Separator for energy storage devices and energy storage devices including the same

Abstract

To provide a separator for a power storage device that has high adhesive strength with an electrode, a small thermal shrinkage rate, and can improve the cycle characteristics and output characteristics of the power storage device, and a power storage device having the separator.SOLUTION: A separator for a power storage device includes a substrate which is a polyolefin microporous membrane containing polyolefin as a main component, and a coating layer disposed on at least one surface of the substrate, and the polyolefin microporous membrane has a crystal long period of 37.0 nm or more as measured by small-angle X-ray scattering (SAXS), the substrate has a basis weight of 3.0 g / m2 or more and 7.0 g / m2 or less, and the substrate has a pin puncture strength of 273 gf or more and 700 gf or less, and the coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer, the particulate polymer including particulate polymer protruding from the coating layer by at least 0.1 times the thickness of the inorganic filler portion of the coating layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a separator for energy storage devices and an energy storage device including the same. [Background technology]

[0002] The development of energy storage devices, typified by lithium-ion secondary batteries, is actively underway. Generally, energy storage devices include a positive electrode, a negative electrode, and a microporous membrane separator between them. The separator has the function of preventing direct contact between the positive and negative electrodes and allowing ions to pass through the electrolyte held in the micropores. The separator is required to have safety properties such as the ability to quickly stop the battery reaction in the event of abnormal overheating (fuse properties) and the ability to maintain its shape even at high temperatures to prevent the dangerous situation of the positive and negative electrodes directly reacting (short-circuit resistance properties).

[0003] On the other hand, non-aqueous secondary batteries such as lithium-ion batteries are available in a variety of shapes, including cylindrical, prismatic, and pouch types, depending on their application. The manufacturing method of batteries also differs depending on the shape of the battery, but for example, in the manufacture of prismatic batteries, there is a process of pressing a wound or laminate of electrodes and polyolefin microporous membranes and inserting it into a rectangular outer casing.

[0004] In recent years, in order to increase the capacity of energy storage devices, efforts have been made to reduce the volume of energy storage devices by heat-pressing a laminate of electrodes and separators, or by heat-pressing a wound laminate of electrodes and separators. In this process, in order to fix the electrodes and separators after heat-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 function under predetermined conditions is placed on the separator base material to improve the adhesion between the entire separator and the electrodes.

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

[0006] For example, Patent Document 1 describes a separator having a porous coating layer containing organic polymer particles, with the aim of enhancing safety by increasing the bonding force between the separator and the electrode and thereby strengthening the integration of the separator and the electrode, without performing a humidification phase separation process of the organic binder polymer or a secondary coating of the 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 having a surface coating containing polymer binder particles of different particle sizes, with the aim of suppressing deformation of an energy storage device due to the expansion of electrode volume during charging. These polymer binder particles of different particle sizes form a gap between the separator and the electrode that allows for internal expansion of the energy storage device.

[0008] Patent Document 3 describes a separator having a composite material coating containing inorganic particles, polymer particles, and a binder, with the aim of further improving existing separators and methods for manufacturing the same, by providing good thermal stability and good adhesion to electrodes, thereby ensuring the safety and flatness of energy storage devices. The polymer particles are dispersed in the inorganic particles and protrude from the surface of the inorganic particles.

[0009] Patent Document 4 describes a separator comprising a functional layer containing inorganic particles and particulate polymer, with the aim of improving adhesiveness, heat resistance, and electrolyte injection properties. In this functional layer, when viewed from above, the area occupied by inorganic particles per unit area of ​​the functional layer surface exceeds 90%, the volume-average particle diameter of the particulate polymer is within a specific range, and the volume-average particle diameter of the particulate polymer is greater than the thickness of the inorganic particle layer.

[0010] Patent Document 5 describes a separator comprising a functional layer containing inorganic particles and particulate polymer, with the aim of providing a functional layer for electrochemical elements that exhibits excellent process adhesion and excellent cycle characteristics for electrochemical elements. This functional layer has a particle shedding area, and when the surface of the functional layer for electrochemical elements is viewed in plan view, the ratio of the area of ​​the particle shedding area to the total area of ​​the particulate polymer and the particle shedding area is 0.1% or more and 40.0% or less, and the volume average particle diameter of the particulate polymer is greater than the thickness of the inorganic particle layer containing the inorganic particles.

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

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

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

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

[0015] [Patent Document 1] Korean Published Patent Publication No. 10-2016-0118979 [Patent Document 2] International Publication No. 2019 / 089492 [Patent Document 3] Chinese Patent No. 105958000 Specification [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 [Overview of the project] [Problems that the invention aims to solve]

[0016] However, these conventional separators for lithium-ion secondary batteries and separators made of polyolefin microporous membranes had the following problems.

[0017] For example, Patent Documents 1 and 3 use secondary particulate adhesive polymers, which have the problem of uneven separator thickness distribution. Furthermore, due to the poor dispersibility of the adhesive polymer in its paint state, areas of adhesion occur on the separator, resulting in uneven adhesion to the electrode, a decrease in overall adhesion strength, and deterioration of heat resistance. Patent Document 2 lacks a heat-resistant layer with inorganic fillers, which has the problem of not being able to provide sufficient heat resistance to the separator. Patent Documents 4 and 5 have insufficient bonding strength of the coating layer, and there is still room for improvement in suppressing powder shedding during the manufacturing process and adhesion strength to the electrode.

[0018] On the other hand, the pressing process used in the manufacturing of batteries using conventional polyolefin microporous membranes, as described in Patent Documents 6-9, can sometimes result in a decrease in the battery's cycle characteristics and output characteristics. This phenomenon is also particularly pronounced when using high-capacity electrodes that are prone to expansion.

[0019] In view of the above circumstances, the present disclosure aims to provide a separator for energy storage devices that has high adhesion to electrodes, low thermal shrinkage rate, and can improve the cycle characteristics and output characteristics of the energy storage device, and an energy storage device having the same. [Means for solving the problem]

[0020] Examples of embodiments of this disclosure are listed below. [1] A separator for an energy storage device comprising a substrate which is a polyolefin microporous film mainly composed of polyolefin, and a coating layer disposed on at least one surface of the substrate, The above substrate has a film thickness of 1 μm to 30 μm and an air permeability of 500 sec / 100 cm. 3 The following conditions apply, and the post-compression porosity measured after compressing the above 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 above coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The particulate polymer described above includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, in a power storage device separator. [2] A separator for an energy storage device comprising a substrate which is a polyolefin microporous film mainly composed of polyolefin, and a coating layer disposed on at least one surface of the substrate, The crystal period of the above polyolefin microporous film, as measured by small-angle X-ray scattering (SAXS), is 37.0 nm or greater. The above coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The particulate polymer described above includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, in a power storage device separator. [3] The above substrate has a film thickness of 1 μm to 30 μm and an air permeability of 500 sec / 100 cm. 3 A separator for energy storage devices as described in item [2], wherein the above substrate has a post-compression porosity of 30% or more, as measured after compression under the conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes. [4] In the above coating layer, the amount of the particulate polymer 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 above coating layer. A separator for an energy storage device according to any one of items [1] to [3], wherein the coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer. [5] A separator for an energy storage device according to item [4], wherein when the thickness of the inorganic filler portion of the coating layer is L1, and the maximum distance from the substrate-coating layer boundary to the outer surface of the inorganic filler of the coating layer formed in the inclined shape is L2, the average value of the inclination ratio L2 / L1 of the coating layer is 1.2 or more. [6] A separator for an energy storage device according to item [4] or [5], wherein when L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the substrate-coating layer boundary 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 substrate-coating layer boundary to the contour of the protruding particulate polymer, the average value of the coverage rate (L2-L1) / (L3-L1) of the protruding portion of the protruding particulate polymer is 0.4 or more. [7] A separator for an energy 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 (meth)acrylic polymers, styrene-butadiene copolymers, and copolymers containing fluorine atoms. [8] A separator for energy storage devices 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] A separator for energy storage devices according to any one of items [1] to [6], wherein the particulate polymer includes a copolymer containing a polyfunctional (meth)acrylate as a monomer.

[10] A storage device including a separator for a storage device as described in any one of items [1] to [9].

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

[11] A separator for an energy storage device comprising a substrate which is a polyolefin microporous film mainly composed of polyolefin, and a coating layer disposed on at least one surface of the substrate, The above coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The particulate polymer described above includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, in a power storage device separator.

[12] The above substrate has a film thickness of 1 μm to 30 μm and an air permeability of 500 sec / 100 cm. 3 A storage device separator as described in item

[11] , wherein the post-compression porosity measured in a compression test under the conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more.

[13] The energy storage device separator described in item

[11] or

[12] , wherein the crystal long period measured by small-angle X-ray scattering (SAXS) of the polyolefin microporous film is 37.0 nm or longer.

[14] A separator for an energy 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 inorganic filler contained in the coating layer.

[15] A separator for an energy storage device according to any one of items

[11] to

[14] , wherein the coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer.

[16] A separator for an energy storage device according to any one of items

[11] to

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

[17] A separator for energy storage devices according to any one of items

[11] to

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

[18] A separator for an energy storage device according to any one of items

[11] to

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

[19] A separator for an energy 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] A separator for an energy storage device according to any one of items

[11] to

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

[11] to

[20] , wherein L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the substrate-coating layer boundary to the outer surface of the inorganic filler of the coating layer formed on the slope, and L3 is the maximum distance from the substrate-coating layer boundary to the contour of the protruding particulate polymer, and the average value of the coverage ratio (L2-L1) / (L3-L1) of the protruding portion of the protruding particulate polymer is 0.4 or more. [twenty two] A separator for an energy 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 particulate polymers contained in the coating layer. [twenty three] A separator for energy storage devices according to any one of items

[11] to

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

[11] to

[23] , wherein the methylene chloride soluble content in the separator for the energy storage device is 0.05% by mass or more and 0.80% by mass or less, based on the total mass of the separator for the energy storage device. [twenty five] A separator for energy storage devices as described in 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 above coating layer contains a water-soluble polymer, and is a separator for energy storage devices as described in any one of items

[11] to

[25] .

[27] The separator for energy storage devices according to item

[26] , wherein the content of the above-mentioned 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 above-mentioned inorganic filler.

[28] A separator for an energy storage device according to any one of items

[11] to

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

[29] A separator for an energy 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 (meth)acrylic polymers, styrene-butadiene copolymers, and copolymers containing fluorine atoms.

[30] A separator for energy storage devices 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] A separator for energy storage devices according to any one of items

[11] to

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

[32] A separator for energy storage devices according to any one of items

[11] to

[31] , wherein the above-mentioned particulate polymer is the primary particle.

[33] A separator for energy storage devices as described in item

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

[34] A separator for energy storage devices as described in any one of items

[11] to

[33] , wherein the thermal shrinkage rate in the TD direction at 130°C for 1 hour is 5% or less.

[35] A separator for energy storage devices as described in any one of items

[11] to

[34] , wherein the thermal shrinkage rate in the TD direction at 150°C for 1 hour is 5% or less.

[36] A storage device including a separator for a storage device as described in any one of items

[11] to

[35] . [Effects of the Invention]

[0022] This disclosure provides a separator for energy storage devices that has high adhesion to electrodes, low thermal shrinkage, and can improve the cycle characteristics and output characteristics of the energy storage device, as well as an energy storage device having the same. [Brief explanation of the drawing]

[0023] [Figure 1] This is a schematic diagram of the surface of the coating layer of the separator for the energy storage device in this embodiment. [Figure 2] This is a schematic diagram of the AA section in Figure 1. [Figure 3] This is an example of a power approximation curve relating porosity and air permeability after compression. [Modes for carrying out the invention]

[0024] The following describes in detail an exemplary embodiment of this disclosure (hereinafter abbreviated as "this embodiment"), but this disclosure is not limited to this embodiment.

[0025] In this specification, the longitudinal direction (MD) refers to the machine direction of continuous microporous membrane molding, and the width direction (TD) refers to the direction that intersects 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 combined in any way. Furthermore, the presence of a specific component as the main component of a particular component means that the content of that specific component constitutes the largest mass within the mass of that component. Unless otherwise specified, the physical properties or numerical values ​​described herein are measured or calculated by the methods described in the examples.

[0027] 《Separator for energy storage devices》 The separator for the energy storage device of this embodiment includes a substrate which is a polyolefin microporous film mainly composed of polyolefin, 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 particulate polymer is 1 to 50 parts by mass per 100 parts by mass of inorganic filler, preferably 3 to 50 parts by mass, more preferably 5 to 30 parts by mass, and even more preferably 10 to 25 parts by mass. By having an amount of particulate polymer of 1 to 50 parts by mass, it is possible to increase the adhesion to the electrode while maintaining ion permeability. Furthermore, from the viewpoint of improving heat shrinkage resistance, 10 parts by mass or less is preferable.

[0029] <Amount of particulate polymer protrusion> The particulate polymer includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer.

[0030] In this specification, "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 fillers stacked on top of it (the layer of inorganic fillers), and is measured from an SEM image of the cross-section of the coating layer. The "inorganic filler portion" refers to the portion that does not contain particulate polymers, which is located at least 1.5D horizontally (in the direction of the surface of the coating layer) from the center of each protruding particulate polymer, where D is the diameter of each protruding particulate polymer. The measurement conditions are described in the Examples section.

[0031] By ensuring that the protrusion of the particulate polymer is 0.1 times or more the thickness of the inorganic filler portion of the coating layer, the adhesion to the electrode can be enhanced. Furthermore, because the protrusion of the particulate polymer is 0.1 times or more 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, suppressing distortion of the wound body and improving cycle characteristics. In particular, by combining a substrate having the characteristics (6) and / or (7) described later with a particulate polymer with a large particle diameter that protrudes to the extent of 0.1 times or more the thickness of the coating layer, it has been found that not only is the air permeability of the substrate portion that does not come into contact with the particulate polymer when bonded to the electrode maintained at a good level, but the air permeability is also maintained at a good level in the substrate portion that comes into contact with the electrode via the particulate polymer (the portion that receives the load), resulting in excellent cycle characteristics and output characteristics. From this viewpoint, it is preferable that the protrusion of the particulate polymer is 0.2 times or more, or 0.3 times or more. From the viewpoint of suppressing the shedding of particulate polymer from the separator, the protrusion of 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, "protrusion" means that the particulate polymer protrudes toward the surface 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 the "protruding portion"), the particulate polymer does not need to be exposed to the surface of the coating layer, and at least a part or all of the protruding portion may be covered with the inorganic filler. From the viewpoint of preventing the particulate polymer from sliding off the coating layer and obtaining higher adhesive strength, it is preferable that at least a part of the periphery of the protruding portion is covered with the inorganic filler. Furthermore, from the viewpoint of ensuring a contact area between the particulate polymer and the electrode and obtaining higher adhesive strength, it is preferable that the central part of the protruding portion is exposed to the surface of the coating layer.

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

[0034] In this specification, "a state in which 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 line measured from the SEM image of the cross-section of the coating layer to the contour of the protruding particulate polymer is 1.1 times or more the thickness (L1) of the inorganic filler portion of the coating layer.

[0035] <Inclined morphology of the coating layer, contact ratio between particulate polymer and substrate, 180° peel strength, average number of adjacent particulate polymers, and ratio of average particle size> The separator for the energy storage device of this embodiment preferably has one or more of the following features (1) to (5): (1) The coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer; (2) 20% or more of the protruding particulate polymer is in contact with the surface of the substrate; (3) The 180° peel strength of the coating layer from the substrate (hereinafter also 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 also simply referred to as "average number of adjacent particulate polymers") is less than 2; (5) The ratio of the average particle size of the protruding particulate polymer to the average particle size of the inorganic filler, i.e., the ratio calculated as average particle size of particulate polymer / average particle size of inorganic filler (hereinafter also simply referred to as "ratio of average particle size") is greater than 10. By having at least one of the above features (1) to (5), it is possible to provide a separator for energy storage devices that has higher adhesion to electrodes and a lower thermal shrinkage rate.

[0036] Feature (1): For separators used in energy storage devices, it is preferable that the coating layer is formed in a sloping manner so that it becomes thicker towards the protruding particulate polymer. This prevents the particulate polymer from sliding off the coating layer and increases the adhesion to the electrodes. In this specification, "sloping manner" 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 of the coating layer formed in a sloping manner, the average value of the slope ratio L2 / L1 of the coating layer is 1.1 or more. For an example of the relationship between L1 and L2, please refer to the schematic diagram in Figure 2. It is preferable that the thickness of the coating layer changes continuously so that it gradually becomes thicker towards the protruding particulate polymer, and it is preferable that there are no discontinuous changes where the coating layer is missing. The absence of gaps in the coating layer tends to improve heat resistance and cycle characteristics. The slope may be gentler the further it is from the protruding particulate polymer and steeper the closer it is to the protruding portion of the particulate polymer. Furthermore, if the inorganic filler covers at least part or all of the protruding portion, the slope on the protruding portion may become gentler again towards the center of the protruding portion. The average value of the slope ratio L2 / L1 of the coating layer is preferably 1.2 or higher, 1.3 or higher, 1.4 or higher, 1.5 or higher, or 1.7 or higher.

[0037] The coating layer may be formed in a sloping manner so that it becomes thicker towards the protruding particulate polymer, thereby coating at least part or all of the protruding portion by allowing the inorganic filler to rest along the contour of the particulate polymer. Preferably, the inorganic filler covers a portion of the periphery of the protruding portion by resting along the contour of the particulate polymer. Furthermore, it is preferable that the area near the center of the protruding portion is exposed on the surface of the coating layer. If L3 is 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 furthest from the substrate-coating layer boundary), then the average value of the coating rate of the protruding portion (L2-L1) / (L3-L1) is preferably 0.4 or more. For an example of the relationship between L1, L2, and L3, please refer to the schematic diagram in Figure 2. By having an average value of 1.1 or more for the slope ratio L2 / L1, or an average value of 0.4 or more for the coating rate (L2-L1) / (L3-L1), the particulate polymer is prevented from sliding off the coating layer, and the adhesion force to the electrode is increased. The upper limit of the average value of the gradient ratio L2 / L1 is not particularly limited, but from the viewpoint of ensuring the contact area between the particulate polymer and the electrode and increasing the adhesive strength to the electrode, it 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. Also, 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 contour of the protruding particulate polymer (the point furthest 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 and increases the adhesive strength to the electrode. A coverage ratio of 0.8 or less increases the contact area between the particulate polymer and the electrode and further increases the adhesive strength to the electrode.

[0038] Feature (2): The separator for energy storage devices has a contact rate between the particulate polymer protruding from the coating layer and the substrate surface, preferably 20% or more, more preferably 50% or more, and even more preferably 70% or more. The "contact rate" is calculated from an image obtained by observing the cross-section of the coating layer of the separator for energy storage devices using a scanning electron microscope (SEM). Increasing the amount of particulate polymer protruding from the coating layer and in contact with the substrate further increases the bonding strength between the substrate and the particulate polymer, improving the 180° peel strength and increasing the adhesion strength to the electrodes. There is no particular upper limit to the contact rate between the particulate polymer protruding from the coating layer and the substrate surface, but it may be less than 100% or 100%.

[0039] Feature (3): The separator for energy storage devices has a 180° peel strength of preferably 200 gf / cm or more, more preferably 230 gf / cm or more, and even more preferably 250 gf / cm or more. "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 a 180° angle with respect to the substrate. A 180° peel strength of 200 gf / cm or more increases the adhesion to the electrodes 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): The separator for energy storage devices preferably has an average number of adjacent particulate polymers of less than two, more preferably less than one. "Adjacent" means that, as seen in images of the coating layer surface of the separator for energy storage devices observed with a scanning electron microscope (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. 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, increases adhesion to electrodes, suppresses thermal shrinkage, and ensures uniformity of the coating layer thickness. The lower limit of the average number of adjacent particulate polymers is not particularly limited, but may be greater than 0 or 0.

[0041] Features (5): In separators for energy storage devices, 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 taken when observing the surface of the coating layer of the separator for energy storage devices with a scanning electron microscope (SEM). The measurement conditions are described in the Examples section. A ratio of average particle size greater than 10 makes it easier for the particulate polymer to form a structure that protrudes from the surface of the coating layer, thereby increasing the adhesion to the electrodes and suppressing thermal shrinkage. From the viewpoint of balancing the permeability and adhesion of the separator, the upper limit of the ratio of average particle size is preferably 50 or less, more preferably 35 or less, and even more preferably 25 or less, 22 or less, and 20 or less.

[0042] The separator for the energy storage device of this embodiment is any combination of the above features (1) to (5), namely: (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), ( 3) and (5); (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 a combination of (1), (2), (3), (4) and (5). Among these, from the viewpoint of higher adhesive strength and lower thermal shrinkage rate, a combination of (1), (2), and (3) is preferred, namely, that the coating layer is formed in a sloping manner 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 particulate polymer particles with a radius of 10 μm or less> In this embodiment, the separator for the energy storage device has a number of other protruding particulate polymers within a radius of 10 μm from any one protruding particulate polymer, preferably less than 60, more preferably less than 40, even more preferably less than 15, and even more preferably less than 5. This suppresses 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 it may be 1 or more in order to make the particulate polymers appropriately dense and improve the adhesive strength.

[0044] <Methylene chloride soluble components> The separator for energy storage devices of this embodiment has a methylene chloride soluble content of preferably 0.05% to 0.80% by mass, more preferably 0.10% to 0.60% by mass, and even more preferably 0.15% to 0.50% by mass, based on the total mass of the separator for energy storage devices. The "soluble content" of methylene chloride refers to the components extracted into the methylene chloride when the separator is immersed in methylene chloride. Mainly, plasticizers mixed during the manufacturing of the base material are extracted as methylene chloride soluble content. By containing 0.10% by mass or more of methylene chloride soluble content, the bonding strength between the base material and the coating layer is further increased, making it easier to adjust the 180° peel strength to 200 gf / cm or more. By having a methylene chloride soluble content of 0.60% by mass or less, the internal resistance of the battery can be lowered. 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, and number of extractions in the plasticizer extraction process during substrate manufacturing if it is a batch process, and adjusting the extraction time, type of extraction solvent, temperature of the extraction solvent, and supply amount of the extraction solvent if it is a continuous process.

[0045] <Metallic cations> In this embodiment, the separator for energy storage devices has a total amount of metal cations in the coating layer that is preferably 0.1 ppm to 100 ppm, more preferably 0.1 ppm to 70 ppm, and even more preferably 0.1 ppm to 50 ppm, based on the total mass of the coating layer. When the total amount of metal cations is adjusted to be low, the inorganic filler and particulate polymer are more easily dispersed and coated during the formation of the coating layer. Examples of metal cations include sodium ions (Na). + ), calcium ions (Ca 2+ ) and magnesium ions (Mg 2+ Examples include the following. One method for adjusting the total amount of metal cations to between 0.1 ppm and 100 ppm is to wash the filler, which is the raw material for the coating layer, with water before use. The washing can be done once or two or more times, but the more times it is washed, the lower the total amount of metal cations contained in the filler becomes.

[0046] <Thermal contraction rate> In this embodiment, the separator for the energy storage device has a thermal shrinkage rate of TD of 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1% at 130°C for 1 hour. The thermal shrinkage rate of TD at 150°C for 1 hour is preferably 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%. Here, if the thermal shrinkage rate of TD is 5% or less, it is possible to more effectively suppress the occurrence of short circuits in areas other than where external force is applied when heat is generated due to a short circuit during a collision test. This makes it possible to more reliably prevent the temperature rise of the entire battery, and the smoke and fire that may occur as a result. The thermal shrinkage rate of the separator can be adjusted by appropriately combining the stretching operation and heat treatment of the base material as described above. At the same time as suppressing the thermal shrinkage rate of TD, the thermal shrinkage of MD is also preferably 5% or less, more preferably 0% to 3%, and even more preferably 0% to 1%.

[0047] <Air permeability of the separator> The air permeability of the separator for energy storage devices is preferably 10 seconds / 100 cm. 310,000 seconds / 100 cm or more 3 Preferably 10 seconds / 100 cm or less 3 1,000 seconds / 100 cm or more 3 More preferably 50 seconds / 100 cm or less 3 500 seconds / 100 cm or more 3 Particularly preferably 80 seconds / 100 cm or less 3 250 seconds / 100 cm or more 3 It is less than this. By this, high ion permeability can be obtained. The air permeability is the air permeability resistance measured in accordance with JIS P-8117.

[0048] 〈Base material〉 The base material is a polyolefin microporous membrane containing polyolefin as a main component, and preferably has the following characteristics (6), (7) or a combination thereof. (6) The film thickness is 1 μm to 30 μm, and the air permeability is 500 sec / 100 cm 3 or less, and the porosity after compression measured in a compression test under the conditions of a temperature of 70 °C, a pressure of 8 MPa, and a compression time of 3 minutes is 30% or more. (7) The crystal long period measured by the small-angle X-ray scattering (SAXS) method of the polyolefin microporous membrane is 37.0 nm or more.

[0049] Characteristic (6): Although not bound by theory, the polyolefin microporous membrane has an air permeability of 500 sec / 100 cm or less and a porosity after compression of 30% or more within the range of a film thickness of 1 μm to 30 μm. For example, in the production of a non-aqueous secondary battery using a polyolefin microporous membrane as a separator, the electrical resistance of the polyolefin microporous membrane can be reduced or the increase in electrical resistance can be suppressed after the pressing process. It is considered that high output and high cycle characteristics of the non-aqueous secondary battery can be achieved by this. The suppression of the increase in resistance by the polyolefin microporous membrane is remarkable when using an electrode that is likely to expand and contract in the cell of the non-aqueous secondary battery, and is more remarkable when using a high-capacity electrode used in an in-vehicle battery or the like, or a silicon (Si)-containing negative electrode. The method of performing a compression test under the conditions of a temperature of 70 °C, a pressure of 8 MPa, and a compression time of 3 minutes will be described in detail in the examples.​​

[0050] The post-compression porosity is thought to be related to the structure of the main component of the polyolefin microporous membrane, which is responsible for reducing resistance and / or suppressing resistance increase in non-aqueous secondary batteries. From the viewpoint described above, the post-compression porosity of the polyolefin microporous membrane is preferably 31% or more, more preferably 32% or more, and even more preferably 33% or more. The upper limit of the post-compression porosity of the polyolefin microporous membrane can be determined according to the porosity before compression, and may be, for example, preferably 60% or less, and even more preferably 50% or less.

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

[0052] Comparing the porosity of polyolefin microporous membranes before and after compression testing 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 non-aqueous secondary batteries, thereby achieving high power output and high cycle characteristics. The porosity of polyolefin microporous membranes before or before compression testing (hereinafter simply referred to as "porosity") is measured by the method described in the examples, and its preferred numerical range will be described later.

[0053] In addition to the reduction in electrical resistance and suppression of resistance increase described above, the film thickness of the polyolefin microporous film 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 miniaturization. The film thickness of the microporous film can be optimized, for example, by the distance between the cast rolls, the stretching ratio in the stretching process, etc.

[0054] The air permeability of the polyolefin microporous membrane before compression is as described in the example section "Air permeability before compression (seconds / 100cm)". 3 The air permeability of the polyolefin microporous membrane can be measured by the method described in ). In addition to the reduction in electrical resistance and suppression of resistance increase described above, the air permeability of the microporous membrane and the output of non-aqueous secondary batteries are preferably 400 sec / 100 cm. 3 More preferably, 300 sec / 100 cm 3 More preferably, 200 sec / 100 cm 3 The following is particularly preferable: 160 sec / 100 cm 3 The following is preferred, and from the viewpoint of the mechanical strength of the microporous membrane, 40 sec / 100 cm 3 That concludes the explanation. The air permeability of the microporous membrane can be optimized in the same way as the post-compression porosity control methods described above.

[0055] Features (7): Although not bound by theory, polyolefin microporous membranes, by having a crystal period of 37.0 nm or longer, surprisingly exhibit improved structural uniformity and compressibility, and consequently, improved reaction uniformity within non-aqueous secondary batteries. This suggests that, for example, high power output and high cycle characteristics can be achieved even after the pressing process in the fabrication of non-aqueous secondary batteries using polyolefin microporous membranes as separators. The improvement in structural uniformity and compressibility of polyolefin microporous membranes is particularly noticeable when using electrodes that are prone to expansion and contraction within the cell of a non-aqueous secondary battery, and is even more pronounced when using high-capacity electrodes or silicon (Si)-containing negative electrodes used in automotive batteries, etc.

[0056] SAXS measurements of polyolefin microporous membranes will be described in detail in the examples. Although not bound by theory, the crystal period obtained by SAXS measurement is thought to be related to the structure of polyethylene, which improves the structural uniformity and compressibility of the membrane and the reaction uniformity in non-aqueous secondary batteries. Furthermore, the crystal period of polyolefin microporous membranes is thought to correlate with the post-compression porosity of the membrane. From the viewpoint described above, the crystal 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 length period of a polyolefin microporous film can be adjusted to within the numerical range described above by controlling, for example, the molecular weight of the polyolefin raw material, the molecular weight and content of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, the stretching coefficient during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, and the heat setting temperature during the biaxial stretching process, in the manufacturing process of the polyolefin microporous film.

[0058] The minimum thickness of the polyolefin microporous film is 1 μm or more in order to maintain mechanical strength and insulation. To improve battery safety by ensuring sufficient resin per unit area, the film thickness is preferably 2 μm or more, more preferably 3 μm or more. To ensure insulation when lithium dendrites grow, the film thickness is preferably 6 μm or more, more preferably 10 μm or more. From the viewpoint of increasing the capacity of non-aqueous secondary batteries, the film thickness of the polyolefin microporous film is preferably 16 μm or less. The film thickness of the microporous film can be adjusted by controlling the distance between the cast rolls, the stretching ratio in the stretching process, etc.

[0059] The air permeability of the polyolefin microporous membrane before compression is preferably 30 sec / 100 cm. 3 More than 250sec / 100cm 3 More preferably, 40 sec / 100 cm 3 More than 200sec / 100cm 3More preferably, 50 sec / 100 cm 3 More than 180sec / 100cm 3 More preferably, 60 sec / 100 cm 3 More than 150sec / 100cm 3 The following applies: The air permeability of the microporous membrane before compression is preferably 40 sec / 100 cm, from the viewpoint of ensuring puncture resistance. 3 Therefore, from the viewpoint of output characteristics, 200 sec / 100 cm is preferred. 3 The following applies:

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

[0061] From the viewpoint of improving the shutdown performance and other aspects when forming a polyolefin microporous membrane for non-aqueous secondary batteries, it is preferable that the porous membrane is formed from a polyolefin resin composition in which polyolefin resin accounts for 50% to 100% by mass of the resin components constituting the porous membrane.

[0062] Polyolefins are advantageous for reducing the thickness of separators because they exhibit excellent coating properties when a coating solution is applied to their film, thereby increasing the active material ratio in energy storage devices and increasing the capacity per unit volume. The polyolefin microporous film can be the same material used as the substrate for conventional separators, and it is preferable that it is a porous film with fine pores that is ionically conductive but not electrically conductive, and has high resistance to organic solvents.

[0063] (Material of the base material) The substrate is a polyolefin microporous membrane containing polyolefin as the main component. "Containing as the main component" means that the mass of the component in question (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, even more preferably 95 parts by mass or more, and particularly preferably 98 parts by mass or more, and may be 100 parts by mass, based on the total mass of the substrate.

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

[0065] Polyolefins, among others, include polyethylene, polypropylene, and polybutene, which are particularly suitable from the viewpoint of reducing or suppressing the increase in electrical resistance of the membrane, as well as the compressive resistance and structural uniformity of the membrane. More specifically, examples include 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 can be used individually or in combination of two or more. Among these, 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 is preferred as the polyolefin, from the viewpoint of shutdown characteristics where pores are closed by thermal melting. In particular, high-density polyethylene is preferred because it has a low melting point and high strength, and its density measured according to JIS K 7112 is 0.93 g / cm³. 3 Polyethylene meeting the above criteria is even more preferable. 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 preferable that the main component of the polyolefin is polyethylene, and it is preferable that the polyethylene content relative to the total mass of polyolefin in the substrate is 50 parts by mass or more.

[0067] To improve the heat resistance of the substrate, the polyolefin microporous film more preferably contains polypropylene and a polyolefin other than polypropylene. Examples of polyolefin resins other than polypropylene include homopolymers using ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, as well as 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 a similar viewpoint, the content ratio of olefin resins other than polypropylene, such as polyethylene, relative to the total mass of polyolefin in the polyolefin microporous film (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 viewpoint of crystallinity, high strength, and compressive resistance when forming a polyolefin microporous membrane for non-aqueous secondary batteries, it is preferable that the polyolefin resin porous membrane is formed from a polyethylene composition in which polyethylene accounts for 50% to 100% by mass of the resin components constituting the microporous membrane. More preferably, the proportion of polyethylene in the resin components constituting the porous membrane is 60% to 100% by mass, even more preferably 70% to 100% by mass, and even 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 a 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 preferable because it tends to result in high strength due to the entanglement of polymers. On the other hand, a viscosity-average molecular weight of 6,000,000 or less is preferable from the viewpoint of improving moldability in the extrusion and stretching processes.

[0071] When the porous polyolefin resin membrane contains polyethylene as a main component, the lower limit of Mv of at least one type of 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 Mv of polyethylene may be, for example, 2,000,000 or less. From a similar viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin constituting the porous polyolefin resin 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 also be 100% by mass. From the viewpoint of reduced fluidity when the membrane melts and short-circuit resistance during nail penetration tests, the proportion of polyethylene with an Mv of 600,000 or more in the polyolefin resin constituting the porous polyolefin resin membrane is preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and even more preferably 70% by mass or more, and may also 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, 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 with a viscosity-average molecular weight of less than 1 million alone, a mixture of a polyolefin with a viscosity-average molecular weight of 2 million and a polyolefin with a viscosity-average molecular weight of 270,000, where the viscosity-average molecular weight of the mixture is less than 1 million, may be used.

[0074] The base material may contain other resins besides polyolefins, such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimidamide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, and other resins.

[0075] The base material may contain any additives. Such additives are not particularly limited and include, for example, plasticizers, polymers other than polyolefins, inorganic particles, antioxidants such as phenolic, phosphorus-based, and sulfur-based antioxidants, metal soaps such as calcium stearate and zinc stearate, ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging 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 polyolefin resin in the polyolefin microporous film.

[0076] The substrate preferably contains a plasticizer. When the substrate contains a plasticizer, the bonding strength between the substrate and the coating layer is improved, making it easier to control the 180° peel strength to 200 gf / cm or higher. The amount of plasticizer is preferably 0.1 parts by mass or more and 1.6 parts by mass or less, more preferably 0.2 parts by mass or more and 1.2 parts by mass or less, and even more preferably 0.3 parts by mass or more and 1.0 part by mass or less, based on the total mass of the substrate. By having the amount of plasticizer within the above range, it is possible to improve the bonding strength between the substrate and the coating layer while lowering 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 as the plasticizer.

[0077] When a porous polyolefin resin film contains polyethylene as its main component, the MDND (110) crystallite size of the polyethylene is preferably 28 nm or less. The MDND (110) crystallite size of polyethylene can be measured by X-ray diffraction (XRD) or wide-angle X-ray scattering (WAXS), as detailed in the examples.

[0078] While not limited to theory, when the MDND (110) crystallite size of polyethylene is 28.0 nm or less, the polyolefin microporous film containing that polyethylene tends to become rigid, improving the film's compressive resistance. This allows for both high power output and high cycle characteristics even after the pressing process in the manufacturing of non-aqueous secondary batteries. From this viewpoint, the MDND (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 MDND (110) crystallite size of polyethylene is 22.0 nm or less, the film's rigidity increases, improving its compressive resistance. The MDND (110) crystallite size of polyethylene can be adjusted to within the numerical range described above by controlling, for example, the molecular weight of the polyolefin raw material, the molecular weight of the polyethylene raw material, the stretching ratio during the biaxial stretching process, the preheating coefficient during the biaxial stretching process, and the stretching coefficient during the biaxial stretching process in the manufacturing process of polyolefin microporous membranes.

[0079] The polyolefin resin contained in the porous polyolefin resin film has a melting point preferably in the range of 120°C to 150°C, more preferably 125°C to 140°C, and / or the DSC 1st peak temperature preferably in the range of 136°C to 144°C, from the viewpoint of making the film rigid and improving its compressive resistance.

[0080] When forming a polyolefin microporous membrane as a separator for non-aqueous secondary batteries, from the viewpoint of crystallinity, high strength, compressibility, and suppression of electrical resistance, 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, even more preferably 80% by mass or more, and 100% by mass or less, preferably 97% by mass or less, and even more preferably 95% by mass or less, based on the total mass of the polyolefin resin. Furthermore, a polyethylene (PE) proportion of 100% by mass in the polyolefin resin is preferable from the viewpoint of strength development. A PE proportion of 50% by mass or more in the polyolefin resin is also preferable 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; antioxidants such as phenolic, phosphorus-based, and sulfur-based agents; 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, based on 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 polyolefins in the manufacturing process of the polyolefin microporous membrane. Furthermore, multilayer polyolefin resin microporous membranes having a structure in which two or more layers of the same or different types of polyolefin resin microporous membranes are laminated can also be adjusted as described above.

[0083] (Structure of the base material) Polyolefin microporous membranes have a porous structure in which a large number of very small pores come together to form dense interconnected pores. As a result, they exhibit excellent ion permeability and high strength when containing electrolytes.

[0084] The average thickness of the polyolefin microporous film 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 viewpoint of high ion permeability and good rate characteristics, and from the viewpoint of reducing the volume occupied by the separator in high-capacity batteries to improve battery capacity. The average thickness of the polyolefin microporous film can be adjusted within the above numerical range by controlling the distance between the cast rolls, the cast clearance, the stretching ratio during the biaxial stretching process, the HS ratio, the HS temperature, etc.

[0085] 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 viewpoint of reducing the electrical resistance of the membrane after the pressing process in the manufacture of a non-aqueous secondary battery equipped with a microporous membrane as a separator, thereby achieving both high output and high cycle characteristics of the battery, and from the viewpoint of achieving a certain membrane strength and low air permeability. Furthermore, from the viewpoint of battery safety and achieving a certain membrane strength and low air permeability, it 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, the stretching ratio, the heat-fixing temperature, the stretching ratio during heat-fixing, the relaxation rate during heat-fixing, or by combining these.

[0086] The pore size of the microporous film is preferably 30 nm to 70 nm, more preferably 35 nm to 60 nm, when measured by the half-dry method, from the viewpoint of achieving high ion permeability, excellent dielectric strength, and high strength. The pore size of the microporous film can be adjusted, for example, by controlling the stretching temperature, stretching ratio, heat-fixing temperature, stretching ratio during heat-fixing, and relaxation rate during heat-fixing, or by a combination thereof.

[0087] The melt flow index (MI) of a 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 even more preferably 0.01 to 0.4, from the viewpoint of reducing the fluidity of the membrane when it melts and suppressing short circuits between electrodes due to separator flow in the exothermic state during nail penetration testing. The MI of a polyolefin microporous membrane can be adjusted to the above numerical range by, for example, controlling the molecular weight and blending ratio of polymer raw materials such as polyolefins.

[0088] Regarding the molecular weight distribution of polyolefin microporous membranes measured by GPC, from the viewpoint of reducing fluidity during membrane melting and short-circuit resistance during nail penetration tests, polyethylene components with a Mw of 1,000,000 or more constitute 7% or more by mass of the total eluted components, more preferably 9% or more by mass, even more preferably 12% or more by mass, and even more preferably 15% or more by mass. Furthermore, from the viewpoint of suppressing excessive stress when the membrane shrinks in a high-temperature environment, polyethylene components with a Mw of 1,000,000 or more constitute 57% or less by mass, more preferably 42% or less by mass, even more preferably 33% or less by mass, and even more preferably 27% or less by mass, based on the total eluted components. The molecular weight distribution of polyolefin microporous membranes can be adjusted within the above numerical range by, for example, controlling the type, molecular weight, and blending ratio of polyolefin raw materials.

[0089] The puncture strength of the microporous film, which has not been converted to basis weight (hereinafter simply referred to as 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 post-compression porosity, crystallinity, and electrical resistance of the polyolefin microporous film. The puncture strength is more preferably 300 gf to 690 gf, and even more preferably 310 gf to 680 gf. A puncture strength of 200 gf / 20 μm or more is preferable from the viewpoint of suppressing film rupture due to detached active material, etc., when the separator is wound together with the electrode, and from the viewpoint of suppressing concerns about short circuits due to the expansion and contraction of the electrode accompanying charging and discharging. On the other hand, a puncture strength of 2000 gf / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured according to the method described in the examples. The puncture strength can be adjusted by adjusting the stretching ratio of the substrate and / or the stretching temperature, etc.

[0090] From the viewpoint of suppressing thermal runaway in non-aqueous secondary batteries, the basis weight of the polyolefin microporous membrane is preferably 3.0 g / m². 2 From the viewpoint of increasing battery capacity, a preferred value is 10 g / m². 2 The following applies: The basis weight of the polyolefin microporous membrane is more preferably 3.0 g / m². 2 More than 7.0g / m 2 More preferably, 3.0 g / m 2 More than 6.0g / m 2 The following is the result: Improved compression resistance allows for battery safety even at lower basis weights.

[0091] From the viewpoint of safety for non-aqueous secondary batteries containing microporous membranes, the dielectric strength per unit area of ​​the microporous membrane is preferably 0.13 kV / (g / m²). 2 That's all.

[0092] The tensile breaking strength of polyolefin microporous membranes, both MD and TD, should preferably have an upper limit of 5000 kgf / cm², from the viewpoint of ensuring the necessary membrane strength for winding and laminating electrodes and separators in the manufacturing process of non-aqueous secondary batteries. 2 The following, more preferably, is 4500 kgf / cm².2 More preferably, 4000 kgf / cm² 2 More preferably, 3500 kgf / cm² 2 The following is particularly preferred: 3,000 kgf / cm² 2 The following applies. The lower limit is preferably 500 kgf / cm². 2 More than 700 kgf / cm² 2 More preferably, 1,000 kgf / cm² 2 More preferably, 1500 kgf / cm² 2 In particular, 2000 kgf / cm² is preferred. 2 In particular, 2500 kgf / cm² is preferred. 2 That concludes the explanation. Furthermore, the upper limit of the tensile breaking strength of the polyolefin microporous membrane is preferably 5000 kgf / cm² for both MD and TD, from the viewpoint of suppressing thermal shrinkage of the polyolefin microporous membrane. 2 It is lower than that.

[0093] The closer the tensile breaking strengths of the MD and TD of a polyolefin microporous membrane, the more uniformly the membrane will rupture during nail-piercing tests of non-aqueous secondary batteries, minimizing the short-circuit area and thus improving the safety of the nail-piercing test. Furthermore, the closer the tensile breaking strengths of the MD and TD of a polyolefin microporous membrane, the less likely the membrane is to tear in the direction of weakness when foreign matter is introduced or when subjected to external impact, improving safety and resulting in a more isotropic structure, which improves the battery's cycle characteristics. From this viewpoint, the ratio of the tensile breaking strength of the MD to the tensile breaking strength of the TD (MD / TD tensile breaking strength ratio) of a polyolefin microporous membrane is preferably 0.5 to 2.0, more preferably 0.7 to 1.5, even more preferably 0.7 to 1.4, even 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 of the polyolefin microporous membrane can be adjusted to within the numerical range described above by controlling, for example, the stretch ratio and HS ratio during the biaxial stretching process.

[0094] When the tensile elongation at break of a polyolefin microporous membrane, both MD and TD, is controlled within an appropriate numerical range, the membrane stretches and ruptures appropriately during the nail-piercing test of a non-aqueous secondary battery, minimizing the short-circuit area and thus improving the safety of the nail-piercing test. If the tensile elongation at break is too high, the nail-piercing area stretches too much, causing the surrounding area to be pulled and the film thickness in the surrounding area to thin, leading to a short circuit over a large area. From this viewpoint, the tensile elongation at break of a polyolefin microporous membrane, 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 of the MD and / or TD of a polyolefin microporous membrane can be adjusted within the numerical range described above by controlling, for example, the stretching ratio and HS ratio during the biaxial stretching process.

[0095] The closer the tensile elongation values ​​of the MD and TD of a polyolefin microporous membrane, the more the membrane stretches and ruptures appropriately during the nail-piercing test of a non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nail-piercing test. From this viewpoint, the ratio of the MD tensile elongation to the TD tensile elongation (MD / TD tensile elongation ratio) of a polyolefin microporous membrane is preferably 0.3 to 2.0, more preferably 0.35 to 1.5, even more preferably 0.4 to 1.3, and even more preferably 0.5 to 1.2. The MD / TD tensile elongation ratio of a polyolefin microporous membrane can be adjusted to the numerical range described above by controlling, for example, the stretching ratio and HS ratio during the biaxial stretching process.

[0096] The tensile modulus of polyolefin microporous membranes is preferably 1,000 kg / cm² for 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 a non-aqueous secondary battery during a nail puncture test, causing deformation of the separator and electrodes. 2 ~10,000 kg / cm 2 More preferably 2,000 kg / cm² 2 ~90,000 kg / cm 2 That is the case.

[0097] The closer the tensile modulus values ​​of the MD and TD of a polyolefin microporous membrane, the more uniformly the membrane will rupture during the nail-piercing test of a non-aqueous secondary battery, thereby minimizing the short-circuit area and improving the safety of the nail-piercing test. From this viewpoint, the ratio of the tensile modulus of the MD to the tensile modulus of the TD 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 even more preferably 0.5 to 1.3. The MD / TD tensile modulus ratio of a polyolefin microporous membrane can be adjusted to the numerical range described above by controlling, for example, the stretching ratio and HS ratio during the biaxial stretching process.

[0098] The shutdown (fuse) temperature of the porous membrane is preferably 150°C or lower, more preferably 149°C or lower. The upper limit of the shutdown temperature means that if some abnormal reaction occurs and the internal temperature of the battery rises, the pores of 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, thus improving safety. On the other hand, from the viewpoint of not degrading battery performance even when exposed to high temperatures exceeding 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 value of the surface smoothness between one side and the other side of the polyolefin microporous membrane is preferably 20,000 sec / 10cm. 3 Over 200,000sec / 10cm 3 More preferably, 30,000 sec / 10cm 3 Over 180,000sec / 10cm 3 More preferably, 40,000 sec / 10cm 3 Over 160,000sec / 10cm 3The following is particularly preferred: 50,000 sec / 10cm 3 Over 140,000sec / 10cm 3 The following is the result: Surface smoothness of 20,000 sec / 10cm 3 If the surface smoothness is lower, the physical distance between the polyolefin microporous membrane and the electrode material becomes non-uniform, which can lead to non-uniform battery reactions and degraded cycle characteristics. 3 If the value is higher, the distance between the polyolefin microporous membrane and the electrode material decreases, and the void formed between the microporous membrane and the electrode material becomes smaller, which can hinder the uniform penetration of the electrolyte and worsen the cycle characteristics. The surface smoothness of the polyolefin microporous membrane can be adjusted to within the numerical range described above 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 during the biaxial stretching process, the MD / TD stretching temperature during the biaxial stretching process, the heating coefficient per unit resin of the resin composition during the biaxial stretching process, the HS ratio, and the HS temperature.

[0100] <Coating layer> The separator for the energy 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 side of the substrate or on both sides. "Disposed on the surface" means that it may be disposed on all of the surface of the substrate or on part of it. The coating layer is intended to be directly bonded to the electrodes. It is preferable that the substrate and the electrodes are bonded via the coating layer so that the coating layer is directly bonded to the electrodes. The coating layer is preferably a coated layer formed by applying a coating solution containing an inorganic filler and a particulate polymer to the substrate.

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

[0102] (Inorganic filler) While not particularly limited, inorganic fillers are preferably those with a melting point of 200°C or higher, high electrical insulation properties, and electrochemical stability within the range of use for energy storage devices such as lithium-ion secondary batteries. Examples of such inorganic fillers include inorganic oxides (oxide-based ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride-based 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 hydroxide oxide, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These can be used individually or in combination of two or more. Among these, at least one selected from the group consisting of alumina, barium sulfate, and aluminum hydroxide oxide (boehmite) is preferred as the inorganic filler.

[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 50 nm or more for the inorganic filler is preferable from the viewpoint of maintaining voids for ions to permeate the coating layer and improving rate characteristics. An average particle size of 2000 nm or less for the inorganic filler is preferable from the viewpoint of increasing the weight ratio of the 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, especially when the thickness of the coating layer is small, it forms a uniform coating layer thickness and improves heat shrinkage resistance. The average particle size of the inorganic filler is preferably, for example, between 250 nm and 450 nm. This is because it allows for a high degree of compatibility between rate characteristics and heat shrinkage resistance. The "average particle size" of the inorganic filler was measured by the method described in the examples. As a method for adjusting the particle size and distribution of the inorganic filler, for example, a method of reducing the particle size by crushing the inorganic filler using an appropriate grinding device such as a ball mill, bead mill, or jet mill. The particle size distribution of the inorganic filler can be such that there is one peak in the frequency graph relative to the particle size. However, it may also be such that there are two peaks or a trapezoidal chart with no peaks. 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 0.55 or less of the particle size distribution 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 increasing the adhesion strength with the electrode.

[0104] Examples of inorganic filler shapes include plate-like, flaky, needle-like, columnar, spherical, polyhedral, and lumpy (block-like) shapes. Multiple types of inorganic fillers having these shapes may be used in combination. From the viewpoint of improving the gradient of the coating layer and increasing the adhesion to the electrode, a block shape is preferred. Regardless of the aspect ratio, a block shape is preferred over a spherical shape for the filler. When the shape of the filler is close to spherical, surface contact of the particulate polymer with the substrate is inhibited due to the surface tension and Newtonian fluidity of the paint, which is undesirable.

[0105] The aspect ratio of the inorganic filler is preferably 1.0 to 2.5, more preferably 1.1 to 2.0. An aspect ratio of 2.5 or less is preferable from the viewpoint of suppressing the amount of moisture adsorption by the separator and suppressing capacity degradation when repeated cycles are performed, suppressing deformation at temperatures exceeding the melting point of the substrate, and improving the gradient of the coating layer and increasing the adhesion strength to the electrode. The reason why the gradient increases when the aspect ratio of the inorganic filler is 1.0 to 2.5 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, obtained by dividing the standard deviation (SD) of the volume-average particle size of the inorganic filler by the value of 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 ratio of the coating layer and increasing the adhesion strength to the electrode. The reason why the gradient ratio increases when the particle size distribution of the inorganic filler is 0.55 or less is thought to be that the uniformity of the particles increases and the contact rate between particles improves, making it easier to form a laminated structure.

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

[0108] (particulate polymer) Particulate polymers are particles of thermoplastic polymers. From the viewpoint of improving adhesion between the separator and the electrode, it is preferable that the particulate polymer contains a thermoplastic polymer with 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 described in JIS K7121 and is determined from the DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the point where the curve of the stepwise transition portion intersects a straight line extending the low-temperature baseline in the DSC curve toward the high-temperature side and a straight line equidistant in the vertical axis direction from the straight line extending the high-temperature baseline in the DSC curve toward the low-temperature side can be adopted as the glass transition temperature. More specifically, it can be determined according to the method described in the examples. Furthermore, "glass transition" refers to the change in heat flow that occurs on the endothermic side due to the change in state of the polymer test specimen in DSC. Such a change in heat flow is observed as a stepwise change in the shape of the DSC curve. A "stepwise change" refers to the portion of the DSC curve from the previous low-temperature baseline to a new high-temperature baseline. Furthermore, a combination of a stepwise change and a peak is also included in the definition of a stepwise change. In addition, in the stepwise change portion, if the upper side is considered the exothermic side, it can also be described as the point where the curve changes from an upward-convex curve to a downward-convex curve. A "peak" in the DSC curve refers to the portion where the curve moves away from the low-temperature baseline and then 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 to 110°C, more preferably 50°C or higher, even more preferably 80°C or higher, and even more preferably 90°C or higher, and is particularly preferably greater than 90°C from the viewpoint of improving the adhesive strength after electrolyte injection. A Tg of 20°C or higher for the particulate polymer is preferable from the viewpoint of suppressing adhesion (blocking) between adjacent separators via the coating layer during storage and transportation of separators for energy storage devices, and during the manufacturing process of energy storage devices. On the other hand, a Tg of 110°C or lower for the particulate polymer is preferable from the viewpoint of obtaining good adhesion to electrodes. The Tg of the particulate polymer can be appropriately adjusted, for example, by changing the type of monomer used when manufacturing the particulate polymer, and, if the particulate polymer is a copolymer, by changing the blending ratio of each monomer. In other words, for each monomer used in the production of particulate polymers, the approximate glass transition temperature can be estimated from the generally available Tg of the homopolymer (for example, as listed in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the monomer blending ratio. For example, copolymers obtained by copolymerizing monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid in high proportions, which give homopolymers with a Tg of approximately 100°C, will have a high Tg, while copolymers obtained by copolymerizing monomers such as n-butyl acrylate and 2-ethylhexyl acrylate in high proportions, which give homopolymers with a Tg of approximately -50°C, will have a low Tg. Furthermore, the Tg of a copolymer can also be estimated using the FOX formula, which is shown below. 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + W i / Tg i +···W n / Tg n Here, in the formula, 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 from 1 to n, and n is the number of types of monomers that make up the copolymer. However, in this embodiment, the glass transition temperature Tg of the particulate polymer is the value measured by the method using DSC described above.

[0110] 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, relative to the thickness of the coating layer, from the viewpoint 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 refers to the volume average particle diameter 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, a form in which two or more primary particles are in contact and form an aggregate is called a "secondary particle."

[0111] The particle size distribution MV / MN of the particulate polymer, obtained by dividing the volume-average particle diameter MV of the particulate polymer by the number-average particle diameter 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 viewpoint of ensuring uniformity of the thickness of the coating layer, improving cycle characteristics, improving adhesion to the electrode, reducing the amount of particulate polymer on the smaller particle size side of the distribution embedded in the coating layer, improving adhesion to the electrode, 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 to 10 μm, more preferably 1 μm to 5 μm, and even more preferably 2 μm to 4 μm. The fact that the particulate polymer is 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 adhesion to the electrode, suppresses thermal shrinkage, and ensures uniformity of the thickness of the coating layer. When the average particle size of the primary particles is 1 μm to 10 μm, the particulate polymer is more likely to form a structure that protrudes from the surface of the coating layer, which increases the adhesion to the electrode and suppresses thermal shrinkage.

[0113] Examples of thermoplastic polymers include (meth)acrylic polymers, conjugated diene polymers, polyvinyl alcohol resins, and fluororesins.

[0114] From the viewpoint of high adhesion to electrodes and low thermal shrinkage, thermoplastic polymers more preferably contain (meth)acrylic polymers. "(meth)acrylic polymer" means a polymer or copolymer containing a (meth)acrylic compound as a monomer. Such (meth)acrylic compounds can be represented by the following general formula. CH2=CR Y1 -COO-R Y2 In the formula, R Y1 R represents a hydrogen atom or a methyl group. Y2 R represents a hydrogen atom or a monovalent hydrocarbon group. Y2If the group is a monovalent hydrocarbon group, it may have substituents and may also have heteroatoms. Examples of monovalent hydrocarbon groups include linear alkyl groups, cycloalkyl groups, and aryl groups, which may be linear or branched. Examples of substituents include hydroxyl groups and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. (meth)acrylic compounds can be used individually 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 hydroxyl groups, and aryl esters of (meth)acrylates.

[0115] More specifically, examples of linear alkyl (meth)acrylates include linear alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, and isopropyl groups; linear alkyl groups having 4 or more carbon atoms, such as n-butyl, isobutyl, t-butyl, n-hexyl, 2-ethylhexyl groups; and lauryl groups. An example of an aryl (meth)acrylate is phenyl (meth)acrylate.

[0116] Examples of (meth)acrylates 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; as well as (meth)acrylates having an aromatic ring, such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0117] Conjugated diene polymers are polymers that have a conjugated diene compound as a monomer unit and are preferred because they are easily compatible with electrodes. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugated pentadienes, substituted and side-chain conjugated hexadienes, which may be used individually or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Conjugated diene polymers may also contain (meth)acrylic compounds or other monomers as monomer units, as described later. Examples of such monomers include styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, and acrylonitrile-butadiene-styrene copolymers and their hydrides.

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

[0119] Fluorine-containing resins are preferred from the viewpoint of dielectric strength, and examples include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers containing fluorine atoms, such as vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. Fluorine-containing resins are preferably copolymers 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. More preferably, the copolymer containing (meth)acrylate as a monomer contains 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 energy storage devices that has higher adhesion to electrodes and a lower thermal shrinkage rate.

[0121] The particulate polymer preferably contains a crosslinkable monomer. The crosslinkable monomer is not particularly limited, but examples include monomers having two or more radically polymerizable double bonds, and monomers having functional groups that give a self-crosslinking structure during or after polymerization. These can be used individually 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 difunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specifically, 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 can be used individually or in combination of two or more. In particular, from the same viewpoint as above, at least one of trimethylolpropane triacrylate or trimethylolpropane trimethacrylate is preferred.

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

[0124] Specific examples of resins used in resin binders include, for example, polyolefins such as polyethylene and polypropylene; fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; fluororubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; styrene-butadiene copolymer and its hydride, acrylonitrile-butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, methacrylic acid ester-acrylic acid ester copolymer, and styrene Examples include rubbers such as ylene-acrylic acid copolymers, acrylonitrile-acrylic acid 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, or resins that do not have a melting point but have a decomposition temperature of 200°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester. These can be used individually or in combination of two or more.

[0125] The resin binder may include, for example, a resin latex binder. As the resin latex binder, for example, a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable thereto can be used. Here, examples of aliphatic conjugated diene monomers include butadiene and isoprene, examples of unsaturated carboxylic acid monomers include (meth)acrylic acid, and examples of other monomers include styrene. There are no particular restrictions on the polymerization method of such copolymers, but emulsion polymerization is preferred. There are no particular restrictions on the emulsion polymerization method, and known methods can be used. There are no particular restrictions on the method of adding monomers and other components, and any of a single addition method, a divided addition method, or a continuous addition method can be employed, and the polymerization method can be a one-step polymerization, a two-step polymerization, or a multi-step polymerization of three or more steps.

[0126] Specific examples of resin binders include the following (1) to (7). (1) Polyolefins, such as polyethylene, polypropylene, ethylene propylene rubber, and modified versions thereof; (2) Conjugated diene polymers, for example, styrene-butadiene copolymers and their hydrides, acrylonitrile-butadiene copolymers and their hydrides, acrylonitrile-butadiene-styrene copolymers and their hydrides; (3) Acrylic polymers, for example, methacrylic acid ester-acrylic acid ester copolymers, styrene-acrylic acid ester copolymers, and acrylonitrile-acrylic acid ester copolymers; (4) Polyvinyl alcohol-based resins, for example, polyvinyl alcohol and polyvinyl acetate; (5) Fluorine-containing resins, for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; (6) Cellulose derivatives, such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; and (7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers that do not have a melting point but have 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 size (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 size of the resin binder can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, and pH.

[0128] From the viewpoint of improving 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 permeability, the glass transition temperature of the resin binder is preferably -60°C or higher.

[0129] From the viewpoint of improving 180° peel strength, the volume-average particle size (D50) of the resin binder is preferably 1 or more times, more preferably 2 or more times, and even more preferably 2.5 or more times, the average pore size of the polyolefin microporous film. By selecting the volume-average particle size (D50) of the resin binder in this way, it becomes possible to retain the resin binder on the surface of the polyolefin microporous film, thereby improving 180° peel strength. From the viewpoint of improving rate characteristics, the volume-average particle size (D50) of the resin binder is preferably 10 times or less the average pore size of the polyolefin microporous film. The content ratio of the resin binder in the coating layer may be, for example, more than 0 parts by mass and 80 parts by mass or less, 1 part by mass and 20 parts by mass or less, 2 parts by mass and 10 parts by mass or less, or 3 parts by mass and 5 parts by mass or less, 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. From the viewpoint of ion permeability, 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, and from the viewpoint of adhesion between the substrate and the particulate polymer, it is more preferably less than 20°C, even more preferably less than 15°C, and particularly preferably less than 0°C.

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

[0132] The content of water-soluble polymer in the coating layer is preferably 0.04 parts by mass or more and less than 2 parts by mass, more preferably 0.04 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.1 parts by mass or more and 1 part by mass or less, per 100 parts by mass of inorganic filler. A water-soluble polymer content of 0.04 parts by mass or more increases the binding properties between inorganic components, further suppressing thermal shrinkage. It also suppresses sedimentation of components during slurry preparation of the coating layer, enabling stable dispersion. A water-soluble polymer content of 5 parts by mass or less suppresses streaks and unevenness during coating layer formation.

[0133] Water-soluble polymers also contribute to the bonding of inorganic fillers within the coating layer. From the viewpoint of suppressing thermal shrinkage of the separator, the water-soluble polymer preferably has a weight loss rate of less than 10% at 150°C, when the weight at 50°C is taken as 100% in thermogravimetric measurements.

[0134] The water-soluble polymer may be a polymer derived from natural products, a synthetic product, a semi-synthetic product, etc., but from the viewpoint of paint formulation of inorganic and organic components, particularly water-based paint formulation, it is preferable that it be an anionic, cationic, amphoteric, or nonionic polymer, and more preferably an anionic, cationic, or amphoteric polymer.

[0135] Examples of anionic polymers include starch modifiers such as carboxymethyl starch and starch phosphate; anionic cellulose derivatives such as carboxymethylcellulose; ammonium salts or alkali metal salts of polyacrylic acid; gum arabic; carrageenan; chondroitin sulfate sodium; sulfonic acid compounds such as polystyrene sulfonate sodium, polyisobutylene sulfonate sodium, and naphthalene sulfonic acid condensate salts; and polyethylene iminzanate salts. Among these, from the viewpoint of achieving an appropriate balance between rigidity, rate characteristics, and cycle characteristics for energy storage devices, anionic polymers containing metal salts as countercations are preferred; anionic cellulose derivatives and ammonium salts or alkali metal salts of polyacrylic acid are also preferred; from the viewpoint of balancing heat resistance and rate characteristics, alkali metal salts of polyacrylic acid are even more preferred, and sodium polyacrylate is even more preferred.

[0136] Ammonium salts or alkali metal salts of polyacrylic acid are derived from multiple carboxylic acid groups -COO - This refers to a polymer in which at least one of its parts forms a salt with an ammonium ion or an alkali metal ion. Examples of alkali metal ions include sodium ions (Na). + ), potassium ions (K + Examples include:

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

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

[0139] Monomers copolymerizable with monomer (C i ) or monomer (C ii ) include, for example, (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 ammonium salts or alkali metal salts of polymers or copolymers obtained by polymerizing or copolymerizing monomers 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. It is desirable that the ammonium salts or alkali metal salts of polyacrylic acid described in (I) to (III) above 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; polyvinylimidazolines; dicyandiamide condensates; epichlorohydrin-dimethylamine condensates; and polyethyleneimines.

[0143] Examples of amphoteric polymers include dimethylaminoethyl (meth)acrylate quaternary salt-acrylic acid copolymers and Hoffmann decomposition products of polyacrylamide.

[0144] Examples of nonionic polymers include starch and its derivatives; cellulose derivatives such as methylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose, and their ammonium salts or alkali metal salts; gums such as guar gum and their modified forms; and synthetic polymers such as polyvinyl alcohol, polyacrylamide, polyethylene glycol, polymethyl vinyl ether, polyisopropylacrylamide, and copolymers of vinyl alcohol and other monomers, and their modified forms.

[0145] Water-soluble polymers may or may not have amide bond-containing cyclic structures. A 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. A water-soluble polymer having an amide bond-containing cyclic structure may have one or more amide bond-containing cyclic structures.

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

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

[0148] (Additives) The coating layer may consist only of inorganic fillers, particulate polymers, and any water-soluble polymers, or it may further contain other additives. Examples of additives include low molecular weight dispersants other than water-soluble polymers; thickeners; defoamers; and pH adjusters such as ammonium hydroxide. Specific examples of low molecular weight dispersants include monomers having multiple ammonium salts or alkali metal salts of carboxylic acids (C ii Examples include nonpolymerizable compounds having multiple ammonium salts or alkali metal salts of carboxylic acids (e.g., sodium alginate and sodium hyaluronate).

[0149] A specific example of an antifoaming agent is the following formula (A): [ka] {where, R 5 ~R 8 It is preferable to use a surfactant (acetylene-based surfactant) containing an ethoxylated acetylene glycol represented by}, where n and m are independent of each other, and n and m are independent of each other, and n + m = 0 to 40.

[0150] Specific examples of alkyl groups having 1 to 10 carbon atoms include linear, branched, and cyclic 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 groups.

[0151] Specific examples of acetylene glycol represented by formula (A) include 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 5,8-dimethyl-6-dodecine-5,8-diol, 2,4,7,9-tetramethyl-5-decine-4,7-diol, 4,7-dimethyl-5-decine-4,7-diol, 2,3,6,7-tetramethyl-4-octin-3,6-diol, 3,6-dimethyl-4-octin-3,6-diol, 2,5-dimethyl-3-hexyne-2,5-diol, ethoxylated derivative of 2,4,7,9-tetramethyl-5-decine-4,7-diol (number of moles of ethylene oxide added: 1.3), and 2,4,7,9-tetramethyl-5-decine-4,7-diol. Examples include ethoxylated compounds (4 moles of ethylene oxide added), ethoxylated compounds of 3,6-dimethyl-4-octyne-3,6-diol (4 moles of ethylene oxide added), ethoxylated compounds of 2,5,8,11-tetramethyl-6-dodecine-5,8-diol (6 moles of ethylene oxide added), ethoxylated compounds of 2,4,7,9-tetramethyl-5-decine-4,7-diol (10 moles of ethylene oxide added), ethoxylated compounds of 2,4,7,9-tetramethyl-5-decine-4,7-diol (30 moles of ethylene oxide added), and ethoxylated compounds of 3,6-dimethyl-4-octyne-3,6-diol (20 moles of ethylene oxide added). The defoaming agent may be used alone or in combination of two or more types.

[0152] Acetylene-based surfactants can also be obtained commercially. Examples of such commercially available products include Olfin SPC (manufactured by Nisshin Chemical Industry Co., Ltd., 80 parts by mass of active ingredient, pale yellow liquid), Olfin AF-103 (manufactured by Nisshin Chemical Industry Co., Ltd., pale brown liquid), Olfin AF-104 (manufactured by Nisshin Chemical Industry Co., Ltd., pale brown liquid), Olfin SK-14 (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AK-02 (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin AF-201F (manufactured by Nisshin Chemical Industry Co., Ltd., short yellow viscous liquid), Olfin D-10PG (manufactured by Nisshin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow liquid), Olfin E- Examples include 1004 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1010 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1020 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow liquid), Olfin E-1030W (manufactured by Nisshin Chemical Industry Co., Ltd., 75 parts by mass of active ingredient, pale yellow liquid), Surfinol 420 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), Surfinol 440 (manufactured by Nisshin Chemical Industry Co., Ltd., 100 parts by mass of active ingredient, pale yellow viscous substance), and Surfinol 104E (manufactured by Nisshin Chemical Industry Co., Ltd., 50 parts by mass of active ingredient, pale yellow viscous substance).

[0153] As an additive surfactant, polyether surfactants and / or silicone surfactants can be used in place of or in combination with acetylene surfactants. Typical 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 copolymer. Among these, polyethylene glycol is particularly preferred. These surfactants may be used individually or in combination of two or more.

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

[0155] Silicone-based surfactants may be linear, branched, or cyclic, as long as they contain at least a silicone chain, and may contain either a hydrophobic group or a hydrophilic group. Specific examples of hydrophobic groups 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 groups; cyclic alkyl groups such as cyclohexyl groups; and aromatic hydrocarbon groups such as phenyl groups. Specific examples of hydrophilic groups include amino groups, thiol groups, hydroxyl groups, alkoxy groups, carboxylic acids, sulfonic acids, phosphoric acid, nitric acid, and their organic and inorganic salts, ester groups, aldehyde groups, glycerol groups, and heterocyclic groups. Representative examples of silicone-based 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 also be obtained as commercial products. Examples of such commercial 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, BYK-349 (above are product names, manufactured by BYK Chemie Japan Co., Ltd.), KM-80, KF-351A, KF-352A, KF-353, KF-354L, KF-355A, KF-615A, KF-945, KF-640, KF-642, KF-643, KF-6020, X-22-4515, KF-6011, KF-6012, KF-6015, KF-6017 (above are product names, manufactured by Shin-Etsu Chemical Co., Ltd.), SH-28PA, SH8400, SH-190, SF-8428 (above are product names, manufactured by Toray Dow Corning Co., Ltd.), Polyflow KL-245, Polyflow KL-270, Polyflow KL-100 (above are product names, manufactured by Kyoeisha Chemical Co., Ltd.), Silface SAG002, Silface SAG005, and Silface SAG0085 (above are product names, manufactured by Nitto Chemical Industry Co., Ltd.), etc.

[0157] (Amount of the coating layer) The amount of the coating layer with respect to the substrate, that is, the amount of the coating layer per unit area of one surface of the substrate, is preferably 0.5 g / m 2 or more, more preferably 1.0 g / m 2 or more in terms of weight, and preferably 0.15 cm 3 / m 2 or more, more preferably 0.30 cm 3 / m 2 or more in terms of volume. The upper limit of the amount of the coating layer is preferably 10.0 g / m 2 or less, more preferably 7.0 g / m 2 or less in terms of weight, and preferably 3.50 cm 3 / m 2 or less, more preferably 2.50 cm 3 / m 2The following applies: It is preferable for the amount of the coating layer to be greater than or equal to the lower limit above, in terms of improving the adhesion between the coating layer and the electrode and suppressing thermal shrinkage. It is preferable for the amount of the coating layer to be less than or equal to the upper limit above, from the viewpoint of suppressing a decrease in ion permeability.

[0158] (Thickness of the coating layer) The thickness of either of the coating layers (the thickness of the inorganic filler portion of the coating layer) disposed on at least one of the substrates 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. When the thickness of the coating layer is 0.3 μm or more, the thermal shrinkage rate can be further suppressed, making it easier to make the adhesive force between the electrode and the substrate uniform, and as a result, the characteristics of the energy storage device can be improved. When the thickness of the coating layer is 1.3 μm or less, the decrease in ion permeability can be suppressed, and it is preferable in that a thin film separator for energy storage devices can be obtained. That is, by making the separator thinner, it is possible to manufacture an energy storage device with a large capacity per unit volume. On the other hand, from the viewpoint of preventing the particulate polymer from sliding off the coating layer, it 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 particulate polymer in the coating solution applied to the substrate, the amount of coating solution applied, the application method, and the application conditions. However, the method for adjusting the thickness of the coating layer is not limited to these methods.

[0159] Figure 1 is a schematic diagram of the surface of the coating layer of the separator for the energy storage device of this embodiment. As schematically shown in Figure 1, the surface of the coating layer (10) contains an inorganic filler (1) and particulate polymers (2) of thermoplastic polymers protruding from the coating layer. In Figure 1, the particulate polymers exist in a primary particle state without agglomerating with other particulate polymers.

[0160] Figure 2 is a cross-sectional view of the separator for the energy storage device shown in Figure 1. As schematically shown in Figure 2, the coating layer (20) is formed in a sloping manner, starting from an inorganic filler portion located at least 1.5D horizontally (in the surface direction of the coating layer) from the volume center of each particulate polymer, and becoming continuously thicker as it approaches the protruding particulate polymer (2). The slope of the sloping coating layer is gentler as it moves away from the protruding particulate polymer and steeper as it approaches the protruding particulate polymer. The inorganic filler (1) covers a portion of the periphery of the protruding portion by resting along the contour of the particulate polymer, while the area near the center of the protruding portion is exposed on the surface of the coating layer.

[0161] Manufacturing method for separators for energy storage devices <Method for manufacturing the base material> (Method for manufacturing polyolefin microporous membranes) The method for manufacturing the substrate is not particularly limited, and known manufacturing methods can be employed. For example, either a wet porosization method or a dry porosization method may be used. Examples of wet porosization methods include, for example, when the substrate is a polyolefin microporous film, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded together to form a sheet, and optionally stretched, and then the plasticizer is extracted to create porosity; a method in which a polyolefin resin composition mainly containing a polyolefin-based resin is melt-kneaded together, extruded at a high draw ratio, and then porosized by peeling off the polyolefin crystal interface by heat treatment and stretching; a method in which a polyolefin resin composition and an inorganic filler are melt-kneaded together to form a sheet, and then porosized by peeling off the interface between the polyolefin and the inorganic filler by stretching; and a method in which a polyolefin resin composition is dissolved, immersed in a poor solvent for polyolefin, and the polyolefin is solidified while the solvent is removed to create porosity.

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

[0163] Extrusion process (A): In step (A), the polyolefin composition is extruded to form a gel-like sheet. The polyolefin composition may contain a polyolefin resin, a pore-forming agent, etc. It is preferable that the resin contained in the polyolefin composition consists only of polyolefin, without containing non-resin components such as fine particles or high heat-resistant resins with significantly different melting points, from the viewpoint of uniformizing the tensile stress and improving the air permeability and air permeability distribution of the resulting film. The gel-like sheet can be obtained by melt-kneading the polyolefin resin and the pore-forming agent and forming it into a sheet.

[0164] First, the polyolefin resin and the pore-forming agent are melt-mixed. One method of melt-mixing is to put the polyolefin resin and, if necessary, other additives into a resin mixing device such as an extruder, kneader, laboplast mill, mixing roll, or Banbury mixer, and mix the resin components while introducing the pore-forming agent in a desired ratio.

[0165] The polyolefin resin contained in the polyolefin composition can be determined according to the predetermined resin raw material of the resulting polyolefin microporous membrane. Specifically, the polyolefin resin used in the extrusion process (A) may be any of the polyolefin resins described as components of the polyolefin microporous membrane.

[0166] The plasticizer content in the resin composition is preferably 66% to 90% by mass, more preferably 68% to 88% by mass, and even more preferably 70% to 80% by mass. Adjusting the plasticizer content to 66% or more by mass tends to lower the melt viscosity of the resin composition and suppress melt fracture, thereby improving film-forming properties during extrusion. On the other hand, adjusting the plasticizer content to 90% by mass or less can suppress the elongation of the raw material during the film-forming process.

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

[0168] From the viewpoint of adjusting the molecular weight, MI, puncture strength, basis weight equivalent puncture strength, difference R between the maximum and minimum values ​​of the air permeability at TD3 points, air permeability and porosity before compression, and thermal shrinkage rate of the high molecular weight raw materials contained in the polyolefin composition to be within the numerical ranges described above, at least one of the raw materials has a lower limit of Mv of preferably 700,000 or more, and an upper limit of, for example, 2,000,000 or less. From a similar viewpoint, the proportion of high molecular weight raw materials with an 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 its main component, from the viewpoint of adjusting the post-compression porosity, crystal length period, or crystallite size of the resulting microporous film to within the numerical range described above, the lower limit of the Mv of 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 a similar viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin 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, in order to adjust the molecular weight, MI, puncture strength, puncture strength equivalent to basis weight, difference R between the maximum and minimum values ​​of the air permeability at TD3 points, air permeability and porosity before compression, and thermal shrinkage rate of the resulting microporous membrane to within the numerical ranges described above, the Mv of polyethylene in 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 a similar viewpoint, the proportion of polyethylene with an Mv of 700,000 or more in the polyolefin resin 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 also be 100% by mass.

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

[0172] Pore-forming materials include plasticizers, inorganic materials, or combinations thereof. While not particularly limited, it is preferable to use a non-volatile solvent capable of forming a homogeneous solution 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. These plasticizers may be recovered and reused after extraction by operations such as distillation.

[0173] Among plasticizers, liquid paraffin is preferred because, when the polyolefin resin is polyethylene or polypropylene, it has high compatibility with these materials, and when the molten mixture is stretched, interfacial delamination between the resin and the plasticizer is less likely to occur, making it easier to perform uniform stretching.

[0174] The inorganic material is not particularly limited and includes, for example, oxide-based ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride-based 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, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These can be used individually or in combination of two or more. Among these, silica is particularly preferred due to 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 the two is preferably 3% by mass or more, more preferably 10% by mass or more, and from the viewpoint of ensuring high strength, it is preferably 60% by mass or less, more preferably 50% by mass or less.

[0176] Next, the molten mixture is formed into a sheet to obtain a gel-like sheet. When molten mixing is performed using an extruder, the ratio of the extrusion speed of the polyolefin composition, i.e., the extruder discharge rate Q (kg / hour) to the extruder screw rotation speed N (rpm) (Q / N, unit: kg / (h·rpm)) is preferably 0.1 to 7.0, more preferably 0.5 to 6.0, and even more preferably 1.0 to 5.0. When molten mixing is performed under conditions of Q / N between 0.1 and less than 7.0, the liquid paraffin that has phase-separated from the resin disperses more easily, resulting in a denser pore structure and a tendency to increase strength.

[0177] One method for manufacturing a sheet-like molded product is to extrude a molten mixture into a sheet shape through a T-die or the like, and then cool and solidify it by contacting it with a heat conductor to a temperature sufficiently lower than the crystallization temperature of the resin component. Examples of heat conductors used for cooling and solidification include metals, water, air, and plasticizers. Among these, it is preferable to use metal rolls because they have high heat conduction efficiency. When contacting the extruded gel-like sheet with metal rolls, sandwiching it between the rolls is even more preferable because it further increases the efficiency of heat conduction, the sheet becomes oriented, increasing film strength and improving the surface smoothness of the sheet.

[0178] By controlling the cast clearance when extruding the molten mixture from the T-die into a sheet, the average thickness of the resulting microporous film before compression can be adjusted to within the numerical range described above. From this viewpoint, for example, in the case of a cast roll, the distance between the rolls is preferably 200 μm to 3,000 μm, more preferably 500 μm to 2,500 μm. If the distance between the rolls of the cast roll is 200 μm or more, the risk of film breakage in the subsequent stretching process can be reduced, and if the distance between the rolls is 3,000 μm or less, the cooling rate is fast and uneven cooling can be prevented. Furthermore, from the viewpoint of obtaining a thin film and achieving the stretching ratio necessary to improve compressibility by enhancing surface orientation and crystallinity, 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 body or gel sheet may be rolled. The rolling can be carried out, for example, by a method using rolls or the like. By performing rolling, the orientation of the surface layer portion in particular can be increased. The rolling surface magnification is preferably more than 1 time and 3 times or less, more preferably more than 1 time and 2 times or less. When the rolling magnification exceeds 1 time, the surface orientation increases, and the film strength of the finally obtained porous membrane tends to increase. When the rolling magnification is 3 times or less, the orientation difference between the surface layer portion and the center inside is small, and a uniform porous structure in the film thickness direction can be formed.

[0180] Biaxial stretching step (B): In step (B), the gel sheet obtained in step (A) is stretched. Step (B) is performed before step (C) for extracting the pore-forming material from the sheet. In step (B), the stretching treatment of the gel sheet is performed at least once in the longitudinal direction and the width direction (that is, by biaxial stretching) from the viewpoint of controlling the bending rigidity of the polyolefin microporous membrane.

[0181] Examples of the stretching method include methods such as simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, and stretching a large number of times. Among them, from the viewpoints of improving the film strength, the uniformity of stretching, and the fact that the trunk structure is likely to be isotropic in the plane and the safety of the nail puncture test is improved due to the isotropic dispersion of stress during the nail puncture test, simultaneous biaxial stretching is preferable. Simultaneous biaxial stretching refers to a stretching method in which MD stretching and TD stretching are performed simultaneously, and the stretching magnification in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD and TD stretching are performed independently, and when stretching is performed in MD or TD, the other direction is in an unconstrained state or a state fixed to a constant length.

[0182] In process (B), from the viewpoint of adjusting the porosity, crystal long period, or crystallite size of the obtained microporous membrane within the numerical ranges described above, it is preferable to preheat the gel sheet immediately before stretching in the stretching furnace, and it is more preferable 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, preferably 130000 °C·m to 300000 °C·m, more preferably 150000 °C·m to 300000 °C·m, still more preferably 180000 °C·m to 300000 °C·m. When the preheating furnace is divided into a plurality of rooms with different air velocities, it is calculated as the air velocity of the entire preheating furnace from the sum of "the air velocity of each room × the furnace length of each room / the furnace length of the entire preheating furnace".

[0183] In the MD stretching of process (B), from the viewpoints of adjusting the porosity, crystal long period, or crystallite size of the obtained microporous membrane within the numerical ranges described above, highly orienting polyethylene as the main component to form a highly rigid stem, and in addition to strengthening the membrane by stretching orientation, improving the compressibility by increasing crystallinity, it is preferable to adjust the MD stretching ratio. The MD stretching ratio is preferably 5 times or more, more preferably 5 times or more and 10 times or less, still more preferably 5 times or more and 9 times or less, even more preferably 6 times or more and 10 times or less, and particularly preferably 6 times or more and 8 times or less. The MD stretching ratio can be adjusted according to, for example, the MD stretching temperature, MD stretching air velocity, MD stretching time, and MD stretching coefficient, etc.

[0184] From the same viewpoint as above, and from the viewpoint of improving the permeability and air permeability distribution of the film obtained by uniformly applying stress even to high molecular weight resins, 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 -12°C to the melting point of the main component is preferable for stretch molding as it applies appropriate stress to the film. More preferably, the MD stretching temperature is -10°C to the melting point of the main component, and even more preferably -8°C to the melting point of the main component. The MD stretching temperature can be adjusted according to, for example, the MD stretching ratio, MD stretching wind speed, MD stretching time, and MD stretching coefficient.

[0185] In step (B), the TD stretching is preferably adjusted from the viewpoint of adjusting the post-compression porosity, crystal length period, or crystallite size of the resulting microporous film to within the numerical range described above, from the viewpoint of highly oriented polyethylene as the main component to form a highly rigid trunk, and from the viewpoint of improving compressibility by increasing crystallinity in addition to increasing the strength of the film through stretch orientation. The TD stretching ratio is preferably 5 times or more, more preferably 5 times or more and 10 times or less, even more preferably 5 times or more and 9 times or less, even more preferably 6 times or more and 10 times or less, and particularly preferably 6 times or more and 8 times or less. The TD stretching ratio can be adjusted, for example, according to the TD stretching temperature, TD stretching wind speed, TD stretching time, and TD stretching coefficient.

[0186] It is preferable to adjust the TD stretching temperature in step (B) from the viewpoint of facilitating uniform TD stretching in step (B) even when the polyolefin composition subjected to step (A) has a high molecular weight composition, thereby improving the cycle characteristics of the non-aqueous secondary battery equipped with the resulting microporous film, and from the viewpoint of uniformly applying stress even to high molecular weight resins to improve the permeability and air permeability distribution of the resulting film. 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, and 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 according to, for example, the TD stretching ratio, TD stretching wind speed, TD stretching time, and TD stretching 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, and more preferably 5.8 or more and 7.0 or less, from the viewpoint of adjusting the post-compression porosity, crystal length period, or crystallite size of the obtained microporous film to within the numerical range described above. When this ratio is adjusted to 5.7 or more, the sheet becomes easier to stretch by applying more heat during preheating immediately before stretching, making it easier to achieve a uniform structure, and the cycle characteristics of the non-aqueous secondary battery with the final microporous film tend to improve. When this ratio is adjusted to 7.0 or more, uneven stretching tends to occur, resulting in an uneven film structure, and the cycle characteristics of the non-aqueous secondary battery with the final microporous film tend to deteriorate. The stretching coefficient is a value obtained by multiplying the stretching temperature by the stretching air velocity and the residence time of the film during the stretching process, preferably between 20,000°C·m and 50,000°C·m, and more preferably between 30,000°C·m and 50,000°C·m. If the stretching furnace is divided into multiple chambers with different air velocities, the total air velocity of the stretching furnace was calculated from the sum of "air velocity in each chamber × furnace length of each chamber / total furnace length of the stretching furnace". The residence time in the stretching furnace was calculated from "total furnace length of the stretching furnace / average velocity of the entire stretching furnace".

[0188] In step (B), it is preferable to adjust the biaxial stretching ratio from the viewpoint of adjusting the puncture strength, basis weight equivalent puncture strength, difference R between the maximum and minimum values ​​of the air permeability at TD3 points, air permeability and porosity before compression, thermal shrinkage rate, and tensile breaking strength and MD / TD tensile breaking strength ratio of the obtained microporous membrane to within the numerical ranges described above. The biaxial stretching ratio is preferably 5x5x or more, more preferably 5x5x to 10x10x, and even more preferably 6x6x to 10x10x. From a similar viewpoint, it is preferable that the biaxial stretching ratio is a simultaneous biaxial stretching ratio.

[0189] In step (B), it is preferable to adjust the biaxial stretching temperature in order to adjust the puncture strength and basis weight puncture strength of the obtained microporous membrane, the difference R between the maximum and minimum values ​​of the air permeability at TD3 points, the air permeability and porosity before compression, the thermal shrinkage rate, and the tensile breaking strength and MD / TD tensile breaking strength ratio to within the numerical ranges described above. The biaxial stretching temperature is preferably 122°C to 147°C, more preferably 123°C to 146°C, even more preferably 124°C to 145°C, and even more preferably 127°C to 140°C.

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

[0191] In step (B), it is preferable to adjust the heating coefficient per unit resin in order to adjust the puncture strength, basis weight puncture strength, the difference R between the maximum and minimum values ​​of the air permeability at TD3 points, the air permeability and porosity before compression, and the thermal shrinkage rate of the resulting microporous membrane to within the numerical ranges described above. The heating coefficient per unit resin is given by the following formula (I): Heating coefficient per unit resin = (Biaxial stretching temperature - 115°C) ÷ PC ···(I) This value is expressed by the formula and is preferably 0.26°C / % or higher. From the viewpoint of increasing the amount of heat applied per unit resin, making the stretch stress uniform, and improving the distribution of permeability of the resulting film, this value is more preferably 0.26°C / % to 1.2°C / %, even more preferably 0.34°C / % to 1.0°C / %, even more preferably 0.37°C / % to 0.98°C / %, and particularly preferably 0.40°C / % to 0.95°C / %. However, in the case of a dry method in which the film is manufactured and porosified in the absence of liquid, the amount of heat required to uniformize the stretch stress is greater because plasticization has not occurred, so this value is 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 molded body to obtain a porous membrane. Methods for removing the pore-forming material include, for example, immersing the sheet-like molded body in an extraction solvent to extract the pore-forming material and then thoroughly drying it. The extraction method for the pore-forming material may be either batch or continuous. To suppress shrinkage of the porous membrane, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. The amount of residual pore-forming material in the porous membrane is preferably less than 1% by mass relative to the total mass of the porous membrane.

[0193] When extracting pore-forming materials, it is preferable to use an extraction solvent that is a poor solvent for polyolefin resins, a good solvent for pore-forming materials, 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-chlorinated 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 inorganic materials are used as pore-forming materials, aqueous solutions of sodium hydroxide, potassium hydroxide, etc., can be used as extraction solvents.

[0194] Heat setting process (D): In the heat-setting process (D), the microporous film is heat-treated for heat-setting (HS) after plasticizer extraction in process (C) in order to suppress shrinkage of the polyolefin microporous film. Heat treatment of the porous film may include a stretching operation performed in an atmosphere at a predetermined temperature and a predetermined stretching ratio for the purpose of adjusting the physical properties, and / or a relaxation operation performed in an atmosphere at a predetermined temperature and a predetermined relaxation rate for the purpose of reducing stretching stress. The relaxation operation is the operation of shrinking the film after the stretching operation. These heat treatments can be performed using a tenter or a roll stretcher. It is preferable that the heat-setting, including stretching and relaxation operations after plasticizer extraction, be performed in TD.

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

[0196] The TD stretching temperature in step (D) is preferably 130°C to 150°C, more preferably 132°C to 145°C, and even more preferably 133°C to 140°C. This reduces the TD thermal shrinkage at 120°C of the resulting film, thereby improving safety in nail penetration tests of non-aqueous secondary batteries.

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

[0198] The thermal fixation ratio in step (D), i.e., the post-relaxation ratio, can be adjusted from the viewpoint of crystallizing polyethylene, the main component of the microporous membrane, to form a rigid core, and from the viewpoint of adjusting the average film thickness before compression, puncture strength and basis weight equivalent puncture strength, the difference R between the maximum and minimum values ​​of the air permeability at TD3 points, air permeability and porosity before compression, thermal shrinkage rate, and tensile breaking strength and MD / TD tensile breaking strength ratio of the resulting microporous membrane to within the numerical ranges described above. 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 allows the stretch orientation to increase the strength of the membrane, optimize the balance between compressibility and permeability by controlling the porosity, and in addition, relax the stress inside the membrane to reduce TD thermal shrinkage at a temperature of 120°C, thereby improving safety in nail puncture tests of non-aqueous secondary batteries.

[0199] The thermal fixing temperature, i.e., relaxation temperature, of step (D) can be adjusted from the viewpoint of adjusting the average thickness of the resulting microporous film before compression to within the numerical range described above, reducing the TD thermal shrinkage of the resulting microporous film at a temperature of 120°C, and improving safety in nail penetration tests of non-aqueous secondary batteries. The relaxation temperature of step (D) is preferably 130°C to 150°C, more preferably 132°C to 145°C, even more preferably 133°C to 140°C, and even more preferably 135°C to 140°C.

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

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

[0202] <Method for disposing a coating layer> A coating layer is disposed on at least one side of a base material manufactured as described above. The method for disposing the coating layer is not particularly limited, and examples thereof include a method of applying a coating liquid containing an inorganic filler and a particulate polymer to the base material and removing the medium.

[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 the coating liquid as it is.

[0204] As the medium of the coating liquid, those that can uniformly and stably disperse or dissolve an inorganic filler, a particulate polymer, and, if necessary, a water-soluble polymer are preferable. Examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, methanol, toluene, hot xylene, methylene chloride, and hexane. As the medium of the coating liquid, preferably, it is water or a mixed medium composed of water and a water-soluble organic medium. The water-soluble organic medium is not particularly limited, and examples thereof include ethanol and methanol. Among these, water is more preferable. When the coating liquid is applied to the base material, if the coating liquid penetrates into the interior of the base material, the particulate polymer containing the polymer is likely to block the surface and interior of the pores of the base material, and the permeability is likely to decrease. In this regard, in the case of an aqueous dispersion using water as the medium of the coating liquid, it is difficult for the coating liquid to penetrate into the interior of the base material, and the particulate polymer containing the polymer is likely to mainly exist on the outer surface of the base material. Therefore, it is preferable because the decrease in permeability can be more effectively suppressed.

[0205] The coating liquid may optionally contain additives. Examples of the additives for the coating liquid include dispersants such as surfactants; thickeners; wetting agents; defoaming agents; and various additives such as pH adjusters containing acids and alkalis.

[0206] Methods for dispersing or dissolving inorganic fillers, particulate polymers, and optionally water-soluble polymers in a coating medium include, for example, ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloidal mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc.

[0207] The preferred procedure for preparing the coating solution is to first add a water-soluble polymer to a coating solution containing dispersed inorganic fillers, and then add a resin binder and particulate polymer. By preparing the coating solution in this order, the water-soluble polymer adsorbs and protects the metal ions contained in the inorganic fillers, preventing aggregation of the resin binder and particulate polymer.

[0208] From the viewpoint of adjusting the gradient of the coating layer and the contact ratio between the particulate polymer and the substrate surface, the viscosity of the coating solution is preferably 20 mPa·s to 80 mPa·s, more preferably 60 mPa·s or less, and even more preferably 40 mPa·s or less. A viscosity of 20 mPa·s to 80 mPa·s is preferable from the viewpoint of increasing the gradient of the coating layer and increasing the contact ratio between the particulate polymer and the substrate surface, as the particulate polymer settles more quickly during the process of removing the solvent from the coating film after coating and forming the coating layer. Means for controlling the viscosity of the coating solution include adjusting the aspect ratio of the inorganic filler, the coefficient of variation of the particle size distribution of the inorganic filler, and the type of thickener. By using these means, the viscosity of the coating solution can be lowered during the immobilization process of the coating solution (formation of the 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 of the coating layer and increased adhesion to the electrode.

[0209] The substrate may be surface-treated before coating. Surface treatment is preferable because it makes it easier to apply the coating solution, improves the 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. Corona discharge treatment is one example of a surface treatment method.

[0210] The method for applying the coating solution 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 coating methods include gravure coater, small-diameter gravure coater, reverse roll coater, transfer roll coater, kiss coater, dip coater, knife coater, air doctor coater, blade coater, rod coater, squeeze coater, cast coater, die coater, screen printing, spray coating, and inkjet coating. Of these, the gravure coater or spray coating method is preferred from the viewpoint of providing a high degree of freedom in the coating shape of the particulate polymer and easily obtaining a desirable area ratio.

[0211] The coating method is preferably one in which the coating is applied at a high shear rate, such as by a gravure coater, and the shear rate is preferably 40,000 sec. -1 Over 120,000 seconds -1 The following is true: When the shear rate is within this range, the dispersion of the particulate polymer as primary particles is good, and it becomes easier to control the 180° peel strength to 200 gf / cm or higher.

[0212] There are no particular limitations on the method for removing the medium from the coating film after application, as long as it does not adversely affect the substrate and the coating layer. For example, methods include drying at a temperature below the melting point while fixing the substrate, drying under reduced pressure at low temperatures, and immersing the particulate polymer in a medium that is a poor solvent for particulate polymers to solidify the particulate polymer into particles while simultaneously extracting the medium.

[0213] <Fabrication of the separator coil> The obtained separator for energy storage devices is preferably wound into a wound body. By winding the separator into a wound body, it can be easily and quickly unwound, thereby increasing productivity in the production process of energy storage devices.

[0214] Energy storage devices The energy storage device of this embodiment includes the separator for the energy storage device of this embodiment. The energy storage device is not particularly limited, but examples include batteries such as non-aqueous electrolyte secondary batteries, capacitors, and condensers. Among these, batteries are preferred in order to take advantage of the benefits of the separator for the energy storage device of this embodiment, 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 separator for the energy storage device of this embodiment disposed between the positive and negative electrodes, and a non-aqueous electrolyte. The energy storage device of this embodiment, by including the separator for the energy storage device, has excellent characteristics such as energy storage performance, and in the case of a lithium-ion secondary battery, it has excellent battery characteristics.

[0215] When the energy storage device of this embodiment is a lithium-ion secondary battery, there are no limitations on the positive electrode, negative electrode, and non-aqueous electrolyte, and known ones can be used. As the positive electrode, a positive electrode having a positive electrode active material layer containing a positive electrode active material on a positive electrode current collector is preferably used. Examples of positive electrode current collectors include aluminum foil. Examples of positive electrode active materials include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. The positive electrode active material layer may appropriately contain a binder, conductive material, etc., in addition to the positive electrode active material.

[0216] As the negative electrode, a negative electrode having a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector can be suitably used. Examples of negative electrode current collectors include copper foil. Examples of negative electrode active materials include carbon materials such as graphite, non-graphitizable carbonaceous materials, easily graphitizable carbonaceous materials, and composite carbonaceous materials; as well as silicon, tin, metallic lithium, and various alloy materials.

[0217] The non-aqueous electrolyte is not particularly limited, but an electrolyte in which the electrolyte is dissolved in an organic solvent can be used. Examples of organic solvents include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of electrolytes include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0218] Manufacturing method for energy storage devices The method for manufacturing an energy 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 manufactured 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, the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are stacked in that order and wound into a circular or flat spiral shape to obtain a wound body. The wound body can then be placed in a device container (e.g., a battery container) and further injected with electrolyte to manufacture the device. Alternatively, the electrodes and separator may be folded to form a wound body, which can then be placed in a device container (e.g., an aluminum film) and injected with electrolyte to manufacture the device.

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

[0220] The pressing temperature is the temperature at which adhesion can be effectively achieved. 1.00 It is preferable to carry out the procedure at the above temperature. 1.00T is the temperature at which the minimum value of DDSC (Differential Scanning Calorimetry) is obtained, where DDSC is the derivative of the heat flow difference per unit time measured by DSC with respect to temperature, is observed between 0°C and 150°C. 1.00 Pressing at the above temperature allows the coating layer to deform sufficiently, resulting in good adhesion. For example, 35°C or higher is preferred. To suppress clogging of holes or thermal shrinkage in the separator due to hot pressing, the press temperature is preferably lower than the melting point of the material contained in the base material, and more preferably 130°C or lower. The press pressure is preferably 20 MPa or lower from the viewpoint of suppressing clogging of holes in the separator. The press time may be 1 second or less when using a roll press, and several hours when using a surface press, and preferably 2 hours or less from the viewpoint of productivity. By using the separator for energy storage devices of this embodiment and going through the above manufacturing process, press back when the wound body consisting of electrodes and separators is press-molded can be suppressed. Therefore, yield reduction in the device assembly process can be suppressed and production process time can be shortened.

[0221] Adhesion may be imparted to the wound material without pressing. Specifically, an example is a method in which the wound material is placed in a device can, an electrolyte is injected, and adhesion is imparted between the separator coating layer and the opposing electrode by the pressure generated inside the device can when manufacturing the energy storage device, or by the pressure associated with the expansion and contraction of the electrodes due to the charging and discharging of the energy storage device.

[0222] The energy storage devices manufactured as described above, particularly lithium-ion secondary batteries, possess the separator of this embodiment, which has high adhesion to electrodes and a low thermal shrinkage rate, and therefore exhibit excellent battery characteristics (rate characteristics) and long-term continuous operation resistance (cycle characteristics). [Examples]

[0223] The embodiments of this disclosure will be specifically described below with reference to examples and comparative examples, but this disclosure is not limited to these examples and comparative examples.

[0224] Measurement and Evaluation Methods <Thickness of the coating layer and amount of particulate polymer protrusion> The separator was frozen and fractured, and its cross-section was examined using a scanning electron microscope (SEM, model S-4800, Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a sample of the separator was cut to approximately 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then fractured with a hammer. The fractured sample was coated with osmium vapor deposition and observed at an acceleration voltage of 1.0 kV and 30,000x magnification. The thickness of the coating layer (μm) was measured from the substrate-coating layer boundary to the outer surface of the coating layer in the inorganic filler portion of the coating layer using the SEM image. The "inorganic filler portion" refers to the portion located at least 1.5D 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 using the area circle equivalent 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 outline of the particulate polymer in the portion of the coating layer where the particulate polymer protruded was measured. The maximum distance to the outline of the particulate polymer was measured at 20 points, and the average value was calculated. The amount of protrusion of the particulate polymer (μm) was determined by subtracting the thickness of the inorganic filler portion of the coating layer from the maximum distance to the outline of the particulate polymer, and the ratio of the amount of protrusion of the particulate polymer to the thickness of the inorganic filler portion of the coating layer was calculated.

[0225] <180° peel strength> A separator cut to 2mm x 7mm was attached to a glass plate with double-sided tape on the side opposite to the coating layer to be measured, and tape (product name "Mending Tape MP-12", manufactured by 3M) was applied to the coating layer. 5mm of the tape tip was peeled off, and the tape tip was clamped in a chuck on a tensile testing machine (model "AG-IS, SLBL-1kN", manufactured by Shimadzu Corporation) so that the tape peeled off at a 180° angle to the surface direction of the separator. A tensile test was performed at a tensile speed of 50mm / sec, 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] <Slope of the coating layer> The separator was frozen and fractured, and its cross-section was examined using a scanning electron microscope (SEM, model S-4800, HITACHI). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a sample of the separator was cut to approximately 1.5 mm × 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 coated with osmium vapor deposition and observed at an acceleration voltage of 1.0 kV and magnification of 30,000x. As schematically shown in Figure 2, 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 using an SEM image of the fractured sample cross-section, and the thickness L1 (μm) of the inorganic filler portion of the coating layer was measured. Note that the "inorganic filler portion" refers to the portion that is 1.5D or more 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 substrate-coating layer boundary to the outer surface of the inorganic filler in the inclined coating layer, and the maximum distance L3 (μm) to the contour of the protruding particulate polymer were measured, and the inclination ratio L2 / L1 of the coating layer and the coverage ratio (L2-L1) / (L3-L1) of the protruding portion were calculated. The inclination ratio L2 / L1 of the coating layer and the coverage ratio (L2-L1) / (L3-L1) of the protruding portion were measured at 200 points, and the average value was calculated.

[0227] <Contact ratio between protruding particulate polymer and substrate> The separator was frozen and fractured, and its cross-section was examined using a scanning electron microscope (SEM, model S-4800, Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a sample of the separator was cut to approximately 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then fractured with a hammer. The fractured sample was coated with osmium vapor deposition and observed at an acceleration voltage of 1.0 kV and magnification of 30,000x. From the SEM image, the number of particles in contact with the substrate was measured for 200 particulate polymers with fractured surfaces that protruded from the thickness of the inorganic filler portion of the coating layer, and this was defined as the contact ratio between the protruding particulate polymers and the substrate.

[0228] <Percentage of particulate polymer particles protruding from the thickness of the inorganic filler portion of the coating layer> The separator was frozen and fractured, and its cross-section was examined using a scanning electron microscope (SEM, model S-4800, Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a sample of the separator was cut to approximately 1.5 mm × 2.0 mm and stained with ruthenium. The stained sample and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then fractured with a hammer. The fractured sample was coated with osmium vapor deposition and observed at an accelerating voltage of 1.0 kV and 30,000x magnification. 200 particulate polymers were observed in the fracture surface using SEM images, and the number of particulate polymers protruding beyond the thickness of the inorganic filler portion of the coating layer was counted. This was then expressed as the ratio of particulate polymers protruding beyond the thickness of the inorganic filler portion of the coating layer.

[0229] <Average number of adjacent particulate polymers> Elemental mapping was performed on the surface of an osmium-deposited separator for energy storage devices using a scanning electron microscope (SEM) (model "SU-8220", Hitachi Corporation) and energy-dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", Oxford University Press). The SEM detector was set to secondary electrons, with an accelerated transfer voltage of 3kV and 20 mapping integrations, and carbon atom mapping measurements were performed at a magnification of 10,000x. In the carbon atom mapping, circular areas were considered as a single particulate polymer, and the number of particles with an outer edge distance of 0.2 μm or less was measured for all particulate polymers in one field of view. This measurement was performed in three fields of view, and the average value of all measurements was taken as the average number of adjacent particulate polymers.

[0230] <Ratio of the average particle size of prominent particulate polymers to the average particle size of inorganic fillers> The cross-section of an osmium-deposited separator for energy storage devices was observed using a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi) at an acceleration voltage of 1.0 kV and magnification of 10,000x. Specifically, the area-circle equivalent diameter was measured for 200 arbitrary inorganic filler particles, and the volume-average particle diameter MV was determined from these values ​​and used as the average particle size. Similarly, an SEM image of the cross-section of an osmium-deposited separator for energy storage devices was observed, and the area-circle equivalent diameter was measured for 200 particulate polymer particles protruding from the thickness of the inorganic filler portion of the coating layer. The volume-average particle diameter MV was determined from these values ​​and used as the average particle size. From the average particle size of the inorganic filler or the average particle size of the particulate polymer obtained by the above method, the ratio of the average particle size of the protruding particulate polymer to the average particle size of the inorganic filler was calculated.

[0231] <Number of particulate polymer particles with a radius of 10 μm or less> Elemental mapping was performed on the surface of an osmium-deposited separator for energy storage devices using a scanning electron microscope (SEM) (model "SU-8220", Hitachi Corporation) and energy-dispersive X-ray spectroscopy (EDX) (model "ULTIM EXTREME", Oxford University Press). The SEM detector was set to secondary electrons, with an accelerated transfer of 3kV and 20 mapping integrations, and carbon atom mapping measurements were performed at a magnification of 50 millionx. In the carbon atom mapping, circular areas were considered as a single particulate polymer, and the number of particulate polymers within a radius of 10 μm from any given particulate polymer was measured for all particulate polymers in one field of view, and the average value was calculated.

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

[0233] <Total amount of metal cations> 0.60 g of separator was placed in a Teflon® pressurized decomposition container, 10 ml of sulfuric acid was added, and the container was sealed. The container was then heated in an air bath at 200°C for 15 hours. After cooling, the solution in the container was transferred to a 100 ml resin volumetric flask and made up to prepare the sample solution. The sample solution was measured using 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 created from standard solutions.

[0234] <Thermal contraction rate> As a sample, a separator was cut to 100 mm on the medium-length side (MD) and 100 mm on the medium-length side (TD), and left to stand in an oven at 130°C or 150°C for 1 hour. During this time, the sample was sandwiched between two pieces of paper to prevent direct contact with the hot air. After removing the sample from the oven and allowing it to cool, its length (mm) was measured, and the thermal shrinkage rate was calculated using the following formula. Measurements were taken for both MD and TD, and the larger value was used as the thermal shrinkage rate. Thermal shrinkage rate (%) = {(100 - length after heating) / 100} × 100

[0235] <Viscosity average molecular weight> Based on ASTM-D4020, the intrinsic viscosity [η] (dl / g) at 135°C in decalin solvent was determined. For polyethylene, the calculation was performed 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> Using a Waters ALC / GPC 150C™ (trademark), standard polystyrene was measured under the following conditions to create a calibration curve. Similarly, chromatograms were measured for each of the polymers listed below under the same conditions, and the weight-average molecular weight of each polymer was calculated based on the calibration curve using the method described below. Columns: 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> By multiplying each molecular weight component in the obtained calibration curve 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), molecular weight distribution curves in polyethylene equivalent or polypropylene equivalent were obtained, 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 compositions or resin microporous membranes> The Q-factor value of the polyolefin with the largest mass fraction was used, and the weight-average molecular weight and number-average molecular weight were calculated in the same manner as for polyethylene.

[0239] <Meltflow Index (MI)> The melt flow index (MI) of a microporous membrane was measured according to JIS K7210:1999 (Plastics - Melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastic plastics). A load of 21.6 kgf was applied to the membrane at 190°C, and the amount of resin (g) that flowed out of a 2 mm diameter, 10 mm long orifice in 10 minutes was measured. The MI was rounded to the first decimal place.

[0240] <DSC measurement> Differential Scanning Calorimetric (DSC) measurements were performed using a Shimadzu DSC60. First, a PO microporous film was punched out into a 5mm diameter circle, and several sheets were stacked to form a 3mg sample. This sample was placed in a 5mm diameter aluminum open sample pan, a clamping cover was placed on top, and it was fixed inside the aluminum pan with a sample sealer. Under a nitrogen atmosphere, the temperature was increased 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 cooling rate of 10°C / min. Subsequently, after holding at 30°C for 5 minutes, the temperature was increased again from 30°C to 200°C at a heating rate of 10°C / min (second heating). The temperature at which the melting endothermic curve of the second heating was maximized was defined as the melting point of the PO microporous film. If there were multiple maximum values, the first peak and the largest peak were detected. The temperature at which the largest melting endothermic curve reaches its maximum can be used as the melting point (Tm) of the PO microporous film.

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

[0242] <Weight (g / m 2 )〉 Basis is measured per unit area (1 m²). 2 This is the weight (g) of the polyolefin microporous membrane per unit area (1m x 1m). After sampling a 1m x 1m area, the weight was measured using a Shimadzu Corporation electronic balance (AUW120D). If sampling a 1m x 1m area is not possible, the weight was measured by cutting out an appropriate area and then measured per unit area (1m). 2 The weight was converted to grams per unit.

[0243] <Average film thickness (μm) of microporous membrane before compression> The thickness was measured using a micro-thickness gauge (Type KBN, terminal diameter Φ5mm) manufactured by Toyo Seiki, at an ambient temperature of 23±2℃. To measure the thickness, a 10cm × 10cm sample of the microporous membrane was first collected. Multiple layers of this membrane were then stacked to a thickness of 15μm or more, and the thickness was measured at nine points. The average value was then calculated. The thickness of a single microporous membrane was then determined by dividing this average value by the number of layers stacked.

[0244] <Porosity before compression (%)> A sample measuring 3cm x 3cm, 1cm x 1cm, 5cm x 5cm, or 10cm x 10cm is cut from the polyolefin microporous membrane, and its volume (cm³) is measured based on the average film thickness measurement results. 3 The values ​​and mass (g) were determined. 3 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 using the density of the polyolefin resin and other components used, along with their respective mixing ratios.

[0245] <Porosity after compression (%)> Two 0.8mm thick rubber cushioning materials, two 0.1mm thick PET films, and two microporous membranes were prepared. These were laminated in the following order: one cushioning material, one PET film, two microporous membranes, one PET film, and one cushioning material. The resulting laminate was placed in a press machine. A compression test was performed by applying pressure by clamping the cushioning material surfaces on both sides of the laminate with the press machine. The compression test was performed under conditions of a temperature of 70°C, a pressure of 8 MPa, and a compression time of 3 minutes. The compressibility after pressure release was measured as needed. The compressibility was measured between 2 and 24 hours after pressure release. After the compression test, the pressure was released, the microporous membranes were removed from the laminate, and the microporous membranes after the compression test were used as samples. The porosity after compression (%) was measured using the same method as for "porosity before compression (%)" described above.

[0246] Under conditions of a temperature of 30°C and a compression time of 3 minutes, the same compression tests were performed at pressures of 2.5 MPa, 5 MPa, 7.5 MPa, and 10 MPa. Furthermore, one hour after pressure release, the microporous membrane was removed from the laminate, and the average film 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 film thickness after compression. Finally, using power approximation, an approximate curve as shown in Figure 3 was created for the porosity and air permeability after compression from four measurement points compressed at the four pressures described above. In Figure 3, membrane types A to C are commercially available polyolefin separators.

[0247] <Air permeability before compression (seconds / 100cm)> 3 )〉 The air permeability was measured using the "EGO2" air permeability meter manufactured by Asahi Seiko Co., Ltd. The measured air permeability was obtained by taking measurements at three points along the width of the membrane: 5 cm from both ends and one point in the center, and then calculating the average value of these measurements.

[0248] <Puncture strength and puncture strength equivalent to basis weight> A microporous membrane was fixed using a Kato Tech KES-G5 (trademark) handy compression tester with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the central part of the fixed microporous membrane with a needle tip radius of curvature of 0.5 mm and a puncture speed of 2 mm / sec under room temperature of 23°C and 40% humidity. The puncture strength (gf) was measured as the maximum puncture load. The measured values ​​for the puncture test were taken at three points along the TD of the membrane: two points 10% inward from both ends toward the center, and one point in the center. The average value of these measurements was then calculated.

[0249] The puncture strength converted to base 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, regarding the puncture strength and basis weight equivalent puncture strength of a separator having at least one layer on a polyolefin microporous membrane substrate, the properties were evaluated using the puncture strength and basis weight equivalent puncture strength of the polyolefin microporous membrane substrate, from the viewpoint of evaluating the strength of the resin and the strength per basis weight.

[0250] <Pore size (nm): Half-dry> Following the half-dry method, the average pore size (nm) was measured using a palm porometer (Porous Materials, Inc.: CFP-1500AE). Perfluoropolyester (product name "Galwick," surface tension 15.6 dyn / cm) manufactured by the same company was used as the immersion solution. The applied pressure and air permeability were measured for both the dry and wet curves. The average pore size dHD (nm) was calculated from the pressure PHD (Pa) at which the half-moon curve of the dry curve intersected the wet curve, using the following formula, and was defined as the pore size. dHD = 2860 × γ / PHD

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

[0252] <Measurement of withstand voltage per unit area before compression> A single sheet measuring MD10cm × TD10cm was cut from near the center of the width direction of a polyolefin microporous membrane, sandwiched between 5mm diameter aluminum plates, and the withstand voltage per unit area before compression was measured using a Kikusui Electronics TOS9201 withstand voltage meter. For the measurement conditions, a DC voltage was applied starting from 0V, with a voltage boosting rate of 100V / sec, and the voltage value (kV) when a current of 0.2mA flowed was taken as the withstand voltage measurement of the microporous membrane. A total of 25 points were measured at 15mm intervals (5 MD points × 5 TD points), and the average value was taken as the withstand voltage measurement. The withstand voltage per unit area was calculated as the ratio of the unit area to the withstand voltage (withstand voltage / unit area).

[0253] <Crystal structure analysis> The crystal long period in polyolefin microporous films was measured using small-angle transmission X-ray scattering with a Rigaku NANOPIX detector. CuKα rays were irradiated onto the sample, and scattering was detected by a semiconductor detector, HyPix-6000. The sample-detector distance was 1312 mm, and the output was 40 kV, 30 mA. A point focus optical system was used, 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 and the X-ray incidence direction were perpendicular.

[0254] The crystallite size of the polyethylene MDND plane (110) in a polyolefin microporous film was measured using a Rigaku NANOPIX system by transmission wide-angle X-ray scattering. CuKα rays were irradiated onto the sample, and scattering was detected using an imaging plate. The sample-detector distance was 110 mm, and the output was 40 kV, 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 sample surface and the X-ray incidence direction formed an angle of 11.0°. At this time, the X-ray incidence direction and the sample's MD were perpendicular.

[0255] <Crystal long period [nm]> A SAXS profile I(q) was obtained from the X-ray scattering pattern obtained from HyPix-6000 by ring averaging. In the linear-linear plot of the obtained one-dimensional profile I(q), 0.1 nm -1 <q<0.6nm -1 A linear baseline was drawn within the range, and a Gaussian function was used for fitting. The position with the maximum intensity was identified as the peak position q, which originates from the crystal's long period. m The crystal period was calculated using the following formula. d = 2π / q m {where d(nm): crystal long period q m (nm -1 ): Lamellar-derived peak positions in the SAXS profile}

[0256] <Crystallite size> The obtained XRD profile was separated into three peaks in the range from 2θ = 10.0° to 2θ = 30.0°: an orthorhombic (110) plane diffraction peak, an orthorhombic (200) plane diffraction peak, and an amorphous peak. The crystallite size was calculated from the full width at half maximum (FMAX) of the (110) plane diffraction peak according to Scherrer's equation (Equation 1). The (110) plane diffraction peak and the (200) plane diffraction peak were approximated by the Voigt function, and the amorphous peak was approximated by the Gauss function. The peak position of the amorphous peak was fixed at 2θ = 19.6° and the FMAX was fixed at 6.3°, while the peak position and FMAX of the crystalline peak were not fixed during peak separation. The crystallite size was calculated from the FMAX of the (110) plane diffraction peak calculated by peak separation using Scherrer's equation (Equation below). D(110) = Kλ / (βcosθ) {In the formula, D(110): crystallite size (nm)} K: 0.9 (constant) λ: Wavelength of X-ray (nm) β:(β1 2 -β2 2 ) 0.5 β1: Full width at half maximum (rad) of the peak (hkl) calculated as a result of peak separation. β2: Total width at half maximum (rad) of the incident beam. θ: Bragg angle} Furthermore, it is preferable to measure the crystal period and crystallite size based on crystal structure analysis in the substrate state before coating. However, due to the principles of X-ray structural analysis, the same results can be obtained even if the measurement is taken on the separator after coating, or if the coating layer is peeled off from the separator after coating and measured.

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

[0258] <Average pore size of polyolefin microporous membranes> It is known that the fluid inside a capillary follows a Knudsen flow when the mean free path of the fluid is greater than the pore diameter of the capillary, and a Poiseuille flow when it is smaller. Therefore, we assume that the airflow in the permeability measurement of the thermoplastic polymer-containing layer follows a Knudsen flow, and the water flow in the permeability measurement of the substrate follows a Poiseuille flow.

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

[0260] Here, R gas This 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 The water permeability (cm 3 / (cm 2 The following formula was used to obtain the result from (·sec·Pa). R liq =water permeability / 100

[0262] The water permeability was determined as follows: A thermoplastic polymer-containing layer, pre-soaked in ethanol, was placed in a 41mm diameter stainless steel permeable cell. After washing the ethanol off this layer with water, water was passed through it under a differential pressure of approximately 50,000 Pa, and the amount of water permeable (cm³) after 120 seconds was calculated. 3 From this, the amount of water permeable per unit time, unit pressure, and unit area was calculated and defined as the degree of water permeability.

[0263] Furthermore, ν is the gas constant R (=8.314), absolute temperature T (K), pi (π), and the average molecular weight of air M (=2.896 × 10⁻¹⁶). -2 It was calculated using the following formula from kg / mol. ν = ((8R × T) / (π × M)) 1 / 2

[0264] <Glass transition temperature of thermoplastic polymers> An aqueous dispersion containing a thermoplastic polymer (solids content = 38-42 parts by mass, pH = 9.0) was placed in an aluminum dish in an appropriate amount and allowed 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 DSC curves under a nitrogen atmosphere and DSC curves were obtained using a DSC analyzer (Shimadzu Corporation, model "DSC6220"). The measurement conditions were as follows. First stage heating program: Starts at 30°C, heating increases at a rate of 10°C per minute. After reaching 150°C... Hold for 5 minutes. Second stage cooling program: Cools down from 110°C at a rate of 10°C per minute. Maintains at -50°C for 5 minutes after reaching -50°C. Third stage heating program: Heat from -50°C to 150°C at a rate of 10°C per minute. DSC and DDSC data are acquired during this third stage heating.

[0265] The glass transition temperature was determined from the obtained DSC curve using the method described in JIS-K7121. Specifically, the glass transition temperature (Tg) was defined as the temperature at the point where the curve representing the stepwise transition intersects a straight line obtained by extending the low-temperature baseline of the DSC curve toward the high-temperature side, and a straight line equidistant in the vertical direction from the straight line obtained by extending the high-temperature baseline of the DSC curve toward the low-temperature side, with the curve representing the stepwise transition portion.

[0266] <Aspect ratio of inorganic fillers in the coating layer> The surface of an osmium-deposited separator for energy storage devices was observed using a scanning electron microscope (SEM) (model "S-4800", manufactured by Hitachi) at an acceleration voltage of 1.0 kV and magnification of 10,000x. The aspect ratio was determined by image processing of the inorganic fillers in the coating layer using SEM images. Even when inorganic fillers were bonded to each other, those with clearly discernible vertical and horizontal lengths were selected, and the aspect ratio was calculated based on these. Specifically, 10 objects with clearly discernible vertical and horizontal lengths were selected, and the average value obtained by dividing the major axis of each inorganic filler by the minor axis was used as the aspect ratio. If there were fewer than 10 objects with clearly discernible vertical and horizontal lengths in one field of view, 10 were selected from images of multiple fields of view.

[0267] <Particle size distribution of inorganic fillers> The particle size distribution of inorganic fillers was measured using a particle size analyzer (Nikkiso Co., Ltd., product name "Microtrac UPA150"). The sample solution used for measurement was the pre-coating dispersion. 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 fillers was calculated by dividing the standard deviation (SD) of the volume-average particle size obtained by the D50 value.

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

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

[0270] <Rate Characteristics> a. Fabrication of the positive electrode The positive electrode active material is nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co=1:1:1 (elemental ratio), density 4.70 g / cm³). 3 ) is added in 90.4 parts by mass, and graphite powder (KS6) (density 2.26 g / cm³) is added as a conductive additive. 3 1.6 parts by mass of (number average particle size 6.5 μm), and acetylene black powder (AB) (density 1.95 g / cm³). 3 3.8 parts by mass of (number average particle size 48 nm), and polyvinylidene fluoride (PVdF) (density 1.75 g / cm³) as a binder. 3A slurry was prepared by mixing ) in a ratio of 4.2 parts by mass and dispersing them in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, the positive electrode was fabricated by compression molding using a roll press. The amount of positive electrode active material applied at this time was 109 g / m². 2 That was the case.

[0271] b. Fabrication of the negative electrode Graphite powder A (density 2.23 g / cm³) is used as the negative electrode active material. 3 87.6 parts by mass of (number average particle size 12.7 μm), and graphite powder B (density 2.27 g / cm³) 3 A slurry was prepared by dispersing 9.7 parts by mass of (number average particle size 6.5 μm), 1.4 parts by mass (solid content equivalent) of ammonium carboxymethylcellulose (solid content concentration 1.83 parts by mass aqueous solution) and 1.7 parts by mass (solid content equivalent) of diene rubber latex (solid content concentration 40 parts by mass aqueous solution) in purified water as binders. This slurry was applied to one side of a 12 μm thick copper foil, which would serve as the negative electrode current collector, using a die coater. After drying at 120°C for 3 minutes, the negative electrode was manufactured by compression molding with a roll press. The amount of negative electrode active material applied at this time was 5.2 g / m². 2 That was the case.

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

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

[0274] e. Evaluation of rate characteristics The simple battery assembled in d. was charged at 25°C with a current of 3mA (approximately 0.5C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 3mA to maintain the 4.2V voltage, for a total of approximately 6 hours. After that, it was discharged at a current of 3mA until the battery voltage reached 3.0V. Next, at 25°C, it was charged at a current of 6mA (approximately 1.0C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 6mA to maintain the 4.2V voltage, for a total of approximately 3 hours. After that, the discharge capacity when discharged at a current of 6mA until the battery voltage reached 3.0V was defined as the 1C discharge capacity (mAh). Next, at 25°C, it was charged at a current of 6mA (approximately 1.0C) until the battery voltage reached 4.2V, and then the current was gradually reduced from 6mA to maintain the 4.2V voltage, for a total of approximately 3 hours. Subsequently, the discharge capacity when the battery was discharged to a voltage of 3.0V at a current of 12mA (approximately 2.0C) was defined as the 2C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was defined as the rate characteristic. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100 Evaluation Criteria for Rate Characteristics (%) A (Good): Rate characteristics are over 85% B (Acceptable): Rating characteristics are between 80% and 85%. C (Poor): Rate characteristics are 80% or less.

[0275] <Adhesion to electrodes (before electrolyte injection)> The separator was cut into a rectangle measuring 20 mm wide x 70 mm long, and this was placed on top of a positive electrode cut to a size of 15 mm x 60 mm to form a laminate of separator and electrode. This laminate was then 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 using IMADA Corporation's Force Gauge ZP5N and MX2-500N (product name) at a peel speed of 50 mm / min during a 90° peel test. The average peel strength over a 40 mm length under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength of 5 N / m or more B (Acceptable): Peel strength of 2 N / m or more, and less than 5 N / m C (Defective): Peel strength of 1 N / m or more, but less than 2 N / m. D (Not acceptable): Peel strength less than 1 N / m

[0276] <Adhesion strength to electrodes (after electrolyte injection)> The separator was cut into a rectangle measuring 20 mm wide x 70 mm long, and this was placed on top of a positive electrode cut to a size of 15 mm x 60 mm to form a laminate of separator and electrode. This laminate was then inserted into an aluminum laminate film, and 0.4 ml of electrolyte (a mixture containing 1 mol / L of LiPF6 with an EC / DEC ratio of 1 / 2) was added. After sealing, it was left to stand for 12 hours and then 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 using IMADA Corporation's Force Gauge ZP5N and MX2-500N (product name) at a peel speed of 50 mm / min during a 90° peel test. The average peel strength over a 40 mm length under the above conditions was used as the peel strength. Adhesion evaluation criteria A (Good): Peel strength of 5 N / m or more B (Acceptable): Peel strength of 2 N / m or more, and less than 5 N / m C (Defective): Peel strength of 1 N / m or more, but less than 2 N / m. D (Not acceptable): Peel strength less than 1 N / m

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

[0278] <Cycle characteristics and strain of the electrode-separator windings> a. Fabrication of the positive electrode The positive electrode active material is nickel, cobalt, and aluminum composite oxide (NCA) (Ni:Co:Al = 90:5:5 (elemental ratio), density 3.50 g / cm³). 3 A slurry was prepared by mixing 100 parts by mass of () as the conductive material, 1.25 parts by mass of acetylene black powder (AB) as the conductive material, and 1.0 part by mass of polyvinylidene fluoride (PVdF) as the binder, and dispersing these in N-methylpyrrolidone (NMP). This slurry was applied to both sides of a 15 μm thick aluminum foil, which would serve as the positive electrode current collector, using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to produce the positive electrode. The amount of positive electrode active material applied at this time was 456 g / m². 2 That was the case.

[0279] b. Fabrication of the negative electrode A slurry was prepared by dispersing 86.0 parts by mass of graphite powder and 4.5 parts by mass of silicon dioxide (SiO) as the negative electrode active material, and 1 part by mass of sodium carboxymethylcellulose and 1.0 part by mass 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, which would serve as the negative electrode current collector, using a die coater. After drying at 120°C for 3 minutes, the negative electrode was fabricated by compression molding using a roll press. The amount of negative electrode active material applied at this time was 266 g / m². 2 That was the case.

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

[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 wound into a spiral to create a coiled body. This coiled body was placed inside a cylindrical battery case with an outer diameter of 21 mm and a height of 70 mm, and the non-aqueous electrolyte was then injected and sealed to assemble the battery.

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

[0283] f. Evaluation of the state of the wound body after cycle characteristics After the cycle characteristic test conducted in e., the battery was disassembled, and the windings of the electrode-separator were checked for distortion. Distortion was detected in some cases, and absent in others. Distortion was detected if there was a gap of 0.5 mm or more, and absent if there was a gap of less than 0.5 mm.

[0284] Examples of substrate manufacturing <Manufacturing of polyolefin microporous membrane substrates B1-B11> (1) As shown in Table 1, raw material resin compositions were obtained by adjusting the proportions of polyethylene with an Mv of 700,000 or more (PE1: Mv 900,000, PE3: Mv 800,000, PE4: Mv 700,000, PE6: Mv 770,000), polyethylene with an Mv of 700,000 or less (PE2: Mv 250,000, PE5: Mv 370,000), and polypropylene (PP, Mv 400,000). Next, polyolefin compositions were obtained by blending the raw material resin compositions with a plasticizer (liquid paraffin) and 0.1% by mass of antioxidant so that the resin content (PC) shown in Table 1 was obtained. Next, the polyolefin compositions were fed into a twin-screw extruder, and the molten polyolefin compositions were extruded to form a gel-like sheet, which was then cooled and solidified using a cast roll. (2) Using a simultaneous biaxial stretcher, the cooled and solidified sheet was subjected to a biaxial stretching process 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 create a porous structure. (4) Furthermore, the obtained porous materials were thermally fixed using a uniaxial stretcher under the conditions shown in Table 1 to obtain polyolefin microporous film substrates B1 to B11. The obtained polyolefin microporous films were evaluated according to the method described above. The evaluation results are shown in Table 2.

[0285] [Table 1]

[0286] [Table 2]

[0287] 《Examples of preparation of aqueous dispersions (particulate polymers)》 <Preparation of aqueous dispersion A1> In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 70.4 parts by mass of deionized water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., indicated as "KH1025" in the table; the same applies hereinafter), and 0.5 parts by mass of "Adekaria Soap SR1025" (registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution, indicated as "SR1025" in the table; the same applies hereinafter) were added, and the internal temperature of the reaction vessel was raised to 95°C. Then, while maintaining the internal temperature of the vessel at 95°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (indicated as "APS(aq)" in the table; the same applies hereinafter) were 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 Industry Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane (AcSi), 3.0 parts by mass of KH1025, and SR1025. A mixture of 3.0 parts by mass of sodium p-styrenesulfonate (NaSS), 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 deionized water was mixed in a homomixer for 5 minutes to prepare an emulsion. The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. Dropping began 5 minutes after the ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. The internal temperature of the vessel was maintained at 80°C during the addition of the emulsion. At this time, a stirring bar placed in the reaction vessel was continuously stirred using a magnetic stirrer.

[0289] After the addition of the emulsifier dropwise was complete, the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH=9.0 using an aqueous solution of ammonium hydroxide (25% by mass aqueous solution) to obtain 40 parts by mass of acrylic copolymer latex (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 by the method described above. The results are shown in Table 3.

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

[0291] <Preparation of aqueous dispersion A1-1> Aqueous dispersion A1-1 was synthesized by taking a portion of aqueous dispersion A1 and performing multi-stage polymerization using this as a seed polymer. Specifically, first, a mixture of 20 parts by mass of aqueous dispersion A1 (in terms of solid content) and 70.4 parts by mass of deionized water was 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. Then, 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 constitutes the initial preparation.

[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-styrene sulfonate (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 ammonium persulfate aqueous solution was added to the reaction vessel, and the entire amount of emulsion was added dropwise over 150 minutes. The internal temperature of the vessel was maintained at 80°C during the addition of the emulsion. At this time, a stirring bar placed inside the reaction vessel was continuously stirred using a magnetic stirrer.

[0293] After the addition of the emulsifier dropwise was complete, the reaction vessel was kept at a temperature of 80°C and stirred for 90 minutes, then cooled to room temperature to obtain an emulsion. The obtained emulsion was adjusted to pH=9.0 using an aqueous solution of ammonium hydroxide (25% by mass aqueous solution) to obtain 40 parts by mass of acrylic copolymer latex (aqueous dispersion A1-1). The obtained aqueous dispersion A1-1 was evaluated using the method described above. The results are shown in Table 3.

[0294] <Preparation of aqueous dispersions A1-2 to A1-4> Copolymer latexes (aqueous dispersions A1-2 to A1-4) were obtained by adjusting the number of multi-stage polymerization steps. Each of the obtained aqueous dispersions was evaluated using the method described above. The results are shown in Table 3.

[0295] <Preparation of aqueous dispersions A2-1, A3-1 to A3-4 and A4-1> Copolymer latexes (aqueous dispersions A2-1, A3-1 to A3-4, and A4-1) were obtained in the same manner as aqueous dispersion A1-1, except that the composition of the seed polymer, monomers, other raw materials, the number of multi-stage polymerization steps, and the polymerization conditions were changed as shown in Table 2. Each of the obtained aqueous dispersions was evaluated using the method described above. The results are shown in Tables 3 and 4.

[0296] <Aqueous dispersion A5~A6> SB latex (Tg: 33℃, particle size: 300nm, toluene-insoluble content: 95%, swelling degree: 1.4 times) was used as aqueous dispersion A5. PVdF-HFP (product name LBG, Arkema), which has a primary particle size of 200nm and whose primary particles aggregate to form secondary particles of 2030nm, 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 mass aqueous solution SR1025: "Adekaria Soap SR1025" registered trademark, manufactured by ADEKA Corporation, 25% by mass aqueous solution NaSS: Sodium p-styrene sulfonate

[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] Examples of separator manufacturing <Example 1> To 100 parts by mass of water, 0.3 parts by mass of an aqueous solution of ammonium polycarboxylate (Sunopco SN Dispersant 5468) and 100 parts by mass of aluminum hydroxide oxide (boehmite) as an inorganic filler were mixed and treated with a bead mill to obtain a pre-coating dispersion. To the pre-coating dispersion, 1 part by mass of carboxymethylcellulose (CMC) as a water-soluble polymer component was mixed with 100 parts by mass of inorganic filler. Subsequently, 4 parts by mass of an acrylic latex suspension (solid content concentration 40% by mass, volume average particle size 150 nm, glass transition temperature -40°C) as a resin binder and 20 parts by mass of aqueous dispersion A1-3 (particulate polymer) were mixed and uniformly dispersed to prepare a coating solution (solid content 40 parts by mass) containing a thermoplastic polymer.

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

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

[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 removed using the following method to prepare a substrate sample for measurement. First, the cut separator was placed on a backing sheet, and the four sides of the separator were secured with adhesive tape (packaging OPP tape). Adhesive tape was similarly applied to the parts not covered by the tape. After applying pressure with a roller over the tape, the tape was peeled off to remove the coating layer attached to the tape. The opposite side was then treated in the same manner to obtain a substrate sample without a coating layer. The results of measuring the physical properties of the substrate using this sample are shown in Table 2.

[0306] <Comparative Examples 1-7> The separators of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1, except that the composition of the polyolefin microporous membrane, the coating solution, and the coating conditions were changed as described in Tables 5 to 10.

[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 energy storage devices of this disclosure can be suitably used in various energy 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 energy storage device comprising a substrate which is a polyolefin microporous film mainly composed of polyolefin, and a coating layer disposed on at least one surface of the substrate, The crystal period of the aforementioned polyolefin microporous film, as measured by small-angle X-ray scattering (SAXS), is 37.0 nm or greater. The basis weight of the aforementioned substrate is 3.0 g / m² or more and 7.0 g / m² or less. The puncture strength of the aforementioned substrate is 273 gf or more and 700 gf or less, and The coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The particulate polymer includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, in a separator for an energy storage device.

2. A separator for an energy storage device comprising a substrate which is a polyolefin microporous film mainly composed of a polyolefin, and a coating layer disposed on at least one surface of the substrate, The polyethylene MDND plane (110) crystallite size measured by wide-angle X-ray scattering using the transmission method of the aforementioned polyolefin microporous membrane is 10.0 nm to 28.0 nm, and The coating layer comprises an inorganic filler and a particulate polymer of a thermoplastic polymer. The particulate polymer includes particulate polymer protruding from the coating layer to a thickness of 0.1 times or more the thickness of the inorganic filler portion of the coating layer, in a separator for an energy storage device.

3. The separator for an energy storage device according to claim 1 or 2, wherein the film thickness of the substrate is 1 μm to 30 μm and the air permeability is 500 sec / 100 cm³ or less.

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. The separator for an energy storage device according to claim 1 or 2, wherein the coating layer is formed in a sloping manner so as to become thicker toward the protruding particulate polymer.

5. A separator for an energy storage device according to claim 4, wherein when the thickness of the inorganic filler portion of the coating layer is L1, and the maximum distance from the substrate-coating layer boundary line to the outer surface of the inclined inorganic filler of the coating layer is L2, the average value of the inclination ratio L2 / L1 of the coating layer is 1.2 or more.

6. A separator for an energy storage device according to claim 4, wherein when L1 is the thickness of the inorganic filler portion of the coating layer, L2 is the maximum distance from the substrate-coating layer boundary line to the outer surface of the inclined inorganic filler of the coating layer, and L3 is the maximum distance from the substrate-coating layer boundary line to the contour of the protruding particulate polymer, the average value of the coverage rate (L2-L1) / (L3-L1) of the protruding portion of the protruding particulate polymer is 0.4 or more.

7. The separator for an energy storage device according to claim 1 or 2, wherein the particulate polymer comprises at least one selected from the group consisting of (meth)acrylic polymers, styrene-butadiene copolymers, and copolymers containing fluorine atoms.

8. The separator for an energy storage device according to claim 1 or 2, 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 energy storage device according to claim 1 or 2, wherein the particulate polymer comprises a copolymer containing a polyfunctional (meth)acrylate as a monomer.

10. A storage device comprising a separator for a storage device according to claim 1 or 2.

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