JP2021150281A - Coated positive electrode active material particles for lithium-ion battery, positive electrode for lithium-ion battery, and manufacturing method of coated positive electrode active material particles for lithium-ion battery - Google Patents

Abstract

To provide coated cathode active material particles for a lithium-ion battery that can suppress side reactions occurring between an electrolyte and the coated positive electrode active material particles and prevent the internal resistance of the lithium-ion battery from increasing.SOLUTION: A coated positive electrode active material particle for a lithium-ion battery has at least a part of the surface coated with a coating layer. The coating layer contains a polymer compound, a conductive aid, and ceramic particles.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing coated positive electrode active material particles for a lithium ion battery, positive electrode for a lithium ion battery, and coated positive electrode active material particles for a lithium ion battery.

In recent years, reduction of carbon dioxide emissions has been urgently desired for environmental protection. In the automobile industry, expectations are high for the reduction of carbon dioxide emissions by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and the development of secondary batteries for driving motors, which holds the key to their practical application, is enthusiastic. It is done. As a secondary battery, attention is focused on a lithium ion battery that can achieve high energy density and high output density.

For example, Patent Document 1 describes a polymer of a monomer composition containing an ester compound of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth) acrylic acid and an anionic monomer. A resin composition for coating an active material containing a polymer having an acid value of 30 to 700, and a coating layer containing the resin composition for coating an active material are provided on at least a part of the surface of the active material. The coating active material is disclosed.

JP-A-2017-160294

Lithium-ion batteries have come to be widely used in various applications, for example, they may be used in a high temperature environment.
In a conventional lithium-ion battery using a coating active material, when used in a high temperature environment, a side reaction occurs between the electrolytic solution and the coating active material, and the lithium ion battery deteriorates (specifically, inside). There was a problem that the resistance value may increase), and there was room for improvement.

The present invention is for a lithium ion battery that can suppress side reactions that occur between the electrolytic solution and the coated positive electrode active material particles and prevent the internal resistance value of the lithium ion battery from increasing even when used in a high temperature environment. It is an object of the present invention to provide coated positive electrode active material particles. Another object of the present invention is to provide a positive electrode for a lithium ion battery containing the coated positive electrode active material particles for a lithium ion battery, and a method for producing the coated positive electrode active material particles for a lithium ion battery.

As a result of diligent studies to solve the above problems, the present inventors have formed a coating layer containing a polymer compound, a conductive additive and ceramic particles on the surface of the positive electrode active material particles, thereby forming an electrolytic solution and a coating positive electrode activity. We have found that it is possible to suppress side reactions that occur with substance particles and prevent the internal resistance value of the lithium ion battery from increasing, and arrived at the present invention.

That is, the present invention is a coated positive electrode active material particle for a lithium ion battery in which at least a part of the surface of the positive electrode active material particle is coated with a coating layer, and the coating layer is a polymer compound, a conductive auxiliary agent, and ceramic particles. Coated positive electrode active material particles for lithium ion batteries; , 1 to 10% by weight based on the weight of the positive electrode for the lithium ion battery; positive electrode activity containing the coated positive electrode active material particles for the lithium ion battery and an electrolytic solution containing an electrolyte and a solvent. A positive electrode for a lithium ion battery including a material layer, wherein the positive electrode active material layer is a positive electrode for a lithium ion battery made of a non-bonded body of the coated positive electrode active material particles for the lithium ion battery; positive electrode active material particles, a polymer. It is a method for producing coated positive electrode active material particles for a lithium ion battery, which comprises a step of mixing a compound, a conductive auxiliary agent, ceramic particles and an organic solvent and then removing the solvent.

According to the present invention, the coated positive electrode active material for a lithium ion battery can suppress side reactions that occur between the electrolytic solution and the coated positive electrode active material particles, and can prevent the internal resistance value of the lithium ion battery from increasing. Particles can be obtained.

FIG. 1 is a graph showing the relationship between the storage days of the lithium ion batteries obtained in each of the examples and the comparative examples and the internal resistance value.

[Coated positive electrode active material particles for lithium-ion batteries]
The coated positive electrode active material particles for a lithium ion battery of the present invention (hereinafter, also simply referred to as “coated positive electrode active material particles”) are coated positive electrode active material particles in which at least a part of the surface of the positive electrode active material particles is coated with a coating layer. The coating layer contains a polymer compound, a conductive additive, and ceramic particles.
In the coated positive electrode active material particles of the present invention, the coating layer contains a polymer compound, a conductive additive, and ceramic particles to suppress side reactions that occur between the electrolytic solution and the coated positive electrode active material particles. It is possible to prevent the internal resistance value of the lithium ion battery from increasing.

As the positive electrode active material particles, composite oxide of lithium and transition metal {composite oxide is a transition metal is one _{(LiCoO 2, LiNiO 2, LiAlMnO} 4, LiMnO 2 and LiMn ₂ O _4, etc.), transition metal elements There composite oxide is a two (e.g. _{LiFeMnO 4, LiNi 1-x Co} x O 2, LiMn 1-y Co y O 2, LiNi 1/3 Co 1/3 Al 1/3 O 2 and _{LiNi 0.8} Co _0.15 Al _0.05 O ₂₎ and a composite oxide metal element is three or more [e.g. _{LiM a M 'b M''} c O 2 (M, different transition metals M' and M '' are each It is an element and satisfies a + b + c = 1. For example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), etc.}, lithium-containing transition metal phosphate (for example, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and LiNiPO). ₄ ), transition metal oxides (eg MnO ₂ and V ₂ O ₅ ), transition metal sulfides (eg MoS ₂ and TiS ₂ ) and conductive polymers (eg polyaniline, polypyrrole, polythiophene, polyacetylene and poly-p-phenylene). And polyvinylcarbazole) and the like, and two or more kinds may be used in combination.
The lithium-containing transition metal phosphate may be one in which a part of the transition metal site is replaced with another transition metal.

The volume average particle size of the positive electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 35 μm, and further preferably 2 to 30 μm from the viewpoint of the electrical characteristics of the battery. preferable.

The coating layer contains a polymer compound, a conductive auxiliary agent, and ceramic particles.
As the polymer compound, for example, a resin containing a polymer containing the acrylic monomer (a) as an essential constituent monomer is preferable.
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-mentioned monomer composition, the content of acrylic acid (a0) is preferably more than 90% by weight and 98% by weight or less based on the weight of the whole monomer. From the viewpoint of the flexibility of the coating layer, the content of acrylic acid (a0) is more preferably 93.0 to 97.5% by weight based on the weight of the entire monomer, and 95.0 to 97. It is more preferably 0% by weight.

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

Examples of the monomer (a1) having a carboxyl group or an acid anhydride group other than acrylic acid (a0) include monocarboxylic acids having 3 to 15 carbon atoms such as methacrylic acid, crotonic acid, and cinnamic acid; (anhydrous) maleic acid and fumal. Dicarboxylic acids having 4 to 24 carbon atoms such as acids, (anhydrous) itaconic acid, citraconic acid, and mesaconic acid; trivalent to tetravalent or higher valent polycarboxylic acids having 6 to 24 carbon atoms such as aconitic acid, etc. Can be mentioned.

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

In the monomer (a2) represented by the general formula (1), R ¹ represents a hydrogen atom or a methyl group. R ¹ is preferably a methyl group.
R ² is a linear or branched alkyl group having 4 to 12 carbon atoms, or is preferably a branched alkyl group having 13 to 36 carbon atoms.

(A21) ^{Ester compound in which R 2} is a linear or branched alkyl group having 4 to 12 carbon atoms Examples of the linear alkyl group having 4 to 12 carbon atoms include a butyl group, a pentyl group, a hexyl group, a heptyl group and an octyl group. Examples thereof include a nonyl group, a decyl group, an undecyl group and a dodecyl group.
As the branched alkyl group having 4 to 12 carbon atoms, 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-Methylheptyl 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-dimethylheptyl 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-Mech Rudecyl 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-methylundesyl group, 3-methylundesyl group, 4-methylundesyl group, 5-methylundesyl group, 6-methylundesyl group, 7 -Methylundecyl group, 8-methylundesyl group, 9-methylundesyl group, 10-methylundesyl 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 and the like can be mentioned. Of these, a 2-ethylhexyl group is particularly preferable.

(A22) An ^{ester compound in which R 2} is a branched alkyl group having 13 to 36 carbon atoms. Examples of the branched alkyl group having 13 to 36 carbon atoms include a 1-alkylalkyl group [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyl octadecyl group, 1-octyl hexadecyl group, 1-decyl tetradecyl group, 1-undecyl tridecyl group, etc.], 2-alkylalkyl group [2-methyldodecyl group, 2-hexyl octadecyl group, 2- Octyl hexadecyl group, 2-decyl tetradecyl group, 2-undecyl tridecyl group, 2-dodecyl hexadecyl group, 2-tridecyl pentadecyl group, 2-decyl octadecyl group, 2-tetradecyl octadecyl group, 2- Hexadecyl octadecyl group, 2-tetradecyl eicosyl group, 2-hexadecyl eicosyl group, etc.] 3-34-alkylalkyl groups (3-alkylalkyl groups, 4-alkylalkyl groups, 5-alkylalkyl groups, 32 -Alkylalkyl groups, 33-alkylalkyl groups, 34-alkylalkyl groups, etc.), as well as propylene oligomers (7-11 mer), ethylene / propylene (molar ratio 16 / 1-1 / 11) oligomers, isobutylene oligomers (mole ratio 16 / 1-1 / 11) One or more branched alkyl groups such as residues obtained by removing hydroxyl groups from oxoalcohols obtained from 7 to 8 mer) and α-olefin (5 to 20 carbon atoms) oligomers (4 to 8 mer). Examples thereof include mixed alkyl groups contained therein.

The polymer compound constituting the coating layer may contain an ester compound (a3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid as the acrylic monomer (a).
Examples of the monohydric aliphatic alcohol having 1 to 3 carbon atoms constituting the ester compound (a3) include methanol, ethanol, 1-propanol and 2-propanol.
In addition, (meth) acrylic acid means acrylic acid or methacrylic acid.

The polymer compound constituting the coating layer is a polymer of a monomer composition containing an acrylic acid (a0) and at least one of a monomer (a1), a monomer (a2) and an ester compound (a3). More preferably, it is a polymer of a monomer composition containing an acrylic acid (a0) and at least one of a monomer (a1), an ester compound (a21) and an ester compound (a3). It is more preferably a polymer of a monomer composition containing an acrylic acid (a0) and any one of a monomer (a1), a monomer (a2) and an ester compound (a3), and an acrylic acid (a0). ) And any one of the monomer (a1), the ester compound (a21) and the ester compound (a3).
As the polymer compound constituting the coating layer, for example, acrylic acid using maleic acid as the monomer (a1), a copolymer of acrylic acid and maleic acid, and 2-ethylhexyl methacrylate as the monomer (a2). And a copolymer of 2-ethylhexyl methacrylate, a copolymer of acrylic acid and methyl methacrylate using methyl methacrylate as the ester compound (a3), and the like.

The total content of the monomer (a1), the monomer (a2) and the ester compound (a3) is 2.0 to 9.9 based on the weight of the entire monomer from the viewpoint of suppressing the volume change of the positive electrode active material particles. It is preferably% by weight, more preferably 2.5 to 7.0% by volume.

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

Examples of the structure having a polymerizable unsaturated double bond include a vinyl group, an allyl group, a styrenyl group and a (meth) acryloyl group.
Examples of the anionic group include a sulfonic acid group and a carboxyl group.
Anionic monomers having a polymerizable unsaturated double bond and an anionic group are compounds obtained by combining these, and examples thereof include vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid and (meth) acrylic acid. Be done.
The (meth) acryloyl group means an acryloyl group or a methacryloyl group.
Examples of the cation constituting the salt (a4) of the anionic monomer include lithium ion, sodium ion, potassium ion, ammonium ion and the like.

Further, the polymer compound constituting the coating layer is copolymerized with acrylic acid (a0), the monomer (a1), the monomer (a2) and the ester compound (a3) as the acrylic monomer (a) as long as the physical properties are not impaired. It may contain a possible radically polymerizable monomer (a5).
As the radically polymerizable monomer (a5), a monomer containing no active hydrogen is preferable, and the following monomers (a51) to (a58) can be used.

(A51) A hydro formed from a linear aliphatic monool having 13 to 20 carbon atoms, an alicyclic monool having 5 to 20 carbon atoms, or an aromatic aliphatic monool having 7 to 20 carbon atoms and (meth) acrylic acid. Calvir (meth) acrylate Examples of the monool include (i) linear aliphatic monool (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, nonadecil alcohol, arachidyl alcohol). Etc.), (iii) alicyclic monool (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol, etc.), (iii) aromatic aliphatic monool (benzyl alcohol, etc.) and a mixture of two or more thereof. Can be mentioned.

(A52) Poly (n = 2 to 30) Oxyalkylene (2 to 4 carbon atoms) Alkyl (1 to 18 carbon atoms) Ether (meth) Acrylate [Methanol ethylene oxide (hereinafter abbreviated as EO) 10 mol adduct (meth) ) Acrylate, propylene oxide of methanol (hereinafter abbreviated as PO) 10 mol adduct (meth) acrylate, etc.]

(A53) Nitrogen-containing vinyl compound (a53-1) Amide group-containing vinyl compound (i) (Meta) acrylamide compound having 3 to 30 carbon atoms, such as N, N-dialkyl (1 to 6 carbon atoms) or dialalkyl (carbon number) 7 to 15) (meth) acrylamide (N, N-dimethylacrylamide, N, N-dibenzylacrylamide, etc.), diacetoneacrylamide (ii) Excluding the above (meth) acrylamide compound, containing an amide group having 4 to 20 carbon atoms Vinyl compounds such as N-methyl-N-vinylacetamide, cyclic amides [pyrrolidone compounds (6 to 13 carbon atoms, for example, N-vinylpyrrolidone, etc.)]

(A53-2) (Meta) Acrylate Compound (i) Dialkyl (1 to 4 Carbons) Aminoalkyl (1 to 4 Carbons) (Meta) Acrylate [N, N-Dimethylaminoethyl (Meta) Acrylate, N, N -Diethylaminoethyl (meth) acrylate, t-butylaminoethyl (meth) acrylate, morpholinoethyl (meth) acrylate, etc.]
(Ii) Quaternary ammonium group-containing (meth) acrylate {tertiary amino group-containing (meth) acrylate [N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, etc.] Compounds (quaternized with a quaternary agent such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate), etc.}

(A53-3) Heterocyclic-containing vinyl compound A pyridine compound (7 to 14 carbon atoms, for example 2- or 4-vinylpyridine), an imidazole compound (5 to 12 carbon atoms, for example N-vinylimidazole), a pyrrole compound (carbon number). 6 to 13, for example N-vinylpyrrole), pyrrolidone compounds (6 to 13 carbon atoms, for example N-vinyl-2-pyrrolidone)

(A53-4) Nitrile Group-Containing Vinyl Compound A nitrile group-containing vinyl compound having 3 to 15 carbon atoms, such as (meth) acrylonitrile, cyanostyrene, and cyanoalkyl (1 to 4 carbon atoms) acrylate.

(A53-5) Other Nitrogen-Containing Vinyl Compounds Nitro group-containing vinyl compounds (8 to 16 carbon atoms, for example, nitrostyrene) and the like.

(A54) Vinyl Hydrocarbons (a54-1) Aliphatic Vinyl Hydrocarbons Olefins having 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.

(A54-2) Alicyclic vinyl hydrocarbons Cyclic unsaturated compounds having 4 to 18 or more carbon atoms, such as cycloalkene (eg, cyclohexene), (di) cycloalkadiene [eg, (di) cyclopentadiene], terpenes ( For example, pinene and limonen), inden

(A54-3) Aromatic Vinyl Hydrocarbons Aromatic unsaturated compounds having 8 to 20 or more carbon atoms, such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, and butyl. Styrene, phenylstyrene, cyclohexylstyrene, benzylstyrene

(A55) Vinyl ester An aliphatic vinyl ester [alkenyl ester of an aliphatic carboxylic acid (mono- or dicarboxylic acid) having 4 to 15 carbon atoms (for example, vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, etc. Vinyl methoxyacetate)]
Aromatic vinyl ester [containing 9 to 20 carbon atoms, for example, an alkenyl ester of an aromatic carboxylic acid (mono- or dicarboxylic acid) (for example, vinylbenzoate, diallylphthalate, methyl-4-vinylbenzoate), and an aromatic ring of an aliphatic carboxylic acid. Ester (eg acetoxystyrene)]

(A56) Vinyl Ether aliphatic vinyl ether [3 to 15 carbon atoms, for example, vinyl alkyl (1 to 10 carbon atoms) ether (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.), vinyl alkoxy (1 to 6 carbon atoms) Alkyl (1 to 4 carbon atoms) ether (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) allyloxyalkane (2 to 6 carbon atoms) (dialyloxyethane, trialiloxietan, tetraallyloxybutane, tetramethallyloxyethane, etc.)], Aromatic vinyl ether (8 to 20 carbon atoms, for example vinyl phenyl ether, phenoxystyrene)

(A57) Vinyl Ketones An aliphatic vinyl ketone (carbon number 4 to 25, for example vinyl methyl ketone, vinyl ethyl ketone), aromatic vinyl ketone (carbon number 9 to 21, for example vinyl phenyl ketone)

(A58) Unsaturated dicarboxylic acid diester An unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms, for example, a dialkyl fumarate (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms). ), Dialkyl maleate (two alkyl groups are linear, branched or alicyclic groups with 1-22 carbon atoms).

When the radically polymerizable monomer (a5) is contained, the content thereof is preferably 0.1 to 3.0% by weight based on the weight of the entire monomer.

The preferable lower limit of the weight average molecular weight of the polymer compound constituting the coating layer is 3,000, the more preferable lower limit is 5,000, and the further preferable lower limit is 7,000. On the other hand, the preferable upper limit of the weight average molecular weight of the polymer compound is 100,000, and the more preferable upper limit is 70,000.

The weight average molecular weight of the polymer compounds constituting the coating layer can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.
Equipment: Alliance GPC V2000 (manufactured by Waters)
Solvents: orthodichlorobenzene, DMF, THF
Standard substance: Polystyrene sample concentration: 3 mg / ml
Column stationary phase: PLgel 10 μm, two MIXED-B in series (manufactured by Polymer Laboratories)
Column temperature: 135 ° C

The polymer compounds constituting the coating layer are known polymerization initiators {azo-based initiator [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.} It can be produced by a polymerization method (lumpy 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 0.05 to 2% by weight, based on the total weight of the monomers, from the viewpoint of adjusting the weight average molecular weight to a preferable range. More preferably, it is 0.1 to 1.5% by weight, and the polymerization temperature and the polymerization time are adjusted according to the type of the polymerization initiator and the like, but the polymerization temperature is preferably −5 to 150 ° C. (more preferably). The reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

Solvents used in solution polymerization include, for example, esters (2-8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (1-8 carbon atoms, such as methanol, ethanol and octanol), hydrocarbons (carbon atoms). Examples thereof include 4 to 8, for example n-butane, cyclohexane and toluene), amides (for example, N, N-dimethylformamide (hereinafter abbreviated as DMF)) and ketones (3 to 9 carbon atoms, for example, methyl ethyl ketone), and weight average. From the viewpoint of adjusting the molecular weight to a preferable range, the amount used is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, still 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, still more preferably 30 to 80% by weight.

Examples of the dispersion medium in emulsification polymerization and suspension polymerization include water, alcohol (for example, ethanol), ester (for example, ethyl propionate), and light naphtha, and examples of emulsifier include higher fatty acid (10 to 24 carbon atoms) metal salt. (For example, sodium oleate and sodium stearate), higher alcohol (10 to 24 carbon atoms) sulfate ester metal salt (for example, sodium lauryl sulfate), tetramethyldecine ethoxylated, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. Can be mentioned. Further, polyvinyl alcohol, polyvinylpyrrolidone and the like may be added as stabilizers.
The monomer concentration of the solution or dispersion is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, even more preferably 15 to 85% by weight, and the amount of the polymerization initiator used is based on the total weight of the monomers. It is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight.
For 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. ..

The polymer compound constituting the coating layer is a cross-linking agent (A') having a reactive functional group that reacts the polymer compound with a carboxyl group {preferably a polyepoxy compound (a'1) [polyglycidyl ether (bisphenol A). Diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, etc.) and polyglycidyl amine (N, N-diglycidyl aniline and 1,3-bis (N, N-diglycidyl aminomethyl)), etc.] and / or It may be a crosslinked polymer formed by cross-linking with a polyol compound (a'2) (ethylene glycol or the like)}.

Examples of the method of cross-linking the polymer compound constituting the coating layer using the cross-linking agent (A') include a method of coating the positive electrode active material particles with the polymer compound constituting the coating layer and then cross-linking. Specifically, after producing the coating active material particles by mixing the positive electrode active material particles and the resin solution containing the polymer compound constituting the coating layer and removing the solvent, a solution containing the cross-linking agent (A') is prepared. By mixing with the coating active material particles and heating, a solvent removal and a cross-linking reaction are caused, and a reaction in which the polymer compound constituting the coating layer is cross-linked by the cross-linking agent (A') is carried out in the positive electrode active material particles. There is a method of raising it on the surface.
The heating temperature is adjusted according to the type of the cross-linking agent, but is preferably 70 ° C. or higher when the polyepoxy compound (a'1) is used as the cross-linking agent, and 70 ° C. or higher when the polyol compound (a'2) is used. It is preferably 120 ° C. or higher.

The conductive auxiliary agent is preferably selected from materials having conductivity.
Preferred conductive aids are 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 lamps). Black, etc.), etc.], and mixtures thereof, etc. may be mentioned.
These conductive auxiliaries may be used alone or in combination of two or more. Further, it may be used as these alloys or metal oxides.
Among them, from the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, gold, copper, titanium and mixtures thereof are more preferable, and silver, gold, aluminum, stainless steel and carbon are particularly preferable. It is preferably carbon.
Further, as these conductive auxiliaries, a conductive material [preferably a metal one among the above-mentioned conductive auxiliaries] may be coated around a particle-based ceramic material or a resin material by plating or the like.

The shape (form) of the conductive auxiliary agent is not limited to the particle form, and may be a form other than the particle form, and is a form practically used as a so-called filler-based conductive auxiliary agent such as carbon nanofibers and carbon nanotubes. You may.

The average particle size of the conductive auxiliary agent is not particularly limited, but is preferably about 0.01 to 10 μm from the viewpoint of the electrical characteristics of the battery.
In the present specification, the “particle size of the conductive auxiliary agent” means the maximum distance L among the distances between any two points on the contour line of the conductive auxiliary agent. The value of the "average particle size" is the average value of the particle size of the particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

The ratio of the polymer compound constituting the coating layer to the conductive auxiliary agent is not particularly limited, but from the viewpoint of the internal resistance of the battery and the like, the polymer compound (resin solid content weight) constituting the coating layer by weight ratio. : The conductive auxiliary agent is preferably 1: 0.01 to 1:50, more preferably 1: 0.2 to 1: 3.0.

Examples of the ceramic particles include metal carbide particles, metal oxide particles, and glass-ceramic particles.

The metal carbide particles, for example silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide _(Mo 2 C), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), vanadium carbide (VC ), Zirconium carbide (ZrC) and the like.

Examples of the metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), tin oxide (SnO ₂ ), titania (TIO ₂ ), zirconia (ZrO ₂ ), and the like. Indium oxide (In ₂ O ₃ ), Li ₂ B ₄ O ₇ , Li ₄ Ti ₅ O ₁₂ , Li ₂ Ti ₂ O ₅ , LiTaO ₃ , LiNbO ₃ , LiAlO ₂ , Li ₂ ZrO ₃ , Li ₂ WO ₄ , Li ₂ TiO ₃ , Li ₃ PO ₄ , Li ₂ MoO ₄ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , Li ₂ SiO ₃ , and ABO ₃ (However, A is Ca, Sr, Ba, La, Pr. At least one selected from the group consisting of 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. Species), and examples thereof include perovskite-type oxide particles.
_{The metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al 2} O ₃ ), and silicon dioxide (SiO ₂ ) from the viewpoint of preferably suppressing side reactions that occur between the electrolytic solution and the coated positive electrode active material particles. ) And lithium tetraborate (Li ₂ B ₄ O ₇ ) are preferable.

The ceramic particles are preferably glass ceramic particles from the viewpoint of preferably suppressing side reactions that occur between the electrolytic solution and the coated positive electrode active material particles.
These may be used alone or in combination of two or more.

The glass-ceramic particles are preferably lithium-containing phosphoric acid compounds having a rhombohedral crystal system, and the chemical formula thereof is represented by Li _x M " ₂ P ₃ O ₁₂ (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. Further, a part of P may be replaced with Si or B, and a part of O may be replaced with F, Cl or the like. 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 and the} like can be used.
Further, materials having different compositions may be mixed or composited, or the surface may be coated with a glass electrolyte or the like. Alternatively, it is preferable to use glass-ceramic particles that precipitate the crystal phase of the lithium-containing phosphoric acid compound having a NASICON-type structure by heat treatment.
Examples of the glass electrolyte include the glass electrolyte described in JP-A-2019-96478.

_{Here, the blending ratio of Li 2} O in the glass-ceramic particles is preferably 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, F, and is a LISION type. A solid electrolyte that has a perovskite type, β-Fe ₂ (SO ₄ ) _{type 3} and Li ₃ In ₂ (PO ₄ ) _{type 3} crystal structure and conducts Li ions at room temperature of 1 × ^10-5 S / cm or more. May be used.

The above-mentioned ceramic particles may be used alone or in combination of two or more.

The volume average particle diameter of the ceramic particles is preferably 1 to 1000 nm, more preferably 1 to 500 nm, and even more preferably 1 to 150 nm from the viewpoint of energy density and electric resistance value.
In the present specification, the volume average particle size means the particle size (Dv50) at an integrated value of 50% in the particle size distribution obtained by the microtrack method (laser diffraction / scattering method). The microtrack method is a method for obtaining a particle size distribution using scattered light obtained by irradiating particles with laser light. A microtrack or the like manufactured by Nikkiso Co., Ltd. can be used for measuring the volume average particle size.

The weight ratio of the ceramic particles is preferably 0.5 to 5.0% by weight based on the weight of the coated positive electrode active material particles.
By containing the ceramic particles in the above range, side reactions that occur between the electrolytic solution and the coated positive electrode active material particles can be suitably suppressed.
The weight ratio of the ceramic particles is more preferably 2.0 to 4.0% by weight based on the weight of the coated positive electrode active material particles.

At least a part of the surface of the positive electrode active material particles is coated with a coating layer.
From the viewpoint of cycle characteristics, the positive electrode active material particles preferably have a coverage of 30 to 95% obtained by the following formula.
Coverage (%) = {1- [BET specific surface area of coated positive electrode active material particles / (BET specific surface area of positive electrode active material particles x weight ratio of positive electrode active material particles contained in coated positive electrode active material + conductive auxiliary agent BET specific surface area x weight ratio of conductive aid contained in coated positive electrode active material particles + BET specific surface area of ceramic particles x weight ratio of ceramic particles contained in coated positive electrode active material particles)]} x 100

[Manufacturing method of coated positive electrode active material particles for lithium-ion batteries]
The method for producing coated positive electrode active material particles for a lithium ion battery of the present invention (hereinafter, also simply referred to as “method for producing coated positive electrode active material particles”) includes positive electrode active material particles, a polymer compound, a conductive additive, ceramic particles and the like. It has a step of removing the solvent after mixing the organic solvent.

The organic solvent is not particularly limited as long as it is an organic solvent capable of dissolving a polymer compound, and a known organic solvent can be appropriately selected and used.

In the method for producing coated positive electrode active material particles, first, the positive 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 positive electrode active material particles, the polymer compound constituting the coating layer, the conductive auxiliary agent and the ceramic particles are mixed is not particularly limited, and for example, the polymer compound constituting the coating layer mixed in advance, the conductive auxiliary agent and the ceramic are not particularly limited. The resin composition composed of particles may be further mixed with the positive electrode active material particles, or the positive electrode active material particles, the polymer compound constituting the coating layer, the conductive auxiliary agent and the ceramic particles may be mixed at the same time. The positive electrode active material particles may be mixed with the polymer compound constituting the coating layer, and the conductive auxiliary agent and the ceramic particles may be further mixed.

The coated positive electrode active material particles of the present invention can be obtained by coating the positive electrode active material particles with a coating layer containing a polymer compound, a conductive auxiliary agent, and ceramic particles. For example, the positive electrode active material particles are universally mixed. The resin solution containing the polymer compound constituting the coating layer was added dropwise over 1 to 90 minutes in a state of being put in a machine and stirred at 30 to 500 rpm, the conductive auxiliary agent and the ceramic particles were mixed, and the mixture was kept stirred. It can be obtained by raising the temperature to ~ 200 ° C., reducing the pressure to 0.007 to 0.04 MPa, and then holding for 10 to 150 minutes to remove the solvent.

The blending ratio of the positive electrode active material particles and the resin composition containing the polymer compound, the conductive auxiliary agent and the ceramic particles constituting the coating layer is not particularly limited, but the positive electrode active material particles: resin in terms of weight ratio. The composition is preferably 1: 0.001 to 0.1.

[Positive electrode for lithium-ion batteries]
The positive electrode for a lithium ion battery of the present invention (hereinafter, also simply referred to as “positive electrode”) includes a positive electrode active material layer containing the coated positive electrode active material particles of the present invention and an electrolytic solution containing an electrolyte and a solvent.

The coated positive electrode active material particles contained in the positive electrode active material layer are preferably 40 to 95% by weight based on the weight of the positive electrode active material layer from the viewpoint of dispersibility of the positive electrode active material particles and electrode moldability. More preferably, it is ~ 90% by weight.

As the electrolyte, an electrolyte used in a known electrolytic solution can be used, for example, a lithium salt of an inorganic anion such as _{LiPF 6} , LiBF ₄ , LiSbF ₆ , _{LiAsF 6} , LiClO ₄ and LiN (FSO ₂ ) _{2, LiN.} Examples thereof include lithium salts of organic anions such as (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) _{3. Of these, LiN (FSO 2} ) ₂ is preferable from the viewpoint of battery output and charge / discharge cycle characteristics.

As the solvent, a non-aqueous solvent used in a known electrolytic solution can be used, and for example, a lactone compound, a cyclic or chain carbonate ester, a chain carboxylic acid ester, a cyclic or chain ether, a phosphoric acid ester, or a nitrile compound can be used. , Amid compounds, sulfones, sulfolanes and mixtures thereof can be used.

Examples of the lactone compound include a 5-membered ring (γ-butyrolactone, γ-valerolactone, etc.) and a 6-membered ring (δ-valerolactone, etc.) lactone compound.

Examples of the cyclic carbonate 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, di-n-propyl carbonate and the like. ..

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

Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,4-dioxane and the like. Examples of the chain ether include dimethoxymethane and 1,2-dimethoxyethane.

Phosphate esters include trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl 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- Examples thereof include dioxaphosphoran-2-one and 2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one.

Examples of the nitrile compound include acetonitrile and the like. Examples of the amide compound include DMF and the like. Examples of the sulfone include dimethyl sulfone and diethyl sulfone.

One of these solvents may be used alone, or two or more of these solvents may be used in combination.

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, and 1.8 to 4.0 mol / L. It is more preferably 2.0 to 3.5 mol / L, and particularly preferably 2.0 to 3.5 mol / L.
Since such an electrolytic solution has an appropriate viscosity, a liquid film can be formed between the coated positive electrode active material particles, and a lubricating effect (position adjusting ability of the coated positive electrode active material particles) is imparted to the coated positive electrode active material particles. can do.

The positive electrode active material layer may further contain a conductive auxiliary agent in addition to the conductive auxiliary agent contained in the coating layer of the coated positive electrode active material particles as required. The conductive auxiliary agent contained in the coating layer as needed is integrated with the coated positive electrode active material particles, whereas the conductive auxiliary agent contained in the positive electrode active material layer is contained separately from the coated positive electrode active material particles. Can be distinguished by.
As the conductive additive that may be contained in the positive electrode active material layer, those described in [Coated positive electrode active material particles for lithium ion batteries] can be used.

When the positive electrode active material layer contains a conductive auxiliary agent, the total content of the conductive auxiliary agent contained in the positive electrode and the conductive auxiliary agent contained in the coating layer is based on the weight of the positive electrode active material layer excluding the electrolytic solution. It is preferably less than 4% by weight, more preferably less than 3% by weight. On the other hand, the total content of the conductive auxiliary agent contained in the positive electrode and the conductive auxiliary agent contained in the coating layer is 2.5% by weight or more based on the weight of the positive electrode active material layer excluding the electrolytic solution. preferable.

The positive electrode active material layer preferably does not contain a binder.
In the present specification, the binder means a drug that cannot reversibly fix the positive electrode active material particles to each other and the positive electrode active material particles to the current collector, and is starch, polyvinylidene fluoride, or polyvinyl alcohol. , Carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, known solvent-drying type binders for lithium ion batteries such as polyethylene and polypropylene.
These binders are used by dissolving or dispersing in a solvent, and solidify by volatilizing and distilling off the solvent to irreversibly fix the positive electrode active material particles and the positive electrode active material particles and the current collector. To do.

The positive electrode active material layer may contain an adhesive resin. The adhesive resin means a resin that does not solidify even when the solvent component is volatilized and dried, and is a material different from the binder and is distinguished.
Further, while the coating layer constituting the coated positive electrode active material particles is fixed to the surface of the positive electrode active material particles, the adhesive resin reversibly fixes the surfaces of the positive electrode active material particles to each other. The adhesive resin can be easily separated from the surface of the positive electrode active material particles, but the coating layer cannot be easily separated. Therefore, the coating layer and the adhesive resin are different materials.

The adhesive resin contains 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 an essential constituent monomer, and the above low Tg monomer. Examples thereof include polymers in which the total weight ratio of the above is 45% by weight or more based on the total weight of the constituent monomers.
When an adhesive resin is used, it is preferable to use 0.01 to 10% by weight of the adhesive resin with respect to the total weight of the positive electrode active material particles.

In the first aspect of the positive electrode for a lithium ion battery of the present invention, the weight ratio of the polymer compound contained in the positive electrode for a lithium ion battery is 1 to 10% by weight based on the weight of the positive electrode for a lithium ion battery.
Here, the “polymer compound” means a polymer compound, a binder and an adhesive resin constituting the coating layer, and in the positive electrode for a lithium ion battery of the present invention, the polymer compound constituting the coating layer The total weight ratio with the adhesive resin is equal to the above-mentioned "weight ratio of polymer compound" and does not contain any binder (0% by weight).

In the second aspect of the positive electrode for a lithium ion battery of the present invention, the positive electrode active material layer is composed of a non-bonded body of coated positive electrode active material particles for a lithium ion battery.
Here, in the non-bound body, the positions of the positive electrode active material particles are not fixed in the positive electrode active material layer, and the positive electrode active material particles and the positive electrode active material particles and the current collector are irreversibly fixed to each other. Means not.
When the positive electrode active material layer is a non-bonded body, since the positive electrode active material particles are not irreversibly fixed to each other, they can be separated without causing destruction at the interface between the positive electrode active material particles, and the positive electrode active material can be separated. Even when stress is applied to the layer, the movement of the positive electrode active material particles can prevent the positive electrode active material layer from being destroyed, which is preferable.
The positive electrode active material layer which is a non-binder can be obtained by a method such as forming a slurry for a positive electrode active material layer containing positive electrode active material particles, an electrolytic solution, etc. and not containing a binder into a positive electrode active material layer. ..

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.

The positive electrode for a lithium ion battery of the present invention collects, for example, a slurry for a positive electrode active material layer containing the coated positive electrode active material particles of the present invention, an electrolytic solution containing an electrolyte and a solvent, and if necessary, a conductive auxiliary agent and the like. It can be produced by applying it to and then drying it. Specifically, after applying the slurry for the positive electrode active material layer on the current collector with a coating device such as a bar coater, the non-woven fabric is allowed to stand on the positive electrode active material particles to absorb the solvent. Examples thereof include a method of removing the particles and pressing the particles with a press machine if necessary.

Examples of the material constituting the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel and alloys thereof, as well as calcined carbon, a conductive polymer material, 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 and a deposited 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.

It is preferable that the positive electrode for a lithium ion battery further includes a current collector, and the positive electrode active material layer is provided on the surface of the current collector. For example, it is preferable that the positive electrode of the present invention 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.

As the conductive polymer material constituting the resin current collector, for example, a resin to which a conductive agent is added can be used.
As the conductive agent constituting the conductive polymer material, the same conductive agent as the conductive auxiliary agent which is an arbitrary component of the coating layer can be preferably used.
Examples of the resin constituting the conductive polymer material include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyether nitrile (PEN), and poly. Tetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin or a mixture thereof. And so on.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferable, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferable. (PMP).
The resin current collector can be obtained by a known method described in Japanese Patent Application Laid-Open No. 2012-150905 and International Publication No. 2015/005116.

[Lithium-ion battery]
A lithium ion battery can be obtained by storing the positive electrode of the present invention in a cell container together with a separator in combination with opposite electrodes, injecting an electrolytic solution, and sealing the cell container.
Further, the positive electrode of the present invention is formed on one surface of the current collector, the negative electrode is formed on the other surface to produce a bipolar (bipolar) type electrode, and the bipolar (bipolar) type electrode is laminated with the separator. It can also be obtained by storing in a cell container, injecting an electrolytic solution, and sealing the cell container.

As the separator, a porous film made of polyethylene or polypropylene, a laminated film of a porous polyethylene film and a porous polypropylene, a non-woven fabric made of synthetic fibers (polyester fiber, aramid fiber, etc.) or glass fiber, and silica on the surface thereof. , Known separators for lithium ion batteries, such as those to which ceramic fine particles such as alumina and titania are attached.

Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to the Examples as long as the gist of the present invention is not deviated. Unless otherwise specified, parts mean parts by weight and% means% by weight.

<Preparation of polymer compounds for coating>
150 parts of DMF was placed in a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, and the temperature was raised to 75 ° C. Next, a monomer composition containing 91 parts of acrylic acid, 9 parts of methyl methacrylate and 50 parts of DMF, and 0.3 parts of 2,2'-azobis (2,4-dimethylvaleronitrile) and 2,2'- A solution of 0.8 parts of azobis (2-methylbutyronitrile) dissolved in 30 parts of DMF was continuously added dropwise over 2 hours with a dropping funnel while blowing nitrogen into a four-necked flask. Radical polymerization was carried out. After completion of the dropping, the reaction was continued at 75 ° C. for 3 hours. Then, the temperature was raised to 80 ° C. and the reaction was continued for 3 hours to obtain a copolymer solution having a resin concentration of 30%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 150 ° C. and 0.01 MPa for 3 hours, and DMF was distilled off to obtain a copolymer. This copolymer was roughly pulverized with a hammer and then additionally pulverized in a mortar to obtain a powdery polymer compound for coating.

<Preparation of electrolytic solution>
An electrolytic solution was prepared by dissolving _{LiN (FSO 2} ) ₂ in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and propylene carbonate (PC) at a ratio of 2.0 mol / L.

<Example 1>
[Preparation of coated positive electrode active material particles A]
One part of the polymer compound for coating was dissolved in 3 parts of DMF to obtain a polymer compound solution for coating.
84 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) were placed in a universal mixer high-speed mixer FS25 [manufactured by EarthTechnica Co., Ltd.] at room temperature. With stirring at 720 rpm, 9 parts of the coating polymer compound solution was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Next, 3 parts of acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.] and glass ceramic particles 1 (trade name "lithium ion conductive glass ceramics LICGC ^TM PW-01 (1 μm)" which are conductive aids in a stirred state. ) ”[Manufactured by O'Hara Co., Ltd.]) The four parts were added in 2 minutes while being divided, and stirring was continued for 30 minutes.
Then, the pressure was reduced to 0.01 MPa while maintaining the stirring, then the temperature was raised to 140 ° C. while maintaining the stirring and the degree of pressure reduction, and the stirring, the degree of pressure reduction and the temperature were maintained for 8 hours to distill off the volatile components. ..
The obtained powder was classified with a sieve having an opening of 200 μm to obtain coated positive electrode active material particles A.

[Preparation of resin current collector]
With a twin-screw extruder, 70 parts of polypropylene [trade name "SunAllomer PL500A", manufactured by SunAllomer Ltd.], 25 parts of carbon nanotubes [trade name "FloTube9000", manufactured by CNano] and a dispersant [trade name "Umex 1001" , Sanyo Kasei Kogyo Co., Ltd.] 5 parts were melt-kneaded under the conditions of 200 ° C. and 200 rpm to obtain a resin mixture.
The obtained resin mixture was passed through a T-die extrusion film forming machine and stretched and rolled to obtain a conductive film for a resin current collector having a film thickness of 100 μm. Next, the obtained conductive film for a resin current collector was cut to a size of 17.0 cm × 17.0 cm, nickel was vapor-deposited on one side, and then a terminal (5 mm × 3 cm) for taking out a current was connected. A resin current collector was obtained.

[Manufacturing positive electrodes for lithium-ion batteries]
42 parts of electrolytic solution and 4.2 parts of carbon fiber [Donna Carbo 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] are mixed and kneaded by planetary stirring. Mix at 2000 rpm for 5 minutes using the apparatus {Awatori Rentaro [manufactured by Shinky Co., Ltd.]}, and then add 30 parts of the electrolytic solution and 206 parts of the coated positive electrode active material particles A, and then further Awatori kneading. Mix with Taro at 2000 rpm for 2 minutes, add 20 parts of the electrolyte, stir with Awatori Kentarou for 1 minute at 2000 rpm, add 2.3 more parts of the electrolyte, and then add Awatori Kentarou. Was mixed at 2000 rpm for 2 minutes to prepare a slurry for the positive electrode active material layer. The obtained slurry for the positive electrode active material layer ^{was applied to one side of the above resin current collector so that the grain size was 80 mg / cm 2,} and pressed at a pressure of 1.4 MPa for about 10 seconds to obtain a thickness of 340 μm. A positive electrode for a lithium ion battery (16.2 cm × 16.2 cm) according to Example 1 was produced.

[Manufacturing of lithium-ion batteries]
The obtained positive electrode was combined with a counter electrode Li metal via a separator (Celguard # 3501) to prepare a laminated cell.

<Example 2>
[Preparation of coated positive electrode active material particles B]
Same as Example 1 except that the glass-ceramic particles 1 are changed to glass-ceramic particles 2 (trade name "lithium ion conductive glass ceramics LICGC ^TM PW-01 (0.4 μm)" [manufactured by O'Hara Co., Ltd.]). The coated positive electrode active material particles B were obtained.

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles B, and a lithium ion battery was obtained.

<Example 3>
[Preparation of coated positive electrode active material particles C]
The coated positive electrode active material is the same as in Example 1 except that the glass-ceramic particles 1 are changed to lithium tetraborate (trade name “lithium tetraborate, anhydrous”, [manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.]). Particle C was obtained.

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles C, and a lithium ion battery was obtained.

<Example 4>
[Preparation of coated positive electrode active material particles D]
The coated positive electrode active material particles D were obtained in the same manner as in Example 1 except that the glass-ceramic particles 1 were changed to zinc oxide (item “ZnO”, [manufactured by Kanto Chemical Co., Ltd.]).

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles D, and a lithium ion battery was obtained.

<Example 5>
[Preparation of coated positive electrode active material particles E]
The coated positive electrode active material particles E were obtained in the same manner as in Example 1 except that the glass-ceramic particles 1 were changed to aluminum oxide (item “Al ₂ O _{3”, [manufactured by Kanto Chemical Co., Ltd.]).}

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles E, and a lithium ion battery was obtained.

<Example 6>
[Preparation of coated positive electrode active material particles F]
The coated positive electrode active material particles F were obtained in the same manner as in Example 1 except that the glass-ceramic particles 1 were changed to silicon dioxide 1 (item “SiO _{2”, [manufactured by Kanto Chemical Co., Ltd.]).}

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles F, and a lithium ion battery was obtained.

<Example 7>
[Preparation of coated positive electrode active material particles G]
The coated positive electrode active material particles G were obtained in the same manner as in Example 1 except that the glass-ceramic particles 1 were changed to silicon dioxide 2 (trade name “Aerosil 300”, [manufactured by Toshin Kasei Co., Ltd.]). ..

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles G, and a lithium ion battery was obtained.

<Comparative example 1>
[Preparation of coated positive electrode active material particles H]
The coated positive electrode active material particles H were obtained in the same manner as in Example 1 except that the glass-ceramic particles 1 were not added.

[Manufacturing of lithium-ion batteries]
A positive electrode for a lithium ion battery was produced in the same manner as in Example 1 except that the coated positive electrode active material particles A were changed to the coated positive electrode active material particles H, to obtain a lithium ion battery.

Table 1 shows the types of ceramic particles used in Examples and Comparative Examples, the volume average particle diameter, the amount of addition based on the coated positive electrode active material particles, and the weight ratio of the coated resin in the positive electrode for a lithium ion battery.
The volume average particle size was measured by the method described in the present specification.

<Measurement of internal resistance value>
The lithium ion batteries obtained in each Example and Comparative Example were charged and discharged once at 25 ° C. Then, it was fully charged and stored in an environment of 60 ° C.
Using an impedance measuring device (Chemical Impedance Analyzer IM3590 manufactured by Hioki Electric Co., Ltd.), the internal resistance value at a frequency of 1100 Hz was measured after 0 days (immediately after full charge), after storage for 7 days, and after storage for 14 days.
The results are shown in Table 2 and FIG.

From Table 2 and FIG. 1, it was confirmed that in the examples, the increase in the internal resistance value of the lithium ion battery can be prevented even after 14 days.

The coated positive electrode active material particles of the present invention are particularly useful as positive electrode active materials for lithium ion batteries used for mobile phones, personal computers, hybrid vehicles and electric vehicles.

Claims (6)

Positive electrode active material particles Coated positive electrode active material particles for lithium ion batteries in which at least a part of the surface is coated with a coating layer.
Coated positive electrode active material particles for a lithium ion battery in which the coating layer contains a polymer compound, a conductive auxiliary agent, and ceramic particles. The coated positive electrode active material particles for a lithium ion battery according to claim 1, wherein the weight ratio of the ceramic particles is 0.5 to 5.0% by weight based on the weight of the coated positive electrode active material particles. The coated electrode active material particles for a lithium ion battery according to claim 1 or 2, wherein the volume average particle diameter of the ceramic particles is 1 to 1000 nm. A positive electrode for a lithium ion battery comprising a positive electrode active material layer containing the coated positive electrode active material particles for a lithium ion battery according to any one of claims 1 to 3 and an electrolytic solution containing an electrolyte and a solvent.
A positive electrode for a lithium ion battery in which the weight ratio of the polymer compound contained in the positive electrode for a lithium ion battery is 1 to 10% by weight based on the weight of the positive electrode for a lithium ion battery. A positive electrode for a lithium ion battery comprising a positive electrode active material layer containing the coated positive electrode active material particles for a lithium ion battery according to any one of claims 1 to 3 and an electrolytic solution containing an electrolyte and a solvent.
The positive electrode active material layer is a positive electrode for a lithium ion battery made of a non-bonded body of the coated positive electrode active material particles for the lithium ion battery. The coated positive electrode active material particles for a lithium ion battery according to any one of claims 1 to 3, further comprising a step of mixing the positive electrode active material particles, a polymer compound, a conductive auxiliary agent, ceramic particles and an organic solvent and then removing the solvent. Manufacturing method.

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