Insulating paste for current collectors in lithium-ion secondary batteries

Abstract

To provide an insulation paste having good storability, dispersibility, and coating workability, with which an insulation layer having good finish properties after coating and good adhesion to a current collector can be obtained.SOLUTION: An insulation paste for a lithium ion secondary battery current collector contains an inorganic filler (A), a binder (B), a dispersion resin (C), and a solvent (D). The paste has a viscosity (shear rate 1s-1) of 2,000 mPa s or more, and a TI value (the ratio of the viscosity at a shear rate of 1 s-1 to the viscosity at a shear rate of 1,000 s-1)of larger than 1.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an insulating paste to be applied onto a current collector of a positive electrode and / or a negative electrode of a lithium ion secondary battery, and to a method for producing an insulating layer obtained by applying the paste. [Background technology]

[0002] Lithium-ion secondary batteries include those in which positive and negative electrodes are stacked or wound. These positive and negative electrodes are manufactured by applying a mixture layer to both sides of a metal foil (current collector), drying, and pressing. Many positive and negative electrodes have exposed portions at the ends of the metal foil as a current path. Techniques have been disclosed to prevent short circuits (insulate) these exposed portions. For example, Patent Document 1 discloses a lithium-ion secondary battery including an insulating layer. This insulating layer prevents short circuits between the positive and negative electrode plates, but the layer has poor storage stability and coating workability, making it difficult to obtain a satisfactory finish. Furthermore, if a physical load is applied during pressing, the insulating layer may fall off, making it impossible to ensure stable insulation. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-232425 Summary of the Invention [Problem to be solved by the invention]

[0004] The problem to be solved by the present invention is to provide an insulating paste having good storage properties (pigment sedimentation, viscosity), dispersibility, and coating workability, and to provide an insulating layer having good finish after coating and good adhesion to a current collector. [Means for solving the problem]

[0005] As a result of intensive research to solve the above problems, the inventors have discovered an insulating paste for a current collector of a lithium ion secondary battery, which contains an inorganic filler (A), a binder (B), a dispersion resin (C), and a solvent (D), and the viscosity of the paste (shear rate 1 s -1 ) is 2000 mPa·s or more, and the TI value (shear rate 1000 s -1 Viscosity of 1s -1 The inventors have found that the above-mentioned problems can be solved by an insulating paste characterized by a viscosity ratio of the above-mentioned viscosity (the ratio of the viscosity of the above-mentioned viscosity) being greater than 1, and have thus completed the present invention.

[0006] That is, the present invention provides the following insulating paste and insulating layer. Item 1. An insulating paste for a lithium ion secondary battery current collector containing an inorganic filler (A), a binder (B), a dispersion resin (C), and a solvent (D), wherein the viscosity of the paste (shear rate 1 s -1 ) is 2000 mPa·s or more, and the TI value (shear rate 1000 s -1 Viscosity of 1s -1 An insulating paste characterized in that the viscosity ratio of the insulating paste to ... Item 2. An insulating paste for a lithium ion secondary battery current collector according to Item 1, characterized in that the dispersed resin (C) contains a polar group-containing acrylic resin (c) which is a copolymer of raw material monomers including a polymerizable unsaturated monomer (c1) having a polar functional group and a polymerizable unsaturated monomer (c2) having a hydrocarbon group having 4 or more carbon atoms, and the weight-average molecular weight of the copolymer is 1,000 to 100,000. Item 3. The insulating paste for a lithium ion secondary battery current collector according to Item 1 or 2, wherein the inorganic filler (A) is at least one selected from the group consisting of alumina, silica, TiO2, BaTiO3, ZrO2, boehmite, zeolite, apatite, and kaolin. Item 4. The insulating paste for a lithium ion secondary battery current collector according to any one of Items 1 to 3, wherein the binder (B) is modified or unmodified polyvinylidene fluoride. Item 5. The insulating paste for a lithium ion secondary battery current collector according to any one of Items 1 to 4, wherein the solvent (D) is N-methyl-2-pyrrolidone. Item 6. An insulating paste for a current collector of a lithium ion secondary battery, characterized in that the insulating paste according to any one of Items 1 to 5 does not substantially contain an electrode active material. Item 7. A method for producing an insulating layer for a current collector of a lithium ion secondary battery, comprising applying the insulating paste according to any one of Items 1 to 6 to a part or all of a current collector, and then heating and drying the paste to form an insulating layer. Item 8. A method for producing an insulating layer for a current collector of a lithium ion secondary battery, wherein the insulating layer according to Item 7 is non-porous. Item 9. The method for producing an insulating layer for a current collector of a lithium ion secondary battery according to Item 7 or 8, wherein the current collector is made of aluminum or a composite metal thereof. [Effects of the Invention]

[0007] The insulating paste of the present invention is an insulating paste having good storage properties (pigment settling property, viscosity), dispersibility, and coating workability, and the insulating layer obtained has good finish and adhesion. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below.

[0009] In this specification, unless otherwise specified, the phrase "a resin contains a monomer X, which is a raw material thereof" means that the resin is a (co)polymer of raw material monomers, including the monomer X. In addition, in this specification, the term "(co)polymer" means a polymer or a copolymer.

[0010] In this specification, "(meth)acrylate" means acrylate and / or methacrylate, "(meth)acrylic acid" means acrylic acid and / or methacrylic acid, "(meth)acryloyl" means acryloyl and / or methacryloyl, and "(meth)acrylamide" means acrylamide and / or methacrylamide.

[0011] Furthermore, in the specification, the term "insulating layer" may be alternatively referred to as an "insulating film," a "coating film," or a "film."

[0012] Insulating paste The insulating paste of the present invention is an insulating paste for a current collector of a lithium ion secondary battery, which contains an inorganic filler (A), a binder (B), a dispersion resin (C), and a solvent (D).

[0013] The viscosity of the above insulating paste (shear rate 1 s -1 From the viewpoint of storage stability and finish quality, the viscosity is usually 2000 mPa·s or higher, preferably 2000 to 7000 mPa·s, and more preferably 2500 to 5000 mPa·s. If the viscosity is 7000 mPa·s or higher, coating workability and finish quality will decrease, while if it is 2000 mPa·s or lower, storage stability (pigment sedimentation), finish quality, and sagging will decrease. In addition, the TI value (shear rate 1000 s -1 Viscosity of 1s -1 The viscosity ratio (ratio of viscosity of the mixture to the viscosity of the mixture) is usually greater than 1, preferably 2 to 10, and more preferably 3 to 6. For example, if the TI value is 1 or more, the shear rate during coating (1000 s -1 The viscosity decreases after coating (shear rate is 1 s -1 The viscosity of the insulating layer (coating film) is high (approximately 100%), so the insulating layer does not flow and the finish is good.

[0014] The viscosity can be measured, for example, by a cone and plate type viscometer "Mars2" (trade name, manufactured by HAAKE).

[0015] The sodium content in the insulating paste is typically adjusted to 450 ppm or less, preferably 10 to 350 ppm, more preferably 10 to 300 ppm, and even more preferably 10 to 200 ppm, from the viewpoint of storage stability (suppressing a decrease in the viscosity of the insulating paste during storage (hereinafter referred to as storage viscosity thinning)). If the sodium content exceeds 450 ppm, viscosity thinning occurs during storage at high temperatures, which may result in a decrease in pigment sedimentation and finish quality (including sagging). Furthermore, the insulating paste may contain sodium ions due to carryover from various raw materials (especially inorganic fillers, described below) or contamination during the manufacturing process, and completely removing these ions would be economical.

[0016] The cause of the above-mentioned storage viscosity reduction is not fully understood, but one possible reason is that, for example, the viscosity of the paste is normally maintained by interactions between the inorganic filler (A), binder (B), and dispersion resin (C) through hydrogen bonds. However, when the paste contains more than a certain amount of sodium ions, this interaction is gradually broken down, causing the viscosity of the insulating paste to decrease.

[0017] The sodium content in the insulating paste can be measured, for example, using an ICP optical emission spectrometer. Specifically, the sample (insulating paste) is dissolved in a nitric acid / sulfuric acid mixture (mixing ratio: 1 / 1), and the sodium content can be measured using an ICP optical emission spectrometer (Shimadzu Corporation, "ICPS-8100").

[0018] Inorganic filler (A) The inorganic filler (A) that can be used in the insulating paste of the present invention can be any non-conductive inorganic filler, and examples thereof include alumina, silica, TiO2, BaTiO3, ZrO2, boehmite, zeolite, apatite, and kaolin. One type can be used alone, or two or more types can be used in combination. Of these, alumina and / or boehmite are preferred. Alumina is aluminum oxide represented by Al2O3, and boehmite is alumina monohydrate represented by the composition γ-AlO(OH).

[0019] The volume average particle size of the inorganic filler (A) in the insulating paste of the present invention is preferably 0.5 to 7 μm.

[0020] The particle size can be measured, for example, using a particle size distribution measuring device (manufactured by Microtrac-Bell, product name: Microtrac MT3000).

[0021] When boehmite is used as the inorganic filler (A), particular attention must be paid to the sodium content in the insulating paste. Since sodium hydroxide is generally used in the manufacturing process of aluminum hydroxide, which is the raw material for boehmite, boehmite also contains a certain amount of sodium ions. Although it is possible to remove sodium ions by washing, etc., it is economically difficult to completely remove them.

[0022] Specifically, the sodium content of the boehmite is usually 2000 ppm or less, preferably 40 to 1500 ppm, and more preferably 200 to 1200 ppm, based on the solid content of the boehmite.

[0023] Binder (B) The binder (B) that can be used in the insulating paste of the present invention is a copolymer having a polymerizable unsaturated group-containing monomer represented by the following formula (1) as a constituent component, and can be synthesized by copolymerizing a monomer containing the polymerizable unsaturated group-containing monomer.

[0024] [ka]

[0025] (wherein R1 to R4 are atoms selected from hydrogen, fluorine and chlorine, or linear, branched and / or cyclic organic groups.) The polymerizable unsaturated group-containing monomer can be used without any particular limitation as long as it has the structure of the above formula (1), and examples thereof include vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, fatty acid vinyl ester, vinyl ether, vinylpyrrolidone, styrene, (meth)acryloyl group-containing monomers, and (meth)acrylamide group-containing monomers, and these can be used alone or in combination of two or more.

[0026] The method for polymerizing the above-mentioned polymerizable unsaturated group-containing monomer may be a polymerization method known per se, for example, For example, the polymerizable unsaturated group-containing monomer may be solution polymerized in an organic solvent. However, the polymerization method is not limited to this, and examples thereof include bulk polymerization, emulsion polymerization, and suspension polymerization. When solution polymerization is carried out, it may be continuous polymerization or batch polymerization, and the monomer is It may be added all at once, or in portions, or may be added continuously or intermittently. You may do so. Various modifications can also be made after polymerization (for example, hydrolysis after polymerization, acetalization, reaction with other resins for grafting, etc.). The polymerization initiator used in the polymerization is not particularly limited, and may be a peroxide. Known radical initiators such as azo initiators, redox initiators, and organic halide initiators A chlorine polymerization initiator can be used.

[0027] As the solvent used in the polymerization, any known solvent can be used without any particular limitation. In this case, the organic solvents mentioned below in relation to the dispersing resin (C) can be suitably used.

[0028] The polymerization reaction temperature is not particularly limited, but is usually set in the range of about 30 to 200°C. It is possible.

[0029] Examples of the binder (B) include polyvinylidene fluoride, polyvinyl alcohol, polyvinyl acetal, acrylic resin, polyvinyl acetate, polyvinyl chloride, polystyrene, polyvinyl ether, polyvinylpyrrolidone, etc. These can be used alone or in combination of two or more. Among them, polyvinylidene fluoride is preferred due to its insulating properties and coating film strength (i.e., cohesive force).

[0030] The weight average molecular weight of the binder (B) is preferably greater than 100,000, more preferably within the range of 110,000 to 5,000,000, and even more preferably within the range of 200,000 to 2,000,000.

[0031] Dispersion resin (C) The dispersing resin (C) that can be used in the present invention preferably contains at least one acrylic resin, and particularly preferably contains a polar group-containing acrylic resin that is a copolymer of raw material monomers including at least one polymerizable unsaturated monomer having a polar group.

[0032] If the dispersing resin (C) contains polar groups such as acid groups, it improves adhesion to the substrate and pigment dispersibility, but if there are too many, the polarity increases too much, resulting in poor finish. The presence of low-polarity monomers with 4 or more carbon atoms increases compatibility with the low-polarity fluororesin, improving the finish. Dispersibility also improves slightly.

[0033] For this reason, it is more preferable that the polar group-containing acrylic resin is a copolymer of raw material monomers containing a polymerizable unsaturated monomer (c1) having a polar functional group and a polymerizable unsaturated monomer (c2) having a hydrocarbon group having 4 or more carbon atoms, and that the weight-average molecular weight of the copolymer is 1,000 to 100,000.Polyvinyl alcohol (PVA) has high polarity, and therefore has poorer finish properties than such a polar group-containing acrylic resin (c).

[0034] <Polar group-containing acrylic resin (c)> The polar group-containing acrylic resin (c) contains a polymerizable unsaturated monomer (c1) having a polar functional group and a polymerizable unsaturated monomer (c2) having a hydrocarbon group having 4 or more carbon atoms, thereby achieving both dispersibility of the inorganic filler (A), compatibility with the binder (B), and adhesion to the current collector.

[0035] <Polymerizable unsaturated monomer having a polar group (c1)> The polymerizable unsaturated monomer having the polar group can be any polymerizable unsaturated monomer having a polar group without any particular limitation. Examples of the polar group include a carboxyl group, a phosphate group, a sulfonic acid group, an amino group, a quaternary base, a hydroxyl group, and a polyalkylene glycol group. The polymerizable unsaturated monomer may have multiple polar groups.

[0036] Specific examples of the polymerizable unsaturated monomer having a polar group include, for example, carboxyl group-containing polymerizable unsaturated monomers such as (meth)acrylic acid, maleic acid, crotonic acid, and β-carboxyethyl acrylate; phosphoric acid group-containing polymerizable unsaturated monomers such as 2-(meth)acryloyloxyethyl acid phosphate and 2-(meth)acryloyloxypropyl acid phosphate; sulfonic acid group-containing polymerizable unsaturated monomers such as 2-acrylamido-2-methylpropanesulfonic acid, 2-sulfoethyl (meth)acrylate, allylsulfonic acid, and 4-styrenesulfonic acid, as well as sodium salts and ammonium salts of these sulfonic acids; amino group-containing polymerizable unsaturated monomers such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, N,N-dimethylaminopropyl (meth)acrylamide, and adducts of glycidyl (meth)acrylate and amines; 2-(methacryloyloxy)ethyltrimethyl Examples of suitable polymerizable unsaturated monomers include quaternary base-containing polymerizable unsaturated monomers such as ammonium chloride; monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; ε-caprolactone-modified monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms; N-hydroxymethyl (meth)acrylamide; allyl alcohol; and hydroxyl group-containing polymerizable unsaturated monomers such as (meth)acrylates having a polyoxyalkylene chain with a hydroxyl group at the molecular terminal; and polyalkylene glycol group-containing polymerizable unsaturated monomers such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate. Among these, preferred are polymerizable unsaturated monomers having an acid group, and more preferred are polymerizable unsaturated monomers having a phosphoric acid group. These may be used alone or in combination of two or more.

[0037] The raw material monomers preferably contain 1 to 80 mass % of polymerizable unsaturated monomers having polar groups, more preferably 5 to 70 mass %, and even more preferably 20 to 60 mass %.

[0038] When the content of the polymerizable unsaturated monomer having a polar group in the raw material monomer is within the above range, compatibility with the binder, pigment dispersibility, and adhesion are improved.

[0039] Furthermore, when the polar group-containing acrylic resin (c) contains acid groups, the acid value is preferably 200 mgKOH / g or less, more preferably within the range of 5 to 150 mgKOH / g; when it contains amino groups, the amine value is preferably 200 mgKOH / g or less, more preferably within the range of 5 to 150 mgKOH / g; and when it contains hydroxyl groups, the hydroxyl value is preferably 200 mgKOH / g or less, more preferably within the range of 5 to 150 mgKOH / g.

[0040] The acid value of the polar group-containing acrylic resin (c) can be measured according to JIS K-5601-2-1 (1999), and the amine value of the polar group-containing acrylic resin (a) can be measured according to JIS K7237 (1995).

[0041] <Polymerizable unsaturated monomer (c2) having an alkyl group having 4 or more carbon atoms> From the viewpoint of compatibility with the binder (B), the raw material monomer of the polar group-containing acrylic resin (c) includes a polymerizable unsaturated monomer having an alkyl group having 4 or more carbon atoms, which is particularly suitable when the binder (B) is polyvinylidene fluoride, which has a relatively low polarity.

[0042] The polymerizable unsaturated monomer having an alkyl group of 4 or more carbon atoms can be a straight-chain, branched, or cyclic alkyl group, etc., and can be used without any particular limitation, as long as it is a polymerizable unsaturated monomer having an alkyl group of 4 or more carbon atoms. Specific examples include straight-chain, branched, or cyclic alkyl group-containing (meth)acrylates such as styrene, naphthyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, lauryl (meth)acrylate, stearyl (meth)acrylate, isostearyl acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and tridecyl (meth)acrylate, and these can be used alone or in combination of two or more.

[0043] The polymerizable unsaturated monomer having an alkyl group with 4 or more carbon atoms preferably has 4 to 24 carbon atoms, more preferably 8 to 20 carbon atoms, and particularly preferably 10 to 17 carbon atoms. In addition, the polymerizable unsaturated monomer having a linear or branched alkyl group structure is preferred.

[0044] In the raw material monomers, the polymerizable unsaturated monomer having an alkyl group having 4 or more carbon atoms is contained in an amount of preferably 1 to 95 mass %, more preferably 10 to 80 mass %, and even more preferably 20 to 60 mass %.

[0045] When the content of the polymerizable unsaturated monomer having an alkyl group with 4 or more carbon atoms in the raw material monomer falls within the above range, the dispersibility and storage stability are improved.

[0046] <Other polymerizable unsaturated monomers> As the raw material monomer for obtaining the polar group-containing acrylic resin (c), other polymerizable unsaturated monomers besides the above-mentioned polymerizable unsaturated monomers having a polar group and polymerizable unsaturated monomers having an alkyl group with 4 or more carbon atoms can also be suitably used. Examples of other polymerizable unsaturated monomers include polymerizable unsaturated monomers having an alkyl group with 3 or less carbon atoms, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and isopropyl (meth)acrylate; and polymerizable unsaturated monomers having two or more polymerizable unsaturated groups in one molecule.

[0047] The polar group-containing acrylic resin (c) can be produced by a conventionally known polymerization method. For example, it can be produced by solution polymerization of a polymerizable unsaturated monomer (raw material monomer) in an organic solvent, but this is not limiting. For example, bulk polymerization, emulsion polymerization, suspension polymerization, etc. may also be used. When solution polymerization is carried out, continuous polymerization or batch polymerization may be used, and the polymerizable unsaturated monomer may be charged all at once or in portions, or may be added continuously or intermittently.

[0048] The radical polymerization initiator used in the polymerization can be a conventionally known method. For example, cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide, methylcyclohexanone peroxide, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(t-butylperoxy)cyclohexane, n-butyl-4,4-bis(t-butylperoxy)valerate, cumene hydroperoxide, 2,5-dimethylhexane-2,5-dihydroperoxide, 1,3-bis(t-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, diisopropylbenzene peroxide, t-butylcumyl peroxide, decanoyl peroxide, lauroyl peroxide, benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, di-t-amyl peroxide, bis(methyl methyl cyclohexane), ... Peroxide polymerization initiators such as tert-butylcyclohexyl peroxydicarbonate, tert-butyl peroxybenzoate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and tert-butylperoxy-2-ethylhexanoate; 2,2'-azobis(isobutyronitrile), 1,1-azobis(cyclohexane-1-carbonitrile), azocumene, and 2,2'-azobis(2-methylbutyronitrile) Examples of azo polymerization initiators include 2,2'-azobisdimethylvaleronitrile, 4,4'-azobis(4-cyanovaleric acid), 2-(t-butylazo)-2-cyanopropane, 2,2'-azobis(2,4,4-trimethylpentane), 2,2'-azobis(2-methylpropane), and dimethyl 2,2'-azobis(2-methylpropionate), and these can be used alone or in combination of two or more.

[0049] The solvent used for the polymerization or dilution is not particularly limited, and examples thereof include water, organic solvents, and mixtures thereof. In particular, it is preferable to use an organic solvent. Examples of the organic solvent include hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, and cyclobutane; aromatic solvents such as toluene and xylene; ketone solvents such as methyl isobutyl ketone; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol; ethyl acetate, n-butyl acetate, isobutyl acetate, butyl butyrate, ethylene glycol monomethyl ether acetate, Examples of known solvents include ester solvents such as butyl carbitol acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone; alcohol solvents such as ethanol, isopropanol, n-butanol, s-butanol, and isobutanol; and amide solvents such as Equamide (trade name, manufactured by Idemitsu Kosan Co., Ltd.), N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, N-methylpropioamide, and N-methyl-2-pyrrolidone. These can be used alone or in combination of two or more. However, if the solvent used in polymerizing and / or diluting the polar group-containing acrylic resin (c) is not removed by a solvent removal step, it will be carried over into the insulating paste of the present invention. Therefore, it is preferable to use the solvent so that it falls within the solubility parameter range specified for the solvent (D) described below.

[0050] In solution polymerization in an organic solvent, a method is used in which a polymerization initiator, a polymerizable unsaturated monomer component, and a solvent are mixed and heated while stirring, or a method is used in which a solvent is charged into a reaction vessel to suppress a temperature rise in the system due to the heat of reaction, and the polymerizable unsaturated monomer component and the polymerization initiator are mixed or separately added dropwise over a predetermined time while stirring at a temperature of 60°C to 200°C and blowing in an inert gas such as nitrogen or argon as necessary.

[0051] The polymerization can generally be carried out for about 1 to 10 hours. After each polymerization stage, an additional catalyst step may be performed, in which the reaction vessel is heated while a polymerization initiator is added dropwise, as needed.

[0052] The weight average molecular weight (Mw) of the polar group-containing acrylic resin (c) obtained as described above is preferably within the range of 1,000 to 100,000, more preferably 2,000 to 95,000, even more preferably 3,000 to 90,000, and particularly preferably 5,000 to 80,000.

[0053] When the weight average molecular weight of the polar group-containing acrylic resin (c) is within the above range, the dispersibility and storage stability are improved.

[0054] In this specification, the weight-average molecular weight is a value obtained by converting the retention time (retention volume) measured using a gel permeation chromatograph (GPC) into the molecular weight of polystyrene using the retention time (retention volume) of a standard polystyrene of known molecular weight measured under the same conditions. Specifically, the measurement can be performed using a gel permeation chromatograph "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) and four columns "TSKgel G-4000HXL," "TSKgel G-3000HXL," "TSKgel G-2500HXL," and "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation) under the conditions of a mobile phase of tetrahydrofuran, a measurement temperature of 40°C, a flow rate of 1 mL / min, and a detector RI.

[0055] <Other resins> In the present invention, the dispersing resin (C) can be any known resin that can be used together with the acrylic resin as needed, without any particular limitation, and specific examples include polyester resins, epoxy resins, urethane resins, epoxy resins, polyether resins, fluororesins, silicone resins, polycarbonate resins, melamine resins, chlorine-based resins, fluorine-based resins, cellulose-based resins, polybutadiene rubber, and modified or composite resins thereof. These resins can be used alone or in combination with the acrylic resin.

[0056] Solvent (D) As the solvent (D) that can be used in the insulating paste of the present invention, conventionally known solvents can be used without any particular limitation. Specifically, for example, hydrocarbon solvents such as n-butane, n-hexane, n-heptane, n-octane, cyclopentane, cyclohexane, cyclobutane, etc.; aromatic solvents such as toluene and xylene, etc.; ketone solvents such as methyl isobutyl ketone, etc.; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol, etc.; ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol mono, Examples of suitable solvents include ester-based solvents such as methyl ether acetate and butyl carbitol acetate; ketone-based solvents such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone; alcohol-based solvents such as ethanol, isopropanol, n-butanol, sec-butanol and isobutanol; and amide-based solvents such as Equamide (trade name: manufactured by Idemitsu Kosan Co., Ltd., an amide-based solvent), N,N-dimethylformamide, N,N-dimethylacetamide, N-methylformamide, N-methylacetamide, N-methylpropioamide and N-methyl-2-pyrrolidone. These solvents can be used alone or in combination of two or more.

[0057] In particular, the solvent (D) that can be used in the insulating paste of the present invention preferably contains a solvent having a polar functional group such as a hydroxyl group, a carboxyl group, an amide group, an amino group, or an ether group, from the viewpoint of the solubility of the dispersed resin (C) and the dispersion stability of the insulating paste, and N-methyl-2-pyrrolidone is particularly preferred.

[0058] Furthermore, from the viewpoint of dispersibility of the insulating paste and preventing deterioration or hydrolysis of the resin, it is preferable that the insulating paste is substantially free of water. Here, "substantially free of water" generally means that the water content is 1 mass % or less, based on the total amount of the insulating paste.

[0059] In the present invention, the moisture content of the insulating paste can be measured by Karl Fischer coulometric titration. Specifically, the moisture content can be measured using a Karl Fischer moisture meter (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name: MKC-610) with the temperature of the moisture vaporizer (manufactured by Kyoto Electronics Manufacturing Co., Ltd., product name: ADP-611) attached to the meter set to 130°C.

[0060] Insulating paste manufacturing The insulating paste of the present invention may contain, as necessary, other components such as pigments, resins, additives, etc., in addition to the inorganic filler (A), binder (B), dispersion resin (C), and solvent (D). It is preferable that the insulating paste of the present invention does not substantially contain an electrode active material.

[0061] Examples of the additives include neutralizing agents, pigment dispersants, binders, antifoaming agents, preservatives, rust inhibitors, plasticizers, and antistatic agents.

[0062] The solid content of the inorganic filler (A) in the insulating paste is usually 5 to 40 mass%, preferably 10 to 30 mass%, and more preferably 18 to 26 mass%, which is suitable from the viewpoints of insulation properties, coating workability, pigment sedimentation properties, dispersibility, etc.

[0063] In this specification, the term "solid content" refers to the residue remaining after removing volatile components, and the residue may be solid or liquid at room temperature. The solid content mass can be calculated by multiplying the sample mass before drying by the solid content percentage, which is the ratio of the amount of material remaining after drying to the mass before drying. The drying conditions for determining the solid content can be, for example, 105°C for 3 hours.

[0064] The content of the inorganic filler (A) solid content in the insulating paste solid content is usually 50 to 99 mass %, preferably 70 to 80 mass %, which is suitable from the viewpoints of insulation properties, coating workability, pigment sedimentation and dispersibility.

[0065] The content of the binder (B) solid content in the insulating paste is usually 2 to 10 mass %, preferably 4 to 7 mass %, which is suitable from the viewpoints of coating workability, adhesion, and the like.

[0066] The content of the binder (B) solid content in the insulating paste solid content is usually 5 to 40 mass %, preferably 10 to 28 mass %, which is suitable from the viewpoints of insulation properties, coating workability, adhesion, dispersibility, etc.

[0067] The content of the dispersed resin (C) solid content in the insulating paste is usually 0.1 to 5 mass %, preferably 0.2 to 2 mass %, which is suitable from the viewpoints of dispersibility, coating workability, adhesion, etc.

[0068] The content of the dispersed resin (C) solid content in the insulating paste solid content is usually 0.05 to 4 mass %, preferably 0.1 to 3.0 mass %, which is suitable from the viewpoints of dispersibility, coating workability, adhesion, etc.

[0069] The ratio of the solid content of the dispersed resin (C) to the solid content of the inorganic filler (A) in the insulating paste is: The ratio of inorganic filler (A) / dispersion resin (C) is usually 100 / 0.5 to 100 / 15, preferably 100 / 1.0 to 100 / 6, which is suitable from the viewpoints of dispersibility, coating workability, adhesion, and the like.

[0070] The insulating paste can be prepared by uniformly mixing and dispersing the above-mentioned components using a conventionally known dispersing machine, such as a disperser, a paint shaker, a sand mill, a ball mill, a pebble mill, an LMZ mill, a DCP pearl mill, a planetary ball mill, a homogenizer, a twin-screw kneader, or a thin film rotary high-speed mixer.

[0071] Insulation layer The insulating paste is applied (coated) to a current collector to form an insulating layer (insulating film, coated film). In the present invention, insulation refers to a material having a volume resistivity of 1.0×10 6 This means that the resistance is Ω·cm or more.

[0072] In the present invention, an insulating layer (insulating film, coating film) refers to a solid film formed by applying a liquid insulating paste to a substrate (charger) and then heating and drying it. The film can be peeled off from the substrate to obtain an insulating film, or it can be applied to both sides of a plate-shaped substrate (collector) to obtain an insulating material. Furthermore, the insulating layer (insulating film, coating film) of the present invention is preferably non-porous.

[0073] The current collector to be coated is not particularly limited as long as it is made of metal, but is preferably aluminum or a composite metal thereof, and may be degreased or surface-treated.

[0074] The method for applying the insulating paste is not particularly limited as long as it can be applied within a certain film thickness range, and examples include roller coating, brush coating, atomization coating, dipping coating, applicator coating, shower coat coating, roll coater coating, and die coater coating.

[0075] The dry thickness is preferably 1 to 50 μm, more preferably 2 to 20 μm, and the drying temperature is preferably 60 to 300° C., more preferably 80 to 200° C.

[0076] By heating and drying, it is preferable that 90% or more of the solvent contained in the insulating paste is removed, more preferably 95% or more, and particularly preferably 99% or more. [Example]

[0077] The present invention will be further described below with reference to examples and comparative examples.

[0078] The synthesis methods of various resins, the manufacturing methods of insulating pastes, insulating layers and secondary batteries, and the evaluation and testing methods are all methods known in the art.

[0079] However, the present invention is not limited to this, and various modifications and variations are possible within the technical spirit of the present invention and the scope of equivalents of the claims.

[0080] In each example, "parts" indicates parts by mass, and "%" indicates % by mass.

[0081] <Production of acrylic resin> Manufacturing Example 1 A reaction vessel equipped with a stirring heater and a cooling tube was charged with 40 parts of N-methyl-2-pyrrolidone, and after replacing the atmosphere with nitrogen, the temperature was maintained at 115° C. The following monomer mixture was added dropwise to the reaction vessel over a period of 4 hours. <Monomer mixture> 30 parts styrene n-Butyl acrylate 20 parts Lauryl methacrylate 15 parts Methyl methacrylate 35 parts t-Butyl peroxy-2-ethylhexanoate (polymerization initiator) 3 parts One hour after the completion of the dropwise addition, a solution of 0.5 parts of t-butylperoxy-2-ethylhexanoate in 10 parts of N-methyl-2-pyrrolidone was added dropwise over one hour. After the dropwise addition, the mixture was maintained at 115°C for an additional hour. N-methyl-2-pyrrolidone was then added to the mixture to a solids content of 50%, yielding an acrylic resin (C-1) solution with a solids content of 50%. The acrylic resin (C-1) had a weight-average molecular weight (Mw) of 18,000.

[0082] Manufacturing Examples 2-17 Solutions of acrylic resins (C-2) to (C-17) were produced in the same manner as in Production Example 1, except that the monomer compositions were as shown in Table 1 below.

[0083] The weight average molecular weight (Mw) of each resin is shown in Table 1 below.

[0084] [Table 1]

[0085] <Insulating paste manufacturing> Example 1 80 parts of boehmite, 20 parts of polyvinylidene fluoride (PVDF) (weight average molecular weight 500,000, unmodified), 4.8 parts of acrylic resin (C-1) solution (resin solid content 2.4 parts), and 250 parts of N-methyl-2-pyrrolidone (NMP) were placed in a container and thoroughly dispersed using a planetary mixer to obtain insulating paste (X-1). This process was carried out at room temperature of about 20 degrees.

[0086] Examples 2 to 28 and Comparative Examples 1 to 3 Insulating pastes (X-2) to (X-31) were produced in the same manner as in Example 1, except that the raw material compositions were as shown in Table 2 below.

[0087] The viscosity (shear rate 1 s) of the obtained insulating paste measured using a cone and plate type viscometer "Mars2" (product name, manufactured by HAAKE) is shown in Table 2 below. -1 , viscosity unit is mPa s) and TI value (shear rate 1000 s -1 Viscosity of 1s -1 The viscosity ratio of the

[0088] Additionally, an insulating layer (coating film) was prepared using the method described below, and evaluation tests were conducted on the insulating paste and insulating layer (coating film). The evaluation results for adhesion, dispersibility, finish (surface), and pigment sedimentation are shown in Table 2 below. If even one of the items was unsatisfactory, the insulating paste was deemed unsatisfactory. In addition, since the dispersibility of Comparative Example 1 was unacceptable, the pigment settling property was not evaluated.

[0089] [Table 2]

[0090] The amounts of filler, binder and dispersing resin in the table are values ​​of solid content. *1 Polyvinyl alcohol (saponification degree 99%, weight average molecular weight 20,000) was used as the dispersing resin.

[0091] The moisture content of the insulating pastes prepared in the above examples and comparative examples was all less than 0.8 mass %.

[0092] Example 29 80 parts of boehmite (1-1), 20 parts of polyvinylidene fluoride (PVDF) (weight average molecular weight 500,000, unmodified), 4.8 parts of acrylic resin (C-3) solution (resin solid content 2.4 parts), and 250 parts of N-methyl-2-pyrrolidone (NMP) were placed in a container and thoroughly dispersed using a planetary mixer to obtain an insulating paste (X-29).

[0093] Examples 30 to 36 Insulating pastes (X-30) to (X-36) were produced in the same manner as in Example 1, except that the raw material compositions were as shown in Table 3 below.

[0094] The viscosity of the obtained insulating paste was measured using a cone and plate type viscometer "Mars2" (product name, manufactured by HAAKE), and the measured viscosity (shear rate 1 s -1 , viscosity unit is mPa s) and TI value (shear rate 1000 s -1 Viscosity at shear rate 1s -1 The viscosity ratio of the

[0095] The sodium content of the insulating paste is also shown in the table. The sodium content was measured by the method described in the present specification.

[0096] The results of evaluation of storage stability (viscosity reduction rate) as determined by the method described below are also shown.

[0097] [Table 3]

[0098] The amounts of inorganic filler, binder and dispersing resin in the table are values ​​of solid content.

[0099] The sodium content of the insulating pastes (X-31) to (X-33) was adjusted by adding sodium hydroxide to the paste.

[0100] The moisture content of the insulating pastes prepared in the above examples was all less than 0.8 mass %.

[0101] The inorganic fillers in the table are as follows: Boehmite (1-1): Volume average particle size (D50) 1.3 μm, sodium content 500 ppm Boehmite (1-2): Volume average particle size (D50) 1.3 μm, sodium content 1000 ppm Boehmite (1-3): Volume average particle size (D50) 1.3 μm, sodium content 2000 ppm

[0102] <Evaluation test> <Adhesion> The resulting insulating paste was applied to an aluminum current collector using an applicator and then dried at 80°C for 60 minutes to form a coating film (20 μm dry film thickness). Next, a 300 μm thick PET film was attached to the coating film of a test plate consisting of a laminate of the current collector and coating film with double-sided tape for reinforcement. The resulting laminate was cut into 10 cm long, 1 cm wide strips with a cutter, spanning the thickness from the PET to the coating film. Double-sided tape was then applied to the current collector surface of the horizontally placed sample, and the sample was adhesively fixed to a tinplate. A 180° peel test was then performed using an "Ez-Test" (Shimadzu Corporation) at a tensile speed of 10 cm / min. The coating film was peeled from the current collector by clamping one of the two shorter edges of the sample. The adhesion between the current collector and the coating film (insulating layer) was evaluated according to the following criteria: AC: Pass, D: Fail. A: 10N / m or more, very good. B: 3N / m or more and less than 10N / m, good. C: 1 N / m or more and less than 3 N / m, which is at a level that does not pose a problem in practical use. D: Less than 1N / m, not practical.

[0103] <Dispersibility> Dispersibility (degree of dispersion) was evaluated by the particle gauge method in accordance with JIS K5600-2-5. Specifically, the paste was dropped onto a particle gauge table, thinly spread into the gauge groove with a scraper, and the particle size of the largest particle observed on the gauge was measured. The measurement was performed three times, and the average value was taken as the measured value.

[0104] The dispersibility of the obtained insulating paste was evaluated according to the following criteria, where AD is pass and E is fail. A: The pigment is dispersed at a particle size of less than 15 μm. The dispersibility is very good. B: The pigment is dispersed at a particle size of 15 μm or more and less than 20 μm. Dispersibility is good. C: The pigment is dispersed at a size of 20 μm or more and less than 25 μm, but no aggregates are visible. Dispersibility is standard. D: The pigment is dispersed at a particle size of 25 μm or more, but no aggregates are visible to the naked eye. Dispersibility is somewhat poor. E: 50 μm aggregates were observed. Dispersibility was very poor.

[0105] <Finish (surface)> The obtained insulating paste was applied to an aluminum current collector using an applicator, and then dried at 80°C for 60 minutes to form a coating film (dry film thickness 15 μm). Each test plate was visually inspected for gloss (luster), unevenness, and smoothness. AD was a pass, and E was a fail. A: There is a slight loss of shine, but the finish is very good. B: There is some loss of gloss, but unevenness and smoothness are good and there is no problem in practical use. C: Although gloss loss is observed, unevenness and smoothness are good and at a level that does not pose a problem in practical use. D: Although gloss loss and unevenness are observed, there is smoothness and it is at a level that does not pose a problem in practical use. E: Loss of gloss and unevenness are observed, and the smoothness is poor, and there is clearly a problem.

[0106] <Pigment settling> The obtained insulating paste was stored at 40°C for 60 days, and the pigment sedimentation was checked. The state after 60 days of storage was evaluated according to the following criteria: AC is pass, D is fail. A: No change. B: Very slight settling of filler was observed, but when the paste was stirred by hand, it immediately returned to its pre-storage state, so there was no problem. C: Settling of the filler was observed, and the paste did not return to the state before storage even when stirred by hand, but when the paste was stirred with a disperser, it returned to the state before storage. D: Significant settling of the filler was observed, and the paste did not return to its pre-storage state even after stirring with a disperser.

[0107] <Storage stability (viscosity reduction rate)> The obtained insulating paste was stored at 40° C. for 30 days. The viscosity was checked before and after storage, and the storage stability (viscosity reduction rate) was evaluated according to the following criteria. AC is pass, and D is fail. The viscosity was measured using a cone and plate type viscometer "Mars2" (product name, manufactured by HAAKE) at a shear rate of 1 s -1 is the value. Viscosity reduction rate (%) = 100 - (viscosity after storage) / (viscosity before storage) x 100 A: The viscosity reduction rate is less than 7% (including cases where the viscosity after storage is equal to or greater than the viscosity before storage). B: The viscosity reduction rate after storage is 7% or more and less than 30%. C: The viscosity reduction rate after storage is 30% or more and less than 50%. D: The viscosity reduction rate after storage is 50% or more.

Claims

1. An insulating paste for a current collector of a lithium ion secondary battery, comprising an inorganic filler (A), a binder (B), a dispersion resin (C) having a phosphate group, and a solvent (D), wherein the viscosity of the paste (shear rate 1 s －１ ) is 2000 mPa·s or more, and the TI value (shear rate 1000 s －１ Viscosity of 1s －１ The insulating paste is characterized in that the viscosity ratio of the paste to the viscosity of the insulating paste is greater than 1.

2. An insulating paste for a lithium ion secondary battery current collector, comprising: an inorganic filler (A), a binder (B), a dispersion resin (C), and a solvent (D), the dispersion resin (C) contains a polar group-containing acrylic resin (c) which is a copolymer of raw material monomers including a polymerizable unsaturated monomer (c1) having a polar functional group and a polymerizable unsaturated monomer (c2) having a hydrocarbon group having 4 or more carbon atoms, and the weight average molecular weight of the copolymer is 1,000 to 100,000; The viscosity of the paste (shear rate 1 s-1) is 2000 mPa·s or more, and the TI value (ratio of the viscosity at 1 s-1 to the viscosity at a shear rate of 1000 s-1) is greater than 1.

3. An insulating paste for a lithium ion secondary battery current collector, comprising: an inorganic filler (A); a binder (B); a dispersion resin (C) having a phosphate group; and a solvent (D), The sodium content of the paste is 10 to 350 ppm; The viscosity of the paste (shear rate 1 s-1) is 2000 mPa·s or more, and the TI value (ratio of the viscosity at 1 s-1 to the viscosity at a shear rate of 1000 s-1) is greater than 1.

4. The inorganic filler (A) is alumina, silica, TiO ２ , BaTiO ３ , ZrO ２ 4. The insulating paste for a lithium ion secondary battery current collector according to claim 1, wherein the insulating paste is at least one selected from the group consisting of quartz, boehmite, zeolite, apatite, and kaolin.

5. 5. The insulating paste for a lithium ion secondary battery current collector according to claim 1, wherein the binder (B) is modified or unmodified polyvinylidene fluoride.

6. 6. The insulating paste for a lithium ion secondary battery current collector according to claim 1, wherein the solvent (D) is N-methyl-2-pyrrolidone.

7. 7. An insulating paste for a current collector of a lithium ion secondary battery, comprising the insulating paste according to claim 1, which is substantially free of an electrode active material.

8. A method for producing an insulating layer for a lithium ion secondary battery current collector, comprising applying the insulating paste according to any one of claims 1 to 7 to a part or all of a current collector, and then heating and drying the applied paste to form an insulating layer.

9. 9. A method for producing an insulating layer for a current collector of a lithium ion secondary battery, wherein the insulating layer according to claim 8 is non-porous.

10. 10. The method for producing an insulating layer for a current collector of a lithium ion secondary battery according to claim 8, wherein the current collector is made of aluminum or a composite metal thereof.

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