Separator for energy storage devices

Abstract

To provide a separator for energy storage devices that can achieve both adhesion to electrodes and electrolyte injection properties, even when using a microporous film containing inorganic particles as the substrate. [Solution] A substrate containing polyolefin resin and inorganic particles, A separator for an energy storage device, comprising a thermoplastic polymer-containing layer on the first main surface of the substrate, the second main surface of the substrate, or both sides thereof, wherein the thermoplastic polymer is arranged in a dot-like pattern, The substrate contains the inorganic particles in an amount of 7% to 40% by volume relative to the total content of the polyolefin resin and the inorganic particles. The porosity of the substrate is 52% or more and 85% or less. The average particle size D50i of the primary particles of the inorganic particles is between 5 nm and 20 nm. The ratio D50a / D50i of the average particle size D50a of the thermoplastic polymer to the average particle size D50i of the primary particles of the inorganic particles is 15 or more and 60 or less. A separator for energy storage devices is provided, wherein the compressibility of the thermoplastic polymer is 30% or less when a pressure of 1 MPa is applied in an environment with a temperature of 90°C and a humidity of 40%.

Description

【Technical Field】 【0001】 The present invention relates to a separator for a power storage device and the like. 【Background Art】 【0002】 In recent years, the development of power storage devices represented by non-aqueous electrolyte batteries has been actively carried out. Usually, in a non-aqueous electrolyte battery such as a lithium-ion battery, a microporous membrane is provided as a separator between the positive and negative electrodes. Such a separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolyte held in the micropores. 【0003】 In addition to the conventionally required safety-related performances such as the characteristic (fuse characteristic) that the battery reaction is promptly stopped when the separator is abnormally heated and the performance (short-circuit prevention characteristic) of maintaining the shape even at high temperatures and preventing a dangerous situation where the positive electrode material and the negative electrode material directly react, improvement in adhesion to the electrode is required from the viewpoints of uniformizing the charge and discharge current and suppressing lithium dendrites. 【0004】 In addition to safety and adhesion to the electrode, in order to impart various functions to the separator, improvement of the microporous membrane itself, coating, and lamination of a functional layer on the microporous membrane have been studied (Patent Documents 1 to 2). 【0005】 For example, Patent Document 1 describes forming a thermoplastic polymer-containing layer in a dot pattern on at least one side of a microporous membrane as a separator substrate and adjusting the dot diameter and dot pitch from the viewpoint of achieving both adhesion and liquid injection property. 【0006】 Patent Document 2 describes using a microporous membrane containing inorganic particles as a separator substrate in order to improve safety. 【Prior Art Documents】 【Patent Documents】 【0007】 【Patent Document 1】 International Publication No. 2023 / 038069 [Patent Document 2] International Publication No. 2018 / 216819 [Overview of the Initiative] [Problems that the invention aims to solve] 【0008】 When a separator comprising a microporous membrane as a separator substrate and an adhesive layer coated or laminated on at least one side of the microporous membrane is used in the cell assembly of an energy storage device, the liquid injection performance during the electrolyte injection process may deteriorate. Therefore, a technique is known in which a dot-shaped thermoplastic polymer-containing layer is provided on the substrate in order to improve adhesion to the electrodes while maintaining liquid injection performance. As a separator substrate, microporous membranes containing inorganic particles offer excellent ion permeability and electrolyte penetration because they allow for high porosity while maintaining high strength and low thermal shrinkage. However, microporous membranes containing inorganic particles with high porosity are prone to deformation during heat pressing, making it difficult to improve adhesion to electrodes even with a dot-shaped thermoplastic polymer layer, and sometimes failing to ensure proper electrolyte injection. 【0009】 The present disclosure aims to provide a separator for energy storage devices that can achieve both adhesion to electrodes and electrolyte injection properties even when using an inorganic particle-containing microporous film as a substrate, and an energy storage device including the same. [Means for solving the problem] 【0010】 In other words, the present invention is as follows. [1] A substrate containing polyolefin resin and inorganic particles, A separator for an energy storage device, comprising a thermoplastic polymer-containing layer on the first main surface of the substrate, the second main surface of the substrate, or both sides thereof, wherein the thermoplastic polymer is arranged in a dot-like pattern, The substrate contains the inorganic particles in an amount of 7% to 40% by volume relative to the total content of the polyolefin resin and the inorganic particles. The porosity of the substrate is 52% or more and 85% or less. The average particle size D50i of the primary particles of the inorganic particles is between 5 nm and 20 nm. The ratio D50a / D50i of the average particle size D50a of the thermoplastic polymer to the average particle size D50i of the primary particles of the inorganic particles is 15 or more and 60 or less. A separator for energy storage devices, wherein the compressibility of the thermoplastic polymer is 30% or less when a pressure of 1 MPa is applied in an environment with a temperature of 90°C and a humidity of 40%. [2] The substrate has a thermoplastic polymer-containing layer arranged in a dot-like pattern on its second main surface, A separator for an energy storage device according to [1], having an inorganic filler-containing layer on the first main surface of the substrate. [3] A separator for an energy storage device according to [1] or [2], wherein the inorganic particles are present as secondary particles in the substrate. [4] A separator for an energy storage device according to any one of [1] to [3], wherein the D50a is 300 nm or more and 700 nm or less. [5] A separator for an energy storage device according to any one of [1] to [4], wherein the air permeability of the substrate is 50 seconds / 100cc or less. [6] The contact angle between the separator and the propylene carbonate on at least one side is 40° or less, and A separator for an energy storage device according to any one of [1] to [5], wherein the contact angle with water on at least one side of the separator is 85° or less. [7] A separator for energy storage devices as described in any of [1] to [6], wherein the adhesive strength when pressed with the negative electrode at a temperature of 90°C, a pressure of 1 MPa, and for 5 seconds is 1.0 N / m or more and 10.0 N / m or less. [8] The dot diameter of the thermoplastic polymer-containing layer is 20 μm or more and 1,000 μm or less, and the coverage rate of the thermoplastic polymer-containing layer on the substrate surface is 5% to 50%. A separator for an energy storage device according to any one of [1] to [7], wherein the average dot height of the thermoplastic polymer-containing layer is 0.2 μm or more and 10 μm or less. [9] A separator for an energy storage device according to any one of [1] to [8], wherein the thermoplastic polymer has a core-shell structure.

[10] A separator for energy storage devices as described in any of [1] to [9], having a puncture strength of 200 gf or more and 1000 gf or less.

[11] An energy storage device comprising a separator for energy storage devices as described in any of [1] to

[10] , a positive electrode, a negative electrode, and a non-aqueous electrolyte. [Effects of the Invention] 【0011】 According to this disclosure, it is possible to provide a separator for an energy storage device that can achieve both adhesion to electrodes and electrolyte injection properties even when using an inorganic particle-containing microporous film as the substrate, and an energy storage device including the same. [Modes for carrying out the invention] 【0012】 The following describes in detail embodiments for carrying out the present invention (hereinafter referred to as "this embodiment"). It should be noted that the present invention is not limited to the following embodiments, and can be implemented in various modifications within the scope of its gist. Furthermore, unless otherwise specified, the characteristic values ​​described in this embodiment are intended to be values ​​measured by the method described in the [Examples] section or by a method that would be understood to those skilled in the art to be equivalent thereto. 【0013】 In the following description, the upper or lower limits in a numerical range described in stages may be replaced with the upper or lower limits in other numerical ranges described in stages. Also, in the following description, the upper or lower limits in a certain numerical range may be replaced with the values ​​described in the examples. Furthermore, the term "process" in the following description may include not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as the function of that "process" is achieved. 【0014】 <Separator for energy storage devices> The separator for energy storage devices according to this embodiment (hereinafter also simply referred to as "separator") has a base material and a thermoplastic polymer-containing layer on the first main surface of the base material, the second main surface of the base material, or both of these surfaces, in which thermoplastic polymer is arranged in a dot-like pattern. Herein, in this disclosure, the first main surface of the substrate means at least one surface of the substrate (in one embodiment, one side of the substrate), and if the separator of this disclosure comprises an inorganic filler-containing layer, the surface on which the inorganic filler-containing layer exists is defined as the first main surface of the substrate. Furthermore, in this disclosure, the second main surface of the substrate means the surface located opposite the first main surface of the substrate, and if the separator of this disclosure comprises an inorganic filler-containing layer, the surface on which the inorganic filler-containing layer does not exist is defined as the second main surface of the substrate. 【0015】 The separator of this embodiment may have a thermoplastic polymer-containing layer on the first main surface of the substrate, the second main surface of the substrate, or both of these surfaces, and optionally, an inorganic filler-containing layer may be present between the substrate surface and the thermoplastic polymer-containing layer, or on the substrate surface where the thermoplastic polymer-containing layer is not formed. The separator of this embodiment has a thermoplastic polymer-containing layer arranged in a dot-like pattern on the second main surface of the substrate, and an inorganic filler-containing layer arranged on the first main surface of the substrate, thereby exhibiting excellent oxidation resistance and heat resistance. 【0016】 In this embodiment, the separator achieves both adhesion to the electrode and electrolyte injection properties even when an inorganic particle-containing microporous membrane is used as the substrate, by ensuring that the compressibility of the thermoplastic polymer contained in the thermoplastic polymer-containing layer at high temperatures is below a certain value, and by controlling the ratio of the average particle size of the thermoplastic polymer contained in the thermoplastic polymer-containing layer to the average particle size of the primary particles of the inorganic particles contained in the substrate within a specific numerical range. 【0017】 (Dot-like pattern in the thermoplastic polymer-containing layer) In this embodiment, the thermoplastic polymer-containing layer has the thermoplastic polymer arranged in a dot-like pattern. The diameter of the dots in the thermoplastic polymer-containing layer is between 20 μm and 1,000 μm. The coverage rate of the thermoplastic polymer-containing layer on the substrate surface is 5-50%. It is preferable that the average dot height of the thermoplastic polymer-containing layer is 0.2 μm or more and 10 μm or less. 【0018】 The term "dot pattern" refers to a polyolefin microporous membrane that contains portions of a thermoplastic polymer and portions that do not, with the portions containing the thermoplastic polymer existing in an island-like manner. Note that the thermoplastic polymer-containing layer may consist of independent portions. 【0019】 In this embodiment, the dot-like pattern of the thermoplastic polymer-containing layer is as follows: 20 μm ≤ dot diameter ≤ 1,000 μm 0.2 μm ≤ average dot height ≤ 10 μm By optimizing the design to satisfy these requirements and controlling capillary action, the liquid injection properties were improved, resulting in a separator that balances adhesion to the electrodes with electrical resistance. Furthermore, achieving both adhesion to the electrodes and electrolyte injection properties with the separator contributes to improving the productivity of energy storage devices equipped with the separator. 【0020】 In this disclosure, electrolyte injection properties refer to the ease with which the electrolyte penetrates the electrodes and separators during the electrolyte injection process in the cell assembly of an energy storage device using a separator, and are expressed as the short time required from the start of injection to the completion of penetration. 【0021】 In this embodiment, a separator that balances adhesion to electrodes and electrical resistance was realized by optimizing the diameter and average height of the dots in the dot-like pattern of the thermoplastic polymer-containing layer within the above numerical range, and by optimizing the coverage rate of the thermoplastic polymer-containing layer on the substrate surface, as described later. 【0022】 The diameter of the dots in the thermoplastic polymer-containing layer is preferably 20 μm to 1000 μm, more preferably 50 μm to 800 μm, even more preferably 100 μm to 700 μm, particularly preferably 145 μm to 600 μm, and most preferably 150 μm to 600 μm, from the viewpoint of achieving both adhesion to the electrode and electrolyte injection, as well as increasing the penetration distance. The diameter of the dots in the thermoplastic polymer-containing layer is measured according to the measurement method described in the examples below. 【0023】 The distance between dots in the thermoplastic polymer-containing layer is preferably 100 μm to 3000 μm, more preferably 200 μm to 2500 μm, even more preferably 400 μm to 2000 μm, and particularly preferably 500 μm to 1500 μm, from the viewpoint of ensuring sufficient gaps between multiple dots to secure pathways for electrolyte penetration and to allow for good air release. The inter-dot distance in the thermoplastic polymer-containing layer is measured according to the measurement method described in the examples below. 【0024】 The dot-to-dot distance / dot diameter of the thermoplastic polymer-containing layer is preferably 0.5 to 4, more preferably 0.7 to 3.8, even more preferably 1 to 3.5, even more preferably within the range of 1.3 to 3.5, and particularly preferably 2 to 3.3, from the viewpoint of achieving an excellent balance between adhesion to the electrode and the ease of electrolyte injection. 【0025】 Regarding the dot-like pattern of the thermoplastic polymer-containing layer, the average dot height is preferably 0.2 μm to 10 μm, more preferably 0.3 μm to 10 μm, even more preferably 0.3 μm to 5 μm, particularly preferably 0.3 μm to 3 μm, and most preferably 0.3 μm to 1 μm, from the viewpoint of appropriately maintaining the distance between the separator and the electrode and improving the wettability of the separator. The average dot height of the thermoplastic polymer-containing layer is measured according to the measurement method described in the examples below. 【0026】 From the viewpoint of ensuring good air release, the arrangement angle of the dots in the thermoplastic polymer-containing layer is preferably less than 40°, and although there is no lower limit to the arrangement angle, it may be, for example, 0° or greater. 【0027】 Regarding the dot-like pattern of the thermoplastic polymer-containing layer, the change in the distance between dots before and after penetration of the electrolyte into the separator is preferably 0% to 20%, and more preferably 0% to 10%. When the change in the distance between dots before and after immersion of the electrolyte into the separator falls within the above numerical range, there is a tendency for excellent balance between adhesion and liquid injection. 【0028】 The dot pattern of the thermoplastic polymer-containing layer identified above can be achieved, for example, in the separator manufacturing process by optimizing the thermoplastic polymer-containing coating solution, adjusting the polymer concentration or amount of the coating solution and the coating method or conditions, or by modifying the printing plate. 【0029】 The components of the separator according to this embodiment are described below. 【0030】 [Thermoplastic polymer-containing layer] The thermoplastic polymer-containing layer according to this embodiment contains a thermoplastic polymer. In battery manufacturing, it is preferable to use a thermoplastic polymer with a low compressibility so that the dot-like pattern does not collapse even when heat pressing is performed. In one embodiment, the thermoplastic polymer of this embodiment has a compressibility of 30% or less when a pressure of 1 MPa is applied in an environment of 90°C and 40% humidity. Furthermore, the thermoplastic polymer of this embodiment is preferably 25% or less, more preferably 15% or less, and even more preferably 5% or less when a pressure of 1 MPa is applied in an environment of 90°C and 40% humidity. On the other hand, from the viewpoint of the thermoplastic polymer following the irregularities of the electrode surface and forming anchors to exhibit high adhesive strength, the thermoplastic polymer of this embodiment is preferably 0.1% or more, and more preferably 1.0% or more, when a pressure of 1 MPa is applied in an environment of 90°C and 40% humidity. The thermoplastic polymer of this embodiment has a compressibility below a certain value at high temperatures, so it is less likely to be crushed when hot-pressed during cell molding, the liquid absorption paths formed by the dot-like pattern do not become narrow, resulting in good liquid absorption and improved adhesion to electrodes. The compressibility of the thermoplastic polymer is measured according to the measurement method described in the examples below. Furthermore, the compressibility of thermoplastic polymers at high temperatures (e.g., 90°C or higher) can be controlled by selecting the type of monomer used, adjusting the monomer blend ratio, adjusting the polymer's network structure through crosslinking, and adjusting the polymer's molecular weight. 【0031】 [Contact angle between thermoplastic polymer-containing layer and electrolyte] From the viewpoint of excellent electrolyte pouring properties, resistance to air pockets, and short pouring time, the thermoplastic polymer-containing layer preferably has a contact angle with the electrolyte of 0° to 90°, more preferably 2° to 60°, and even more preferably 4° to 40°. The contact angle of the thermoplastic polymer-containing layer with the electrolyte is preferably measured on the surface where the thermoplastic polymer-containing layer is formed in a dot-like pattern. 【0032】 The contact angle between the thermoplastic polymer-containing layer and the electrolyte can be adjusted to within the numerical range described above by controlling, for example, the ratio of the total coverage area of ​​the thermoplastic polymer-containing layer to the substrate surface, the particle size of the thermoplastic polymer, the corona treatment intensity of the substrate surface, the drying rate, the viscosity of the paint, the pH of the paint, etc., during the process of forming the thermoplastic polymer-containing layer. 【0033】 (Thermoplastic polymer) The thermoplastic polymer used in this embodiment is not particularly limited, but examples include: polyolefin resins such as polyethylene, polypropylene, and α-polyolefin; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene and copolymers containing these; diene polymers containing conjugated dienes such as butadiene and isoprene as monomer units, or copolymers containing these and their hydrides; acrylic polymers containing acrylic acid esters, methacrylic acid esters, etc. as monomer units, or copolymers containing these and their hydrides; rubbers such as ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, and carboxymethylcellulose; resins with a melting point and / or glass transition temperature of 180°C or higher, such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester, and mixtures thereof. Furthermore, monomers having at least one group selected from the group consisting of hydroxyl group, sulfonic acid group, carboxyl group, amide group, and cyano group can also be used as monomers when synthesizing the thermoplastic polymer. 【0034】 Among these thermoplastic polymers, diene polymers, acrylic polymers, or fluorine polymers are preferred due to their excellent binding properties with electrode active materials, as well as their strength and flexibility. 【0035】 (Diene polymer) Diene polymers are polymers that include monomer units obtained by polymerizing conjugated dienes having two conjugated double bonds, such as butadiene and isoprene, although these are not particularly limited. Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-phenyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, 1,3-hexadiene, 4,5-diethyl-1,3-octadiene, and 3-butyl-1,3-octadiene. These may be polymerized individually or copolymerized. 【0036】 The proportion of monomer units obtained by polymerizing conjugated dienes in a diene polymer is not particularly limited, but for example, it is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more, of the total diene polymer. 【0037】 The above-mentioned diene polymers are not particularly limited, but examples include homopolymers of conjugated dienes such as polybutadiene and polyisoprene, and copolymers of conjugated dienes with copolymerizable monomers. The copolymerizable monomers are not particularly limited, but examples include the (meth)acrylate monomers described later and the monomers listed below (hereinafter also referred to as "other monomers"). 【0038】 "Other monomers" are not particularly limited, but include, for example, α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; styrene monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; olefins such as ethylene and propylene; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; methyl vinyl ether and ethyl vinyl ether Examples include vinyl ethers such as butyl vinyl ether; vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole; acrylic acid esters and / or methacrylic acid ester compounds such as methyl acrylate and methyl methacrylate; hydroxyalkyl group-containing compounds such as β-hydroxyethyl acrylate and β-hydroxyethyl methacrylate; and amide monomers such as acrylamide, N-methylolacrylamide, and acrylamide-2-methylpropanesulfonic acid. These may be used individually or in combination of two or more. 【0039】 (Acrylic polymer) The acrylic polymer is not particularly limited, but preferably a polymer containing monomer units obtained by polymerizing (meth)acrylate monomers. 【0040】 In this specification, "(meth)acrylic acid" refers to "acrylic acid or methacrylic acid," and "(meth)acrylate" refers to "acrylate or methacrylate." 【0041】 (Meth)acrylate monomers are not particularly limited, but examples include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate. Examples include alkyl(meth)acrylates such as acrylate, lauryl(meth)acrylate, n-tetradecyl(meth)acrylate, and stearyl(meth)acrylate; hydroxyl group-containing(meth)acrylates such as hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, and hydroxybutyl(meth)acrylate; amino group-containing(meth)acrylates such as aminoethyl(meth)acrylate; and epoxy group-containing(meth)acrylates such as glycidyl(meth)acrylate. 【0042】 The proportion of monomer units obtained by polymerizing (meth)acrylate monomers is not particularly limited, but is, for example, 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more of the total acrylic polymer. Examples of acrylic polymers include homopolymers of (meth)acrylate monomers and copolymers of these with copolymerizable monomers. Examples of copolymerizable monomers include the "other monomers" listed in the section on diene polymers above, and one or more of these may be used in combination. 【0043】 (Fluorine-based polymer) The fluorinated polymer is not particularly limited, but examples include homopolymers of vinylidene fluoride and copolymers of vinylidene fluoride with monomers that can copolymerize with it. Fluorinated polymers are preferred from the viewpoint of electrochemical stability. 【0044】 The proportion of monomer units obtained by polymerizing vinylidene fluoride is not particularly limited, but for example, it is 40% by mass or more, preferably 50% by mass or more, and more preferably 60% by mass or more. Monomers copolymerizable with vinylidene fluoride are not particularly limited, but examples include fluorine-containing ethylenically unsaturated compounds such as vinyl fluoride, tetrafluoroethylene, trifluorochloroethylene, hexafluoropropylene, hexafluoroisobutylene, perfluoroacrylic acid, perfluoromethacrylic acid, and fluoroalkyl esters of acrylic acid or methacrylic acid; fluorine-free ethylenically unsaturated compounds such as cyclohexyl vinyl ether and hydroxyethyl vinyl ether; and fluorine-free diene compounds such as butadiene, isoprene, and chloroprene. 【0045】 Among fluorinated polymers, homopolymers of vinylidene fluoride, vinylidene fluoride / tetrafluoroethylene copolymers, and vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers are preferred. Particularly preferred fluorinated polymers are vinylidene fluoride / tetrafluoroethylene / hexafluoropropylene copolymers, whose monomer composition is typically 30-90% by mass of vinylidene fluoride, 9-50% by mass of tetrafluoroethylene, and 1-20% by mass of hexafluoropropylene. These fluororesin particles may be used individually or in mixtures of two or more types. 【0046】 Furthermore, monomers having a hydroxyl group, carboxyl group, amino group, sulfonic acid group, amide group, or cyano group can also be used as monomers when synthesizing the above thermoplastic polymer. 【0047】 The monomers having a hydroxyl group are not particularly limited, but examples include vinyl monomers such as pentenol. 【0048】 The monomers having a carboxyl group are not particularly limited, but examples include unsaturated carboxylic acids having an ethylenic double bond, such as (meth)acrylic acid and itaconic acid, and vinyl monomers such as pentenoic acid. 【0049】 The monomer having an amino group is not particularly limited, but examples include 2-aminoethyl methacrylate. 【0050】 The monomers having a sulfonic acid group are not particularly limited, but examples include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)alisulfonic acid, styrene sulfonic acid, ethyl (meth)acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, and 3-alyloxy-2-hydroxypropanesulfonic acid. 【0051】 The monomers having an amide group are not particularly limited, but examples include acrylamide, methacrylamide, N-methylolacrylamide, and N-methylolmethacrylamide. 【0052】 The monomers having a cyano group are not particularly limited, but examples include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-cyanoethyl acrylate. 【0053】 The thermoplastic polymer used in this embodiment may be used alone or as a mixture of two or more polymers, but it is preferable to use a mixture of two or more polymers. The thermoplastic polymer may be used with a solvent, and the solvent should be one that can uniformly and stably disperse the thermoplastic polymer. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, hexane, etc., with aqueous solvents being preferred. The thermoplastic polymer can also be used in the form of latex. 【0054】 (Glass transition temperature of thermoplastic polymers) From the viewpoint of exhibiting adhesive strength between the separator electrode and the separator, ensuring sufficient distance between the electrode and the separator in an energy storage device, and shortening the electrolyte injection time, it is preferable that the thermoplastic polymer has thermal properties such that at least two glass transition temperatures, at least one of which is in the region below 20°C, and at least one of which is in the region between 40°C and 110°C. 【0055】 Here, the glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). In this disclosure, the glass transition temperature may also be expressed as Tg. 【0056】 Specifically, it is determined by the intersection of a straight line extending the baseline on the low-temperature side of the DSC curve toward the high-temperature side, and a tangent line at the inflection point of the stepwise transition portion of the glass transition. For more details, refer to the method described in the examples. 【0057】 Here, "glass transition" refers to the endothermic change in heat energy associated with the state change of the polymer specimen in DSC. Such a heat energy change is observed in the DSC curve as a step-like change or a shape that combines a step-like change with a peak. 【0058】 A "step-like change" in a DSC curve refers to the portion where the curve deviates from the previous baseline and transitions to a new baseline. This also includes shapes that combine peaks and step-like changes. 【0059】 An "inflection point" is the point in the stepwise transition section where the gradient of the DSC curve is at its maximum. It can also be described as the point in the stepwise transition section where an upward-convex curve changes to a downward-convex curve. 【0060】 A "peak" in a DSC curve refers to the portion of the curve that moves away from the baseline and then returns to the baseline. 【0061】 "Baseline" refers to the DSC curve in the temperature range where no transitions or reactions occur in the test specimen. 【0062】 In this embodiment, by having at least one of the glass transition temperatures of the thermoplastic polymer used be in the region below 20°C, excellent adhesion to the substrate, such as a microporous film, is achieved, resulting in excellent adhesion between the separator and the electrode. It is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer used be in the region of 15°C or lower, and even more preferable that it be in the region of -30°C to 15°C. Furthermore, it is preferable that at least one of the glass transition temperatures of the thermoplastic polymer used be in the region of -20°C to 5°C, and more preferably in the region of -10°C to 0°C. Glass transition temperatures that exist in the region below 20°C are particularly preferably found only in the region between -30°C and 15°C, as this enhances adhesion between the thermoplastic polymer and the microporous film while maintaining good handling properties. 【0063】 In this embodiment, by having at least one of the glass transition temperatures of the thermoplastic polymer used be in the range of 40°C to 110°C, excellent adhesion and handling properties between the separator and the electrode are achieved, and furthermore, the distance between the electrode surface and the separator substrate surface can be maintained in the energy storage device, and the electrolyte injection time can be shortened. It is more preferable that at least one of the glass transition temperatures of the thermoplastic polymer used be in the range of 45°C to 100°C, and even more preferable that it be in the range of 50°C to 95°C. Within the range that does not hinder the effects of the present invention, a glass transition temperature of 70°C or higher is preferable from the viewpoint of handling properties. 【0064】 The ability of a thermoplastic polymer to have two glass transition temperatures can be achieved, for example, by blending two or more thermoplastic polymers, and by using a thermoplastic polymer having a core-shell structure, but is not limited to these methods. In this disclosure, a core-shell structure refers to a double-layer structure comprising a polymer belonging to the central part (hereinafter referred to as the core) and a polymer belonging to the outer shell (hereinafter referred to as the shell). The core-shell structure is formed by seed polymerization of polymers, and since the polymers belonging to the shell and core each contain polymers with different compositions, the glass transition temperatures of the core and shell may be different. 【0065】 In particular, polymer blends or core-shell structures are preferred because they allow control of the overall glass transition temperature of the thermoplastic polymer by combining polymers with high and low glass transition temperatures, and because they allow for the imparting of multiple functions to the thermoplastic polymer as a whole. The thermoplastic polymer in this embodiment is preferably a polymer blend, a core-shell structure, or both. 【0066】 For example, in the case of polymer blends, by blending two or more polymers, particularly those with a glass transition temperature of 20°C or higher and those with a glass transition temperature of less than 20°C, it is possible to achieve both resistance to stickiness and wettability to polyolefin microporous films. When blending, the mixing ratio of polymers with a glass transition temperature of 20°C or higher to polymers with a glass transition temperature of less than 20°C is preferably in the range of 0.1:99.9 to 99.9:0.1, more preferably 5:95 to 95:5, even more preferably 50:50 to 95:5, and even more preferably 60:40 to 90:10. 【0067】 For example, in the case of a core-shell structure, the adhesion or compatibility with other materials such as polyolefin microporous membranes can be adjusted by changing the shell polymer. Furthermore, by adjusting the polymer belonging to the core portion, it is possible to create a polymer with improved adhesion to electrodes after hot pressing, for example. Additionally, viscoelasticity can be controlled by combining a highly viscous polymer with a highly elastic polymer, preventing stickiness to the substrate. 【0068】 Furthermore, when the thermoplastic polymer has a core-shell structure, the glass transition temperature of the thermoplastic polymer constituting the core is not particularly limited, but is preferably 40°C to 110°C, more preferably 45°C to 100°C, and even more preferably 50°C to 95°C. Also, when the thermoplastic polymer has a core-shell structure, the glass transition temperature of the thermoplastic polymer constituting the shell is not particularly limited, but is preferably 40°C to 200°C, more preferably 50°C to 180°C, and even more preferably 95°C to 150°C. Furthermore, it is preferable that the glass transition temperature of the thermoplastic polymer constituting the shell is higher than that of the thermoplastic polymer constituting the core, as this prevents stickiness to the substrate. 【0069】 In this embodiment, the glass transition temperature, or Tg, of the thermoplastic polymer can be appropriately adjusted, for example, by changing the monomer components used to produce the thermoplastic polymer and the input ratio of each monomer. That is, it can be roughly estimated from the Tg of the homopolymer of each monomer used in the production of the thermoplastic polymer (for example, as described in "Polymer Handbook" (A WILEY-INTERSCIENCE PUBLICATION)) and the blending ratio of the monomers. For example, copolymers containing high proportions of monomers such as styrene, methyl methacrylate, and acrylonitrile, which give polymers with a Tg of approximately 100°C, can be obtained with a high Tg. On the other hand, copolymers containing high proportions of monomers such as butadiene, which gives polymers with a Tg of approximately -80°C, or n-butyl acrylate and 2-ethylhexyl acrylate, which give polymers with a Tg of approximately -50°C, can be obtained with a low Tg. 【0070】 Furthermore, the Tg of the polymer can be estimated using FOX's formula (Equation (1) below). The glass transition temperature of the thermoplastic polymer in this embodiment is determined by the method using DSC described above. 1 / Tg = W1 / Tg1 + W2 / Tg2 + ... + W i / Tg i +···W n / Tg n (1) {In formula (1), Tg(K) is the Tg of the copolymer, Tg i (K) is the Tg and W of the homopolymer of each monomer i. i This indicates the mass fraction of each monomer. 【0071】 (Structure of the thermoplastic polymer-containing layer) In the thermoplastic polymer-containing layer, it is preferable that a thermoplastic polymer having a glass transition temperature of 40°C to 110°C is present on the outermost surface side of the separator for the energy storage device, and that a thermoplastic polymer having a glass transition temperature of less than 20°C is present on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. The "outermost surface" refers to the surface of the thermoplastic polymer-containing layer that is in contact with the electrode when the separator for the energy storage device and the electrode are laminated. The "interface" refers to the surface of the thermoplastic polymer-containing layer that is in contact with the polyolefin microporous membrane. 【0072】 In a thermoplastic polymer-containing layer, the presence of a thermoplastic polymer with a glass transition temperature of 40°C to 110°C on the outermost surface side of the separator for energy storage devices results in superior adhesion with the polyolefin microporous membrane, and consequently, superior adhesion between the separator and the electrode. Furthermore, the presence of a thermoplastic polymer with a glass transition temperature of less than 20°C on the interface side between the polyolefin microporous membrane and the thermoplastic polymer-containing layer results in superior adhesion and handling between the separator and the electrode. By having such a thermoplastic polymer-containing layer, the separator tends to exhibit improved adhesion and handling between the separator and the electrode. 【0073】 The above structure can be achieved by (a) the thermoplastic polymer consisting of granular (particle) thermoplastic polymer (hereinafter also referred to as thermoplastic polymer particles) and a binder polymer that adheres the granular thermoplastic polymer to the polyolefin microporous membrane with the granular thermoplastic polymer exposed on the surface, the glass transition temperature of the granular thermoplastic polymer being in the range of 40°C to 110°C, and a thermoplastic polymer with a glass transition temperature of less than 20°C being present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer, and (b) the thermoplastic polymer having a laminated structure, the glass transition temperature of the thermoplastic polymer in the outermost layer when used as a separator being in the range of 40°C to 110°C, and a thermoplastic polymer with a glass transition temperature of less than 20°C being present at the interface between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. Note that (b) the thermoplastic polymer may have a laminated structure with each polymer having a different Tg. 【0074】 (Average particle size of thermoplastic polymer: D50a) The structure of the thermoplastic polymer in this embodiment is not particularly limited. For example, it can be configured in a granular form. By having such a structure, it tends to be excellent in the adhesiveness between the separator and the electrode and the handling property of the separator. Here, the granular form refers to a state in which each thermoplastic polymer has a contour as measured by a scanning electron microscope (SEM), and it may be an elongated shape, a spherical shape, a polygonal shape, or the like. 【0075】 The average particle size D50a of the granular thermoplastic polymer is preferably 150 nm or more and 1000 nm or less, more preferably 300 nm or more and 700 nm or less, and still more preferably 300 nm or more and 500 nm or less from the viewpoints of excellent dot formation property and expressing the adhesive force between the separator and the electrode while improving the electrolyte injection property. D50a is measured according to the measurement method in the examples described later. Note that D50a can be adjusted to a desired range by adjusting conditions such as the composition of the thermoplastic polymer, the reaction temperature, and the reaction time. 【0076】 (Areal density per side of the thermoplastic polymer-containing layer) In the separator according to this embodiment, the areal density per side of the thermoplastic polymer-containing layer is preferably 0.03 g / m 2 or more and 0.3 g / m 2 or less, more preferably 0.04 g / m 2 or more and 0.15 g / m 2 or less, and most preferably 0.06 g / m 2 or more and 0.10 g / m 2 or less. The areal density of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating solution or the coating amount of the polymer solution. From the viewpoint of suppressing the deformation of the cell shape accompanying the expansion and contraction of the electrode and improving the cycle characteristics of the battery within a range that does not hinder the effects of this embodiment, the areal density of the thermoplastic polymer-containing layer is preferably 0.06 g / m 2 or more. 【0077】 (Coverage rate of the substrate surface by the thermoplastic polymer-containing layer) In this embodiment, the total coverage area ratio (coverage rate) of the thermoplastic polymer-containing layer on the substrate surface is preferably 5% to 50%, more preferably 6% to 40%, and even more preferably 7% to 30%, from the viewpoint of improving the pourability of the electrolyte by controlling capillary action while maintaining adhesion to the separator electrodes. The total coverage area ratio S (coverage rate) of the thermoplastic polymer-containing layer present on the substrate surface is calculated from the following formula, and more specifically, by the method described in the examples. S(%) = Total coverage area of ​​thermoplastic polymer-containing layer ÷ Surface area of ​​substrate × 100 The total coverage area ratio (coverage rate) of the thermoplastic polymer-containing layer can be adjusted by changing the polymer concentration of the coating liquid or the amount of polymer solution applied, as well as the coating method and coating conditions. 【0078】 [Base material] Since separators require both insulating properties and ion permeability, separator substrates are generally formed from insulating materials with a porous structure, such as paper, polyolefin nonwoven fabrics, or resin microporous membranes. In particular, for separator substrates used in energy storage devices such as non-aqueous secondary batteries, which comprise a positive electrode and a negative electrode capable of intercalating and releasing lithium, and a non-aqueous electrolyte solution obtained by dissolving an electrolyte in a non-aqueous solvent, polyolefin microporous membranes that have oxidation-reduction resistance and can construct a dense and uniform porous structure are preferred. 【0079】 (Polyolefin microporous membrane) The polyolefin microporous membrane of this embodiment is formed from a resin composition containing a polyolefin resin and inorganic particles. The substrate of this embodiment also contains a polyolefin resin and inorganic particles. When an adhesive layer consisting of a thermoplastic polymer-containing layer is present on the substrate surface, the ability to inject electrolyte solution is usually reduced, which poses a challenge in terms of reduced productivity of energy storage devices. However, by using a polyolefin microporous membrane (high porosity substrate) containing polyolefin resin and inorganic particles, which is the substrate of this embodiment, and combining it with a thermoplastic polymer-containing layer arranged in a dot pattern, both adhesion and liquid injection properties can be achieved. 【0080】 The polyolefin resin used in this embodiment is not particularly limited, and examples include polymers (homopolymers, copolymers, multi-stage polymers, etc.) obtained by polymerizing monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene. These polymers can be used individually or in combination of two or more. The content of the polyolefin resin contained in the polyolefin microporous membrane is preferably 60% by volume or more, more preferably 70% by volume or more, even more preferably 78% by volume or more, and may be 85% by volume or more, based on the polyolefin microporous membrane (excluding the void portion). 【0081】 Furthermore, as the polyolefin resin, for example, low-density polyethylene (density 0.910 g / cm³) 3 More than 0.930g / cm 3 (less than), linear low-density polyethylene (density 0.910 g / cm³) 3 More than 0.940g / cm 3 (less than), medium-density polyethylene (density 0.930 g / cm³) 3 More than 0.942g / cm 3 (less than), high-density polyethylene (density 0.942 g / cm³) 3 (The above) Ultra-high molecular weight polyethylene (density 0.910 g / cm³) 3 More than 0.970g / cm 3 Examples include isotactic polypropylene, atactic polypropylene, polybutene, and ethylene propylene rubber (less than 100%). These can be used individually or in combination of two or more. In particular, using polyethylene alone, polypropylene alone, or a mixture of polyethylene and polypropylene is preferable from the viewpoint of obtaining a uniform film. From the viewpoint of improving heat resistance, it is more preferable for the polyolefin resin to contain polyethylene and polypropylene as main components, and even more preferable to contain 50% by mass or more of polyethylene and 8% by mass ± 5% by mass of polypropylene. Here, containing a specific component as a main component means that the content of that specific component is 50% by mass or more. Polyethylenes include polyethylene with a viscosity-average molecular weight of less than 1 million, and polyethylenes with a viscosity-average molecular weight of 1 million or more and a density of 0.942 g / cm³. 3 Using at least one of the following ultra-high molecular weight polyethylenes is preferable from the viewpoint of balancing strength and permeability and maintaining an appropriate fuse temperature. 【0082】 Furthermore, the resin composition may be mixed with various known additives as needed, such as antioxidants such as phenolic, phosphorus-based, or sulfur-based agents; metal soaps such as calcium stearate or zinc stearate; ultraviolet absorbers, light stabilizers, antistatic agents, anti-fogging agents, and coloring pigments. 【0083】 The viscosity-average molecular weight of the polyolefin resin (measured according to the measurement method described later in the examples; if multiple types of polyolefin resins are used, this refers to the value measured for each polyolefin resin) is preferably 50,000 or more, more preferably 100,000 or more, and the upper limit is preferably 10 million or less, more preferably 3 million or less, or 1 million or less. Setting the viscosity-average molecular weight to 50,000 or more is preferable from the viewpoint of maintaining high melt tension during melt molding and ensuring good moldability, or from the viewpoint of providing sufficient entanglement and increasing the strength of the microporous film. On the other hand, setting the viscosity-average molecular weight to 10 million or less is preferable from the viewpoint of achieving uniform melt kneading and improving the moldability of the sheet, especially thickness moldability. Setting the viscosity-average molecular weight to 1 million or less is preferable from the viewpoint of further improving thickness moldability. 【0084】 The inorganic particles are not particularly limited and include, for example, oxide-based ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, zinc oxide, and iron oxide; nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride; silicon carbide, calcium carbonate, aluminum sulfate, barium sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amethyst, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass fibers. These can be used individually or in combination of two or more. Among the above, silica, zinc oxide, alumina, titanium, and magnesia are more preferred from the viewpoint of electrochemical stability, and silica and zinc oxide are even more preferred. 【0085】 From the viewpoint of achieving both wettability with thermoplastic polymer coating liquid and electrolyte, it is necessary to set the content of inorganic particles in the polyolefin microporous film within a predetermined range. The content of inorganic particles in the polyolefin microporous film is preferably 7% to 40% by volume, more preferably 10% to 30% by volume, and particularly preferably 20% to 30% by volume, based on the total content of polyolefin resin and inorganic particles. 【0086】 In this embodiment, the lower limit of the average particle size D50i of the primary inorganic particles contained in the polyolefin microporous membrane is 5 nm or more, or 10 nm or more, or 15 nm or more. Furthermore, the upper limit of the average particle size D50i of the primary inorganic particles contained in the polyolefin microporous membrane in this embodiment is preferably 20 nm or less. The average particle size D50i of the primary inorganic particles in the polyolefin microporous film is preferably 5 nm to 20 nm, more preferably 10 nm to 20 nm, and particularly preferably 15 nm to 20 nm. Inorganic particles are preferably present as secondary particles in the polyolefin microporous membrane. By controlling D50i within a predetermined range, inorganic particles become more easily aggregated, which reduces the contact angle between the polyolefin microporous membrane and the electrolyte, thereby improving the electrolyte injection performance. Furthermore, the reduced contact angle with water improves coating properties to the substrate, and the bonding strength between the thermoplastic polymer-containing layer and the substrate is improved, resulting in improved adhesion between the separator and the electrode and reduced shedding of thermoplastic polymer powder. The D50i is measured according to the measurement method described in the examples below. Furthermore, D50i can be adjusted by adjusting the reaction conditions and crushing conditions during the preparation of inorganic particles, as well as by combining these conditions. 【0087】 The ratio of the average particle size D50a of the thermoplastic polymer to the average particle size D50i of the primary inorganic particles, D50a / D50i, is preferably 15 to 60, and more preferably 19 to 45. By setting D50a / D50i within a predetermined range, the interfacial strength between the thermoplastic polymer-containing layer and the substrate is improved, resulting in improved adhesion between the thermoplastic polymer-containing layer and the substrate, adhesion between the separator and the electrode, and prevention of powder shedding of the thermoplastic polymer. Furthermore, improved wettability with the electrolyte and wettability (ease of coating) with the thermoplastic polymer can also be achieved. 【0088】 [Method for manufacturing polyolefin microporous membranes] The method for producing a polyolefin microporous membrane is not particularly limited, but examples include an extrusion step (a) in which a resin composition containing a polyolefin resin, inorganic particles, and a pore-forming material is melt-kneaded and extruded; a sheet molding step (b) in which the extruded product obtained in step (a) is formed into a sheet; a primary stretching step (c) in which the sheet-shaped product obtained in step (b) is stretched at least once in at least one axial direction; an extraction step (d) in which the pore-forming material is extracted from the primary stretched membrane obtained in step (c); and a heat-setting step (f) in which the extracted membrane obtained in step (d) is heat-set at a predetermined temperature. Depending on the embodiment, a secondary stretching step (e) may be performed in which the extracted membrane obtained in step (d) is stretched at least in one axial direction. 【0089】 The above method for manufacturing a polyolefin microporous membrane makes it possible to provide a polyolefin microporous membrane that exhibits excellent performance in high-temperature environments and high heat resistance when used as a separator for lithium-ion secondary batteries and other electrochemical devices. In particular, by adopting a method in which the membrane is stretched only in the lateral direction in the primary stretching step (c), and then stretched only in the longitudinal direction in the secondary stretching step (e) after the extraction step (d), it tends to become even easier to achieve both the permeability and heat resistance associated with the above performance. It should be noted that the method for manufacturing a polyolefin microporous membrane in this embodiment is not limited to the above manufacturing method, and various modifications are possible without departing from the gist of the method. 【0090】 [Extrusion process (a)] The extrusion process (a) is a process of melting and kneading a resin composition containing a polyolefin resin, inorganic particles, and a pore-forming material, and then extruding it. In the extrusion process (a), other components may be mixed with the resin composition as needed. 【0091】 (Optional additives) In step (a), the resin composition containing polyolefin may contain any additives. The additives are not particularly limited, but examples include polymers other than polyolefin resin; antioxidants such as phenolic compounds, phosphorus compounds, and sulfur compounds; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total amount of these additives added is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polyolefin resin. 【0092】 The method of kneading in step (a) is not particularly limited, but for example, one method is to pre-mix some or all of the raw materials using a Henschel mixer, ribbon blender, tumbler blender, etc. as needed, and then melt-knead all of the raw materials using a screw extruder such as a single-screw extruder or twin-screw extruder; a kneader; a mixer, etc. Among these methods, melt mixing is preferably performed using a screw in a twin-screw extruder. In this case, the Q / N ratio (Q: extrusion rate [kg / hr], N: screw rotation speed [rpm]) is preferably 0.3 or higher, and more preferably 0.5 or higher. The upper limit is preferably 1.5 or lower, and more preferably 1.2 or lower. When the Q / N ratio is 0.3 or higher, uniform dissolution of the polymer into the plasticizer is possible without severing of the polymer molecular chains, so a higher strength microporous film tends to be obtained. When it is 1.5 or lower, it is possible to unravel the loosening between polymer molecular chains and apply sufficient shear force to highly disperse inorganic particles. Furthermore, when performing melt mixing, it is preferable to add the plasticizer in two or more stages. Moreover, when adding the additive in multiple stages, it is preferable to adjust the amount added in the first stage so that it is 80% or less by weight of the total amount added, from the viewpoint of suppressing aggregation of inorganic particles and ensuring uniform dispersion. By uniformly dispersing the inorganic particles, the viscosity of the polyolefin microporous membrane near its melting point is improved, making pore blockage less likely and improving cycle characteristics and output characteristics at high temperatures. Furthermore, by uniformly dispersing the inorganic particles, when the polyolefin microporous membrane is exposed to 150°C, there is less variation in the membrane properties and the membrane ruptures quickly. This makes short circuits over large areas more likely, which is preferable from the viewpoint of improving the safety of the cell. 【0093】 When a pore-forming agent is used in step (a), the temperature of the melt-mixing section is preferably less than 200°C from the viewpoint of dispersibility of inorganic particles. The lower limit of the temperature of the melt-mixing section is above the melting point of the polyolefin from the viewpoint of uniformly dissolving the polyolefin resin in the plasticizer. 【0094】 In this embodiment, during the kneading process, although not particularly limited, it is preferable to first mix the polyolefin raw material with an antioxidant at a predetermined concentration, then replace the surrounding atmosphere of the mixture with a nitrogen atmosphere, and perform melt kneading while maintaining the nitrogen atmosphere. The temperature during melt kneading is preferably 160°C or higher, more preferably 180°C or higher, and preferably less than 300°C. 【0095】 In step (a), the kneaded material obtained after the above kneading is extruded by an extruder such as a T-die or an annular die. At this time, it may be single-layer extrusion or laminated extrusion. The conditions during extrusion are not particularly limited, and known methods can be used, for example. 【0096】 [Sheet forming process (b)] The sheet forming process (b) is a process of forming the extruded material obtained in the extrusion process (a) into a sheet. The sheet-like molded product obtained in the sheet forming process (b) may be a single layer or a laminate. The method of sheet forming is not particularly limited, but one example is a method of solidifying the extruded material by compression and cooling. The compression cooling method is not particularly limited, but examples include a method of directly contacting the extruded material with a cooling medium such as cold air or cooling water; or a method of contacting the extruded material with a metal roll or press machine cooled with a refrigerant. Among these, the method of contacting the extruded material with a metal roll or press machine cooled with a refrigerant is preferred because it allows for easy control of the film thickness. In the process of forming the molten material into a sheet after the melting and kneading in step (a), it is preferable to set the temperature higher than the set temperature of the extruder. The upper limit of the set temperature is preferably 300°C or less, and more preferably 260°C or less, from the viewpoint of thermal degradation of the polyolefin resin. 【0097】 [Primary stretching process (c)] The primary stretching step (c) is a step in which the sheet-like molded product obtained in the sheet forming step (b) is stretched at least once in at least one axial direction. This stretching step (a stretching step performed before the next extraction step (d)) will be called "primary stretching," and the film obtained by primary stretching will be called "primary stretched film." In primary stretching, the sheet-like molded product can be stretched in at least one direction, and may be performed in both MD and TD directions, or in only one of MD or TD directions. 【0098】 The primary stretching method is not particularly limited, but examples include uniaxial stretching using a roll stretching machine; TD uniaxial stretching using a tenter; sequential biaxial stretching using a roll stretching machine and a tenter, or a combination of multiple tenters; and simultaneous biaxial stretching using a simultaneous biaxial tenter or inflation molding. 【0099】 The stretching ratio of the MD and / or TD in the primary stretching is preferably 2 times or more, more preferably 3 times or more. A stretching ratio of 2 times or more in the MD and / or TD in the primary stretching tends to further improve the strength of the resulting polyolefin microporous film. Alternatively, the stretching ratio of the MD and / or TD in the primary stretching is preferably 10 times or less, more preferably 8 times or less, or 5 times or less. A stretching ratio of 10 times or less in the MD and / or TD in the primary stretching tends to further suppress stretch fracture. When performing biaxial stretching, either sequential stretching or simultaneous biaxial stretching may be used, but the stretching ratio in each axial direction is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 8 times or less, or 3 times or more and 5 times or less. 【0100】 The primary stretching temperature is not particularly limited and can be selected by referring to the raw material resin composition and concentration contained in the resin composition. From the viewpoint of preventing fracture due to excessive stretching stress and balancing strength and thermal shrinkage, the stretching temperature is preferably in the range from 30°C below the melting point Tm of the polyolefin microporous membrane to the melting point Tm (Tm-30°C to Tm°C). When the resin that is the main component of the polyolefin microporous membrane is polyethylene, the stretching temperature is preferably 110°C or higher, and from the viewpoint of increasing the strength of the microporous membrane, it is preferably 130°C or lower. Specifically, the stretching temperature is preferably 100 to 135°C, more preferably 110 to 130°C, and even more preferably 115 to 129°C. 【0101】 [Extraction step (d)] The extraction step (d) is a step of extracting pore-forming material from the primary stretched film obtained in the primary stretching step (c) to obtain an extracted film. Methods for removing the pore-forming material include, for example, immersing the primary stretched film in an extraction solvent to extract the pore-forming material and then drying it thoroughly. The method for extracting the pore-forming material may be either batch or continuous. Furthermore, it is preferable that the residual amount of pore-forming material, particularly plasticizer, in the microporous film be less than 1% by mass. In addition, the amount of inorganic particles extracted by this step is preferably 1% by mass or less, and more preferably substantially 0% by mass, of the amount blended in the microporous film. 【0102】 When extracting the pore-forming material, it is preferable to use an extraction solvent that is a poor solvent for the polyolefin resin, a good solvent for the pore-forming plasticizer, and has a boiling point lower than the melting point of the polyolefin resin. Such extraction solvents are not particularly limited, but examples 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. 【0103】 [Secondary stretching process (e)] The secondary stretching step (e) is a step in which the extracted film obtained in the extraction step (d) is stretched in at least one axial direction. This stretching step (the stretching step performed after the extraction step (d)) will be called "secondary stretching," and the film obtained by secondary stretching will be called "secondary stretched film." In secondary stretching, the porous film obtained through the extraction step (d) can be stretched in at least one direction, and this may be done in both MD and TD directions, or in only one of MD or TD directions. 【0104】 The stretching ratio of the MD in secondary stretching is preferably 1.1 times or more, more preferably 2.0 times or more, and even more preferably 3.0 times or more. Similarly, the stretching ratio of the TD in secondary stretching is preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 2.0 times or more. When stretching in two axial directions, the stretching ratio in at least one of the MD and TD directions is preferably 1.1 times or more, and more preferably 2.0 times or more. 【0105】 Furthermore, the stretching process in this embodiment may involve either primary stretching only or primary and secondary stretching. The final total stretching ratio in each axial direction is preferably 2 times or more, more preferably 3 times or more, and even more preferably 5 times or more. The final total area stretching ratio is preferably 9 times or more, more preferably 16 times or more, and even more preferably 25 times or more. When the total stretching ratio and total area stretching ratio are within the above range, the strength and permeability of the resulting polyolefin microporous film tend to be further improved. In addition, from the viewpoint of dimensional stability and prevention of breakage during stretching, the total stretching ratio in each axial direction is preferably less than 20 times, and the total area stretching ratio is preferably 200 times or less. 【0106】 The secondary stretching temperature is not particularly limited and can be selected by referring to the raw material resin composition and concentration contained in the resin composition. From the viewpoint of preventing fracture due to excessive stretching stress, the stretching temperature is preferably in the range from 30°C below the melting point Tm of the polyolefin microporous membrane to the melting point Tm of the polyolefin microporous membrane (Tm-30°C to Tm°C). When the main component of the polyolefin microporous membrane is polyethylene, the stretching temperature is preferably 110°C or higher, and from the viewpoint of increasing the strength of the microporous membrane, it is preferably 130°C or lower. The stretching temperature is more preferably 115 to 129°C, and even more preferably 118 to 127°C. Furthermore, the porosity of the secondary stretched film is preferably 55% or higher, and more preferably 60% or higher. A porosity of 55% or higher in the secondary stretched film is preferable from the viewpoint of suppressing thermal shrinkage, as it allows for a higher heat-fixing temperature in the next step (f), and as a result, the cycle characteristics and output characteristics in high-temperature environments can be improved. Also, from the viewpoint of strength, the porosity of the secondary stretched film is preferably 90% or lower. 【0107】 [Heat setting process (f)] The heat-setting step (f) is a step in which the secondary stretched film obtained in the secondary stretching step (e) or the extracted film obtained in the extraction step (d) is heat-set at a predetermined temperature. The method of heat treatment in this step is not particularly limited, but examples include a heat-setting method that uses a tenter or roll stretcher to perform stretching and relaxation operations. 【0108】 The stretching operation in the heat-setting step (f) is an operation in which the polyolefin microporous film is stretched in at least one of the MD and TD directions, and may be performed in both directions of MD and TD, or in only one of MD or TD. The stretch ratios of MD and TD in the heat-setting process (f) are preferably 1.4 times or more, and more preferably 1.5 times or more. There is no particular upper limit to the stretch ratios of MD and TD in the heat-setting process (f), but 5 times or less is preferred. If the stretch ratio is outside the above range, shrinkage stress near the melting point tends to remain, worsening thermal shrinkage. Furthermore, if the stretch ratio is within the above range, the strength and porosity of the porous film tend to improve. 【0109】 The stretching temperature in this stretching operation is not particularly limited, but it is preferably 20°C lower than the melting point Tm of the polyolefin microporous film (i.e., stretching temperature ≥ Tm-20°C), more preferably 20°C lower than the melting point Tm-15°C of the polyolefin microporous film, and even more preferably 20°C lower than the melting point Tm-10°C of the polyolefin microporous film, up to the melting point Tm (Tm-10°C to Tm). When the stretching temperature is within the above range, the thermal shrinkage rate of the resulting polyolefin microporous film tends to be reduced, and the porosity and strength tend to be improved. 【0110】 The relaxation operation in the heat-setting step (f) is an operation to shrink the polyolefin microporous film in at least one of the MD and TD directions, and may be performed in both directions, or in only one of the MD or TD directions. The relaxation rate in the heat-setting step (f) is preferably 5% or more, more preferably 7% or more, and even more preferably 10% or more. A relaxation rate of 5% or more in the heat-setting step (f) tends to improve the heat resistance in oven tests. Furthermore, the relaxation rate is preferably 30% or less from the viewpoint of film quality, and even more preferably 25% or less from the viewpoint of increasing the relaxation temperature. Here, "relaxation rate" refers to the value obtained by subtracting the dimensions of the membrane after the relaxation operation from the dimensions of the membrane before the relaxation operation and dividing the result by the dimensions of the membrane before the relaxation operation. If both MD and TD are relaxed, it is the value obtained by multiplying the relaxation rate of MD by the relaxation rate of TD. Relaxation rate (%) = (Dimensions of the membrane before relaxation (m) - Dimensions of the membrane after relaxation (m)) / (Dimensions of the membrane before relaxation (m)) × 100 【0111】 The relaxation temperature in this relaxation operation is not particularly limited, but to obtain the separator according to this embodiment, a range from the melting point Tm-5°C to the melting point Tm+15°C (Tm-5°C to Tm+15°C) is more preferable, a range from the melting point Tm-3°C to the melting point Tm+10°C (Tm-3°C to Tm+10°C) is even more preferable, and a range from the melting point Tm-1°C to the melting point Tm+8°C (Tm-1°C to Tm+8°C) is particularly preferable. The fact that the temperature during the relaxation operation is within the above range not only removes residual stress caused by the stretching process, but also firmly fixes the orientation of the molecular chains. Therefore, it is preferable from the viewpoint of preventing an increase in AC electrical resistance near the melting point of the polyolefin microporous film and improving battery performance. 【0112】 [Other processes] The method for manufacturing a polyolefin microporous film according to this embodiment may include steps other than those described in steps (a) to (f). These other steps are not particularly limited, but for example, in addition to the heat-setting step, a lamination step may be used to obtain a laminated polyolefin microporous film by stacking multiple single-layer polyolefin microporous films. Furthermore, the method for manufacturing a polyolefin microporous film according to this embodiment may also include a surface treatment step, such as electron beam irradiation, plasma irradiation, surfactant application, or chemical modification, applied to the surface of the polyolefin microporous film. 【0113】 (Physical properties of polyolefin microporous membranes) The thickness of the polyolefin microporous membrane in this embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 4 μm or more, even more preferably 5 μm or more, with an upper limit of preferably 30 μm or less, more preferably 20 μm or less, even more preferably 16 μm or less, even more preferably 12 μm or less, and particularly preferably 9 μm or less. A thickness of 2 μm or more for the polyolefin microporous membrane is preferable from the viewpoint of improving mechanical strength. On the other hand, a film thickness of 30 μm or less is preferable because it reduces the volume occupied by the separator, which tends to be advantageous in terms of increasing the capacity of the battery. Furthermore, a film thickness of 12 μm or less, or 9 μm or less, is preferable from the viewpoint of shortening the electrolyte filling time because it reduces the amount of electrolyte to be filled. The thickness of the polyolefin microporous membrane is measured according to the measurement method described in the examples below. 【0114】 The thickness of the polyolefin microporous film can be adjusted by adjusting the sheet thickness in step (b), the stretching ratio in step (c), the stretching temperature, etc., or by combining these. 【0115】 In this embodiment, the lower limit of the porosity of the polyolefin microporous membrane is preferably 52% or more, and the upper limit of the porosity is preferably 85% or less, more preferably 80% or less. Setting the porosity to 52% or more is preferable from the viewpoint of ensuring good output characteristics. On the other hand, setting the porosity to 85% or less is preferable from the viewpoint of ensuring puncture strength and dielectric strength. From the viewpoint of improving liquid injection, the porosity of the polyolefin microporous membrane in this embodiment is preferably 52% to 85%, more preferably 55% to 75%, and even more preferably 60% to 70%. The porosity of the polyolefin microporous membrane is measured according to the measurement method described in the examples below. 【0116】 The porosity can be adjusted by adjusting the ratio of polyolefin resin / inorganic particles / plasticizer in step (a), the stretching temperature and stretching ratio in step (c), controlling the heat-fixing temperature, stretching ratio during heat-fixing, and relaxation rate during heat-fixing in step (f), or by combining these. 【0117】 In this embodiment, the lower limit of the air permeability of the polyolefin microporous membrane is preferably 20 seconds / 100cc or more, more preferably 30 seconds / 100cc or more, and the upper limit of the air permeability is preferably 50 seconds / 100cc or less, more preferably 45 seconds / 100cc or less, even more preferably 40 seconds / 100cc or less, and particularly preferably 35 seconds / 100cc or less. Setting the air permeability to 20 seconds / 100cc or more is preferable from the viewpoint of suppressing the self-discharge of the battery. On the other hand, setting the air permeability to 50 seconds / 100cc or less is preferable from the viewpoint of suppressing the resistance of the battery and obtaining good charge-discharge characteristics. The air permeability of the polyolefin microporous membrane is measured according to the measurement method described in the examples below. 【0118】 The above air permeability can be adjusted by adjusting the ratio of polyolefin resin / inorganic particles / plasticizer in step (a), the stretching temperature and stretching ratio in step (c), controlling the heat setting temperature, stretching ratio during heat setting, and relaxation rate during heat setting in step (f), or by combining these. 【0119】 Basis weight (g / m²) of polyolefin microporous membrane 2 The puncture strength when converted to (hereinafter referred to as the basis weight equivalent puncture strength) is 50 gf / (g / m²). 2 ) or more, or 60 gf / (g / m³) 2 It is preferable that it is 50 gf / (g / m³). 2 ) or more or 60 gf / (g / m³) 2Polyolefin microporous membranes having a basis weight equivalent puncture strength of 70 gf / (g / m²) or higher tend to be less prone to rupture during impact tests of energy storage devices. From the viewpoint of improving the safety of energy storage devices, such as impact resistance, while maintaining the strength of the polyolefin microporous membrane, the basis weight equivalent puncture strength is more preferably 70 gf / (g / m²). 2 ) More preferably 80 gf / (g / m³) 2 ) or more. The puncture strength converted to base weight is not limited, but for example, 200 gf / (g / m 2 ) or less, 150gf / (g / m 2 ) or less, or 140 gf / (g / m³) 2 It can be less than or equal to ). Note that the CCS unit "gf" can be converted to the SI unit "N" according to the formula: 1N ≈ 102.0gf. 【0120】 The puncture strength of the polyolefin microporous membrane, which has not been converted to basis weight (hereinafter simply referred to as puncture strength), has a lower limit of preferably 200 gf or more, and more preferably 300 gf or more. A puncture strength of 200 gf or more is preferable from the viewpoint of suppressing the rupture of the polyolefin microporous membrane in impact tests. Furthermore, the upper limit of the puncture strength of the polyolefin microporous membrane is preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 700 gf or less, from the viewpoint of stability during film formation. The lower limit can be used as long as it is a value that allows for stable production during film formation and battery manufacturing. The upper limit is set in balance with other characteristics. Puncture strength can be increased by the shear force applied to the molded product during extrusion or by increasing the orientation of molecular chains due to stretching. However, as strength increases, thermal stability deteriorates due to increased residual stress, so it is controlled according to the purpose. In one embodiment, from the viewpoint of improving battery safety (resistance to foreign matter and impact resistance), the puncture strength of the polyolefin microporous membrane is 200 gf or more and 1000 gf or less. 【0121】 In this embodiment, the average pore size of the polyolefin microporous film is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more as the lower limit. Setting the average pore size to 0.15 μm or less is preferable when used as a separator for energy storage devices, from the viewpoint of suppressing self-discharge of the energy storage device and suppressing capacity reduction. The average pore size can be adjusted by changing the stretching ratio when manufacturing the polyolefin microporous film. 【0122】 In this embodiment, the short-circuit temperature, which is an indicator of the heat resistance of the polyolefin microporous membrane, is preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. Setting the short-circuit temperature to 140°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for an energy storage device. 【0123】 [Inorganic filler-containing layer] Furthermore, the separator for the energy storage device according to this embodiment may include an inorganic filler-containing layer containing an inorganic filler and a resin binder. The inorganic filler-containing layer may be located on at least a portion of the surface of the polyolefin microporous membrane, at least a portion of the surface of the thermoplastic polymer-containing layer, and / or between the polyolefin microporous membrane and the thermoplastic polymer-containing layer. The inorganic filler-containing layer may be provided on the first main surface or the second main surface of the polyolefin microporous membrane, or on both sides thereof. The inorganic filler-containing layer contributes to improving thermal stability and other properties. Hereinafter, a microporous membrane to which an inorganic filler-containing layer is attached will also be referred to as a multilayer porous membrane. 【0124】 (Inorganic filler) The inorganic filler used in the inorganic filler-containing layer is not particularly limited, but it is preferable to have a melting point of 200°C or higher, high electrical insulation properties, and electrochemical stability within the operating range of lithium-ion secondary batteries. 【0125】 Examples of inorganic filler materials include oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, barium sulfate, aluminum hydroxide, aluminum hydroxide oxide or boehmite, 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. Among these, at least one selected from the group consisting of aluminum hydroxide oxide, alumina, boehmite, and barium sulfate is preferred from the viewpoint of stability in lithium-ion secondary batteries. Furthermore, as boehmite, synthetic boehmite is preferred as it can reduce ionic impurities that adversely affect the characteristics of electrochemical elements. 【0126】 Examples of inorganic filler shapes include plate-like, flaky, polyhedral, needle-like, columnar, granular, spherical, spindle-shaped, and block-like shapes, and multiple types of inorganic fillers having the above shapes may be used in combination. Among these, block-like shapes are preferred from the viewpoint of balancing permeability and heat resistance. 【0127】 The aspect ratio of the inorganic filler is preferably 1.0 to 5.0, and more preferably 1.1 to 3.0. An aspect ratio of 5.0 or less is preferable from the viewpoint of suppressing the amount of moisture adsorption of the multilayer porous membrane and suppressing capacity degradation when repeated cycles are performed, and from the viewpoint of suppressing deformation of the polyolefin microporous membrane at temperatures exceeding its melting point. 【0128】 The specific surface area of ​​the inorganic filler is 3.0 m². 2 / g or more 17m 2 It is preferable that it be less than or equal to / g, and more preferably 5.0m 2 / g or more 15m 2It is less than or equal to / g, and more preferably 6.5m 2 / g or more 13m 2 It is less than / g. The specific surface area is 17m². 2 Having a specific surface area of ​​3.0 m² or less is preferable from the viewpoint of suppressing the amount of moisture adsorbed by the multilayer porous membrane and suppressing capacity degradation when repeated cycles are performed, and the specific surface area is 3.0 m² or less. 2 A value of 1 / g or higher is preferable from the viewpoint of suppressing deformation of the polyolefin microporous membrane at temperatures exceeding its melting point. The specific surface area of ​​the inorganic filler is measured using the BET adsorption method. 【0129】 The average particle size D50f of the inorganic particles is preferably 0.1 μm or more and 3.0 μm or less, more preferably 0.2 μm or more and 1.0 μm or less, and even more preferably 0.3 μm or more and 0.7 μm or less. A D50f of 0.1 μm or more is preferable from the viewpoint of suppressing the amount of moisture adsorption of the multilayer porous film and suppressing capacity degradation when repeated cycles are performed, and a D50f of 3.0 μm or less is preferable from the viewpoint of suppressing deformation of the polyolefin microporous film at temperatures exceeding the melting point. Furthermore, D50f is measured in accordance with the measurement method described in the examples below. Methods for adjusting the average particle size D50f of inorganic fillers as described above include, for example, grinding the inorganic fillers using a ball mill, bead mill, jet mill, etc., to obtain the desired particle size distribution, or preparing fillers with multiple particle size distributions and then blending them. 【0130】 The proportion of inorganic filler in the inorganic filler-containing layer can be appropriately determined from the viewpoint of the binding properties of the inorganic filler, the permeability and heat resistance of the multilayer porous film, etc., but it is preferably 50% by mass or more and less than 100% by mass, more preferably 70% by mass or more and 99.99% by mass or less, even more preferably 80% by mass or more and 99.9% by mass or less, and particularly preferably 90% by mass or more and 99% by mass or less. 【0131】 (Resin binder) While there are no particular limitations on the type of resin binder, when using the multilayer porous membrane in this embodiment as a separator for lithium-ion secondary batteries, it is preferable to use one that is insoluble in the electrolyte of the lithium-ion secondary battery and electrochemically stable within the operating range of the lithium-ion secondary battery. 【0132】 Specific examples of resin binders are listed below (1) to (7). 1) Polyolefins: for example, 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, acrylonitrile-acrylic acid ester copolymers; 4) Polyvinyl alcohol-based resins: for example, polyvinyl alcohol, polyvinyl acetate; 5) Fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer; 6) Cellulose derivatives: for example, ethylcellulose, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose; 7) Resins with 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: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester. 【0133】 From the viewpoint of further improving safety during short circuits, 3) acrylic polymers, 5) fluororesins, and 7) polyamides as polymers are preferred. As for polyamides, all aromatic polyamides, particularly polymetaphenylene isophthalamide, are preferred from the viewpoint of durability. 【0134】 From the viewpoint of compatibility between the resin binder and the electrode, 2) conjugated diene polymers are preferred, and from the viewpoint of voltage resistance, 3) acrylic polymers and 5) fluororesins are preferred. 【0135】 The above 2) Conjugated diene polymers are polymers that contain conjugated diene compounds as monomer units. 【0136】 Examples of the above-mentioned 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-conjugated hexadienes, etc. These may be used individually or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. 【0137】 The above 3) Acrylic polymer is a polymer that contains a (meth)acrylic compound as a monomer unit. The above (meth)acrylic compound refers to at least one selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters. 【0138】 Examples of (meth)acrylic acid esters used in the acrylic polymers described in 3) above include alkyl (meth)acrylic acid esters, such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2-ethylhexyl methacrylate; and epoxy group-containing (meth)acrylic acid esters, such as glycidyl acrylate and glycidyl methacrylate. These may be used individually or in combination of two or more. Among these, 2-ethylhexyl acrylate (EHA) and butyl acrylate (BA) are particularly preferred. 【0139】 From the viewpoint of safety in impact tests, acrylic polymers are preferably polymers that contain EHA or BA as the main constituent units. The main constituent units refer to monomers and corresponding polymer portions that account for 40 mol% or more of the total raw materials for forming the polymer. 【0140】 The above 2) conjugated diene polymers and 3) acrylic polymers may also be obtained by copolymerizing them with other monomers that can copolymerize with them. Examples of other copolymerizable monomers that can be used include unsaturated alkyl carboxylates, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated monomers containing hydroxyalkyl groups, unsaturated carboxylic acid amide monomers, crotonic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, etc. These may be used individually or in combination of two or more. Among the above, unsaturated alkyl carboxylate monomers are particularly preferred. Examples of unsaturated alkyl carboxylate monomers include dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, etc. These may be used individually or in combination of two or more. 【0141】 Furthermore, the conjugated diene polymer described in 2) above may be obtained by copolymerizing the above (meth)acrylic compound as another monomer. 【0142】 The resin binder is preferably in the form of latex, and more preferably an acrylic polymer latex, from the viewpoint of having strong binding force between multiple inorganic particles even at high temperatures exceeding room temperature, and suppressing thermal shrinkage. 【0143】 The average particle size of the resin binder is preferably 50 nm to 500 nm, more preferably 60 nm to 460 nm, and even more preferably 80 nm to 250 nm. When the average particle size of the resin binder is 50 nm or more, when an inorganic filler-containing layer containing inorganic filler and binder is laminated on at least one side of a polyolefin microporous film, ion permeability does not easily decrease, and high power characteristics are easily obtained. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics, and high safety is easily obtained. When the average particle size of the resin binder is 500 nm or less, good bonding properties are exhibited, and when a multilayer porous film is formed, thermal shrinkage is good, and safety tends to be superior. 【0144】 The average particle size of resin binders can be controlled by adjusting the polymerization time, polymerization temperature, raw material composition ratio, raw material input order, and pH. 【0145】 A dispersant such as a surfactant may be added to the coating solution containing the inorganic filler and resin binder to stabilize dispersion or improve coating properties. The dispersant is adsorbed onto the surface of the inorganic particles in the slurry and stabilizes the inorganic filler particles by electrostatic repulsion, etc. Examples include polycarboxylates, sulfonates, and polyoxyethers. The amount of dispersant added is preferably 0.2 parts by weight or more and 5.0 parts by weight or less in terms of solid content, and more preferably 0.3 parts by weight or more and 1.0 part by weight or less, per 100 parts by weight of inorganic filler. 【0146】 (Physical properties, composition, and formation method of inorganic filler-containing layer) The thickness of the inorganic filler-containing layer is preferably 0.5 μm to 5.0 μm, more preferably 0.7 μm to 4.0 μm, even more preferably 0.8 μm to 3.9 μm, even more preferably 1.0 μm to 3.0 μm, and particularly preferably 1.5 μm to 2.0 μm. A thickness of 0.5 μm or more for the inorganic filler-containing layer is preferable from the viewpoint of suppressing deformation at temperatures exceeding the melting point of the microporous membrane. A thickness of 5.0 μm or less for the inorganic filler-containing layer is preferable from the viewpoint of improving battery capacity and suppressing the amount of moisture adsorbed by the multilayer porous membrane. Furthermore, a thickness of 3.9 μm or less, more preferably 2.0 μm or less for the inorganic filler-containing layer is preferable from the viewpoint of shortening the injection time because the amount of electrolyte to be filled can be reduced. The thickness of the inorganic filler-containing layer is measured according to the measurement method described in the examples below. 【0147】 The layer density in the inorganic filler-containing layer is 1.10 g / (m²). 2 ·μm) or more 3.00g / (m 2 It is preferable that the size is less than or equal to μm, and more preferably 1.20 g / (m²). 2 ·μm) or more 2.90g / (m 2 (μm) or less, more preferably 1.40 g / (m 2 ·μm) or more 2.70g / (m 2 (μm) or less, particularly preferably 1.50 g / (m 2 ·μm) or more 2.50g / (m 2 The thickness is less than or equal to μm. The layer density in the inorganic filler-containing layer is 1.10 g / (m³). 2 A layer density of 3.00 g / (m³) or greater is preferable from the viewpoint of suppressing deformation of the polyolefin microporous film at temperatures exceeding its melting point. 2 Having a particle size of (μm) or less is preferable from the viewpoint of maintaining the ion permeability of the inorganic filler-containing layer and suppressing capacity degradation when repeated cycles are performed. 【0148】 One method for forming an inorganic filler-containing layer is to apply a coating solution containing an inorganic filler and a resin binder to at least one side of a microporous film mainly composed of a polyolefin resin to form an inorganic filler-containing layer. 【0149】 The solvent for the coating solution containing an inorganic filler and a resin binder is preferably one that can uniformly and stably disperse the inorganic filler and the resin binder. Examples include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane. 【0150】 The coating solution containing the inorganic filler and the resin binder may contain various additives such as dispersants (including surfactants), thickeners, wetting agents, defoamers, and pH adjusters (including acids and alkalis) to improve dispersion stabilization and coating properties. While it is preferable that these additives can be removed during solvent removal, they may remain in the inorganic filler-containing layer if they are electrochemically stable within the operating range of lithium-ion secondary batteries, do not inhibit the battery reaction, and are stable up to approximately 200°C. 【0151】 The method for dispersing the inorganic filler and resin binder in the solvent of the coating solution is not particularly limited as long as it can achieve the dispersion characteristics of the coating solution required for the coating process. Examples include ball mills, bead mills, planetary ball mills, vibrating ball mills, sand mills, colloid mills, attritors, roll mills, high-speed impeller dispersion, dispersers, homogenizers, high-speed impact mills, ultrasonic dispersion, and mechanical stirring using stirring blades, etc. 【0152】 The method for applying a coating solution containing an inorganic filler and a resin binder to a microporous film is not particularly limited as long as it can achieve the required layer thickness and coating area. Examples 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, and spray coating. 【0153】 Furthermore, it is preferable to surface-treat the surface of the microporous membrane, which serves as the separator substrate, prior to applying the coating solution containing the inorganic filler and the resin binder, as this facilitates the application of the coating solution and improves the adhesion between the inorganic filler-containing layer and the microporous membrane surface after coating. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the microporous membrane, and examples include corona discharge treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation. 【0154】 Regarding the method for removing the solvent from the coating film after coating with a coating solution containing an inorganic filler and a resin binder, there are no particular limitations as long as the method does not adversely affect the microporous film. Examples include drying the microporous film at a temperature below its melting point while fixing it in place, or drying it under reduced pressure at a low temperature. From the viewpoint of controlling the shrinkage stress in the MD direction of the microporous film and multilayer porous film, it is preferable to appropriately adjust the drying temperature, winding tension, etc. 【0155】 [Physical properties and composition of separators] From the viewpoint of excellent electrolyte pouring performance, resistance to air pockets, and short pouring time, the contact angle between the separator and the electrolyte (e.g., propylene carbonate) on one or both sides of the separator is preferably 0° to 40°, more preferably 2° to 30°, and even more preferably 4° to 20°. Since the pouring performance improves as the contact angle between the separator and the electrolyte on one or both sides of the separator decreases, the contact angle between the separator and the electrolyte on one or both sides is preferably 40° or less, more preferably 30° or less, even more preferably 20° or less, and particularly preferably 15° or less. The contact angle of the electrolyte on one or both sides of the separator is preferably measured on the side where the thermoplastic polymer-containing layer is formed, and more preferably on the side where the thermoplastic polymer-containing layer is formed in a dot pattern. Even when measuring the contact angle with the electrolyte on one or both sides of the separator on a side where the thermoplastic polymer-containing layer is not formed, the procedure can be carried out in the same way as on the side where the thermoplastic polymer-containing layer is formed. The contact angle between the separator and the electrolyte (e.g., propylene carbonate: PC) on one or both sides is measured by the method described in the examples. 【0156】 From the viewpoint of excellent coatability, the contact angle of the separator with water on one or both sides of the separator is preferably 20° to 85°, more preferably 25° to 75°, and even more preferably 30° to 65°. The lower the contact angle of the separator with water on one or both sides of the separator, the higher the affinity between the coating liquid and the substrate, and the better the coatability. Therefore, the contact angle of the separator with water on one or both sides of the separator is preferably 85° or less, more preferably 75° or less, even more preferably 65° or less, and particularly preferably 50° or less. The contact angle with water on one or both sides of the separator is preferably measured on the side where the thermoplastic polymer-containing layer is formed, and more preferably on the side where the thermoplastic polymer-containing layer is formed in a dot pattern. Even when measuring the water contact angle on one or both sides of the separator on a side where the thermoplastic polymer-containing layer is not formed, the procedure can be carried out in the same way as on the side where the thermoplastic polymer-containing layer is formed. The contact angle with water on one or both sides of the separator is measured by the method described in the examples. 【0157】 In one embodiment, the separator of this embodiment has excellent liquid pourability and coating properties because the contact angle with propylene carbonate on at least one side of the separator is 40° or less, and the contact angle with water on at least one side of the separator is 85° or less. 【0158】 The lower limit of the thickness of the separator for energy storage devices is preferably 2.5 μm or more, more preferably 4.5 μm or more, and even more preferably 5.5 μm or more, from the viewpoint of ensuring the strength of the separator for energy storage devices. On the other hand, the upper limit of the thickness of the separator for energy storage devices is preferably 35 μm or less, more preferably 18 μm or less, from the viewpoint of obtaining good charge / discharge characteristics, and even more preferably 14 μm or less, particularly preferably 12 μm or less, and most preferably 9 μm or less, from the viewpoint of achieving both good charge / discharge characteristics and liquid injection properties. 【0159】 The lower limit of the air permeability of the separator for energy storage devices is preferably 10 seconds / 100cc or more, more preferably 20 seconds / 100cc or more, even more preferably 30 seconds / 100cc or more, and most preferably 40 seconds / 100cc or more. The upper limit is preferably 500 seconds / 100cc or less, more preferably 300 seconds / 100cc or less, and even more preferably 200 seconds / 100cc or less. Setting the air permeability of the separator for energy storage devices to 10 seconds / 100cc or higher is preferable from the viewpoint of further suppressing the self-discharge of the energy storage device when used as a separator for energy storage devices. On the other hand, setting the air permeability of the separator for energy storage devices to 500 seconds / 100cc or lower is preferable from the viewpoint of obtaining good charge and discharge characteristics. The air permeability of separators for energy storage devices can be adjusted by changing the stretching temperature and stretching ratio when manufacturing the polyolefin microporous membrane, the composition and thickness of the inorganic filler-containing layer, and the total coverage area ratio and form of the thermoplastic polymer-containing layer. 【0160】 The separator for the energy storage device has a shutdown temperature, which is an indicator of the safety of the energy storage device, preferably 160°C or lower, more preferably 155°C or lower, even more preferably 150°C or lower, and most preferably 145°C or lower. 【0161】 The separator for energy storage devices has a short-circuit temperature, which is an indicator of heat resistance, preferably 140°C or higher, more preferably 150°C or higher, and even more preferably 160°C or higher. A short-circuit temperature of 160°C or higher is preferable from the viewpoint of safety of the energy storage device when used as a separator for energy storage devices. 【0162】 The puncture strength of the separator for energy storage devices is preferably 200 gf or more, more preferably 300 gf or more. Separators for energy storage devices with a puncture strength of 200 gf or more are preferred from the viewpoint of suppressing the rupture of the polyolefin microporous membrane in impact tests. Furthermore, the upper limit of the puncture strength of the separator for energy storage devices is preferably 1000 gf or less, more preferably 800 gf or less, and even more preferably 700 gf or less, from the viewpoint of stability during film formation. The lower limit can be used as long as it is a value that allows for stable production of film formation and battery manufacturing. The upper limit is set in balance with other characteristics. Puncture strength can be increased by the shear force applied to the molded product during extrusion or by increasing the orientation of molecular chains due to stretching. However, as strength increases, thermal stability deteriorates due to increased residual stress, so it is controlled according to the purpose. 【0163】 [Method for manufacturing separators] The method for forming a thermoplastic polymer-containing layer on a polyolefin microporous membrane is not particularly limited, and one example is a method of applying a coating solution containing a thermoplastic polymer to the polyolefin microporous membrane. 【0164】 The method for applying a coating solution containing a thermoplastic polymer to a polyolefin microporous film is not particularly limited as long as it can achieve the required layer thickness and coating area. Examples 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, spray coater coating, and inkjet coating. Of these, the gravure coater, spray coating, or inkjet coating method is preferred from the viewpoint of offering a high degree of freedom in the coating shape of the thermoplastic polymer and easily obtaining a desirable area ratio. Furthermore, from the viewpoint of adjusting the dot-like pattern of the thermoplastic polymer-containing layer as described above, the gravure coater, inkjet coating, and coating methods that allow for easy adjustment of the printing plate are preferred. 【0165】 When coating a polyolefin microporous film with a thermoplastic polymer, if the coating solution penetrates into the interior of the microporous film, the thermoplastic polymer will fill the surface and interior of the pores, reducing permeability. Therefore, a poor solvent for the thermoplastic polymer is preferred as the coating solution medium. 【0166】 When a poor solvent for a thermoplastic polymer is used as the medium for the coating solution, the coating solution does not penetrate into the interior of the microporous film, and the thermoplastic polymer mainly exists on the surface of the microporous film, which is preferable from the viewpoint of suppressing a decrease in permeability. Water is preferred as such a medium. In addition, there are no particular limitations on the medium that can be used in combination with water, but examples include ethanol and methanol. 【0167】 From the viewpoint of adjusting the dot-like pattern of the thermoplastic polymer-containing layer as described above, it is preferable to optimize the thermoplastic polymer-containing coating solution (also simply called paint) using the thermoplastic polymer, poor solvent, etc., described above. 【0168】 With regard to the coating solution containing thermoplastic polymers, from the viewpoint of adjusting the contact angle between the thermoplastic polymer-containing layer or separator and the electrolyte to the numerical range described above, it is preferable that the paint viscosity be in the range of 30 mPa·s to 100 mPa·s, and more preferably in the range of 50 mPa·s to 80 mPa·s. When the paint viscosity is within the range described above, the appropriate thickening suppresses leveling and brings about an uneven structure of thermoplastic polymer particles on the dot surface, which tends to improve the wettability of the electrolyte. 【0169】 With regard to the coating solution containing thermoplastic polymers, the paint pH is preferably in the range of 5 to 7.9, and more preferably in the range of 5.5 to 7.7, from the viewpoint of adjusting the contact angle between the thermoplastic polymer-containing layer or separator and the electrolyte to the numerical range described above. A paint pH within the range described above moderately suppresses electrostatic repulsion and reduces dispersion stability, thereby suppressing close packing of thermoplastic polymer particles during the drying process, and thereby improving the wettability of the electrolyte due to the uneven structure created by the thermoplastic polymer particles. 【0170】 Furthermore, surface treatment of the microporous film as a separator substrate prior to coating is preferable because it facilitates the application of the coating solution and improves the adhesion between the microporous film and the thermoplastic polymer. The surface treatment method is not particularly limited as long as it does not significantly impair the porous structure of the microporous film, and examples include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation. 【0171】 In the case of corona discharge treatment, the corona treatment intensity of the substrate surface is 1 W / (m²) from the viewpoint of adjusting the contact angle between the thermoplastic polymer-containing layer or separator and the electrolyte to within the numerical range described above. 2 / min) or more 40W / (m 2 It is preferable that the range is 3W / (m²) or less, and 2 / min) or more 32W / (m 2 It is more preferable that the range be less than or equal to 5W / (m 2 / min) or more 25W / (m 2 It is even more preferable that the corona treatment intensity is within the range of ( / min) or less. By introducing hydrophilic groups to the substrate surface with corona treatment intensity within the above range, the affinity with the electrolyte is improved, and wettability tends to be improved. Furthermore, it is also preferable to perform corona discharge treatment after the dot-like pattern of the thermoplastic polymer-containing layer has been formed by coating. 【0172】 Regarding the method for removing the solvent from the coating film after coating with a thermoplastic polymer-containing coating solution, there are no particular limitations as long as the method does not adversely affect the microporous film. For example, methods include drying at a temperature below the melting point while fixing the microporous film, drying under reduced pressure at low temperatures, and immersing the thermoplastic polymer in a poor solvent to solidify the thermoplastic polymer while simultaneously extracting the solvent. 【0173】 In drying a thermoplastic polymer-containing coating film, the drying rate is set to 0.03 g / (m²) from the viewpoint of adjusting the contact angle between the thermoplastic polymer-containing layer or separator and the electrolyte to within the numerical range described above. 2 ·s) or more 4.0g / (m 2 It is preferable that it be within the range of 0.05 g / (m 2 ·s) or more 3.5g / (m 2 It is more preferable that it be within the range of 0.1g / (m 2 ·s) or more 3.0g / (m 2It is even more preferable that the drying speed is within the following range. When the drying speed is within the above range, an appropriate drying speed suppresses leveling, brings about an uneven structure of thermoplastic polymer particles on the dot surface, and tends to improve the wettability of the electrolyte. From a similar viewpoint, when drying a thermoplastic polymer-containing coating film, it is also preferable to raise the temperature by heating or other means to the extent that the particle shape of the thermoplastic polymer-containing layer is not impaired. 【0174】 [Laminate] The laminate according to this embodiment is formed by laminating a separator and an electrode. The separator in this embodiment can be used as a laminate by bonding it to the electrode. The laminate has excellent handling properties during winding and rate characteristics for energy storage devices, and furthermore, it has excellent adhesion and permeability between the thermoplastic polymer and the polyolefin microporous membrane. Therefore, although the application of the laminate is not particularly limited, it can be suitably used, for example, in batteries such as non-aqueous electrolyte secondary batteries or energy storage devices such as capacitors. 【0175】 The electrodes used in the laminate of this embodiment can be those described in the section on energy storage devices below. The method for manufacturing the laminate using the separator of this embodiment is not particularly limited, but for example, the separator and electrodes of this embodiment can be stacked and heated and / or pressed as necessary. Heating and / or pressing can be performed when stacking the electrodes and separator. Alternatively, the laminate can be manufactured by heating and / or pressing a wound body obtained by winding the electrodes and separator into a circular or flat spiral shape after stacking them. 【0176】 Furthermore, the laminate can also be manufactured by laminating a positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape, and heating and / or pressing as necessary. In lamination, from the viewpoint of efficiently exhibiting the effects of this disclosure, it is preferable that the side of the separator having the inorganic filler-containing layer described above faces the positive electrode, with respect to the substrate of the separator. 【0177】 More specifically, the separator of this embodiment can be prepared as a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 1 to 4000 m (preferably 1 to 2000 m), and the separator can be stacked in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, and heated and / or pressed as necessary to manufacture it. 【0178】 The heating temperature is preferably 40 to 120°C. The heating time is preferably 5 seconds to 30 minutes. The pressing pressure is preferably 1 to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The order of heating and pressing is also flexible; heating can be done before pressing, after pressing, or simultaneously. Of these, heating and pressing simultaneously is preferred. 【0179】 <Energy storage devices> The separator according to this embodiment can be used as a separator in batteries, capacitors, or other devices, or for separating materials. In particular, when used as a separator for energy storage devices, it is possible to provide excellent adhesion to electrodes and superior battery performance. The following describes preferred embodiments when the energy storage device is a non-aqueous electrolyte secondary battery. The energy storage device of this embodiment includes a separator for the energy storage device of this embodiment, a positive electrode, a negative electrode, and a non-aqueous electrolyte. 【0180】 When manufacturing a non-aqueous electrolyte secondary battery using the separator of this embodiment, there are no limitations on the positive electrode, negative electrode, or non-aqueous electrolyte; known ones can be used. 【0181】 The cathode material is not particularly limited, but examples include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFe polyolefin 4. 【0182】 The negative electrode material is not particularly limited, but examples include carbon materials such as graphite, non-graphitizable carbon, easily graphitizable carbon, and composite carbon bodies; silicon, tin, metallic lithium, and various alloy materials. 【0183】 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 (PC), ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of electrolytes include lithium salts such as LiClO4, LiBF4, and LiPF6. 【0184】 The method for manufacturing an energy storage device using the separator of this embodiment is not particularly limited, but in the case of a secondary battery, for example, the separator of this embodiment may be manufactured as a vertically elongated separator with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 1 to 4000 m (preferably 1 to 2000 m), the separator may be stacked in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, wound into a circular or flat spiral to obtain a wound body, the wound body may be placed in a battery case, and then an electrolyte may be injected to manufacture the device. 【0185】 In this case, the laminate described above may be formed by heating and / or pressing the wound body. Alternatively, the laminate described above may be wound in a circular or flat spiral shape as the wound body for manufacturing. Furthermore, the energy storage device may be manufactured by laminating a positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator in a flat plate shape, or by laminating the above laminate with a bag-shaped film, injecting an electrolyte, and optionally performing a heating and / or pressing step. The heating and / or pressing step described above can be performed before and / or after the electrolyte injection step. 【0186】 In an energy storage device comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, it is preferable that the separator be positioned such that the side having the inorganic filler-containing layer described above faces the positive electrode, relative to the substrate, from the viewpoint of efficiently exhibiting the effects of this disclosure. 【0187】 The separator according to this embodiment exhibits excellent battery performance (rate characteristics, cycle characteristics) as the adhesive strength measured after pressing the thermoplastic polymer-containing layer on top of the negative electrode at a pressure of 1 MPa, a temperature of 90°C, and 5 seconds is between 1.0 N / m and 10.0 N / m. This improves handling during cell fabrication and reduces thermal shrinkage of the inorganic particle-containing microporous film as it adheres to the electrode. From the viewpoint of achieving excellent battery performance (rate characteristics, cycle characteristics), improved handling during cell fabrication, and the effect of the inorganic particle-containing microporous film adhering to the electrode and becoming less susceptible to thermal shrinkage, the adhesive strength of the separator according to this embodiment is preferably 1.0 N / m or more and 10.0 N / m or less, more preferably 1.2 N / m or more and 5.0 N / m or less, even more preferably 1.5 N / m or more and 3.0 N / m or less, and particularly preferably 1.7 N / m or more and 3.0 N / m or less. The adhesive strength when the thermoplastic polymer-containing layer of the separator according to this embodiment is placed on top of the negative electrode and pressed at a pressure of 1 MPa, a temperature of 90°C, and 5 seconds is measured by the method described in the examples. 【0188】 Unless otherwise specified, the measured values ​​of the various parameters mentioned above are those measured in accordance with the measurement methods described in the examples below. [Examples] 【0189】 The embodiment will be described in detail below based on examples and comparative examples, but this embodiment is not limited to these examples. The methods for measuring and evaluating various physical properties used in the following examples and comparative examples are as follows. Unless otherwise specified, all measurements and evaluations were performed under conditions of room temperature of 23°C, 1 atmosphere, and relative humidity of 50%. 【0190】 [Measurement method] <Viscosity-average molecular weight (hereinafter also referred to as "Mv")> Based on ASRM-D4020, the intrinsic viscosity [η] at 135°C in decalin solvent was determined, and the Mv of polyethylene was calculated using the following formula. [η] = 6.77 × 10 -4 ×Mv 0.67 Furthermore, the Mv of polypropylene was calculated using the following formula. [η] = 1.10 × 10 -4 Mv 0.80 【0191】 <Average particle size D50i of primary inorganic particles contained in polyolefin microporous membrane> The average particle size D50i of inorganic particles was measured using a scanning electron microscope (SEM). Specifically, a 10 μm × 10 μm field image magnified by the SEM was taken directly, or printed from the negative, and then loaded into an image analysis system. The average value of the circular equivalent diameter (diameter of a circle with the same area) of each particle, calculated from the image analysis results, was defined as the average particle size D50i of inorganic particles. However, if the staining boundary was unclear when inputting from the photograph into the image analysis system, the photograph was traced, and this figure was used for input into the image analysis system. 【0192】 <Average particle size of thermoplastic polymer: D50a> The average particle size D50a of thermoplastic polymers was calculated by observing 100 particles of different thermoplastic polymers using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi) at a magnification that allows for the measurement of the diameter of a single particle (for example, 10,000x for thermoplastic polymers of approximately 0.5 μm). Furthermore, the average volume particle size D50a of the thermoplastic polymer particles was defined as the particle size at which the cumulative frequency of the thermoplastic polymer particle size distribution reaches 50%. 【0193】 <Average particle size of inorganic filler particles: D50f> The average particle size D50f of inorganic filler particles was calculated by observing them using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi) at a magnification that allows for the measurement of the diameter of a single particle (for example, 10,000x magnification for inorganic filler particles of approximately 0.5 μm). The average particle size was then calculated by measuring the particle sizes of 100 different inorganic filler particles. Furthermore, the particle size at which the cumulative frequency of the particle size of the inorganic filler particles reaches 50% was defined as the average volume particle size of the inorganic filler particles, D50f. 【0194】 <Measurement of the thickness of the inorganic filler-containing layer> The separator sample was cross-sectionally processed using BIB (Broad Ion Beam). Cross-section machining was performed using a Hitachi High-Tech IM4000 under the following conditions: argon beam, accelerating voltage of 3kV, and beam current of 25-35μA. To suppress thermal damage during machining, the sample was cooled as needed until immediately before machining. Specifically, the sample was left in a -40°C cooling device overnight. This resulted in obtaining a smooth separator cross-section. The thickness of the inorganic filler-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi). The sample was coated with osmium, observed under conditions of an acceleration voltage of 1.0 kV and magnification of 5000x, and the thickness of the inorganic filler-containing layer was calculated. 【0195】 <Balance of polyolefin microporous film and coating basis of thermoplastic polymer-containing layer> Samples measuring 10 cm x 10 cm were cut from a polyolefin microporous membrane, a polyolefin microporous membrane with an inorganic filler-containing layer, and a polyolefin microporous membrane with an inorganic filler-containing layer and a thermoplastic polymer-containing layer. The mass of the cut samples was measured using an electronic balance AEL-200 manufactured by Shimadzu Corporation. Multiplying the obtained mass by 100 gives 1 m 2 Weight (g / m²) of polyolefin microporous membrane per unit 2 ) was calculated. The basis weight of the thermoplastic polymer-containing layer was calculated from the difference in basis weight of the polyolefin microporous film before and after the formation of the thermoplastic polymer-containing layer. 【0196】 <Thickness of polyolefin microporous membrane (μm)> Measurements were taken at room temperature (23°C) using a micro-thickness gauge, KBM (trademark), manufactured by Toyo Seiki. 【0197】 <Porosity (%) of polyolefin microporous membranes> A 10cm x 10cm square sample was cut from a polyolefin microporous membrane, and its volume (cm³) was measured. 3 The values ​​(g) and mass were determined, and the calculation was performed using the following formula. Porosity = (Volume of sample - Mass of sample / Density of sample membrane) / Volume of sample × 100 The film density of the sample was calculated using the density and mixing ratio of the polyolefin resin and inorganic particles used. 【0198】 <Air permeability of polyolefin microporous membrane (seconds / 100cc)> In accordance with JIS P-8117, the air permeability was defined as the air permeability resistance measured using a Gurley-type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd. 【0199】 <Puncture strength (gf) of polyolefin microporous membranes> A polyolefin 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 polyolefin microporous membrane at a 25°C atmosphere with a needle tip radius of curvature of 0.5 mm and a puncture speed of 2 mm / second, to obtain the puncture strength (gf) as the maximum puncture load. Furthermore, the puncture strength converted to basis weight can also be calculated from the puncture strength and basis weight. 【0200】 <Glass transition temperature of thermoplastic polymers (°C)> An appropriate amount of thermoplastic polymer coating solution was placed in an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes. Approximately 17 mg of the dried film was placed in an aluminum container for measurement, and DSC and DDSC curves under a nitrogen atmosphere were obtained using a DSC analyzer (Shimadzu Corporation, DSC6220). The measurement conditions were as follows. (First stage heating program) Start at 70°C, increasing the temperature at a rate of 15°C per minute. Once it reaches 110°C, maintain that temperature for 5 minutes. (Second stage cooling program) The temperature is reduced from 110°C at a rate of 40°C per minute. After reaching -50°C, it is maintained for 5 minutes. (3rd stage heating program) The temperature was increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third stage of temperature increase. The glass transition temperature (Tg) was defined as the intersection point of the baseline (a straight line extending the baseline in the obtained DSC curve toward the higher temperature side) and the tangent line at the inflection point (the point where the curve, which is convex upwards, changes to a curve, which is convex downwards). 【0201】 <Dot diameter and distance between dots> The dot diameter of the coating pattern was defined as the region where the thermoplastic polymer is continuously present when observed using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi) at a magnification that allows observation of one dot in one field of view (for example, 300x magnification for a dot diameter of approximately 200 μm). A region where the thermoplastic polymer is continuously present is a region with a width exceeding 10 μm in a continuous manner. This region is formed, for example, by the continuous density and contact of thermoplastic polymer particles in the planar direction. The pattern of the region where the thermoplastic polymer is continuously present was defined by visually excluding regions with a width of 10 μm or less from the SEM image. Furthermore, the region where the thermoplastic polymer is continuously present was defined visually so as not to include regions where the thermoplastic polymer is discontinuously scattered. 【0202】 The dot diameter in the region where the thermoplastic polymer was continuously present was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). The separator sample was photographed using coaxial reflected light at a magnification that allowed for the measurement of at least five dot diameters (for example, 100x magnification for a dot diameter of approximately 200 μm). The command "Measurement / Scale" was selected, then "Planar Measurement" and "Diameter". 【0203】 For example, in the case of clover-shaped dots formed on an inorganic filler-containing layer containing inorganic particles and a resin binder, the diameter of the circle circumscribing the region where the thermoplastic polymer is continuously present was used. The diameter of each circumscribing circle was measured for multiple (5) dots, and their average value was calculated as the dot diameter. 【0204】 Furthermore, in cases where the dots were teardrop-shaped (for example, dots formed directly on a polyolefin microporous membrane) or elliptical in shape, the diameter of the largest circle inscribed within the region where the thermoplastic polymer continuously existed was used. For multiple (5) dots, the diameter of the largest inscribed circle for each was measured, and the average value of these measurements was calculated as the dot diameter. 【0205】 The inter-dot distance in the thermoplastic polymer-containing layer was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). The separator sample was photographed at 100x magnification (coaxial incident light), and in measurement mode, an arbitrary dot was selected. The distance from the center of its circumscribed circle to the centers of dots located vertically, horizontally, and diagonally to the arbitrary dot was measured, and the average of these measurements was defined as the inter-dot distance. 【0206】 <Total coverage area ratio of thermoplastic polymer-containing layer relative to the substrate surface (%)> The total coverage area ratio of the thermoplastic polymer-containing layer coating pattern on the substrate surface was measured using a microscope (model: VHX-7000, manufactured by Keyence Corporation). The separator sample was photographed using coaxial incident light at a magnification that allowed for simultaneous observation of 10 or more dots (for example, 100x magnification for dots with a diameter of approximately 200 μm). From the command "Measurement / Scale," select "Automatic Area Measurement (Particle Count)," "Extraction Method Brightness (Standard)," and "Fill Holes." Select an appropriate brightness (preferably between -10 and 10) to binarize the covered and uncoated areas of the thermoplastic polymer-containing layer, and measure the total coverage area ratio of the thermoplastic polymer-containing layer. If the contrast is unclear, another light source (model: PD2-1024, manufactured by CCS Corporation) may be used. 【0207】 <Dot average height of the thermoplastic polymer-containing layer> The separator as a sample was cross-sectionally processed by BIB (Broad Ion Beam). The cross-sectional processing was carried out using IM4000 manufactured by Hitachi High-Tech Corporation under the processing conditions of argon as the beam species, an acceleration voltage of 3 kV, and a beam current of 25 to 35 μA. During processing, in order to suppress thermal damage, the separator was cooled until immediately before processing as necessary. Specifically, the separator was left in a cooling device at -40°C for one day and night. As a result, a smooth cross-section of the separator was obtained. The height of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by HITACHI). After osmium evaporation, observations were made under the conditions of an acceleration voltage of 1.0 kV and a magnification of 5000 times. The maximum thickness of the thermoplastic polymer-containing layer was measured at 5 observation points, and their average value was calculated as the average height. In the case of a dot pattern, the dot average height is calculated by the same method as above, with the distance from the substrate surface to the dot apex along the thickness direction of the thermoplastic polymer-containing layer taken as the dot maximum thickness. 【0208】 <Compression ratio of the thermoplastic polymer> The compression ratio of the thermoplastic polymer used in each example and comparative example was measured using a plate-like sample of the thermoplastic polymer. The plate-like sample for measurement was prepared by the following method. First, an appropriate amount of the thermoplastic polymer coating liquid was taken in a petri dish and dried in an environment of room temperature 23°C, 1 atmosphere, and relative humidity 50% for one day or more to remove the moisture in the coating liquid and create a dry solid. The dry solid was pulverized in a mortar to a powder form, and 1 g was collected. The collected dry solid was sandwiched between two 10 cm × 10 cm square PET films and pressed at a temperature of 150°C and a pressure of 3 MPa for 2 minutes to prepare a compression plate. The displacement amount T of the plate thickness before and after compression was measured using a thermomechanical analyzer (TMA). Using a TMA (manufactured by NETZSCH: TMA4000SE+HC9700, probe: quartz 0.5 mmφ probe), the measurement conditions were: sample atmosphere N2, load: 20.00 g, temperature program: temperature 90°C, humidity 40%, hold for 30 minutes, and the displacement amount T was measured. The thickness of the plate-like sample before compression was measured at room temperature of 23°C using a micrometer KBM (trademark) manufactured by Toyo Seiki. The displacement amount T and the thickness of the plate-like sample before compression were applied to the formula: compression ratio = displacement amount T / thickness of the plate-like sample before compression × 100, and the compression ratio of the thermoplastic polymer was calculated. 【0209】 <Adhesion to electrodes> The separators for the power storage devices obtained in each of the examples and comparative examples were cut into rectangular shapes with a width of 20 mm and a length of 70 mm. As adherends, a positive electrode (manufactured by Enertech, positive electrode material: LiCoO2, conductive assistant: acetylene black, L / W: 36 mg / cm on both sides 2 , thickness of Al current collector: 15 μm, thickness of the positive electrode after pressing: 120 μm), and a negative electrode (manufactured by Enertech, negative electrode material: graphite, conductive assistant: acetylene black, L / W: 20 mg / cm on both sides 2 , thickness of Cu current collector: 10 μm, thickness of the negative electrode after pressing: 140 μm) were each cut into rectangular shapes with a width of 15 mm and a length of 60 mm. The thermoplastic polymer-containing layer of the cut separator and the cut positive electrode or negative electrode were overlapped so as to face each other to obtain a laminate. The thermoplastic polymer-containing layer on the first main surface of the base material faced the positive electrode, and the thermoplastic polymer-containing layer on the second main surface of the base material faced the negative electrode. The separator and the negative electrode or positive electrode were overlapped. Then, each laminate was pressed under the following conditions. Pressing pressure: 1 MPa Temperature: 90°C Pressing time: 5 seconds 【0210】 For the laminate after pressing, a 90° peel test was performed at a peel rate of 50 mm / min using a force gauge ZP5N and MX2-500N (product name) manufactured by IMADA Co., Ltd. to fix the electrode and grip and pull the separator, and the peel strength was measured. At this time, the average value of the peel strength in the peel test for a length of 40 mm performed under the above conditions was adopted as the adhesive force to the electrode. When a separator achieving an adhesive strength of 1.0 N / m or more, obtained by this method, is used in an energy storage device, good adhesion is achieved between it and the opposing positive and negative electrodes. 【0211】 <Pouring properties of electrolyte> The separators for energy storage devices obtained in each example and comparative example, and the cathode (manufactured by enertech, positive electrode material: LiCoO2, conductive additive: acetylene black, L / W: 36 mg / cm² on both sides) used as the substrate. 2 (Aluminum current collector thickness: 15 μm, positive electrode thickness after pressing: 120 μm) or negative electrode (manufactured by enertech, negative electrode material: graphite, conductive additive: acetylene black, L / W: 20 mg / cm² on both sides) 2 The copper current collector (thickness: 10 μm) and the negative electrode (thickness after pressing: 140 μm) were each cut into rectangular shapes with a width of 26 mm and a length of 76 mm. A laminate was obtained by stacking a separator and either a negative electrode or a positive electrode such that the thermoplastic polymer-containing layer on the first main surface of the substrate faced the positive electrode, and the thermoplastic polymer-containing layer on the second main surface of the substrate faced the negative electrode. Then, each laminate was pressed under the following conditions. Press pressure: 2 MPa Temperature: 100℃ Press time: 5 seconds 【0212】 The pressed laminate was sandwiched between two glass plates (Matsunami Glass Co., Ltd., S1214, size: 76 x 26 mm, thickness: 1.2-1.5 mm), and the top was secured with two clips (ASKUL double clips, 15 mm wide) and attached to a 100 mm long rod. An electrolyte solution (Kishida Chemical Co., Ltd., LBG-64955, propylene carbonate (PC)) was placed in a cup so that the pressed laminate was immersed to a height of 2 mm from the bottom. The rod with the laminate attached was placed on the rim of the cup, and the electrolyte solution was absorbed from the lower end of the laminate. The time it took for the electrolyte solution to spread throughout the entire pressed laminate was measured by visual observation and defined as the injection time. The electrolyte infusion rate test was performed on both sides of the separator (the first main surface of the substrate and the second main surface of the substrate), and the longer infusion time was defined as the rate-limiting infusion time of the separator. 【0213】 In automotive batteries, increasing cell width increases the time required for liquid injection, which can become a bottleneck in the cell manufacturing process. To solve this problem, it is desirable to keep the liquid injection process to 60 hours or less. Assuming a typical automotive battery size (e.g., 200 mm width), energy storage devices using separators that achieve a liquid injection completion time of 20 minutes or less using this method, for both the positive electrode and separator laminate and the negative electrode and separator laminate, can reduce the liquid injection time to 60 hours or less. Energy storage devices using separators obtained by this method, which achieve a rate-determining injection time of 20 minutes or less, exhibit good electrolyte penetration at the interfaces between the opposing positive and negative electrodes, thereby improving the overall injection performance of the cell. 【0214】 <Measuring the contact angle with the electrolyte> Using a dynamic contact angle meter (Kyowa Interface Science Co., Ltd., model DCA-VM), a 2 μL droplet of electrolyte (Kishida Chemical Co., Ltd., LBG-64955, propylene carbonate (PC)) was prepared on the tip of a syringe needle. This droplet was then applied to the surface of the separators for energy storage devices obtained in each example and comparative example, and the contact angle was taken at 6000 ms from the point of liquid separation. The contact angle was measured in a constant temperature room under conditions of 23°C and 42% humidity. The contact angle with the electrolyte was measured on both sides of the separator (the first main surface of the substrate and the second main surface of the substrate). 【0215】 <Measuring the contact angle with water> Using a dynamic contact angle meter (Kyowa Interface Science Co., Ltd., model DCA-VM), a 2 μL droplet of deionized water was prepared on the tip of a syringe needle. This droplet was then placed on the surface of the separators for energy storage devices obtained in each example and comparative example, and the contact angle was taken at 6000 ms from the point of liquid separation. The contact angle was measured in a constant temperature room under conditions of 23°C and 42% humidity. The contact angle with water was measured on both sides of the separator (the first main surface of the substrate and the second main surface of the substrate). 【0216】 <Preparation of positive and negative electrodes for rate characteristic testing> 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 90.4% by mass, and graphite powder (KS6) (density 2.26 g / cm³) is used as a conductive additive. 3 , 1.6% by mass of number-average particle size 6.5 μm, and acetylene black powder (AB) (density 1.95 g / cm³). 3 3.8% by mass of (number average particle size 48 nm), and polyvinylidene fluoride (PVdF) (density 1.75 g / cm³) as a binder. 3 A slurry was prepared by mixing the two substances in a ratio of 4.2% 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. Graphite powder A (density 2.23 g / cm³) is used as the negative electrode active material. 3 87.6% 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% by mass of (number average particle size 6.5 μm), 1.4% by mass (on a solid content basis) of ammonium carboxymethylcellulose (1.83% by mass aqueous solution) and 1.7% by mass (on a solid content basis) of diene rubber latex (40% by mass aqueous solution) as binders in purified water. 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. 【0217】 <Preparation of non-aqueous electrolyte for rate characteristic testing> 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:ethyl methyl carbonate = 1:2 (volume ratio) containing 1% by mass of vinylene carbonate. 【0218】 <Battery Assembly> The separator or substrate was cut into a 24 mm diameter circle, and the positive and negative electrodes for rate characteristic testing were each cut into 16 mm 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 lid were insulated, 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. A simple battery (energy storage device) was assembled by injecting 0.4 mL of non-aqueous electrolyte for rate characteristic testing into this container and sealing it. 【0219】 <Rate Characteristics> The assembled simple battery was charged at 25°C with a current of 3mA (approximately 0.5C) until the battery voltage reached 4.2V. Then, the current was gradually reduced from 3mA to maintain the 4.2V voltage. This first charge (initial charge) after battery fabrication took a total of approximately 6 hours. After that, the battery was discharged at a current of 3mA until the battery voltage reached 3.0V. Next, at 25°C, the battery was charged to a voltage of 4.2V with a current of 6mA (approximately 1.0C), and then the current was gradually reduced from 6mA to maintain the voltage at 4.2V, for a total of approximately 3 hours. After that, the discharge capacity when the battery was discharged to a voltage of 3.0V with a current of 6mA was defined as the 1C discharge capacity (mAh). Next, at 25°C, the battery was charged to a voltage of 4.2V with a current of 6mA (approximately 1.0C), and then the current was gradually reduced from 6mA to maintain the voltage at 4.2V, for a total of approximately 3 hours. After that, the discharge capacity when the battery voltage was discharged to 3.0V with a current of 12mA (approximately 2.0C) was defined as the 2C discharge capacity (mAh). The ratio of the 2C discharge capacity to the 1C discharge capacity was then calculated, and this value was defined as the rate characteristic. Note that a current of 6mA is approximately 1C when charging and discharging a simple battery at a temperature of 25°C. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) × 100 Evaluation criteria A (Good): Rate characteristic is over 85% B (Acceptable): Rate characteristic is over 80% and 85% or less C (Unacceptable): Rate characteristic is 80% or less 【0220】 <Polyolefin microporous membrane> (Manufacture of inorganic particle-containing microporous membrane 1) High-density polyethylene "SH800" (manufactured by Asahi Kasei Corporation) with a viscosity-average molecular weight (Mv) of 250,000 and a density of 0.957 g / cm 3 was 11.5 parts by mass, ultra-high molecular weight polyethylene "UH850" (manufactured by Asahi Kasei Corporation) with a viscosity-average molecular weight (Mv) of 2,000,000 and a density of 0.937 g / cm 3 was 7.7 parts by mass, silica "R972" (manufactured by Nippon Aerosil Co., Ltd.) with an average primary particle diameter of 16 nm as inorganic particles, 15.4 parts by mass of liquid paraffin (LP) "Smoyl P-350P" (manufactured by Matsumura Petrochemical Research Institute, Inc.) as a plasticizer, and 0.1 part by mass of pentaerythrityl-tetrakis-[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate] as an antioxidant were premixed in a Henschel mixer. The obtained mixture was supplied to the feed port of a twin-screw co-rotating extruder by a feeder and melt-kneaded. Also, liquid paraffin was added by side feed to the twin-screw extruder cylinder in two portions so that the ratio of the amount of liquid paraffin in the total mixture (100 parts by mass) extruded was 68 parts by mass. The addition ratio for the two times was 1st time / 2nd time = 7 / 3. The melt-kneading conditions were carried out under the conditions of a screw rotation speed of 60 rpm and an extrusion amount of 65 kg / h. The Q / N ratio (Q: extrusion amount [kg / hr], N: screw rotation speed [rpm]) at this time was 1.08. The set temperature was 160°C for the kneading section and 230°C for the T-die. Subsequently, the melt-kneaded material was extruded into a sheet shape from the T-die and cooled with a cooling roll controlled at a surface temperature of 70°C to obtain a sheet-shaped molded product with a thickness of 1800 μm. 【0221】 The obtained sheet-like molded material was guided into a simultaneous biaxial stretching machine to obtain a primary stretched film (primary stretching step). The set stretching conditions were an MD ratio of 7 times, a TD ratio of 7 times, and a stretching temperature of 117°C. Next, the obtained primary stretched film was guided into a methylene chloride bath and thoroughly immersed to extract and remove the liquid paraffin, which is a plasticizer, and then the methylene chloride was dried off to obtain an extracted film. 【0222】 Next, the extracted membrane was guided into a TD uniaxial tenter for thermal fixation. As a heat-setting process, the material was stretched under conditions of a stretching temperature of 135°C and a stretching ratio of 1.6 times, followed by a relaxation operation at a relaxation temperature of 144°C and a relaxation rate of 10%. The various properties of the obtained polyolefin microporous film (inorganic-containing microporous film 1) were evaluated using the method described above. The results are shown in Table 1. Furthermore, when the obtained microporous membrane was calcined at 600°C for 30 minutes and the amount of silica was calculated from the remaining weight, it was found to be 10% by volume. This indicates that the incorporated silica was hardly extracted and remained in the microporous membrane. 【0223】 [Manufacturing of microporous membranes containing inorganic particles 2-13] Inorganic particle-containing microporous membranes 2 to 13 were obtained in the same manner as inorganic particle-containing microporous membrane 1, except that the inorganic particle content and other factors were appropriately changed as manufacturing conditions to adjust the physical properties (membrane thickness, basis weight, porosity, air permeability, puncture strength, etc.). 【0224】 For the obtained inorganic particle-containing microporous membranes 1 to 13, the physical properties (membrane thickness, porosity, air permeability, and puncture resistance, etc.) were measured as needed using the method described above. 【0225】 <Thermoplastic polymer> <Preparation of thermoplastic polymer 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", and 0.5 parts by mass of "Adekaria Soap SR1025" were added as the initial charge, 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% by mass aqueous solution) (indicated as "APS(aq)" in the table; the same applies hereafter) were added. 【0226】 On the other hand, 0.1 parts by mass of methacrylic acid (MAA), 0.1 parts by mass of acrylic acid (AA), 38.5 parts by mass of methyl methacrylate (MMA), 19.6 parts by mass of n-butyl acrylate (BA), 31.9 parts by mass of 2-ethylhexyl acrylate (EHA), 2 parts by mass of 2-hydroxyethyl methacrylate (HEMA), 5 parts by mass of acrylamide (AM), 2.8 parts by mass of glycidyl methacrylate (GMA), 0.7 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. 【0227】 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% aqueous solution) to obtain a 40% by mass acrylic copolymer latex (thermoplastic polymer a1). The glass transition temperature (Tg) of the thermoplastic polymer contained in the obtained thermoplastic polymer a1 was evaluated using the method described above. The results are shown in Table 2. 【0228】 <Preparation of thermoplastic polymers a2-a8> Thermoplastic polymers a2 to a8 were obtained in the same manner as thermoplastic polymer a1, except that the composition of the emulsion was changed as shown in Table 2, and the glass transition temperature (Tg) was evaluated using the method described above. The results obtained are shown in Table 2. 【0229】 Thermoplastic polymers a1 to a8 were mixed in the combinations and proportions shown in Table 3 to prepare thermoplastic polymer-containing paints A1 to A7. The volume-average particle size (D50a) of the obtained thermoplastic polymer-containing paints A1 to A7 was measured using the method described above. The results are shown in Table 3. 【0230】 <Explanation of abbreviations in the table> ·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 【0231】 Initiator APS(aq): Ammonium persulfate (2% by mass aqueous solution) 【0232】 • Monomer MAA: Methacrylic acid AA: Acrylic acid MMA: Methyl methacrylate BA: n-butyl acrylate 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 【0233】 (Dot coating of thermoplastic polymer-containing layers onto polyolefin microporous films) <Example 1> Under the conditions for the dot pattern, coverage area ratio, and coating basis shown in Table 1, a thermoplastic polymer A1 mixed in the proportions described in Table 1 was applied as a coating solution to one side (the second main surface of the substrate) of a polyolefin microporous film 1 using gravure printing. By adjusting the drive roll conditions and drying at 40°C, the water in the coating solution was removed to obtain the separator for the energy storage device of Example 1. The properties of the obtained separator were evaluated using the method described above. The results are shown in Table 1. The obtained separator had a dot diameter of 200 μm and an average dot height of 0.3 μm. 【0234】 <Comparative Example 5> As shown in Table 1, Comparative Example 5, a separator for an energy storage device, was obtained in the same manner as in Example 1, except that the conditions such as the type of thermoplastic polymer, dot pattern, coverage area ratio, and coating basis were changed, and the coating conditions were changed to gravure coating, in which the thermoplastic polymer-containing coating was uniformly applied to the entire surface of one side (the second main surface of the substrate) of the polyolefin microporous film using uniform dispersion coating (indicated as "solid" in the table). The obtained separator was evaluated using the method described above. The results are shown in Table 1. 【0235】 <Examples 2-6 and 9-13, Comparative Examples 1-4 and 6-9> As shown in Table 1, separators for energy storage devices were obtained in the same manner as in Example 1, except that conditions such as the type of thermoplastic polymer, dot pattern, coverage area ratio, and coating basis were changed, and the separators had thermoplastic polymer-containing layers on one side of the polyolefin microporous film (the first main surface of the substrate or the second main surface of the substrate) or on both sides of the polyolefin microporous film (the first main surface of the substrate and the second main surface of the substrate). The properties of the obtained separators were evaluated using the method described above. The results are shown in Table 1. 【0236】 <Example 7> Under the conditions for the dot pattern, coverage area ratio, and coating basis shown in Table 1, an inorganic filler-containing layer was formed on one side (the first main surface of the substrate) of a polyolefin microporous film 1. Subsequently, a thermoplastic polymer A1, mixed in the proportions shown in Table 1, was applied as a coating liquid to the second main surface of the substrate using gravure printing. By adjusting the drive roll conditions and drying at 40°C, the water in the coating liquid was removed to obtain the separator for the energy storage device of Example 7. The obtained separator was evaluated using the method described above. The results are shown in Table 1. 【0237】 <Example 8> A separator for an energy storage device of Example 8 was obtained in the same manner as in Example 7, except that a thermoplastic polymer A1, mixed in the proportions shown in Table 1, was applied as a coating liquid to the inorganic filler-containing layer and the second main surface of the substrate using gravure printing. The obtained separator was evaluated using the method described above. The results are shown in Table 1. 【0238】 [Table 1-1] 【0239】 [Table 1-2] 【0240】 [Table 1-3] 【0241】 [Table 1-4] 【0242】 [Table 1-5] 【0243】 [Table 2] 【0244】 Table 3

Claims

[Claim 1] A substrate containing polyolefin resin and inorganic particles, A separator for an energy storage device, comprising a thermoplastic polymer-containing layer on the first main surface of the substrate, the second main surface of the substrate, or both sides thereof, wherein the thermoplastic polymer is arranged in a dot-like pattern, The substrate contains the inorganic particles in an amount of 7% to 40% by volume relative to the total content of the polyolefin resin and the inorganic particles. The porosity of the substrate is 52% or more and 85% or less. The average particle size D50i of the primary particles of the inorganic particles is 5 nm or more and 20 nm or less. The ratio D50a / D50i of the average particle size D50a of the thermoplastic polymer to the average particle size D50i of the primary particles of the inorganic particles is 15 or more and 60 or less. A separator for energy storage devices, wherein the compressibility of the thermoplastic polymer is 30% or less when a pressure of 1 MPa is applied in an environment with a temperature of 90°C and a humidity of 40%. [Claim 2] The substrate has a thermoplastic polymer-containing layer arranged in a dot-like pattern on its second main surface, The separator for an energy storage device according to claim 1, wherein the first main surface of the substrate has an inorganic filler-containing layer. [Claim 3] The separator for an energy storage device according to claim 1 or 2, wherein the inorganic particles are present as secondary particles in the substrate. [Claim 4] The separator for an energy storage device according to claim 1 or 2, wherein the D50a is 300 nm or more and 700 nm or less. [Claim 5] The separator for an energy storage device according to claim 1 or 2, wherein the air permeability of the substrate is 50 seconds / 100 cc or less. [Claim 6] The contact angle between the separator and the propylene carbonate on at least one side is 40° or less, and A separator for an energy storage device according to claim 1 or 2, wherein the contact angle with water on at least one side of the separator is 85° or less. [Claim 7] A separator for an energy storage device according to claim 1 or 2, wherein the adhesive force when pressed with the negative electrode at a temperature of 90°C, a pressure of 1 MPa, and for 5 seconds is 1.0 N / m or more and 10.0 N / m or less. [Claim 8] The dot diameter of the thermoplastic polymer-containing layer is 20 μm or more and 1,000 μm or less, and the coverage rate of the thermoplastic polymer-containing layer on the substrate surface is 5% to 50%. The separator for an energy storage device according to claim 1 or 2, wherein the average dot height of the thermoplastic polymer-containing layer is 0.2 μm or more and 10 μm or less. [Claim 9] The separator for an energy storage device according to claim 1 or 2, wherein the thermoplastic polymer has a core-shell structure. [Claim 10] A separator for an energy storage device according to claim 1 or 2, wherein the puncture strength is 200 gf or more and 1000 gf or less. [Claim 11] An energy storage device comprising a separator for energy storage devices according to claim 1 or 2, a positive electrode, a negative electrode, and a non-aqueous electrolyte.

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