Separators for power storage devices

Abstract

To provide a separator for a power storage device and the like that can improve the cycle characteristics of a power storage device.SOLUTION: A separator for a power storage device includes a substrate, and a thermoplastic polymer-containing layer formed on at least one substrate surface of the substrate and containing a thermoplastic polymer, and satisfies a relationship represented by B90 / B10<7 {B90 and B10 represent the maximum peel strength for 90% RH and maximum peel strength for 10% RH, respectively, as defined herein}.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a separator for an electricity storage device, a laminate or wound body using the same, an electricity storage device, etc. [Background technology]

[0002] The development of energy storage devices, such as lithium-ion secondary batteries, has been actively pursued. Energy storage devices typically have a microporous membrane (separator) between the positive and negative electrodes. The separator prevents direct contact between the positive and negative electrodes and allows ions to pass through the electrolyte solution held in the micropores.

[0003] Separators are required to have safety-related properties, such as the ability to quickly stop the battery reaction in the event of abnormal heating (fuse properties), and the ability to maintain their shape even at high temperatures and prevent dangerous situations in which the positive and negative electrodes would directly react (short-circuit resistance).

[0004] Furthermore, with growing environmental awareness, electricity storage devices for electric vehicles (EVs), on-board components, etc. are attracting increasing attention, and a technology is being used to reduce the volume by heat-pressing a laminate or wound body of electrodes and a separator in order to increase the capacity of the electricity storage device. In order to fix the electrode and separator after pressing and maintain the volume at the time of pressing, a technology is also being used in which a thermoplastic polymer-containing layer that exhibits adhesive properties under specified conditions is disposed on the separator to improve adhesion between the separator and the electrode, thereby also suppressing press-back of the laminate or wound body.

[0005] However, a "blocking" phenomenon is expected, in which separators having a thermoplastic polymer-containing layer adhere to each other. In this case, when unwinding a separator from a wound body in which only the separator is wound, a stress equivalent to the blocking force between the separators is required, which may cause a problem of unwinding failure, making it difficult to unwind a separator of the desired length uniformly without wrinkles. Therefore, efforts have been made to achieve both blocking resistance and adhesion to electrodes for the separator.

[0006] For example, Patent Document 1 describes a separator for an electricity storage device that aims to achieve both blocking resistance and adhesion to electrodes. The separator has a thermoplastic polymer-containing layer formed on at least one side of a substrate, and specifies the ratio of two peel strengths measured under two conditions for a separator wound body. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 6580234 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, increasing environmental awareness and safety have led to demands for improving the cycle characteristics of electricity storage devices. Even if conventional separators for electricity storage devices have been designed with attention to blocking resistance, adhesion to electrodes, etc., as described in, for example, Cited Document 1, there is still room for further improvement in the cycle characteristics of electricity storage devices.

[0009] The present invention has been made in view of the above circumstances, and aims to provide a separator for an electricity storage device that can improve the cycle characteristics of the electricity storage device, as well as a laminate or wound body using the separator, and an electricity storage device. [Means for solving the problem]

[0010] The present inventors have conducted studies to solve the above-mentioned problems and have found that the above-mentioned problems can be solved by using a separator for an electricity storage device having the following configuration, thereby completing the present invention. That is, the present invention is as follows. [1] A separator for an electric storage device comprising a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate and containing a thermoplastic polymer, wherein the separator for an electric storage device comprises a compound represented by the following formula: B90 / B10<7 {wherein B90 and B10 are defined as follows: Two of the separators for the electricity storage device were prepared and stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 90%, and then one surface (A) of each of the separators for the electricity storage device was laminated with the other surface (A) to form a laminate (AA). RH90 A laminate (AB) formed by laminating the surface (A) and the surface (B) opposite thereto. RH90 and a laminate (BB) formed by laminating the surfaces (B) together. RH90 Each laminate was pressed for 2 minutes under conditions of a temperature of 40°C and a pressure of 1 MPa, and the maximum peel strength (N / m) of all the laminates was measured individually, and the maximum value was designated as B90; Two of the separators for the electricity storage device were prepared and stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then a laminate (AA) was formed by laminating one surface (A) of the separator for the electricity storage device with the surface (A) of the separator for the electricity storage device. RH10 A laminate (AB) formed by laminating the surface (A) and the surface (B) opposite thereto. RH10 and a laminate (BB) formed by laminating the surfaces (B) together. RH10 Each laminate was pressed for 2 minutes under conditions of a temperature of 40°C and a pressure of 1 MPa. The maximum peel strength (N / m) of all the laminates measured individually was designated as B10. A separator for an electricity storage device that satisfies the relationship expressed by the following formula: [2] The separator for an electricity storage device has the following configuration: (1) the substrate and the thermoplastic polymer-containing layer formed on one side of the substrate; (2) the substrate and the thermoplastic polymer-containing layers formed on both sides of the substrate; (3) the substrate, an inorganic coating layer formed on one side of the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) the substrate, an inorganic coating layer formed on one side of the substrate, the thermoplastic polymer-containing layer formed on the inorganic coating layer on the side opposite to the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; 2. The separator for an electricity storage device according to item 1, comprising at least one of the following: [3] 3. The separator for an electricity storage device according to item 1 or 2, wherein the B90 is less than 10 N / m. [4] A separator for an electricity storage device, comprising: a substrate; and a thermoplastic polymer-containing layer formed on at least a portion of at least one surface of the substrate, the thermoplastic polymer being represented by the following formula: T10-T90<10 {wherein T90 and T10 are defined as follows: The thermoplastic polymer was stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 90%, and then the thermoplastic polymer was sealed in an aluminum hermetic pan. The glass transition temperature (°C) measured by DSC (differential scanning calorimetry) was defined as T90. The thermoplastic polymer is stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then the thermoplastic polymer is sealed in an aluminum hermetic pan and the glass transition temperature (°C) measured by DSC is defined as T10. A separator for an electricity storage device that satisfies the relationship expressed by the following formula: [5] Item 5. The separator for an electricity storage device according to item 4, wherein the T90 is 30°C or higher. [6] The separator for an electricity storage device is subjected to the following conditions: {Condition: The measurement value P10 is determined as follows: Two of the separators for an electricity storage device were prepared, and the separators for an electricity storage device were stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then one surface (A) of each of the separators for an electricity storage device was laminated with the other surface (A) of each separator to form a laminate (AA). RH10 A laminate (AB) formed by laminating the surface (A) and the surface (B) opposite thereto. RH10 and a laminate (BB) formed by laminating the surfaces (B) together. RH10 Each laminate is pressed for 5 seconds under conditions of a temperature of 90°C and a pressure of 1 MPa. The maximum peel strength of all the laminates measured individually is defined as P10 (N / m). 6. The separator for an electricity storage device according to any one of items 1 to 5, wherein a measured value P10 measured by JIS Z 2004-2008 is 5 N / m or more. [7] 7. The separator for an electricity storage device according to any one of items 1 to 6, wherein the thermoplastic polymer has a mass swelling ratio of 2 to less than 7 times with respect to an electrolyte solution (volume ratio of ethylene carbonate (EC) / diethyl carbonate (DEC)=2 / 3). [8] 8. The separator for an electricity storage device according to any one of items 1 to 7, wherein the coverage area of ​​the thermoplastic polymer relative to the substrate is 5% or more and 70% or less. [9] 9. The separator for an electricity storage device according to any one of items 1 to 8, wherein the thermoplastic polymer comprises a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer.

[10] the thermoplastic polymer has at least two glass transition temperatures; At least one of the glass transition temperatures is in a region below 20°C; and 10. The separator for an electricity storage device according to any one of items 1 to 9, wherein at least one of the glass transition temperatures is in a range of 20° C. or higher.

[11] 11. The separator for an electricity storage device according to any one of items 1 to 10, wherein the thermoplastic polymer is a water-insoluble particulate thermoplastic polymer and comprises a copolymer having an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units, and the proportions of the aromatic vinyl compound monomer and the nitrile group-containing monomer in the water-insoluble particulate thermoplastic polymer are each 10% by mass or more. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a separator for an electricity storage device that can improve the cycle characteristics of the electricity storage device, as well as a laminate or wound body using the separator, and an electricity storage device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Below, we will explain in detail the form for implementing the present invention (hereinafter simply referred to as the ``present embodiment''), but the present invention is not limited to the present embodiment and various modifications are possible within the scope of the gist of the present invention.

[0013] As used herein, "(meth)acrylic" refers to "acrylic" and its corresponding "methacrylic", "(meth)acrylate" refers to "acrylate" and its corresponding "methacrylate", and "(meth)acryloyl" refers to "acryloyl" and its corresponding "methacryloyl".

[0014] Furthermore, the term "on" in this specification does not limit the positional relationship of each component to "directly on top." For example, the expression "a thermoplastic polymer-containing layer formed on a substrate" does not exclude an embodiment in which an optional layer (a layer having heat resistance, for example, an inorganic filler porous layer) is included between the substrate and the thermoplastic polymer-containing layer.

[0015] Furthermore, in this specification, unless otherwise specified, the symbol "to" means that the numerical values ​​before and after it are included as upper and lower limits.

[0016] <Separators for electricity storage devices> One aspect of the present invention provides a separator for an electricity storage device (hereinafter also simply referred to as "separator") comprising a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate and containing a thermoplastic polymer. Both an embodiment in which the thermoplastic polymer-containing layer is formed on only one surface of the separator and an embodiment in which the thermoplastic polymer-containing layer is formed on both surfaces of the separator are within the scope of the present invention.

[0017] The separator can be disposed between positive and negative electrodes in an electricity storage device, such as a non-aqueous electrolyte secondary battery, a condenser, a capacitor, etc. In particular, when the separator is disposed between the positive and negative electrodes of a lithium ion secondary battery, the separator tends to have excellent electrical insulation, ion permeability, fuse characteristics, short-circuit characteristics, electricity storage performance, etc.

[0018] (Embodiment 1) The separator according to embodiment 1 includes a substrate and a thermoplastic polymer-containing layer formed on at least one surface of the substrate and containing a thermoplastic polymer, and the thermoplastic polymer-containing layer is represented by the following formula: B90 / B10<7 {wherein B90 and B10 are defined as follows: Two separators were prepared and stored for one day in an environment with a temperature of 35°C and a relative humidity (RH) of 90%, and then the separators were stacked together with one side (A) of the separator facing each other to form a laminate (AA). RH90 , a laminate (AB) formed by laminating the surface (A) and the opposite surface (B) RH90 , and a laminate (BB) formed by laminating the surfaces (B) together. RH90 Each laminate was pressed for 2 minutes under conditions of a temperature of 40°C and a pressure of 1 MPa, and the maximum peel strength (N / m) of all the laminates was measured individually, and the maximum value was designated as B90; Two separators were prepared and stored for one day in an environment of 35°C temperature and 10% relative humidity (RH). Then, one side (A) of the separator was laminated with the other side (A) to form a laminate (AA). RH10 , a laminate (AB) formed by laminating the surface (A) and the opposite surface (B)RH10 , and a laminate (BB) formed by laminating the surfaces (B) together. RH10 Each laminate was pressed for 2 minutes under conditions of a temperature of 40°C and a pressure of 1 MPa. The maximum peel strength (N / m) of all the laminates measured individually was designated as B10. The characteristic is that the relationship expressed by

[0019] By satisfying the above formula B90 / B10<7, the separator according to embodiment 1 can reduce the amount of moisture carried over into the separator when incorporated into an electricity storage device, thereby improving cycle characteristics, and can also suppress blocking of the separator under high humidity conditions. The method for measuring the peel strengths B10 and B90 is described in detail in the Examples. Furthermore, controlling B90 / B10 as shown in the above formula is thought to contribute to suppressing the blocking phenomenon that occurs when a separator wound body is stored under high humidity conditions in this technical field. Furthermore, from the viewpoint of not only improving the cycle characteristics of the electricity storage device but also preventing defects when the separator is unwound, B90 according to embodiment 1 is preferably less than 10 N / m.

[0020] Furthermore, without wishing to be bound by theory, it is believed that if the separator satisfies the above formulae B90 / B10<7 and B90<10 N / m, poor unwinding of the separator when unwinding it from the wound body can be prevented, the amount of moisture adsorbed by the separator can be reduced, and in the manufacture of an electricity storage device using the separator, the amount of moisture carried over into the device can be reduced, thereby improving the cycle characteristics or yield of the electricity storage device.

[0021] From the viewpoints of cycle characteristics, blocking resistance, prevention of feeding failure, etc., the separator more preferably satisfies B90<8 N / m, even more preferably satisfies B90<5 N / m, and particularly preferably satisfies B90<2 N / m. From the viewpoint of reducing the amount of water carried over into the electricity storage device and improving the cycle characteristics of the electricity storage device, the separator preferably satisfies B90 / B10<6, more preferably satisfies B90 / B10<5, and even more preferably satisfies B90 / B10<4. Furthermore, with regard to the peel strength measured as described above, it is preferable that there is no change or that the change is significantly small due to RH during storage of the separator, and therefore the lower limit of B90 / B10 is preferably 1 or more.

[0022] The B10, B90 and B90 / B10 values ​​relating to the peel strength of the separator can be adjusted within the above-described ranges by controlling the physical properties and composition of the thermoplastic polymer-containing layer, for example, by using a thermoplastic polymer unit that is difficult to swell in an electrolyte solution in the art, by introducing a hydrophobic block or a functional group, by containing both a unit derived from an aromatic vinyl compound monomer and a unit derived from a nitrile group-containing monomer, or by controlling the content ratio of both.

[0023] (Embodiment 2) The separator according to embodiment 2 includes a substrate and a thermoplastic polymer-containing layer formed on at least a portion of at least one surface of the substrate and containing a thermoplastic polymer, wherein the thermoplastic polymer is a compound represented by the following formula: T10-T90<10 {wherein T90 and T10 are defined as follows: The thermoplastic polymer was stored for one day in an environment of 35°C and 90% relative humidity (RH), and then sealed in an aluminum hermetic pan. The glass transition temperature (°C) measured by DSC (differential scanning calorimetry) was taken as T90. Furthermore, the thermoplastic polymer is stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then the thermoplastic polymer is sealed in an aluminum hermetic pan and the glass transition temperature (°C) measured by DSC is defined as T10. The characteristic is that the relationship expressed by

[0024] When the thermoplastic polymer according to embodiment 2 satisfies the above formula T10-T90<10, the amount of moisture carried over into the separator when incorporated into an energy storage device can be reduced, improving cycle characteristics and further improving the blocking resistance of the separator. The method for measuring the glass transition temperatures T10 and T90 is described in detail in section (6) of the Examples. Furthermore, thermoplastic polymers that satisfy the formula T10-T90<10 tend to exhibit this effect when a hydrophobic molecular skeleton or hydrophobic functional groups are introduced, which is thought to contribute to the suppression of blocking when a separator wound body is stored in a high-humidity environment in this technical field.

[0025] Furthermore, without wishing to be bound by theory, it is thought that when the thermoplastic polymer satisfies the above formula T10-T90<10, poor payout of the separator from the wound body is prevented, the amount of moisture adsorbed by the separator is reduced, and in the manufacture of an electricity storage device using the separator, the amount of moisture carried over into the device is reduced, thereby improving the cycle characteristics or yield of the electricity storage device.

[0026] From the viewpoint of reducing the amount of moisture carried over from the separator to the electricity storage device and thereby improving the cycle characteristics of the electricity storage device, the thermoplastic polymer contained in the thermoplastic polymer-containing layer preferably satisfies T10-T90<9, more preferably T10-T90<7, and even more preferably T10-T90<6. Furthermore, with regard to the glass transition temperature of the thermoplastic polymer measured as described above, the less the difference in value between the multiple RH conditions during separator storage, or the smaller the difference in value, the less likely blocking tends to occur. Therefore, it is preferable that T10-T90≒0 or T10-T90=0, and it may also be T10-T90≧0.

[0027] From the viewpoint of reducing the amount of moisture carried over from the separator to the electricity storage device and improving cycle characteristics, T90 according to the second embodiment is preferably 30° C. or higher, and more preferably 31° C. or higher.

[0028] The T10, T90, and T10-T90 values ​​relating to the glass transition temperatures of the thermoplastic polymer can be adjusted within the above-described ranges by controlling the physical properties or structure of the thermoplastic polymer, for example, by making it difficult for the polymer to swell in an electrolyte, by introducing a hydrophobic molecular skeleton or a hydrophobic functional group, by containing both a unit derived from an aromatic vinyl compound monomer and a unit derived from a nitrile group-containing monomer, or by controlling the content ratio of both.

[0029] Preferred embodiments of each member that can constitute the separator will be described in detail below.

[0030] [Base material] The substrate itself may be a material that has been conventionally used as a separator. A porous membrane is preferred as the substrate, and a porous membrane with fine pores that is non-electronically conductive, ionically conductive, and highly resistant to organic solvents is even more preferred. Examples of such porous membranes include microporous membranes primarily composed of polyolefin resins (e.g., polyethylene, polypropylene, polybutene, and polyvinyl chloride), mixtures thereof, or copolymers of these monomers; microporous membranes primarily composed of resins such as polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene; woven polyolefin fibers (woven fabrics); nonwoven polyolefin fibers; paper; and aggregates of insulating material particles. These may be used alone or in combination of two or more. Among these, from the viewpoint of reducing the thickness of the separator to increase the ratio of active material in the electricity storage device and thus increasing the capacity per volume, a polyolefin microporous membrane containing a polyolefin resin as a main component is preferred. When a coating liquid is applied to the polyolefin microporous membrane through a process, the polyolefin microporous membrane has excellent coatability, and is therefore advantageous for reducing the thickness of the separator. Incidentally, "containing a polyolefin-based resin as a main component" means that the content exceeds 50% by mass of the total mass of the substrate.

[0031] When a polyolefin microporous membrane is used as a substrate, the content of polyolefin resin in the polyolefin microporous membrane is not particularly limited. However, from the viewpoint of shutdown performance when used as a separator, it is preferable that 50% to 100% by mass of all components constituting the polyolefin microporous membrane is polyolefin resin. The content of polyolefin resin is more preferably 60% to 100% by mass of all components constituting the polyolefin microporous membrane, more preferably 70% to 100% by mass, even more preferably 75% to 100% by mass, 85% to 100% by mass, 90% to 100% by mass, or even more preferably 95% to 100% by mass, particularly preferably 98% to 100% by mass, and may be 100% by mass.

[0032] The polyolefin resin is not particularly limited, but may be a polyolefin resin that can be used in ordinary extrusion, injection, inflation, blow molding, etc. Examples of polyolefin resins include homopolymers containing ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, etc. as monomers, as well as copolymers and multistage polymers of two or more of these monomers. These homopolymers, copolymers, and multistage polymers may be used alone or in combination of two or more.

[0033] Representative examples of polyolefin resins include, but are not limited to, polyethylene, polypropylene, and polybutene. More specifically, low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ultra-high molecular weight polyethylene, isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, polybutene, and ethylene-propylene rubber. These may be used alone or in combination of two or more. From the viewpoint of shutdown properties in which pores are closed by thermal melting, it is preferable that the polyolefin resin is primarily composed of polyethylene, such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, and ultra-high molecular weight polyethylene. In particular, high-density polyethylene is preferred because of its low melting point and high strength, and a density of 0.93 g / cm measured according to JIS K 7112 is preferred. 3 Polyethylenes in which the above-mentioned conditions are satisfied are more preferred. The polymerization catalyst used in producing these polyethylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts.

[0034] To improve the heat resistance of the substrate, the polyolefin microporous membrane preferably contains polypropylene and a polyolefin resin other than polypropylene. The three-dimensional structure of the polypropylene is not limited, and may be any of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. Examples of polyolefin resins other than polypropylene include homopolymers containing ethylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers, as well as copolymers and multi-stage polymers of two or more of these monomers, specific examples of which are already described above. The polymerization catalyst used to produce the polypropylene is not particularly limited, and examples include Ziegler-Natta catalysts and metallocene catalysts.

[0035] The content ratio of polypropylene to the total amount of polyolefin in the polyolefin microporous membrane (polypropylene / polyolefin) is preferably 1 to 35 mass%, more preferably 3 to 20 mass%, and even more preferably 4 to 10 mass%, from the viewpoint of achieving both heat resistance and a good shutdown function. From the same viewpoint, the content ratio of olefin resins other than polypropylene, such as polyethylene, to the total amount of polyolefin in the polyolefin microporous membrane (olefin resins other than polypropylene / polyolefin) is preferably 65 to 99 mass%, more preferably 80 to 97 mass%, and even more preferably 90 to 96 mass%. Examples of polyolefin resins other than polyethylene and polypropylene include polybutene, ethylene-propylene random copolymer, and polymethylpentene.

[0036] The viscosity average molecular weight of the polyolefin resin constituting the polyolefin microporous membrane is not particularly limited, but is preferably from 30,000 to 12,000,000, more preferably from 50,000 to less than 2,000,000, and even more preferably from 100,000 to less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferred because it increases the melt tension during melt molding, improving moldability, and also tends to result in higher strength due to entanglement of polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferred because it facilitates uniform melt-kneading and tends to improve sheet moldability, particularly thickness stability. Furthermore, a viscosity average molecular weight of less than 1,000,000 is preferred because it tends to facilitate pore blocking during temperature rise and provide better shutdown function. From the standpoint of moldability, a viscosity average molecular weight of less than 1,000,000 is also preferred. The viscosity average molecular weight (Mv) is calculated according to ASTM-D4020 using decalin as the solvent and the intrinsic viscosity [η] measured at 135°C using the following formula: Polyethylene: [η] = 6.80 × 10 -4 Mv 0.67 (Chiang's formula) Polypropylene: [η] = 1.10 × 10 -4 Mv 0.80 For example, instead of using a polyolefin having a viscosity average molecular weight of less than 1 million alone, a mixture of a polyolefin having a viscosity average molecular weight of 2 million and a polyolefin having a viscosity average molecular weight of 270,000, the viscosity average molecular weight of which is less than 1 million, may be used.

[0037] The substrate may also contain any additives. Such additives are not particularly limited and include, for example, polymers other than polyolefins; inorganic particles; phenolic, phosphorus-based, and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers; antistatic agents; antifogging agents; and coloring pigments. The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polyolefin resin in the polyolefin microporous membrane.

[0038] The porosity of the substrate is preferably 20 to 80%, more preferably 35 to 70%, still more preferably 40 to 60%, and particularly preferably 40 to 50%. It is preferable to set the porosity of the substrate to 20% or more from the viewpoint of more effectively and reliably ensuring the permeability of the separator. It is preferable to set the porosity of the substrate to 80% or less from the viewpoint of more effectively and reliably ensuring the pin puncture strength. The porosity can be calculated, for example, by the volume (cm) of the substrate sample. 3 ), mass (g), membrane density (g / cm 3 ) to the following formula: Porosity = (volume - mass / film density) / volume x 100 Here, for example, in the case of a polyolefin microporous membrane made of polyethylene, the membrane density can be calculated as 0.95 (g / cm 3 The porosity can be adjusted by changing the stretch ratio of the polyolefin microporous membrane.

[0039] The air permeability of the substrate is preferably 10 seconds / 100 cm 3 More than 50 seconds / 100cm is preferable. 3More than 1,000 seconds / 100 cm is preferable. 3 Less than 500 seconds / 100cm, preferably less than 500 seconds / 100cm 3 Less than 200 seconds / 100 cm, more preferably 3 The air permeability of the substrate is 10 seconds / 100 cm 3 It is preferable to set the air permeability of the substrate to 1000 sec / 100 cm or more from the viewpoint of suppressing self-discharge of the electricity storage device. 3 The following is preferable from the viewpoint of obtaining good charge / discharge characteristics. The air permeability is the air permeability resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the substrate, etc.

[0040] The average pore size of the substrate is preferably 0.15 μm or less, more preferably 0.1 μm or less, and preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is suitable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. The average pore size can be adjusted by changing the stretching ratio when manufacturing the substrate.

[0041] The pin puncture strength of the substrate is preferably 200 gf / 20 μm or more, more preferably 250 gf / 20 μm or more, even more preferably 300 gf / 20 μm or more, and preferably 2,000 gf / 20 μm or less, more preferably 1,000 gf / 20 μm or less. A pin puncture strength of 200 gf / 20 μm or more is preferable from the viewpoint of preventing film rupture due to fallen active material, etc., when the separator is wound together with the electrodes, and from the viewpoint of preventing the risk of short circuit due to expansion and contraction of the electrodes during charge and discharge. A pin puncture strength of 2,000 gf / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The pin puncture strength is measured according to the method described in the Examples. The pin puncture strength can be adjusted by adjusting the stretch ratio and / or stretching temperature of the substrate.

[0042] The thickness of the substrate is preferably 2 μm or more, more preferably 5 μm or more, and preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. A substrate thickness of 2 μm or more is preferred from the viewpoint of improving mechanical strength. A substrate thickness of 100 μm or less is preferred because it reduces the volume occupied by the separator in the electricity storage device, which tends to be advantageous in terms of increasing the capacity of the electricity storage device.

[0043] [Thermoplastic polymer-containing layer] The thermoplastic polymer-containing layer contains a thermoplastic polymer. The thermoplastic polymer-containing layer may be disposed on the entire surface of the substrate, or on a portion thereof. It is preferable to dispose the thermoplastic polymer-containing layer on only a portion of the surface of the substrate so that the resulting electricity storage device exhibits high ion permeability.

[0044] The thermoplastic polymer-containing layer is intended to be directly bonded to the electrode. At least one thermoplastic polymer-containing layer provided in the separator is preferably arranged so as to be directly bonded to the electrode, for example, so that at least a portion of the substrate and the electrode are bonded via the thermoplastic polymer-containing layer.

[0045] The coating amount of the thermoplastic polymer-containing layer on the substrate, i.e., the amount of the thermoplastic polymer-containing layer formed (placed amount) per surface area of ​​the substrate, is 0.01 g / m 2 It is preferable that the content is 0.02 g / m or more. 2 It is more preferable that the coating amount is 2.0 g / m or more. 2 It is preferable that the content is 1.5 g / m or less. 2 It is more preferable that it is 1.0 g / m or less. 2 It is more preferable that it is 0.5 g / m or less. 2 It is particularly preferable that the coating amount is 0.01 g / m or less. 2A coating amount of 2.0 g / m or more is preferable from the viewpoint of improving the adhesive strength between the thermoplastic polymer-containing layer and the electrode, realizing more uniform charge / discharge, and improving device characteristics (e.g., battery cycle characteristics) by improving the measured value P10 of the obtained separator, for example, as described below. 2 The following is preferable from the viewpoint of the characteristics (rate characteristics) of the electricity storage device and the prevention of a decrease in ion permeability.

[0046] The ratio of the area of ​​the surface on which the thermoplastic polymer-containing layer is present to the total area of ​​the surface of the substrate on which the thermoplastic polymer-containing layer is disposed, i.e., the coverage area ratio of the thermoplastic polymer-containing layer to the substrate, is preferably 70% or less, more preferably 50% or less, and particularly preferably 40% or less. This surface coverage is preferably 5% or more, more preferably 10% or more, and even more preferably 12% or more. Setting the coverage area ratio to 70% or less suppresses clogging of the pores of the substrate by the particulate polymer, improves the permeability of the separator, and ultimately improves the rate characteristics of an electricity storage device including the separator. On the other hand, setting the coverage area ratio to 5% or more is preferable from the viewpoint of, for example, improving the measured value P10 described below and further improving adhesion to the electrode. The coverage area ratio is measured by observing the surface on which the thermoplastic polymer-containing layer is formed of the resulting separator using an SEM, and in detail, is measured according to the method described in the Examples. The coverage area ratio can be adjusted, for example, in the separator manufacturing method described below, by changing the type or concentration of the particulate polymer in the coating liquid to be applied to the surface of the substrate, the amount of the coating liquid to be applied, the coating method, and the coating conditions, although the method for adjusting the coverage area is not limited thereto.

[0047] When the thermoplastic polymer-containing layer is disposed on only a portion of the surface of the substrate, the form (pattern) of the thermoplastic polymer is not particularly limited, but it is preferable that the thermoplastic polymer be dispersed throughout the entire surface of the substrate or be present in an islands-in-a-sea pattern. When the thermoplastic polymer is present in an islands-in-a-sea pattern, its arrangement pattern can be, for example, a dotted pattern, a striped pattern, a lattice pattern, a striped pattern, a tortoiseshell pattern, a random pattern, or a combination thereof. Among these, a dotted pattern is preferred from the viewpoint of preventing overlapping of the thermoplastic polymer-containing layers when the separator is wound. Furthermore, from the viewpoint of blocking resistance, a dotted pattern is preferable to a state in which the thermoplastic polymer is dispersed throughout the entire surface of the substrate (e.g., a solid coating). When the arrangement pattern is a dotted pattern, the dot diameter is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 80 μm or more. Furthermore, the dot diameter is preferably 1,000 μm or less, more preferably 800 μm or less, and even more preferably 500 μm or less. A dot diameter of 10 μm or more allows for better ion flow in the electrolyte, resulting in even better permeability. A dot diameter of 1,000 μm (1 mm) or less allows for more uniform adhesion of the separator to the electrode, resulting in even more uniform in-plane current density. Furthermore, by providing areas within the dot pattern where the thermoplastic polymer is not applied, the in-plane current density can be made even more uniform.

[0048] When the thermoplastic polymer-containing layer is partially disposed, it is desirable that the coverage area ratio is uniform within a certain area range. Specifically, when the separator surface is observed with an SEM, the variation rate of the coverage area ratio, expressed by the following formula, is preferably within ±50% within an observation field of 10 mm × 10 mm or more. (Change in coverage area ratio (%)) = (C1-C2) / C1 x 100 Here, C1 represents the coverage area ratio in any observation field of view of 10 mm × 10 mm or more, and C2 represents the coverage area ratio in any other observation field of view of 10 mm × 10 mm or more. For example, for a separator in which a thermoplastic polymer-containing layer is partially disposed, if the measurement value of the coverage area ratio in a 10 mm × 10 mm observation field of view is 50%, it is preferable that the coverage area ratio in any other 10 mm × 10 mm observation field of view be 25% or more and 75% or less when any other part of the separator is observed.

[0049] The thickness of the thermoplastic polymer-containing layer is preferably 0.01 μm or more, more preferably 0.1 μm or more, and even more preferably 0.3 μm or more, per surface of the substrate. The thickness is preferably 5.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less, per surface of the substrate. A thickness of 0.01 μm or more is preferable from the viewpoint of uniformly exhibiting adhesive strength between the electrode and the substrate, thereby improving device characteristics. A thickness of 5.0 μm or less is preferable from the viewpoint of suppressing a decrease in ion permeability. The thickness of the thermoplastic polymer-containing layer can be adjusted, for example, by changing the type or concentration of the particulate polymer in the coating solution applied to the substrate, the amount of the coating solution applied, the coating method, and the coating conditions. However, the thickness adjustment method is not limited thereto. The thickness of the thermoplastic polymer-containing layer is measured according to the method described in the Examples.

[0050] The mass swelling degree of the thermoplastic polymer used in the electrolyte solution (hereinafter also referred to as "electrolyte swelling degree") is preferably 2 times or more and less than 7 times, more preferably 3 times to 6 times, and even more preferably 4 times to 5 times. When the electrolyte swelling degree of the thermoplastic polymer is 2 times or more, the amount of water carried over into the separator or the electricity storage device can be reduced, and the cycle characteristics of the electricity storage device can be improved. When the electrolyte swelling degree of the thermoplastic polymer is less than 7 times, an increase in electrical resistance can be suppressed. The electrolyte swelling degree can be measured by the method described in the Examples. The electrolyte used to measure the electrolyte swelling degree can be a non-aqueous solvent, and can be one or more carbonate-based solvents, a mixture of multiple carbonate-based solvents, or the like, and can be a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio of EC / DEC = 2 / 3).

[0051] (particulate polymer) The thermoplastic polymer contained in the thermoplastic polymer-containing layer may contain a particulate polymer. The thermoplastic polymer is preferably water-insoluble and particulate, from the viewpoint of adjusting the B10, B90, B90 / B10, T10, T90, T10-T90, etc. measured under specific conditions within the above-described numerical ranges. In the following description, "ethylenically unsaturated monomer" refers to a monomer having one or more ethylenically unsaturated bonds in the molecule. By including a particulate polymer in the thermoplastic polymer, both excellent adhesion to the electrode and ion permeability can be achieved.

[0052] Specific examples of particulate polymers include acrylic polymers, conjugated diene polymers, acrylic polymers, polyvinyl alcohol resins, and fluorine-containing resins. Among these, from the viewpoint of polymer stability in an electricity storage device, acrylic polymers are preferred as thermoplastic polymers, and copolymers containing monomer units of (meth)acrylic acid ester monomers are more preferred. Furthermore, from the viewpoint of voltage resistance, acrylic polymers and fluorine-containing resins are also preferred, and conjugated diene polymers are also preferred from the viewpoint of compatibility with electrodes. Furthermore, from the viewpoint of more effectively and reliably achieving the effects of the present invention, it is preferable that the particulate polymer contains a particulate copolymer. One type of particulate polymer is used alone, or two or more types are used in combination.

[0053] The thermoplastic polymer contained in the thermoplastic polymer-containing layer preferably contains 60% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more of the particulate polymer, based on the total amount of the thermoplastic polymer. The thermoplastic polymer-containing layer may contain a thermoplastic polymer other than the particulate polymer to an extent that does not impair the effects of the present invention.

[0054] Conjugated diene polymers are polymers containing a conjugated diene compound as a monomer unit. Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated pentadiene, and substituted and side-chain conjugated hexadienes. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is particularly preferred. Furthermore, conjugated diene polymers may contain, as a monomer unit, a (meth)acrylic compound or other monomer, as described below. Examples of such monomers include styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, and acrylonitrile-butadiene-styrene copolymers and their hydrogenated products.

[0055] Examples of polyvinyl alcohol resins include polyvinyl alcohol, polyvinyl acetate, etc. Examples of fluorine-containing resins include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer.

[0056] An acrylic polymer is a polymer having a (meth)acrylic compound as a monomer unit, i.e., a polymerization unit. The (meth)acrylic compound refers to at least one compound selected from the group consisting of (meth)acrylic acid and (meth)acrylic acid esters. Examples of such compounds include compounds represented by the following formula: CH2=CR Y1 -COO-R Y2 In the formula, R Y1 represents a hydrogen atom or a methyl group, and R Y2 represents a hydrogen atom or a monovalent hydrocarbon group. Y2 When is a monovalent hydrocarbon group, it may have a substituent and may have a heteroatom in the chain. Examples of monovalent hydrocarbon groups include linear or branched chain alkyl groups, cycloalkyl groups, and aryl groups. Examples of substituents include hydroxyl groups and phenyl groups, and examples of heteroatoms include halogen atoms and oxygen atoms. The (meth)acrylic compounds may be used alone or in combination of two or more. Examples of such (meth)acrylic compounds include (meth)acrylic acid, linear alkyl (meth)acrylates, cycloalkyl (meth)acrylates, (meth)acrylates having a hydroxyl group, and phenyl group-containing (meth)acrylates.

[0057] R Y2More specifically, examples of the chain alkyl group that is one of the above include chain alkyl groups having 1 to 3 carbon atoms, such as methyl, ethyl, n-propyl, and isopropyl groups; n-butyl, isobutyl, t-butyl, n-hexyl, and 2-ethylhexyl groups; and chain alkyl groups having 4 or more carbon atoms, such as lauryl groups. Y2 An example of an aryl group is a phenyl group. Y2 Specific examples of the (meth)acrylic acid ester monomer having the formula (I) include (meth)acrylates having a chain alkyl group such as methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate; and (meth)acrylates having an aromatic ring such as phenyl (meth)acrylate and benzyl (meth)acrylate.

[0058] Among these, from the viewpoint of improving the adhesiveness of the separator to the electrode (electrode active material), a monomer having a chain alkyl group with 4 or more carbon atoms, more specifically, R Y2 is a chain alkyl group having 4 or more carbon atoms. More specifically, at least one selected from the group consisting of butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate is preferred. The upper limit of the number of carbon atoms in the chain alkyl group having 4 or more carbon atoms is not particularly limited, and may be, for example, 14, but 7 is preferred. These (meth)acrylic acid ester monomers may be used alone or in combination of two or more.

[0059] The (meth)acrylic acid ester monomer may be a monomer having a chain alkyl group having 4 or more carbon atoms, or may be a monomer having R Y2 It is also preferable to include a monomer having a cycloalkyl group as the cycloalkyl group. This also further improves the adhesiveness of the separator to the electrodes. More specific examples of such a monomer having a cycloalkyl group include cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. The number of carbon atoms constituting the alicyclic ring of the cycloalkyl group is preferably 4 to 8, more preferably 6 to 7, and particularly preferably 6. The cycloalkyl group may or may not have a substituent. Examples of the substituent include a methyl group and a t-butyl group. Among these, at least one selected from the group consisting of cyclohexyl acrylate and cyclohexyl methacrylate is preferred in terms of good polymerization stability during the preparation of the acrylic polymer. These may be used alone or in combination of two or more.

[0060] The acrylic polymer preferably contains a crosslinkable monomer as the (meth)acrylic acid ester monomer instead of or in addition to the above-mentioned monomers, preferably in addition to the above-mentioned monomers. The crosslinkable monomer is not particularly limited, but examples thereof include a monomer having two or more radically polymerizable double bonds, and a monomer having a functional group that gives a self-crosslinking structure during or after polymerization. These may be used alone or in combination of two or more.

[0061] Examples of monomers having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylates. The polyfunctional (meth)acrylate may be at least one selected from the group consisting of bifunctional (meth)acrylates, trifunctional (meth)acrylates, and tetrafunctional (meth)acrylates. Specific examples include polyoxyethylene diacrylate, polyoxyethylene dimethacrylate, polyoxypropylene diacrylate, polyoxypropylene dimethacrylate, neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used alone or in combination of two or more. From the same viewpoints as above, at least one of trimethylolpropane triacrylate and trimethylolpropane trimethacrylate is preferred.

[0062] Examples of monomers having a functional group that gives a self-crosslinking structure during or after polymerization include monomers having an epoxy group, monomers having a methylol group, monomers having an alkoxymethyl group, and monomers having a hydrolyzable silyl group. Preferred examples of monomers having an epoxy group include ethylenically unsaturated monomers having an alkoxymethyl group, and specific examples include glycidyl (meth)acrylate, 2,3-epoxycyclohexyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, and allyl glycidyl ether.

[0063] Examples of monomers having a methylol group include N-methylolacrylamide, N-methylolmethacrylamide, dimethylolacrylamide, and dimethylolmethacrylamide. Examples of monomers having an alkoxymethyl group include ethylenically unsaturated monomers having an alkoxymethyl group, such as N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. Examples of monomers having a hydrolyzable silyl group include vinylsilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane. These may be used alone or in combination of two or more.

[0064] The acrylic polymer may further contain other monomers as monomer units to improve various qualities and physical properties. Examples of such monomers include carboxyl group-containing monomers (excluding (meth)acrylic acid), amide group-containing monomers, nitrile group-containing monomers, hydroxyl group-containing monomers, and aromatic vinyl compound monomers (excluding divinylbenzene). Furthermore, various vinyl monomers having functional groups such as sulfonic acid groups or phosphoric acid groups, as well as vinyl acetate, vinyl propionate, vinyl versatate, vinylpyrrolidone, methyl vinyl ketone, butadiene, ethylene, propylene, vinyl chloride, and vinylidene chloride may also be used as needed. These may be used alone or in combination. Furthermore, such other monomers may simultaneously belong to two or more of the above-mentioned monomers.

[0065] Examples of monomers having an amide group include (meth)acrylamide, and examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth)acrylate.

[0066] Examples of the nitrile group-containing monomer that can be used include acrylic nitrile group-containing monomers such as (meth)acrylonitrile, cyanide nitrile group-containing monomers such as α-cyanoacrylate and dicyanovinylidene, and fumarate nitrile group-containing monomers such as fumaronitrile. Among these, from the viewpoint of adjusting B10, B90, B90 / B10, T10, T90, T10-T90, and the like measured under specific conditions within the above-described numerical ranges, the viewpoint of the polymerizability and economic efficiency of the monomer, and the viewpoint of cyclization upon heating or the hydrophobicity of the resulting copolymer, preferred are ethylenically unsaturated monomers having a cyano group, more preferred are (meth)acrylonitrile, and even more preferred are acrylonitrile and / or methacrylonitrile.

[0067] Examples of aromatic vinyl monomers include styrene, styrene sulfonic acid, butoxystyrene, vinyltoluene, vinylnaphthalene, and α-methylstyrene. Among them, styrene is preferred from the viewpoint of adjusting B10, B90, B90 / B10, T10, T90, T10-T90, etc., measured under specific conditions, to fall within the above-described numerical ranges, and from the viewpoint of the hydrophobicity of the resulting copolymer.

[0068] The proportion of the (meth)acrylic compound in the acrylic polymer as a monomer unit, i.e., a polymerization unit, is preferably 5% by mass or more and 95% by mass or less, based on 100% by mass of the acrylic polymer. The lower limit is more preferably 15% by mass, even more preferably 20% by mass, and particularly preferably 30% by mass. A monomer unit content of 5% by mass or more is preferred in terms of adhesion to the substrate and oxidation resistance. On the other hand, a more preferred upper limit is 92% by mass, an even more preferred upper limit is 80% by mass, and a particularly preferred upper limit is 60% by mass. A monomer content of 95% by mass or less is preferred because adhesion to the substrate is improved.

[0069] When the acrylic polymer has a chain alkyl (meth)acrylate or a cycloalkyl (meth)acrylate as a monomer unit, the total content thereof is preferably 3% by mass or more and 92% by mass or less, more preferably 10% by mass or more and 90% by mass or less, even more preferably 15% by mass or more and 75% by mass or less, and particularly preferably 25% by mass or more and 55% by mass or less, relative to 100% by mass of the acrylic polymer. A content of these monomers of 3% by mass or more is preferred in terms of improving oxidation resistance, and 92% by mass or less is preferred in terms of improving adhesion to the substrate.

[0070] When the acrylic polymer has (meth)acrylic acid as a monomer unit, the content thereof is preferably 0.1% by mass or more and 5% by mass or less relative to 100% by mass of the acrylic polymer. When the content of the monomer is 0.1% by mass or more, the separator tends to have improved cushioning properties in a swollen state, and when it is 5% by mass or less, the polymerization stability tends to be good.

[0071] When the acrylic polymer has a crosslinkable monomer as a monomer unit, the content of the crosslinkable monomer in the acrylic polymer is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 5% by mass or less, and even more preferably 0.1% by mass or more and 3% by mass or less, relative to 100% by mass of the acrylic polymer. When the content of the monomer is 0.01% by mass or more, the electrolyte resistance is further improved, and when it is 10% by mass or less, the decrease in cushioning property in a swollen state can be further suppressed.

[0072] In the case of a water-insoluble particulate thermoplastic polymer, from the viewpoint of adjusting B10, B90, B90 / B10, T10, T90, T10-T90, etc. measured under specific conditions within the numerical ranges explained above, the particulate polymer preferably includes or is a copolymer having one or both of an aromatic vinyl compound monomer and a nitrile group-containing monomer as monomer units, and more preferably includes or is an acrylic copolymer having a (meth)acrylic acid ester monomer, an aromatic vinyl compound monomer, and a nitrile group-containing monomer as monomer units. Furthermore, from the viewpoint of reducing the amount of moisture carried over from the separator to the electricity storage device and improving the cycle characteristics, it is preferable that the proportions of the aromatic vinyl compound monomer and the nitrile group-containing monomer in the water-insoluble particulate thermoplastic polymer are each 10% by mass or more, it is more preferable that the proportion of the aromatic vinyl compound monomer in the water-insoluble particulate thermoplastic polymer is 12 to 30% by mass and the proportion of the nitrile group-containing monomer is 15 to 60% by mass, and it is even more preferable that the proportion of the aromatic vinyl compound monomer is 14 to 25% by mass and the proportion of the nitrile group-containing monomer is 20 to 55% by mass.

[0073] The acrylic polymer can be obtained, for example, by a conventional emulsion polymerization method. There are no particular limitations on the emulsion polymerization method, and any conventionally known method can be used.

[0074] For example, an acrylic polymer can be obtained by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous medium in a dispersion system containing the basic components of the above-mentioned monomers, surfactant, radical polymerization initiator, and other additives used as needed. For the polymerization, various methods can be used as needed, such as a method in which the composition of the supplied monomer composition is kept constant throughout the entire polymerization process, or a method in which the composition of the resulting resin dispersion particles is changed in morphology by gradually or continuously changing the composition during the polymerization process. When the acrylic polymer is obtained by emulsion polymerization, it may be in the form of, for example, an aqueous dispersion (latex) containing water and particulate acrylic polymer dispersed in the water.

[0075] A surfactant is a compound having at least one hydrophilic group and one lipophilic group in one molecule. The surfactant is not particularly limited, but polyether surfactants are preferred. The surfactant will be described later, so a detailed description will be omitted here. The radical polymerization initiator is a compound that initiates addition polymerization of monomers by radical decomposition using heat or a reducing substance. Radical polymerization initiators will be described later, so further explanation is omitted here.

[0076] Among the forms of thermoplastic polymers, from the viewpoints of improving the adhesiveness between the separator and the electrode, the high-temperature storage characteristics and cycle characteristics of the electricity storage device, and achieving a thin film of the bond between the electrode and the separator, an acrylic copolymer latex formed from an emulsion containing a monomer, an emulsifier, an initiator, and water is preferred.

[0077] The glass transition temperature Tg (different from the T10 and T90 described above) of the particulate polymer is preferably -50°C or higher, more preferably -30°C or higher, even more preferably 20°C or higher, and even more preferably 40°C or higher, from the viewpoints of adhesion to electrodes and ion permeability. The glass transition temperature of the particulate polymer is preferably 200°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC). Specifically, the temperature at the intersection of a line extending the low-temperature baseline of the DSC curve toward the high-temperature side and a tangent to the inflection point of the stepwise change in the glass transition can be used as the glass transition temperature. More specifically, the glass transition temperature can be determined according to the method described in item (5) of the Examples. Furthermore, "glass transition" refers to a change in heat quantity that occurs on the endothermic side in DSC due to a change in the state of the polymer test piece. Such a change in heat quantity is observed as a stepwise change in the DSC curve. A "step change" refers to the portion of a DSC curve where the curve leaves the previous low-temperature baseline and transitions to a new high-temperature baseline. A step change also includes a combination of a step change and a peak. Furthermore, an "inflection point" refers to the point where the gradient of the DSC curve in the step change portion is at its maximum. It can also be expressed as the point where the curve changes from an upwardly convex curve to a downwardly convex curve, with the upper side considered to be the heat-generating side. A "peak" refers to the portion of a DSC curve where the curve leaves the low-temperature baseline and returns to the same baseline. A "baseline" refers to the DSC curve in the temperature range where no transition or reaction occurs in the test specimen.

[0078] The glass transition temperature Tg of the particulate polymer can be appropriately adjusted, for example, by changing the type of monomer used in producing the particulate polymer, or, if the particulate polymer is a copolymer, by changing the blending ratio of each monomer. That is, for each monomer used in producing the particulate polymer, the glass transition temperature can be roughly estimated from the generally-disclosed Tg of its homopolymer (for example, as described in "Polymer Handbook" (A Wiley-Interscience Publication)) and the blending ratio of the monomer. For example, a copolymer obtained by copolymerizing a high ratio of monomers such as methyl methacrylate, acrylonitrile, and methacrylic acid to give a homopolymer with a Tg of about 100°C will have a high Tg, while a copolymer obtained by copolymerizing a high ratio of monomers such as n-butyl acrylate and 2-ethylhexyl acrylate to give a homopolymer with a Tg of about -50°C will have a low Tg. The Tg of the copolymer can also be roughly calculated by the FOX formula represented by the following mathematical formula (1). 1 / Tg=W1 / Tg1+W2 / Tg2+········+W i / Tg i +·····W n / Tg n (1) where Tg(K) is the Tg of the copolymer, and Tg i (K) is the Tg of the homopolymer of monomer i, and W i is the mass fraction of each monomer. However, as the glass transition temperature Tg of the particulate polymer in this embodiment, a value measured by the above-mentioned method using DSC is adopted.

[0079] From the viewpoints of wettability to the substrate, adhesion between the substrate and the thermoplastic polymer-containing layer, and adhesion to the electrode, it is preferable that the thermoplastic polymer-containing layer contains a polymer having a glass transition temperature of less than 40°C. From the viewpoint of ion permeability, the glass transition temperature is more preferably -100°C or higher, even more preferably -50°C or higher, and particularly preferably -40°C or higher. From the viewpoint of adhesion between the substrate and the thermoplastic polymer-containing layer, the glass transition temperature is more preferably lower than 20°C, even more preferably lower than 15°C, and particularly preferably lower than 0°C.

[0080] From the viewpoint of adhesion of the thermoplastic polymer-containing layer to the electrode and resistance to powder shedding, the particulate polymer preferably has at least two glass transition temperatures. In other words, it is preferable that the thermoplastic polymer-containing layer contains two or more types of thermoplastic polymers having different glass transition temperatures. More preferably, at least one of the glass transition temperatures is in a range below 20°C, and at least one of the glass transition temperatures is in a range of 20°C or higher.

[0081] When the particulate polymer has a glass transition temperature (Tg) of less than 20°C and a Tg of 20°C or higher, the former Tg is preferably -100°C or higher, more preferably -50°C or higher, and even more preferably -40°C or higher from the viewpoint of blocking resistance, and is preferably less than -20°C, more preferably less than -15°C, and even more preferably less than -10°C from the viewpoint of binding strength and powder shedding resistance, and the latter Tg is preferably 20°C or higher, more preferably 40°C or higher, and even more preferably 50°C or higher from the viewpoint of blocking resistance, and is preferably less than 100°C, more preferably less than 90°C, and even more preferably less than 80°C from the viewpoint of adhesive strength.

[0082] Methods for making a particulate polymer have at least two glass transition temperatures include, but are not limited to, blending two or more types of particulate polymers and using a particulate polymer with a core-shell structure. A core-shell structure is a polymer with a double structure having a central portion and an outer shell portion covering the central portion, with the types or compositions of the polymers constituting each portion being different from each other. In particular, in polymer blends and core-shell structures, the glass transition temperature of the entire particulate polymer can be controlled by combining a polymer with a high glass transition temperature and a polymer with a low glass transition temperature. In addition, multiple functions can be imparted to the entire particulate polymer.

[0083] For example, when two or more types of particulate polymers are blended, it is possible to more favorably achieve both stickiness resistance and substrate application by blending one or more polymers having a glass transition temperature (Tg) in the range of 20° C. or higher with one or more polymers having a glass transition temperature in the range below 20° C. From the viewpoint of achieving both adhesiveness and blocking resistance, the mixing ratio of the polymers when blended is preferably in the range of 0.1:99.9 to 99.9:0.1, more preferably 5:95 to 95:5, still more preferably 50:50 to 95:5, and particularly preferably 60:40 to 90:10, as the ratio of the polymer having a glass transition temperature in the range of 20° C. or higher to the polymer having a glass transition temperature in the range below 20° C.

[0084] When particulate polymers having two or more Tg's are present in the thermoplastic polymer-containing layer, the particulate polymer having a higher Tg has an average particle size (D50) of preferably 10 to 1000 nm, more preferably 100 to 800 nm, and even more preferably 200 to 700 nm, from the viewpoint of suppressing the amount of moisture carried over into the separator or the electricity storage device. The average particle size (D50) of the particulate polymer is measured according to the method described in the examples below.

[0085] Two or more kinds of particulate polymers each having a different average particle size (D50) can be contained in the thermoplastic polymer-containing layer. For example, it is preferable to use a combination of a particulate polymer having an arithmetic mean particle size of 10 nm to 300 nm (hereinafter referred to as "small particle size") and a particulate polymer having an arithmetic mean particle size of more than 100 nm to 2000 nm (hereinafter referred to as "large particle size").

[0086] Furthermore, from the viewpoint of blocking resistance and powder shedding resistance, two or more types of particulate polymers may exist not only separately in the thermoplastic polymer-containing layer but also as a core-shell structure. When a particulate polymer having a core-shell structure is used, the adhesion and compatibility of the thermoplastic polymer-containing layer to other components (e.g., substrates) can be adjusted by selecting the type of polymer in the outer shell. Furthermore, the adhesion to electrodes after heat pressing can be improved by selecting the type of polymer in the center. Alternatively, the viscoelasticity of the thermoplastic polymer-containing layer can be controlled by combining a highly viscous polymer with a highly elastic polymer.

[0087] The glass transition temperature of the outer shell portion (shell) of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably less than 20° C., more preferably 15° C. or less, and even more preferably −30° C. to 15° C. The glass transition temperature of the central portion (core) of the thermoplastic polymer having a core-shell structure is not particularly limited, but is preferably 20° C. or more, more preferably 20° C. to 200° C., and even more preferably 50° C. to 200° C.

[0088] The particulate polymer described above can be produced by known polymerization methods, except for using the monomers described above. Examples of suitable polymerization methods include solution polymerization, emulsion polymerization, and bulk polymerization. Emulsion polymerization is particularly preferred for obtaining a particulate dispersion. The emulsion polymerization method is not particularly limited, and conventionally known methods can be used. For example, a polymer can be obtained by polymerizing a monomer composition consisting of the above-mentioned monomers in an aqueous medium in a dispersion system containing the basic components of the above-mentioned monomers, surfactant, radical polymerization initiator, and other additive components used as needed. During polymerization, various methods can be used as needed, such as a method in which the composition of the supplied monomer composition is kept constant throughout the entire polymerization process, or a method in which the composition of the particles in the resulting resin dispersion is changed gradually or continuously during the polymerization process to change the morphology of the resulting resin dispersion. When the polymer is obtained by emulsion polymerization, it may be in the form of an aqueous dispersion (latex) containing water and a particulate polymer dispersed in the water.

[0089] A surfactant is a compound having at least one hydrophilic group and one lipophilic group in one molecule. Examples of surfactants include polyether surfactants; anionic surfactants such as non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, naphthalene sulfonate-formaldehyde condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrenated phenyl ether sulfates, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates; and nonionic surfactants such as non-reactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkylalkanolamides, and polyoxyethylene alkylphenyl ethers. In addition to these, so-called reactive surfactants may be used, which are surfactants having a hydrophilic group and a lipophilic group and an ethylenic double bond introduced into their chemical structure.

[0090] Examples of anionic surfactants among reactive surfactants include ethylenically unsaturated monomers having a sulfonic acid group, a sulfonate group, or a sulfate ester group, and salts thereof. Compounds having a sulfonic acid group or its ammonium or alkali metal salt (ammonium sulfonate group or alkali metal sulfonate group) are preferred. Specific examples include alkylaryl sulfosuccinate salts (e.g., ELEMINOL (trademark) JS-20 manufactured by Sanyo Chemical Industries, Ltd., and LATEMURU (trademark) S-120, S-180A, and S-180 manufactured by Kao Corporation), polyoxyethylene alkylpropenylphenyl ether sulfate salts (e.g., AQUALON (trademark) HS-10 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-polyoxyethylene sulfate salts (e.g., ADEKA REASOAP (trademark) SE-10N manufactured by ADEKA Corporation), ammonium α- Examples include sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (for example, AQUALON KH-10 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), styrenesulfonate (for example, Spinomer (trademark) NaSS manufactured by Tosoh Organic Chemical Co., Ltd.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-polyoxyethylene sulfate (for example, Adeka Reasop SR-10 manufactured by ADEKA Corporation), and sulfate of polyoxyethylene polyoxybutylene (3-methyl-3-butenyl) ether (for example, LATEMURU PD-104 manufactured by Kao Corporation).

[0091] Examples of nonionic surfactants among reactive surfactants include α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene (e.g., ADEKA REASOAP NE-20, NE-30, and NE-40 manufactured by ADEKA Corporation), polyoxyethylene alkylpropenylphenyl ether (e.g., Aqualon RN-10, RN-20, RN-30, and RN-50 manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), α-[2-[(allyloxy)-1-(alkyloxymethyl)ethyl]-ω-hydroxypolyoxyethylene (e.g., ADEKA REASOAP ER-10 manufactured by ADEKA Corporation), and polyoxyethylene polyoxybutylene(3-methyl-3-butenyl)ether (e.g., Latemul PD-420 manufactured by Kao Corporation). The surfactant is preferably used in an amount of 0.1 to 5 parts by mass per 100 parts by mass of the monomer composition. The surfactants may be used alone or in combination of two or more.

[0092] In addition to the method of adding the surfactant as a raw material during the polymerization reaction of the particulate polymer, the surfactant can also be added after the polymerization reaction. Adding the surfactant after the polymerization reaction allows the surface energy of the thermoplastic polymer layer formed on the substrate surface to be adjusted. Adjusting the surface energy of the thermoplastic polymer layer makes it possible to adjust the contact angle of the separator surface on which the thermoplastic polymer is formed. Adding the surfactant after the polymerization reaction is preferable from the viewpoint of adjusting the surface energy of the thermoplastic polymer layer without being affected by the polymerization reaction conditions. Adding the surfactant after the polymerization reaction results in a large amount of free surfactant being present in the slurry, and it is believed that a large amount of surfactant will be present on the outermost surface of the binder when the slurry is dried. As a result, the surface energy of the thermoplastic polymer layer can be adjusted with a smaller amount than when the surfactant is added as a raw material during the polymerization reaction. The surfactant added after the polymerization reaction of the particulate polymer can be the same as the surfactant added during the polymerization reaction, but since the polymerization reaction has already finished when the surfactant is added after the polymerization reaction, it is preferable to use a surfactant that is not a reactive surfactant. Among these, the polyether surfactants or the anionic surfactants are preferred from the viewpoints that they easily suppress foaming of the slurry, furthermore, the dispersing effect increases with the amount added, making it easy to ensure dispersibility, and they have the effect of significantly changing the surface tension of the polyolefin microporous membrane with a small amount. The surfactant to be added later is preferably used in an amount of 0.05 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the monomer composition. By using an amount of 0.05 parts by weight or more, it is possible to sufficiently adjust the surface energy, and by using an amount of 20 parts by weight or less, it is possible to prevent the surface energy of the thermoplastic polymer layer from becoming too high and prone to blocking.

[0093] The radical polymerization initiator initiates the addition polymerization of monomers by radical decomposition using heat or a reducing substance, and both inorganic and organic initiators can be used. The radical polymerization initiator can be a water-soluble or oil-soluble polymerization initiator. Examples of water-soluble polymerization initiators include peroxodisulfates, peroxides, water-soluble azobis compounds, and peroxide-reducing agent redox systems. Examples of peroxodisulfates include potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of peroxides include hydrogen peroxide, t-butyl hydroperoxide, t-butylperoxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis(N-hydroxyethylisobutyramide), 2,2-azobis(2-amidinopropane) dihydrochloride, and 4,4-azobis(4-cyanopentanoic acid). Examples of peroxide-reducing agent redox systems include combinations of the above peroxides with one or more reducing agents, such as sodium sulfoxylate formaldehyde, sodium hydrogen sulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid and its salts, cuprous salts, and ferrous salts.

[0094] The radical polymerization initiator may be used in an amount of preferably 0.05 parts by mass or more and 2 parts by mass or less relative to 100 parts by mass of the monomer composition. The radical polymerization initiator may be used singly or in combination of two or more kinds.

[0095] When a monomer composition containing an ethylenically unsaturated monomer (P) having a polyalkylene glycol group, an ethylenically unsaturated monomer (A) having a cycloalkyl group, and another monomer (B) is emulsion polymerized to form a dispersion in which polymer particles are dispersed in a solvent (water), the solid content of the resulting dispersion is preferably 30% by mass or more and 70% by mass or less. To maintain long-term dispersion stability, the pH of the dispersion is preferably adjusted to a range of 5 to 12. The pH is preferably adjusted using ammonia, sodium hydroxide, potassium hydroxide, or amines such as dimethylaminoethanol, and more preferably using ammonia (water) or sodium hydroxide.

[0096] The aqueous dispersion contains a polymer obtained by polymerizing a monomer composition containing the specific monomer as particles (polymer particles) dispersed in water. In addition to water and the polymer, the aqueous dispersion may contain solvents such as methanol, ethanol, and isopropyl alcohol, as well as dispersants, lubricants, thickeners, and disinfectants. Since the thermoplastic polymer-containing layer can be easily formed by coating, it is preferable to form a particulate polymer by emulsion polymerization and use the resulting particulate polymer emulsion as the aqueous latex.

[0097] (Other components contained in the thermoplastic polymer-containing layer) In addition to the thermoplastic polymer, the thermoplastic polymer-containing layer may optionally contain other components, such as inorganic substances. Examples of inorganic substances include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers, which may be used alone or in combination of two or more. The content of the inorganic substance in the thermoplastic polymer-containing layer may be 5% by mass or less, or may exceed 0% by mass, relative to the total amount of the thermoplastic polymer-containing layer, so as to prevent cohesive failure of the inorganic substance.

[0098] [Any layer] The separator may include any layer other than the substrate and the thermoplastic polymer-containing layer, such as an inorganic filler porous layer, as long as it can achieve the effects of B10, B90, B90 / B10, T10, T90, T10-T90, etc., adjusted within the numerical ranges described above. The inorganic filler porous layer can be disposed, for example, on one side of the substrate, on both sides of the substrate, between the substrate and the thermoplastic polymer-containing layer, or so as to form at least one outer surface of the separator. The inorganic filler porous layer contains an inorganic filler and a resin binder and has a plurality of pores.

[0099] (inorganic filler) The inorganic filler is not particularly limited, but can be one that has a melting point of 200°C or higher, has high electrical insulation properties, and is electrochemically stable within the range of use of an electricity storage device such as a lithium ion secondary battery.

[0100] The inorganic filler is not particularly limited, but examples thereof include inorganic oxides (oxide ceramics) such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; inorganic nitrides (nitride ceramics) such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum oxide hydroxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fiber. These may be used alone or in combination of two or more.

[0101] The inorganic filler has an average particle size D50 of preferably 0.01 μm or more, more preferably 0.2 μm or more, and even more preferably 0.4 μm or more. The inorganic filler also has an average particle size D50 of preferably 4.0 μm or less, more preferably 3.5 μm or less, and even more preferably less than 1.0 μm. An inorganic filler with an average particle size D50 of 0.01 μm or more is preferred from the viewpoint of reducing the amount of moisture adsorbed by the separator. An inorganic filler with an average particle size D50 of 4.0 μm or less is preferred from the viewpoint of the heat resistance of the separator. Examples of methods for adjusting the particle size and particle size distribution of the inorganic filler include pulverizing the inorganic filler using an appropriate pulverizing device such as a ball mill, a bead mill, or a jet mill to reduce the particle size. The particle size distribution of the inorganic filler can be such that a graph of particle size versus frequency has one peak, but it may also be such that the graph has two peaks or a trapezoidal chart with no peak.

[0102] The average particle size of the particulate polymer may be larger than the average pore size of the inorganic filler porous layer. For example, the average particle size of the particulate polymer is, for example, 1.2 times or more, 1.5 times or more, or even 1.8 times or more, and 6.0 times or less, or even 3.0 times or less, relative to the average pore size of the inorganic filler porous layer. The average pore size of the inorganic filler porous layer quantitatively defines the gaps between inorganic fillers, between inorganic fillers and binders, or between binders in the inorganic filler porous layer. The content of the particulate polymer in the inorganic filler porous layer is, for example, 20% by volume or less, 15% by volume or less, 10% by volume or less, or even 5% by volume or less, relative to the total amount of the inorganic filler porous layer.

[0103] When measuring the average pore diameter of the inorganic filler porous layer, it is advisable to observe the cross section of the separator in a region that is not involved in ion conduction. The average pore diameter of the inorganic filler porous layer may be measured, for example, on a separator immediately after production, that is, a separator that has not yet been incorporated into an electricity storage device. Alternatively, if the separator has been incorporated into an electricity storage device, it may be measured on the so-called "edge" portion of the separator (a region near the outer edge of the separator that is not involved in ion conduction). The inorganic filler porous layer has an average pore size of, for example, 0.01 μm or more, 0.05 μm or more, 0.1 μm or more, or even 0.2 μm or more, and an average pore size of 5 μm or less, 3 μm or less, 0.7 μm or less, or even 0.5 μm or less.

[0104] The average pore size of the inorganic filler porous layer is an index representing the size of voids formed between inorganic fillers bound together by a resin binder in the inorganic filler porous layer formed on at least one surface of the substrate. The average pore size of the inorganic filler porous layer is determined by the method for forming the inorganic filler porous layer, and can be adjusted, for example, by the properties of the inorganic filler used, the properties of the inorganic filler porous layer slurry used to form the inorganic filler porous layer, and the method for forming the inorganic filler porous layer.

[0105] Examples of the shape of the inorganic filler include plate-like, scale-like, needle-like, columnar, spherical, polyhedral, and block-like shapes. A combination of inorganic fillers having these shapes may be used. The content of the inorganic filler in the inorganic filler porous layer is, for example, 20% by mass or more but less than 100% by mass, 30% by mass or more but less than 80% by mass, 35% by mass or more but less than 70% by mass, or even 40% by mass or more but less than 60% by mass, relative to the total amount of the inorganic filler porous layer.

[0106] (resin binder) The type of resin contained in the inorganic filler porous layer is not particularly limited, but can be a resin that is insoluble in the electrolyte of an electric storage device such as a lithium-ion secondary battery and is electrochemically stable within the range of use of the electric storage device such as a lithium-ion secondary battery. In addition to the resin binder (A) contained in the inorganic filler porous layer and the particulate polymer (B) contained in the thermoplastic polymer-containing layer, a binder binder (C) contained in the thermoplastic polymer-containing layer and binding the particulate polymer (B) to the substrate or the inorganic filler porous layer may also be used as the resin of the resin binder. The resin binder (A) and the binder binder (C) are usually not particulate in the separator. On the other hand, the particulate polymer (B) is particulate in the separator, and the particulate polymer (B) can contain a different type of resin from the resin binder (A) and the binder binder (C).

[0107] Specific examples of such resins include polyolefins such as polyethylene and polypropylene; fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene; fluorine-containing rubbers such as vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer and ethylene-tetrafluoroethylene copolymer; rubbers such as styrene-butadiene copolymer and its hydrogenated product, acrylonitrile-butadiene copolymer and its hydrogenated product, acrylonitrile-butadiene-styrene copolymer and its hydrogenated product, methacrylate-acrylate copolymer, styrene-acrylate copolymer, acrylonitrile-acrylate copolymer, ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate; cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and resins having 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. These may be used alone or in combination of two or more.

[0108] The resin binder may include, for example, a resin latex binder. Examples of the resin latex binder include a copolymer of an unsaturated carboxylic acid monomer and another monomer copolymerizable therewith. Examples of the aliphatic conjugated diene monomer include butadiene and isoprene, examples of the unsaturated carboxylic acid monomer include (meth)acrylic acid, and examples of the other monomer include styrene. While there are no particular limitations on the polymerization method for such copolymers, emulsion polymerization is preferred. There are no particular limitations on the emulsion polymerization method, and known methods can be used. There are no particular limitations on the method for adding the monomers and other components, and any of a batch addition method, a divided addition method, and a continuous addition method can be used. The polymerization method can be one-stage polymerization, two-stage polymerization, or multi-stage polymerization with three or more stages.

[0109] Specific examples of the resin binder include the following 1) to 7). 1) Polyolefins: for example, polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof; 2) Conjugated diene polymers: for example, styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof; 3) Acrylic polymers: for example, methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers; 4) Polyvinyl alcohol-based resins: for example, polyvinyl alcohol and polyvinyl acetate; 5) Fluorine-containing resins: for example, polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer; 6) Cellulose derivatives: for example, ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose; and 7) Resins having a melting point and / or glass transition temperature of 180°C or higher, or polymers having no melting point but a decomposition temperature of 200°C or higher: for example, polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, and polyester.

[0110] When the resin binder is a resin latex binder, its average particle size (D50) is, for example, 50 to 500 nm, 60 to 460 nm, or even 80 to 250 nm. The average particle size of the resin binder can be controlled by adjusting, for example, the polymerization time, polymerization temperature, raw material composition ratio, raw material charging order, pH, etc. The content ratio of the resin binder in the inorganic filler porous layer is, for example, more than 0 mass% and 80 mass% or less, 1 mass% or more and 20 mass% or less, 2 mass% or more and 10 mass% or less, or even 3 mass% or more and 5 mass% or less, relative to the total amount of the inorganic filler porous layer. The content of the particulate polymer contained in the inorganic filler porous layer can be, for example, less than 5 vol%, less than 3 vol%, or even less than 2 vol% of the content of the particulate polymer contained in the separator.

[0111] The thickness of the inorganic filler porous layer is preferably 0.5 μm or more, more preferably 1.0 μm or more, from the viewpoint of heat resistance, and is preferably 10.0 μm or less, more preferably 6.0 μm or less, from the viewpoint of suppressing the amount of moisture adsorbed by the separator. The layer density of the inorganic filler porous layer is, for example, 0.5 g / (m 2 ·μm) or more 3.0g / (m 2 μm) or less, and even 0.7 to 2.0 cm 3 Furthermore, the peel strength between the substrate and the inorganic filler porous layer is not particularly limited, but can be determined so as to prevent cohesive failure of the inorganic material due to blocking.

[0112] (Laminate of substrate and inorganic filler porous layer) The laminate of the substrate and the inorganic filler porous layer may have a thickness of, for example, 2.5 to 110.0 μm and an air permeability of 50 to 400 seconds / 100 cm 3 and / or the TD heat shrinkage at 130°C may be 1.0 to 5.0%.

[0113] <Various separator characteristics> The separator satisfies the following conditions: {Condition: The measurement value P10 is determined as follows: Two separators were prepared and stored for one day in an environment of 35°C and 10% relative humidity (RH), and then the separators were stacked together with one side (A) of the separator facing each other to form a laminate (AA). RH10 , a laminate (AB) formed by laminating the surface (A) and the opposite surface (B) RH10 , and a laminate (BB) formed by laminating the surfaces (B) together. RH10 Each laminate is pressed for 5 seconds under conditions of a temperature of 90°C and a pressure of 1 MPa. The maximum peel strength of all the laminates measured individually is defined as P10 (N / m). It is preferable that the measured value P10 measured by is 5 N / m or more.

[0114] The method for measuring the P10 value is described in detail in the Examples. When the measured P10 value of a separator under the above conditions is 5 N / m or more, the adhesiveness between the separator and the electrode tends to be ensured or improved. Furthermore, when a separator having a P10 value of 5 N / m or more is used for laminating, winding, assembling, etc. with an electrode, the assembly speed and productivity improve, leading to so-called tact time improvement. From this perspective, the measured P10 value of the separator is more preferably greater than 5 N / m, even more preferably greater than 10 N / m, and particularly preferably greater than 15 N / m. The upper limit of the measured P10 value is not particularly limited, and may be, for example, 30 N / m or less, 25 N / m or less, or 20 N / m or less.

[0115] The measured value P10 for the separator peel strength can be adjusted within the above-described range by controlling the physical properties and composition of the thermoplastic polymer-containing layer, for example, by controlling the glass transition temperature of the thermoplastic polymer. The measured value P10 can also be adjusted by using a thermoplastic polymer unit that is less likely to swell in the electrolyte, introducing a hydrophobic block or functional group, or controlling the content or proportions of both a unit derived from an aromatic vinyl compound monomer and a unit derived from a nitrile group-containing monomer, in addition to controlling the glass transition temperature of the thermoplastic polymer.

[0116] The separator preferably has an air permeability of 10 seconds / 100 cm 3 More than 10,000 seconds / 100cm 3 More preferably, it is 10 seconds / 100 cm or less. 3 More than 1000 seconds / 100cm 3 More preferably, it is 50 seconds / 100 cm or less. 3 More than 500 seconds / 100cm 3 It is particularly preferably 100 seconds / 100 cm or less. 3 More than 300 seconds / 100cm 3As a result, when the separator is applied to an electricity storage device, it exhibits high ion permeability. This air permeability is the air permeability resistance measured in accordance with JIS P-8117, the same as the air permeability of the polyolefin porous substrate.

[0117] The separator has a puncture strength of preferably 200 g / 20 μm or more, more preferably 250 g / 20 μm or more, even more preferably 300 g / 20 μm or more, and preferably 2000 g / 20 μm or less, more preferably 1000 g / 20 μm or less. A puncture strength of 200 g / 20 μm or more is preferable from the viewpoint of preventing film rupture due to fallen active material when the separator is wound with electrodes, and from the viewpoint of preventing the risk of short circuit due to expansion and contraction of electrodes during charge and discharge. A puncture strength of 2000 g / 20 μm or less is preferable from the viewpoint of reducing width contraction due to orientation relaxation during heating. The puncture strength is measured according to the method described in the Examples. The puncture strength can be adjusted by adjusting the stretch ratio and / or stretching temperature of the substrate.

[0118] The total thickness of the separator is preferably 2 μm or more, more preferably 5 μm or more, and preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less. A total thickness of 2 μm or more is preferable from the viewpoint of improving mechanical strength. A total thickness of 100 μm or less is preferable because it reduces the volume occupied by the separator in the electricity storage device, which tends to be advantageous in terms of increasing the capacity of the electricity storage device.

[0119] <Preparing two separators and stacking them> To measure the separator peel strength values ​​B10, B90, and P10, two separators are prepared and laminated as described above. Preparing two separators for measuring the values ​​B10, B90, and P10 means forming a laminate using two members of equal area derived from the same separator.

[0120] When measuring the B10, B90, and P10 peel strength values ​​of the separator, it is preferable to press the laminate in an environment maintained at a relative humidity (RH) corresponding to each value. If it is difficult to simultaneously control the humidity and press the laminate due to factors such as the storage facility, lamination equipment, pressing equipment, and ambient environment, the laminate may be stored in a humidity control device such as an oven and adjusted to a predetermined humidity, and immediately thereafter, the laminate may be placed in a container such as an aluminum pouch, sealed, and transferred to pressing equipment, where it may be quickly pressed.

[0121] In measuring the values ​​B10, B90, and P10, the laminate may be formed by the method detailed in the examples, for example, the following method: (A) A method of forming a laminate by cutting two sheets of equal area from a sheet or disc-shaped separator and stacking them; (a) A method of folding a sheet or a leaf separator in half; and (c) A method of folding a sheet or a single-leaf separator and then cutting it to the desired size; The method can be performed by at least one selected from the group consisting of:

[0122] <Separator layer structure> The separators according to the first and second embodiments include a substrate and a thermoplastic polymer-containing layer disposed on at least one surface of the substrate, and more specifically, have a layer structure in which a thermoplastic polymer-containing layer is disposed on one or both surfaces of the substrate. Such a layer structure of the separator significantly enhances the effects of B10, B90, B90 / B10, T10, T90, T10-T90, P10, and the like, which are adjusted to fall within the numerical ranges described above.

[0123] More specifically, the separators according to the first and second embodiments, or separators whose measured value P10 satisfies the above-described conditions, have the following configuration from the viewpoints of improving the cycle characteristics of the electricity storage device, achieving both adhesiveness and anti-blocking properties, preventing misalignment when unwound, and reducing the amount of moisture carried over into the electricity storage device: (1) a substrate and a thermoplastic polymer-containing layer formed on one side of the substrate; (2) a substrate and a thermoplastic polymer-containing layer formed on both sides of the substrate; (3) a substrate, an inorganic coating layer formed on one side of the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) a substrate, an inorganic coating layer formed on one side of the substrate, a thermoplastic polymer-containing layer formed on the side of the inorganic coating layer opposite the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate; Each layer structure and a laminate formed from a separator having the same will be described below.

[0124] (1) A substrate and a thermoplastic polymer-containing layer formed on one side of the substrate In the layer structure (1), if the thermoplastic polymer-containing layer side of the separator is defined as surface (B) and the side on which the thermoplastic polymer-containing layer is not formed is defined as surface (A), there is generally no adhesion between surfaces (A), which are the exposed surfaces of the substrates, so a laminate (BB) of surfaces (B) or a laminate (AB) of surfaces (A) and (B) is preferred. More specifically, in the measurement of B90, B10 or P10 of the separator of layer structure (1), laminate (BB) RH90,RH10 or laminate (AB) RH90,RH10 It is preferable that the peel strength of the pressed body is the maximum value.

[0125] (2) A substrate and a thermoplastic polymer-containing layer formed on both sides of the substrate In the layer structure (2), a thermoplastic polymer-containing layer is disposed on both sides of the separator (i.e., both sides (A, B)), and therefore, in terms of adhesive strength of the thermoplastic polymer-containing layer, a laminate (AA) of the surfaces (A) together, a laminate (BB) of the surfaces (B) together, or a laminate (AB) of the surfaces (A) and (B) are all preferred. More specifically, in measuring B90, B10, or P10 of the separator of the layer structure (2), the laminate (AA) RH90,RH10 , laminate (BB) RH90,RH10 or laminate (AB) RH90,RH10 Any of the pressed bodies can have a maximum peel strength.

[0126] (3) A substrate, an inorganic coating layer formed on one side of the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate In the layer structure (3), if the inorganic coating layer side of the separator is defined as surface (A) and the thermoplastic polymer-containing layer side is defined as surface (B), there is generally no adhesion between the inorganic coating surfaces (A), and from the viewpoint of observing peeling between multiple thermoplastic polymer-containing layers rather than peeling between the substrate and the inorganic layer or cohesive failure of the inorganic layer, a laminate (BB) of surfaces (B) is preferred. More specifically, in measuring B90, B10, or P10 of a separator having the layer structure (3), the laminate (BB) RH90,RH10 It is preferable that the peel strength of the pressed body is at a maximum value. The inorganic coating layer may be, for example, an inorganic filler porous layer formed by a coating method.

[0127] (4) A substrate, an inorganic coating layer formed on one side of the substrate, a thermoplastic polymer-containing layer formed on the side of the inorganic coating layer opposite the substrate, and a thermoplastic polymer-containing layer formed on the other side of the substrate. In the layer structure (4), if the thermoplastic polymer-containing layer formed in contact with the inorganic coating layer of the separator is defined as surface (A) and the thermoplastic polymer-containing layer formed in contact with the substrate surface is defined as surface (B), a laminate (BB) of surfaces (B) is preferred from the viewpoint of observing peeling between multiple thermoplastic polymer-containing layers rather than peeling between the substrate and the inorganic layer or cohesive failure of the inorganic layer. More specifically, in measuring B90, B10, or P10 of a separator having the layer structure (4), the laminate (BB) RH90,RH10 It is preferable that the peel strength of the pressed body is at a maximum value. The inorganic coating layer may be, for example, an inorganic filler porous layer formed by a coating method.

[0128] <Separator manufacturing method> [Method of manufacturing the substrate] The method for producing substrate is not particularly limited, and can adopt known production method, for example, can adopt either wet porosity method or dry porosity method.Example of wet porosity method includes, for example, when substrate is polyolefin microporous film, melt-knead polyolefin resin composition and plasticizer, form into sheet, then optionally stretch, then extract plasticizer to make porous; melt-knead polyolefin resin composition that comprises polyolefin resin as main component, extrude with high draw ratio, then heat treatment and stretch to peel polyolefin crystal interface to make porous; melt-knead polyolefin resin composition and inorganic filler, form into sheet, then stretch to peel polyolefin and inorganic filler interface to make porous; and dissolve polyolefin resin composition, then immerse in poor solvent for polyolefin, solidify polyolefin and simultaneously remove solvent to make porous.

[0129] The nonwoven fabric or paper substrate may be prepared by any known method, including, for example, a chemical bonding method in which a web is immersed in a binder and dried to bond the fibers together, a thermal bonding method in which heat-melting fibers are mixed into the web and the fibers are partially melted to bond the fibers together, a needle punch method in which a web is repeatedly pierced with barbed needles to mechanically entangle the fibers, and a hydroentanglement method in which a high-pressure water jet is sprayed from a nozzle onto the web through a net (screen) to entangle the fibers.

[0130] As an example of a method for producing a polyolefin microporous membrane, a method of melt-kneading a polyolefin resin composition and a plasticizer, forming the composition into a sheet, and then extracting the plasticizer will be described below. First, the polyolefin resin composition and the plasticizer are melt-kneaded. Examples of melt-kneading methods include adding a polyolefin resin and, if necessary, other additives to a resin kneading device such as an extruder, kneader, Labo Plastomill, kneading roll, or Banbury mixer, and then introducing and kneading the plasticizer at a desired ratio while heating and melting the resin components. In this case, it is preferable to pre-knead the polyolefin resin, other additives, and plasticizer in a predetermined ratio using a Henschel mixer or the like before adding them to the resin kneading device. More preferably, only a portion of the plasticizer is added during pre-kneading, and the remaining plasticizer is kneaded while being side-fed into the resin kneading device.

[0131] As the plasticizer, a nonvolatile solvent capable of forming a homogeneous solution at or above the melting point of the polyolefin can be used. Specific examples of such nonvolatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; and higher alcohols such as oleyl alcohol and stearyl alcohol. Among these, liquid paraffin is preferred.

[0132] The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and molded into a sheet. For example, the mass fraction of the plasticizer in a composition consisting of the polyolefin resin composition and the plasticizer is preferably 30% by mass or more and 80% by mass or less, more preferably 40% by mass or more and 70% by mass or less. By setting the mass fraction of the plasticizer within this range, it is preferable to achieve both melt tension during melt molding and the ability to form a uniform and fine pore structure.

[0133] Next, the molten kneaded product obtained by heating, melting, and kneading as described above is molded into a sheet. Examples of methods for producing a sheet-shaped molded product include extruding the molten kneaded product into a sheet through a T-die or the like, contacting it with a thermal conductor, and solidifying it by cooling to a temperature sufficiently lower than the crystallization temperature of the resin component. Thermal conductors used for cooling and solidifying include metal, water, air, and plasticizer itself, but metal rolls are preferred due to their high thermal conductivity. In this case, sandwiching the molten kneaded product between the metal rolls when contacting them further increases the thermal conductivity efficiency, orients the sheet, increasing film strength and improving the surface smoothness of the sheet, making it more preferable. When extruding into a sheet through a T-die, the die lip spacing is preferably 400 μm or more and 3000 μm or less, and more preferably 500 μm or more and 2500 μm or less.

[0134] The sheet-like molded article thus obtained is then preferably stretched. Either uniaxial stretching or biaxial stretching can be suitably used as the stretching treatment. Biaxial stretching is preferred from the viewpoint of the strength of the resulting microporous membrane. When the sheet-like molded article is stretched in the biaxial direction at a high magnification, the molecules are oriented in the plane direction, and the finally obtained porous substrate becomes less likely to tear and has high pin puncture strength. Examples of stretching methods include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improved pin puncture strength, stretching uniformity, and shutdown properties.

[0135] The areal stretching ratio is preferably in the range of 20 to 100 times, more preferably in the range of 25 to 50 times. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction and 4 to 10 times in the TD direction, more preferably in the range of 5 to 8 times in the MD direction and 5 to 8 times in the TD direction. A stretching ratio within this range is preferred in that it can impart more sufficient strength, prevent film rupture during the stretching step, and achieve high productivity. The MD direction means the machine direction when, for example, a polyolefin microporous membrane is continuously molded, and the TD direction means the direction crossing the MD direction at an angle of 90°.

[0136] The sheet-like molded article obtained as described above may be further rolled. Rolling can be carried out, for example, by a pressing method using a double belt press or the like. Rolling can particularly increase the orientation of the surface layer portion of the sheet-like molded article. The rolling area ratio is preferably more than 1 and not more than 3, and more preferably more than 1 and not more than 2. A rolling ratio within this range is preferred in that it increases the film strength of the finally obtained porous substrate and allows for the formation of a more uniform porous structure in the thickness direction of the film.

[0137] Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. For example, a method for removing the plasticizer includes immersing the sheet-like molded body in an extraction solvent to extract the plasticizer, followed by thorough drying. The plasticizer extraction method may be either a batch method or a continuous method. To prevent the porous substrate from shrinking, it is preferable to restrain the edges of the sheet-like molded body during the immersion and drying process. Furthermore, it is preferable that the amount of plasticizer remaining in the porous substrate is less than 1% by mass.

[0138] It is preferable to use an extraction solvent that is a poor solvent for polyolefin resins and a good solvent for plasticizers, and has a boiling point lower than the melting point of polyolefin resins. Examples of such extraction solvents include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine-based halogenated solvents such as hydrofluoroethers and hydrofluorocarbons; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by operations such as distillation.

[0139] In order to suppress shrinkage of the porous substrate, a heat treatment such as heat setting or heat relaxation may be performed after the stretching step or after the formation of the porous substrate. The porous substrate may also be subjected to post-treatment such as hydrophilization treatment with a surfactant or crosslinking treatment with ionizing radiation or the like.

[0140] Here is an example of a dry porosity method, which is different from the above-mentioned wet porosity method. First, a film is produced by directly stretching and oriented after melt-kneading in an extruder without using a solvent, and then a microporous membrane is produced by sequentially undergoing an annealing step, a cold stretching step, and a hot stretching step. In the dry porosity method, a method in which a molten resin is stretched and oriented through a T-die from an extruder, an inflation method, etc. can be used, and the method is not particularly limited.

[0141] [Method of disposing the thermoplastic polymer-containing layer] A thermoplastic polymer-containing layer is disposed on at least one surface of the substrate produced as described above. When an inorganic filler porous layer is disposed on the surface of the substrate, a thermoplastic polymer-containing layer is disposed on all or part of the surface of the inorganic filler porous layer, or a thermoplastic polymer-containing layer is disposed on the surface of the substrate on which the inorganic filler porous layer is not formed. The method for disposing the thermoplastic polymer-containing layer is not particularly limited, and for example, a method of applying a coating liquid containing a particulate polymer to the inorganic filler porous layer or the substrate can be mentioned.

[0142] As the coating liquid, a dispersion in which a particulate polymer is dispersed in a solvent that does not dissolve the polymer can be preferably used. Particularly preferably, the particulate polymer is synthesized by emulsion polymerization, and the emulsion obtained by the emulsion polymerization can be used as it is as the coating liquid.

[0143] The shape of the application of the thermoplastic polymer to the substrate can be determined so as to obtain the arrangement pattern of the thermoplastic polymer described above. The amount of the thermoplastic polymer applied to the substrate can be determined depending on the application shape, and may be, for example, the same as the amount of the thermoplastic polymer-containing layer formed per area of ​​one side of the substrate described above.

[0144] The method for applying a coating liquid containing a particulate polymer onto a substrate is not particularly limited as long as it can achieve a desired coating pattern, coating film thickness, and coating area. Examples include gravure coater method, small-diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, and inkjet coating method. Among these, gravure coater method or spray coating method is preferred from the viewpoints of having a high degree of freedom in the coating shape of the particulate polymer and being able to easily obtain a preferred area ratio.

[0145] The medium for the coating liquid is preferably water or a mixed solvent consisting of water and a water-soluble organic medium. The water-soluble organic medium is not particularly limited, but examples thereof include ethanol, methanol, etc. Among these, water is more preferred. When the coating liquid is applied to a substrate, if the coating liquid penetrates into the substrate, the particulate polymer containing the polymer will clog the surface and interior of the pores of the substrate, easily reducing permeability. In this regard, when water is used as the solvent or dispersion medium for the coating liquid, the coating liquid is less likely to penetrate into the substrate, and the particulate polymer containing the polymer will tend to be present mainly on the outer surface of the substrate, which is preferable because it can more effectively suppress the reduction in permeability. Furthermore, examples of solvents or dispersion media that can be used in combination with water include ethanol and methanol.

[0146] The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate and the thermoplastic polymer-containing layer. Examples include a method of drying the substrate at a temperature below its melting point while fixing it, a method of drying under reduced pressure at a low temperature, and a method of immersing the substrate in a poor solvent for the particulate polymer to solidify the particulate polymer into particles and simultaneously extracting the solvent.

[0147] The drying temperature during or after coating of the thermoplastic polymer-containing layer is preferably 30°C to 80°C, more preferably 35°C to 60°C, and even more preferably 40°C to 60°C. A drying temperature of 30°C or higher is preferred from the viewpoints of ensuring reliable drying and suppressing the amount of moisture carried over from the thermoplastic polymer-containing layer to the separator or electricity storage device. A drying temperature of 80°C or lower is preferred from the viewpoints of suppressing changes in the separator properties due to heat, such as wrinkling and sagging.

[0148] [Method for forming inorganic filler porous layer] When an inorganic filler porous layer is disposed on at least one surface of a substrate, the method for forming the inorganic filler porous layer is not particularly limited and can be formed by a known method. For example, a method of applying a coating liquid containing an inorganic filler and, if necessary, a resin binder to the substrate can be mentioned. When the substrate contains a resin, such as a polyolefin microporous film, a raw material containing an inorganic filler and a resin binder and a raw material for the substrate containing a resin can be laminated and extruded by a co-extrusion method, or the substrate and the inorganic filler porous layer (film) can be produced separately and then bonded together.

[0149] The solvent for the coating liquid is preferably one that can uniformly and stably disperse or dissolve the inorganic filler and, if necessary, the resin binder, and examples thereof include N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, water, ethanol, toluene, hot xylene, methylene chloride, and hexane.

[0150] The coating liquid may contain various additives such as dispersants such as surfactants, thickeners, wetting agents, antifoaming agents, and pH adjusters including acids and alkalis.

[0151] Examples of methods for dispersing or dissolving the inorganic filler and, if necessary, the resin binder in the medium of the coating liquid include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, high-speed impeller dispersion, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and mechanical stirring using a stirring blade or the like.

[0152] Examples of methods for applying the coating liquid to the substrate include gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method, squeeze coater method, cast coater method, die coater method, screen printing method, and spray coating method.

[0153] The method for removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the substrate. For example, there are methods such as drying the substrate at a temperature below the melting point of the material constituting the substrate while fixing it, drying under reduced pressure at a low temperature, and immersing the substrate in a poor solvent for the resin binder to solidify the resin binder and simultaneously extract the solvent. Furthermore, some of the solvent may remain as long as it does not significantly affect the device characteristics.

[0154] When the coating solution is removed from the coating film by drying, the average pore size of the inorganic filler porous layer can be adjusted by changing the drying conditions. It is believed that if the drying conditions are strengthened and the drying speed is increased, the inorganic filler will be fixed in its original arrangement without adjusting its shape from a fully dispersed state, resulting in a larger average pore size. On the other hand, if the drying conditions are relaxed, the dispersed inorganic filler will attempt to adopt a more energetically stable structure as the solvent dries, resulting in a smaller average pore size of the inorganic filler porous layer. Furthermore, if the viscosity of the coating solution is low, it will be easier to adopt a stable structure, resulting in a smaller average pore size of the inorganic filler porous layer. Furthermore, the dispersion state of the inorganic filler is also affected by the type of inorganic filler, the type of solvent, the presence or absence of an added surfactant, and the type of surfactant.

[0155] The average pore size of the inorganic filler porous layer can be reduced by calendering the laminate of the inorganic filler porous layer and the substrate. The method of calendering is not particularly limited, and a method of drying the coating liquid and then conveying it while applying pressure with nip rolls may be used.

[0156] <Electricity storage device> An electricity storage device including a separator may be similar to a conventionally known device except for the inclusion of the separator for the electricity storage device. The electricity storage device is not particularly limited, but examples thereof include batteries such as non-aqueous electrolyte secondary batteries, condensers, and capacitors. Among these, from the viewpoint of more effectively obtaining the benefits of the effects of the present invention, batteries are preferred, non-aqueous electrolyte secondary batteries are more preferred, and lithium ion secondary batteries are even more preferred. Since the electricity storage device includes the separator of this embodiment, the device has excellent device characteristics such as electricity storage performance. Furthermore, lithium ion secondary batteries have excellent battery characteristics.

[0157] The electrode used to measure the peel strength from the electrode may be either a positive electrode or a negative electrode, but it is appropriate to use a positive electrode in order to properly understand the effect of the separator. In particular, when the electricity storage device is a lithium ion secondary battery, it is appropriate to measure the peel strength after overlapping a positive electrode for a lithium ion secondary battery, in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector, with the positive electrode active material layer facing the surface of the separator on which the thermoplastic polymer-containing layer is formed, and then hot-pressing as described above.

[0158] When a lithium ion secondary battery is produced using the separator, there are no limitations on the positive electrode, negative electrode, and non-aqueous electrolyte, and known materials can be used for each. A suitable positive electrode is one in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector. Examples of the positive electrode current collector include aluminum foil. Examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO2, LiNiO2, spinel-type LiMnO4, and olivine-type LiFePO4. In addition to the positive electrode active material, the positive electrode active material layer may also contain a binder, a conductive material, and the like.

[0159] The negative electrode may preferably be formed by forming a negative electrode active material layer containing a negative electrode active material on a negative electrode current collector. Examples of the negative electrode current collector include copper foil. Examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbon, graphitizable carbon, and composite carbon materials; silicon, tin, metallic lithium, and various alloy materials.

[0160] The non-aqueous electrolyte is not particularly limited, but may be an electrolyte solution prepared by dissolving an electrolyte in an organic solvent. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO4, LiBF4, and LiPF6.

[0161] <Method of manufacturing an electricity storage device> The method for producing an electricity storage device using a separator is not particularly limited. For example, the following method can be exemplified. First, a separator having a vertically elongated shape with a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) is produced. Next, the positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator are laminated in this order, and wound into a circular or flat spiral to obtain a wound body. The wound body is then housed in a device can (e.g., a battery can), and an electrolyte solution is then injected into the device can to produce the device. Alternatively, the electrode and separator may be folded to form a wound body, which is then placed in a device container (e.g., an aluminum film) and the electrolyte solution is then injected into the device can to produce the device.

[0162] At this time, the wound body can be pressed. Specifically, a method can be exemplified in which a separator, a current collector, and an electrode having an active material layer formed on at least one surface of the current collector are stacked together so that the thermoplastic polymer-containing layer of the former faces the active material layer, and then pressed.

[0163] The pressing temperature is preferably, for example, 20°C or higher, which is a temperature at which adhesiveness can be effectively achieved. Furthermore, in order to prevent clogging of pores in the separator or thermal shrinkage due to heat pressing, the pressing temperature is preferably lower than the melting point of the material contained in the substrate, and more preferably 120°C or lower. The pressing pressure is preferably 20 MPa or lower, from the viewpoint of preventing clogging of pores in the separator. The pressing time may be 1 second or less when using a roll press, or may be several hours of surface pressing, but is preferably 2 hours or less from the viewpoint of productivity. Using the separator for an electricity storage device of this embodiment through the above-described manufacturing process can prevent press-back when a wound body consisting of electrodes and a separator is press-molded. Therefore, this is preferable because it can prevent a decrease in yield in the device assembly process and shorten the production process time.

[0164] The electricity storage device, particularly the lithium ion secondary battery, manufactured as described above has a separator with high adhesiveness and reduced ionic resistance, and therefore has excellent battery characteristics (rate characteristics) and durability against long-term continuous operation (cycle characteristics). [Example]

[0165] The physical property evaluations described in the Examples section were carried out according to the following methods.

[0166] (1) Solids Approximately 1 g of the aqueous dispersion of the thermoplastic polymer was weighed out onto an aluminum dish, and the weight of the aqueous dispersion weighed out was designated (a) g. This was dried in a hot air dryer at 130°C for 1 hour, and the dry weight of the thermoplastic polymer after drying was designated (b) g. The solid content was calculated using the following formula: Solid content=(b) / (a)×100 [%]

[0167] (2) Average particle size of particulate polymer (D50) The average particle size (D50) of the particulate polymer was measured using a particle size measuring device (manufactured by Nikkiso Co., Ltd., product name "Microtrac UPA150") The measurement conditions were a loading index of 0.20 and a measurement time of 300 seconds, and the 50% particle size (D50) value in the obtained data was recorded as the average particle size.

[0168] (3) Thickness of the substrate (μm) The thickness of the substrate was measured by observing the cross section of the substrate using an SEM (Model S-4800, manufactured by Hitachi Corporation).

[0169] (4) Thickness of the thermoplastic polymer-containing layer The separator was freeze-fractured, and its cross section was observed using an SEM (Model S-4800, manufactured by Hitachi). The thickness of the thermoplastic polymer-containing layer was measured from the obtained field of view. Specifically, a sample of approximately 1.5 mm x 2.0 mm and ethanol were placed in a gelatin capsule, frozen with liquid nitrogen, and then the sample was fractured with a hammer. The fractured sample was osmium-deposited and observed at an accelerating voltage of 1.0 kV and 30,000x magnification to calculate the thickness of the thermoplastic polymer-containing layer. Note that the thickness of the thermoplastic polymer-containing layer was determined by the boundary line between the visible and invisible parts of the substrate cross section in the SEM image and the shortest distance from the line parallel to this that contacts the thermoplastic polymer-containing layer and is furthest from the substrate. In addition, when a thermoplastic polymer-containing layer is present on the inorganic filler porous layer, the thickness of the thermoplastic polymer-containing layer can be determined as the distance from the substrate to the thermoplastic polymer-containing layer minus the thickness of the inorganic filler porous layer.

[0170] (5) Glass transition temperature Tg of thermoplastic polymer An appropriate amount of a water dispersion containing a thermoplastic polymer (solid content = 38-42% by mass, pH = 9.0) was placed on an aluminum dish and dried in a hot air dryer at 130°C for 30 minutes to obtain a dry film. Approximately 10 mg of the dry film was placed in an aluminum container for measurement, and a DSC curve under a nitrogen atmosphere and a DSC curve were obtained using a DSC measurement device (Shimadzu Corporation, model name "DSC6220"). The measurement conditions were as follows: First stage temperature increase program: Start at 70°C, increase temperature at a rate of 15°C per minute, and maintain at 110°C for 5 minutes. Second stage temperature reduction program: Reduce the temperature from 110°C at a rate of 40°C per minute. After reaching -50°C, maintain the temperature for 5 minutes. Third-stage temperature increase program: Temperature increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were collected during this third-stage temperature increase. The intersection of the baseline (a straight line extending the baseline of the obtained DSC curve to the higher temperature side) and the tangent at the inflection point (the point where the upward convex curve changes to a downward convex curve) was determined as the glass transition temperature (Tg). Note that the Tg described in this section is shown in Tables 3 and 5 as the glass transition temperature Tg of the particulate polymer.

[0171] (6) Glass transition temperatures T10 and T90 of thermoplastic polymers after storage for one day The glass transition temperatures T10 and T90 of the thermoplastic polymer after storage for 1 day were measured as follows. A thermoplastic polymer (a mixture of multiple thermoplastic polymers is also acceptable) was stored for one day at 35°C and 10% relative humidity (RH), and then 10 mg of the polymer was placed in an aluminum hermetic pan (Hitachi High-Tech Science Corporation, K-YSSC000E031) and sealed. Thereafter, the glass transition temperature T10 (°C) was measured by DSC (differential scanning calorimetry) under the following conditions: Heating program: Starts at 0°C, heats up to 100°C at a rate of 3°C per minute

[0172] A thermoplastic polymer (a mixture of multiple thermoplastic polymers is also acceptable) was stored for one day at 35°C and 90% relative humidity (RH), and then 10 mg was placed in an aluminum hermetic pan (Hitachi High-Tech Science Corporation, K-YSSC000E031, capacity 15 μL) and sealed. Thereafter, the glass transition temperature T90 (°C) was measured by DSC (differential scanning calorimetry) under the following conditions. Heating program: Starts at 0°C, heats up to 100°C at a rate of 3°C per minute

[0173] Table 5 shows the measurement results of T10 and T90, and the value obtained by subtracting T90 from T10 (T10-T90).

[0174] (7) Swelling ratio of thermoplastic polymer to electrolyte (times) A thermoplastic polymer or a latex containing the same (a mixture of multiple thermoplastic polymers or a latex containing the same may also be used) was left to stand in an oven at 80°C for 9 hours, and then vacuum dried at 80°C for 12 hours to obtain a dried polymer. Approximately 0.5 g of the obtained dried product was weighed and the mass before immersion (W A This dried sample was placed in a 50 mL vial together with 10 g of a mixed solvent of ethylene carbonate (EC):diethyl carbonate (DEC) = 2:3 (volume ratio) at 25°C, and after immersion for 24 hours, the sample was taken out and wiped with towel paper, and immediately afterwards the mass was measured. The mass after immersion (W B ) was decided. The degree of swelling of the thermoplastic polymer in the electrolyte was calculated by the following formula. Swelling ratio (times) = W B / W A In the above formula, if the polymer sample neither swells nor dissolves in the mixed solvent, the swelling degree is 1.

[0175] (8) Viscosity average molecular weight Mv In accordance with ASTM-D4020, the intrinsic viscosity [η] was determined in decalin solvent at 135° C. Using this [η] value, the viscosity average molecular weight Mv was calculated from the relationship of the following mathematical formula. For polyethylene: [η] = 0.00068 × Mv 0.67 For polypropylene: [η] = 1.10 × 10 -4 ×Mv 0.80

[0176] (9) Porosity (%) A 10cm x 10cm square sample was cut from the substrate and its volume (cm 3 ) and mass (g). Using these values, the density of the substrate was calculated as 0.95 (g / cm 3) and the porosity was calculated using the following formula: Porosity (%) = (1 - mass / volume / 0.95) x 100

[0177] (10) Air permeability (sec / 100cm 3 ) The air permeability of the substrate, the laminate of the substrate and the inorganic filler porous layer, or the separator was determined as the air permeability resistance measured in accordance with JIS P-8117 using a Gurley air permeability meter G-B2 (model name) manufactured by Toyo Seiki Co., Ltd. When the thermoplastic polymer-containing layer is present on only one side of the substrate, the needle can be pierced from the side where the thermoplastic polymer-containing layer is present.

[0178] (11)Piercing strength (gf / 20μm or g / 20μm) Using a Kato Tech handy compression tester, model KES-G5, the substrate or separator was fixed in place with a sample holder having an opening diameter of 11.3 mm. Next, a puncture test was performed on the center of the fixed substrate or separator using a needle with a tip radius of curvature of 0.5 mm at a puncture speed of 2 mm / sec in a 25°C atmosphere to measure the maximum puncture load. The maximum puncture load was converted to a value per 20 μm of thickness and used as the puncture strength (gf / 20 μm or g / 20 μm). When the thermoplastic polymer was present on only one side of the substrate, the needle could be punctured from the side where the thermoplastic polymer was present.

[0179] (12) Average particle size D50 of inorganic filler (μm) The average particle size of the inorganic filler, along with its particle size distribution, was measured using a particle size measuring device (product name "Microtrac UPA150" manufactured by Nikkiso Co., Ltd.) under the following measurement conditions: loading index = 0.20, measurement time 300 seconds, and the 50% particle size (D50) value of the obtained data was recorded as the average particle size.

[0180] (13) Thickness of inorganic filler porous layer (μm) The difference between the thickness of the substrate obtained by the method described in the "Thickness of substrate" section above and the thickness of the multilayer porous membrane obtained by the method described in the "Thickness of multilayer porous membrane" section below was calculated.

[0181] (14) Thickness (μm) of the laminate (multilayer porous membrane) of the substrate and the inorganic filler porous layer The measurement object was a multilayer porous membrane, and the thickness was measured by the same method as described in the "Thickness of substrate" section above.

[0182] (15) 130°C heat shrinkage rate (%) of the laminate (multilayer porous film) of the substrate and inorganic filler porous layer The laminate was cut into a sample of 100 mm in the TD direction and 100 mm in the MD direction and left to stand in an oven at 130°C for 1 hour. The sample was sandwiched between two pieces of paper to prevent direct exposure to hot air. The sample was removed from the oven and cooled, after which its length (mm) was measured and the TD thermal shrinkage was calculated using the following formula. TD heat shrinkage rate (%) = 100 - TD length after heating (mm)

[0183] (16) Total thickness of separator (μm) The measurement object was a separator, and the measurement was performed by the same method as described in the above column "Thickness of substrate." Depending on the presence or absence of pattern coating or an inorganic filler porous layer, the total thickness of the separator may be equal to the thickness of the substrate or the multilayer porous membrane.

[0184] (17) Coverage area ratio (%) of thermoplastic polymer-containing layer The coverage area ratio of the thermoplastic polymer-containing layer was measured using a scanning electron microscope (SEM) (model: S-4800, manufactured by Hitachi Corporation). The separator sample was osmium-deposited and observed at an accelerating voltage of 1.0 kV and 50x magnification, and the surface coverage ratio was calculated using the following formula. Note that the region of the substrate surface where the porous structure was not visible in the SEM image was defined as the thermoplastic polymer-containing layer region. Coverage area ratio (%) of thermoplastic polymer-containing layer = area of ​​thermoplastic polymer-containing layer ÷ (area including pores of substrate + area of ​​thermoplastic polymer-containing layer) × 100 The coverage area ratio for each sample was calculated by taking the above measurement three times and averaging the results.

[0185] (18) Peel strength B10 (N / m) Two rectangular separator test pieces measuring 20 mm wide and 70 mm long were cut from the separator, and the two cut separator test pieces were stored in a test box at a temperature of 35°C and a relative humidity (RH) of 10% for one day. Then, the two stored separator test pieces were used to prepare the following laminate: (AA) RH10 : A laminate formed by laminating the surface (A) of one test piece with the surface (A) of another test piece; (AB) RH10 : A laminate formed by laminating a surface (A) of one test piece with a surface (B) opposite to the surface (A) of another test piece; (BB) RH10 : A laminate formed by laminating the surface (B) opposite to the surface (A) of one test piece with the surface (B) of another test piece.

[0186] Each laminate was pressed under the following conditions. Temperature 40℃ Press pressure: 1 MPa Pressing time: 2 minutes

[0187] Laminate after pressing (AA) RH10 , laminate (AB) RH10 , and laminate (BB) RH10 For each laminate, a 90° peel test was performed at a peel rate of 50 mm / min using a force gauge ZP5N manufactured by Imada Co., Ltd., and the peel strength was measured. The average peel strength value in the 40 mm length peel test performed under the above conditions was used as the peel strength. Next, the maximum peel strength (N / m) of all the laminates individually measured was used as B10 (N / m).

[0188] (19) Peel strength B90 (N / m) Two rectangular separator test pieces measuring 20 mm wide and 70 mm long were cut from the separator, and the two cut separator test pieces were stored in a test box at a temperature of 35°C and a relative humidity (RH) of 90% for one day. Then, the two stored separator test pieces were used to prepare the following laminate: (AA) RH90 : A laminate formed by laminating the surface (A) of one test piece with the surface (A) of another test piece; (AB) RH90 : A laminate formed by laminating a surface (A) of one test piece with a surface (B) opposite to the surface (A) of another test piece; (BB) RH90 : A laminate formed by laminating the surface (B) opposite to the surface (A) of one test piece with the surface (B) of another test piece.

[0189] Each laminate was pressed under the following conditions. Temperature: 40℃ Press pressure: 1 MPa Pressing time: 2 minutes

[0190] Laminate after pressing (AA) RH90 , laminate (AB) RH90 , and laminate (BB) RH90 For each laminate, a 90° peel test was performed at a peel speed of 50 mm / min using an Imada ZP5N force gauge to measure the peel strength. The average peel strength value for a 40 mm length of the peel test performed under the above conditions was used as the peel strength. Next, the maximum peel strength (N / m) measured individually for all laminates was used as the peel strength B90 (N / m). The ratio B90 / B10 of the B90 to the peel strength B10 of the laminate was also calculated.

[0191] (20) Peel strength P10 (N / m) Laminate (AA) made with two separator specimens for measuring peel strength B10 (N / m) RH10 , laminate (AB) RH10 , and laminate (BB) RH10Each laminate was prepared in a state before being pressed to measure the peel strength B10 (N / m).

[0192] Next, each laminate was pressed under the following conditions. Temperature: 90℃ Press pressure: 1 MPa Press time: 5 seconds

[0193] Laminate after pressing (AA) RH10 , laminate (AB) RH10 , and laminate (BB) RH10 For each laminate, a 90° peel test was performed at a peel rate of 50 mm / min using a force gauge ZP5N manufactured by Imada Co., Ltd., and the peel strength was measured. The average value of the peel strength in the 40 mm length peel test performed under the above conditions was used as the peel strength. Next, the maximum value of the peel strengths measured individually for all laminates was used as the peel strength P10 (N / m).

[0194] (21) Blocking resistance (amount of misalignment when feeding the separator) A rectangular separator measuring 30 mm wide and 2000 m long was wound to form a wound body. The formed wound body was stored stably at 35°C for 30 days. After storage, the wound body was placed in an automatic winding device, and the length of the separator that could be unwound evenly and wrinkle-free within 20 m of the inner layer of the wound body was measured, and blocking resistance (referred to in the table as "amount of misalignment when unwinding the separator") was evaluated based on the following evaluation criteria. Evaluation criteria for blocking resistance 〇 (Very good): The separator was fed out uniformly and without wrinkles, and the length was over 1m △ (Good): The separator was fed out evenly and without wrinkles, and the length was over 95 cm and 1 m or less × (bad): The length of the separator that can be fed out uniformly and without wrinkles is 95 m or less.

[0195] (22) Adhesion to electrodes The substrate, multilayer porous membrane, or separator and the positive electrode (manufactured by Enertech, positive electrode material: LiCoO, conductive additive: acetylene black, binder: PVdF, LiCoO / acetylene black / PVdF (mass ratio) = 95 / 2 / 3, L / W: 36 mg / cm on both sides) were used as the adherend. 2 , Density: 3.9g / cm 3 The separator and positive electrode active material were stacked so that the thermoplastic polymer layer of the separator and the positive electrode active material faced each other to obtain a laminate, which was then pressed under the following conditions: The room temperature during evaluation was 23°C and the humidity was 30%. Press pressure: 1 MPa Temperature: 100℃ Press time: 5 seconds

[0196] The laminate after pressing was subjected to a 90° peel test at a peel speed of 50 mm / min to measure the peel strength, by fixing the electrode and gripping and pulling the substrate, the multilayer porous membrane, or the separator using force gauges ZP-5N and MX2-500N (product name) manufactured by Imada Co., Ltd. At this time, the average value of the peel strength in the peel test over a length of 40 mm conducted under the above conditions was adopted as the peel strength, and the adhesion to the electrode was evaluated according to the following criteria. ○ (Good): Peel strength is 5 N / m or more. △ (slightly poor): Peel strength is 3 N / m or more and less than 5 N / m. × (bad): Peel strength is less than 3 N / m.

[0197] Regarding the above-mentioned "adhesion to electrode" test, Table 1 shows the test results when a substrate was used instead of the separator, and Table 2 shows the test results when a multilayer porous membrane was used instead of the separator. As can be seen from Tables 1 and 2, the polyolefin microporous membrane or multilayer porous membrane alone, i.e., without a thermoplastic polymer layer, does not exhibit significant adhesion to electrodes.

[0198] (23) Powder shedding A 10 cm x 10 cm square sample was cut from the separator for an electricity storage device and its mass (g) was measured. One side was attached to cardboard and fixed, and then a 5 cm diameter, 900 g weight covered with cotton cloth was placed on the inorganic filler porous layer side (however, if there was no inorganic filler porous layer, either the exposed substrate side or the thermoplastic polymer-containing layer side could be used). These were then rubbed together at 50 rpm for 10 minutes. The mass (g) was then accurately measured again, and the powder shedding rate was measured using the following formula: Powder shedding (mass%) = {(mass before rubbing (g) - mass after rubbing (g)) / mass before rubbing} x 100 Next, the powder shedding was ranked according to the following evaluation criteria. ◯ (Good): Powder shedding is less than 2%. △ (Acceptable): Powder shedding is 2% or more but less than 10%. × (bad): Powder shedding rate exceeds 10%.

[0199] (24) Rate characteristics a. Preparation of the positive electrode The positive electrode active material was nickel, manganese, and cobalt composite oxide (NMC) (Ni:Mn:Co = 1:1:1 (element ratio), density 4.70 g / cm 3 ) as 90.4 mass%, and graphite powder (KS6) (density 2.26 g / cm) as a conductive additive. 3 1.6 mass% of acetylene black powder (AB) (density 1.95 g / cm 3 3.8 mass% of polyvinylidene fluoride (PVdF) (density 1.75 g / cm 3) as a binder. 3 ) were mixed at a ratio of 4.2% by mass and dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one side of a 20 μm thick aluminum foil, which would serve as a positive electrode current collector, using a die coater, dried at 130°C for 3 minutes, and then compression-molded using a roll press to prepare a positive electrode. The amount of positive electrode active material applied at this time was 109 g / m 2 It was.

[0200] b. Preparation of negative electrode Graphite powder A (density 2.23 g / cm) was used as the negative electrode active material. 3 , number average particle diameter 12.7 μm) at 87.6 mass%, and graphite powder B (density 2.27 g / cm 3 A slurry was prepared by dispersing 9.7% by mass of carboxymethylcellulose (number average particle diameter 6.5 μm) and 1.4% by mass (solids content equivalent) of ammonium salt of carboxymethylcellulose (aqueous solution with a solids content of 1.83% by mass) and 1.7% by mass (solids content equivalent) of diene rubber latex (aqueous solution with a solids content of 40% by mass) in purified water. This slurry was applied to one side of a 12 μm-thick copper foil serving as a negative electrode current collector using a die coater, dried at 120°C for 3 minutes, and then compression-molded using a roll press to produce a negative electrode. The amount of negative electrode active material applied was 5.2 g / m 2 It was.

[0201] c. Preparation of non-aqueous electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=1:2 (volume ratio) to a concentration of 1.0 mol / L.

[0202] d. Battery assembly The separator, substrate, or multilayer porous membrane was cut into a 24 mm diameter circle, and the positive electrode and negative electrode were each cut into a 16 mm diameter circle. The negative electrode, separator, substrate, or multilayer porous membrane, and positive electrode were stacked in this order, with the active material surfaces of the positive electrode and negative electrode facing each other, and then placed in a lidded stainless steel metal container. The container and lid were insulated, with the container in contact with the copper foil of the negative electrode, and the lid in contact with the aluminum foil of the positive electrode. A battery was assembled by pouring 0.4 ml of the nonaqueous electrolyte into the container and sealing it.

[0203] e. Evaluation of rate characteristics The simple battery assembled in step d was charged at 25°C at a current of 3 mA (approximately 0.5 C) up to a battery voltage of 4.2 V, and then the current was reduced from 3 mA to maintain the voltage at 4.2 V. This was the initial charging method for a total of approximately 6 hours after the battery was assembled. It was then discharged at a current of 3 mA down to a battery voltage of 3.0 V. Next, the battery was charged at 25°C at a current of 6 mA (approximately 1.0 C) up to a battery voltage of 4.2 V, and then the current was reduced from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. After that, the battery was discharged at a current of 6 mA down to a battery voltage of 3.0 V, and the discharge capacity was taken as the 1 C discharge capacity (mAh). Next, the battery was charged at 25°C at a current of 6 mA (approximately 1.0 C) up to a battery voltage of 4.2 V, and then the current was reduced from 6 mA to maintain 4.2 V, for a total of approximately 3 hours. The battery was then discharged at a current of 12 mA (approximately 2.0 C) down to a battery voltage of 3.0 V, and the discharge capacity was recorded as the 2C discharge capacity (mAh). Then, the ratio of the 2C discharge capacity to the 1C discharge capacity was calculated, and this value was taken as the rate characteristic. Rate characteristic (%) = (2C discharge capacity / 1C discharge capacity) x 100

[0204] Evaluation criteria for rate characteristics (%) ◎ (Extremely good): Rate characteristics are 95% or more. ○ (Good): Rate characteristics are 85% or more and less than 95%. △ (Acceptable): Rate characteristics are 80% or more and less than 85%. × (bad): Rate characteristics are less than 80%.

[0205] (25) Cycle characteristics Using the simple batteries assembled as in items a to d of the "rate characteristics" above, cycle characteristics were also evaluated. The above battery was charged at a constant current of 1 / 3C to a voltage of 4.2V, then charged at a constant voltage of 4.2V for 8 hours, and then discharged at a current of 1 / 3C to a cutoff voltage of 3.0V. Next, the battery was charged at a constant current of 1C to a voltage of 4.2V, then charged at a constant voltage of 4.2V for 3 hours, and then discharged at a current of 1C to a cutoff voltage of 3.0V. Finally, the battery was charged at a constant current of 1C to 4.2V, and then charged at a constant voltage of 4.2V for 3 hours as a preconditioning step. 1C refers to the current value required to discharge the battery's reference capacity in 1 hour. The pretreated battery was discharged at a temperature of 25°C at a discharge current of 1 A to a discharge cut-off voltage of 3 V, and then charged at a charge current of 1 A to a charge cut-off voltage of 4.2 V. This cycle was repeated. The cycle characteristics were evaluated using the capacity retention rate after 200 cycles relative to the initial capacity (capacity at the first cycle) according to the following criteria. <Evaluation criteria for cycle characteristics> ◎ (Excellent): Capacity retention of 90% to 100% Good: Capacity retention of 85% or more but less than 90% △ (Acceptable): Capacity retention rate between 80% and 85% × (bad): Capacity retention rate less than 80%

[0206] [Production Example 1] (Production of polyolefin microporous membrane B1) 45 parts by mass of a homopolymer high-density polyethylene having an Mv of 700,000, 45 parts by mass of a homopolymer high-density polyethylene having an Mv of 300,000, and 10 parts by mass of a mixture of a homopolymer polypropylene having an Mv of 400,000 and a homopolymer polypropylene having an Mv of 150,000 (mass ratio = 4:3) were dry-blended using a tumbler blender. 1 part by mass of tetrakis-[methylene-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane as an antioxidant was added to 99 parts by mass of the resulting polyolefin mixture, and the mixture was again dry-blended using the tumbler blender to obtain a mixture. The resulting mixture was fed into a twin-screw extruder using a feeder under a nitrogen atmosphere. Liquid paraffin (kinematic viscosity at 37.78°C: 7.59 x 10) was also added. -5 m 2 / s) was injected into the extruder cylinder using a plunger pump. The operating conditions of the feeder and pump were adjusted so that the proportion of liquid paraffin in 100 parts by mass of the total mixture extruded was 65 parts by mass, i.e., so that the proportion of the resin composition was 35 parts by mass.

[0207] Next, they were melt-kneaded in a twin-screw extruder while heating to 230°C, and the resulting melt-kneaded mixture was extruded through a T-die onto a cooling roll controlled at a surface temperature of 80°C. The extrudate was brought into contact with the cooling roll, cast, and cooled to solidify, yielding a sheet-like molded product. This sheet was stretched at a ratio of 7x6.4 at a temperature of 112°C using a simultaneous biaxial stretching machine, then immersed in methylene chloride to extract and remove the liquid paraffin, dried, and stretched 2x in the transverse direction at a temperature of 130°C using a tenter stretching machine. The stretched sheet was then relaxed approximately 10% in the width direction and heat-treated to obtain polyolefin microporous membrane B1 as the substrate.

[0208] The properties of the obtained polyolefin microporous membrane B1 were measured by the above-mentioned methods. The obtained polyolefin microporous membrane was also evaluated by the above-mentioned methods as a separator. The results are shown in Table 1. Before using the substrate B1, the substrate B1 was subjected to a corona treatment to adjust the surface tension.

[0209] [Production Example 2] (Production of polyolefin microporous membrane B2) A separator manufactured by Celgard, model H1609, was used as the polyolefin microporous membrane B2 and was evaluated in the same manner as in Production Example 1. The results are shown in Table 1.

[0210] [Table 1]

[0211] [Production Example 1-1] (Formation of multilayer porous membrane B1-1) The acrylic latex used as the resin binder for the inorganic particle layer was prepared by the following method. 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and 0.5 parts by mass of "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) were added to a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer. The temperature inside the reaction vessel was then raised to 80°C. While maintaining the temperature at 80°C, 7.5 parts by mass of a 2% aqueous solution of ammonium persulfate was added to obtain an initial mixture. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the emulsion was added dropwise from the dropping tank to the reaction vessel over 150 minutes. The emulsion was prepared by mixing 70 parts by weight of butyl acrylate, 29 parts by weight of methyl methacrylate, 1 part by weight of methacrylic acid, 3 parts by weight of emulsifiers "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) and "ADEKA REASOAP SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation), 7.5 parts by weight of a 2% aqueous solution of ammonium persulfate, and 52 parts by weight of ion-exchanged water in a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was maintained at 80°C for 90 minutes and then cooled to room temperature. The pH of the resulting emulsion was adjusted to 8.0 with a 25% aqueous solution of ammonium hydroxide, and a small amount of water was added to obtain an acrylic latex with a solids content of 40%. The resulting acrylic latex had a number-average particle size of 145 nm and a glass transition temperature of -23°C.

[0212] A dispersion was prepared by uniformly dispersing 95 parts by weight of aluminum hydroxide oxide (block-shaped, average particle size 1.4 μm) as an inorganic filler and 0.4 parts by weight (solids equivalent) of an aqueous solution of ammonium polycarboxylate (SN Dispersant 5468, manufactured by San Nopco, solids concentration 40%) as an ionic dispersant in 100 parts by weight of water. The resulting dispersion was crushed using a bead mill (cell volume 200 cc, zirconia bead diameter 0.1 mm, filling amount 80%) to adjust the particle size distribution of the inorganic particles to D50 = 0.7 μm, producing an inorganic particle-containing slurry. To the dispersion with the adjusted particle size distribution, 2.0 parts by weight (solids equivalent) of the acrylic latex prepared above as a resin binder was added to obtain an inorganic particle-containing slurry. Substrate B1 was continuously unwound from a mother roll, and the inorganic particle-containing slurry was coated on one side of the substrate B1 using a gravure reverse coater. The coated substrate was dried in a dryer at 60°C to remove water, yielding a multilayer porous membrane B1-1 having an inorganic filler porous layer on one side of the substrate B1. This was wound up to obtain a mother roll. The aluminum hydroxide oxide contained in the inorganic filler porous layer was 95 mass%, and the thickness of the inorganic filler porous layer was 4.0 μm per side. The physical properties of the multilayer porous membrane B1-1 were measured and evaluated according to the methods described above, and the results are shown in Table 2.

[0213] [Production Example 1-2] (Formation of multilayer porous membrane B1-2) A multilayer porous membrane B1-2 was formed in the same manner as in Production Example 1-1, except that the inorganic filler material was changed as shown in Table 2. Table 2 shows the measurement and evaluation results of the multilayer porous membrane B1-2.

[0214] [Production Example 1-3] (Formation of multilayer porous membrane B1-3) A multilayer porous membrane B1-3 was formed in the same manner as in Production Example 1-1, except that the shape and average particle size D50 of the inorganic filler were changed as shown in Table 2. The measurement and evaluation results of the multilayer porous membrane B1-3 are shown in Table 2.

[0215] [Table 2]

[0216] <Synthesis of particulate polymer>

[0217] (Production Example A1) Synthesis of aqueous dispersion A1 (referred to as "raw polymer" in the table, and the same applies hereinafter) A reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer was charged with 70.4 parts by mass of ion-exchanged water, 0.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., referred to as "KH1025" in the tables; the same applies hereinafter), and 0.5 parts by mass of "Adeka Reasoap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, referred to as "SR1025" in the tables; the same applies hereinafter), and the internal temperature of the reaction vessel was raised to 80°C. Subsequently, while maintaining the internal temperature of the vessel at 80°C, 7.5 parts by mass of ammonium persulfate (2% aqueous solution) (referred to as "APS(aq)" in the tables; the same applies hereinafter) was added.

[0218] On the other hand, a mixture of 38.5 parts by mass of methyl methacrylate, 19.6 parts by mass of n-butyl acrylate, 31.9 parts by mass of 2-ethylhexyl acrylate, 0.1 parts by mass of methacrylic acid, 0.1 parts by mass of acrylic acid, 2 parts by mass of 2-hydroxyethyl methacrylate, 5 parts by mass of acrylamide, 2.8 parts by mass of GMA: glycidyl methacrylate, 0.7 parts by mass of trimethylolpropane triacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd.), 0.3 parts by mass of γ-methacryloxypropyltrimethoxysilane, 3 parts by mass of “Aqualon KH1025”, 3 parts by mass of “ADEKA REASOAP SR1025”, 0.05 parts by mass of sodium p-styrenesulfonate, 7.5 parts by mass of ammonium persulfate (2% aqueous solution), and 52 parts by mass of ion-exchanged water was mixed for 5 minutes using a homomixer to prepare an emulsion.

[0219] The resulting emulsion was added dropwise from the dropping tank to the reaction vessel. The addition began 5 minutes after the addition of the aqueous ammonium persulfate solution to the reaction vessel, and the entire amount of the emulsion was added dropwise over 150 minutes. During the addition of the emulsion, the temperature inside the vessel was maintained at 80°C.

[0220] After the emulsion was added dropwise, the internal temperature of the reaction vessel was maintained at 80°C for 90 minutes, and then cooled to room temperature to obtain an emulsion. The pH of the resulting emulsion was adjusted to 9.0 using an aqueous ammonium hydroxide solution (25% aqueous solution), yielding a copolymer latex with a concentration of 40% by mass (raw polymer A1). The resulting raw polymer (aqueous dispersion) A1 was evaluated using the methods described above. The results are shown in Table 3.

[0221] (Production Examples A2 to A12) Synthesis of Water Dispersions A2 to A12 Copolymer latexes (raw polymers A2 to A12) were obtained in the same manner as in the synthesis of raw polymer (aqueous dispersion) A1, except that the compositions of the monomers and other raw materials were changed as shown in Table 3 or Table 4, respectively. The obtained raw polymers (aqueous dispersions) A2 to A12 were evaluated by the methods described above. The obtained results are shown in Table 3 or Table 4.

[0222] [Table 3]

[0223] [Table 4]

[0224] The abbreviations for the raw material names in Tables 3 and 4 have the following meanings: <Emulsifier> KH1025: "Aqualon KH1025" registered trademark, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., 25% aqueous solution SR1025: "ADEKA REASOAP SR1025" registered trademark, manufactured by ADEKA Corporation, 25% aqueous solution NaSS: Sodium p-styrenesulfonate <Initiator> APS: Ammonium persulfate (2% aqueous solution) <Monomer> ((Meth)acrylic acid monomer) MAA: methacrylic acid AA: acrylic acid ((Meth)acrylic acid ester) MMA: methyl methacrylate BA: n-butyl acrylate EHA: 2-ethylhexyl acrylate CHMA: Cyclohexyl methacrylate (aromatic vinyl compound monomer) St: styrene (nitrile group-containing monomer) AN: Acrylonitrile (Other functional group-containing monomers) HEMA: 2-hydroxyethyl methacrylate AM: acrylamide (Crosslinking monomer) GMA: Glycidyl methacrylate A-TMPT: Trimethylolpropane triacrylate AcSi: γ-methacryloxypropyltrimethoxysilane

[0225] Example 1 A thermoplastic polymer-containing coating solution (5% solids by mass) was prepared by uniformly dispersing 10 parts by mass of aqueous dispersion A1 and 90 parts by mass of aqueous dispersion A2 in water. A polyoxyethylene alkyl ether surfactant, a polyether surfactant, was added as a surfactant to the coating solution at 0.005% by mass. Furthermore, carboxymethyl cellulose was added as a thickener to the coating solution at 1% by mass, and the viscosity of the coating solution was adjusted to 30 mPa·s.

[0226] Then, a gravure coater was used to coat the thermoplastic polymer at a coating amount of 0.15 g / m 2 The coating solution was applied to both sides of the multilayer porous membrane B1-1. At this time, the coverage area ratio of the thermoplastic polymer to one side of the polyolefin porous substrate B1 was 20%, and the coating shape was dot-like. After that, the coating solution after application was dried at 40 ° C to remove water, and a separator was obtained, which had an inorganic filler porous layer and a thermoplastic polymer layer thereon on one side of the polyolefin porous substrate B1, and a thermoplastic polymer layer on the other side of B1.

[0227] <Examples 2 to 21> As shown in Table 5, separators for power storage devices were produced in the same manner as in Example 1, except that the composition of the thermoplastic polymer-containing coating liquid, the conditions for forming the thermoplastic polymer-containing layer, the multilayer porous membrane, and the separator properties were changed. In Example 7, the thermoplastic polymer-containing coating liquid was applied to the entire surface of the multilayer porous membrane B1-1 so that 50% of the surface opposite the inorganic filler porous layer was covered with the thermoplastic polymer-containing layer, and therefore the coating shape in Table 5 is shown as "uniformly dispersed." In addition, in Examples 18 and 19, the thermoplastic polymer-containing coating liquid was applied to both surfaces of polyolefin porous substrates B1 and B2, respectively, without using a multilayer porous membrane.

[0228] <Comparative Examples 1 to 3, Examples 22 to 25> As shown in Table 5, separators for power storage devices were produced in the same manner as in Example 1, except that the composition of the thermoplastic polymer-containing coating liquid, the conditions for forming the thermoplastic polymer-containing layer, the multilayer porous membrane, the separator physical properties, etc. were changed. In Example 23, the thermoplastic polymer-containing coating liquid was applied in a solid manner so that 50% of the surface of the multilayer porous membrane B1-1 opposite to the inorganic filler porous layer was covered with the thermoplastic polymer-containing layer, and therefore the coating shape in Table 5 is shown as "uniformly dispersed".

[0229] The thermoplastic polymer-containing coating solution, thermoplastic polymer-containing layer, separator, and battery formed in the examples and comparative examples were evaluated by the methods described above. The evaluation results are shown in Table 5.

[0230] [Table 5-1]

[0231] [Table 5-2]

[0232] [Table 5-3]

[0233]

Table 5-4

[0234]

Table 5-5

[0235]

Table 5-6

Claims

1. A separator for an electricity storage device comprising: a substrate; and a thermoplastic polymer-containing layer formed on at least one surface of the substrate, the thermoplastic polymer-containing layer containing a thermoplastic polymer, the thermoplastic polymer is a water-insoluble particulate thermoplastic polymer and includes a copolymer having, as monomer units, an aromatic vinyl compound monomer and a nitrile group-containing monomer; a proportion of the aromatic vinyl compound monomer in the water-insoluble particulate thermoplastic polymer is 10% by mass or more and 30% by mass or less, and a proportion of the nitrile group-containing monomer in the water-insoluble particulate thermoplastic polymer is 10% by mass or more and 60% by mass or less, The thermoplastic polymer has the following formula: T10-T90<10 {wherein T90 and T10 are defined as follows: The thermoplastic polymer was stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 90%, and then the thermoplastic polymer was sealed in an aluminum hermetic pan. The glass transition temperature (°C) measured by DSC (differential scanning calorimetry) was defined as T90. The thermoplastic polymer is stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then the thermoplastic polymer is sealed in an aluminum hermetic pan and the glass transition temperature (°C) measured by DSC is defined as T10. and The separator for an electricity storage device has the following formula: B90 / B10<7 {wherein B90 and B10 are defined as follows: Two of the separators for an electricity storage device were prepared and stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 90%, and then one surface (A) of each of the separators for an electricity storage device was laminated with the other surface (A) of each separator to form a laminate (A-A). ＲＨ９０ A laminate (A-B) formed by laminating the surface (A) and the surface (B) opposite thereto. ＲＨ９０ , and a laminate (B-B) formed by laminating the surfaces (B) together ＲＨ９０ Each laminate was pressed for 2 minutes under conditions of a temperature of 40°C and a pressure of 1 MPa, and the maximum peel strength (N / m) of all the laminates was measured individually, and the maximum value was designated as B90; Two of the separators for an electricity storage device were prepared and stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then a laminate (A-A) was formed by laminating one surface (A) of the separator for an electricity storage device with the surface (A) of the separator for an electricity storage device. ＲＨ１０ A laminate (A-B) formed by laminating the surface (A) and the surface (B) opposite thereto. ＲＨ１０ , and a laminate (B-B) formed by laminating the surfaces (B) together ＲＨ１０ Each laminate was pressed for 2 minutes at a temperature of 40°C and a pressure of 1 MPa. The maximum peel strength (N / m) of all the laminates was measured individually, and the value was designated as B10. A separator for an electricity storage device that satisfies the relationship expressed by the following formula:

2. The separator for an electricity storage device has the following configuration: (1) the substrate and the thermoplastic polymer-containing layer formed on one side of the substrate; (2) the substrate and the thermoplastic polymer-containing layers formed on both sides of the substrate; (3) the substrate, an inorganic coating layer formed on one side of the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; and (4) the substrate, an inorganic coating layer formed on one side of the substrate, the thermoplastic polymer-containing layer formed on the inorganic coating layer on the side opposite to the substrate, and the thermoplastic polymer-containing layer formed on the other side of the substrate; The separator for an electricity storage device according to claim 1 , comprising at least one of the following:

3. The separator for an electricity storage device according to claim 1 or 2, wherein the B90 is less than 10 N / m.

4. A separator for an electricity storage device comprising: a substrate; and a thermoplastic polymer-containing layer that contains a thermoplastic polymer and is formed on at least a portion of at least one surface of the substrate, the thermoplastic polymer is a water-insoluble particulate thermoplastic polymer and includes a copolymer having, as monomer units, an aromatic vinyl compound monomer and a nitrile group-containing monomer; a proportion of the aromatic vinyl compound monomer in the water-insoluble particulate thermoplastic polymer is 10% by mass or more and 30% by mass or less, and a proportion of the nitrile group-containing monomer in the water-insoluble particulate thermoplastic polymer is 10% by mass or more and 60% by mass or less; and The thermoplastic polymer has the following formula: T10-T90<10 {wherein T90 and T10 are defined as follows: The thermoplastic polymer was stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 90%, and then the thermoplastic polymer was sealed in an aluminum hermetic pan. The glass transition temperature (°C) measured by DSC (differential scanning calorimetry) was defined as T90. The thermoplastic polymer is stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then the thermoplastic polymer is sealed in an aluminum hermetic pan and the glass transition temperature (°C) measured by DSC is defined as T10. A separator for an electricity storage device that satisfies the relationship expressed by the following formula:

5. The separator for an electricity storage device according to any one of claims 1 to 4, wherein the T90 is 30°C or higher.

6. The separator for an electricity storage device is subjected to the following conditions: {Condition: The measurement value P10 is determined as follows: Two of the electricity storage device separators were prepared, and the electricity storage device separators were stored for one day in an environment of a temperature of 35°C and a relative humidity (RH) of 10%, and then one surface (A) of each of the electricity storage device separators was laminated with the other surface (A) of each of the electricity storage device separators to form a laminate (A-A). ＲＨ１０ A laminate (A-B) formed by laminating the surface (A) and the surface (B) opposite thereto. ＲＨ１０ , and a laminate (B-B) formed by laminating the surfaces (B) together ＲＨ１０ Each laminate is pressed for 5 seconds at a temperature of 90°C and a pressure of 1 MPa. The maximum peel strength of all the laminates measured individually is defined as P10 (N / m). The separator for an electricity storage device according to any one of claims 1 to 5, wherein a measured value P10 measured by

7. The thermoplastic polymer has a mass swelling degree with respect to an electrolytic solution (volume ratio of ethylene carbonate (EC) / diethyl carbonate (DEC) = 2 / 3) of 2 times or more and less than 7 times. The separator for an electricity storage device according to any one of claims 1 to 6.

8. 8. The separator for an electricity storage device according to claim 1, wherein the coverage area ratio of the thermoplastic polymer to the substrate is 5% or more and 70% or less.

9. 9. The power storage device separator according to claim 1, wherein the thermoplastic polymer comprises a copolymer containing a monomer unit of a (meth)acrylic acid ester monomer.

10. the thermoplastic polymer has at least two glass transition temperatures; At least one of the glass transition temperatures is in a region below 20°C; and The separator for an electricity storage device according to any one of claims 1 to 9, wherein at least one of the glass transition temperatures is in a range of 20°C or higher.

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