Raw material for coating material for secondary battery separator, coating material for secondary battery separator, secondary battery separator, and secondary battery

Abstract

This starting material for a coating material for a secondary battery separator comprises a water-soluble acrylic resin and polyvinyl alcohol. The degree of saponification of the polyvinyl alcohol is at least 85 mol%.

Description

[Technical Field]

[0001] The present invention relates to a coating material raw material for secondary battery separators, a coating material for secondary battery separators, a secondary battery separator, and a secondary battery, and more particularly to a coating material raw material for secondary battery separators, a coating material for secondary battery separators containing the coating material raw material for secondary battery separators, a secondary battery separator having a coating film of the coating material for secondary battery separators, and a secondary battery having the secondary battery separator. [Background technology]

[0002] Conventionally, a separator is provided in a secondary battery to separate the positive electrode from the negative electrode and to allow ions in the electrolyte to pass through.

[0003] As such a separator, for example, a polyolefin porous film is known.

[0004] On the other hand, a coating layer may be provided on the surface of the separator to impart various physical properties. Such a coating layer is formed, for example, by applying a coating material for a secondary battery separator to the surface of the separator and drying it.

[0005] As such a coating material for secondary battery separators, for example, a coating material for secondary battery separators has been proposed that contains a coating material raw material for secondary battery separators that includes a water-soluble polymer obtained by polymerizing a water-soluble polymer raw material that includes methacrylamide and methacrylic acid, and an inorganic filler (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-103676 Summary of the Invention [Problem to be solved by the invention]

[0007] On the other hand, if the separator changes shape due to heat shrinkage, it may cause a short circuit between the positive electrode and the negative electrode, so the coating layer is required to have heat resistance.

[0008] The coating layer is also required to have good adhesion to the separator.

[0009] The present invention provides a coating material raw material for secondary battery separators that has excellent heat resistance and adhesion, a coating material for secondary battery separators that contains the coating material raw material for secondary battery separators, a secondary battery separator that has a coating film of the coating material for secondary battery separators, and a secondary battery that has the secondary battery separator. [Means for solving the problem]

[0010] The present invention [1] is a raw material for a coating material for a secondary battery separator, which contains a water-soluble acrylic resin and polyvinyl alcohol, and the degree of saponification of the polyvinyl alcohol is 85 mol % or more.

[0011] The present invention [2] includes the coating material raw material for secondary battery separators according to the above [1], in which the content of the polyvinyl alcohol is 5 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the water-soluble acrylic resin.

[0012] The present invention [3] includes the coating material raw material for secondary battery separators according to the above [1], wherein the polyvinyl alcohol is at least one selected from the group consisting of unmodified polyvinyl alcohol and anionic group-modified polyvinyl alcohol.

[0013] The present invention [4] includes the raw material for a coating material for a secondary battery separator according to the above [1], wherein the water-soluble acrylic resin has a weight average molecular weight of 10,000 or more and 150,000 or less.

[0014] The present invention [5] includes a coating material for a secondary battery separator, which includes the raw material for a coating material for a secondary battery separator according to any one of the above [1] to [4] and inorganic particles.

[0015] The present invention [6] includes a secondary battery separator comprising a porous membrane and a coating film of the coating material for secondary battery separators according to the above [5], which is disposed on at least one side of the porous membrane.

[0016] The present invention [7] includes a secondary battery comprising a positive electrode, a negative electrode, and the secondary battery separator described in the above [6] disposed between the positive electrode and the negative electrode. [Effects of the Invention]

[0017] The coating material raw material for a secondary battery separator of the present invention is a water-soluble acrylic resin and a kenyl group having a predetermined value or more. transformation It contains polyvinyl alcohol with a high viscosity, which gives it excellent heat resistance and adhesion.

[0018] The coating material for a secondary battery separator of the present invention contains the raw material for a coating material for a secondary battery separator of the present invention, and therefore has excellent heat resistance and adhesion.

[0019] The secondary battery separator of the present invention has a coating film of the coating material for a secondary battery separator of the present invention, and therefore has excellent heat resistance and adhesion.

[0020] The secondary battery of the present invention includes the secondary battery separator of the present invention, and therefore has excellent heat resistance and adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0021] The coating material raw material for a secondary battery separator contains a water-soluble acrylic resin and polyvinyl alcohol.

[0022] <Water-soluble acrylic resin> The water-soluble acrylic resin is a polymer obtained by polymerizing a water-soluble acrylic resin raw material.

[0023] The term "water-soluble acrylic resin" is defined as an acrylic resin that has been dried, and when 1 g of the resin is dissolved in 100 ml of water by stirring for 24 hours, and then filtered through a 300 mesh wire screen, the residual solid content is 0.1% or less.

[0024] The water-soluble acrylic resin raw material includes, for example, (meth)acrylamide and a carboxy group-containing vinyl monomer.

[0025] {(Meth)acrylamide} (Meth)acrylamide refers to methacrylamide and / or acrylamide. As the (meth)acrylamide, methacrylamide is preferred from the viewpoint of ion permeability.

[0026] The (meth)acrylamide content is, for example, 60 parts by mass or more, preferably 75 parts by mass or more, and for example, 98 parts by mass or less, preferably 90 parts by mass or less, more preferably 85 parts by mass or less, relative to 100 parts by mass of the total amount of the water-soluble acrylic resin raw materials.

[0027] {Carboxy group-containing vinyl monomer} The carboxy group-containing vinyl monomer is a vinyl monomer that is copolymerizable with (meth)acrylamide and contains a carboxy group.

[0028] Examples of the carboxyl group-containing vinyl monomer include monocarboxylic acids, dicarboxylic acids, and salts thereof. Examples of the monocarboxylic acid include (meth)acrylic acid. Examples of the dicarboxylic acid include itaconic acid, maleic acid, fumaric acid, itaconic anhydride, maleic anhydride, and fumaric anhydride.

[0029] The carboxyl group-containing vinyl monomer is preferably a monocarboxylic acid. The carboxyl group-containing vinyl monomer is more preferably (meth)acrylic acid. The carboxyl group-containing vinyl monomer is even more preferably methacrylic acid.

[0030] The carboxyl group-containing vinyl monomers can be used alone or in combination of two or more kinds.

[0031] The content of the carboxy group-containing vinyl monomer is, relative to 100 parts by mass of the total amount of the water-soluble acrylic resin raw materials, for example, 1 part by mass or more, preferably 3 parts by mass or more, and for example, 35 parts by mass or less, preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 7 parts by mass or less.

[0032] {Copolymerizable monomer} The water-soluble acrylic resin raw material may also contain a copolymerizable monomer that is copolymerizable with (meth)acrylamide and the carboxy group-containing vinyl monomer.

[0033] Examples of copolymerizable monomers include (meth)acrylic acid alkyl esters, functional group-containing vinyl monomers (excluding carboxy group-containing vinyl monomers), vinyl esters, aromatic vinyl monomers, N-substituted unsaturated carboxylic acid amides, heterocyclic vinyl compounds, vinylidene halide compounds, α-olefins, dienes, and crosslinkable vinyl monomers.

[0034] Examples of alkyl (meth)acrylates include alkyl (meth)acrylates having an alkyl moiety with 1 to 12 carbon atoms. Examples of alkyl (meth)acrylates having an alkyl moiety with 1 to 12 carbon atoms include alkyl (meth)acrylates having an alkyl moiety with 1 to 4 carbon atoms and alkyl (meth)acrylates having an alkyl moiety with 5 to 12 carbon atoms. Examples of alkyl (meth)acrylates having an alkyl moiety with 1 to 4 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and t-butyl (meth)acrylate. Examples of alkyl(meth)acrylates having an alkyl moiety with 5 to 12 carbon atoms include n-amyl(meth)acrylate, isoamyl(meth)acrylate, n-hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, decyl(meth)acrylate, dodecyl(meth)acrylate, and octadecyl(meth)acrylate.

[0035] Examples of functional group-containing vinyl monomers (excluding carboxy group-containing vinyl monomers) include sulfonic acid group-containing vinyl monomers, phosphoric acid group-containing vinyl monomers, hydroxyl group-containing vinyl monomers, amino group-containing vinyl monomers, glycidyl group-containing vinyl monomers, cyano group-containing vinyl monomers, and acetoacetoxy group-containing vinyl monomers.

[0036] Examples of sulfonic acid group-containing vinyl monomers include allyl sulfonic acid, methallyl sulfonic acid, and acrylamido t-butyl sulfonic acid. The sulfonic acid group-containing vinyl monomers also include their salts. Examples of salts of sulfonic acid group-containing vinyl monomers include alkali metal salts (e.g., sodium salts, potassium salts), and ammonium salts. Specific examples include sodium allyl sulfonate, sodium methallyl sulfonate, and ammonium methallyl sulfonate.

[0037] Examples of the phosphate group-containing vinyl monomer include 2-methacrylamide, R Examples include oleyloxyethyl acid phosphate.

[0038] Examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate and 2-hydroxypropyl (meth)acrylate. Preferred examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl (meth)acrylate. More preferred examples of hydroxyl group-containing vinyl monomers include 2-hydroxyethyl methacrylate.

[0039] Examples of amino group-containing vinyl monomers include 2-aminoethyl (meth)acrylate, 2-(N-methylamino)ethyl (meth)acrylate, and 2-(N,N-dimethylamino)ethyl (meth)acrylate.

[0040] An example of the glycidyl group-containing vinyl monomer is glycidyl (meth)acrylate.

[0041] Examples of the cyano group-containing vinyl monomer include (meth)acrylonitrile, and preferred examples of the cyano group-containing vinyl monomer include acrylonitrile.

[0042] An example of an acetoacetoxy group-containing vinyl monomer is acetoacetoxyethyl (meth)acrylate.

[0043] Examples of vinyl esters include vinyl acetate and vinyl propionate.

[0044] Examples of aromatic vinyl monomers include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, and chlorostyrene.

[0045] An example of the N-substituted unsaturated carboxylic acid amide is N-methylol (meth)acrylamide.

[0046] An example of the heterocyclic vinyl compound is vinylpyrrolidone.

[0047] Examples of vinylidene halide compounds include vinylidene chloride and vinylidene fluoride.

[0048] Examples of α-olefins include ethylene and propylene.

[0049] An example of the dienes is butadiene.

[0050] Examples of crosslinkable vinyl monomers include vinyl monomers containing two or more vinyl groups, such as methylenebis(meth)acrylamide, divinylbenzene, polyethylene glycol chain-containing di(meth)acrylate, trimethylolpropane tetraacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate.

[0051] As the copolymerizable monomer, preferably, a functional group-containing vinyl monomer is used, and more preferably, a hydroxyl group-containing vinyl monomer is used.

[0052] The copolymerizable monomers can be used alone or in combination of two or more kinds.

[0053] The content ratio of the copolymerizable monomer relative to 100 parts by mass of the total amount of the water-soluble acrylic resin raw materials is, for example, 3 parts by mass or more, preferably 5 parts by mass or more, more preferably 12 parts by mass or more, and for example, 30 parts by mass or less, preferably 20 parts by mass or less.

[0054] The water-soluble acrylic resin can be obtained by polymerizing a water-soluble acrylic resin raw material by a known method.

[0055] Specifically, for example, a water-soluble acrylic resin raw material and a polymerization initiator are mixed with water, the water-soluble acrylic resin raw material is polymerized, and then, if necessary, aging is carried out.

[0056] The polymerization initiator is not particularly limited, and examples thereof include water-soluble initiators, oil-soluble initiators, and redox initiators. Examples of water-soluble initiators include persulfates (e.g., ammonium persulfate, potassium persulfate), hydrogen peroxide, organic hydroperoxides, 4,4'-azobis(4-cyanovaleric acid), and the like. ) Examples of oil-soluble initiators include benzoyl peroxide and azobisisobutyronitrile.

[0057] As the polymerization initiator, a water-soluble initiator is preferably used. As the polymerization initiator, a persulfate is more preferably used. As the polymerization initiator, ammonium persulfate is further preferably used.

[0058] The mixing ratio of the polymerization initiator relative to 100 parts by mass of the water-soluble acrylic resin raw material is, for example, 0.01 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, and for example, 3 parts by mass or less, preferably 1 part by mass or less.

[0059] The polymerization initiators can be used alone or in combination of two or more kinds.

[0060] The polymerization temperature under normal pressure is, for example, 30° C. or more, preferably 50° C. or more, and for example, 95° C. or less, preferably 85° C. or less. The polymerization time is, for example, 0.5 hours or more, preferably 1.5 hours or more, and for example, 20 hours or less, preferably 10 hours or less.

[0061] The aging time is, for example, 0.5 hours or more, preferably 1.5 hours or more, and for example, 6 hours or less, preferably 4 hours or less.

[0062] In the above polymerization, known additives such as a pH adjuster, a metal ion sequestering agent (e.g., ethylenediaminetetraacetic acid and its salts), and a molecular weight regulator (chain transfer agent) (e.g., mercaptans, low-molecular-weight halogen compounds) can be blended in an appropriate ratio from the viewpoint of improving production stability.

[0063] Before or after the polymerization, a neutralizing agent such as ammonia may be added to adjust the pH to within the range of 6 to 11.

[0064] As a result, a water-soluble acrylic resin (aqueous solution containing the water-soluble acrylic resin) is obtained as a polymer of the water-soluble acrylic resin raw material.

[0065] In the aqueous solution containing the water-soluble acrylic resin, the solid content concentration of the water-soluble acrylic resin is, for example, 10% by mass or more and, for example, 50% by mass or less.

[0066] The weight average molecular weight of the water-soluble acrylic resin is, from the viewpoint of improving ion permeability, for example, 10,000 or more, preferably 50,000 or more, more preferably 68,000 or more, and for example, 500,000 or less, preferably 200,000 or less, and from the viewpoint of improving ion permeability, more preferably 150,000 or less, even more preferably 100,000 or less, particularly preferably 80,000 or less.

[0067] The method for measuring the weight average molecular weight will be described in detail in the examples below.

[0068] The water-soluble acrylic resin has a glass transition temperature (Tg) of, for example, 100°C or higher, preferably 150°C or higher, more preferably 210°C or higher, and even more preferably 220°C or higher, and for example, 270°C or lower, preferably 250°C or lower, and more preferably 225°C or lower.

[0069] The glass transition temperature (Tg) can be calculated by the FOX formula.

[0070] The content of the water-soluble acrylic resin is, for example, 60 parts by mass or more, preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and for example, 98 parts by mass or less, preferably 90 parts by mass or less, per 100 parts by mass of the total amount of the water-soluble acrylic resin and polyvinyl alcohol.

[0071] <Polyvinyl alcohol> Polyvinyl alcohol is a component that imparts wettability to the raw material of the coating material for secondary battery separators and improves adhesion.

[0072] Polyvinyl alcohol is a material that has a specified value or more transformation Has a degree.

[0073] Specifically, the ken of polyvinyl alcohol transformation The degree is 85 mol % or more, preferably 90 mol % or more, more preferably 95 mol % or more, particularly preferably 98 mol % or more, and for example, 100 mol % or less, preferably 99 mol % or less.

[0074] Polyvinyl alcohol transformation If the degree is equal to or higher than the lower limit, the heat resistance and adhesion are improved.

[0075] On the other hand, the ken of polyvinyl alcohol transformation If the degree is less than the lower limit, the heat resistance and adhesion will be reduced.

[0076] Examples of polyvinyl alcohol include unmodified polyvinyl alcohol and modified polyvinyl alcohol.

[0077] Examples of modified polyvinyl alcohols include anionic group-modified polyvinyl alcohols (for example, carboxyl group-modified polyvinyl alcohols, sulfo group-modified polyvinyl alcohols), and hydrophobic group-modified polyvinyl alcohols.

[0078] As the polyvinyl alcohol, preferably, from the viewpoint of improving ion permeability, at least one selected from the group consisting of unmodified polyvinyl alcohol and anionic group-modified polyvinyl alcohol is selected.

[0079] The polyvinyl alcohol may be used alone or in combination of two or more kinds.

[0080] The content of polyvinyl alcohol is, for example, 5 parts by mass or more, preferably 10 parts by mass or more, from the viewpoint of coatability, and for example, 90 parts by mass or less, and preferably 50 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, from the viewpoint of ion permeability, relative to 100 parts by mass of the water-soluble acrylic resin.

[0081] The content of polyvinyl alcohol is, for example, 2 parts by mass or more, preferably 10 parts by mass or more from the viewpoint of improving coatability, and for example, 60 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, more preferably 20 parts by mass or less, from the viewpoint of improving ion permeability, relative to 100 parts by mass of the total amount of the water-soluble acrylic resin and polyvinyl alcohol.

[0082] In addition, when the content of polyvinyl alcohol is within the above range, the wettability is excellent, and therefore, a coating film having excellent heat resistance and adhesion can be formed on the surface of the porous film, even without performing a surface treatment (for example, a corona discharge treatment, described later).

[0083] Polyvinyl alcohol can also be prepared as an aqueous solution of polyvinyl alcohol, where the solid content of polyvinyl alcohol in the aqueous solution is, for example, 5% by mass or more and, for example, 50% by mass or less.

[0084] In addition, the raw material for the coating material for the secondary battery separator has a ken content of at least the above-mentioned predetermined value. transformation Polyvinyl alcohol having a viscosity of less than the above-mentioned predetermined value transformation It may also contain polyvinyl alcohol having a different viscosity (hereinafter referred to as other polyvinyl alcohol).

[0085] The content of the other polyvinyl alcohol is, for example, 10 mass % or less, preferably 5 mass % or less, and more preferably 1 mass % or less, relative to the raw material (solid content) of the coating material for a secondary battery separator.

[0086] The coating material raw material for secondary battery separators preferably does not contain other polyvinyl alcohols.

[0087] <Preparation of raw material for coating material for secondary battery separator> The coating material raw material for secondary battery separators is prepared by mixing a water-soluble acrylic resin (aqueous solution containing a water-soluble acrylic resin) and polyvinyl alcohol.

[0088] In addition, the raw material for the coating material for the secondary battery separator may contain, as necessary, a wetting agent, a dispersant, a hydrophilic resin, a moistening agent, an antifoaming agent, a pH adjuster, etc. Adjustment In other words, the raw material for a coating material for a secondary battery separator contains additives as needed.

[0089] On the other hand, this coating material raw material for secondary battery separators contains a water-soluble acrylic resin and polyvinyl alcohol, and therefore has excellent wettability. Therefore, the coating material raw material for secondary battery separators has excellent wettability even without containing a wetting agent. That is, the coating material raw material for secondary battery separators preferably contains a water-soluble acrylic resin and polyvinyl alcohol, but does not contain a wetting agent.

[0090] The coating material raw material for secondary battery separators contains a water-soluble acrylic resin and polyvinyl alcohol, and therefore has excellent heat resistance and adhesion.

[0091] Such a coating material raw material for a secondary battery separator can be suitably used particularly as a coating material raw material for a secondary battery separator.

[0092] Hereinafter, the coating material for secondary battery separators obtained using this raw material for coating material for secondary battery separators will be described in detail.

[0093] <Coating material for secondary battery separators> The coating material for a secondary battery separator is a mixture of the above-mentioned coating material raw material for a secondary battery separator, inorganic particles, and of include.

[0094] Inorganic particles include, for example, oxides, nitrides, carbides, sulfates, hydroxides, and potassium titanate. Oxides include, for example, alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide. Nitrides include, for example, silicon nitride, titanium nitride, and boron nitride. Carbides include, for example, silicon carbide and calcium carbonate. Sulfates include, for example, magnesium sulfate and aluminum sulfate. Hydroxides include, for example, aluminum hydroxide and aluminum oxide hydroxide. Silicates include, for example, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand, and glass.

[0095] The inorganic particles are preferably hydroxide particles, and more preferably aluminum oxide hydroxide particles.

[0096] The inorganic particles have an average median diameter D50 of, for example, 0.1 μm or more, preferably 0.5 μm or more, and for example, 5 μm or less, preferably 1 μm or less.

[0097] The inorganic particles can be used alone or in combination of two or more kinds.

[0098] The blending ratio of the inorganic particles will be described later.

[0099] To produce a coating material for a secondary battery separator, first, inorganic particles and, if necessary, a dispersant are mixed with water to prepare an aqueous dispersion of inorganic particles. When a dispersant is mixed, the coating material for a secondary battery separator contains the dispersant.

[0100] Examples of the dispersant include ammonium polycarboxylate and sodium polycarboxylate, and preferably ammonium polycarboxylate.

[0101] The mixing ratio of the dispersant (solid content) relative to 100 parts by mass of the inorganic particles is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and for example, 10 parts by mass or less, preferably 3 parts by mass or less.

[0102] The dispersants can be used alone or in combination of two or more kinds.

[0103] Next, the raw material for a coating material for a secondary battery separator (aqueous dispersion of the raw material for a coating material for a secondary battery separator) is blended into the aqueous dispersion of inorganic particles and stirred.

[0104] The stirring method is not particularly limited, and examples thereof include a ball mill, a bead mill, a planetary ball mill, a vibrating ball mill, a sand mill, a colloid mill, an attritor, a roll mill, a high-speed impeller dispersion, a stirrer, a disperser, a homogenizer, a high-speed impact mill, ultrasonic dispersion, and a stirring blade.

[0105] The coating material for a secondary battery separator may contain the above-mentioned additives in an appropriate ratio as needed. That is, the coating material for a secondary battery separator contains the above-mentioned additives as needed. The coating material for a secondary battery separator preferably does not contain a wetting agent.

[0106] These additives can be used alone or in combination of two or more kinds.

[0107] This allows the production of a coating material for a secondary battery separator. The coating material for a secondary battery separator is obtained as an aqueous dispersion in which the material is dispersed in water.

[0108] The solid content concentration of the aqueous dispersion of the coating material for a secondary battery separator is, for example, 10 mass % or more, preferably 20 mass % or more, more preferably 30 mass % or more, and for example, 50 mass % or less.

[0109] In the coating material (solid content) for secondary battery separators, the content of the raw material (solid content) for secondary battery separators is, for example, 3.0 parts by mass or more, preferably 4.2 parts by mass or more, and 10.0 parts by mass or less, preferably 7.0 parts by mass or less, more preferably 6.0 parts by mass or less, relative to 100 parts by mass of the total amount of the coating material raw material (solid content) for secondary battery separators and the inorganic particles. The content of the inorganic particles is, for example, 90.0 parts by mass or more, preferably 93.0 parts by mass or more, more preferably 94.0 parts by mass or more, and for example, 97.0 parts by mass or less, preferably 95.8 parts by mass or less, relative to 100 parts by mass of the total amount of the coating material raw material (solid content) for secondary battery separators and the inorganic particles.

[0110] In addition, in the coating material (solid content) for secondary battery separators, the content of the raw material (solid content) for secondary battery separator coating material is, for example, 3.0 parts by mass or more, preferably 4.4 parts by mass or more, and for example, 10.0 parts by mass or less, preferably 7.0 parts by mass or less, more preferably 5.0 parts by mass or less, relative to 100 parts by mass of the total amount of inorganic particles.

[0111] The coating material for a secondary battery separator contains a raw material for the coating material for a secondary battery separator, and therefore a secondary battery separator having a coating film obtained using the coating material for a secondary battery separator has excellent heat resistance and adhesion.

[0112] Hereinafter, a secondary battery separator obtained by using this coating material for a secondary battery separator will be described in detail.

[0113] <Secondary battery separator> The secondary battery separator includes a porous membrane and a coating film of a coating material for a secondary battery separator that is disposed on at least one surface of the porous membrane.

[0114] [Porous membrane] Examples of the porous membrane include a polyolefin porous membrane and an aromatic polyamide porous membrane. Examples of the polyolefin porous membrane include a polyethylene porous membrane and a polypropylene porous membrane. A preferred example of the porous membrane is a polyolefin porous membrane.

[0115] The thickness of the porous membrane is, for example, 1 μm or more, and, for example, 40 μm or less, preferably 20 μm or less.

[0116] [Coating film] The coating film provides heat resistance to the porous film and is made of a coating material for a secondary battery separator.

[0117] The thickness of the coating film is, for example, 1 μm or more, preferably 3 μm or more, and for example, 10 μm or less, preferably 8 μm or less.

[0118] [Method for manufacturing secondary battery separator] The method for manufacturing a secondary battery separator includes a first step of preparing a porous membrane, and a second step of applying a separator coating material to at least one surface of the porous membrane.

[0119] (1st step) In the first step, a porous membrane is prepared.

[0120] (2nd process) In the second step, a coating material for a secondary battery separator is applied to at least one surface of the porous membrane, and then dried as necessary, to obtain a coated membrane.

[0121] To apply the coating material for a secondary battery separator to at least one surface of the porous membrane, first, if necessary, one surface of the porous membrane is subjected to a surface treatment to form a surface treatment layer on one surface of the porous membrane. That is, in such a case, the secondary battery separator comprises a porous membrane, a surface treatment layer, and a coating film of a coating material for a secondary battery separator.

[0122] Examples of surface treatments include corona discharge treatment, glow discharge treatment, plasma treatment, and ozone treatment. In this manufacturing method, preferably, no surface treatment is performed in order to improve ion permeability. In other words, the secondary battery separator preferably does not include a surface treatment layer.

[0123] The coating method for applying the coating material for secondary battery separators is not particularly limited, and examples thereof include a wire bar method, a gravure coater method, a small-diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a microgravure coater method, a knife coater method, an air doctor coater method, a blade coater method, a rod coater method, a squeeze coater method, a cast coater method, a die coater method, a screen printing method, and a spray coating method. A preferred coating method is the wire bar method.

[0124] The drying temperature is, for example, 40°C or higher and, for example, 80°C or lower.

[0125] In this way, a secondary battery separator is manufactured, which includes a porous membrane and a coating film of the above-mentioned coating material for a secondary battery separator that is disposed on at least one surface of the porous membrane.

[0126] In the above description, the coating film of the coating material for a secondary battery separator is disposed on at least one side of the porous membrane, but the coating film can also be disposed on both sides of the porous membrane.

[0127] This secondary battery separator includes a coating film of the above-described coating material for a secondary battery separator. Therefore, the secondary battery separator has excellent heat resistance and adhesion. Therefore, this secondary battery separator can be suitably used in the manufacture of secondary batteries.

[0128] <Secondary battery> The secondary battery comprises a positive electrode, a negative electrode, the above-mentioned secondary battery separator disposed between the positive electrode and the negative electrode, and an electrolyte impregnated in the positive electrode, the negative electrode, and the above-mentioned secondary battery separator.

[0129] As the positive electrode, for example, a known electrode including a positive electrode current collector and a positive electrode active material laminated on the positive electrode current collector is used.

[0130] Examples of the positive electrode current collector include conductive materials such as aluminum, titanium, stainless steel, nickel, baked carbon, conductive polymers, and conductive glass.

[0131] The positive electrode active material is not particularly limited, but examples thereof include known positive electrode active materials such as lithium-containing transition metal oxides, lithium-containing phosphates, and lithium-containing sulfates.

[0132] These positive electrode active materials can be used alone or in combination of two or more.

[0133] As the negative electrode, for example, a known electrode including a negative electrode current collector and a negative electrode active material laminated on the negative electrode current collector is used.

[0134] The negative electrode current collector may be made of a conductive material such as copper or nickel.

[0135] The negative electrode active material is not particularly limited, but may be a carbon active material, such as graphite, soft carbon, or hard carbon.

[0136] These negative electrode active materials can be used alone or in combination of two or more.

[0137] When a lithium ion battery is used as the secondary battery, the electrolyte may be, for example, a solution in which a lithium salt is dissolved in a carbonate compound such as ethylene carbonate (EC), propylene carbonate (PC), or ethyl methyl carbonate (EMC).

[0138] To manufacture a secondary battery, for example, a separator for the secondary battery is sandwiched between a positive electrode and a negative electrode, and these are housed in a battery casing (cell), and an electrolyte is injected into the battery casing. In this way, a secondary battery can be obtained.

[0139] The secondary battery includes the secondary battery separator, and therefore has excellent heat resistance and adhesion.

[0140] <Action and effect> The raw material for the coating material for secondary battery separators is a water-soluble acrylic resin and a kenyl chloride resin with a specified value or more. transformation It contains polyvinyl alcohol with a high viscosity, which gives it excellent heat resistance and adhesion.

[0141] For details, see Polyvinyl Alcohol transformation If the viscosity is too low, the wettability tends to decrease, which makes it difficult to form a uniform coating film and reduces heat resistance and adhesion.

[0142] On the other hand, the raw material for the coating material for the secondary battery separator is a kenyl polyvinyl alcohol. transformation Since the degree of wettability is equal to or greater than a predetermined value, wettability can be improved, resulting in the formation of a uniform coating film, and improved heat resistance and adhesion.

[0143] The coating material for a secondary battery separator contains the above-mentioned raw materials for the coating material for a secondary battery separator, and therefore has excellent heat resistance and adhesion.

[0144] The secondary battery separator has a coating film of the above-mentioned coating material for secondary battery separators, and therefore has excellent heat resistance and adhesion.

[0145] The secondary battery includes the above-mentioned secondary battery separator, and therefore has excellent heat resistance and adhesion. [Example]

[0146] Specific numerical values ​​of blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be replaced with the corresponding upper limit values ​​(numeric values ​​defined as "not more than" or "less than") or lower limit values ​​(numeric values ​​defined as "not less than" or "exceeding") of blending ratios (content ratios), physical property values, parameters, etc. described in the above "Description of the Invention." Furthermore, unless otherwise specified in the following description, "parts" and "%" are based on mass.

[0147] <Ingredient details> The trade names and abbreviations of the components used in each example and each comparative example are described in detail below. Mam: methacrylamide AM: acrylamide Mac: methacrylic acid HEMA: 2-hydroxyethyl methacrylate St: styrene BA: n-butyl acrylate Kuraray Poval 60-98: Unmodified polyvinyl alcohol, ken transformation 98mol%~99mol%, manufactured by Kuraray Co., Ltd. Kuraray Poval 28-98: Unmodified polyvinyl alcohol, ken transformation 98mol%~99mol%, manufactured by Kuraray Co., Ltd. Kuraray Poval 5-98: Unmodified polyvinyl alcohol, ken transformation 98mol%~99mol%, manufactured by Kuraray Co., Ltd. Kuraray Poval 44-88: Unmodified polyvinyl alcohol, ken transformation 87mol%~89mol%, manufactured by Kuraray Co., Ltd. Kuraray Poval 40-80E: Unmodified polyvinyl alcohol, Ken transformation 80mol%, manufactured by Kuraray Co., Ltd. AF17: Carboxyl group modified polyvinyl alcohol, ken transformation Over 96 mol% ABV, manufactured by Nippon Vaccination & Poval Co., Ltd. Gohsenol CKS50: Sulfo-modified polyvinyl alcohol, ken transformation99mol%, manufactured by Mitsubishi Chemical Corporation Exeval RS-2117: Hydrophobic group modification Sex vinyl alcohol, transformation 98mol%~99mol%, manufactured by Kuraray Co., Ltd. EXCEVAL RS-1113: Hydrophobically modified unmodified polyvinyl alcohol, transformation 98mol%~99mol%, manufactured by Kuraray Co., Ltd. Olfine E1010: Wetting agent (acetylene surfactant), manufactured by Nissin Chemical Industry Co., Ltd. Ammonium polycarboxylate: Dispersant, ammonium polycarboxylate aqueous solution, product name SN5468, manufactured by San Nopco

[0148] <Production of water-soluble acrylic resin> Manufacturing Example 1 Stirrer, reflux cooling vessel A separable flask with a lid was charged with 200.0 parts by mass of distilled water, and the atmosphere was replaced with nitrogen gas. The temperature was then raised to 80°C. Next, 0.6 parts by mass of ammonium persulfate was added, and the water-soluble acrylic resin raw materials listed below were added continuously over 3 hours. The mixture was then maintained for another 3 hours to complete the polymerization. Ammonia water was added to adjust the pH to 9.0, and an appropriate amount of water was added to obtain an aqueous solution of the water-soluble polymer (solid content 15.0% by mass). {Water-soluble acrylic resin raw material} Methacrylamide 80.0 parts by mass Methacrylic acid 5.0 parts by mass 2-Hydroxyethyl methacrylate 15.0 parts by mass 25% ammonia water 3.0 parts by mass Distilled water 300.0 parts by mass

[0149] Production Examples 2, 3, 5 and 6 An aqueous solution of a water-soluble polymer (solid content: 15.0% by mass) was obtained in the same manner as in Production Example 1. However, the formulation of the water-soluble acrylic resin raw material was changed according to the description in Table 1.

[0150] <Production of acrylic emulsion> Production Example 4 A separable flask equipped with a stirrer was charged with 0.4 parts by mass of dodecylbenzenesulfonic acid as a surfactant and 300 parts by mass of water. The mixture was stirred while purging with nitrogen and heated to 70°C. Next, 1 part by mass of potassium persulfate was added as a polymerization initiator, and the following emulsion was continuously added over 3 hours. The mixture was then stirred at 80°C for 5 hours to allow the reaction to proceed. The mixture was then cooled and adjusted to pH 9 with 25% aqueous ammonia. An appropriate amount of water was then added to obtain an aqueous dispersion of acrylic resin particles (solids concentration 20% by mass). The particle size of the acrylic resin particles was 0.2 μm.

[0151] {Preparation of emulsion} To an aqueous solution containing 170 parts by mass of water and 1.0 part by mass of dodecylbenzenesulfonic acid, 55 parts by mass of n-butyl acrylate, 30 parts by mass of styrene, 5 parts by mass of methacrylic acid, and 10 parts by mass of 2-hydroxyethyl methacrylate were continuously added with stirring to obtain an emulsion.

[0152] <Preparation of Polyvinyl Alcohol> The polyvinyl alcohols listed in Tables 2 and 3 were prepared as follows: . Ingredients Specifically, 90 parts by mass of water was placed in a separable flask equipped with a stirrer, and 10 parts by mass of polyvinyl alcohol was added little by little while stirring, and then the temperature was raised to 95°C and maintained for 3 hours. After confirming that the polyvinyl alcohol had completely dissolved, the mixture was cooled, and an appropriate amount of water was added to prepare a 10% aqueous solution of polyvinyl alcohol.

[0153] <Production of raw materials for coating materials for secondary battery separators, coating materials for secondary battery separators, and secondary battery separators> Examples 1 to 13 and Comparative Examples 1 to 3 (Manufacturing raw materials for coating materials for secondary battery separators) A water-soluble acrylic resin and polyvinyl alcohol were mixed according to the formulations shown in Tables 2 and 3. This produced a coating material raw material for a secondary battery separator. In Comparative Example 2, an acrylic emulsion was used instead of the water-soluble acrylic resin. The values ​​shown in Tables 2 and 3 are the solid content values.

[0154] (Manufacturing coating materials for secondary battery separators) A dispersant was added to 123 parts by mass of water according to the formulations shown in Tables 2 and 3. Next, while stirring with a disperser (1000 rpm), 100 parts by mass of boehmite (aluminum hydroxide oxide, manufactured by Navaltec, trade name "Apilar AOH60", average median diameter D50: 0.9 μm) was gradually added as inorganic particles. After the addition, the mixture was further stirred with a homogenizer (5000 rpm). This resulted in an aqueous dispersion of inorganic particles (solid concentration of inorganic particles: 45% by mass).

[0155] Next, the raw material for the coating material for a secondary battery separator was blended into the aqueous dispersion of inorganic particles, and water was added appropriately, followed by stirring.

[0156] The mixture was then filtered through a 300 mesh (48 μm filtration particle size) filter to produce a coating material for secondary battery separators (a dispersion of a coating material for secondary battery separators). The solid content of the dispersion of the coating material for secondary battery separators was 40 mass %.

[0157] (Manufacturing secondary battery separators) [1st step] As the porous membrane, a polyolefin porous membrane (without surface treatment (corona treatment)) was prepared.

[0158] [Second process] Using a wire bar, the above-mentioned coating material for secondary battery separators (dispersion of coating material for secondary battery separators) was applied to one side of the polyolefin porous membrane, and then dried at 50° C. Thereby, a coating film (thickness 2 μm) of the coating material for secondary battery separators was formed on one side of the polyolefin porous membrane, and a secondary battery separator was thus produced.

[0159] <Evaluation> [Weight average molecular weight] For the water-soluble acrylic resin or acrylic emulsion of each manufacturing example, the weight average molecular weight was calculated in terms of standard polyethylene glycol / polyethylene oxide based on the following conditions: Amount The results are shown in Table 1. {conditions} Apparatus: GPC apparatus: Apparatus name: P KP-22, manufactured by Fromm Sample concentration: 0.1 (w / v)% Sample injection volume: 100 μL Eluent: 0.2M NaNO3 / acrylonitrile (AN) = 90 / 10 Flow rate: 1.0ml / min Measurement temperature: 40℃ Column: ShodexohPAK SB-806M HQ x 2

[0160] [Glass transition temperature] The glass transition temperature (Tg) of the water-soluble acrylic resin or acrylic emulsion of each production example was calculated using the following FOX equation. The results are shown in Table 1. 1 / Tg=W1 / Tg1+W2 / Tg2++W n / Tg n (1) [wherein Tg is the glass transition temperature of the copolymer (unit: K), Tg i (i=1, 2, . . . n) is the glass transition temperature (unit: K) when monomer i forms a homopolymer, W i (i=1, 2,...n) represents the mass fraction of monomer i in all monomers.]

[0161] [Heat resistance] The secondary battery separators of each example and comparative example were cut into 5 cm x 5 cm pieces to serve as test specimens. These test specimens were left in an oven at 150°C for 1 hour. The lengths of each side of the test specimen were measured before and after leaving the oven. The shrinkage rate was calculated from the lengths of each side before and after shrinkage according to the following formula (2). The results are shown in Tables 2 and 3. Shrinkage rate (%) = {average length of one side before shrinkage (cm) - average length of one side after shrinkage (cm)} / average length of one side before shrinkage (cm) x 100 (2)

[0162] [Ion permeability] For the secondary battery separators of each example and each comparative example, the air permeability resistance was measured in accordance with JIS-P-8117 using an Oken-type air permeability smoothness tester manufactured by Asahi Seiko Co., Ltd. The amount of decrease in air permeability relative to the air permeability of the porous membrane itself was taken as Δ air permeability. Specifically, Δ air permeability was calculated based on the following formula (3). The smaller the Δ air permeability, the better the ion permeability was evaluated. The results are shown in Tables 2 and 3. ΔAir permeability = Measured air permeability - 180 (Air permeability of the porous membrane itself) (3)

[0163] [Adhesion] The coating film on the secondary battery separator of each Example and Comparative Example was rubbed with an eraser, and the degree of peeling of the coating film was evaluated based on the following criteria. The results are shown in Tables 2 and 3. 1 item: 100g load After rubbing it heavily once, the coating peeled off. 2 items: 100g load After rubbing it heavily 2-3 times, the coating came off. 3 items: 100g load After rubbing it heavily 4-5 times, the coating came off. 4 points: 100g load Even after rubbing five times with heavy weight, the coating did not peel off. load After rubbing it heavily five times, the coating peeled off. 5 points: 100g load Even after rubbing five times with heavy weight, the coating did not peel off. load Even after rubbing it heavily five times, the coating did not come off.

[0164] <Consideration> Water-soluble acrylic resin and a specified value or more of ken transformation Polyvinyl alcohol with high viscosity Example Examples 1 to 13 are Comparative Example 1 which does not contain polyvinyl alcohol, Comparative Example 2 which does not contain a water-soluble acrylic resin but contains an acrylic emulsion, and Comparative Example 3 which does not contain a water-soluble acrylic resin but contains an acrylic emulsion. transformation It can be seen that the heat resistance and adhesion are superior to those of Comparative Example 3, which contains polyvinyl alcohol having a high viscosity.

[0165] [Table 1]

[0166] [Table 2]

[0167] [Table 3]

[0168] The above invention is provided as an exemplary embodiment of the present invention, but this is merely an example and should not be interpreted as limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0169] The coating material raw material for secondary battery separators, the coating material for secondary battery separators, and the secondary battery separators of the present invention are suitably used in the production of secondary batteries.

Claims

1. Contains a water-soluble acrylic resin and polyvinyl alcohol, The polyvinyl alcohol has a saponification degree of 85 mol % or more.

2. 2. The coating material raw material for a secondary battery separator according to claim 1, wherein a content ratio of the polyvinyl alcohol is 5 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the water-soluble acrylic resin.

3. 2. The coating material raw material for a secondary battery separator according to claim 1, wherein the polyvinyl alcohol is at least one selected from the group consisting of unmodified polyvinyl alcohol and anionic group-modified polyvinyl alcohol.

4. 2. The coating material raw material for a secondary battery separator according to claim 1, wherein the water-soluble acrylic resin has a weight average molecular weight of 10,000 or more and 150,000 or less.

5. A coating material for a secondary battery separator, comprising the coating material raw material for a secondary battery separator according to any one of claims 1 to 4 and inorganic particles.

6. A porous membrane; a coating film of the coating material for a secondary battery separator according to claim 5, which is disposed on at least one surface of the porous membrane; A secondary battery separator comprising:

7. A secondary battery comprising: a positive electrode; a negative electrode; and the secondary battery separator according to claim 6 disposed between the positive electrode and the negative electrode.

Images