JP6896477B2 - Coated negative electrode active material for lithium-ion batteries - Google Patents

Description

The present invention relates to a coated negative electrode active material for a lithium ion battery.

In recent years, there has been an urgent need to reduce carbon dioxide emissions 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 secondary battery that can achieve high energy density and high output density.

Regarding lithium-ion secondary batteries, further improvement of battery characteristics is required. Above all, there is a strong demand for improvement of cycle characteristics, and development of non-aqueous electrolytes and active materials for the purpose of improving cycle characteristics. At the same time, surface treatment of active materials is being studied.

Among them, as a surface treatment of an active material having improved cycle characteristics, a coating active material for a non-aqueous secondary battery electrode in which a specific hydroxy acid compound covers at least a part of the surface of the active material has been proposed (patented). Reference 1).

Japanese Unexamined Patent Publication No. 2011-210668

However, in the non-aqueous electrolyte secondary battery using the coating active material for the non-aqueous secondary battery electrode described in Patent Document 1, the coating layer from the surface of the coating active material generated by the expansion and contraction of the electrode due to charge and discharge. There is a problem in the charge / discharge characteristics of the lithium ion battery, such as the fact that sufficient rate characteristics may not be obtained due to peeling or the like.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a coated negative electrode active material for a lithium ion battery having excellent rate characteristics.

The present inventors have arrived at the present invention as a result of diligent studies to solve the above problems.
That is, the present invention is a coated negative electrode active material for a lithium ion battery, wherein at least a part of the surface of the negative electrode active material for a lithium ion battery is coated with a coating layer containing a polymer compound and a conductive agent. The coverage obtained by the above formula is 10 to 45%.
Coverage (%) = {1- [BET specific surface area of coated negative electrode active material / (BET specific surface area of uncoated negative electrode active material x weight ratio of negative electrode active material contained in coated negative electrode active material + conductive agent BET specific surface area x weight ratio of conductive agent contained in coated negative electrode active material)]} x 100

By using the coated negative electrode active material for a lithium ion battery of the present invention, a lithium ion battery having excellent rate characteristics can be obtained.

Hereinafter, the present invention will be described in detail.
In the present specification, when the term lithium ion battery is used, the concept includes a lithium ion secondary battery.

The present invention is a coated negative electrode active material for a lithium ion battery, wherein at least a part of the surface of the negative electrode active material for a lithium ion battery is coated with a coating layer containing a polymer compound and a conductive agent, and the following calculation is performed. It is a coated negative electrode active material for a lithium ion battery, characterized in that the coverage obtained by the formula is 10 to 45%.
Coverage (%) = {1- [BET specific surface area of coated negative electrode active material / (BET specific surface area of uncoated negative electrode active material x weight ratio of negative electrode active material contained in coated negative electrode active material + conductive agent BET specific surface area x weight ratio of conductive agent contained in coated negative electrode active material)]} x 100
In the above formula, the coated negative electrode active material is the coated negative electrode active material constituting the negative electrode coated active material for the lithium ion battery of the present invention, and the negative electrode active material constituting the coated negative electrode active material is for the lithium ion battery. It is a negative electrode active material.

In the coated negative electrode active material for a lithium ion battery of the present invention, the coverage obtained by the above formula is 10 to 45%.
A negative electrode produced by using a coated negative electrode active material for a lithium ion battery having a coverage in the above range has a high electrode density and good rate characteristics.
If the coverage exceeds 45%, the Coulomb efficiency and rate characteristics deteriorate. On the other hand, if the coverage is less than 10%, the durability of the negative electrode may be insufficient, and the rate characteristics may be deteriorated.

As the negative electrode active material for a lithium ion battery constituting the coated negative electrode active material for a lithium ion battery of the present invention, a conventionally known negative electrode active material can be preferably used. For example, lithium ions are inserted and removed by applying a certain potential. A compound that can be separated and capable of inserting and removing lithium ions at a lower potential than the positive electrode active material for a lithium ion battery used for the counter electrode can be used.
Examples of the negative electrode active material for a lithium ion battery include carbon-based materials [graphite, non-graphitizable carbon, amorphous carbon, fired resin (for example, phenol resin, furan resin, etc. fired and carbonized), cokes (for example, carbonized). Pitch coke, needle coke, petroleum coke, etc.) and carbon fiber, etc.], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composite (carbon particles whose surface is coated with silicon and / or silicon carbide, etc.) Silicon particles or silicon oxide particles coated with carbon and / or silicon carbide, silicon carbide, etc.) and silicon alloys (silicon-aluminum alloy, silicon-lithium alloy, silicon-nickel alloy, silicon-iron alloy, silicon- Titanium alloy, silicon-manganese alloy, silicon-copper alloy, silicon-tin alloy, etc.)], conductive polymers (eg, polyacetylene and polypyrrole, etc.), metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (such as tin, aluminum, zirconium, titanium, etc.) Examples thereof include titanium oxides and lithium-titanium oxides) and metal alloys (for example, lithium-tin alloys, lithium-aluminum alloys and lithium-aluminum-manganese alloys) and mixtures of these with carbon-based materials.
Among the negative electrode active materials for lithium ion batteries, those that do not contain lithium or lithium ions inside may be pre-doped with a part or all of the negative electrode active materials containing lithium or lithium ions in advance.

Among these, carbon-based materials, silicon-based materials and mixtures thereof are preferable from the viewpoint of battery capacity and the like, graphite, non-graphitizable carbon and amorphous carbon are more preferable as carbon-based materials, and silicon-based materials are more preferable. , Silicon oxide and silicon-carbon composites are more preferred.

The volume average particle size of the negative electrode active material for a lithium ion battery is preferably 0.01 to 100 μm, more preferably 0.1 to 20 μm, and further preferably 2 to 10 μm from the viewpoint of the electrical characteristics of the battery. preferable.

In the present specification, the volume average particle size of the negative electrode active material for a lithium ion battery 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.

Subsequently, the coating layer constituting the coating negative electrode active material for the lithium ion battery of the present invention will be described.
The coating layer contains a polymer compound and a conductive agent, and covers at least a part of the negative electrode active material for a lithium ion battery.
When the periphery of the negative electrode active material for a lithium ion battery is coated with a coating layer, the volume change of the negative electrode can be alleviated and the expansion of the negative electrode can be suppressed. Further, the wettability of the coated negative electrode active material for a lithium ion battery to a non-aqueous solvent can be improved.

As the polymer compound constituting the coating layer, a polymer compound having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more is preferable.

The liquid absorption rate when immersed in the electrolytic solution is calculated by the following formula by measuring the weight of the polymer compound before and after immersion in the electrolytic solution.
Liquid absorption rate (%) = [(Weight of polymer compound after immersion in electrolyte solution-Weight of polymer compound before immersion in electrolyte solution) / Weight of polymer compound before immersion in electrolyte solution] × 100
The electrolytic solution for determining the liquid absorption rate is preferably a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed in a volume ratio of EC: DEC = 3: 7 and LiPF ₆ as an electrolyte is 1 mol / mol /. An electrolytic solution dissolved so as to have a concentration of L is used.
Immersion in the electrolytic solution for determining the liquid absorption rate is performed at 50 ° C. for 3 days. By immersing at 50 ° C. for 3 days, the polymer compound becomes a saturated liquid absorbing state. The saturated liquid absorbing state means a state in which the weight of the polymer compound does not increase even if it is further immersed in the electrolytic solution.
The electrolytic solution used in manufacturing the lithium ion battery is not limited to the above electrolytic solution, and other electrolytic solutions may be used.

When the liquid absorption rate is 10% or more, lithium ions can easily permeate the polymer compound, so that the ion resistance in the negative electrode active material layer can be kept low. If the liquid absorption rate is less than 10%, the conductivity of lithium ions becomes low, and the performance as a lithium ion battery may not be sufficiently exhibited.
The liquid absorption rate is preferably 20% or more, and more preferably 30% or more.
The preferable upper limit value of the liquid absorption rate is 400%, and the more preferable upper limit value is 300%.

For the tensile elongation at break in the saturated liquid absorption state, the polymer compound is punched out in a dumbbell shape and immersed in the electrolytic solution at 50 ° C. for 3 days in the same manner as the above measurement of the liquid absorption rate to saturate the polymer compound. As a state, it can be measured according to ASTM D683 (test piece shape TypeII). The tensile elongation at break is a value calculated by the following formula as the elongation at break until the test piece breaks in the tensile test.
Tensile fracture elongation (%) = [(Test piece length at break-Test piece length before test) / Test piece length before test] x 100

When the tensile elongation at break of the polymer compound in the saturated liquid absorption state is 10% or more, the polymer compound has appropriate flexibility, so that the coating layer is peeled off due to the volume change of the negative electrode active material during charging and discharging. It becomes easier to suppress that.
The tensile elongation at break is preferably 20% or more, and more preferably 30% or more.
Further, the preferable upper limit value of the tensile elongation at break is 400%, and the more preferable upper limit value is 300%.

Subsequently, the polymer compound constituting the coating layer will be specifically described.
Examples of the polymer compound constituting the coating layer include thermoplastic resins and thermosetting resins. For example, vinyl resin (A), urethane resin (B), polyester resin, polyamide resin, epoxy resin, polyimide resin, etc. Examples thereof include silicone resin, phenol resin, melamine resin, urea resin, aniline resin, ionomer resin, polycarbonate, polysaccharoid (sodium alginate, etc.) and mixtures thereof.
Among these, a polymer compound having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more is more preferable.

The vinyl resin (A) is a resin containing a polymer (A1) containing the vinyl monomer (a) as an essential constituent monomer.
In particular, the polymer (A1) preferably contains a vinyl monomer (a1) having a carboxyl group or an acid anhydride group as the vinyl monomer (a) or a vinyl monomer (a2) represented by the following general formula (2). ..
CH ₂ = C (R ¹ ) COOR ² (2)
[In the formula (2), 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 4 to 36 carbon atoms. ]
Of the vinyl resins (A), those having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more are more preferable.

Examples of the vinyl monomer (a1) having a carboxyl group or an acid anhydride group include monocarboxylic acids having 3 to 15 carbon atoms such as (meth) acrylic acid (a11), crotonic acid, and itaconic acid; (anhydrous) maleic acid and fumal. Dicarboxylic acids with 4 to 24 carbon atoms such as acids, (anhydrous) itaconic acid, citraconic acid, and mesaconic acid; trivalent to tetravalent or higher valent polycarboxylic acids with 6 to 24 carbon atoms such as aconitic acid, etc. Can be mentioned. Among these, (meth) acrylic acid (a11) is preferable, and methacrylic acid is more preferable.

In the vinyl monomer (a2) represented by the general formula (2), 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.
The branched alkyl group having 4 to 12 carbon atoms includes a 1-methylpropyl group (sec-butyl group), a 2-methylpropyl group, a 1,1-dimethylethyl group (tert-butyl group), a 1-methylbutyl group, and 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.

(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 ( 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 (A1) preferably further contains an ester compound (a3) of a monohydric aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid.
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.

The content of the ester compound (a3) is preferably 10 to 60% by weight, preferably 15 to 55% by weight, based on the total weight of the polymer (A1) from the viewpoint of suppressing the volume change of the negative electrode active material. Is more preferable, and 20 to 50% by weight is further preferable.

Further, the polymer (A1) preferably further contains a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group.
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 and / 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.

The content of the salt (a4) of the anionic monomer is preferably 0.1 to 15% by weight, preferably 1 to 15% by weight, based on the total weight of the polymer compounds from the viewpoint of internal resistance and the like. More preferably, it is more preferably 2 to 10% by weight.

The polymer (A1) preferably contains (meth) acrylic acid (a11) and an ester compound (a21), more preferably contains an ester compound (a3), and further contains a salt of an anionic monomer (a1). It is particularly preferable to include a4).

The polymer compound is (meth) acrylic acid (a11), an ester compound (a21) represented by the following general formula (1), an ester of a monovalent aliphatic alcohol having 1 to 3 carbon atoms and (meth) acrylic acid. A monomer composition comprising the compound (a3) and a salt (a4) of an anionic monomer having a polymerizable unsaturated double bond and an anionic group is polymerized to obtain the above ester compound (a21). The weight ratio of the (meth) acrylic acid (a11) to the above (meth) acrylic acid (a11) [the ester compound (a21) / the (meth) acrylic acid (a11)] is preferably 10/90 to 90/10.
CH ₂ = C (R ¹ ) COOR ² (1)
[R ¹ is a hydrogen atom or a methyl group, and R ² is a linear or branched alkyl group having 4 to 12 carbon atoms. ]
When the weight ratio of the ester compound (a21) to the (meth) acrylic acid (a11) is 10/90 to 90/10, the polymer obtained by polymerizing the ester compound (a21) has good adhesion to the negative electrode active material and can be peeled off. It becomes difficult to do.
The weight ratio is preferably 30/70 to 85/15, more preferably 40/60 to 70/30.

The monomer constituting the polymer (A1) includes a vinyl monomer (a1) having a carboxyl group or an acid anhydride group, a vinyl monomer (a2) represented by the above general formula (2), and 1 carbon number. In addition to the ester compound (a3) of the monovalent aliphatic alcohol of ~ 3 and (meth) acrylic acid and the salt (a4) of the anionic monomer having a polymerizable unsaturated double bond and an anionic group. , A copolymerizable vinyl monomer (a5) containing no active hydrogen may be contained.
Examples of the copolymerizable vinyl monomer (a5) containing no active hydrogen include the following (a51) to (a58).
(A51) 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, and araxyl 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, methanol propylene oxide (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 pyridine compound (7 to 14 carbon atoms, for example 2- or 4-vinylpyridine), imidazole compound (5 to 12 carbon atoms, for example N-vinylimidazole), 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, isobutylene, 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 limonene), 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, vinyl benzoate, diallyl phthalate, methyl-4-vinyl benzoate), 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) allyloxyalkanes (2 to 6 carbon atoms) (dialyloxyethane, trialiloxiethan, tetraaryloxybutane, tetramethalyloxyethane, 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). ), Dialkylmaleate (two alkyl groups are linear, branched or alicyclic groups with 1-22 carbon atoms)

Among those exemplified as (a5) above, (a51), (a52) and (a53) are preferable from the viewpoint of withstand voltage.

In the polymer (A1), a vinyl monomer (a1) having a carboxyl group or an acid anhydride group, a vinyl monomer (a2) represented by the above general formula (2), and a monovalent aliphatic alcohol having 1 to 3 carbon atoms. And (meth) acrylic acid ester compound (a3), anionic monomer salt (a4) having a polymerizable unsaturated double bond and an anionic group, and a copolymerizable vinyl monomer containing no active hydrogen (a4). The content of a5) is 0.1 to 80% by weight for (a1), 0.1 to 99.9% by weight for (a2), and 0 to 0 for (a3), based on the weight of the polymer (A1). It is preferable that 60% by weight, (a4) is 0 to 15% by weight, and (a5) is 0 to 99.8% by weight.
When the content of the monomer is within the above range, the liquid absorbency into the electrolytic solution becomes good.
More preferable contents are (a1) from 15 to 60% by weight, (a2) from 5 to 60% by weight, (a3) from 10 to 60% by weight, (a4) from 0.1 to 15% by weight, and (a5). ) Is 5 to 69.9% by weight, and more preferable contents are (a1) 25 to 49% by weight, (a2) 15 to 39% by weight, (a3) 15 to 39% by weight, and (a4). ) Is 1 to 15% by weight, and (a5) is 20 to 44% by weight.

The preferred lower limit of the number average molecular weight of the polymer (A1) is 3,000, more preferably 50,000, still more preferably 100,000, particularly preferably 200,000, and the preferred upper limit is 2,000,000. It is preferably 1,500,000, more preferably 1,000,000, and particularly preferably 800,000.

The number average molecular weight of the polymer (A1) can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.
Equipment: Alliance GPC V2000 (manufactured by Waters)
Solvent: Ortodichlorobenzene Standard substance: Polystyrene detector: RI
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 solubility parameter (hereinafter abbreviated as SP value) of the polymer (A1) is preferably ^{9.0 to 20.0 (cal / cm 3} ) ^1/2. The SP value of the polymer (A1) ^{is more preferably 10.0 to 18.0 (cal / cm 3} ) ^1/2 , and 11.5 to 14.0 (cal / cm ³ ) ^1/2 . Is even more preferable. When the SP value of the polymer (A1) is 9.0 to 20.0 (cal / cm ³ ) ^1/2, it is preferable from the viewpoint of the liquid absorbency of the electrolytic solution.
The SP value is calculated by the Fedors method. The SP value can be expressed by the following equation.
SP value (δ) = (ΔH / V) ^1/2
However, in the formula, ΔH represents the molar heat of vaporization (cal) and V represents the molar volume (cm ³ ).
Further, ΔH and V are the total molar heat of vaporization (ΔH) of the atomic group described in “POLYMER ENGINEERING AND SCIENCE, 1974, Vol. 14, No. 2, ROBERT F. FEDORS. The total molar volume (V) can be used.
The SP value is an index indicating that those having similar values are easily mixed with each other (high compatibility), and those having different values are difficult to mix with each other.

The glass transition point of the polymer (A1) [hereinafter abbreviated as Tg, measuring method: DSC (scanning differential thermal analysis) method] is preferably 80 to 200 ° C., more preferably 90 ° C. from the viewpoint of battery heat resistance. It is ~ 180 ° C., more preferably 100 to 150 ° C.

The polymer (A1) can be produced by a known polymerization method (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.).
In the polymerization, known polymerization initiators {azo-based initiators [2,2'-azobis (2-methylpropionitrile), 2,2'-azobis (2,4-dimethylvaleronitrile, etc.)], peroxides It can be carried out using a system initiator (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.)}.
The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, still more preferably 0.1 to 1.5% by weight, based on the total weight of the monomer. ..

Solvents used in the case of solution polymerization include, for example, esters (2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (1 to 8 carbon atoms, such as methanol, ethanol and octanol), and hydrocarbons (carbon numbers 1 to 8). Examples thereof include 4 to 8, for example n-butane, cyclohexane and toluene) and ketones (3 to 9 carbon atoms, for example, methyl ethyl ketone), and the amount used is preferably 5 to 900% by weight, more preferably 5 to 900% by weight based on the total weight of the monomers. It is 10 to 400% by weight, more preferably 30 to 300% by weight, and 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 amount used is preferably 2% by weight or less, more preferably 0.5% by weight or less, still more preferably 0.3% by weight or less based on the total weight of the monomer.

The in-system temperature in the polymerization reaction is preferably −5 to 150 ° C., more preferably 30 to 120 ° C., further preferably 50 to 110 ° C., and the reaction time is preferably 0.1 to 50 hours, more preferably 2 to 2. It is 24 hours, and the end point of the reaction is preferably 5% by weight or less, more preferably 1% by weight or less, still more preferably 0.5% by weight, based on the total amount of unreacted monomers used. % Or less. The amount of unreacted monomer can be confirmed by using a known quantification method such as gas chromatography.

The polymer (A1) contained in the vinyl resin (A) is a crosslinked polymer obtained by cross-linking the polymer (A1) with a polyepoxy compound (a'1) and / or a polyol compound (a'2). May be good.
In the crosslinked polymer, it is preferable to crosslink the polymer (A1) with a crosslinking agent (A') having a reactive functional group that reacts with an active hydrogen such as a carboxyl group in the polymer (A1). It is preferable to use the polyepoxy compound (a'1) and / or the polyol compound (a'2) as the agent (A').

The polyepoxide compound (a'1) has an epoxy equivalent of 80 to 2,500, for example, glycidyl ether [bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, pyrogallol triglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol. Diglycidyl ether, neopentyl glycol diglycidyl ether, trimethylolpropan triglycidyl ether, glycerin triglycidyl ether, polyethylene glycol (Mw200-2,000) diglycidyl ether, polypropylene glycol (Mw200-2,000) diglycidyl ether, bisphenol Diglycidyl ether of 1 to 20 mol of alkylene oxide of A]; glycidyl ester (phthalic acid diglycidyl ester, trimellitic acid triglycidyl ester, dimer acid diglycidyl ester, adipate diglycidyl ester, etc.); glycidyl amine [ N, N-diglycidyl aniline, N, N-diglycidyl toluidine, N, N, N', N'-tetraglycidyl diaminodiphenylmethane, N, N, N', N'-tetraglycidyl xylylene diamine, 1,3 -Bis (N, N-diglycidyl aminomethyl) cyclohexane, N, N, N', N'-tetraglycidyl hexamethylenediamine, etc.]; aliphatic epoxides (epoxidized polybutadiene, epoxidized soybean oil, etc.); alicyclic Examples include epoxides (limonendioxide, dicyclopentadiendioxide, etc.).

Examples of the polyol compound (a'2) include low-molecular-weight polyhydric alcohols {aliphatic or alicyclic diols having 2 to 20 carbon atoms [ethylene glycol (hereinafter abbreviated as EG), diethylene glycol (hereinafter abbreviated as DEG), propylene glycol. , 1,3-butylene glycol, 1,4-butanediol (hereinafter abbreviated as 14BG), 1,6-hexanediol, 3-methylpentanediol, neopentyl glycol, 1,9-nonanediol, 1,4-dihydroxy Cyclohexane, 1,4-bis (hydroxymethyl) cyclohexane, 2,2-bis (4,4'-hydroxycyclohexyl) propane, etc.]; aromatic ring-containing diols with 8 to 15 carbon atoms [m- or p-xylylene glycol] , 1,4-Bis (hydroxyethyl) benzene, etc.]; Triol with 3 to 8 carbon atoms (glycerin, trimethylolpropane, etc.); Polyhydric alcohols of tetravalent or higher [pentaerythritol, α-methylglucoside, sorbitol, xylit, etc. Mannit, glucose, fructose, sucrose, dipentaerythritol, polyglycerin (polymerization degree 2 to 20), etc.], etc.}, and their alkylene (carbon number 2 to 4) oxide adduct (polymerization degree 2 to 30), etc. Can be mentioned.

The amount of the cross-linking agent (A') used is the equivalent ratio of the active hydrogen-containing group in the polymer (A1) to the reactive functional group in the cross-linking agent (A') from the viewpoint of the liquid absorbency of the electrolytic solution. The amount is preferably 1: 0.01 to 1: 2, more preferably 1: 0.02 to 1: 1.

Examples of the method of cross-linking the polymer (A1) with the cross-linking agent (A') include a method of coating the negative electrode active material for a lithium ion battery with the polymer (A1) and then cross-linking. Specifically, the negative electrode active material for lithium ion batteries is coated with the polymer (A1) by mixing the negative electrode active material for lithium ion batteries with a resin solution containing the polymer (A1) and removing the solvent. After producing the active material, a solution containing the cross-linking agent (A') is mixed with the coated negative electrode active material and heated to cause a solvent removal and a cross-linking reaction, so that the polymer (A1) becomes a cross-linking agent (A1). A method of causing a reaction of being crosslinked by A') to become a polymer compound on the surface of the negative electrode active material for a lithium ion battery can be mentioned.
The heating temperature is preferably 70 ° C. or higher when the polyepoxy compound (a'1) is used as the cross-linking agent, and 120 ° C. or higher when the polyol compound (a'2) is used.

Urethane resin (B) is preferable as the polymer compound constituting the coating layer.
Of the urethane resins (B), those having a liquid absorption rate of 10% or more when immersed in an electrolytic solution and a tensile elongation at break in a saturated liquid absorption state of 10% or more are more preferable.

The urethane resin (B) is a resin obtained by reacting an active hydrogen component (b1) and an isocyanate component (b2).

The active hydrogen component (b1) preferably contains at least one selected from the group consisting of polyether diols, polycarbonate diols and polyester diols.

Examples of the polyether diol include polyoxyethylene glycol (hereinafter abbreviated as PEG), polyoxyethylene oxypropylene block copolymer diol, and polyoxyethylene oxytetramethylene block copolymer diol; EG, propylene glycol, 14BG, 1,6-hexa. Ethethylene oxide adducts of low molecular weight glycols such as methylene glycol, neopentyl glycol, bis (hydroxymethyl) cyclohexane, 4,4'-bis (2-hydroxyethoxy) -diphenylpropane; with PEG having a number average molecular weight of 2,000 or less. , Dicarboxylic acid [an aliphatic dicarboxylic acid having 4 to 10 carbon atoms (for example, succinic acid, adipic acid, sebacic acid, etc.), aromatic dicarboxylic acid having 8 to 15 carbon atoms (for example, terephthalic acid, isophthalic acid, etc.), etc.] Condensed polyether ester diols obtained by reacting with more than one species; and mixtures of two or more of these.
When the polyether diol contains oxyethylene units, the content of the oxyethylene units is preferably 20% by weight or more, more preferably 30% by weight or more, still more preferably 40% by weight or more.
Further, polyoxypropylene glycol, polyoxytetramethylene glycol (hereinafter abbreviated as PTMG), polyoxypropylene oxytetramethylene block copolymer diol and the like can also be mentioned.
Of these, PEG, polyoxyethylene oxypropylene block copolymer diol and polyoxyethylene oxytetramethylene block copolymer diol are preferable, and PEG is more preferable.
Further, only one type of polyether diol may be used, or a mixture of two or more types thereof may be used.

Examples of the polycarbonate diol include polyhexamethylene carbonate diol.

Examples of the polyester diol include a condensed polyester diol obtained by reacting a low molecular weight diol and / or a polyether diol having a number average molecular weight of 1,000 or less with one or more of the above-mentioned dicarboxylic acids, and a lactone having 4 to 12 carbon atoms. Examples thereof include a polylactone diol obtained by ring-opening polymerization of. Examples of the low-molecular-weight diol include low-molecular-weight glycols exemplified in the section of the above-mentioned polyether diol. Examples of the polyether diol having a number average molecular weight of 1,000 or less include polyoxypropylene glycol and PTMG. Examples of the lactone include ε-caprolactone and γ-valerolactone. Specific examples of the polyester diol include polyethylene adipate diol, polybutylene adipate diol, polyneopentylene adipate diol, poly (3-methyl-1,5-pentylene adipate) diol, polyhexamethylene adipate diol, and polycaprolactone diol. And a mixture of two or more of these.

Further, the active hydrogen component (b1) may be a mixture of two or more of the above-mentioned polyether diol, polycarbonate diol and polyester diol.

The active hydrogen component (b1) preferably contains a high molecular weight diol (b11) having a number average molecular weight of 2,500 to 15,000 as an essential component. Examples of the polymer diol (b11) include the above-mentioned polyether diol, polycarbonate diol, polyester diol and the like.
When the number average molecular weight of the polymer diol (b11) is 2,500 to 15,000, the hardness of the urethane resin (B) is moderately soft, and the strength of the coating layer formed on the negative electrode active material is strong. Therefore, it is preferable.
Further, the number average molecular weight of the polymer diol (b11) is more preferably 3,000 to 12,500, and further preferably 4,000 to 10,000.
The number average molecular weight of the polymer diol (b11) can be calculated from the hydroxyl value of the polymer diol.
The hydroxyl value can be measured according to the description of JIS K1557-1.

Further, a polymer diol (b11) having a number average molecular weight of 2,500 to 15,000 as an active hydrogen component (b1) is an essential component, and the solubility parameter (SP value) of the polymer diol (b11) is 8.0 to 8.00. It is preferably 12.0 (cal / cm ³ ) ^1/2. More preferably SP value of the polymer diol (b11) is ^{8.5~11.5 (cal / cm 3) 1/2} , in 9.0~11.0 (cal ^/ cm ^{3) 1/2} It is more preferable to have. When the SP value of the polymer diol (b11) is 8.0 to 12.0 (cal / cm ³ ) ^1/2, it is preferable from the viewpoint of the liquid absorbency of the electrolytic solution of the urethane resin (B).

Further, a polymer diol (b11) having a number average molecular weight of 2,500 to 15,000 as an active hydrogen component (b1) is an essential component, and the content of the polymer diol (b11) is the weight of the urethane resin (B). It is preferably 20 to 80% by weight based on. The content of the polymer diol (b11) is more preferably 30 to 70% by weight, further preferably 40 to 65% by weight.
When the content of the polymer diol (b11) is 20 to 80% by weight, it is preferable from the viewpoint of the liquid absorbency of the electrolytic solution of the urethane resin (B).

Further, it is preferable that the polymer diol (b11) having a number average molecular weight of 2,500 to 15,000 and the chain extender (b13) as essential components are used as the active hydrogen component (b1).
Examples of the chain extender (b13) include low molecular weight diols having 2 to 10 carbon atoms (for example, EG, propylene glycol, 14BG, DEG, 1,6-hexamethylene glycol, etc.); diamines [fats having 2 to 6 carbon atoms]. Group diamines (eg ethylenediamine, 1,2-propylene diamine, etc.), alicyclic diamines with 6 to 15 carbon atoms (eg, isophorone diamine, 4,4'-diaminodicyclohexylmethane, etc.), aromatic diamines with 6 to 15 carbon atoms. (For example, 4,4'-diaminodiphenylmethane, etc.)]; Monoalkanolamine (for example, monoethanolamine, etc.); Hydrazin or a derivative thereof (for example, dihydrazide adipate, etc.) and a mixture of two or more thereof can be mentioned. Of these, preferred are low molecular weight diols, more preferred are EG, DEG and 14BG.
The combination of the polymer diol (b11) and the chain extender (b13) is a combination of PEG as the polymer diol (b11) and EG as the chain extender (b13), or as a polymer diol (b11). A combination of the polycarbonate diol and EG as the chain extender (b13) is preferable.

Further, the active hydrogen component (b1) contains a polymer diol (b11) having a number average molecular weight of 2,500 to 15,000, a diol (b12) other than the polymer diol (b11), and a chain extender (b13). The equivalent ratio [(b11) / (b12)] between (b11) and (b12) is 10/1 to 30/1, and the equivalent ratio between (b11) and the total equivalents of (b12) and (b13) { It is preferable that (b11) / [(b12) + (b13)]} is 0.9 / 1 to 1.1 / 1.
The equivalent ratio [(b11) / (b12)] of (b11) and (b12) is more preferably 13/1 to 25/1, and even more preferably 15/1 to 20/1.

The diol (b12) other than the high molecular weight diol (b11) is a diol and is not contained in the above-mentioned high molecular weight diol (b11), but is contained in the low molecular weight diol having 2 to 10 carbon atoms of the chain extender (b13). If it does not exist, the present invention is not particularly limited, and specific examples thereof include a diol having a number average molecular weight of less than 2,500 and a diol having a number average molecular weight of more than 15,000.
Examples of the type of diol include the above-mentioned polyether diol, polycarbonate diol, polyester diol and the like.

As the isocyanate component (b2), those conventionally used for urethane resin production can be used. Such isocyanates include aromatic diisocyanates having 6 to 20 carbon atoms (excluding carbons in NCO groups, the same applies hereinafter), aliphatic diisocyanates having 2 to 18 carbon atoms, and alicyclic diisocyanates having 4 to 15 carbon atoms. Aromatic aliphatic diisocyanates having 8 to 15 carbon atoms, modified products of these diisocyanates (carbodiimide modified products, urethane modified products, uretdione modified products, etc.) and mixtures of two or more of these are included.

Specific examples of the aromatic diisocyanate include 1,3- or 1,4-phenylenediocyanate, 2,4- or 2,6-tolylene diisocyanate, 2,4'-or 4,4'-diphenylmethane diisocyanate (hereinafter referred to as "these". , Diphenylmethane diisocyanate is abbreviated as MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanate Examples thereof include natodiphenyl methane and 1,5-naphthylene diisocyanate.

Specific examples of the aliphatic diisocyanate include ethylene diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, lysine diisocyanate, and 2,6-diisocyanatomethyl caproate. Examples thereof include bis (2-isocyanatoethyl) carbonate and 2-isocyanatoethyl-2,6-diisocyanatohexanoate.

Specific examples of the alicyclic diisocyanate include isophorone diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, cyclohexylene diisocyanate, methylcyclohexylene diisocyanate, and bis (2-isocyanatoethyl) -4-cyclohexylene-1,2. -Dicarboxylate, 2,5- or 2,6-norbornane diisocyanate and the like can be mentioned.

Specific examples of the aromatic aliphatic diisocyanate include m- or p-xylylene diisocyanate, α, α, α', α'-tetramethylxylylene diisocyanate and the like.

Of these, preferred are aromatic diisocyanates and alicyclic diisocyanates, more preferred are aromatic diisocyanates, and even more preferred are MDIs.

When the urethane resin (B) contains the polymer diol (b11) and the isocyanate component (b2), the equivalent ratio of (b2) / (b11) is preferably 10/1 to 30/1, more preferably 11/1. It is ~ 28/1, more preferably 15/1 to 25/1. When the ratio of the isocyanate component (b2) exceeds 30 equivalents, a hard coating layer is formed.
When the urethane resin (B) contains a polymer diol (b11), a chain extender (b13) and an isocyanate component (b2), the equivalent ratio of (b2) / [(b11) + (b13)] is preferable. It is 0.9 / 1 to 1.1 / 1, more preferably 0.95 / 1 to 1.05 / 1. If it is out of this range, the urethane resin may not have a sufficiently high molecular weight.

The number average molecular weight of the urethane resin (B) is preferably 40,000 to 500,000, more preferably 50,000 to 400,000, and even more preferably 60,000 to 300,000. If the number average molecular weight of the urethane resin (B) is less than 40,000, the strength of the coating layer is low, and if it exceeds 500,000, the solution viscosity is high, and a uniform coating layer may not be obtained.

The number average molecular weight of the urethane resin (B) is measured by GPC using dimethylformamide (hereinafter abbreviated as DMF) as a solvent and polyoxypropylene glycol as a standard substance. The sample concentration may be 0.25% by weight, the column stationary phase may be one each of TSKgel SuperH2000, TSKgel SuperH3000, and TSKgel SuperH4000 [all manufactured by Tosoh Corporation] connected, and the column temperature may be 40 ° C.

The urethane resin (B) can be produced by reacting the active hydrogen component (b1) with the isocyanate component (b2).
For example, a polymer diol (b11) and a chain extender (b13) are used as the active hydrogen component (b1), and the isocyanate component (b2), the polymer diol (b11), and the chain extender (b13) are reacted at the same time. Examples thereof include a shot method and a prepolymer method in which a polymer diol (b11) and an isocyanate component (b2) are first reacted and then a chain extender (b13) is continuously reacted.
Further, the urethane resin (B) can be produced in the presence or absence of a solvent inert to the isocyanate group. Suitable solvents for use in the presence of a solvent include amide solvents [DMF, dimethylacetamide, N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), etc.], sulfoxide solvents (dimethyl sulfoxide, etc.), and ketones. Solvents (methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic solvents (toluene, xylene, etc.), ether solvents (dioxane, tetrahydrofuran, etc.), ester solvents (ethyl acetate, butyl acetate, etc.) and mixtures of two or more of these. Can be mentioned. Of these, preferred are amide solvents, ketone solvents, aromatic solvents and mixtures of two or more of these.

In the production of the urethane resin (B), the reaction temperature may be the same as the temperature adopted for the known urethanization reaction, preferably 20 to 100 ° C. when a solvent is used, and 20 to 220 ° C. when no solvent is used. preferable.

If necessary to accelerate the reaction, known catalysts used in the urethanization reaction [for example, amine-based catalysts (triethylamine, triethylenediamine, etc.), tin-based catalysts (dibutyltin dilaurate, etc.)] can be used.

Further, if necessary, a polymerization inhibitor [for example, a monohydric alcohol (for example, ethanol, isopropanol, butanol, etc.), a monovalent amine (dimethylamine, dibutylamine, etc.), etc.] can be used.

Subsequently, the conductive agent contained in the coating layer will be described.
The conductive agent contained in the coating layer is selected from materials having conductivity.
Specifically, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, etc.), etc.), etc. ], And a mixture thereof, etc., but is not limited to these.
These conductive agents may be used alone or in combination of two or more. Moreover, you may use these alloys or metal oxides. From the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, copper, titanium and mixtures thereof are preferable, silver, aluminum, stainless steel and carbon are more preferable, and carbon is even more preferable. Further, these conductive agents may be those obtained by coating a conductive material (a metal material among the above-mentioned conductive agent materials) around a particle-based ceramic material or a resin material by plating or the like.

The average particle size of the conductive agent is not particularly limited, but is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, and 0. It is more preferably 03 to 1 μm. In the present specification, the “particle size” means the maximum distance L among the distances between any two points on the contour line of the conductive 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 shape (form) of the conductive agent is not limited to the particle form, and may be a form other than the particle form, or may be a form practically used as a so-called filler-based conductive resin composition such as carbon nanotubes. ..

The conductive agent may be a conductive fiber whose shape is fibrous.
As conductive fibers, carbon fibers such as PAN-based carbon fibers and pitch-based carbon fibers, conductive fibers in which a metal having good conductivity or graphite is uniformly dispersed in synthetic fibers, and a metal such as stainless steel are used. Examples thereof include fibrous metal fibers, conductive fibers in which the surface of organic fibers is coated with metal, and conductive fibers in which the surface of organic fibers is coated with a resin containing a conductive substance. Among these conductive fibers, carbon fibers are preferable. Further, a polypropylene resin kneaded with graphene is also preferable.
When the conductive agent is a conductive fiber, the average fiber diameter thereof is preferably 0.1 to 20 μm.

The ratio of the total weight of the polymer compound and the conductive agent to the weight of the negative electrode active material for the lithium ion battery is not particularly limited, but is preferably 2.1 to 25% by weight.

The ratio of the weight of the polymer compound to the weight of the coated negative electrode active material for a lithium ion battery is not particularly limited, but is preferably 0.1 to 11% by weight, and preferably 1 to 10% by weight. More preferred. The ratio of the weight of the conductive agent to the weight of the lithium ion battery-coated negative electrode active material is not particularly limited, but is preferably 2 to 14% by weight, more preferably 2 to 12% by weight.

The ratio of the weight of the polymer compound contained in the coating layer to the weight of the conductive agent contained in the coating layer is not particularly limited, but is preferably 13 to 500% by weight, preferably 13 to 35% by weight. More preferably. When the ratio of the weight of the polymer compound contained in the coating layer to the weight of the conductive agent contained in the coating layer is in the above range, the internal resistance is low, which is preferable.

The conductivity of the coating layer is preferably 0.0001 to 10 mS / cm, more preferably 0.01 to 5 mS / cm.
The conductivity of the coating layer can be determined by the four-terminal method.
When the conductivity of the coating layer is 0.0001 mS / cm or more, the internal resistance of the lithium ion battery does not become too high, which is preferable.

Hereinafter, the method for producing the coated negative electrode active material for a lithium ion battery of the present invention described above will be described.
The coated negative electrode active material for a lithium ion battery of the present invention may be produced by mixing a polymer compound, a conductive agent and a negative electrode active material for a lithium ion battery, or a polymer compound and a conductive agent are mixed and coated. After preparing the material, it may be produced by mixing the coating material with the negative electrode active material for a lithium ion battery.
When the negative electrode active material for lithium ion batteries, the polymer compound, and the conductive agent are mixed, the mixing order is not particularly limited, but after mixing the negative electrode active material for lithium ion batteries and the polymer compound, further It is preferable to add a conductive agent and further mix.
By the above method, at least a part of the surface of the negative electrode active material for a lithium ion battery is coated with a coating layer containing a polymer compound and a conductive agent.

As the negative electrode active material for lithium ion batteries, the polymer compound and the conductive agent used in the above method for producing the coated negative electrode active material for lithium ion batteries, those described in the coated negative electrode active material for lithium ion batteries of the present invention are used. It can be preferably used.

The coated negative electrode active material for a lithium ion battery of the present invention is, for example, a polymer solution containing a polymer compound in a state where the negative electrode active material for a lithium ion battery is placed in a universal mixer and stirred at 30 to 50 rpm. It can be obtained by dropping and mixing over a minute, further mixing the conductive agent, raising the temperature to 50 to 200 ° C. with stirring, reducing the pressure to 0.007 to 0.04 MPa, and then holding the mixture for 10 to 150 minutes.

The blending ratio of the negative electrode active material for lithium ion batteries and the polymer compound is not particularly limited, but the weight ratio of the negative electrode active material for lithium ion batteries: polymer compound = 1: 0.001 to 0.1. It is preferable to have.

When the coated negative electrode active material for a lithium ion battery of the present invention is used as a negative electrode, the coated negative electrode active material for a lithium ion battery and the conductive material are 30 to 60 weights based on the weight of the dispersion medium (water, electrolyte or solvent). The dispersion liquid dispersed at a concentration of% and slurried is applied to the current collector with a coating device such as a bar coater, and when water or a solvent is used as the dispersion medium, it is dried to electrolyze it as a dispersion medium. When a liquid is used, the excess electrolyte may be absorbed by an absorber such as a sponge, or the dispersion medium may be removed by suction through a mesh, and if necessary, pressed with a press machine.
If necessary, a known electrode binder [polyvinylidene fluoride (PVdF) or the like] contained in the negative electrode for a lithium ion battery may be added to the dispersion liquid, but it is preferable not to add the electrode binder. .. In a conventionally known negative electrode for a lithium ion battery that does not use a coated negative electrode active material as the negative electrode active material, it is necessary to maintain the conductive path by fixing the negative electrode active material in the negative electrode with an electrode binder. However, when the coated negative electrode active material for a lithium ion battery of the present invention is used, the conductive path can be maintained without fixing the negative electrode active material in the negative electrode by the action of the coating layer, so an electrode binder is added. You don't have to. By not adding the binder for the electrode, the negative electrode active material is not immobilized in the negative electrode, so that the ability to alleviate the volume change of the negative electrode active material is further improved.
The conductive material used for manufacturing the electrode is different from the conductive agent contained in the coating layer, exists outside the coating layer of the coating active material, and has electron conductivity from the surface of the coating active material in the active material layer. Has the function of improving.

Among the dispersion media, examples of water include ion-exchanged water and ultrapure water.
Among the dispersion media, as the electrolytic solution, the same electrolytic solution (described later) used when producing a lithium ion battery using the negative electrode containing the coated negative electrode active material for the lithium ion battery of the present invention may be used. it can.
Among the dispersion media, the solvent used is the same as the non-aqueous solvent constituting the electrolytic solution used when producing a lithium ion battery using the negative electrode containing the coated negative electrode active material for the lithium ion battery of the present invention. In addition to these, 1-methyl-2-pyrrolidone, dimethylacetamide, N, N-dimethylaminopropylamine and the like can be used.
Examples of the current collector include a metal foil such as copper, aluminum, titanium, stainless steel and nickel, a resin current collector made of a conductive polymer (described in Japanese Patent Application Laid-Open No. 2012-150905, etc.), and conductive carbon. Examples include sheets and conductive glass sheets.
Examples of the binder for the electrode include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene and polypropylene.

As the conductive material used together with the coated negative electrode active material for the lithium ion battery in the manufacture of the electrode, the same conductive material as that contained in the coating layer can be used.

When producing a lithium ion battery using a negative electrode containing a coated negative electrode active material for a lithium ion battery of the present invention, the electrodes to be opposite electrodes are combined, housed in a cell container together with a separator, and an electrolytic solution is injected into the cell. It can be manufactured by a method of sealing the container or the like.
Further, a positive electrode is formed on one surface of the current collector and a negative electrode is formed on the other surface to prepare a bipolar electrode, and the bipolar electrode is laminated with a separator and stored in a cell container to store an electrolytic solution. It can also be obtained by injecting and sealing the cell container.

Examples of the separator include a microporous film made of polyethylene and polypropylene, a multilayer film of a porous polyethylene film and polypropylene, a non-woven fabric made of polyester fiber, aramid fiber, glass fiber, etc., and silica, alumina, titania, etc. on their surfaces. Examples thereof include known separators for lithium ion batteries, such as those to which the ceramic fine particles of the above are attached.

As the electrolytic solution to be injected into the cell container, a known electrolytic solution containing an electrolyte and a non-aqueous solvent, which is used in the production of a known lithium ion battery, can be used.

As the electrolyte, those used in known electrolytes can be used, for example, lithium salts of inorganic acids such as _{LiPF 6} , LiBF ₄ , LiSbF ₆ , _{LiAsF 6} and LiClO _{4 , LiN (CF 3} SO ₂ ). _2. Lithium salts of organic acids such as LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC (CF ₃ SO ₂ ) _{3 can be mentioned. Of these, LiPF 6} is preferable from the viewpoint of battery output and charge / discharge cycle characteristics.

As the non-aqueous solvent, those used in known electrolytic solutions can be used, for example, a lactone compound, a cyclic or chain carbonate, a chain carboxylic acid ester, a cyclic or chain ether, a phosphoric acid ester, and a nitrile. Compounds, amide compounds, sulfones, sulfolanes and the like 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 lactone compound (δ-valerolactone, etc.).

Examples of the cyclic carbonate include propylene carbonate, ethylene carbonate and butylene carbonate.
Examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, 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 type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

Among the non-aqueous solvents, lactone compounds, cyclic carbonates, chain carbonates and phosphate esters are preferable from the viewpoint of battery output and charge / discharge cycle characteristics, and lactone compounds, cyclic carbonates and chains are more preferable. A carbonic acid ester is particularly preferable, and a mixed solution of a cyclic carbonic acid ester and a chain carbonic acid ester is particularly preferable. The most preferable is a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC), or a mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC).

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.

<Production Example 1: Preparation of coating polymer compound and its solution>
70.0 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 compounding solution containing 20.0 parts of butyl methacrylate, 55.0 parts of acrylate, 22.0 parts of methyl methacrylate, 3 parts of sodium allylsulfonate and 20 parts of DMF, and 2,2'-azobis (2). , 4-Dimethylvaleronitrile) 0.4 parts and 2,2'-azobis (2-methylbutyronitrile) 0.8 parts dissolved in 10.0 parts of DMF Initiator solution and nitrogen in a 4-neck flask. Radical polymerization was carried out by continuously dropping the mixture in a dropping funnel over 2 hours with stirring. After completion of the dropping, the temperature was raised to 80 ° C. and the reaction was continued for 5 hours to obtain a copolymer solution having a resin concentration of 50%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 120 ° C. and 0.01 MPa for 3 hours to distill off DMF to obtain a polymer compound for coating.

<Manufacturing Example 2: Fabrication of Silicon-based Material>
Silicon particles (manufactured by Sigma Aldrich Japan, volume average particle diameter 1.5 μm) are placed in a horizontal heating furnace, and chemical vapor deposition at 1100 ° C / 1000 Pa and an average residence time of about 2 hours while aerating methane gas into the horizontal heating furnace. The operation was carried out to obtain a silicon-based material (volume average particle diameter 1.5 μm) whose surface was coated with carbon with a carbon content of 2% by weight.

<Example 1>
[Creation of coated negative electrode active material]
Manufactured in a state where 100 parts of non-graphitizable carbon powder 1 (volume average particle diameter 20 μm), which is a carbon-based material, is placed in a universal mixer high-speed mixer FS25 [manufactured by Arstecnica Co., Ltd.] and stirred at room temperature and 720 rpm. The coating polymer compound obtained in Example 1 was dissolved in isopropanol at a concentration of 19.8% by weight, and 8.7 parts of the coating polymer compound solution obtained was added dropwise over 2 minutes and stirred for another 5 minutes. did.
Then, in a stirred state, 5.2 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.], which is a conductive agent, was 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 a mesh size of 212 μm to obtain a coated negative electrode active material (N-1) according to Example 1.

<Examples 2 to 4>
The same procedure as in Example 1 was carried out except that the solid content concentration and the number of copies of the polymer compound solution for coating and the number of copies of the conductive agent were changed as shown in Table 1, and the coating according to Examples 2 to 4 was carried out. Negative electrode active materials (N-2) to (N-4) were obtained.
The solid content concentration of the coating polymer compound solution was adjusted by changing the amount of isopropanol in which the coating polymer compound was dissolved.

<Example 5>
20 parts of the refractory carbon powder 1 (volume average particle diameter 20 μm) and 80 parts of the silicon-based material produced in Production Example 2 were placed in a universal mixer high-speed mixer FS25 [manufactured by Arstecnica Co., Ltd.] at room temperature. With stirring at 720 rpm, 8.7 parts of the coating polymer compound solution obtained by dissolving the coating polymer compound obtained in Production Example 1 in isopropanol at a concentration of 19.8% by weight was applied over 2 minutes. Was added dropwise, and the mixture was further stirred for 5 minutes.
Then, in a stirred state, 5.2 parts of acetylene black [Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.], which is a conductive agent, was 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 a mesh size of 212 μm to obtain a coated negative electrode active material (N-5) according to Example 5.

<Example 6>
The same procedure as in Example 5 was carried out except that the number of copies of the carbon-based material and the silicon-based material was changed as shown in Table 1, to obtain a coated negative electrode active material (N-6) according to Example 6.

<Comparative Examples 1 to 3>
The same procedure as in Example 1 was carried out except that the type of the negative electrode active material, the solid content concentration and the number of copies of the coating polymer compound solution, and the number of copies of the conductive agent were changed as shown in Table 1, and comparative examples were performed. The coated negative electrode active materials (N'-1) to (N'-3) according to Nos. 1 to 3 were obtained.

<Comparative example 4>
The same procedure as in Example 5 was carried out except that the number of copies of the carbon-based material and the silicon-based material were changed as shown in Table 1, and the coated negative electrode active material (N'-4) according to Comparative Example 4 was obtained. ..

In Table 1, as the non-graphitizable carbon powder 1, a non-graphitizable carbon powder having a volume average particle diameter of 20 μm is used, and as the non-graphitizable carbon powder 2, a non-graphitizable carbon powder having a volume average particle diameter of 5 μm is used. Using.

Non-graphitizable carbon powders 1 and 2 which are negative electrode active materials before coating, acetylene black which is a conductive agent, silicon-based materials obtained in Production Example 2, and obtained in Examples 1 to 6 and Comparative Examples 1 to 4. The BET specific surface area of each of the coated negative electrode active materials was measured by the following method, and the coverage was calculated from the values and shown in Table 1.
Coverage (%) = {1- [BET specific surface area of coated negative electrode active material / (BET specific surface area of uncoated negative electrode active material x weight ratio of negative electrode active material contained in coated negative electrode active material + conductive agent BET specific surface area x weight ratio of conductive agent contained in coated negative electrode active material)]} x 100

[Measurement method of BET specific surface area]
According to the method for measuring the specific surface area of powder (solid) by JIS Z8830 gas adsorption, the measurement was performed with the following equipment and measurement conditions.
Measuring device: Micromeritex ASAP-2010
Adsorbed gas: N ₂
Dead volume measurement gas: He
Adsorption temperature: 77K
Measurement pretreatment: 100 ° C., vacuum drying for 10 minutes Measurement mode: Isothermal adsorption process and desorption process Measurement relative pressure P / P0: Approximately 0 to 0.99
Equilibrium setting time: 180 sec per relative pressure

[Calculation of coverage]
The coverage was calculated using the BET specific surface area obtained above and the above formula.
The BET specific surface area of acetylene black is 67.7 m ² / g, the BET specific surface area of the refractory carbon powder 1 is 3.43 m ² / g, and the BET specific surface area of the refractory carbon powder 2 is 3.84 m ² / g. g, the BET specific surface area of the silicon-based material obtained in Production Example 2 is 22.5 m ² / g, and the BET specific surface area of the coated negative electrode active materials obtained in Examples 1 to 6 and Comparative Examples 1 to 4 is It was as shown in Table 1.

[Manufacturing of lithium-ion battery for negative electrode evaluation]
20 parts of an electrolytic solution for a lithium ion battery and carbon fiber [Osaka Gas] prepared by dissolving _{LiPF 6} in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and diethyl carbonate (DEC) at a ratio of 1 mol / L. Donna Carbo Mild S-243 manufactured by Chemical Co., Ltd .: Average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS / cm] 2 parts and planetary stirring type mixing and kneading device ]} Is mixed at 2000 rpm for 7 minutes, and then 50 parts of the above electrolytic solution and 98 parts of the coated negative electrode active material obtained in Examples 1 to 6 or Comparative Examples 1 to 4 are added, and then further kneading. Mix by Taro at 2000 rpm for 1.5 minutes, add 25 parts of the above electrolyte, and then stir with Awatori Kentarou at 2000 rpm for 1 minute. After adding 50 parts of the electrolyte, stir with Awatori Kentarou. Was mixed at 2000 rpm for 1.5 minutes to prepare a negative electrode active material slurry.
Each of the obtained negative electrode active material slurries was applied to one side of an aramid separator [manufactured by Nippon Bileen Co., Ltd.] and pressed at a pressure of 10 MPa for about 10 seconds to have a thickness of about 350 μm in Examples 1 to 6 and Comparative Example 1. The negative electrode for the lithium ion battery according to No. 4 was produced.
A copper foil (3 cm x 3 cm) with a terminal (5 mm x 3 cm), two separators (made of Cellguard 2500 PP) (5 cm x 5 cm), and a copper foil with a terminal (5 mm x 3 cm) (3 cm x 3 cm) are placed in the same direction. Laminate in order so that the two terminals come out, sandwich it between two commercially available heat-sealing aluminum laminate films (8 cm x 8 cm), heat-sealing one side where the terminals come out, and laminate for negative evaluation. A cell was prepared.
Next, a negative electrode (3 cm × 3 cm) for a lithium ion battery according to Examples 1 to 6 or Comparative Examples 1 to 4 is inserted between one of the copper foils and the separator in a direction in which the aramid separator having the negative electrode and the separator are in contact with each other. 70 μL of the electrolytic solution was injected into the electrode to absorb the electrolytic solution into the electrode. Next, 70 μL of the electrolytic solution was injected onto the separator.
Then, a lithium foil was inserted between the separator and the other copper foil, and the two sides orthogonal to the first heat-sealed side were heat-sealed. After that, 70 μL of electrolytic solution is injected from the opening, and the laminated cell is sealed by heat-sealing the opening while evacuating the inside of the cell using a vacuum sealer, and the negative electrode evaluation lithium ion batteries 1 to 6 and the negative electrode are compared. Lithium ion batteries 1 to 4 for use were obtained.
The rate characteristics, internal resistance and Coulomb efficiency were measured by the following methods, and the results are shown in Table 2.

<Measurement of rate characteristics of lithium-ion batteries>
At 45 ° C., the charge / discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.] is used to evaluate the negative electrode evaluation lithium ion batteries 1 to 6 and the negative electrode comparison lithium ion batteries 1 to 4 by the following method. went.
It was discharged to 10 mV with a current of 0.1 C by a constant current constant voltage charging method (also referred to as CCCV mode), then paused for 10 minutes, and then charged to 1.5 V with a current of 0.1 C.
Then, it was discharged to 10 mV with a current of 0.1 C, paused for 10 minutes, and then charged to 1.5 V with a current of 1.0 C.
Then, after resting for 10 minutes, it is charged to 1.5V at 0.5C, then after resting for 10 minutes, it is continuously charged to 1.5V at 0.2C, and after resting for another 10 minutes, it is continuously charged with a current of 0.1C. It was charged to 1.5V.
From the charging capacity when charging to 1.5V with a current of 1.0C and the charging capacity when finally charging to 1.5V with a current of 0.1C, the rate characteristics (at 0.1C) are as follows. The ratio of the charge capacity of 1 to the charge capacity at 1.0 C) was calculated. It should be noted that the larger the value of the rate characteristic, the smaller the decrease in capacity and the better the battery characteristic.
[Rate characteristic (%)] = [Charging capacity at 1.0C] ÷ [Charging capacity at 0.1C] x 100

<Measurement of internal resistance of lithium-ion battery>
In the same manner as the above-mentioned measurement of the rate characteristics, the voltage and current after 0 seconds of charging at 1.0 C and the voltage and current after 10 seconds of charging at 1.0 C were measured, and the internal resistance was calculated by the following formula. The smaller the internal resistance, the better the battery characteristics.
The voltage after 0 seconds of charging is a voltage measured at the same time as charging (also referred to as a charging voltage).
[Internal resistance (Ω)] = [(voltage after 0 seconds of charging at 1.0C)-(voltage after 10 seconds of charging at 1.0C)] ÷ [(current after 0 seconds of charging at 1.0C)- (Current after 10 seconds of charging at 1.0C)]

<Evaluation of Coulomb efficiency of lithium-ion batteries>
The Coulomb efficiency was calculated by the following formula using the initial charge capacity at 0.1 C and the initial discharge capacity at 0.1 C obtained by the above measurement of the rate characteristics. The higher the Coulomb efficiency, the better the battery characteristics.
Coulomb efficiency (%) = (first charge capacity at 0.1C) ÷ (first discharge capacity at 0.1C) x 100

It can be seen that the lithium ion battery using the coated negative electrode active material for the lithium ion battery of the present invention is particularly excellent in rate characteristics.

The coated negative electrode active material for lithium ion batteries of the present invention is particularly useful as a negative electrode active material for bipolar secondary batteries and lithium ion secondary batteries used for mobile phones, personal computers, hybrid vehicles and electric vehicles. Is.

Claims (3)

A coated negative electrode active material for a lithium ion battery, wherein at least a part of the surface of the negative electrode active material for a lithium ion battery is coated with a coating layer containing a polymer compound and a conductive agent.
The negative electrode active material for a lithium ion battery is a graphitizable carbon or a mixture of graphitizable carbon and a silicon-based material.
The polymer compound is obtained by polymerizing a monomer composition containing acrylic acid, butyl methacrylate, methyl methacrylate, and sodium allylsulfonate, and the weight ratio of butyl methacrylate to acrylic acid [butyl methacrylate / Acrylic acid] is 10/90 to 90/10,
The conductive agent is acetylene black and
A coated negative electrode active material for a lithium ion battery, wherein the coverage obtained by the following formula is 10 to 45%.
Coverage (%) = {1- [BET specific surface area of coated negative electrode active material / (BET specific surface area of uncoated negative electrode active material x weight ratio of negative electrode active material contained in coated negative electrode active material + conductive agent BET specific surface area x weight ratio of conductive agent contained in coated negative electrode active material)]} x 100 The ratio of the weight of the polymer compound to the weight of the coated negative electrode active material for a lithium ion battery is 0.1 to 11% by weight, and the ratio of the weight of the conductive agent to the weight of the coated negative electrode active material for a lithium ion battery. The coated negative electrode active material for a lithium ion battery according to claim 1, wherein the amount is 2 to 14% by weight. The coated negative electrode active material for a lithium ion battery according to claim 1 or 2 , wherein the ratio of the weight of the polymer compound contained in the coating layer to the weight of the conductive agent contained in the coating layer is 13 to 500% by weight. ..