Coated negative electrode active material particles for lithium-ion batteries, negative electrode for lithium-ion batteries, and method for manufacturing coated negative electrode active material particles for lithium-ion batteries

Abstract

To provide a coated negative electrode active material particle for lithium-ion battery, capable of preventing an internal resistance value of a lithium-ion battery by suppressing side reaction generated between electrolyte and a coated negative electrode active material particle.SOLUTION: A coated negative electrode active material particle for lithium-ion battery is a coated negative electrode active material particle for lithium-ion battery in which at least a part of a negative electrode active material particle surface is covered with a coated layer. The coated layer includes a polymer compound, a conductive assistant and a ceramic particle.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated negative electrode active material particles for lithium-ion batteries, a negative electrode for lithium-ion batteries, and a method for producing coated negative electrode active material particles for lithium-ion batteries. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions for environmental protection. The automotive industry is hoping that the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) will reduce carbon dioxide emissions, and the development of secondary batteries for motor drives, which are key to the practical application of these vehicles, is being actively pursued. Among secondary batteries, lithium-ion batteries, which can achieve high energy density and high power density, are attracting attention.

[0003] For example, Patent Document 1 discloses a polymer of a monomer composition comprising an ester compound of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid and an anionic monomer, wherein the polymer has an acid value of 30 to 700, and a coated active material having a coating layer comprising the above-mentioned active material coating resin composition on at least a part of the surface of the active material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-160294 [Overview of the project] [Problems that the invention aims to solve]

[0005] Lithium-ion batteries are now widely used in a variety of applications, including, for example, in high-temperature environments. Conventional lithium-ion batteries using coating active materials have a problem in that when used in high-temperature environments, side reactions can occur between the electrolyte and the coating active material, causing the lithium-ion battery to degrade (specifically, its internal resistance increases), and there was room for improvement.

[0006] The present invention aims to provide coated negative electrode active material particles for lithium-ion batteries that can suppress side reactions occurring between the electrolyte and coated negative electrode active material particles, even when used in high-temperature environments, thereby preventing an increase in the internal resistance of the lithium-ion battery. The present invention also aims to provide a negative electrode for lithium-ion batteries containing the above-mentioned coated negative electrode active material particles, and a method for manufacturing the above-mentioned coated negative electrode active material particles for lithium-ion batteries. [Means for solving the problem]

[0007] As a result of diligent research to solve the above problems, the present inventors have found that by forming a coating layer containing a polymer compound, a conductive additive, and ceramic particles on the surface of the negative electrode active material particles, side reactions occurring between the electrolyte and the coated negative electrode active material particles can be suppressed, thereby preventing an increase in the internal resistance of the lithium-ion battery, and thus arrived at the present invention.

[0008] In other words, the present invention relates to coated negative electrode active material particles for lithium-ion batteries in which at least a portion of the surface of the negative electrode active material particles is coated with a coating layer, wherein the coating layer comprises a polymer compound, a conductive additive, and ceramic particles; a negative electrode for lithium-ion batteries comprising the coated negative electrode active material particles, wherein the weight percentage of the polymer compound contained in the negative electrode for lithium-ion batteries is 1 to 10% by weight based on the weight of the negative electrode for lithium-ion batteries; a negative electrode for lithium-ion batteries comprising a negative electrode active material layer comprising the coated negative electrode active material particles and an electrolyte containing an electrolyte and a solvent, wherein the negative electrode active material layer consists of an unbound form of the coated negative electrode active material particles for lithium-ion batteries; and a method for producing coated negative electrode active material particles for lithium-ion batteries, comprising a step of desolving after mixing the negative electrode active material particles, a polymer compound, a conductive additive, ceramic particles, and an organic solvent. [Effects of the Invention]

[0009] According to the present invention, it is possible to obtain coated negative electrode active material particles for lithium-ion batteries that can suppress side reactions occurring between the electrolyte and coated negative electrode active material particles, thereby preventing an increase in the internal resistance of the lithium-ion battery. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a graph showing the relationship between the storage time and internal resistance value of lithium-ion batteries obtained in each example and comparative example. [Modes for carrying out the invention]

[0011] [Active material particles for coated negative electrodes of lithium-ion batteries] The coated negative electrode active material particles for lithium-ion batteries of the present invention (hereinafter also simply referred to as "coated negative electrode active material particles") are coated negative electrode active material particles in which at least a part of the surface of the negative electrode active material particle is coated with a coating layer, wherein the coating layer comprises a polymer compound, a conductive additive, and ceramic particles. In the coated negative electrode active material particles of the present invention, since the coating layer contains a polymer compound, a conductive assistant, and ceramic particles, side reactions occurring between the electrolytic solution and the coated negative electrode active material particles can be suppressed, and an increase in the internal resistance value of the lithium ion battery can be prevented.

[0012] Examples of the negative electrode active material particles include carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, resin sintered bodies (such as those obtained by sintering and carbonizing phenolic resins and furan resins, etc.), cokes (such as pitch coke, needle coke, and petroleum coke, etc.), and carbon fibers, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (those obtained by coating the surface of carbon particles with silicon and / or silicon carbide, those obtained by coating the surface of silicon particles or silicon oxide particles with carbon and / or silicon carbide, and silicon carbide, etc.), and silicon alloys (such as silicon-aluminum alloys, silicon-lithium alloys, silicon-nickel alloys, silicon-iron alloys, silicon-titanium alloys, silicon-manganese alloys, silicon-copper alloys, and silicon-tin alloys, etc.), etc.], conductive polymers (such as polyacetylene and polypyrrole, etc.), metals (such as tin, aluminum, zirconium, and titanium, etc.), metal oxides (such as titanium oxides and lithium titanium oxides, etc.), and metal alloys (such as lithium-tin alloys, lithium-aluminum alloys, and lithium-aluminum-manganese alloys, etc.), etc., and mixtures of these with carbon-based materials, etc. Among the above negative electrode active material particles, those that do not contain lithium or lithium ions inside may be subjected to a pre-doping treatment in which a part or all of the negative electrode active material particles are made to contain lithium or lithium ions in advance.

[0013] From the perspective of the electrical characteristics of the battery, the volume average particle diameter of the negative electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 60 μm, and even more preferably 2 to 40 μm.

[0014] In this specification, the volume-average particle diameter refers to the particle size at 50% of the integrated value in the particle size distribution determined by the microtrac method (laser diffraction / scattering method) (Dv50). The microtrac method is a method for determining the particle size distribution using scattered light obtained by irradiating particles with laser light. For measuring the volume-average particle diameter, a microtrac manufactured by Nikkiso Co., Ltd. or similar can be used.

[0015] The coating layer contains a polymer compound, a conductive additive, and ceramic particles. The polymer compound is preferably a resin containing a polymer in which acrylic monomer (a) is an essential constituent monomer. Specifically, the polymer compound constituting the coating layer is preferably a polymer of a monomer composition containing acrylic acid (a0) as the acrylic monomer (a). In the above monomer composition, from the viewpoint of the flexibility of the coating layer, the content of acrylic acid (a0) is preferably 90% or more and 95% or less by weight, based on the total weight of the monomer.

[0016] The polymer compound constituting the coating layer may contain, as the acrylic monomer (a), a monomer (a1) having a carboxyl group or an acid anhydride group other than acrylic acid (a0).

[0017] Examples of monomers (a1) having a carboxyl group or acid anhydride group other than acrylic acid (a0) include monocarboxylic acids with 3 to 15 carbon atoms such as methacrylic acid, crotonic acid, and cinnamic acid; dicarboxylic acids with 4 to 24 carbon atoms such as maleic anhydride, fumaric acid, itaconic anhydride, citraconic acid, and mesaconic acid; and polycarboxylic acids with 6 to 24 carbon atoms and a valency of 3 to 4 or higher, such as aconitic acid.

[0018] The polymer compound constituting the coating layer may contain, as acrylic monomer (a), monomer (a2) represented by the following general formula (1). CH2=C(R 1 )COOR 2 (1) [In formula (1), R 1R is a hydrogen atom or a methyl group, 2 This is a linear alkyl group with 4 to 12 carbon atoms or a branched alkyl group with 3 to 36 carbon atoms.

[0019] In the monomer (a2) represented by the above general formula (1), R 1 R represents a hydrogen atom or a methyl group. 1 It is preferable that it be a methyl group. R 2 It is preferable that the element is a linear or branched alkyl group having 4 to 12 carbon atoms, or a branched alkyl group having 13 to 36 carbon atoms.

[0020] (a21)R 2 Ester compounds in which C4 is a linear or branched alkyl group having 4 to 12 carbon atoms. Examples of linear alkyl groups having 4 to 12 carbon atoms include butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl groups. Branched alkyl groups with 4 to 12 carbon atoms include 1-methylpropyl group (sec-butyl group), 2-methylpropyl group, 1,1-dimethylethyl group (tert-butyl group), 1-methylbutyl group, 1,1-dimethylpropyl group, 1,2-dimethylpropyl group, 2,2-dimethylpropyl group (neopentyl group), 1-methylpentyl group, 2-methylpentyl group, 3-methylpentyl group, 4-methylpentyl group, 1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 1,3-dimethylbutyl group, 2,2-dimethylbutyl group, 2, 3-dimethylbutyl group, 1-ethylbutyl group, 2-ethylbutyl group, 1-methylhexyl group, 2-methylhexyl group, 2-methylhexyl group, 4-methylhexyl group, 5-methylhexyl group, 1-ethylpentyl group, 2-ethylpentyl group, 3-ethylpentyl group, 1,1-dimethylpentyl group, 1,2-dimethylpentyl group, 1,3-dimethylpentyl group, 2,2-dimethylpentyl group, 2,3-dimethylpentyl group, 2-ethylpentyl group, 1-methylheptyl group, 2-methylheptyl group, 3-methylheptyl group, 4-methyl Tylheptyl group, 5-methylheptyl group, 6-methylheptyl group, 1,1-dimethylhexyl group, 1,2-dimethylhexyl group, 1,3-dimethylhexyl group, 1,4-dimethylhexyl group, 1,5-dimethylhexyl group, 1-ethylhexyl group, 2-ethylhexyl group, 1-methyloctyl group, 2-methyloctyl group, 3-methyloctyl group, 4-methyloctyl group, 5-methyloctyl group, 6-methyloctyl group, 7-methyloctyl group, 1,1-dimethylheptyl group, 1,2-dimethylheptyl group, 1,3-dimethyl Heptyl group, 1,4-dimethylheptyl group, 1,5-dimethylheptyl group, 1,6-dimethylheptyl group, 1-ethylheptyl group, 2-ethylheptyl group, 1-methylnonyl group, 2-methylnonyl group, 3-methylnonyl group, 4-methylnonyl group, 5-methylnonyl group, 6-methylnonyl group, 7-methylnonyl group, 8-methylnonyl group, 1,1-dimethyloctyl group, 1,2-dimethyloctyl group, 1,3-dimethyloctyl group, 1,4-dimethyloctyl group, 1,5-dimethyloctyl group, 1,6-dimethyloctyl group, 1,7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyldecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1,1-dimethylnonyl group, 1,2-dimethylnonyl group, 1,3-dimethylnonyl group, 1,4-dimethylnonyl group, 1,5-dimethylnonyl group, 1,6-dimethylnonyl group, 1,7-dimethylnonyl group, 1,8-dimethylnonyl group, 1-ethylnonyl group, 2-ethylnonyl group, 1-methylundecyl group, 2-methylundecyl group, 3-methylundecyl group, 4-methylundecyl group, 5-methylundecyl group, 6-methylundecyl group, 7-methylundecyl group, 8-methylundecyl group, 9-methylundecyl group, 10-methylundecyl group, 1,1-dimethyldecyl group, 1,2-dimethyldecyl group, 1,3-dimethyldecyl group, 1,4-dimethyldecyl group, 1,5-dimethyldecyl group, 1,6-dimethyldecyl group, 1,7-dimethyldecyl group, 1,8-dimethyldecyl group, 1,9-dimethyldecyl group, 1-ethyldecyl group, 2-ethyldecyl group, etc. are exemplified. Among these, particularly, 2-ethylhexyl group is preferable.,

[0021] (a22)R 2 an ester compound in which R is a branched alkyl group having 13 to 36 carbon atoms Branched alkyl groups with 13 to 36 carbon atoms include 1-alkylalkyl groups [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyloctadecyl group, 1-octylhexadecyl group, 1-decyltetradecyl group, 1-undecyltridecyl group, etc.], and 2-alkylalkyl groups [2-methyldodecyl group, 2-hexyloctadecyl group, 2-octylhexadecyl group, 2-decyltetradecyl group, 2-undecyltridecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2-decyloctadecyl group, 2-tetradecyloctadecyl group, 2-hexadecyloctadecyl group, 2-tetradecyleicosyl Examples include groups such as 2-hexadecyleicosyl groups, 3-34-alkylalkyl groups (3-alkylalkyl groups, 4-alkylalkyl groups, 5-alkylalkyl groups, 32-alkylalkyl groups, 33-alkylalkyl groups, and 34-alkylalkyl groups), and mixed alkyl groups containing one or more branched alkyl groups, such as residues obtained by removing hydroxyl groups from oxo alcohols obtained from propylene oligomers (7-11 units), ethylene / propylene (molar ratio 16 / 1-1 / 11) oligomers, isobutylene oligomers (7-8 units), and α-olefin (5-20 carbon atoms) oligomers (4-8 units).

[0022] The polymer compound constituting the coating layer may contain, as acrylic monomer (a), an ester compound (a3) ​​of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth)acrylic acid. Examples of monovalent aliphatic alcohols having 1 to 3 carbon atoms that constitute the ester compound (a3) ​​include methanol, ethanol, 1-propanol, and 2-propanol. Note that (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0023] The polymer compound constituting the coating layer is preferably a polymer of a monomer composition comprising acrylic acid (a0) and at least one of monomer (a1), monomer (a2), and ester compound (a3); more preferably a polymer of a monomer composition comprising acrylic acid (a0) and at least one of monomer (a1), ester compound (a21), and ester compound (a3); even more preferably a polymer of a monomer composition comprising acrylic acid (a0) and any one of monomer (a1), monomer (a2), and ester compound (a3); and most preferably a polymer of a monomer composition comprising acrylic acid (a0) and any one of monomer (a1), ester compound (a21), and ester compound (a3). Examples of polymer compounds constituting the coating layer include a copolymer of acrylic acid and maleic acid using maleic acid as monomer (a1), a copolymer of acrylic acid and 2-ethylhexyl methacrylate using 2-ethylhexyl methacrylate as monomer (a2), and a copolymer of acrylic acid and methyl methacrylate using methyl methacrylate as ester compound (a3).

[0024] The total content of monomer (a1), monomer (a2), and ester compound (a3) ​​is preferably 2.0 to 9.9% by weight, and more preferably 2.5 to 7.0% by weight, based on the total weight of the monomers, from the viewpoint of suppressing volume changes of the negative electrode active material particles.

[0025] The polymer compound constituting the coating layer preferably does not contain an anionic monomer salt (a4) having a polymerizable unsaturated double bond and an anionic group as the acrylic monomer (a).

[0026] Examples of structures having polymerizable unsaturated double bonds include vinyl groups, allyl groups, styrenyl groups, and (meth)acryloyl groups. Examples of anionic groups include sulfonic acid groups and carboxyl groups. Anionic monomers, which have polymerizable unsaturated double bonds and anionic groups, are compounds obtained by combining these, and examples include vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, and (meth)acrylic acid. Note that (meth)acryloyl group refers to either an acryloyl group or a methacryloyl group. Examples of cations constituting the salt (a4) of anionic monomers include lithium ions, sodium ions, potassium ions, and ammonium ions.

[0027] Furthermore, the polymer compound constituting the coating layer may contain, to the extent that it does not impair the physical properties, a radical polymerizable monomer (a5) as the acrylic monomer (a), which can copolymerize with acrylic acid (a0), monomer (a1), monomer (a2), and ester compound (a3). As the radical polymerizable monomer (a5), monomers that do not contain active hydrogen are preferred, and the monomers listed below (a51) to (a58) can be used.

[0028] (a51) Hydrocarbyl (meth)acrylate formed from a linear aliphatic monool with 13-20 carbon atoms, an alicyclic monool with 5-20 carbon atoms, or an aromatic aliphatic monool with 7-20 carbon atoms and (meth)acrylic acid. Examples of the above monools include (i) linear aliphatic monools (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecyl alcohol, arachidyl alcohol, etc.), (ii) alicyclic monools (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol, etc.), (iii) aromatic aliphatic monools (benzyl alcohol, etc.), and mixtures of two or more of these.

[0029] (a52) Poly(n=2~30) oxyalkylene (2~4 carbon atoms) alkyl (1~18 carbon atoms) ether (meth)acrylate [meth)acrylate of methanol ethylene oxide (hereinafter abbreviated as EO), meth)acrylate of methanol propylene oxide (hereinafter abbreviated as PO), etc.]

[0030] (a53) Nitrogen-containing vinyl compounds (a53-1) Amide group-containing vinyl compound (i) (meth)acrylamide compounds having 3 to 30 carbon atoms, such as N,N-dialkyl (1 to 6 carbon atoms) or dialkyl (7 to 15 carbon atoms) (meth)acrylamide (N,N-dimethylacrylamide, N,N-dibenzylacrylamide, etc.), and diacetone acrylamide. (ii) Vinyl compounds containing amide groups with 4 to 20 carbon atoms, excluding the (meth)acrylamide compounds mentioned above, such as N-methyl-N-vinylacetamide and cyclic amides [pyrrolidone compounds (with 6 to 13 carbon atoms, such as N-vinylpyrrolidone)].

[0031] (a53-2) (meth)acrylate compound (i) Dialkyl (C1-C4) aminoalkyl (C1-C4) (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, etc.] (ii) Quaternary ammonium group-containing (meth)acrylates {quaternary amino group-containing (meth)acrylates [N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.] (quaternary products obtained by quaternizing using quaternizing agents such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate, etc.)}

[0032] (a53-3) Heterocyclic vinyl compounds Pyridine compounds (7-14 carbon atoms, e.g., 2- or 4-vinylpyridine), imidazole compounds (5-12 carbon atoms, e.g., N-vinylimidazole), pyrrole compounds (6-13 carbon atoms, e.g., N-vinylpyrrole), pyrrolidone compounds (6-13 carbon atoms, e.g., N-vinyl-2-pyrrolidone)

[0033] (a53-4) Nitrile group-containing vinyl compound Vinyl compounds containing nitrile groups with 3 to 15 carbon atoms, such as (meth)acrylonitrile, cyanostyrene, and cyanoalkyl (1 to 4 carbon atoms) acrylates.

[0034] (a53-5) Other nitrogen-containing vinyl compounds Nitro group-containing vinyl compounds (8-16 carbon atoms, e.g., nitrostyrene), etc.

[0035] (a54) Vinyl hydrocarbons (a54-1) Aliphatic vinyl hydrocarbons Olefins with 2 to 18 or more carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), dienes with 4 to 10 or more carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.), etc.

[0036] (a54-2) Alicyclic vinyl hydrocarbons Cyclic unsaturated compounds with 4 to 18 or more carbon atoms, such as cycloalkenes (e.g., cyclohexene), (di)cycloalkadienes [e.g., (di)cyclopentadiene], terpenes (e.g., pinene and limonene), and indene.

[0037] (a54-3) Aromatic vinyl hydrocarbons Aromatic unsaturated compounds with 8 to 20 or more carbon atoms, such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butylstyrene, phenylstyrene, cyclohexylstyrene, and benzylstyrene.

[0038] (a55) Vinyl ester Aliphatic vinyl esters [C4-C15, e.g., alkenyl esters of aliphatic carboxylic acids (mono- or dicarboxylic acids) (e.g., vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, vinyl methoxyacetate)] Aromatic vinyl esters [C9-C20, e.g., alkenyl esters of aromatic carboxylic acids (mono- or dicarboxylic acids) (e.g., vinyl benzoate, diallyl phthalate, methyl-4-vinyl benzoate), aromatic ring-containing esters of aliphatic carboxylic acids (e.g., acetoxystyrene)]

[0039] (a56) vinyl ether Aliphatic vinyl ethers [3-15 carbon atoms, e.g., vinyl alkyl (1-10 carbon atoms) ethers (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.), vinyl alkoxy (1-6 carbon atoms) alkyl (1-4 carbon atoms) ethers (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether, vinyl-2-ethyl mercaptoethyl ether, etc.), poly(2-4)(meth)allyloxyalkanes (2-6 carbon atoms) (diallyloxyethane, triallyloxyethane, tetraallyloxybutane, tetramethallyloxyethane, etc.)], aromatic vinyl ethers [8-20 carbon atoms, e.g., vinyl phenyl ether, phenoxystyrene]

[0040] (a57) Vinyl ketone Aliphatic vinyl ketones (4-25 carbon atoms, e.g., vinyl methyl ketone, vinyl ethyl ketone), aromatic vinyl ketones (9-21 carbon atoms, e.g., vinyl phenyl ketone)

[0041] (a58) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diesters with 4 to 34 carbon atoms, for example, dialkyl fumarates (two alkyl groups consisting of linear, branched, or alicyclic groups with 1 to 22 carbon atoms), dialkyl maleates (two alkyl groups consisting of linear, branched, or alicyclic groups with 1 to 22 carbon atoms).

[0042] If a radical polymerizable monomer (a5) is included, its content is preferably 0.1 to 3.0% by weight based on the total weight of the monomer.

[0043] The preferred lower limit for the weight-average molecular weight of the polymer compound constituting the coating layer is 3,000, the more preferred lower limit is 5,000, and the still preferred lower limit is 7,000. On the other hand, the preferred upper limit for the weight-average molecular weight of the above polymer compound is 100,000, and the more preferred upper limit is 70,000.

[0044] The weight-average molecular weight of the polymer compounds constituting the coating layer can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions. Equipment: Alliance GPC V2000 (Waters Corporation) Solvents: Orthodichlorobenzene, DMF, THF Standard material: Polystyrene Sample concentration: 3 mg / ml Column stationary phase: PLgel 10 μm, MIXED-B x 2 in series (Polymer Laboratories, Inc.) Column temperature: 135℃

[0045] The polymer compounds constituting the coating layer can be produced by known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) using known polymerization initiators {azo-based initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), etc.], peroxide-based initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.), etc.}. The amount of polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, and even more preferably 0.1 to 1.5% by weight, based on the total weight of the monomer, from the viewpoint of adjusting the weight-average molecular weight to a preferred range. The polymerization temperature and polymerization time are adjusted according to the type of polymerization initiator, but the polymerization temperature is preferably -5 to 150°C (more preferably 30 to 120°C), and the reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

[0046] Examples of solvents used in solution polymerization include esters (2-8 carbon atoms, e.g., ethyl acetate and butyl acetate), alcohols (1-8 carbon atoms, e.g., methanol, ethanol, and octanol), hydrocarbons (4-8 carbon atoms, e.g., n-butane, cyclohexane, and toluene), amides (e.g., N,N-dimethylformamide (hereinafter abbreviated as DMF)), and ketones (3-9 carbon atoms, e.g., methyl ethyl ketone). From the viewpoint of adjusting the weight-average molecular weight to a preferred range, the amount used is preferably 5-900% by weight, more preferably 10-400% by weight, and even more preferably 30-300% by weight, based on the total weight of the monomers. The monomer concentration is preferably 10-95% by weight, more preferably 20-90% by weight, and even more preferably 30-80% by weight.

[0047] Examples of dispersion media in emulsion polymerization and suspension polymerization include water, alcohol (e.g., ethanol), ester (e.g., ethyl propionate), and light naphtha. Examples of emulsifiers include metal salts of higher fatty acids (10-24 carbon atoms) (e.g., sodium oleate and sodium stearate), metal ester salts of higher alcohols (10-24 carbon atoms) (e.g., sodium lauryl sulfate), ethoxylated tetramethyldecinediol, sodium sulfoethyl methacrylate, and dimethylaminomethyl methacrylate. Furthermore, stabilizers such as polyvinyl alcohol and polyvinylpyrrolidone may be added. The monomer concentration of the solution or dispersion is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, and even more preferably 15 to 85% by weight, and the amount of polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomer. During polymerization, known chain transfer agents, such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and / or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.), can be used.

[0048] The polymer compound constituting the coating layer may be a crosslinked polymer obtained by crosslinking the polymer compound with a crosslinking agent (A') {preferably a polyepoxy compound (a'1) [such as polyglycidyl ether (bisphenol A diglycidyl ether, propylene glycol diglycidyl ether, and glycerin triglycidyl ether) and polyglycidylamine (N,N-diglycidylaniline and 1,3-bis(N,N-diglycidylaminomethyl))] and / or a polyol compound (a'2) (such as ethylene glycol)} which has a reactive functional group that reacts with a carboxyl group.

[0049] One method for crosslinking the polymer compounds constituting the coating layer using a crosslinking agent (A') is to coat the negative electrode active material particles with the polymer compounds constituting the coating layer and then crosslink them. Specifically, one method involves mixing negative electrode active material particles with a resin solution containing the polymer compounds constituting the coating layer and desolventing the solution to produce coated active material particles, then mixing a solution containing the crosslinking agent (A') with the coated active material particles and heating the mixture to induce desolventing and a crosslinking reaction, causing the polymer compounds constituting the coating layer to be crosslinked by the crosslinking agent (A') on the surface of the negative electrode active material particles. The heating temperature is adjusted according to the type of crosslinking agent, but is preferably 70°C or higher when using a polyepoxy compound (a'1) as the crosslinking agent, and preferably 120°C or higher when using a polyol compound (a'2).

[0050] The conductive additive is preferably selected from materials that have electrical conductivity. Preferred conductive additives include metals [aluminum, stainless steel (SUS), silver, gold, copper, and titanium, etc.], carbon [graphite and carbon black (acetylene black, Ketjen black, furnace black, channel black, and thermal lamp black, etc.)], and mixtures thereof. These conductive additives may be used individually or in combination of two or more. They may also be used as alloys or metal oxides. In particular, from the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, gold, copper, titanium, and mixtures thereof are more preferred, even more preferably silver, gold, aluminum, stainless steel, and carbon, and especially preferably carbon. Furthermore, these conductive additives may also be made by coating a particulate ceramic material or resin material with a conductive material [preferably a metallic conductive additive from the above-mentioned conductive additives] by plating or the like.

[0051] The shape (form) of the conductive additive is not limited to particle form; it may also be in a form other than particle form, such as carbon nanofibers or carbon nanotubes, which are already in practical use as so-called filler-type conductive additives.

[0052] The average particle size of the conductive additive is not particularly limited, but from the viewpoint of the electrical characteristics of the battery, it is preferably about 0.01 to 10 μm. In this specification, "particle diameter of the conductive additive" means the maximum distance L between any two points on the contour line of the conductive additive. The value of "average particle diameter" shall be the value calculated as the average particle diameter of particles observed within several to tens of fields of view using observation methods such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0053] The ratio of the polymer compound to the conductive additive constituting the coating layer is not particularly limited, but from the viewpoint of the internal resistance of the battery, the weight ratio of the polymer compound (resin solids weight) to the conductive additive constituting the coating layer is preferably 1:0.01 to 1:50, and more preferably 1:0.2 to 1:3.0.

[0054] Examples of ceramic particles include metal carbide particles, metal oxide particles, and glass ceramic particles.

[0055] Examples of metal carbide particles include silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide (Mo2C), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), vanadium carbide (VC), and zirconium carbide (ZrC).

[0056] Examples of metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al2O3), silicon dioxide (SiO2), tin oxide (SnO2), titania (TiO2), zirconia (ZrO2), indium oxide (In2O3), Li2B4O7, and Li4Ti5O. 12 Examples include perovskite-type oxide particles represented as Li2Ti2O5, LiTaO3, LiNbO3, LiAlO2, Li2ZrO3, Li2WO4, Li2TiO3, Li3PO4, Li2MoO4, Li3BO3, LiBO2, Li2CO3, Li2SiO3, and ABO3 (where A is at least one selected from the group consisting of Ca, Sr, Ba, La, Pr, and Y, and B is at least one selected from the group consisting of Ni, Ti, V, Cr, Mn, Fe, Co, Mo, Ru, Rh, Pd, and Re). From the viewpoint of effectively suppressing side reactions occurring between the electrolyte and the coated negative electrode active material particles, zinc oxide (ZnO), aluminum oxide (Al2O3), silicon dioxide (SiO2), and lithium tetraborate (Li2B4O7) are preferred as metal oxide particles.

[0057] As for the ceramic particles, glass ceramic particles are preferable from the viewpoint of effectively suppressing side reactions that occur between the electrolyte and the coated negative electrode active material particles. These may be used individually or in combination of two or more types.

[0058] The glass ceramic particles are preferably lithium-containing phosphate compounds having a rhombohedral crystal system, and their chemical formula is Li x M"2P3O 12 It can be expressed as (X = 1 to 1.7). Here, M'' is one or more elements selected from the group consisting of Zr, Ti, Fe, Mn, Co, Cr, Ca, Mg, Sr, Y, Sc, Sn, La, Ge, Nb, and Al. Furthermore, some of the P may be substituted with Si or B, and some of the O may be substituted with F, Cl, etc. For example, Li 1.15 Ti 1.85 Al 0.15 Si 0.05 P 2.95 O 12 Li 1.2 Ti 1.8 Al 0.1 Ge 0.1 Si 0.05 P 2.95 O 12 The following can be used. Furthermore, materials of different compositions may be mixed or compounded, and the surface may be coated with a glass electrolyte or the like. Alternatively, it is preferable to use glass ceramic particles that precipitate a crystalline phase of a lithium-containing phosphate compound having a NASICON-type structure by heat treatment. Examples of glass electrolytes include the glass electrolyte described in Japanese Patent Publication No. 2019-96478.

[0059] Here, it is preferable that the proportion of Li2O in the glass ceramic particles is 8% by mass or less in terms of oxide. Even if it is not a NASICON-type structure, it is composed of Li, La, Mg, Ca, Fe, Co, Cr, Mn, Ti, Zr, Sn, Y, Sc, P, Si, O, In, Nb, and F, and has liSICON-type, perovskite-type, β-Fe2(SO4)3-type, and Li3In2(PO4)3-type crystal structures, and Li ions can be released at room temperature in a quantity of 1 × 10⁻¹⁶. -5 A solid electrolyte with conductivity of S / cm or higher may also be used.

[0060] The ceramic particles described above may be used individually or in combination of two or more types.

[0061] The volume-average particle diameter of the ceramic particles is preferably 1 to 1200 nm, more preferably 1 to 500 nm, and even more preferably 1 to 150 nm, from the viewpoint of energy density and electrical resistance.

[0062] The weight percentage of ceramic particles is preferably 0.5 to 5.0% by weight, based on the weight of the coated negative electrode active material particles. By including ceramic particles within the above range, side reactions occurring between the electrolyte and the coated negative electrode active material particles can be effectively suppressed. The weight percentage of ceramic particles is more preferably 2.0 to 4.0% by weight, based on the weight of the coated negative electrode active material particles.

[0063] The negative electrode active material particles have at least a portion of their surface covered with a coating layer. From the viewpoint of cycle characteristics, the negative electrode active material particles preferably have a coverage rate of 30 to 95%, as calculated by the following formula. Coverage (%) = {1 - [BET specific surface area of ​​coated negative electrode active material particles / (BET specific surface area of ​​negative electrode active material particles × weight ratio of negative electrode active material particles contained in coated negative electrode active material + BET specific surface area of ​​conductive additive × weight ratio of conductive additive contained in coated negative electrode active material particles + BET specific surface area of ​​ceramic particles × weight ratio of ceramic particles contained in coated negative electrode active material particles)]} × 100

[0064] [Method for manufacturing coated negative electrode active material particles for lithium-ion batteries] The present invention provides a method for producing coated negative electrode active material particles for lithium-ion batteries (hereinafter also simply referred to as "method for producing coated negative electrode active material particles"), which comprises a step of mixing negative electrode active material particles, a polymer compound, a conductive additive, ceramic particles, and an organic solvent, followed by a step of desolventing.

[0065] The organic solvent is not particularly limited as long as it is an organic solvent capable of dissolving polymer compounds, and any known organic solvent can be appropriately selected and used.

[0066] In the method for producing coated negative electrode active material particles, first, the negative electrode active material particles, the polymer compound constituting the coating layer, the conductive additive, and the ceramic particles are mixed in an organic solvent. The order in which the negative electrode active material particles, the polymer compound constituting the coating layer, the conductive additive, and the ceramic particles are mixed is not particularly limited. For example, a resin composition consisting of the polymer compound constituting the coating layer, the conductive additive, and the ceramic particles, which have been mixed in advance, may be further mixed with the negative electrode active material particles. Alternatively, the negative electrode active material particles, the polymer compound constituting the coating layer, the conductive additive, and the ceramic particles may be mixed simultaneously. Alternatively, the polymer compound constituting the coating layer may be mixed with the negative electrode active material particles, and then the conductive additive and ceramic particles may be further mixed.

[0067] The coated negative electrode active material particles of the present invention can be obtained by coating the negative electrode active material particles with a coating layer containing a polymer compound, a conductive additive, and ceramic particles. For example, the negative electrode active material particles can be placed in a universal mixer and stirred at 30 to 500 rpm, then a resin solution containing the polymer compound constituting the coating layer is added dropwise over 1 to 90 minutes and mixed, followed by mixing in the conductive additive and ceramic particles, raising the temperature to 50 to 200°C while stirring, reducing the pressure to 0.007 to 0.04 MPa, and holding for 10 to 150 minutes to desolvent the mixture.

[0068] The blending ratio of the negative electrode active material particles to the resin composition containing the polymer compound, conductive additive, and ceramic particles constituting the coating layer is not particularly limited, but it is preferable that the weight ratio of negative electrode active material particles to resin composition is 1:0.001 to 0.1.

[0069] [Negative electrode for lithium-ion batteries] The negative electrode for lithium-ion batteries of the present invention (hereinafter also simply referred to as "negative electrode") comprises a negative electrode active material layer containing coated negative electrode active material particles of the present invention and an electrolyte solution containing an electrolyte and a solvent.

[0070] The coated negative electrode active material particles contained in the negative electrode active material layer are preferably 40 to 95% by weight, and more preferably 60 to 90% by weight, based on the weight of the negative electrode active material layer, from the viewpoint of dispersibility of the negative electrode active material particles and electrode moldability.

[0071] As the electrolyte, electrolytes used in known electrolytes can be used, such as lithium salts of inorganic anions such as LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, and LiN(FSO2)2, and lithium salts of organic anions such as LiN(CF3SO2)2, LiN(C2F5SO2)2, and LiC(CF3SO2)3. Of these, LiN(FSO2)2 is preferred from the viewpoint of battery output and charge / discharge cycle characteristics.

[0072] As the solvent, any non-aqueous solvent used in known electrolytes can be used. For example, lactone compounds, cyclic or linear carbonate esters, linear carboxylic acid esters, cyclic or linear ethers, phosphate esters, nitrile compounds, amide compounds, sulfones, sulfolanes, and mixtures thereof can be used.

[0073] Examples of lactone compounds include lactone compounds with a 5-membered ring (such as γ-butyrolactone and γ-valerolactone) and a 6-membered ring (such as δ-valerolactone).

[0074] Examples of cyclic carbonate esters include propylene carbonate, ethylene carbonate (EC), and butylene carbonate (BC). Examples of linear carbonate esters include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate.

[0075] Examples of linear carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

[0076] Examples of cyclic ethers include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 1,4-dioxane. Examples of linear ethers include dimethoxymethane and 1,2-dimethoxyethane.

[0077] Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(trifluoromethyl) phosphate, tri(trichloromethyl) phosphate, tri(trifluoroethyl) phosphate, tri(triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2-dioxaphosphoran-2-one, and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.

[0078] Examples of nitrile compounds include acetonitrile. Examples of amide compounds include DMF. Examples of sulfones include dimethyl sulfone and diethyl sulfone.

[0079] These solvents may be used individually or in combination of two or more.

[0080] The concentration of the electrolyte in the electrolyte solution is preferably 1.2 to 5.0 mol / L, more preferably 1.5 to 4.5 mol / L, even more preferably 1.8 to 4.0 mol / L, and particularly preferably 2.0 to 3.5 mol / L. Since such an electrolyte has appropriate viscosity, it can form a liquid film between the coated negative electrode active material particles, and can impart a lubricating effect (the ability to adjust the position of the coated negative electrode active material particles) to the coated negative electrode active material particles.

[0081] The negative electrode active material layer may further contain a conductive additive in addition to the conductive additive that is optionally included in the coating layer of the coated negative electrode active material particles described above. The conductive additive included in the coating layer is integrated with the coated negative electrode active material particles, whereas the conductive additive included in the negative electrode active material layer is included separately from the coated negative electrode active material particles. As for conductive additives that may be included in the negative electrode active material layer, those described in [Coated negative electrode active material particles for lithium-ion batteries] can be used.

[0082] When the negative electrode active material layer contains a conductive additive, the total content of the conductive additive in the negative electrode and the conductive additive in the coating layer is preferably less than 4% by weight, and more preferably less than 3% by weight, based on the weight of the negative electrode active material layer excluding the electrolyte. On the other hand, the total content of the conductive additive in the negative electrode and the conductive additive in the coating layer is preferably 2.5% by weight or more, based on the weight of the negative electrode active material layer excluding the electrolyte.

[0083] The negative electrode active material layer preferably does not contain a binder. In this specification, "binding agent" refers to a chemical agent that cannot reversibly fix the negative electrode active material particles to each other or to the negative electrode active material particles to the current collector, and includes known solvent-drying type lithium-ion battery binding agents such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, and polypropylene. These binders are used by dissolving or dispersing them in a solvent, and solidify by volatilizing or distilling off the solvent, irreversibly fixing the negative electrode active material particles to each other and to the current collector.

[0084] The negative electrode active material layer may contain an adhesive resin. An adhesive resin is a resin that retains its adhesive properties without solidifying even after the solvent components are evaporated and dried, and is a different material from a binder and should be distinguished. Furthermore, while the coating layer constituting the coated negative electrode active material particles is fixed to the surface of the negative electrode active material particles, the adhesive resin reversibly fixes the surfaces of the negative electrode active material particles together. The adhesive resin can be easily separated from the surface of the negative electrode active material particles, but the coating layer cannot be easily separated. Therefore, the coating layer and the adhesive resin are different materials.

[0085] Examples of adhesive resins include polymers that contain at least one low-Tg monomer selected from the group consisting of vinyl acetate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, butyl acrylate, and butyl methacrylate as essential constituent monomers, and the total weight percentage of the low-Tg monomers is 45% by weight or more based on the total weight of the constituent monomers. When using an adhesive resin, it is preferable to use an amount of adhesive resin that is 0.01 to 10% by weight relative to the total weight of the negative electrode active material particles.

[0086] In a first embodiment of the lithium-ion battery anode of the present invention, the weight percentage of the polymer compound contained in the lithium-ion battery anode is 1 to 10% by weight, based on the weight of the lithium-ion battery anode. Here, "polymer compound" refers to the polymer compound, binder, and adhesive resin that constitute the coating layer. In the lithium-ion battery negative electrode of the present invention, the total weight ratio of the polymer compound and adhesive resin that constitute the coating layer is equal to the "weight ratio of polymer compound" mentioned above, and no binder is included (0% by weight).

[0087] In a second embodiment of the negative electrode for lithium-ion batteries of the present invention, the negative electrode active material layer consists of unbound bodies of coated negative electrode active material particles for lithium-ion batteries. Here, "non-bonded" means that the positions of the negative electrode active material particles are not fixed within the negative electrode active material layer, and that the negative electrode active material particles are not irreversibly fixed to each other, nor to the current collector. When the negative electrode active material layer is non-bonded, the negative electrode active material particles are not irreversibly fixed to each other, so they can be separated without fracture at the interfaces between the negative electrode active material particles. Furthermore, even when stress is applied to the negative electrode active material layer, the movement of the negative electrode active material particles prevents the layer from being fractured, which is preferable. A non-binding negative electrode active material layer can be obtained by methods such as using a slurry for negative electrode active material layers that contains negative electrode active material particles, electrolyte, etc., but does not contain a binder, as the negative electrode active material layer.

[0088] From the viewpoint of battery performance, the thickness of the negative electrode active material layer is preferably 150 to 600 μm, and more preferably 200 to 550 μm.

[0089] The negative electrode for lithium-ion batteries of the present invention can be manufactured, for example, by applying a slurry for the negative electrode active material layer, which contains the coated negative electrode active material particles, electrolyte, and solvent of the present invention, and optionally a conductive additive, to a current collector and then drying it. Specifically, one method is to apply the slurry for the negative electrode active material layer onto the current collector using a coating device such as a bar coater, then remove the solvent by placing a nonwoven fabric on the negative electrode active material particles to absorb the liquid, and press it with a press machine if necessary.

[0090] Materials that make up the current collector include metallic materials such as copper, aluminum, titanium, stainless steel, nickel and their alloys, as well as calcined carbon, conductive polymer materials, conductive glass, and the like. The shape of the current collector is not particularly limited and may be a sheet-like current collector made of the above material, or a deposited layer made of fine particles composed of the above material. The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm.

[0091] The negative electrode for a lithium-ion battery preferably further comprises a current collector, and the negative electrode active material layer is provided on the surface of the current collector. For example, the negative electrode of the present invention preferably comprises a resin current collector made of a conductive polymer material, and the negative electrode active material layer is provided on the surface of the resin current collector.

[0092] As the conductive polymer material constituting the resin current collector, for example, a resin to which a conductive agent has been added can be used. As the conductive agent constituting the conductive polymer material, the same type as the conductive additive that is an optional component of the coating layer can be suitably used. Examples of resins that make up conductive polymer materials include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyethernitrile (PEN), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resins, silicone resins, or mixtures thereof. From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), and polycycloolefin (PCO) are preferred, and more preferably polyethylene (PE), polypropylene (PP), and polymethylpentene (PMP). Resin current collectors can be obtained by known methods described in Japanese Patent Publication No. 2012-150905 and International Publication No. 2015 / 005116, etc.

[0093] [Lithium-ion battery] A lithium-ion battery can be obtained by combining the negative electrode of the present invention with a counter electrode, housing them together with a separator in a cell container, injecting an electrolyte, and sealing the cell container. Alternatively, the present invention can be obtained by forming the negative electrode on one side of a current collector and the positive electrode on the other side to create a bipolar electrode, stacking the bipolar electrode with a separator and housing it in a cell container, injecting an electrolyte, and sealing the cell container.

[0094] Examples of separators include known separators for lithium-ion batteries such as porous films made of polyethylene or polypropylene, laminated films of porous polyethylene film and porous polypropylene, nonwoven fabrics made of synthetic fibers (polyester fibers and aramid fibers, etc.) or glass fibers, and those on which ceramic fine particles such as silica, alumina, and titania are attached to the surface. [Examples]

[0095] The present invention will now be specifically described with reference to examples, but the present invention is not limited to these examples unless it deviates from the spirit of the invention. Unless otherwise specified, parts refer to parts by weight, and % refers to % by weight.

[0096] <Preparation of polymer compounds for coatings> 150 parts of DMF were placed in a four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen gas inlet tube, and the temperature was raised to 75°C. Next, a monomer composition containing 91 parts acrylic acid, 9 parts methyl methacrylate, and 50 parts DMF, along with an initiator solution containing 0.3 parts 2,2'-azobis(2,4-dimethylvaleronitrile) and 0.8 parts 2,2'-azobis(2-methylbutyronitrile) dissolved in 30 parts DMF, were continuously added dropwise over 2 hours using a dropping funnel while blowing nitrogen into the four-necked flask under stirring to carry out radical polymerization. After the dropwise addition was complete, the reaction was continued at 75°C for 3 hours. Next, the temperature was raised to 80°C and the reaction was continued for 3 hours to obtain a copolymer solution with a resin concentration of 30%. The obtained copolymer solution was transferred to a Teflon® vat and dried under reduced pressure at 150°C and 0.01 MPa for 3 hours, and the DMF was removed by distillation to obtain the copolymer. This copolymer was coarsely ground with a hammer, and then further ground in a mortar to obtain a powdered polymer compound for coating.

[0097] <Preparation of electrolyte solution> An electrolyte was prepared by dissolving LiN(FSO2)2 at a ratio of 2.0 mol / L in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) (volume ratio 1:1).

[0098] <Example 1> [Fabrication of coated negative electrode active material particles A] One part of the coating polymer compound was dissolved in three parts of DMF to obtain a coating polymer compound solution. 76 parts of negative electrode active material particles (hard carbon powder, volume average particle size 25 μm) were placed in a universal mixer high-speed mixer FS25 [(manufactured by Earth Technica Co., Ltd.)], and while stirring at room temperature and 720 rpm, 9 parts of the coating polymer compound solution were added dropwise over 2 minutes, and the mixture was stirred for a further 5 minutes. Next, while stirred, 9 parts of acetylene black [Denka Black®, manufactured by Denka Co., Ltd.], 2 parts of carbon nanofiber [Teijin Limited], and glass ceramic particles (product name "Lithium Ion Conductive Glass Ceramics LICGC") are added. TM PW-01 (1 μm) [manufactured by Ohara Co., Ltd.] (volume average particle size 1000 nm) was added in four parts over a period of 2 minutes, and stirring was continued for 30 minutes. Subsequently, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and reduced pressure. The stirring, reduced pressure, and temperature were maintained for 8 hours to remove volatile components by distillation. The obtained powder was classified using a sieve with a mesh size of 200 μm to obtain coated negative electrode active material particles A.

[0099] [Manufacturing of resin current collectors] A resin mixture was obtained by melt-kneading 70 parts of polypropylene [product name "Sun Allomer PL500A", manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotubes [product name: "FloTube9000", manufactured by CNano] and 5 parts of dispersant [product name "Yumex 1001", manufactured by Sanyo Chemical Industries, Ltd.] in a twin-screw extruder at 200°C and 200 rpm. The obtained resin mixture was passed through a T-die extrusion film molding machine and stretched and rolled to obtain a conductive film for resin current collectors with a thickness of 100 μm. Next, the obtained conductive film for resin current collectors was cut to 17.0 cm × 17.0 cm, nickel deposition was applied to one side, and then a current extraction terminal (5 mm × 3 cm) was attached to obtain a resin current collector.

[0100] [Fabrication of negative electrodes for lithium-ion batteries] 42 parts of electrolyte and 4.2 parts of carbon fiber [Donacarbo Milled S-243, manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm] were mixed at 2000 rpm for 5 minutes using a planetary stirring type mixing and kneading device {Awatori Rentaro [manufactured by Shinky Co., Ltd.]}. Subsequently, 30 parts of the electrolyte and 206 parts of the coated negative electrode active material particles A were added, and the mixture was further mixed at 2000 rpm for 2 minutes using the Awatori Rentaro. After adding another 20 parts of the electrolyte, the mixture was stirred at 2000 rpm for 1 minute using the Awatori Rentaro, and after adding another 2.3 parts of the electrolyte, the mixture was stirred at 2000 rpm for 2 minutes using the Awatori Rentaro to prepare a slurry for the negative electrode active material layer. The obtained slurry for the negative electrode active material layer had a basis weight of 80 mg / cm³. 2 To achieve this, the above resin current collector was coated on one side and pressed at a pressure of 1.4 MPa for approximately 10 seconds to produce a lithium-ion battery negative electrode (16.2 cm × 16.2 cm) according to Example 1 with a thickness of 340 μm.

[0101] [Manufacturing of lithium-ion batteries] The obtained negative electrode was combined with a counter electrode made of Li metal via a separator (Cellgard #3501) to fabricate a laminate cell.

[0102] <Example 2> [Fabrication of coated negative electrode active material particles B] Coated negative electrode active material particles B were obtained in the same manner as in Example 1, except that the glass ceramic particles were replaced with lithium tetraborate (product name "Lithium Tetraborate, Anhydrous," manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., volume average particle size 35.5 nm).

[0103] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particles A to coated negative electrode active material particles B, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0104] <Example 3> [Fabrication of coated negative electrode active material particles C] Coated negative electrode active material particles C were obtained in the same manner as in Example 1, except that the glass ceramic particles were replaced with zinc oxide (product "ZnO", manufactured by Kanto Chemical Co., Ltd., volume average particle size 65.4 nm).

[0105] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particle A to coated negative electrode active material particle C, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0106] <Example 4> [Fabrication of coated negative electrode active material particles D] Coated negative electrode active material particles D were obtained in the same manner as in Example 1, except that the glass ceramic particles were replaced with aluminum oxide (product "Al2O3", manufactured by Kanto Chemical Co., Ltd., volume average particle size 35.0 nm).

[0107] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particle A to coated negative electrode active material particle D, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0108] <Example 5> [Fabrication of coated negative electrode active material particles E] Coated negative electrode active material particles E were obtained in the same manner as in Example 1, except that the glass ceramic particles were replaced with silicon dioxide 1 (item "SiO2", manufactured by Kanto Chemical Co., Ltd., volume average particle size 51.2 nm).

[0109] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particles A to coated negative electrode active material particles E, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0110] <Example 6> [Fabrication of coated negative electrode active material particles F] Coated negative electrode active material particles F were obtained in the same manner as in Example 1, except that the glass ceramic particles were replaced with silicon dioxide II (product name "Aerosil 300", manufactured by Toshin Kasei Co., Ltd., volume average particle size 7.0 nm).

[0111] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particles A to coated negative electrode active material particles F, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0112] <Comparative Example 1> [Fabrication of coated negative electrode active material particles G] Coated negative electrode active material particles G were obtained in the same manner as in Example 1, except that glass ceramic particles were not added.

[0113] [Manufacturing of lithium-ion batteries] Except for changing coated negative electrode active material particles A to coated negative electrode active material particles G, a negative electrode for a lithium-ion battery was fabricated in the same manner as in Example 1, and a lithium-ion battery was obtained.

[0114] Table 1 shows the types of ceramic particles used in the examples and comparative examples, the volume-average particle diameter, the amount added based on the weight of the coated negative electrode active material particles, and the weight ratio of the coating resin in the lithium-ion battery negative electrode. The volume-average particle size was measured using the method described herein.

[0115] [Table 1]

[0116] <Measurement of internal resistance> The lithium-ion batteries obtained in each example and comparative example were charged to a voltage of 4.2V at 25°C using a charge / discharge measurement device "Battery Analyzer Model 1470" [manufactured by Toyo Technica Co., Ltd.] with a constant current of 0.05C, and then charged again at a constant voltage of 4.2V until the current value was 0.01C. After a 10-minute rest, the batteries were discharged to a voltage of 2.5V with a constant current of 0.01C, and then charged to a voltage of 4.2V with a constant current of 0.05C. The charged lithium-ion batteries were then stored in a 60°C environment. An impedance measuring device (HIOKI E.E. CORPORATION, Chemical Impedance Analyzer IM3590) was used to measure the internal resistance at a frequency of 1000 Hz after 0 days (immediately after full charge), after 7 days of storage, and after 14 days of storage. The results are shown in Table 2 and Figure 1.

[0117] [Table 2]

[0118] Table 2 and Figure 1 confirm that, in the examples, it is possible to prevent an increase in the internal resistance of the lithium-ion battery even after 14 days. [Industrial applicability]

[0119] The coated negative electrode active material particles of the present invention are particularly useful as negative electrode active material for lithium-ion batteries used in mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims

1. Coated negative electrode active material particles for lithium-ion batteries, wherein at least a portion of the surface of the negative electrode active material particles is coated with a coating layer, The coating layer comprises a polymer compound, a conductive additive, and ceramic particles. The aforementioned polymer compound is a resin containing a polymer in which acrylic monomer (a) is an essential constituent monomer. The weight percentage of the ceramic particles is 0.5 to 5.0% by weight, based on the weight of the coated negative electrode active material particles. A coated negative electrode active material particle for lithium-ion batteries, wherein the weight ratio of the polymer compound constituting the coating layer to the conductive additive is 1:0.01 to 1:

50.

2. The coated negative electrode active material particles for lithium-ion batteries according to claim 1, wherein the volume-average particle diameter of the ceramic particles is 1 to 1200 nm.

3. A lithium-ion battery negative electrode comprising a negative electrode active material layer containing coated negative electrode active material particles for lithium-ion batteries according to claim 1 or 2, and an electrolyte solution containing an electrolyte and a solvent, A lithium-ion battery anode in which the weight percentage of the polymer compound contained in the lithium-ion battery anode is 1 to 10% by weight, based on the weight of the lithium-ion battery anode.

4. A lithium-ion battery negative electrode comprising a negative electrode active material layer containing coated negative electrode active material particles for lithium-ion batteries according to claim 1 or 2, and an electrolyte solution containing an electrolyte and a solvent, The negative electrode active material layer is a negative electrode for a lithium-ion battery, comprising unbound bodies of the coated negative electrode active material particles for lithium-ion batteries.

5. A method for producing coated negative electrode active material particles for lithium-ion batteries according to claim 1 or 2, comprising the step of mixing negative electrode active material particles, a polymer compound, a conductive additive, ceramic particles, and an organic solvent, and then desolventing the mixture.

Images