WO2023204215A1

WO2023204215A1 - Electrode composition for lithium ion batteries, coated negative electrode active material particles for lithium ion batteries, method for producing coated negative electrode active material particles for lithium ion batteries, negative electrode for lithium ion batteries, and lithium ion battery

Info

Publication number: WO2023204215A1
Application number: PCT/JP2023/015512
Authority: WO
Inventors: 石賀渉; 磯村省吾; 堀江英明; 横溝大悟; 大前直也
Original assignee: Ａｐｂ株式会社
Priority date: 2022-04-18
Filing date: 2023-04-18
Publication date: 2023-10-26

Abstract

The purpose of the present invention is to provide an electrode composition for lithium ion batteries, which enables the production of an electrode that has high electron conductivity even when the thickness of the electrode is large and also has satisfactory moldability.　Provided is an electrode composition for lithium ion batteries, which contains an electroconductive filler, in which the electroconductive filler comprises at least two types of electroconductive fillers having different aspect ratio from each other and each of the aspect ratios of the electroconductive fillers is 2.00 to 7.00.

Description

Electrode composition for lithium ion batteries, coated negative electrode active material particles for lithium ion batteries, method for producing coated negative electrode active material particles for lithium ion batteries, negative electrode for lithium ion batteries, and lithium ion batteries

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

Lithium ion batteries have been widely used in a variety of applications in recent years as secondary batteries that can achieve high energy density and high power density, and various studies are being conducted to develop higher performance lithium ion batteries.
In particular, increasing the capacity of batteries is strongly desired, and various studies are underway.

For example, Patent Document 1 discloses a method of increasing the energy density of a battery by increasing the film thickness of an electrode to reduce the relative proportions of a current collector and a separator.

Moreover, Patent Document 2 discloses a method of improving the deterioration of electronic conductivity when the film thickness of an electrode is increased by using two types of conductive fibers together.

Japanese Patent Application Publication No. 9-204936 Japanese Patent Application Publication No. 2016-189325 Japanese Patent Application Publication No. 2017-188452 Japanese Patent Application Publication No. 2020-009751

However, as the range of applications of lithium ion batteries expands, higher capacity is required, and conventional studies are no longer sufficient.

The present invention has been made in view of the above-mentioned problems, and provides an electrode composition for lithium ion batteries that can produce an electrode that has high electronic conductivity and good formability even when the film is thick. The purpose is to

The inventors of the present invention have diligently studied the above-mentioned problems and found that when a conductive filler with a small aspect ratio (for example, less than 2.00) is used, the conductive path becomes short and the electron conductivity in the electrode becomes unstable. It was discovered that the internal resistance value of the electrode increases.
On the other hand, the present inventors found that the use of conductive fillers with large aspect ratios (e.g., greater than 7.00) causes steric hindrance (inhibits the construction of conductive paths), and as a result, It has been found that the moldability during molding deteriorates, particularly when the film thickness of the electrode is increased, the deterioration of the moldability becomes remarkable. After further intensive study, the present inventors found that by using two or more types of conductive fillers with aspect ratios in a specific range, all of the above-mentioned problems were solved, and even with a large film thickness, electronic conductivity was achieved. The present invention was achieved by discovering that it is possible to obtain an electrode composition for lithium ion batteries that can produce an electrode with high moldability and good moldability.

That is, the present invention provides an electrode composition for a lithium ion battery containing a conductive filler, wherein the conductive filler is composed of two or more types having different aspect ratios, and the aspect ratio of the conductive filler is It also relates to an electrode composition for a lithium ion battery in which the ratio is 2.00 to 7.00.

It is possible to provide an electrode composition for a lithium ion battery that can produce an electrode with high electron conductivity and good moldability even if the film thickness is large.

[Electrode composition for lithium ion batteries]
The present invention provides an electrode composition for a lithium ion battery containing a conductive filler, wherein the conductive filler is composed of two or more types having different aspect ratios, and each of the conductive fillers has an aspect ratio of 2. The present invention relates to an electrode composition for lithium ion batteries having a molecular weight of .00 to 7.00.

(conductive filler)
The electrode composition for a lithium ion battery of the present invention contains a conductive filler, and the conductive filler is composed of two or more types having different aspect ratios.

The aspect ratio of each conductive filler is 2.00 to 7.00.
The conductive filler may be one containing two or more types in the range of 2.00 to 7.00, but conductive filler A with a value of 2.00 or more and less than 4.00, and conductive filler A with a value of 2.00 or more and less than 4.00. It is preferable to contain less than 7.00% of conductive filler B.
By containing such a conductive filler, the conductive filler A covers the electrode active material particles described below and contributes to improving the conductivity of the surface of the electrode active material particles, and the conductive filler B contributes to improving the conductivity of the electrode active material particle surface. The conductivity between the electrode active material particles can be improved by serving as a connection between the electrode active material particles.
Note that the conductive filler may contain two or more types of conductive filler A and two or more types of conductive filler B.

The aspect ratio of the conductive filler can be measured, for example, under the following measurement conditions.
Measuring equipment: PITA-04 (particle shape image analysis device, manufactured by Seishin Enterprise Co., Ltd.)
Camera: Monochrome CCD camera (1 pixel 2.8μm x 2.8μm), maximum 54fps
Number of observed particles: 5000

As the conductive filler, metals [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black], mixtures thereof, etc. can be used as long as they satisfy the above-mentioned aspect ratio. be able to.

The shape (form) of the conductive filler is not limited to the particle form, as long as it satisfies the aspect ratio described above, and may be in a form other than the particle form, such as a so-called filler type such as fibrous (carbon nanofiber). It may be in a form that has been put into practical use as a conductive resin composition.

It is preferable that the conductive filler consists of flaky graphite and fibrous graphite.
The flaky graphite corresponds to the above-mentioned conductive filler A, and can be coated to cover the electrode active material particles described below to improve the conductivity of the surface of the electrode active material particles.
Further, fibrous graphite corresponds to the above-mentioned conductive filler B, and can play a role of connecting electrode active material particles, which will be described later, to improve the conductivity between electrode active material particles.

Specific examples of flaky graphite include UP-5-α (manufactured by Nippon Graphite Co., Ltd., aspect ratio: 2.3), CNP15 (manufactured by Ito Graphite Industries Co., Ltd., aspect ratio: 3.9) FT-4. (manufactured by East Japan Carbon Co., Ltd., aspect ratio: 3.2).

Specific examples of fibrous graphite include ZEONANO SG101 (carbon nanotubes, manufactured by Nippon Zeon Co., Ltd., aspect ratio: 6.8), SWNT carbon nanotubes (manufactured by Meijo Nano Carbon Co., Ltd., aspect ratio: 6.7), etc. can be mentioned.

The average particle diameter when the conductive filler is particulate, the fiber diameter when it is fibrous, etc. are not particularly limited as long as the aspect ratio described above is satisfied.
When the conductive filler is in the form of particles, the average particle size may be, for example, 0.01 to 10 μm.
Further, when the conductive filler is fibrous, the average fiber diameter may be 0.1 to 20 μm.
In addition, in this specification, "particle diameter" means the maximum distance L among the distances between any two points on the contour line of a particle. The value of "average particle diameter" is the average value of the particle diameter of particles observed in several to several dozen fields of view using observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

In the lithium ion battery electrode composition of the present invention, the weight proportion of the conductive filler is preferably 1 to 6% by weight based on the weight of the lithium ion battery electrode composition.

When containing the conductive filler A and conductive filler B described above as the conductive filler, the weight ratio of the conductive filler A is 1.5 to 4.5 weight based on the weight of the lithium ion battery electrode composition. % is preferable.
Further, the weight proportion of the conductive filler B is preferably 0.5 to 2% by weight based on the weight of the electrode composition for a lithium ion battery.
Further, it is preferable that the weight ratio of the conductive filler A is larger than that of the conductive filler B.

(Coated electrode active material particles)
The electrode composition for a lithium ion battery of the present invention preferably contains coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound.
From the viewpoint of suitably imparting electronic conductivity, the conductive filler is preferably contained in the coating layer, more preferably contained outside the coating layer, and is preferably contained in the coating layer and outside the coating layer. It is more preferable that it be contained.

The electrode active material particles may be either positive electrode active material particles or negative electrode active material particles.

As the positive electrode active material particles, composite oxides of lithium and transition metals {complex oxides containing one type of transition metal (LiCoO ₂ , LiNiO ₂ , LiAlMnO ₄ , LiMnO ₂ and LiMn ₂ O ₄ etc.), transition metal elements _Composite _oxides _having _two _types _of _{_} _{_} _{_} _{_} _{_} _{_} Co _0.15 Al _0.05 O ₂ ) and a composite oxide containing three or more types of transition metal elements [e.g. LiM _a M' _b M'' _c O ₂ (M, M' and M'' are different transitions) It is a metal element and satisfies a+b+c=1. For example, LiNi _1/3 Mn _1/3 Co _1/3 O ₂ ), etc.), lithium-containing transition metal phosphates (for example, LiFePO ₄ , LiCoPO ₄ , LiMnPO ₄ and LiNiPO ₄ ), transition metal oxides (e.g. MnO ₂ and V ₂ O ₅ ), transition metal sulfides (e.g. MoS ₂ and TiS ₂ ) and conductive polymers (e.g. polyaniline, polypyrrole, polythiophene, polyacetylene and poly-p- phenylene and polyvinylcarbazole), and two or more types may be used in combination.
Note that the lithium-containing transition metal phosphate may be one in which some of the transition metal sites are replaced with another transition metal.

The volume average particle diameter of the positive electrode active material particles is preferably from 0.01 to 100 μm, more preferably from 0.1 to 35 μm, and even more preferably from 2 to 30 μm, from the viewpoint of electrical characteristics of the battery. preferable.
In this specification, the volume average particle diameter means the particle diameter (Dv50) at 50% of the integrated value in the particle size distribution determined by the Microtrack method (laser diffraction/scattering method). The microtrack method is a method of determining particle size distribution using scattered light obtained by irradiating particles with laser light. Note that, for measuring the volume average particle diameter, a Microtrack manufactured by Nikkiso Co., Ltd., etc. can be used.

The negative electrode active material particles include carbon-based materials [graphite, non-graphitizable carbon (hard carbon), amorphous carbon, fired resin bodies (for example, carbonized phenolic resins, furan resins, etc.); Cokes (e.g. pitch coke, needle coke, petroleum coke, etc.) and carbon fibers], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites (carbon particles whose surfaces are coated with silicon and/or silicon carbide) silicon particles or silicon oxide particles whose surfaces are coated with carbon and/or silicon carbide, silicon carbide, etc.) and silicon alloys (silicon-aluminum alloys, silicon-lithium alloys, silicon-nickel alloys, silicon-iron alloys) conductive polymers (e.g. polyacetylene and polypyrrole, etc.), metals (tin, aluminum, zirconium, titanium, etc.), Metal oxides (titanium oxide and lithium titanium oxide, etc.), metal alloys (for example, lithium-tin alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.), and mixtures of these with carbon-based materials, etc. Can be mentioned.
Among the negative electrode active material particles, those that do not contain lithium or lithium ions inside may be subjected to a pre-doping treatment in which part or all of the negative electrode active material particles contain lithium or lithium ions.

The volume average particle diameter of the negative electrode active material particles is preferably from 0.01 to 100 μm, more preferably from 0.1 to 60 μm, and even more preferably from 2 to 40 μm, from the viewpoint of the electrical characteristics of the battery. preferable.

In the coated electrode active material particles, a coating layer that covers at least a portion of the surface of the electrode active material particles contains a polymer compound.

The polymer compound is preferably a resin containing a polymer having the acrylic monomer (a) as an essential constituent monomer, for example.
Specifically, the polymer compound constituting the coating layer of the coated electrode active material particles is preferably a polymer of a monomer composition containing acrylic acid (a0) as the acrylic monomer (a).
In the above monomer composition, the content of acrylic acid (a0) is preferably more than 90% by weight and not more than 98% by weight based on the weight of the entire monomer. From the viewpoint of flexibility of the coating layer, the content of acrylic acid (a0) is more preferably 93.0 to 97.5% by weight, more preferably 95.0 to 97.5% by weight, based on the weight of the entire monomer. More preferably, it is 0% by weight.

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

Monomers (a1) having a carboxyl group or acid anhydride group other than acrylic acid (a0) include monocarboxylic acids having 3 to 15 carbon atoms such as methacrylic acid, crotonic acid, and cinnamic acid; (anhydrous) maleic acid, fumaric acid; acids, (anhydrous) dicarboxylic acids with 4 to 24 carbon atoms such as itaconic acid, citraconic acid, and mesaconic acid; polycarboxylic acids with 6 to 24 carbon atoms, trivalent to tetravalent or higher valences such as aconitic acid, etc. can be mentioned.

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

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

Monomer (a2) is classified into (a21) and (a22) depending on the group of R ² .
(a21) Ester compound in which R ² is a straight chain or branched alkyl group having 4 to 12 carbon atoms Examples of straight chain alkyl groups having 4 to 12 carbon atoms include butyl group, pentyl group, hexyl group, heptyl group, octyl group, Examples include nonyl group, decyl group, undecyl group, and dodecyl group.
Examples of branched alkyl groups having 4 to 12 carbon atoms include 1-methylpropyl group (sec-butyl group), 2-methylpropyl group, 1,1-dimethylethyl group (tert-butyl group), 1-methylbutyl group, , 1-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, 3-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, 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 group, 6-methylnonyl group, 7-methylnonyl group, 8-methylnonyl group, 1,1-dimethyloctyl group, 1,2-dimethyloctyl group, 1,3-dimethyloctyl group, 1,4-dimethyloctyl group, 1 , 5-dimethyloctyl group, 1,6-dimethyloctyl group, 1,7-dimethyloctyl group, 1-ethyloctyl group, 2-ethyloctyl group, 1-methyldecyl group, 2-methyldecyl group, 3-methyldecyl group, 4-methyldecyl group, 5-methyldecyl group, 6-methyldecyl group, 7-methyldecyl group, 8-methyldecyl group, 9-methyldecyl group, 1,1-dimethylnonyl group, 1,2-dimethylnonyl group, 1,3- Dimethylnonyl group, 1,4-dimethylnonyl group, 1,5-dimethylnonyl group, 1,6-dimethylnonyl group, 1,7-dimethylnonyl group, 1,8-dimethylnonyl group, 1-ethylnonyl group, 2 -Ethylnonyl group, 1-methylundecyl group, 2-methylundecyl group, 3-methylundecyl group, 4-methylundecyl group, 5-methylundecyl group, 6-methylundecyl group, 7-methylundecyl group Decyl group, 8-methylundecyl group, 9-methylundecyl group, 10-methylundecyl group, 1,1-dimethyldecyl group, 1,2-dimethyldecyl group, 1,3-dimethyldecyl group, 1, 4-dimethyldecyl group, 1,5-dimethyldecyl group, 1,6-dimethyldecyl group, 1,7-dimethyldecyl group, 1,8-dimethyldecyl group, 1,9-dimethyldecyl group, 1-ethyldecyl group , 2-ethyldecyl group, etc. Among these, 2-ethylhexyl group is particularly preferred.

(a22) Ester compound in which R ² is a branched alkyl group having 13 to 36 carbon atoms The branched alkyl group having 13 to 36 carbon atoms includes a 1-alkylalkyl group [1-methyldodecyl group, 1-butyleicosyl group, 1-hexyloctadecyl group, 1-octylhexadecyl group, 1-decyltetradecyl group, 1-undecyltridecyl group, etc.], 2-alkylalkyl group [2-methyldodecyl group, 2-hexyloctadecyl group, 2- Octylhexadecyl group, 2-decyltetradecyl group, 2-undecyltridecyl group, 2-dodecylhexadecyl group, 2-tridecylpentadecyl group, 2-decyloctadecyl group, 2-tetradecyloctadecyl group, 2- hexadecyl octadecyl group, 2-tetradecyl eicosyl group, 2-hexadecyl eicosyl group, etc.], 3-34-alkylalkyl group (3-alkylalkyl group, 4-alkylalkyl group, 5-alkylalkyl group, 32 -alkylalkyl group, 33-alkylalkyl group, 34-alkylalkyl group, etc.), propylene oligomer (7-11mer), ethylene/propylene (molar ratio 16/1-1/11) oligomer, isobutylene oligomer ( One or more branched alkyl groups, such as residues obtained by removing the hydroxyl group from oxo alcohols obtained from α-olefins (7- to 8-mer) and α-olefin (5-10 carbon atoms) oligomers (4- to 8-mer), etc. Examples include mixed alkyl groups.

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

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

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

The polymer compound constituting the coating layer preferably does not contain, as the acrylic monomer (a), 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 anionic groups include sulfonic acid groups and carboxyl groups.
Anionic monomers having a polymerizable unsaturated double bond and an anionic group are compounds obtained by a combination of these, and include, for example, vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid, and (meth)acrylic acid. It will be done.
In addition, a (meth)acryloyl group means an acryloyl group or a methacryloyl group.
Examples of the cations constituting the anionic monomer salt (a4) include lithium ions, sodium ions, potassium ions, and ammonium ions.

In addition, the polymer compound constituting the coating layer may be copolymerized with acrylic acid (a0), monomer (a1), monomer (a2), and ester compound (a3) as acrylic monomer (a) to the extent that physical properties are not impaired. It may also contain a radically polymerizable monomer (a5).
The radically polymerizable monomer (a5) is preferably a monomer that does not contain active hydrogen, and the following monomers (a51) to (a58) can be used.

(a51) at least one monol selected from a linear aliphatic monool having 13 to 20 carbon atoms, an alicyclic monool having 5 to 20 carbon atoms, and an aromatic aliphatic monool having 7 to 20 carbon atoms; and (meth) Hydrocarbyl (meth)acrylate formed from acrylic acid The above monools include (i) straight chain aliphatic monools (tridecyl alcohol, myristyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, (nonadecyl alcohol, arachidyl alcohol, etc.), (ii) alicyclic monools (cyclopentyl alcohol, cyclohexyl alcohol, cycloheptyl alcohol, cyclooctyl alcohol, etc.), (iii) aromatic aliphatic monools (benzyl alcohol, etc.), and these Examples include mixtures of two or more of these.

(a52) Poly(n=2-30) oxyalkylene (carbon number 2-4) alkyl (carbon number 1-18) ether (meth)acrylate [10 mol adduct of methanol with ethylene oxide (hereinafter abbreviated as EO) (meth) ) acrylate, 10 mole adduct of methanol with propylene oxide (hereinafter abbreviated as PO) (meth)acrylate, etc.]

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

(a53-2) (meth)acrylate compound (i) Dialkyl (1 to 4 carbon atoms) Aminoalkyl (1 to 4 carbon atoms) (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N - diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, etc.]
(ii) Quaternary ammonium group-containing (meth)acrylate {tertiary amino group-containing (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.] compounds (quaternized using a quaternizing agent such as methyl chloride, dimethyl sulfate, benzyl chloride, dimethyl carbonate, etc.), etc.}

(a53-3) Heterocycle-containing vinyl compounds, pyridine compounds (7 to 14 carbon atoms, e.g. 2- or 4-vinylpyridine), imidazole compounds (5 to 12 carbon atoms, e.g. N-vinylimidazole), pyrrole compounds (carbon atoms 6 to 13 carbon atoms, e.g. N-vinylpyrrole), pyrrolidone compounds (6 to 13 carbon atoms, e.g. N-vinyl-2-pyrrolidone)

(a53-4) Nitrile group-containing vinyl compound Nitrile group-containing vinyl compound having 3 to 15 carbon atoms, such as (meth)acrylonitrile, cyanostyrene, cyanoalkyl (1 to 4 carbon atoms) acrylate

(a53-5) Other nitrogen-containing vinyl compounds Nitro group-containing vinyl compounds (8 to 16 carbon atoms, such as nitrostyrene), etc.

(a54) Vinyl hydrocarbon (a54-1) Aliphatic vinyl hydrocarbon Olefin having 2 to 18 or more carbon atoms (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), Dienes having 4 to 10 carbon atoms or more (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.), etc.

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

(a54-3) Aromatic vinyl hydrocarbon Aromatic unsaturated compounds having 8 to 20 carbon atoms or more, such as styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropylstyrene, butyl Styrene, phenylstyrene, cyclohexylstyrene, benzylstyrene

(a55) Vinyl ester aliphatic vinyl ester [carbon number 4-15, e.g. alkenyl ester of aliphatic carboxylic acid (mono- or dicarboxylic acid) (e.g. vinyl acetate, vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, vinyl methoxy acetate)]
Aromatic vinyl esters [9 to 20 carbon atoms, such as alkenyl esters of aromatic carboxylic acids (mono- or dicarboxylic acids) (such as vinyl benzoate, diallyl phthalate, methyl-4-vinyl benzoate), aromatic ring-containing aliphatic carboxylic acids ester (e.g. acetoxystyrene)]

(a56) Vinyl ether aliphatic vinyl ether [3 to 15 carbon atoms, such as 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 (1-4 carbon atoms) ether (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether, vinyl-2-ethyl mercaptoethyl ether, etc.), poly(2-4)(meth)allyloxyalkane (carbon number 2-6) (diallyloxyethane, triaryloxyethane, tetraallyloxybutane, tetramethallyloxyethane, etc.)], Aromatic vinyl ether (8 to 20 carbon atoms, e.g. vinyl phenyl ether, phenoxystyrene)

(a57) Vinyl ketone Aliphatic vinyl ketone (4 to 25 carbon atoms, e.g. vinyl methyl ketone, vinyl ethyl ketone), aromatic vinyl ketone (9 to 21 carbon atoms, e.g. vinyl phenyl ketone)

(a58) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms, such as dialkyl fumarate (two alkyl groups are linear, branched, or alicyclic groups having 1 to 22 carbon atoms) ), dialkyl maleate (two alkyl groups are linear, branched or alicyclic groups having 1 to 22 carbon atoms)

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

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

The weight average molecular weight of the polymer compound constituting the coating layer can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.
Equipment: Alliance GPC V2000 (manufactured by Waters)
Solvent: Orthodichlorobenzene, N,N-dimethylformamide (hereinafter abbreviated as DMF), tetrahydrofuran Standard material: polystyrene Sample concentration: 3 mg/ml
Column stationary phase: PLgel 10μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
Column temperature: 135℃

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

Solvents used in solution polymerization include, for example, esters (with 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (with 1 to 8 carbon atoms, such as methanol, ethanol and octanol), hydrocarbons (with 1 to 8 carbon atoms, such as methanol, ethanol and octanol), 4 to 8, such as n-butane, cyclohexane, and toluene), amides (such as DMF), and ketones (3 to 9 carbon atoms, such as methyl ethyl ketone). The amount used is preferably 5 to 900% by weight, more preferably 10 to 400% by weight, even more preferably 30 to 300% by weight, based on the total weight of the monomers, 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.

Dispersion media in emulsion polymerization and suspension polymerization include water, alcohol (e.g. ethanol), ester (e.g. ethyl propionate), light naphtha, etc., and emulsifiers include higher fatty acid (carbon number 10-24) metal salts. (e.g. sodium oleate and sodium stearate), higher alcohol (10-24 carbon atoms) sulfate ester metal salt (e.g. sodium lauryl sulfate), ethoxylated tetramethyldecynediol, sodium sulfoethyl methacrylate, dimethylaminomethyl methacrylate, etc. can be 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, 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. The amount is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight.
During polymerization, known chain transfer agents such as mercapto compounds (dodecyl mercaptan, n-butyl mercaptan, etc.) and/or halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used. .

The polymer compound constituting the coating layer is a crosslinking agent (A') having a reactive functional group that reacts with a carboxyl group of the polymer compound {preferably a polyepoxy compound (a'1) [polyglycidyl ether (bisphenol A) diglycidyl ether, propylene glycol diglycidyl ether, glycerin triglycidyl ether, etc.) and polyglycidylamines (N,N-diglycidylaniline and 1,3-bis(N,N-diglycidylaminomethyl)), etc.] and/or A crosslinked polymer formed by crosslinking with a polyol compound (a'2) (ethylene glycol, etc.) may also be used.

Examples of the method of crosslinking the polymer compound constituting the coating layer using the crosslinking agent (A') include a method in which electrode active material particles are coated with the polymer compound constituting the coating layer and then crosslinked.
Specifically, after producing coated electrode active material particles by mixing electrode active material particles and a resin solution containing a polymer compound constituting the coating layer and removing the solvent, a solution containing a crosslinking agent (A') is prepared. By mixing and heating the coated electrode active material particles, a solvent removal and crosslinking reaction is caused, and a reaction in which the polymer compound constituting the coating layer is crosslinked by the crosslinking agent (A') is caused to occur in the electrode active material. One example is a method in which this occurs on the surface of particles.
The heating temperature is adjusted depending on the type of crosslinking agent, but when using the polyepoxy compound (a'1) as the crosslinking agent, it is preferably 70°C or higher, and when using the polyol compound (a'2), it is preferably 70°C or higher. Preferably it is 120°C or higher.

The coating layer may contain a conductive aid and ceramic particles in addition to the polymer compound.

Examples of conductive aids include metals with aspect ratios other than 2.00 to 7.00 [nickel, aluminum, stainless steel (SUS), silver, copper, titanium, etc.], carbon [graphite and carbon black], and mixtures thereof. Can be mentioned.

The weight proportion of the conductive additive is 0.5 to 3% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries.

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

Examples of metal carbide particles include silicon carbide (SiC), tungsten carbide (WC), molybdenum carbide ( _Mo2C ), titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), and vanadium carbide (VC). ), zirconium carbide (ZrC), and the like.

Examples of metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), tin oxide (SnO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), _Indium oxide ( _In2O3 ) _, _Li2B4O7 _, _Li4Ti5O12 _, _Li2Ti2O5 _, _LiTaO3 _, _LiNbO3 , _LiAlO2 _, _Li2ZrO3 _, _Li2WO4 _, Li ₂ TiO ₃ , Li ₃ PO ₄ , Li ₂ MoO ₄ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , Li ₂ SiO ₃ and ABO ₃ (However, A is Ca, Sr, Ba, La, Pr and Y, and B is at least one selected from the group consisting of Ni, Ti, V, Cr, Mn, Fe, Co, Mo, Ru, Rh, Pd, and Re. Examples include perovskite-type oxide particles represented by (which is a species).
As the metal oxide particles, zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) and lithium tetraborate (Li ₂ B ₄ O ₇ ) are preferred.

The glass ceramic particles are preferably lithium-containing phosphoric acid compounds having a rhombohedral crystal system, and the chemical formula thereof is represented by Li _x M'' ₂ P ₃ O ₁₂ (X=1 to 1.7).
Here, M" is one or more elements selected from the group consisting of Zr, Ti, Fe, Mn, Co, Cr, Ca, Mg, Sr, Y, Sc, Sn, La, Ge, Nb, and Al. Also, part of P may be replaced with Si or B, and part of O may be replaced with F, Cl, etc. For example, Li _1.15 Ti _1.85 Al _0.15 Si _0.05 P _{2. 95} O ₁₂ , Li _1.2 Ti _1.8 Al _0.1 Ge _0.1 Si _0.05 P _2.95 O ₁₂ , etc. can be used.
Furthermore, materials with different compositions may be mixed or composited, and the surface may be coated with a glass electrolyte or the like. Alternatively, it is preferable to use glass ceramic particles that precipitate a crystalline phase of a lithium-containing phosphate compound having a NASICON type structure by heat treatment.
Examples of the glass electrolyte include the glass electrolyte described in JP-A-2019-96478.

Here, the blending ratio of Li ₂ O in the glass ceramic particles is preferably 8% by mass or less in terms of oxide.
Even if it is not a NASICON type structure, it is composed of Li, La, Mg, Ca, Fe, Co, Cr, Mn, Ti, Zr, Sn, Y, Sc, P, Si, O, In, Nb, F, and LISICON type, A solid electrolyte that has a perovskite type, β-Fe ₂ (SO ₄ ) ₃ type, and Li ₃ In ₂ (PO ₄ ) ₃ type crystal structure and conducts Li ions at a rate of 1×10 ^-5 S/cm or more at room temperature. May be used.

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

The volume average particle diameter of the ceramic particles is preferably from 1 to 1000 nm, more preferably from 1 to 500 nm, even more preferably from 1 to 150 nm, from the viewpoint of energy density and electrical resistance value.

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

The coated electrode active material particles may have two or more coating layers. When there are two or more coating layers, the composition of the polymer compound contained in each coating layer may be the same or different.
Moreover, when a conductive filler is contained in a coating layer, the type of conductive filler contained in each coating layer may be the same or different.
Furthermore, when the coating layer contains a conductive additive and ceramic particles, the types of the conductive additive and ceramic particles contained in each coating layer may be the same or different.

The method for producing coated electrode active material particles preferably includes, for example, a step of mixing electrode active material particles, a polymer compound, a conductive filler, optionally used ceramic particles, and an organic solvent, and then removing the solvent.

The organic solvent is not particularly limited as long as it can dissolve the polymer compound, and any known organic solvent can be appropriately selected and used.

In the method for producing coated electrode active material particles, first, electrode active material particles, a polymer compound constituting the coating layer, a conductive filler, and optionally used ceramic particles are mixed in an organic solvent.
The order in which the electrode active material particles, the polymer compound forming the coating layer, the conductive filler, and the ceramic particles are mixed is not particularly limited. For example, the polymer compound forming the coating layer, the conductive filler, and the ceramic are mixed in advance. The resin composition consisting of the particles may be further mixed with the electrode active material particles, or the electrode active material particles, the polymer compound constituting the coating layer, the conductive filler, and the ceramic particles may be mixed at the same time. Alternatively, a polymer compound constituting the coating layer may be mixed with the electrode active material particles, and further a conductive filler and ceramic particles may be mixed therein.

The coated electrode active material particles can be obtained by coating the electrode active material particles with a coating layer containing a polymer compound, a conductive filler, and optionally used ceramic particles. Place in a mixer and stir at 30 to 500 rpm, dropwise mix the resin solution containing the polymer compound constituting the coating layer over 1 to 90 minutes, and if conductive filler and ceramic particles are used, add them. It can be obtained by mixing, raising the temperature to 50 to 200°C while stirring, reducing the pressure to 0.007 to 0.04 MPa, and holding for 10 to 150 minutes to remove the solvent.

When the coated electrode active material particles have two coating layers, for example, after forming the first coating layer according to the above method, a resin solution containing a polymer compound constituting the second coating layer, a conductive filler and Using ceramic particles, coated electrode active material particles in which a second coating layer is provided on a first coating layer can be obtained by the same procedure as the above method. Even when the coated electrode active material particles have three or more coating layers, the coated electrode active material particles can be obtained by forming a coating layer on the surface of the electrode active material particles using the same method.

The blending ratio of the electrode active material particles and the resin composition containing the polymer compound, conductive filler, and optionally used ceramic particles constituting the coating layer is not particularly limited; It is preferable that the ratio of material particles to resin composition is 1:0.001 to 0.1.

At least a portion of the surface of the electrode active material particles is coated with a coating layer.
The electrode active material particles preferably have a coverage rate of 10 to 90%, more preferably 15 to 65%, obtained by the following calculation formula, from the viewpoint of suitably imparting charge/discharge performance.
Coverage rate (%) = {1-[BET specific surface area of coated electrode active material particles/(BET specific surface area of electrode active material particles x weight percentage of electrode active material particles contained in coated electrode active material particles + conductive filler) BET specific surface area x weight percentage of conductive filler contained in coated electrode active material particles + BET specific surface area of ceramic particles x weight percentage of ceramic particles contained in coated electrode active material particles)} x 100

Here, the above calculation formula will be explained in detail.
"BET specific surface area of electrode active material particles x weight ratio of electrode active material particles contained in covered electrode active material particles" corresponds to the surface area of electrode active material particles contained in covered electrode active material particles.
Further, "BET specific surface area of conductive filler x weight ratio of conductive filler contained in coated electrode active material particles" corresponds to the surface area of conductive filler contained in coated electrode active material particles.
Furthermore, "BET specific surface area of ceramic particles x weight percentage of ceramic particles contained in coated electrode active material particles" corresponds to the surface area of ceramic particles contained in coated electrode active material particles.
Therefore, "BET specific surface area of electrode active material particles x weight percentage of electrode active material particles contained in coated electrode active material particles + BET specific surface area of conductive filler x amount of conductive filler contained in coated electrode active material particles""Weight percentage + BET specific surface area of ceramic particles x weight percentage of ceramic particles contained in coated electrode active material particles" is calculated as follows: ceramic particles).

On the other hand, "BET specific surface area of coated electrode active material particles" is [(Surface area of the part of the electrode active material particles not covered with resin) + (Surface area of the part of the conductive filler not covered with resin). (Surface area of the part not covered with resin) + (Surface area of the part of the ceramic particles not covered with resin) + (Surface area of resin)]
Since (the surface area of the resin) is extremely small compared to (the surface area of the electrode active material particles), (the surface area of the conductive filler), and (the surface area of the ceramic particles), (the surface area of the resin) is set to "zero". Then, "BET specific surface area of coated electrode active material particles" is [(Surface area of the part of the electrode active material particles not covered with resin) + (part of the conductive filler not covered with resin) surface area) + (surface area of the portion of the ceramic particles not covered with resin)].

In other words, the total surface area of the materials constituting the coated electrode active material particles (electrode active material particles + conductive filler + ceramic particles) before coating is calculated by "BET specific surface area of the electrode active material particles x contained in the coated electrode active material particles. Weight percentage of electrode active material particles + BET specific surface area of conductive filler x weight percentage of conductive filler contained in coated electrode active material particles + BET specific surface area of ceramic particles x ceramic contained in coated electrode active material particles The total surface area of the "parts not covered with resin" after being coated with the resin is the "BET specific surface area of the coated electrode active material particles."
Therefore, "BET specific surface area of coated electrode active material particles" is calculated as "BET specific surface area of electrode active material particles x weight percentage of electrode active material particles contained in coated electrode active material particles + BET specific surface area of conductive filler x coating". The value divided by "weight percentage of conductive filler contained in electrode active material particles + BET specific surface area of ceramic particles x weight percentage of ceramic particles contained in coated electrode active material particles" is the value that constitutes the coated electrode active material particles. This is the percentage of the surface of the "portion not covered with resin" among the surfaces of the electrode active material particles, conductive filler, and ceramic particles.
Then, the coated electrode The ratio of the area of the "portion covered with resin" among the surfaces of the electrode active material particles, conductive filler, and ceramic particles that constitute the active material particles can be determined.

(Lithium ion battery electrode)
The electrode composition for lithium ion batteries of the present invention can form an electrode active material layer by combining with an electrolytic solution containing an electrolyte and a solvent.
Moreover, the electrode active material layer can form a lithium ion battery electrode by combining with a current collector.

As the electrolyte, solvent, and current collector described above, electrolytes, solvents, and current collectors used in known lithium ion batteries can be appropriately selected and used.

Preferably, the electrode active material layer does not contain a binder.
In addition, in this specification, a binder means a drug that cannot reversibly fix coated electrode active material particles or coated electrode active material particles and a current collector, and includes starch, polyvinylidene fluoride, Examples include known solvent-dried binders for lithium ion batteries such as polyvinyl alcohol, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, and polypropylene.
These binders are used by being dissolved or dispersed in a solvent, and are solidified by volatilizing or distilling off the solvent, thereby irreversibly binding the coated electrode active material particles to each other and the coated electrode active material particles to the current collector. It is to be fixed at

The electrode active material layer may contain adhesive resin.
Adhesive resin refers to a resin that does not solidify even after drying after volatilizing the solvent component and remains adhesive, and is a different material from a binder and is distinguished from it.
Further, while the coating layer constituting the covered electrode active material particles is fixed to the surface of the electrode active material particles, the adhesive resin reversibly fixes the surfaces of the electrode active material particles to each other. Although the adhesive resin can be easily separated from the surface of the electrode active material particles, the coating layer cannot be easily separated.
Therefore, the coating layer and the adhesive resin are different materials.

The adhesive resin contains as an essential constituent monomer 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. Examples include polymers in which the total weight proportion of is 45% by weight or more based on the total weight of the constituent monomers.
When using an adhesive resin, it is preferable to use 0.01 to 10% by weight of the adhesive resin based on the total weight of the electrode active material particles.

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

The electrode active material layer may contain other types of electrode active material particles in addition to the above-mentioned coated electrode active material particles, and can be blended within a range that does not affect the cycle characteristics of the battery.
As the electrode active material particles, the above-mentioned positive electrode active material particles or negative electrode active material particles can be used.
Further, the other types of electrode active material particles may be coated electrode active material particles.

The thickness of the electrode current collector is not particularly limited, but is preferably 5 to 150 μm.

The electrode for a lithium ion battery is produced, for example, by applying the electrode composition for a lithium ion battery of the present invention on a current collector, pressing it with a press to form an electrode active material layer, and then pouring an electrolyte solution. be able to.
Further, the electrode composition for lithium ion batteries of the present invention is applied onto a release film and pressed to form an electrode active material layer, and after the electrode active material layer is transferred to a current collector, an electrolytic solution is poured. You can.

<Lithium ion battery>
The lithium ion battery preferably includes the above-described lithium ion battery electrode, a separator, and an electrode serving as a counter electrode.

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

The electrode serving as the counter electrode is not particularly limited, and may be the electrode for lithium ion batteries described above, and electrodes used in known lithium ion batteries can be appropriately selected and used.

A lithium ion battery can be manufactured by, for example, stacking the above-described lithium ion battery electrode, separator, and counter electrode in this order, and then injecting an electrolyte as necessary.

The following items are disclosed in this specification.

The present disclosure (1) is an electrode composition for a lithium ion battery containing a conductive filler, wherein the conductive filler is composed of two or more types having different aspect ratios, and the aspect ratio of the conductive filler is This is an electrode composition for a lithium ion battery in which the average number is 2.00 to 7.00.

The present disclosure (2) is the electrode composition for a lithium ion battery according to the present disclosure (1), in which the conductive filler includes flaky graphite and fibrous graphite.

The present disclosure (3) is the lithium ion battery according to the present disclosure (1) or (2), wherein the weight percentage of the conductive filler is 1 to 6% by weight based on the weight of the lithium ion battery electrode composition. It is an electrode composition for

The present disclosure (4) includes coated electrode active material particles in which at least a part of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound, and the conductive filler is contained in the coating layer and in the coating. This is an electrode composition for a lithium ion battery in any combination of any one of (1) to (3) of the present disclosure contained outside the layer.

EXAMPLES Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the examples unless it departs from the gist of the present invention. In addition, unless otherwise specified, parts mean parts by weight, and % means weight %.

<Conductive filler>
The following materials were used as the conductive filler.
(Conductive filler A)
Acetylene black (aspect ratio: 1.0)
(Conductive filler B)
Flaky graphite (aspect ratio: 2.2)
(Conductive filler C)
Fibrous graphite (aspect ratio: 6.6)
(Conductive filler D)
Carbon nanofiber (aspect ratio: 17.0)
<Cathode active material particles>
LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder (volume average particle diameter 4 μm)
<Ceramic particles>
Silicon dioxide (AEROSIL 200, manufactured by Nippon Aerosil Co., Ltd.)
<Conductivity aid>
Conductive aid A (Ketjen Black, EC300J, manufactured by Lion Specialty Chemicals Co., Ltd., aspect ratio: 1.0)
Conductive aid B (carbon fiber, Dona Carbo Milled S-243, manufactured by Osaka Gas Chemical Co., Ltd., aspect ratio: 9.8)

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

(Example 1)
One part of the coating polymer compound was dissolved in 3 parts of DMF to obtain a coating polymer compound solution.
88.0 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) were placed in a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.]. While stirring at room temperature and 720 rpm, 15.2 parts of the coating polymer compound solution was added dropwise over 2 minutes, followed by further stirring for 5 minutes.
Next, in a stirred state, 3.0 parts of conductive filler B, 2.0 parts of conductive filler C, 2.0 parts of silicon dioxide (AEROSIL 200, manufactured by Nippon Aerosil Co., Ltd.), and a conductive additive were added. A (Ketjen Black, EC300J, manufactured by Lion Specialty Chemicals Co., Ltd.) 0.7 part, conductive aid B (carbon fiber, Dona Carbo Milled S-243, manufactured by Osaka Gas Chemicals Co., Ltd.) 0.5 part was added in portions over 2 minutes, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to prepare an electrode composition for a lithium ion battery, which is coated positive electrode active material particles.

(Examples 2 to 8, Comparative Examples 1 to 6)
An electrode composition for a lithium ion battery was produced in the same manner as in Example 1, except that the amounts of each material added were changed as shown in Table 1.

(Example 9)
One part of the coating polymer compound was dissolved in 3 parts of DMF to obtain a coating polymer compound solution.
Put 89.0 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) into a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.]. While stirring at room temperature and 720 rpm, 15.2 parts of the coating polymer compound solution was added dropwise over 2 minutes, followed by further stirring for 5 minutes.
Next, in a stirred state, 1.0 part of conductive filler C, 2.0 parts of silicon dioxide (AEROSIL 200, manufactured by Nippon Aerosil Co., Ltd.), and conductive additive A (Ketjen Black, EC300J, Lion Specialty Chemicals) were added. Co., Ltd.) and 0.5 part of conductive aid B (carbon fiber, Dona Carbo Milled S-243, Osaka Gas Chemical Co., Ltd.) were added in portions over 2 minutes, and stirred for 30 minutes. continued.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
3.0 parts of conductive filler B was added, and the resulting powder was classified using a sieve with an opening of 200 μm to prepare an electrode composition for a lithium ion battery, which is coated positive electrode active material particles.

(Example 10, 12)
An electrode composition for a lithium ion battery was produced in the same manner as in Example 9, except that the type of conductive filler and the amount added were changed as shown in Table 1.
In addition, the conductive filler described as inside the coating layer in Table 1 was added at the same stage as silicon dioxide and the conductive additive, and the conductive filler described as outside the coating layer was added after volatile content was distilled off. This is a conductive filler added before post-classification.

(Example 11)
92.8 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) were placed in a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.]. While stirring at room temperature and 720 rpm, 3.0 parts of conductive filler B, 1.0 part of conductive filler C, 2.0 parts of silicon dioxide (AEROSIL 200, manufactured by Nippon Aerosil Co., Ltd.), and conductive aid A ( Divide 0.7 parts of Ketjen Black, EC300J, manufactured by Lion Specialty Chemicals Co., Ltd., and 0.5 parts of conductive aid B (carbon fiber, Dona Carbo Milled S-243, manufactured by Osaka Gas Chemicals Co., Ltd.). The mixture was added over 2 minutes while stirring, and stirring was continued for 30 minutes.
The obtained powder was classified using a sieve with an opening of 200 μm to prepare an electrode composition for a lithium ion battery, which is a positive electrode active material particle.

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

[Preparation of current collector]
In a twin-screw extruder, 70 parts of polypropylene [trade name "Sun Allomer PL500A", manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotubes [trade name "FloTube9000", manufactured by CNano], and a dispersant [trade name "Yumex 1001"] were added. , manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200° C. and 200 rpm to obtain a resin mixture.
The obtained resin mixture was passed through a T-die extrusion film forming machine and stretched and rolled to obtain a conductive film for a resin current collector having a thickness of 100 μm. Next, the obtained conductive film for a resin current collector was cut into a circular shape with a diameter of 15 mm or 16 mm, one side was evaporated with nickel, and a terminal (5 mm x 3 cm) for current extraction was connected to the resin. A current collector was obtained.
Note that a circular resin current collector with a diameter of 15 mm was used as the resin current collector for the positive electrode, and a circular resin current collector with a diameter of 16 mm was used as the resin current collector.

[Preparation of positive electrode for lithium ion battery]
(Examples 1 to 10, 12, Comparative Examples 1 to 6)
Each of the prepared electrode compositions for lithium ion batteries was filled into a mold with a diameter of 15 mm so that the basis weight of the positive electrode active material particles was 50 mg/cm ² , and a press machine (HANDTAB-100T15, Ichihashi Seiki Co., Ltd.) was used. A positive electrode active material layer (thickness: 213 μm) was formed by tablet-forming at a pressure of 1 ton/cm ² (manufactured by J.D. Co., Ltd.), and after pouring 50 μl of electrolyte from above, it was laminated on one side of the resin current collector. A positive electrode for a lithium ion battery (circular with a diameter of 15 mm) was produced.

(Example 11)
The prepared electrode composition for lithium ion batteries and 50 μl of electrolyte were stirred using a powder mixer, and the resulting mixture was placed on a mold of Φ15 mm so that the basis weight of the positive electrode active material particles was 50 mg/cm ² . A positive electrode active material layer (thickness: 213 μm) was formed by tableting with a press machine (HANDTAB-100T15, manufactured by Ichihashi Seiki Co., Ltd.) at a pressure of 1 ton/cm ² , and 50 μl of the electrolyte was added. After injecting the solution from above, it was laminated on one side of the resin current collector to produce a positive electrode for a lithium ion battery (circular with a diameter of 15 mm).

[Preparation of coated negative electrode active material particles]
One part of the above-mentioned coating polymer compound was dissolved in 3 parts of DMF to obtain a coating polymer compound solution.
80.04 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, 37.92 parts of the molecular compound solution was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Next, 9.48 parts of acetylene black (Denka Black (registered trademark) manufactured by Denka Co., Ltd.), which is a conductive additive, was added in portions over 2 minutes while stirring, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles.

[Preparation of negative electrode for lithium ion battery]
99 parts of the prepared coated negative electrode active material particles were mixed with 1 part of carbon fiber [Dona Carbo Milled S-243 manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm, electrical conductivity 200 mS/cm]. A negative electrode precursor was prepared.
The produced negative electrode precursor was filled into a Φ16 mold so that the basis weight of negative electrode active material particles was 23.4 mg/cm ² , and 1 ton was filled with a press machine (HANDTAB-100T15, manufactured by Ichihashi Seiki Co., Ltd.). A negative electrode active material layer (thickness: 300 μm) was formed by compression molding at a pressure of /cm ² and was laminated on one side of the resin current collector to produce a negative electrode for a lithium ion battery (circular with a diameter of 16 mm). .

[Fabrication of lithium ion battery]
The produced positive electrode for a lithium ion battery and the negative electrode for a lithium ion battery were combined via a separator (#3501 manufactured by Celgard) to produce a lithium ion battery.

[Measurement of DC resistance value (DCR)]
Each of the produced lithium ion batteries was charged at constant current and constant voltage at 0.1C at 25°C to an upper limit voltage of 4.2V (depth of charge (SOC: state of charge) is approximately 80%) (stopping condition: constant). Current value is less than 0.01C in voltage mode).
Thereafter, after a 10-minute rest, the battery was discharged to 2.5V using a constant current method (0.1C). Then, DCR (Direct Current Resistance) was measured based on the following formula using the cell voltage (V1) immediately before the start of discharge in the constant current discharge process and the cell voltage (V2) 10 seconds after discharge. .
In addition, those whose direct current resistance value (DCR) was 15.7 Ω·cm ² or less were judged to have passed.

<Moldability evaluation>
Each of the prepared electrode compositions for lithium ion batteries was filled into a mold with a diameter of 15 mm so that the basis weight of the positive electrode active material particles was 100 mg/cm ² , and a press machine (HANDTAB-100T15, Ichihashi Seiki Co., Ltd.) was used. The thickness (μm) of the tablet was measured after it was compressed into a tablet at a pressure of 0.5 ton/ ^cm2 .
Regarding Example 11, a mixture obtained by stirring the electrode composition for a lithium ion battery and 50 μl of the electrolytic solution using a powder mixer was placed on a mold with a diameter of 15 mm so that the basis weight of the positive electrode active material particles was 100 mg/kg. The mixture was filled to a thickness of cm ² and tableted using a press machine (HANDTAB-100T15, manufactured by Ichihashi Seiki Co., Ltd.) at a pressure of 0.5 ton/cm ² , and the thickness (μm) was measured.
It should be noted that the thinner the cathode active material particles can achieve a predetermined basis weight, the better the moldability can be judged to be, and the better the moldability can be judged to be if the thickness is 480 μm or less. .

From Table 2, it was confirmed that by using the electrode compositions for lithium ion batteries of Examples, electrodes with high electronic conductivity and good moldability could be produced even if the film thickness was large.

The present invention also relates to a method for producing coated negative electrode active material particles for lithium ion batteries and coated negative electrode active material particles for lithium ion batteries described below. The above-mentioned electrode composition for a lithium ion battery may have this negative electrode active material particle.

Lithium ion batteries have recently been used for various purposes as secondary batteries that can achieve high energy density and high output density.
With the expansion of uses for lithium ion batteries, further improvements in battery characteristics are required, and in particular, there is a strong desire to improve cycle characteristics, and various studies are being conducted with the aim of improving cycle characteristics.

For example, in Patent Document 3, coated negative electrode active material particles for lithium ion batteries in which at least a part of the surface of the negative electrode active material particles for lithium ion batteries are coated with a coating layer containing a polymer compound and a conductive agent, It has been reported that the cycle characteristics of lithium ion batteries can be improved by adjusting the coverage within a certain range.

In recent years, as studies have progressed, it has been found that the three-dimensional structure of the conductive additive in the coating layer of the coated negative electrode active material particles has a significant effect on the cycle characteristics of the battery.
That is, in the coating layer, conductivity is exhibited by the conductive additives forming a three-dimensional structure that allows them to exchange electrons with each other.

In conventional coated negative electrode active material particles for lithium ion batteries, when a volume change occurs in the coated negative electrode active material during charging and discharging, the conductive additive becomes steric in the process in which the coating layer follows the volume change of the coated negative electrode active material particles. The structure was destroyed and the network between the conductive additives was cut, resulting in a decrease in conductivity, which resulted in a problem in that the cycle characteristics of the lithium ion battery deteriorated.

Therefore, in order to improve the cycle characteristics of lithium ion batteries, a three-dimensional structure of the conductive additive is required that will not be destroyed even if the coated negative electrode active material particles repeatedly expand and contract during charging and discharging.

The present invention meets the above requirements, and aims to provide coated negative electrode active material particles for lithium ion batteries that can improve the cycle characteristics of lithium ion batteries.

The present inventors have conducted extensive studies on the above-mentioned problems, and have found that the three-dimensional structure of the conductive additive is determined by the shearing force applied to each material containing the conductive additive during the manufacturing process of coated negative electrode active material particles. . Furthermore, it has been found that the coverage of the coated negative electrode active material particles is similarly determined by the shear force. That is, as the shear force increases, the coverage of the coated negative electrode active material particles decreases, and as the shear force decreases, the coverage of the coated negative electrode active material particles increases.
Based on the above findings, the present inventors constructed a conductive additive with an optimized three-dimensional structure by applying shearing force so that the coverage of the coated negative electrode active material particles was 80% or more. The inventors have discovered that the cycle characteristics of lithium ion batteries can be improved as a result, and have thus arrived at the present invention.

That is, the present invention provides coated negative electrode active material particles for lithium ion batteries, in which at least a part of the surface of the negative electrode active material particles for lithium ion batteries is coated with a coating layer containing a polymer compound and a conductive additive. The weight ratio of the conductive additive is 6.1 to 10.5% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries, and the coverage obtained by the following formula is 80%. The above coated negative electrode active material particles for lithium ion batteries; a first coating step in which the negative electrode active material particles, the polymer compound, the conductive agent, and the organic solvent are mixed and then the solvent is removed to obtain the first coated negative electrode active material particles; , relates to a method for producing coated negative electrode active material particles for a lithium ion battery, comprising a second coating step of mixing the first coated negative electrode active material particles, a polymer compound, a conductive aid, and an organic solvent, and then removing the solvent.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material contained in coated negative electrode active material particles + BET specific surface area of conductive aid x weight ratio of conductive aid contained in coated negative electrode active material particles)] x 100

It is possible to provide coated negative electrode active material particles for lithium ion batteries that can improve the cycle characteristics of lithium ion batteries.

<Coated negative electrode active material particles for lithium ion batteries>
The coated negative electrode active material particles for lithium ion batteries of the present invention are lithium ion batteries in which at least a part of the surface of the negative electrode active material particles for lithium ion batteries is coated with a coating layer containing a polymer compound and a conductive additive. coated negative electrode active material particles for lithium ion batteries, in which the weight ratio of the conductive additive is 6.1 to 10.5% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries, and the weight ratio is calculated using the following calculation formula: The coverage obtained is 80% or more.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles) + BET specific surface area of the conductive aid × weight ratio of the conductive aid contained in the coated negative electrode active material particles)]}×100

(Negative electrode active material particles)
Negative electrode active material particles for lithium ion batteries (also simply referred to as negative electrode active material particles) include carbon-based materials [graphite, non-graphitizable carbon (hard carbon), amorphous carbon, fired resin bodies (such as phenol resin and Cokes (e.g. pitch coke, needle coke, petroleum coke, etc.) and carbon fibers], silicon-based materials [silicon, silicon oxide (SiOx), silicon-carbon composites] (carbon particles whose surfaces are coated with silicon and/or silicon carbide, silicon particles or silicon oxide particles whose surfaces are coated with carbon and/or silicon carbide, silicon carbide, etc.) and silicon alloys (silicon-aluminum alloys, conductive polymers (e.g. polyacetylene, polypyrrole, etc.) , metals (tin, aluminum, zirconium, titanium, etc.), metal oxides (titanium oxides and lithium/titanium oxides, etc.), and metal alloys (such as lithium-tin alloys, lithium-aluminum alloys, lithium-aluminum-manganese alloys, etc.) ), and mixtures of these and carbon-based materials.
Among the negative electrode active material particles, those that do not contain lithium or lithium ions inside may be subjected to a pre-doping treatment in which part or all of the negative electrode active material particles contain lithium or lithium ions.

From the viewpoint of increasing electric capacity, the negative electrode active material particles are preferably non-graphitizable carbon or a mixture of non-graphitizable carbon and a silicon-based material.

The volume average particle diameter of the negative electrode active material particles is preferably from 0.01 to 100 μm, more preferably from 0.1 to 60 μm, and even more preferably from 2 to 40 μm, from the viewpoint of the electrical characteristics of the battery. preferable.
In this specification, the volume average particle diameter means the particle diameter (Dv50) at 50% of the integrated value in the particle size distribution determined by the Microtrack method (laser diffraction/scattering method). The microtrack method is a method of determining particle size distribution using scattered light obtained by irradiating particles with laser light. Note that, for measuring the volume average particle diameter, a Microtrack manufactured by Nikkiso Co., Ltd., etc. can be used.

The weight percentage of the negative electrode active material particles is preferably 75 to 90% by weight, more preferably 79 to 87% by weight, based on the weight of the coated negative electrode active material particles for lithium ion batteries.

(polymer compound)
In the coated negative electrode active material particles for lithium ion batteries of the present invention, at least a portion of the surface of the negative electrode active material particles is coated with a coating layer containing a polymer compound and a conductive aid.
The covering layer may have a first covering layer and a second covering layer covering at least a portion of the surface of the first covering layer.
The polymer compounds constituting the first coating layer and the second coating layer may be the same or different, and may be appropriately selected from among the polymer compounds described below.

In particular, the polymer compound is a monomer composition containing a (meth)acrylic acid alkyl ester monomer from the viewpoint of imparting strength to the negative electrode for lithium ion batteries using the coated negative electrode active material for lithium ion batteries. Preferably, it is formed by polymerization.
Note that (meth)acrylic acid means acrylic acid and/or methacrylic acid.

(Meth)acrylic acid alkyl ester copolymer is an acrylic polymer that essentially has a constituent unit derived from (meth)acrylic acid alkyl ester monomer, and constitutes (meth)acrylic acid alkyl ester copolymer. It is preferable that the weight proportion of the (meth)acrylic acid alkyl ester monomer in the monomer composition is 90% by weight or more based on the weight of the monomer composition.

The weight ratio (wt%) of the (meth)acrylic acid alkyl ester monomer is determined by dissolving the polymer in a supercritical fluid and analyzing the resulting oligomer component by gas chromatography-mass spectrometry (GC-MS). It can be measured by the following methods.

Examples of (meth)acrylic acid alkyl ester monomers include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, methyl methacrylate, methyl acrylate, and Examples include 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate containing a hydroxyl group at the end.
Further, polyfunctional acrylates are also included in the above (meth)acrylic acid alkyl ester monomers. Examples of the polyfunctional acrylate include 1,6-hexanediol methacrylate and ethylene glycol dimethacrylate.
From the viewpoint of stability of the electrode shape, the weight proportion of the polyfunctional acrylate is preferably 0.1 to 3% by weight based on the total weight of the monomers.

The (meth)acrylic acid alkyl ester copolymer contains two or more types of (meth)acrylic acid alkyl ester monomers as constituent monomers, and the total content thereof is 90% by weight based on the total weight of the constituent monomers. % or more. Preferred combinations of the above (meth)acrylic acid alkyl ester monomers include a combination of n-butyl acrylate, 2-hydroxyethyl acrylate and acrylonitrile, a combination of 2-ethylhexyl methacrylate and 2-ethylhexyl acrylate, and a combination of n-butyl acrylate and 2-ethylhexyl acrylate. Examples include a combination of ethylhexyl acrylate, a combination of methyl acrylate and n-butyl acrylate, or a combination of methyl methacrylate and iso-butyl methacrylate.

The (meth)acrylic acid alkyl ester copolymer preferably contains (meth)acrylic acid monomer as a constituent monomer as a monomer other than the above-mentioned (meth)acrylic acid alkyl ester monomer. When (meth)acrylic acid monomer is included as a constituent monomer, it is possible to neutralize by-products such as lithium hydroxide generated within the battery and prevent corrosion of the electrodes. The weight proportion of the (meth)acrylic acid monomer is preferably 0.1 to 10% by weight based on the total weight of the constituent monomers.

The (meth)acrylic acid alkyl ester copolymer may contain a monovinyl monomer copolymerizable with the (meth)acrylic acid alkyl ester monomer as a constituent monomer.
As the monovinyl monomer, a monovinyl monomer containing a fluoro group, siloxane, etc. (dimethylsiloxane, etc.) can be used.

The preferable lower limit of the weight average molecular weight of the (meth)acrylic acid alkyl ester copolymer is 10,000, more preferably 50,000, still more preferably 100,000, and the preferable upper limit is 1,000,000, more preferably 800,000, more preferably 500,000, particularly preferably 400,000.

The weight average molecular weight of a polymer compound can be determined by gel permeation chromatography (hereinafter abbreviated as GPC) measurement under the following conditions.
Equipment: “HLC-8120GPC” [manufactured by Tosoh Corporation]
Column: "TSKgel GMHXL" (2 columns), "TSKgel Multipore HXL-M each connected one column" [both manufactured by Tosoh Corporation]
Sample solution: 0.25% by weight tetrahydrofuran solution Solution injection volume: 10 μL
Flow rate: 0.6mL/min Measurement temperature: 40℃
Detection device: Refractive index detector Reference material: Standard polystyrene [manufactured by Tosoh Corporation]

The polymer compound is a known polymerization initiator {azo initiator [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile), 2,2 A known polymerization method (bulk polymerization , solution polymerization, emulsion polymerization, suspension polymerization, etc.).
The amount of the polymerization initiator used is preferably 0.01 to 5% by weight, more preferably 0.05 to 2% by weight, based on the total weight of the monomer, from the viewpoint of adjusting the weight average molecular weight to a preferable range. More preferably, it is 0.1 to 1.5% by weight, and the polymerization temperature and time are adjusted depending on the type of polymerization initiator, etc., but the polymerization temperature is preferably -5 to 150°C, (more preferably 30 to 120°C), and the reaction time is preferably 0.1 to 50 hours (more preferably 2 to 24 hours).

Solvents used in solution polymerization include, for example, esters (with 2 to 8 carbon atoms, such as ethyl acetate and butyl acetate), alcohols (with 1 to 8 carbon atoms, such as methanol, ethanol and octanol), hydrocarbons (with 1 to 8 carbon atoms, such as methanol, ethanol and octanol), 4 to 8, such as n-butane, cyclohexane, and toluene), amides (such as dimethylformamide, hereinafter abbreviated as DMF), and ketones (3 to 9 carbon atoms, such as methyl ethyl ketone), and the weight average molecular weight is adjusted to a preferable range. From the viewpoint of the is 10 to 95% by weight, more preferably 20 to 90% by weight, even more preferably 30 to 80% by weight.

(conductivity aid)
In the coated negative electrode active material particles for lithium ion batteries of the present invention, the coating layer contains a conductive additive.
Items common to the conductive additive contained in the first coating layer and the second coating layer described above will be described without particular distinction.

Examples of conductive aids include metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite (flake graphite (UP)), carbon black (acetylene black, Ketjen black, furnace black, channel black, thermal lamp black, etc.), carbon nanofibers (CNF), etc.], and mixtures thereof.

The conductive aid is preferably acetylene black and/or flaky graphite from the viewpoint of improving the cycle characteristics of a lithium ion battery using coated negative electrode active material particles for a lithium ion battery.

The weight proportion of the conductive additive is 6.1 to 10.5% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries.
By setting the weight ratio of the conductive agent within the above range, the shearing force applied to each material containing the conductive agent during the manufacturing process of coated negative electrode active material particles can be suitably adjusted, and the three-dimensional structure of the conductive agent can be adjusted. It can be constructed in an optimized state.
The weight proportion of the conductive additive is preferably 6.8 to 10.5% by weight, and preferably 6.8 to 7.5% by weight, based on the weight of the coated negative electrode active material particles for lithium ion batteries. More preferred.

The ratio of the polymer compound that makes up the coating layer and the conductive additive is not particularly limited, but from the viewpoint of internal resistance of the battery, etc., the weight ratio of the polymer compound that makes up the coating layer (resin solid content weight) : The ratio of the conductive aid is preferably 1:0.01 to 1:50, more preferably 1:0.2 to 1:3.0.

(others)
In the coated negative electrode active material particles for lithium ion batteries of the present invention, the coating layer may further contain ceramic particles.
Examples of the ceramic particles include metal carbide particles, metal oxide particles, glass ceramic particles, and the like.

Here, the blending ratio of Li ₂ O in the glass ceramic particles is preferably 8% by mass or less in terms of oxide.
Even if it is not a NASICON type structure, it is composed of Li, La, Mg, Ca, Fe, Co, Cr, Mn, Ti, Zr, Sn, Y, Sc, P, Si, O, In, Nb, F, and LISICON type, Using a solid electrolyte that has a perovskite type, β-Fe ₂ (SO ₄ ) ₃ type, and Li ₃ In ₂ (PO ₄ ) ₃ type crystal structure and conducts Li ions at a rate of 1 × 10 ^-5 S/cm or more at room temperature. It's okay.

The weight proportion of the ceramic particles is preferably 0.5 to 5.0% by weight based on the weight of the coated negative electrode active material particles.
By containing the ceramic particles in the above range, side reactions occurring between the electrolytic solution and the coated negative electrode active material particles can be suppressed.

(Coverage rate)
The coated negative electrode active material particles for lithium ion batteries of the present invention have a coverage rate of 80% or more obtained by the following calculation formula.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles) + BET specific surface area of the conductive aid × weight ratio of the conductive aid contained in the coated negative electrode active material particles)]}×100

Since the coated negative electrode active material particles for lithium ion batteries of the present invention have a coverage rate within the above range, the shearing force applied to each material including a conductive aid during the manufacturing process of the coated negative electrode active material particles can be suitably adjusted. It is possible to construct a conductive additive with an optimized three-dimensional structure.
The coverage rate is preferably 83% or more. Further, the coverage rate is preferably 95% or less, more preferably 92% or less.

Here, the above calculation formula will be explained in detail.
"BET specific surface area of negative electrode active material particles when not coated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles" corresponds to the surface area of negative electrode active material particles contained in coated negative electrode active material particles. do.
Further, "BET specific surface area of the conductive additive x weight percentage of the conductive additive contained in the coated negative electrode active material particles" corresponds to the surface area of the conductive additive contained in the coated negative electrode active material particles.
Therefore, "BET specific surface area of uncoated negative electrode active material particles x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles + BET specific surface area of conductive additive x contained in coated negative electrode active material particles""Weight percentage of conductive aid" corresponds to "total surface area of materials (negative electrode active material particles + conductive aid) contained in coated negative electrode active material particles before coating".

On the other hand, "BET specific surface area of coated negative electrode active material particles" is [(Surface area of the part of the negative electrode active material particles not covered with resin) + (Surface area of the part of the conductive additive not covered with resin) (Surface area of non-containing parts) + (Surface area of resin)]
Since (the surface area of the resin) is extremely small compared to (the surface area of the negative electrode active material particles) and (the surface area of the conductive additive), if (the surface area of the resin) is set to "zero," The BET specific surface area of material particles is expressed as [(Surface area of the part of the negative electrode active material particles not covered with resin) + (Surface area of the part of the conductive additive not covered with resin)]. Ru.

In other words, the total surface area of the materials (negative electrode active material particles + conductive additive) constituting the coated negative electrode active material particles before coating is calculated as follows: The weight ratio of the negative electrode active material particles contained + the BET specific surface area of the conductive additive x the weight ratio of the conductive additive contained in the coated negative electrode active material particles. The total surface area of the "absent part" is the "BET specific surface area of the coated negative electrode active material particles."
Therefore, "BET specific surface area of coated negative electrode active material particles" is calculated as "BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles + BET of conductive support agent". The value divided by "specific surface area x weight percentage of the conductive additive contained in the coated negative electrode active material particles" is calculated based on the ratio of "resin This is the percentage of the surface that is not covered by
Then, by subtracting [the ratio of the surface of the "portion not covered with resin" among the surfaces of the negative electrode active material particles and the conductive additive that constitute the coated negative electrode active material particles] from 1, the coated negative electrode active material particles are calculated. The area ratio of the "portion covered with resin" among the surfaces of the negative electrode active material particles constituting the material particles and the conductive additive can be determined.

The coverage rate of the coated negative electrode active material particles for lithium ion batteries can be determined by adjusting the content of the negative electrode active material particles, conductive agent, and polymer compound, and the volume average particle diameter of the negative electrode active material particles within the above-mentioned preferred ranges. It can be suitably satisfied.

(The bulk density)
The coated negative electrode active material particles for lithium ion batteries of the present invention have a ratio of a loose bulk density of the coated negative electrode active material particles for lithium ion batteries to a firm bulk density of the coated negative electrode active material particles for lithium ion batteries measured by a tapping method. It is preferably 0.60 to 0.85.
By setting the ratio of the loose bulk density to the hard bulk density of the coated negative electrode active material particles for lithium ion batteries within the above range, the cycle characteristics of the lithium ion battery can be suitably improved.
The ratio of loose bulk density to hard bulk density of the coated negative electrode active material particles for lithium ion batteries is more preferably 0.60 to 0.70.

In this specification, the loose bulk density is the bulk density measured in accordance with JIS K 6219-2 (2005) using a cylindrical container with a capacity of 100 cm ³ and a diameter of 30 mm. ) is the bulk density measured according to JIS K 5101-12-2 (2004) with a falling height of 5 mm and a number of tamps (also referred to as tapping or vertical vibration) of 2000 times. Note that the loose bulk density and hardened density each use the average value of five measurements.

<Method for producing coated negative electrode active material particles for lithium ion batteries>
The method for producing coated negative electrode active material particles for lithium ion batteries of the present invention includes the step of mixing negative electrode active material particles, a polymer compound, a conductive agent, and an organic solvent, and then removing the solvent to obtain first coated negative electrode active material particles. and a second coating step in which the first coated negative electrode active material particles are mixed with a polymer compound, a conductive additive, and an organic solvent, and then the solvent is removed.

For example, when each polymer compound is dissolved in an organic solvent and added as a resin solution, the negative electrode active material particles are placed in a universal mixer and stirred at a stirring speed (peripheral speed) of 1 to 7 m/s. A resin solution containing a polymer compound constituting one coating layer (also referred to as coating polymer compound solution) is mixed dropwise over a period of 1 to 90 minutes, and the temperature is raised to 50 to 200°C while stirring, and the temperature is increased to 0.007 to 200°C. After reducing the pressure to 0.04 MPa and holding it for 2 to 9 hours to remove the solvent, at least a part of the surface of the negative electrode active material particles is coated with the first coating layer by mixing a conductive additive and optionally used ceramic particles. particles coated with can be obtained.
By forming the second coating layer using the same procedure as described above, coated negative electrode active material particles in which the second coating layer is provided on the first coating layer can be obtained.

In the first coating step, the stirring speed (peripheral speed) is preferably 2 to 5 m/s, more preferably 2.5 to 4 m/s.
Note that the stirring speed in the first coating step refers to the speed of stirring performed from the time when the negative electrode active material particles are placed in the universal mixer until the entire coating polymer compound solution is dropped.

In the first coating step, the stirring time is preferably 1 to 90 minutes, more preferably 2 to 60 minutes.
Note that the stirring time in the first coating step is the time from when all the materials constituting the first coating layer, such as the coating polymer compound solution and conductive agent, are added until the temperature starts to increase for solvent removal. means the time of

In the first coating step, the drying time is preferably 3 to 7 hours, more preferably 4 to 6 hours.
Note that the drying time in the first coating step means the time from the start of temperature increase and pressure reduction for solvent removal until the completion of solvent removal.

In the second coating step, the stirring speed (peripheral speed) is preferably 1 to 5 m/s, more preferably 2 to 4.5 m/s.
Note that the stirring speed in the second coating step refers to the speed of stirring performed from the time when the negative electrode active material particles forming the first coating layer are placed in the universal mixer until the entire coating polymer compound solution is dropped. do.

In the second coating step, the stirring time is preferably 1 to 90 minutes, more preferably 3 to 60 minutes.
Note that the stirring time in the second coating step is the period from when all the materials constituting the second coating layer, such as the coating polymer compound solution and conductive agent, are added until the temperature starts to be raised for solvent removal. means the time of

In the second coating step, the drying time is preferably 1.5 to 10 hours, more preferably 2 to 9 hours.
Note that the drying time in the second coating step means the time from the start of temperature increase and pressure reduction for solvent removal until the completion of solvent removal.

The negative electrode active material particles on which the first coating layer is formed (before the second coating step) preferably have a BET specific surface area of 0.8 to 1.2 m ² /g, and preferably 0.9 to 1.1 m ² /g. It is more preferable that
When the negative electrode active material particles forming the first coating layer have such a BET specific surface area, the coverage can be suitably satisfied in the second coating step.
Incidentally, the BET specific surface area can be measured by the method described in Examples described later.

The coated negative electrode active material particles produced by the method for producing coated negative electrode active material particles for lithium ion batteries of the present invention preferably have a BET specific surface area of 0.25 to 0.8 m ² /g, preferably 0.3 More preferably, it is 0.75 m ² /g.
When the coated negative electrode active material particles have such a BET specific surface area, the coverage can be suitably satisfied.

By performing the first coating step and the second coating step in this manner, the coverage rate can be suitably adjusted.

The organic solvent is not particularly limited as long as it is an organic solvent that can dissolve the polymer compound, and any known organic solvent can be appropriately selected and used.

<Negative electrode for lithium ion batteries>
The negative electrode for a lithium ion battery preferably includes a negative electrode active material layer containing the coated negative electrode active material particles of the present invention, an electrolytic solution containing an electrolyte and a solvent, and a negative electrode current collector.

As the electrolyte, solvent, and negative electrode current collector described above, electrolytes, solvents, and negative electrode current collectors used in known lithium ion batteries can be appropriately selected and used.

The negative electrode active material layer may further contain a conductive additive in addition to the conductive additive contained in the coating layer of the coated negative electrode active material particles described above. They can be distinguished from each other in that the conductive agent contained in the coating layer is integrated with the coated negative electrode active material particles, whereas the conductive agent contained in the negative electrode active material layer is contained separately from the coated negative electrode active material particles.
As the conductive additive that the negative electrode active material layer may contain, the conductive additive described in the above-mentioned coated negative electrode active material particles for lithium ion batteries can be used.

Preferably, the negative electrode active material layer does not contain a binder.
In addition, in this specification, a binder means a drug that cannot reversibly fix coated negative electrode active material particles or coated negative electrode active material particles and a current collector, and includes starch, polyvinylidene fluoride, Examples include known solvent-dried binders for lithium ion batteries such as polyvinyl alcohol, carboxymethylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, styrene-butadiene rubber, polyethylene, and polypropylene.
These binders are used by being dissolved or dispersed in a solvent, and solidify by volatilizing or distilling off the solvent, thereby irreversibly binding the coated negative electrode active material particles to each other and the coated negative electrode active material particles to the current collector. It is to be fixed at

The negative electrode active material layer may contain adhesive resin.
Adhesive resin refers to a resin that does not solidify even after drying after volatilizing a solvent component and remains adhesive, and is a different material from a binder and is distinguished from it.
Further, while the coating layer constituting the coated negative electrode active material particles is fixed to the surface of the negative electrode active material particles, the adhesive resin reversibly fixes the surfaces of the negative electrode active material particles to each other. Although the adhesive resin can be easily separated from the surface of the negative electrode active material particles, the coating layer cannot be easily separated.
Therefore, the coating layer and the adhesive resin are different materials.

The adhesive resin contains as an essential constituent monomer 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. Examples include polymers in which the total weight proportion of is 45% by weight or more based on the total weight of the constituent monomers.
When using a sticky resin, it is preferable to use 0.01 to 10% by weight of the sticky resin based on 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, silicon-based negative electrode active material particles, and the like. 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.

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

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

<Lithium ion battery>
The lithium ion battery preferably includes the above-described negative electrode for a lithium ion battery, a separator, and a positive electrode.

The positive electrode is not particularly limited, and any positive electrode used in known lithium ion batteries can be appropriately selected and used.

A lithium ion battery can be manufactured, for example, by stacking a positive electrode, a separator, and the above-described negative electrode for lithium ion batteries in this order, and then injecting an electrolyte as necessary.

The following items are disclosed in this specification.

The present disclosure (5) provides coated negative electrode active material particles for lithium ion batteries, in which at least a part of the surface of the negative electrode active material particles for lithium ion batteries is coated with a coating layer containing a polymer compound and a conductive additive. The weight ratio of the conductive additive is 6.1 to 10.5% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries, and the coverage obtained by the following formula is 80%. % or more of coated negative electrode active material particles for lithium ion batteries.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles) + BET specific surface area of the conductive aid × weight ratio of the conductive aid contained in the coated negative electrode active material particles)]}×100

The present disclosure (6) provides the lithium ion battery according to the present disclosure (5), wherein the negative electrode active material particles for lithium ion batteries are non-graphitizable carbon or a mixture of non-graphitizable carbon and a silicon-based material. These are coated negative electrode active material particles for batteries.

In the present disclosure (7), the polymer compound is formed by polymerizing a monomer composition containing an alkyl (meth)acrylate monomer, and the alkyl (meth)acrylate in the monomer composition is provided. The coated negative electrode active material particles for a lithium ion battery according to (5) or (6) of the present disclosure, wherein the weight ratio of the monomer is 90% by weight or more based on the weight of the monomer composition.

The present disclosure (8) is the coated negative electrode active material particle for a lithium ion battery according to any one of the present disclosure (5) to (7), wherein the conductive additive is acetylene black and/or flaky graphite.

The present disclosure (9) provides that the ratio of the loose bulk density of the coated negative electrode active material particles for lithium ion batteries to the firm bulk density of the coated negative electrode active material particles for lithium ion batteries measured by a tapping method is 0.60 to 0. The coated negative electrode active material particles for a lithium ion battery according to any one of (5) to (8) of the present disclosure have a particle diameter of .85.

The present disclosure (10) includes a first coating step of mixing negative electrode active material particles, a polymer compound, a conductive aid, and an organic solvent and then removing the solvent to obtain first coated negative electrode active material particles; The coated negative electrode active for a lithium ion battery according to any one of the present disclosure (5) to (9), comprising a second coating step of removing the solvent after mixing the active material particles, a polymer compound, a conductive aid, and an organic solvent. This is a method for producing material particles.
[Example]

(Example 201)
[Preparation of polymer compound covering negative electrode active material particles]
150 parts of DMF was charged into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen gas introduction tube, and the temperature was raised to 75°C. Next, a monomer composition containing 91 parts of acrylic acid, 9 parts of methyl methacrylate, and 50 parts of DMF, and 0.3 part of 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'- An initiator solution prepared by dissolving 0.8 parts of azobis(2-methylbutyronitrile) in 30 parts of DMF was continuously added dropwise into a four-necked flask using a dropping funnel over 2 hours under stirring while blowing nitrogen. Radical polymerization was performed. After the dropwise addition was completed, the reaction was continued at 75°C for 3 hours.
Next, the temperature was raised to 80°C and the reaction was continued for 3 hours to obtain a copolymer solution with a resin concentration of 30%. The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 150° C. and 0.01 MPa for 3 hours, and DMF was distilled off to obtain a copolymer. This copolymer was roughly pulverized with a hammer, and then further pulverized in a mortar to obtain a powdery polymer compound.

[Preparation of coated negative electrode active material particles]
(First coating step)
One part of the polymer compound was dissolved in 3 parts of DMF to obtain a polymer compound solution.
79.0 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm, manufactured by JFE Chemical Co., Ltd.) were placed in a universal mixer high-speed mixer FS25 [manufactured by Earth Technica Co., Ltd.] at room temperature and at a peripheral speed of 2. While stirring at a speed of .6 m/s, 21.80 parts of a polymer compound solution (5.45 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 60 minutes.
Next, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 4 hours to distill off volatile components. , a first coating layer was formed.
Thereafter, while stirring, 5.45 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm] as a conductive aid was added in portions over 2 minutes, and stirring was continued for 30 minutes.

(Second coating step)
24.20 parts (6.05 parts in terms of solid content) of the polymer compound solution was added dropwise to the negative electrode active material particles on which the first coating layer was formed over 2 minutes while stirring, and the mixture was further stirred for 5 minutes. Next, 4.04 parts of acetylene black (AB) (manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm), which is a conductive additive, was divided while stirring at a circumferential speed of 2.6 m/s. The mixture was added over 2 minutes while stirring, and stirring was continued for 60 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and reduced pressure, and the stirring, reduced pressure, and temperature were maintained for 2 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 106 μm to produce coated negative electrode active material particles having the compositions shown in Table 3.
In addition, the composition shown in Table 3 is expressed in "wt%" using the negative electrode active material particles, the polymer compound, and the conductive aid used in the formation of the first coating layer and the second coating layer. It is a value.

(Examples 202 to 208, Comparative Examples 201 and 204)
Same as Example 201 except that the amounts of negative electrode active material particles, polymer compound, and conductive aid used, as well as the stirring time, stirring speed (peripheral speed), and drying time were changed to the values listed in Table 3. coated negative electrode active material particles were prepared.
Note that the stirring time, stirring speed, and drying time in the first coating step and the second coating step mean the stirring time, stirring speed, and drying time described in this specification.

(Comparative example 202)
[Preparation of polymer compound covering negative electrode active material particles]
70.0 parts of DMF was charged into a four-neck 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 mixture containing 20.0 parts of butyl methacrylate, 55.0 parts of acrylic acid, 22.0 parts of methyl methacrylate, 3 parts of sodium allylsulfonate, and 20 parts of DMF, and 2,2'-azobis(2 , 4-dimethylvaleronitrile) and 0.8 parts of 2,2'-azobis(2-methylbutyronitrile) dissolved in 10.0 parts of DMF were placed in a four-necked flask under nitrogen gas. was continuously added dropwise over a period of 2 hours using a dropping funnel while stirring to carry out radical polymerization. After the dropwise addition was completed, the temperature was raised to 80°C and the reaction was continued for 5 hours to obtain a copolymer solution with 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 and obtain a coating polymer.

[Preparation of coated negative electrode active material particles]
87.6 parts of non-graphitizable carbon powder (volume average particle diameter 20 μm), which is the negative electrode active material particles, was placed in a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.] and stirred at room temperature and 720 rpm. , 58.6 parts of the coating polymer compound solution obtained by dissolving the coating polymer compound obtained in the example in isopropanol at a concentration of 19.8% by weight (11.6 parts in solid content) The mixture was added dropwise over 2 minutes and stirred for an additional 5 minutes.
Next, while stirring, 0.8 part of acetylene black (Denka Black (registered trademark) manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive aid was added in portions over 2 minutes, and stirring was continued for 30 minutes. Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. . The obtained powder was classified using a sieve with an opening of 212 μm to produce coated negative electrode active material particles according to Comparative Example 202.
The compositions shown in Table 3 are values expressed in "wt%" of the amounts of the negative electrode active material particles, polymer compound, and conductive aid used to form the coating layer.
Furthermore, in Table 3, the stirring time and drying time are listed in the "first coating step" column.

(Comparative example 203)
Coated negative electrode active material particles were produced in the same manner as Comparative Example 202, except that the amounts of negative electrode active material particles, polymer compound, and conductive aid were changed to the values listed in Table 3.

<Measurement of bulk density>
The loose bulk density and hard bulk density of the obtained coated negative electrode active material particles were measured using the method described in this specification, and the ratio of the loose bulk density to the hard bulk density was calculated. The results are shown in Table 4.

<Measurement of coverage>
BET specific surface area of negative electrode active material particles when uncoated × weight ratio of negative electrode active material particles contained in coated negative electrode active material particles, and BET specific surface area of conductive aid × conductivity contained in coated negative electrode active material particles The weight proportion of the auxiliary agent was measured.
Next, the BET specific surface areas of the coated negative electrode active material particles produced in Examples and Comparative Examples were measured.
Thereafter, the coverage was calculated using the following formula.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles) + BET specific surface area of the conductive aid × weight ratio of the conductive aid contained in the coated negative electrode active material particles)]}×100

[Method of measuring BET specific surface area]
The BET specific surface area was measured using the following apparatus and measurement conditions in accordance with JIS Z8830 method for measuring the specific surface area of powder (solid) by gas adsorption.
Measuring device: Micromeritex ASAP-2010
Adsorbed gas: _N2
Dead volume measuring gas: He
Adsorption temperature: 77K
Measurement pretreatment: Vacuum drying at 100°C for 10 minutes Measurement mode: Isothermal adsorption and desorption processes Measured relative pressure P/P0: Approximately 0 to 0.99
Equilibrium setting time: 180 seconds per relative pressure

"BET specific surface area after the first coating step" described in Table 4 means "BET specific surface area of the negative electrode active material particles forming the first coating layer ( "before the second coating step)" and "coated BET specific surface area" indicates "BET specific surface area of the prepared coated negative electrode active material particles."
Note that Comparative Examples 202 and 203 do not have the second coating step, so the column for the BET specific surface area after the first coating step is left blank, and only "coated BET specific surface area" is written.

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

[Preparation of resin current collector]
In a twin-screw extruder, 70 parts of polypropylene [trade name: "Sun Allomer PL500A", manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotubes [trade name: "FloTube9000", manufactured by CNano], and a dispersant [trade name: "Umex 1001"] were added. '', manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200° C. and 200 rpm to obtain a resin mixture.
The obtained resin mixture was passed through a T-die extrusion film forming machine and stretched and rolled to obtain a conductive film for a resin current collector having a thickness of 100 μm. Next, the obtained conductive film for a resin current collector was cut into a size of 17.0 cm x 17.0 cm, nickel vapor deposition was performed on one side, and a terminal for current extraction (5 mm x 3 cm) was connected. A resin current collector was obtained.

[Preparation of negative electrodes 1 to 12 for lithium ion batteries]
42 parts of electrolytic solution, 1.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], and carbon fiber [Donna Carbo Milled S-243 manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average Fiber diameter 13 μm, electric conductivity 200 mS/cm] and 0.9 parts were mixed at 2000 rpm for 5 minutes using a planetary stirring type mixing and kneading device {Awatori Rentaro (registered trademark) [manufactured by Shinky Co., Ltd.]}, Subsequently, after adding 30 parts of the above electrolytic solution and 97.8 parts each of the above coated negative electrode active material particles 1 to 12, they were further mixed for 2 minutes at 2000 rpm with a foaming Rentaro, and 20 parts of the above electrolytic solution was further added. After that, stirring with a foaming Rentaro was performed at 2000 rpm for 1 minute, and after adding 2.3 parts of the above electrolyte solution, stirring was performed with a foaming Rentaro for 2 minutes at 2000 rpm to prepare a slurry for a negative electrode active material layer. .
The obtained slurry for negative electrode active material layer was applied to one side of the resin current collector so that the basis weight was 80 mg/cm ² and pressed for about 10 seconds at a pressure of 1.4 MPa to form negative electrode 1 for lithium ion batteries. ~12 were made. Each of negative electrodes 1 to 12 for lithium ion batteries had a thickness of 340 μm and a rectangular shape of 190×90 mm.

[Preparation of coated positive electrode active material particles]
One part of the coating polymer compound was dissolved in 3 parts of DMF to obtain a coating polymer compound solution.
90.12 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) were placed in a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.]. While stirring at room temperature and 720 rpm, 12.56 parts of coating polymer compound solution (3.14 parts in terms of solid content) was added dropwise over 2 minutes, followed by further stirring for 5 minutes.
Next, in a stirred state, 3.14 parts of acetylene black (Denka Black (registered trademark) manufactured by Denka Co., Ltd.), which is a conductive aid, and glass ceramic particles (trade name: "Lithium ion conductive glass ceramics LICGC ^TM PW-01") were added. 1 μm)" [manufactured by OHARA Co., Ltd.]) was added in portions over 2 minutes, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated positive electrode active material particles.

[Preparation of positive electrode for lithium ion battery]
42 parts of electrolyte, 0.5 part of Ketjenblack [trade name "EC300J", manufactured by Lion Specialty Chemicals Co., Ltd.], and 1.0 part of carbon fiber [Dona Carbo Milled S-243, manufactured by Osaka Gas Chemicals Co., Ltd.] 30 parts of the above electrolyte and 98.5 parts of the above coated positive electrode active material particles were mixed for 5 minutes at 2000 rpm using a planetary stirring type mixing and kneading device {Awatori Rentaro [manufactured by Shinky Co., Ltd.]}. After adding 1.0 parts of the electrolyte, the electrolyte was further mixed for 2 minutes at 2000 rpm with a foaming Rentaro, and 20 parts of the electrolyte was further added, and the electrolyte was stirred with a foaming Rentaro for 1 minute at 2000 rpm. After 3 more parts were added, the mixture was stirred by a foaming Rentaro for 2 minutes at 2000 rpm to prepare a slurry for a positive electrode active material layer. The obtained slurry for the positive electrode active material layer was applied to one side of the resin current collector so that the basis weight was 80 mg/cm ² , and pressed at a pressure of 1.4 MPa for about 10 seconds to form a lithium layer with a thickness of 340 μm. A positive electrode (190 cm x 90 cm) for an ion battery was produced.

Lithium ion batteries 1 to 12 were produced by combining and sealing a separator with any of the lithium ion battery positive electrode and lithium ion battery negative electrodes 1 to 12 produced above. As the separator, Celgard #3501 was used. The capacity retention rates of the obtained lithium ion batteries 1 to 12 were measured. The results are shown in Table 4.

[Measurement of capacity retention rate (cycle characteristics)]
A charge/discharge test was conducted on lithium ion batteries 1 to 12 at 45° C. using a charge/discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.] according to the following method.
After charging to 4.2V using a constant current/constant voltage method (0.1C), after a 10 minute rest, the battery was discharged to 2.6V using a constant current method (0.1C).
The discharged capacity at this time was defined as [discharge capacity (mAh)].
A 10-cycle repeated test was conducted to determine the 10-cycle capacity retention rate (%).

From Table 4, it was confirmed that the negative electrode active material particles for lithium ion batteries of Examples 201 to 208 could improve the cycle characteristics of lithium ion batteries.

The present invention also relates to coated negative electrode active material particles for lithium ion batteries, negative electrodes for lithium ion batteries, and lithium ion batteries described below. The above-mentioned electrode composition for a lithium ion battery may have this negative electrode active material particle.

Lithium ion batteries have been used in a variety of applications in recent years as secondary batteries that can achieve high energy density and high output density, and various battery components are being studied.
Among them, carbon-based materials such as graphite and amorphous carbon used as negative electrode active materials are being widely studied because they are low cost and have excellent cycle life.

A negative electrode active material made of a carbon-based material causes side reactions such as a decomposition reaction of an electrolytic solution using the surface of the active material as a reaction site during charging and discharging. As a result, a decrease in battery performance was observed, such as an increase in the irreversible capacity of the battery and an increase in internal resistance.
In order to suppress this side reaction, a widely adopted method is to form a film (SEI: Solid Electrolyte Interface, also referred to as SEI surface film) on the surface of the negative electrode active material to prevent the negative electrode active material from coming into direct contact with the electrolyte. ing. For example, Patent Document 4 discloses a method of suppressing side reactions by using a polymer compound having a specific acid value as a coating resin for a negative electrode active material.

However, the coated negative electrode active material disclosed in Patent Document 4, in which at least a portion of the surface of the negative electrode active material is coated with a polymer compound, has a problem that the electrode strength is not sufficient when the electrode is produced by compression molding. there were. Particularly in these days when lithium ion batteries are required to have higher capacities and electrodes are becoming thicker in order to achieve higher capacities, there is a strong desire to solve this problem.

The present invention solves the above-mentioned problems, and when producing an electrode by compression molding, the present invention provides an electrode that has a low initial internal resistance value and a low rate of increase in resistance after charging and discharging, has a high capacity retention rate, and has excellent electrode strength. An object of the present invention is to provide coated negative electrode active material particles for lithium ion batteries that can be used to produce lithium ion battery coated negative electrode active material particles.

In the present invention, at least a part of the surface of negative electrode active material particles for lithium ion batteries is coated with a first coating layer, and at least a part of the surface of the first coating layer is coated with a second coating layer. Coated negative electrode active material particles for lithium ion batteries, wherein the first coating layer comprises an ester compound (a11) of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid and an anionic monomer. The polymer compound (P1) has a glass transition temperature of 20° C. and a conductive additive (C1). above, the second coating layer comprises coated negative electrode active material particles for lithium ion batteries containing a polymer compound (P2) having a glass transition temperature of 20° C. or lower and a conductive agent (C2); the above coating for lithium ion batteries; The present invention relates to a lithium ion battery negative electrode comprising a non-binding body containing negative electrode active material particles and a conductive filler; and a lithium ion battery comprising the above lithium ion battery negative electrode.

According to the present invention, when producing an electrode by compression molding, lithium can be used to produce an electrode that has a low initial internal resistance value and a low rate of increase in resistance after charging and discharging, has a high capacity retention rate, and has excellent electrode strength. Coated negative electrode active material particles for ion batteries can be provided.

The present invention will be explained in detail below.
The present invention relates to coated negative electrode active material particles for lithium ion batteries.
In addition, in this specification, when describing a lithium ion battery, it is a concept that also includes a lithium ion secondary battery.

The coated negative electrode active material particles for lithium ion batteries of the present invention are obtained by coating at least a part of the surface of the negative electrode active material particles for lithium ion batteries with a first coating layer, and at least a part of the surface of the first coating layer. is coated with a second coating layer. The first coating layer is provided primarily to suppress side reactions between the negative electrode active material particles for lithium ion batteries and the electrolyte. The second coating layer is provided mainly for the purpose of maintaining the strength of the electrode when the electrode is formed using the coated negative electrode active material particles for lithium ion batteries of the present invention.

As the negative electrode active material particles, carbon-based materials [graphite, non-graphitizable carbon (hard carbon), amorphous carbon, fired resin bodies (for example, those obtained by firing and carbonizing phenol resin and furan resin, etc.), Cokes (e.g. pitch coke, needle coke, petroleum coke, etc.) and carbon fibers], silicon-based materials [silicon, silicon oxide (SiO _x ), silicon-carbon composites (carbon particles whose surfaces are made of silicon and/or silicon carbide) 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- conductive polymers (e.g. polyacetylene, polypyrrole, etc.), metals (tin, aluminum, zirconium, titanium, etc.) , metal oxides (titanium oxide and lithium titanium oxide, etc.), metal alloys (for example, lithium-tin alloy, lithium-aluminum alloy, lithium-aluminum-manganese alloy, etc.), and mixtures of these with carbon-based materials, etc. can be mentioned.
Among the negative electrode active material particles, those that do not contain lithium or lithium ions inside may be subjected to a pre-doping treatment in which part or all of the negative electrode active material particles contain lithium or lithium ions.

(First coating layer)
The first coating layer includes a polymer compound (P1) and a conductive aid (C1).
The polymer compound (P1) has a monomer composition comprising an ester compound (a11) of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid and an anionic monomer (a12). It is a polymer of substances, and its glass transition temperature (Tg) exceeds 20°C. Note that (meth)acrylic acid in this specification means methacrylic acid or acrylic acid.

In this specification, Tg is a value measured by the method specified in ASTM D3418-82 (DSC method). The Tg of the polymer compound (P1) is preferably 40°C or higher, more preferably 60°C or higher from the viewpoint of suppressing side reactions.

First, the ester compound (a11) will be explained.
The ester compound (a11) is an ester compound of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid. Examples of monovalent aliphatic alcohols having 1 to 12 carbon atoms include monovalent branched or straight chain aliphatic alcohols having 1 to 12 carbon atoms, such as 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, neopentyl alcohol, etc.), hexyl alcohol (1-hexanol, 2-hexanol and 3-hexanol) -hexanol, etc.), heptyl alcohol (n-heptyl alcohol, 1-methylhexyl alcohol, 2-methylhexyl alcohol, etc.), octyl alcohol (n-octyl alcohol, 1-methylheptanol, 1-ethylhexanol, 2-methylheptyl alcohol) alcohol and 2-ethylhexanol), nonyl alcohol (n-nonyl alcohol, 1-methyloctanol, 1-ethylheptanol, 1-propylhexanol, 2-ethylheptyl alcohol, etc.), decyl alcohol (n-decyl alcohol, - Methylnonyl alcohol, 2-methylnonyl alcohol, 2-ethyloctyl alcohol, etc.), undecyl alcohol (n-undecyl alcohol, 1-methyldecyl alcohol, 2-methyldecyl alcohol, 2-ethylnonyl alcohol, etc.), lauryl Examples include alcohols (n-lauryl alcohol, 1-methylundecyl alcohol, 2-methylundecyl alcohol, 2-ethyldecyl alcohol, 2-butyloctyl alcohol, etc.).

Preferred ester compounds (a11) include methyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-methylhexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. , dodecyl (meth)acrylate, among which methyl methacrylate, butyl methacrylate, dodecyl methacrylate, and 2-ethylhexyl methacrylate are more preferred.

The anionic monomer (a12) will be explained.
The anionic monomer (a12) is a monomer having a radically polymerizable 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, etc., and preferred anionic groups include phosphonic acid group, sulfonic acid group, carboxyl group, etc.

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

Examples of the radically polymerizable unsaturated carboxylic acid 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. . Examples of 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), and pentenoic acid (2-methylbutanoic acid and substituted butanoic acid such as 3-methylbutanoic acid). - including substituted pentenoic acids such as methylpentenoic acid and 3-methylpentenoic acid), hexenoic acid (including substituted hexenoic acids such as 2-methylhexenoic acid and 3-methylhexenoic acid), heptenoic acid (including substituted hexenoic acids such as 2-methylhexenoic acid and 3-methylhexenoic acid), (including substituted heptenoic acids such as 3-methylheptenoic acid) and octenoic acid (including substituted octenoic acids such as 2-methyloctenoic acid and 3-methyloctenoic acid).
Examples of the radically polymerizable unsaturated aromatic monocarboxylic acid 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 anion), butenesulfonic acid (including substituted butenesulfonic acids such as 1-methylbutenesulfonic acid and 2-methylbutenesulfonic acid) ), pentensulfonic acid (including substituted pentensulfonic acids such as 1-methylpentensulfonic acid and 2-methylpentensulfonic acid), hexenesulfonic acid (substituted pentensulfonic acids such as 1-methylhexenesulfonic acid and 2-methylhexenesulfonic acid) (including hexenesulfonic acid) and heptenesulfonic acid (including substituted heptenesulfonic acids such as 1-methylheptensulfonic acid and 2-methylheptensulfonic acid).
Examples of the radically polymerizable unsaturated aromatic monosulfonic acid having 8 carbon atoms include styrene sulfonic 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, and acrylamidealkylphosphonic acid. Diphosphonic acid, phosphonomethylated vinylamine, (meth)acrylicphosphonic acid, and the like can be mentioned.
These anionic monomers may be a mixture.
In addition, by containing the anionic monomer, the toughness of the polymer compound (P1) is improved, making it less susceptible to stress due to expansion and contraction of the negative electrode active material particles associated with lithium ion deintercalation reactions during charging and discharging. .

These anionic monomers may be used alone or in combination of two or more. Among them, when the acid value of the polymer is 30 to 500, the anionic monomer (a12) is a radically polymerizable unsaturated carboxylic acid having 3 to 9 carbon atoms or a radically polymerizable unsaturated carboxylic acid having 2 to 8 carbon atoms. It is preferable to use in combination at least two selected from the group consisting of saturated sulfonic acids and radically polymerizable unsaturated phosphonic acids having 2 to 9 carbon atoms, and radically polymerizable unsaturated carboxylic acids having 3 to 9 carbon atoms and 2 to 9 carbon atoms. It is more preferable to use a radically polymerizable unsaturated sulfonic acid having 1 to 8 carbon atoms or a radically polymerizable unsaturated phosphonic acid having 2 to 9 carbon atoms in combination.

The content of the ester compound (a11) contained in the monomer composition is based on the total weight of the ester compound (a11) and the anionic monomer (a12) from the viewpoint of adhesiveness with the negative electrode active material particles. The amount is preferably 1 to 99% by weight, more preferably 20 to 80% by weight, and even more preferably 30 to 70% by weight.

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

Preferably, the monomer composition further includes a salt of an anionic monomer (a13). When the monomer composition contains the anionic monomer salt (a13), the internal resistance of the lithium ion battery can be reduced.

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

When the monomer composition contains the anionic monomer salt (a13), the content of the ester compound (a11) contained in the monomer composition is determined from the viewpoint of adhesion to the active material, etc. , preferably 5 to 95% by weight, more preferably 20 to 80% 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 30 to 70% by weight.

When the monomer composition contains a salt of an anionic monomer (a13), the content of the anionic monomer (a12) contained in the monomer composition is determined from the viewpoint of ionic conductivity. It is preferably 10 to 90% by weight, more preferably 20 to 80% by weight, based on the total weight of the compound (a11), the anionic monomer (a12) and the salt of the anionic monomer (a13). The content is more preferably 30 to 70% by weight.

When the monomer composition contains an anionic monomer salt (a13), the content of the anionic monomer salt (a13) contained in the monomer composition is determined from the viewpoint of internal resistance, etc. , the ester compound (a11), the anionic monomer (a12) and the salt of the anionic monomer (a13) are preferably 0.1 to 10% by weight, more preferably 0. The amount is 5 to 10% by weight, more preferably 1 to 10% by weight.

The weight average molecular weight of the polymer compound (P1) is preferably from 20,000 to 96,000 from the viewpoint of adhesion to the active material, and in the method for obtaining the polymer described below, the polymerization conditions are preferably set. By setting the weight average molecular weight within this range, the weight average molecular weight can be set within a preferable range.
Note that the weight average molecular weight of the polymer compound (P1) in this specification is measured by gel permeation chromatography (hereinafter abbreviated as GPC) measured under the following conditions.
<GPC measurement conditions>
Equipment: Alliance GPC V2000 (manufactured by Waters)
Solvent: Orthodichlorobenzene Standard material: Polystyrene Sample concentration: 3mg/ml
Column stationary phase: PLgel 10μm, MIXED-B 2 in series (manufactured by Polymer Laboratories)
Column temperature: 135℃

In addition to the ester compound (a11), the anionic monomer (a12), and the salt of the anionic monomer (a13), the monomer composition includes a copolymerizable vinyl monomer (c) that does not contain active hydrogen. "Hereinafter, referred to as copolymerizable vinyl monomer (c)" may be included.

Examples of the copolymerizable vinyl monomer (c) include the following (c1) to (c5).

(c1) Formed from a branched or straight-chain 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. The monools mentioned above include (i) branched or straight-chain aliphatic monools having 13 to 20 carbon atoms (tridecyl alcohol, tetradecyl alcohol, pentadecyl alcohol, cetyl alcohol, heptadecyl alcohol, stearyl alcohol, isostearyl alcohol, nonadecyl alcohol, arachidyl alcohol, etc.), (ii) alicyclic monool having 5 to 20 carbon atoms (cyclohexyl alcohol, etc.), (iii) aromatic aliphatic monool having 7 to 20 carbon atoms (benzyl alcohol, etc.) and mixtures of two or more thereof.

(c2) Poly(n=2-30) oxyalkylene (2-4 carbon atoms) alkyl (1-18 carbon atoms) ether (meth)acrylate [10 mole adduct of methanol with ethylene oxide (hereinafter abbreviated as EO) (meth) acrylate, 10 mole adduct of methanol with propylene oxide (hereinafter abbreviated as PO) (meth)acrylate, etc.].

(c3) Nitrogen-containing vinyl compound (c3-1) Amide group-containing vinyl compound (i) (meth)acrylamide compound having 3 to 30 carbon atoms, such as N,N-dialkyl (1 to 6 carbon atoms) or dialkyl (carbon number 7-15) (meth)acrylamide (N,N-dimethylacrylamide, N,N-dibenzylacrylamide, etc.) and diacetone acrylamide.
(ii) Vinyl compounds containing an amide group having 4 to 20 carbon atoms, excluding the above (meth)acrylamide compounds, such as N-methyl-N-vinylacetamide, cyclic amides [pyrrolidone compounds having 6 to 13 carbon atoms (N-vinylpyrrolidone)] etc)].

(c3-2) (meth)acrylate compound (i) dialkyl (1 to 4 carbon atoms) aminoalkyl (1 to 4 carbon atoms) (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N -diethylaminoethyl (meth)acrylate, t-butylaminoethyl (meth)acrylate, morpholinoethyl (meth)acrylate, etc.].
(ii) Halogenating quaternary ammonium group-containing (meth)acrylate {tertiary amino group-containing (meth)acrylate [N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, etc.] Quaternized products etc. that have been quaternized using a quaternizing agent such as alkyl}.

(c3-3) Heterocycle-containing vinyl compounds Pyridine compounds with 7 to 14 carbon atoms (2- or 4-vinylpyridine, etc.), imidazole compounds with 5 to 12 carbon atoms (N-vinylimidazole, etc.), 6 to 13 carbon atoms pyrrole compounds (such as N-vinylpyrrole) and pyrrolidone compounds having 6 to 13 carbon atoms (such as N-vinyl-2-pyrrolidone).

(c3-4) Nitrile group-containing vinyl compound A nitrile group-containing vinyl compound having 3 to 15 carbon atoms [(meth)acrylonitrile, cyanostyrene, cyanoalkyl (1 to 4 carbon atoms) acrylate, etc.].

(c3-5) Other vinyl compounds Nitro group-containing vinyl compounds having 8 to 16 carbon atoms (nitrostyrene, etc.), etc.

(c4) vinyl hydrocarbon (c4-1) aliphatic vinyl hydrocarbon olefin having 2 to 18 carbon atoms or more (ethylene, propylene, butene, isobutylene, pentene, heptene, diisobutylene, octene, dodecene, octadecene, etc.), Dienes having 4 to 10 or more carbon atoms (butadiene, isoprene, 1,4-pentadiene, 1,5-hexadiene, 1,7-octadiene, etc.), etc.

(c4-2) Alicyclic vinyl hydrocarbon Cyclic unsaturated compounds having 4 to 18 carbon atoms or more {cycloalkenes (cyclohexene, etc.), (di)cycloalkadienes [(di)cyclopentadiene, etc.], terpenes (pinene, etc.) , limonene and indene, etc.)}.

(c4-3) Aromatic vinyl hydrocarbon Aromatic unsaturated compounds having 8 to 20 carbon atoms or more and derivatives thereof (styrene, α-methylstyrene, vinyltoluene, 2,4-dimethylstyrene, ethylstyrene, isopropyl styrene, butylstyrene, phenylstyrene, cyclohexylstyrene, benzylstyrene, etc.).

(c5) Vinyl ester, vinyl ether, vinyl ketone and unsaturated dicarboxylic acid diester (c5-1) Vinyl ester aliphatic vinyl ester [alkenyl ester of aliphatic carboxylic acid (mono- or dicarboxylic acid) having 4 to 15 carbon atoms (vinyl acetate) , vinyl propionate, vinyl butyrate, diallyl adipate, isopropenyl acetate, vinyl methoxy acetate, etc.).
Aromatic vinyl esters [alkenyl esters of aromatic carboxylic acids (mono- or dicarboxylic acids) having 9 to 20 carbon atoms (vinyl benzoate, diallyl phthalate, methyl-4-vinyl benzoate, etc.) and aromatic ring-containing esters of aliphatic carboxylic acids (acetoxystyrene, etc.)].

(c5-2) Vinyl ether aliphatic vinyl ether [vinyl alkyl having 3 to 15 carbon atoms (1 to 10 carbon atoms) ether (vinyl methyl ether, vinyl butyl ether, vinyl 2-ethylhexyl ether, etc.), vinyl alkoxy (having 1 to 6 carbon atoms) ) Alkyl (1-4 carbon atoms) ethers (vinyl-2-methoxyethyl ether, methoxybutadiene, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxydiethyl ether and vinyl-2- ethyl mercaptoethyl ether, etc.), poly(2-4)(meth)allyloxyalkanes (2-6 carbon atoms) (diallyloxyethane, triaryloxyethane, tetraallyloxybutane, tetramethallyloxyethane, etc.), etc. ].
Aromatic vinyl ethers having 8 to 20 carbon atoms (vinylphenyl ether, phenoxystyrene, etc.).

(c5-3) Vinyl ketone Aliphatic vinyl ketone having 4 to 25 carbon atoms (vinyl methyl ketone, vinyl ethyl ketone, etc.).
Aromatic vinyl ketones having 9 to 21 carbon atoms (vinylphenyl ketones, etc.).

(c5-4) Unsaturated dicarboxylic acid diester Unsaturated dicarboxylic acid diester having 4 to 34 carbon atoms [dialkyl fumarate (two alkyl groups are linear, branched, or alicyclic, having 1 to 22 carbon atoms) ) and dialkyl maleate (the two alkyl groups are linear, branched, or alicyclic groups having 1 to 22 carbon atoms)].

When the monomer composition contains a copolymerizable vinyl monomer (c), the content of the copolymerizable vinyl monomer (c) is 4% based on the total weight of the monomer components contained in the monomer composition. It is preferably .5 to 6.5% by weight. In the present invention, the monomer component refers to a monomer component having polymerizability such as an ester compound (a11), an anionic monomer (a12), and a salt of an anionic monomer (a13). However, when the monomer composition contains the copolymerizable vinyl monomer (c), the total weight of the monomer components also includes the weight of the copolymerizable vinyl monomer (c).

The acid value of the polymer compound (P1) is 30 to 700 from the viewpoint of suppressing volume change of the active material. If the acid value is lower than 30 or higher than 700, the interfacial resistance between the coated active materials increases and good electrical properties cannot be exhibited. Although the acid value can be adjusted depending on the type of active material and electrolyte used, it is more preferably 500 to 700 from the viewpoint of electrical properties.
In addition, the acid value of the polymer compound (P1) in this specification is measured by the method of JIS K 0070-1992, and the acid value of the polymer compound (P1) is determined by the amount of anionic monomer contained in the monomer composition. The above range can be achieved by adjusting the content of body (a12).

The polymer compound (P1) consists of an ester compound (a11), an anionic monomer (a12), a salt of the anionic monomer (a13) used as necessary, and a copolymerizable vinyl monomer (c). It can be obtained by polymerizing a monomer composition, and known polymerization methods (bulk polymerization, solution polymerization, emulsion polymerization, suspension polymerization, etc.) can be used as the polymerization method.
During polymerization, known polymerization initiators {azo initiators [2,2'-azobis(2-methylpropionitrile), 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2' -azobis(2-methylbutyronitrile), etc.], peroxide-based initiators (benzoyl peroxide, di-t-butyl peroxide, lauryl peroxide, etc.), 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 monomer components contained in the monomer composition.

Solvents used in solution polymerization include ester solvents [preferably ester compounds having 2 to 8 carbon atoms (e.g. ethyl acetate and butyl acetate)], alcohols [preferably aliphatic alcohols having 1 to 8 carbon atoms (e.g. methanol, ethanol, isopropanol and octanol)], hydrocarbons with a linear, branched or cyclic structure having 5 to 8 carbon atoms (e.g. pentane, hexane, heptane, octane, cyclohexane, toluene and xylene), amide solvents [e.g. N-dimethylformamide (hereinafter abbreviated as DMF) and dimethylacetamide] and ketone solvents [preferably a ketone compound having 3 to 9 carbon atoms (for example, methyl ethyl ketone)], etc., and the amount used is included in the monomer composition. It is usually 50 to 200% by weight based on the total weight of the monomer components, and the concentration of the monomer composition is usually 30 to 70% by weight.

Examples of solvents (dispersion media) used in emulsion polymerization and suspension polymerization include water, alcohol (e.g. ethanol), ester solvents (e.g. ethyl propionate), light naphtha, etc., and examples of emulsifiers such as higher fatty acids (C10-24) metal salts (e.g. sodium oleate and sodium stearate), higher alcohol (C10-24) sulfate ester metal salts (e.g. sodium lauryl sulfate), ethoxylated tetramethyldecynediol, methacrylic acid sulfonate. Examples include ethyl sodium and dimethylaminomethyl methacrylate. Furthermore, polyvinyl alcohol, polyvinylpyrrolidone, etc. may be added as a stabilizer.
The concentration of the monomer composition in emulsion polymerization or suspension polymerization is usually 5 to 95% by weight, and the amount of polymerization initiator used is usually 0.01 to 5% by weight based on the total weight of the monomer composition. From the viewpoint of adhesive strength and cohesive strength, it is 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 halogenated hydrocarbons (carbon tetrachloride, carbon tetrabromide, benzyl chloride, etc.) can be used. The amount used is usually 2% by weight or less based on the total weight of the monomer components contained in the monomer composition, and preferably 0.5% by weight or less from the viewpoint of resin strength.

In addition, the temperature in the system during the polymerization reaction is usually -5 to 150°C, preferably 30 to 120°C, the reaction time is usually 0.1 to 50 hours, preferably 2 to 24 hours, and the end point of the polymerization reaction is The amount of reacted monomer is usually 5% by weight or less, preferably 1% by weight or less based on the total weight of monomer components contained in the monomer composition, and the amount of unreacted monomer is The amount can be confirmed by a known method for quantifying monomer content such as gas chromatography.

The weight proportion of the polymer compound (P1) in the coated negative electrode active material particles for lithium ion batteries is preferably 0.7 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. When the weight ratio of the polymer compound (P1) is within the above range, the internal resistance increase rate of the electrode can be suppressed to a low level. The weight proportion of the polymer compound (P1) is more preferably 1.0 to 9.0% by weight, even more preferably 2.0 to 6.0% by weight.

The conductive aid (C1) is not particularly limited, and examples thereof include particles and fibers, such as metals [aluminum, stainless steel (SUS), silver, gold, copper, titanium, etc.], carbon [graphite (flake carbon black (acetylene black, Ketjen black, furnace black, channel black, thermal lamp black, etc.), carbon nanofiber (CNF), etc.], and mixtures thereof. The conductive aid (C1) may be used alone or in combination of two or more.

The ratio of the polymer compound (P1) and the conductive agent (C1) constituting the first coating layer is not particularly limited, but from the viewpoint of internal resistance of the battery, etc. The ratio of molecular compound (P1) (resin solid content weight) to conductive aid (C1) is preferably 1:0.01 to 1:50, more preferably 1:0.1 to 1:3.0. preferable.

The first coating layer may further contain ceramic particles in addition to the polymer compound (P1) and the conductive aid (C1).
Examples of the ceramic particles include metal carbide particles, metal oxide particles, glass ceramic particles, and the like.

Examples of metal oxide particles include zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ), tin oxide (SnO ₂ ), titania (TiO ₂ ), zirconia (ZrO ₂ ), _Indium oxide ( _In2O3 ) _, _Li2B4O7 _, _Li4Ti5O12 _, _Li2Ti2O5 _, _LiTaO3 _, _LiNbO3 , _LiAlO2 _, _Li2ZrO3 _, _Li2WO4 _, Li ₂ TiO ₃ , Li ₃ PO ₄ , Li ₂ MoO ₄ , Li ₃ BO ₃ , LiBO ₂ , Li ₂ CO ₃ , Li ₂ SiO ₃ and ABO ₃ (However, A is Ca, Sr, Ba, La, Pr and Y, and B is at least one selected from the group consisting of Ni, Ti, V, Cr, Mn, Fe, Co, Mo, Ru, Rh, Pd, and Re. Examples include perovskite-type oxide particles represented by (species).
As the metal oxide particles, zinc oxide (ZnO), aluminum oxide (Al ₂ O ₃ ), silicon dioxide (SiO ₂ ) and lithium tetraborate (Li ₂ B ₄ O ₇ ) are preferred.

(Second coating layer)
The second coating layer includes a polymer compound (P2) and a conductive aid (C2).
The polymer compound (P2) has a glass transition temperature (Tg) of 20°C or lower.

Examples of the polymer compound (P2) include adhesive resins having a Tg of 20°C or less. Adhesive resin refers to a resin that does not solidify even when a solvent component is evaporated and is dried, but remains adhesive, and is a different material from a binder, and these are distinguished from each other. The second coating layer is the outermost surface of the coated negative electrode active material particles, and the surfaces of the coated negative electrode active material particles are reversibly fixed to each other by the adhesive resin contained in the second coating layer. Although the adhesive resin can be easily separated from the surface of the negative electrode active material particles, the binder usually cannot be easily separated. Therefore, the binder and the adhesive resin are different materials.
The polymer compound (P2) is preferably at least one selected from the group consisting of urethane resin, (meth)acrylic acid alkyl ester copolymer, and styrene-butadiene rubber.

The urethane resin is preferably a urethane resin obtained by reacting the active hydrogen component (b1) and the isocyanate component (b2).
Since the urethane resin has flexibility, by covering the negative electrode active material particles with the urethane resin, the volume change of the electrode can be alleviated and the expansion of the electrode can be suppressed.

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

Examples of polyether diols include polyoxyethylene glycol (hereinafter abbreviated as PEG), polyoxyethylene oxypropylene block copolymer diol, polyoxyethylene oxytetramethylene block copolymer diol; ethylene glycol, propylene glycol, 1,4-butane. Ethylene oxide adducts of low molecular weight glycols such as diol, 1,6-hexamethylene glycol, neopentyl glycol, bis(hydroxymethyl)cyclohexane, 4,4'-bis(2-hydroxyethoxy)-diphenylpropane, number average molecular weight 2 ,000 or less and dicarboxylic acids [aliphatic dicarboxylic acids with 4 to 10 carbon atoms (e.g. succinic acid, adipic acid, sebacic acid, etc.), aromatic dicarboxylic acids with 8 to 15 carbon atoms (e.g. terephthalic acid, isophthalic acid, etc.) ) etc.] and mixtures of two or more of these.
Among these, PEG, polyoxyethylene oxypropylene block copolymer diol and polyoxyethylene oxytetramethylene block copolymer diol are preferred, and PEG is particularly preferred.

The polycarbonate diol includes one or more alkylene diols having an alkylene group having 4 to 12 carbon atoms, preferably 6 to 10 carbon atoms, and more preferably 6 to 9 carbon atoms, and a low-molecular carbonate compound (for example, By condensing a dialkyl carbonate having an alkyl group with 1 to 6 carbon atoms, an alkylene carbonate having an alkylene group having 2 to 6 carbon atoms, and a diaryl carbonate having an aryl group having 6 to 9 carbon atoms while performing a dealcoholization reaction. Polycarbonate polyols (e.g. polyhexamethylene carbonate diol) produced are mentioned.

Examples of polyester diols include condensed polyester diols obtained by reacting low-molecular diols and/or polyether diols with a number average molecular weight of 1,000 or less with one or more of the aforementioned dicarboxylic acids, and lactones having 4 to 12 carbon atoms. Examples include polylactone diol obtained by ring-opening polymerization of . Examples of the low-molecular diol include the low-molecular glycols exemplified in the section of the polyether diol. Examples of the polyether diol having a number average molecular weight of 1,000 or less include polyoxypropylene glycol and polytetramethylene ether glycol. 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 mixtures of two or more thereof.

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

The active hydrogen component (b1) desirably contains a polymeric 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, and polyester diol.
The polymer diol (b11) is preferable because the hardness of the urethane resin is moderately soft and the strength of the coating is strong.
Further, the number average molecular weight of the polymer diol (b11) is more preferably 3,000 to 12,500, and even more 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.
Furthermore, the hydroxyl value can be measured according to the description in JIS K1557-1.

Further, it is preferable that the active hydrogen component (b1) contains a polymeric diol (b11) as an essential component, and the content of the polymeric diol (b11) is 20 to 80% by weight based on the weight of the urethane resin. The content of the polymeric diol (b11) is more preferably 30 to 70% by weight, and even more preferably 40 to 65% by weight.
It is preferable that the content of the polymeric diol (b11) is 20 to 80% by weight in terms of absorption of the electrolyte by the urethane resin.

Further, it is desirable that the active hydrogen component (b1) contains a polymeric diol (b11) having a number average molecular weight of 2,500 to 15,000 and a chain extender (b13) as essential components.
Examples of the chain extender (b13) include low-molecular diols having 2 to 10 carbon atoms [e.g., ethylene glycol, propylene glycol, 1,4-butanediol, diethylene glycol, 1,6-hexamethylene glycol, etc.]; diamines [carbon Aliphatic diamines having 2 to 6 carbon atoms (e.g. ethylene diamine, 1,2-propylene diamine, etc.), alicyclic diamines having 6 to 15 carbon atoms (e.g. isophorone diamine, 4,4'-diaminodicyclohexylmethane, etc.), 6 carbon atoms ~15 aromatic diamines (e.g., 4,4'-diaminodiphenylmethane, etc.); monoalkanolamines (e.g., monoethanolamine, etc.); hydrazine or derivatives thereof (e.g., adipic acid dihydrazide, etc.), and mixtures of two or more of these. can be mentioned. Among these, preferred are low molecular weight diols, and particularly preferred are ethylene glycol, diethylene glycol and 1,4-butanediol.
The combination of polymer diol (b11) and chain extender (b13) is a combination of PEG as polymer diol (b11) and ethylene glycol as chain extender (b13), or a combination of polymer diol (b11) as PEG and ethylene glycol as chain extender (b13). A combination of polycarbonate diol and ethylene glycol as chain extender (b13) is preferred.

As the isocyanate component (b2), those conventionally used in polyurethane production can be used. Such isocyanates include aromatic diisocyanates having 6 to 20 carbon atoms (excluding the carbon in the NCO group, the same applies hereinafter), aliphatic diisocyanates having 2 to 18 carbon atoms, alicyclic diisocyanates having 4 to 15 carbon atoms, Included are 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 thereof.

Specific examples of the aromatic diisocyanate include 1,3- or 1,4-phenylene diisocyanate, 2,4- or 2,6-tolylene diisocyanate, and 2,4'- or 4,4'-diphenylmethane diisocyanate (hereinafter referred to as , diphenylmethane diisocyanate is abbreviated as MDI), 4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocyanatobiphenyl, 3,3'-dimethyl-4,4'-diisocya Examples include natodiphenylmethane 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, 2,6-diisocyanatomethyl caproate, Bis(2-isocyanatoethyl) carbonate, 2-isocyanatoethyl-2,6-diisocyanatohexanoate, and the like.

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

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

Among these, aromatic diisocyanates and alicyclic diisocyanates are preferred, aromatic diisocyanates are more preferred, and MDI is particularly preferred.

When the urethane resin contains the polymeric diol (b11) and the isocyanate component (b2), the preferred equivalent ratio of (b2)/(b11) is 10 to 30/1, more preferably 11 to 28/1. If the ratio of the isocyanate component (b2) exceeds 30 equivalents, a hard coating will result.
The number average molecular weight of the urethane resin is preferably 40,000 to 500,000, more preferably 50,000 to 400,000. If the number average molecular weight of the urethane resin is less than 40,000, the strength of the coating will be low, and if it exceeds 500,000, the solution viscosity will be high and a uniform coating may not be obtained.

The number average molecular weight of the urethane resin is measured by gel permeation chromatography (hereinafter abbreviated as GPC) using DMF as a solvent and polyoxypropylene glycol as a standard substance. The sample concentration is 0.25% by weight, the column stationary phase is one each of TSKgel Super H2000, TSKgel Super H3000, and TSKgel Super H4000 (all manufactured by Tosoh Corporation) connected together, and the column temperature is 40°C.

The urethane resin can be produced by reacting the active hydrogen component (b1) and the isocyanate component (b2).
For example, a method in which 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 simultaneously reacted. Examples include the shot method and the prepolymer method in which the polymer diol (b11) and the isocyanate component (b2) are first reacted and then the chain extender (b13) is reacted.
In addition, urethane resins are manufactured in the presence of solvents that are inert to isocyanate groups, such as solvents [DMF, dimethylacetamide, etc.], sulfoxide-based solvents (dimethylsulfoxide, etc.), ketone-based 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. Among these, preferred are amide solvents, ketone solvents, aromatic solvents, and mixtures of two or more thereof.

The reaction temperature during the production of urethane resin is preferably 20 to 100°C when a solvent is used, and 20 to 220°C when no solvent is used.
The urethane resin can be manufactured using manufacturing equipment commonly employed in the industry. Moreover, when a solvent is not used, a manufacturing device such as a kneader or an extruder can be used. The solution viscosity of the urethane resin produced in this way, measured as a 30% by weight (solid content) DMF solution, is usually 10 to 10,000 poise/20°C, and practically preferred is 100 to 2,000 poise. /20℃.

(Meth)acrylic acid alkyl ester copolymer is an acrylic polymer that essentially has a constituent unit derived from (meth)acrylic acid alkyl ester monomer, and constitutes (meth)acrylic acid alkyl ester copolymer. The weight proportion of the (meth)acrylic acid alkyl ester monomer in the monomer is 50% by weight or more based on the total weight of the monomers.
The weight ratio (wt%) of the (meth)acrylic acid alkyl ester monomer is determined by dissolving the polymer in a supercritical fluid and analyzing the resulting oligomer component by gas chromatography-mass spectrometry (GC-MS). It can be measured by the following methods.
If the weight ratio of the (meth)acrylic acid alkyl ester monomer in the monomers constituting the (meth)acrylic acid alkyl ester copolymer is less than 50% by weight based on the total weight of the monomers, it is suitable. It does not have a strong adhesive force, and the stability of the electrode shape becomes low.

Examples of the (meth)acrylic acid alkyl ester monomers include 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, n-butyl acrylate, n-butyl methacrylate, iso-butyl methacrylate, methyl methacrylate, methyl acrylate, and alkyl chains. Examples include 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate containing a hydroxyl group at the terminal thereof.
Further, polyfunctional acrylates are also included in the above (meth)acrylic acid alkyl ester monomers. Examples of the polyfunctional acrylate include 1,6-hexanediol methacrylate and ethylene glycol dimethacrylate. From the viewpoint of stability of the electrode shape, the weight proportion of the polyfunctional acrylate is preferably 0.1 to 3% by weight based on the total weight of the monomers.

The (meth)acrylic acid alkyl ester copolymer contains two or more types of (meth)acrylic acid alkyl ester monomers as constituent monomers, and the total content thereof is 50% by weight based on the total weight of the constituent monomers. % or more. Preferred combinations of the above (meth)acrylic acid alkyl ester monomers include a combination of n-butyl acrylate, 2-hydroxyethyl acrylate and acrylonitrile, a combination of 2-ethylhexyl methacrylate and 2-ethylhexyl acrylate, and a combination of n-butyl acrylate and 2-ethylhexyl acrylate. Examples include a combination of ethylhexyl acrylate, a combination of methyl acrylate and n-butyl acrylate, or a combination of methyl methacrylate and iso-butyl methacrylate.

The (meth)acrylic acid alkyl ester copolymer preferably contains (meth)acrylic acid monomer as a constituent monomer as a monomer other than the above-mentioned (meth)acrylic acid alkyl ester monomer. When (meth)acrylic acid monomer is included as a constituent monomer, it is possible to neutralize by-products such as lithium hydroxide generated within the battery and prevent corrosion of the electrodes.
The weight proportion of the (meth)acrylic acid monomer is preferably 0.1 to 15% by weight based on the total weight of the constituent monomers.

The (meth)acrylic acid alkyl ester copolymer can be produced in the same manner as for the above-mentioned polymer compound (P1).

As the styrene-butadiene rubber, for example, those commercially available for use as a battery binder can be used. Commercial products of styrene-butadiene rubber include, for example, product names: TRD104A (manufactured by JSR Corporation), BM-400B (manufactured by Nippon Zeon Corporation), and the like.
The amount of bound styrene in the styrene-butadiene rubber is not particularly limited, but from the viewpoint of improving the strength of the electrode, it is, for example, 10 to 60% by mass, preferably 15 to 55% by mass.
Note that the amount of bound styrene can be measured by ¹ H-NMR.

The weight proportion of the polymer compound (P2) in the coated negative electrode active material particles for lithium ion batteries is preferably 0.3 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. When the weight ratio of the polymer compound (P2) is within the above range, the strength of the electrode can be improved. The weight proportion of the polymer compound (P2) is more preferably 0.5 to 9.0% by weight, and still more preferably 3.0 to 6.0% by weight.

The conductive aid (C2) is not particularly limited, and those exemplified as the conductive aid (C1) can be used. The conductive aid (C2) may be used alone or in combination of two or more.

The ratio of the polymer compound (P2) and the conductive agent (C2) constituting the second coating layer is not particularly limited, but from the viewpoint of internal resistance of the battery, etc., the proportion of the polymer compound (P2) constituting the second coating layer is The ratio of molecular compound (P2) (resin solid content weight) to conductive aid (C2) is preferably 1:0.01 to 1:50, more preferably 1:0.1 to 1:3.0. preferable.

The second coating layer may further contain ceramic particles in addition to the polymer compound (P2) and the conductive aid (C2). Examples of the ceramic particles include the same ceramic particles that are optionally used in the first coating layer.

In the coated negative electrode active material particles for lithium ion batteries of the present invention, the weight proportion of the polymer compound (P1) is 0.7 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. , and the weight proportion of the polymer compound (P2) is preferably 0.3 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. When the weight ratio of the polymer compound (P1) and the polymer compound (P2) is within the above range, the strength of the obtained electrode is high and the rate of increase in internal resistance can be suppressed.

At least a portion of the surface of the negative electrode active material particles is coated with a first coating layer.
From the viewpoint of cycle characteristics, the negative electrode active material particles preferably have a first coating layer coverage of 30 to 95%, which is obtained by the following calculation formula.
Coverage rate (%) = {1 - [BET specific surface area of negative electrode active material particles coated with the first coating layer / (BET specific surface area of negative electrode active material particles when not coated x negative electrode coated with the first coating layer) Weight ratio of the negative electrode active material particles contained in the active material particles + BET specific surface area of the conductive agent (C1) x weight of the conductive agent (C1) contained in the negative electrode active material particles coated with the first coating layer ratio + BET specific surface area of optionally included ceramic particles × weight ratio of ceramic particles optionally included in the negative electrode active material particles coated with the first coating layer)]}×100

In the coated negative electrode active material particles of the present invention, at least a portion of the surface of the first coating layer is coated with the second coating layer.
In the coated negative electrode active material particles of the present invention, from the viewpoint of electrode strength, the coverage ratio of the second coating layer to the first coating layer is preferably 30 to 95%. The coverage of the second coating layer can be obtained by calculation from the BET specific surface area of the sample coated with the first coating layer and the BET specific surface area of the second coating layer.
Coverage rate (%) = {1 - [BET specific surface area of negative electrode active material particles covered with second coating layer / (BET specific surface area of negative electrode active material particles covered with first coating layer x second coating layer) Weight proportion of the negative electrode active material particles contained in the coated negative electrode active material particles + BET specific surface area of the conductive aid (C1) × conductive aid contained in the negative electrode active material particles coated with the second coating layer ( Weight ratio of C1) + BET specific surface area of optionally included ceramic particles x weight ratio of ceramic particles optionally included in the negative electrode active material particles coated with the second coating layer)}×100

The coated negative electrode active material particles of the present invention may have a portion on the surface of the negative electrode active material particle where the first coating layer is not formed, and a portion where the surface of the negative electrode active material particle is coated with the second coating layer. You can.

The method for producing the coated negative electrode active material particles of the present invention is not particularly limited, but for example, the negative electrode active material particles, the polymer compound (P1), the conductive agent (C1), and optionally used ceramic particles are mixed and then the coated negative electrode active material particles are mixed. A step of forming a first coating layer, and a second coating by mixing the negative electrode active material particles on which the first coating layer has been formed, a polymer compound (P2), a conductive agent (C2), and optionally used ceramic particles. It is preferable to include a step of forming a layer.

In each step, the order in which negative electrode active material particles, polymer compounds (P1), (P2), conductive aids (C1), (C2), and optionally used ceramic particles are mixed is not particularly limited. A resin composition consisting of a polymer compound, a conductive agent, and ceramic particles mixed in the above may be further mixed with negative electrode active material particles, or a resin composition consisting of a polymer compound, a conductive agent, and ceramic particles mixed with negative electrode active material particles, a polymer compound, a conductive agent, and ceramic particles may be further mixed with They may be mixed at the same time, or the polymer compound may be mixed with the negative electrode active material particles, and then the conductive additive and ceramic particles may be mixed.

In the step of forming the first coating layer and the step of forming the second coating layer, the polymer compound (P1) and the polymer compound (P2) are each dissolved in an organic solvent and added in the form of a resin solution. Examples include a method in which the resin solution is added by a spray method, a method in which the polymer compound (P1) and the polymer compound (P2) are used in powder form, and the like.
The organic solvent is not particularly limited as long as it can dissolve the polymer compound (P1) and the polymer compound (P2), and any known organic solvent can be appropriately selected and used.
When adding the resin solution by a spray method, a spray system using a nozzle of WA-101-102P (manufactured by Anest Iwata Co., Ltd.) can be used, for example.
When the polymer compound (P1) and the polymer compound (P2) are used in powder form, the particle size of the powder is not particularly limited. The particle size of the powder may be changed depending on the desired thickness of the coating layer.

In the step of forming the first coating layer and the step of forming the second coating layer, the methods of adding the polymer compound (P1) and the polymer compound (P2) may be the same or different. Good too. Specifically, the following combinations (i) to (iv) may be mentioned.
(i) Put the negative electrode active material particles and the polymer compound (P1) solution into a mixer, mix them, remove the solvent, and then mix the conductive aid (C1) to form a first coating layer, and further conductive Method of adding the auxiliary agent (C2), adding the polymer compound (P2) solution, mixing, and removing the solvent. (ii) Putting the negative electrode active material particles and the powdered polymer compound (P1) in a mixer and heating and mixing. After that, a conductive additive (C1) is mixed to form a first coating layer, and a conductive additive (C2) is further added, a polymer compound (P2) solution is added and mixed, and the solvent is removed ( iii) After putting the negative electrode active material particles and the polymer compound (P1) solution into a mixer and mixing them and removing the solvent, the conductive additive (C1) is mixed to form a first coating layer, and then the conductive additive (C1) is mixed. (iv) Put the negative electrode active material particles and the powdered polymer compound (P1) into a mixer. After heating and mixing, the conductive additive (C1) is mixed to form a first coating layer, and the conductive additive (C2) is further added, and the polymer compound (P2) solution is added by a spray method and mixed. How to remove solvent

For example, when the polymer compound (P1) and the polymer compound (P2) are dissolved in an organic solvent and added as a resin solution, the negative electrode active material particles are placed in a universal mixer and stirred at 30 to 500 rpm. , the resin solution containing the polymer compound (P1) constituting the first coating layer was mixed dropwise over 1 to 90 minutes, the conductive agent (C1) and optionally used ceramic particles were mixed, and the mixture was stirred for 50 minutes. By raising the temperature to ~200°C, reducing the pressure to 0.007~0.04 MPa, and holding it for 10~150 minutes to remove the solvent, at least a part of the surface of the negative electrode active material particles is covered with the first coating layer. particles can be obtained. By forming the second coating layer using the same procedure as described above, coated negative electrode active material particles in which the second coating layer is provided on the first coating layer can be obtained.

In the case of a spray method, the above resin solution can be added using a spray system using a nozzle of WA-101-102P (manufactured by Anest Iwata Co., Ltd.). An example of a method for adding a resin solution by spraying is a method in which a resin solution with a solid content concentration of about 10% is heated to 40° C. and the above-mentioned spray system is used. When the viscosity of the resin solution is high, it is preferable to use it at a diluted concentration.
When using powdered polymeric compounds (P1) and (P2), for example, the solid polymeric compounds (P1) and (P2) are crushed in a mortar (manufactured by Osaka Chemical Co., Ltd., a crusher such as Force Mill can also be used). The powdered polymer compounds (P1) and (P2) can be added by crushing and passing through a 200 mesh (opening 75 μm).

[Negative electrode for lithium ion batteries]
The negative electrode for lithium ion batteries of the present invention (hereinafter also simply referred to as "negative electrode") is characterized by being composed of a non-binding body containing coated negative electrode active material particles for lithium ion batteries of the present invention and a conductive filler. .

Here, a non-bound body means that the coated negative electrode active material particles for lithium ion battery and the conductive filler are not fixed in position by a binder (also referred to as a binder). That is, the coated negative electrode active material particles for a lithium ion battery and the conductive filler are in a state where they can each move in response to an external force.

When the negative electrode is made of a non-binder, the coated negative electrode active material particles and the conductive filler are not irreversibly fixed by the binder. Irreversible fixation means that the coated negative electrode active material particles and the conductive filler are adhesively fixed using the following known solvent drying binder for lithium ion batteries, and the coated negative electrode that has been adhesively fixed is In order to separate the active material particles and the conductive filler, it is necessary to mechanically destroy the interface between the coated negative electrode active material particles and the conductive filler. On the other hand, in the case of a non-binding body, the coated negative electrode active material particles and the conductive filler are not irreversibly adhesively fixed, so the interface between the coated negative electrode active material particles and the conductive filler is not mechanically destroyed. Can be separated.

The negative electrode of the present invention preferably does not contain a solvent-drying binder.
Examples of the solvent-drying binder include known binders for lithium ion batteries such as starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. These binders are used by being dissolved or dispersed in a solvent, and by volatilizing or distilling off the solvent, the surface becomes solid without exhibiting stickiness, and the coated negative electrode active material particles and the conductive filler are bonded to each other, and This is to firmly fix the coated negative electrode active material particles, the conductive filler, and the current collector.

The negative electrode of the present invention preferably includes a negative electrode active material layer containing coated negative electrode active material particles, a conductive filler, and an electrolytic solution containing an electrolyte and a solvent.

As the electrolyte, electrolytes used in known electrolytes can be used, such as lithium salts of inorganic anions such as LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ and LiN(FSO ₂ ) ₂ , LiN Examples include lithium salts of organic anions such as (CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ and LiC(CF ₃ SO ₂ ) ₃ . Among these, LiN(FSO ₂ ) ₂ is preferred from the viewpoint of battery output and charge/discharge cycle characteristics.

As the solvent, nonaqueous solvents used in known electrolyte solutions can be used, such as lactone compounds, cyclic or chain carbonates, chain carboxylic esters, cyclic or chain ethers, phosphate esters, and nitrile compounds. , amide compounds, sulfones, sulfolanes and mixtures thereof can be used.

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

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

Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, and methyl propionate.

Examples of the cyclic ether include tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, and 1,4-dioxane. Examples of 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, 2-ethoxy-1,3,2-dioxaphosphoran-2-one, 2-trifluoroethoxy-1,3,2-dioxaphosphoran-2-one and 2 -methoxyethoxy-1,3,2-dioxaphosphorane-2-one and the like.

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 dimethylsulfone and diethylsulfone.

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

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

The negative electrode of the present invention contains a conductive filler in addition to the conductive additive (C1) and the conductive additive (C2) contained in the first coating layer and the second coating layer of the coated negative electrode active material particles described above. There is. The conductive additive (C1) and conductive additive (C2) contained in the first coating layer and the second coating layer are integrated with the coated negative electrode active material particles, whereas the conductive filler is integrated with the coated negative electrode active material particles. They can be distinguished by being included separately.
The conductive filler may be the same as or different from the conductive additive (C1) contained in the first coating layer and the conductive additive (C2) contained in the second coating layer.
As the conductive filler that may be included in the negative electrode of the present invention, the same one as exemplified as the conductive aid (C1) can be used.

When the negative electrode active material layer contains a conductive filler, the conductive filler contained in the negative electrode, the conductive agent (C1) contained in the first coating layer, and the conductive agent (C2) contained in the second coating layer. Although the total content of is not particularly limited, it is preferably 0.5 to 20% by weight based on the weight of the negative electrode active material layer excluding the electrolyte.

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

The negative electrode of the present invention can be produced, for example, by applying a negative electrode slurry containing coated negative electrode active material particles, a conductive filler, and an electrolytic solution to a current collector, and then drying the slurry. Specifically, after applying the negative electrode slurry onto the current collector using a coating device such as a bar coater, the solvent is removed by placing a nonwoven fabric on the active material and absorbing the liquid, and then pressing if necessary. Examples include a method of pressing with a machine.

In the negative electrode of the present invention, materials constituting the current collector include metal materials such as copper, aluminum, titanium, stainless steel, nickel, and alloys thereof, as well as calcined carbon, conductive polymer materials, conductive glass, etc. can be mentioned.
The shape of the current collector is not particularly limited, and may be a sheet-like current collector made of the above-mentioned material or a deposited layer made of fine particles made of the above-mentioned material.
The thickness of the current collector is not particularly limited, but is preferably 50 to 500 μm.

As described above, the negative electrode of the present invention preferably further includes a current collector, and the negative electrode active material layer is provided on the surface of the current collector. For example, the negative electrode of the present invention preferably includes a resin current collector made of a conductive polymer material, and the negative electrode active material layer is provided on the surface of the resin current collector.

As the conductive polymer material constituting the resin current collector, for example, a resin containing a conductive agent can be used.
As the conductive agent constituting the conductive polymer material, the same conductive agent (C1) of the first coating layer can be suitably used.
Examples of resins constituting the conductive polymer material include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polycycloolefin (PCO), polyethylene terephthalate (PET), polyethernitrile (PEN), and polyethylene terephthalate (PET). Tetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), epoxy resin, silicone resin, or these Examples include mixtures.
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 a known method described in JP-A No. 2012-150905, Re-Table No. 2015/005116, and the like.

[Lithium ion battery]
The lithium ion battery of the present invention is characterized by comprising the negative electrode for lithium ion batteries of the present invention.

The lithium ion battery of the present invention is obtained by combining an electrode serving as a counter electrode, housing the cell container together with a separator in a cell container, injecting an electrolytic solution, and sealing the cell container.
In addition, a positive electrode is formed on one side of the current collector and a negative electrode is formed on the other side to create a bipolar (bipolar) type electrode, and the bipolar (bipolar) type electrode is laminated with a separator to form a cell container. It can also be obtained by storing the cell, injecting electrolyte, and sealing the cell container.
By using the negative electrode of the present invention, the lithium ion battery of the present invention can be obtained.

Note that the following inventions are described in this specification.
[11] Lithium obtained by coating at least a part of the surface of negative electrode active material particles for lithium ion batteries with a first coating layer, and at least a part of the surface of the first coating layer by coating with a second coating layer. Coated negative electrode active material particles for ion batteries, wherein the first coating layer comprises an ester compound (a11) of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid, and an anionic monomer. The polymer compound (P1) is a polymer of a monomer composition containing (a12) and a conductive additive (C1), and the polymer compound (P1) has a glass transition temperature of more than 20°C. , the second coating layer is a coated negative electrode active material particle for a lithium ion battery containing a polymer compound (P2) having a glass transition temperature of 20° C. or lower and a conductive additive (C2).
[12] The weight proportion of the polymer compound (P1) in the coated negative electrode active material particles for lithium ion batteries is 0.7 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. and the weight proportion of the polymer compound (P2) in the coated negative electrode active material particles for lithium ion batteries is 0.3 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. The coated negative electrode active material particles for lithium ion batteries according to [11] above.
[13] [11] or [12] above, wherein the polymer compound (P2) is at least one selected from the group consisting of urethane resin, (meth)acrylic acid alkyl ester copolymer, and styrene-butadiene rubber. The coated negative electrode active material particles for lithium ion batteries as described in .
[14] A negative electrode for a lithium ion battery comprising a non-binding body comprising the coated negative electrode active material particles for a lithium ion battery according to any one of [11] to [13] above and a conductive filler.
[15] A lithium ion battery comprising the negative electrode for a lithium ion battery according to [14] above.
[Example]

EXAMPLES Next, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the examples unless it departs from the gist of the present invention. In addition, unless otherwise specified, "part" means "part by weight" and "%" means percent by weight.
<Tg measurement method>
The measurement was performed using DSC20 and SSC/580 manufactured by Seiko Electronics Co., Ltd. according to the method specified in ASTM D3418-82 (DSC method).

[Preparation of polymer compound (P1) used for first coating layer]
150 parts of DMF was charged into a four-necked flask equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen gas introduction tube, and the temperature was raised to 75°C. Next, a monomer composition containing 91 parts of acrylic acid, 9 parts of methyl methacrylate, and 50 parts of DMF, and 0.3 part of 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'- An initiator solution prepared by dissolving 0.8 parts of azobis(2-methylbutyronitrile) in 30 parts of DMF was continuously added dropwise into a four-necked flask using a dropping funnel over 2 hours under stirring while blowing nitrogen. Radical polymerization was performed. After the dropwise addition was completed, the reaction was continued at 75°C for 3 hours.
Next, the temperature was raised to 80°C and the reaction was continued for 3 hours to obtain a copolymer solution with a resin concentration of 30%.
The obtained copolymer solution was transferred to a Teflon (registered trademark) vat and dried under reduced pressure at 150° C. and 0.01 MPa for 3 hours, and DMF was distilled off to obtain a copolymer. This copolymer was roughly pulverized with a hammer, and then further pulverized in a mortar to obtain a powdery polymer compound (P1). The Tg of the obtained polymer compound (P1) was measured and found to be 105°C.

[Polymer compound (P2-1) used for second coating layer]
As the polymer compound (P2-1) used for the second coating layer, a urethane emulsion (product name: Ucoat, manufactured by Sanyo Chemical Industries, Ltd., Tg: -70°C) was used.

[Preparation of polymer compound (P2-2) used for second coating layer]
In a four-necked colben equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen gas introduction tube, 30 parts of 2-ethylhexyl acrylate, 60 parts of 2-ethylhexyl methacrylate, 5 parts of acrylic acid, and 4.0 parts of n-butyl methacrylate were added. 5 parts of 1,6-hexanediol dimethacrylate, 0.5 parts of toluene, and 390 parts of toluene were charged and the temperature was raised to 75°C. 10 parts of toluene, 0.200 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) and 0.200 parts of 2,2'-azobis(2-methylbutyronitrile) were mixed. Radical polymerization was carried out by continuously dropping the polymerization initiator mixture into the obtained monomer mixture using a dropping funnel over a period of 4 hours while blowing nitrogen into a Kolben. After dropping, a solution of 0.800 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) dissolved in 12.4 parts of toluene was added using a dropping funnel for 6 to 8 hours after starting polymerization. I added it continuously. Further, polymerization was continued for 2 hours, and 488 parts of toluene was added to obtain a polymer compound (P2-2) solution with a resin concentration of 10% by weight. The molecular weight of the obtained polymer compound (P2-2) was measured by GPC, and the Mw was 510,000. The Tg of the obtained polymer compound (P2-2) was measured and found to be -21°C.

[Polymer compound used for second coating layer (P2-3)]
As the polymer compound (P2-3) used for the second coating layer, styrene-butadiene rubber (product name: TRD104A, manufactured by JSR Corporation, Tg: 7° C.) was used.

[Preparation of polymer compound (P2-4) used for second coating layer]
Into a four-necked colben equipped with a stirrer, a thermometer, a reflux condenser, a dropping funnel, and a nitrogen gas introduction tube, 30 parts of n-butyl acrylate, 20 parts of 2-hydroxyethyl acrylate, 50 parts of acrylonitrile, and 390 parts of toluene were charged. The temperature was raised to ℃. 10 parts of toluene, 0.200 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) and 0.200 parts of 2,2'-azobis(2-methylbutyronitrile) were mixed. While blowing nitrogen into the resulting monomer mixture, a polymerization initiator was continuously added dropwise using a dropping funnel over a period of 4 hours to carry out radical polymerization. After dropping, a solution of 0.800 parts of 2,2'-azobis(2,4-dimethylvaleronitrile) dissolved in 12.4 parts of toluene was added using a dropping funnel for 6 to 8 hours after starting polymerization. I added it continuously. Furthermore, polymerization was continued for 2 hours, and 488 parts of toluene was added to obtain a polymer compound (P2-4) solution with a resin concentration of 10% by weight. The molecular weight of the obtained polymer compound (P2-4) was measured by GPC, and the Mw was 460,000. The Tg of the obtained polymer compound (P2-4) was measured and found to be 16°C.

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

Example 301 [Preparation of coated negative electrode active material particles 1]
(Formation of first coating layer)
1 part of polymer compound (P1) was dissolved in 3 parts of DMF to obtain a polymer compound (P1) solution.
77.3 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, a polymer compound was added. 21.2 parts of the (P1) solution (5.3 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, while stirring, 5.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive additive (C1), was added in portions over 2 minutes, and stirring was continued for 30 minutes. did.

(Formation of second coating layer)
Further, while stirring, 23.6 parts (5.9 parts in terms of solid content) of the polymer compound (P2-1) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, in a stirred state, 4.0 parts of acetylene black (AB) (manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm), which is a conductive aid (C2), was added in portions for 2 minutes. and continued stirring for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 1 having the composition shown in Table 5.

Example 302 [Preparation of coated negative electrode active material particles 2]
Table 5 shows the results in the same manner as in Example 301 except that 59.0 parts (5.9 parts in terms of solid content) of the polymer compound (P2-2) solution was used instead of the polymer compound (P2-1). Coated negative electrode active material particles 2 having the composition shown were obtained.

Example 303 [Preparation of coated negative electrode active material particles 3]
Instead of the polymer compound (P2-1), 23.6 parts of an aqueous solution of the polymer compound (P2-3) diluted with ultrapure water to a resin concentration of 25% by weight (5.9 parts in terms of solid content) Coated negative electrode active material particles 3 having the compositions shown in Table 5 were obtained in the same manner as in Example 301 except that .

Example 304 [Preparation of coated negative electrode active material particles 4]
Table 5 was carried out in the same manner as in Example 301, except that 59.0 parts of polymer compound (P2-4) solution (5.9 parts in terms of solid content) was used instead of polymer compound (P2-1) solution. Coated negative electrode active material particles 4 having the composition shown below were obtained.

Example 305 [Preparation of coated negative electrode active material particles 5]
(Creation of powdered polymer compound P1)
The polymer compound P1 solution was placed in a vacuum dryer at 140°C, and the solvent was completely volatilized to obtain a P1 solid. The obtained P1 solid was crushed in a mortar (manufactured by Osaka Chemical Co., Ltd.) and passed through a 200 mesh (opening 75 μm) to create a powdery polymer compound P1.
(Formation of first coating layer)
77.3 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a multipurpose mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, powdered 5.3 parts of the polymer compound (P1) was added, heated to 140°C, and further stirred for 60 minutes. Next, while stirring, 5.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive additive (C1), was added in portions over 2 minutes, and stirring was continued for 30 minutes. did.

(Formation of second coating layer)
Further, while stirring, 59.0 parts of the polymer compound (P2-2) solution (5.9 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, in a stirred state, 4.0 parts of acetylene black (AB) (manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm), which is a conductive aid (C2), was added in portions for 2 minutes. and continued stirring for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 5 having the composition shown in Table 5.

Example 306 [Preparation of coated negative electrode active material particles 6]
(Formation of first coating layer)
1 part of polymer compound (P1) was dissolved in 3 parts of DMF to obtain a polymer compound (P1) solution.
77.3 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, a polymer compound was added. 21.2 parts (5.3 parts in terms of solid content) of the (P1) solution was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, while stirring, 5.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive additive (C1), was added in portions over 2 minutes, and stirring was continued for 30 minutes. did.

(Formation of second coating layer)
Furthermore, in a stirred state, 59.0 parts of the polymer compound (P2-2) solution at 40°C (5.9 parts in terms of solid content) was sprayed with a spray system using a WA-101-102P (manufactured by Anest Iwata) nozzle. ) was added by spraying over 2 minutes (spray amount: 100 ml/min), and the mixture was further stirred for 5 minutes. Next, in a stirred state, 4.0 parts of acetylene black (AB) (manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm), which is a conductive aid (C2), was added in portions for 2 minutes. and continued stirring for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 6 having the composition shown in Table 5.

Example 307 [Preparation of coated negative electrode active material particles 7]
(Formation of first coating layer)
77.3 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a multipurpose mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, powdered 5.3 parts of the polymer compound (P1) was added, heated to 140°C, and further stirred for 60 minutes. Next, while stirring, 5.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], which is a conductive additive (C1), was added in portions over 2 minutes, and stirring was continued for 30 minutes. did.

(Formation of second coating layer)
Furthermore, in a stirred state, 59.0 parts of the polymer compound (P2-2) solution (5.9 parts in terms of solid content) at 40°C was sprayed with a spray system using a WA-101-102P (manufactured by Anest Iwata) nozzle. ) was added by spraying over 2 minutes (spray amount: 100 ml/min), and the mixture was further stirred for 5 minutes. Next, in a stirred state, 4.0 parts of acetylene black (AB) (manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm), which is a conductive aid (C2), was added in portions for 2 minutes. and continued stirring for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 7 having the composition shown in Table 5.

Example 308 [Preparation of coated negative electrode active material particles 8]
80.9 parts of negative electrode active material particles, 4.0 parts of polymer compound (P1) solution (1.0 parts in terms of solid content), 5.5 parts of conductive aid (C1), and polymer compound (P2). -2) The composition shown in Table 5 was prepared in the same manner as in Example 302, except that the solution was changed to 62.0 parts (6.2 parts in terms of solid content) and the conductive aid (C2) was changed to 4.2 parts. Coated negative electrode active material particles 8 were obtained.

Example 309 [Preparation of coated negative electrode active material particles 9]
74.5 parts of negative electrode active material particles, 34.8 parts of polymer compound (P1) solution (8.7 parts in terms of solid content), 5.1 parts of conductive aid (C1), and polymer compound (P2). -2) The composition shown in Table 5 was prepared in the same manner as in Example 302, except that the solution was changed to 57.0 parts (5.7 parts in terms of solid content) and the conductive aid (C2) was changed to 3.9 parts. Coated negative electrode active material particles 9 were obtained.

Example 310 [Preparation of coated negative electrode active material particles 10]
81.8 parts of negative electrode active material particles, 22.4 parts of polymer compound (P1) solution (5.6 parts in terms of solid content), 5.6 parts of conductive aid (C1), and polymer compound (P2). -2) The composition shown in Table 5 was prepared in the same manner as in Example 302, except that the solution was changed to 5.0 parts (0.5 parts in terms of solid content) and the conductive aid (C2) was changed to 4.2 parts. Coated negative electrode active material particles 10 were obtained.

Example 311 [Preparation of coated negative electrode active material particles 11]
79.7 parts of negative electrode active material particles, 22.0 parts of polymer compound (P1) solution (5.5 parts in terms of solid content), 5.5 parts of conductive aid (C1), and polymer compound (P2). -2) The composition shown in Table 5 was prepared in the same manner as in Example 302, except that the solution was changed to 31.0 parts (3.1 parts in terms of solid content) and the conductive aid (C2) was changed to 4.1 parts. Coated negative electrode active material particles 11 were obtained.

Example 312 [Preparation of coated negative electrode active material particles 12]
74.9 parts of negative electrode active material particles, 20.4 parts of polymer compound (P1) solution (5.1 parts in terms of solid content), 5.1 parts of conductive aid (C1), and polymer compound (P2). -2) The composition shown in Table 5 was prepared in the same manner as in Example 302, except that the solution was changed to 87.0 parts (8.7 parts in terms of solid content) and the conductive aid (C2) was changed to 3.9 parts. Coated negative electrode active material particles 12 were obtained.

Comparative Example 301 [Preparation of coated negative electrode active material particles 13]
1 part of polymer compound (P1) was dissolved in 3 parts of DMF to obtain a polymer compound (P1) solution.
86.0 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, a polymer compound was added. 23.6 parts of the (P1) solution (5.9 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, while stirring, 5.9 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm] was added in portions over 2 minutes, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 13 having the composition shown in Table 6.

Comparative Example 302 [Preparation of coated negative electrode active material particles 14]
86.7 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, a polymer compound was added. 66.0 parts of the (P2-2) solution (6.6 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes. Next, 4.5 parts of acetylene black (AB) [manufactured by Denka Co., Ltd., trade name "Denka Black", volume average particle diameter 35 nm] was added in portions over 2 minutes, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 14 having the composition shown in Table 6.

Comparative Example 303 [Preparation of coated negative electrode active material particles 15]
1 part of polymer compound (P1) was dissolved in 3 parts of DMF to obtain a polymer compound (P1) solution.
77.3 parts of negative electrode active material particles (hard carbon powder, volume average particle diameter 25 μm) were placed in a universal mixer, High Speed Mixer FS25 [manufactured by Earth Technica Co., Ltd.], and while stirring at room temperature and 720 rpm, a polymer compound was added. (P1) solution 23.6 parts (5.9 parts in terms of solid content) and polymer compound (P2-2) solution 59.0 parts (5.9 parts in terms of solid content) were added simultaneously for 2 minutes. It was added dropwise and further stirred for 5 minutes. Next, in a stirred state, 5.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm] and acetylene black (AB) [manufactured by Denka Co., Ltd., trade name "Denka Black", volume 4.0 parts (average particle diameter: 35 nm) were added in portions over 2 minutes, and stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated negative electrode active material particles 15 having the composition shown in Table 6.

[Preparation of resin current collector]
In a twin-screw extruder, 70 parts of polypropylene [trade name: "Sun Allomer PL500A", manufactured by Sun Allomer Co., Ltd.], 25 parts of carbon nanotubes [trade name: "FloTube9000", manufactured by CNano], and a dispersant [trade name: "Umex 1001"] were added. '', manufactured by Sanyo Chemical Industries, Ltd.] were melt-kneaded at 200° C. and 200 rpm to obtain a resin mixture.
The obtained resin mixture was passed through a T-die extrusion film forming machine and stretched and rolled to obtain a conductive film for a resin current collector having a film thickness of 100 μm. Next, the obtained conductive film for a resin current collector was cut into a size of 17.0 cm x 17.0 cm, nickel vapor deposition was performed on one side, and a terminal (5 mm x 3 cm) for current extraction was connected. A resin current collector was obtained.

[Preparation of negative electrodes 1 to 15 for lithium ion batteries]
97.8 parts each of the prepared coated negative electrode active material particles 1 to 15, 1.3 parts of graphite (UP) [flake graphite, volume average particle diameter 4.5 μm], and carbon fiber [Donna Carbo manufactured by Osaka Gas Chemicals Co., Ltd.] Milled S-243: average fiber length 500 μm, average fiber diameter 13 μm, electrical conductivity 200 mS/cm] was mixed with 0.9 part to prepare a negative electrode precursor.
The prepared negative electrode precursor was filled into a Φ16 mold so that the basis weight of the negative electrode active material was 23.4 mg/cm ² , and then pressed to a pressure of 1 ton/cm using a press machine (HANDTAB-100T15, manufactured by Ichihashi Seiki Co., Ltd.). A negative electrode active material layer (thickness: 300 μm) was formed by compression molding at a pressure of ² , and was laminated on one side of the resin current collector to produce a negative electrode for a lithium ion battery (circular with a diameter of 16 mm).

(electrode strength)
The strengths of the lithium ion battery negative electrodes 1 to 15 obtained above were measured as follows.
The yield stress of the obtained lithium ion battery negative electrodes 1 to 15 (sample size: circular with a diameter of 16 mm) was measured using Autograph [manufactured by Shimadzu Corporation] in accordance with ISO178 (Plastic - How to determine bending properties). The electrode strength was evaluated using the following criteria.
First, each sample of negative electrode for lithium ion batteries was set in a jig with a distance between supporting points of 5 mm, and a load cell (rated load: 20 N) set in an autograph was lowered toward the electrode at a speed of 1 mm/min until it yielded. The yield stress at the point was calculated. The results are shown in Table 7.

[Measurement of internal resistance increase rate]
Negative electrodes 1 to 15 for lithium ion batteries were evaluated by the following method at 25° C. using a charge/discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.].
After charging to 4.2V using a constant current/constant voltage method (0.1C), after a 10 minute break, the battery was discharged to 2.5V using a constant current method (0.1C). The voltage and current after 0 seconds of discharge at 0.1C and the voltage and current after 10 seconds of discharge at 0.1C were measured using the constant current constant voltage method (also referred to as CCCV mode), and the internal resistance was calculated using the following formula. . It means that the smaller the internal resistance, the better the battery characteristics.
Note that the voltage after 0 seconds of discharge is the voltage measured at the same time as discharge (also referred to as voltage during discharge).
[Internal resistance (Ω cm ² )] = [(Voltage after 0 seconds of discharge at 0.1C) - (Voltage after 10 seconds of discharge at 0.1C)] ÷ [(Voltage after 0 seconds of discharge at 0.1C) Current) - (Current after 10 seconds of discharge at 0.1C)] x [Opposing area of electrodes (cm ² )] To measure the internal resistance, a 20-cycle repeated test was carried out, and the internal resistance (initial internal The "internal resistance increase rate (%)" was determined by comparing the internal resistance at the 20th cycle (internal resistance at the 20th cycle/internal resistance at the 2nd cycle). The results are shown in Table 7.

[Preparation of coated positive electrode active material particles]
1 part of polymer compound (P1) was dissolved in 3 parts of DMF to obtain a polymer compound (P1) solution.
90.12 parts of positive electrode active material particles (LiNi _0.8 Co _0.15 Al _0.05 O ₂ powder, volume average particle diameter 4 μm) were placed in a universal mixer high speed mixer FS25 [manufactured by Earth Technica Co., Ltd.]. While stirring at room temperature and 720 rpm, 12.56 parts of polymer compound (P1) solution (3.14 parts in terms of solid content) was added dropwise over 2 minutes, and the mixture was further stirred for 5 minutes.
Next, while stirring, 3.14 parts of acetylene black (Denka Black (registered trademark) manufactured by Denka Co., Ltd.), which is a conductive additive, and 2.10 parts of ceramic particles (SiO ₂ ) were added in portions for 2 minutes. , stirring was continued for 30 minutes.
Thereafter, the pressure was reduced to 0.01 MPa while maintaining stirring, and then the temperature was raised to 140°C while maintaining stirring and the degree of vacuum, and the stirring, degree of vacuum, and temperature were maintained for 8 hours to distill off volatile components. .
The obtained powder was classified using a sieve with an opening of 200 μm to obtain coated positive electrode active material particles.

[Preparation of positive electrode for lithium ion battery]
98.5 parts of the prepared coated positive electrode active material particles and carbon fiber [Dona Carbo Milled S-243 manufactured by Osaka Gas Chemical Co., Ltd.: average fiber length 500 μm, average fiber diameter 13 μm: electrical conductivity 200 mS/cm] 1.0 and 0.5 part of Ketjen Black [EC300J manufactured by Lion Specialty Chemicals Co., Ltd.] to prepare a positive electrode precursor.
The prepared positive electrode precursor was filled into a mold of Φ15 so that the basis weight of the positive electrode active material was 50 mg/cm ² , and then pressed with a press machine (HANDTAB-100T15, manufactured by Ichihashi Seiki Co., Ltd.) at 1 ton/cm ² . A positive electrode active material layer (thickness: 213 μm) was formed by compression molding under pressure, and was laminated on one side of the resin current collector to produce a positive electrode for a lithium ion battery (circular shape with a diameter of 15 mm).

[Fabrication of lithium ion battery]
A separator was combined with any of the positive electrode for lithium ion battery and negative electrode for lithium ion battery 1 to 15 produced above, and an electrolytic solution was added and sealed to produce lithium ion batteries 1 to 15. The electrolytic solution was added so as to account for 160% of the total void volume of each of the positive electrode, negative electrode, and separator. As the separator, Celgard #3501 was used. The capacity retention rates of the obtained lithium ion batteries 1 to 15 were measured. The results are shown in Table 8.

[Measurement of capacity retention rate]
A charge/discharge test was conducted on lithium ion batteries 1 to 15 at 25° C. using a charge/discharge measuring device "HJ-SD8" [manufactured by Hokuto Denko Co., Ltd.] according to the following method.
After charging to 4.2V using a constant current/constant voltage method (0.1C), after a 10 minute rest, the battery was discharged to 2.5V using a constant current method (0.1C).
The discharged capacity at this time was defined as [discharge capacity (mAh)].
A 20-cycle repeated test was conducted to determine the 20-cycle capacity retention rate (%).

The negative electrodes and batteries obtained using coated negative electrode active material particles 1 to 12 for lithium ion batteries of Examples 301 to 312 were compared with those obtained using coated negative electrode active material particles 13 to 15 of Comparative Examples 301 to 303. Therefore, the electrode strength was excellent, the initial internal resistance was low, the rate of increase in internal resistance was low, and the capacity retention rate was high.
The coated negative electrode active material particles 13 and 15 of Comparative Examples 301 and 303 could not be formed into electrodes, and the rate of increase in internal resistance was also high. The coated negative electrode active material particles 14 of Comparative Example 302 had a high internal resistance increase rate.
The electrode of Example 303 using the polymer compound (P2-3) had higher electrode strength than Examples 301, 302, and 304, which differed only in the type of polymer compound (P2).
In Examples 305 to 307, coated negative electrode active material particles for lithium ion batteries were produced using the same formulation as in Example 302 except for changing the method of preparing the polymer compound, but the internal resistance increase rate was lower than that in Example 302. No major differences were observed, except for a slightly higher value.
In Examples 302, 308, and 309 in which the blending amount of the polymer compound (P1) was changed, the rate of increase in internal resistance was lower as the amount of the polymer compound (P1) increased.
In Examples 302 and 310 to 312 in which the amount of the polymer compound (P2-2) was changed, the electrode strength increased as the amount of the polymer compound (P2-2) increased.

The electrode composition for lithium ion batteries, the coated negative electrode active material particles for lithium ion batteries, and the negative electrode for lithium ion batteries of the present invention can be used particularly for stationary power supplies, mobile phones, personal computers, hybrid vehicles, electric vehicles, etc. It is useful for producing lithium-ion batteries. The lithium ion battery of the present invention is particularly useful as a lithium ion battery for mobile phones, personal computers, hybrid vehicles, and electric vehicles.

Claims

An electrode composition for a lithium ion battery containing a conductive filler,
The conductive filler is composed of two or more types having different aspect ratios,
An electrode composition for a lithium ion battery, wherein the conductive filler has an aspect ratio of 2.00 to 7.00.
The electrode composition for a lithium ion battery according to claim 1, wherein the conductive filler comprises flaky graphite and fibrous graphite.
The electrode composition for a lithium ion battery according to claim 1, wherein the weight percentage of the conductive filler is 1 to 6% by weight based on the weight of the electrode composition for a lithium ion battery.
Containing coated electrode active material particles in which at least a portion of the surface of the electrode active material particles is coated with a coating layer containing a polymer compound,
The electrode composition for a lithium ion battery according to claim 1 or 2, wherein the conductive filler is contained in the coating layer and outside the coating layer.
The electrode composition for a lithium ion battery according to claim 1 has negative electrode active material particles,
Coated negative electrode active material particles for lithium ion batteries, in which at least a part of the surface of the negative electrode active material particles is covered with a coating layer containing a polymer compound and a conductive additive,
The weight ratio of the conductive additive is 6.1 to 10.5% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries,
Coated negative electrode active material particles for lithium ion batteries having a coverage rate of 80% or more obtained by the following calculation formula.
Coverage rate (%) = {1-[BET specific surface area of coated negative electrode active material particles/(BET specific surface area of negative electrode active material particles when uncoated x weight percentage of negative electrode active material particles contained in coated negative electrode active material particles) + BET specific surface area of the conductive aid × weight ratio of the conductive aid contained in the coated negative electrode active material particles)]}×100
The coated negative electrode active material particles for a lithium ion battery according to claim 5, wherein the negative electrode active material particles for a lithium ion battery are non-graphitizable carbon or a mixture of non-graphitizable carbon and a silicon-based material.
The polymer compound is obtained by polymerizing a monomer composition containing an alkyl (meth)acrylate monomer, and the weight ratio of the alkyl (meth)acrylate monomer in the monomer composition is The coated negative electrode active material particles for a lithium ion battery according to claim 5 or 6, wherein the amount is 90% by weight or more based on the weight of the monomer composition.
The coated negative electrode active material particles for a lithium ion battery according to claim 5 or 6, wherein the conductive additive is acetylene black and/or flaky graphite.
Claim 5, wherein the ratio of the loose bulk density of the coated negative electrode active material particles for lithium ion batteries to the firm bulk density of the coated negative electrode active material particles for lithium ion batteries measured by a tapping method is 0.60 to 0.85. or 6. The coated negative electrode active material particles for lithium ion batteries according to 6.
A first coating step in which the negative electrode active material particles, the polymer compound, the conductive agent, and the organic solvent are mixed and then the solvent is removed to obtain first coated negative electrode active material particles;
The coated negative electrode active material particles for a lithium ion battery according to claim 5 or 6, further comprising a second coating step of removing the solvent after mixing the first coated negative electrode active material particles with a polymer compound, a conductive aid, and an organic solvent. manufacturing method.
The electrode composition for a lithium ion battery according to claim 1 has negative electrode active material particles,
A coated negative electrode active for a lithium ion battery, wherein at least a part of the surface of the negative electrode active material particles is coated with a first coating layer, and at least a part of the surface of the first coating layer is coated with a second coating layer. A material particle,
The first coating layer is a monomer composition comprising an ester compound (a11) of a monovalent aliphatic alcohol having 1 to 12 carbon atoms and (meth)acrylic acid and an anionic monomer (a12). a polymer compound (P1) which is a polymer of
The second coating layer is a coated negative electrode active material particle for a lithium ion battery containing a polymer compound (P2) having a glass transition temperature of 20° C. or lower and a conductive additive (C2).
The weight proportion of the polymer compound (P1) in the coated negative electrode active material particles for lithium ion batteries is 0.7 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries,
A weight ratio of the polymer compound (P2) in the coated negative electrode active material particles for lithium ion batteries is 0.3 to 9.0% by weight based on the weight of the coated negative electrode active material particles for lithium ion batteries. Item 12. The coated negative electrode active material particles for lithium ion batteries according to item 11.
The lithium ion battery according to claim 11 or 12, wherein the polymer compound (P2) is at least one selected from the group consisting of urethane resin, (meth)acrylic acid alkyl ester copolymer, and styrene-butadiene rubber. coated negative electrode active material particles.
A negative electrode for a lithium ion battery comprising a non-binding body comprising the coated negative electrode active material particles for a lithium ion battery according to claim 11 or 12 and a conductive filler.
A lithium ion battery comprising the negative electrode for a lithium ion battery according to claim 14.