Battery material composition, polymer layer for secondary battery, separator for secondary battery, electrode for secondary battery, and secondary battery

Abstract

The present invention provides a battery material composition capable of improving the output characteristics of a secondary battery, a polymer layer for a secondary battery, a separator for a secondary battery, an electrode for a secondary battery, and a secondary battery. [Solution] A battery material composition comprising (i) a fluorine-containing polymer (A) containing polymerization units based on vinylidene fluoride and polymerization units based on tetrafluoroethylene and an acrylic polymer (B), or (ii) a copolymer (C) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on acrylic monomer, or (iii) a copolymer (D) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on chlorotrifluoroethylene.

Description

[Technical Field]

[0001] This disclosure relates to battery material compositions, polymer layers for secondary batteries, separators for secondary batteries, electrodes for secondary batteries, and secondary batteries. [Background technology]

[0002] The use of vinylidene fluoride / tetrafluoroethylene polymers and vinylidene fluoride / hexafluoropropylene polymer-acrylic compositions for separator coatings is being considered (see, for example, Patent Documents 1-3). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-33913 [Patent Document 2] Special Publication No. 2022-539128 [Patent Document 3] Special Publication No. 2024-511117 [Overview of the project] [Problems that the invention aims to solve]

[0004] This disclosure aims to provide a battery material composition, a polymer layer for secondary batteries, a separator for secondary batteries, an electrode for secondary batteries, and a secondary battery that can improve the output characteristics of secondary batteries. [Means for solving the problem]

[0005] (1) The present disclosure is a composition for battery material comprising (i) a fluorine-containing polymer (A) containing polymerization units based on vinylidene fluoride and polymerization units based on tetrafluoroethylene and an acrylic polymer (B), or (ii) a copolymer (C) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on acrylic monomer, or (iii) a copolymer (D) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on chlorotrifluoroethylene.

[0006] Disclosure (2) further comprises the battery material composition according to Disclosure (1), which includes at least one inorganic particle selected from the group consisting of metal oxide particles and metal hydroxide particles.

[0007] Disclosure (3) is a battery material composition according to Disclosure (2), wherein the inorganic particles are at least one selected from the group consisting of aluminum oxide, magnesium oxide, and aluminum hydroxide.

[0008] Disclosure (4) is a battery material composition according to Disclosure (2) or (3), wherein the content of the inorganic particles is 20 to 99% by mass of the solid content of the battery material composition.

[0009] The present disclosure (5) states that the fluorine-containing polymer (A) is at least one selected from the group consisting of vinylidene fluoride / tetrafluoroethylene / chlorotrifluoroethylene copolymer and vinylidene fluoride / tetrafluoroethylene copolymer. The acrylic polymer (B) is a battery material composition in any combination of any of the disclosures (1) to (4) above, which is at least one selected from the group consisting of an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer copolymer, an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / an epoxy group-containing acrylic monomer copolymer, and an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / a silyl group-containing acrylic monomer copolymer.

[0010] The present disclosure (6) states that the copolymer (C) comprises a fluorine-containing polymer portion (A') containing polymerization units based on vinylidene fluoride and polymerization units based on tetrafluoroethylene, and an acrylic polymer portion (B') containing polymerization units based on acrylic monomer. The fluorine-containing polymer portion (A') is at least one selected from the group consisting of vinylidene fluoride / tetrafluoroethylene / chlorotrifluoroethylene copolymer and vinylidene fluoride / tetrafluoroethylene copolymer. The acrylic polymer portion (B') is a battery material composition in any combination of any of the disclosures (1) to (5), which is at least one selected from the group consisting of an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer copolymer, an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / an epoxy group-containing acrylic monomer copolymer, and an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / a silyl group-containing acrylic monomer copolymer.

[0011] Disclosure (7) is a battery material composition in any combination of any of Disclosures (1) to (6) used to form a layer between the electrodes and separator of a secondary battery.

[0012] Disclosure (8) is a battery material composition in any combination with any of Disclosures (1) to (7) for separator coating.

[0013] Disclosure (9) is a battery material composition in any combination with any of Disclosures (1) to (7) for electrode coating.

[0014] Disclosure (10) is a polymer layer for a secondary battery, formed using the battery material composition described in Disclosure (7), and provided between the electrodes and separator of a secondary battery.

[0015] The present disclosure (11) is a separator for a secondary battery comprising a porous substrate and a porous membrane formed on the porous substrate using the battery material composition described in the present disclosure (8).

[0016] Disclosure (12) relates to an electrode for a secondary battery comprising a film formed using the battery material composition described in Disclosure (9).

[0017] The present disclosure (13) is a secondary battery comprising at least one selected from the group consisting of the polymer layer for secondary batteries described in the present disclosure (10), the separator for secondary batteries described in the present disclosure (11), and the electrode for secondary batteries described in the present disclosure (12).

[0018] This disclosure (14) is the secondary battery described in this disclosure (13), which is a lithium-ion secondary battery. [Effects of the Invention]

[0019] According to this disclosure, it is possible to provide a battery material composition capable of improving the output characteristics of a secondary battery, a polymer layer for a secondary battery, a separator for a secondary battery, an electrode for a secondary battery, and a secondary battery. [Modes for carrying out the invention]

[0020] The following provides a detailed explanation of this disclosure.

[0021] This disclosure relates to a battery material composition (hereinafter also referred to as the composition of this disclosure) comprising (i) a fluorine-containing polymer (A) containing polymerization units based on vinylidene fluoride (VdF) and polymerization units based on tetrafluoroethylene (TFE) and an acrylic polymer (B), or (ii) a copolymer (C) containing polymerization units based on VdF, polymerization units based on TFE and polymerization units based on acrylic monomer, or (iii) a copolymer (D) containing polymerization units based on VdF, polymerization units based on TFE and polymerization units based on chlorotrifluoroethylene (CTFE).

[0022] The composition of this disclosure contains a specific polymer, which can improve the output characteristics (rate characteristics) of a secondary battery. The reason for this is not clear, but it is thought to be due to the uniformity of the polymer network, high electrolyte retention, and the good formation of conductive paths for carrier ions. Furthermore, the compositions of this disclosure also exhibit excellent dispersion stability of inorganic particles when they are included. It is believed that the polymer described above functions as a dispersant, thereby improving the dispersibility of the inorganic particles. When the dispersibility of inorganic particles is good, the inorganic particles are less likely to aggregate, so good conductive paths are formed, and the output characteristics of the secondary battery are improved.

[0023] The composition of the present disclosure relating to the embodiment of (i) above comprises a fluorine-containing polymer (A) containing polymerization units based on VdF (hereinafter also referred to as VdF units) and polymerization units based on TFE (hereinafter also referred to as TFE units), and an acrylic polymer (B). The composition of the present disclosure relating to the embodiment of (i) above preferably contains particles of a fluorine-containing polymer (A) and particles of an acrylic polymer (B). Furthermore, it is preferable that the fluorine-containing polymer (A) and the acrylic polymer (B) exist as separate particles.

[0024] In the above fluorine-containing polymer (A), the mass ratio of VdF units to TFE units (VdF / TFE) is preferably 40 / 60 or more, more preferably 50 / 50 or more, even more preferably 60 / 40 or more, even more preferably 65 / 35 or more, particularly preferably 72 / 28 or more, and also preferably 99 / 1 or less, more preferably 92 / 8 or less, even more preferably 85 / 15 or less, and even more preferably 81 / 19 or less.

[0025] The total amount of VdF units and TFE units in the above-mentioned fluorine-containing polymer (A) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and also preferably 100% by mass or less, more preferably 99.5% by mass or less, even more preferably 99% by mass or less, even more preferably 98.5% by mass or less, and particularly preferably 98% by mass or less.

[0026] In this specification, the content of each polymerization unit can be calculated by appropriately combining NMR, FT-IR, elemental analysis, and X-ray fluorescence analysis depending on the type of monomer.

[0027] The above-mentioned fluorine-containing polymer (A) may consist only of VdF units and TFE units, or it may contain polymerization units based on other monomers (hereinafter also referred to as other monomer units) together with the VdF units and TFE units.

[0028] Examples of other monomers include fluoroolefins copolymerizable with VdF and TFE, and non-fluorinated monomers copolymerizable with VdF and TFE, with fluoroolefins copolymerizable with VdF and TFE being preferred.

[0029] Examples of the above fluorinated olefin include hexafluoropropylene (HFP), perfluoro(alkyl vinyl ether) (PAVE),

[0030] [Chemical formula]

[0031] and other perfluorinated olefins; non-perfluorinated olefins such as chlorotrifluoroethylene (CTFE), vinyl fluoride (VF), trifluoroethylene, trifluoropropylene, hexafluoroisobutene, 2,3,3,3-tetrafluoropropene, 1,3,3,3-tetrafluoropropene, 1,1,3,3,3-pentafluoropropene, etc. Examples of perfluoro(alkyl vinyl ether) include perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) (PEVE), perfluoro(propyl vinyl ether) (PPVE), etc.

[0032] In addition, as the above fluorinated olefin, a functional group-containing fluorinated olefin can also be used. Examples of the functional group-containing fluorinated olefin include, for example, the general formula: CX 1 2=CX 2 -(Rf) m -Y 1 (where Y 1 is -OH, -COOM 2 , -SO2F, -SO3M 2 (M 2 is a hydrogen atom, NH4 group or an alkali metal), carboxylate, carboxyester group, epoxy group or cyano group; X 1 and X 2 are the same or different and are each a hydrogen atom or a fluorine atom; Rf is a divalent fluorine-containing alkylene group or fluorine-containing oxyalkylene group having 1 to 40 carbon atoms, or a divalent fluorine-containing alkylene group or fluorine-containing oxyalkylene group containing an ether bond and having 2 to 40 carbon atoms; m is 0 or 1).

[0033] Specific examples of the above-mentioned functional group-containing fluoroolefins include, for example,

[0034] [ka]

[0035] [ka]

[0036] These are some examples.

[0037] As the fluoroolefin mentioned above, iodine-containing monomers, such as perfluoro(6,6-dihydro-6-iodo-3-oxa-1-hexene) and perfluoro(5-iodo-3-oxa-1-pentene) perfluorovinyl ethers described in Japanese Patent Publication No. 5-63482 and Japanese Patent Publication No. 62-12734, can also be used.

[0038] In particular, at least one of the above fluoroolefins selected from the group consisting of HFP and CTFE is preferred, and CTFE is more preferred.

[0039] The content of polymerization units based on fluoroolefins copolymerizable with the above VdF and TFE is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, and may be 0% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and even more preferably 2% by mass or more.

[0040] The total amount of polymerization units based on fluoroolefins, including VdF and TFE, is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and may be 100% by mass or less, or 99.5% by mass or less, based on the total polymerization units of the fluorine-containing polymer (A).

[0041] As the fluorine-containing polymer (A) mentioned above, at least one selected from the group consisting of VdF / TFE / CTFE copolymer (VTC) and VdF / TFE copolymer (VT) is preferred, and VdF / TFE / CTFE copolymer is more preferred, in that it can further improve the output characteristics of the secondary battery. The preferred composition of the VdF / TFE / CTFE copolymer is VdF / TFE / CTFE = 50-95 / 1-49 / 49-1 (mass%), and the more preferred composition is VdF / TFE / CTFE = 55-90 / 1-44 / 44-1 (mass%).

[0042] The average particle size of the above-mentioned fluorine-containing polymer (A) is preferably 50 nm or more, preferably 70 nm or more, preferably 300 nm or less, and more preferably 250 nm or less. The above average particle size may be the average particle size in an aqueous dispersion. The average particle size of the above-mentioned fluorine-containing polymer (A) is measured by dynamic light scattering. Specifically, an aqueous dispersion is prepared with a polymer solid content concentration of approximately 1.0% by mass, and the particle size is measured using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) at 25°C for 70 cumulative measurements. The refractive index of the solvent (water) is assumed to be 1.3328, and the viscosity of the solvent (water) is assumed to be 0.8878 mPa·s.

[0043] The method for producing the above-mentioned fluorine-containing polymer (A) is not particularly limited and can be produced by conventionally known polymerization methods, such as emulsion polymerization. The emulsifier used in the above emulsion polymerization may be a reactive emulsifier, a non-reactive emulsifier, or a combination thereof. Examples of non-reactive emulsifiers include conventionally known anionic emulsifiers, nonionic emulsifiers, or combinations thereof. In some cases, amphoteric emulsifiers may also be used. The above emulsion polymerization can be carried out, for example, by the method described in Japanese Patent Application Publication No. 2017-052879. Emulsion polymerization is performed using the following formula (1): CH2 = CHCH2 - OR (1) (In the formula, R is an oxygen atom, a nitrogen atom, and / or a hydrocarbon group which may have a polar group.) It is preferable to carry out the procedure in the presence of compound (1) shown in the diagram. Polymerization using compound (1) can be carried out, for example, by the method described in International Publication No. 2010 / 104142 or International Publication No. 2011 / 024856.

[0044] The above acrylic polymer (B) contains polymerization units based on acrylic monomers (hereinafter also referred to as acrylic monomer units). Examples of the above acrylic monomers include (meth)acrylic acid, (meth)acrylic acid esters, etc., and one or more types may be used. In this specification, "(meth)acrylic acid" means acrylic acid or methacrylic acid.

[0045] The above acrylic polymer (B) preferably contains polymerization units based on at least one acrylic monomer selected from the group consisting of acrylic acid esters, methacrylic acid esters, and acrylic monomers containing crosslinkable groups; more preferably contains methacrylic acid ester units and polymerization units based on at least one acrylic monomer selected from the group consisting of acrylic acid esters and acrylic monomers containing crosslinkable groups; and even more preferably contains methacrylic acid ester units, acrylic acid ester units, and acrylic monomer units containing crosslinkable groups.

[0046] As the above acrylic acid ester, alkyl acrylates having 1 to 10 carbon atoms in the alkyl group are preferred. Among these, at least one selected from the group consisting of methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, and cyclohexyl acrylate is more preferred, at least one selected from the group consisting of n-butyl acrylate and 2-ethylhexyl acrylate is even more preferred, and n-butyl acrylate is even more preferred. The above acrylic acid ester may not contain the crosslinking group described later.

[0047] The content of polymerization units based on the above acrylic acid ester is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, even more preferably 1% by mass or more, even more preferably 5% by mass or more, and also preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0048] As the methacrylic acid ester mentioned above, alkyl methacrylate esters having 1 to 10 carbon atoms in the alkyl group are preferred. Among these, at least one selected from the group consisting of methyl methacrylate, n-propyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, 2-ethylhexyl methacrylate, and cyclohexyl methacrylate is more preferred, and at least one selected from the group consisting of methyl methacrylate, n-butyl methacrylate, and cyclohexyl methacrylate is even more preferred. The methacrylic acid ester mentioned above may not contain the crosslinking group described later.

[0049] The content of the polymerization units based on the above methacrylic acid ester is preferably 1% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, even more preferably 40% by mass or more, particularly preferably 50% by mass or more, and also preferably 99% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0050] The above-mentioned acrylic monomer containing a crosslinkable group is preferably an acrylic monomer having a crosslinkable group that can be crosslinked by heating.

[0051] The crosslinkable groups in the above-mentioned acrylic monomer containing crosslinkable groups are functional groups that can be crosslinked by heating. Examples of crosslinkable groups that can be crosslinked by heating include epoxy groups, carboxyl groups, hydroxyl groups, amino groups, methylolamide groups, silyl groups, carbodiimide groups, oxazoline groups, blocked isocyanate groups, and ethyleneimine groups, with at least one selected from the group consisting of epoxy groups, carboxyl groups, and silyl groups being preferred.

[0052] Examples of acrylic monomers containing crosslinkable groups with epoxy groups include glycidyl compounds such as glycidyl acrylate and glycidyl methacrylate (GMA). At least one selected from the group consisting of glycidyl acrylate and glycidyl methacrylate is preferred due to its good stability during polymerization. When the crosslinkable group-containing acrylic monomer contains epoxy groups, the film-forming properties between particles and adhesion to the substrate during coating are further improved.

[0053] Examples of acrylic monomers containing a crosslinkable group having a carboxyl group include one or more of the following: acrylic acid, 2-acryloyloxyethyl phthalate, 2-acryloyloxyethyl hexahydrophthalate, methacrylic acid, 2-methacryloyloxyethyl phthalate, and 2-methacryloyloxyethyl hexahydrophthalate. At least one selected from the group consisting of acrylic acid (AA) and methacrylic acid (MAA) is preferred due to the good stability of the emulsion. When the crosslinkable group-containing acrylic monomer contains a carboxyl group, the film-forming properties between particles and adhesion to the substrate during coating are further improved.

[0054] Examples of acrylic monomers containing a crosslinkable group having a hydroxyl group include one or more of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.

[0055] Examples of acrylic monomers containing crosslinkable groups with amino groups include one or more of aminoethyl acrylate, dimethylaminoacrylate, diethylaminoethyl acrylate, aminoethyl methacrylate, dimethylamino methacrylate, diethylaminoethyl methacrylate, and 2-(O-[1'-methylpropyleneamino]carboxyamino)ethyl methacrylate.

[0056] Examples of acrylic monomers containing a crosslinkable group having a methylolamide group include one or more types such as methylolated acrylamide and alkoxymethylacrylamide.

[0057] Examples of acrylic monomers containing a crosslinkable group having a silyl group include: CH2=CHCOO(CH2)3Si(OCH3)3, CH2=CHCOO(CH2)3Si(CH3)(OCH3)2, CH2=CHCOO(CH2)3Si(OC2H5)3, CH2=CHCOO(CH2)3Si(CH3)(OC2H5)2, CH2=C(CH3)COO(CH2)3Si(OCH3)3, CH2=C(CH3)COO(CH2)3Si(CH3)(OCH3)2, CH2=C(CH3)COO(CH2)3Si(OC2H5)3, CH2=C(CH3)COO(CH2)3Si(CH3)(OC2H5)2, CH2=C(CH3)COO(CH2)2O(CH2)3Si(OCH3)3, CH2=C(CH3)COO(CH2)2(CH2)3Si(CH3)(OCH3)2, CH2=C(CH3)COO(CH2) 11 Si(OCH3)3, CH2=C(CH3)COO(CH2) 11 Si(CH3)(OCH3)2, Examples include one or more of the following: In particular, at least one selected from the group consisting of γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-methacryloxypropylmethyldiethoxysilane is preferred, with γ-methacryloxypropyltriethoxysilane being more preferred.

[0058] These crosslinkable group-containing acrylic monomers may be used in combination of two or more types, regardless of the type of crosslinkable group. For example, combinations of epoxy group-containing acrylic monomer and carboxyl group-containing acrylic monomer, epoxy group-containing acrylic monomer and hydroxyl group-containing acrylic monomer, epoxy group-containing acrylic monomer and amino group-containing acrylic monomer, epoxy group-containing acrylic monomer and methylolamide group-containing acrylic monomer, carboxyl group-containing acrylic monomer and carbodiimide group-containing acrylic monomer, carboxyl group-containing acrylic monomer and oxazoline group-containing acrylic monomer, hydroxyl group-containing acrylic monomer and blocked isocyanate group-containing acrylic monomer, hydroxyl group-containing acrylic monomer and ethyleneimine group-containing acrylic monomer, hydroxyl group-containing acrylic monomer and carboxyl group-containing acrylic monomer, hydroxyl group-containing acrylic monomer and methylolamide group-containing acrylic monomer, methylolamide group-containing acrylic monomer and ethyleneimine group-containing acrylic monomer, methylolamide group-containing acrylic monomer and carboxyl group-containing acrylic monomer, amino group-containing acrylic monomer and ethyleneimine group-containing acrylic monomer, and carboxyl group-containing acrylic monomer and silyl group-containing acrylic monomer are examples of such combinations. In particular, when epoxy group-containing acrylic monomers and carboxyl group-containing acrylic monomers are used in combination, the stability of the emulsion becomes especially excellent.

[0059] The above-mentioned crosslinkable group-containing acrylic monomer is preferably at least one selected from the group consisting of carboxyl group-containing acrylic monomers, epoxy group-containing acrylic monomers, and silyl group-containing acrylic monomers, and a combination of a carboxyl group-containing acrylic monomer and at least one selected from the group consisting of epoxy group-containing acrylic monomers and silyl group-containing acrylic monomers is more preferred. The above crosslinkable group-containing acrylic monomer is preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, glycidyl acrylate, glycidyl methacrylate, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-methacryloxypropylmethyldiethoxysilane; more preferably at least one selected from the group consisting of acrylic acid, methacrylic acid, glycidyl methacrylate, and γ-methacryloxypropyltriethoxysilane; and even more preferably a combination of at least one selected from the group consisting of acrylic acid and methacrylic acid and at least one selected from the group consisting of glycidyl methacrylate and γ-methacryloxypropyltriethoxysilane.

[0060] The content of polymerization units based on the above crosslinkable group-containing acrylic monomer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, even more preferably 1.0% by mass or more, and also preferably 40% by mass or less, more preferably 35% by mass or less, even more preferably 30% by mass or less, even more preferably 25% by mass or less, even more preferably 20% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

[0061] Other examples of the above-mentioned acrylic monomers include 2-ethoxyethyl acrylate, 2-methoxyethyl acrylate, 2-ethoxyethyl methacrylate, and 2-methoxyethyl methacrylate.

[0062] The total amount of acrylic monomer units in the above acrylic polymer (B) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and may be 100% by mass or less, or 99.5% by mass or less, based on the total polymerization units of the acrylic polymer (B).

[0063] The above acrylic polymer (B) may consist only of the above acrylic monomer units, or it may contain polymerization units based on other monomers other than the above acrylic monomer, to the extent that it does not impair the effects of the present disclosure. Examples of other monomers include aromatic vinyl monomers, epoxy group-containing monomers other than the above crosslinkable group-containing acrylic monomers, unsaturated carboxylic acid monomers other than the above crosslinkable group-containing acrylic monomers, vinyl ether monomers, olefin monomers, hydrolyzable silyl group-containing vinyl monomers, vinyl ester monomers, and the like.

[0064] Examples of aromatic vinyl monomers include styrenes such as styrene and α-methylstyrene. Examples of epoxy group-containing monomers include allyl glycidyl ether.

[0065] Examples of unsaturated carboxylic acid monomers include vinyl acetic acid, crotonic acid, cinnamic acid, 3-allyloxypropionic acid, 3-(2-alyloxyethoxycarbonyl)propionic acid, itaconic acid, itaconic acid monoester, maleic acid, maleic acid monoester, maleic anhydride, fumaric acid, fumaric acid monoester, vinyl phthalate, vinyl pyromellitic acid, and undecylenic acid.

[0066] Examples of vinyl ether monomers include alkyl vinyl ethers and hydroxyl group-containing vinyl ethers. Examples of hydroxyl group-containing vinyl ethers include 2-hydroxyethyl vinyl ether, 3-hydroxypropyl vinyl ether, 2-hydroxypropyl vinyl ether, 2-hydroxy-2-methylpropyl vinyl ether, 4-hydroxybutyl vinyl ether, 4-hydroxy-2-methylbutyl vinyl ether, 5-hydroxypentyl vinyl ether, 6-hydroxyhexyl vinyl ether, 2-hydroxyethyl allyl ether, 4-hydroxybutyl allyl ether, and glycerol monoallyl ether.

[0067] Examples of olefin monomers include ethylene, propylene, n-butene, isobutene, and styrene.

[0068] Examples of hydrolyzable silyl group-containing vinyl monomers include, CH2=CHSi(OCH3)3, CH2=CHSi(CH3)(OCH3)2, CH2=C(CH3)Si(OCH3)3, CH2=C(CH3)Si(CH3)(OCH3)2, CH2=CHSi(OC2H5)3, CH2=CHSi(OC3H7)3, CH2=CHSi(OC4H9)3, CH2=CHSi(OC6H 13 )3, CH2=CHSi(OC8H 17 )3, CH2=CHSi(OC 10 H 21 )3, CH2=CHSi(OC 12 H 25 )3, CH2=CHCH2OCO(o-C6H4)COO(CH2)3Si(OCH3)3, CH2=CHCH2OCO(o-C6H4)COO(CH2)3Si(CH3)(OCH3)2, CH2=CH(CH2)4Si(OCH3)3, CH2=CH(CH2)8Si(OCH3)3, CH2=CHO(CH2)3Si(OCH3)3, CH2=CHCH2O(CH2)3Si(OCH3)3, CH2=CHCH2OCO(CH2) 10 Si(OCH3)3 These are some examples.

[0069] Examples of vinyl ester monomers include vinyl acetate, vinyl propionate, vinyl butyrate, vinyl isobutyrate, vinyl pivalate, vinyl caproate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl cyclohexylcarboxylate, vinyl benzoate, and p-t-butylvinyl benzoate, among other vinyl carboxylates.

[0070] The above acrylic polymer (B) is selected from the group consisting of alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer copolymer, alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / epoxy group-containing acrylic monomer copolymer, and alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / silyl group-containing acrylic monomer copolymer. At least one of the following is preferred, and at least one selected from the group consisting of methyl methacrylate (MMA) / n-butyl acrylate (n-BA) / acrylic acid (AA) copolymer, MMA / n-BA / n-butyl methacrylate (n-MBA) / methacrylic acid (MAA) / γ-methacryloxypropyltriethoxysilane copolymer, MMA / n-BA / cyclohexyl methacrylate (CHMA) / MAA / glycidyl methacrylate (GMA) copolymer, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer, and MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane copolymer. A preferred composition of the MMA / n-BA / AA copolymer is, for example, MMA / n-BA / AA = 1~99 / 0.5~40 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / CHMA / MAA / GMA copolymer is, for example, MMA / n-BA / CHMA / MAA / GMA = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane = 1~70 / 1~70 / 0.5~5 / 0.5~10 (mass%).

[0071] The average particle size of the above acrylic polymer (B) is preferably 50 nm or more, preferably 70 nm or more, preferably 300 nm or less, and more preferably 250 nm or less. The above average particle size may be the average particle size in an aqueous dispersion. The average particle size of the above acrylic polymer (B) is measured by dynamic light scattering. Specifically, an aqueous dispersion is prepared with a polymer solid content concentration of approximately 1.0% by mass, and the particle size is measured using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) at 25°C for 70 cumulative measurements. The refractive index of the solvent (water) is assumed to be 1.3328, and the viscosity of the solvent (water) is assumed to be 0.8878 mPa·s.

[0072] The method for producing the above-mentioned acrylic polymer (B) is not particularly limited and can be produced by conventionally known polymerization methods.

[0073] The mass ratio ((A) / (B)) of the above-mentioned fluorine-containing polymer (A) to the above-mentioned acrylic polymer (B) is preferably 1 / 99 or more, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, even more preferably 30 / 70 or more, particularly preferably 35 / 65 or more, and also preferably 99 / 1 or less, more preferably 90 / 10 or less, even more preferably 80 / 20 or less, and even more preferably 75 / 25 or less, in order to further improve the output characteristics of the secondary battery.

[0074] The total amount of the above-mentioned fluorine-containing polymer (A) and the above-mentioned acrylic polymer (B) is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, particularly preferably 20% by mass or more, and also preferably 100% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, even more preferably 55% by mass or less, and particularly preferably 40% by mass or less.

[0075] The composition of the present disclosure relating to the embodiment of (ii) above comprises a copolymer (C) containing VdF units, TFE units, and acrylic monomer units. The composition of the present disclosure is preferably in the embodiment of (ii) above in that it can further improve the output characteristics of the secondary battery.

[0076] The copolymer (C) described above may contain VdF units, TFE units, and acrylic monomer units, but it is preferable to include a fluorine-containing polymer portion (A') containing VdF units and TFE units, and an acrylic polymer portion (B') containing acrylic monomer units, in order to further improve the output characteristics of the secondary battery. The fluorine-containing polymer portion (A') and the acrylic polymer portion (B') may or may not be chemically bonded. Furthermore, the composition of the present disclosure relating to the embodiment of (ii) above preferably contains copolymer (C) particles. In this case, it is preferable that the fluorine-containing polymer portion (A') and the acrylic polymer portion (B') are present within a single particle.

[0077] The mass ratio (VdF / TFE) of VdF units to TFE units in the copolymer (C) described above is preferably 40 / 60 or more, more preferably 50 / 50 or more, even more preferably 60 / 40 or more, even more preferably 65 / 35 or more, particularly preferably 72 / 28 or more, and also preferably 99 / 1 or less, more preferably 92 / 8 or less, even more preferably 85 / 15 or less, and even more preferably 81 / 19 or less.

[0078] The total amount of VdF units and TFE units is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, particularly preferably 85% by mass or more, and also preferably 100% by mass or less, more preferably 99.5% by mass or less, even more preferably 99% by mass or less, even more preferably 98.5% by mass or less, and particularly preferably 98% by mass or less.

[0079] The above-mentioned fluorine-containing polymer portion (A') may consist only of VdF units and TFE units, or it may contain other monomer units along with the VdF units and TFE units.

[0080] Other monomers mentioned above include monomers similar to those that can be used in the fluorine-containing polymer (A) in the embodiment of (i) above. Among these, fluoroolefins copolymerizable with VdF and TFE are preferred, at least one selected from the group consisting of HFP and CTFE is more preferred, and CTFE is even more preferred.

[0081] The content of polymerization units based on fluoroolefins copolymerizable with the above VdF and TFE is preferably 50% by mass or less, more preferably 45% by mass or less, even more preferably 35% by mass or less, even more preferably 30% by mass or less, and may be 0% by mass or more, preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and even more preferably 2% by mass or more.

[0082] The total amount of polymerization units based on fluoroolefins, including VdF and TFE, is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and may be 100% by mass or less, or 99.5% by mass or less, based on the total polymerization units of the fluorine-containing polymer portion (A').

[0083] As the fluorine-containing polymer portion (A') described above, at least one selected from the group consisting of VdF / TFE / CTFE copolymer (VTC) and VdF / TFE copolymer (VT) is preferred, and VdF / TFE / CTFE copolymer is more preferred, in that it can further improve the output characteristics of the secondary battery. The preferred composition of the VdF / TFE / CTFE copolymer is VdF / TFE / CTFE = 50-95 / 1-49 / 49-1 (mass%), and the more preferred composition is VdF / TFE / CTFE = 55-90 / 1-44 / 44-1 (mass%).

[0084] The acrylic monomer in the copolymer (C) described above can be the same monomer as the acrylic monomer that can be used in the acrylic polymer (B) in the form described in (i) above, and the preferred form is also the same.

[0085] The total amount of acrylic monomer units in the copolymer (C) is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and may be 100% by mass or less, or 99.5% by mass or less, relative to the total polymerization units of the acrylic polymer portion (B').

[0086] The acrylic polymer portion (B') may consist solely of the acrylic monomer units, or it may contain polymerization units based on other monomers other than the acrylic monomer, to the extent that it does not impair the effects of the present disclosure. Examples of other monomers include those similar to other monomers that can be used in the acrylic polymer (B) in the form of (i) above.

[0087] The above acrylic polymer portion (B') is selected from the group consisting of an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer copolymer, an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / epoxy group-containing acrylic monomer copolymer, and an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / silyl group-containing acrylic monomer copolymer. At least one of the selected copolymers is preferred, and at least one selected from the group consisting of methyl methacrylate (MMA) / n-butyl acrylate (n-BA) / acrylic acid (AA) copolymer, MMA / n-BA / n-butyl methacrylate (n-MBA) / methacrylic acid (MAA) / γ-methacryloxypropyltriethoxysilane copolymer, MMA / n-BA / cyclohexyl methacrylate (CHMA) / MAA / glycidyl methacrylate (GMA) copolymer, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer, and MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane copolymer is more preferred. A preferred composition of the MMA / n-BA / AA copolymer is, for example, MMA / n-BA / AA = 1~99 / 0.5~40 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / CHMA / MAA / GMA copolymer is, for example, MMA / n-BA / CHMA / MAA / GMA = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / n-MBA / MAA / γ-methacryloxypropyltriethoxysilane = 1~50 / 5~40 / 1~70 / 0.5~5 / 0.5~10 (mass%). A preferred composition of the MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane copolymer is, for example, MMA / n-BA / AA / γ-methacryloxypropyltriethoxysilane = 1~70 / 1~70 / 0.5~5 / 0.5~10 (mass%).

[0088] The mass ratio ((A') / (B')) of the above-mentioned fluorine-containing polymer portion (A') to the above-mentioned acrylic polymer portion (B') is preferably 1 / 99 or more, more preferably 10 / 90 or more, even more preferably 20 / 80 or more, even more preferably 30 / 70 or more, particularly preferably 35 / 65 or more, and also preferably 99 / 1 or less, more preferably 90 / 10 or less, even more preferably 80 / 20 or less, and even more preferably 75 / 25 or less, in order to further improve the output characteristics of the secondary battery.

[0089] The average particle size of the copolymer (C) is preferably 50 nm or more, preferably 70 nm or more, preferably 300 nm or less, and more preferably 250 nm or less. The above average particle size may be the average particle size in an aqueous dispersion. The average particle size of the copolymer (C) described above is measured by dynamic light scattering. Specifically, an aqueous dispersion is prepared with a polymer solids content concentration of approximately 1.0% by mass, and the particle size is measured using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) at 25°C for 70 cumulative measurements. The refractive index of the solvent (water) is assumed to be 1.3328, and the viscosity of the solvent (water) is assumed to be 0.8878 mPa·s.

[0090] The method for producing the copolymer (C) is not particularly limited and can be produced by conventionally known polymerization methods, such as emulsion polymerization. Among these, seed polymerization is particularly preferred. Seed polymerization is not particularly limited and can be carried out by conventionally known methods and conditions, but for example, one method involves producing particles of a fluorine-containing polymer corresponding to the fluorine-containing polymer portion (A') and polymerizing an acrylic monomer to form the acrylic polymer portion (B') in the presence of these particles. The particles of the fluorine-containing polymer corresponding to the above-mentioned fluorine-containing polymer portion (A') may be produced in the form of an aqueous dispersion, and the polymerization of the acrylic monomer may be carried out in the aqueous dispersion. Particles of the fluorine-containing polymer corresponding to the above-mentioned fluorine-containing polymer portion (A') can be produced, for example, by the same method as that used for the fluorine-containing polymer (A) described above. Polymerization of acrylic monomers (seed polymerization) can be carried out, for example, by the method described in International Publication No. 2010 / 104142.

[0091] The content of the copolymer (C) is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 10% by mass or more, even more preferably 15% by mass or more, particularly preferably 20% by mass or more, and also preferably 100% by mass or less, more preferably 80% by mass or less, even more preferably 70% by mass or less, even more preferably 65% ​​by mass or less, even more preferably 60% by mass or less, even more preferably 55% by mass or less, and particularly preferably 40% by mass or less.

[0092] The composition of the present disclosure relating to the embodiment of (iii) above comprises a copolymer (D) containing VdF units, TFE units, and polymerization units based on CTFE (hereinafter also referred to as CTFE units). The composition of the present disclosure is preferably in the embodiment of (iii) above in that it can further improve the cycle characteristics of the secondary battery at high temperatures (e.g., 50 to 100°C, preferably 60 to 80°C).

[0093] The copolymer (D) described above may consist only of VdF units, TFE units, and CTFE units, or it may contain other monomer units along with VdF units, TFE units, and CTFE units. However, the VdF / TFE / CTFE copolymer (VTC) is preferred because it can further improve the output characteristics of the secondary battery.

[0094] Other monomers mentioned above include other monomers other than CTFE that can be used in the fluorine-containing polymer (A) in the form of (i) above, and preferred monomers are the same as in the case of the fluorine-containing polymer (A) in the form of (i) above.

[0095] The content of VdF units in the copolymer (D) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, particularly preferably 72% by mass or more, and also preferably 95% by mass or less, and more preferably 90% by mass or less. The content of TFE units in the copolymer (D) is preferably 2% by mass or more, more preferably 3% by mass or more, preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less, relative to the total polymerization units of copolymer (D). The content of CTFE units in the copolymer (D) is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 8% by mass or more, and preferably 25% by mass or less, and more preferably 20% by mass or less, relative to the total polymerization units of copolymer (D).

[0096] As the copolymer (D) mentioned above, VdF / TFE / CTFE copolymer (VTC) is preferred because it can further improve the output characteristics and high-temperature cycle characteristics of the secondary battery. The preferred composition of the VdF / TFE / CTFE copolymer is VdF / TFE / CTFE = 50-95 / 1-49 / 49-1 (mass%), and the more preferred composition is VdF / TFE / CTFE = 55-90 / 1-44 / 44-1 (mass%).

[0097] From the viewpoint of improving the cycling properties at high temperatures, the melting point of the copolymer (D) is preferably 80°C or higher, more preferably 90°C or higher, preferably 150°C or lower, and more preferably 140°C or lower. The fact that the copolymer (D) has a melting point of 90°C or higher is preferable because it prevents the resin from flowing excessively during the drying process, moderately suppresses the formation of a continuous coating film, and allows the porous structure to be maintained. In this specification, the melting point of the polymer can be measured by the method described in the examples below.

[0098] The compositions of this disclosure preferably further contain a solvent. Examples of the solvent include water and organic solvents, with water being preferred. Water and organic solvents may be used in combination. Examples of the organic solvent include amide solvents such as N-methyl-2-pyrrolidone; ketone solvents such as acetone; and cyclic ether solvents such as tetrahydrofuran. The composition of the present disclosure relating to the embodiment of (i) above is preferably an aqueous dispersion containing a fluorine-containing polymer (A) and an acrylic polymer (B), and is also preferably an aqueous dispersion containing particles of the fluorine-containing polymer (A) and particles of the acrylic polymer (B). The composition of the present disclosure relating to the embodiment of (ii) above is preferably an aqueous dispersion containing copolymer (C), and is also preferably an aqueous dispersion containing copolymer (C) particles. The composition of the present disclosure relating to the embodiment of (iii) above is preferably an aqueous dispersion containing copolymer (D), and is also preferably an aqueous dispersion containing copolymer (D) particles.

[0099] The compositions of this disclosure preferably further contain at least one inorganic particle selected from the group consisting of metal oxide particles and metal hydroxide particles, but may not contain it. When the compositions contain the inorganic particles, the resulting separator has excellent heat resistance (thermal stability). The compositions of this disclosure exhibit excellent dispersion stability, even when they contain inorganic particles.

[0100] The content of the inorganic particles is preferably 20 to 99% by mass of the solid content of the composition. When the content of the inorganic particles is within the above range, a separator can be obtained in which a porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. Furthermore, a separator with high heat resistance and low thermal shrinkage can be realized. The content of the inorganic particles is more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 55% by mass or more, particularly preferably 60% by mass or more, and more preferably 97% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0101] The inorganic particles described above preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and preferably 0.001 μm or more. The average particle diameter mentioned above is a value obtained by measuring with a dynamic light scattering particle analyzer.

[0102] As for the metal oxide particles mentioned above, from the viewpoint of improving the ion conductivity and shutdown effect of the separator, at least one selected from the group consisting of aluminum oxide, magnesium oxide, silicon oxide, titanium oxide, vanadium oxide, and copper oxide is preferred, and at least one selected from the group consisting of aluminum oxide and magnesium oxide is more preferred.

[0103] The above metal oxide particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and preferably 0.001 μm or more. The average particle diameter mentioned above is a value obtained by measuring with a dynamic light scattering particle analyzer.

[0104] Particularly preferred metal oxide particles are aluminum oxide particles or silicon oxide particles with an average particle diameter of 5 μm or less, due to their excellent ionic conductivity.

[0105] The content of the above-mentioned metal oxide particles is preferably 20 to 99% by mass of the solid content of the above-mentioned composition. When the content of the above-mentioned metal oxide particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. Furthermore, a separator with high heat resistance and low thermal shrinkage can be realized. The content of the above metal oxide particles is more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 55% by mass or more, particularly preferably 60% by mass or more, and more preferably 97% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0106] As for the metal hydroxide particles mentioned above, from the viewpoint of improving the ion conductivity and shutdown effect of the separator, at least one selected from the group consisting of magnesium hydroxide, calcium hydroxide, aluminum hydroxide, chromium hydroxide, zirconium hydroxide, and nickel hydroxide is preferred, and aluminum hydroxide is more preferred.

[0107] The above metal hydroxide particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and preferably 0.001 μm or more. The average particle diameter mentioned above is a value obtained by measuring with a dynamic light scattering particle analyzer.

[0108] The content of the above-mentioned metal hydroxide particles is preferably 20 to 99% by mass of the solid content of the above-mentioned composition. When the content of the above-mentioned metal hydroxide particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. Furthermore, a separator with high heat resistance and low thermal shrinkage can be realized. The content of the above metal hydroxide particles is more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, even more preferably 55% by mass or more, particularly preferably 60% by mass or more, and more preferably 97% by mass or less, even more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% by mass or less.

[0109] The inorganic particles mentioned above are preferably at least one selected from the group consisting of aluminum oxide, magnesium oxide, and aluminum hydroxide.

[0110] The compositions of this disclosure preferably further contain organic particles. The organic particles are preferably non-conductive crosslinked polymers, and more preferably crosslinked polystyrene, crosslinked polymethacrylate, and crosslinked acrylate.

[0111] The above organic particles preferably have an average particle diameter of 20 μm or less, more preferably 10 μm or less, even more preferably 5 μm or less, and preferably 0.001 μm or more. The average particle size mentioned above is a value obtained by measurement using a transmission electron microscope.

[0112] The content of the above-mentioned organic particles is preferably 0 to 49% by mass of the solid content of the above-mentioned composition. When the content of the above-mentioned organic particles is within the above range, a separator can be obtained in which a composite porous membrane having a pore size and porosity that does not hinder the permeation of lithium ions is laminated. The content of the above organic particles is more preferably 2% by mass or more, even more preferably 5% by mass or more, more preferably 37% by mass or less, and even more preferably 35% by mass or less, based on the solid content of the above composition.

[0113] The compositions of this disclosure may further contain other components not described above. Examples of other components include other resins, rubbers, and so on. Preferred resins to be used in combination include, for example, one or more of the following: polyacrylonitrile, polyamide-imide, polyvinylidene fluoride (PVdF), and VdF / HFP copolymer resins. Preferred rubbers to be used in combination include, for example, one or more types of VdF / HFP copolymer rubber, VdF / TFE / HFP copolymer rubber, and acrylic rubber. These rubbers may or may not be crosslinked.

[0114] Particularly preferred resins or rubbers to be used in combination include acrylic rubber from the viewpoint of improving ionic conductivity, and VdF / HFP copolymer rubber, VdF / TFE / HFP copolymer rubber, and VdF / HFP resin from the viewpoint of improving both ionic conductivity and oxidation resistance.

[0115] The VdF / HFP copolymer rubber preferably has a molar ratio of 80 / 20 to 65 / 35 in terms of VdF units to HFP units. The VdF / TFE / HFP copolymer rubber preferably has a molar ratio of 80 / 5 / 15 to 60 / 30 / 10 for VdF units, HFP units, and TFE units. The VdF / HFP resin preferably has a molar ratio of 98 / 2 to 85 / 15 in terms of VdF units / HFP units. VdF / HFP resin preferably has a melting point of 100 to 200°C.

[0116] The amount of other resins or rubbers added is preferably 400 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less, relative to 100 parts by mass of the total amount of fluorine-containing polymer (A) and acrylic polymer (B), or 100 parts by mass of copolymer (C), or 100 parts by mass of copolymer (D). The lower limit varies depending on the desired effect, but is about 10 parts by mass.

[0117] The compositions of this disclosure may further contain a viscosity-adjusting thickener (stabilizer). Examples of such thickeners (stabilizers) include carboxyalkylcellulose, alkylcellulose, and hydroxyalkylcellulose.

[0118] The solid content concentration of the composition of this disclosure is not particularly limited, but may be, for example, 10% by mass or more, 20% by mass or more, 30% by mass or more, 35% by mass or more, or 65% by mass or less, 60% by mass or less, 55% by mass or less, or 50% by mass or less.

[0119] The compositions of this disclosure can be prepared by mixing the components. The mixing method is not particularly limited, and conventionally known methods can be employed.

[0120] The compositions disclosed herein are used as materials for batteries such as secondary batteries, and are preferably used to form a layer between the electrodes and separator of a secondary battery. A polymer layer for secondary batteries, formed using the composition of the present disclosure and provided between the electrodes and separator of a secondary battery, is also part of the present disclosure.

[0121] The method for forming a layer between the electrode and the separator is not particularly limited, and conventionally known methods may be employed. Specifically, the composition of this disclosure may be applied to the surface of the electrode that contacts the separator and / or the surface of the separator that contacts the electrode, and dried as necessary. Alternatively, a film may be prepared in advance from the above composition, and the film may be sandwiched between the electrode and the separator and laminated by a method such as lamination. An example of a method for producing the above-mentioned coating is to cast the composition of this disclosure onto a film having a smooth surface, such as a polyester film or an aluminum film, and then peel it off.

[0122] The compositions disclosed herein are preferably separator coating compositions used for coating separators in secondary batteries and the like, and are also preferably used to form a porous film on a porous substrate constituting a separator. A separator for a secondary battery comprising a porous substrate and a porous membrane formed on the porous substrate using the composition of the present disclosure is also one of the present disclosures.

[0123] The porous membrane described above is preferably provided on a porous substrate, and more preferably provided directly on the porous substrate. Furthermore, the porous membrane may be provided on only one side of the porous substrate, or on both sides. Also, the porous membrane may be provided so as to cover the entire porous substrate on which the porous membrane is provided, or so as to cover only a part of it.

[0124] The mass of the porous membrane described above is 0.5 to 50.0 g / m² when the porous membrane is formed on only one side of the porous substrate. 2 A range of 0.5 g / m² is preferred. 2 Using less than 50.0 g / m² may result in insufficient adhesion to the electrodes. 2 If the amount is too high, it tends to inhibit ion conduction and degrade the battery's load characteristics, which is undesirable. When forming the above porous film on both the front and back surfaces of a porous substrate, the mass of the porous film should be 0.1 to 6.0 g / m². 2 It is preferable.

[0125] The porous substrates mentioned above refer to substrates that have voids or cavities inside. Examples of such substrates include microporous membranes, porous sheets made of fibrous materials such as nonwoven fabrics and laminated sheets, or composite porous membranes in which one or more other porous layers are laminated onto these microporous membranes or porous sheets. A microporous membrane refers to a membrane that has a large number of fine pores inside, in which these fine pores are interconnected, and which allows gas or liquid to pass from one side to the other.

[0126] The materials constituting the porous substrate can be either electrically insulating organic or inorganic materials. In particular, from the viewpoint of providing the substrate with a shutdown function, it is preferable to use a thermoplastic resin as the constituent material of the substrate. Here, the shutdown function refers to the function that, when the battery temperature rises, melts the thermoplastic resin and blocks the pores of the porous substrate, thereby blocking ion movement and preventing thermal runaway of the battery. Suitable thermoplastic resins have a melting point of less than 200°C, and polyolefins are particularly preferred.

[0127] As a porous substrate using polyolefin, a polyolefin microporous membrane is preferred. As the polyolefin microporous membrane, a conventional polyolefin microporous membrane used in separators for non-aqueous secondary batteries, which has sufficient mechanical properties and ion permeability, can be used. Furthermore, from the viewpoint of having the shutdown function described above, it is preferable that the polyolefin microporous membrane contains polyethylene.

[0128] Polyolefins with a weight-average molecular weight of 100,000 to 5,000,000 are preferable. If the weight-average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. If it is greater than 5,000,000, the shutdown characteristics may deteriorate or molding may become difficult.

[0129] Such polyolefin microporous membranes can be manufactured by, for example, the following methods: (i) extruding molten polyolefin resin from a T-die to form a sheet, (ii) subjecting the sheet to a crystallization treatment, (iii) stretching the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane. Another method involves (i) melting polyolefin resin together with a plasticizer such as liquid paraffin, extruding it from a T-die, and cooling it to form a sheet, (ii) stretching the sheet, (iii) extracting the plasticizer from the sheet, and (iv) heat-treating the sheet in sequence to form a microporous membrane.

[0130] As porous sheets made of fibrous materials, porous sheets can be made of fibrous materials made of polyester such as polyethylene terephthalate, polyolefins such as polyethylene and polypropylene, heat-resistant polymers such as aromatic polyamides and polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides, or mixtures thereof.

[0131] The above-mentioned porous substrate may be a composite porous substrate in which a functional layer is further laminated. The above-mentioned composite porous substrate is preferable in that further functionality can be added by a functional layer. As a functional layer, for example, from the viewpoint of providing heat resistance, a porous layer made of a heat-resistant resin or a porous layer made of a heat-resistant resin and an inorganic filler can be used. Examples of heat-resistant resins include one or more heat-resistant polymers selected from aromatic polyamides, polyimides, polyethersulfones, polysulfones, polyetherketones, and polyetherimides. Suitable inorganic fillers include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. As for composite formation methods, methods include coating the porous sheet with a functional layer, joining with an adhesive, and heat-pressing.

[0132] The porous substrate in this disclosure preferably contains at least one resin selected from the group consisting of polyethylene, polypropylene, polyimide, polyamide, polyethylene terephthalate, polyester, and polyacetal.

[0133] In this disclosure, the film thickness of the porous substrate is preferably in the range of 5 to 50 μm from the viewpoint of obtaining good mechanical properties and internal resistance.

[0134] The method for laminating the porous film on the porous substrate is not particularly limited, and conventionally known methods may be employed. Specifically, preferred methods include roll coating the composition of this disclosure onto the porous substrate, dipping the porous substrate into the composition, and coating the porous substrate with the composition and then immersing it in a suitable solidification solution. If necessary, it is also preferable to dry the composition applied on the porous substrate. Alternatively, a film made of the above-mentioned porous membrane may be prepared in advance, and the film and the porous substrate may be laminated together by a method such as lamination. An example of a method for producing a film consisting of the above-mentioned porous membrane is a method in which the composition of the present disclosure is cast onto a film having a smooth surface, such as a polyester film or an aluminum film, and then peeled off.

[0135] The compositions disclosed herein are preferably electrode coating compositions used for coating electrodes of secondary batteries and the like, and are also preferably used to form a film on an electrode. An electrode for a secondary battery having a film formed using the composition of this disclosure is also part of this disclosure.

[0136] The method for forming a film on the electrode is not particularly limited, and conventionally known methods may be employed. Specifically, a method of roll-coating the electrode with the composition of this disclosure, a method of dipping the electrode in the composition, and a method of applying the composition to the electrode and then immersing it in a suitable solidifying solution are preferred. If necessary, it is also preferable to dry the composition applied to the electrode. Alternatively, a film may be prepared in advance from the above composition, and the film and the electrode may be laminated together by a method such as lamination. An example of a method for producing the above-mentioned coating is to cast the composition of this disclosure onto a film having a smooth surface, such as a polyester film or an aluminum film, and then peel it off.

[0137] Preferably, the above-mentioned film is formed on the electrode mixture layer constituting the electrode and / or on the current collector.

[0138] This disclosure also relates to a secondary battery comprising at least one selected from the group consisting of the polymer layer for secondary batteries of this disclosure, the separator for secondary batteries of this disclosure, and the electrode for secondary batteries of this disclosure.

[0139] Examples of secondary batteries in this disclosure include alkali metal ion secondary batteries, with lithium ion secondary batteries, sodium ion secondary batteries, and potassium ion secondary batteries being preferred, lithium ion secondary batteries and sodium ion secondary batteries being more preferred, and lithium ion secondary batteries being even more preferred.

[0140] The above secondary battery can adopt a known structure and typically comprises a positive electrode and a negative electrode capable of intercepting and releasing ions (e.g., lithium ions), and an electrolyte.

[0141] The positive electrode consists of a positive electrode active material layer containing positive electrode active material and a current collector.

[0142] The positive electrode active material is not particularly limited as long as it is capable of electrochemically intercalating and releasing carrier ions such as alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferred. Specific examples include alkali metal-containing transition metal composite oxides, alkali metal-containing transition metal phosphate compounds, sulfur-based materials, and conductive polymers. Among these, alkali metal-containing transition metal composite oxides that produce high voltage are particularly preferred as the positive electrode active material. Examples of the alkali metal ions include lithium ions, sodium ions, and potassium ions. In a preferred embodiment, the alkali metal ions may be lithium ions or sodium ions. That is, in this embodiment, the alkali metal ion secondary battery is a lithium-ion secondary battery or a sodium-ion secondary battery.

[0143] Examples of the alkali metal-containing transition metal composite oxides mentioned above include: Formula: M a Mn 2-b M 1 b O4 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0.9 ≤ a; 0 ≤ b ≤ 1.5; M) 1Alkali metal-manganese spinel composite oxides (such as lithium-manganese spinel composite oxides) are represented by at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. Formula:MNi 1-c M 2 c O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ c ≤ 0.5; M 2 (This refers to an alkali metal-nickel composite oxide (such as a lithium-nickel composite oxide) represented by at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge), or Formula:MCo 1-d M 3 d O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K; 0 ≤ d ≤ 0.5; M 3 Examples include alkali metal-cobalt composite oxides (such as lithium-cobalt composite oxides) represented by at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.

[0144] In particular, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are used because they offer high energy density and can provide high-output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 is preferred, and it is preferable that the compound is represented by the following general formula (3). MNi h Co i Mn j M5 k O2(3) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 5 (This represents at least one element selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, where (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.)

[0145] Examples of the alkali metal-containing transition metal phosphate compounds mentioned above include the following general formula (4): M e M 4 f (PO4) g (4) (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, M 4 A compound represented by ( ) is at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni, and Cu, and satisfies 0.5 ≤ e ≤ 3, 1 ≤ f ≤ 2, and 1 ≤ g ≤ 3. In the above, M is preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li. That is, lithium-containing transition metal phosphate compounds are preferred as the alkali metal-containing transition metal phosphate compounds.

[0146] The transition metals used in the lithium-containing transition metal phosphate compounds are preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and those in which some of the transition metal atoms that make up the main body of these lithium transition metal phosphate compounds are substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si. The lithium-containing transition metal phosphate compounds are preferably those having an olivine-type structure.

[0147] Other positive electrode active materials include lithium-nickel composite oxides. The lithium-nickel composite oxide is defined by the following general formula (5): Li y Ni 1-x M x O2(5) A positive electrode active material represented by the formula (wherein x is 0.01 ≤ x ≤ 0.7, y is 0.9 ≤ y ≤ 2.0, and M represents a metal atom (excluding Li and Ni)) is preferred.

[0148] Other cathode active materials include MFePO4 and MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 Other examples include O2, MV3O6, and M2MnO3. In particular, M2MnO3 and MNi 0.5 Mn 1.5 Positive electrode active materials such as O2 are preferable because their crystalline structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4V or a voltage of 4.6V or higher. Therefore, electrochemical devices such as secondary batteries using positive electrode materials containing the positive electrode active materials exemplified above are preferable because, even when stored at high temperatures, the remaining capacity does not decrease easily, the rate of resistance increase does not change easily, and the battery performance does not deteriorate even when operated at high voltages.

[0149] Other positive electrode active materials include M2MnO3 and MM 6 O2(wherein M is at least one metal selected from the group consisting of Li, Na, and K, M 6 Examples include solid solution materials with transition metals such as Co, Ni, Mn, and Fe.

[0150] Examples of the above solid solution material include the general formula Mx[Mn (1-y) M 7 y ]O z It is an alkali metal manganese oxide represented by the formula. Here, M is at least one metal selected from the group consisting of Li, Na, and K, and M 7It consists of at least one metal element other than M and Mn, and includes, for example, one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, the values of x, y, and z in the formula are in the ranges of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 A manganese-containing solid solution material in which LiNiO2 or LiCoO2 is solid-dissolved based on Li2MnO3 such as Li 1.2 Mn 0.5 Co 0.14 Ni 0.14 O2 is preferable because it can provide an alkali metal ion secondary battery having a high energy density.

[0151] Examples of the sulfur-based material include materials containing sulfur atoms, and at least one selected from the group consisting of elemental sulfur, metal sulfides, and organic sulfur compounds is preferable, and elemental sulfur is more preferable. The metal sulfide may be a metal polysulfide. The organic sulfur compound may be an organic polysulfide.

[0152] Examples of the metal sulfide include compounds represented by LiS x (0 < x ≤ 8); compounds represented by Li2S x (0 < x ≤ 8); compounds having a two-dimensional layered structure such as TiS2 and MoS2; compounds such as Schubert compounds having a strong three-dimensional skeleton structure represented by the general formula Me x Mo6S8 (Me is various transition metals including Pb, Ag, and Cu), etc.

[0153] Examples of the organic sulfur compound include carbon sulfide compounds, etc.

[0154] The organic sulfur compound may be supported on a material having pores such as carbon and used as a carbon composite material. The sulfur content in the carbon composite material is preferably 10 to 99% by mass, more preferably 20% by mass or more, still more preferably 30% by mass or more, particularly preferably 40% by mass or more, and also preferably 85% by mass or less with respect to the carbon composite material because the cycle performance is further excellent and the overvoltage is further reduced. If the positive electrode active material is elemental sulfur, the amount of sulfur contained in the positive electrode active material is equal to the amount of elemental sulfur.

[0155] Examples of conductive polymers include p-doped and n-doped conductive polymers. Other examples of conductive polymers include polyacetylene-based polymers, polyphenylene-based polymers, heterocyclic polymers, ionic polymers, ladder and network polymers, etc.

[0156] Furthermore, including lithium phosphate in the positive electrode active material is preferable because it improves continuous charging characteristics. There are no restrictions on the use of lithium phosphate, but it is preferable to use a mixture of the positive electrode active material and lithium phosphate. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of the positive electrode active material and lithium phosphate, with an upper limit of preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0157] Furthermore, a positive electrode active material may be used in which a substance of a different composition is attached to its surface. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0158] These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent and impregnating them into the positive electrode active material, followed by drying; dissolving or suspending a surface-adhering substance precursor in a solvent and impregnating it into the positive electrode active material, then reacting it by heating or other means; or adding it to the positive electrode active material precursor and simultaneously firing it. When attaching carbon, a method of mechanically attaching carbonaceous material afterwards, such as activated carbon, can also be used.

[0159] The amount of surface-adhered material is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, relative to the positive electrode active material by mass, with a lower limit of preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less. The surface-adhered material can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, thereby improving battery life. However, if the amount of adhesion is too small, the effect will not be fully realized, and if it is too large, it may hinder the movement of lithium ions in and out, potentially increasing resistance.

[0160] The particle shapes of the positive electrode active material can include conventionally used shapes such as lumpy, polyhedral, spherical, ellipsoidal, plate-like, needle-like, and columnar. Furthermore, primary particles may aggregate to form secondary particles.

[0161] The tap density of the positive electrode active material is preferably 0.5 g / cm³. 3 More preferably 0.8 g / cm³ 3 More preferably 1.0 g / cm³ 3 The above is the case. If the tap density of the positive electrode active material falls below the above lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, as does the amount of conductive material and binder required, which may restrict the filling rate of the positive electrode active material into the positive electrode active material layer and thus limit the battery capacity. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. Generally, a higher tap density is preferable, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions using the electrolyte as a medium within the positive electrode active material layer becomes the rate-limiting step, which may lead to a decrease in load characteristics. Therefore, the upper limit is preferably 4.0 g / cm³. 3 More preferably, 3.7 g / cm³ 3 More preferably, 3.5 g / cm³ 3 The following applies: The tap density mentioned above is the powder packing density (tap density) g / cm³ obtained when 5-10 g of positive electrode active material powder is placed in a 10 ml glass graduated cylinder and tapped 200 times with a stroke of approximately 20 mm. 3 We will seek it as follows.

[0162] The median diameter d50 of the positive electrode active material particles (or secondary particle diameter if primary particles aggregate to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more. It is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it falls below the lower limit, it may not be possible to obtain a high-tap density product, and if it exceeds the upper limit, the diffusion of lithium within the particles will take time, which may lead to problems such as a decrease in battery performance. Here, by mixing two or more of the above positive electrode active materials having different median diameters d50, the packing performance during positive electrode fabrication can be further improved.

[0163] The median diameter d50 is measured using a known laser diffraction / scattering particle size distribution analyzer. When using the HORIBA LA-920 as the particle size distribution analyzer, a 0.1% by mass aqueous solution of sodium hexametaphosphate is used as the dispersion medium, and the measurement is performed after ultrasonic dispersion for 5 minutes with the measurement refractive index set to 1.24.

[0164] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more. The upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. Exceeding the upper limit makes it difficult to form spherical secondary particles, which can adversely affect powder packing properties and significantly reduce the specific surface area, potentially leading to a decrease in battery performance such as output characteristics. Conversely, below the lower limit usually results in problems such as poor reversibility of charge and discharge due to underdeveloped crystals. The average primary particle diameter mentioned above is measured by observation using a scanning electron microscope (SEM). Specifically, it is determined by taking a 10,000x magnification photograph, finding the longest value of the intercept between the left and right boundaries of the primary particle relative to a horizontal line for any 50 primary particles, and then taking the average value.

[0165] The BET specific surface area of the positive electrode active material is preferably 0.1 m 2 / g or more, more preferably 0.2 m 2 / g or more, still more preferably 0.3 m 2 / g or more, and the upper limit is preferably 50 m 2 / g or less, more preferably 40 m 2 / g or less, still more preferably 30 m 2 / g or less. If the BET specific surface area is smaller than this range, the battery performance is likely to deteriorate. If it is larger, the tap density is difficult to increase, and problems may easily occur in the processability during the formation of the positive electrode active material layer. The above BET specific surface area is defined as a value measured by the nitrogen adsorption BET one-point method by the gas flow method using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.), with the sample pre-dried at 150 °C for 30 minutes under nitrogen flow, and then using a nitrogen-helium mixed gas accurately adjusted so that the relative pressure value of nitrogen with respect to atmospheric pressure becomes 0.3.

[0166] When the secondary battery of the present disclosure is used as a large lithium-ion secondary battery for hybrid vehicles or distributed power sources, high output is required. Therefore, it is preferable that the particles of the positive electrode active material are mainly secondary particles. The particles of the positive electrode active material preferably contain fine particles with an average particle diameter of the secondary particles of 40 μm or less and an average primary particle diameter of 1 μm or less in a volume percentage of 0.5 to 7.0%. By containing fine particles with an average primary particle diameter of 1 μm or less, the contact area with the electrolyte becomes larger, and the diffusion of lithium ions between the electrode binder and the electrolyte can be made faster. As a result, the output performance of the battery can be improved.

[0167] For the production of positive electrode active materials, general methods for producing inorganic compounds are used. In particular, various methods can be considered for producing spherical or ellipsoidal active materials. For example, a method can be used in which transition metal raw materials are dissolved or pulverized and dispersed in a solvent such as water, the pH is adjusted while stirring to produce and recover spherical precursors, these are dried as needed, and then a Li source such as LiOH, Li2CO3, or LiNO3 is added and calcined at a high temperature to obtain the active material.

[0168] For the manufacture of the positive electrode, the positive electrode active material may be used alone, or two or more materials with different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples include combinations with ternary systems such as O2, combinations of LiCoO2 and LiMn2O4 or a combination in which part of the Mn is substituted with other transition metals, or combinations of LiFePO4 and LiCoO2 or a combination in which part of the Co is substituted with other transition metals.

[0169] The content of the positive electrode active material is preferably 50 to 99.5% by mass of the positive electrode mixture, and more preferably 80 to 99% by mass, in order to achieve high battery capacity. Furthermore, the content in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is too low, the electrical capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0170] The positive electrode active material layer is preferably formed from a positive electrode mixture containing the positive electrode active material.

[0171] The above positive electrode mixture may further contain a binder, a thickener, a conductive material, etc.

[0172] As the binder mentioned above, any material can be used as long as it is safe for the components used in electrode manufacturing, for example, resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, nitrocellulose; rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), ethylene-propylene rubber; styrene-butadiene-styrene block copolymer or its hydrogenated additive; EPDM (ethylene Examples include thermoplastic elastomer polymers such as propylene-diene terpolymer, styrene-ethylene-butadiene-styrene copolymer, styrene-isoprene-styrene block copolymer, or hydrogenated versions thereof; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene-α-olefin copolymer; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymer, and tetrafluoroethylene-ethylene copolymer; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). These may be used individually or in any combination and ratio of two or more types.

[0173] The binder content is typically 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, as a percentage of the binder in the positive electrode active material layer, and is typically 50% by mass or less, preferably 40% by mass or less, more preferably 30% by mass or less, and most preferably 10% by mass or less. If the binder content is too low, the positive electrode active material cannot be sufficiently held, resulting in insufficient mechanical strength of the positive electrode and potentially degrading battery performance such as cycle characteristics. On the other hand, if it is too high, it may lead to a decrease in battery capacity and conductivity.

[0174] Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, polyvinyl pyrrolidone, and salts thereof. It may be used alone or in any combination and ratio of two or more kinds.

[0175] The proportion of the thickener relative to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and is usually in the range of 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If it is below this range, the coating property may be significantly reduced. If it exceeds this range, problems such as a decrease in the proportion of the active material in the positive electrode active material layer, a decrease in the battery capacity, and an increase in the resistance between the positive electrode active materials may occur.

[0176] As the conductive material, known conductive materials can be arbitrarily used. Specific examples include metal materials such as copper, nickel, and gold, graphite (graphite) such as natural graphite and artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerenes, and amorphous carbons such as VGCF. These may be used alone or in any combination and ratio of two or more kinds.

[0177] The conductive material is usually used so as to contain 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more in the positive electrode active material layer, and is usually 5% by mass or less, preferably 3% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0178] When the above positive electrode mixture is made into a slurry, the solvent for forming the slurry is not particularly limited as long as it can dissolve or disperse the positive electrode active material, the conductive material, the binder, and, if necessary, the thickener used. Either an aqueous solvent or an organic solvent may be used. Examples of the aqueous solvent include water, a mixed solvent of alcohol and water, and the like. Examples of the organic solvent include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, and the like.

[0179] The above positive electrode mixture may further contain a thermoplastic resin. Examples of the thermoplastic resin include polyvinylidene fluoride, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polyethylene oxide, and the like. It may be used alone or in combination of two or more in any combination and ratio.

[0180] The proportion of the thermoplastic resin with respect to the positive electrode active material is usually 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and is usually in the range of 3.0% by mass or less, preferably 2.5% by mass or less, more preferably 2.0% by mass or less. By adding the thermoplastic resin, the mechanical strength of the electrode can be improved. Also, if it exceeds this range, problems such as a decrease in the proportion of the positive electrode active material in the electrode mixture and a decrease in the capacity of the battery, or an increase in the resistance between the active materials may occur.

[0181] Suitable materials for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0182] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0183] Furthermore, roughening the surface of the current collector is also preferable from the viewpoint of improving the adhesion between the current collector and the positive electrode active material layer and reducing electrical contact resistance. The surface roughness of the current collector, expressed as Sa (arithmetic mean height), is preferably about 260 nm or more, more preferably about 280 nm or more, and even more preferably about 300 nm or more.

[0184] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver. Carbon is particularly preferred because of its low weight.

[0185] The thickness of the positive electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer, after subtracting the thickness of the metal foil of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0186] The ratio of the thickness of the current collector to the thickness of the positive electrode active material layer is not particularly limited, but the value of (the thickness of the positive electrode active material layer on one side immediately before injecting the electrolytic solution) / (the thickness of the current collector) is preferably 20 or less, more preferably 15 or less, and most preferably 10 or less. Also, it is preferably 0.5 or more, more preferably 0.8 or more, and most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during charge and discharge at a high current density. If it is below this range, the volume ratio of the current collector to the positive electrode active material increases, and the capacity of the battery may decrease.

[0187] The positive electrode can be manufactured by a conventional method. For example, a method can be mentioned in which the above-mentioned positive electrode active material, a binder, a thickener, a conductive material, a solvent, etc. are added to form a slurry-like positive electrode mixture, which is applied to a current collector, dried, and then pressed to increase the density. The above-mentioned densification can be carried out by hand pressing, roller pressing, etc. Also, a method can be mentioned in which a positive electrode mixture sheet is produced by adding the above-mentioned binder, conductive material, etc. to the above-mentioned positive electrode active material, and the positive electrode mixture sheet and the current collector are laminated via an adhesive and vacuum dried.

[0188] The density of the positive electrode active material layer is preferably 1.0 g / cm 3 or more, more preferably 1.3 g / cm 3 or more, still more preferably 1.5 g / cm 3 or more, and also preferably 5 g / cm 3 or less, more preferably 3.80 g / cm 3 or less. If it exceeds this range, the permeability of the electrolytic solution near the current collector / active material interface decreases, and in particular, the charge and discharge characteristics at a high current density may decrease and high output may not be obtained. Also, cracks may easily occur in the positive electrode active material layer. If it is below the above range, the conductivity between the active materials decreases, the battery resistance increases, and high output may not be obtained.

[0189] From the viewpoint of increasing high output and stability at high temperatures, it is preferable that the area of ​​the positive electrode active material layer be large relative to the outer surface area of ​​the battery casing. Specifically, it is preferable that the sum of the positive electrode area relative to the surface area of ​​the secondary battery casing be 15 times or more in area ratio, and more preferably 40 times or more. The outer surface area of ​​the battery casing refers to the total area calculated from the length, width, and thickness of the case portion filled with the power generation elements, excluding the terminal protrusions, in the case of a bottomed rectangular shape. In the case of a bottomed cylindrical shape, it is the geometric surface area approximating the case portion filled with the power generation elements, excluding the terminal protrusions, as a cylinder. The sum of the positive electrode area refers to the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which positive electrode mixture layers are formed on both sides via a current collector foil, it refers to the sum of the areas calculated separately for each surface.

[0190] Furthermore, a positive electrode surface may be fitted with a substance of a different composition. Examples of surface-fitted substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0191] The negative electrode consists of a negative electrode active material layer containing the negative electrode active material and a current collector.

[0192] The negative electrode active material is not particularly limited and includes, for example, metallic materials such as lithium metal; carbonaceous materials such as artificial graphite, graphite carbon fiber, resin-fired carbon, pyrolysis vapor-grown carbon, coke, mesocarbon microbeads (MCMB), furfuryl alcohol resin-fired carbon, polyacene, pitch-based carbon fiber, vapor-grown carbon fiber, natural graphite, and non-graphitizable carbon; silicon-containing compounds such as silicon and silicon alloys; Li4Ti5O 12 Examples include alkali metal-containing metal composite oxide materials and conductive polymers. These may be used individually or in any combination of two or more types. In particular, materials containing at least a portion of carbonaceous material, or silicon-containing compounds, can be used with particular preference.

[0193] The above-mentioned negative electrode active material preferably contains silicon as a constituent element. By including silicon as a constituent element, a high-capacity battery can be manufactured.

[0194] Preferred silicon-containing materials include silicon particles, particles having a structure in which silicon fine particles are dispersed in a silicon-based compound, silicon oxide particles represented by the general formula SiOx (0.5 ≤ x ≤ 1.6), or mixtures thereof. Using these materials makes it possible to obtain a negative electrode mixture for lithium-ion secondary batteries that has higher initial charge-discharge efficiency, higher capacity, and excellent cycle characteristics.

[0195] In this disclosure, silicon oxide refers to a general term for amorphous silicon oxides, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ≤ x ≤ 1.6). x is preferably 0.8 ≤ x < 1.6, and more preferably 0.8 ≤ x < 1.3. This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metallic silicon to produce silicon monoxide gas, which is then cooled and precipitated.

[0196] Particles having a structure in which silicon nanoparticles are dispersed in a silicon-based compound can be obtained, for example, by calcining a mixture of silicon nanoparticles and a silicon-based compound, or by heat-treating silicon oxide particles before disproportionation, represented by the general formula SiOx, in an inert, non-oxidizing atmosphere such as argon at a temperature of 400°C or higher, preferably 800-1,100°C, to carry out a disproportionation reaction. The material obtained by the latter method is particularly preferable because the silicon microcrystals are uniformly dispersed. Through the disproportionation reaction described above, the size of the silicon nanoparticles can be made to 1-100 nm. It is desirable that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is silicon dioxide. Furthermore, it can be confirmed by transmission electron microscopy that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

[0197] The physical properties of the silicon-containing particles can be appropriately selected according to the target composite particles. For example, the average particle size is preferably 0.1 to 50 μm, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. The above average particle size is represented by the weight average particle size in the particle size distribution measurement by the laser diffraction method.

[0198] The BET specific surface area is preferably 0.5 to 100 m 2 / g, more preferably 1 to 20 m 2 / g. If the BET specific surface area is 0.5 m 2 / g or more, there is no risk of deterioration of the adhesiveness when processed into an electrode and deterioration of the battery characteristics. Also, if it is 100 m 2 / g or less, the ratio of silicon dioxide on the particle surface increases, and there is no risk of decrease in battery capacity when used as a negative electrode material for a lithium-ion secondary battery.

[0199] By carbon coating the above silicon-containing particles, conductivity is imparted and improvement in battery characteristics can be observed. As methods for imparting conductivity, there are methods of mixing the above silicon-containing particles with conductive particles such as graphite, methods of coating the surface of the above silicon-containing particles with a carbon film, and methods of combining both. Among them, the method of coating with a carbon film is preferred, and the method of chemical vapor deposition (CVD) is more preferred.

[0200] As the above negative electrode active material, a material containing an alkali metal is also preferred. For a battery using an alkali metal as the negative electrode, temperature adjustment is particularly important in terms of performance and handling properties, and the effect by using the above refrigerant composition can be significantly exhibited. The above alkali metal may be a single alkali metal. As the above alkali metal, at least one selected from the group consisting of lithium, sodium, and potassium is preferred, at least one selected from the group consisting of lithium and sodium is more preferred, and lithium is particularly preferred.

[0201] The content of the above-mentioned negative electrode active material is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 60% by mass or more, in order to increase the volume of the resulting electrode mixture. The upper limit is preferably 99% by mass or less, and more preferably 98% by mass or less.

[0202] The above-mentioned negative electrode active material layer is preferably formed from a negative electrode mixture containing the negative electrode active material.

[0203] The above-mentioned negative electrode mixture may further contain a binder, a thickener, a conductive material, etc.

[0204] Examples of the binders mentioned above include those similar to the binders that can be used for the positive electrode as described above. The ratio of the binder to the negative electrode active material is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 0.6% by mass or more, preferably 20% by mass or less, more preferably 15% by mass or less, even more preferably 10% by mass or less, and particularly preferably 8% by mass or less. If the ratio of the binder to the negative electrode active material exceeds the above range, the proportion of binder that does not contribute to the battery capacity increases, which may lead to a decrease in battery capacity. Also, if it falls below the above range, it may lead to a decrease in the strength of the negative electrode.

[0205] In particular, when a rubbery polymer such as SBR is included as the main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. Furthermore, when a fluorine-based polymer such as polyvinylidene fluoride is included as the main component, the ratio to the negative electrode active material is usually 1% by mass or more, preferably 2% by mass or more, more preferably 3% by mass or more, and usually 15% by mass or less, preferably 10% by mass or less, and more preferably 8% by mass or less.

[0206] Examples of the thickening agents mentioned above include those similar to the thickening agents that can be used in the positive electrode as described above. The ratio of the thickening agent to the negative electrode active material is usually 0.1% by mass or more, preferably 0.5% by mass or more, more preferably 0.6% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, and more preferably 2% by mass or less. If the ratio of the thickening agent to the negative electrode active material falls below the above range, the coating properties may be significantly reduced. If it exceeds the above range, the proportion of negative electrode active material in the negative electrode active material layer decreases, which may lead to problems such as a decrease in battery capacity or an increase in resistance between negative electrode active materials.

[0207] Examples of conductive materials for the negative electrode include metallic materials such as copper and nickel, and carbon materials such as graphite and carbon black.

[0208] When the above-mentioned negative electrode mixture is prepared as a slurry, there are no particular restrictions on the type of solvent used to form the slurry, as long as it is capable of dissolving or dispersing the negative electrode active material, binder, and any thickeners and conductive materials used as needed. Either an aqueous solvent or an organic solvent may be used. Examples of aqueous solvents include water and alcohol, while examples of organic solvents include N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethylacetamide, hexamethylphosphoramide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, and hexane.

[0209] The above-mentioned negative electrode mixture may further contain a thermoplastic resin. Examples of thermoplastic resins include those similar to those that can be used for the positive electrode.

[0210] The ratio of thermoplastic resin to negative electrode active material is typically 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.10% by mass or more, and typically within the range of 3.0% by mass or less, preferably 2.5% by mass or less, and more preferably 2.0% by mass or less. Adding thermoplastic resin can improve the mechanical strength of the electrode. If the ratio exceeds this range, the proportion of electrode active material in the electrode mixture decreases, which may lead to problems such as a decrease in battery capacity or an increase in resistance between active materials.

[0211] Suitable materials for the negative electrode current collector include metals such as copper, nickel, titanium, tantalum, and stainless steel, or their alloys; and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly copper, nickel, or their alloys, are preferred.

[0212] Examples of current collector shapes include metal foil, metal cylinders, metal coils, metal plates, expanded metal, punched metal, and foamed metal in the case of metal materials, and carbon plates, carbon thin films, and carbon cylinders in the case of carbon materials. Of these, metal foil is preferred. The metal foil may be formed into a mesh shape as appropriate. The thickness of the metal foil is arbitrary, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, and more preferably 50 μm or less. If the metal foil is thinner than this range, it may lack the necessary strength as a current collector. Conversely, if the metal foil is thicker than this range, its handling may be impaired.

[0213] Furthermore, roughening the surface of the current collector is also preferable from the viewpoint of improving the adhesion between the current collector and the negative electrode active material layer and reducing electrical contact resistance. The surface roughness of the current collector, expressed as Sa (arithmetic mean height), is preferably about 260 nm or more, more preferably about 280 nm or more, and even more preferably about 300 nm or more.

[0214] Furthermore, it is preferable that a conductive additive is applied to the surface of the current collector, as this reduces the electrical contact resistance between the current collector and the negative electrode active material layer. Examples of conductive additives include carbon and precious metals such as gold, platinum, and silver. Carbon is particularly preferred because of its low weight.

[0215] The negative electrode can be manufactured by conventional methods. For example, one method involves adding the aforementioned binder, thickener, conductive material, solvent, etc., to the negative electrode material to form a slurry, applying it to a current collector, drying it, and then pressing it to increase its density. When using alloy materials, methods such as vapor deposition, sputtering, or plating can be used to form a thin film layer (negative electrode active material layer) containing the aforementioned negative electrode active material. Another method involves adding the aforementioned binder, conductive material, etc., to the negative electrode active material to produce a negative electrode mixture sheet, laminating the negative electrode mixture sheet and the current collector with an adhesive, and then vacuum drying it.

[0216] The density of the negative electrode mixture is preferably 1.0 g / cm³. 3 More preferably 1.2 g / cm³ 3 More preferably 1.3 g / cm³ 3 More preferably, 1.4 g / cm³ 3 In particular, 1.5 g / cm³ is preferred. 3 The above applies, and preferably 2.2 g / cm³. 3 More preferably, 2.1 g / cm³ 3 More preferably, 2.0 g / cm³ 3 More preferably, 1.9 g / cm³ 3 The following is particularly preferred: 1.8 g / cm³ 3 The following range applies. Exceeding this range can cause the negative electrode active material particles to break down, potentially leading to an increase in the initial irreversible capacity and a deterioration in high-current-density charge-discharge characteristics due to reduced electrolyte penetration near the current collector / negative electrode active material interface. It can also make the negative electrode active material layer more prone to cracking. Furthermore, below the above range can reduce conductivity between the active materials, increasing battery resistance and potentially preventing high output power from being achieved.

[0217] The thickness of the negative electrode is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer, after subtracting the thickness of the metal foil of the current collector, is preferably 10 μm or more, more preferably 20 μm or more, and preferably 500 μm or less, and more preferably 450 μm or less, as a lower limit for one side of the current collector.

[0218] Furthermore, a negative electrode with a different composition attached to its surface may also be used. Examples of surface-attached substances include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

[0219] In a secondary battery equipped with electrodes for secondary batteries according to the present disclosure, it is preferable that at least one of the positive electrode and the negative electrode described above is provided with a coating formed using the composition of the present disclosure.

[0220] The secondary battery in this disclosure may be a secondary battery that uses an electrolyte, or it may be a solid-state secondary battery. In this specification, a solid-state secondary battery may be any secondary battery containing a solid electrolyte, and may be a semi-solid secondary battery containing a solid electrolyte and a liquid component as the electrolyte, or an all-solid-state secondary battery containing only a solid electrolyte as the electrolyte.

[0221] The secondary battery using the above-mentioned electrolyte can use the same electrolyte as that used in known secondary batteries. These will be described in detail below.

[0222] A non-aqueous electrolyte is preferably used as the electrolyte. As the non-aqueous electrolyte, a known electrolyte salt dissolved in a known organic solvent for dissolving electrolyte salts can be used.

[0223] The organic solvent for dissolving the electrolyte salt is not particularly limited, but one or more of the following can be used: known hydrocarbon solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; and fluorinated solvents such as fluoroethylene carbonate, fluoroether, and fluorinated carbonate.

[0224] Examples of electrolyte salts include LiClO4, LiAsF6, LiBF4, LiPF6, LiN(SO2CF3)2, and LiN(SO2C2F5)2. LiPF6, LiBF4, LiN(SO2CF3)2, LiN(SO2C2F5)2, or combinations thereof are particularly preferred due to their good cycling properties.

[0225] The concentration of the electrolyte salt is preferably 0.8 mol / liter or higher, and more preferably 1.0 mol / liter or higher. The upper limit depends on the organic solvent used to dissolve the electrolyte salt, but is usually 1.5 mol / liter or lower.

[0226] A secondary battery using the above-mentioned electrolyte is preferably further equipped with a separator. In a secondary battery equipped with the secondary battery separator of this disclosure, it is preferable to use the secondary battery separator of this disclosure described above as the separator.

[0227] The material of the outer casing is not particularly limited as long as it is a stable material for the electrolyte used. Specifically, metals such as nickel-plated steel sheets, stainless steel, aluminum or aluminum alloys, magnesium alloys, or laminated films of resin and aluminum foil can be used. From the viewpoint of weight reduction, aluminum or aluminum alloys or laminated films are preferably used.

[0228] Outer cases using metals may be sealed by welding the metals together using laser welding, resistance welding, or ultrasonic welding, or by using a crimped structure with the metals connected via a resin gasket. Outer cases using laminate film may be sealed by heat-fusing the resin layers together. To improve sealing performance, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when a sealed structure is formed by heat-fusing the resin layers via a current collector terminal, since it is a joint between metal and resin, a resin having polar groups or a modified resin with introduced polar groups is preferably used as the interposing resin.

[0229] The shape of the secondary battery using the above-mentioned electrolyte is arbitrary, and examples include cylindrical, prismatic, laminated, coin-type, and large-sized shapes. The shape and configuration of the positive electrode, negative electrode, and separator can be changed and used according to the shape of each battery.

[0230] The above-mentioned solid-state secondary battery is preferably an all-solid-state secondary battery. The above-mentioned solid-state secondary battery is preferably a lithium-ion battery, and is also preferably a sulfide-based solid-state secondary battery. The above-mentioned solid-state secondary battery preferably comprises a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the positive electrode and the negative electrode.

[0231] The solid electrolyte used in the composite material for solid-state secondary batteries may be either a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, using a sulfide-based solid electrolyte has the advantage of flexibility.

[0232] The above sulfide-based solid electrolytes are not particularly limited and include Li2S-P2S5, Li2S-P2S3, Li2S-P2S3-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiI-Li2S-SiS2-P2S5, Li2S-SiS2-Li4SiO4, Li2S-SiS2-Li3PO4, Li3PS4-Li4GeS4, Li3.4 P 0.6 Si 0.4 S4, Li 3.25 P 0.25 Ge 0.76 S4, Li 4-x Ge 1-x P x S4(x=0.6~0.8), Li 4+y Ge 1-y Ga y S4(y=0.2~0.3), LiPSCl, LiCl, Li 7-x-2y PS 6-x-y Cl x (0.8≦x≦1.7, 0 <y≦-0.25x+0.5)、Li 10 SnP2S 12 Any of the following, or a mixture of two or more, can be used.

[0233] The above sulfide-based solid electrolyte preferably contains lithium. A lithium-containing sulfide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device with high energy density.

[0234] The oxide-based solid electrolyte described above is preferably a compound that contains oxygen atoms (O), has the ionic conductivity of a metal belonging to Group 1 or Group 2 of the periodic table, and is also an electronically insulating compound.

[0235] Specific examples of compounds include, for example, Li xa La ya TiO3 [xa=0.3~0.7, ya=0.3~0.7] (LLT), Li xb La yb Zr zb M bb mb O nb (M bb (The elements are Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn, and xb satisfies 5 ≤ ​​xb ≤ 10, yb satisfies 1 ≤ yb ≤ 4, zb satisfies 1 ≤ zb ≤ 4, mb satisfies 0 ≤ mb ≤ 2, and nb satisfies 5 ≤ ​​nb ≤ 20.) , Li xc Byc M cc zc O nc (M cc (The element is C, S, Al, Si, Ga, Ge, In, Sn, and xc satisfies 0 ≤ xc ≤ 5, yc satisfies 0 ≤ yc ≤ 1, zc satisfies 0 ≤ zc ≤ 1, and nc satisfies 0 ≤ nc ≤ 6.) Li xd (Al,Ga) yd (Ti,Ge) zd Si ad P md O nd (wherein 1≦xd≦3, 0≦yd≦2, 0≦zd≦2, 0≦ad≦2, 1≦md≦7, 3≦nd≦15), Li (3-2xe) M ee xe D ee O(xe represents a number between 0 and 0.1, M ee D represents a divalent metal atom. ee ) represents a halogen atom or a combination of two or more halogen atoms. ), Li xf Si yf O zf (1≦xf≦5, 0 <yf≦3、1≦zf≦10)、Li xg S yg O zg (1 ≤ xg ≤ 3, 0 <yg≦2、1≦zg≦10)、Li3BO3-Li2SO4、Li2O-B2O3-P2O5、Li2O-SiO2、Li6BaLa2Ta2O 12 Li3PO (4-3 / 2w) N w (where w < 1), Li has a LISICON (Lithium superionic conductor) type crystal structure. 3.5 Zn 0.25 La, which has a perovskite crystal structure, is GeO4. 0.51 Li 0.34 TiO 2.94 , La 0.55 Li 0.35 LiTi2P3O has a TiO3, NASICON (Natrium superionic conductor) type crystal structure. 12 Li 1+xh+yh (Al,Ga) xh (Ti,Ge) 2-xhSi yh P 3-yh O 12 (where 0≦xh≦1, 0≦yh≦1), Li7La3Zr2O has a garnet-type crystal structure. 12 Examples include (LLZ). Furthermore, ceramic materials in which elements have been substituted into LLZ are also known. For example, Li, which is partially substituted into LLZ. 6.24 La3Zr2Al 0.24 O 11.98 Li 6.25 Al 0.25 La3Zr2O 12 or Li substituted with Ta 6.6 La3Zr 1.6 Ta 0.4 O 12 Li substituted with Nb 6.75 La3Zr 1.75 Nb 0.25 O 12 Examples include the following. Other examples include LLZ-based ceramic materials in which at least one element, Mg (magnesium) and A (A is at least one element selected from the group consisting of Ca (calcium), Sr (strontium), and Ba (barium)), is substituted into LLZ. Phosphorus compounds containing Li, P, and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON and LiPOD, in which some of the oxygen in lithium phosphate is replaced with nitrogen. 1 (D 1 Examples include at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, etc. Also, LiA 1 ON(A 1 (At least one selected from Si, B, Ge, Al, C, Ga, etc.) can also be preferably used. Specific examples include Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2 and Li2O-Al2O3-SiO2-P2O5-TiO2.

[0236] The above oxide-based solid electrolyte is preferably lithium-containing. A lithium-containing oxide-based solid electrolyte is used in solid-state batteries that use lithium ions as carriers and is particularly preferred in that it is an electrochemical device with high energy density.

[0237] The above oxide-based solid electrolyte is preferably an oxide having a crystalline structure. Oxides having a crystalline structure are particularly preferred in terms of good Li ion conductivity. Examples of oxides having a crystalline structure include perovskite type (La 0.51 Li 0.34 TiO 2.94 etc.), NASICON type (Li 1.3 Al 0.3 Ti 1.7 (PO4)3, garnet type (Li7La3Zr2O 12 Examples include (LLZ, etc.). Among these, the garnet type is preferred.

[0238] The volume-average particle size of oxide-based solid electrolytes is not particularly limited, but is preferably 0.01 μm or larger, and more preferably 0.03 μm or larger. The upper limit is preferably 100 μm or smaller, and more preferably 50 μm or smaller. The average particle size of oxide-based solid electrolyte particles is measured using the following procedure: A 1% by mass dispersion of oxide-based solid electrolyte particles is prepared in a 20 ml sample bottle using water (or heptane if the substance is unstable in water). The diluted dispersion sample is irradiated with 1 kHz ultrasound for 10 minutes and used immediately afterward. Using this dispersion sample, data is acquired 50 times using a laser diffraction / scattering particle size distribution analyzer LA-920 (manufactured by HORIBA) at a temperature of 25°C using a quartz cell to obtain the volume-average particle size. For other detailed conditions, refer to JIS Z 8828:2013 "Particle Size Analysis - Dynamic Light Scattering Method" as needed. Five samples are prepared for each level, and their average value is adopted.

[0239] The above-mentioned solid-state secondary battery may include a separator between the positive electrode and the negative electrode. Examples of the separator include porous membranes such as polyethylene and polypropylene, and nonwoven fabrics such as resin nonwoven fabrics such as polypropylene and glass fiber nonwoven fabrics. It is also preferable to use the secondary battery separator for which this disclosure was disclosed above as the separator for the solid secondary battery described above.

[0240] The above-mentioned solid-state secondary battery may further include a battery case. The shape of the battery case is not particularly limited as long as it can accommodate the positive electrode, negative electrode, solid electrolyte layer, etc., as described above, but specific examples include cylindrical, prismatic, coin-shaped, laminated, etc.

[0241] The above-mentioned solid-state secondary battery can be manufactured, for example, by sequentially stacking a positive electrode, a solid electrolyte layer sheet, and a negative electrode, and then pressing them together.

[0242] Although embodiments have been described above, it should be understood that various modifications to the form and details are possible without departing from the spirit and scope of the claims. [Examples]

[0243] The present disclosure will now be explained with reference to examples, but the present disclosure is not limited to such examples.

[0244] Each physical property was measured using the following method.

[0245] <Polymer composition> Measurements were taken by NMR using the following equipment and conditions. NMR measuring instrument: Manufactured by VARIAN Corporation 1 H-NMR measurement conditions: 400MHz (tetramethylsilane = 0 ppm) 19 F-NMR measurement conditions: 376MHz (trichlorofluoromethane = 0 ppm)

[0246] <Average particle size of polymers> The measurement was performed using dynamic light scattering. Specifically, an aqueous dispersion was prepared with a polymer solids content of approximately 1.0% by mass, and the measurement was performed using an ELSZ-1000S (manufactured by Otsuka Electronics Co., Ltd.) at 25°C for 70 cumulative measurements. The refractive index of the solvent (water) was 1.3328, and the viscosity of the solvent (water) was 0.8878 mPa·s.

[0247] <Melting point of polymers> The obtained dispersion was dried at 40°C, and the resulting solid content was used as the measurement sample. The melting point was measured by differential scanning calorimetry (DSC) in accordance with ASTM D3418. Before measurement, to remove the thermal history of the sample, it was heated above its melting point to completely melt it, and then cooled before being subjected to DSC measurement. The heating and cooling rates were set to 10°C / min.

[0248] <Average particle size of inorganic particles> The measurements were taken using a dynamic light scattering particle detector. Measurement device: NANOTRAC WAVE EX-150 manufactured by NANOTRAC WAVE Corporation Measurement method: Dynamic light scattering method The emulsion to be measured was diluted with pure water to a measurable concentration to prepare the sample, and the measurement was performed at room temperature. The number-average diameter of the obtained data was defined as the average particle size.

[0249] Example 1 <Preparation of Polymer A> 571.4 g of an aqueous dispersion (solid content concentration 45.5% by mass) of VdF / TFE / CTFE copolymer (=61.0 / 19.0 / 20.0 (mass%)) (VTC) particles as a fluorine-containing polymer was placed in a 2.0 L glass separable flask. 37.1 g of Newcol 707SF (manufactured by Nippon Emulsifier Co., Ltd.) and 161.0 g of water were added as emulsifiers and thoroughly mixed to prepare an aqueous dispersion. Next, 109.2 g (98.0% by mass) of methyl methacrylate (MMA), 1.1 g (1.0% by mass) of n-butyl acrylate (n-BA), and 1.1 g (1.0% by mass) of acrylic acid (AA) were added to a 1.0 L glass flask to prepare a monomer solution. The internal temperature of the separable flask was raised to 80°C, and the entire amount of the monomer solution was added to the aqueous dispersion of VdF / TFE / CTFE copolymer particles over 3 hours. Polymerization was carried out while simultaneously adding 20.0 g of ammonium persulfate (APS) (1% by mass aqueous solution) dropwise at 30-minute intervals for seven separate additions. After 5 hours from the start of polymerization, the reaction solution was cooled to room temperature to terminate the reaction, and aqueous dispersion A of polymer A with an average particle size of 155 nm was obtained (solid content concentration 48.0% by mass). The composition of the acrylic polymer portion in the obtained polymer A was MMA / n-BA / AA = 98.0 / 1.0 / 1.0 (mass % ratio). The mass ratio of the fluorine-containing polymer portion to the acrylic polymer portion in the obtained polymer A (fluorine-containing polymer / acrylic polymer) was 70 / 30. Table 1 shows the composition of polymer A in the obtained aqueous dispersion A.

[0250] <Preparation of separator coating compositions and separators for secondary batteries> To the aqueous dispersion A of polymer A obtained above, high-purity alumina powder (Al2O3) (average particle size 0.67 μm) was added as inorganic particles so that polymer A / alumina = 5 / 95 (mass%), and the mixture was mixed using a ball mill at 25°C for 12 hours to obtain a slurry-like coating liquid (separator coating composition) in which alumina was dispersed in an aqueous solvent. The solid content concentration of the slurry-like coating liquid was adjusted to 50% by mass using water. The resulting slurry coating solution was applied to both sides of a porous polyolefin film (polypropylene, 22 μm thick) as a porous substrate using a bar coater (coating amount (porous film amount) 15 g / m²). 2 Next, the film was left to stand in a 90°C oven for 2 hours to evaporate the solvent, thereby obtaining a secondary battery separator in which a polymer A / alumina composite porous film was formed on a polyolefin porous film.

[0251] <Manufacturing of positive electrodes> 97 parts lithium cobalt oxide and 1.5 parts acetylene black were mixed with 1.5 parts of NMP solution of polyvinylidene fluoride (KF7200, manufactured by Kureha Advanced Material Co., Ltd.) as a binder for the positive electrode, in a solid-state equivalent ratio. The mixture was then mixed in a rotating / revolving mixer to obtain a positive electrode slurry. The obtained slurry was coated onto one side of a 22 μm thick aluminum foil, dried with hot air at 120°C for 2 hours, and then roll-pressed to achieve an electrode mixture coating amount of 25 mg / cm². 2 A positive electrode with an electrode density of 3.8 g / cc was obtained.

[0252] <Manufacturing of negative electrodes> 97 parts of artificial graphite were mixed with 1.5 parts of styrene-butadiene rubber as a binder for the negative electrode, and mixed using a planetary mixer. Then, 1.5 parts of carboxymethylcellulose as a thickener and water as a dispersion medium were added to the resulting mixture and mixed further to obtain a negative electrode slurry. The obtained slurry was coated onto one side of an 18 μm thick copper foil, dried with hot air at 100°C for 2 hours, and then roll-pressed to achieve an electrode mixture coating amount of 9.5 mg / cm². 2 A negative electrode with an electrode density of 1.5 g / cc was obtained.

[0253] <Secondary battery> The separator (cut to a size of 7.7cm x 4.6cm), positive electrode (cut to a size of 7.2cm x 4.1cm), and negative electrode (cut to a size of 7.3cm x 4.2cm) obtained above were combined in the order of positive electrode, separator, and negative electrode, and this set was laminated with aluminum film to create a secondary battery (lithium-ion secondary battery).

[0254] Next, a full-cell type lithium-ion secondary battery was manufactured by injecting electrolyte into laminated batteries that had been dried in a 70°C vacuum dryer for more than 12 hours, ensuring no air remained, and then sealing them. The electrolyte used was prepared by dissolving LiPF6 at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 7:3 volume ratio), and then adding 1% by mass of vinylene carbonate (VC). Here, LiPF6, EC, EMC, and VC were battery-grade products manufactured by Kishida Chemical Industries.

[0255] Examples 2-6 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 1, except that the mixing ratio of polymer A and high-purity alumina powder was changed as shown in Table 2.

[0256] Example 7 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 1, except that high-purity alumina powder was not included and the solid content concentration of the slurry coating solution was adjusted to 30% by mass.

[0257] Example 8 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that magnesium oxide powder (MgO) (average particle size 0.54 μm) was used instead of high-purity alumina powder.

[0258] Example 9 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aluminum hydroxide powder (Al(OH)3) (average particle size 1.5 μm) was used instead of high-purity alumina powder.

[0259] Example 10 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion B of polymer B was used instead of aqueous dispersion A of polymer A.

[0260] <Preparation of Polymer B> Seed polymerization was carried out in the same manner as in Example 1, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain aqueous dispersion B of polymer B with an average particle size of 180 nm (solids concentration 48.5% by mass). Table 1 shows the composition of polymer B in the obtained aqueous dispersion B.

[0261] Example 11 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion C of polymer C was used instead of aqueous dispersion A of polymer A.

[0262] <Preparation of Polymer C> Seed polymerization was carried out in the same manner as in Example 1, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain an aqueous dispersion C of polymer C with an average particle size of 201 nm (solids content concentration 47.0% by mass). Table 1 shows the composition of polymer C in the obtained aqueous dispersion C.

[0263] Example 12 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion D of polymer D was used instead of aqueous dispersion A of polymer A.

[0264] <Preparation of Polymer D> Seed polymerization was carried out in the same manner as in Example 1, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain an aqueous dispersion D of polymer D with an average particle size of 165 nm (solids concentration 32.0% by mass). Table 1 shows the composition of polymer D in the obtained aqueous dispersion D.

[0265] Example 13 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion E of polymer (blend) E was used instead of aqueous dispersion A of polymer A.

[0266] <Preparation of Polymer (Blend) E> In a 1.0 L glass flask, 143 g of water was placed, and in a separate 1.0 L container, 117 g of water, 145 g of methyl methacrylate (MMA) (58.0% by mass), 87.5 g of n-butyl acrylate (n-BA) (35.0% by mass), 5.0 g of acrylic acid (AA) (2.0% by mass), 12.5 g of γ-methacryloxypropyltriethoxysilane (5.0% by mass), and 7.1 g of Newcol 707SF (manufactured by Nippon Emulsifier Co., Ltd.) were added and thoroughly mixed to prepare a monomer emulsion dispersion solution by mechanical emulsification. The internal temperature of the separable flask was raised to 80°C, and the entire amount of the monomer emulsion dispersion solution was added over 5 hours. Polymerization was carried out while simultaneously adding the entire amount of 25.0 g of ammonium persulfate (APS) (10% by mass aqueous solution) over 5 hours. Five hours after the start of polymerization, the reaction solution was cooled to room temperature to terminate the reaction, and a neutralizing agent was added to obtain an aqueous dispersion of acrylic copolymer with a pH of 7 and an average particle size of 180 nm (solid content concentration 47.0% by mass). Next, 500g of deionized water and an appropriate amount of surfactant were placed in a 2L stainless steel autoclave, and the system was thoroughly purged with nitrogen gas before the pressure was reduced. Subsequently, a mixed monomer of VdF / TFE / CTFE (=61.0 / 19.0 / 20.0 mass%) was injected into the polymerization tank under pressure so that the system pressure was 0.58~0.63 MPa, and the temperature was raised to 70°C. Then, an appropriate amount of polymerization initiator and continuous transfer agent were injected under pressure with nitrogen gas, and the reaction was started while stirring. As polymerization progressed and the internal pressure began to decrease, a VdF / TFE / CTFE mixed monomer (=61.0 / 19.0 / 20.0 mass%) was supplied to maintain an internal pressure of 0.58-0.63 MPa. After the predetermined amount had been charged from the start of polymerization, the autoclave was cooled, and 12 g of Newcol 707SF (manufactured by Nippon Emulsifier Co., Ltd.) and a neutralizing agent were added to obtain an aqueous dispersion of a fluorine-containing polymer with a pH of 7 and an average particle size of 125 nm (solid content concentration 45.5 mass%). In a 0.5L container, 106.4g (solid content concentration 47.0% by mass) of the above-mentioned acrylic copolymer aqueous dispersion and 109.9g (solid content concentration 45.5% by mass) of the fluorine-containing polymer aqueous dispersion were thoroughly mixed to obtain aqueous dispersion E. Table 1 shows the composition of polymer (blend) E in the obtained aqueous dispersion E.

[0267] Comparative Example 1 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion F of polymer F was used instead of aqueous dispersion A of polymer A.

[0268] <Preparation of Polymer F> 500g of deionized water and an appropriate amount of surfactant were placed in a 2L stainless steel autoclave. After thoroughly replacing the system with nitrogen gas, the pressure was reduced. Next, a VdF / TFE (=78.0 / 22.0 mass%) mixed monomer was injected into the polymerization tank under pressure so that the system pressure was 0.58~0.63 MPa, and the temperature was raised to 70°C. Then, an appropriate amount of polymerization initiator and continuous transfer agent were injected under pressure with nitrogen gas, and the reaction was started while stirring. When the internal pressure began to decrease as polymerization progressed, the VdF / TFE mixed monomer (=78.0 / 22.0 mass%) was supplied to maintain the internal pressure at 0.58~0.63 MPa. After the predetermined amount had been added since the start of polymerization, the autoclave was cooled to obtain an aqueous dispersion F of polymer F with a solid content of 20.5 mass% and an average particle size of 120 nm. Table 1 shows the composition of polymer F in the obtained aqueous dispersion F.

[0269] Comparative Example 2 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by following the same procedure as in Example 3, except that aqueous dispersion G of polymer G was used instead of aqueous dispersion A of polymer A.

[0270] <Preparation of Polymer G> Seed polymerization was carried out in the same manner as in Example 1, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain an aqueous dispersion G of polymer G with an average particle size of 120 nm (solid content concentration 27.2% by mass). Table 1 shows the composition of polymer G in the obtained aqueous dispersion G.

[0271] Comparative Example 3 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion H of polymer H was used instead of aqueous dispersion A of polymer A.

[0272] <Preparation of Polymer H> Seed polymerization was carried out in the same manner as in Example 1, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain aqueous dispersion H of polymer H with an average particle size of 112 nm (solids concentration 20.8% by mass). Table 1 shows the composition of polymer H in the obtained aqueous dispersion H.

[0273] Comparative Example 4 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 7, except that aqueous dispersion H of polymer H was used instead of aqueous dispersion A of polymer A.

[0274] Example 14 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion I of polymer I was used instead of aqueous dispersion A of polymer A.

[0275] <Preparation of Polymer I> Seed polymerization was carried out in the same manner as for polymer F, except that the type and amount of monomers were changed to achieve the composition shown in Table 1, to obtain aqueous dispersion I of polymer I with an average particle size of 120 nm (solids content concentration 45.5% by mass). Table 1 shows the composition of polymer I in the obtained aqueous dispersion I. The melting point of polymer I was 89°C.

[0276] Example 15 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 7, except that aqueous dispersion I of polymer I was used instead of aqueous dispersion A of polymer A.

[0277] Example 16 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 3, except that aqueous dispersion J of polymer J was used instead of aqueous dispersion A of polymer A.

[0278] <Preparation of Polymer J> 200g of deionized water was placed in a 2L stainless steel autoclave, and the system was thoroughly purged with nitrogen gas before the pressure was reduced. Next, a VdF / TFE / CTFE (=84.0 / 5.0 / 11.0 mass%) mixed monomer was injected into the polymerization tank under pressure to achieve a system pressure of 0.5 MPa, and the temperature was raised to 80°C. Then, an appropriate amount of polymerization initiator was injected under pressure with nitrogen gas, and the reaction was started while stirring. As polymerization progressed and the internal pressure began to decrease, the VdF / TFE / CTFE (=84.0 / 5.0 / 11.0 mass%) mixed monomer was supplied to maintain an internal pressure of 0.75-0.80 MPa. After the predetermined amount had been charged since the start of polymerization, the autoclave was cooled to obtain an aqueous dispersion J of polymer J with a solid content of 10.0 mass% and an average particle size of 120 nm. The composition of polymer J in the obtained aqueous dispersion J is shown in Table 1. The melting point of polymer J was 128°C.

[0279] Example 17 A separator coating composition, a separator for a secondary battery, and a secondary battery were manufactured by performing the same procedure as in Example 7, except that aqueous dispersion J of polymer J was used instead of aqueous dispersion A of polymer A.

[0280] [Table 1]

[0281] In Table 1, "fluorine-containing polymer" and "acrylic polymer" for a single polymer refer to the "fluorine-containing polymer portion" and the "acrylic polymer portion," respectively. Furthermore, the abbreviations in Table 1 are as follows: MMA: Methyl methacrylate n-BA:n-butyl acrylate n-MBA:n-butyl methacrylate CHMA: Cyclohexyl methacrylate MAA: Methacrylic acid AA: Acrylic acid GMA: Glycidyl methacrylate

[0282] The separator coating compositions used in Examples 1-17 and Comparative Examples 1-4, as well as the resulting secondary battery separators and secondary batteries, were evaluated as described below. The results are shown in Table 2.

[0283] <Evaluation of dispersion stability of separator coating compositions> The slurry-like coating solution (separator coating composition) obtained in each experimental example was stored at 25°C for 5 days. After storage, the supernatant of the slurry-like coating solution was taken, placed in an aluminum cup, and dried at 150°C for 2 hours. The mass of the residue was measured, and the solid content concentration of the supernatant after storage was determined.

[0284] <Evaluation of output characteristics (rate characteristics) of secondary batteries> A lithium-ion secondary battery placed in a constant temperature bath at 25°C was charged to 4.35V using the constant current-constant voltage method at a rate of 0.2C-0.05C, and then discharged to 3V using the constant current method at 0.2C to determine the 0.2C discharge capacity. Next, the battery was charged to 4.35V using the constant current-constant voltage method at a rate of 0.2C-0.05C, and then discharged to 3V using the constant current method at 5.0C to determine the 5.0C discharge capacity. The average value of 5 cells was used as the measured value, and the output characteristics (rate characteristics) were evaluated from the value expressed as the ratio of the 5.0C discharge capacity to the 0.2C discharge capacity (5.0C discharge capacity / 0.2C discharge capacity (%)).

[0285] <Evaluation of cycle characteristics of secondary batteries at high temperatures> Lithium-ion secondary batteries placed in a 60°C constant temperature bath were subjected to 200 cycles of alternating constant current-constant voltage charging at a 1C-0.05C rate and constant current discharge at a 1C rate within a voltage range of 4.35V to 3.0V. High-temperature cycle characteristics were evaluated from the ratio of the discharge capacity at cycle 1 to the discharge capacity at cycle 200 (discharge capacity at cycle 200 / discharge capacity at cycle 1 (%)).

[0286] [Table 2]

[0287] The abbreviations in Table 2 are as follows: X:Al2O3 Y:MgO Z:Al(OH)3

Claims

1. A battery material composition comprising (i) a fluorine-containing polymer (A) containing polymerization units based on vinylidene fluoride and polymerization units based on tetrafluoroethylene and an acrylic polymer (B), or (ii) a copolymer (C) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on acrylic monomer, or (iii) a copolymer (D) containing polymerization units based on vinylidene fluoride, polymerization units based on tetrafluoroethylene and polymerization units based on chlorotrifluoroethylene.

2. Furthermore, the battery material composition according to claim 1 further comprises at least one inorganic particle selected from the group consisting of metal oxide particles and metal hydroxide particles.

3. The battery material composition according to claim 2, wherein the inorganic particles are at least one selected from the group consisting of aluminum oxide, magnesium oxide, and aluminum hydroxide.

4. The battery material composition according to claim 2 or 3, wherein the content of the inorganic particles is 20 to 99% by mass of the solid content of the battery material composition.

5. The fluorine-containing polymer (A) is at least one selected from the group consisting of vinylidene fluoride / tetrafluoroethylene / chlorotrifluoroethylene copolymer and vinylidene fluoride / tetrafluoroethylene copolymer. The battery material composition according to claim 1 or 2, wherein the acrylic polymer (B) is at least one selected from the group consisting of an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer copolymer, an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / an epoxy group-containing acrylic monomer copolymer, and an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / an alkyl acrylate ester having 1 to 10 C1 of the alkyl group / a carboxyl group-containing acrylic monomer / a silyl group-containing acrylic monomer copolymer.

6. The copolymer (C) comprises a fluorine-containing polymer portion (A') containing polymerization units based on vinylidene fluoride and polymerization units based on tetrafluoroethylene, and an acrylic polymer portion (B') containing polymerization units based on acrylic monomer. The fluorine-containing polymer portion (A') is at least one selected from the group consisting of vinylidene fluoride / tetrafluoroethylene / chlorotrifluoroethylene copolymer and vinylidene fluoride / tetrafluoroethylene copolymer. The battery material composition according to claim 1 or 2, wherein the acrylic polymer portion (B') is at least one selected from the group consisting of an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer copolymer, an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / epoxy group-containing acrylic monomer copolymer, and an alkyl methacrylate ester having 1 to 10 C1 of the alkyl group / alkyl acrylate ester having 1 to 10 C1 of the alkyl group / carboxyl group-containing acrylic monomer / silyl group-containing acrylic monomer copolymer.

7. A battery material composition according to claim 1 or 2, used to form a layer between the electrodes and separator of a secondary battery.

8. A battery material composition according to claim 1 or 2, which is for use as a separator coating.

9. A battery material composition according to claim 1 or 2, which is for electrode coating.

10. A polymer layer for a secondary battery, formed using the battery material composition described in claim 7, and provided between the electrodes and separator of a secondary battery.

11. A separator for a secondary battery comprising a porous substrate and a porous membrane formed on the porous substrate using the battery material composition according to claim 8.

12. An electrode for a secondary battery comprising a film formed using the battery material composition described in claim 9.

13. A secondary battery comprising at least one selected from the group consisting of a polymer layer for secondary batteries according to claim 10, a separator for secondary batteries according to claim 11, and an electrode for secondary batteries according to claim 12.

14. The secondary battery according to claim 13, which is a lithium-ion secondary battery.

Images