WO2022239547A1

WO2022239547A1 - Porous film, separator for secondary battery, and secondary battery

Info

Publication number: WO2022239547A1
Application number: PCT/JP2022/015369
Authority: WO
Inventors: 加門慶一; 甲斐信康; 西村直哉; 久万琢也; 佃明光
Original assignee: 東レ株式会社
Priority date: 2021-05-10
Filing date: 2022-03-29
Publication date: 2022-11-17
Also published as: JPWO2022239547A1; KR20240006493A; CN117203846A

Abstract

The present invention addresses the problem of providing a porous film that has excellent adherence to an electrode, thermal dimensional stability, and low resistance. Provided is a porous film comprising a porous substrate and a porous layer disposed on at least one side of the substrate, the porous layer containing inorganic particles and organic resin particles. The porous substrate has an arithmetic mean height (Sa) of 0.09-0.3 µm, per 2200 µm squared of the surface that is in contact with the porous layer. When all the structural components of the porous layer are 100 vol%, the volume content ratio α of the inorganic particles and the occupancy ratio β of the inorganic particles in the surface area of the porous layer satisfies β/α < 1.

Description

Porous film, secondary battery separator and secondary battery

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

Secondary batteries such as lithium-ion batteries are used in automotive applications such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as well as portable applications such as smartphones, tablets, mobile phones, laptops, digital cameras, digital video cameras, and handheld game consoles. It is widely used in digital devices, electric tools, electric motorcycles, electric assist bicycles, etc.

Lithium ion batteries generally have a secondary battery separator and an electrolyte 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. have a configuration.

Polyolefin-based porous substrates are used as separators for secondary batteries. The characteristics required for secondary battery separators are the ability to contain electrolyte in the porous structure and enable ion movement, and the ability to close the porous structure by melting when the lithium ion battery overheats. and a shutdown characteristic that stops the discharge by stopping ion migration.

Also, in order to improve the energy density of lithium-ion batteries, the battery form is being replaced from the wound type to the laminated type. In the case of the laminated type, in the manufacturing process of a secondary battery using an electrode laminate in which a positive electrode, a separator, and a negative electrode are laminated, when the electrode laminate is transported, the laminate structure may be maintained, or the electrode laminate may be rolled into a cylinder. When inserting into a mold, square, etc. can, in order to keep the shape at that time, or to increase the energy density by putting more electrode laminates in the can, or to laminate type A battery is required to have adhesiveness (dry adhesiveness) between the separator and the electrode before being impregnated with the electrolytic solution in order to prevent the shape from being deformed after being inserted into the outer packaging material. Therefore, in the above process, the electrode laminate may be subjected to hot pressing. Lithium-ion batteries are also required to have good battery characteristics such as adhesion (wet adhesion) to electrodes impregnated with electrolyte, high output, and long life.

In response to the above requirement for dry adhesion, in Patent Document 1, an adhesive layer formed on a heat-resistant layer is laminated to develop dry adhesion with the electrode. In Patent Document 2, the dry adhesion 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. Further, it is known that smoothing the outermost surface of the separator improves the dry adhesion to the electrode (Patent Document 3). In addition, it is being studied to improve the yield during battery production and the yield during initial charge/discharge by developing both dry adhesiveness and wet adhesiveness (Patent Document 4).

WO2013/151144 WO2018/034094 WO2014/021293 WO2016/098684

As mentioned above, dry adhesion between electrodes and separators is required due to the heat press process in the manufacturing process of secondary batteries. Furthermore, due to the increase in the size of batteries, the electrode laminate is required to be increased in size and to have a higher capacity, and it is necessary to improve not only the dry adhesion to the electrodes but also the wet adhesion. In addition, due to the increase in demand for laminated type batteries, productivity improvement is also required, and it is also necessary to shorten the heat press time for improving adhesiveness. In order to improve the adhesiveness with the electrode, it has been studied to increase the amount of organic resin particles responsible for adhesion with the electrode, but there is a problem that the rate characteristics and battery life deteriorate due to the increase in battery resistance.

In view of the above problems, the object of the present invention is to provide a porous film having excellent adhesion (dry adhesion, wet adhesion) with electrodes, thermal dimensional stability, and low resistance.

Therefore, the present inventors focused on the adhesiveness with the electrode by high pressure heat press for shortening the heat press time, and as a result of extensive studies, the arithmetic mean height of the porous substrate was set to a certain height. It has been found that organic resin particles are unevenly distributed on the surface layer and layer-separated from the inorganic particles, resulting in excellent dry adhesion to electrodes, thermal dimensional stability, and low resistance. Furthermore, they have found that by appropriately selecting the composition of the organic resin particles, in addition to the properties described above, the wet adhesion is also excellent.

In order to solve the above problems, the porous film of the present invention has the following configuration.
(1) A porous film having a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate, wherein the porous substrate comprises: Inorganic particles having an arithmetic mean height (Sa) of 0.09 μm or more and 0.3 μm or less in a 2200 μm square of the surface on the side in contact with the porous layer, and when the volume of all constituent components of the porous layer is 100% by volume and the occupancy ratio β (area %) of the inorganic particles in the surface portion of the porous layer satisfies β/α<1.
(2) The porous film according to (1), wherein the porous film has an arithmetic mean height (Sa) of 0.085 μm or more and 0.3 μm or less in a 2200 μm square of the surface on the side having the porous layer.
(3) The porous material according to (1) or (2), wherein the volume content α of the inorganic particles is 30% by volume or more and 80% by volume or less when the volume of all constituent components of the porous layer is 100% by volume. sex film.
(4) The porous film according to any one of (1) to (3), wherein the occupancy β of the inorganic particles in the porous surface portion is greater than 0.
(5) The porous substrate according to any one of (1) to (4), wherein the surface in contact with the porous layer has an arithmetic mean roughness (Ra) of 40 nm or more and 300 nm or less in a 12 nm square. porous film.
(6) The porous substrate has a protruding ridge height (Spk) of 0.10 μm or more and 0.40 μm or less in a 2200 μm square on the surface on the side in contact with the porous layer of (1) to (5). A porous film according to any one of the preceding claims.
(7) The porous film according to any one of (1) to (6), wherein the porous layer has a surface free energy of 10 mN/m or more and 80 mN/m or less.
(8) The porous film according to any one of (1) to (7), wherein the porous substrate is a polyolefin microporous film (9) The inorganic particles are an inorganic hydroxide, an inorganic oxide and an inorganic sulfuric acid The porous film according to any one of (1) to (8), which is a particle composed of at least one selected from the group consisting of compounds.
(10) The organic resin particles are fluorine-containing (meth)acrylate monomers, unsaturated carboxylic acid monomers, (meth)acrylate monomers, styrene-based monomers, olefin-based monomers, and diene-based monomers. Any one of (1) to (9), which has a polymer polymerized using at least one monomer selected from the group consisting of a monomer, an acrylamide-based monomer, and a vinylidene fluoride monomer. The porous film according to .
(11) With respect to the organic resin particles, the ratio of the fluorine-containing (meth)acrylate monomer is 20% by mass or more and 80% by mass or less when the total constituent monomer components of the organic resin particles are 100% by mass. The porous film according to (10).
(12) The porous film according to (11), wherein the organic resin particles contain a polymer polymerized only with a fluorine-containing (meth)acrylate monomer.
(13) The porous film according to any one of (10) to (12), wherein the number of fluorine atoms contained in one molecule of the fluorine-containing (meth)acrylate monomer is 3 or more and 13 or less.
(14) The porous film according to (12) or (13), wherein the organic resin particles further comprise a polymer or copolymer polymerized using a (meth)acrylate monomer having a hydroxyl group.
(15) With respect to the organic resin particles, the ratio of the (meth)acrylate monomer having a hydroxyl group is greater than 0% by mass and 7.0% by mass when the total constituent monomer components of the organic resin particles are 100% by mass. 15. The porous film of claim 14, wherein:
(16) Regarding the polymer contained in the organic resin particles, the glass transition of the polymer when at least one of the monomers that are the raw materials of the polymer is polymerized only with that monomer. The porous film according to any one of (10) to (15), which is a monomer having a temperature of -100°C or higher and 0°C or lower.
(17) The monomer having a glass transition temperature of −100° C. or more and 0° C. or less when polymerized only by the monomer accounts for 100% by mass of the total constituent monomer components of the organic resin particles. , the porous film according to (16), which is greater than 0% by mass and 10.0% by mass or less.
(18) The porous film according to any one of (1) to (17), wherein the porous layer contains at least two types of organic resin particles.
(19) The porous film according to any one of (1) to (18), wherein the organic resin particles have an average particle size of 100 nm or more and 500 nm or less.
(20) The porous film according to any one of (1) to (19), wherein the film thickness of the porous substrate is 3 μm or more and 15 μm or less.
(21) The porous film according to any one of (1) to (20), wherein the porous layer has a thickness of 2 μm or more and 8 μm or less.
(22) A secondary battery separator comprising the porous film according to any one of (1) to (21).
(23) A secondary battery using the secondary battery separator according to (22).
(24) A porous film having a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate,
The porous substrate is made of a polyolefin microporous membrane whose surface in contact with the porous layer has an arithmetic mean height (Sa) of 0.09 μm or more in a 2200 μm square,
The inorganic particles are particles composed of at least one selected from the group consisting of inorganic hydroxides, inorganic oxides and inorganic sulfates,
The organic resin particles contain a fluorine-containing (meth)acrylate monomer, an unsaturated carboxylic acid monomer, a (meth)acrylic acid ester monomer, a styrene monomer, an olefin monomer, and a diene monomer. is a polymer polymerized using at least one monomer selected from the group consisting of a polymer, an amide-based monomer, and a vinylidene fluoride monomer,
When the volume of all constituent components of the porous layer is 100% by volume, the volume content ratio α of the inorganic particles is 30% by volume or more and 80% by volume or less,
The battery separator, wherein the relationship between the volume content α of the inorganic particles and the occupation ratio β of the inorganic particles in the surface portion of the porous layer satisfies β>0 and β/α<1.

According to the present invention, it is possible to provide a porous film having excellent adhesiveness (dry adhesiveness, wet adhesiveness) with electrodes, thermal dimensional stability, and low resistance. In particular, when subjected to high-pressure heat pressing, excellent dry adhesion can be exhibited. Further, by using the porous film as a battery separator, it is possible to improve the yield in the battery manufacturing process and provide a secondary battery having excellent battery life and rate characteristics.

The porous film of the present invention is a porous film having a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate, wherein the porous The base material has an arithmetic mean height (Sa) of 0.09 μm or more in a 2200 μm square of the surface on the side in contact with the porous layer, and the amount of inorganic particles when the volume of all constituent components of the porous layer is 100% by volume. The volume content α (% by volume) and the occupation ratio β (% by area) of the inorganic particles in the surface portion of the porous layer satisfy β/α<1.

The porous film of the present invention will be described in detail below.

The porous film of the present invention has an arithmetic mean height (Sa) of 0.09 μm or more and 0.3 μm or less in a 2200 μm square on the surface of the porous substrate on the side in contact with the porous layer. By setting the lower limit of the arithmetic mean height (Sa) to 0.09 μm or more, the adhesion to the electrode can be further improved. In addition, by setting the upper limit of the arithmetic mean height (Sa) to 0.3 μm or less, it is possible to prevent the ion transport from becoming too strong due to excessively strong adhesion to the electrode, resulting in a high resistance.

Until now, in order to improve the dry adhesion with the electrodes, it has been studied to smooth the adhesive layer provided on the outermost surface of the separator. Furthermore, in recent years, in order to improve the yield of dry adhesion between the separator and the electrode before impregnating with the electrolyte, the pressing pressure in the adhesion process (heat press) with the electrode has been greatly increased to improve the adhesion between the separator and the electrode. It has been studied to greatly shorten the time required for the bonding process. In that case, in order to improve the dry adhesion, the outermost surface of the separator needs to be pressed deeply by the electrode so that it follows the unevenness of the active material present in the electrode, but the outermost surface is smooth. It was found that the dry adhesion to the electrode decreased because it did not follow the unevenness.

In addition, in order to improve the dry and wet adhesion with the electrode, it is being considered to increase the content of the organic resin particles responsible for adhesion with the electrode. However, an increase in the amount of organic resin particles may hinder ion transport and deteriorate the resistance of the membrane. Therefore, there has been a problem in achieving both dry adhesion and wet adhesion to electrodes and maintaining low resistance of the film.

For the porous film of the present invention, the arithmetic mean height (Sa) in 2200 μm square of the surface of the porous substrate on the side in contact with the porous layer is 0.09 μm or more and 0.3 μm or less, so that dry adhesion with the electrode found to improve performance. By setting the arithmetic mean height (Sa) of the surface of the porous substrate on the side in contact with the porous layer within the above range, the arithmetic mean height of the surface of the porous layer is also improved, and the step of bonding with the electrode (hot press) In this case, it can follow the unevenness of the active material present in the electrode, and exhibits high dry adhesion to the electrode. The dry adhesion to the electrode can be improved without increasing the amount of the organic resin particles while reducing the cost, and the improvement of the dry adhesion improves the uniformity of ion transport and lowers the resistance. Therefore, a battery using the porous film of the present invention can achieve both rate characteristics and battery life. The lower limit of the arithmetic mean height (Sa) on the surface of the porous substrate of 2200 μm square is preferably 0.012 μm or more.

Here, the arithmetic mean height (Sa) in 2200 μm square of the surface of the porous substrate on the side in contact with the porous layer, By adjusting various manufacturing conditions such as the magnification, stretching temperature, and dry re-stretching after stretching, it is possible to achieve a predetermined range.

The porous layer in the present invention contains inorganic particles and organic resin particles. The porous layer has a volume content rate α (% by volume) of inorganic particles when the volume of all constituent components of the porous layer is 100% by volume, and an occupation rate β ( area %) satisfies β/α<1. When β/α is less than 1, it means that the occupancy rate of the inorganic particles in the surface portion of the porous layer is lower than the content rate of the inorganic particles in the entire porous layer. It shows that it is unevenly distributed on the surface of the Since the organic resin particles are unevenly distributed on the surface portion of the porous layer, a large amount of organic resin particles are present on the surface portion, thereby exhibiting sufficient adhesiveness to the electrode.

It should be noted that the volume content α of the inorganic particles and the occupation ratio β of the inorganic particles described above are obtained by the method described in the Examples section.

The porous film of the present invention uses a porous substrate having an arithmetic mean height (Sa) of 0.09 μm or more and 0.3 μm or less at 2200 μm on the surface of the porous substrate on the side in contact with the porous layer. And, when the total constituent components of the porous layer are 100% by volume, the porous layer has a volume content rate α (% by volume) of the inorganic particles and an occupation rate β of the inorganic particles at the surface of the porous layer ( area %) satisfies β/α<1, high dry adhesion and wet adhesion to the electrode can be obtained, especially when high-pressure heat pressing is performed, and good battery characteristics can be obtained. β/α is more preferably 0.5 or less, still more preferably 0.3 or less. Although the lower limit of β/α is not particularly limited, it is preferably 0.01 or more.

In order to form a porous layer in which β/α is within the above range, it may be formed through a two-step coating process using two types of coating liquids, or one step using one type of coating liquid. It is more preferable to form in the coating step of . If it can be formed by a one-stage coating process, the cost can be reduced by reducing the number of times of coating. For a one-stage coating process, for example, the surface free energy of the organic resin particles, the viscosity of the coating liquid, the solid content concentration, and the drying temperature can be adjusted appropriately to set β/α within a predetermined range. It becomes possible. Details will be described later.

The volume content α of the inorganic particles is preferably 30% by volume or more and 80% by volume or less, more preferably 40% by volume or more and 70% by volume or less, when the volume of all constituent components of the porous layer is 100% by volume. and more preferably 50% by volume or more and 60% by volume or less. By setting the volume content α of the inorganic particles to 30% by volume or more, sufficient thermal dimensional stability can be obtained. Moreover, by making it 80 volume % or less, the content of the organic resin particles becomes sufficient, and dry adhesion and wet adhesion to the electrode are improved.

The occupancy β of the inorganic particles on the surface of the porous layer is preferably greater than 0%. More preferably, it is 1% or more, and still more preferably 5% or more. When β is greater than 0%, the cost can be reduced by reducing the number of times of coating by a one-step coating process or by reducing the cost of coating materials by reducing raw materials. Although the upper limit is not particularly limited, it is preferably less than 50%. More preferably less than 30%, still more preferably less than 20%. When it is less than 50%, the adhesiveness with the electrode is improved. β=0 means that no inorganic particles are present on the surface of the porous layer and all are present in the porous layer. The surface portion of the porous layer is a surface layer having a depth that affects the adhesiveness between the outer surface of the porous layer and the electrode, and is shown in the image obtained using SEM-EDX, which will be described later. .

[Porous layer]
In the porous film of the present invention, a porous layer containing inorganic particles and organic resin particles is formed on at least one surface of a porous substrate which will be described later in detail.

The lower limit of the film thickness of the porous layer is preferably 2 μm or more, more preferably 3 μm or more, and still more preferably 4 μm or more. The upper limit of the film thickness of the porous layer is preferably 8 μm or less, preferably 7 μm or less, and more preferably 6 μm or less. The film thickness of the porous layer as used herein refers to the total thickness of the porous layers provided on the porous substrate. By setting the film thickness of the porous layer to 2 μm or more, sufficient thermal dimensional stability and uneven distribution of the organic resin tend to occur, and adhesion to the electrode can be obtained. Further, by setting the thickness to 8 μm or less, a porous structure is obtained, and rate characteristics and battery life are improved. Moreover, it is advantageous in terms of cost.

The surface free energy of the porous layer is preferably 10 mN/m or more and 80 mN/m or less, more preferably 15 mN/m or more and 70 mN/m or less, and still more preferably 20 mN/m or more and 60 mN/m or less. By making it 10 mN/m or more, the coating stability of the porous layer is improved. Further, by making it 80 mN/m or less, uneven surface distribution due to layer separation of the organic resin particles is likely to occur, and β/α can be easily controlled.

Also, the porous layer preferably has a glass transition temperature of 20°C or more and less than 80°C. The lower limit is more preferably 30°C or higher, still more preferably 40°C or higher. Also, the upper limit is more preferably 70° C. or lower, still more preferably 60° C. or lower. By setting the glass transition temperature to 20° C. or higher, swelling in the electrolyte is suppressed, and wet adhesion, rate characteristics, and battery life are improved. Moreover, by making it below 80 degreeC, the dry adhesiveness with an electrode improves more. In order to set the glass transition temperature in an appropriate range, it can be appropriately selected from a specific group of monomers.

(1) Organic Resin Particles Organic resin particles improve adhesion to electrodes. The resin constituting the organic resin particles is preferably a resin having adhesiveness to the electrode, and by unevenly distributing the organic resin particles on the surface layer of the porous film, the ion permeability is improved and the rate characteristics are improved. In addition, β/α can be lowered by lowering the surface free energy of the organic resin particles.

Examples of organic resin particles include fluorine-containing (meth)acrylate monomers, unsaturated carboxylic acid monomers, (meth)acrylic acid ester monomers, styrene monomers, olefin monomers, and diene monomers. It is preferable to have a polymer polymerized by using at least one monomer selected from the group consisting of polyimides, acrylamide-based monomers, and vinylidene fluoride monomers. Among these, in particular, the organic resin particles are a mixture of a polymer polymerized only with a fluorine-containing (meth)acrylate monomer and other polymers, or a mixture of a fluorine-containing (meth)acrylate monomer and other monomers. It is desirable to have a copolymer with As a result, by lowering the surface free energy of the organic resin particles, the organic resin particles can be unevenly distributed on the surface side, and the adhesion of the porous layer to the electrode can be improved. In this specification, "(meth)acrylate" means both "acrylate" and "methacrylate".

Polymers polymerized using fluorine-containing (meth)acrylate monomers contain repeating units obtained by polymerizing fluorine-containing (meth)acrylates.

Fluorine-containing (meth)acrylate monomers include 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3,3-pentafluoropropyl (meth)acrylate, 2-(perfluorobutyl ) ethyl (meth) acrylate, 3-(perfluorobutyl)-2-hydroxypropyl (meth) acrylate, 2-(perfluorohexyl) ethyl (meth) acrylate, 3-perfluorohexyl-2-hydroxypropyl (meth) acrylates, 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. One fluorine-containing (meth)acrylate monomer may be used alone, or two or more may be used in combination at an arbitrary ratio.

The proportion of the fluorine-containing (meth)acrylate monomer used in the organic resin particles is preferably greater than 20% by mass, more preferably 22%, based on 100% by mass of all constituent monomer components of the organic resin particles. % by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. Also, it is preferably 80% by mass or less, more preferably 60% by mass or less, still more preferably 50% by mass or less, still more preferably 40% by mass or less, and most preferably 35% by mass or less. Within the above range, the organic resin particles are likely to be unevenly distributed on the surface layer, and sufficient adhesiveness to the electrode can be obtained.

Whether or not the fluorine-containing (meth)acrylate monomer is used in the organic resin particles, and the proportion of the fluorine-containing (meth)acrylate monomer used in the organic resin particles are measured using a known method. can do. For example, first, the porous layer is removed from the porous film using an organic solvent such as water and alcohol, and then the organic solvent such as water and alcohol is sufficiently dried to obtain the constituents contained in the porous layer. An organic solvent capable of dissolving the organic resin component is added to the resulting 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. Using the obtained organic resin component, nuclear magnetic resonance spectroscopy ( ¹ H-NMR, ¹⁹ F-NMR, ¹³ C-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescence It can be calculated from the intensity of the signal derived from the fluorine-containing (meth)acrylate monomer by X-ray analysis (EDX), elemental analysis, pyrolysis gas chromatograph mass spectrometer (pyrolysis GC/MS), etc. can. In particular, after confirming the use of a fluorine-containing (meth)acrylate monomer by pyrolysis GC/MS, ¹³ C-NMR (a solid NMR sample tube was charged with the above organic resin component and an appropriate amount of solvent (deuterated chloroform)). The ratio of the fluorine-containing (meth)acrylate monomer used can be obtained by filling and standing overnight and then measuring by the DD/MAS method).

Also, the number of fluorine atoms contained in one molecule of the fluorine-containing (meth)acrylate monomer is preferably 3 or more and 13 or less. The number of fluorine atoms is more preferably 3 or more and 11 or less, still more preferably 3 or more and 9 or less. By setting the amount within the above range, the surface free energy of the organic resin particles can be reduced, and the coatability can be achieved at the same time. When the number of fluorine atoms is 3 or more, the surface free energy of the organic resin particles is sufficiently reduced, and the adhesiveness to the electrode is sufficient. Moreover, when the number of fluorine atoms is 13 or less, the coatability to the porous substrate is ensured, and the productivity is improved.

The number of fluorine atoms in the fluorine-containing (meth)acrylate can be measured using a known method. For example, first, the porous layer is removed from the porous film using an organic solvent such as water and alcohol, and then the organic solvent such as water and alcohol is sufficiently dried to obtain the constituents contained in the porous layer. An organic solvent capable of dissolving the organic resin component is added to the resulting constituent components to dissolve only the organic resin component and separate it 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. Using the obtained organic resin component, nuclear magnetic resonance spectroscopy ( ¹ H-NMR, ¹⁹ F-NMR, ¹³ C-NMR), infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), fluorescence It can be calculated from the intensity of the signal derived from the fluorine-containing (meth)acrylate monomer by X-ray analysis (EDX), elemental analysis, pyrolysis gas chromatograph mass spectrometer (pyrolysis GC/MS), etc. can. Among these, pyrolysis GC/MS is particularly useful.

Examples of unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, and crotonic acid. One type of unsaturated carboxylic acid monomer may be used alone, or two or more types may be used in combination at an arbitrary ratio.

(Meth)acrylate monomers include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, and octyl acrylate. , 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, cyclohexyl acrylate, hydroxyethyl acrylate, benzyl acrylate, isobornyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, Acrylics such as hydroxymethyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, 5-hydroxypentyl acrylate, 6-hydroxyhexyl acrylate, 7-hydroxyheptyl acrylate, 8-hydroxyoctyl acrylate acid ester; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, t-butylcyclohexyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, Octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, hydroxyethyl methacrylate, benzyl methacrylate, isobornyl methacrylate, dicyclopentanyl methacrylate, dicyclopentenyl methacrylate, hydroxymethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 5-hydroxypentyl methacrylate, 6-hydroxyhexyl methacrylate, 7-hydroxyheptyl methacrylate, 8-hydroxyoctyl methacrylate, etc. and methacrylic acid esters of. The (meth)acrylic acid ester monomers may be used singly or in combination of two or more at any ratio.

Among the above (meth)acrylic acid ester monomers, it is preferable to use a (meth)acrylate monomer having a hydroxyl group. By using a (meth)acrylate monomer having a hydroxyl group, the glass transition temperature of the organic resin particles can be adjusted and the dry adhesion to the electrode can be improved. The (meth)acrylate monomers having a hydroxyl group may be used singly or in combination of two or more at any ratio. Hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate (4-HBA), and 2-hydroxypropyl acrylate (2-HPA) are particularly preferred.

Styrenic monomers include styrene, α-methylstyrene, paramethylstyrene, t-butylstyrene, chlorostyrene, chloromethylstyrene, hydroxymethylstyrene and the like. Examples of olefinic monomers include ethylene and propylene. Examples of diene-based monomers include butadiene and isoprene.

Examples of acrylamide-based monomers include acrylamide. Among these, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The vinylidene fluoride monomer may be a homopolymer using a vinylidene fluoride monomer alone or a copolymer with other monomers. Monomers copolymerizable with vinylidene fluoride include, for example, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, vinyl fluoride, (meth)acrylic acid, methyl (meth)acrylate, (meth)acrylic acid (Meth)acrylic acid esters such as ethyl, vinyl acetate, vinyl chloride, acrylonitrile and the like. These may be used individually by 1 type, and may be used in combination of 2 or more types by arbitrary ratios.

The organic resin particles are a mixture containing a polymer polymerized using a fluorine-containing (meth)acrylate monomer and a polymer polymerized using a (meth)acrylate monomer having a hydroxyl group, or It preferably contains a copolymer polymerized using a monomer mixture containing a fluorine-containing (meth)acrylate monomer and a hydroxyl group-containing (meth)acrylate monomer.

The content of the polymer or copolymer polymerized using a (meth)acrylate monomer having a hydroxyl group contained in the organic resin particles is 0 when the total constituent components of the organic resin particles are 100% by mass. More than mass % and 7.0 mass % or less are preferable. It is more preferably 0.5% by mass or more and 5.0% by mass or less, and still more preferably 1.0% by mass or more and 3.0% by mass or less. When this content is greater than 0% by mass, the polymerization stability of the organic resin particles is improved. In addition, by making it 7.0% by mass or less, sufficient dry adhesion with the electrode can be obtained, and by suppressing swelling in the electrolytic solution, sufficient wet adhesion with the electrode can be obtained. , the distance between the electrodes becomes constant, and the decrease in capacity during initial charge/discharge can be suppressed, so that the yield during initial charge/discharge is improved.

The content of the polymer or copolymer polymerized using the (meth)acrylate monomer having a hydroxyl group contained in the organic resin particles can be measured using a known method. For example, first, the porous layer is detached from the porous film using an organic solvent such as water and alcohol, and then the organic solvent such as water and alcohol is sufficiently dried to obtain the constituents contained in the porous layer. An organic solvent capable of dissolving the organic resin component is added to the resulting 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. Using the obtained organic resin component, after confirming the presence or absence of a (meth)acrylate monomer having a hydroxyl group by pyrolysis GC/MS, ¹³ C-NMR (solid NMR sample tube with the above organic resin component) Amount of solvent (heavy chloroform) is filled, left to stand overnight, and then measured by DD/MAS method) to determine the content of the copolymer polymerized using the (meth)acrylate monomer having a hydroxyl group. be able to.

When obtaining a copolymer polymerized by using a fluorine-containing (meth)acrylate monomer and a (meth)acrylate monomer having a hydroxyl group, a monomer having two or more reactive groups per molecule is used. It is preferred to carry out the polymerization using a monomer. By using a monomer having two or more reactive groups per molecule, it has excellent electrolyte resistance with suppressed swelling in the electrolyte, dry adhesion with the electrode, and electrode in the electrolyte. It is possible to obtain polymer particles having excellent wet adhesiveness with.

As the monomer having two or more reactive groups per molecule, for example, it is preferable to use a (meth)acrylate monomer having two or more reactive groups per molecule, and alkylene glycol di(meth) ) acrylates and urethane di(meth)acrylates are more preferred.

The polymer contained in the organic resin particles has a glass transition temperature of − It is preferable that a monomer having a temperature of 100° C. or higher and 0° C. or lower is used and polymerized. The glass transition temperature range is more preferably -70°C or higher and -10°C or lower, more preferably -50°C or higher -20°C. Here, the glass transition temperature is the midpoint glass transition temperature measured by differential scanning calorimetry (DSC) according to JIS K7121:2012. The midpoint glass transition temperature is defined as the temperature at the point where a straight line equidistant in the vertical axis direction from the extended straight line of each base line intersects with the curve of the stepwise change portion of the glass transition.

The ratio of the monomer having a glass transition temperature of −100° C. or more and 0° C. or less when polymerized only by the monomer is 100% by mass of the total constituent monomer components of the organic resin particles. , it is preferably greater than 0% by mass and 10.0% by mass or less. This ratio is more preferably 1% by mass or more and 7.0% by mass or less, and still more preferably 3.0% by mass or more and 5.0% by mass or less. When the amount is greater than 0% by mass, the organic resin particles are softened and the adhesiveness is improved. On the other hand, by setting this ratio to 10.0% by mass or less, the softening of the organic resin particles is less likely to occur, and the swelling of the organic resin particles in the electrolytic solution can be suppressed. When the proportion of the monomer having a glass transition temperature of −100° C. or more and 0° C. or less when polymerized only by the monomer is reduced, the rate of decrease in wet adhesion after dry adhesion tends to be suppressed. , which is advantageous in terms of improving wet adhesion.

The porous layer of the porous film of the present invention may contain organic resin particles that impart different functions in addition to organic resin particles that have adhesiveness to electrodes. That is, the porous layer can contain at least two types of organic resin particles. As the organic resin particles imparting different functions, an emulsion binder is used to adhere the organic resin particles to each other or to adhere the organic resin particles and the inorganic particles to each other, or to provide a binder function to adhere the organic resin particles to the porous substrate. You can use it as Adhesion is improved by the binder function, and adhesion to the electrode can be further improved. As the organic resin particles, a resin that is electrochemically stable within the battery usage range is preferable.

In the present invention, the organic resin particles include, in addition to those having a particle shape, those partially formed into a film and fused with the surrounding particles and 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 is preferably 100 nm or more and 500 nm or less. The lower limit is more preferably 120 nm or more, still more preferably 150 nm or more, and most preferably 170 nm or more. Also, the upper limit is more preferably 400 nm or less, still more preferably 300 nm or less, and most preferably 250 nm or less. By setting the average particle size to 100 nm or more, a porous structure is obtained, and rate characteristics and battery life are further improved. Further, by setting the thickness to 500 nm or less, the film thickness of the porous layer becomes appropriate, and the rate characteristics and battery life can be further improved.

The average particle size of organic resin particles can be measured using the following method. An image (image 1) obtained by imaging the surface of the porous layer at a magnification of 30,000 times using a field emission scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.), and only inorganic particles are contained in the same field of view. An EDX image (image 2) of the element 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. Particles that do not contain the element that only the inorganic particles in Image 2 have are defined as organic resin particles. If the particles cannot be visually distinguished, the organic resin particles are defined as those containing elemental fluorine by elemental analysis. Next, for the organic resin particles, draw a circumscribed rectangle (including a square) with the smallest area for each organic resin on Image 1, and measure the length of the long side (one side in the case of a square) of the particle. The particle diameters of all the organic resin particles found in Image 1 were measured, and the arithmetic average value was taken as the average particle diameter. However, if 50 organic resin particles are not observed in image 1, a plurality of images are taken, and the total number of particles of all the organic resin particles contained in the plurality of images reaches 50. I took a picture and found it. The organic resin particles were measured, and the arithmetic average value was taken as the average particle size.

(2) Inorganic Particles The porous layer of the porous film of the present invention contains inorganic particles. When the porous layer contains inorganic particles, it is possible to impart thermal dimensional stability and suppress short circuits due to foreign matter.

Specific examples of 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; Poorly soluble ionic crystal particles such as barium fluoride and barium sulfate may be used. The inorganic particles are preferably particles composed of at least one selected from the group consisting of inorganic hydroxides, inorganic oxides and inorganic sulfates. Among them, aluminum oxide which is effective in increasing strength, and organic resins. Particularly preferred are boehmite and barium sulfate, which are effective in reducing wear of parts during the process of dispersing particles and inorganic particles. Furthermore, one type of these inorganic particles may be used, or two or more types may be mixed and used.

The shape of the inorganic particles used may be spherical, plate-like, needle-like, rod-like, elliptical, etc. Any shape may be used. Among them, a spherical shape is preferable from the viewpoint of surface modification properties, dispersibility, and coatability.

(3) Binder The porous layer of the porous film of the present invention is composed of: It may contain a binder. As the binder, a resin that is electrochemically stable within the battery usage range is preferred. In addition, binders include organic solvent-soluble binders, water-soluble binders, emulsion binders, and the like, and may be used alone or in combination.

When using a binder soluble in an organic solvent and a water-soluble binder, the preferred viscosity of the binder itself is preferably 10000 mPa·s or less when the concentration is 15% by mass. It is more preferably 8000 mPa·s or less, still more preferably 5000 mPa·s or less. When the concentration is 15% by mass and the viscosity is 10,000 mPa s or less, the viscosity increase of the coating material can be suppressed, and the organic resin particles are unevenly distributed on the surface, thereby improving dry adhesion and wet adhesion with the electrode. .

When an emulsion binder is used, the dispersant includes water and organic solvents such as alcohol solvents such as ethanol and ketone solvents such as acetone. from the point of view of the mixability of The particle size of the emulsion binder is 30-1000 nm, preferably 50-500 nm, more preferably 70-400 nm, still more preferably 80-300 nm. By setting the particle size of the emulsion binder to 30 nm or more, an increase in air permeability can be suppressed, and battery characteristics are improved. Further, by setting the thickness to 1000 nm or less, sufficient adhesion between the porous layer and the porous substrate can be obtained.

Resins that can be used as binders include, for example, polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone, polyetherketone, Resins such as polycarbonate, polyacetal, polyvinyl alcohol, polyethylene glycol, cellulose ether, acrylic resin, polyethylene, polypropylene, polystyrene, and urethane can be used. Among these, it is particularly preferable to use an acrylic resin because stronger adhesion can be obtained by interacting with the organic resin particles. In addition, by using polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer (hereinafter sometimes referred to as "polyvinylidene fluoride resin"), the adhesiveness with the electrode in the electrolytic solution is further improved. , is particularly preferred. These resins may be used singly or in combination of two or more if necessary.

Also, the vinylidene fluoride content of the polyvinylidene fluoride-based resin is preferably 80% by mass or more and less than 100% by mass of the components constituting the resin. More preferably, it is 85% by mass or more and 99% by mass or less. More preferably, it is 90% by mass or more and 98% by mass or less. If the vinylidene fluoride content is less than 80% by mass, sufficient mechanical strength cannot be obtained, and although the adhesiveness to the electrode is exhibited, the strength is weak and the adhesiveness may be easily peeled off. Moreover, when the vinylidene fluoride content is 100% by mass, the electrolytic solution resistance is lowered, and sufficient adhesiveness may not be obtained.

When using a water-soluble binder, the content in the porous layer is preferably 0.5% by mass or more with respect to the total amount of the organic resin particles and the inorganic particles. It is more preferably 1% by mass or more, still more preferably 1.5% by mass or more. Moreover, 10 mass % or less is preferable. More preferably 8% by mass or less, still more preferably 6% by mass or less. By setting the content 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. Moreover, by making it 10% by mass or less, an increase in air permeability can be suppressed, and battery characteristics are improved.

When using an emulsion binder, the content in the porous layer is preferably 1% by mass or more with respect to the total amount of the organic resin particles and the inorganic particles. It is more preferably 5% by mass or more, still more preferably 7.5% by mass or more, and most preferably 10% by mass or more. Also, it is preferably 30% by mass or less, more preferably 25% by mass or less, and still more preferably 20% by mass or less. Sufficient adhesion between the porous layer and the porous substrate can be obtained by setting the content of the emulsion binder to 1% by mass or more. Moreover, by making it 30% by mass or less, an increase in air permeability can be suppressed, and battery characteristics are improved. In particular, the content of 7.5% by mass or more and 20% by mass or less not only promotes the adhesion of the organic resin particles and the inorganic particles and the adhesion of these particles to the substrate, but also interacts with the organic resin particles, and the electrodes. dry adhesion and wet adhesion are also improved.

(4) Formation of Porous Layer A method for forming the porous layer will be described below.

The porous layer may be formed through a two-step coating process, or may be formed through a one-step coating process. When forming by a two-step coating process, a coat layer containing inorganic particles is formed in the first step, and a coat layer containing organic resin particles is formed in the second step in this order. Since the coating liquid containing the organic resin particles is present on the surface layer, the adhesion to the electrode can be easily ensured. In this case, the coating layer containing the organic resin particles can be made thinner, or the amount of the organic resin particles can be reduced to such an extent that the organic resin particles are locally present on the surface, so that the cost can be reduced.

The two-step coating process involves preparing a coating liquid consisting of inorganic particles and a solvent, coating the coating liquid on a porous substrate, drying the solvent of the coating liquid, and then organic resin particles and the solvent. In this method, a coating solution is prepared, the coating solution is applied onto the inorganic particle coating layer, and the solvent of the coating solution is dried to form a porous layer, thereby obtaining a porous film. Spray coating may be used as the coating method.

In the one-step coating process, a coating solution comprising organic resin particles, inorganic particles and a solvent is prepared, the coating solution is applied onto a porous substrate, and the solvent of the coating solution is dried to form a porous layer. , a method of obtaining a porous film.

The coating method is not particularly limited, but the latter can reduce costs by reducing the number of coatings. Therefore, the method for forming the porous layer by the latter method will be described below.

(i) First, a coating liquid is prepared by dispersing organic resin particles at a predetermined concentration. The coating liquid is prepared by dispersing, suspending, or emulsifying organic resin particles in a solvent. The solvent for the water-based dispersion coating liquid is not necessarily limited, but is not particularly limited as long as it can disperse, suspend or emulsify the organic resin particles in a solid state. Examples include organic solvents such as methanol, ethanol, 2-propanol, acetone, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, N-methylpyrrolidone, dimethylacetamide, dimethylformamide and dimethylformamide. From the viewpoints of low environmental load, safety, and economy, water-based emulsions in which an organic resin is emulsified in water or a mixture of water and alcohol are preferred. When water is used, a solvent other than water may be added.

The solid content concentration of the coating liquid is preferably 5% or more and 40% or less. By setting it to the predetermined range, both coating stability and uneven surface distribution during coating and drying can be achieved. Moreover, the solution viscosity of the coating liquid is preferably 5 mPa·s or more and 50 mPa·s or less. By setting it to the predetermined range, both the dispersibility of the coating liquid and the surface uneven distribution during coating and drying can be achieved. By adjusting the solid content concentration of the coating liquid to be low and the viscosity to be low within the above preferable range, the organic resin particles can be adjusted so as to be unevenly distributed in the outer layer.

In addition, film-forming aids, dispersants, thickeners, stabilizers, antifoaming agents, leveling agents, etc. may be added to the coating liquid as necessary.

Examples of methods for dispersing the coating liquid include ball mills, bead mills, sand mills, roll mills, homogenizers, ultrasonic homogenizers, high-pressure homogenizers, ultrasonic devices, and paint shakers. Among them, by selecting a dispersing method (bead mill, sand mill) in which a high pressure is applied to the inorganic particles and the organic resin particles during dispersing, the dispersibility is improved and the surface uneven distribution of the organic resin particles is more likely to occur. A plurality of these mixing and dispersing machines may be combined for stepwise dispersion.

(ii) Next, the obtained coating liquid is applied onto the porous substrate. Coating methods include, for example, 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 methods, etc. can be used. The coating method is not limited to these, and the coating method may be selected according to preferable conditions such as the organic resin, binder, dispersant, leveling agent, solvent to be used, and base material.

(iii) After that, the solvent of the coating liquid is dried to form a porous layer. The drying temperature is preferably 40°C or higher and 100°C or lower. By doing so, the porous layer is uniformly dried, and the arithmetic mean height (Sa) in 2200 μm square of the porous film surface on the side in contact with the porous layer is the height of the porous substrate surface on the side in contact with the porous layer. It becomes susceptible to the arithmetic mean height (Sa) in 2200 μm square, and the adhesiveness with the electrode is improved. If the temperature is less than 40°C, the solvent in the coating liquid will not dry. On the other hand, if the drying temperature is higher than 100° C., the amount of heat during drying increases and the shape of the particles cannot be maintained, resulting in film formation. Therefore, it is possible to achieve both good adhesiveness with the electrode and cost reduction by improving the coating and drying speeds by setting the content to a predetermined range.

[Porous substrate]
In the present invention, the porous substrate has a structure in which micropores are formed therein and these micropores are connected from one surface to the other surface. Examples of porous substrates include microporous membranes, non-woven fabrics, and porous membrane sheets made of fibrous materials. Arithmetic average height (Sa) in 2200 μm square of the porous substrate surface on the side in contact with the porous layer, 12 nm square, from the viewpoint of being electrically insulating, electrically stable, and stable to the electrolytic solution and the manufacturing method. The porous base material is preferably a polyolefin microporous membrane because of ease of adjustment of the arithmetic mean roughness (Ra) in 2200 μm square and the height of protruding peaks (Spk) in 2200 μm square. That is, it is preferably a porous membrane made of polyolefin. Resins constituting the polyolefin microporous membrane include polyethylene, polypropylene, ethylene-propylene copolymers, and mixtures thereof. The polyolefin microporous membrane may be a single membrane or a laminated membrane having a plurality of layers. Examples thereof include a single membrane containing 90% by mass or more of polyethylene and a laminated membrane made of polyethylene and polypropylene.

The lower limit of the arithmetic mean roughness (Ra) of the surface of the porous base material on the side in contact with the porous layer on a 12 nm square is preferably 40 nm or more and 300 nm, more preferably 80 nm or more, and still more preferably 120 nm or more. By setting the arithmetic mean roughness (Ra) to 40 nm or more, the arithmetic mean roughness of the porous substrate is also improved, and since fine unevenness exists in a local range of 12 nm square, it follows the unevenness of the active material in the electrode. Therefore, dry adhesion and wet adhesion to the electrode can be further improved. In addition, by setting the arithmetic mean roughness (Ra) to 300 nm or less, excessive adhesion to the electrode can be suppressed, and good rate characteristics and battery life can be exhibited.

The height (Spk) of protruding peaks in a 2200 μm square on the surface of the porous substrate on the side in contact with the porous layer is preferably 0.10 μm or more and 0.40 μm or less, and the lower limit is more preferably 0.12 μm or more. 0.15 μm or more is more preferable. The upper limit of the protruding peak height (Spk) is more preferably 0.30 μm or less, and even more preferably 0.25 μm or less. In addition, by setting the height (Spk) of the protruding ridges to 0.10 μm or more, there are sufficient protruding portions on the porous base material, and when the porous layer is formed, the porous base material and the porous base material The peelability of the porous layer is improved to form a strong porous layer. By improving the releasability, it is possible to further improve dry adhesion and wet adhesion to the electrode. On the other hand, by setting the protruding peak height (Spk) to 0.40 μm or less, the porous layer appropriately enters the porous base material, and the rate characteristics and battery life can be exhibited.

The thickness of the porous substrate is preferably 3 μm or more and 15 μm or less, more preferably 5 μm or more as the lower limit, and more preferably 12 μm or less as the upper limit.

Next, the method for manufacturing the porous base material will be explained. Here, the method for producing the porous substrate is not particularly limited, but the method for producing a polyolefin microporous membrane will be described below as an example.

(a) First, a plasticizer is added to the polyolefin resin composition described above in a twin-screw extruder, and melt-kneaded to prepare a resin solution.

The polyolefin resin composition is composed of a polyolefin resin, and may be a single composition or a mixture of two or more polyolefin resins. Polyolefin resins include, but are not limited to, polyethylene, polypropylene, and the like. As the polyethylene resin, ultra-high molecular weight polyethylene, high density polyethylene, and medium density polyethylene low density may be used as a single composition, or a mixture of different molecular weights may be used. It is preferable to use a mixture of two or more polyethylenes selected from the group consisting of ultra ^- high molecular weight polyethylene, high-density polyethylene, medium-density polyethylene and low-density polyethylene. A mixture of A) and polyethylene (B) having an Mw of 1×10 ⁴ or more and less than 9×10 ⁴ is preferable, and it is more preferable to contain an ultra-high molecular weight polyethylene having an Mw of 1×10 ⁶ or more. The ratio of ultra high molecular weight polyethylene (A) and polyethylene (B) is 50% by mass, with the total of ultra high molecular weight polyethylene (A) and polyethylene (B) being 100% by mass. It is preferable in it being above.

The plasticizer is preferably liquid at room temperature so that it can be stretched at a relatively high magnification. Specific examples include aliphatic hydrocarbons such as nonane, decane, decalin, paraxylene, undecane, dodecane, and liquid paraffin. As for the mixing ratio of the polyolefin resin composition and the plasticizer, the content of the polyolefin resin composition is preferably 10% by mass or more and 50% by weight or less.

By providing the polyolefin resin composition, the content of the plasticizer, and the cooling step, the arithmetic mean height (Sa) and the height of the protruding peaks (Spk ), the arithmetic mean roughness (Ra) in 12 nm square can be adjusted to a large extent, and it becomes easy to set it within a predetermined range.

(b) Next, the resin solution is fed from the extruder to a die, extruded into a sheet, and cooled to form a gel sheet.

(c) After that, the gel-like sheet is stretched. The gel-like sheet is preferably stretched at a predetermined magnification by a tenter method, a roll method, an inflation method, or a combination thereof. The stretched area ratio is preferably 4 times or more and 100 times or less, more preferably 12 times or more and 64 times or less, and particularly preferably 25 times or more and 49 times or less. The lower the draw ratio, the higher the arithmetic mean height (Sa) and protruding peak height (Spk) in 2200 μm square of the surface of the porous substrate on the side in contact with the porous layer, and the arithmetic mean roughness (Ra) in 12 nm square. can be increased.

(d) After that, the plasticizer is removed using a washing solvent, and the polyolefin microporous membrane can be obtained by drying.

(e) In addition to the above steps, stretching (also called dry re-stretching) may be performed after the drying step. The second stretching can be performed by a tenter method or the like while heating the polyolefin microporous membrane in the same manner as the stretching described above. The re-stretching ratio is preferably 1.01 to 2.0 times in the case of uniaxial stretching, and preferably 1.01 to 2.0 times in the case of biaxial stretching. The lower the re-stretching ratio, the higher the arithmetic average height (Sa) and protruding peak height (Spk) in 2200 μm square of the surface of the porous substrate on the side in contact with the porous layer, and the arithmetic average roughness (Ra) in 12 nm square. can be increased.

[Porous film]
The porous film of the present invention preferably has an arithmetic mean height (Sa) of 0.085 μm or more and 0.3 μm or less in a 2200 μm square on the surface on which the porous layer is provided. More preferably, it is 0.010 μm or more. By setting it to the above range, it is possible to further improve the adhesiveness with the electrode by following the unevenness of the active material existing in the electrode during the bonding step (heat press) with the electrode described above. . In the porous film, the arithmetic mean height (Sa) in 2200 μm square of the surface on the side where the porous layer is provided is the arithmetic mean height (Sa) in 2200 μm square of the surface of the porous substrate in contact with the porous layer ( Sa) tends to be greatly affected, and the arithmetic mean height (Sa) in a 2200 μm square of the surface of the porous substrate on the side in contact with the porous layer is appropriately selected within the above preferable range. can be within

[Secondary battery]
The porous film of the present invention can be suitably used as a separator for secondary batteries such as lithium ion batteries. A lithium-ion battery has a configuration in which a secondary battery separator 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 obtained by laminating a positive electrode material composed of an active material, a binder _resin , and a conductive aid _on a current collector. Lithium-containing transition metal oxides having a layered structure, spinel-type manganese oxides such as LiMn ₂ O ₄ , and iron-based compounds such as LiFePO ₄ can be used. A resin having high oxidation resistance may be used as the binder resin. Specific examples include fluorine resins, acrylic resins, styrene-butadiene resins, and the like. Carbon materials such as carbon black and graphite are used as conductive aids. As the current collector, a metal foil is suitable, and an aluminum foil is often used in particular.

The negative electrode is obtained by laminating a negative electrode material composed of an active material and a binder resin on a current collector, and the active material includes carbon materials such as artificial graphite, natural graphite, hard carbon and soft carbon, tin and silicon. , metal materials such as metallic lithium, and lithium titanate (Li ₄ Ti ₅ O ₁₂ ). A fluorine resin, an acrylic resin, a styrene-butadiene resin, or the like is used as the binder resin. As the current collector, metal foil is suitable, and copper foil is often used in particular.

The electrolytic solution serves as a field for transferring ions between the positive electrode and the negative electrode in the secondary battery, and is made by dissolving the electrolyte in an organic solvent. Examples of electrolytes include LiPF ₆ , LiBF ₄ , and LiClO ₄ , and LiPF ₆ is preferably used from the viewpoint of solubility in organic solvents and ionic conductivity. Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, etc. Two or more of these organic solvents may be used in combination.

As a method for producing a secondary battery, first, an active material and a conductive agent are dispersed in a solution of a binder resin to prepare a coating liquid for an electrode. A positive electrode and a negative electrode are obtained by drying. The film thickness of the coating film after drying is preferably 50 μm or more and 500 μm or less. A secondary battery separator is placed between the obtained positive electrode and negative electrode so as to be in contact with the active material layer of each electrode, enclosed in an outer packaging material such as an aluminum laminate film, and after injecting an electrolytic solution, the negative electrode lead and the Install a safety valve and seal the exterior material. The secondary battery thus obtained has high adhesion between the electrode and the secondary battery separator, has excellent rate characteristics and battery life, and can be manufactured at low cost.

The present invention will be described in detail below with reference to examples, but the present invention is not limited by these. In the description below, "%" and "parts" represent "% by mass" and "parts by mass", respectively.

The present invention will be specifically described below with reference to examples, but the present invention is not limited by these.

[Measuring method]
(1) Arithmetic mean height (Sa) in 2200 μm square on the surface of the porous substrate on the side in contact with the porous layer, protruding peak height (Spk)
20 g of water was used to remove the porous layer from a 5 cm×5 cm sample cut out from the porous film, and the water was sufficiently dried to obtain the target porous substrate. In addition, when it is not possible to sufficiently desorb with water, an organic solvent such as alcohol is used, and after the desorption, it is sufficiently dried. Next, the obtained porous substrate was attached to a metal frame having an outer size of 6 cm square and an inner size of 3 cm square so as not to cause wrinkles. Using a scanning white light interference microscope VS-1540 manufactured by Hitachi High-Tech Science Co., Ltd., the surface roughness was measured under the following conditions, and the three-dimensional surface roughness parameters (Sa, Spk) were calculated according to ISO 25178. When the porous layer is formed on both sides of the porous substrate, 4 points on each side, 8 points in total, are measured on both surfaces of the substrate on the side in contact with the porous layer under the same conditions. The values were averaged. In addition, when a porous layer is formed on one side of the porous substrate, 4-point measurement is performed on the surface of the porous substrate on the side in contact with the porous layer side under the same conditions, and the measured values are averaged. did.
・Objective lens: 5x ・Tube lens: 0.5x ・Wavelength filter: 530white
・Camera: High pixel ・Measurement mode: Wave
・Cutoff: None.

(2) Volume content rate α of inorganic particles in the porous layer (volume content rate α)
A 10 cm×10 cm sample cut out from the porous film was used to extract the porous layer using 40 g of water, and the water was sufficiently dried to obtain the constituent components of the porous layer. In addition, an organic solvent such as alcohol may be used when water cannot be used to sufficiently desorb. After measuring the mass of the total amount of the constituent components obtained, the constituent components were burned at a high temperature at which the organic resin component melts and decomposes, 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 constituent components)×100. In addition, the content of the organic resin component in the porous layer was calculated in mass % by the formula ((mass of the total amount of the constituent components−mass of the inorganic particles)/(mass of the total amount of the constituent ingredients))×100. Next, the density of each of the inorganic particles and the organic resin component was measured with a hydrometer. The volume content of the inorganic particles in the porous layer was calculated in volume % from the mass content (% by mass) of the inorganic particles and the organic resin component obtained above and the density of the inorganic particles and the organic resin component. The above measurements were performed on five samples, and the measured values were averaged.

(3) Occupancy β of inorganic particles on the surface of the porous layer (occupancy β)
The surface of the porous layer of the sample in which Pt/Pd was deposited on the porous film for 30 seconds was measured with SEM-EDX (Hitachi SE8200) at a magnification of 10,000 and an acceleration voltage of 5.0 kV, and the inorganic elements of the inorganic particles were analyzed. did Using image analysis software (Toyo Technica, SPIP 6.0.10), after masking and removing the element symbol display, magnification display, scale bar, and acceleration voltage display part in the EDX image, "particle / hole analysis" mode, the threshold level of the threshold is set to 130 nm as a detection method, and the area ratio (%), which is a parameter representing the area of the portion corresponding to the inorganic element of the inorganic particle with respect to the area of the image as a percentage, is the occupancy rate of the inorganic particle. β. The above measurements were performed on five samples, and the measured values were averaged.

(4) Arithmetic mean height (Sa) in 2200 μm square of the porous film surface on the side where the porous layer is provided
A sample of 5 cm×5 cm cut out from the porous film was pasted on a metal frame with an outer size of 6 cm square and an inner size of 3 cm square so as not to cause wrinkles. Using a scanning white light interference microscope VS-1540 manufactured by Hitachi High-Tech Science Co., Ltd., the surface roughness was measured under the following conditions, and the three-dimensional surface roughness parameter (Sa) was calculated according to ISO 25178. Under the same conditions, both surfaces of the porous film were measured at 4 points on each side, 8 points in total, and the measured values were averaged. When the porous layer was provided on one side, the values measured at four points on the surface on which the porous layer was provided were averaged.
・Objective lens: 5x ・Tube lens: 0.5x ・Wavelength filter: 530white
・Camera: High pixel ・Measurement mode: Wave
・Cutoff: None.

(5) Arithmetic mean roughness (Ra) of 12 nm square on the surface of the porous substrate on the side in contact with the porous layer
50 g of water was used to remove the porous layer from a sample cut out from the porous film to a size of 12 cm×12 cm, and the water was sufficiently dried to obtain the target porous substrate. In addition, when it is not possible to sufficiently desorb with water, an organic solvent such as alcohol is used, and after the desorption, it is sufficiently dried. Using a scanning probe microscope (Seiko Instruments SPA-500), the porous substrate is fixed to the sample stage with carbon tape, the cantilever is SI-DF40, the measurement area is 12 μm square, and the amplitude attenuation rate is −0. Arithmetic mean roughness (Ra) was measured in DFM mode with a scanning frequency of 0.5 Hz. When porous layers are formed on both sides of the porous substrate, measure 3 points on each side, 6 points in total, on both surfaces of the porous substrate under the same conditions, and average the measured values. did. In addition, when a porous layer is formed on one side of the porous substrate, three-point measurement is performed on the surface of the porous substrate on the porous layer side under the same conditions, and the measured values are arithmetically averaged. .

(6) Surface free energy of porous layer The surface of a sample cut into 100 mm × 100 mm from the porous film is subjected to contact angle measurement with water, ethylene glycol, methylene iodide, and formamide, and the porous layer is calculated according to the Young-Dupre equation. The surface free energy (mN/m) of the thin layer was measured. The above measurements were performed on five samples, and the measured values were arithmetically averaged.

(7) Film thickness of the porous layer At the center of the sample cut out from the porous film to 100 mm × 100 mm, cut out a cross section of the sample with a microtome, and examine the cross section with a field emission scanning electron microscope (manufactured by Hitachi, Ltd. S -800, acceleration voltage of 26 kV) and a magnification of 10,000 times, and the distance from the interface with the porous substrate to the highest point on the surface was measured. 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 film thickness of the porous layer. Regarding the interface between the porous base material and the porous layer, the interface was defined as a place where the inorganic particles were no longer observed in the region where the inorganic particles were present. The above measurements were performed on five samples, and the measured values were arithmetically averaged.

(8) Film Thickness of Porous Film The film thickness at the central portion of a sample of 100 mm×100 mm cut out from the porous film was measured with a contact thickness meter (Lightmatic manufactured by Mitutoyo Co., Ltd.). The above measurements were performed on five samples, and the measured values were arithmetically averaged.

(9) Glass transition temperature of porous film The midpoint glass transition temperature of the porous film measured by differential scanning calorimetry (DSC) in accordance with the provisions of "JIS K7121: 2012 Method for measuring the transition temperature of plastics" . The midpoint glass transition temperature was taken as the temperature at the point where a straight line equidistant from the extended straight line of each base line intersects the curve of the stepwise change portion of the glass transition. The above measurements were performed on three samples, and the measured values were arithmetically averaged.

(10) Peel Strength Between Porous Substrate and Porous Layer A sample of 25 mm wide and 100 mm long was cut out of the porous film and attached to an acrylic plate having a thickness of 2 cm. Next, a tape (manufactured by 3M, product number 810-3-15) cut into 18 mm width and 150 mm length was attached to the sample by roll pressing at 0.5 MPa, 25° C., 0.2 m/min. Thereafter, the tape was peeled off at 180 degrees under the condition of a peeling speed of 300 mm/min, and the peel strength was taken as the average value from 30 mm to 70 mm in the length direction.
・Excellent peel strength: The porous substrate and the porous layer were peeled off with a stronger force.
- "Excellent" peel strength: The porous base material and the porous layer were separated with a strong force.
- Peel strength is "good": The porous substrate and the porous layer were peeled with a slightly strong force.
- Peel strength is "Fair": The porous substrate and the porous layer were peeled off with a weak force.
- "Poor" peel strength: The porous substrate and the porous layer were peeled off with an extremely weak force.

The magnitude of the force required for peeling is "excellent" > "excellent" > "good" > "acceptable" > "bad".

(11) Thermal shrinkage (thermal dimensional stability)
For three samples of 100 mm × 100 mm cut out from the porous film, mark the midpoint of one side and the midpoint of the opposite side of each sample, measure the length between the midpoints, and place in an oven at 150 ° C. without tension. Heat treatment was performed for 30 minutes at the bottom. For the sample after heat treatment, measure the length between the midpoints of the same place as before heat treatment, calculate the thermal shrinkage rate from the following formula, "Excellent", 10% or more and less than 20% as "Good", 20% or more and less than 40% as "Fair", 40% or more as "Bad").
Thermal shrinkage rate (%)=[(length between midpoints before heat treatment−length between midpoints after heat treatment)/(length between midpoints before heat treatment)]×100.

(12) Dry Adhesion with Electrode Active material is Li(Ni _5/10 Mn _2/10 Co _3/10 )O ₂ , binder is vinylidene fluoride resin, and conductive aid is acetylene black and graphite positive electrode 20 mm×50 mm. and a porous film of 25 mm × 55 mm are placed so that the active material and the porous layer are in contact, and hot press is performed for 10 seconds at a pressure of 5 MPa in a heating environment of 70 ° C. to bond the electrode and the porous film. . Next, it was manually peeled off using tweezers, and the adhesive strength was evaluated in the following 5 stages. Similarly, the adhesive strength between the porous film and the negative electrode in which the active material is graphite, the binder is vinylidene fluoride resin, and the conductive agent is carbon black, is measured. It was determined as adhesive strength.
・Excellent adhesion strength: The electrode and the porous film were separated with a stronger force.
- Adhesive strength is "excellent": The electrode and the porous film were separated with a strong force.
- "Good" adhesion strength: The electrode and the porous film were separated with a slightly strong force.
・Adhesion strength is “Fair”: The electrode and the porous film were peeled off with a weak force.
- "Poor" adhesive strength: The electrode and the porous film were separated with very weak force.

(13) Wet Adhesion to Electrode A negative electrode (width 20 mm×length 70 mm) containing graphite as an active material, vinylidene fluoride resin as a binder, and carbon black as a conductive aid was used as an electrode. A porous film (width 25 mm × length 80 mm) was placed so that the ends of the electrode and the porous film overlapped in the length direction, and the active material and the porous layer were in contact, and the condition a (70 C. for 6 seconds at a pressure of 5 MPa) to adhere the electrode and the porous film to prepare a test piece. The test piece is placed in a bag-shaped aluminum laminate film with three pieces closed, and after the electrolytic solution injection process (1 g of electrolytic solution is impregnated from the porous film side of the test piece), the aluminum is sealed using a vacuum sealer. The remaining one side of the laminate film was enclosed. Here, the electrolytic solution used was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate:diethyl carbonate=1:1 (volume ratio) so as to have a concentration of 1 mol/liter. Next, the aluminum laminate film after enclosing this test piece was stored in a 60° C. environment for 17 hours under static conditions. The test piece was taken out from the aluminum laminate film, and the electrolytic solution on the surface of the test piece was wiped. After that, the adhesive strength was evaluated in the following 5 stages by manually peeling using tweezers.
・Excellent adhesion strength: The electrode and the porous film were separated with a stronger force.
- Adhesive strength is "excellent": The electrode and the porous film were separated with a strong force.
- "Good" adhesion strength: The electrode and the porous film were separated with a slightly strong force.
・Adhesion strength is “Fair”: The electrode and the porous film were peeled off with a weak force.
- "Poor" adhesive strength: The electrode and the porous film were separated with very weak force.

(14) Battery production The positive electrode sheet contains 96 parts by mass of Li(Ni _5/10 Mn _2/10 Co _3/10 )O ₂ as a positive electrode active material, and 1.0 parts by mass of acetylene black and graphite as positive electrode conductive aids. Each positive electrode slurry was prepared by dispersing 2 parts by mass of polyvinylidene fluoride as a positive electrode binder in N-methyl-2-pyrrolidone using a planetary mixer. (Coating basis weight: 10.0 mg/cm ² ). This positive electrode sheet was cut into a size of 40 mm×40 mm. At this time, a current-collecting tab bonding portion without an active material layer was cut out to a size of 5 mm×5 mm outside 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 bonding portion. For 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 resulting negative electrode slurry was coated on a copper foil, dried, and rolled to prepare a negative electrode slurry (coating basis weight: 6.6 mg/cm ² ). This negative electrode sheet was cut into a size of 45 mm×45 mm. At this time, a current-collecting tab bonding portion without an active material layer was cut out to a size of 5 mm×5 mm outside the active material surface. A copper tab having the same size as the positive electrode tab was ultrasonically welded to the tab bonding portion. Next, the porous film was cut into a size of 55 mm×55 mm, and the positive electrode and the negative electrode were superimposed on both sides of the porous film so that the active material layer separated the porous film, and the positive electrode coated portion was entirely opposed to the negative electrode coated portion. Arranged to obtain an electrode group. After that, hot pressing was performed for 10 seconds at a pressure of 5 MPa in a heating environment of 70° C. to bond the positive electrode, the porous film, and the negative electrode. The above positive electrode, porous film, and negative electrode were sandwiched between a sheet of aluminum laminate film of 90 mm×200 mm. An electrolytic solution prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate:ethyl methyl carbonate=3:7 (volume ratio) at a concentration of 1 mol/liter was used. 1.5 g of the electrolytic solution was poured into a bag-shaped aluminum laminate film, and the short sides of the aluminum laminate film were heat-sealed while being impregnated under reduced pressure to obtain a laminate type battery.

(14) Discharge load characteristics Discharge load characteristics were tested according to the following procedure, and evaluated by the discharge capacity retention rate. Using the laminate type battery, the discharge capacity when discharged at 0.5 C at 25 ° C. and the discharge capacity when discharged at 10 C at 25 ° C. are measured, (discharge capacity at 7 C) / ( Discharge capacity at 0.5 C)×100 was used to calculate the discharge capacity retention rate. Here, the charging conditions were constant current charging at 0.5C and 4.3V, and the discharging conditions were constant current discharge at 2.7V. Five laminate-type batteries were produced, and the average of the measurement results of the three batteries after removing the maximum and minimum discharge capacity retention rates was taken as the capacity retention rate. A discharge capacity retention rate of less than 40% was rated as "bad", 45% or more and less than 50% as "good", 50% or more and less than 55% as "excellent", and 55% or more as "excellent".

(15) Life characteristics Life characteristics were tested according to the following procedure, and evaluated by the discharge capacity retention rate.
<1st to 300th cycles>
Charging and discharging were set as one cycle, charging conditions were constant current charging at 2C and 4.3V, and discharging conditions were constant current discharging at 2C and 2.7V, 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 the formula of (discharge capacity at 300th cycle)/(discharge capacity at 1st cycle)×100. Five laminate-type batteries were produced, and the average of the measurement results of the three batteries after removing the maximum and minimum discharge capacity retention rates was taken as the capacity retention rate. The life characteristics are "bad" when the discharge capacity retention rate is less than 50%; The life characteristics of 70% or more were evaluated as "excellent".

(Example 1)
Dispersion A
120 parts of ion-exchanged water and 1 part of Adekaria Sorb SR-1025 (an emulsifier manufactured by Adeka Corporation) were charged into a reactor, and stirring was started. To this, 0.4 parts 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- Trifluoroethyl methacrylate (3FM) 30 parts, cyclohexyl acrylate (CHA) 54 parts, hydroxyethyl methacrylate (HEMA) 5 parts, alkylene glycol dimethacrylate (AGDMA) 11 parts, Adekaria Sorb SR-1025 (emulsifier, manufactured by Adeka Co., Ltd.) 9 and 115 parts of ion-exchanged water are continuously added dropwise at 60° C. over 2 hours. ) (particle size 180 nm, glass transition temperature: 45° C.).

Dispersion Z
Using alumina particles (aluminum oxide) having an average particle size of 0.5 μm as inorganic particles, adding water in the same amount as the inorganic particles as a solvent, and carboxymethyl cellulose as a dispersant at 1% by mass relative to the inorganic particles, followed by bead milling. to prepare a dispersion liquid Z.

Coating liquid Dispersion liquid A and dispersion liquid Z are dispersed in water so that the volume content α of the inorganic particles contained in the porous layer is 55% by volume and the solid content concentration is 20% by mass, and mixed with a stirrer. did. The resulting coating liquid had a viscosity of 15 mPa·s. The obtained coating liquid was applied to a polyolefin microporous film (arithmetic mean height (Sa) 0.15 μm, protruding peak height (Spk) 0.19 μm, arithmetic average roughness (Ra) 120 nm, thickness 9 μm), dried for 1 minute in a hot air oven (drying set temperature 50 ° C.), and volatilizing the contained solvent to form a porous layer, A porous film was obtained. Table 1 shows the arithmetic mean height (Sa) of the surface of the porous substrate on the side in contact with the porous layer used in Examples 1 to 32, the coating conditions, the type of inorganic particles, the volume content α, the organic resin Indicates the type of particle. Table 2 shows the β/α of the porous films obtained in Examples 1 to 32, the occupation ratio β of the inorganic particles in the porous surface layer portion, and the arithmetic mean height of the surface of the porous film on the side having the porous layer. (Sa), surface free energy, glass transition temperature (°C) of the porous film, and thickness of the porous layer. Table 3 shows the measurement results of thermal dimensional stability, peel strength, dry adhesion to electrodes, rate characteristics, and life characteristics of the porous films obtained in Examples 1 to 32 and batteries using them.

(Example 2)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.20 µm.

(Example 3)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.30 μm.

(Example 4)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.09 μm.

(Example 5)
A porous film was obtained in the same manner as in Example 1, except that the volume content α of the inorganic particles contained in the porous layer was changed to 30% by volume.

(Example 6)
A porous film was obtained in the same manner as in Example 1, except that the volume content α of the inorganic particles contained in the porous layer was changed to 80% by volume.

(Example 7)
A porous film was obtained in the same manner as in Example 1, except that the solid content concentration of the coating liquid was changed to 10% by mass and the viscosity was changed to 10 mPa·s.

(Example 8)
A porous film was obtained in the same manner as in Example 1, except that the solid content concentration of the coating liquid was changed to 40% by mass and the viscosity was changed to 40 mPa·s.

(Example 9)
Dispersion liquid A and dispersion liquid Z were prepared in the same manner as in Example 1.

Dispersion B
A dispersion liquid B comprising a polymer (polymer B) comprising methyl acrylate as an acrylate monomer was prepared. After that, the dispersion liquid A, the dispersion liquid Z, and the dispersion liquid B were mixed in the porous layer so that the volume content α of the inorganic particles contained in the porous layer was 55% by volume, the content of the organic resin particles (polymer A) was 35% by volume, and the organic resin The particles (polymer B) were dispersed in water so that the content of the particles (polymer B) was 10% by volume and the solid concentration was 20% by mass, and mixed with a stirrer. The resulting coating liquid had a viscosity of 10 mPa·s. Except that the organic resin particles are a mixture of two kinds of particles containing 90% by mass of a polymer A composed of a fluorine-containing methacrylate monomer and 10% by mass of a polymer B (average particle diameter 130 nm) composed of an acrylic acid ester monomer. obtained a porous film in the same manner as in Example 1.

(Example 10)
Dispersion A containing polymer C was prepared in the same manner as dispersion A of Example 1, except that 2,2,2-trifluoroethyl methacrylate (3FM) was replaced with 1H,1H,5H-octafluoropentyl acrylate (8FA). Dispersion C was prepared. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 11)
30 parts of 2,2,2-trifluoroethyl methacrylate (3FM), 54 parts of cyclohexyl acrylate (CHA), and 5 parts of hydroxyethyl methacrylate (HEMA) as monomers for constituting the polymer D that forms the organic resin particles and 11 parts of alkylene glycol dimethacrylate (AGDMA) were replaced with 100 parts of ethyl methacrylate as the methacrylic acid ester monomer. Dispersion D was prepared. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 12)
A porous film was obtained in the same manner as in Example 11, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.30 µm.

(Example 13)
A porous film was obtained in the same manner as in Example 11, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.09 μm.

(Example 14)
30 parts of 2,2,2-trifluoroethyl methacrylate (3FM), 54 parts of cyclohexyl acrylate (CHA), and 5 parts of hydroxyethyl methacrylate (HEMA) as monomers for constituting the polymer E forming the organic resin particles and 11 parts of alkylene glycol dimethacrylate (AGDMA) were replaced with 100 parts of vinylidene fluoride monomer. manufactured. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 15)
A porous film was obtained in the same manner as in Example 1, except that the average particle size of the organic resin particles was 70 nm.

(Example 16)
A porous film was obtained in the same manner as in Example 1, except that the average particle size of the organic resin particles was 100 nm.

(Example 17)
A porous film was obtained in the same manner as in Example 1, except that the average particle size of the organic resin particles was 500 nm.

(Example 18)
A porous film was obtained in the same manner as in Example 1, except that the average particle size of the organic resin particles was 800 nm.

(Example 19)
A porous film was obtained in the same manner as in Example 1, except that the inorganic particles were barium sulfate particles.

(Example 20)
A porous film was obtained in the same manner as in Example 1, except that boehmite particles were used as the inorganic particles.

(Example 21)
A porous film was obtained in the same manner as in Example 1, except that the film thickness of the porous layer was 5 μm.

(Example 22)
A porous film was obtained in the same manner as in Example 1, except that the film thickness of the porous layer was 8 μm.

(Example 23)
Polymer F was obtained by adjusting the amounts of CHA, HEMA, and AGDMA so that the glass transition temperature was 20° C. under the conditions for producing dispersion liquid A of Example 1, with 20 parts of 3FM. A porous film was obtained in the same manner.

(Example 24)
Polymer G was obtained by adjusting the amounts of CHA, HEMA, and AGDMA so that the glass transition temperature was 20° C. under the conditions for producing Dispersion A of Example 1, with the exception that 80 parts of 3FM was used. A porous film was obtained in the same manner.

(Example 25)
A porous film was obtained in the same manner as in Example 1, except that the drying temperature of the coating liquid was set to 70°C.

(Example 26)
A porous film was obtained in the same manner as in Example 1, except that the drying temperature of the coating liquid was set to 100°C.

(Example 27)
Using the same polyolefin microporous membrane as in Example 1 as the porous substrate, the dispersion liquid Z was coated on both sides of the polyolefin microporous membrane using a #9 wire bar, and dried in a hot air oven (drying set temperature 50 ° C.). The first porous layer was formed by drying in the chamber for 1 minute and volatilizing the contained solvent. After that, dispersion liquid A was dispersed in water so as to have a solid content concentration of 7% by mass, and mixed with a stirrer. The resulting coating liquid had a viscosity of 6 mPa·s. The coating liquid is coated on both sides of the first coating layer using a #1.5 wire bar and dried in a hot air oven (drying temperature set at 50°C) for 1 minute to volatilize the contained solvent. A porous film was obtained in the same manner as in Example 6, except that the second porous layer was formed by heating. By setting the solid content concentration and the wire bar to the above values, the occupation ratio β of the inorganic particles in the surface portion of the porous layer was 20%.

(Example 28)
A porous film was obtained in the same manner as in Example 27, except that polymer D was used instead of polymer A.

(Example 29)
Polymer H obtained by selecting a methacrylic acid ester monomer (butyl methacrylate) suitable for constituting the polymer forming the organic resin particles so that the glass transition temperature of the porous layer is 20°C. A porous film was obtained in the same manner as in Example 27, except for using instead of Polymer A.

(Example 30)
Acrylic acid ester monomers (50 parts of methyl acrylate and 50 parts of butyl acrylate) suitable for forming the polymer forming the organic resin particles were selected so that the glass transition temperature of the porous layer was 80°C. A porous film was obtained in the same manner as in Example 1, except that the polymer I obtained in the above step was used in place of the polymer A.

(Example 31)
A porous film was obtained in the same manner as in Example 28, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.10 μm.

(Example 32)
A porous film was obtained in the same manner as in Example 28, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.40 μm.

Polymers in the table represent the following.
Polymer A: A polymer polymerized using a fluorine-containing methacrylate monomer (ratio of fluorine-containing methacrylate monomer to total monomers used: 30% by mass)
Polymer B: polymer polymerized using acrylic acid ester monomer Polymer C: polymer polymerized using fluorine-containing acrylate monomer Polymer D: methacrylic acid ester monomer used Polymer E: polymer polymerized using vinylidene fluoride monomer Polymer F: polymer polymerized using fluorine-containing methacrylate monomer (total monomers used Proportion of fluorine-containing methacrylate monomer accounted for: 20% by mass)
Polymer G: A polymer polymerized using a fluorine-containing methacrylate monomer (ratio of fluorine-containing methacrylate monomer to total monomers used: 80% by mass)
Polymer H: polymer polymerized using methacrylic acid ester monomer Polymer I: copolymer polymerized using acrylic acid ester monomer

(Example 33)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness (Ra) of the polyolefin microporous membrane was changed to 30 nm.

(Example 34)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness (Ra) of the polyolefin microporous membrane was changed to 40 nm.

(Example 35)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness (Ra) of the polyolefin microporous membrane was changed to 200 nm.

(Example 36)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness (Ra) of the polyolefin microporous membrane was changed to 300 nm.

(Example 37)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean roughness (Ra) of the polyolefin microporous membrane was changed to 350 nm.

(Example 38)
A porous film was obtained in the same manner as in Example 1, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.05 μm.

(Example 39)
A porous film was obtained in the same manner as in Example 1, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.10 μm.

(Example 40)
A porous film was obtained in the same manner as in Example 1, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.40 μm.

(Example 41)
A porous film was obtained in the same manner as in Example 1, except that the height (Spk) of the protrusion peaks of the polyolefin microporous membrane was changed to 0.50 μm.

Arithmetic mean height (Sa), arithmetic mean roughness (Ra) or peak height (Spk) of porous substrates used in Examples 33-41, and porosity obtained in Examples 33-41 Tables 4 and 5 show the measurement results of peel strength, dry adhesion to electrodes, rate characteristics, and life characteristics of the film and the battery using it.

(Example 42)
Dispersion J containing polymer J was prepared in the same manner as dispersion A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 43)
Dispersion K containing polymer K was prepared in the same manner as dispersion A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 44)
Dispersion L containing polymer L was prepared in the same manner as dispersion A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 45)
Dispersion M containing polymer M was prepared in the same manner as Dispersion A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 46)
Dispersion N containing polymer N was prepared in the same manner as dispersion A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Thereafter, in the same manner as in Example 1, a porous film was obtained.

(Example 47)
Dispersion liquid O containing polymer O was produced in the same manner as dispersion liquid A of Example 1, except that the composition of the organic resin particles was changed as shown in Table 6. Then, in the same manner as in Example 1, a porous film was obtained.

(Example 48)
A porous film was obtained in the same manner as in Example 44, except that the volume content α of the inorganic particles contained in the porous layer was changed to 30% by volume.

(Example 49)
A porous film was obtained in the same manner as in Example 44, except that the volume content α of the inorganic particles contained in the porous layer was changed to 80% by volume.

(Example 50)
A porous film was obtained in the same manner as in Example 44, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.30 μm.

(Example 51)
A porous film was obtained in the same manner as in Example 44, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.30 μm.

Table 6 shows the arithmetic mean height (Sa) of the porous substrate used in Examples 1 and 42 to 51, the type of monomer used for polymerization of the polymer constituting the organic resin particles, and each monomer The glass transition temperature (°C) of the polymer polymerized using only the monomer for the body, the usage ratio (%) of each monomer, and the glass transition temperature of the polymer polymerized only with the monomer The ratio of the monomers used (denoted as “γ” in Table 6) at −100° C. or higher and 0° C. or lower is shown.

Table 7 shows the types of inorganic particles used in Examples 1 and 42 to 51, the volume content α, and the β/α of the porous films obtained in Examples 1 and 42 to 51. Inorganic particle occupancy β, arithmetic mean height (Sa) of the porous film surface on the side where the porous layer is provided, surface free energy, glass transition temperature (° C.), thermal dimensional stability, peel strength, electrode dry adhesion to electrodes, wet adhesion to electrodes, and rate characteristics and life characteristics of batteries using the porous film.

(Comparative example 1)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.07 μm.

(Comparative example 2)
A porous film was obtained in the same manner as in Example 1, except that the solid content concentration of the coating liquid was changed to 50% by mass and the viscosity was changed to 80 mPa·s.

(Comparative Example 3)
A porous film was obtained in the same manner as in Example 1, except that the drying temperature of the coating liquid was set to 105°C.

(Comparative Example 4)
A porous film was obtained in the same manner as in Example 1, except that the composition shown in Table 8 was used without using the organic resin particles A.

(Comparative Example 5)
A porous film was obtained in the same manner as in Example 1, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.35 μm.

(Comparative Example 6)
A porous film was obtained in the same manner as in Example 44, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.07 μm.

(Comparative Example 7)
A porous film was obtained in the same manner as in Example 44, except that the arithmetic mean height (Sa) of the polyolefin microporous membrane was changed to 0.35 μm.

Table 8 shows the arithmetic mean height (Sa) of the porous substrate used in Comparative Examples 1 to 7, the type of monomer used for polymerization of the polymer constituting the organic resin particles, and each monomer The glass transition temperature (° C.) of the polymer polymerized using only the monomer, the proportion (%) of each monomer used, and the glass transition temperature of the polymer polymerized only with the monomer are −100. ° C. to 0 °C. Table 9 shows the β/α of the porous films obtained in Comparative Examples 1 to 7, the occupancy β of the inorganic particles in the porous surface layer, and the arithmetic of the surface of the porous film on the side where the porous layer is provided. Average height (Sa), surface free energy, glass transition temperature (° C.) and film thickness of porous layer are shown. Table 10 shows the thermal dimensional stability, peel strength, dry adhesion to electrodes, wet adhesion to electrodes, rate characteristics, and life of the porous films obtained in Comparative Examples 1 to 7 and the batteries using them. The measurement results of the characteristics are shown.

(Reference example 1)
For the porous film obtained in Example 1, the dry adhesion to the electrode, the electrolyte pourability, and the rate were determined by setting the hot press conditions for adhesion to the electrode in a heating environment of 75° C. under a pressure of 2 MPa for 10 seconds. Characteristics and life characteristics were measured. Table 11 shows the measurement results obtained in Reference Examples 1 and 2.

(Reference example 2)
For the porous film obtained in Example 3, the dry adhesion to the electrode, the electrolyte pourability, and the rate were determined by setting the hot press conditions for adhesion to the electrode in a heating environment of 75° C. under a pressure of 2 MPa for 10 seconds. Characteristics and life characteristics were measured.

From Tables 1 to 7, Examples 1 to 51 all have a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate. In the film, the porous substrate has an arithmetic mean height (Sa) of 0.09 μm or more and 0.3 μm or less in a 2200 μm square on the surface of the porous substrate on the side in contact with the porous layer. When the volume of all constituent components of the layer is 100% by volume, the volume content α (% by volume) of the inorganic particles and the occupation ratio β (% by mass) of the inorganic particles at the surface of the porous layer are β/α<1. It is a porous film, has excellent dry adhesion to electrodes, and has good rate characteristics and battery life. Examples 42 to 45 and 48 to 51 also have excellent wet adhesion to the electrode by appropriately selecting the composition of the organic resin particles.

On the other hand, in Comparative Examples 1 and 6, the arithmetic mean height (Sa) of the surface of the porous substrate on the side in contact with the porous layer is less than 0.09 μm, so the adhesiveness to the electrode is poor. In Comparative Example 2, since the viscosity and solid content concentration of the coating liquid are out of the preferred range, uneven distribution of the organic resin particles on the surface is hindered, and β/α = 1, so sufficient adhesion to the electrode. is not obtained. In Comparative Example 3, since the drying temperature of the coating liquid exceeded 100° C., the organic resin particles could not retain their particle shape during the drying process, and film formation hindered uneven distribution of the organic resin particles on the surface. , and β/α=1, so sufficient adhesion to the electrode cannot be obtained. Since Comparative Example 4 does not contain organic resin particles, uneven distribution of the organic resin particles on the surface does not occur. In Comparative Examples 5 and 7, since the arithmetic mean height (Sa) of the surface of the porous substrate on the side in contact with the porous layer is larger than 0.3 μm, the adhesion to the electrode becomes too strong, thereby inhibiting ion transport. However, the resistance became high and the battery characteristics deteriorated.

In Reference Examples 1 and 2, when the pressure of the hot press conditions was changed from 5 MPa to 2 MPa for the adhesion between the porous films obtained in Examples 1 and 3 and the electrodes, the pressure in Example 1 was reduced. 3 shows an example in which the dry adhesion to the electrode decreased as the arithmetic mean height (Sa) of the surface of the porous substrate on the side in contact with the porous layer in a 2200 μm square area increased.

Claims

A porous film having a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate, wherein the porous substrate and the porous layer Arithmetic mean height (Sa) in 2200 μm square of the surface of the contact side is 0.09 μm or more and 0.3 μm or less, and the volume content of inorganic particles when the volume of all constituent components of the porous layer is 100% by volume. A porous film in which α (% by volume) and β (% by area) of inorganic particles occupying the surface of the porous layer satisfy β/α<1.
2. The porous film according to claim 1, wherein the porous film has an arithmetic mean height (Sa) of 0.085 μm or more and 0.3 μm or less in a 2200 μm square of the surface of the porous film on the side having the porous layer. .
The porous film according to claim 1 or 2, wherein the volume content α of the inorganic particles is 30% by volume or more and 80% by volume or less when the volume of all constituent components of the porous layer is 100% by volume.
The porous film according to any one of claims 1 to 3, wherein the occupancy β of the inorganic particles in the surface portion of the porous layer is greater than 0%.
5. The porous film according to any one of claims 1 to 4, wherein the porous substrate has an arithmetic mean roughness (Ra) of 40 nm or more and 300 nm or less on a 12 nm square surface on the side in contact with the porous layer.
6. The porous substrate according to any one of claims 1 to 5, wherein the height (Spk) of protruding peaks in a 2200 μm square of the surface on the side in contact with the porous layer is 0.10 μm or more and 0.40 μm or less. porous film.
The porous film according to any one of claims 1 to 6, wherein the porous layer has a surface free energy of 10 mN/m or more and 80 mN/m or less.
The porous film according to any one of claims 1 to 7, wherein the porous substrate is a polyolefin microporous membrane.
The porous film according to any one of claims 1 to 8, wherein the inorganic particles are particles composed of at least one selected from the group consisting of inorganic hydroxides, inorganic oxides and inorganic sulfates.
The organic resin particles are composed of a fluorine-containing (meth)acrylate monomer, an unsaturated carboxylic acid monomer, a (meth)acrylic acid ester monomer, a styrene monomer, an olefin monomer, and a diene monomer. 10. The porous polymer according to any one of claims 1 to 9, comprising a polymer polymerized using at least one monomer selected from the group consisting of , an acrylamide-based monomer, and a vinylidene fluoride monomer. the film.
11. The method according to claim 10, wherein the ratio of the fluorine-containing (meth)acrylate monomer is 20% by mass or more and 80% by mass or less when the total constituent monomer components of the organic resin particles of the organic resin particles are 100% by mass. A porous film as described.
The porous film according to claim 10, wherein the organic resin particles contain a polymer polymerized only with a fluorine-containing (meth)acrylate monomer.
The porous film according to any one of claims 10 to 12, wherein the number of fluorine atoms contained in one molecule of the fluorine-containing (meth)acrylate monomer is 3 or more and 13 or less.
The porous film according to claim 12 or 13, wherein the organic resin particles further contain a polymer or copolymer polymerized using a (meth)acrylate monomer having a hydroxyl group.
Regarding the organic resin particles, the ratio of the (meth)acrylate monomer having a hydroxyl group is more than 0% by mass and 7.0% by mass or less when the total constituent monomer components of the organic resin particles are 100% by mass. 15. The porous film of claim 14.
Regarding the polymer contained in the organic resin particles, the glass transition temperature of the polymer when at least one of the monomers that are the raw materials of the polymer is polymerized only with that monomer is 16. The porous film according to any one of claims 10 to 15, which is a monomer having a temperature of -100°C or higher and 0°C or lower.
The monomer having a glass transition temperature of −100° C. or higher and 0° C. or lower when polymerized only by the monomer alone accounts for 100% by mass of the total constituent monomer components of the organic resin particles. 17. The porous film according to claim 16, which is greater than 0% by weight and 10.0% by weight or less.
The porous film according to any one of claims 1 to 17, wherein the porous layer contains at least two types of organic resin particles.
The porous film according to any one of claims 1 to 18, wherein the organic resin particles have an average particle size of 100 nm or more and 500 nm or less.
The porous film according to any one of claims 1 to 19, wherein the film thickness of the porous substrate is 3 µm or more and 15 µm or less.
The porous film according to any one of claims 1 to 20, wherein the film thickness of the porous layer is 2 µm or more and 8 µm or less.
A secondary battery separator using the porous film according to any one of claims 1 to 21.
A secondary battery using the secondary battery separator according to claim 22.
A porous film having a porous substrate and a porous layer containing inorganic particles and organic resin particles on at least one surface of the porous substrate,
The porous substrate is made of a polyolefin microporous membrane whose surface in contact with the porous layer has an arithmetic mean height (Sa) of 0.09 μm or more in a 2200 μm square,
The inorganic particles are particles composed of at least one selected from the group consisting of inorganic hydroxides, inorganic oxides and inorganic sulfates,
The organic resin particles contain a fluorine-containing (meth)acrylate monomer, an unsaturated carboxylic acid monomer, a (meth)acrylic acid ester monomer, a styrene monomer, an olefin monomer, and a diene monomer. is a polymer polymerized using at least one monomer selected from the group consisting of a polymer, an acrylamide-based monomer, and a vinylidene fluoride monomer,
When the volume of all constituent components of the porous layer is 100% by volume, the volume content ratio α of the inorganic particles is 30% by volume or more and 80% by volume or less,
The battery, wherein the relationship between the volume content α (volume %) of the inorganic particles and the occupation ratio β (area %) of the inorganic particles in the surface portion of the porous layer satisfies β>0 and β/α<1. separator for