Coating composition for electrochemical element separators, electrochemical element separator, and electrochemical element

Abstract

Disclosed is a coating composition for electrochemical element separators, the coating composition containing: (A) a linear organopolysiloxane that contains, in each molecule, at least two alkenyl groups that are each bonded to a silicon atom; (B) a resin-like organopolysiloxane that has an R3SiO1 / 2 unit and an SiO4 / 2 unit (in the formula, each R independently represents a monovalent hydrocarbon group having 1 to 6 carbon atoms, but at least two R moieties in each molecule are alkenyl groups); (C) an organohydrogen polysiloxane that contains, in each molecule, at least two hydrogen atoms that are each bonded to a silicon atom; and (D) a hydrosilylation reaction catalyst. This coating composition for electrochemical element separators enables the achievement of an electrochemical element separator which has excellent tensile strength, and which is capable of maintaining insulation even in cases where combustion occurs.

Description

Coating composition for electrochemical element separator, electrochemical element separator, and electrochemical element

[0001] The present invention relates to a coating composition for an electrochemical element separator, an electrochemical element separator, and an electrochemical element.

[0002] In recent years, with the trend toward cordless electronic devices, the development of high-performance electrochemical elements such as capacitors, lithium-ion batteries, and nickel-metal hydride batteries has been actively promoted. In particular, secondary batteries, which can be used repeatedly by recharging, are used in a variety of devices.

[0003] A secondary battery has two electrodes, an anode and a cathode, immersed in an electrolyte solution, and a separator separating them. Each type of secondary battery is optimized based on the electrode materials, electrolyte, and separator used. The separator not only structurally separates the anode and cathode, but also electrically insulates them to prevent internal short circuits. The separator must also be permeable to ions to allow electrochemical reactions between the anode and cathode.

[0004] In recent years, efforts to improve the energy density of batteries have been active, and separators must have as low an internal resistance as possible to maximize their ion permeability. Separators must have high ion permeability, but they must also be thin for the devices in which they are used. In light of the performance requirements for separators, nonwoven fabric-based separators have been developed.

[0005] Nonwoven fabric separators are more heat-resistant than commonly used polyolefin-based separators, and their high porosity allows for high current densities. This advantage is extremely useful for secondary batteries. However, such high porosity can lead to micro-short circuits due to electrode deposits. Furthermore, because the distribution of voids between fibers is uneven, areas with large voids can experience micro-short circuits due to electrode deposits or short circuits in environments with repeated long-term charge-discharge cycles. Because the density of voids is difficult to control, the short circuit problem is difficult to solve.

[0006] For these reasons, nonwoven fabric separators are required to have the ability to prevent short circuits without impairing high ion permeability. One technique for achieving both performance goals is to appropriately control the porosity. However, for nonwoven fabrics with various pore sizes, it is difficult to appropriately control the porosity according to the pore size. In Patent Document 1, the inventors proposed a technique for achieving this goal by applying particles to the nonwoven fabric to reduce the porosity without impairing the ion permeability. This technique made it possible to prevent short circuits in environments with repeated long-term charge-discharge cycles. However, the particle application process can cause particle aggregation and variations in particle density during application, making it difficult to uniformly reduce the porosity.

[0007] Preventing combustion is also important in lithium-ion batteries. Thin, laminated lithium-ion batteries, in particular, have adjacent battery units, raising concerns that a short circuit or overheating could ignite the battery and spread the fire. To prevent battery fires caused by overheating or damage, the anode and cathode must remain electrically insulated from each other, even in the event of a fire. Therefore, separators must be able to remain electrically insulated and prevent fire spread, even in the unlikely event of a fire.

[0008] Furthermore, nonwoven fabrics have low tensile strength and may tear due to stress resistance. To solve this problem, Patent Document 2 proposes a technique of layering two fibers with different orientation angles of nonwoven fabric fibers. While this technique provides tensile strength sufficient to withstand the stresses encountered during the battery fabrication process, layering two layers of fibers inevitably increases the membrane thickness. In particular, the thickness of the separator is important for secondary batteries, and there has been a strong demand for thinner separators.

[0009] International Publication No. 2023 / 127375 Japanese Patent Application Laid-Open No. 2013-178937

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a coating composition for an electrochemical element separator that provides an electrochemical element separator that has excellent tensile strength and is capable of maintaining insulation even in the event of combustion; an electrochemical element separator that has a coating film made of a cured product of the composition; and an electrochemical element that has the separator and exhibits little deterioration in battery characteristics over long-term charge-discharge cycles.

[0011] As a result of extensive research to achieve the above object, the present inventors have found that by applying a specific curable organopolysiloxane composition (coating composition) to a separator substrate and curing it, an electrochemical element separator can be obtained that has excellent tensile strength even when the substrate has a thin film thickness and is capable of maintaining insulation even when combustion occurs, and that an electrochemical element equipped with this separator has the property of experiencing little deterioration in battery characteristics over long-term charge-discharge cycles, thereby completing the present invention.

[0012] That is, the present invention provides a composition comprising: 1. (A) 100 parts by mass of a linear organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms in one molecule; (B) RSiO 1 / 2 Units and SiO 4 / 21. A coating composition for an electrochemical element separator, comprising: 10 to 50 parts by mass of a resinous organopolysiloxane having units (wherein R each independently represent a monovalent hydrocarbon group having 1 to 6 carbon atoms, with at least two R per molecule being alkenyl groups); (C) an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms per molecule, in an amount such that the number of hydrogen atoms bonded to silicon atoms in component (C) is 0.8 to 3.0 per total of the alkenyl groups bonded to silicon atoms in components (A) and (B); and (D) a hydrosilylation reaction catalyst; 2. A coating composition for an electrochemical element separator, comprising: a substrate; and a coating film formed on at least a portion of the substrate, the coating film being a cured product of one coating composition for an electrochemical element separator, the amount of the coating being 10 to 50 parts by mass per 1 cm of the substrate. 2 2. An electrochemical element separator in which the coating is formed on at least the surface of the substrate, and the amount of the coating is 0.05 to 1.50 mg per 1 cm of the substrate; 2 2. An electrochemical element separator having a weight of 0.05 to 1.20 mg per separator; 4. An electrochemical element separator having a substrate with a plurality of pores and the coating formed inside at least some of the plurality of pores; 5. An electrochemical element separator having a substrate that is a nonwoven fabric; and 6. An electrochemical element comprising any one of the electrochemical element separators of 2 to 5.

[0013] By applying the coating composition for an electrochemical element separator of the present invention to a separator substrate by means of coating or the like and then curing the coating, the tensile strength of the separator can be improved even when the film thickness is small. An electrochemical element separator provided with a coating made of the coating composition of the present invention improves the battery characteristics of an electrochemical element over long-term charge / discharge cycles, prevents the spread of fire in the event of fire, and electrically separates the anode and cathode even after combustion, maintaining insulation, thereby providing a highly reliable electrochemical element.

[0014] The present invention is described in detail below. [1] Coating composition for electrochemical element separator The coating composition for electrochemical element separator according to the present invention (hereinafter simply referred to as "coating composition") is characterized by containing (A) an alkenyl group-containing linear organopolysiloxane, (B) an alkenyl group-containing resinous organopolysiloxane, (C) an organohydrogenpolysiloxane, and (D) a hydrosilylation reaction catalyst.

[0015] (A) Alkenyl Group-Containing Linear Organopolysiloxane Component (A) is the main component (base polymer) of the composition of the present invention, and is a linear organopolysiloxane containing at least two silicon-bonded alkenyl groups (hereinafter referred to as "silicon-bonded alkenyl groups") per molecule.

[0016] The bonding position of the alkenyl group bonded to the silicon atom may be at the molecular chain terminal, non-terminal (i.e., side chain) or both, but component (A) is preferably a linear or partially branched linear organopolysiloxane having an alkenyl group bonded to a silicon atom at at least one molecular chain terminal or both molecular chain terminals. Component (A) may be a single polymer having such a molecular structure, a copolymer consisting of such a molecular structure, or a mixture of such polymers or copolymers.

[0017] The silicon-bonded alkenyl group in component (A) preferably has 2 to 10 carbon atoms, more preferably 2 to 6 carbon atoms. Specific examples include vinyl, allyl, 1-propenyl, isopropenyl, butenyl, isobutenyl, pentenyl, hexenyl, and cyclohexenyl groups, with vinyl being particularly preferred. The content of the silicon-bonded alkenyl group is preferably 0.001 to 10 mol, more preferably 0.001 to 1 mol, per 100 g of component (A). The content of the silicon-bonded alkenyl group is, 29 It can be calculated by Si-NMR measurement.

[0018] In the organopolysiloxane of component (A), the silicon-bonded monovalent organic group other than the silicon-bonded alkenyl group (hereinafter also referred to as the "silicon-bonded organic group") is not particularly limited as long as it does not contain an aliphatic unsaturated bond, and examples include unsubstituted or substituted monovalent hydrocarbon groups that preferably have 1 to 12 carbon atoms, and more preferably 1 to 10 carbon atoms, and that do not contain an aliphatic unsaturated bond. Examples of this unsubstituted or substituted monovalent hydrocarbon group include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, and decyl; cycloalkyl groups such as cyclohexyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as chlorine, fluorine, and bromine. Of these, alkyl groups and aryl groups are preferred, and methyl and phenyl groups are more preferred.

[0019] The viscosity of component (A) at 25°C is not particularly limited, but considering the improvement of the workability of the composition and the mechanical properties of the cured product, it is preferably 100 to 500,000 mPa·s, more preferably 300 to 100,000 mPa·s. In the present invention, viscosity can be measured using a rotational viscometer (e.g., BL type, BH type, BS type, cone-plate type, rheometer, etc.) (the same applies hereinafter). For the same reasons, the number of silicon atoms (or degree of polymerization) in component (A) is preferably 50 to 1,500, more preferably 100 to 1,000, and even more preferably 120 to 800. In the present invention, the degree of polymerization (or molecular weight) can be determined, for example, as the polystyrene-equivalent number-average degree of polymerization (or number-average molecular weight) in gel permeation chromatography (hereinafter referred to as GPC) analysis using toluene or the like as a developing solvent (the same applies hereinafter).

[0020] Specific examples of component (A) include dimethylpolysiloxanes both ends of which are blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers both ends of which are blocked with dimethylvinylsiloxy groups, dimethylsiloxane-diphenylsiloxane copolymers both ends of which are blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers both ends of which are blocked with dimethylvinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymers both ends of which are blocked with dimethylvinylsiloxy groups, and dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymers both ends of which are blocked with dimethylvinylsiloxy groups. copolymer of methylsiloxane, methylvinylsiloxane, and methylphenylsiloxane; methyltrifluoropropylpolysiloxane endblocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane and methyltrifluoropropylsiloxane endblocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane, methyltrifluoropropylsiloxane, and methylvinylsiloxane endblocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane, methyltrifluoropropylsiloxane, and methylvinylsiloxane endblocked with trimethylsiloxy groups; copolymer of dimethylsiloxane and vinylmethylsiloxane endblocked with trimethylsiloxy groups copolymer of vinylsiloxane, vinylmethylsiloxane, and diphenylsiloxane; copolymer of dimethylsiloxane, vinylmethylsiloxane, and methylphenylsiloxane both ends blocked with trimethylsiloxy groups; copolymer of vinylmethylsiloxane and methyltrifluoropropylsiloxane both ends blocked with trimethylsiloxy groups; dimethylpolysiloxane with one end blocked with trimethylsiloxy groups and one end blocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane and methylvinylsiloxane with one end blocked with trimethylsiloxy groups and one end blocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane and methylvinylsiloxane with one end blocked with trimethylsiloxy groups and one end blocked with dimethylvinylsiloxy groups; copolymer of dimethylsiloxane and diphenylsiloxane with one end blocked by trimethylsiloxy group and one end blocked by dimethylvinylsiloxy group; copolymer of dimethylsiloxane and methylphenylsiloxane with one end blocked by trimethylsiloxy group and one end blocked by dimethylvinylsiloxy group; copolymer of dimethylsiloxane, diphenylsiloxane, and methylvinylsiloxane with one end blocked by trimethylsiloxy group and one end blocked by dimethylvinylsiloxy group; copolymer of dimethylsiloxane, methylphenylsiloxane, and methylvinylsiloxane with one end blocked by trimethylsiloxy group and one end blocked by dimethylvinylsiloxy group;Methyltrifluoropropylpolysiloxane capped with one end trimethylsiloxy group and one end dimethylvinylsiloxy group, dimethylsiloxane / methyltrifluoropropylsiloxane copolymer capped with one end trimethylsiloxy group and one end dimethylvinylsiloxy group, dimethylsiloxane / methyltrifluoropropylsiloxane / methylvinylsiloxane copolymer capped with one end trimethylsiloxy group and one end dimethylvinylsiloxy group, dimethylpolysiloxane capped with both ends methyldivinylsiloxy group, both ends capped with methyldivinylsiloxy group Chain dimethylsiloxane-methylvinylsiloxane copolymer, dimethylsiloxane-diphenylsiloxane copolymer both ends blocked with methyldivinylsiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymer both ends blocked with methyldivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymer both ends blocked with methyldivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer both ends blocked with methyldivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer both ends blocked with methyldivinylsiloxy groups, Blocked methyltrifluoropropylpolysiloxane, methyldivinylsiloxy-terminated dimethylsiloxane-methyltrifluoropropylsiloxane copolymer, methyldivinylsiloxy-terminated dimethylsiloxane-methyltrifluoropropylsiloxane-methylvinylsiloxane copolymer, trivinylsiloxy-terminated dimethylpolysiloxane, trivinylsiloxy-terminated dimethylsiloxane-methylvinylsiloxane copolymer, trivinylsiloxy-terminated dimethylsiloxane-diphenylsiloxane copolymer, dimethylsiloxane-methylphenylsiloxane copolymer both ends blocked with trivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-diphenylsiloxane copolymer both ends blocked with trivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer both ends blocked with trivinylsiloxy groups, methyltrifluoropropylpolysiloxane both ends blocked with trivinylsiloxy groups, dimethylsiloxane-methyltrifluoropropylsiloxane copolymer both ends blocked with trivinylsiloxy groups,Examples include diorganopolysiloxanes in which both molecular chain terminals are blocked with triorganosiloxy groups, such as a dimethylsiloxane-methyltrifluoropropylsiloxane-methylvinylsiloxane copolymer in which both terminals are blocked with trivinylsiloxy groups, and branched (straight-chain with some branching) organopolysiloxanes in which one or two of the bifunctional diorganosiloxane units constituting the main chain of these straight-chain diorganopolysiloxanes have been replaced with a branched structure (trifunctional organosilsesquioxane unit).

[0021] (B) Alkenyl group-containing resinous organopolysiloxane Component (B) is RSiO 1 / 2 Units (M units) and SiO 4 / 2 The alkenyl-containing resinous organopolysiloxane comprises an essential structural unit, the Q unit, where each R is independently a monovalent hydrocarbon group having 1 to 6 carbon atoms, and at least two, preferably 3 to 8, alkenyl groups are present in one molecule (total structural units).

[0022] Specific examples of monovalent hydrocarbon groups having 1 to 6 carbon atoms include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, and hexyl; alkenyl groups such as vinyl, allyl, butenyl, pentenyl, and hexenyl; cycloalkyl groups such as cyclohexyl; cycloalkenyl groups such as cyclohexenyl; aryl groups such as phenyl; and halogenated alkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as chlorine, fluorine, or bromine, such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. The multiple R groups contained in component (B) may be the same or different, but from the viewpoint of compatibility with other components, it is preferable that at least 80 mol% of the total number of R groups be methyl groups, and for the same reason, the alkenyl groups are preferably vinyl groups.

[0023] The ratio of M units to Q units in component (B) (M units / Q units) is preferably 0.6 to 1.2, more preferably 0.8 to 1.0, from the viewpoints of preventing gelation and hardness. In addition to the M units and Q units, component (B) may contain any structural unit such as RSiO 2 / 2 Units (D units) and RSiO3 / 2 In order to improve the hardness of the resulting cured product, the total proportion of the M units and Q units in all structural units is preferably 80 mol % or more, and more preferably 90 mol % or more.

[0024] Specific examples of component (B) include copolymers of vinyldimethylsiloxy groups and Q units, copolymers of vinyldimethylsiloxy groups, trimethylsiloxy groups, and Q units, copolymers of vinyldimethylsiloxy groups, dimethylsiloxane, and Q units, copolymers of vinyldimethylsiloxy groups, phenylsilsesquioxane, and Q units, copolymers of vinyldimethylsiloxy groups, dimethylsiloxane, phenylsilsesquioxane, and Q units, and copolymers of trimethylsiloxy groups, vinylmethylsiloxane, and Q units.

[0025] The molecular weight of component (B), as measured by GPC in terms of polystyrene, is preferably 2,000 to 8,000, more preferably 4,000 to 6,000, and this component is usually solid at room temperature.

[0026] The blend amount of component (B) is 10 to 50 parts by mass, and preferably 10 to 40 parts by mass, per 100 parts by mass of component (A). If the blend amount is within this range, molding processing becomes easy.

[0027] (C) Organohydrogenpolysiloxane Component (C) is an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms (Si—H groups) per molecule, and is a component that forms a crosslinked structure through a hydrosilylation reaction with the alkenyl groups in components (A) and (B) above.

[0028] The silicon-bonded organic group other than a silicon-bonded hydrogen atom in component (C) is not particularly limited as long as it does not contain an aliphatic unsaturated bond, and examples thereof include unsubstituted or substituted monovalent hydrocarbon groups that do not contain an aliphatic unsaturated bond and preferably have 1 to 12 carbon atoms, more preferably 1 to 10 carbon atoms. Examples of such unsubstituted or substituted monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, nonyl, and decyl; cycloalkyl groups such as cyclohexyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogenated alkyl groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms such as chlorine, fluorine, or bromine, such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. Of these, alkyl groups and aryl groups are preferred, and methyl groups and phenyl groups are more preferred.

[0029] Specific examples of component (C) include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, methylhydrogenpolysiloxane terminally capped with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer terminally capped with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane copolymer terminally capped with trimethylsiloxy groups, and dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane copolymer terminally capped with trimethylsiloxy groups. , methylhydrogenpolysiloxanes capped at both molecular chain terminals with dimethylhydrogensiloxy groups, dimethylpolysiloxanes capped at both molecular chain terminals with dimethylhydrogensiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymers capped at both molecular chain terminals with dimethylhydrogensiloxy groups, dimethylsiloxane-methylphenylsiloxane copolymers capped at both molecular chain terminals with dimethylhydrogensiloxy groups, dimethylsiloxane-diphenylsiloxane copolymers capped at both molecular chain terminals with dimethylhydrogensiloxy groups, methylphenylpolysiloxanes capped at both molecular chain terminals with dimethylhydrogensiloxy groups, diphenylpolysiloxanes capped at both molecular chain terminals with dimethylhydrogensiloxy groups, and compounds in which some or all of the methyl groups have been replaced with other alkyl groups such as ethyl groups or propyl groups, compounds of the formula: R'3SiO 1 / 2 and a siloxane unit represented by the formula: R'HSiO 1 / 2 and a siloxane unit represented by the formula: SiO 4 / 2 Organosiloxane copolymers consisting of siloxane units represented by the formula: R'HSiO 1 / 2 and a siloxane unit represented by the formula: SiO 4 / 2 Organosiloxane copolymers consisting of siloxane units represented by the formula: R'HSiO 2 / 2 and a siloxane unit represented by the formula: R'SiO 3 / 2or a siloxane unit represented by the formula: HSiO 3 / 2 and mixtures of two or more of these organopolysiloxanes, where R' is a monovalent hydrocarbon group having 1 to 12 carbon atoms and containing no aliphatic unsaturated bonds.

[0030] From the viewpoint of the mechanical properties of the resulting cured product, the amount of component (C) to be blended is an amount such that the number of hydrogen atoms bonded to silicon atoms in component (C) is 0.8 to 3.0, and preferably 1.0 to 2.5, per combined alkenyl group bonded to silicon atoms in components (A) and (B).

[0031] (D) Hydrosilylation Reaction Catalyst The hydrosilylation reaction catalyst of component (D) is a catalyst that promotes crosslinking via a hydrosilylation reaction between alkenyl groups in components (A) and (B) and Si—H groups in component (C).

[0032] The hydrosilylation reaction catalyst is preferably a platinum group metal catalyst, and specific examples include platinum group metal catalysts such as platinum black, platinic chloride, chloroplatinic acid, reaction products of chloroplatinic acid and monohydric alcohols, complexes of chloroplatinic acid and olefins, complexes of chloroplatinic acid and vinyl group-containing (poly)siloxanes, platinum-acetylacetone complexes, and platinum-cyclopentadienyl complexes.

[0033] The amount of component (D) to be blended may be any amount sufficient to cure the composition. From the viewpoints of curability and cost, the amount is preferably 0.5 to 1,000 ppm, and more preferably 1 to 500 ppm, of the metal element (by mass) per 100 parts by mass of the total of components (A), (B), and (C).

[0034] (E) Other Components In addition to the above components (A) to (D), the coating composition of the present invention may contain other components within the range that does not impair the effects of the present invention. Specific examples include a reaction inhibitor for the hydrosilylation reaction, a reinforcing material, an organic solvent, an adhesion promoter (particularly, an organosilicon compound such as a functional alkoxysilane that contains at least one functional group selected from an alkenyl group, an epoxy group, an amino group, a (meth)acryloxy group, a mercapto group, etc. in the molecule but does not contain a SiH group in the molecule), a thixotropy-imparting agent, etc.

[0035] (E1) Reaction Inhibitor The coating composition of the present invention may contain a known reaction inhibitor that has a reaction inhibitor effect on the hydrosilylation catalyst of component (D). Specific examples of the reaction inhibitor include 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclohexanol, 3-methyl-3-trimethylsiloxy-1-butyne, 3-methyl-3-trimethylsiloxy-1-pentyne, 3,5-dimethyl-3-trimethylsiloxy-1-hexyne, 1-ethynyl-1-trimethylsiloxycyclohexanol ... Examples of the solvent include hexane, bis(2,2-dimethyl-3-butynoxy)dimethylsilane, 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 1,1,3,3-tetramethyl-1,3-divinyldisiloxane, and 1,1,dimethyl-1-trimethylsiloxy-ethyne, and preferably 1-ethynyl-1-cyclohexanol and 1,1,dimethyl-1-trimethylsiloxy-ethyne.

[0036] (E2) Reinforcing Material The coating composition of the present invention may contain finely powdered silica as a reinforcing material in order to improve the tensile strength, elongation, tear strength, etc. of the resulting cured product.

[0037] The finely powdered silica preferably has a specific surface area (BET method) of 50 m 2 / g or more, more preferably 50 to 400m 2 / g, and more preferably 100 to 300 m 2 / g. The specific surface area is 50 m 2If the tensile strength is 1 / g or more, sufficient reinforcement can be imparted to the cured product.

[0038] Such finely powdered silica has a specific surface area within the above range (50 m 2 / g or more), known silicas that have conventionally been used as reinforcing fillers for silicone rubbers may also be used, such as fumed silica (dry silica) and precipitated silica (wet silica). Finely powdered silica may be used as is, but in order to impart good fluidity to the composition, it is preferable to use silica that has been treated with an organosilicon compound such as methylchlorosilanes such as trimethylchlorosilane, dimethyldichlorosilane, and methyltrichlorosilane, or hexaorganodisilazanes such as dimethylpolysiloxane, hexamethyldisilazane, divinyltetramethyldisilazane, and dimethyltetravinyldisilazane. The reinforcing silica may be used alone or in combination of two or more types.

[0039] When reinforcing silica is used, the amount blended is preferably 10 to 150 parts by mass, more preferably 30 to 90 parts by mass, and even more preferably 50 to 90 parts by mass, per 100 parts by mass of component (A). When the amount of reinforcing silica blended is 10 parts by mass or more, the reinforcing effect before and after curing is easily obtained, and when it is 150 parts by mass or less, the dispersion of silica in the composition is good, and the processability during curing and molding is excellent.

[0040] (E3) Organic Solvent An organic solvent may be added to the coating composition of the present invention for the purpose of mixing the above components (A) to (D) and the other component (E) added as needed and / or for the purpose of adjusting the concentration. Specific examples of organic solvents include aromatic solvents such as toluene and xylene; aliphatic solvents such as n-heptane, n-hexane, n-octane, and isoparaffin; ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone; ester solvents such as ethyl acetate and isobutyl acetate; and ether solvents such as diisopropyl ether and 1,4-dioxane. These may be used alone or in combination of two or more.

[0041] The coating composition of the present invention can be prepared by mixing the above-mentioned components (A) to (D) and, if necessary, other components (E) using a commonly used mixer / stirrer such as a kneader or planetary mixer, or a kneader.

[0042] [2] Electrochemical element separator The electrochemical element separator of the present invention (hereinafter simply referred to as "separator") is obtained by applying or impregnating the above-mentioned coating composition onto at least a part of a substrate, preferably one or both sides thereof, and then drying and curing the composition by heating, thereby forming a coating film made of a cured product of the coating composition on part or all of the surface of the substrate and, if the substrate has pores, on part or all of the insides of the pores.

[0043] The method for applying the coating composition of the present invention to a substrate is not particularly limited, and examples thereof include a bar coater method, a spin coating method, a dip coating method, an offset printing method, a screen printing method, etc. Alternatively, the substrate may be immersed in the coating composition of the present invention to impregnate the substrate with the coating composition.

[0044] The separator substrate may be any material commonly used in electrochemical devices such as secondary batteries, but nonwoven fabrics are particularly suitable. Examples of nonwoven fabrics include those with fiber diameters of 0.1 to 5 μm (e.g., 0.1 μm, 1 μm, 5 μm, etc.), which vary depending on the construction method, but are not particularly limited in the present invention. Examples of fibers include cellulose fiber, pulp fiber, carbon fiber, glass fiber, ceramic fiber, aramid fiber, vinylon fiber, and polyamide fiber. From the standpoint of flame resistance, aramid fiber is preferred, and its use provides a higher fire spread prevention effect. The thickness of the substrate is preferably 30 μm or less, more preferably 20 μm or less. While the lower limit is not particularly limited, it is preferably 1 μm or more.

[0045] It is preferable to dehydrate the nonwoven fabric before applying the coating composition of the present invention. Specifically, it is preferable to provide a dehydration treatment step in which the nonwoven fabric is dried at a temperature of 130 to 260°C, particularly 140 to 200°C, under normal or reduced pressure for 12 hours or more.

[0046] After applying the coating composition of the present invention, the nonwoven fabric is heated at a temperature of 100 to 150°C under normal pressure or reduced pressure for 1 hour or more to cure the coating composition, thereby completing the bonding between the resin and the fibers.

[0047] Base material 1cm 2 The amount of the coating film made of the cured product of the coating composition per 1000 mm is 0.05 to 1.50 mg, preferably 0.05 to 1.20 mg, and more preferably 0.08 to 1.00 mg. 2 If the density is less than 1.50 mg / cm, sufficient tensile strength cannot be obtained, and the resulting electrochemical element separator will be inferior in battery characteristics and flame retardancy in long-term charge / discharge cycles. 2 If the thickness exceeds 100 μm, the separator membrane thickness increases, causing a problem of increased internal electrical resistance. The thickness of the resulting separator is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 24 μm or less. The lower limit is not particularly limited, but is preferably 1 μm or more.

[0048] [3] Electrochemical element The electrochemical element in which the separator of the present invention is used is not particularly limited, but is preferably a secondary battery comprising positive and negative electrodes, a separator interposed between these electrodes, and a non-aqueous electrolyte, and more preferably a lithium ion secondary battery.

[0049] The positive electrode contains, as positive electrode materials, a positive electrode active material, a conductive agent, a binder, a viscosity adjuster, etc. The positive electrode active material may be lithium or a compound containing lithium, and may be used alone or in appropriate combination of two or more. Specific examples of the compound containing lithium include lithium composite oxides. Among them, in order to increase the energy density, Li pLithium composite oxides mainly composed of MetO2 are preferred. Met is preferably at least one of cobalt, nickel, iron, and manganese, and p is usually a value within the range of 0.05≦p≦1.10. Specific examples of such lithium composite oxides include layered structures such as LiCoO2, LiNiO2, LiFeO2, and Li q Ni r Co 1-r O2 (wherein the values ​​of q and r vary depending on the charge / discharge state of the battery, and are usually 0<q<1, 0.7<r≦1), LiNi 0.8 Co 0.1 Mn 0.1 LiMnO2, spinel structure LiMn2O4, orthorhombic LiMnO2, etc. Furthermore, as a high voltage compatible type, a substituted spinel manganese compound LiMe s Mn 1-s O4 (0<s<1) is also used, where Met is titanium, chromium, iron, cobalt, nickel, copper, zinc, or the like.

[0050] The lithium composite oxide can be prepared, for example, by pulverizing and mixing a carbonate, nitrate, oxide, or hydroxide of lithium and a carbonate, nitrate, oxide, or hydroxide of a transition metal according to the desired composition, and firing the mixture at a temperature in the range of 600 to 1,000°C in an oxygen atmosphere.

[0051] The negative electrode includes negative electrode active materials such as a negative electrode active material, a conductive agent, a binder, and a viscosity modifier. The negative electrode active materials may be used singly or in combination of two or more. Specific examples of negative electrode active materials include carbon materials such as non-graphitizable carbon, graphitizable carbon, graphite, pyrolytic carbons, cokes, glassy carbons, baked organic polymer compounds, carbon fiber, and activated carbon. Materials capable of absorbing and releasing lithium and containing one or more constituent elements selected from metal elements and metalloid elements may also be used.

[0052] Examples of conductive agents that can be used include metal powders and fibers of Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, Si, etc., and graphite such as natural graphite, artificial graphite, various coke powders, mesophase carbon, vapor-grown carbon fiber, pitch-based carbon fiber, PAN-based carbon fiber, and various baked resins. These can be used alone or in combination of two or more types as appropriate.

[0053] Examples of binders used in the positive electrode material and the negative electrode material include polyimide resins, polyamide resins, polyamideimide resins, etc., and more specifically, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), etc. These can be used alone or in combination of two or more types.

[0054] Examples of viscosity modifiers used in the positive electrode material and the negative electrode material include carboxymethyl cellulose, sodium polyacrylate, other acrylic polymers, fatty acid esters, etc. These may be used alone or in combination of two or more.

[0055] The preferred contents (mass % solids) of the components in the positive electrode material are 90 to 98 mass % of the positive electrode active material, 0.5 to 5.0 mass % of the conductive agent, 0.5 to 5.0 mass % of the binder, and 0 to 3.0 mass % of the viscosity modifier. The preferred contents (mass % solids) of the components in the negative electrode material are 75 to 98 mass % of the negative electrode active material, 1 to 20 mass % of the conductive agent, 1 to 20 mass % of the binder, and 0 to 3.0 mass % of the viscosity modifier.

[0056] Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions in which electrolyte salts are dissolved in non-aqueous solvents. Examples of electrolyte salts include light metal salts, such as alkali metal salts (lithium salts, sodium salts, potassium salts, etc.); alkaline earth metal salts (magnesium salts, calcium salts, etc.); and aluminum salts, and one or more of these salts may be selected depending on the purpose. Specific examples of lithium salts include LiBF, LiClO, LiPF, LiAsF, CFSOLi, (CFSO)NLi, CFSOLi, CFCOLi, (CFCO)NLi, CFSOLi, CF 17SOLi, (C2F5SO2)2NLi, (C4F9SO2)(CF3SO2)NLi, (FSO2C6F4)(CF3SO2)NLi, ((CF3)2CHOSO2)2NLi, (CF3SO2)3CLi, (3,5-(CF3)2C6F3)4BLi, LiCF3, LiAlCl4, C4BO8Li, and the like can be mentioned, and one of these can be used alone or two or more can be used in combination.

[0057] The nonaqueous solvent is not particularly limited as long as it can be used as a nonaqueous electrolyte. Generally, aprotic high-dielectric-constant solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, and γ-butyrolactone are used; and aprotic low-viscosity solvents such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, dipropyl carbonate, diethyl ether, tetrahydrofuran, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,3-dioxolane, sulfolane, methyl sulfolane, acetonitrile, propionitrile, anisole, acetate esters such as methyl acetate, and propionate esters are used. It is desirable to use these aprotic high-dielectric-constant solvents and aprotic low-viscosity solvents in combination at an appropriate mixing ratio. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium cations can be used. The counter anion is not particularly limited, but examples include BF4 - , PF6 - , (CF3SO2)2N - The ionic liquid can be used by mixing with the non-aqueous solvent described above.

[0058] They can also be used as solid electrolytes or gel electrolytes. In this case, they can contain glass-based inorganic solid electrolytes, polyether gels, silicone gels, silicone polyether gels, acrylic gels, silicone acrylic gels, acrylonitrile gels, poly(vinylidene fluoride), etc. as polymer materials. These may be polymerized in advance or after injection. They can be used alone or as a mixture of two or more.

[0059] Furthermore, various additives may be added to the non-aqueous electrolyte solution as needed. Examples include vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, 4-vinylethylene carbonate, etc., for the purpose of improving cycle life; biphenyl, alkylbiphenyl, cyclohexylbenzene, t-butylbenzene, diphenyl ether, benzofuran, etc., for the purpose of preventing overcharge; and various carbonate compounds such as carbon dioxide gas, various carboxylic acid anhydrides, and various nitrogen- and sulfur-containing compounds for the purpose of deoxidation and dehydration. Furthermore, compounds in which some of these compounds are fluorine-substituted are also suitable.

[0060] The nonaqueous electrolyte secondary battery includes a battery case that seals the above-mentioned battery configuration, and may have any shape without any particular limitations. Typical examples include a coin-type battery in which electrodes punched into a coin shape and a separator are laminated together, and a prismatic or cylindrical battery in which an electrode sheet and a separator are spirally wound.

[0061] The present invention will be specifically described below with reference to examples and comparative examples. Note that the following examples do not limit the present invention in any way. Note that, hereinafter, "Me" means "methyl group," "Vi" means "vinyl group," and "parts" means "parts by mass."

[0062] [1] Production of Coating Composition for Electrochemical Element Separator [Example 1] As component (A), 18 parts of a dimethylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 1,000 mPa·s at 25°C, and 62 parts of a dimethylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups and having a viscosity of 5,000 mPa·s at 25°C, and as component (B), Me2ViSiO 1 / 2 Units: 6.8 mol%, MeSiO 1 / 2 units at 39.8 mol%, and SiO 4 / 2 25 parts of a resinous organopolysiloxane (weight average molecular weight 6,000) having 53.4 mol% of a unit, and MeHSiO as component (C). 1 / 2 Units: 61.1 mol%, MeSiO 1 / 2 The unit is 0.8 mol%, and SiO 4 / 2A coating composition for electrochemical element separators was obtained by kneading 5 parts of a resinous organohydrogenpolysiloxane having 38.1 mol% of units (an amount such that there were 2.0 moles of silicon-bonded hydrogen atoms in component (C) per mole of silicon-bonded vinyl groups in components (A) and (B)), 0.1 parts of a 1,1-divinyltetramethyldisiloxane complex solution of chloroplatinic acid (platinum concentration: 1% by mass) as component (D), and 0.03 parts of 1-ethynyl-1-cyclohexanol as a hydrosilylation reaction inhibitor. These components were kneaded for 10 minutes in a planetary mixer (PLMG-350, manufactured by Inoue Seisakusho Co., Ltd.).

[0063] [2] Production and evaluation of secondary battery separators [Examples 2-1 to 2-5, Comparative Examples 2-1 to 2-4] 10 x 10 cm 2 A coating solution prepared by diluting the coating composition obtained in Example 1 with n-hexane to the solid content concentration shown in Table 1 was applied to one side of a nonwoven fabric cut to size (a 20 μm thick aramid fiber nonwoven fabric that had been previously heated at 150°C for 12 hours and dehydrated). The nonwoven fabric was placed on a cellulose sheet in advance, and the coating solution that had slipped through the nonwoven fabric was absorbed by the cellulose sheet on the back side. The excess coating solution remaining on the surface of the nonwoven fabric was scraped off with a squeegee, and the nonwoven fabric was then dried and cured in an oven at 120°C for 2 hours to obtain a secondary battery separator having a coating film made of the coating composition. Note that the coating solution was applied to a 1 cm 2 nonwoven fabric. 2 The coating amount per unit area was calculated from the mass of the separator before and after coating and curing.

[0064] The thickness of the obtained secondary battery separator, the combustion test, and the lithium ion battery characteristics were measured by the following methods, and the results are shown in Table 1. In addition, the results of a secondary battery separator in which the coating composition was not applied to the nonwoven fabric are shown in Comparative Example 2-1.

[0065] [Separator Thickness] The thickness of the obtained secondary battery separator was measured using a thickness gauge. The thickness of the original separator without coating was 20 μm. After coating and drying, the thickness of the separator was evaluated as ◯ when it was 22 μm or less, △ when it was more than 22 μm but not more than 25 μm, and × when it was more than 25 μm.

[0066] [Combustion test] The obtained secondary battery separator was cut into a size of 3.5 cm x 6.5 cm, and both ends in the longitudinal direction (6.5 cm direction) were fixed with two stands so that the separator was parallel and maintained in a shape without loosening. A fire was lit from the lower center of the separator, and after leaving it until the fire was extinguished, the separator was visually inspected, and a rating of ◯ was given for those that maintained their shape, and a rating of × was given for those that could not maintain their shape and separated.

[0067] [Cutting Strength Measurement] The resulting secondary battery separator was cut to a size of 2.0 cm x 10.0 cm and pulled in a 180° direction using an autograph manufactured by Shimadzu Corporation to measure the cutting strength. The separator to be measured was sandwiched between the upper and lower fixing parts of the device at the bottom and top, each 2.0 cm wide, and pulled in the longitudinal direction by 10.0 cm. The pulling speed was 5 mm / min, and the torque (N / 2 cm) at the time of cutting was taken as the cutting strength. The cutting strength of the uncoated separator was 3.0 (N / 2 cm). For the cut strength value of the coated separator, a value less than 4.0 was evaluated as ×, a value between 4.0 and 6.0 was evaluated as ◯, and a value greater than 6.0 was evaluated as ⊚.

[0068] [Battery Characteristics Test] The battery characteristics of the lithium ion secondary battery manufactured by the following procedure were evaluated. 0.8 Co 0.1 Mn 0.1 O2 was laminated and bonded to a metal plate, and an extraction electrode (tab) was electrically welded to the upper metal part, which did not have any positive electrode active material, to form the positive electrode material. Polyimide tape was attached to the entire back side, which was not in close contact with the separator, to provide electrical insulation. On the other hand, graphite was laminated and bonded to the metal plate as the negative electrode active material, and an extraction electrode (tab) was electrically welded to the upper metal part, which did not have any negative electrode active material, to form the negative electrode material. Polyimide tape was attached to the entire back side, which was not in close contact with the separator, to provide electrical insulation.

[0069] Next, the polyolefin-coated aluminum film was placed with the polyolefin film facing up, and the negative electrode material, secondary battery separator, and positive electrode material prepared above were laminated in this order. The aluminum film in the portion not laminated with the laminate was folded to form an exterior seal. The separator was positioned so that the coating composition-coated surface faced the positive electrode. Each end face of the aluminum film was heated and pressed at 180°C to seal it under pressure. At this time, only the end face where the extraction electrode was not exposed was left open without being pressure-bonded. The laminate thus obtained was dried under reduced pressure at 130°C for 12 hours.

[0070] In a glove box filled with dry N2, an electrolyte solution was injected into the dried laminate from the end surface that was not crimped. The electrolyte solution was a 1 mol / L LiPF6 [ethylene carbonate: ethylene carbonate (1:1 vol%)] solution. The open end was then welded using a vacuum heating laminator in the glove box, resulting in a lithium-ion secondary battery.

[0071] The lithium ion secondary battery obtained above was subjected to preliminary charge and discharge (chemical conversion treatment), and then charged to 4.1 V at a current value of 0.2 cA in a 30°C constant temperature bath, and then charged at a constant voltage of 4.1 V until the current value reached 0.02 cA. After charging, the battery was repeatedly discharged to 2.7 V at a current value of 0.2 cA. The battery capacity after 200 charge and discharge cycles, assuming the initial capacity to be 100%, was determined and the retention rate was calculated. A retention rate of 90% or more was evaluated as ◯, a retention rate of 85% or more was evaluated as △, and a retention rate of less than 85% was evaluated as ×.

[0072]

[0073] As shown in Table 1, the coating amount was 0.05 to 1.20 mg / cm 2 In the range of 0.02 mg / cm, the separator thickness, cutting strength, combustion test, and battery characteristics all showed good results (Examples 2-1 to 2-5). 2 In the following Comparative Examples 2-1 and 2-2, the breaking strength was 3.1 N / 2 cm or less, and the combustion test and battery characteristics were both insufficient. 2In Comparative Examples 2-3 and 2-4, the cutting strength, the combustion test, and the battery characteristics were good, but the separator thicknesses were 34 μm and 41 μm, respectively, which are unsuitable from the viewpoints of internal electrical resistance and size.

Claims

1. (A) 100 parts by mass of a linear organopolysiloxane containing at least two alkenyl groups bonded to silicon atoms in each molecule, (B) RSiO 1 / 2 Units and SiO 4 / 2 1. A coating composition for an electrochemical element separator, comprising: (a) a resin-like organopolysiloxane having a unit (wherein R each independently represent a monovalent hydrocarbon group having 1 to 6 carbon atoms, with at least two R groups in one molecule being alkenyl groups); (b) an organohydrogenpolysiloxane containing at least two hydrogen atoms bonded to silicon atoms in one molecule, in an amount such that the number of hydrogen atoms bonded to silicon atoms in component (C) is 0.8 to 3.0 per combined alkenyl group bonded to silicon atoms in components (A) and (B); and (c) a hydrosilylation reaction catalyst.

2. A substrate and a coating film made of the cured product of the coating composition for electrochemical element separators according to claim 1 on at least a part of the substrate, the amount of the coating film being 1 cm 2 The electrochemical element separator has a weight of 0.05 to 1.50 mg per unit area.

3. The coating is formed on at least the surface of the substrate, and the amount of the coating is 1 cm 2 3. The electrochemical element separator according to claim 2, wherein the weight is 0.05 to 1.20 mg per unit area.

4. The electrochemical element separator according to claim 3, wherein said substrate has a plurality of pores, and said coating film is formed inside at least some of said plurality of pores.

5. The electrochemical element separator according to claim 4, wherein the substrate is a nonwoven fabric.

6. An electrochemical element comprising the electrochemical element separator according to any one of claims 2 to 5.

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