Coated electrode active material particles for lithium ion batteries and lithium ion batteries

Abstract

To provide a coated electrode active material particle which enables the achievement of a lithium ion battery superior in cycle and rate characteristics.SOLUTION: A coated electrode active material particle for a lithium ion battery comprises a coating layer containing a polymer electrolyte composition. The polymer electrolyte composition contains a polymer (P) of a monomer composition containing a monomer (m1) and / or a monomer (m2), and a monomer (m3), and a lithium salt. In the monomer composition, a total weight percentage of the monomer (m1) and monomer (m2) is 10-60 wt.% to a weight of the monomer composition. A weight percentage of the monomer (m3) in the monomer composition is 40-90 wt.% to the weight of the monomer composition, and a weight percentage of the polymer (P) is 70-90 wt.% to a weight of the polymer electrolyte composition. A weight percentage of the lithium salt is 10-30 wt.% to the weight of the polymer electrolyte composition, and a weight percentage of the polymer electrolyte composition is 1-6 wt.% to a weight of the coated electrode active material particle.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to coated electrode active material particles for lithium ion batteries and lithium ion batteries. [Background technology]

[0002] In recent years, there has been a strong desire to reduce carbon dioxide emissions in order to protect the environment. The automotive industry is hoping to reduce carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs), and is working hard to develop secondary batteries for motor drive, which hold the key to making these vehicles practical. 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 resin composition for coating a non-aqueous secondary battery active material, which comprises a polymer of a monomer composition comprising an ester compound of a monohydric aliphatic alcohol having 1 to 12 carbon atoms with (meth)acrylic acid and an anionic monomer, the polymer having an acid value of 30 to 700; and a coated active material for a non-aqueous secondary battery, which has a coating layer comprising the above-mentioned resin composition for coating an active material on at least a part of the surface of the active material. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-160294 Summary of the Invention [Problem to be solved by the invention]

[0005] According to Patent Document 1, by coating the surface of an active material with a specific resin, the internal resistance of the battery can be reduced, and as a result, the cycle characteristics are improved. However, the resin composition for coating an active material disclosed in Patent Document 1 leaves room for improvement in terms of the cycle characteristics and rate characteristics of lithium ion batteries.

[0006] That is, the present invention has been made in view of the above-mentioned problems, and aims to provide coated electrode active material particles for lithium ion batteries that can provide lithium ion batteries having excellent cycle characteristics and rate characteristics, and a lithium ion battery that includes the coated electrode active material particles for lithium ion batteries. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve these problems and have arrived at the present invention. Specifically, the present invention relates to coated electrode active material particles, at least a portion of the surface of which is coated with a coating layer, the coating layer comprising a polymer electrolyte composition, the polymer electrolyte composition comprising a polymer (P) of a monomer composition comprising a monomer (m1) represented by the following general formula (1) and / or a monomer (m2) represented by the following general formula (2) and a monomer (m3) represented by the following general formula (3), and a lithium salt, and the total weight ratio of the monomer (m1) and the monomer (m2) in the monomer composition is: the weight proportion of the monomer (m3) in the monomer composition is 40 to 90% by weight based on the weight of the monomer composition; the weight proportion of the polymer (P) is 70 to 90% by weight based on the weight of the polymer electrolyte composition; the weight proportion of the lithium salt is 10 to 30% by weight based on the weight of the polymer electrolyte composition; and the weight proportion of the polymer electrolyte composition is 1 to 6% by weight based on the weight of the coated electrode active material particles.

[0008] [ka]

[0009] [In general formula (1), R 1 represents a hydrogen atom or a methyl group.

[0010] [ka]

[0011] [In general formula (2), R 2 represents a hydrogen atom or a methyl group, and X 1 represents an alkylene group having 1 to 2 carbon atoms.]

[0012] [ka]

[0013] [In general formula (3), R 3 represents a hydrogen atom or a methyl group, and R 4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms.]

[0014] The present invention also relates to a lithium ion battery comprising the coated electrode active material particles. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide coated electrode active material particles for lithium ion batteries that can provide lithium ion batteries with excellent cycle characteristics and rate characteristics, and a lithium ion battery that includes the coated electrode active material particles for lithium ion batteries. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. In this specification, "(meth)acrylic acid" means "acrylic acid or methacrylic acid."

[0017] The coated electrode active material particles for lithium ion batteries of the present invention are coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer, the coating layer comprising a polymer electrolyte composition, the polymer electrolyte composition comprising a polymer (P) of a monomer composition comprising a monomer (m1) represented by the following general formula (1) and / or a monomer (m2) represented by the following general formula (2) and a monomer (m3) represented by the following general formula (3), and a lithium salt, and the combination of the monomer (m1) and the monomer (m2) in the monomer composition is The total weight proportion is 10 to 60% by weight based on the weight of the monomer composition, the weight proportion of the monomer (m3) in the monomer composition is 40 to 90% by weight based on the weight of the monomer composition, the weight proportion of the polymer (P) is 70 to 90% by weight based on the weight of the polymer electrolyte composition, the weight proportion of the lithium salt is 10 to 30% by weight based on the weight of the polymer electrolyte composition, and the weight proportion of the polymer electrolyte composition is 1 to 6% by weight based on the weight of the coated electrode active material particles.

[0018] [ka]

[0019] [In general formula (1), R 1 represents a hydrogen atom or a methyl group.

[0020] [ka]

[0021] [In general formula (2), R 2 represents a hydrogen atom or a methyl group, and X 1 represents an alkylene group having 1 to 2 carbon atoms.]

[0022] [ka]

[0023] [In general formula (3), R 3represents a hydrogen atom or a methyl group, and R 4 represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms.]

[0024] Examples of the monomer (m1) represented by the general formula (1) include vinylpyrrolidone and α-methylvinylpyrrolidone. As the monomer (m1), one type of monomer may be used, or two or more types may be used.

[0025] Examples of the monomer (m2) represented by the general formula (2) include (2-oxo-1,3-dioxolan-4-yl)methyl acrylate, (2-oxo-1,3-dioxolan-4-yl)methyl methacrylate, (2-oxo-1,3-dioxolan-4-yl)ethyl acrylate, and (2-oxo-1,3-dioxolan-4-yl)ethyl methacrylate. As the monomer (m2), one type of monomer may be used, or two or more types may be used.

[0026] Examples of the monomer (m3) represented by the general formula (3) include (meth)acrylic acid, 2-ethylhexyl methacrylate, 2-ethylhexyl acrylate, dodecyl methacrylate, dodecyl acrylate, butyl methacrylate, butyl acrylate, methyl methacrylate, methyl acrylate, isononyl acrylate, isononyl methacrylate, isobornyl methacrylate, and isobornyl acrylate. 4 When is an alkyl group having 1 to 12 carbon atoms, the number of carbon atoms in the alkyl group is preferably 1 to 10. As the monomer (m3), one kind of monomer may be used, or two or more kinds of monomers may be used.

[0027] As for the combination of the monomers (m1) and / or (m2) and (m3) in the monomer composition, from the viewpoint of ionic conductivity, the monomer (m1) and the monomer (m3) each having R 4 is a saturated alkyl group having 4 to 12 carbon atoms, and in the monomer (m2) and the monomer (m3), R 4is preferably a hydrogen atom.

[0028] The coated electrode active material particles for lithium ion batteries of the present invention are coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer. In the coated electrode active material particles of the present invention, the coating layer contains a polymer electrolyte composition.

[0029] The polymer electrolyte composition contains a polymer (P) of a monomer composition containing the monomer (m1) and / or the monomer (m2) and the monomer (m3). The total weight proportion of the monomer (m1) and the monomer (m2) in the monomer composition is 10 to 60% by weight based on the weight of the monomer composition. If the total weight proportion of the monomers (m1) and (m2) in the monomer composition is less than 10 wt % based on the weight of the monomer composition, the ionic conductivity of the polymer (P) deteriorates, whereas if it exceeds 60 wt %, the resistance to solubility in an electrolyte solution of the polymer (P) deteriorates. From the viewpoint of resistance to solubility in an electrolyte solution, the total weight proportion of the monomers (m1) and (m2) in the monomer composition is preferably 20 to 55 wt % and more preferably 20 to 50 wt % based on the weight of the monomer composition.

[0030] In the present invention, the weight proportion of the monomer (m3) in the monomer composition is 40 to 90% by weight based on the weight of the monomer composition. If the weight proportion of the monomer (m3) in the monomer composition is less than 40% by weight based on the weight of the monomer composition, the polymer (P) becomes hard and the ionic conductivity deteriorates. If the weight proportion of the monomer (m3) in the monomer composition is more than 90% by weight, the lithium salt described below will be partially released, thereby deteriorating the ionic conductivity of the polymer (P). From the viewpoint of ion conductivity, the weight proportion of the monomer (m3) in the monomer composition is preferably 45 to 80% by weight, and more preferably 50 to 80% by weight, based on the weight of the monomer composition.

[0031] From the viewpoint of ion conductivity and flexibility of the polymer electrolyte composition, the monomer composition preferably further contains a sulfonate salt (m4 (sometimes referred to as monomer (m4))) having a vinyl group. Examples of the sulfonate salt (m4) having a vinyl group include sodium styrenesulfonate, lithium styrenesulfonate, sodium 2-sulfoethyl acrylate, and sodium 2-sulfoethyl methacrylate. From the viewpoint of ionic conductivity, the weight proportion of the sulfonate salt (m4) having a vinyl group in the monomer composition is preferably 1 wt % or less, and more preferably 0.5 wt % or less, based on the weight of the monomer composition.

[0032] The monomer composition may contain a monomer (also referred to as monomer (m5)) other than the monomers (m1), (m2), (m3), and (m4) as long as the physical properties are not impaired. From the viewpoints of ionic conductivity and electrolyte solubility resistance, the weight proportion of the monomer other than the monomers (m1), (m2), (m3), and (m4) in the monomer composition is preferably 3.0 wt% or less, more preferably less than 2.5 wt%, based on the weight of the monomer composition. When the monomer composition contains a monomer (m5) other than the monomers (m1), (m2), (m3), and (m4), the weight proportion of the monomer (m5) may be 0.2 wt% or more, based on the weight of the monomer composition. The monomer (m5) other than the monomers (m1), (m2), (m3), and (m4) is not particularly limited as long as it is polymerizable, and specific examples thereof include 1,6-hexanediol dimethacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, 1,4-butanediol dimethacrylate, trimethylolpropane trimethacrylate, and trimethylolpropane triacrylate.

[0033] The absolute molecular weight of the polymer (P) contained in the polymer electrolyte composition is preferably 15,000 to 100,000, from the viewpoint of the strength and flexibility of the polymer electrolyte composition. The absolute molecular weight can be measured using, for example, a multi-angle light scattering detector (MALS) or static light scattering (SLS) in gel permeation chromatography (GPC). In the present invention, the absolute molecular weight was measured using SLS. The measurement conditions for the absolute molecular weight are as follows: The solvent used in this measurement is not particularly limited as long as it dissolves the polymer (P). The refractive index concentration gradient (dn / dc) of each sample can be measured using a differential refractive index measurement device DRM-3000 attached to the DLS-8000DLS. Device: DLS-8000DSL [Otsuka Electronics Co., Ltd.] Measurement mode: SLS Measurement cell: Cylindrical cell Measurement temperature: 25℃ Number of samples: 4 (different concentrations)

[0034] The weight proportion of the polymer (P) contained in the polymer electrolyte composition is 70 to 90 wt % based on the weight of the polymer electrolyte composition. If the weight proportion of the polymer (P) contained in the polymer electrolyte composition is less than 70 wt % based on the weight of the polymer electrolyte composition, lithium salts will partially precipitate in the polymer electrolyte composition, destabilizing battery performance. If it exceeds 90 wt %, the ionic conductivity of the polymer electrolyte composition will deteriorate. From the viewpoints of resistance to solubility in an electrolyte solution and ion conductivity, the weight ratio of the polymer (P) contained in the polymer electrolyte composition is preferably 75 to 85% by weight.

[0035] The polymer (P) can be produced by polymerizing the monomer composition using a known polymerization initiator {azo initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2-methylbutyronitrile), etc.], peroxide initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.)], etc.} by a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.). The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.03 to 2% by weight, and even more preferably 0.04 to 1.5% by weight based on the total weight of the monomers, from the viewpoint of adjusting the absolute molecular weight within a preferred range, etc. The polymerization temperature and polymerization time are adjusted depending on the type of polymerization initiator, etc., 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).

[0036] Examples of solvents used in solution polymerization include esters (having 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (having 1 to 8 carbon atoms, such as methanol, ethanol, and octanol), hydrocarbons (having 4 to 8 carbon atoms, such as n-butane, cyclohexane, and toluene), amides (such as N,N-dimethylformamide), and ketones (having 3 to 9 carbon atoms, such as methyl ethyl ketone).From the viewpoint of adjusting the absolute molecular weight within a preferred range, the amount of the solvent used is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, and even more preferably 30 to 300% by weight, based on the total weight of the monomers.The monomer concentration is preferably 10 to 95% by weight, more preferably 20 to 90% by weight, and even more preferably 30 to 80% by weight.

[0037] Examples of dispersion media for emulsion polymerization and suspension polymerization include water, alcohols (e.g., ethanol), esters (e.g., ethyl propionate), light naphtha, etc. Examples of emulsifiers include metal salts of higher fatty acids (having 10 to 24 carbon atoms) (e.g., sodium oleate and sodium stearate), metal salts of higher alcohol (having 10 to 24 carbon atoms) sulfates (e.g., sodium lauryl sulfate), ethoxylated tetramethyldecynediol, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. Furthermore, polyvinyl alcohol, polyvinylpyrrolidone, etc. may be added as a stabilizer.

[0038] The monomer concentration in 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 monomers. In the 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.

[0039] The polymer electrolyte composition includes a lithium salt. Examples of the lithium salt include LiSCN, LiN(CN), LiClO, LiBF, LiAsF, LiPF, LiCF, LiCF, Li(CFSO)N, Li(CFSO)C, LiSbF, Li(FSO)N, LiC, F, SO, LiN(SOCFCF), LiPF(CFCF), LiPF(C, F), LiPF(CF), LiCl, LiF, LiBr, LiI, LiB(C, O), lithium difluoro(oxalate)borate, and lithium bis(oxalate)borate. The lithium salt may be one kind or a mixture of two or more kinds, among which LiPF6 or Li(FSO2)2N is preferred.

[0040] The weight ratio of the lithium salt contained in the polymer electrolyte composition is 10 to 30 wt % based on the weight of the polymer electrolyte composition. If the weight ratio of the lithium salt contained in the polymer electrolyte composition is less than 10 wt % based on the weight of the polymer electrolyte composition, the polymer electrolyte composition will not conduct ions, and if it exceeds 30 wt %, the salt will be partially released, causing the battery reaction on the opposing surface to become non-uniform. From the viewpoint of ion conductivity, the weight proportion of the lithium salt contained in the polymer electrolyte composition is preferably 15 to 25% by weight based on the weight of the polymer electrolyte composition.

[0041] The polymer electrolyte composition may further contain additives such as plasticizers, stabilizers, antioxidants, and release agents used in known polymer compounds, within the scope of the present invention.

[0042] The glass transition temperature of the polymer electrolyte composition is preferably −60 to 20° C., more preferably −50 to 0° C. When the glass transition temperature of the polymer electrolyte composition is within the above range, the electrode obtained using the polymer electrolyte composition has a good balance between structural strength and flexibility. The glass transition temperature of the polymer electrolyte composition can be adjusted by the weight proportion of the lithium salt contained in the polymer electrolyte composition.

[0043] The glass transition temperature of the polymer electrolyte composition and the polymer (P) can be measured by, for example, differential scanning calorimetry (DSC). In the present invention, the glass transition temperature is measured by the method (DSC method) specified in ASTM D3418-82. The measurement conditions are described below. Equipment: Q2000 [TA Instruments] Sample pan: aluminum Measurement atmosphere: Nitrogen 50mL / min Temperature Program: (1) Heat up to 50°C at 10°C / min (2) Keep at 50°C for 10 minutes (3) Cool to -80°C at 10°C / min (4) Keep at -80°C for 10 minutes (5) Heat up to 50°C at 10°C / min. From the differential scanning calorimetry curve obtained by the above measurement, a graph is drawn with the endothermic heat quantity on the vertical axis and the temperature on the horizontal axis. The glass transition temperature is determined as the temperature at the intersection of a straight line extending the low-temperature baseline of the graph toward the high-temperature side and a tangent drawn at the point where the gradient of the curve in the stepwise change portion of the glass transition is maximum.

[0044] The method for producing the polymer electrolyte composition is not particularly limited. For example, the polymer electrolyte composition can be obtained by mixing the polymer (P), the lithium salt, and an organic solvent capable of dissolving both the polymer (P) and the lithium salt in a predetermined ratio, and then removing the solvent if necessary. The above mixing is preferably carried out by a conventionally known method, for example, by using a mixer such as a homomixer, homodisper, wave rotor, homogenizer, disperser, paint conditioner, ball mill, magnetic stirrer or mechanical stirrer.

[0045] The organic solvent capable of dissolving both the polymer (P) and the lithium salt is not particularly limited, but examples thereof include N-alkylpyrrolidones such as N,N-dimethylacetamide, N,N-dimethylformamide, and N-methyl-2-pyrrolidone, aprotic polar solvents such as dimethyl sulfoxide and 1,3-dimethyl-2-imidazolidinone, ester solvents such as γ-butyrolactone and butyl acetate, carbonate solvents such as ethylene carbonate and propylene carbonate, alkylene glycol monoalkyl ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol monomethyl ether, and propylene glycol monoethyl ether, alcohol solvents such as isopropyl alcohol, water, and mixtures thereof. Among these, aprotic polar solvents are preferred because they have the highest solubility.

[0046] The coated electrode active material particles for lithium ion batteries of the present invention are coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer. The electrode active material particles include positive electrode active material particles and negative electrode active material particles. The coated electrode active material particles of the present invention may be either coated positive electrode active material particles or coated negative electrode active material particles.

[0047] The positive electrode active material particles are not particularly limited as long as they can be used as a positive electrode active material for lithium ion batteries. Positive electrode active material particles include composite oxides of lithium and transition metals {composite oxides containing one type of transition metal (e.g., LiCoO2, LiNiO2, LiAlMnO4, LiMnO2, and LiMn2O4), composite oxides containing two types of transition metal elements (e.g., LiFeMnO4, LiNi 1-x Co x O2, LiMn 1-y Co y O2, LiNi 1 / 3 Co 1 / 3 Al 1 / 3 O2 and LiNi 0.8 Co 0.15 Al 0.05 O2) and complex oxides containing three or more metal elements [e.g., LiM a M' b M'' c O2 (M, M' and M'' are different transition metal elements, and a + b + c = 1. For example, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2), etc.}, lithium-containing transition metal phosphates (for example, LiFePO4, LiCoPO4, LiMnPO4, and LiNiPO4), transition metal oxides (for example, MnO2 and V2O5), transition metal sulfides (for example, MoS2 and TiS2), and conductive polymers (for example, polyaniline, polypyrrole, polythiophene, polyacetylene, poly-p-phenylene, and polyvinylcarbazole), and two or more of them may be used in combination. The lithium-containing transition metal phosphate may have some of the transition metal sites substituted with other transition metals.

[0048] The negative electrode active material particles are not particularly limited as long as they can be used as a negative electrode active material for a lithium ion battery. Examples of the negative electrode active material particles include carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, resin baked bodies (e.g., baked and carbonized phenolic resins, furan resins, etc.), cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), and carbon fibers], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and / or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and / or silicon carbide, and silicon carbide, etc.], and silicon alloys (silicon-aluminum Examples of the conductive material include silicon-based materials such as aluminum alloys, silicon-lithium alloys, silicon-nickel alloys, silicon-iron alloys, silicon-titanium alloys, silicon-manganese alloys, silicon-copper alloys, and silicon-tin alloys), conductive polymers (for example, polyacetylene and polypyrrole), metals (tin, aluminum, zirconium, and titanium), metal oxides (titanium oxide and lithium-titanium oxide), and metal alloys (for example, lithium-tin alloys, lithium-aluminum alloys, and lithium-aluminum-manganese alloys), as well as mixtures of these with carbon-based materials. Among the 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 lithium or lithium ions are contained in part or all of the negative electrode active material particles in advance.

[0049] From the viewpoint of the electrical characteristics of the battery, the volume average particle diameter of the electrode active material particles is preferably 0.1 to 100 μm, more preferably 1 to 50 μm, and even more preferably 2 to 20 μm. The volume-average particle diameter of electrode active material particles refers to the particle size at 50% of the cumulative value (Dv50) in the particle size distribution determined by the Microtrac method (also known as the laser diffraction / scattering method). The Microtrac method is a method for determining particle size distribution using scattered light obtained by irradiating particles with laser light. A laser diffraction / scattering particle size distribution analyzer (such as the Microtrac manufactured by Microtrac Bell Co., Ltd.) can be used to measure the volume-average particle diameter.

[0050] In the coated electrode active material particles of the present invention, the coating layer preferably contains a conductive additive from the viewpoint of the internal resistance of the battery and the like.

[0051] When the coating layer contains a conductive additive, the conductive additive is preferably selected from materials having electrical conductivity. Preferred conductive additives include metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.)], and mixtures thereof. These conductive additives may be used alone or in combination of two or more, and may also be used as alloys or metal oxides thereof. Among these, from the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, gold, copper, titanium, and mixtures of two or more of these are more preferred, silver, gold, aluminum, stainless steel, and carbon are even more preferred, and carbon is particularly preferred. Furthermore, these conductive additives may be obtained by coating a particulate ceramic material or a resin material with a conductive material (preferably a metal one of the conductive additives mentioned above) by plating or the like.

[0052] The shape (form) of the conductive additive is not limited to a particulate form, and may be a form other than a particulate form, such as carbon nanofibers, carbon nanotubes, or the like, which are forms that are in practical use as so-called filler-based conductive additives.

[0053] The average particle size of the conductive additive is not particularly limited, but is preferably about 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery. In this specification, the "particle diameter of the conductive additive" refers to the longest distance L between any two points on the contour line of the conductive additive. The value of the "average particle diameter" is calculated as the average value of particle diameters of particles observed in several to several tens of fields of view using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0054] When the coating layer contains a conductive additive, the ratio of the polymer (P) constituting the coating layer to the conductive additive is not particularly limited, but from the viewpoint of the internal resistance of the battery, the weight ratio of polymer (P) (resin solid content weight):conductive additive is preferably 1:0.01 to 1:50, and more preferably 1:0.2 to 1:3.0.

[0055] The weight percentage of the polymer electrolyte composition in the coating layer is preferably 30 to 70 wt %. When the weight percentage of the polymer electrolyte composition in the coating layer is within this range, a good balance between electrical conductivity and ionic conductivity is achieved. The weight percentage of the polymer electrolyte composition in the coating layer is more preferably 32 to 65 wt %, and even more preferably 35 to 65 wt %. The conductive assistant is not included in the weight of the polymer electrolyte composition.

[0056] In the present invention, the weight proportion of the polymer electrolyte composition is 1 to 6% by weight based on the weight of the coated electrode active material particles. If the weight proportion of the polymer electrolyte composition is less than 1 wt % based on the weight of the coated electrode active material particles, the rate characteristics of a lithium ion battery including the coated electrode active material particles may be reduced, and the adhesion of the conductive additive may not be maintained, causing an increase in internal resistance, while if it exceeds 6 wt %, the amount of resin is too high, causing an increase in internal resistance.The weight proportion of the polymer electrolyte composition is preferably 1.5 to 5.5 wt %, and more preferably 2.0 to 5.0 wt %, based on the weight of the coated electrode active material particles.

[0057] The coated electrode active material particles of the present invention can be produced by mixing the polymer electrolyte composition constituting the coating layer, the electrode active material particles, and an optional conductive assistant. The order in which the polymer electrolyte composition constituting the coating layer, the electrode active material particles, and the conductive assistant are mixed is not particularly limited. For example, a resin composition comprising the polymer electrolyte composition constituting the coating layer and the conductive assistant, which have been mixed in advance, may be further mixed with the electrode active material particles; the polymer electrolyte composition, the electrode active material particles, and the conductive assistant may be mixed simultaneously; or the polymer electrolyte composition may be mixed with the electrode active material particles, and then the conductive assistant may be mixed therewith.

[0058] The coated electrode active material particles of the present invention can be obtained by coating electrode active material particles with a polymer electrolyte composition. For example, the electrode active material particles are placed in a universal mixer and stirred at 30 to 500 rpm, and a resin solution containing the polymer electrolyte composition is added dropwise over 1 to 90 minutes to mix, and if necessary, a conductive aid is added, and the mixture is heated to 50 to 200°C while stirring, and the pressure is reduced to 0.007 to 0.04 MPa, and the mixture is maintained at this temperature for 10 to 150 minutes.

[0059] A lithium ion battery comprising the coated electrode active material particles of the present invention also constitutes the present invention. The coated electrode active material particles may be coated positive electrode active material particles or coated negative electrode active material particles, or may be coated positive electrode active material particles and coated negative electrode active material particles. The lithium ion battery of the present invention comprises the coated positive electrode active material particles and / or the coated negative electrode active material particles, and preferably comprises a positive electrode containing the coated positive electrode active material particles and / or a negative electrode containing the coated negative electrode active material particles, and more preferably comprises a positive electrode containing the coated positive electrode active material particles and a negative electrode containing the coated negative electrode active material particles.

[0060] An example of a lithium ion battery comprising the coated positive electrode active material particles of the present invention is a lithium ion battery comprising a positive electrode comprising a positive electrode active material layer containing the coated positive electrode active material particles and an electrolytic solution containing an electrolyte and a solvent. The positive electrode active material layer preferably comprises the coated positive electrode active material particles in an unbound state. The term "non-bound" for the coated positive electrode active material particles means that the coated positive electrode active material particles are not fixed in position by a binding agent (also called a binder), i.e., the coated positive electrode active material particles are in a state where they can move in response to an external force.

[0061] When the positive electrode active material layer is made of a non-binder, the coated positive electrode active material particles are not irreversibly fixed to each other by a binder. Irreversibly fixed means that the coated positive electrode active material particles are bonded to each other by a known solvent-drying binder for lithium-ion batteries, as described below. In order to separate the bonded coated positive electrode active material particles, it is necessary to mechanically destroy the interface between the coated positive electrode active material particles. On the other hand, in the case of a non-binder, the positive electrode active material particles are not irreversibly bonded to each other, and therefore can be separated without mechanically destroying the interface between the coated positive electrode active material particles. The same applies to the case where the negative electrode active material layer described below is made of a non-bound body of coated negative electrode active material particles.

[0062] In the positive electrode, the positive electrode active material layer preferably does not contain a solvent-drying type binder. Examples of the solvent-drying binder include known binders for lithium ion batteries, such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, etc. These binders are used by dissolving or dispersing them in a solvent, and by volatilizing or distilling off the solvent, the surface solidifies without exhibiting adhesiveness, thereby firmly fixing the coated positive electrode active material particles to each other and between the coated positive electrode active material particles and the current collector.

[0063] As the electrolyte, electrolytes used in known electrolytic solutions can be used, including, for example, lithium salts of inorganic anions such as LiPF, LiBF, LiSbF, LiAsF, LiClO, and LiN(FSO), and lithium salts of organic anions such as LiN(CFSO), LiN(CFS0), and LiC(CFSO). Of these, LiN(FSO) is preferred from the viewpoint of battery output and charge / discharge cycle characteristics.

[0064] As the solvent, non-aqueous solvents used in known electrolytic solutions can be used, such as lactone compounds, cyclic or chain carbonate esters, chain carboxylic acid esters, cyclic or chain ethers, phosphate esters, nitrile compounds, amide compounds, sulfones, sulfolane, and mixtures of two or more of these.

[0065] Examples of lactone compounds include lactone compounds with five-membered rings (such as γ-butyrolactone and γ-valerolactone) and six-membered rings (such as δ-valerolactone).

[0066] Examples of cyclic carbonates include propylene carbonate, ethylene carbonate (EC), and butylene carbonate (BC). Examples of the chain carbonate ester include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate, and di-n-propyl carbonate.

[0067] Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

[0068] Examples of cyclic ethers include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 1,4-dioxane. Examples of chain ethers include dimethoxymethane and 1,2-dimethoxyethane.

[0069] Examples of phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethylmethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(trifluoromethyl) phosphate, tri(trichloromethyl) phosphate, tri(trifluoroethyl) phosphate, tri(triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphospholan-2-one, 2-trifluoroethoxy-1,3,2-dioxaphospholan-2-one, and 2-methoxyethoxy-1,3,2-dioxaphospholan-2-one.

[0070] Examples of nitrile compounds include acetonitrile, etc. Examples of amide compounds include N,N-dimethylformamide (DMF), etc. Examples of sulfones include dimethyl sulfone and diethyl sulfone, etc.

[0071] These solvents may be used alone or in combination of two or more.

[0072] From the viewpoint of preventing heat generation and expansion of the lithium ion battery, the flash point of the solvent in the electrolyte is preferably 100° C. or higher, more preferably 120° C. or higher, and even more preferably 130° C. or higher. On the other hand, the flash point of the solvent in the electrolyte may be 160° C. or lower.

[0073] In this specification, the flash point of a solvent is a temperature measured by the tag-sealed method specified in JIS K 2265-1-2007.

[0074] Of these solvents, from the viewpoint of ionic conductivity, at least one selected from the group consisting of dimethyl carbonate, propylene carbonate, and ethylene carbonate is preferred, and propylene carbonate and / or ethylene carbonate is more preferred.

[0075] In the positive electrode, the positive electrode active material layer may further contain a conductive additive in addition to the conductive additive contained as needed in the coating layer of the coated positive electrode active material particles. The conductive additive contained as needed in the coating layer is integral with the coated positive electrode active material particles, whereas the conductive additive contained in the positive electrode active material layer is contained separately from the coated positive electrode active material particles. The conductive additive that may be contained in the positive electrode active material layer can be any of those described above for the coated electrode active material particles. When the positive electrode active material layer contains a conductive additive, the conductive additive contained in the positive electrode active material layer may be the same as or different from the conductive additive contained in the coating layer.

[0076] In the case where the positive electrode active material layer contains a conductive additive, the total content of the conductive additive contained in the positive electrode and the coating layer is preferably less than 10 wt %, more preferably less than 7 wt %, based on the weight of the positive electrode active material layer excluding the electrolyte solution. On the other hand, the total content of the conductive additive contained in the positive electrode and the coating layer is preferably 1 wt % or more based on the weight of the positive electrode active material layer excluding the electrolyte solution.

[0077] In the positive electrode, the thickness of the positive electrode active material layer is preferably 150 to 600 μm, more preferably 200 to 450 μm, from the viewpoint of battery performance.

[0078] The positive electrode can be produced, for example, by applying a positive electrode slurry containing coated positive electrode active material particles and an electrolytic solution containing an electrolyte and a solvent to a current collector, followed by drying. Specifically, the positive electrode slurry is applied to a current collector using a coating device such as a bar coater, and then a nonwoven fabric is placed on the slurry to absorb the liquid, thereby removing the solvent, and if necessary, pressing with a press.

[0079] The positive electrode slurry can be prepared, for example, by dispersing the coated positive electrode active material particles of the present invention in an electrolyte solution. The amount of the coated positive electrode active material particles contained in the positive electrode slurry is preferably 40 to 80 wt %, more preferably 45 to 75 wt %, based on the weight of the positive electrode slurry, from the viewpoints of dispersibility of the particles and electrode formability. In the positive electrode slurry, the concentration of the electrolyte in the electrolytic 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. Such an electrolyte solution has an appropriate viscosity, and therefore can form a liquid film between the coated positive electrode active material particles, thereby imparting a lubricating effect (ability to adjust the position of the coated positive electrode active material particles) to the coated positive electrode active material particles.

[0080] The positive electrode preferably further includes a current collector, and the positive electrode active material layer is provided on the surface of the current collector. For example, the positive electrode preferably includes a resin current collector made of a conductive polymer material, and the positive electrode active material layer is provided on the surface of the resin current collector.

[0081] A lithium ion battery including the coated negative electrode active material particles of the present invention may be a lithium ion battery including a negative electrode including a negative electrode active material layer containing the coated negative electrode active material particles and an electrolytic solution containing an electrolyte and a solvent. The negative electrode active material layer preferably comprises the coated negative electrode active material particles in an unbound state. The term "unbound" used for the coated negative electrode active material particles means that the coated negative electrode active material particles are not fixed in position by a binder, i.e., the coated negative electrode active material particles are in a state where they can move in response to an external force.

[0082] In the negative electrode, the negative electrode active material layer preferably does not contain a solvent-drying type binder. Examples of the solvent-drying binder include the above-mentioned known binders for lithium-ion batteries, etc. These binders are used by dissolving or dispersing them in a solvent, and by volatilizing or distilling off the solvent, the surface becomes solidified without exhibiting adhesiveness, thereby firmly fixing the coated negative electrode active material particles to each other and between the coated negative electrode active material particles and the current collector.

[0083] In the negative electrode, the electrolyte and solvent contained in the electrolytic solution can be the same as those described above for the positive electrode.

[0084] In the negative electrode, the negative electrode active material layer may further contain a conductive additive in addition to the conductive additive contained as needed in the coating layer of the coated negative electrode active material particles. The conductive additive contained as needed in the coating layer is integral with the coated negative electrode active material particles, whereas the conductive additive contained in the negative electrode active material layer is contained separately from the coated negative electrode active material particles. The conductive additive that may be contained in the negative electrode active material layer can be any of those described above for the coated electrode active material particles. When the negative electrode active material layer contains a conductive additive, the conductive additive contained in the negative electrode active material layer may be the same as or different from the conductive additive contained in the coating layer.

[0085] In the case where the negative electrode active material layer contains a conductive additive, the total content of the conductive additive contained in the negative electrode and the coating layer is preferably less than 20 wt %, more preferably less than 10 wt %, based on the weight of the negative electrode active material layer excluding the weight of the electrolyte solution. On the other hand, the total content of the conductive additive contained in the negative electrode and the coating layer is preferably 0.5 wt % or more based on the weight of the negative electrode active material layer excluding the weight of the electrolyte solution.

[0086] In the negative electrode, the thickness of the negative electrode active material layer is preferably 150 to 600 μm, more preferably 200 to 450 μm, from the viewpoint of battery performance.

[0087] The negative electrode can be produced, for example, by applying a negative electrode slurry containing coated negative electrode active material particles and an electrolytic solution containing an electrolyte and a solvent to a current collector, followed by drying. Specifically, the negative electrode slurry is applied to a current collector using a coating device such as a bar coater, and then a nonwoven fabric is placed on the slurry to absorb the liquid, thereby removing the solvent, and if necessary, pressing the nonwoven fabric with a press.

[0088] The negative electrode preferably further includes a current collector, and the negative electrode active material layer is provided on a surface of the current collector. For example, the negative electrode preferably includes a resin current collector made of a conductive polymer material, and the negative electrode active material layer is provided on a surface of the resin current collector.

[0089] In the positive and negative electrodes, examples of materials constituting the current collectors include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as baked carbon, conductive polymer materials, and conductive glass. The shape of the current collector is not particularly limited, and may be a sheet-shaped current collector made of the above-mentioned material, or a deposition layer made of fine particles made of the above-mentioned material. The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm.

[0090] The conductive polymer material constituting the resin current collector may be, for example, a resin to which a conductive agent has been added. As the conductive agent constituting the conductive polymer material, the same conductive assistant as the optional component of the coating layer can be suitably used. Examples of resins that constitute the conductive polymer material 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 resin, silicone resin, and mixtures of two or more of these. From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferred, and polyethylene (PE), polypropylene (PP) and polymethylpentene (PMP) are more preferred. The resin current collector can be obtained by known methods such as those described in JP-A-2012-150905 and WO 2015 / 005116.

[0091] The lithium-ion battery of the present invention can be obtained by combining a counter electrode, housing it together with a separator in a cell container, pouring in an electrolyte, and sealing the cell container. Alternatively, the battery can be obtained by forming a bipolar electrode by forming a positive electrode on one side of a current collector and a negative electrode on the other side, laminating the bipolar electrode with a separator, housing it in a cell container, pouring in an electrolyte, and sealing the cell container. The lithium ion battery of the present invention can be obtained by using a positive electrode containing the above-mentioned coated positive electrode active material particles and / or a negative electrode containing the above-mentioned coated negative electrode active material particles. In the lithium ion battery of the present invention, when the positive electrode is a positive electrode containing the coated positive electrode active material particles, the negative electrode is not particularly limited as long as it is usable as a negative electrode for a lithium ion battery, but is preferably a negative electrode containing the above-mentioned coated negative electrode active material particles. In addition, in the lithium ion battery of the present invention, when the negative electrode is a negative electrode containing the above-mentioned coated negative electrode active material particles, the positive electrode is not particularly limited as long as it is usable as a positive electrode for a lithium ion battery, but is preferably a positive electrode containing the above-mentioned coated positive electrode active material particles.

[0092] Examples of the separator 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, aramid fibers, etc.) or glass fibers, and those having ceramic fine particles such as silica, alumina, or titania attached to their surfaces. [Example]

[0093] The present invention will now be described in detail with reference to examples, but the present invention is not limited to these examples as long as they do not deviate from the gist of the present invention. Unless otherwise specified, parts mean parts by weight and % means % by weight.

[0094] The glass transition temperature was measured under the above conditions by the method (DSC method) specified in ASTM D3418-82. The absolute molecular weight of the polymer was measured by the static light scattering method of gel permeation chromatography (GPC).

[0095] <Production Example 1: Synthesis of Polymer (P-1)> A four-neck flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel, and nitrogen gas inlet tube was charged with 300 parts of toluene as a polymerization solvent and heated to 75°C. Next, a monomer mixture containing 30 parts of N-vinylpyrrolidone (hereinafter abbreviated as VP), 65 parts of 2-ethylhexyl acrylate (hereinafter abbreviated as EHA), 4.5 parts of acrylic acid, and 0.5 parts of 1,6-hexanediol dimethacrylate (hereinafter abbreviated as HDMA) and an initiator solution containing 0.03 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) dissolved in 5 parts of toluene were continuously added dropwise over 2 hours using the dropping funnel while stirring and nitrogen was blown into the four-neck flask, to carry out radical polymerization. After the addition was completed, the temperature was raised to 75°C, and the reaction was continued for 1 hour. Next, an initiator solution prepared by dissolving 0.01 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) in 1 part of toluene was added via a dropping funnel, and the reaction was continued for another 3 hours to obtain a toluene solution of polymer (P-1). The toluene solution of the obtained polymer (P-1) was dropped into methanol / ion-exchanged water (1 / 1 volume ratio) to cause reprecipitation, yielding a white block of polymer (P-1). The absolute molecular weight of the obtained polymer (P-1) in a methanol solution measured using a light scattering method was 69,000, and the glass transition temperature was -25°C.

[0096] <Production Examples 2 to 3: Synthesis of Polymers (P-2) to (P-3)> Polymers (P-2) and (P-3) were obtained in the same manner as in Production Example 1, except that the composition of the monomer mixture solution was changed as shown in Table 1. The absolute molecular weights and glass transition temperatures of each were shown in Table 1.

[0097] <Production Examples 4 to 9: Synthesis of Polymers (P-4) to (P-9)> DMF solutions of polymers (P-4) to (P-9) were obtained in the same manner as in Production Example 1, except that the polymerization solvent was changed to 300 parts of N,N-dimethylformamide (hereinafter abbreviated as DMF) and the composition of the monomer mixture solution was changed as shown in Table 1. The obtained DMF solutions were added dropwise to acetone to cause reprecipitation, yielding polymers (P-4) to (P-9). The absolute molecular weights and glass transition temperatures of each are shown in Table 1.

[0098] <Production Examples 10, 11, 13, 15, 16, and 22: Synthesis of Polymers (P-10), (P-11), (P-13), (P-15), (P-16), and (P-22)> Polymers (P-10), (P-11), (P-13), (P-15), (P-16), and (P-22) were obtained in the same manner as in Production Example 1, except that the composition of the monomer mixture solution was changed as shown in Table 1. The absolute molecular weights and glass transition temperatures of each polymer are shown in Table 1.

[0099] <Production Examples 12, 14, and 18 to 20: Synthesis of Polymers (P-12), (P-14), and (P-18) to (P-20)> In Production Example 1, a metering pump (MP-2010, manufactured by Tokyo Rikakikai Co., Ltd.) was used instead of the dropping funnel to dropwisely add a mixture of monomers m1 to m3 listed in Table 1 to 280 parts by weight of the polymerization solvent DMF, an aqueous solution of monomer m4 listed in Table 1 dissolved in 20 parts by weight of ion-exchanged water, and an initiator solution of 0.03 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) dissolved in 5 parts of DMF. The procedure was repeated except that the solvent for preparing the additional initiator solution was also changed to DMF, to obtain DMF solutions of polymers (P-12), (P-14), and (P-18) to (P-20). The resulting DMF solutions were added dropwise to acetone to cause reprecipitation, yielding polymers (P-12), (P-14), and (P-18) to (P-20). The absolute molecular weights and glass transition temperatures of each were listed in Table 1.

[0100] <Production Examples 17 and 21: Synthesis of Polymers (P-17) and (P-21)> DMF solutions of polymers (P-17) and (P-21) were obtained in the same manner as in Production Example 1, except that the polymerization solvent was changed to 300 parts of DMF and the composition of the monomer mixture solution was changed as shown in Table 1. The obtained DMF solutions were added dropwise to acetone to cause reprecipitation, yielding polymers (P-17) and (P-21). The absolute molecular weights and glass transition temperatures of each are shown in Table 1.

[0101] [Table 1]

[0102] The monomers in Table 1 are shown below. VP: N-vinylpyrrolidone PCMA: (2-oxo-1,3-dioxolan-4-yl)methyl methacrylate MMA: Methyl methacrylate BMA: butyl methacrylate EHMA: 2-ethylhexyl methacrylate EHA: 2-ethylhexyl acrylate iNA: Isononyl acrylate IBMA: Isobornyl methacrylate DMA: Dodecyl methacrylate AA: acrylic acid MAA: methacrylic acid NaSS: Sodium styrene sulfonate (prepared as a 10% aqueous solution) LiSS: Lithium styrene sulfonate (prepared as a 10% aqueous solution) NaSEMA: Sodium 2-sulfoethyl methacrylate HDMA: 1,6-hexanediol dimethacrylate TMPTA: Trimethylolpropane triacrylate

[0103] Example 1 (Production of polymer electrolyte composition) 9 parts of the polymer (P-1) obtained in Production Example 1 and 1 part of lithium bis(fluorosulfonyl)imide (hereinafter abbreviated as LiFSI) were dissolved in 40 parts of acetone to prepare an acetone solution of a polymer electrolyte composition (D-1) (solid content concentration: 20%).

[0104] (Production of coated positive electrode active material particles) 91 parts of lithium-nickel-cobalt-aluminum composite oxide (NCA) [manufactured by Toda Kogyo Co., Ltd., volume average particle diameter 6.4 μm] as positive electrode active material particles were placed in a universal mixer, high-speed mixer FS25 [manufactured by Earth Technica Corporation], and while stirring at room temperature and 720 rpm, 15 parts of an acetone solution of the polymer electrolyte composition (D-1) (solid content concentration 20%) and 5 parts of acetylene black [manufactured by Denki Kagaku Kogyo Co., Ltd., Denka Black (registered trademark)] as a conductive additive were added dropwise over 2 minutes, followed by stirring for an additional 5 minutes. While continuing stirring, the pressure was reduced to 0.01 MPa, and then the temperature was raised to 120°C while maintaining stirring and the reduced pressure. The stirring, reduced pressure, and temperature were maintained for 3 hours to distill off the volatiles. The resulting powder was classified using a sieve with 212 µm openings to obtain coated positive electrode active material particles. The ratio of the weight of the polymer electrolyte composition (D-1) to the weight of the coated positive electrode active material particles was 3 wt %.

[0105] (Preparation of electrolyte) An electrolyte solution (X-1) was prepared by mixing ethylene carbonate (39 parts), propylene carbonate (35 parts), and LiFSI (26 parts).

[0106] (Preparation of positive electrode) The coated positive electrode active material particles (99 parts) obtained above, the electrolyte (X-1) (25 parts), and 1 part of carbon nanofiber (product name VGCF-H, manufactured by Showa Denko K.K.) were mixed, and the mixture was mixed at 2000 rpm for 3 minutes using a Thinky Mixer, to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry was applied to an aluminum current collector foil so that the positive electrode active material was coated in an amount of 80 mg / cm. 2 The mixture was applied to one side of the current collector foil so that the thickness became 1.4 MPa, and pressed for about 10 seconds to obtain a positive electrode (15 mmφ).

[0107] (Production of coated negative electrode active material particles) As negative electrode active material particles, 89 parts of non-graphitizable carbon (HC) powder [Carbotron (registered trademark) PS(F) manufactured by Kureha Battery Materials Japan Co., Ltd., number average particle diameter 18 μm] was placed in a universal mixer, high-speed mixer FS25 [manufactured by Earth Technica Corporation], and while stirring at room temperature and 720 rpm, 15 parts of an acetone solution of the polymer electrolyte composition (D-1) (solid content concentration 20%) and 6 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.] as a conductive additive were added dropwise over 2 minutes, followed by stirring for an additional 5 minutes. While continuing stirring, the pressure was reduced to 0.01 MPa, and then the temperature was raised to 120°C while maintaining stirring and the reduced pressure. The stirring, reduced pressure, and temperature were maintained for 3 hours to distill off the volatiles. The resulting powder was classified using a sieve with 212 µm openings to obtain coated negative electrode active material particles.

[0108] (Preparation of negative electrode) The coated negative electrode active material particles (98 parts) obtained above, the electrolyte (X-1) (20 parts), and 2 parts of carbon nanofiber (product name VGCF-H, manufactured by Showa Denko K.K.) were mixed, and the mixture was mixed at 2000 rpm for 3 minutes using a Thinky Mixer, to prepare a negative electrode active material slurry. The obtained negative electrode active material slurry was applied to a copper current collector foil so that the negative electrode active material was coated in an amount of 34 mg / cm. 2 The mixture was applied to one side of the current collector foil so that the thickness became 1.4 MPa, and pressed for about 10 seconds to obtain a negative electrode (15 mmφ).

[0109] (Lithium-ion battery manufacturing) The obtained positive electrode and negative electrode were combined via a separator (#3501 manufactured by Celgard) and an electrolytic solution (X-1) was poured into the combination to prepare a laminate cell (lithium ion battery) (M-1).

[0110] <Example 2> A polymer electrolyte composition (D-2) of Example 2 was prepared in the same manner as in Example 1, except that the polymer (P-1) in Example 1 was replaced with the polymer shown in Table 2. A lithium ion battery (M-2) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-2) was used and the weight proportions of the polymer electrolyte composition, the active material and the conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0111] Example 3 A polymer electrolyte composition (D-3) of Example 3 was prepared in the same manner as in Example 1, except that the polymer (P-1) in Example 1 was replaced with the polymer shown in Table 2 and the solvent was changed from acetone to methanol. A lithium ion battery (M-3) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-3) was used and the weight proportions of the polymer electrolyte composition, the active material and the conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0112] Example 4 A polymer electrolyte composition (D-4) of Example 4 was prepared in the same manner as in Example 3, except that the composition ratio of the positive electrode composition was changed in Example 3. A lithium ion battery (M-4) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-4) was used and the weight ratios of the active material and conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0113] <Example 5> A polymer electrolyte composition (D-5) of Example 5 was prepared in the same manner as in Example 3, except that the composition ratio of the positive electrode composition was changed in Example 3. A lithium ion battery (M-5) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-5) was used and the weight ratios of the active material and conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0114] Example 6 A polymer electrolyte composition (D-6) of Example 6 was prepared in the same manner as in Example 3, except that the polymer (P-4) in Example 3 was replaced with the polymer shown in Table 2. A lithium ion battery (M-6) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-6) was used and the weight proportions of the polymer electrolyte composition, the active material and the conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0115] Example 7 A polymer electrolyte composition (D-7) of Example 7 was prepared in the same manner as in Example 3, except that the polymer (P-4) in Example 3 was replaced with the polymer shown in Table 2. A lithium ion battery (M-7) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-7) was used and the weight proportions of the polymer electrolyte composition, the active material and the conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0116] Example 8 A polymer electrolyte composition (D-8) of Example 8 was prepared in the same manner as in Example 3, except that the polymer (P-4) in Example 3 was replaced with the polymer shown in Table 2. A lithium ion battery (M-8) was prepared in the same manner as in Example 1, except that the polymer electrolyte composition (D-8) was used and the weight proportions of the polymer electrolyte composition, the active material and the conductive additive used in the positive electrode, and the electrolyte solution were changed as shown in Table 2.

[0117] <Comparative Examples 1 to 3> Polymer electrolyte compositions (D-9) to (D-11) of Comparative Examples 1 to 3 were prepared in the same manner as in Example 1, except that the polymer (P-1) in Example 1 was replaced with the polymer shown in Table 2. Lithium ion batteries (M-9) to (M-11) were prepared in the same manner as in Example 1, except that the polymer electrolyte compositions (D-9) to (D-11) were used instead of the polymer electrolyte composition (D-1).

[0118] <Examples 9 to 13, 15 to 20> Polymer electrolyte compositions (D-12) to (D-16) and (D-18) to (D-23) of Examples 9 to 13 and 15 to 20 were prepared in the same manner as in Example 1, except that the polymer (P-1) in Example 1 was replaced with the polymer shown in Table 3. Lithium ion batteries (M-12) to (M-16) and (M-18) to (M-23) were prepared in the same manner as in Example 1, except that the polymer electrolyte compositions (D-12) to (D-16) and (D-18) to (D-23) were used.

[0119] Example 14 A polymer electrolyte composition (D-17) of Example 14 was prepared in the same manner as in Example 7, except that the polymer (P-6) in Example 7 was replaced with the polymer shown in Table 3. A lithium ion battery (M-17) was prepared in the same manner as in Example 7, except that the polymer electrolyte composition (D-17) was used.

[0120] Example 21 A polymer electrolyte composition (D-24) of Example 21 was prepared in the same manner as in Example 7, except that the polymer (P-6) in Example 7 was replaced with the polymer shown in Table 3. A lithium ion battery (M-24) was prepared in the same manner as in Example 7, except that the polymer electrolyte composition (D-24) was used and the electrolyte solution was changed as shown in Table 3.

[0121] <Evaluation of rate characteristics> The lithium-ion batteries (M-1) to (M-24) prepared above were placed in a thermostatic chamber (Espec Corp., PFU-3K) set to 45°C and the temperature was controlled. In this state, the batteries were charged using a charge / discharge device (Hokuto Denko Corp., HJ0501SM8A). The charging current was set to 0.05C, and the batteries were charged using CCCV charging (constant current / constant voltage mode) up to a cutoff voltage of 4.2V. They were then discharged at a constant current of 0.05C down to a cutoff voltage of 2.5V.

[0122] The lithium-ion battery that had undergone the initial charge / discharge process described above was subjected to a second cycle of charge / discharge. Similar charge / discharge processes were performed at discharge rates of 1 C and 0.05 C, and the discharge capacity was measured. The percentage of the discharge capacity at 1 C relative to the discharge capacity at 0.05 C (100 × (discharge capacity at 1 C) / (discharge capacity at 0.05 C)) (%) was calculated and used as an evaluation index for the discharge rate characteristics. The results are shown in Tables 2 and 3 below.

[0123] <Charge / discharge test: Evaluation of cycle characteristics> At 45°C, a charge / discharge test was carried out on the lithium ion batteries (M-1) to (M-24) using a charge / discharge measuring device "HJ-SD8" (manufactured by Hokuto Denko Corporation) according to the following method. After charging to 4.2V using a constant current / constant voltage method (0.05C), the battery was allowed to rest for 10 minutes and then discharged to 2.6V using a constant current method (0.05C). This cycle was repeated 20 times, and the cycle performance (%) was calculated by dividing the discharge capacity obtained in the first cycle by the discharge capacity obtained in the 20th cycle (100 × 20th discharge capacity / 1st discharge capacity). The results are shown in Tables 2 and 3.

[0124] [Table 2]

[0125] [Table 3]

[0126] The descriptions in Tables 2 and 3 are as follows: NCA: Lithium-nickel-cobalt-aluminum composite oxide AB: Acetylene black CF: Carbon nanofiber HC: Non-graphitizable carbon DMC: Dimethyl carbonate EC: Ethylene carbonate PC: Propylene carbonate LiFSI: Lithium bis(fluorosulfonyl)imide LiPF6: Lithium hexafluorophosphate The weight percentage (wt%) of the polymer electrolyte composition in the coating layer in Tables 2 and 3 is the weight percentage of the polymer electrolyte composition in the coating layer of the coated positive electrode active material particles (100 × (weight of polymer electrolyte composition) / (total weight of polymer electrolyte composition and acetylene black)). In Examples 1 to 21 and Comparative Examples 1 to 3, the weight percentage of the polymer electrolyte composition in the coating layer of the coated negative electrode active material particles was 33 wt%. [Industrial Applicability]

[0127] The coated electrode active material particles of the present invention and the lithium ion secondary battery using the same are useful for mobile phones, personal computers, hybrid cars, electric cars, etc.

Claims

1. Coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer, the coating layer comprises a polymer electrolyte composition, The polymer electrolyte composition comprises a polymer (P) of a monomer composition including a monomer (m1) represented by the following general formula (1) and / or a monomer (m2) represented by the following general formula (2) and a monomer (m3) represented by the following general formula (3), and a lithium salt: the total weight ratio of the monomer (m1) and the monomer (m2) in the monomer composition is 10 to 60% by weight based on the weight of the monomer composition; the weight proportion of the monomer (m3) in the monomer composition is 40 to 90% by weight based on the weight of the monomer composition; the weight proportion of the polymer (P) is 70 to 90% by weight based on the weight of the polymer electrolyte composition, the weight ratio of the lithium salt is 10 to 30 wt % based on the weight of the polymer electrolyte composition; The coated electrode active material particles for lithium ion batteries have a weight ratio of the polymer electrolyte composition of 1 to 6% by weight based on the weight of the coated electrode active material particles. 【Chemistry 1】 [In general formula (1), R １ represents a hydrogen atom or a methyl group. 【Chemistry 2】 [In general formula (2), R ２ represents a hydrogen atom or a methyl group, and X １ represents an alkylene group having 1 to 2 carbon atoms. 【Transformation 3】 [In general formula (3), R ３ represents a hydrogen atom or a methyl group, R ４ represents a hydrogen atom or an alkyl group having 1 to 12 carbon atoms.

2. 2. The coated electrode active material particles according to claim 1, wherein the weight ratio of the polymer electrolyte composition in the coating layer is 30 to 70% by weight.

3. 3. The coated electrode active material particles according to claim 1, wherein the monomer composition further contains a sulfonate (m4) having a vinyl group.

4. A lithium ion battery comprising the coated electrode active material particles according to any one of claims 1 to 3.

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