JP2022152880A - Coated Negative Electrode Active Material Particles for Lithium Ion Battery, Negative Electrode for Lithium Ion Battery, and Lithium Ion Battery - Google Patents

Abstract

To provide coated negative electrode active material particles for lithium ion battery, in which titanium composite oxide and titanium oxide are used as a negative electrode active material and a coating layer is formed, the coated negative electrode active material particles having a sufficiently high discharge capacity per volume.SOLUTION: There are provided coated negative electrode active material particles for lithium ion battery, at least part of the surface of negative electrode active material particles being coated with a coating layer containing a polymer compound and a conductive assistant. The negative electrode active material particles include particles comprising a titanium composite oxide and/or a titanium oxide. The weight ratio of the polymer compound in the coated negative electrode active material particles is 0.1-2 wt.% based on the weight of the coated negative electrode active material particles, and the weight ratio of the conductive assistant in the coated negative electrode active material particles is 3-15 wt.% based on the weight of the coated negative electrode active material particles.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to coated negative electrode active material particles for lithium ion batteries, negative electrodes for lithium ion batteries, and lithium ion batteries.

Lithium ion (secondary) batteries have recently been widely used in various applications as secondary batteries capable of achieving high energy density and high output density.
Lithium-ion batteries have been widely used in recent years as secondary batteries that can achieve high energy density and high output density, and various materials are being investigated to develop higher-performance lithium-ion batteries. .

Among them, titanium composite oxides and titanium oxides have excellent input/output characteristics and cycle characteristics, so their use as an alternative to carbon-based materials that have been used as negative electrode active materials in lithium-ion batteries is being investigated. (Patent document 1).

In addition, by using coated electrode active material particles in which at least a part of the surface of the electrode active material particles is covered with a coating layer containing a coating resin and a conductive aid, a solvent removal step that requires a lot of time and energy is performed. There is known a method of producing an electrode for a lithium-ion battery without using a coating (Patent Document 2).

JP 2019-160734 A JP 2016-189325 A

Patent Document 2 considers a carbon-based material as the negative electrode active material, and does not consider using a titanium composite oxide or titanium oxide as the negative electrode active material.
In order to obtain the effects described in Patent Document 2, coated electrode active material particles are formed by forming a coating layer on the surface of titanium composite oxide or titanium oxide particles by the method described in Patent Document 2. As a result, it was found that there was a problem that the discharge capacity per volume became insufficient.

The present invention has been made in view of the above problems, and uses a titanium composite oxide or titanium oxide as a negative electrode active material to provide a coated negative electrode active material particle for a lithium ion battery in which a coating layer is formed. An object of the present invention is to provide coated negative electrode active material particles having a sufficiently high discharge capacity per charge.

The inventors of the present invention have found that when titanium composite oxides and titanium oxides are used as the negative electrode active material, the electrical conductivity of these materials tends to be lower than that of carbon-based materials, so the discharge capacity per volume is reduced. As a result of intensive studies based on this hypothesis, the present inventors found a configuration capable of increasing the discharge capacity per volume and arrived at the present invention.

That is, the present invention provides a coated negative electrode active material particle for a lithium ion battery in which at least a part of the surface of the negative electrode active material particle is coated with a coating layer containing a polymer compound and a conductive aid, The material particles contain particles made of titanium composite oxide and/or titanium oxide, and the weight ratio of the polymer compound in the coated negative electrode active material particles is 0.1 to 0.1 based on the weight of the coated negative electrode active material particles. 2% by weight, and the weight ratio of the conductive aid in the coated negative electrode active material particles is 3 to 15% by weight based on the weight of the coated negative electrode active material particles. .

According to the present invention, a coated negative electrode active material particle for a lithium ion battery in which a titanium composite oxide or titanium oxide is used as a negative electrode active material and a coating layer is formed, the coated negative electrode having a sufficiently high discharge capacity per volume. Active material particles can be provided.

<Coated Negative Electrode Active Material Particles for Lithium Ion Battery>
The coated negative electrode active material particles for lithium ion batteries of the present invention are coated negative electrode active materials for lithium ion batteries in which at least part of the surface of the negative electrode active material particles is coated with a coating layer containing a polymer compound and a conductive aid. particles, wherein the negative electrode active material particles contain particles made of titanium composite oxide and/or titanium oxide, and the weight ratio of the polymer compound in the coated negative electrode active material particles is the same as that of the coated negative electrode active material particles. It is 0.1 to 2% by weight based on the weight, and the weight ratio of the conductive aid in the coated negative electrode active material particles is 3 to 15% by weight based on the weight of the coated negative electrode active material particles. Characterized by

(Negative electrode active material particles)
The negative electrode active material particles include particles made of titanium composite oxide and/or titanium oxide.
A titanium composite oxide is a compound containing titanium, oxygen and other elements, and examples thereof include lithium titanate and titanium niobium oxide.
As the lithium titanate, a spinel type, a ramsdellite type, or the like can be used.
Lithium titanate having a spinel crystal structure includes, for example, compounds represented by the general formula Li _4+x Ti ₅ O ₁₂ (−1≦x≦3).
Lithium titanate having a ramsdellite-type crystal structure includes, for example, compounds represented by the general formula Li _2+x Ti ₃ O ₇ (0≦x≦1).

Titanium niobium oxides include Li _a TiM _b Nb _2+c O _7+d (0≦a≦5, 0≦b≦0.3, −0.3≦c≦0.3, and −0.3≦d≦0. 3, and M is one or more elements selected from Fe, V, Mo, and Ta.).

Titanium oxide is a compound containing only titanium and oxygen, and includes titanium oxide (TiO) and titanium dioxide (TiO ₂ ). The crystal system of titanium dioxide is not particularly limited, and rutile type, anatase type, and brookite type can be used.

The titanium composite oxides and titanium oxides shown above can be used singly or in combination of two or more.

The volume average particle diameter of the negative electrode active material particles is preferably 0.01 to 100 μm, more preferably 0.1 to 20 μm, even more preferably 2 to 10 μm, from the viewpoint of the electrical characteristics of the battery.

(coating layer)
The coating layer contains a polymer compound and a conductive aid.
As the polymer compound, an ester compound (a11) of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid [hereinafter referred to as the ester compound (a11)] and an anionic monomer ( It is preferably a polymer of a monomer composition comprising a12).
In addition, (meth)acrylic acid means acrylic acid and methacrylic acid.

Further, the acid value of the polymer compound is preferably 250-800.
The acid value of the polymer compound herein is measured by the method of JIS K 0070-1992, and the acid value of the polymer compound is the anionic monomer (a12 ) can be adjusted to the above range.
Further, it is more preferable that the polymer compound has an acid value of 270-780.

First, the ester compound (a11) will be described.
The ester compound (a11) is an ester of a monohydric aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid, and the monohydric aliphatic alcohol having 1 to 12 carbon atoms has 1 to 12 carbon atoms. monohydric branched or straight chain aliphatic alcohols, methanol, ethanol, propanol (n-propanol, iso-propanol), butyl alcohol (n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol), pentyl alcohol (n-pentyl alcohol, 2-pentyl alcohol and neopentyl alcohol, etc.), hexyl alcohol (1-hexanol, 2-hexanol and 3-hexanol, etc.), heptyl alcohol (n-heptyl alcohol, 1-methylhexyl alcohol and 2 -methylhexyl alcohol, etc.), octyl alcohol (n-octyl alcohol, 1-methylheptanol, 1-ethylhexanol, 2-methylheptanol and 2-ethylhexanol, etc.), nonyl alcohol (n-nonyl alcohol, 1-methyl octanol, 1-ethylheptanol, 1-propylhexanol and 2-ethylheptyl alcohol, etc.), decyl alcohol (n-decyl alcohol, 1-methylnonyl alcohol, 2-methylnonyl alcohol and 2-ethyloctyl alcohol, etc.), un Decyl alcohol (n-undecyl alcohol, 1-methyldecyl alcohol, 2-methyldecyl alcohol and 2-ethylnonyl alcohol, etc.), lauryl alcohol (n-lauryl alcohol, 1-methylundecyl alcohol, 2-methylundecyl alcohol , 2-ethyldecyl alcohol and 2-butylhexyl alcohol) and the like.

Preferred examples of the ester compound (a11) include methyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-methylhexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. , dodecyl (meth)acrylate, and more preferably methyl methacrylate, butyl methacrylate, dodecyl methacrylate, and 2-ethylhexyl methacrylate.

The anionic monomer (a12) will be explained.
The anionic monomer (a12) is a monomer having a radically polymerizable group and an anionic group, and preferable radically polymerizable groups include a vinyl group, an allyl group, a styrenyl group and a (meth) ) acryloyl group and the like, and preferred anionic groups include phosphonic acid group, sulfonic acid group and carboxyl group.

Preferred examples of the anionic monomer (a12) include a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms, a radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms, and a radically polymerizable unsaturated sulfonic acid having 2 to 9 carbon atoms. at least one selected from the group consisting of polyunsaturated phosphonic acids.

Examples of radically polymerizable unsaturated carboxylic acids having 3 to 9 carbon atoms include radically polymerizable unsaturated aliphatic monocarboxylic acids having 3 to 9 carbon atoms and radically polymerizable unsaturated aromatic monocarboxylic acids having 9 carbon atoms. , The radically polymerizable unsaturated aliphatic monocarboxylic acids having 3 to 9 carbon atoms include (meth)acrylic acid, butanoic acid (including substituted butanoic acids such as 2-methylbutanoic acid and 3-methylbutanoic acid), pentenoic acid ( 2-methylpentenoic acid and substituted pentenoic acids such as 3-methylpentenoic acid), hexenoic acid (including substituted hexenoic acids such as 2-methylhexenoic acid and 3-methylhexenoic acid), heptenoic acid (2- (including substituted heptenoic acids such as methylheptenoic acid and 3-methylheptenoic acid) and octenoic acid (including substituted octenoic acids such as 2-methyloctenoic acid and 3-methyloctenoic acid).
Examples of radically polymerizable unsaturated aromatic monocarboxylic acids having 9 carbon atoms include 3-phenylpropenoic acid and vinylbenzoic acid.

Examples of radically polymerizable unsaturated sulfonic acids having 2 to 8 carbon atoms include radically polymerizable unsaturated aliphatic monosulfonic acids having 2 to 8 carbon atoms and radically polymerizable unsaturated aromatic monosulfonic acids having 8 carbon atoms. .
Examples of radically polymerizable unsaturated aliphatic monosulfonic acids having 2 to 8 carbon atoms include vinylsulfonic acid (including substituted vinylsulfonic acids such as 1-methylvinylsulfonic acid and 2-methylvinylsulfonic acid), allylsulfonic acid ( (including substituted allylsulfonic acids such as 1-methylallylsulfonic acid and 2-methylallylsulfonic acid anions), butenesulfonic acids (including substituted butenesulfonic acids such as 1-methylbutenesulfonic acid and 2-methylbutenesulfonic acid) ), pentenesulfonic acid (including substituted pentenesulfonic acids such as 1-methylpentenesulfonic acid and 2-methylpentenesulfonic acid), hexenesulfonic acid (substituted 1-methylhexenesulfonic acid and 2-methylhexenesulfonic acid). hexenesulfonic acid) and heptenesulfonic acid (including substituted heptenesulfonic acids such as 1-methylheptenesulfonic acid and 2-methylheptenesulfonic acid).
Examples of radically polymerizable unsaturated aromatic monosulfonic acid monomers having 8 carbon atoms include styrenesulfonic acid.

Examples of radically polymerizable unsaturated phosphonic acids having 2 to 9 carbon atoms include vinylphosphonic acid, allylphosphonic acid, vinylbenzylphosphonic acid, 1- or 2-phenylethenylphosphonic acid, (meth)acrylamidoalkylphosphonic acid, acrylamidoalkyl diphosphonic acid, phosphonomethylated vinylamine, (meth)acrylic phosphonic acid and the like.
A mixture of these anionic monomers may be used.
By containing the anionic monomer, the toughness is improved, and the stress caused by the expansion and contraction of the active material accompanying the deinsertion reaction of lithium ions during charge and discharge is less likely to occur.

These anionic monomers may be used singly or in combination of two or more. The anionic monomer (a12) is a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms, a radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms, and a radically polymerizable unsaturated phosphonic acid having 2 to 9 carbon atoms. It is preferable to use at least two selected from the group consisting of acids in combination, a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms and a radically polymerizable unsaturated sulfonic acid having 2 to 8 carbon atoms or 2 to 9 carbon atoms. is more preferably used in combination with a radically polymerizable unsaturated phosphonic acid.

The content of the ester compound (a11) contained in the polymer compound is 5 to 99 based on the total weight of the ester compound (a11) and the anionic monomer (a12) from the viewpoint of adhesion to the active material. % by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight.

In the polymer compound, the content of the anionic monomer (a12) contained in the monomer composition is, from the viewpoint of ion conductivity, the total weight of the ester compound (a11) and the anionic monomer (a12). It is preferably 1 to 99% by weight, more preferably 20 to 80% by weight, still more preferably 30 to 70% by weight, based on the weight.

In the polymer compound, the monomer composition preferably further contains an anionic monomer salt (a13).
When the polymer compound contains the anionic monomer salt (a13), the internal resistance can be reduced.

The anionic monomer salt (a13) will be described.
Examples of the anion of the anionic monomer constituting the salt of the anionic monomer (a13) include the anions of the same anionic monomers as exemplified for the anionic monomer (a12) above, At least one anion selected from the group consisting of vinylsulfonate anions, allylsulfonate anions, styrenesulfonate anions and (meth)acrylate anions is preferred.
The cations constituting the anionic monomer salt (a13) include monovalent inorganic cations, preferably alkali metal cations and ammonium ions, more preferably lithium ions, sodium ions, potassium ions and ammonium ions, Lithium ion is more preferred.
The anionic monomer salt (a13) may be used alone or in combination, and when the anionic monomer salt (a13) has a plurality of anions, the cations are lithium ions and sodium ions. , potassium ions and ammonium ions.

In the polymer compound, when the monomer composition contains an anionic monomer salt (a13), the content of the ester compound (a11) contained in the monomer composition is From the viewpoint of properties and the like, it is preferably 5 to 95% by weight, more preferably 5 to 95% by weight based on the total weight of the ester compound (a11), the anionic monomer (a12) and the salt of the anionic monomer (a13). is 20 to 80% by weight, more preferably 30 to 70% by weight.

In the polymer compound, when the monomer composition contains an anionic monomer salt (a13), the content of the anionic monomer (a12) contained in the monomer composition is From the viewpoint of, the ester compound (a11), the anionic monomer (a12) and the anionic monomer salt (a13) are preferably 10 to 90% by weight based on the total weight, more preferably 20 80% by weight, more preferably 30 to 70% by weight.

In the polymer compound, when the monomer composition contains an anionic monomer salt (a13), the content of the anionic monomer salt (a13) contained in the monomer composition is From the viewpoint of resistance etc., it is preferably 0.1 to 10% by weight based on the total weight of the ester compound (a11), the anionic monomer (a12) and the salt of the anionic monomer (a13), More preferably 0.5 to 10% by weight, still more preferably 1 to 10% by weight.

Polymer compounds include, for example, known polymerization initiators {azo initiators [2,2′-azobis(2-methylpropionitrile), 2,2′-azobis(2,4-dimethylvaleronitrile), 2 , 2'-azobis(2-methylbutyronitrile), 2,2'-azobis(2-methylpropionamidine) dihydrochloride, etc.], peroxide initiators (benzoyl peroxide, di-t-butyl peroxide , lauryl peroxide, etc.), etc.) by known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.).
The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomers, from the viewpoint of adjusting the weight average molecular weight to a preferred range. It is more preferably 0.1 to 1.5% by weight, and the polymerization temperature and polymerization time are adjusted according to the type of polymerization initiator. 30 to 120° C.), and the reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

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

Dispersion media in emulsion polymerization and suspension polymerization include water, alcohols (eg, ethanol), esters (eg, ethyl propionate), light naphtha, etc. Emulsifiers include higher fatty acid (C10-24) metal salts. (e.g. sodium oleate and sodium stearate), higher alcohol (C10-24) sulfate metal salt (e.g. sodium lauryl sulfate), ethoxylated tetramethyldecyndiol, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. is mentioned. Furthermore, polyvinyl alcohol, polyvinylpyrrolidone, etc. may be added as a stabilizer.
The monomer concentration of the solution or dispersion is preferably 5 to 95% by weight, more preferably 10 to 90% by weight, still more preferably 15 to 85% by weight, and the amount of the polymerization initiator used is based on the total weight of the monomers. is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight.
In the polymerization, known chain transfer agents such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and/or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used. .

The polymer compound is a cross-linking agent (A') {preferably a polyepoxy compound (a'1) [polyglycidyl ether (bisphenol A diglycidyl ether, propylene glycol diglycidyl ether and glycerin triglycidyl ether, etc.) and polyglycidylamines (N,N-diglycidylaniline and 1,3-bis(N,N-diglycidylaminomethyl), etc.)] and/or polyol compounds (a' 2) It may be a crosslinked polymer obtained by crosslinking with (ethylene glycol, etc.).

Examples of the method for cross-linking the polymer compound using the cross-linking agent (A′) include a method in which the negative electrode active material particles are coated with the polymer compound and then cross-linked. Specifically, the coated negative electrode active material particles are produced by mixing the negative electrode active material particles and a resin solution containing a polymer compound and removing the solvent, and then the solution containing the cross-linking agent (A′) is added to the coated negative electrode active material. There is a method in which solvent removal and cross-linking reaction are caused by mixing with substance particles and heating to cause cross-linking reaction of the polymer compound with the cross-linking agent (A′) on the surface of the negative electrode active material particles.
The heating temperature is adjusted according to the type of cross-linking agent, and is preferably 70° C. or higher when using the polyepoxy compound (a′1) as the cross-linking agent, and when using the polyol compound (a′2) It is preferably 120° C. or higher.

The weight-average molecular weight of the polymer compound is preferably 20,000 to 96,000 from the viewpoint of adhesiveness with the active material, etc., and the weight-average molecular weight is preferably controlled by setting the polymerization conditions of the polymer within a preferable range. can be a range.
In addition, the weight average molecular weight of the polymer compound in the present specification is measured by gel permeation chromatography (hereinafter abbreviated as GPC) under the following conditions.
<GPC measurement conditions>
Apparatus: Alliance GPC V2000 (manufactured by Waters)
Solvent: ortho-dichlorobenzene Standard material: polystyrene sample Concentration: 3 mg/ml
Column stationary phase: PLgel 10 μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
Column temperature: 135°C

The coating layer contains a conductive aid.
The conductive aid is preferably selected from materials having conductivity.
Preferable conductive aids include metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite and carbon black (acetylene black, ketjen black, furnace black, channel black, thermal lamp black, carbon nanofibers, etc.), and mixtures thereof.
One of these conductive aids may be used alone, or two or more thereof may be used in combination. Moreover, these alloys or metal oxides may be used.
Among them, from the viewpoint of electrical stability, aluminum, stainless steel, carbon, silver, gold, copper, titanium and mixtures thereof are more preferable, silver, gold, aluminum, stainless steel and carbon are more preferable, and particularly Carbon is preferred.
These conductive aids may also be those obtained by coating a conductive material [preferably a metal one of the above-described conductive aids] around a particulate ceramic material or a resin material by plating or the like.

The shape (form) of the conductive aid is not limited to a particle form, and may be in a form other than a particle form, such as carbon nanofibers, carbon nanotubes, etc., which are practically used as so-called filler-type conductive aids. may

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

(Coated negative electrode active material particles for lithium ion batteries)
Coated negative electrode active material particles for a lithium ion battery (hereinafter also simply referred to as coated negative electrode active material particles) are such that at least part of the surface of the negative electrode active material particles is coated with a coating layer containing a polymer compound and a conductive aid. It is a particle that becomes
The weight ratio of the polymer compound in the coated negative electrode active material particles is 0.1 to 2% by weight based on the weight of the coated negative electrode active material particles. Also, the weight ratio is preferably 0.3 to 1.0% by weight.
The weight ratio of the conductive aid in the coated negative electrode active material particles is 3 to 15% by weight based on the weight of the coated negative electrode active material particles. Also, the weight ratio is preferably 6 to 12% by weight.
When the negative electrode active material particles contain particles made of a titanium composite oxide and/or titanium oxide, and the weight ratios of the polymer compound and the conductive aid in the coated negative electrode active material particles are both within the above range, the electrode volume The discharge capacity per unit can be increased. Moreover, it is excellent in cycle characteristics.
The weight ratio of the polymer compound and the weight ratio of the conductive aid in the coated negative electrode active material particles can be measured by thermogravimetry.

When the weight ratio of the polymer compound in the coated negative electrode active material particles is less than 0.1% by weight, the discharge capacity per electrode volume becomes low. Also, the cycle characteristics are not so high even if the negative electrode active material particles are titanium composite oxide and/or titanium oxide.
When the weight ratio of the polymer compound in the coated negative electrode active material particles exceeds 2% by weight, the discharge capacity per electrode volume becomes low.
If the weight ratio of the conductive aid in the coated negative electrode active material particles is less than 3% by weight, the discharge capacity per electrode volume will be low. Also, the cycle characteristics are not so high even if the negative electrode active material particles are titanium composite oxide and/or titanium oxide.
When the weight ratio of the conductive aid in the coated negative electrode active material particles exceeds 15% by weight, the discharge capacity per electrode volume becomes low.

<Method for producing coated negative electrode active material particles for lithium ion battery>
The method for producing the coated negative electrode active material particles for a lithium ion battery according to the present invention is not particularly limited. be able to.
The order in which the negative electrode active material particles, the polymer compound, and the conductive aid are mixed is not particularly limited. Further mixing may be performed, the negative electrode active material particles, the polymer compound and the conductive aid may be mixed at the same time, or the negative electrode active material particles may be mixed with the polymer compound and further mixed with the conductive aid. good.

The coated negative electrode active material particles of the present invention can be obtained by coating the negative electrode active material particles with a polymer compound. For example, the negative electrode active material particles are placed in a universal mixer and stirred at 30 to 500 rpm. , A resin solution containing a polymer compound is dropped and mixed over 1 to 90 minutes, and if necessary, a conductive agent is mixed, and the temperature is raised to 50 to 200 ° C. while stirring to 0.007 to 0.04 MPa. It can be obtained by holding for 10 to 150 minutes after reducing the pressure to.

<Negative electrode for lithium ion battery>
A negative electrode for a lithium ion battery of the present invention is characterized by having the coated negative electrode active material particles of the present invention described above.
The negative electrode for a lithium ion battery of the present invention preferably comprises a negative electrode active material layer containing coated negative electrode active material particles, an electrolytic solution containing an electrolyte and a solvent, and a negative electrode current collector.

(Negative electrode active material layer)
The negative electrode active material layer includes coated negative electrode active material particles and an electrolytic solution. The electrolytic solution contains an electrolyte and a solvent.

_As the _electrolyte , _{electrolytes used} in _{known electrolytic solutions} can be used. 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 are included. Among these, LiN(FSO ₂ ) ₂ is preferable from the viewpoint of battery output and charge/discharge cycle characteristics.

As the solvent, non-aqueous solvents used in known electrolytic solutions can be used. , amide compounds, sulfones, sulfolane and mixtures thereof can be used.

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

Cyclic carbonates include propylene carbonate, ethylene carbonate (EC) and butylene carbonate (BC).
Chain carbonates include dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl-n-propyl carbonate, ethyl-n-propyl carbonate and di-n-propyl carbonate. .

Chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate and methyl propionate.

Cyclic ethers include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane and 1,4-dioxane. Chain ethers include dimethoxymethane and 1,2-dimethoxyethane.

Phosphate esters include trimethyl phosphate, triethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, tripropyl phosphate, tributyl phosphate, tri(trifluoromethyl) phosphate, tri(trichloromethyl) phosphate, Tri(trifluoroethyl) phosphate, tri(triperfluoroethyl) phosphate, 2-ethoxy-1,3,2-dioxaphospholan-2-one, 2-trifluoroethoxy-1,3,2- dioxaphospholan-2-one, 2-methoxyethoxy-1,3,2-dioxaphospholan-2-one and the like.

Acetonitrile etc. are mentioned as a nitrile compound. DMF etc. are mentioned as an amide compound. Sulfones include dimethylsulfone, diethylsulfone, and the like.

One of these solvents may be used alone, or two or more thereof 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. more preferably 2.0 to 3.5 mol/L.

The negative electrode active material layer may further contain a conductive support agent in addition to the conductive support agent contained in the coating layer of the coated negative electrode active material particles described above. It can be distinguished in that the conductive aid contained in the coating layer is integrated with the coated negative electrode active material particles, whereas the conductive aid contained in the negative electrode active material layer is contained separately from the coated negative electrode active material particles.
As the conductive aid that the negative electrode active material layer may contain, those described in <Coated Negative Electrode Active Material Particles for Lithium Ion Battery> can be used.

The negative electrode active material layer preferably does not contain a binder.
In this specification, the binder means an agent that cannot reversibly fix the coated negative electrode active material particles together and the coated negative electrode active material particles and the current collector, and includes starch, polyvinylidene fluoride, Known solvent-drying type binders for lithium ion batteries such as polyvinyl alcohol, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene and polypropylene are included.
These binders are used by being dissolved or dispersed in a solvent, and are solidified by volatilizing and distilling off the solvent to irreversibly bind the coated negative electrode active material particles together and the coated negative electrode active material particles and the current collector. is fixed to

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

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. is 45% by weight or more based on the total weight of the constituent monomers.
When the 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 negative electrode active material particles.

From the viewpoint of battery performance, the thickness of the negative electrode active material layer is preferably 150 to 600 μm, more preferably 200 to 450 μm.

The negative electrode active material layer may contain other types of negative electrode active material particles in addition to the coated negative electrode active material particles of the present invention. Other types of negative electrode active material particles include carbon-based negative electrode active material particles and silicon-based negative electrode active material particles. These other types of negative electrode active material particles can be blended within a range that does not affect the cycle characteristics of the battery.
Further, the other types of negative electrode active material particles may be coated negative electrode active material particles.

(Negative electrode current collector)
A negative electrode for a lithium ion battery preferably includes a negative electrode current collector, and a negative electrode active material layer is provided on the surface of the negative electrode current collector.

Materials constituting the negative electrode current collector include metallic materials such as copper, aluminum, titanium, stainless steel, nickel and alloys thereof, baked carbon, conductive polymer materials, conductive glass, and the like.
The shape of the negative electrode current collector is not particularly limited.

The negative electrode for a lithium ion battery of the present invention preferably includes a resin current collector made of a conductive polymer material, and a negative 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 material is added can be used.
As the conductive material that constitutes the conductive polymer material, the same materials as the conductive aid, which is an optional component of the coating layer, can be preferably used.
Examples of resins constituting the conductive polymer material include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyethernitrile (PEN), poly Tetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin or mixtures thereof etc.
From the viewpoint of electrical stability, polyethylene (PE), polypropylene (PP), polymethylpentene (PMP) and polycycloolefin (PCO) are preferred, and polyethylene (PE), polypropylene (PP) and polymethylpentene are more preferred. (PMP).
The resin current collector can be obtained by known methods described in JP-A-2012-150905, WO 2015/005116, and the like.

Although the thickness of the negative electrode current collector is not particularly limited, it is preferably 5 to 150 μm.

The negative electrode for a lithium ion battery of the present invention can be obtained, for example, by coating a negative electrode current collector with a powder (negative electrode precursor) obtained by mixing the coated negative electrode active material particles of the present invention and, if necessary, a conductive aid, etc., and applying the powder with a press. It can be produced by injecting an electrolytic solution after forming a negative electrode active material layer by pressing.
Alternatively, the negative electrode precursor may be applied onto a release film and pressed to form a negative electrode active material layer, the negative electrode active material layer may be transferred to the negative electrode current collector, and then the electrolytic solution may be injected.

<Lithium-ion battery>
The lithium ion battery of the present invention has the lithium ion battery negative electrode of the present invention.
The lithium ion battery of the present invention preferably comprises the lithium ion battery negative electrode of the present invention, a separator, and a positive electrode.

(separator)
Separators include porous films made of polyethylene or polypropylene, laminated films of porous polyethylene film and porous polypropylene, non-woven fabrics made of synthetic fibers (polyester fibers, aramid fibers, etc.) or glass fibers, and silica on their surfaces. , alumina, titania, and other known separators for lithium ion batteries.

(positive electrode)
The positive electrode preferably includes a positive electrode active material layer and a positive electrode current collector.

The positive electrode active material layer contains positive electrode active material particles.
Examples of positive electrode active material particles include composite oxides of lithium and transition metals {composite oxides containing one type of transition metal (LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO ₂ and LiMn ₂ O ₄ , etc.), transition metal elements are two kinds of composite oxides (for example, 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 containing three or more metal elements [for example, LiM _a M′ _b M″ _c O ₂ (M, M′ and M″ are different transition metals _element and _satisfies a _{+ b + c} = ₁ . 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 polyvinyl carbazole), and two or more thereof may be used in combination.
The lithium-containing transition metal phosphate may have a transition metal site partially substituted with another transition metal.

The volume average particle diameter 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 positive electrode active material particles may be coated positive electrode active material particles in which at least part of the surface is coated with a coating layer containing a polymer compound.
When the positive electrode active material particles are covered with the coating layer, the volume change of the positive electrode is moderated, and the expansion of the positive electrode can be suppressed.

As the coating layer, the same coating layer as described for the coated negative electrode active material particles for a lithium ion battery of the present invention can be suitably used.

The positive electrode active material layer preferably does not contain a binder.
The binder means the one described for the negative electrode.

The positive electrode active material layer may contain an adhesive resin.
As the adhesive resin, the same adhesive resin as an optional component of the negative electrode active material layer can be preferably used.

The positive electrode active material layer may contain a conductive aid.
As the conductive aid, a conductive material similar to the conductive filler contained in the negative electrode active material layer can be preferably used.
The weight ratio of the conductive aid in the positive electrode active material layer is preferably 2 to 10% by weight.

The positive electrode active material layer may contain an electrolytic solution.
As the electrolytic solution, those described for the negative electrode active material layer can be appropriately selected and used.

Although the thickness of the positive electrode active material layer is not particularly limited, it is preferably 150 to 600 μm, more preferably 200 to 450 μm, from the viewpoint of battery performance.

As the positive electrode current collector, a known metal current collector and a resin current collector composed of a conductive resin composition containing a conductive material and a resin (Japanese Patent Application Laid-Open No. 2012-150905 and International Publication No. 2015-005116 etc.) can be used.
The positive electrode current collector is preferably a resin current collector from the viewpoint of battery characteristics and the like.
Although the thickness of the positive electrode current collector is not particularly limited, it is preferably 5 to 150 μm.

The positive electrode can be produced, for example, by a method of applying a mixture containing positive electrode active material particles and an electrolytic solution to the surface of a positive electrode current collector or a substrate and removing excess electrolytic solution.
When the positive electrode active material layer is formed on the surface of the substrate, the positive electrode active material layer may be combined with the positive current collector by a method such as transfer.
The mixture may contain a conductive aid, an adhesive resin, and the like, if necessary.

(Manufacturing method of lithium ion battery)
The lithium-ion battery of the present invention can be produced, for example, by stacking a positive electrode, a separator and a negative electrode for a lithium-ion battery of the present invention in this order, and then pouring an electrolytic solution as necessary.

EXAMPLES Next, the present invention will be specifically described with reference to Examples, but the present invention is not limited to Examples unless it departs from the gist of the present invention. Unless otherwise specified, parts means parts by weight and % means % by weight.

<Preparation of polymer compound A>
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 66.46 parts of DMF and heated to 75°C. Next, 10.0 parts of acrylic acid, 90.0 parts of 2-ethylhexyl methacrylate, and 116.5 parts of DMF were added to a monomer mixture, and 2,2′-azobis(2,4-dimethylvaleronitrile)1. A solution of 7 parts dissolved in 29.15 parts of DMF and a solution of initiator dissolved in 29.15 parts of DMF were continuously added dropwise over 2 hours with stirring into a four-necked flask with a dropping funnel to carry out radical polymerization. After the dropwise addition was completed, the reaction was continued at 75° C. for 3 hours. Then, the temperature was raised to 80° C., and an initiator solution prepared by dissolving 1.7 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) in 29.15 parts of DMF was again stirred with a dropping funnel for 2 hours. dripped continuously. After dropping, the reaction was continued for 3 hours to obtain a solution of polymer compound A with a resin concentration of 30%.

<Preparation of polymer compound B>
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 70.0 parts of DMF and heated to 75°C. Then, a monomer composition containing 100.0 parts of acrylic acid and 20 parts of DMF, 0.3 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) and 2,2′-azobis(2- 0.8 parts of methylbutyronitrile) dissolved in 10.0 parts of DMF and a solution of an initiator dissolved in 10.0 parts of DMF were continuously added dropwise over 2 hours with a dropping funnel under stirring while blowing nitrogen into a four-necked flask to obtain radicals. Polymerization was carried out. After the dropwise addition was completed, 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 solution of polymer compound B with a resin concentration of 50%.

<Preparation of polymer compound C>
A four-necked flask equipped with a stirrer, thermometer, reflux condenser, dropping funnel and nitrogen gas inlet tube was charged with 70.0 parts of DMF and heated to 75°C. Then, 15.0 parts of 2-ethylhexyl methacrylate, 40.0 parts of methyl methacrylate, 10.0 parts of dodecyl methacrylate, 28.0 parts of methacrylic acid, 2.0 parts of vinylsulfonic acid, and 1.0 part of lithium styrenesulfonate. part, a monomer composition containing 4.0 parts of lithium methacrylate and 20 parts of DMF, 0.6 parts of 2,2′-azobis (2,4-dimethylvaleronitrile) and 2,2′-azobis (2 -Methylbutyronitrile) was dissolved in 10.0 parts of DMF and an initiator solution was continuously added dropwise over 2 hours with a dropping funnel while blowing nitrogen into a four-necked flask. Radical polymerization was performed. After completion of dropping, the temperature was raised to 80° C. and the reaction was continued for 5 hours to obtain a solution of polymer compound C with a resin concentration of 50%.

<Preparation of electrolytic solution>
LiPF ₆ was dissolved at a ratio of 1 mol/L in a mixed solvent of ethylene carbonate and propylene carbonate (volume ratio 1:1) to prepare an electrolytic solution for a lithium ion battery.

<Preparation of current collector>
Using a twin-screw extruder, 10 parts of the product name "SunAllomer PB522M" [manufactured by SunAllomer Co., Ltd.], 25 parts of the trade name "SunAllomer PM854X" [manufactured by SunAllomer Co., Ltd.], and the product name "Suntec B680" [Asahi Kasei Chemicals Co., Ltd. )] 10 parts of graphite particles “SNG-WXA1” 40 parts, acetylene black 1 “Ensaco 250G” 10 parts and trade name “Umex 1001 (acid-modified polypropylene)” [manufactured by Sanyo Chemical Industries Co., Ltd.] 5 parts to 180 C., 100 rpm, and a residence time of 5 minutes.
The resin current collector was obtained by extruding the obtained resin current collector material from a T-die and rolling it with a cooling roll temperature-controlled to 50°C.

<Preparation of coated negative electrode active material particles>
The materials used for producing the coated negative electrode active material particles are as follows.
(Negative electrode active material particles)
LTO: Lithium titanate TNO: Titanium niobium oxide HC: Hard carbon (conductive aid)
AB: Acetylene black KB: Ketjen black CNF: Carbon nanofiber

(Examples 1 to 11, Comparative Examples 1 to 9)
The negative electrode active material particles were placed in a universal mixer High Speed Mixer FS25 [manufactured by Earthtechnica Co., Ltd.], and while stirring at room temperature and 720 rpm, the solution of the polymer compound was added dropwise over 2 minutes, followed by further stirring for 5 minutes. .
Then, while being stirred, the conductive additive was added in portions over 26 minutes, and the stirring was continued for 30 minutes. Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, then the temperature was raised to 140°C while stirring and the degree of pressure reduction were maintained, and the volatile matter was distilled off while maintaining the stirring, the degree of pressure reduction, and the temperature for 8 hours. . The obtained powder was classified with a sieve having an opening of 212 μm to obtain coated negative electrode active material particles.
Table 1 shows the blending ratio (% by weight) of each material used for producing the coated negative electrode active material particles.
In Comparative Examples 1 to 3, no polymer compound was used, so no coating layer was formed. Therefore, these particles cannot be regarded as coated negative electrode active material particles.

<Preparation of negative electrode for evaluation>
5 g of the coated negative electrode active material particles and 0.0505 g of carbon fiber [Donacarb Milled S-242 manufactured by Osaka Gas Chemicals Co., Ltd.] as a conductive additive are combined with flaky graphite [UP-5-α manufactured by Nippon Graphite Co., Ltd.]. 0.2632 g was mixed for 3 minutes at 1500 rpm using a planetary stirring type mixing kneader {Awatori Mixer [manufactured by Thinky Co., Ltd.]}.
Furthermore, the step of adding 0.14 g of the electrolyte and mixing for 1 minute at 1500 rpm was repeated twice, and a total of 0.28 g of the electrolyte was added to obtain a negative electrode composition.
0.055 g of the above negative electrode composition was weighed, placed in a cylindrical bottomed container having an inner diameter of 15 mm, and compressed by a pressure device to obtain a cylindrical negative electrode active material layer.

<Cycle characteristics evaluation>
A 1 mm thick PP sheet (manufactured by AS ONE) was cut into a 2 cm square, and a hole of φ18 mm was provided in the center. The prepared negative electrode active material layer and the Li foil cut to φ15 mm are placed on both electrodes with a PP separator (manufactured by Celgard) of φ18 mm sandwiched between them. , the electrolytic solution is injected so that the volume of the voids in the negative electrode active material layer and the separator is 110% by volume, and the resin current collector and copper foil are placed on the outside of the negative electrode active material layer and the Li foil, respectively. A piece cut into 2 cm squares was arranged. This was heat-sealed under reduced pressure to prepare an evaluation cell.
The evaluation cell was connected to a charge/discharge device, and cycle characteristics were evaluated under the following conditions.
CC-CV (cut-off current 0.01 C) charge to 1.5 V at 0.01 C, rest for 1 hour, then discharge to 0 V at 0.1 C CC-CV (cut-off current 0.01 C). rice field.
The discharge capacity at this time was defined as the initial capacity _X0 . This was repeated ₁₀₀ times to obtain capacity X1 at the 100th cycle. This X ₁ /X ₀ was taken as the 100 cycle discharge capacity retention rate.
Table 1 shows the discharge capacity per electrode volume obtained using the initial capacity X ₀ and the 100-cycle discharge capacity retention rate.

From the results in Table 1, the lithium ion battery produced using the coated negative electrode active material particles for a lithium ion battery of the present invention has a sufficiently high discharge capacity per electrode volume and a high discharge capacity retention rate. Recognize.
In Examples 10 and 11, in which titanium niobium oxide was used as the negative electrode active material, the discharge capacity per electrode volume was particularly high.
Comparative Examples 1 and 2 did not use a polymer compound, and the discharge capacity and the discharge capacity retention rate were low.
Comparative Example 3 used neither a polymer compound nor a conductive aid, and did not function as a negative electrode.
In Comparative Example 4, the content of the conductive aid was too small, and the discharge capacity per electrode volume was low.
In Comparative Examples 5 and 6, the content of the conductive aid was too large, and the discharge capacity per electrode volume was low.
In Comparative Example 7, the amount of polymer compound used was too small, and the discharge capacity per electrode volume was low.
In Comparative Example 87, the amount of the polymer compound used was too large, and the amount of the conductive aid used was too large, resulting in a low discharge capacity per electrode volume.
Since Comparative Example 9 uses a carbon-based negative electrode active material as the negative electrode active material, the discharge capacity retention rate is low.

The coated negative electrode active material particles for lithium ion batteries of the present invention can be used particularly in lithium ion batteries used for stationary power sources, mobile phones, personal computers, hybrid automobiles, and electric automobiles.

Claims (4)

A coated negative electrode active material particle for a lithium ion battery, wherein at least part of the surface of the negative electrode active material particle is coated with a coating layer containing a polymer compound and a conductive aid,
The negative electrode active material particles contain particles made of titanium composite oxide and / or titanium oxide,
The weight ratio of the polymer compound in the coated negative electrode active material particles is 0.1 to 2% by weight based on the weight of the coated negative electrode active material particles,
Coated negative electrode active material particles for lithium ion batteries, wherein the weight ratio of the conductive aid in the coated negative electrode active material particles is 3 to 15% by weight based on the weight of the coated negative electrode active material particles. 2. The coated negative electrode active material particles for lithium ion batteries according to claim 1, wherein the polymer compound has an acid value of 250 to 800. A negative electrode for a lithium ion battery, comprising the coated negative electrode active material particles for a lithium ion battery according to claim 1 or 2. A lithium ion battery comprising the lithium ion battery negative electrode according to claim 3 .