a plasticizer. When the substrate contains a plasticizer, the adhesive strength between the substrate and the coating layer is improved, making it easier to control the 180° peel strength to 200 gf / cm or more. The amount of plasticizer is preferably 0.1 to 1.6 parts by mass, more preferably 0.2 to 1.2 parts by mass, and even more preferably 0.3 to 1.0 parts by mass, based on the total mass of the substrate. By using a plasticizer amount within the above range, the adhesive strength between the substrate and the coating layer can be improved while reducing the internal resistance of the battery. Examples of plasticizers include hydrocarbons such as liquid paraffin, esters such as dioctyl phthalate and dibutyl phthalate, and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

[0077] When the polyolefin resin porous membrane contains polyethylene as a main component, the polyethylene preferably has a crystallite size of 28 nm or less in the M, D, and N, D planes (110) of the crystallites. The M, D, and N, D plane (110) crystallite size of the polyethylene can be measured by X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS), as described in detail in the Examples.

[0078] Without being limited by theory, when the M, D, N, and D (110) crystallite size of polyethylene is 28.0 nm or less, the polyolefin microporous membrane containing the polyethylene tends to be rigid and the compression resistance of the membrane is improved, thereby achieving both high output and high cycle characteristics even after the pressing step in the production of a nonaqueous secondary battery. From this perspective, the M, D, N, and D (110) crystallite size of polyethylene is more preferably 27.0 nm or less, even more preferably 10.0 nm to 27.0 nm, even more preferably 15.0 nm to 26.0 nm, particularly preferably 15.0 nm to 25.0 nm, and particularly preferably 15.0 nm to 22.0 nm. In particular, when the M, D, N, and D (110) crystallite size of polyethylene is 22.0 nm or less, the membrane becomes more rigid and the compression resistance is improved. The M, D, N, and D plane (110) crystallite size of polyethylene can be adjusted within the above-described numerical ranges, for example, by controlling the molecular weight of the polyolefin raw material, the molecular weight of the polyethylene raw material, the stretch ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretch coefficient during the biaxial stretching process, etc. in the production process of the polyolefin microporous membrane.

[0079] From the viewpoint of making the film rigid and improving its compression resistance, the polyolefin resin contained in the polyolefin resin porous film preferably has a melting point in the range of 120°C or higher and 150°C or lower, more preferably 125°C or higher and 140°C or lower, and / or a DSC first peak temperature in the range of 136°C to 144°C.

[0080] From the viewpoints of crystallinity, high strength, compression resistance, and suppressed electrical resistance when a polyolefin microporous membrane is formed as a separator for a nonaqueous secondary battery, the proportion of polyethylene in the polyolefin resin is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more, based on the mass of the entire polyolefin resin, and is 100% by mass or less, preferably 97% by mass or less, and more preferably 95% by mass or less. A polyethylene (PE) proportion of 100% by mass in the polyolefin resin is preferred from the viewpoint of strength development. A PE proportion of 50% by mass or more in the polyolefin resin is also preferred from the viewpoint of highly responsive fuse behavior.

[0081] The polyolefin resin composition may contain any additives. Examples of additives include polymers other than polyolefin resins; inorganic fillers; phenolic, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. From the viewpoint of improving shutdown performance and the like, the total amount of these additives added is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less, relative to 100% by mass of the polyolefin resin.

[0082] The type, molecular weight, and composition of the polyolefin resin constituting the polyolefin resin porous membrane can be adjusted, for example, by controlling the type, molecular weight, and blending ratio of polymer raw materials such as polyolefin in the production process of the polyolefin resin microporous membrane. Also, a multilayer polyolefin resin microporous membrane having a structure in which two or more layers of the same or different polyolefin resin microporous membranes are laminated can be prepared as described above.

[0083] (Structure of base material) A polyolefin microporous membrane has a porous structure in which a large number of very small pores gather to form dense interconnected pores, and is therefore characterized by excellent ion permeability when containing an electrolyte solution, as well as high strength.

[0084] The average thickness of the polyolefin microporous membrane before compression is preferably 1 μm to 16 μm, more preferably 3 μm to 13 μm, and even more preferably 5 μm to 12 μm, from the viewpoints of high ion permeability and good rate characteristics, and of reducing the volume occupied by the separator in a high-capacity battery to improve battery capacity. The average thickness of the polyolefin microporous membrane can be adjusted within the above range by controlling the distance between the cast rolls, the cast clearance, the stretch ratio during the biaxial stretching step, the HS ratio, the HS temperature, etc.

[0085] For example, in the production of a nonaqueous secondary battery using the microporous membrane as a separator, the porosity of the microporous membrane before compression is preferably 20% or more, more preferably 35% or more, even more preferably 38% or more, even more preferably 40% or more, and particularly preferably 45% or more, from the viewpoints of reducing the electrical resistance of the membrane after the pressing step to achieve both high output and high cycle characteristics of the battery and achieving a certain level of membrane strength and low air permeability. From the viewpoints of battery safety and achieving a certain level of membrane strength and low air permeability, the porosity is preferably 70% or less, more preferably 65% ​​or less, and even more preferably 60% or less. The porosity of the microporous membrane can be adjusted by controlling the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, stretching ratio, heat setting temperature, stretching ratio during heat setting, relaxation rate during heat setting, etc., or by combining these.

[0086] To achieve high ion permeability, excellent voltage resistance, and high strength, the pore size of the microporous membrane is preferably 30 to 70 nm, more preferably 35 to 60 nm, as measured by the half-dry method. The pore size of the microporous membrane can be adjusted, for example, by controlling the stretching temperature, stretching ratio, heat setting temperature, stretching ratio during heat setting, relaxation rate during heat setting, etc., or a combination of these.

[0087] The melt flow index (MI) of the polyolefin microporous membrane is preferably 1.0 or less, more preferably 0.001 to 1.0, even more preferably 0.005 to 0.8, and still more preferably 0.01 to 0.4, from the viewpoint of reducing the fluidity of the membrane when molten and suppressing inter-electrode short-circuiting due to separator flow in a heat-generating state during a nail penetration test. The MI of the polyolefin microporous membrane can be adjusted within the above numerical range, for example, by controlling the molecular weight and blending ratio of polymer raw materials such as polyolefin.

[0088] With regard to the molecular weight distribution of the polyolefin microporous membrane measured by GPC, from the viewpoints of reducing fluidity when the membrane is melted and short-circuit resistance in a nail penetration test, polyethylene components having a Mw of 1,000,000 or more account for 7% by mass or more of the total eluted components, more preferably 9% by mass or more, even more preferably 12% by mass or more, and even more preferably 15% by mass or more. Furthermore, from the viewpoint of suppressing excessive stress when the membrane shrinks in a high-temperature environment, polyethylene components having a Mw of 1,000,000 or more are preferably 57% by mass or less, more preferably 42% by mass or less, even more preferably 33% by mass or less, and even more preferably 27% by mass or less of the total eluted components. The molecular weight distribution of the polyolefin microporous membrane can be adjusted within the above numerical ranges, for example, by controlling the type, molecular weight, and blending ratio of the polyolefin raw materials.

[0089] The pin puncture strength of the microporous membrane, not converted into basis weight (hereinafter simply referred to as pin puncture strength), is preferably 250 gf or more from the viewpoint of battery safety, and preferably 700 gf or less from the viewpoint of suppressing the porosity, crystallinity, and electrical resistance of the polyolefin microporous membrane after compression. The pin puncture strength is more preferably 300 gf to 690 gf, and even more preferably 310 gf to 680 gf. A pin puncture strength of 200 gf / 20 μm or more is preferred from the viewpoint of suppressing membrane rupture due to fallen active material, etc., when the separator is wound with the electrodes, and from the viewpoint of suppressing the risk of short-circuiting due to expansion and contraction of the electrodes during charge and discharge. On the other hand, a pin puncture strength of 2000 gf / 20 μm or less is preferred from the viewpoint of reducing width shrinkage due to relaxation of orientation during heating. The pin puncture strength is measured according to the method described in the Examples. The pin puncture strength can be adjusted by adjusting the stretch ratio and / or stretching temperature of the substrate.

[0090] The basis weight of the polyolefin microporous membrane is preferably 3.0 g / m from the viewpoint of suppressing thermal runaway of the non-aqueous secondary battery. 2 From the viewpoint of increasing the capacity of the battery, it is preferable to use a material having a thickness of 10 g / m 2 The basis weight of the polyolefin microporous membrane is more preferably 3.0 g / m or less. 2 More than 7.0g / m 2 More preferably, 3.0 g / m or less 2 More than 6.0g / m 2 The improved compression resistance ensures the safety of the battery even at a lower basis weight.

[0091] From the viewpoint of safety of a non-aqueous secondary battery containing a microporous membrane, the withstand voltage per unit area of ​​the microporous membrane is preferably 0.13 kV / (g / m 2 )That's all.

[0092] The upper limit of the tensile breaking strength of the polyolefin microporous membrane in both MD and TD is preferably 5000 kgf / cm from the viewpoint of ensuring the membrane strength required for winding and laminating electrodes and separators in the manufacturing process of a nonaqueous secondary battery. 2 Less than or equal to 4500 kgf / cm2 or less, more preferably 4000 kgf / cm 2 More preferably, 3500 kgf / cm or less 2 Below 3,000 kgf / cm, particularly preferably 2 The lower limit is preferably 500 kgf / cm 2 More preferably, 700 kgf / cm 2 More preferably, 1,000 kgf / cm 2 More preferably, 1500 kgf / cm 2 More than 2000 kgf / cm, particularly preferably 2000 kgf / cm 2 More than 2500 kgf / cm, particularly preferably 2500 kgf / cm 2 The upper limit of the tensile strength at break of the polyolefin microporous membrane is preferably 5000 kgf / cm in both MD and TD from the viewpoint of suppressing thermal shrinkage of the polyolefin microporous membrane. 2 Lower than.

[0093] The closer the MD and TD tensile strengths of a polyolefin microporous membrane are, the more uniformly the membrane breaks during a nail penetration test of a nonaqueous secondary battery, minimizing the short-circuit area and ultimately improving nail penetration test safety. Furthermore, the closer the MD and TD tensile strengths of a polyolefin microporous membrane are, the less likely the membrane will tear in the direction of weaker strength when contaminated with foreign matter or subjected to external impact, improving safety and the more isotropic the structure, improving battery cycle characteristics. From these perspectives, the ratio of the MD tensile strength to the TD tensile strength of a polyolefin microporous membrane (MD / TD tensile strength ratio) is preferably 0.5 to 2.0, more preferably 0.7 to 1.5, even more preferably 0.7 to 1.4, still more preferably 0.7 to 1.3, particularly preferably 0.75 to 1.25, particularly preferably 0.8 to 1.3, and particularly preferably 0.8 to 1.2. The MD / TD tensile strength ratio at break of the polyolefin microporous membrane can be adjusted within the above-described numerical range by, for example, controlling the stretching ratio and HS ratio during the biaxial stretching step.

[0094] When the tensile elongation at break of a polyolefin microporous membrane is controlled within an appropriate range in both MD and TD, the membrane stretches appropriately and breaks during a nail penetration test of a nonaqueous secondary battery, minimizing the area of ​​short circuit and ultimately improving nail penetration test safety. If the tensile elongation at break is too high, the nail penetration portion stretches too much, pulling the surrounding area other than the nail penetration membrane breakage portion, thinning the membrane thickness in the surrounding area and leading to a large-area short circuit. From this perspective, the tensile elongation at break of a polyolefin microporous membrane in both MD and TD is preferably 20% to 200%, more preferably 30% to 150%, even more preferably 40% to 120%, and even more preferably 50% to 110%. The tensile elongation at break in MD and / or TD of the polyolefin microporous membrane can be adjusted within the above-described range by, for example, controlling the stretch ratio and HS ratio during the biaxial stretching process.

[0095] The closer the MD and TD tensile elongation at break of a polyolefin microporous membrane are, the more the membrane will elongate and break appropriately during a nail penetration test of a nonaqueous secondary battery, minimizing the short-circuit area and ultimately improving nail penetration test safety. From this perspective, the ratio of the MD tensile elongation at break to the TD tensile elongation at break of the polyolefin microporous membrane (MD / TD tensile elongation at break ratio) is preferably 0.3 to 2.0, more preferably 0.35 to 1.5, even more preferably 0.4 to 1.3, and still more preferably 0.5 to 1.2. The MD / TD tensile elongation at break ratio of the polyolefin microporous membrane can be adjusted within the above-described numerical range by, for example, controlling the stretch ratio and HS ratio during the biaxial stretching process.

[0096] The tensile modulus of the polyolefin microporous membrane is preferably 1,000 kg / cm in both MD and TD from the viewpoint of improving safety by making it difficult for the separator to rupture and preventing a complete short circuit when a nail penetrates the nonaqueous secondary battery during a nail penetration test, penetrating and deforming the separator and electrodes. 2 ~10,000kg / cm 2 , more preferably 2,000 kg / cm 2 ~90,000kg / cm 2 is.

[0097] The closer the MD and TD tensile moduli of a polyolefin microporous membrane are, the more uniformly the membrane will rupture during a nail penetration test of a nonaqueous secondary battery, minimizing the short-circuit area and ultimately improving nail penetration test safety. From this perspective, the ratio of the MD tensile modulus to the TD tensile modulus of a polyolefin microporous membrane (MD / TD tensile modulus ratio) is preferably 0.3 to 3.0, more preferably 0.35 to 2.0, even more preferably 0.4 to 1.5, and still more preferably 0.5 to 1.3. The MD / TD tensile modulus ratio of a polyolefin microporous membrane can be adjusted within the above-described range by, for example, controlling the stretch ratio and HS ratio during the biaxial stretching process.

[0098] The fuse temperature of the microporous membrane is preferably 150°C or lower, more preferably 149°C or lower. The upper limit of the shutdown temperature means that when an abnormal reaction occurs and the temperature inside the battery rises, the pores in the separator will close before that temperature is reached. Therefore, the lower the shutdown temperature, the more quickly the flow of lithium ions between the electrodes stops at a low temperature, improving safety. On the other hand, to prevent a decrease in battery performance even when exposed to temperatures above 100°C, the fuse temperature of the microporous membrane is preferably 130°C or higher, more preferably 135°C or higher, even more preferably 138°C or higher, and even more preferably 139°C or higher.

[0099] Regarding the surface smoothness of the polyolefin microporous membrane, from the viewpoint of cycle characteristics and rate characteristics under pressure, the average surface smoothness between one side and the other side of the polyolefin microporous membrane is preferably 20,000 sec / 10 cm 3 Over 200,000sec / 10cm 3 Less than 30,000sec / 10cm, preferably less than 30,000sec / 10cm 3 Over 180,000sec / 10cm 3 Less than 40,000 sec / 10 cm, more preferably 3 Over 160,000sec / 10cm 3Below 50,000 sec / 10 cm, especially preferred 3 Over 140,000sec / 10cm 3 Surface smoothness is 20,000sec / 10cm or less. 3 If the surface smoothness is lower than 200,000 sec / 10 cm, the physical distance between the polyolefin microporous membrane and the electrode material becomes uneven, which may cause uneven battery reactions and deteriorate cycle characteristics. 3 If the temperature is higher, the distance between the polyolefin microporous membrane and the electrode material will be reduced, and the voids formed between the microporous membrane and the electrode material will be smaller, which may prevent uniform penetration of the electrolyte and deteriorate cycle characteristics. The surface smoothness of the polyolefin microporous membrane can be adjusted within the above-described numerical range by controlling, for example, the molecular weight and blending ratio of polymer raw materials such as polyolefin, the distance between the cast rolls, the stretching ratio in the biaxial stretching process, the MD / TD stretching temperature in the biaxial stretching process, the heat coefficient per unit resin of the resin composition in the biaxial stretching process, the HS magnification, the HS temperature, etc.

[0100] <Coating layer> The separator for an electricity storage device of this embodiment includes a coating layer disposed on at least one surface of the substrate. That is, the coating layer may be disposed on only one surface of the substrate, or on both surfaces. "Disposed on the surface" means that the coating layer may be disposed on the entire surface of the substrate, or on a portion of the surface. The coating layer is intended to be directly bonded to the electrode. It is preferable that the coating layer is disposed so that the substrate and the electrode are bonded via the coating layer, so that the coating layer is directly bonded to the electrode. The coating layer is preferably a coating layer formed by applying a coating liquid containing an inorganic filler and a particulate polymer to the substrate.

[0101] The coating layer includes an inorganic filler and a particulate polymer of a thermoplastic polymer. The coating layer may further include a resin binder, a water-soluble polymer, and other additives in addition to the particulate polymer of a thermoplastic polymer.

[0102] (inorganic filler) The inorganic filler is not particularly limited, but is preferably one that has a melting point of 200°C or higher, high electrical insulation, and electrochemical stability within the range of use of an electricity storage device such as a lithium-ion secondary battery. Examples of such inorganic fillers include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone or in combination. Among these, the inorganic filler is preferably at least one selected from the group consisting of alumina, barium sulfate, and aluminum oxide hydroxide (boehmite).

[0103] The lower limit of the average particle size of the inorganic filler is preferably 50 nm or more, 100 nm or more, 150 nm or more, 200 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, or 400 nm or more, and the upper limit is preferably 2000 nm or less, 1100 nm or less, 800 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, or 300 nm or less. An average particle size of the inorganic filler of 50 nm or more is preferred from the viewpoint of maintaining voids for ion permeation through the coating layer and improving rate characteristics. An average particle size of the inorganic filler of 2000 nm or less is preferred from the viewpoint of increasing the proportion of inorganic filler in the coating layer and improving heat shrinkage resistance. The average particle size of the inorganic filler is preferably, for example, 180 nm or more and 300 nm or less. This is because, particularly when the coating layer is thin, a uniform coating layer thickness is formed and heat shrinkage resistance is improved. The average particle size of the inorganic filler is also preferably, for example, 250 nm or more and 450 nm or less. This is because it is possible to achieve a high degree of both rate characteristics and heat shrinkage resistance. The "average particle size" of the inorganic filler was measured using the method described in the Examples. Methods for adjusting the particle size and distribution of the inorganic filler include, for example, grinding the inorganic filler using an appropriate grinding device such as a ball mill, a bead mill, or a jet mill to reduce the particle size. The particle size distribution of the inorganic filler can be such that a single peak is obtained in a graph of particle size versus frequency. However, a graph with two peaks or a trapezoidal chart with no peaks may also be obtained. The coefficient of variation of the particle size distribution of the inorganic filler is preferably 0.55 or less, more preferably 0.50 or less, and even more preferably 0.45 or less. A coefficient of variation of the particle size distribution of 0.55 or less is preferable from the viewpoints of suppressing deformation at temperatures exceeding the melting point of the substrate and improving the slope rate of the coating layer and thereby enhancing adhesion to the electrode.

[0104] Examples of the shape of the inorganic filler include plate-like, scale-like, needle-like, columnar, spherical, polyhedral, and block-like. A combination of inorganic fillers having these shapes may be used. A block shape is preferred from the viewpoint of improving the gradient of the coating layer and enhancing adhesion to the electrode. Regardless of the aspect ratio, a block shape is more preferable than a sphere. Filler shapes close to spheres are undesirable because the surface tension and Newtonian fluidity of the paint inhibit surface contact of the particulate polymer with the substrate.

[0105] The aspect ratio of the inorganic filler is preferably 1.0 or more and 2.5 or less, more preferably 1.1 or more and 2.0 or less. An aspect ratio of 2.5 or less is preferable from the viewpoints of suppressing the amount of moisture adsorption by the separator and suppressing capacity deterioration during repeated cycles, suppressing deformation at temperatures exceeding the melting point of the substrate, and improving the gradient of the coating layer and increasing adhesion to the electrode. The reason why the gradient increases when the aspect ratio of the inorganic filler is 1.0 or more and 2.5 or less is thought to be because the orientation of the particles in the coating layer is small, making it easier to form a laminated structure.

[0106] The particle size distribution of the inorganic filler, calculated by dividing the standard deviation SD of the volume average particle size of the inorganic filler by the D50, is preferably 0.55 or less, more preferably 0.50 or less, and even more preferably 0.45 or less. A particle size distribution of 0.55 or less is preferable from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the substrate and from the viewpoint of improving the gradient of the coating layer and enhancing adhesion to the electrode. The reason why the gradient increases when the particle size distribution of the inorganic filler is 0.55 or less is thought to be because the particle uniformity is increased and the contact rate between particles is improved, making it easier to form a laminated structure.

[0107] The amount of the inorganic filler is, for example, 20 to less than 100 parts by mass, 30 to 80 parts by mass, 35 to 70 parts by mass, or even 40 to 60 parts by mass relative to the total mass of the coating layer.

[0108] (particulate polymer) The particulate polymer is a thermoplastic polymer particle. From the viewpoint of enhancing adhesion between the separator and the electrode, the particulate polymer preferably contains a thermoplastic polymer having a glass transition temperature or melting point of 20°C or higher and 200°C or lower. The glass transition temperature refers to the midpoint glass transition temperature as defined in JIS K7121 and is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the glass transition temperature can be determined as the temperature at the point where a line extending the low-temperature baseline of the DSC curve toward the high-temperature side intersects with a line equidistant along the vertical axis from a line extending the high-temperature baseline of the DSC curve toward the low-temperature side, and a curve representing a stepwise change in the glass transition. More specifically, the glass transition temperature can be determined according to the method described in the Examples. Furthermore, the term "glass transition" refers to a change in heat flow occurring on the endothermic side in DSC due to a change in the state of the polymer specimen. Such a change in heat flow is observed as a stepwise change in the DSC curve. The "stepwise change" refers to the portion of the DSC curve where the curve moves away from the previous low-temperature baseline and transitions to a new high-temperature baseline. A step change also includes a combination of a step change and a peak. It can also be expressed as the point in the step change where, if the upper side is the heat generation side, the curve changes from an upwardly convex curve to a downwardly convex curve. A "peak" refers to the portion of a DSC curve where the curve leaves the low-temperature baseline and returns to the same baseline. A "baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test specimen.

[0109] The glass transition temperature (Tg) of the particulate polymer is preferably 20°C or higher and 110°C or lower, more preferably 50°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher. From the viewpoint of improving adhesive strength after injection of an electrolyte solution, it is particularly preferably higher than 90°C. A Tg of the particulate polymer of 20°C or higher is preferred from the viewpoint of preventing adjacent separators from sticking together (blocking) via the coating layer during storage and transportation of the separator for an electricity storage device and during the manufacturing process of the electricity storage device. On the other hand, a Tg of the particulate polymer of 110°C or lower is preferred from the viewpoint of obtaining good adhesive strength with the electrode. The Tg of the particulate polymer can be appropriately adjusted, for example, by changing the type of monomer used in producing the particulate polymer, or, when the particulate polymer is a copolymer, by changing the compounding ratio of each monomer. That is, for each monomer used in the production of a particulate polymer, the glass transition temperature can be roughly estimated from the Tg of the homopolymer generally shown (for example, as described in "Polymer Handbook" (A Wiley-Interscience Publication)) and the blending ratio of the monomers. For example, a copolymer obtained by copolymerizing a high ratio of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of about 100°C will have a high Tg, while a copolymer obtained by copolymerizing a high ratio of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate to give a homopolymer with a Tg of about -50°C will have a low Tg. The Tg of a copolymer can also be roughly calculated by the FOX formula shown below. 1 / Tg=W1 / Tg1+W2 / Tg2++W i / Tg i +···W n / Tg n where Tg(K) is the Tg of the copolymer, and Tg i (K) is the Tg of the homopolymer of monomer i, and W i is the mass fraction of each monomer. i is an integer of 1 to n, and n is the number of types of monomers constituting the copolymer. However, as the glass transition temperature Tg of the particulate polymer in this embodiment, a value measured by the method using DSC is adopted.

[0110] From the viewpoints of adhesion between the separator and the electrode and preventing the particulate polymer from falling off the coating layer, the average particle size of the particulate polymer is preferably 0.5 to 5 times, more preferably 1 to 2 times, even more preferably 1.1 to less than 1.5 times, and particularly preferably 1.2 to 1.4 times the thickness of the coating layer. The "average particle size" of the particulate polymer refers to the volume-average particle size measured by the measurement method described in the Examples. The "primary particles" of the particulate polymer refer to independent particles that are united by covalent bonds. On the other hand, aggregates formed by two or more primary particles are called "secondary particles."

[0111] The particle size distribution MV / MN of the particulate polymer, calculated by dividing the volume-average particle size MV of the particulate polymer by the number-average particle size MN, is preferably 1.60 or less, more preferably 1.30 or less, even more preferably 1.20 or less, even more preferably 1.10 or less, and particularly preferably less than 1.10. Having the particle size distribution of the particulate polymer within the above range is preferable from the viewpoints of ensuring uniformity in the thickness of the coating layer, improving cycle characteristics, and improving adhesion to the electrode, reducing the amount of particulate polymer on the small particle size side of the distribution embedded in the coating layer, improving adhesion to the electrode, and improving heat resistance, and reducing the total thickness of the separator. The lower limit of the particle size distribution MV / MN of the particulate polymer is not particularly limited, but may be, for example, 1.01 or more, or 1.01.

[0112] The particulate polymer contained in the coating layer is preferably in the form of primary particles. The average particle size of the primary particles of the particulate polymer is preferably 1 μm or more and 10 μm or less, more preferably 1 μm or more and 5 μm or less, and even more preferably 2 μm or more and 4 μm or less. The particulate polymer being in the form of primary particles means that the particulate polymer is uniformly dispersed in the coating layer, which improves the 180° peel strength, increases the adhesive strength with the electrode, suppresses thermal shrinkage, and ensures the uniformity of the thickness of the coating layer. When the average particle size of the primary particles is 1 μm or more and 10 μm or less, the particulate polymer is likely to form a structure in which it protrudes from the surface of the coating layer, which increases the adhesive strength with the electrode and suppresses thermal shrinkage.

[0113] Examples of the thermoplastic polymer include (meth)acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluorine-containing resins.

[0114] From the viewpoints of high adhesion to electrodes and low thermal shrinkage, the thermoplastic polymer preferably contains a (meth)acrylic polymer. The term "(meth)acrylic polymer" refers to a polymer or copolymer containing a (meth)acrylic compound as a monomer. Such a (meth)acrylic compound can be represented by the following general formula: CH2=CR Y1 -COO-R Y2 In the formula, R Y1 represents a hydrogen atom or a methyl group, and R Y2 represents a hydrogen atom or a monovalent hydrocarbon group. Y2When is a monovalent hydrocarbon group, it may have a substituent or a heteroatom. Examples of monovalent hydrocarbon groups include linear or branched chain alkyl groups, cycloalkyl groups, and aryl groups. Examples of substituents include hydroxyl groups and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. The (meth)acrylic compounds may be used alone or in combination of two or more. Examples of (meth)acrylic compounds include (meth)acrylic acid, linear alkyl (meth)acrylates, cycloalkyl (meth)acrylates, (meth)acrylates having a hydroxyl group, and (meth)acrylic acid aryl esters.

[0115] More specifically, examples of the chain alkyl (meth)acrylate include (meth)acrylates having a chain alkyl group having 1 to 3 carbon atoms, such as a methyl group, an ethyl group, an n-propyl group, and an isopropyl group; an n-butyl group, an isobutyl group, a t-butyl group, an n-hexyl group, a 2-ethylhexyl group; and a chain alkyl group having 4 or more carbon atoms, such as a lauryl group. Examples of the (meth)acrylic acid aryl ester include phenyl (meth)acrylate.

[0116] Specific examples of the (meth)acrylate include (meth)acrylates having a chain alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; and (meth)acrylates having an aromatic ring such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0117] Conjugated diene polymers are polymers containing conjugated diene compounds as monomer units and are preferred because they are compatible with electrodes. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadienes, and substituted and side-chain conjugated hexadienes. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Conjugated diene polymers may contain (meth)acrylic compounds or other monomers as monomer units, as described below. Examples of such monomers include styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, and acrylonitrile-butadiene-styrene copolymers and their hydrogenated products.

[0118] Examples of polyvinyl alcohol resins include polyvinyl alcohol and polyvinyl acetate.

[0119] Fluorine-containing resins are preferred from the viewpoint of voltage resistance, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers containing fluorine atoms, such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. The fluorine-containing resin is preferably a copolymer containing fluorine atoms.

[0120] Among the thermoplastic polymers listed above, the particulate polymer preferably contains at least one selected from the group consisting of copolymers containing (meth)acrylate as a monomer, styrene-butadiene copolymers, and copolymers containing fluorine atoms. The copolymers containing (meth)acrylate as a monomer more preferably contain copolymers containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers. By including these specific thermoplastic polymers in the particulate polymer, it is possible to provide a separator for an electricity storage device that has higher adhesive strength with electrodes and a smaller thermal shrinkage rate.

[0121] The particulate polymer preferably contains a crosslinkable monomer. The crosslinkable monomer is not particularly limited, but examples thereof include a monomer having two or more radically polymerizable double bonds, a monomer having a functional group that gives a self-crosslinking structure during or after polymerization, etc. These may be used alone or in combination of two or more.

[0122] Examples of monomers having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylates, with polyfunctional (meth)acrylates being preferred. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specific examples include polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. Among these, at least one of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferred from the same viewpoint as above.

[0123] (resin binder) The coating layer preferably contains a resin binder for binding the inorganic fillers together and the inorganic filler and the substrate. The type of resin for the resin binder is not particularly limited, but any resin that is insoluble in the electrolyte of an electricity storage device such as a lithium ion secondary battery and is electrochemically stable within the range of use of the electricity storage device such as a lithium ion secondary battery can be used.

[0124] Specific examples of resins for the resin binder include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene-styrene copolymers and their hydrogenated products, methacrylate-acrylate copolymers, styrene-butadiene copolymers and their hydrogenated products ... Examples of suitable resins include rubbers such as ethylene-acrylate copolymers, acrylonitrile-acrylate copolymers, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins with a melting point of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, or resins with no melting point but a decomposition temperature of 200°C or higher. These may be used alone or in combination of two or more.

[0125] The resin binder may include, for example, a resin latex binder. Examples of the resin latex binder include a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable therewith. Examples of the aliphatic conjugated diene monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth)acrylic acid, and examples of the other monomer include styrene. While there are no particular limitations on the polymerization method for such copolymers, emulsion polymerization is preferred. There are no particular limitations on the emulsion polymerization method, and known methods can be used. There are no particular limitations on the method for adding the monomers and other components, and any of a batch addition method, a divided addition method, and a continuous addition method can be used. The polymerization method can be one-stage polymerization, two-stage polymerization, or multi-stage polymerization with three or more stages.

[0126] Specific examples of the resin binder include the following (1) to (7). (1) Polyolefins, such as polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; (2) Conjugated diene polymers, such as styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; (3) Acrylic polymers, such as methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers; (4) Polyvinyl alcohol-based resins, such as polyvinyl alcohol and polyvinyl acetate; (5) Fluorine-containing resins, such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, and ethylene-tetrafluoroethylene copolymers; (6) Cellulose derivatives, such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and (7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers having no melting point but a decomposition temperature of 200°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0127] When the resin binder is a resin latex binder, its volume average particle diameter (D50) may be, for example, 50 nm to 500 nm, 60 nm to 460 nm, or 80 nm to 250 nm. The volume average particle diameter of the resin binder can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, etc.

[0128] From the viewpoint of improving the 180° peel strength, the glass transition temperature of the resin binder is preferably 25° C. or lower, more preferably 10° C. or lower, and even more preferably −15° C. or lower. From the viewpoint of transparency, the glass transition temperature of the resin binder is preferably −60° C. or higher.

[0129] The volume average particle diameter (D50) of the resin binder is preferably at least 1 time, more preferably at least 2 times, and even more preferably at least 2.5 times the average pore size of the polyolefin microporous membrane from the viewpoint of improving 180° peel strength. Selecting the volume average particle diameter (D50) of the resin binder in this manner enables the resin binder to be retained on the surface of the polyolefin microporous membrane, improving 180° peel strength. From the viewpoint of improving rate characteristics, the volume average particle diameter (D50) of the resin binder is preferably at most 10 times the average pore size of the polyolefin microporous membrane. The content of the resin binder in the coating layer may be, for example, more than 0 part by mass and at most 80 parts by mass, 1 part by mass to 20 parts by mass, 2 parts by mass to 10 parts by mass, or 3 parts by mass to 5 parts by mass, relative to the total amount of the coating layer.

[0130] The Tg of the resin binder is preferably less than 40° C. from the viewpoint of wettability to the substrate, adhesion between the substrate and the particulate polymer, adhesion between the coating layer and the particulate polymer, adhesion between the substrate and the coating layer, and adhesion to the electrode. The Tg of the resin binder is more preferably −100° C. or higher, even more preferably −50° C. or higher, and particularly preferably −40° C. or higher from the viewpoint of ion permeability, and is more preferably less than 20° C., even more preferably less than 15° C., and particularly preferably less than 0° C. from the viewpoint of adhesion between the substrate and the particulate polymer.

[0131] (Water-soluble polymer) The coating layer may further contain a water-soluble polymer in addition to the inorganic filler and the particulate polymer. The water-soluble polymer may be incompatible with the thermoplastic polymer of the particulate polymer. In general, the water-soluble polymer functions as a dispersant in a coating liquid for forming a coating layer containing the inorganic filler and the particulate polymer of the thermoplastic polymer, and functions as a dispersant and / or a water-retaining agent when the coating liquid is a water-based paint.

[0132] The content of the water-soluble polymer in the coating layer is preferably 0.04 parts by mass or more but less than 2 parts by mass, more preferably 0.04 parts by mass or more but 1.5 parts by mass or less, and even more preferably 0.1 parts by mass or more but 1 part by mass or less, relative to 100 parts by mass of the inorganic filler. A water-soluble polymer content of 0.04 parts by mass or more improves the binding strength between inorganic components, further suppressing thermal shrinkage. Furthermore, sedimentation of components during preparation of the coating layer slurry is suppressed, enabling stable dispersion. A water-soluble polymer content of 5 parts by mass or less can suppress streaks and unevenness during coating layer formation.

[0133] The water-soluble polymer also contributes to the binding between inorganic fillers in the coating layer. From the viewpoint of suppressing thermal shrinkage of the separator, the water-soluble polymer preferably exhibits a weight loss rate of less than 10% at 150°C when the weight at 50°C is taken as 100% in thermogravimetry.

[0134] The water-soluble polymer may be a polymer derived from a natural product, a synthetic product, a semi-synthetic product, or the like. However, from the viewpoint of forming inorganic and organic components into paints, particularly water-based paints, the water-soluble polymer is preferably an anionic, cationic, amphoteric, or nonionic polymer, and more preferably an anionic, cationic, or amphoteric polymer.

[0135] Examples of anionic polymers include modified starches such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethyl cellulose; ammonium salts or alkali metal salts of polyacrylic acid; gum arabic; carrageenan; sodium chondroitin sulfate; sulfonic acid compounds such as sodium polystyrene sulfonate, sodium polyisobutylene sulfonate, and naphthalene sulfonic acid condensate salts; and polyethyleneimine xanthate salts. Among these, from the viewpoint of achieving an appropriate balance between the rigidity, rate characteristics, and cycle characteristics of the power storage device, anionic polymers containing a metal salt as a counter cation are preferred; anionic cellulose derivatives and ammonium salts or alkali metal salts of polyacrylic acid are also preferred; from the viewpoint of the balance between heat resistance and rate characteristics, alkali metal salts of polyacrylic acid are more preferred, and sodium polyacrylate is even more preferred.

[0136] The ammonium salt or alkali metal salt of polyacrylic acid is a compound having -COO groups derived from multiple carboxylic acid groups. - It refers to a polymer in which at least one of the moieties forms a salt with an ammonium ion or an alkali metal ion. Examples of alkali metal ions include sodium ions (Na + ), potassium ions (K + ) etc.

[0137] The ammonium salt or alkali metal salt of polyacrylic acid may be at least one of the following (I) to (III): (I) Monomers having one ammonium salt or alkali metal salt of a carboxylic acid (C i ) or a homopolymer of multiple monomers (C i ) copolymers with other monomers; (II) Monomers having a plurality of ammonium salts or alkali metal salts of carboxylic acids (C ii ) homopolymer or monomer (C ii ) and other monomers; and (III) Ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing monomers having one or more carboxylic acids. Monomers having one ammonium salt or alkali metal salt of a carboxylic acid (C i ) include, for example, sodium (meth)acrylate and ammonium (meth)acrylate.

[0138] Monomers having a plurality of ammonium salts or alkali metal salts of carboxylic acids (C ii Examples of the (meth)acryloyloxy)undecane-1,1-dicarboxylic acid include ammonium salts and sodium salts of 11-(methacryloyloxy)undecane-1,1-dicarboxylic acid; ammonium salts, monosodium salts, and disodium salts of ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; and alicyclic polycarboxylic acids having a (meth)acryloyl group.

[0139] Monomer (C i ) or monomer (C ii Examples of monomers copolymerizable with the copolymer include (meth)acrylamide; ethylenically unsaturated dicarboxylic acids such as fumaric acid, maleic acid, itaconic acid, and citraconic acid; and ethylenically unsaturated dicarboxylic acid anhydrides such as maleic anhydride, itaconic anhydride, and citraconic anhydride.

[0140] Examples of the ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing a monomer having one or more carboxylic acids include sodium polyacrylate and ammonium polyacrylate.

[0141] The structures of the ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above may overlap with each other. The ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above preferably have a low content of polyvalent cations when dissolved in water. Examples of polyvalent cations include magnesium ions, calcium ions, and iron ions. Reducing the content of these ions stabilizes the dispersibility of the particulate polymer in the mixed slurry with the particulate polymer.

[0142] Examples of cationic polymers include cationic starch, chitosan, gelatin, homopolymers or copolymers of dimethylaminoethyl (meth)acrylate quaternary salts, homopolymers or copolymers of dimethylallylammonium chloride, polyamidines and their copolymers, polyvinylimidazoline, dicyandiamide condensates, epichlorohydrin-dimethylamine condensates, and polyethyleneimine.

[0143] Examples of amphoteric polymers include dimethylaminoethyl (meth)acrylate quaternary salt-acrylic acid copolymers, Hofmann degradation products of polyacrylamide, and the like.

[0144] Examples of nonionic polymers include starch and its derivatives; cellulose derivatives such as methyl cellulose, hydroxyethyl cellulose, and hydroxypropyl cellulose, and their ammonium salts or alkali metal salts; gums such as guar gum and modified versions thereof; and synthetic polymers and modified versions thereof, such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropyl acrylamide, and copolymers of vinyl alcohol and other monomers.

[0145] The water-soluble polymer may or may not have an amide bond-containing cyclic structure. The water-soluble polymer having an amide bond-containing cyclic structure refers to a homopolymer or copolymer having a group having an amide bond-containing cyclic structure and a backbone derived from a polymerizable double bond. The water-soluble polymer having an amide bond-containing cyclic structure may have one or more amide bond-containing cyclic structures.

[0146] Examples of the group having an amide bond-containing cyclic structure include the group of the following formula (2): [ka] Specific examples of the water-soluble polymer having an amide bond-containing cyclic structure include homopolymers of monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond, such as poly(N-vinylcaprolactam), which is a homopolymer of N-vinylcaprolactam, and polyvinylpyrrolidone (PVP), which is a homopolymer of vinylpyrrolidone; copolymers of two or more monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.); and copolymers of one or more monomers having a group having an amide bond-containing cyclic structure and a polymerizable double bond (N-vinylcaprolactam, vinylpyrrolidone, etc.) with one or more other monomers having a polymerizable double bond (monomers other than the monomer having a group having an amide bond-containing cyclic structure and a polymerizable double bond).

[0147] Examples of monomers copolymerizable with the monomer having a group with an amide bond-containing cyclic structure and a polymerizable double bond include vinyl acyclic amides; (meth)acrylic acid and esters thereof; (meth)acrylamide and derivatives thereof; styrene and derivatives thereof; vinyl esters such as vinyl acetate; α-olefins; basic unsaturated compounds such as vinylimidazole and vinylpyridine and derivatives thereof; carboxyl group-containing unsaturated compounds and acid anhydrides thereof; vinyl sulfonic acid and derivatives thereof; vinyl ethylene carbonate and derivatives thereof; and vinyl ethers.

[0148] (additives) The coating layer may consist of only an inorganic filler, a particulate polymer, and an arbitrary water-soluble polymer, or may further contain additives other than these. Examples of additives include low-molecular-weight dispersants other than water-soluble polymers; thickeners; antifoaming agents; and pH adjusters such as ammonium hydroxide. Specific examples of low-molecular-weight dispersants include monomers (C ) having multiple ammonium salts or alkali metal salts of carboxylic acids. ii ), and non-polymerizable compounds having a plurality of ammonium salts or alkali metal salts of carboxylic acids (for example, sodium alginate and sodium hyaluronate).

[0149] Specific examples of the antifoaming agent include those represented by the following formula (A): [ka] {where, R 5 ~R 8 are each independently an alkyl group having 1 to 10 carbon atoms, and n and m are each independently an integer of 0 or more, provided that n+m=0 to 40. It is preferable to use a surfactant (acetylene-based surfactant) containing an ethoxylated acetylene glycol represented by the formula:

[0150] Specific examples of the alkyl group having 1 to 10 carbon atoms may be linear, branched, or cyclic, and include, for example, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group.

[0151] Specific examples of the acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol, 5,8-dimethyl-6-dodecyne-5,8-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 4,7-dimethyl-5-decyne-4,7-diol, 2,3,6,7-tetramethyl-4-octyne-3,6-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (ethylene oxide addition mole number: 1.3), and 2,4,7,9-tetramethyl-5-decyne-4,7-diol. Examples of the antifoaming agent include an ethoxylated product (number of moles of ethylene oxide added: 4), an ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 4), an ethoxylated product of 2,5,8,11-tetramethyl-6-dodecyne-5,8-diol (number of moles of ethylene oxide added: 6), an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 10), an ethoxylated product of 2,4,7,9-tetramethyl-5-decyne-4,7-diol (number of moles of ethylene oxide added: 30), and an ethoxylated product of 3,6-dimethyl-4-octyne-3,6-diol (number of moles of ethylene oxide added: 20). One type of antifoaming agent may be used alone, or two or more types may be used in combination.

[0152] The acetylene-based surfactant can be obtained as a commercially available product, and examples of such commercially available products include Olfine SPC (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 80 parts by mass, pale yellow liquid), Olfine AF-103 (manufactured by Nissin Chemical Industry Co., Ltd., pale brown liquid), Olfine AF-104 (manufactured by Nissin Chemical Industry Co., Ltd., pale brown liquid), Olfine SK-14 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine AK-02 (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine AF-201F (manufactured by Nissin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfine D-10PG (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50 parts by mass, pale yellow liquid), and Olfine E- Examples of such active ingredients include 1004 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1010 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1020 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow liquid), Olfine E-1030W (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 75 parts by mass, pale yellow liquid), Surfynol 420 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow viscous material), Surfynol 440 (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 100 parts by mass, pale yellow viscous material), and Surfynol 104E (manufactured by Nissin Chemical Industry Co., Ltd., active ingredient 50 parts by mass, pale yellow viscous material).

[0153] As the surfactant additive, polyether surfactants and / or silicone surfactants can be used in place of or in addition to acetylene surfactants. Representative examples of polyether surfactants include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polyoxyethylene oleyl ether, polyoxyethylene stearyl ether, polyoxyethylene lauryl ether, polyoxyethylene dodecyl ether, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, and polyoxyethylene-polyoxypropylene block copolymers. Among these, polyethylene glycol is particularly preferred. These surfactants may be used alone or in combination.

[0154] Polyether surfactants are also available as commercially available products, and examples of such commercially available products include E-D052, E-D054, and E-F010 (manufactured by San Nopco Ltd.).

[0155] The silicone surfactant may be linear, branched, or cyclic, as long as it contains at least a silicone chain, and may contain either a hydrophobic group or a hydrophilic group. Specific examples of the hydrophobic group include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl; cyclic alkyl groups such as cyclohexyl; and aromatic hydrocarbon groups such as phenyl. Specific examples of the hydrophilic group include amino, thiol, hydroxyl, alkoxy, carboxylic acid, sulfonic acid, phosphoric acid, nitric acid, and their organic or inorganic salts, ester, aldehyde, glycerol, and heterocyclic groups. Representative examples of silicone surfactants include dimethyl silicone, methylphenyl silicone, chlorophenyl silicone, alkyl-modified silicone, fluorine-modified silicone, amino-modified silicone, alcohol-modified silicone, phenol-modified silicone, carboxy-modified silicone, epoxy-modified silicone, fatty acid ester-modified silicone, and polyether-modified silicone.

[0156] Silicone surfactants can be obtained as commercially available products, and examples of such commercially available products include BYK-300, BYK-301, BYK-302, BYK-306, BYK-307, BYK-310, BYK-313, BYK-320, BYK-333, BYK-341, BYK-345, BYK-346, BYK-347, BYK-348, and BYK-349 (all trade names, manufactured by BYK-Chemie Japan Co., Ltd.), KM-80, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, and KF-640. , KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.), SH-28PA, SH8400, SH-190, SF-8428 (all trade names, manufactured by Dow Corning Toray Co., Ltd.), Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (all trade names, manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, and Silface SAG0085 (all trade names, manufactured by Nissin Chemical Industry Co., Ltd.).

[0157] (amount of coating layer) The amount of the coating layer relative to the substrate, i.e., the amount of the coating layer per unit area of ​​one surface of the substrate, is preferably 0.5 g / m by weight. 2 More preferably, 1.0 g / m 2 The volume is preferably 0.15 cm or more. 3 / m 2 More than 0.30cm, preferably 3 / m 2 The upper limit of the amount of the coating layer is preferably 10.0 g / m 2 Less than 7.0 g / m 2 The volume is preferably 3.50 cm or less. 3 / m 2 Less than or equal to 2.50 cm, preferably 3 / m 2The amount of the coating layer is preferably equal to or greater than the above lower limit in terms of improving the adhesive strength between the coating layer and the electrode and suppressing thermal shrinkage, and the amount of the coating layer is preferably equal to or less than the above upper limit in terms of suppressing a decrease in ion permeability.

[0158] (Coating layer thickness) The thickness of one of the coating layers disposed on at least one of the substrates (the thickness of the inorganic filler portion of the coating layer) is preferably 0.3 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 2.5 μm or less, and even more preferably 0.7 μm or more and 1.3 μm or less. A coating layer thickness of 0.3 μm or more can further suppress the thermal shrinkage rate and facilitate uniform adhesion between the electrode and the substrate, thereby improving the characteristics of the electricity storage device. A coating layer thickness of 1.3 μm or less is preferable in that it can suppress a decrease in ion permeability and enable the production of a thin-film electricity storage device separator. In other words, reducing the thickness of the separator allows the production of an electricity storage device with a large capacity per volume. On the other hand, from the viewpoint of preventing the particulate polymer from slipping off the coating layer, the thickness is preferably 1.6 μm or more or 2.1 μm or more. The thickness of the coating layer can be adjusted, for example, by changing the type or concentration of the particulate polymer in the coating liquid applied to the substrate, the amount of the coating liquid applied, the coating method, the coating conditions, etc. However, the method for adjusting the thickness of the coating layer is not limited to these.

[0159] Fig. 1 is a schematic diagram of the surface of the coating layer of the separator for an electricity storage device of this embodiment. As shown in Fig. 1, inorganic filler (1) and particulate polymer (2) of a thermoplastic polymer protruding from the coating layer are present on the surface of the coating layer (10). In Fig. 1, the particulate polymer exists in the form of primary particles without agglomerating with other particulate polymers.

[0160] Fig. 2 is a cross-sectional view taken along the line AA of the separator for a power storage device shown in Fig. 1. As shown schematically in Fig. 2, the coating layer (20) is formed in a sloping shape, so that it continuously becomes thicker from an inorganic filler portion 1.5D or more away from the volume center of each particulate polymer in the horizontal direction (the surface direction of the coating layer) toward the protruding particulate polymer (2). The slope of the sloping coating layer becomes gentler the farther away from the protruding particulate polymer and becomes steeper the closer to the protruding particulate polymer. The inorganic filler (1) covers a part of the periphery of the protruding portion so as to ride along the contour of the particulate polymer, and the center of the protruding portion is exposed on the surface of the coating layer.

[0161] <<Method for manufacturing separator for electricity storage device>> <Method for manufacturing substrate> (Method for producing a polyolefin microporous membrane) The method for producing substrate is not particularly limited, and can adopt known production method, for example, can adopt any of wet porosity method or dry porosity method.Example of wet porosity method includes, for example, when substrate is polyolefin microporous film, melt-knead polyolefin resin composition and plasticizer, form into sheet, and then optionally stretch, and then extract plasticizer to make porous; melt-knead polyolefin resin composition that mainly comprises polyolefin resin, extrude at high draw ratio, and then heat-treat and stretch to peel polyolefin crystal interface to make porous; melt-knead polyolefin resin composition and inorganic filler, form into sheet, and then stretch to peel polyolefin and inorganic filler interface to make porous; and dissolve polyolefin resin composition, then immerse in poor solvent for polyolefin, solidify polyolefin and simultaneously remove solvent to make porous.

[0162] The method for producing the polyolefin microporous membrane according to the present disclosure is not particularly limited, but an example includes a method including the following steps: (A) extruding a polyolefin composition comprising a polyolefin resin and a pore-forming material to form a gel-like sheet; (B) biaxially stretching the gel-like sheet to form a stretched sheet; (C) extracting the pore-forming material from the stretched sheet to form a porous membrane; and (D) A step of heat-setting the porous membrane. The manufacturing process and preferred embodiments of the microporous polyolefin membrane are described below.

[0163] Extrusion process (A): In step (A), a polyolefin composition is extruded to form a gel-like sheet. The polyolefin composition may contain a polyolefin resin, a pore-forming agent, etc. The resin contained in the polyolefin composition is preferably composed solely of polyolefin, without containing non-resin components such as fine particles or highly heat-resistant resins with significantly different melting points, from the viewpoints of uniforming the stretching stress and improving the air permeability and air permeability distribution of the resulting film. The gel-like sheet can be obtained by melt-kneading a polyolefin resin and a pore-forming agent and molding the mixture into a sheet.

[0164] First, the polyolefin resin and the pore-forming material are melt-kneaded. Examples of the melt-kneading method include a method in which the polyolefin resin and, if necessary, other additives are charged into a resin kneading device such as an extruder, kneader, Labo Plastomill, kneading roll, or Banbury mixer, and the pore-forming material is introduced at an arbitrary ratio while the resin components are heated and melted, and then kneaded.

[0165] The polyolefin resin contained in the polyolefin composition can be determined depending on the desired resin raw material of the resulting polyolefin microporous membrane. Specifically, the polyolefin resin used in the extrusion step (A) may be the polyolefin resin described as a component of the polyolefin microporous membrane.

[0166] The content of the plasticizer in the resin composition is preferably 66% by mass to 90% by mass, more preferably 68% by mass to 88% by mass, and even more preferably 70% by mass to 80% by mass. By adjusting the plasticizer content to 66% by mass or more, the melt viscosity of the resin composition decreases, melt fracture is suppressed, and film formability during extrusion tends to improve. On the other hand, adjusting the plasticizer content to 90% by mass or less can sometimes suppress elongation of the raw fabric during the film formation process.

[0167] The proportion of the polymer component of the resin composition (hereinafter also referred to simply as "PC") is preferably 20% by mass to 40% by mass, more preferably 22% by mass to 37% by mass, and even more preferably 24% by mass to 33% by mass, based on the total mass of the resin composition, from the viewpoint of uniformly dispersing a high molecular weight resin to uniformly apply elongation stress and improving the ion permeability and air permeability distribution of the resulting membrane.

[0168] For at least one of the high-molecular-weight raw materials contained in the polyolefin composition, the lower limit of Mv is preferably 700,000 or more, and the upper limit may be, for example, 2,000,000 or less, from the viewpoint of adjusting the molecular weight, MI, pin puncture strength, pin puncture strength converted into basis weight, difference R between the maximum and minimum air permeabilities at TD3 points, air permeability and porosity before compression, and heat shrinkage rate of the resulting microporous membrane within the numerical ranges described above. From the same viewpoint, the proportion of high-molecular-weight raw materials with Mv of 700,000 or more in the resin contained in the polyolefin composition is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and may be 100% by mass.

[0169] When the polyolefin composition contains polyethylene as a main component, from the viewpoint of adjusting the post-compression porosity, crystalline long period, or crystallite size of the resulting microporous membrane within the above-described numerical ranges, the lower limit of the Mv of the polyethylene is preferably 600,000 or more, more preferably 700,000 or more, and the upper limit may be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resins constituting the polyolefin composition is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and may be 100% by mass.

[0170] When the polyolefin composition contains polyethylene as the main component, from the viewpoint of adjusting the molecular weight, MI, pin puncture strength, pin puncture strength converted into basis weight, difference R between maximum and minimum air permeabilities at TD3 points, air permeability and porosity before compression, and heat shrinkage of the resulting microporous membrane within the above-described numerical ranges, the Mv of the polyethylene for at least one of the raw materials is preferably 700,000 or more, and the upper limit may be, for example, 2,000,000 or less. From the same viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resins constituting the polyolefin composition is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and may be 100% by mass.

[0171] From the viewpoint of the heat resistance of the resulting microporous film, polypropylene may be mixed into the polyolefin composition. In this case, from the viewpoint of film strength and compression resistance, the proportion of polypropylene relative to the total mass of polyolefin resins in the polyolefin composition is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 15% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less. Furthermore, from the viewpoint of improving moldability, the proportion of polypropylene relative to the total mass of polyolefin resins in the polyolefin composition is preferably 3% by mass or more and 10% by mass or less, more preferably 5% by mass or more and 9% by mass or less.

[0172] Examples of the pore-forming material include plasticizers, inorganic materials, and combinations thereof. The plasticizer is not particularly limited, but it is preferable to use a non-volatile solvent that can form a homogeneous solution at or above the melting point of the polyolefin. Specific examples of non-volatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. After extraction, these plasticizers may be recovered by distillation or other procedures and reused.

[0173] Among plasticizers, liquid paraffin is preferred because, when the polyolefin resin is polyethylene or polypropylene, it has high compatibility with these, and even when the molten kneaded product is stretched, interfacial peeling between the resin and the plasticizer is unlikely to occur, making it easier to perform uniform stretching.

[0174] The inorganic material is not particularly limited and includes, for example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone or in combination of two or more. Among these, silica is particularly preferred because of its ease of extraction.

[0175] From the viewpoint of obtaining good isolation between the polyolefin resin composition and the inorganic material, the mass of the inorganic material relative to the total mass of these is preferably 3 mass% or more, more preferably 10 mass% or more, and from the viewpoint of ensuring high strength, it is preferably 60 mass% or less, more preferably 50 mass% or less.

[0176] The melt-kneaded product is then formed into a sheet to obtain a gel-like sheet. When melt-kneading is performed using an extruder, the ratio of the extrusion rate of the polyolefin composition, i.e., the extruder output Q (kg / h) to the extruder screw rotation speed N (rpm) (Q / N, unit: kg / (h·rpm)) is preferably 0.1 or more and 7.0 or less, more preferably 0.5 or more and 6.0 or less, and even more preferably 1.0 or more and 5.0 or less. When melt-kneading is performed under conditions of Q / N of 0.1 or more and less than 7.0, the liquid paraffin that has phase-separated from the resin becomes more easily dispersed, resulting in a denser pore structure and tending to increase strength.

[0177] Examples of methods for producing a sheet-like molded product include extruding a molten mixture into a sheet through a T-die or the like, contacting it with a thermal conductor, and solidifying it by cooling it to a temperature sufficiently lower than the crystallization temperature of the resin component. Thermal conductors used for cooling and solidifying include metal, water, air, and plasticizers. Among these, metal rolls are preferred because of their high thermal conductivity. It is more preferable to sandwich the extruded gel-like sheet between the metal rolls when bringing it into contact with them, as this further increases the thermal conductivity, orients the sheet, increasing its film strength and tending to improve the surface smoothness of the sheet.

[0178] By controlling the cast clearance when the molten mixture is extruded into a sheet from a T-die, the average thickness of the resulting microporous membrane before compression can be adjusted within the numerical range described above. From this viewpoint, for example, in the case of a casting roll, the distance between the rolls is preferably 200 μm or more and 3,000 μm or less, more preferably 500 μm or more and 2,500 μm or less. When the distance between the rolls of the casting roll is 200 μm or more, the risk of membrane breakage in the subsequent stretching step can be reduced, and when the distance between the rolls is 3,000 μm or less, the cooling rate is high and cooling unevenness can be prevented. Furthermore, from the viewpoint of obtaining a thin film and achieving the stretch ratio necessary to enhance planar orientation and crystallinity and improve compressibility, the cast thickness is preferably 500 μm to 2,200 μm, more preferably 700 μm to 2,000 μm.

[0179] The extruded sheet-like molded product or gel-like sheet may be rolled. Rolling can be carried out, for example, by a method using a roll or the like. Rolling can increase the orientation, particularly in the surface layer portion. The rolling area ratio is preferably more than 1 to 3 times, more preferably more than 1 to 2 times. If the rolling ratio exceeds 1, the surface orientation increases, and the membrane strength of the finally obtained porous membrane tends to increase. If the rolling ratio is 3 times or less, the difference in orientation between the surface layer portion and the central interior is small, and a uniform porous structure tends to be formed in the thickness direction of the membrane.

[0180] Biaxial stretching process (B): In step (B), the gel-like sheet obtained in step (A) is stretched. Step (B) is performed before step (C), in which the pore-forming material is extracted from the sheet. In step (B), the gel-like sheet is stretched at least once in the longitudinal direction and once in the transverse direction (i.e., by biaxial stretching) to control the bending rigidity of the polyolefin microporous membrane.

[0181] Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Among these, simultaneous biaxial stretching is preferred from the viewpoints of improving film strength and uniformity of stretching, as well as the fact that the backbone structure is likely to become isotropic in-plane and stress is isotropically dispersed during a nail penetration test, thereby improving nail penetration test safety. Simultaneous biaxial stretching refers to a stretching method in which MD stretching and TD stretching are performed simultaneously, and the stretching ratios in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD and TD stretching are performed independently, and while stretching is performed in MD or TD, the other direction is left unconstrained or fixed at a fixed length.

[0182] In step (B), from the viewpoint of adjusting the post-compression porosity, crystal long period, or crystallite size of the resulting microporous membrane within the above-described numerical ranges, it is preferable to preheat the gel-like sheet in the stretching furnace immediately before stretching, and more preferably to increase the preheating coefficient. The preheating coefficient is a value obtained by multiplying the preheating temperature by the preheating air velocity and the preheating time, and is preferably 130,000°C·m to 300,000°C·m, more preferably 150,000°C·m to 300,000°C·m, and even more preferably 180,000°C·m to 300,000°C·m. When the preheating furnace is divided into multiple chambers with different air velocities, the total air velocity of the preheating furnace is calculated as the sum of the air velocity of each chamber multiplied by the furnace length of each chamber divided by the total furnace length.

[0183] In the MD stretching of step (B), it is preferable to adjust the MD stretch ratio from the viewpoints of adjusting the post-compression porosity, crystal long period, or crystallite size of the resulting microporous membrane within the numerical ranges described above, of highly orienting the polyethylene as the main component to form a highly rigid backbone, and of improving compressibility by increasing crystallinity in addition to increasing the membrane strength through stretch orientation. The MD stretch ratio is preferably 5 times or more, more preferably 5 to 10 times, even more preferably 5 to 9 times, still more preferably 6 to 10 times, and particularly preferably 6 to 8 times. The MD stretch ratio can be adjusted depending on, for example, the MD stretching temperature, MD stretching wind speed, MD stretching time, and MD stretch coefficient.

[0184] From the same viewpoint as above, and from the viewpoint of uniformly applying stress even to high molecular weight resins to obtain membranes with good permeability and air permeability distribution, the lower limit of the MD stretching temperature is preferably 122.0°C or higher, more preferably 123.0°C or higher, even more preferably 124.0°C or higher, even more preferably 125.0°C or higher, particularly preferably 126.0°C or higher, and most preferably 127.0°C or higher. The upper limit of the MD stretching temperature is preferably 145.0°C or lower, more preferably 140.0°C or lower, and even more preferably 131.0°C or lower. It is presumed that an MD stretching temperature of from the melting point of the main component minus 12°C to the melting point applies appropriate stress to the membrane, which is preferable for stretch molding. The MD stretching temperature is more preferably from the melting point of the main component minus 10°C to the melting point, and even more preferably from the melting point of the main component minus 8°C to the melting point. The MD stretching temperature can be adjusted according to, for example, the MD stretching ratio, the MD stretching wind speed, the MD stretching time, the MD stretching coefficient, and the like.

[0185] In the TD stretching of step (B), it is preferable to adjust the TD stretch ratio from the viewpoints of adjusting the post-compression porosity, crystal long period, or crystallite size of the resulting microporous membrane within the above-described numerical ranges, of highly orienting the polyethylene as the main component to form a highly rigid backbone, and of improving compressibility by increasing crystallinity in addition to increasing the membrane strength through stretch orientation. The TD stretch ratio is preferably 5 times or more, more preferably 5 times to 10 times, even more preferably 5 times to 9 times, still more preferably 6 times to 10 times, and particularly preferably 6 times to 8 times. The TD stretch ratio can be adjusted, for example, depending on the TD stretching temperature, TD stretching wind speed, TD stretching time, and TD stretch coefficient.

[0186] Even if the polyolefin composition used in step (A) has a high molecular weight, it is preferable to adjust the TD stretching temperature in step (B) to facilitate uniform TD stretching in step (B) and improve the cycle characteristics of the resulting nonaqueous secondary battery equipped with the microporous membrane. Furthermore, it is preferable to uniformly apply stress to even high-molecular-weight resins, thereby improving the permeability and air permeability distribution of the resulting membrane. The lower limit of the TD stretching temperature is preferably 122.0°C or higher, more preferably 123.0°C or higher, even more preferably 124.0°C or higher, even more preferably 125.0°C or higher, particularly preferably 126.0°C or higher, and particularly preferably 127.0°C or higher. The upper limit is preferably 145.0°C or lower, more preferably 140.0°C or lower, and even more preferably 131.0°C or lower. The TD stretching temperature can be adjusted depending on, for example, the TD stretch ratio, TD stretching wind speed, TD stretching time, and TD stretch coefficient.

[0187] In step (B), the ratio of the preheating coefficient to the stretching coefficient (preheating coefficient / stretching coefficient) is preferably adjusted to 5.7 or more and 7.0 or less, more preferably 5.8 or more and 7.0 or less, to adjust the post-compression porosity, crystalline long period, or crystallite size of the resulting microporous membrane within the above-described numerical ranges. When this ratio is adjusted to 5.7 or more, the sheet is more easily stretched by applying more heat during preheating immediately before stretching, which tends to result in a more uniform structure and improve the cycle characteristics of the nonaqueous secondary battery comprising the final microporous membrane. When this ratio is adjusted to 7.0 or more, uneven stretching tends to occur, resulting in a nonuniform membrane structure and tending to deteriorate the cycle characteristics of the nonaqueous secondary battery comprising the final microporous membrane. The stretching coefficient is a value obtained by multiplying the stretching temperature by the stretching air speed and the residence time of the membrane during the stretching process, and is preferably 20,000°C·m to 50,000°C·m, and more preferably 30,000°C·m to 50,000°C·m. When the stretching furnace is divided into multiple chambers with different air speeds, the air speed of the entire furnace is calculated as the sum of the air speed of each chamber multiplied by the furnace length of each chamber divided by the total furnace length of the entire furnace. The residence time in the stretching furnace is calculated as the total furnace length divided by the average speed of the entire furnace.

[0188] In step (B), the biaxial stretching ratio is preferably adjusted to adjust the pin puncture strength, the pin puncture strength converted into basis weight, the difference R between the maximum and minimum air permeabilities at three TD points, the air permeability and porosity before compression, the heat shrinkage, the tensile break strength, and the MD / TD tensile break strength ratio of the resulting microporous membrane within the above-described numerical ranges. The biaxial stretching ratio is preferably 5x5 or more, more preferably 5x5 to 10x10, and even more preferably 6x6 to 10x10. From the same viewpoint, the biaxial stretching ratio is preferably a simultaneous biaxial stretching ratio.

[0189] In step (B), the biaxial stretching temperature is preferably adjusted to adjust the pin puncture strength and basis weight-equivalent pin puncture strength, the difference R between the maximum and minimum air permeabilities at three TD points, the air permeability and porosity before compression, the heat shrinkage, the tensile break strength, and the MD / TD tensile break strength ratio of the resulting microporous membrane within the above-described numerical ranges. The biaxial stretching temperature is preferably 122°C or higher and 147°C or lower, more preferably 123°C or higher and 146°C or lower, even more preferably 124°C or higher and 145°C or lower, and still more preferably 127°C or higher and 140°C or lower.

[0190] The PC of the gel-like sheet subjected to step (B) is preferably 22% to 30%, more preferably 25% to 32%, from the viewpoint of increasing the amount of heat applied per unit resin, uniforming the stretching stress, and increasing the distribution of permeability of the resulting membrane.

[0191] In step (B), it is preferable to adjust the heat coefficient per unit resin from the viewpoint of adjusting the pin puncture strength, the pin puncture strength converted into basis weight, the difference R between the maximum and minimum air permeabilities at TD3 points, the air permeability and porosity before compression, and the thermal shrinkage rate of the resulting microporous membrane within the above-described numerical ranges. The heat coefficient per unit resin is calculated using the following formula (I): Heating coefficient per unit resin = (biaxial stretching temperature - 115°C) ÷ PC (I) and is preferably 0.26°C / % or more. From the viewpoint of increasing the amount of heat applied per unit resin, uniforming the stretching stress, and increasing the distribution of permeability in the resulting membrane, this value is more preferably 0.26°C / % or more and 1.2°C / % or less, even more preferably 0.34°C / % or more and 1.0°C / % or less, even more preferably 0.37°C / % or more and 0.98°C / % or less, and particularly preferably 0.40°C / % or more and 0.95°C / % or less. However, in the case of a dry method in which membrane production and porosity are carried out in the absence of liquid, a larger amount of heat is required to uniform the stretching stress because the membrane is not plasticized, and this is therefore excluded from the value calculated by the above formula.

[0192] Extraction process (C): In step (C), the pore-forming material is removed from the sheet-like formed body to obtain a porous membrane. For example, a method for removing the pore-forming material may be used, such as immersing the sheet-like formed body in an extraction solvent to extract the pore-forming material and then thoroughly drying the sheet-like formed body. The pore-forming material may be extracted by either a batch method or a continuous method. To prevent the porous membrane from shrinking, it is preferable to restrain the edges of the sheet-like formed body during the immersion and drying process. The amount of pore-forming material remaining in the porous membrane is preferably less than 1% by mass relative to the total mass of the porous membrane.

[0193] The extraction solvent used to extract the pore-forming material is preferably a poor solvent for the polyolefin resin, a good solvent for the pore-forming material, and has a boiling point lower than the melting point of the polyolefin resin. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation. When an inorganic material is used as the pore-forming material, an aqueous solution of sodium hydroxide, potassium hydroxide, or the like can be used as the extraction solvent.

[0194] Heat setting process (D): In the heat setting step (D), the microporous membrane is heat-treated for heat setting (HS) after the plasticizer extraction in step (C) to suppress shrinkage of the polyolefin microporous membrane. Examples of heat treatments for the porous membrane include stretching at a predetermined temperature and a predetermined stretch ratio to adjust physical properties, and / or relaxation at a predetermined temperature and a predetermined relaxation rate to reduce stretching stress. The relaxation operation refers to a membrane shrinkage operation after the stretching operation. These heat treatments can be carried out using a tenter or roll stretching machine. Heat setting, including stretching and relaxation operations after plasticizer extraction, is preferably carried out in TD.

[0195] In step (D), from the viewpoint of adjusting the post-compression porosity, crystal long period, or crystallite size of the resulting microporous membrane to fall within the above-described numerical ranges, it is preferable to preheat the microporous membrane immediately before stretching. Preheating in step (D) can be controlled, for example, by the preheating temperature.

[0196] The TD stretching temperature in the TD stretching operation in step (D) is preferably 130° C. or higher and 150° C. or lower, more preferably 132° C. or higher and 145° C. or lower, and even more preferably 133° C. or higher and 140° C. or lower, thereby reducing the TD heat shrinkage of the resulting film at a temperature of 120° C. and improving the safety of the nonaqueous secondary battery in a nail penetration test.

[0197] The TD stretching ratio in the TD stretching operation in step (D) is preferably 1.1 or more, more preferably 1.4 or more, and even more preferably 1.5 or more. The TD stretching ratio in step (D) is preferably 3 or less, more preferably 2.5 or less. By adjusting the TD stretching ratio in step (D) within the above numerical range, the stretch orientation increases the strength of the membrane, and the porosity can be controlled to optimize the balance between compressibility and permeability. In addition, stress inside the membrane is alleviated to suppress thermal shrinkage; specifically, the TD thermal shrinkage at a temperature of 120°C is reduced, thereby improving safety in a nail penetration test.

[0198] The heat setting ratio in step (D), i.e., the post-relaxation ratio, can be adjusted to crystallize polyethylene, the main component of the microporous membrane, to form a rigid backbone, and to adjust the average membrane thickness before compression, pin puncture strength and basis weight equivalent pin puncture strength, the difference R between the maximum and minimum air permeabilities at three TD points, the air permeability before compression and porosity, heat shrinkage, and the tensile strength at break and MD / TD tensile strength at break ratio of the resulting microporous membrane within the above-described numerical ranges. The post-relaxation ratio in step (D) is preferably 1.4 times or more, more preferably 1.5 times or more, and even more preferably 1.5 times or more and 3 times or less. This increases the membrane strength through stretch orientation, controls porosity, and optimizes the balance between compressibility and permeability. Additionally, it relieves internal stress in the membrane, reduces TD heat shrinkage at 120°C, and improves safety in a nail penetration test for nonaqueous secondary batteries.

[0199] The heat setting temperature, i.e., the relaxation temperature, in step (D) can be adjusted to adjust the average thickness of the resulting microporous membrane before compression within the above-described range, reduce the TD heat shrinkage of the resulting microporous membrane at 120°C, and improve the safety of nonaqueous secondary batteries in a nail penetration test. The relaxation temperature in step (D) is preferably 130°C or higher and 150°C or lower, more preferably 132°C or higher and 145°C or lower, even more preferably 133°C or higher and 140°C or lower, and still more preferably 135°C or higher and 140°C or lower.

[0200] A polyolefin microporous membrane can be obtained by the production method including steps (A) to (D). The total stretching ratio of the finally obtained polyolefin microporous membrane is preferably 60 times or more, more preferably 61 times to 81 times, in order to crystallize polyethylene, which is the main component of the microporous membrane, and form a rigid backbone.

[0201] Throughout steps (A) to (D), the PC content of the resin composition, gel-like sheet, or porous membrane is preferably 22% by mass to 30% by mass, more preferably 25% by mass to 32% by mass, from the viewpoint of increasing the amount of heat applied per unit resin, uniforming the stretching stress, and increasing the distribution of permeability in the finally obtained membrane.

[0202] <Method of Arranging the Coating Layer> A coating layer is formed on at least one surface of the substrate produced as described above. The method for forming the coating layer is not particularly limited, and examples thereof include a method in which a coating liquid containing an inorganic filler and a particulate polymer is applied to the substrate, and the medium is then removed.

[0203] As the coating liquid, a dispersion in which an inorganic filler and a particulate polymer are dispersed in a solvent or dispersion medium (hereinafter simply referred to as "medium") that does not dissolve the particulate polymer can be used. Preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as it is as the coating liquid.

[0204] The medium for the coating liquid is preferably one that can uniformly and stably disperse or dissolve the inorganic filler, the particulate polymer, and optionally the water-soluble polymer. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, and hexane. The medium for the coating liquid is preferably water or a mixed medium consisting of water and a water-soluble organic medium. Examples of the water-soluble organic medium include, but are not limited to, ethanol and methanol. Among these, water is more preferred. When the coating liquid is applied to a substrate, if the coating liquid penetrates into the substrate, the particulate polymer containing the polymer will clog the surface and interior of the pores in the substrate, easily reducing permeability. In this regard, an aqueous dispersion using water as the medium for the coating liquid is preferred because the coating liquid is less likely to penetrate into the substrate and the particulate polymer containing the polymer will be more likely to be present mainly on the outer surface of the substrate, thereby more effectively suppressing the reduction in permeability.

[0205] The coating liquid may contain any additives, such as dispersants such as surfactants, thickeners, wetting agents, antifoaming agents, and pH adjusters including acids and alkalis.

[0206] Examples of methods for dispersing or dissolving the inorganic filler, the particulate polymer, and, if necessary, the water-soluble polymer in the medium of the coating liquid include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade or the like.

[0207] The procedure for preparing the coating solution is preferably to first add the water-soluble polymer to the coating solution in which the inorganic filler is dispersed, and then add the resin binder and the particulate polymer. By preparing the coating solution in this order, the water-soluble polymer adsorbs and protects the metal ions contained in the inorganic filler, and aggregation of the resin binder and the particulate polymer can be prevented.

[0208] From the viewpoint of adjusting the gradient rate of the coating layer and the contact rate between the particulate polymer and the substrate surface, the viscosity of the coating solution is preferably 20 mPa·s or more and 80 mPa·s or less, more preferably 60 mPa·s or less, and even more preferably 40 mPa·s or less. A coating solution viscosity of 20 mPa·s or more and 80 mPa·s or less is preferable from the viewpoint of accelerating the settling of the particulate polymer and increasing the gradient rate of the coating layer and the contact rate between the particulate polymer and the substrate surface during the process of removing the solvent from the coating film after coating to form a coating layer. Methods for controlling the viscosity of the coating solution include adjusting the aspect ratio of the inorganic filler, the coefficient of variation of the inorganic filler particle size distribution, and the type of thickener. Using these methods, the viscosity of the coating solution can be reduced during the process of immobilizing the coating solution (forming a coating layer by drying) and the meniscus of the coating solution on the particulate polymer can be improved (wettability can be improved), resulting in an improved gradient rate of the coating layer and increased adhesion to the electrode.

[0209] The substrate may be surface-treated before coating. Surface treatment is preferred because it makes it easier to apply the coating liquid, improves adhesion between the substrate and the thermoplastic polymer, and makes it easier to control the 180° peel strength to 200 gf / cm or more. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation. An example of a surface treatment is corona discharge treatment.

[0210] The method for applying the coating liquid onto the substrate is not particularly limited as long as it can achieve the desired coating pattern, coating film thickness, and coating area. Examples of the coating method include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, and inkjet coating method. Among these, gravure coater method or spray coating method is preferred from the viewpoints of high degree of freedom in the coating shape of the particulate polymer and easy achievement of a preferred area ratio.

[0211] The coating method is preferably a gravure coater method or the like, and the shear rate is preferably 40,000 sec -1 Over 120,000sec -1 When the shear rate is within this range, the particulate polymer is well dispersed as primary particles, and it is easier to control the 180° peel strength to 200 gf / cm or more.

[0212] The method for removing the medium from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate and the coating layer. Examples include a method of drying the substrate at a temperature below its melting point while fixing it, a method of drying it under reduced pressure at a low temperature, and a method of immersing the substrate in a medium that is a poor solvent for the particulate polymer to solidify the particulate polymer into particles and simultaneously extracting the medium.

[0213] <Preparation of Separator Wound Body> The obtained separator for an electricity storage device is preferably wound into a wound body. By forming the separator into a wound body, it can be easily unwound at high speed, thereby increasing productivity in the production process of electricity storage devices.

[0214] <Energy storage device> The electricity storage device of this embodiment includes the electricity storage device separator of this embodiment. The electricity storage device is not particularly limited, but examples include batteries such as non-aqueous electrolyte secondary batteries, condensers, and capacitors. Among these, to take advantage of the advantages of the electricity storage device separator of this embodiment, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred. A lithium ion secondary battery has a positive electrode, a negative electrode, the electricity storage device separator of this embodiment disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. By including the electricity storage device separator of this embodiment, the electricity storage device of this embodiment has excellent properties such as electricity storage performance, and in the case of a lithium ion secondary battery, excellent battery properties.

[0215] When the power storage device of this embodiment is a lithium-ion secondary battery, the positive electrode, negative electrode, and non-aqueous electrolyte are not limited, and known materials can be used. A positive electrode having a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. In addition to the positive electrode active material, the positive electrode active material layer may also contain a binder, a conductive material, and the like, as appropriate.

[0216] The negative electrode may preferably have a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and composite carbon; silicon, tin, metallic lithium, and various alloy materials.

[0217] The non-aqueous electrolyte is not particularly limited, but may be an electrolyte solution prepared by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0218] <Method for manufacturing an electricity storage device> The method for producing an electricity storage device using the separator of this embodiment is not particularly limited. For example, the following method can be exemplified. First, the separator of this embodiment is produced by the method described above. The size and shape of the separator may be, for example, a vertically elongated shape with a width of 10 to 500 mm, preferably 80 to 500 mm, and a length of 200 to 10,000 m, preferably 1,000 to 6,000 m. Next, positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are stacked in this order and wound into a circular or flat spiral to obtain a wound body. The wound body is placed in a device can (e.g., a battery can) and then an electrolyte solution is poured into the device. Alternatively, the device may be produced by folding the electrodes and separator to form a wound body, placing the wound body in a device container (e.g., an aluminum film), and pouring the electrolyte solution into the device container.

[0219] At this time, the wound body can be pressed. Specifically, a method can be exemplified in which a separator, a current collector, and an electrode having an active material layer formed on at least one surface of the current collector are stacked so that the coating layer and the active material layer face each other, and then pressed.

[0220] The pressing temperature is set to T 1.00 It is preferable to carry out the reaction at a temperature of T 1.00T is the temperature at which the minimum DDSC value is reached between 0°C and 150°C, when the DDSC is the value obtained by differentiating the heat flow difference per unit time measured by DSC (differential scanning calorimetry) with respect to temperature. 1.00 Pressing at a temperature above this level allows the coating layer to deform sufficiently, resulting in good adhesive strength. For example, a temperature of 35°C or higher is preferred. To prevent clogging of pores or thermal shrinkage in the separator due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the substrate, more preferably 130°C or lower. To prevent clogging of pores in the separator, the pressing pressure is preferably 20 MPa or lower. The pressing time may be 1 second or less when using a roll press, or several hours when using a surface press, and is preferably 2 hours or less from the viewpoint of productivity. Using the separator for an electricity storage device of this embodiment and undergoing the above-described manufacturing process can prevent press-back during press molding of a wound body consisting of electrodes and a separator. This can prevent a decrease in yield in the device assembly process and shorten the production process time.

[0221] Adhesion may be imparted to the wound body without pressing. Specifically, an example of such a method is to house the wound body in a device can, inject an electrolyte solution, and impart adhesion between the coating layer of the separator and the opposing electrode by pressure generated in the device can when manufacturing an electricity storage device, or by pressure accompanying expansion and contraction of the electrodes due to charging and discharging of the electricity storage device.

[0222] The electricity storage device, particularly the lithium ion secondary battery, manufactured as described above has excellent battery characteristics (rate characteristics) and durability against long-term continuous operation (cycle characteristics) because it is equipped with the separator of the present embodiment, which has high adhesion to the electrodes and a small thermal shrinkage rate. [Example]

[0223] Hereinafter, embodiments of the present disclosure will be specifically described with reference to examples and comparative examples, but the present disclosure is not limited to these examples and comparative examples.

[0224] <<Measurement and Evaluation Methods>> <Thickness of Coating Layer and Amount of Protrusion of Particulate Polymer> The separator was freeze-fractured, and its cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an acceleration voltage of 1.0 kV and 30,000x magnification. In the SEM image, the distance from the substrate-coating layer boundary to the outer surface of the inorganic filler portion of the coating layer was measured as the thickness of the coating layer (μm). The "inorganic filler portion" refers to a portion that is 1.5D or more away from each protruding particulate polymer, where D is the diameter of each protruding particulate polymer. The "diameter of each protruding particulate polymer" was measured as the equivalent circle diameter. The thickness of the coating layer was measured at 20 points and the average value was calculated. The maximum distance (μm) from the substrate-coating layer boundary to the contour of the particulate polymer in the coating layer where the particulate polymer protruded was measured. The maximum distance to the contour of the particulate polymer was measured at 20 points, and the average value was calculated. The protrusion amount (μm) of the particulate polymer was calculated by subtracting the thickness of the inorganic filler portion of the coating layer from the maximum distance to the contour of the particulate polymer, and the ratio of the protrusion amount of the particulate polymer to the thickness of the inorganic filler portion of the coating layer was calculated.

[0225] <180° peel strength> A 2mm x 7mm separator was cut out and attached to a glass plate with double-sided tape on the side opposite the coating layer to be measured. Tape (product name: Mending Tape MP-12, manufactured by 3M) was then attached to the coating layer. 5mm of the tape tip was peeled off, and the tip of the tape was clamped in a chuck using a tensile tester (model AG-IS, SLBL-1kN, manufactured by Shimadzu Corporation) so that the tape was peeled off at an angle of 180° relative to the surface of the separator. The tensile test was performed at a pulling speed of 50mm / s, a temperature of 25°C, and a relative humidity of 40%, and the tensile strength (N / m) was measured. Note that 1gf / cm can be converted to 0.98N / m.

[0226] <Gradient rate of coating layer> The separator was freeze-fractured, and its cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 30,000x magnification. As shown schematically in Figure 2, in the SEM image of the fractured sample cross section, the distance from the substrate-coating layer boundary to the outer surface of the coating layer in the inorganic filler portion of the coating layer was measured as the thickness L1 (μm) of the inorganic filler portion of the coating layer. Note that the "inorganic filler portion" refers to the portion that is at least 1.5D away from each protruding particulate polymer, where D is the volume average particle diameter of the protruding particulate polymer. Furthermore, the maximum distance L2 (μm) from the boundary line between the substrate and coating layer to the outer surface of the inorganic filler in the coating layer, which is formed in a sloping manner, and the maximum distance L3 (μm) to the outline of the protruding particulate polymer were measured, and the slope ratio L2 / L1 of the coating layer and the coverage ratio of the protruding portion (L2-L1) / (L3-L1) were calculated. The slope ratio L2 / L1 of the coating layer and the coverage ratio of the protruding portion (L2-L1) / (L3-L1) were measured at 200 points, and the average values ​​were calculated.

[0227] <Contact ratio between protruding particulate polymer and substrate> The separator was freeze-fractured, and its cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 30,000x magnification. Of the particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer in the SEM image, the number of particles in contact with the substrate was counted for 200 particulate polymers with fractured cross sections, and this was determined as the contact ratio between the protruding particulate polymers and the substrate.

[0228] <Proportion of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer> The separator was freeze-fractured, and the cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a separator sample was cut into a size of approximately 1.5 mm x 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was vapor-deposited with osmium and observed at an accelerating voltage of 1.0 kV and 30,000x magnification. 200 particulate polymers present on the fractured surface were observed using SEM images, and the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer was counted and recorded as the percentage of the number of particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer.

[0229] <Average number of adjacent particulate polymers> The surface of the osmium-deposited separator for a power storage device was subjected to elemental mapping using a scanning electron microscope (SEM) (model "SU-8220", manufactured by Hitachi) and energy dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", manufactured by Oxford). At this time, secondary electrons were selected as the SEM detector, and carbon atom mapping measurements were performed at a magnification of 10,000 with an acceleration transmission of 3 kV and 20 mapping accumulations. In the carbon atom mapping, an area that appeared circular was defined as one particulate polymer, and the number of particles whose outer edges were 0.2 μm or less was counted for all particulate polymers in one field of view. This measurement was performed in three fields of view, and the average of all the measurement values ​​was taken as the average number of adjacent particulate polymers.

[0230] <Ratio of Average Particle Size of Protruding Particulate Polymer to Average Particle Size of Inorganic Filler> The cross section of the osmium-deposited separator for a power storage device was observed using a scanning electron microscope (SEM) (model "S-4800," manufactured by Hitachi) at an accelerating voltage of 1.0 kV and 10,000x magnification to measure the average particle diameter. Specifically, the equivalent circle diameter of 200 random inorganic filler particles was measured, and the volume average particle diameter MV was calculated from these values, which was used as the average particle diameter. Similarly, an SEM image of the cross section of the osmium-deposited separator for a power storage device was observed, and the equivalent circle diameter of 200 particulate polymers protruding from the thickness of the inorganic filler portion of the coating layer was measured, and the volume average particle diameter MV was calculated from these values, which was used as the average particle diameter. From the average particle diameter of the inorganic filler or the average particle diameter of the particulate polymer determined by the above method, the ratio of the average particle diameter of the protruding particulate polymer to the average particle diameter of the inorganic filler was calculated.

[0231] <Number of polymer particles within a radius of 10 μm> The surface of the osmium-deposited separator for power storage devices was subjected to elemental mapping using a scanning electron microscope (SEM) (model "SU-8220", manufactured by Hitachi) and energy dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", manufactured by Oxford). Secondary electrons were selected as the SEM detector, and carbon atom mapping measurements were performed at a magnification of 50 million times with an acceleration transmission of 3 kV and 20 mapping accumulations. In the carbon atom mapping, a circular area was defined as one particulate polymer, and the number of particulate polymers present within a radius of 10 μm from any one particulate polymer was counted for all particulate polymers in one field of view, and the average value was calculated.

[0232] <Methylene chloride solubles> The methylene chloride soluble content in the substrate and separator was measured using the following method. A 100 x 100 mm sample of the substrate or separator was neutralized and weighed using a precision balance (W0 (g)). Next, 200 ml of methylene chloride was added to a sealed container, and the separator was immersed at room temperature for 15 minutes. The separator was then removed, dried at room temperature for 3 hours, neutralized in the same manner as above, and weighed using a precision balance (W1 (g)). The methylene chloride soluble content was calculated using the following formula. Methylene chloride solubles (%) = {(W1-W0) / W0} x 100

[0233] <Total amount of metal cations> 0.60 g of separator was placed in a Teflon (registered trademark) pressure decomposition vessel, 10 ml of sulfuric acid was added, and the vessel was sealed and heated in an air bath at 200°C for 15 hours. After cooling, the solution in the vessel was transferred to a 100 ml resin measuring flask and diluted to volume to prepare a sample solution. The sample solution was measured using an inductively coupled plasma atomic emission spectrometry (ICP-OES) (model "ICPE-9000", manufactured by Shimadzu Corporation), and the content of each element was calculated using a calibration curve prepared from the standard solution.

[0234] <Heat shrinkage rate> The separator was cut into samples of 100 mm in the MD and 100 mm in the TD, and left to stand in an oven at 130°C or 150°C for 1 hour. The sample was sandwiched between two pieces of paper to prevent the hot air from directly hitting the sample. After removing the sample from the oven and cooling, the length (mm) was measured and the thermal shrinkage was calculated using the formula below. Measurements were performed in both the MD and TD, and the larger value was taken as the thermal shrinkage. Heat shrinkage rate (%) = {(100 - length after heating) / 100} x 100

[0235] <Viscosity average molecular weight> The intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent was determined based on ASTM-D4020. For polyethylene, the calculation was made using the following formula: [η]=6.77×10 -4 M v 0.67 For polypropylene, Mv was calculated using the following formula: [η]=1.10×10 -4 M v 0.80

[0236] <Weight average molecular weight and number average molecular weight> A calibration curve was created by measuring standard polystyrene under the following conditions using a Waters ALC / GPC 150C (trademark). Chromatograms of the following polymers were also measured under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the following method. Column: Tosoh GMH6-HT (trademark) x 2 + GMH6-HTL (trademark) x 2 Mobile phase: o-dichlorobenzene Detector: Differential refractometer Flow rate: 1.0ml / min Column temperature: 140℃ Sample concentration: 0.1 wt%

[0237] <Weight average molecular weight and number average molecular weight of polyethylene and polypropylene> Each molecular weight component in the obtained calibration curve was multiplied by 0.43 (Q factor of polyethylene / Q factor of polystyrene=17.7 / 41.3) or 0.64 (Q factor of polypropylene / Q factor of polystyrene=26.4 / 41.3) to obtain a molecular weight distribution curve in terms of polyethylene or polypropylene, and the weight average molecular weight and number average molecular weight were calculated.

[0238] <Weight-average molecular weight and number-average molecular weight of resin composition or microporous resin membrane> The weight-average molecular weight and number-average molecular weight were calculated using the Q factor value of the polyolefin with the largest mass fraction, in the same manner as for polyethylene.

[0239] <Melt Flow Index (MI)> The melt flow index (MI) of the microporous membrane was measured according to JIS K7210:1999 (Melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastics). A load of 21.6 kgf was applied to the membrane at 190°C, and the amount of resin (g) flowing through an orifice 2 mm in diameter and 10 mm in length in 10 minutes was measured. The value was rounded to one decimal place to obtain the MI.

[0240] <DSC measurement> DSC (Differential Scanning Calorimetry) was measured using a Shimadzu DSC60. First, a 5 mm diameter circle was punched out of the PO microporous membrane, and several sheets were stacked together to obtain a 3 mg measurement sample. This sample was placed in a 5 mm diameter aluminum open sample pan, a clamping cover was placed on top, and the sample was fixed inside the aluminum pan with a sample sealer. Under a nitrogen atmosphere, the sample was heated from 30°C to 200°C at a heating rate of 10°C / min (first heating), held at 200°C for 5 minutes, and then cooled from 200°C to 30°C at a heating rate of 10°C / min. Subsequently, the sample was held at 30°C for 5 minutes, and then heated again from 30°C to 200°C at a heating rate of 10°C / min (second heating). The maximum temperature in the melting endothermic curve during the second heating was determined as the melting point of the PO microporous membrane. When there were multiple maxima, the first peak and the largest peak were detected. The temperature at the largest maximum on the melting endothermic curve can be used as the melting point (Tm) of the microporous PO membrane.

[0241] 〈Density (g / cm 3 )〉 The density of the sample was measured by the density gradient tube method (23°C) in accordance with JIS K7112:1999.

[0242] <Weight (g / m 2 )〉 The basis weight is the unit area (1m 2 The weight (g) of the polyolefin microporous membrane per unit area (1 m) was measured using an electronic balance (AUW120D) manufactured by Shimadzu Corporation after sampling to 1 m x 1 m. If it was not possible to sample to 1 m x 1 m, the membrane was cut to an appropriate area, the weight was measured, and the unit area (1 m) was used. 2 The weight was converted to weight (g) per unit.

[0243] <Average thickness of microporous membrane before compression (μm)> The thickness was measured at an ambient temperature of 23±2°C using a Toyo Seiki microthickness gauge (Type KBN, terminal diameter Φ5mm). When measuring the thickness, the microporous membrane was sampled in a 10 cm × 10 cm area, and multiple microporous membranes were stacked to a total thickness of 15 μm or more. The thickness was measured at nine locations and the average value was calculated. The average value was divided by the number of stacked membranes to determine the thickness of one microporous membrane.

[0244] <Porosity before compression (%)> A sample of 3 cm x 3 cm square, 1 cm x 1 cm square, 5 cm x 5 cm square, or 10 cm x 10 cm square was cut from the polyolefin microporous membrane, and its volume (cm) was calculated based on the average membrane thickness measurement. 3 ) and mass (g). These values ​​and density (g / cm 3 ) and the porosity (%) before compression was calculated using the following formula: Porosity (%) = (volume - mass / density of mixed composition) / volume × 100 The density of the mixed composition was calculated from the density and mixing ratio of the polyolefin resin and other components used.

[0245] <Porosity after compression (%)> Two 0.8 mm-thick rubber buffers, two 0.1 mm-thick PET films, and two microporous membranes were prepared. These were stacked in the following order: one buffer, one PET film, two microporous membranes, one PET film, and one buffer. The resulting laminate was placed in a press. A compression test was performed by clamping both buffer surfaces of the laminate with the press and applying pressure. The compression test was performed at a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes. If necessary, the compression ratio after pressure relaxation was measured. The compression ratio was measured between 2 and 24 hours after pressure relaxation. After the compression test, the pressure was relaxed, and the microporous membrane was removed from the laminate. The microporous membrane after the compression test was used as a sample. The porosity after compression (%) was measured using the same method as in the "Porosity before compression (%)" above.

[0246] The same compression test as above was conducted at a temperature of 30°C for 3 minutes under pressures of 2.5 MPa, 5 MPa, 7.5 MPa, and 10 MPa. One hour after the pressure was released, the microporous membrane was removed from the laminate, and the average membrane thickness (average of 9 points) and air permeability after compression were measured. The porosity after compression was calculated from the basis weight and the average membrane thickness after compression. Finally, an approximate curve, as shown in Figure 3, was created using power approximation for the porosity and air permeability after compression from the four measurement points compressed at the four pressures mentioned above. In Figure 3, membrane types A to C are commercially available polyolefin separators.

[0247] <Air permeability before compression (sec / 100cm 3 )〉 The air permeability was measured using an Oken-type air permeability measuring instrument, "EGO2," manufactured by Asahi Seiko Co., Ltd. The air permeability was measured at three points along the width of the membrane: 5 cm from both ends and one point in the center, and the average value was calculated.

[0248] <Puncture strength and puncture strength converted into basis weight> Using a Kato Tech handy compression tester KES-G5™, a microporous membrane was fixed in a sample holder with an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed microporous membrane at a room temperature of 23°C and a humidity of 40% with a needle tip curvature radius of 0.5 mm and a puncture speed of 2 mm / sec. The puncture strength (gf) was measured as the maximum puncture load. The puncture test measurement was taken at three points along the membrane's transverse travel (TD): two points 10% inward from both ends toward the center and one point in the center, and the average of these measurements was calculated.

[0249] The puncture strength converted into basis weight is calculated using the following formula. Penetration strength converted to basis weight [gf / (g / m 2 )]=Piercing strength [gf] / Weight [g / m 2 ] Here, with regard to the pin puncture strength and equivalent pin puncture strength per unit area of ​​a separator having at least one layer provided on a polyolefin microporous membrane substrate, the properties were evaluated using the pin puncture strength and equivalent pin puncture strength per unit area of ​​the polyolefin microporous membrane substrate from the perspective of evaluating the strength of the resin and the strength per unit area.

[0250] <Pore diameter (nm): Half dry> The average pore size (nm) was measured using a perm porometer (Porous Materials, Inc.: CFP-1500AE) according to the half-dry method. The immersion liquid used was a perfluoropolyester manufactured by the same company (trade name "Galwick", surface tension 15.6 dyn / cm). The applied pressure and air permeability were measured for the dry and wet curves. The average pore size dHD (nm) was calculated using the following formula from the pressure PHD (Pa) at which the half-dry curve intersects with the wet curve. dHD=2860×γ / PHD

[0251] <Fuse (shutdown) temperature> Two 10 μm thick Ni foils (A, B) were prepared. One Ni foil, A, was masked with Teflon® tape, leaving a rectangular area 15 mm long and 10 mm wide. A measurement sample separator was placed on the other Ni foil, B, and both ends of the separator were fixed with Teflon® tape. This Ni foil, B, was immersed in a 1 mol / L lithium fluoroborate solution (solvent: a propylene carbonate / ethylene carbonate / γ-butyl lactone mixed solvent with a volume ratio of 1 / 1 / 2) to impregnate the separator with the electrolyte. The Ni foils (A, B) were then bonded together and held down on both sides with clips between two glass plates. The Ni foil electrode thus prepared was placed in an oven at 25°C and heated to 200°C at a rate of 2°C / min. The impedance change during this process was measured under conditions of 1 V and 1 kHz using an electrical resistance measurement device "AG-4311" (manufactured by Ando Electric Co., Ltd.). In this measurement, the temperature at which the impedance value reached 1000Ω was taken as the fuse (shutdown) temperature (°C).

[0252] <Measurement of withstand voltage per unit area before compression> A 10cm MD x 10cm TD strip was cut from the center of the width direction of the polyolefin microporous membrane and sandwiched between 5mm diameter aluminum plates. The pre-compression breakdown voltage per unit area was measured using a Kikusui Electronics Corporation (TOS9201) voltage tester. The measurement conditions were as follows: DC voltage was applied starting from 0V and increasing at a rate of 100V / sec. The voltage (kV) at which a current of 0.2mA flowed was taken as the measured voltage of the microporous membrane. Measurements were taken at 5 points in MD x 5 points in TD at 15mm intervals, for a total of 25 points, and the average value was taken as the measured voltage. The breakdown voltage per unit area was calculated as the ratio of the breakdown voltage to the unit area (voltage / unit area).

[0253] <Crystal structure analysis> The crystalline long period in the polyolefin microporous membrane was measured by small-angle X-ray scattering in transmission using a Rigaku NANOPIX. The sample was irradiated with CuKα radiation, and scattering was detected using a semiconductor detector, HyPix-6000. The sample-to-detector distance was 1312 mm, and the output was 40 kV, 30 mA. A point focus was used for the optical system, with slit diameters of 1st slit: φ=0.55 mm, 2nd slit: open, and guard slit: φ=0.35 mm. The sample was set so that the sample surface was perpendicular to the X-ray incidence direction.

[0254] The crystallite size of the polyethylene MD / ND plane (110) in the polyolefin microporous membrane was measured by wide-angle X-ray scattering using a Rigaku NANOPIX in transmission mode. The sample was irradiated with CuKα radiation, and scattering was detected using an imaging plate. Measurements were performed at a sample-to-detector distance of 110 mm and at an output of 40 kV and 30 mA. A point focus optical system was used, with slit diameters of 1st slit: φ = 1.2 mm, and guard slit: φ = 0.35 mm. The sample was set so that the angle between the sample surface and the X-ray incidence direction was 11.0°. The X-ray incidence direction and the MD of the sample were perpendicular.

[0255] <Crystal long period [nm]> For the X-ray scattering pattern obtained from the HyPix-6000, the SAXS profile I(q) was obtained by circular averaging. The linear-linear plot of the obtained one-dimensional profile I(q) was -1 <q<0.6nm -1 A straight line baseline was drawn in the range and fitted with a Gaussian function. The position of maximum intensity was determined as the peak position q m The crystal long period was calculated using the following formula: d=2π / q m {In the formula, d(nm): Crystal long period q m (nm -1 ): Peak position of lamellae in the SAXS profile}

[0256] <Crystallite size> The XRD profile obtained was separated into three peaks: the orthorhombic (110) diffraction peak, the orthorhombic (200) diffraction peak, and the amorphous peak, in the range from 2θ = 10.0° to 2θ = 30.0°. The crystallite size was calculated from the full width at half maximum of the (110) diffraction peak using the Scherrer equation (Equation 1). The (110) diffraction peak and the (200) diffraction peak were approximated using a Voigt function, and the amorphous peak was approximated using a Gaussian function. The amorphous peak's position was fixed at 2θ = 19.6° and its full width at half maximum was 6.3°, while the crystalline peak's position and full width at half maximum were not fixed. The crystallite size was calculated from the full width at half maximum of the (110) diffraction peak calculated by peak separation using the Scherrer equation (see below). D(110)=Kλ / (βcosθ) {wherein D(110): crystallite size (nm) K: 0.9 (constant) λ: X-ray wavelength (nm) β:(β1 2 -β2 2 ) 0.5 β1: Full width at half maximum (rad) of the (hkl) peak calculated as a result of peak separation β2: Full width at half maximum of the incident beam divergence (rad) θ: Bragg angle} It is preferable to measure the crystal long period and crystallite size based on crystal structure analysis on the substrate before coating. However, due to the principles of X-ray structure analysis, the same results are obtained whether the measurement is performed on the separator after coating or after peeling the coating layer from the separator after coating.

[0257] 〈Smoothness (sec / 10cm 3 )〉 In accordance with ISO 8791-5:2020, the smoothness of the polyolefin microporous membrane was measured in an atmosphere at a temperature of 30°C and a humidity of 40% using an air permeability smoothness meter EYO-5 manufactured by Asahi Seiko Co., Ltd., with a stainless steel nozzle with an inner diameter of 0.15 mm and a length of 50 mm. The surface smoothness was measured for each of one surface and the other surface of the polyolefin microporous membrane, and the average smoothness of the one surface and the other surface was calculated as described above.

[0258] <Average pore diameter of polyolefin microporous membrane> It is known that the fluid inside a capillary follows Knudsen flow when the mean free path of the fluid is larger than the pore diameter of the capillary, and follows Poiseuille flow when it is smaller. Therefore, it is assumed that the air flow in measuring the air permeability of a thermoplastic polymer-containing layer follows Knudsen flow, and the water flow in measuring the water permeability of a substrate follows Poiseuille flow.

[0259] The average pore size d (μm) of the polyolefin microporous membrane is expressed as the air permeation rate constant R gas (m 3 / (m 2 ·sec·Pa)), water permeation rate constant R liq (m 3 / (m 2 The following equation was used to calculate the thickness of the film from the air pressure (m / sec), the molecular velocity of air (ν), the viscosity of water (η), the standard pressure (Ps) (=101325 Pa), the porosity (ε) (%), and the film thickness (L) (μm). d=2ν×(R liq / R gas )×(16η / 3Ps)×10 6

[0260] where R gas was calculated from the air permeability (sec) using the following formula: R gas =0.0001 / (air permeability × (6.424 × 10 -4 )×(0.01276×101325))

[0261] Also, R liq is the permeability (cm 3 / (cm 2 sec Pa)) using the following formula: R liq =water permeability / 100

[0262] The water permeability was determined as follows: A thermoplastic polymer-containing layer, which had been immersed in ethanol beforehand, was placed in a stainless steel liquid permeation cell with a diameter of 41 mm. After washing the ethanol out of this layer with water, water was passed through the cell at a differential pressure of about 50,000 Pa. The amount of water permeated (cm) after 120 seconds was measured. 3 ) the amount of water permeable per unit time, unit pressure and unit area was calculated, and this was taken as the permeability.

[0263] Also, ν is the gas constant R (= 8.314), absolute temperature T (K), pi (π), and the average molecular weight of air M (= 2.896 × 10 -2 kg / mol) using the following formula: ν=((8R×T) / (π×M)) 1 / 2

[0264] <Glass transition temperature of thermoplastic polymer> An appropriate amount of a water dispersion containing a thermoplastic polymer (solid content = 38 to 42 parts by mass, pH = 9.0) was placed in an aluminum dish and left to stand at room temperature for 24 hours to obtain a dried film. Approximately 17 mg of this dried film was placed in an aluminum container for measurement, and a DSC curve under a nitrogen atmosphere and a DSC curve were obtained using a DSC measurement device (Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows. First stage temperature increase program: Start at 30°C, increase temperature at a rate of 10°C per minute. After reaching 150°C Maintain for 5 minutes. Second stage temperature reduction program: Reduce the temperature from 110°C at a rate of 10°C per minute. After reaching -50°C, maintain the temperature for 5 minutes. Third-stage temperature increase program: Increase the temperature from -50°C to 150°C at a rate of 10°C per minute. DSC and DDSC data were collected during this third-stage temperature increase.

[0265] The glass transition temperature of the obtained DSC curve was determined by the method described in JIS-K 7121. Specifically, the glass transition temperature (Tg) was determined as the temperature at the point where a line extending the low-temperature baseline of the DSC curve toward the high-temperature side and a line equidistant in the vertical direction from the line extending the high-temperature baseline of the DSC curve toward the low-temperature side intersect with the curve of the stepwise change in the glass transition.

[0266] <Aspect ratio of inorganic filler in coating layer> The surface of the osmium-deposited separator for a power storage device was observed using a scanning electron microscope (SEM) (model "S-4800," manufactured by Hitachi) at an accelerating voltage of 1.0 kV and 10,000x magnification to measure the aspect ratio. The inorganic filler in the coating layer was image-processed from the SEM image to determine the aspect ratio. Even when inorganic fillers were bonded to each other, those in which the length and width of each inorganic filler were clearly recognizable were selected, and the aspect ratio was calculated based on these. Specifically, 10 inorganic fillers with clearly recognizable length and width were selected, and the average value obtained by dividing the long axis by the short axis of each inorganic filler was used as the aspect ratio. If there were fewer than 10 inorganic fillers with clearly recognizable length and width in one field of view, 10 were selected from images of multiple fields of view.

[0267] <Particle size distribution of inorganic filler> The particle size distribution of the inorganic filler was measured using a particle size measuring device (product name "Microtrac UPA150" manufactured by Nikkiso Co., Ltd.) The sample solution to be measured was the pre-coating dispersion liquid, and the measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds. The particle size distribution (Cv value) of the inorganic filler was calculated by dividing the standard deviation SD of the volume average particle size in the obtained data by the D50 value.

[0268] <Volume average particle diameter (D50) of thermoplastic polymer (particulate polymer) in aqueous dispersion and volume average particle diameter (D50) of resin binder> The volume average particle diameter (D50) of the thermoplastic polymer (particulate polymer) in the aqueous dispersion and the volume average particle diameter (D50) of the resin binder were measured using a particle diameter measuring device (product name "Microtrac UPA150" manufactured by Nikkiso Co., Ltd.) The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds, and the particle diameter (D50) value at which the cumulative volume of the obtained data reached 50% was recorded as the volume average particle diameter (D50).

[0269] <Particle size distribution of particulate polymer> The cross section of the osmium-deposited separator for a power storage device was measured by observing it with a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi) at an acceleration voltage of 1.0 kV and a magnification of 10,000. Specifically, the area-equivalent circle diameter was measured for 200 random particulate polymers, and the number-average particle diameter MN and volume-average particle diameter MV were calculated from these values, and the particle size distribution of the particulate polymer was calculated as MV / MN.

[0270] <Rate characteristics> a. Preparation of the positive electrode The positive electrode active material was nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) as a conductive additive, graphite powder (KS6) (density 2.26 g / cm 3 1.6 parts by mass of acetylene black powder (AB) (density 1.95 g / cm 3 3.8 parts by mass of polyvinylidene fluoride (PVdF) (density 1.75 g / cm 3) as a binder. 3) were mixed in a ratio of 4.2 parts by mass, and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil that would serve as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 109 g / m 2 It was.

[0271] b. Preparation of negative electrode Graphite powder A (density 2.23 g / cm) was used as the negative electrode active material. 3 87.6 parts by mass of graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7 parts by mass of carboxymethylcellulose (number average particle diameter 6.5 μm) and 1.4 parts by mass (solids equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solids concentration of 1.83 parts by mass) and 1.7 parts by mass (solids equivalent) of diene rubber latex (aqueous solution with a solids concentration of 40 parts by mass) in purified water. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied was 5.2 g / m 2 It was.

[0272] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0273] d. Battery assembly The separator or substrate was cut into a 24 mm diameter circle, and the positive and negative electrodes were each cut into a 16 mm diameter circle. The negative electrode, separator or substrate, and positive electrode were stacked in this order, with the active material surfaces of the positive and negative electrodes facing each other, and then placed in a lidded stainless steel container. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode, and the lid in contact with the aluminum foil of the positive electrode. A battery was assembled by pouring 0.4 ml of the nonaqueous electrolyte into the container and sealing it.

[0274] e. Evaluation of rate characteristics The simplified battery assembled in d. was charged at 25°C at a current of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, and then tapered from 3 mA to maintain 4.2 V. This initial charge was performed for a total of approximately 6 hours. It was then discharged at 3 mA to a battery voltage of 3.0 V. Next, at 25°C, it was charged at a current of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and then tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The discharge capacity at 6 mA to a battery voltage of 3.0 V was recorded as the 1C discharge capacity (mAh). Next, at 25°C, it was charged at a current of 6 mA (approximately 1.0 C) to a battery voltage of 4.2 V, and then tapered from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The discharge capacity when the battery was subsequently discharged at a current value of 12 mA (approximately 2.0 C) to a battery voltage of 3.0 V was taken as the 2 C discharge capacity (mAh).The ratio of the 2 C discharge capacity to the 1 C discharge capacity was then calculated, and this value was taken as the rate characteristic. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) x 100 Evaluation criteria for rate characteristics (%) A (Good): Rate characteristics are over 85% B (Acceptable): Rate characteristics are over 80% and less than 85% C (bad): Rate characteristics are 80% or less

[0275] <Adhesion strength with electrode (before electrolyte injection)> The separator was cut into a rectangular shape of 20 mm wide x 70 mm long, and was layered on a positive electrode cut to a size of 15 mm x 60 mm to form a separator and electrode laminate, and this laminate was pressed under the following conditions. Temperature: 90℃ Press pressure: 1 MPa Press time: 5 seconds The peel strength between the separator and electrode after pressing was measured by a 90° peel test at a peel rate of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. The average value of the peel strength in the 40 mm length peel test conducted under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength is 5N / m or more B (Acceptable): Peel strength is 2N / m or more and less than 5N / m C (poor): Peel strength is 1N / m or more and less than 2N / m D (unacceptable): Peel strength is less than 1N / m

[0276] <Adhesion strength with electrode (after electrolyte injection)> The separator was cut into a rectangular shape measuring 20 mm wide x 70 mm long, and placed on top of a positive electrode cut to 15 mm x 60 mm to form a separator-electrode laminate. This laminate was then inserted into an aluminum laminate film, and 0.4 ml of electrolyte (a mixture of EC / DEC = 1 / 2 containing 1 mol / L LiPF6) was added. After sealing, the battery was left to stand for 12 hours and pressed under the following conditions. Temperature: 90℃ Press pressure: 1 MPa Press time: 1 minute The peel strength between the separator and electrode after pressing was measured by a 90° peel test at a peel rate of 50 mm / min using force gauges ZP5N and MX2-500N (product name) manufactured by Imada Co., Ltd. The average value of the peel strength in the 40 mm length peel test conducted under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength is 5N / m or more B (Acceptable): Peel strength is 2N / m or more and less than 5N / m C (poor): Peel strength is 1N / m or more and less than 2N / m D (unacceptable): Peel strength is less than 1N / m

[0277] <Powder shedding> A 12 mm wide x 100 mm long tape (manufactured by 3M) was attached to the raw polymer coating layer of the separator. The force required to peel the tape from the sample at a rate of 50 mm / min was measured using a 90° peel strength tester (manufactured by IMADA, product name IP-5N). Based on the measurement results, the adhesive strength was evaluated according to the following criteria. A (good): 59N / m (6gf / mm) or more B (tolerance): 40N / m or more and less than 59N / m C (poor): Less than 40N / m

[0278] <Cycle characteristics and distortion of electrode-separator winding> a. Preparation of the positive electrode The positive electrode active material was nickel, cobalt, and aluminum composite oxide (NCA) (Ni:Co:Al = 90:5:5 (element ratio), density 3.50 g / cm 3 100 parts by mass of acetylene black powder (AB) as a conductive material, 1.25 parts by mass of acetylene black powder (AB) as a conductive material, and 1.0 part by mass of polyvinylidene fluoride (PVdF) as a binder were mixed and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to both sides of a 15 μm thick aluminum foil that served as a positive electrode current collector using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 456 g / m 2 It was.

[0279] b. Preparation of negative electrode A slurry was prepared by dispersing 86.0 parts by weight of graphite powder and 4.5 parts by weight of silicon oxide (SiO) as the negative electrode active material, and 1 part by weight of sodium carboxymethyl cellulose and 1.0 part by weight of styrene-butadiene rubber (SBR) as binders in purified water. This slurry was applied to both sides of a 7.5 μm-thick copper foil that served as the negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied was 266 g / m. 2 It was.

[0280] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate=25:70:5 (weight ratio) to a concentration of 1.4 mol / L.

[0281] d. Battery assembly A positive electrode (63 mm wide), a negative electrode (64 mm wide), and a separator (67 mm wide) were stacked and spirally wound to form a wound body, which was then placed in a cylindrical battery can with an outer diameter of 21 mm and a height of 70 mm, and the nonaqueous electrolyte solution was poured into the can and sealed to assemble the battery.

[0282] e. Evaluation of cycle characteristics The battery assembled in step d was charged at 25°C at a current of 3 mA (approximately 0.5 C) to a battery voltage of 4.2 V, and then charged to a current of 50 mA while maintaining 4.2 V. The battery was then discharged at 0.2 C to a battery voltage of 2.5 V, and the initial capacity was determined. Next, the battery was charged at 0.3 C to a battery voltage of 4.2 V, and then charged to a current of 50 mA while maintaining 4.2 V, and then discharged at 1 C to a battery voltage of 2.5 V. This cycle was repeated, and the cycle characteristics were evaluated using the capacity retention rate after 500 cycles relative to the initial capacity (capacity at the first cycle) according to the following criteria. A: 80% or more capacity retention rate B: Capacity retention rate of 75% or more but less than 80% C: Capacity retention rate of less than 75%

[0283] f. Evaluation of the condition of the winding after cycle characteristics After the cycle characteristic test performed in e., the battery was disassembled and the electrode-separator wound body was checked for distortion. If distortion was present, it was judged as present, and if no distortion was present, it was judged as absent. If there was a gap of 0.5 mm or more, it was judged as present, and if there was a gap of less than 0.5 mm, it was judged as absent.

[0284] <<Example of substrate manufacturing>> <Production of Polyolefin Microporous Membrane Substrates B1 to B11> (1) As shown in Table 1, a raw resin composition was prepared by adjusting the proportions of polyethylene with a Mv of 700,000 or more (PE1: Mv 900,000, PE3: Mv 800,000, PE4: Mv 700,000, PE6: Mv 770,000), polyethylene with a Mv of 700,000 or less (PE2: Mv 250,000, PE5: Mv 370,000), and polypropylene (PP, Mv 400,000). Next, the raw resin composition, a plasticizer (liquid paraffin), and 0.1% by mass of an antioxidant were blended to obtain the resin content (PC) shown in Table 1, thereby obtaining a polyolefin composition. The polyolefin composition was then fed into a twin-screw extruder, and the molten polyolefin composition was extruded to form a gel-like sheet, which was then cooled and solidified using a cast roll. (2) The cooled and solidified sheet was biaxially stretched using a simultaneous biaxial stretching machine under the conditions shown in Table 1 to obtain a stretched sheet. (3) The stretched sheet was then immersed in methylene chloride to extract and remove the liquid paraffin, and then dried to make it porous. (4) The resulting porous materials were then heat-set using a uniaxial stretching machine under the conditions shown in Table 1 to obtain polyolefin microporous membrane bases B1 to B11. The resulting polyolefin microporous membranes were evaluated according to the methods described above. The evaluation results are shown in Table 2.

[0285] [Table 1]

[0286] [Table 2]

[0287] <Preparation example of aqueous dispersion (particulate polymer)> <Preparation of Aqueous Dispersion A1> A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., referred to as "KH1025" in the tables; the same applies hereinafter), and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, referred to as "SR1025" in the tables; the same applies hereinafter), and the internal temperature of the reaction vessel was raised to 95°C. Subsequently, while maintaining the internal temperature of the vessel at 95°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution by mass) (referred to as "APS(aq)" in the tables; the same applies hereinafter) was added.

[0288] On the other hand, 71.5 parts by mass of methyl methacrylate (MMA), 18.9 parts by mass of n-butyl acrylate (BA), 2 parts by mass of 2-ethylhexyl acrylate (EHA), 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 0.4 parts by mass of glycidyl methacrylate (GMA), 0.4 parts by mass of trimethylolpropane triacrylate (A-TMPT) (manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3.0 parts by mass of KH1025, SR1025 A mixture of 3.0 parts by mass of ammonium persulfate, 0.05 parts by mass of sodium p-styrenesulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% by mass aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the addition of the ammonium persulfate aqueous solution to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. During the dropwise addition of the emulsion, the temperature inside the vessel was maintained at 80°C. During this time, the stirring bar placed inside the reaction vessel was constantly stirred using a magnetic stirrer.

[0289] After the dropwise addition of the emulsified liquid was completed, the internal temperature of the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the obtained emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% by weight aqueous solution), yielding an acrylic copolymer latex with a concentration of 40 parts by weight (aqueous dispersion A1). The glass transition temperature (Tg) and volume average particle size (D50) of the thermoplastic polymer contained in the obtained aqueous dispersion A1 were evaluated using the methods described above. The results are shown in Table 3.

[0290] <Preparation of Aqueous Dispersions A2, A3, and A4> Aqueous dispersions A2 to A4 were obtained and their physical properties were evaluated in the same manner as for aqueous dispersion A1, except that the compositions of the emulsions were changed as shown in Tables 3 and 4. The results are shown in Tables 3 and 4.

[0291] <Preparation of Aqueous Dispersion A1-1> A portion of the aqueous dispersion A1 was taken and used as a seed polymer to carry out multi-stage polymerization to synthesize aqueous dispersion A1-1. Specifically, a mixture of 20 parts by mass of aqueous dispersion A1 (solid content equivalent) and 70.4 parts by mass of ion-exchanged water was first added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, and the internal temperature of the reaction vessel was raised to 80°C. Thereafter, while maintaining the internal temperature of the vessel at 80°C, 7.5 parts by mass of ammonium persulfate (2% by mass aqueous solution) was added. This completes the initial charging process.

[0292] On the other hand, a mixture of 71.5 parts by mass of methyl methacrylate (MMA), 18.9 parts by mass of n-butyl acrylate (BA), 2 parts by mass of 2-ethylhexyl acrylate (EHA), 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 0.4 parts by mass of glycidyl methacrylate (GMA), 0.7 parts by mass of trimethylolpropane triacrylate (A-TMPT), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3 parts by mass of KH1025, 3 parts by mass of SR1025, 0.05 parts by mass of sodium p-styrenesulfonate (NaSS), 7.5 parts by mass of ammonium persulfate (2% by mass aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. The addition began 5 minutes after the addition of the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the addition of the emulsion, the temperature inside the vessel was maintained at 80°C. At this time, the stirring bar placed inside the reaction vessel was constantly stirred with a magnetic stirrer.

[0293] After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C while stirring for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the resulting emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% by weight aqueous solution), yielding an acrylic copolymer latex with a concentration of 40 parts by weight (aqueous dispersion A1-1). The resulting aqueous dispersion A1-1 was evaluated using the methods described above. The results are shown in Table 3.

[0294] <Preparation of Aqueous Dispersions A1-2 to A1-4> Copolymer latexes (water dispersions A1-2 to A1-4) were obtained by adjusting the number of multi-stage polymerizations. The obtained water dispersions were each evaluated by the above-mentioned methods. The obtained results are shown in Table 3.

[0295] <Preparation of Aqueous Dispersions A2-1, A3-1 to A3-4, and A4-1> Copolymer latexes (water dispersions A2-1, A3-1 to A3-4, and A4-1) were obtained in the same manner as for water dispersion A1-1, except that the compositions of seed polymer, monomer, and other raw materials, the number of multi-stage polymerizations, and the polymerization conditions were changed as shown in Table 2. The obtained water dispersions were each evaluated by the above-mentioned methods. The obtained results are shown in Tables 3 and 4.

[0296] <Aqueous dispersion A5~A6> SB latex (Tg: 33°C, particle size: 300 nm, toluene insoluble content: 95%, swelling ratio: 1.4) was used as aqueous dispersion A5. PVdF-HFP (product name LBG, Arkema) with a primary particle size of 200 nm and agglomerated to form secondary particles of 2030 nm was used as aqueous dispersion A6.

[0297] [Table 3]

[0298] [Table 4]

[0299] ·emulsifier KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% by weight aqueous solution SR1025: "ADEKA REASOAP SR1025" registered trademark, manufactured by ADEKA Corporation, 25% by weight aqueous solution NaSS: Sodium p-styrenesulfonate

[0300] Initiator APS(aq): Ammonium persulfate (2% by mass aqueous solution)

[0301] Monomer MAA: methacrylic acid AA: acrylic acid MMA: methyl methacrylate BA: n-butyl acrylate BMA: n-butyl methacrylate EHA: 2-ethylhexyl acrylate CHMA: Cyclohexyl methacrylate St: styrene AN: Acrylonitrile HEMA: 2-hydroxyethyl methacrylate AM: acrylamide GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

[0302] <Separator manufacturing example> Example 1 A pre-coating dispersion was prepared by mixing 0.3 parts by weight of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468 manufactured by San Nopco) and 100 parts by weight of aluminum oxide hydroxide (boehmite) as an inorganic filler with 100 parts by weight of water, followed by processing with a bead mill. To the pre-coating dispersion, 1 part by weight of carboxymethyl cellulose (CMC) as a water-soluble polymer component was added per 100 parts by weight of the inorganic filler. This was then mixed with 4 parts by weight of an acrylic latex suspension (solids concentration 40% by weight, volume average particle size 150 nm, glass transition temperature -40°C) as a resin binder, and 20 parts by weight of aqueous dispersion A1-3 (particulate polymer). The mixture was uniformly dispersed to prepare a coating solution containing a thermoplastic polymer (solids content 40 parts by weight).

[0303] Both surfaces of the polyolefin microporous membrane B1 were treated by corona discharge treatment. Then, a coating solution was applied to one surface (side (A)) of the polyolefin microporous membrane B1 using a gravure coater. The shear rate of the gravure coater was 80,000 sec -1The coating area ratio of the coating layer to the polyolefin microporous membrane at this time was 100%. The applied coating liquid was then dried at 60°C to remove water. The coating liquid was then similarly applied to the surface (surface (B)) opposite to surface (A) of polyolefin microporous membrane B1, and again dried in the same manner as above. In this way, a separator having coating layers formed on both surfaces of polyolefin microporous membrane B1 was obtained.

[0304] Examples 2 to 27 Separators of Examples 2 to 27 were obtained in the same manner as in Example 1, except that the polyolefin microporous membrane, the composition of the coating solution, the coating conditions, etc. were changed as shown in Tables 5 to 11. In the separator of Comparative Example 5, the particulate polymer was dispersed in the form of secondary particles. The alumina used was "AKP3000" manufactured by Sumitomo Chemical Co., Ltd.

[0305] Example 28 A separator for Example 28 was obtained in the same manner as in Example 1. The coating layer of the obtained separator was peeled off using the following method to prepare a substrate sample for measurement. First, the cut separator was placed on a backing sheet, and the four edges of the separator were fixed with adhesive tape (packaging OPP tape). Adhesive tape was similarly applied to the uncovered portion. Pressure was applied from above this tape with a roll, and then the tape was peeled off to remove the coating layer adhering to the tape. The opposite side was then treated in the same manner to obtain a substrate sample without a coating layer. The physical properties of the substrate were measured using this sample, and the results are shown in Table 2.

[0306] Comparative Examples 1 to 7 Separators of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1, except that the polyolefin microporous membrane, the composition of the coating solution, the coating conditions, etc. were changed as shown in Tables 5 to 10, respectively.

[0307] [Table 5]

[0308] [Table 6]

[0309] [Table 7]

[0310] [Table 8]

[0311] [Table 9]

[0312] [Table 10]

[0313] [Table 11] [Industrial Applicability]

[0314] The separator for an electricity storage device of the present disclosure can be suitably used in various electricity storage devices, preferably lithium ion secondary batteries. [Explanation of symbols]

[0315] 1. Inorganic filler 2 Particulate polymer 10 Base material 20 Covering layer

Claims

1. A separator for an electricity storage device, comprising: a substrate that is a polyolefin microporous film containing a polyolefin as a main component; and a coating layer disposed on at least one surface of the substrate, The thickness of the substrate is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm ３ or less, and the porosity after compression measured after compressing the substrate under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more, the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer.

2. A separator for an electricity storage device, comprising: a substrate that is a polyolefin microporous film containing a polyolefin as a main component; and a coating layer disposed on at least one surface of the substrate, the polyolefin microporous membrane has a crystalline long period measured by small-angle X-ray scattering (SAXS) method of 37.0 nm or more; the coating layer contains an inorganic filler and a particulate polymer of a thermoplastic polymer; The particulate polymer includes particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer.

3. The thickness of the substrate is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm ３ 3. The separator for an electricity storage device according to claim 2, wherein the porosity after compression is 30% or more when measured after compressing the substrate under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes.

4. In the coating layer, the amount of the particulate polymer is 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the inorganic filler contained in the coating layer, 4. The separator for an electricity storage device according to claim 1, wherein the coating layer is formed in a gradient shape so that the coating layer becomes thicker toward the protruding particulate polymer.

5. 5. The separator for an electricity storage device according to claim 4, wherein, when a thickness of the inorganic filler portion of the coating layer is L1 and a maximum distance from a boundary line between the substrate and the coating layer to an outer surface of the inorganic filler in the coating layer formed in the inclined shape is L2, an average value of a slope rate L2 / L1 of the coating layer is 1.2 or more.

6. 5. The separator for an electricity storage device according to claim 4, wherein the average value of the coverage rate of the protruding portions of the protruding particulate polymer, (L2-L1) / (L3-L1), is 0.4 or more, where L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the boundary line between the substrate and the coating layer to the outer surface of the inorganic filler of the coating layer formed in the inclined shape, and L3 is the maximum distance from the boundary line between the substrate and the coating layer to the outline of the protruding particulate polymer.

7. The separator for an electricity storage device according to any one of claims 1 to 3, wherein the particulate polymer comprises at least one selected from the group consisting of a (meth)acrylic polymer, a styrene-butadiene copolymer, and a copolymer containing a fluorine atom.

8. The separator for an electricity storage device according to any one of claims 1 to 3, wherein the particulate polymer comprises a copolymer containing (meth)acrylic acid, butyl (meth)acrylate, and ethylhexyl (meth)acrylate as monomers.

9. 4. The power storage device separator according to claim 1, wherein the particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

10. An electricity storage device comprising the separator for an electricity storage device according to any one of claims 1 to 3.

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