JP2021184378A - Porous film, separator for secondary battery, and secondary battery - Google Patents

Abstract

To provide a porous film having excellent thermal dimensional stability and adhesiveness to an electrode and having excellent battery characteristics at low cost.SOLUTION: A porous film includes a porous base, and a porous layer containing inorganic particles and an organic resin on at least one surface of the porous base, and when an inner layer, an intermediate layer, and an outer layer are used, (a) the content α of the organic resin present in the outer layer is 30% or more and 60% or less, (b) the content β of the organic resin present in the intermediate layer is 10% or more and 25% or less, and (c) the content γ of the organic resin present in the inner layer is 30% or more and 60% or less for the content of all organic resins.SELECTED DRAWING: None

Description

The present invention relates to a porous film, a separator for a secondary battery and a secondary battery.

Secondary batteries such as lithium-ion batteries are used in automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, and are portable such as smartphones, tablets, mobile phones, laptop computers, digital cameras, digital video cameras, and portable game machines. It is widely used in digital devices, electric tools, electric motorcycles, electric assist assisted bicycles, etc.

In a lithium ion battery, generally, a separator for a secondary battery and an electrolyte are interposed between a positive electrode in which a positive electrode active material is laminated on a positive electrode current collector and a negative electrode in which a negative electrode active material is laminated on a negative electrode current collector. Has a configuration.

A polyolefin-based porous substrate is used as the separator for the secondary battery. The characteristics required for a separator for a secondary battery include the characteristic that an electrolytic solution is contained in the porous structure to enable ion transfer, and the porous structure is closed by melting with heat when the lithium ion battery generates abnormal heat. The shutdown characteristic is that the discharge is stopped by stopping the ion movement.

In addition, with the increase in capacity and output of secondary batteries, high safety is required for the separator for secondary batteries, and the positive electrode and negative electrode generated by the thermal shrinkage of the separator for secondary batteries at high temperatures. Thermal dimensional stability is required to prevent a short circuit due to contact with the battery.

Further, in the manufacturing process of the secondary battery, in order to maintain the laminated body structure when transporting the laminated body in which the positive electrode, the separator and the negative electrode are laminated, or in order to maintain the laminated body structure, or to form the wound laminated body of the positive electrode, the separator and the negative electrode into a cylindrical shape. , When inserting into a can such as a square type, the laminate is hot-pressed before insertion, but in order to prevent the shape from collapsing at that time, or by hot-pressing the laminate, more laminates can be obtained. Adhesion of the separator and electrode before impregnation with the electrolytic solution to put the body in a can to increase the energy density, and also to prevent the shape from deforming after being inserted into the exterior material in the laminated mold. Sex is required.

On the other hand, lithium-ion batteries are also required to have excellent battery characteristics such as high output and long life, and are required to exhibit good durability of battery characteristics without deteriorating high output characteristics. Has been done.
Further, it is required to provide a separator for a secondary battery satisfying the above characteristics at a low cost.

In response to these demands, Patent Document 1 aims to achieve both adhesiveness to electrodes and blocking resistance by laminating an adhesive layer formed on a heat-resistant layer. Further, in Patent Document 2, the adhesiveness to the electrode is enhanced by satisfying a specific relationship between the particle size of the particulate polymer and the particle size of the inorganic particles. However, the blocking resistance test described in Patent Documents 1 and 2 has insufficient test conditions, and the technique described in Patent Document 1 has insufficient blocking resistance under appropriate test conditions, and the blocking resistance is insufficient. If the above is improved, the adhesiveness with the electrode becomes insufficient. In addition, the adhesive layer swells by performing hot pressing, the porosity decreases by filling the voids of the electrode active material and the separator, and the ion transport rate decreases, so that the battery characteristics also deteriorate. Further, since Patent Document 1 is a high-cost secondary battery separator for coating an adhesive layer on a heat-resistant layer, the techniques described in Patent Documents 1 and 2 have thermal dimensional stability and adhesion. It is difficult to achieve both properties and battery characteristics at low cost.

Japanese Patent No. 6191597 International Publication No. 2018/034094

As described above, the adhesiveness between the electrode and the separator is required by the hot pressing process in the manufacturing process of the secondary battery. In addition, excellent battery characteristics are also required, and it is necessary to achieve both thermal dimensional stability, adhesiveness, high output characteristics, and long battery life at low cost.

In view of the above problems, an object of the present invention is to provide a porous film having excellent thermal dimensional stability and adhesiveness to an electrode, and having excellent discharge characteristics and cycle characteristics at low cost.

Therefore, the present inventors have made extensive studies in order to provide a low-cost porous film having excellent thermal dimensional stability, adhesiveness to electrodes, and excellent battery characteristics.
In order to solve the above problems, the porous film of the present invention has the following constitution.

(1) A porous base material and a porous layer containing inorganic particles and an organic resin are provided on at least one surface of the porous base material, and the porous layer is divided into three equal parts in the thickness direction, respectively. A porous film satisfying the following (a) to (c) when the inner layer in contact with the porous substrate, the intermediate layer adjacent to the inner layer, and the outer layer adjacent to the intermediate layer are used.
(A) The content α of the organic resin present in the outer layer is 30% or more and 60% or less of the content of all the organic resins.
(B) The content β of the organic resin present in the intermediate layer is 10% or more and 25% or less of the content of all the organic resins.
(C) The content γ of the organic resin present in the inner layer is 30% or more and 60% or less of the content of all the organic resins.
(2) The porous film according to (1), wherein the organic resin is organic resin particles.
(3) The organic resin is an organic resin A having a mixture containing a polymer containing a fluorine-containing (meth) acrylate monomer or a copolymer containing a fluorine-containing (meth) acrylate monomer. The porous film according to 1) or (2).
(4) The porous film according to (3), wherein the organic resin further contains a binder.
(5) The binder is polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone, polyetherketone, polycarbonate, polyacetal, polyvinyl. The porous film according to (4), which is at least one binder selected from the group consisting of alcohol, polyethylene glycol, cellulose ether, acrylic resin, polyethylene, polypropylene, polystyrene, and urethane.
(6) The porous film according to (4) or (5), wherein the binder is an acrylic resin.
(7) The organic resin A is a mixture containing a polymer composed of a fluorine-containing (meth) acrylate monomer and a polymer composed of a (meth) acrylate monomer having a hydroxyl group, or a fluorine-containing (meth) acrylate simple substance. It has a copolymer containing a (meth) acrylate monomer having a weight and a hydroxyl group, and the content of the (meth) acrylate monomer having a hydroxyl group is 100% by mass of all the constituents of the organic resin particles. The porous film according to (3), wherein the amount is 1% by mass or more and 30% by mass or less.
(8) The porous film according to (7), wherein the (meth) acrylate monomer having a hydroxyl group has a glass transition temperature of −100 ° C. or higher and 0 ° C. or lower of a homopolymer composed of the monomer.
(9) The organic resin A further contains a monomer having two or more reactive groups per molecule, and a single amount having two or more reactive groups per molecule contained in the organic resin A. The porous film according to (7) or (8), wherein the content of the body is 1% by mass or more and 10% by mass or less.
(10) The porous film according to (9), wherein the monomer having two or more reactive groups per molecule is an alkylene glycol di (meth) acrylate or a urethane di (meth) acrylate.
(11) The porous film according to any one of (1) to (10), wherein the organic resin contains an organic resin B that does not contain fluorine.
(12) The content of the inorganic particles contained in the porous layer is 60% by mass or more and 95% by mass or less when all the constituents of the porous layer are 100% by mass, (1) to (11). The porous film according to any one of.
(13) A separator for a secondary battery using the porous film according to any one of (1) to (12).
(14) A secondary battery using the separator for a secondary battery according to (13).

According to the porous film of the present invention, a porous base material and a porous layer containing inorganic particles and an organic resin are provided on at least one surface of the porous base material, and the porous layer is formed in the thickness direction 3 When the inner layer, the intermediate layer, and the outer layer are equally divided, (a) the content α of the organic resin present in the outer layer is 30% or more and 60% or less with respect to the total content of the organic resin, (b). Excellent thermal dimensional stability by satisfying the content β of the organic resin present in the intermediate layer is 10% or more and 25% or less, and (c) the content γ of the organic resin existing in the inner layer is 30% or more and 60% or less. A porous film can be obtained that can provide a secondary battery having properties and adhesiveness to an electrode and having excellent battery characteristics at low cost.

The porous film of the present invention is composed of a porous base material and a porous layer, and a porous layer containing inorganic particles and an organic resin having adhesiveness to an electrode is laminated on at least one surface of the porous base material. It is a porous film.
Hereinafter, the present invention will be described in detail.

As used herein, the term "polymer composed of a fluorine-containing (meth) acrylate monomer" refers to a homopolymer composed of a fluorine-containing (meth) acrylate monomer or a common weight containing a fluorine-containing (meth) acrylate monomer. It means coalescence. Further, the "organic resin" includes "organic resin A", and as "organic resin A", a homopolymer composed of a fluorine-containing (meth) acrylate monomer and a homopolymer composed of a (meth) acrylate monomer having a hydroxyl group. , A homopolymer composed of monomers constituting a specific monomer group, and a copolymer composed of a fluorine-containing (meth) acrylate monomer and a (meth) acrylate monomer having a hydroxyl group.

[Porous layer]
The porous layer of this embodiment contains an organic resin composed of inorganic particles and an organic resin A. Further, the organic resin may optionally contain a binder and an organic resin B in addition to the organic resin A.

The porous layer is divided into three equal parts in the thickness direction, and when the inner layer is in contact with the porous substrate, the intermediate layer is adjacent to the inner layer, and the outer layer is adjacent to the intermediate layer, the following (a) to (c) are used. ), The porous film can obtain high adhesiveness to an electrode, excellent thermal dimensional stability, and battery characteristics.
(A) When the content of the organic resin existing in the outer layer is α, the value of α is 30% or more and 60% or less when the content of all the organic resins constituting the porous layer is 100%. The α is preferably 35% or more and 55% or less, and more preferably 40% or more and 50% or less. If the value of α is less than 30%, sufficient adhesion to the electrode cannot be obtained. On the other hand, when the value of α is larger than 60%, the adhesive strength between the porous layer and the porous substrate is lowered, and peeling may occur when the porous layer is adhered to the electrode.
(B) When the content of the organic resin present in the intermediate layer is β, the value of β is 10% or more and 25% or less when the content of all the organic resins constituting the porous layer is 100%. The β is preferably 12% or more and 22% or less, and more preferably 15% or more and 20% or less. If the value of β is less than 10%, the ion permeability may decrease and the battery characteristics may decrease. On the other hand, if it exceeds 25%, the α value decreases, so that sufficient adhesiveness to the electrode cannot be obtained, and the γ value, which will be described later, decreases, so that the adhesive strength between the porous layer and the porous substrate decreases. However, peeling may occur when it is adhered to the electrode.
(C) When the content of the organic resin existing in the inner layer is γ, the value of γ is 30% or more and 60% or less when the content of all the organic resins constituting the porous layer is 100%. The γ is preferably 35% or more and 55% or less, and more preferably 40% or more and 50% or less. When the value of γ is less than 30%, the adhesive strength between the porous layer and the porous substrate is lowered, and peeling may occur when the porous layer is adhered to the electrode. On the other hand, when the value of γ is larger than 60%, the value of α decreases and sufficient adhesion to the electrode cannot be obtained.

Of the outer layer, intermediate layer, and inner layer obtained by dividing the porous layer into three equal parts in the thickness direction, the inner layer is the layer including the interface between the porous base material and the porous layer, and the outer layer is the most of the porous layer. It is a surface and a layer in contact with an electrode. Further, the intermediate layer is a layer interposed between the inner layer and the outer layer.

For the organic resin contents α, β and γ in the outer layer, intermediate layer and inner layer, for example, the cross section of the porous layer is observed with a cross section SEM image and a cross section SEM-EDX image of a carbon element by an electrolytic radiation scanning electron microscope. Can be determined by doing. Based on the cross-sectional SEM image, the porous layer is divided into three equal parts in the thickness direction, and each region of the outer layer, the intermediate layer and the inner layer is determined. The cross-sectional SEM image and the cross-sectional SEM-EDX image of the carbon element are superimposed, and the area of the carbon element caused by the organic resin contained in each region of the outer layer, the intermediate layer and the inner layer is analyzed by image analysis software. The total area of the carbon elements in the outer layer, the intermediate layer, and the inner layer obtained is 100% of the total of the organic resins present in the porous layer, and the area ratio of the carbon elements in the outer layer, the intermediate layer, and the inner layer is calculated. However, the content of the organic resin can be α, β and γ.

(Organic resin)
(1) Organic resin A
As used herein, the porous layer contains an organic resin. The form of the organic resin is not particularly limited, but it is preferably organic resin particles. By using organic resin particles, ion permeability is improved and battery characteristics are improved.

The organic resin contains the organic resin A. It is desirable that the organic resin A has a mixture containing a polymer composed of a fluorine-containing (meth) acrylate monomer or a copolymer containing a fluorine-containing (meth) acrylate monomer. As a result, the surface free energy of the organic resin A can be reduced, and when the coating liquid containing the organic resin A is applied to the porous substrate, the organic resin A can be unevenly distributed on the surface side. , The adhesiveness of the porous layer to the electrode can be improved. In the present invention, "(meth) acrylate" means acrylate and / or methacrylate.

The polymer composed of the fluorine-containing (meth) acrylate monomer contains a repeating unit obtained by polymerizing the fluorine-containing (meth) acrylate.
Examples of the fluorine-containing (meth) acrylate monomer include 2,2,2-trifluoroethyl (meth) acrylate, 2,2,3,3,3-pentafluoropropyl (meth) acrylate, and 2- (perfluorobutyl). ) Ethyl (meth) acrylate, 3- (perfluorobutyl) -2-hydroxypropyl (meth) acrylate, 2- (perfluorohexyl) ethyl (meth) acrylate, 3-perfluorohexyl-2-hydroxypropyl (meth) Acrylate, 3- (Perfluoro-3-methylbutyl) -2-hydroxypropyl (meth) acrylate, 1H, 1H, 3H-tetrafluoropropyl (meth) acrylate, 1H, 1H, 5H-octafluoropentyl (meth) acrylate, 1H, 1H, 7H-dodecafluoroheptyl (meth) acrylate, 1H-1- (trifluoromethyl) trifluoroethyl (meth) acrylate, 1H, 1H, 3H-hexafluorobutyl (meth) acrylate, 1, 2, 2 , 2-Tetrafluoro-1- (trifluoromethyl) ethyl (meth) acrylate, 2- (perfluorooctyl) ethyl (meth) acrylate and the like. As the fluorine-containing (meth) acrylate monomer, one type may be used alone, or two or more types may be used in combination at any ratio.

The content of the fluorine-containing (meth) acrylate monomer contained in the organic resin A is preferably larger than 20% by mass, more preferably 22% by mass, when all the constituents of the organic resin A are 100% by mass. As mentioned above, it is more preferably 25% by mass or more, and further preferably 30% by mass or more. Further, it is preferably 80% by mass or less, more preferably 70% by mass or less, further preferably 60% by mass or less, still more preferably 50% by mass or less, particularly preferably 40% by mass or less, and most preferably 35% by mass or less. .. Within the above range, sufficient adhesion to the electrode can be obtained.

The content of the fluorine-containing (meth) acrylate monomer contained in the organic resin A can be measured by using a known method. For example, first, the porous layer is desorbed from the porous film using an organic solvent such as water and alcohol, and the organic solvent such as water and alcohol is sufficiently dried to obtain a constituent component contained in the porous layer. An organic solvent that dissolves the organic resin component is added to the obtained constituent component to dissolve only the organic resin component. Subsequently, the organic solvent is dried from the solution in which the organic resin component is dissolved, and only the organic resin component is extracted. ^{Nuclear magnetic resonance (1} H-NMR, ¹⁹ F-NMR, ¹³ C-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescence using the obtained organic resin components. It can be calculated from the signal intensity indicating a fluorine-containing (meth) acrylate monomer by an X-ray analysis method (EDX), an elemental analysis method, a thermal decomposition gas chromatograph mass spectrometer (thermal decomposition GC / MS), or the like. In particular, after confirming the presence or absence of a fluorine-containing (meth) acrylate monomer by thermal decomposition GC / MS, ¹³ C-NMR (solid NMR sample tube is filled with the organic resin component and an appropriate amount of solvent (deuterated chloroform). , Measured by the DD / MAS method after standing overnight), the content of the fluorine-containing (meth) acrylate monomer can be determined.

The number of fluorine atoms in the fluorine-containing (meth) acrylate constituting the fluorine-containing (meth) acrylate monomer is preferably 3 or more and 13 or less. It is more preferably 3 or more and 11 or less, and further preferably 3 or more and 9 or less. Within the above range, it is possible to achieve both low surface free energy and coatability of the organic resin A. When the number of fluorine atoms is 3 or more, the surface free energy of the organic resin A is sufficiently reduced, and the adhesiveness with the electrode is sufficient. Further, when the number of fluorine atoms is 13 or less, the coatability on the porous substrate is guaranteed and the productivity is improved.

The number of fluorine atoms in the fluorine-containing (meth) acrylate can be measured by using a known method. For example, first, the porous layer is desorbed from the porous film using an organic solvent such as water and alcohol, and the organic solvent such as water and alcohol is sufficiently dried to obtain a constituent component contained in the porous layer. An organic solvent that dissolves the organic resin component is added to the obtained constituent component to dissolve only the organic resin component, and the particles are separated from the inorganic particles. Subsequently, the organic solvent is dried from the solution in which the organic resin component is dissolved, and only the organic resin component is extracted. ^{Nuclear magnetic resonance (1} H-NMR, ¹⁹ F-NMR, ¹³ C-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescence using the obtained organic resin components. It can be calculated from the signal intensity indicating a fluorine-containing (meth) acrylate monomer by an X-ray analysis method (EDX), an elemental analysis method, a thermal decomposition gas chromatograph mass spectrometer (thermal decomposition GC / MS), or the like. Of these, pyrolysis GC / MS is particularly useful.

The organic resin A is a mixture containing a polymer composed of a fluorine-containing (meth) acrylate monomer and a polymer composed of a (meth) acrylate monomer having a hydroxyl group, or a fluorine-containing (meth) acrylate monomer and a hydroxyl group. It is preferable to contain a copolymer containing a (meth) acrylate monomer having the above. By containing a mixture containing a polymer composed of a (meth) acrylate monomer having a hydroxyl group, or a copolymer containing a fluorine-containing (meth) acrylate monomer and a (meth) acrylate monomer having a hydroxyl group. The glass transition temperature of the organic resin A can be adjusted to obtain organic resin particles having excellent adhesion to the electrode.

The content of the (meth) acrylate monomer having a hydroxyl group is preferably in the range of 1% by mass or more and 30% by mass or less when all the constituents of the organic resin A are 100% by mass. It is more preferably larger than 2% by mass, further preferably 4% by mass or more, further preferably 6% by mass or more, particularly preferably 10% by mass or more, particularly preferably more than 10% by mass, and most preferably 12% by mass or more. .. Further, it is more preferably 25% by mass or less, still more preferably 20% by mass or less. By setting the content of the (meth) acrylate monomer having a hydroxyl group contained in the organic resin A to 1% by mass or more, sufficient adhesion to the electrode can be obtained, and by improving the affinity with the electrolytic solution, the battery can be used. The characteristics can be improved, and the thermal dimensional stability can be improved by improving the adhesiveness with the porous substrate and the inorganic particles. Further, particles having excellent stability after particle formation can be obtained. Further, when the content is 30% by mass or less, particles having excellent stability after particle formation can be obtained, side reactions in the secondary battery can be suppressed, and excellent battery characteristics can be imparted.

The content of the (meth) acrylate monomer having a hydroxyl group contained in the organic resin A can be measured by using a known method. For example, first, the porous layer is desorbed from the porous film using an organic solvent such as water and alcohol, and the organic solvent such as water and alcohol is sufficiently dried to obtain a constituent component contained in the porous layer. An organic solvent that dissolves the organic resin component is added to the obtained constituent component to dissolve only the organic resin component. Subsequently, the organic solvent is dried from the solution in which the organic resin component is dissolved, and only the organic resin component is extracted. ^{Nuclear magnetic resonance (1} H-NMR, ¹⁹ F-NMR, ¹³ C-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescence using the obtained organic resin components. It can be calculated from the signal intensity indicating a (meth) acrylate monomer having a hydroxyl group by X-ray analysis method (EDX), elemental analysis method, thermal decomposition gas chromatograph mass spectrometer (thermal decomposition GC / MS), or the like. .. In particular, after confirming the presence or absence of a (meth) acrylate monomer having a hydroxyl group by thermal decomposition GC / MS, ¹³ C-NMR (solid NMR sample tube is filled with the organic resin component and an appropriate amount of solvent (deuterated chloroform). Then, after allowing to stand overnight, the content of the (meth) acrylate monomer having a hydroxyl group can be determined by the DD / MAS method).

Examples of the (meth) acrylate monomer having a hydroxyl group include hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 6-hydroxyhexyl methacrylate, and 7-hydroxy. Examples thereof include methacrylic acid esters such as hepticyl methacrylate and 8-hydroxyoctyl methacrylate. As the (meth) acrylate monomer having a hydroxyl group, one type may be used alone, or two or more types may be used in combination at any ratio. In particular, 2-hydroxyethyl acrylate, 4-hydroxybutyl acrylate, and 2-hydroxypropyl acrylate are preferable.

In the (meth) acrylate monomer having a hydroxyl group, the glass transition temperature of the homopolymer composed of the monomer is preferably −100 ° C. or higher, more preferably −70 ° C. or higher, still more preferably −50 ° C. or higher. Within the above range, sufficient adhesion to the electrode can be obtained. The glass transition temperature (Tg) of the homopolymer composed of the (meth) acrylic acid ester monomer (C) having a hydroxyl group is preferably 0 ° C. or lower, more preferably -10 ° C. or lower, still more preferably -20 ° C. or lower. be. Here, the glass transition temperature is the intermediate point glass transition temperature measured by differential scanning calorimetry (DSC) according to JIS K7121: 2012. The midpoint glass transition temperature is the temperature at the intersection of a straight line equidistant from the extended straight line of each baseline in the vertical direction and the curve of the stepwise change portion of the glass transition.

The organic resin A preferably further contains a monomer having two or more reactive groups per molecule. A polymer consisting of a monomer having two or more reactive groups per molecule or a copolymer consisting of a fluorine-containing (meth) acrylate monomer and a monomer having two or more reactive groups per molecule. May be contained. A polymer consisting of a monomer having two or more reactive groups per molecule or a copolymer consisting of a fluorine-containing (meth) acrylate monomer and a monomer having two or more reactive groups per molecule. By containing the above, polymer particles having excellent electrolytic solution resistance with suppressed swelling property to the electrolytic solution and excellent adhesiveness to the electrode can be obtained. "Polymer composed of a monomer having two or more reactive groups per molecule" is a homopolymer composed of a monomer having two or more reactive groups per molecule or two or more per molecule. Refers to a copolymer containing a monomer having a reactive group of.

The content of the monomer having two or more reactive groups per molecule is preferably 1% by mass or more and 10% by mass or less when the total amount of the organic resin A is 100% by mass. It is more preferably 3% by mass or more, further preferably 5% by mass or more, and particularly preferably 6% by mass or more. Further, it is more preferably 9% by mass or less, still more preferably 8% by mass or less. By using 1% by mass or more of the monomers having two or more reactive groups per molecule, sufficient adhesion to the electrode can be obtained, and by suppressing excessive swelling to the electrolytic solution, the battery can be used. The characteristics can be improved. Further, by setting the content to 10% by mass or less, polymer particles having excellent stability can be obtained.

As the polymer composed of a monomer having two or more reactive groups per molecule, a monomer capable of forming a crosslinked structure at the time of polymerization can be used. As the monomer having two or more reactive groups per molecule, it is particularly preferable to use a (meth) acrylate monomer having two or more reactive groups per molecule, and it is preferable to use an alkylene glycol di (meth). It is more preferable to use acrylate and urethane di (meth) acrylate.

More specifically, a monomer having two or more reactive groups per molecule is a monofunctional monomer having a thermally crosslinkable crosslinkable group and one or more olefinic double bonds per molecule. Examples include the body and polyfunctional monomers having two or more olefinic double bonds per molecule. The number of olefinic double bonds may be one per molecule or two or more. Examples of thermally crosslinkable crosslinkable groups include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof.

Examples of the epoxy group which is a thermally crosslinkable group and the monofunctional monomer having one or more olefinic double bonds per molecule include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and the like. Unsaturated glycidyl ethers such as o-allylphenylglycidyl ethers; butadiene monoepoxides, chloroprene monoepoxides, 4,5-epoxide-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5, Diene or polyene monoepoxides such as 9-cyclododecadiene; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl. Aacrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, 4-methyl-3-cyclohexene carboxylic acid. Examples thereof include glycidyl esters of unsaturated carboxylic acids such as glycidyl esters of acids.

Examples of monofunctional monomers having a thermally crosslinkable crosslinkable N-methylolamide group and one or more olefinic double bonds per molecule are methylols such as N-methylol (meth) acrylamide. Examples include (meth) acrylamides having a group.

Examples of monofunctional monomers having an oxazoline group, which is a thermally crosslinkable group, and one or more olefinic double bonds per molecule are 2-vinyl-2-oxazoline and 2-vinyl-4. -Methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl- 2-Oxazoline and 2-isopropenyl-5-ethyl-2-oxazoline can be mentioned.

Examples of polyfunctional monomers having two or more olefinic double bonds per molecule are allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, and triethylene glycol di (meth). ) Acrylate, Tetraethylene glycol di (meth) acrylate, Trimethylol propan-tri (meth) acrylate, Dipropylene glycol diallyl ether, Polyglycol diallyl ether, Triethylene glycol divinyl ether, Hydroquinone diallyl ether, Tetraallyl oxyethane, Trimethylol Examples thereof include propane-diallyl ether, allyl or vinyl ether of other polyfunctional alcohols, triallylamine, methylenebisacrylamide, divinylbenzene, alkylene glycol di (meth) acrylate, and urethane di (meth) acrylate.

For a monomer having two or more reactive groups per molecule, the glass transition temperature of the homopolymer composed of the monomer is preferably −50 ° C. or higher and 0 ° C. or lower. More preferably, it is −45 ° C. or higher and 0 ° C. or lower. Here, the glass transition temperature is the intermediate point glass transition temperature measured by differential scanning calorimetry (DSC) according to JIS K7121: 2012. The midpoint glass transition temperature is the temperature at the intersection of a straight line equidistant from the extended straight line of each baseline in the vertical direction and the curve of the stepwise change portion of the glass transition.

In the present invention, the polymer composed of a fluorine-containing (meth) acrylate monomer can include a polymer composed of a monomer arbitrarily selected from a specific monomer group. Further, the copolymer containing a fluorine-containing (meth) acrylate monomer may be a copolymer containing a monomer arbitrarily selected from a specific monomer group. By forming a copolymer containing a monomer selected from a specific monomer group, the surface free energy of the organic resin A and the glass transition temperature can be adjusted to predetermined conditions.

It is also possible to form a core-shell type in which a polymer composed of a monomer selected from a specific monomer group is used as a core and a copolymer containing a fluorine-containing (meth) acrylate monomer is formed as a shell around the polymer. .. The core-shell type in the present specification includes a type in which the core portion is completely covered by the shell portion and a type in which the core portion is partially covered and the core portion and the shell portion coexist.

Examples of the monomers constituting the specific monomer group include unsaturated carboxylic acid monomers, (meth) acrylate monomers, styrene-based monomers, olefin-based monomers, diene-based monomers, and amides. Examples include system monomers.
Examples of the monomers constituting these specific monomer groups include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, and n-butyl acrylate. Isobutyl acrylate, t-butyl acrylate, pentyl acrylate, neopentyl acrylate, isoamyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, dodecyl acrylate, 2-dimethylaminoethyl acrylate. , 2-Diethylaminoethyl acrylate, 2-dipropylaminoethyl acrylate, 2-diphenylaminoethyl acrylate, 3- (N, N-dimethylamino) propyl acrylate, n-tetradecyl acrylate, stearyl acrylate, cyclohexyl acrylate and other acrylic acids. Esters; Methyl Methacrylate, Ethyl Methacrylate, n-propyl Methacrylate, Isopropyl Methacrylate, n-Butyl Methacrylate, t-Butyl Methacrylate, Isobutyl Methacrylate, t-Butyl Cyclohexyl Methacrylate, Pentyl Methacrylate, Neopentyl Methacrylate, Isoamyl Methacrylate, Hexyl Methacrylate, Heptyl Methacrylate , Octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, dodecyl methacrylate, 2-dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, 2-dipropylaminoethyl methacrylate, 2-diphenylaminoethyl methacrylate, 3 Examples thereof include methacrylic acid esters such as-(N, N-dimethylamino) propyl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate and cyclohexyl methacrylate. More preferably, isobornyl (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, cyclohexyl (meth) acrylate, benzyl (meth) acrylate, methyl (meth) acrylate, n-butyl (meth) acrylate. ) Acrylate and the like can be mentioned. As the monomer constituting a specific monomer group, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The content of the monomer selected from the specific monomer group contained in the organic resin A is preferably 20% by mass or more, more preferably 20% by mass, when all the constituents of the organic resin A are 100% by mass. It is 30% by mass or more, more preferably 40% by mass or more, and most preferably 50% by mass or more. Further, it is preferably 80% by mass or less. It is more preferably 75% by mass or less, further preferably 70% by mass or less, and most preferably 65% by mass or less. By setting the content of the specific monomer group contained in the organic resin A to 20% by mass or more, sufficient adhesiveness to the electrode can be obtained. Further, when the content is 80% by mass or less, the swelling property to the electrolytic solution can be suppressed, and excellent battery characteristics can be obtained.

Among the specific monomer group, at least one of the (meth) acrylate monomers has a (meth) acrylate having a cyclic hydrocarbon group of a monocyclic group for the purpose of reducing the particle fusion property at the time of producing the organic resin A. It is preferably a (meth) acrylate monomer unit substituted with a monomer or one or more alkyl groups. In the case of a (meth) acrylate monomer having a cyclic hydrocarbon group having a monocyclic group, the reduction in particle fusion property becomes remarkable, which is more preferable.

The content of the acrylate monomer having a cyclic hydrocarbon group of a monocyclic group and the methacrylate monomer having a cyclic hydrocarbon group of a monocyclic group contained in the organic resin A is the entire composition of the organic resin A. When the component is 100% by mass, it is preferably 20% by mass or more, more preferably 30% by mass or more, further preferably 40% by mass or more, and most preferably 50% by mass or more. Further, it is preferably 80% by mass or less, more preferably 75% by mass or less, further preferably 70% by mass or less, and most preferably 65% by mass or less. By setting the content of the (meth) acrylate monomer having a cyclic hydrocarbon group having a monocyclic group contained in the organic resin A to 20% by mass or more, sufficient adhesiveness to the electrode can be obtained. Further, when the content is 80% by mass or less, the swelling property to the electrolytic solution can be suppressed, and excellent battery characteristics can be obtained.

Further, for the purpose of adjusting the glass transition temperature to a predetermined temperature or improving the chemical resistance to the chain carbonate constituting the non-aqueous electrolyte solution of the secondary battery, styrene, α-methylstyrene, paramethylstyrene, t. -Organic resin A contains monomers such as styrene-based such as butylstyrene, chlorostyrene, chloromethylstyrene and hydroxymethylstyrene, olefin-based such as ethylene and propylene, diene-based such as butadiene and isoprene, and amide-based such as acrylamide. Can be included in. Of these, one type may be used alone, or two or more types may be contained in any combination at any ratio.

The polymerization method of the homopolymer composed of the fluorine-containing (meth) acrylate monomer forming the organic resin A and the copolymer containing the fluorine-containing (meth) acrylate monomer is not particularly limited, and is, for example, a solution polymerization method. , Suspension polymerization method, bulk polymerization method, emulsification polymerization method and the like may be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, living radical polymerization and the like may be used. The polymerization gives an aqueous solution in which the organic resin A is dispersed in an aqueous solvent. The aqueous solution thus obtained may be used as it is, or the organic resin A may be taken out from the aqueous solution and used. The organic resin preferably contains a monomer that arbitrarily constitutes a specific monomer group, and by using a copolymer, it is possible to suppress swelling property to the electrolytic solution and improve the adhesive strength. can.

At the time of polymerization, examples of the emulsifier include a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. Of these, one type may be used alone, or two or more types may be used in combination.

Examples of the cationic surfactant include alkylpyridinium chloride, alkyltrimethylammonium chloride, dialkyldimethylammonium chloride, alkyldimethylbenzylammonium chloride and the like.

Examples of the anionic surfactant include alkyl sulfate ester sodium salt, alkylbenzene sulfonic acid sodium salt, succinic acid dialkyl ester sulfonic acid sodium salt, alkyldiphenyl ether disulfonic acid sodium salt, polyoxyethylene alkyl ether sulfate sodium salt, and polyoxyethylene. Examples thereof include alkylphenyl ether sodium sulfate. Among these, sodium lauryl sulfate, sodium dodecylbenzene sulfonic acid salt, sodium polyoxyethylene alkyl ether sulfate, sodium lauryl sulfate and the like are preferable.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl aryl ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester and the like. Generally, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether and the like are used.

Examples of the amphoteric tenside include lauryl betaine, hydroxyethyl imidazoline sulfate sodium salt, imidazoline sulfonic acid sodium salt and the like.

Further, as an emulsifier, a fluorine-based surfactant such as perfluoroalkyl carboxylate, perfluoroalkyl sulfonate, perfluoroalkyl phosphate ester, perfluoroalkyl polyoxyethylene, perfluoroalkyl betaine, perfluoroalkoxyfluorocarboxylate ammonium, etc. Activators can also be used.

Furthermore, so-called reactive emulsifiers that can be copolymerized with fluorine-containing (meth) acrylate monomers, such as styrene sulfonic acid sodium salt, allylalkyl sulfonic acid sodium salt, polyoxyethylene alkyl allylphenyl ether ammonium sulfate salt, and polyoxyethylene alkyl. Allylphenyl ether and the like can be used, and it is particularly preferable to use 2- (1-allyl) -4-nonylphenoxypolyethylene glycol sulfate ammonium salt in combination with 2- (1-allyl) -4-nonylphenoxypolyethylene glycol. ..

The amount of the emulsifier used is preferably 0.05 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total amount of the monomers contained in the organic resin A.

As the polymerization initiator, a water-soluble polymerization initiator such as sodium persulfate, potassium persulfate, ammonium persulfate, or hydrogen peroxide, or a redox-based polymerization initiator that combines these water-soluble polymerization initiators and a reducing agent is used. can do. Among these, potassium persulfate and ammonium persulfate are preferable. Examples of the reducing agent include sodium pyrobisulfite, sodium hydrogen sulfite, sodium sulfite, sodium thiosulfate, L-ascorbic acid or a salt thereof, sodium formaldehyde sulfoxylate, ferrous sulfate, glucose and the like. Among these, L-ascorbic acid or a salt thereof is preferable.

The amount of the polymerization initiator used is preferably 0.1 part by mass or more and 3 parts by mass or less per 100 parts by mass of the total amount of the monomers contained in the organic resin A.

The organic resin A in the present specification preferably has a particle shape, and may be organic resin particles A. The organic resin particles A include those having a particle shape and those having a partially formed film and fused with surrounding particles and a binder. The shape is not particularly limited and may be spherical, polygonal, flat, fibrous or the like.

The average particle size of the organic resin particles A is preferably 0.01 μm or more. It is more preferably 0.082 μm or more, further preferably 0.10 μm or more, and most preferably 0.12 μm or more. Further, it is preferably 5 μm or less, more preferably 1 μm or less, still more preferably 0.5 μm or less, and most preferably 0.3 μm or less. By setting the average particle size to 0.01 μm or more, a porous structure is formed and the battery characteristics are improved. Further, when the thickness is 5 μm or less, the film thickness of the porous layer becomes appropriate, and deterioration of battery characteristics can be suppressed.

The average particle size of the organic resin particles A can be measured by using the following method. Using an electrolytic radiation scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.), the surface of the porous layer is placed on an image with a magnification of 30,000 and a porous layer composed of inorganic particles and organic resin particles. An EDX image of an element contained only in particles is obtained. The image size is 4.0 μm × 3.0 μm, the number of pixels is 1,280 pixels × 1,024 pixels, and the size of one pixel is 3.1 nm × 2.9 nm. In the obtained EDX image, particles other than the inorganic particles are referred to as the organic resin particles A of the present invention. When it cannot be visually distinguished, the organic resin particles A are those containing a fluorine element by elemental analysis. Draw a square or rectangle with the smallest area that completely surrounds one particle on the image, that is, draw a square or rectangle with the edges of the particle touching the four sides of the square or rectangle, and in the case of a square, one side. In the case of a length or a square, the length of the long side (major axis diameter) is used as the particle size, the particle size of each organic resin particle A on the image is measured, and the arithmetic average value is used as the average particle size. .. If 50 organic resin particles A are not observed in the captured images, a plurality of images are captured so that the total of all the organic resin particles A contained in the plurality of images is 50 or more. The organic resin particles A were measured, and the arithmetic mean value thereof was taken as the average particle size.

The organic resin A is preferably an organic resin that does not contain an inorganic component from the viewpoint of adhesiveness to the electrode. By using the organic resin A as the organic resin particles, it may be possible to impart stronger adhesiveness to the electrode.

The glass transition temperature of the organic resin A is preferably 20 ° C. or higher. It is more preferably 25 ° C. or higher, further preferably 30 ° C. or higher, and most preferably 35 ° C. or higher. Further, it is preferably 60 ° C. or lower, more preferably 55 ° C. or lower, still more preferably 50 ° C. or lower, and most preferably 45 ° C. or lower. By setting the glass transition temperature to 20 ° C. or higher, the swelling property to the electrolytic solution is suppressed and the battery characteristics are improved. Further, when the temperature is 60 ° C. or lower, the adhesiveness with the electrode becomes good. In order to keep the glass transition temperature in an appropriate range, it can be appropriately selected from a specific group of monomers.

(2) Binder The organic resin may contain a binder in addition to the organic resin A in order to bring the organic resins into close contact with each other and in order to bring the organic resin and the inorganic particles into close contact with each other and to bring the organic resin into close contact with the porous substrate. .. As the binder, a resin that is electrochemically stable within the range of use of the battery is preferable. Examples of the binder include a binder soluble in an organic solvent, a water-soluble binder, an emulsion binder and the like, and the binder may be used alone or in combination.

When a binder soluble in an organic solvent and a water-soluble binder are used, the preferable viscosity of the binder itself is preferably 10,000 mPa · s or less when the concentration is 15% by mass. It is more preferably 8000 mPa · s or less, and further preferably 5000 mPa · s or less. When the concentration is 15% by mass and the viscosity is 10,000 mPa · s or less, the increase in the viscosity of the coating material can be suppressed, and the organic resin A is unevenly distributed on the surface, so that the adhesiveness with the electrode is improved.

When an emulsion binder is used, examples of the dispersant include alcohol-based solvents such as ethanol and ketone-based solvents such as acetone as water and organic solvents, but the aqueous dispersion system is easy to handle and mixes with other components. It is preferable from the viewpoint of sex. The particle size of the emulsion binder is 30 to 1000 nm, preferably 50 to 500 nm, more preferably 70 to 400 nm, and even more preferably 80 to 300 nm. By setting the particle size of the emulsion binder to 30 nm or more, an increase in air permeability can be suppressed and the battery characteristics are improved. Further, when the nm is 1000 nm or less, sufficient adhesion between the porous layer and the porous substrate can be obtained.

The resin used for the binder is, for example, polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone, polyetherketone, polycarbonate, etc. Examples thereof include resins such as polyacetal, polyvinyl alcohol, polyethylene glycol, cellulose ether, acrylic resin, polyethylene, polypropylene, polystyrene and urethane. It is preferable to use an acrylic resin from the viewpoint of compatibility with an organic resin and electrical stability. These resins may be used alone or in admixture of two or more, if necessary.

When a water-soluble binder is used, the amount added is preferably 0.5% by mass or more with respect to the total amount of the organic resin A and the inorganic particles. It is more preferably 1% by mass or more, still more preferably 1.5% by mass or more. Further, it is preferably 10% by mass or less. It is more preferably 8% by mass or less, still more preferably 6% by mass or less. By setting the addition amount of the water-soluble binder to 0.5% by mass or more, sufficient adhesion between the porous layer and the porous substrate can be obtained. Further, when the content is 10% by mass or less, an increase in air permeability can be suppressed and the battery characteristics are improved.

When the emulsion binder is used, the addition amount is preferably 1% by mass or more with respect to the total amount of the organic resin A and the inorganic particles. It is more preferably 5% by mass or more, still more preferably 7.5% by mass or more. Further, it is preferably 30% by mass or less, more preferably 25% by mass or less, still more preferably 20% by mass or less. By setting the addition amount of the emulsion binder to 1% by mass or more, sufficient adhesion between the porous layer and the porous substrate can be obtained. Further, when the content is 30% by mass or less, an increase in air permeability can be suppressed and the battery characteristics are improved. In particular, when the content is 7.5% by mass or more and 20% by mass or less, not only the adhesion between the organic resin A and the inorganic particles and the adhesion of these particles to the substrate are promoted, but also the interaction with the organic resin A is exhibited, and the electrode and the electrode. Adhesion is also improved.

When the organic resin contains the organic resin and the above-mentioned added amount of the binder, the surface free energy of the organic resin can be adjusted, and when the coating liquid containing the organic resin is applied to the porous substrate, the surface free energy of the organic resin can be adjusted. Promotes the uneven distribution of the organic resin not only in the outer layer but also in the inner layer.

(3) Organic resin B
As the electrode adhesion aid and the substrate adhesion aid, the organic resin may contain a fluorine-free organic resin B in addition to the organic resin A and the binder. When the organic resin B is contained, it interacts with the organic resin A, and a part thereof may be unevenly distributed on the surface to improve the adhesiveness between the porous layer and the electrode. Further, the presence at the interface between the porous layer and the porous base material may improve the adhesion to the base material. Examples of the resin used for the organic resin B are fluorine-free resins, and examples thereof include acrylic resins, polyethylene, polypropylene, polystyrene, and urethane. It is preferable to use acrylic resin, polyethylene, or polypropylene from the viewpoint of adhesiveness to the electrode and adhesion to the porous substrate. The glass transition temperature of the organic resin B is preferably 10 ° C. or higher. It is more preferably 20 ° C. or higher, further preferably 30 ° C. or higher, and most preferably 40 ° C. or higher. Further, it is preferably 100 ° C. or lower. It is more preferably 90 ° C. or lower, further preferably 80 ° C. or lower, and most preferably 70 ° C. or lower. By setting the glass transition temperature to 10 ° C. or higher, the swelling property to the electrolytic solution can be suppressed and the battery characteristics are improved. Further, when the temperature is 100 ° C. or lower, sufficient adhesion to the electrode can be obtained, and adhesion to the porous substrate can be obtained.

The amount of the organic resin B added is preferably 0.1% by mass or more with respect to the total amount of the organic resin A and the inorganic particles. It is more preferably 0.3% by mass or more, further preferably 0.5% by mass or more, and most preferably 1.0% by mass or more. Further, it is preferably 30% by mass or less, more preferably 25% by mass or less, further preferably 20% by mass or less, still more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 3% by mass or less. .. By setting the addition amount of the organic resin B to 0.1% by mass or more, sufficient adhesion to the electrode can be obtained, and sufficient adhesion between the porous layer and the porous substrate can be obtained. Further, when the content is 30% by mass or less, an increase in air permeability can be suppressed and the battery characteristics are improved.

The organic resin B preferably has a particle shape, and may be the organic resin particles B. The particle size is preferably 10 nm or more. It is more preferably 30 nm or more, further preferably 50 nm or more, still more preferably 80 nm or more, and most preferably 100 nm or more. Further, it is preferably 500 nm or less, more preferably 400 nm or less, further preferably 300 nm or less, still more preferably 250 nm or less, particularly preferably 200 nm or less, and most preferably 150 nm or less. By setting the particle size of the organic resin particles B to 10 nm or more, an increase in air permeability can be suppressed and the battery characteristics are improved. Further, when the thickness is 500 nm or less, the surface is unevenly distributed and sufficient adhesiveness can be obtained.

(Inorganic particles)
In the present invention, the porous layer preferably contains inorganic particles. Since the porous layer contains inorganic particles, it is possible to impart thermal dimensional stability and suppression of short circuits due to foreign substances.

Specifically, the inorganic particles include inorganic oxide particles such as aluminum oxide, boehmite, silica, titanium oxide, zirconium oxide, iron oxide, and magnesium oxide, inorganic nitride particles such as aluminum nitride and silicon nitride, calcium fluoride, and foot. Examples thereof include sparingly soluble ionic crystal particles such as barium oxide and barium sulfate. Among the inorganic particles, aluminum oxide, which is effective in increasing the strength, and boehmite and barium sulfate, which are effective in reducing component wear in the dispersion process of the organic resin particles A and the inorganic particles, are particularly preferable. Further, these inorganic particles may be used alone or in combination of two or more.

The average particle size of the inorganic particles used is preferably 0.05 μm or more. It is more preferably 0.10 μm or more, still more preferably 0.20 μm or more. Further, it is preferably 5.0 μm or less. It is more preferably 3.0 μm or less, further preferably 1.0 μm or less, and particularly preferably 0.6 μm or less. By setting the thickness to 0.05 μm or more, an increase in air permeability can be suppressed, so that the battery characteristics are improved. Further, since the pore diameter becomes small, the impregnation property of the electrolytic solution may decrease, which may affect the productivity. When the thickness is 5.0 μm or less, not only sufficient thermal dimensional stability can be obtained, but also the film thickness of the porous layer becomes appropriate, and deterioration of battery characteristics can be suppressed.

The average particle size of the inorganic particles was measured by the following method. Using an electrolytic radiation scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.), the surface of the porous layer is placed on an image with a magnification of 30,000 and a porous layer composed of inorganic particles and organic resin particles. An EDX image of the element contained only in the particles was obtained. The image size at that time is 4.0 μm × 3.0 μm. The number of pixels was 1,280 pixels × 1,024 pixels, and the size of one pixel was 3.1 nm × 2.9 nm. Then draw a square or rectangle with the smallest area that completely encloses one of the inorganic particles identified from the resulting EDX image, i.e. a square or rectangle with the ends of the particles touching the four sides of the square or rectangle. Draw a rectangle, measure the particle size of all inorganic particles on the image as the length of one side in the case of a square, and the length of the long side (major axis diameter) in the case of a rectangle, and measure the arithmetic average value. Was taken as the average particle size. If 50 particles are not observed in the captured images, multiple images are captured and the inorganic particles are arranged so that the total of all the inorganic particles contained in the plurality of images is 50 or more. The measurement was performed, and the arithmetic mean value was taken as the average particle size.

Examples of the shape of the inorganic particles used include a spherical shape, a plate shape, a needle shape, a rod shape, an elliptical shape, and the like, and any shape may be used. Among them, it is preferable that it is spherical from the viewpoint of surface modifier, dispersibility, and coatability.

(Formation of porous layer)
The porous film of the present invention has a porous base material and a porous layer containing inorganic particles and an organic resin on at least one surface of the porous base material, and the porous layer is divided into three equal parts in the thickness direction. However, when the inner layer, the intermediate layer, and the outer layer are used, the content α of the organic resin present in the outer layer is (a) 30% or more and 60% or less with respect to the content of all the organic resins, (b). ) The content β of the organic resin present in the intermediate layer is 10% or more and 25% or less, and (c) the content γ of the organic resin present in the inner layer is 30% or more and 60% or less.

By using such a porous film, a low-cost porous film having excellent thermal dimensional stability and adhesiveness to an electrode and having excellent battery characteristics can be obtained, and the formation of the porous layer thereof can be obtained. The method will be described below.

The porous layer contains an organic resin and inorganic particles. The organic resin is made of organic resin A and may optionally contain a binder and organic resin B. The porous layer preferably contains 2% by mass or more of the organic resin A when the total constituent components of the porous layer are 100% by mass. Further, it preferably contains 30% by mass or less. The organic resin A is more preferably 4% by mass or more. Further, it is more preferably contained in an amount of 20% by mass or less, still more preferably 15% by mass or less. By setting the content of the organic resin A in the porous layer to 2% by mass or more, sufficient adhesiveness to the electrode can be obtained. Further, by setting the content of the organic resin A in the porous layer to 30% by mass or less, sufficient thermal dimensional stability can be obtained. A known method may be used for measuring the content of the organic resin A in the porous layer. For example, first, the porous layer is desorbed from the porous film using an organic solvent such as water and alcohol, and the organic solvent such as water and alcohol is sufficiently dried to obtain a constituent component contained in the porous layer. After measuring the mass of the total amount of the obtained constituent component, an organic solvent for dissolving the organic resin component is added to the obtained component component to dissolve only the organic resin component. Subsequently, the organic solvent is dried from the solution in which the organic resin component is dissolved, and only the organic resin component is extracted. ^{Nuclear magnetic resonance (1} H-NMR, ¹⁹ F-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescent X-ray analysis (1 H-NMR, 19 F-NMR), fluorescent X-ray analysis (1 H-NMR, 19 F-NMR), X-ray photoelectron spectroscopy (XPS), using the obtained organic resin components. EDX), gas chromatograph mass spectrometry, matrix-assisted laser desorption / ionization flight time mass spectrometry (MALDI-TOF-MS), elemental analysis, and the like are used to measure the mass of particle A alone. The content of the organic resin A in the porous layer can be calculated from the formula (mass of the organic resin A / mass of the total amount of the constituent components) × 100.

The content of the inorganic particles in the porous layer is preferably 60% by mass or more, more preferably 65% by mass or more, still more preferably 70% by mass or more, assuming that all the constituents of the porous layer are 100% by mass. Most preferably, it is 75% by mass or more. Further, it is preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less. Sufficient thermal dimensional stability can be obtained by setting the content of the inorganic particles in the porous layer to 60% by mass or more. Further, when the content of the particles B in the porous layer is 95% by mass or less, the content of the organic resin becomes sufficient and the adhesiveness with the electrode can be obtained.

A water-based dispersion coating liquid is prepared by dispersing the organic resin constituting the porous layer at a predetermined concentration. The aqueous dispersion coating liquid is prepared by dispersing, suspending, or emulsifying an organic resin in a solvent. At least water is used as the solvent of the aqueous dispersion coating liquid, and a solvent other than water may be added. The solvent other than water is not particularly limited as long as it is a solvent that does not dissolve the organic resin and can be dispersed, suspended or emulsified in a solid state. Examples thereof include organic solvents such as methanol, ethanol, 2-propanol, acetone, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, N-methylpyrrolidone, dimethylacetamide, dimethylformamide and dimethylformamide. From the viewpoint of low environmental load, safety and economy, a water-based emulsion obtained by emulsifying an organic resin in water or a mixture of water and alcohol is preferable. By appropriately adjusting the concentration of the aqueous dispersion coating liquid, the organic resin A can be adjusted so as to be unevenly distributed in the outer layer.

Further, a film-forming auxiliary, a dispersant, a thickener, a stabilizer, an antifoaming agent, a leveling agent and the like may be added to the coating liquid, if necessary.

Examples of the method for dispersing the coating liquid include a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, an ultrasonic device, and a paint shaker. These plurality of mixing and dispersing machines may be combined to carry out stepwise dispersion.

Next, the obtained coating liquid is applied onto the porous substrate, dried, and the porous layer is laminated. Examples of coating methods include dip coating, gravure coating, slit die coating, knife coating, comma coating, kiss coating, roll coating, bar coating, spray coating, dip coating, spin coating, screen printing, inkjet printing, and pad printing. , Other types of printing etc. are available. The coating method is not limited to these, and the coating method may be selected according to preferable conditions such as the organic resin to be used, the binder, the dispersant, the leveling agent, the solvent to be used, and the base material. Further, in order to improve the coatability, for example, the surface treatment of the coated surface such as corona treatment or plasma treatment may be performed on the porous substrate.

The film thickness of the porous layer is preferably 1.0 μm or more. It is more preferably larger than 1.0 μm, still more preferably 2.0 μm or more, still more preferably 2.5 μm or more, and most preferably 4.0 μm or more. Further, it is preferably 10.0 μm or less. It is more preferably 8.0 μm or less, further preferably 7.0 μm or less, still more preferably 6.0 μm or less, and particularly preferably 5.0 μm or less. The film thickness of the porous layer here means the film thickness of the porous layer in the case of a porous film having a porous layer on one side of the porous substrate, and is porous on both sides of the porous substrate. In the case of a porous film having layers, it means the total thickness of both porous layers. When the film thickness of the porous layer is 1.0 μm or more, sufficient thermal dimensional stability and adhesion to the electrode can be obtained. Further, when the thickness is 10.0 μm or less, the structure becomes porous and the battery characteristics are improved. It is also advantageous in terms of cost.

[Porous substrate]
In the present embodiment, the porous base material is a base material having pores inside. Further, in the present embodiment, examples of the porous substrate include a porous membrane having pores inside, a non-woven fabric, and a porous membrane sheet made of a fibrous material. The material constituting the porous substrate is preferably composed of a resin that is electrically insulating, electrically stable, and also stable to the electrolytic solution. Further, the resin used from the viewpoint of imparting a shutdown function is preferably a thermoplastic resin having a melting point of 200 ° C. or lower. The shutdown function here is a function of closing the porous structure by melting with heat when the lithium ion battery heats up abnormally, stopping the ion movement, and stopping the power generation.

Examples of the thermoplastic resin include a polyolefin-based resin, and the porous substrate is preferably a polyolefin-based porous substrate. Further, the polyolefin-based porous substrate is more preferably a polyolefin-based porous substrate having a melting point of 200 ° C. or lower. Specific examples of the polyolefin resin include polyethylene, polypropylene, an ethylene-propylene copolymer, and a mixture thereof. For example, a single-layer porous substrate containing 90% by mass or more of polyethylene, polyethylene. And a multi-layered porous substrate made of polypropylene and the like.

As a method for producing a porous base material, a method of forming a sheet of a polyolefin resin and then stretching it to make it porous, or a method of dissolving a polyolefin resin in a solvent such as liquid paraffin to form a sheet and then extracting the solvent. There is a method of making it porous.

The thickness of the porous substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more, and 30 μm or less. By setting the thickness of the porous substrate to 50 μm or less, it is possible to suppress an increase in the internal resistance of the porous substrate. Further, when the thickness of the porous substrate is 3 μm or more, the porous substrate can be manufactured and sufficient mechanical properties can be obtained.

The thickness of the porous substrate can be measured by observing the cross section with a microscope. When the porous layer is laminated, the vertical distance between the interface between the porous base material and the porous layer is measured as the thickness of the porous base material. Five pieces were cut into a size of 100 mm × 100 mm, and the central part of the sample was observed and measured for each of the five pieces, and the average value was taken as the thickness of the porous substrate.

The air permeability of the porous substrate is preferably 50 seconds / 100 cc or more and 1,000 seconds / 100 cc or less. More preferably, it is 50 seconds / 100 cc or more, and 500 seconds / 100 cc or less. When the air permeability is 1,000 seconds / 100 cc or less, sufficient ion mobility can be obtained and the battery characteristics can be improved. When it is 50 seconds / 100 cc or more, sufficient mechanical properties can be obtained.

[Porosity film]
The porous film of the present embodiment is a porous film having the above-mentioned porous layer on at least one side of the porous substrate. The porous layer is preferably sufficiently porous to have ion permeability, and the air permeability of the porous film is preferably 50 seconds / 100 cc or more and 1,000 seconds / 100 cc or less. More preferably, it is 50 seconds / 100 cc or more and 500 seconds / 100 cc or less. More preferably, it is 50 seconds / 100 cc or more and 300 seconds / 100 cc or less. When the air permeability is 1,000 seconds / 100 cc or less, sufficient ion mobility can be obtained and the battery characteristics can be improved. When it is 50 seconds / 100 cc or more, sufficient mechanical properties can be obtained.

[Secondary battery]
The porous film of the present embodiment can be suitably used as a separator for a secondary battery such as a lithium ion battery. The lithium ion battery has a configuration in which a separator for a secondary battery and an electrolyte are interposed between a positive electrode in which a positive electrode active material is laminated on a positive electrode current collector and a negative electrode in which a negative electrode active material is laminated on a negative electrode current collector. There is.

The positive electrode is a positive electrode material composed of an active material, a binder resin, and a conductive auxiliary agent laminated on a current collector, and examples of the active material include LiCoO ₂ , LiNiO ₂ , and Li (NiCoMn) O ₂ . Examples thereof include a layered lithium-containing transition metal oxide, a spinel-type manganese oxide such as _{LiMn 2} O ₄ , and an iron-based compound such as _{LiFePO 4.} As the binder resin, a resin having high oxidation resistance may be used. Specific examples thereof include fluororesin, acrylic resin and styrene-butadiene resin. As the conductive auxiliary agent, a carbon material such as carbon black or graphite is used. As the current collector, a metal foil is suitable, and in particular, an aluminum foil is often used.

The negative electrode is a negative electrode material composed of an active material and a binder resin laminated on a current collector, and the active material includes carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, tin, silicon, and the like. Examples thereof include lithium alloy-based materials, metal materials such as Li, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). As the binder resin, a fluororesin, an acrylic resin, a styrene-butadiene resin and the like are used. As the current collector, a metal foil is suitable, and in particular, a copper foil is often used.

The electrolytic solution is a place for moving ions between the positive electrode and the negative electrode in the secondary battery, and has a structure in which the electrolyte is dissolved in an organic solvent. As the _electrolyte, LiPF 6, LiBF _4, and the like LiClO ₄ and the like, solubility in organic solvents, LiPF ₆ is preferably used in view of ion conductivity. Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and the like, and two or more kinds of these organic solvents may be mixed and used.

As a method for producing a secondary battery, first, an active material and a conductive auxiliary agent are dispersed in a solution of a binder resin to prepare a coating liquid for electrodes, and this coating liquid is applied onto a current collector to prepare a solvent. By drying, a positive electrode and a negative electrode can be obtained, respectively. The film thickness of the coating film after drying is preferably 50 μm or more and 500 μm or less. A separator for a secondary battery is placed between the obtained positive electrode and the negative electrode so as to be in contact with the active material layer of each electrode, sealed in an exterior material such as an aluminum laminate film, and after injecting an electrolytic solution, a negative electrode lead or a negative electrode is used. Install a safety valve and seal the exterior material. The secondary battery thus obtained has high adhesiveness between the electrode and the separator for the secondary battery, has excellent battery characteristics, and can be manufactured at low cost.

Hereinafter, the present invention will be described in detail with reference to Examples, but this does not limit the present invention. In the following description, "%" and "part" represent "% by mass" and "part by mass". The measurement method used in this example is shown below.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto. The measurement method used in this example is shown below.
[Measuring method]
(1) Air permeability Using the Oken type air permeability measuring device (EG01-5-1MR manufactured by Asahi Seiko Co., Ltd.), the central part of 100 mm x 100 mm size is measured in accordance with JIS P 8117 (2009). bottom. The above measurement was carried out on three samples, the measured values were averaged, and the average value was taken as the air permeability (seconds / 100 cc).

(2) A porous film was cut out to a film thickness of 100 mm × 100 mm. Next, in the central part of the sample, a sample cross section is cut out with a microtome, and the cross section is observed with an electrolytic radiation scanning electron microscope (S-800 manufactured by Hitachi, Ltd., acceleration voltage 26 kV) at a magnification of 10000 times. Then, the highest point from the interface with the porous substrate was taken as the thickness, and in the case of one side, only one side was measured, and in the case of both sides, both sides were measured, and the total was taken as the thickness of the porous layer. Regarding the interface between the porous base material and the porous layer, the place where the inorganic particles are no longer confirmed in the region where the inorganic particles are present is defined as the interface. The above measurement was performed on 5 samples, and the measured values were averaged.

(3) Content of Inorganic Particles Contained in the Porous Layer The porous layer is desorbed from a 10 cm × 10 cm porous film using 40 g of water, and an organic solvent such as water and alcohol is sufficiently dried to make the porous layer porous. The constituents contained in the layer were obtained. After measuring the mass of the total amount of the obtained constituent components, the constituent components were burned at a high temperature such that the organic resin components were melted and decomposed, and the mass of only the inorganic particles was measured. The content of the inorganic particles in the porous layer was calculated in% by mass from the formula (mass of inorganic particles / mass of total amount of constituents) × 100.

(4) Glass transition temperature of organic resin A The intermediate point glass transition temperature measured by differential scanning calorimetry (DSC) according to the provisions of "JIS K7121: 2012 Plastic transition temperature measurement method" was used. The midpoint glass transition temperature was defined as the temperature at the intersection of a straight line equidistant from the extended straight line of each baseline in the vertical direction and the curve of the stepwise change portion of the glass transition.

(5) Organic resin content α, β, γ
The porous layer measured in "(2) Film thickness of the porous layer" was divided into three to form an outer layer, an intermediate layer, and an inner layer, and the organic resin contents α, β, and γ existing in each region were obtained. , Calculated using the following method. First, a sample cross section is cut out with a microtom, and the cross section is used with an electrolytic radiation scanning electron microscope (S-800 manufactured by Hitachi, Ltd., acceleration voltage 26 kV) at a magnification of 10000 times with a cross section SEM image in the same field. A cross-sectional SEM-EDX image of the carbon element was acquired. Next, the film thickness of the porous layer was measured from "(2) Film thickness of the porous layer" using a cross-sectional SEM image. The film thickness was divided into three, and each region of the outer layer, the intermediate layer, and the inner layer was determined. By superimposing the cross-sectional SEM image and the cross-sectional SEM-EDX image of the carbon element, each region of the outer layer, the intermediate layer, and the inner layer was compared with the cross-sectional SEM-EDX image of the carbon element. Analysis was performed for each region of the outer layer, the middle layer, and the inner layer. The following analysis was performed using image analysis software (Toyo Technica, SPIP). After emphasizing the boundary of the organic resin A with a general-purpose plug-in (PrugIn_BoundaryDropper (Particle7x7)) for the HighSensor image, the area of the carbon element included in the visual field is calculated by automatic calculation of the threshold value without including the edge of the image image. bottom.
Calculated as the area of carbon elements contained in the outer layer region x 100 / (area of carbon elements contained in all regions of the outer layer, middle layer, and inner layer), and the same measurements were performed for the five samples, and the average thereof. The value was defined as the organic resin content α (%). Calculated as the area of carbon elements contained in the region of the intermediate layer x 100 / (area of carbon elements contained in all regions of the outer layer, intermediate layer, and inner layer), and the same measurement was performed for 5 samples, and the average thereof. The value was defined as the organic resin content β (%). Calculated as the area of carbon elements contained in the inner layer region x 100 / (area of carbon elements contained in all regions of the outer layer, middle layer, and inner layer), and the same measurements were performed for 5 samples, and the average thereof. The value was defined as the organic resin content γ (%).

(6) Appearance of coating film A sample having a size of 100 × 200 mm was placed on black drawing paper, the appearance of the coating film was observed, and the evaluation was made based on the following indexes.
・ Excellent coating film appearance: No coating streaks or coating film appearance ・ Good coating film appearance: Some of coating film streaks or coating film repellent can be confirmed Some repellent is confirmed ・ The appearance of the coating film is bad: Coating streaks and coating repellent are confirmed, and evaluation is difficult.

(7) Thermal shrinkage (thermal dimensional stability)
The length from the midpoint of one side to the midpoint of the opposite side of each sample was measured from three samples having a size of 100 mm × 100 mm, and heat treatment was performed in an oven at 150 ° C. for 30 minutes under no tension. The sample was taken out after the heat treatment, the length between the midpoints at the same location as before the heat treatment was measured, and the heat shrinkage rate was calculated from the following formula. Calculated at two locations from one sample at the same time, and the average value of all the values is the heat shrinkage rate (thermal dimensional stability). Was good, 20% or more and less than 40% was acceptable, and 40% or more was bad.
Heat shrinkage rate (%) = [(length between midpoints before heat treatment-length between midpoints after heat treatment) / (length between midpoints before heat treatment)] × 100.

(8) Adhesion to the base material A transparent double-sided tape (manufactured by 3M, product number 665) cut to a width of 18 mm and a length of 100 mm is attached to an acrylic plate having a thickness of 2 cm. Next, the porous film cut to a length of 20 mm and 200 mm was roll-pressed at 0.5 MPa, 25 ° C. and 0.2 m / min, and the transparent double-sided tape and the porous film were attached. Then, the peeling adhesion strength of 180 degrees was measured under the condition of the peeling speed of 300 mm / min.
-Excellent adhesive strength: The porous base material and the porous layer were peeled off with a stronger force.
-Excellent adhesive strength: The porous base material and the porous layer were peeled off with a strong force.
-Good adhesive strength: The porous base material and the porous layer were peeled off with a slightly strong force.
-Adhesive strength is possible: The porous base material and the porous layer were peeled off with a weak force.
-Poor adhesive strength: The porous base material and the porous layer were peeled off with extremely weak force.

(9) Adhesion to electrodes The active material is Li (Ni _5/10 Mn _2/10 Co _3/10 ) O ₂ , the binder is vinylidene fluoride resin, and the conductive auxiliary agent is acetylene black and graphite positive electrode 15 mm x 100 mm. The porous film is placed so that the active material and the porous layer are in contact with each other, hot-pressed with a thermal roll press machine at 0.5 MPa, 100 ° C., 0.2 m / min, and manually peeled off using a tweezers. The adhesive strength was evaluated in the following four stages. Similarly, the adhesive strength between the negative electrode of graphite as the active material, vinylidene fluoride resin as the binder, and carbon black as the conductive auxiliary agent and the porous film was also measured, and the average adhesive strength was obtained by integrating the evaluation results of the positive electrode and the negative electrode. It was judged as the adhesive strength.
-Excellent adhesive strength: The electrode and the porous film peeled off with a stronger force.
-Excellent adhesive strength: The electrode and the porous film peeled off with a strong force.
-Good adhesive strength: The electrode and the porous film peeled off with a slightly strong force.
-Adhesive strength is possible: The electrode and the porous film peeled off with a weak force.
-Poor adhesive strength: The electrode and the porous film peeled off with extremely weak force.

(10) Battery production The positive electrode sheet contains _{92 parts by mass of Li (Ni 5/10} Mn _2/10 Co _3/10 ) O ₂ as the positive electrode active material and 2.5 parts by mass of acetylene black and graphite as the positive electrode conductive aid. A positive electrode slurry in which 3 parts by mass of polyvinylidene fluoride as a positive electrode binder was dispersed in N-methyl-2-pyrrolidone using a planetary mixer was applied on an aluminum foil, dried, and rolled. (Applyance: 9.5 mg / cm ² ).
This positive electrode sheet was cut out to a size of 40 mm × 40 mm. At this time, the tab adhesive portion for current collection without the active material layer was cut out so as to have a size of 5 mm × 5 mm on the outside of the active material surface. An aluminum tab having a width of 5 mm and a thickness of 0.1 mm was ultrasonically welded to the tab adhesive portion.
In the negative electrode sheet, 98 parts by mass of natural graphite as a negative electrode active material, 1 part by mass of carboxymethyl cellulose as a thickener, and 1 part by mass of a styrene-butadiene copolymer as a negative electrode binder are dispersed in water using a planetary mixer. The negative electrode slurry was coated, dried, and rolled on a copper foil (applied grain: 5.5 mg / cm ² ).
This negative electrode sheet was cut out to a size of 45 mm × 45 mm. At this time, the tab adhesive portion for current collection without the active material layer was cut out so as to have a size of 5 mm × 5 mm on the outside of the active material surface. A copper tab of the same size as the positive electrode tab was ultrasonically welded to the tab bonding portion.
Next, the porous film is cut into a size of 55 mm × 55 mm, and the positive electrode and the negative electrode are laminated on both sides of the porous film so that the active material layer separates the porous film so that the positive electrode coating portion faces the negative electrode coating portion. The electrodes were arranged to obtain a group of electrodes. The positive electrode, the porous film, and the negative electrode were sandwiched between one 90 mm × 200 mm aluminum laminated film, the long sides of the aluminum laminated film were folded, and the two long sides of the aluminum laminated film were heat-sealed to form a bag.
_{An electrolytic solution prepared by dissolving LiPF 6} as a solute at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) was used. 1.5 g of an electrolytic solution was injected into a bag-shaped aluminum laminated film, and the short sides of the aluminum laminated film were heat-sealed while impregnated under reduced pressure to form a laminated battery.

(11) Discharge load characteristics The discharge load characteristics were tested by the following procedure and evaluated by the discharge capacity retention rate.
Using the above laminated battery, the discharge capacity when discharged at 0.5 C at 25 ° C. and the discharge capacity when discharged at 10 C were measured, and (discharge capacity at 10 C) / (discharge capacity at 0.5 C). Discharge capacity) × 100 was used to calculate the discharge capacity retention rate. Here, the charging condition was 0.5C, 4.3V constant current charging, and the discharging condition was 2.7V constant current discharging. The capacity retention rate was defined as the average of the three measurement results obtained by producing five laminated batteries and removing the results that maximized and minimized the discharge capacity retention rate. A discharge capacity retention rate of less than 40% was bad, 45% or more and less than 50% was good, 50% or more and less than 55% was excellent, and 55% or more was excellent.

(12) Charge / discharge cycle characteristics The charge / discharge cycle characteristics of the above-mentioned laminated battery were tested by the following procedure and evaluated by the discharge capacity retention rate.
<1st to 300th cycles>
Charging and discharging were set to one cycle, charging conditions were set to 2C, 4.3V constant current charging, and discharging conditions were set to 2C, 2.7V constant current discharging, and charging and discharging were repeated 300 times at 25 ° C.
<Calculation of discharge capacity maintenance rate>
The discharge capacity retention rate was calculated by (discharge capacity in the 300th cycle) / (discharge capacity in the first cycle) × 100. The capacity retention rate was defined as the average of the three measurement results obtained by producing five laminated batteries and removing the results that maximized and minimized the discharge capacity retention rate. If the discharge capacity retention rate is less than 50%, the charge / discharge cycle characteristics are poor, if 50% or more and less than 60%, the charge / discharge cycle characteristics are good, if 60% or more and less than 70%, the charge / discharge cycle characteristics are excellent, and 70% or more is charge / discharge. The cycle was excellent.

(Example 1)
120 parts of ion-exchanged water and 1 part of Adecaria Sorb SR-1025 (emulsifier manufactured by Adeca Corporation) were charged into the reactor, and stirring was started. To this, 0.4 part of 2,2'-azobis (2- (2-imidazolin-2-yl) propane) (manufactured by Wako Pure Chemical Industries, Ltd.) was added under a nitrogen atmosphere, and 2,2,2- 30 parts of trifluoroethyl methacrylate (3FMA), 14 parts of 4-hydroxybutyl acrylate (4-HBA), 56 parts of cyclohexyl acrylate (CHA), 9 parts of Adecaria Sorb SR-1025 (embroidery manufactured by Adeca Co., Ltd.), 115 parts of ion-exchanged water. The mixture composed of parts was continuously added dropwise at 60 ° C. over 2 hours, and the polymerization treatment was carried out for 4 hours after the completion of the addition, and the organic resin particles A made of the organic resin of the copolymer (average particle size 170 nm, glass transition temperature). A dispersion A containing 40 ° C.) was produced.
Alumina particles (aluminum oxide) with an average particle size of 0.5 μm are used as the inorganic particles, the same amount of water as the inorganic particles is added as a solvent, and 1% by mass of carboxymethyl cellulose is added as a dispersant to the inorganic particles, and then a bead mill is used. To prepare a dispersion liquid B.
The dispersion liquid A and the dispersion liquid B are dispersed in water so that the content of the inorganic particles contained in the porous layer is 70% by mass, mixed with a stirrer, and further used as an acrylic emulsion binder (acrylic particles). , 100 nm) was added in an amount of 17% by mass based on the total amount of the organic resin particles A and the inorganic particles to prepare a coating liquid.
The obtained coating liquid was coated on both sides of a polyethylene porous substrate (thickness 9 μm, air permeability 60 seconds / 100 cc) using a wire bar, and placed in a hot air oven (drying set temperature 50 ° C.) for 1 minute. By drying and volatilizing the contained solvent, a porous layer was formed, and the porous film of the present invention was obtained. Regarding the obtained porous film, the film thickness of the porous layer, the air permeability, the content α of the organic resin, the content β of the organic resin, the content γ of the organic resin, the appearance of the coating film, and the heat shrinkage rate (thermal dimensions). Table 2 shows the measurement results of stability), adhesion to the porous substrate, adhesion to the electrode, discharge load characteristics, and charge / discharge cycle characteristics.

(Example 2)
As shown in Table 1-1, the composition ratio of the organic resin particles A is 30 parts of 2,2,2-trifluoroethyl methacrylate (3FMA), 2 parts of 4-hydroxybutyl acrylate (4-HBA), and alkylene glycol dimethacrylate. The porous film of the present invention was prepared in the same manner as in Example 1 except that it was changed to 7 parts (PDE-600 manufactured by Nichiyu Co., Ltd., homopolymer Tg: -34 ° C.) and 68 parts of cyclohexyl acrylate (CHA). Obtained. Table 2 shows the measurement results of the porous film.

(Example 3)
The porous film of the present invention was obtained in the same manner as in Example 2 except that the film thickness of the porous layer was set to the film thickness shown in Table 2. Table 2 shows the measurement results of the porous film.

(Example 4)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-1. Table 2 shows the measurement results of the porous film.

(Example 5)
The porous film of the present invention was obtained in the same manner as in Example 4 except that the film thickness of the porous layer was set to the film thickness shown in Table 2. Table 2 shows the measurement results of the porous film.

(Example 6)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-1. Table 2 shows the measurement results of the porous film.

(Example 7)
The porous film of the present invention was obtained in the same manner as in Example 6 except that the film thickness of the porous layer was set to the film thickness shown in Table 2. Table 2 shows the measurement results of the porous film.

(Example 8)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-1. Table 2 shows the measurement results of the porous film.

(Example 9)
The porous film of the present invention was obtained in the same manner as in Example 8 except that the film thickness of the porous layer was set to the film thickness shown in Table 2. Table 2 shows the measurement results of the porous film.

(Example 10)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-1. Table 2 shows the measurement results of the porous film.

(Example 11)
The porous film of the present invention was obtained in the same manner as in Example 10 except that the film thickness of the porous layer was set to the film thickness shown in Table 2. Table 2 shows the measurement results of the porous film.

(Example 12)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-2. Table 2 shows the measurement results of the porous film.

(Example 13)
The porous film of the present invention is the same as in Example 8 except that 2.2% by mass of the organic resin particles B (polyethylene, melting point 80 ° C.) is added to the total amount of the organic resin particles A and the inorganic particles. Got Table 2 shows the measurement results of the porous film.

(Example 14)
The porous film of the present invention was obtained in the same manner as in Example 8 except that the organic resin A was in the form of crumbs instead of particles. Table 2 shows the measurement results of the porous film.

(Example 15)
The porous film of the present invention is the same as in Example 8 except that 2.2% by mass of the organic resin particles B (polypropylene, melting point 60 ° C.) is added to the total amount of the organic resin particles A and the inorganic particles. Got Table 2 shows the measurement results of the porous film.

(Example 16)
The porous film of the present invention was obtained in the same manner as in Example 8 except that the content of the inorganic particles contained in the porous layer was 55% by mass. Table 2 shows the measurement results of the porous film. Table 2 shows the measurement results of the porous film.

(Example 17)
Except that the content of the inorganic particles contained in the porous layer was 90% by mass, and the acrylic emulsion binder (acrylic particles, 100 nm) was 7.5% by mass with respect to the total amount of the organic resin particles A and the inorganic particles. The porous film of the present invention was obtained in the same manner as in Example 8. Table 2 shows the measurement results of the porous film. Table 2 shows the measurement results of the porous film.

(Example 18)
The porous film of the present invention was obtained in the same manner as in Example 8 except that the inorganic particles were barium sulfate. Table 2 shows the measurement results of the porous film.

(Example 19)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-2. Table 2 shows the measurement results of the porous film.

(Example 20)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-2 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 21)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-2. Table 2 shows the measurement results of the porous film.

(Example 22)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-2 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 23)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 24)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-3 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 25)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 26)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-3 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 27)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 28)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-3 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 29)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 30)
The porous film of the present invention is the same as in Example 1 except that the composition of the organic resin particles A is changed to the composition shown in Table 1-3 and the film thickness of the porous layer is changed to the film thickness shown in Table 2. Got Table 2 shows the measurement results of the porous film.

(Example 31)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 32)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 33)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-3. Table 2 shows the measurement results of the porous film.

(Example 34)
The porous film of the present invention was obtained in the same manner as in Example 1 except that the composition of the organic resin particles A was changed to the composition shown in Table 1-4. Table 2 shows the measurement results of the porous film.

(Comparative Example 1)
A porous film was obtained in the same manner as in Example 1 except that the composition ratio of the organic resin particles A was changed to the composition shown in Table 1-4. Table 2 shows the measurement results of the porous film.

(Comparative Example 2)
A porous film was obtained in the same manner as in Example 1 except that the composition ratio of the organic resin particles A was changed to the composition shown in Table 1-4. Table 2 shows the measurement results of the porous film.

(Comparative Example 3)
An attempt was made to prepare the organic particles A in the same manner as in Example 1 except that the composition ratio of the organic resin particles A was changed to the composition shown in Table 1-4, but stable particles could not be obtained. Therefore, the porous layer could not be formed, and the porous film could not be measured.

(Comparative Example 4)
A porous film was obtained in the same manner as in Example 1 except that the composition was changed to the composition shown in Table 1-4 without using the organic resin particles A. Table 2 shows the measurement results of the porous film.

From Table 1-1, Table 1-2, Table 1-3, Table 1-4 and Table 2, all of Examples 1 to 34 are inorganic on at least one surface of the porous base material and the porous base material. The inner layer, the middle layer, and the outer layer, which have a porous layer containing an organic resin having adhesiveness to particles and electrodes and the porous layer is divided into three equal parts in the thickness direction, are all organic resins. The content α of the organic resin present in the outer layer is 30% or more and 60% or less, and (b) the content β of the organic resin present in the intermediate layer is 10% or more and 25% or less. (C) Since the porous film satisfies the content γ of the organic resin present in the inner layer of 30% or more and 60% or less, sufficient thermal dimensional stability, adhesion to the electrode, and good battery characteristics are obtained. can get.

On the other hand, in Comparative Example 1, since the content α of the organic resin in the outer layer is less than 30% by mass and the content β of the organic resin in the intermediate layer exceeds 25% by mass, the adhesiveness to the electrode is inferior. In Comparative Example 2, since the content γ of the organic resin in the inner layer is less than 30% by mass and the content β of the organic resin in the intermediate layer exceeds 25% by mass, the adhesiveness between the porous substrate and the porous layer is high. Since it is not sufficient, sufficient adhesion to the electrode cannot be obtained. In Comparative Example 3, since the content of the (meth) acrylate monomer having a hydroxyl group exceeds 30% by mass, a stable organic resin A cannot be obtained. This organic resin A cannot form a porous layer. In Comparative Example 4, since the porous layer does not contain the organic resin, sufficient adhesiveness to the electrode and sufficient adhesiveness to the porous substrate cannot be obtained.

Claims (14)

A porous base material and a porous layer containing inorganic particles and an organic resin are provided on at least one surface of the porous base material, and the porous layer is divided into three equal parts in the thickness direction, and each of the porous groups is divided into three equal parts. A porous film satisfying the following (a) to (c) when the inner layer in contact with the material, the intermediate layer adjacent to the inner layer, and the outer layer adjacent to the intermediate layer are used.
(A) The content α of the organic resin present in the outer layer is 30% or more and 60% or less of the content of all the organic resins.
(B) The content β of the organic resin present in the intermediate layer is 10% or more and 25% or less of the content of all the organic resins.
(C) The content γ of the organic resin present in the inner layer is 30% or more and 60% or less of the content of all the organic resins. The porous film according to claim 1, wherein the organic resin is organic resin particles. Claim 1 or claim 1, wherein the organic resin is a mixture containing a polymer containing a fluorine-containing (meth) acrylate monomer, or an organic resin A having a copolymer containing a fluorine-containing (meth) acrylate monomer. The porous film according to claim 2. The porous film according to claim 3, wherein the organic resin further contains a binder. The binder is polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone, polyetherketone, polycarbonate, polyacetal, polyvinyl alcohol, polyethylene. The porous film according to claim 4, which is at least one binder selected from the group consisting of glycol, cellulose ether, acrylic resin, polyethylene, polypropylene, polystyrene, and urethane. The porous film according to claim 4 or 5, wherein the binder is an acrylic resin. The organic resin A is a mixture containing a polymer composed of a fluorine-containing (meth) acrylate monomer and a polymer composed of a (meth) acrylate monomer having a hydroxyl group, or a fluorine-containing (meth) acrylate monomer. When it has a copolymer containing a (meth) acrylate monomer having a hydroxyl group and the content of the (meth) acrylate monomer having a hydroxyl group is 100% by mass of all the constituents of the organic resin A. The porous film according to claim 3, wherein the porous film is 1% by mass or more and 30% by mass or less. The porous film according to claim 7, wherein the (meth) acrylate monomer having a hydroxyl group has a glass transition temperature of −100 ° C. or higher and 0 ° C. or lower of the homopolymer composed of the monomer. The organic resin A further contains a monomer having two or more reactive groups per molecule, and contains a monomer having two or more reactive groups per molecule contained in the organic resin A. The porous film according to claim 7 or 8, wherein the reactivity is 1% by mass or more and 10% by mass or less. The porous film according to claim 9, wherein the monomer having two or more reactive groups per molecule is an alkylene glycol di (meth) acrylate or a urethane di (meth) acrylate. The porous film according to any one of claims 1 to 10, wherein the organic resin contains an organic resin B that does not contain fluorine. Any of claims 1 to 11, wherein the content of the inorganic particles contained in the porous layer is 60% by mass or more and 95% by mass or less when all the constituents of the porous layer are 100% by mass. The porous film described in. A separator for a secondary battery using the porous film according to any one of claims 1 to 12. A secondary battery using the separator for a secondary battery according to claim 13.