KR102067562B1 - Negative electrode for secondary cell, secondary cell, slurry composition, and manufacturing method - Google Patents

Abstract

As a negative electrode for secondary batteries containing a negative electrode active material, a particulate-form binder, and a water-soluble polymer, the said water-soluble polymer is 0.1 weight%-15 weight% of a sulfonic acid group containing monomeric unit, and 0.5 weight%-10 fluorine-containing (meth) acrylic acid ester monomeric units The negative electrode for secondary batteries which is a copolymer containing weight%, The secondary battery etc. containing it.

Description

Negative electrode for secondary battery, secondary battery, slurry composition, and manufacturing method {NEGATIVE ELECTRODE FOR SECONDARY CELL, SECONDARY CELL, SLURRY COMPOSITION, AND MANUFACTURING METHOD}

The present invention relates to a method for producing a negative electrode for a secondary battery, a secondary battery, a slurry composition, and a negative electrode for a secondary battery.

Background Art In recent years, the popularity of portable terminals such as notebook computers, mobile phones, PDAs (Personal Digital Assistants) and the like is remarkable. As a secondary battery used as a power source for these portable terminals, for example, a nickel hydride secondary battery, a lithium ion secondary battery, and the like are frequently used. As portable terminals are required for more comfortable portability, miniaturization, thinning, weight reduction, and high performance are rapidly progressing. As a result, portable terminals are being used in various places. In addition, the secondary battery is required to be smaller, thinner, lighter and higher in performance as with the portable terminal.

In order to improve the performance of secondary batteries, improvements in electrodes, electrolytes and other battery members have been studied. Among these, the electrode usually mixes an electrode active material and a conductive agent such as conductive carbon, if necessary, with a liquid composition in which a polymer to be a binder (binder) is dispersed or dissolved in a solvent such as water or an organic solvent. A slurry composition is obtained, and this slurry composition is apply | coated to an electrical power collector, and it is manufactured by drying. In addition to the examination of the electrode active material and the current collector itself, the electrode is also examined for a binder for binding the electrode active material to the current collector and various additives (see Patent Documents 1 to 4, for example).

For example, Patent Literature 1 and Patent Literature 2 describe a slurry for a negative electrode of a non-aqueous secondary battery containing a carbon material active material, a water dispersion emulsion resin, and a binder composed of a water-soluble high molecular compound. As the water-soluble high molecular compound, polyvinyl alcohol, carboxymethyl cellulose, sodium polyacrylate, and the like are described. According to this, the effect that the coating film strength and coating film density of a battery become favorable is described.

In patent document 3, it is 0.02-13 weight% of fluorine-containing unsaturated monomers, 10-38 weight% of aliphatic conjugated diene monomers, 0.1-10 weight% of ethylenically unsaturated carboxylic acid monomers, and 49-88.88 weight% of other monomers copolymerizable with these. The binder for secondary battery electrodes which consists of copolymer latex obtained by emulsion-polymerizing the monomer composition comprised is described. According to this, the effect which is excellent in mix | blending stability, blocking resistance, fall resistance, and binding force is described.

Moreover, patent document 4 describes the binder for secondary battery electrodes which consists of a polymer which has a monomeric unit derived from fluorine atom containing monomers, such as alkyl (meth) acrylate. And the purpose which can add a cellulose polymer, a polyacrylate, etc. in order to improve applicability | paintability or a charge / discharge characteristic is described. According to this, it is described that the electrode which is consistently good in binding property with an active material is obtained.

Japanese Unexamined Patent Publication No. 2003-308841 Japanese Unexamined Patent Publication No. 2003-217573 Japanese Unexamined Patent Publication No. 2010-146870 Japanese Laid-Open Patent Publication 2002-42819

In a secondary battery, the particles of the electrode active material contained in the negative electrode may expand and contract with charging and discharging. If such expansion and contraction are repeated, there is a possibility that the negative electrode gradually expands and the secondary battery is deformed. Therefore, development of the technology which can suppress the expansion of such a negative electrode is desired.

Moreover, the capacity | capacitance fell in the conventional secondary battery, for example, when it preserve | stores in the high temperature environment of 60 degreeC. Therefore, the development of the technology which can suppress the fall of the capacity of the said secondary battery even if the secondary battery is preserve | saved in a high temperature environment is also desired.

Moreover, in a secondary battery, also in any of a high temperature environment and a low temperature environment, it is calculated | required that favorable characteristics, such as cycling characteristics and an output characteristic, are favorable.

This invention was devised in view of the above-mentioned subject, and it can suppress the expansion of the negative electrode accompanying charge and discharge, and even if it is preserve | saved in a high temperature environment, capacity is hard to fall, and also in any of a high temperature environment and a low temperature environment, A secondary battery negative electrode capable of realizing a secondary battery having good characteristics, a slurry composition for negative electrode capable of producing the negative electrode for secondary battery, a method for producing a negative electrode for secondary battery, and the negative electrode for secondary battery It is an object to provide a secondary battery.

MEANS TO SOLVE THE PROBLEM As a result of earnestly examining in order to solve said subject, the water-soluble polymer which contains a sulfonic acid group containing monomeric unit and a fluorine-containing (meth) acrylic acid ester monomeric unit in a specific ratio each in the electrode active material layer of the negative electrode for secondary batteries By containing, it was found that the expansion of the negative electrode accompanying charging and discharging can be suppressed and that the capacity can be less easily reduced even when stored in a high temperature environment, thereby completing the present invention.

That is, according to the present invention, the following [1] to [11] are provided.

[1] A negative electrode for a secondary battery containing a negative electrode active material, a particulate binder, and a water-soluble polymer,

The water-soluble polymer,

0.1 wt% to 15 wt% of a sulfonic acid group-containing monomer unit, and

The negative electrode for secondary batteries which is a copolymer containing 0.5 weight%-10 weight% of a fluorine-containing (meth) acrylic acid ester monomeric unit.

[2] The negative electrode for secondary batteries as described in [1], in which the water-soluble polymer contains an ethylenically unsaturated carboxylic monomer unit.

[3] The negative electrode for secondary batteries according to [2], in which the ethylenically unsaturated carboxylic monomer is an ethylenically unsaturated monocarboxylic acid monomer.

[4] The negative electrode for secondary batteries according to any one of [1] to [3], in which the negative electrode active material can occlude and release lithium and contains a metal.

[5] The negative electrode for secondary batteries according to [4], wherein the metal is silicon.

[6] The negative electrode for secondary batteries according to any one of [1] to [5], in which the particulate binder contains a polymer containing an aliphatic conjugated diene monomer unit.

[7] The negative electrode for secondary batteries according to [6], in which the polymer containing the aliphatic conjugated diene monomeric unit further contains an aromatic vinyl monomer unit.

[8] A secondary battery comprising a positive electrode, a negative electrode, an electrolyte solution, and a separator, wherein the negative electrode is the negative electrode for secondary battery according to any one of [1] to [7].

[9] A slurry composition containing a negative electrode active material, a particulate binder, and a water-soluble polymer,

The water-soluble polymer,

0.1 wt% to 15 wt% of a sulfonic acid group-containing monomer unit,

The slurry composition for secondary battery negative electrodes which is a copolymer containing 0.5 weight%-10 weight% of a fluorine-containing (meth) acrylic acid ester monomeric unit.

[10] The slurry composition for negative electrodes according to [9], in which the water-soluble polymer contains an ethylenically unsaturated carboxylic monomer unit.

[11] A method for producing a negative electrode for secondary batteries, comprising applying the slurry composition for secondary battery negative electrodes as described in [9] or [10] onto a current collector and drying it.

According to the negative electrode for secondary batteries of this invention, expansion of the negative electrode accompanying charge / discharge can be suppressed, it is difficult to reduce a capacity | capacitance even if it preserve | stores in high temperature environment, and the characteristic is favorable also in either high temperature environment or low temperature environment. Secondary battery can be realized.

The secondary battery of the present invention can suppress expansion of the negative electrode accompanying charging and discharging, hardly lowers the capacity even when stored in a high temperature environment, and has excellent characteristics in either the high temperature environment or the low temperature environment.

When the slurry composition for negative electrodes of this invention is used, the negative electrode for secondary batteries of this invention can be manufactured. Moreover, since the slurry composition for negative electrodes of this invention has high stability, long term storage is possible and it is easy to use.

According to the manufacturing method of the negative electrode for secondary batteries of this invention, the negative electrode for secondary batteries of this invention can be manufactured.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment and an example are shown and this invention is demonstrated in detail. However, this invention is not limited to embodiment described below and an illustration, You may change arbitrarily and implement in the range which does not deviate from the Claim of this invention, and its equal range.

In the following description, (meth) acrylic acid means acrylic acid and methacrylic acid. In the following description, when a substance is water-soluble, in 25 degreeC, when 0.5 g of the substance is melt | dissolved in 100 g of water, it means that an insoluble content is less than 0.5 weight%. Moreover, when a substance is water-insoluble, when a substance is melt | dissolved in 100 g of water at 25 degreeC, it means that an insoluble content is 90 weight% or more.

[One. Negative electrode for secondary battery]

The negative electrode for secondary batteries of this invention (henceforth "the negative electrode of this invention suitably") contains a negative electrode active material, a particulate-form binder, and a water-soluble polymer. Usually, the negative electrode of this invention is equipped with an electrical power collector and the negative electrode active material layer formed in the surface of the said electrical power collector, and a negative electrode active material layer contains said negative electrode active material, a particulate-form binder, and a water-soluble polymer.

[1-1. Negative Electrode Active Material]

A negative electrode active material is an electrode active material for negative electrodes, and is a substance which delivers an electron in the negative electrode of a secondary battery.

For example, when the secondary battery of this invention is a lithium ion secondary battery, the substance which can occlude and discharge | release lithium is normally used as a negative electrode active material.

Carbon is mentioned as an example of a preferable negative electrode active material. As carbon, natural graphite, artificial graphite, carbon black, etc. are mentioned, for example, It is preferable to use natural graphite especially.

As another example of a preferable negative electrode active material, the substance containing a metal is mentioned. In particular, a negative electrode active material containing at least one selected from the group consisting of tin, silicon, germanium and lead is preferable. This is because the negative electrode active material containing these elements has a small irreversible capacity.

Among these, the negative electrode active material containing silicon is preferable. By using the negative electrode active material containing silicon, it becomes possible to enlarge the electric capacity of a lithium ion secondary battery. In general, the negative electrode active material containing silicon expands and contracts greatly (for example, about five times) with charge and discharge. However, in the negative electrode of the present invention, the battery is caused by the expansion and contraction of the silicon-containing negative electrode active material. The fall of performance can be suppressed.

Examples of the active material containing silicon include an active material made of metal silicon, an active material made of silicon and a compound of another element (hereinafter referred to as "silicon-based active material"), and an active material made of metal silicon and a silicon-based active material And combinations thereof.

In addition, the negative electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, it can use combining two or more types of said negative electrode active material. Especially, it is preferable to use the negative electrode active material containing the carbon and the active material containing a silicon in combination. When a combination of an active material containing carbon and silicon is used as the negative electrode active material, insertion and desorption of Li into one or both of the metal silicon and the silicon-based active material occurs at high potentials, and insertion and desorption of Li into carbon at low potentials occurs. It is assumed that this happens. For this reason, since expansion and contraction are suppressed, the cycling characteristics of a lithium ion secondary battery can be improved.

Silicon as the active material, for example, SiO, SiO _2, and the like _{SiO x (0.01 ≤ x <2} ), SiC, SiOC, a SiO _x, SiC and SiOC is preferred. Especially, since the expansion of the negative electrode active material itself is suppressed, it is particularly preferable to use SiO _x as the silicon-based active material. SiO _x is a compound which can be formed from one or both of SiO and SiO ₂ and metallic silicon. This SiO _x can be produced by, for example, cooling and precipitation of the silicon monoxide gas generated by heating a mixture of SiO ₂ and metal silicon.

When using the active material containing carbon and silicon in combination, it is preferable that the active material containing silicon is compounded with conductive carbon. By complexing with conductive carbon, expansion of the negative electrode active material itself can be suppressed.

As a method of compounding, for example, the method of compounding by coating the active material containing silicon with carbon; The method of compounding by granulating the mixture containing electroconductive carbon and the active material containing a silicon, etc. are mentioned.

When using the negative electrode active material which combines carbon and the active material containing a silicon, it is preferable that the quantity of a silicon atom is 0.1 weight part-50 weight part with respect to 100 weight part of total carbon atoms in a negative electrode active material. Thereby, a conductive path is formed satisfactorily and the electroconductivity in a negative electrode can be made favorable.

When using a negative electrode active material containing carbon and an active material containing silicon in combination, the weight ratio ("weight of carbon" / "weight of active material containing silicon") of the active material containing carbon and silicon is preferably 50/50 or more, More preferably, it is 70/30 or more, Preferably it is 97/3 or less, More preferably, it is 90/10 or less. Thereby, the cycling characteristics of a secondary battery can be improved.

(Shape of Negative Electrode Active Material)

It is preferable that the negative electrode active material was grain-sorted. If the shape of the particles is spherical, a higher density electrode can be formed at the time of electrode molding.

In the case where the negative electrode active material is a particle, the volume average particle diameter is appropriately selected from balance with other constituent requirements of the secondary battery, and is usually 0.1 μm or more, preferably 1 μm or more, more preferably 5 μm or more, Usually it is 100 micrometers or less, Preferably it is 50 micrometers or less, More preferably, it is 30 micrometers or less. Here, the volume average particle diameter adopts a particle diameter such that the cumulative volume calculated from the small diameter side is 50% in the particle size distribution measured by the laser diffraction method.

The specific surface area of the negative electrode active material is usually 2 m 2 / g or more, preferably 3 m 2 / g or more, more preferably 5 m 2 / g or more, and usually 20 m 2 / g or less, from the viewpoint of output density improvement, Preferably it is 15 m <2> / g or less, More preferably, it is 10 m <2> / g or less. The specific surface area of a negative electrode active material can be measured by a BET method, for example.

1-2. Particulate Binder]

A particulate-form binder is a component which binds an electrode active material to the surface of an electrical power collector in a negative electrode. In the negative electrode of the present invention, desorption of the negative electrode active material from the negative electrode active material layer is reduced when the particulate binder binds the negative electrode active material. Moreover, the particulate-form binder normally binds particle | grains other than the negative electrode active material contained in a negative electrode active material layer, and also achieves the role which maintains the intensity | strength of a negative electrode active material layer.

As a particulate-form binder, it is preferable to use the thing excellent in the performance which hold | maintains a negative electrode active material, and high adhesiveness with respect to an electrical power collector. Usually, as a particulate binder, what contains a polymer is used, Especially what consists of a polymer substantially can be used. The polymer of the particulate binder may be a homopolymer or a copolymer.

The polymer of the particulate binder preferably contains an aliphatic conjugated diene monomer unit. Aliphatic conjugated diene monomeric units are low rigidity and flexible repeating units. Therefore, sufficient adhesiveness of a negative electrode active material layer and an electrical power collector can be obtained by using the polymer containing an aliphatic conjugated diene monomeric unit as a particulate-form binder.

An aliphatic conjugated diene monomeric unit is a repeating unit obtained by superposing | polymerizing an aliphatic conjugated diene monomer. Examples of aliphatic conjugated diene monomers include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear chains Conjugated pentadienes, substituted and side chain conjugated hexadienes; and the like. Especially, 1, 3- butadiene is preferable.

An aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the polymer of a particulate-form binder may contain only one type of aliphatic conjugated diene monomeric unit, and may contain it combining two or more types by arbitrary ratios.

In the polymer of the particulate binder, the proportion of the aliphatic conjugated diene monomer unit is preferably 20% by weight or more, more preferably 30% by weight or more, preferably 70% by weight or less, more preferably 60% by weight or less, Especially preferably, it is 55 weight% or less. By setting the proportion of the aliphatic conjugated diene monomer unit to be equal to or greater than the lower limit of the above range, the flexibility of the negative electrode can be increased, and by using the aliphatic conjugated diene monomer unit or less, the sufficient adhesion between the negative electrode active material layer and the current collector can be obtained, or the electrolyte resistance of the electrode is increased. You can do it.

The polymer of the particulate binder preferably contains an aromatic vinyl monomer unit. The aromatic vinyl monomer unit is stable, and the solubility in the electrolyte solution of the polymer containing the aromatic vinyl monomer unit can be lowered to stabilize the negative electrode active material layer.

An aromatic vinyl monomer unit is a repeating unit obtained by superposing | polymerizing an aromatic vinyl monomer. As an example of an aromatic vinyl monomer, styrene, (alpha) -methylstyrene, vinyltoluene, divinylbenzene, etc. are mentioned. Especially, styrene is preferable. It is preferable that the polymer of a particulate-form binder contains an aromatic vinyl monomeric unit, and as mentioned previously, it is preferable that the polymer of a particulate-form binder contains aliphatic conjugated diene monomeric units, such as butadiene. Therefore, it is preferable that the polymer of a particulate-form binder is a polymer containing an aliphatic conjugated diene monomeric unit and an aromatic vinyl monomeric unit, for example, a styrene butadiene copolymer is preferable.

An aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the polymer of a particulate-form binder may contain only one type of aromatic vinyl monomer, and may contain it combining two or more types by arbitrary ratios.

When using an aromatic vinyl monomer, the polymer of a particulate-form binder may contain the unreacted aliphatic conjugated diene monomer and the unreacted aromatic vinyl monomer as a residual monomer. In that case, the amount of the unreacted aliphatic conjugated diene monomer contained in the polymer of the particulate binder is preferably 50 ppm or less, more preferably 10 ppm or less, and the amount of the unreacted aromatic vinyl monomer contained in the polymer of the particulate binder is Preferably it is 1000 ppm or less, More preferably, it is 200 ppm or less. When the amount of the aliphatic conjugated diene monomer contained in the polymer of the particulate binder is suppressed in the above range, when the negative electrode slurry composition according to the present invention is applied and dried on the surface of the current collector to produce the negative electrode, It is possible to prevent roughness due to occurrence or environmental load caused by odor. Moreover, if the quantity of the aromatic vinyl monomer which the polymer of a particulate-form binder contains is suppressed in the said range, the environmental load and the roughness of the negative electrode surface which generate | occur | produce by drying conditions can be suppressed, and also the electrolyte resistance of the polymer of a particulate-form binder will be suppressed. It can increase.

In the polymer of the particulate binder, the proportion of the aromatic vinyl monomer unit is preferably 30% by weight or more, more preferably 35% by weight or more, preferably 79.5% by weight or less, and more preferably 69% by weight or less. By carrying out the ratio of an aromatic vinyl monomer unit more than the lower limit of the said range, the electrolyte resistance of the negative electrode for secondary batteries of this invention can be improved, and below the upper limit, the slurry composition for negative electrodes which concerns on this invention to an electrical power collector When it apply | coats, sufficient adhesiveness of a negative electrode active material layer and an electrical power collector can be obtained.

The polymer of the particulate binder preferably contains an ethylenically unsaturated carboxylic monomer unit. The ethylenically unsaturated carboxylic acid monomer unit contains a carboxyl group (-COOH group) that enhances the adsorption property to the negative electrode active material and the current collector, and is a high strength repeating unit, and thus can stably prevent detachment of the negative electrode active material from the negative electrode active material layer. In addition, the strength of the negative electrode can be improved.

An ethylenic unsaturated carboxylic monomer unit is a repeating unit obtained by superposing | polymerizing an ethylenic unsaturated carboxylic monomer. Examples of the ethylenically unsaturated carboxylic acid monomers include monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. Especially, it is preferable to use the monomer chosen from the group which consists of acrylic acid, methacrylic acid, and itaconic acid individually or in combination from a viewpoint of the stability of the slurry composition for negative electrodes which concerns on this invention.

An ethylenic unsaturated carboxylic monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the polymer of a particulate-form binder may contain only one type of ethylenically unsaturated carboxylic monomer unit, and may contain it combining two or more types by arbitrary ratios.

In the polymer of the particulate binder, the proportion of ethylenically unsaturated carboxylic monomer units is preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, preferably 10% by weight. % Or less, More preferably, it is 8 weight% or less, Especially preferably, it is 7 weight% or less. By making the ratio of an ethylenic unsaturated carboxylic monomer unit more than the lower limit of the said range, the stability of the slurry composition for negative electrodes which concerns on this invention can be improved, and also below the upper limit, the viscosity of the slurry for negative electrodes which concerns on this invention Can be prevented from becoming excessively high to facilitate handling.

The polymer of a particulate-form binder may contain arbitrary repeating units other than what was mentioned above, unless the effect of this invention is remarkably impaired. As a monomer corresponding to said arbitrary repeating unit, a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, the unsaturated monomer containing a hydroxyalkyl group, an unsaturated carboxylic amide monomer, etc. are mentioned, for example. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As a vinyl cyanide monomer, an acrylonitrile, methacrylonitrile, the (alpha)-chloro acrylonitrile, the (alpha)-ethyl acrylonitrile, etc. are mentioned, for example. Especially, acrylonitrile and methacrylonitrile are preferable. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As the unsaturated carboxylic acid alkyl ester monomer, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate , Dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate, and the like. Especially, methyl methacrylate, ethyl acrylate, and butyl acrylate are preferable. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As the unsaturated monomer containing a hydroxyalkyl group, for example, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, Hydroxybutyl methacrylate, 3-chloro-2-hydroxypropylmethacrylate, di- (ethyleneglycol) maleate, di- (ethyleneglycol) itaconate, 2-hydroxyethylmaleate, bis (2 -Hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. Especially, (beta) -hydroxyethyl acrylate is preferable. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As an unsaturated carboxylic amide monomer, acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N- dimethyl acrylamide, etc. are mentioned, for example. Especially, acrylamide and methacrylamide are preferable. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Moreover, as a monomer which comprises the polymer of a particulate-form binder, you may use the monomer used in normal emulsion polymerization, such as ethylene, propylene, vinyl acetate, a vinyl propionate, a vinyl chloride, vinylidene chloride, for example. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Preferably the weight average molecular weight of the polymer of a particulate-form binder is 10000 or more, More preferably, it is 20000 or more, Preferably it is 2000000 or less, More preferably, it is 500000 or less. When the weight average molecular weight of the polymer of a particulate-form binder exists in the said range, it is easy to make the intensity | strength of the negative electrode of this invention and the dispersibility of a negative electrode active material favorable. The weight average molecular weight of the polymer of a particulate-form binder can be calculated | required as a value of polystyrene conversion using tetrahydrofuran as a developing solvent by gel permeation chromatography (GPC).

The glass transition temperature of the particulate binder is preferably -75 ° C or higher, more preferably -55 ° C or higher, particularly preferably -35 ° C or higher, preferably 40 ° C or lower, preferably 30 ° C or lower, more preferably. Preferably it is 20 degrees C or less, Especially preferably, it is 15 degrees C or less. When the glass transition temperature of a particulate-form binder is the said range, characteristics, such as the softness | flexibility, binding property, and winding property of a negative electrode, adhesiveness of a negative electrode active material layer and an electrical power collector, are highly balanced, and are preferable.

Typically, the particulate binder becomes a water-insoluble polymer. Therefore, in the slurry composition for negative electrodes of this invention, a particulate-form binder does not melt | dissolve in the water which is a solvent, but becomes a particle and disperse | distributes. When a particulate-form binder is melt | dissolved in water and an organic solvent (for example, N-methyl- 2-pyrrolidone), a binder will adsorb | suck to a negative electrode active material and the output characteristic of the secondary battery obtained as a result will fall. By the particulate binder being a water-insoluble polymer, the above problem can be prevented. In the slurry composition for negative electrodes, the particulate binder is preferably dispersed in water in the form of particles. As a slurry composition for negative electrodes, when the binder melt | dissolves in organic solvents, such as NMP (N-methyl- 2-pyrrolidone), and does not hold the particulate form, a binder is adsorb | sucked to the surface of a negative electrode active material, and outputs. Properties are degraded.

The number average particle diameter of the particles of the particulate binder is preferably 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, and more preferably 400 nm or less. The number average particle diameter of a particulate-form binder exists in the said range, and the intensity | strength and flexibility of the negative electrode obtained can be made favorable. Presence of particle | grains can be measured easily by a transmission electron microscopy method, a coulter counter, a laser diffraction scattering method, etc.

A particulate-form binder is manufactured by superposing | polymerizing the monomer composition containing the monomer mentioned above in an aqueous solvent, for example.

The ratio of each monomer in a monomer composition is usually with the ratio of repeating units (for example, an aliphatic conjugated diene monomer unit, an aromatic vinyl monomer unit, an ethylenically unsaturated carboxylic monomer unit, etc.) in the polymer of a particulate-form binder. Do the same.

The aqueous solvent is not particularly limited as long as it can disperse the particles of the particulate binder, and usually, the boiling point at normal pressure is usually 80 ° C. or higher, preferably 100 ° C. or higher, and usually 350 ° C. or lower, preferably Is selected from aqueous solvents up to 300 ° C. Hereinafter, the example of the aqueous solvent is given. In the following examples, the number in parentheses after the solvent name is the boiling point at normal pressure (unit C), and the decimal point is rounded off or truncated.

Examples of the aqueous solvent include water (100); ketones such as diacetone alcohol (169) and γ-butyrolactone (204); ethyl alcohol (78), isopropyl alcohol (82), and normal propyl alcohol (97) Alcohols such as propylene glycol; propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171), 3 -Methoxy-3-methyl-1-butanol (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether Glycol ethers such as (188); ethers such as 1,3-dioxolane (75), 1,4-dioxolane (101), tetrahydrofuran (66), and the like. Among them, water is not particularly flammable and is particularly preferable from the viewpoint of easily obtaining a dispersion of particles of a particulate binder. You may use water as a main solvent and mix and use aqueous solvents other than water mentioned above in the range which the dispersion state of the particle | grains of a particulate-form binder can be ensured.

A polymerization method is not specifically limited, For example, any method, such as a solution polymerization method, suspension polymerization method, block polymerization method, and emulsion polymerization method, can also be used. As a polymerization method, any method, such as ionic polymerization, radical polymerization, a living radical polymerization, can be used, for example. It is easy to obtain a high molecular weight, and since a polymer is obtained in the state disperse | distributed in water as it is, the process of re-dispersion is unnecessary and can be used for manufacture of the slurry composition for negative electrodes which concerns on this invention as it is. Among them, emulsion polymerization is particularly preferred.

An emulsion polymerization method is normally performed by a conventional method. For example, it is performed by the method as described in "Experimental chemistry lecture" Vol. 28, (publisher: Maruzen, Japan Chemical Society). That is, additives such as water, a dispersant, an emulsifier, and a crosslinking agent, a polymerization initiator, and a monomer are added to a closed container with a stirrer and a heating device to a predetermined composition, and the composition in the container is stirred to emulsify the monomer in water It is a method of starting superposition | polymerization by raising a temperature, stirring. Or after emulsifying the said composition, it is the method of starting a reaction similarly in a sealed container.

As a polymerization initiator, for example, lauroyl peroxide, diisopropyl peroxy dicarbonate, di-2-ethylhexyl peroxy dicarbonate, t-butyl peroxy pivalate, 3,3,5-trimethylhexanoyl peroxide, etc. Organic peroxides; azo compounds such as α, α'-azobisisobutyronitrile; ammonium persulfate; potassium persulfate, and the like. A polymerization initiator may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

An emulsifier, a dispersing agent, a polymerization initiator, etc. are generally used in these polymerization methods, Usually, the usage-amount is also used as the quantity generally used. Moreover, in superposition | polymerization, seed particle | grains may be employ | adopted and seed polymerization may be performed.

The polymerization temperature and the polymerization time can be arbitrarily selected according to the polymerization method, the kind of the polymerization initiator, or the like. Usually, the polymerization temperature is about 30 ° C. or more and the polymerization time is about 0.5 hour to 30 hours.

Moreover, you may use additives, such as amines, as a polymerization adjuvant.

Moreover, the aqueous dispersion liquid of the particle | grains of a particulate-form binder obtained by these methods is, for example, hydroxide of an alkali metal (for example, Li, Na, K, Rb, Cs), ammonia, an inorganic ammonium compound (for example, NH). ₄ Cl, etc.), an organic amine compound (e.g., ethanolamine, diethylamine, etc.), and mixed with a basic aqueous solution, and the pH is usually adjusted to 5-10, preferably 5-9 do. Especially, since pH adjustment by alkali metal hydroxide improves the binding property (fill strength) of an electrical power collector and a negative electrode active material, it is preferable.

The particle | grains of the particulate-form binder mentioned above may be composite polymer particle which consists of two or more types of polymers. The composite polymer particles can also be obtained by a method of polymerizing at least one monomer component by a conventional method, followed by polymerization of at least one other monomer component by a conventional method (two-stage polymerization method) or the like. Thus, by polymerizing a monomer in stages, the particle | grains of the core shell structure which have the core layer which exists in particle | grains, and the shell layer which covers the said core layer can be obtained.

The amount of the particulate binder is preferably 0.3 parts by weight or more, more preferably 0.5 parts by weight or more, preferably 8 parts by weight or less, more preferably 4 parts by weight or less, particularly preferably 100 parts by weight of the negative electrode active material. Preferably 2 parts by weight or less. By setting the amount of the particulate binder in the above-described range, the viscosity of the slurry composition for negative electrodes according to the present invention is optimized, and the application to the current collector can be smoothly performed. Moreover, with respect to the negative electrode of this invention, sufficient adhesive strength of an electrical power collector and a negative electrode active material layer is obtained, without increasing resistance. As a result, peeling of the particulate-form binder from the negative electrode active material layer in the process of performing a pressurization process to a negative electrode active material layer can be suppressed.

1-3. Water Soluble Polymer]

In the negative electrode of the present invention, the water-soluble polymer contained in the negative electrode active material layer is a copolymer containing a sulfonic acid group-containing monomer unit in a predetermined ratio and a fluorine-containing (meth) acrylic acid ester monomer unit in a predetermined ratio. By containing the water-soluble polymer of the negative electrode of the present invention, it is possible to suppress the expansion of the negative electrode accompanying charging and discharging, and to realize a secondary battery in which capacity is hardly reduced even when stored in a high temperature environment. Moreover, by using such a water-soluble polymer, the applicability | paintability at the time of apply | coating the slurry composition for negative electrodes of this invention to an electrical power collector, and the adhesiveness with respect to the electrical power collector of the negative electrode active material layer in the secondary battery of this invention, The high temperature cycle characteristics and the low temperature output characteristics are usually excellent.

Since the water-soluble polymer contains a sulfonic acid group-containing monomer unit, the dispersion stability of the negative electrode active material can be improved, desorption of the negative electrode active material from the negative electrode active material layer, or chemical change of the negative electrode active material itself can be suppressed. High temperature storage characteristics and low temperature output characteristics of the battery can be improved. In addition, when the water-soluble polymer contains a fluorine-containing (meth) acrylic acid ester monomer unit, the swellability of the water-soluble polymer (the degree to which the water-soluble polymer is swollen by absorbing water when the water-soluble polymer is immersed in water) is improved, In addition, the water-soluble polymer can be elastically deformed, and as a result, the properties of the slurry are improved, and further, the performance of the battery is improved. It is thought that these effects are combined and the above-mentioned effect is exhibited.

Specifically, when the negative electrode active material expands or contracts in the negative electrode, the water-soluble polymer can elastically deform in accordance with the expansion or contraction of the negative electrode active material, so that the expansion of the negative electrode accompanying charge and discharge can be suppressed. Conventionally, when the negative electrode active material repeats expansion and contraction, the particulate binder cannot be brought into close contact with the negative electrode active material, and a gap is formed between the negative electrode active materials or between the negative electrode active material and the conductive agent, and the negative electrode active material and the conductive in the negative electrode In some cases, the electrical connection of the agent was hindered. If the above electrical connection is impaired, there is a possibility that the electric capacity of the secondary battery is lowered. However, if the water-soluble polymer can elastically deform following the expansion or contraction of the negative electrode active material, the occurrence of the gap can be suppressed to maintain the electrical connection, thereby improving the cycle characteristics.

In the negative electrode, the water-soluble polymer can be adsorbed onto the surface of the negative electrode active material to cover the negative electrode active material, thereby forming a protective layer. By this protective layer, decomposition of the electrolyte solution in a high temperature environment and decomposition of the electrolyte solution accompanying charge and discharge can be suppressed. When the electrolyte solution is decomposed, bubbles are formed around the negative electrode active material, and this bubble may inhibit the transfer of electrons and lower the electric capacity of the secondary battery. However, if decomposition of electrolyte solution can be suppressed by a water-soluble polymer, the fall of the above-mentioned electric capacity can be suppressed and high temperature storage characteristic and high temperature cycling characteristic can be improved.

In addition, the protective layer formed of a water-soluble polymer has higher ionic conductivity than a protective layer formed of a conventional additive such as carboxymethyl cellulose (hereinafter, appropriately referred to as "CMC"). This is inferred because the water-soluble polymer has swelling property to the electrolyte solution (when the water-soluble polymer is immersed in the electrolyte solution, the water-soluble polymer swells by absorbing the electrolyte solution). Because of the high ion conductivity, the diffusion resistance (that is, the resistance which prevents the diffusion of ions) is lowered, so that the secondary battery of the present invention has high output characteristics, and particularly excellent low temperature output characteristics. Thus, even if it has swelling property with respect to electrolyte solution, since the solvent of electrolyte solution cannot swell through the protective layer easily, the effect which suppresses decomposition of electrolyte solution as mentioned above is fully exhibited.

In addition, the water-soluble polymer has high solubility in water and can be easily adsorbed onto the negative electrode active material. For this reason, in the whole slurry composition for negative electrodes of this invention, a water-soluble polymer can cover the surface of the particle | grains of a negative electrode active material, and can improve the dispersibility of the particle | grains of a negative electrode active material. Therefore, since the agglomerate of a negative electrode active material hardly arises at the time of application | coating of the slurry composition for negative electrodes, a coating film with a uniform film thickness and a composition can be easily formed. Moreover, in the negative electrode active material layer obtained from the coating film formed in this way, since a negative electrode active material is disperse | distributed favorably, the electric capacity of a secondary battery can be improved.

In addition, since the water-soluble polymer is highly flexible and flexible, it is easy to adhere to the surface of the current collector and the surface of the negative electrode active material without a gap. For this reason, a water-soluble polymer can supplement binding to the electrical power collector and a negative electrode active material by a particulate-form binder, and can improve adhesive force. Therefore, it is possible to improve the adhesiveness with respect to the electrical power collector of a negative electrode active material layer.

(Sulfonic acid group-containing monomer unit)

Sulfonic acid group-containing monomer unit contained in the water-soluble polymer is a repeating unit obtained by polymerizing a monomer containing a sulfonic acid group (-SO ₃ H). Examples of the monomer containing sulfonic acid include a sulfonic acid group-containing monomer or salt thereof having no functional group other than a sulfonic acid group, a monomer containing an amide group and a sulfonic acid group or a salt thereof, and a monomer containing a hydroxyl group and a sulfonic acid group or a salt thereof Can be mentioned. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of sulfonic acid group containing monomeric unit, and may contain it combining two or more types by arbitrary ratios.

As a sulfonic acid group containing monomer which does not have a functional group other than a sulfonic acid group, For example, the monomer which sulfonated one of the conjugated double bonds of diene compounds, such as isoprene and butadiene, vinylsulfonic acid, styrene sulfonic acid, allyl sulfonic acid, and sulfoethyl methacrylate , Sulfopropyl methacrylate, sulfobutyl methacrylate and the like. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As a monomer containing an amide group and a sulfonic acid group, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) etc. are mentioned, for example. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

As a monomer containing a hydroxyl group and a sulfonic acid group, 3-aryloxy-2-hydroxypropanesulfonic acid (HAPS) etc. are mentioned, for example. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Among these, monomers containing styrene sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and other amide groups and sulfonic acid groups, and salts thereof are preferable.

The ratio of the sulfonic acid group-containing monomer unit in the water-soluble polymer is 0.1% by weight or more, preferably 1% by weight or more, while 15% by weight or less, preferably 10% by weight or less. When the presence density of the sulfonic acid group which a water-soluble polymer has has increased, the dispersibility of the slurry for negative electrodes improves. Moreover, since a sulfonic acid group produces a crosslinking reaction at the time of normally manufacturing the negative electrode of this invention, a crosslinked structure is formed by a sulfonic acid group in a negative electrode active material layer. In this case, when the water-soluble polymer has a sufficient amount of sulfonic acid group, the number of crosslinked structures can be increased to increase the strength of the negative electrode active material layer, and the high temperature storage characteristics and the low temperature output characteristics of the secondary battery can be improved. Therefore, it is preferable that a water-soluble polymer contains many sulfonic acid group containing monomeric units as mentioned above. However, if the sulfonic acid group-containing monomer unit is too large, relatively other monomer units may be reduced, and the adsorption and strength of the water-soluble polymer to the negative electrode active material may be reduced, so that the amount of the sulfonic acid group-containing monomer unit is less than or equal to the upper limit of the above range. It is desirable to be.

(Fluorine-containing (meth) acrylic acid ester monomer unit)

The fluorine-containing (meth) acrylic acid ester monomeric unit contained in the water-soluble polymer is a repeating unit obtained by polymerizing the fluorine-containing (meth) acrylic acid ester monomer as units other than the sulfonic acid group-containing monomer unit described above.

As a fluorine-containing (meth) acrylic acid ester monomer, the monomer represented by following formula (I) is mentioned, for example.

[Formula 1]

In said formula (I), R <^1> represents a hydrogen atom or a methyl group.

In said Formula (I), R <^2> represents the hydrocarbon group containing a fluorine atom. Carbon number of a hydrocarbon group is 1 or more normally, and is 18 or less normally. Moreover, one may be sufficient as the number of the fluorine atoms which R <^2> contains, and two or more may be sufficient as it.

Examples of the fluorine-containing (meth) acrylic acid ester monomer represented by formula (I) include (meth) acrylic acid fluoride, aryl (meth) acrylate, and aralkyl (meth) acrylate. Especially, alkyl (meth) acrylic-acid fluoride is preferable. Specific examples of such monomers include (meth) acrylic acid trifluoromethyl, (meth) acrylic acid 2,2,2-trifluoroethyl, (meth) acrylic acid β- (perfluorooctyl) ethyl, and (meth) acrylic acid 2 , 2,3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-perfluoro-1-nonyl , (Meth) acrylic acid 1H, 1H, 11H-perfluorodecyl, perfluorooctyl (meth) acrylate, (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri (Meth) acrylic acid perfluoroalkyl esters, such as fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl, etc. are mentioned.

A fluorine-containing (meth) acrylic acid ester monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of fluorine-containing (meth) acrylic acid ester monomeric unit, and may contain it combining two or more types by arbitrary ratios.

The proportion of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is 0.5% by weight or more, preferably 1% by weight or more, and 10% by weight or less, preferably 5% by weight or less. Low temperature output characteristics of a secondary battery can be improved by making the quantity of a fluorine-containing (meth) acrylic acid ester monomeric unit more than the lower limit of the said range. Moreover, by using below an upper limit, a water-soluble polymer becomes excessively flexible and it can prevent that durability of a negative electrode falls.

(Arbitrary unit)

The water-soluble polymer can contain repeating units other than the sulfonic acid group containing monomeric unit and fluorine-containing (meth) acrylic acid ester monomeric unit mentioned above, unless the effect of this invention is remarkably impaired. Such a repeating unit can be made into the repeating unit obtained by superposing | polymerizing the monomer copolymerizable with a sulfonic acid group containing monomer and a fluorine-containing (meth) acrylic acid ester monomer.

(Any unit: ethylenic unsaturated carboxylic monomer unit)

For example, the water soluble polymer may contain ethylenically unsaturated carboxylic monomer units. An ethylenic unsaturated carboxylic monomer unit is a repeating unit obtained by superposing | polymerizing an ethylenic unsaturated carboxylic monomer.

As an ethylenic unsaturated carboxylic monomer, an ethylenic unsaturated monocarboxylic acid and its derivative (s), ethylenic unsaturated dicarboxylic acid, its acid anhydride, derivatives thereof, etc. are mentioned, for example. Among these, since the water solubility of the water-soluble polymer from which ethylenic unsaturated monocarboxylic acid is obtained can be improved more, it is preferable.

Acrylic acid, methacrylic acid, crotonic acid, etc. are mentioned as an example of ethylenic unsaturated monocarboxylic acid. Examples of derivatives of ethylenically unsaturated monocarboxylic acids include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-dia Minoacrylic acid etc. are mentioned. Maleic acid, fumaric acid, itaconic acid, etc. are mentioned as an example of ethylenic unsaturated dicarboxylic acid. As an example of the acid anhydride of ethylenic unsaturated dicarboxylic acid, maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, etc. are mentioned. Examples of the derivative of ethylenically unsaturated dicarboxylic acid include maleic acid substituted with a hydrocarbon group such as methyl maleic acid, dimethyl maleic acid and phenyl maleic acid; halogenated maleic acid such as chloromaleic acid, dichloromaleic acid and fluoromaleic acid; And maleic acid esters such as methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate. Among these, ethylenic unsaturated monocarboxylic acids, such as acrylic acid and methacrylic acid, are preferable. It is because the dispersibility with respect to the water of the obtained water-soluble polymer can be improved more.

An ethylenic unsaturated carboxylic monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of ethylenically unsaturated carboxylic monomer unit, and may contain it combining two or more types by arbitrary ratios.

In the water-soluble polymer, the proportion of the ethylenically unsaturated carboxylic monomer unit is preferably 5% by weight or more, more preferably 10% by weight or more, preferably 35% by weight or less, and more preferably 30% by weight or less. to be. By making the quantity of an ethylenic unsaturated carboxylic monomer unit more than the lower limit of the said range, the adsorption property of the water-soluble polymer with respect to the negative electrode active material can be improved, and the dispersibility of a negative electrode active material and adhesiveness with respect to an electrical power collector can be improved. Moreover, since the flexibility of a water-soluble polymer can be improved by using below an upper limit, the flexibility of a negative electrode can be improved, a lack of a negative electrode or a crack can be prevented, and durability can be improved.

(Arbitrary unit: (meth) acrylic acid ester monomeric unit)

For example, a water-soluble polymer can contain a (meth) acrylic acid ester monomeric unit. The (meth) acrylic acid ester monomeric unit is a repeating unit obtained by superposing | polymerizing the (meth) acrylic acid ester monomer. However, among the (meth) acrylic acid ester monomers, those corresponding to the sulfonic acid group-containing monomer or the fluorine-containing (meth) acrylic acid ester monomer described above are included in the sulfonic acid group-containing monomer or the fluorine-containing (meth) acrylic acid ester monomer in the calculation of the amount ratio. It does not contain in the (meth) acrylic acid ester monomer. For example, what contains fluorine among the (meth) acrylic acid ester monomers is distinguished from a (meth) acrylic acid ester monomer as a fluorine-containing (meth) acrylic acid ester monomer.

As the (meth) acrylic acid ester monomer, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate Acrylate alkyl esters such as heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; methyl methacrylate; , Ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate Acrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate Agent, and the like n- tridecyl methacrylate, stearyl methacrylate such as methacrylic acid alkyl ester.

The (meth) acrylic acid ester monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of (meth) acrylic acid ester monomeric unit, and may contain it combining two or more types by arbitrary ratios.

In the water-soluble polymer, the proportion of the (meth) acrylic acid ester monomer unit is preferably 30% by weight or more, more preferably 35% by weight or more, particularly preferably 40% by weight or more, and preferably 70% by weight. It is as follows. By making the quantity of a (meth) acrylic acid ester monomeric unit below the upper limit of the said range, adhesiveness with respect to the electrical power collector of a negative electrode active material can be made high, and the flexibility of a negative electrode can be improved by using more than the lower limit of the said range.

(Arbitrary unit: crosslinkable monomer unit)

In addition, for example, the water-soluble polymer may contain a crosslinkable monomer unit. The crosslinkable monomer unit is a structural unit capable of forming a crosslinked structure during or after polymerization by heating or energizing the crosslinkable monomer. By containing a crosslinkable monomer unit, since a water-soluble polymer can be bridge | crosslinked, the strength and stability of the film formed from a water-soluble polymer can be improved.

As a crosslinkable monomer, the monomer which can form a crosslinked structure at the time of superposition | polymerization can be used. As an example of a crosslinkable monomer, the monomer which has a 2 or more reactive group per molecule is mentioned. More specifically, the monofunctional monomer which has a heat crosslinkable crosslinkable group and one olefinic double bond per molecule, and the polyfunctional monomer which has two or more olefinic double bonds per molecule can be mentioned.

As an example of the heat crosslinkable crosslinkable group contained in a monofunctional monomer, an epoxy group, N-methylolamide group, an oxetanyl group, an oxazoline group, and a combination thereof are mentioned. Among these, an epoxy group is more preferable at the point which adjusts bridge | crosslinking and crosslinking density easily.

As an example of the crosslinkable monomer which has an epoxy group as a heat crosslinkable crosslinkable group, and has an olefinic double bond, vinylglycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, o-allylphenyl glycidyl ether Unsaturated glycidyl ethers such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5, Monoepoxides of dienes or polyenes such as 9-cyclododecadiene; alkenyls such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2-epoxy-9-decene Epoxides; and glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl 4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, 4-methyl-3-cyclohexenecar Glycidyl of unsaturated carboxylic acids such as the glycidyl ester of the acids and the like can be mentioned glycidyl esters.

Examples of the crosslinkable monomer having an N-methylolamide group as the heat crosslinkable crosslinkable group and having an olefinic double bond include (meth) acrylamides having methylol groups such as N-methylol (meth) acrylamide and the like. Can be mentioned.

As an example of the crosslinkable monomer which has an oxetanyl group as a heat crosslinkable crosslinkable group, and has an olefinic double bond, 3-((meth) acryloyloxymethyl) oxetane and 3-((meth) acryloyloxy Methyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2- ( (Meth) acryloyloxymethyl) -4-trifluoromethyloxetane etc. are mentioned.

Examples of the crosslinkable monomer having an oxazoline group as the heat crosslinkable crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, and 2-vinyl- 5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, And 2-isopropenyl-5-ethyl-2-oxazoline.

Examples of the polyfunctional monomer having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxy Ethane, trimethylolpropane- diallyl ether, allyl or vinyl ether, polyallylamine, methylenebisacrylamide, divinylbenzene, etc. of the polyfunctional alcohol of that excepting the above are mentioned.

Especially, as a crosslinkable monomer, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are preferable.

In the water-soluble polymer, the content ratio of the crosslinkable monomer unit is preferably 0.1% or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 2% by weight or less. Is 1.5% by weight or less, particularly preferably 1% by weight or less. By carrying out the content rate of a crosslinkable monomer unit in the said range, swelling degree can be suppressed and durability of an electrode can be improved. Here, the ratio of the crosslinkable monomer unit in a water-soluble polymer generally corresponds with the ratio (injection ratio) of the crosslinkable monomer in all the monomers of a water-soluble polymer.

(Arbitrary unit: reactive surfactant monomer unit)

For example, the water-soluble polymer may contain the reactive surfactant monomer unit. A reactive surfactant monomeric unit is a structural unit obtained by superposing | polymerizing a reactive surfactant monomer. The reactive surfactant monomer unit constitutes part of the water soluble polymer and can also function as a surfactant.

A reactive surfactant monomer is a monomer which has a polymeric group copolymerizable with another monomer, and also has surfactant groups (hydrophilic group and hydrophobic group). Typically, the reactive surfactant monomer has a polymerizable unsaturated group, which also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group possessed by the reactive surfactant monomer include vinyl group, allyl group, vinylidene group, propenyl group, isopropenyl group, and isobutylidene group. The kind of such a polymerizable unsaturated group may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

A reactive surfactant monomer is a part which expresses hydrophilicity, and usually has a hydrophilic group. Reactive surfactant monomers are classified into anionic, cationic, and nonionic surfactants according to the type of hydrophilic group.

Examples of the anionic hydrophilic group include -SO ₃ M, -COOM, and -PO (OM) ₂ . M represents a hydrogen atom or a cation here. Examples of the cation include alkali metal ions such as lithium, sodium and potassium; alkaline earth metal ions such as calcium and magnesium; ammonium ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; And ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.

Examples of cationic hydrophilic groups include primary amine salts such as -NH ₂ HX, secondary amine salts such as -NHCH ₃ HX, tertiary amine salts such as -N (CH ₃ ) ₂ HX, and -N ⁺ (CH _{3) 3} X ^-, and the like quaternary amine salts and the like. X represents a halogen group here.

As an example of the nonionic hydrophilic group, -OH is mentioned.

As an example of a preferable reactive surfactant monomer, the compound represented by following formula (II) is mentioned.

[Formula 2]

In Formula (II), R represents a bivalent coupling group. As an example of R, -Si-O- group, a methylene group, and a phenylene group are mentioned.

In Formula (II), R <^3> represents a hydrophilic group. Examples of R ³ include -SO ₃ NH ₄ .

In Formula (II), n represents the integer of 1 or more and 100 or less.

As another example of a preferred reactive surfactant, an alkenyl group having a structural unit having a structure formed by polymerizing ethylene oxide and a structural unit having a structure formed by polymerizing butylene oxide, and further having a terminal double bond at the terminal and- compounds having SO ₃ NH ₄ there may be mentioned (for example, trade name "LA temreu PD-104" and "la temreu PD-105", manufactured by Kao Corporation).

A reactive surfactant monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In the water-soluble polymer, the content of the reactive surfactant unit is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5% by weight or less. Preferably it is 4 weight% or less, Especially preferably, it is 2 weight% or less. By making the content rate of a reactive surfactant unit more than the lower limit of the said range, the dispersibility of a slurry composition can be improved. Moreover, durability of an electrode can be improved by using below an upper limit.

(Any unit: other units)

As an example of the arbitrary unit which a water-soluble polymer can contain, the repeating unit obtained by superposing | polymerizing various arbitrary copolymerizable monomers in addition to what was illustrated above is mentioned. As a monomer which can be copolymerized, For example, Carboxylic acid ester monomer which has 2 or more carbon-carbon double bonds, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylol propane triacrylate; Styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene and divinylbenzene; acrylamide, N Amide monomers such as -methylol acrylamide; α, β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; olefin monomers such as ethylene and propylene; (fluorine such as vinyl chloride and vinylidene chloride) Halogen atom-containing monomers other than the containing (meth) acrylic acid ester monomer; vinyl acetate, vinyl propionate Vinyl ester monomers such as vinyl butyrate and vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl Vinyl ketone monomers such as vinyl ketone; heterocyclic-containing vinyl compound monomers such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; and the like.

Said copolymerizable monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Therefore, the water-soluble polymer may contain only one type of unit based on such a copolymerizable monomer, and may contain it combining two or more types by arbitrary ratios. In the water-soluble polymer, the proportion of units based on such copolymerizable monomers is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight.

(Characteristics of Water-Soluble Polymer)

The weight average molecular weight of the water-soluble polymer is usually smaller than the polymer to be a particulate binder, preferably 500 or more, more preferably 700 or more, particularly preferably 1000 or more, preferably 500000 or less, more preferably 250000 Hereinafter, Especially preferably, it is 100000 or less. By setting the weight average molecular weight of the water-soluble polymer to the lower limit of the above range, the strength of the water-soluble polymer can be increased to form a stable protective layer covering the negative electrode active material. Thus, for example, the dispersibility of the negative electrode active material and the high temperature storage characteristics of the secondary battery. Etc. can be improved. Moreover, since water-soluble polymer can be made flexible by using below the upper limit of the said range, for example, suppression of expansion of a negative electrode, improvement of adhesiveness with respect to the electrical power collector of a negative electrode active material layer, etc. are attained. The weight average molecular weight of a water-soluble polymer can be calculated | required by GPC as the value of polystyrene conversion which made the solution which melt | dissolved 0.85 g / mL sodium nitrate in 10 volume% aqueous solution of dimethylformamide as a developing solvent.

The glass transition temperature of the water-soluble polymer is preferably 0 ° C. or higher, more preferably 5 ° C. or higher, preferably 100 ° C. or lower, and more preferably 50 ° C. or lower. When the glass transition temperature of the water-soluble polymer is in the above range, the adhesion and flexibility of the negative electrode can be made compatible. The glass transition temperature of the water-soluble polymer can be adjusted by combining various monomers.

The viscosity of the water-soluble polymer in the case of 1 wt% aqueous solution is usually 0.1 mPa · s or more, preferably 1 mPa · s or more, more preferably 10 mPa · s or more, and usually 20000 mPa · s or less, preferably Preferably it is 10000 mPa * s or less, More preferably, it is 5000 mPa * s or less. By making said viscosity more than the lower limit of the said range, the intensity | strength of a water-soluble polymer can be made high, the durability of a negative electrode can be improved, and below the upper limit, the applicability | paintability of the slurry composition for negative electrodes is favorable, and a collector and a negative electrode active material The adhesion strength of the layer can be improved. Said viscosity can be adjusted with the molecular weight of a water-soluble polymer, for example. Said viscosity is a value when it measures by 25 degreeC and rotation amount 60rpm using a Brookfield viscometer.

(Method for producing water-soluble polymer)

As a manufacturing method of a water-soluble polymer, the monomer composition containing the sulfonic-acid group containing monomer, the fluorine-containing (meth) acrylic acid ester monomer, and arbitrary monomers as needed, for example can be superposed | polymerized in an aqueous solvent, and can be manufactured, for example. . An aqueous solvent and a polymerization method can be made similar to manufacture of a particulate-form binder, for example. As a result, an aqueous solution in which a water-soluble polymer is dissolved in an aqueous solvent is usually obtained. Although the water-soluble polymer may be taken out from the aqueous solution obtained in this way, normally, the slurry composition for negative electrodes is manufactured using the water-soluble polymer in the state dissolved in the aqueous solvent, and a negative electrode is manufactured using this slurry composition for negative electrodes.

Since the said aqueous solution which contains a water-soluble polymer in an aqueous solvent is acidic normally, you may alkalinize to pH 7-pH 13 as needed. Thereby, the handleability of aqueous solution can be improved and the applicability | paintability of the slurry composition for negative electrodes can be improved. As a method of alkalizing to pH 7-13, For example, Alkali metal aqueous solution, such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution, and potassium hydroxide aqueous solution; Alkaline earth metal aqueous solution, such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution; Alkali aqueous solution, such as aqueous ammonia solution The method of mixing is mentioned. Said aqueous alkali solution may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

(Amount of water soluble polymer)

The amount of the water-soluble polymer is preferably 0.1 part by weight or more, more preferably 0.5 part by weight or more, particularly preferably 1 part by weight or more, preferably 10 parts by weight or less, more preferably 100 parts by weight of the negative electrode active material. Preferably 5 parts by weight or less. By setting the amount of the water-soluble polymer in the above range, suppression of expansion of the negative electrode accompanying charge and discharge; improvement of high temperature storage characteristics, high temperature cycle characteristics, and low temperature output characteristics of the secondary battery; application of the slurry composition for the negative electrode to a current collector Improvement of coating property at the time; And the above-mentioned effects, such as improvement of adhesiveness with respect to the electrical power collector of a negative electrode active material layer, can be exhibited stably.

1-4. Arbitrary components of the negative electrode active material layer]

In the negative electrode of the present invention, the negative electrode active material layer may contain an optional component in addition to the above-described negative electrode active material, particulate binder, and water-soluble polymer. Examples of the optional component include viscosity modifiers, conductive agents, reinforcing materials, leveling agents, electrolyte additives, and the like. These will not be specifically limited if it does not affect battery reaction. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

A viscosity modifier is a component used in order to adjust the viscosity of the slurry composition for negative electrodes of this invention, and to improve the dispersibility and applicability of the slurry composition for negative electrodes. Usually, the viscosity modifier contained in the slurry composition for negative electrodes will remain in a negative electrode active material layer.

As a viscosity modifier, it is preferable to use a water-soluble polysaccharide. As a polysaccharide, a natural high molecular compound, a cellulose semisynthetic high molecular compound, etc. are mentioned, for example. In addition, a viscosity modifier may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Examples of the natural polymer compound include polysaccharides and proteins derived from plants or animals. Moreover, the natural type high molecular compound which became the fermentation process by microorganisms, the process by heat, etc. as needed can also be illustrated. These natural high molecular compounds can be classified as plant natural high molecular compounds, animal natural high polymer compounds, microbial natural high polymer compounds and the like.

As the plant-based natural polymer compound, for example, gum arabic, tragacanth gum, galactan, guar gum, carab gum, karaya gum, carrageenan, pectin, agar, queen's seed (quincelo), algocolloid (algae extract), Starch (derived from rice, corn, potatoes, wheat and the like), glycyrrhizin and the like. Moreover, as an animal-type natural high molecular compound, collagen, casein, albumin, gelatin, etc. are mentioned, for example. Examples of the microbial natural polymer compound include xanthan gum, dextran, succinoglucan and pullulan.

Cellulose semisynthetic polymer compounds can be classified into nonionic, anionic and cationic.

Examples of the nonionic cellulose semisynthetic polymer compound include alkyl celluloses such as methyl cellulose, methyl ethyl cellulose, ethyl cellulose, and microcrystalline cellulose; hydroxyethyl cellulose, hydroxybutyl methyl cellulose, hydroxypropyl cellulose, Hydroxyalkyl celluloses such as hydroxypropyl methyl cellulose, hydroxyethyl methyl cellulose, hydroxypropyl methyl cellulose stearoxy ether, carboxymethyl hydroxyethyl cellulose, alkyl hydroxyethyl cellulose, and nonoxynyl hydroxyethyl cellulose. Can be.

As an anionic cellulose semisynthetic high molecular compound, the alkyl cellulose which substituted the said nonionic cellulose semisynthetic high molecular compound by various induction groups, its sodium salt, ammonium salt, etc. are mentioned. Specific examples thereof include sodium cellulose sulfate, methyl cellulose, methyl ethyl cellulose, ethyl cellulose, carboxymethyl cellulose (CMC) and salts thereof.

Examples of the cationic cellulose semisynthetic polymer compound include low nitrogen hydroxyethyl cellulose dimethyl diallyl ammonium chloride (polyquaternium-4) and chloride O- [2-hydroxy-3- (trimethylammonio) propyl. ] Hydroxyethyl cellulose (polyquaternium-10), chloride O- [2-hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium-24), etc. are mentioned.

Among these, a cellulose semisynthetic high molecular compound, its sodium salt, and its ammonium salt are preferable at the point which can acquire cationic, anionic, and positive characteristic. Among them, anionic cellulose semisynthetic polymer compounds are particularly preferable from the viewpoint of dispersibility of the negative electrode active material.

Moreover, the etherification degree of a cellulose semisynthetic high molecular compound becomes like this. Preferably it is 0.5 or more, More preferably, it is 0.6 or more, Preferably it is 1.0 or less, More preferably, it is 0.8 or less. Here, the degree of etherification refers to the degree of substitution of a hydroxyl group (three) with respect to a substituent on a carboxymethyl group or the like per anhydroglucose unit in cellulose. The degree of etherification can theoretically take the value of 0-3. When the degree of etherification is in the above range, the cellulosic semisynthetic polymer compound is excellent in dispersibility in that it is adsorbed on the surface of the negative electrode active material and also shows compatibility with water, and thus the negative electrode active material is not dispersed to the primary particle level. Can be.

In addition, when using a high molecular compound as a viscosity modifier, the average polymerization degree of the viscosity modifier computed from the intrinsic viscosity calculated | required from a Uberode viscometer becomes like this. Preferably it is 500 or more, More preferably, it is 1000 or more, Preferably it is 2500 or less, More preferably, it is 2000 or less, Especially preferably, it is 1500 or less. The average degree of polymerization of the viscosity modifier may affect the fluidity of the slurry composition for negative electrodes of the present invention, the film uniformity of the negative electrode active material layer, and the process on the process. By setting the average degree of polymerization in the above-described range, the stability over time of the slurry composition for negative electrodes of the present invention is improved, and coating without agglomerates and without thickness nonuniformity becomes possible.

The amount of the viscosity modifier is preferably 0 parts by weight or more, and preferably 0.5 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. By making quantity of a viscosity modifier into the said range, it can be set as the preferable range which is easy to handle the viscosity of the slurry composition for negative electrodes of this invention.

A electrically conductive agent is a component which improves the electrical contact of negative electrode active materials. By containing a electrically conductive agent, the discharge rate characteristic of the secondary battery of this invention can be improved.

As the conductive agent, for example, conductive carbon such as acetylene black, Ketjen black, carbon black, graphite, vapor grown carbon fiber, and carbon nanotube can be used. In addition, a electrically conductive agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The amount of the conductive agent is preferably 1 to 20 parts by weight, more preferably 1 to 10 parts by weight based on 100 parts by weight of the negative electrode active material.

As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used, for example. A reinforcing material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using a reinforcing material, a strong and flexible negative electrode can be obtained, and a secondary battery exhibiting excellent long-term cycle characteristics can be realized.

The amount of the reinforcing material is usually 0.01 parts by weight or more, preferably 1 part by weight or more, and usually 20 parts by weight or less, preferably 10 parts by weight or less, based on 100 parts by weight of the negative electrode active material. By setting the amount of the reinforcing agent in the above range, the secondary battery can exhibit high capacity and high load characteristics.

As a leveling agent, surfactant, such as an alkyl type surfactant, silicone type surfactant, a fluorine type surfactant, and a metal type surfactant, is mentioned, for example. A leveling agent may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using a leveling agent, the cratering which arises at the time of application | coating of the slurry composition for negative electrodes can be prevented, or the smoothness of a negative electrode can be improved.

The amount of the leveling agent is preferably 0.01 part by weight to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. When the leveling agent is in the above range, the productivity, smoothness and battery characteristics at the time of producing the negative electrode are excellent. Moreover, by containing surfactant, dispersibility, such as a negative electrode active material, can be improved in the slurry composition for negative electrodes, and also the smoothness of the negative electrode obtained by it can be improved.

As electrolyte solution additive, vinylene carbonate etc. are mentioned, for example. An electrolyte solution additive may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. By using electrolyte solution additive, decomposition of electrolyte solution can be suppressed, for example.

The amount of the electrolyte additive is preferably 0.01 part by weight to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. By carrying out quantity of electrolyte solution additive in the said range, the secondary battery excellent in cycling characteristics and high temperature characteristic can be implement | achieved.

Moreover, the negative electrode active material layer may contain nano fine particles, such as fumed silica and fumed alumina, for example. Nanoparticles may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. When it contains a nanoparticle, since the thixotropy of the slurry composition for negative electrodes can be adjusted, the leveling property of the negative electrode of this invention obtained by it can be improved.

The amount of the nanoparticles is preferably 0.01 part by weight to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material. When the nanoparticles are in the above range, the stability and productivity of the slurry composition for negative electrodes can be improved, and high battery characteristics can be realized.

1-5. Current collector and negative electrode active material layer]

The negative electrode of this invention usually contains an electrical power collector and the negative electrode active material layer formed in the surface of an electrical power collector, and this negative electrode active material layer contains a negative electrode active material, a particulate-form binder, and a water-soluble polymer. The current collector is usually in the form of a sheet, and the negative electrode active material layer may be formed on at least one side of the sheet-like collector, but is preferably formed on both surfaces.

The current collector for the negative electrode is not particularly limited as long as it is an electrically conductive material and is an electrochemically durable material, but a metal material is preferable because it has heat resistance. As a material of the electrical power collector for negative electrodes, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. are mentioned, for example. Especially, copper is especially preferable as an electrical power collector used for a secondary battery negative electrode. In addition, said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The shape of the current collector is not particularly limited, but a sheet-like one having a thickness of about 0.001 mm to 0.5 mm is preferable.

In order to raise the adhesive strength with a negative electrode active material layer, you may use an electrical power collector, roughening a surface previously. As a roughening method, a mechanical polishing method, an electrolytic polishing method, a chemical polishing method, etc. are mentioned, for example. In the mechanical polishing method, a wire brush provided with abrasive cloth, grindstone, emery buff, steel wire, or the like, on which abrasive particles are fixed, is usually used. Moreover, in order to improve the adhesive strength and electroconductivity of a negative electrode active material layer, you may form an intermediate | middle layer on the surface of an electrical power collector.

The thickness of the negative electrode active material layer formed on the surface of the current collector is usually 5 m or more, preferably 30 m or more, and usually 300 m or less, preferably 250 m or less. By the thickness of a negative electrode active material layer being in the said range, load characteristic and cycling characteristics can be made favorable.

The content rate of the negative electrode active material in a negative electrode active material layer becomes like this. Preferably it is 85 weight% or more, More preferably, it is 88 weight% or more, Preferably it is 99 weight% or less, More preferably, it is 97 weight% or less. By making the content rate of a negative electrode active material into the said range, the negative electrode which shows a high capacity and shows flexibility and binding property can be implement | achieved.

[2. Slurry composition for negative electrodes and manufacturing method of negative electrode]

Although the negative electrode for secondary batteries of this invention can be manufactured by arbitrary manufacturing methods, Preferably, the slurry composition for secondary battery negative electrodes of this invention described below (Hereinafter, "the slurry composition for negative electrodes of this invention" suitably. It can manufacture by the manufacturing method (henceforth "the manufacturing method of the negative electrode of this invention" suitably.) Of the negative electrode for secondary batteries of this invention described below.

2-1. Slurry Composition for Negative Electrodes]

The slurry composition for negative electrodes of this invention is a slurry-like composition containing a negative electrode active material, a particulate-form binder, and a water-soluble polymer.

The slurry composition for negative electrodes of this invention contains a solvent further normally. As the solvent, it is preferable to use water or a mixture of water and a liquid other than water from the viewpoint of reducing the environmental load.

Water functions as a solvent or a dispersion medium in the slurry composition for negative electrodes, and can disperse a negative electrode active material, disperse | distribute a particulate binder in particulate form, or dissolve a water-soluble polymer. It is preferable to combine the liquid dissolving the particulate binder and the water-soluble polymer because the dispersion of the negative electrode active material is stabilized by adsorbing the particulate binder and the water-soluble polymer onto the surface of the negative electrode active material.

It is preferable to select the kind of liquid combined with water from a drying rate or an environmental point of view. Preferable examples include cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate and γ-butyrolactone esters such as ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl Alcohols, such as ether; Amides, such as N-methylpyrrolidone and N, N- dimethylformamide, etc. are mentioned, Especially, N-methylpyrrolidone (NMP) is preferable. These liquids may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

It is preferable to adjust the quantity of the solvent in the slurry composition for negative electrodes so that the viscosity of the slurry composition for negative electrodes of this invention may become a viscosity suitable for application | coating. Specifically, the concentration of the solid content of the slurry composition for negative electrodes of the present invention is preferably 30% by weight or more, more preferably 40% by weight or more, preferably 90% by weight or less, and more preferably 80% by weight or less. Used to adjust the amount to be.

The slurry composition for negative electrodes may contain arbitrary components other than a negative electrode active material, a particulate-form binder, a water-soluble polymer, and a solvent as needed. The amount of the optional component is usually the same as the amount of the optional component contained in the negative electrode active material layer. In such a slurry composition for negative electrodes of the present invention, some of the water-soluble polymers are usually dissolved in water, but some of the water-soluble polymers are adsorbed on the surface of the negative electrode active material, whereby the negative electrode active material is covered with a stable layer of the water-soluble polymer, Dispersibility in the solvent of the negative electrode active material is improved. For this reason, the applicability | paintability at the time of apply | coating to the electrical power collector for the slurry composition for negative electrodes of this invention is favorable.

The preparation method of the slurry composition for negative electrodes of this invention is not specifically limited, It can manufacture by mixing a negative electrode active material, a particulate-form binder, a water-soluble polymer, a solvent, and arbitrary components used as needed. Although the mixing method is not specifically limited, For example, the method of using mixing apparatuses, such as agitation, shaking, and rotation, is mentioned. Moreover, the method using the dispersion kneading apparatuses, such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader, is mentioned.

2-2. Manufacturing method of negative electrode]

By applying the slurry composition for negative electrodes of this invention to the surface of an electrical power collector, and drying as needed, a negative electrode active material layer can be formed on the surface of an electrical power collector, and the negative electrode of this invention can be manufactured.

The method of apply | coating the slurry composition for negative electrodes of this invention to the surface of an electrical power collector is not specifically limited. For example, methods, such as a doctor blade method, a dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, and the brush coating method, are mentioned.

As an example of a drying method, the drying method by the warm air, hot air, low humidity wind drying, vacuum drying, irradiation by (far) infrared rays, an electron beam, etc. are mentioned, for example. Drying time is 1 minute-40 minutes normally, and drying temperature is 40 degreeC-180 degreeC normally.

Moreover, after apply | coating and drying the slurry composition for negative electrodes on the surface of an electrical power collector, it is preferable to pressurize a negative electrode active material layer using a metal mold | die press, a roll press, etc. as needed. By a pressurizing process, the porosity of a negative electrode active material layer can be made low. Porosity becomes like this. Preferably it is 5% or more, More preferably, it is 7% or more, Preferably it is 30% or less, More preferably, it is 20% or less. By setting the porosity to be equal to or higher than the lower limit of the above range, a high volume capacity can be easily obtained, making it difficult to peel the negative electrode active material layer from the current collector, and by setting it to an upper limit or less, high charging efficiency and discharge efficiency can be obtained.

In addition, when a negative electrode active material layer contains a curable polymer, it is preferable to harden the said polymer after formation of a negative electrode active material layer.

[3. Secondary battery]

The secondary battery of this invention is equipped with a positive electrode, a negative electrode, electrolyte solution, and a separator, The said negative electrode is a negative electrode of this invention.

Since the negative electrode of this invention is provided, the secondary battery of this invention can suppress expansion of the negative electrode accompanying charge / discharge, or can make it difficult to reduce capacity, even if stored in a high temperature environment. Moreover, usually, the high temperature cycling characteristics and low temperature output characteristics of the secondary battery of this invention can be improved, or adhesiveness with respect to the electrical power collector of a negative electrode active material layer can also be improved.

3-1. Positive electrode]

The positive electrode is usually provided with a positive electrode active material layer containing a positive electrode active material and a binder for positive electrode formed on the surface of the current collector and the current collector.

The current collector of the positive electrode is not particularly limited as long as it is an electrically conductive and electrochemically durable material. As a current collector of a positive electrode, you may use the electrical power collector used for the negative electrode of this invention, for example. Especially, aluminum is especially preferable.

As the positive electrode active material, for example, when the secondary battery of the present invention is a lithium ion secondary battery, a substance capable of inserting and detaching lithium ions is used. Such positive electrode active materials are roughly classified into those consisting of inorganic compounds and those containing organic compounds.

As a positive electrode active material which consists of inorganic compounds, a transition metal oxide, a transition metal sulfide, the lithium containing composite metal oxide of lithium and a transition metal, etc. are mentioned, for example.

As said transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo etc. are mentioned, for example.

As the transition metal oxide, for example, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , And V ₆ O _13. Among these, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferable in terms of cycle stability and capacity.

Examples of transition metal sulfides, for example, TiS there may be mentioned _2, TiS _3, amorphous MoS _2, FeS or the like.

As a lithium containing composite metal oxide, the lithium containing composite metal oxide which has a layered structure, the lithium containing composite metal oxide which has a spinel structure, the lithium containing composite metal oxide which has an olivine type structure, etc. are mentioned, for example.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co-Ni-Mn, and lithium of Ni-Mn-Al. A composite oxide, the lithium composite oxide of Ni-Co-Al, etc. are mentioned.

As the lithium-containing composite metal oxide having a spinel structure, for example, lithium manganese oxide (LiMn ₂ O ₄₎ or a different part of the Mn transition replaced by a metal _{Li [Mn 3/2 M 1} /2] O 4 ( where M, Cr, Fe, Co, Ni, Cu, etc.) etc. are mentioned.

As a lithium-containing composite metal oxide having an olivine-type structure, for example, Li _X MPO ₄ (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, An olivine-type lithium phosphate compound represented by at least 1 sort (s) chosen from the group which consists of Al, Si, B, and Mo, and X represents the number which satisfy | fills 0 <= X <= 2.

As a positive electrode active material which consists of organic compounds, conductive polymers, such as polyacetylene and poly- p-phenylene, are mentioned, for example.

Moreover, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound. For example, the iron-based oxide may be reduced and calcined in the presence of a carbon source material to produce a composite material covered with a carbon material, and the composite material may be used as a positive electrode active material. Although iron oxide tends to be inadequate in electrical conductivity, it can be used as a high performance positive electrode active material by making it a composite material as mentioned above.

Moreover, you may use what element-substituted the said compound partially as a positive electrode active material. Moreover, you may use the mixture of said inorganic compound and organic compound as a positive electrode active material.

In addition, a positive electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The volume average particle diameter of the particles of the positive electrode active material is usually 1 m or more, preferably 2 m or more, and usually 50 m or less, preferably 30 m or less. By making the volume average particle diameter of the particle | grains of a positive electrode active material into the said range, the quantity of the binder at the time of preparing a positive electrode active material layer can be reduced, and the fall of the capacity of a secondary battery can be suppressed. Moreover, in order to form a positive electrode active material layer, although the slurry composition for positive electrodes containing a positive electrode active material and a binder is prepared normally, it becomes easy to adjust to the appropriate viscosity which is easy to apply | coat the viscosity of this slurry composition for positive electrodes, and it is uniform. One positive electrode can be obtained.

Preferably the content rate of the positive electrode active material in a positive electrode active material layer is 90 weight% or more, More preferably, it is 95 weight% or more, Preferably it is 99.9 weight% or less, More preferably, it is 99 weight% or less. By making content of a positive electrode active material into the said range, the capacity | capacitance of a secondary battery can be made high and the flexibility of a positive electrode and binding property of an electrical power collector and a positive electrode active material layer can be improved.

As the binder for the positive electrode, for example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylics Resins such as ronitrile derivatives; soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, and vinyl soft polymers. In addition, a binder may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Moreover, components other than a positive electrode active material and a binder may contain in the positive electrode active material layer as needed. For example, a viscosity modifier, a electrically conductive agent, a reinforcing material, a leveling agent, electrolyte additive, etc. are mentioned, for example. Moreover, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The thickness of the positive electrode active material layer is usually 5 µm or more, preferably 10 µm or more, and usually 300 µm or less, preferably 250 µm or less. By the thickness of a positive electrode active material layer being in the said range, high characteristic can be implement | achieved in both a load characteristic and an energy density.

The positive electrode can be produced, for example, by the same production method as the above-described negative electrode.

3-2. Electrolyte solution]

As electrolyte solution, what melt | dissolved lithium salt as a supporting electrolyte in a non-aqueous solvent can be used, for example. As the lithium salt, for example, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ And lithium salts such as NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. LiPF ₆ , LiClO ₄ , CF ₃ SO ₃ Li, which is particularly soluble in a solvent and exhibits high dissociation degree, is preferably used. These may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

The amount of the supporting electrolyte is usually 1% by weight or more, preferably 5% by weight or more, and usually 30% by weight or less, preferably 20% by weight or less with respect to the electrolyte solution. Even if the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charge characteristics and discharge characteristics of the secondary battery may be lowered.

As a solvent used for electrolyte solution, if a supporting electrolyte is dissolved, it will not specifically limit. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC). Esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide and the like. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easy to be obtained and the use temperature range is wide. In addition, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Moreover, you may contain an additive in electrolyte solution as needed. As an additive, carbonate type compounds, such as vinylene carbonate (VC), are preferable, for example. In addition, an additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Incidentally, as an electrolyte other than the above, for example, polyethylene oxide, a gel polymer electrolyte impregnated with the electrolytic solution in the polymer electrolyte, such as polyacrylonitrile; may include sulfurized lithium, LiI, such as an inorganic solid electrolyte such as Li ₃ N .

3-3. Separator]

As the separator, a porous substrate having pores is usually used. Examples of the separator include (a) a porous separator having pores, (b) a porous separator having a polymer coat layer formed on one or both sides thereof, and (c) a porous separator having a porous resin coat layer containing inorganic ceramic powder. Can be mentioned. Examples thereof include solid polymer electrolytes such as polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymers. Polymer films for solvent or gel polymer electrolytes; separators coated with a gelled polymer coat layer; separators coated with a porous membrane layer made of an inorganic filler and a dispersant for an inorganic filler.

3-4. Manufacturing Method of Secondary Battery]

The manufacturing method of the secondary battery of this invention is not specifically limited. For example, a secondary battery can be manufactured by superimposing the above-mentioned negative electrode and positive electrode through a separator, winding them along a battery shape, bending them, and placing them in a battery container and injecting and sealing an electrolyte solution in the battery container. Can be. In addition, an overcurrent prevention element such as an expanded metal, a fuse, a PTC element, a lead plate, or the like may be placed, if necessary, to prevent pressure increase inside the battery and overcharge / discharge. The shape of the battery may be, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical shape, a square shape, or a flat type.

Example

Hereinafter, an Example is shown and this invention is demonstrated concretely. However, this invention is not limited to the Example shown below, You may change arbitrarily in the range which does not deviate from the Claim of this invention, and its equal range.

In the following description, "%" and "part" indicating the amount are based on weight unless otherwise specified. In addition, the operation demonstrated below was performed on the conditions of normal temperature and normal pressure, unless there is particular notice. In particular, the evaluation operation of a battery was performed at 25 degreeC unless there is particular notice.

[Assessment Methods]

Evaluation of the characteristic in the Example and the comparative example was performed as follows.

1. adhesion strength

The negative electrode manufactured by the Example and the comparative example was cut into the rectangle of length 100mm and width 10mm, and was used as the test piece. The surface of the negative electrode active material layer faced this test piece, and the cellophane tape was affixed on the surface of the negative electrode active material layer. At this time, what is prescribed | regulated to JIS Z1522 was used as a cellophane tape. In addition, the cellophane tape was fixed on a horizontal test bench. Then, the stress at the time of pulling one end of an electrical power collector perpendicularly upward at 50 mm / min of tensile velocity, and peeling off was measured. This measurement was performed 3 times, the average value was calculated | required, and the said average value was made into peeling strength (N / m). The larger the peeling strength, the larger the binding force to the current collector of the negative electrode active material layer, that is, the larger the bonding strength.

2. Slurry Stability

About the slurry composition for negative electrodes manufactured by the Example and the comparative example, the viscosity (eta) 0 in 25 degreeC and rotation amount 60rpm was measured with the Brookfield viscometer.

Then, after stopping the slurry composition for negative electrodes for 72 hours at 5 degreeC, it returned to 25 degreeC and measured the viscosity (eta) 1 similarly to the above. Comparing the viscosity before and after stopping still, if the rate of change of viscosity (= (η1-η0) / η0 × 100) is less than 10% increase, A, 10% increase or more to less than 30% increase, B, 30% increase or more, C I did it.

3. Applicability

The slurry composition for negative electrodes manufactured by the Example and the comparative example was apply | coated so that the film thickness after drying might be about 150 micrometers on the copper foil of thickness 20micrometer which is an electrical power collector, and it dried. This drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for copper foil at a speed | rate of 0.5 m / min. Then, it heat-processed at 120 degreeC for 2 minutes, and obtained the negative electrode. The obtained negative electrode was cut out to the dimension of 10 * 10cm, and the number of pinholes 0.1 mm or more in diameter was visually measured. The smaller the number of pinholes, the better the applicability.

4. Durable

(1) high temperature storage characteristics

After stopping the lithium ion secondary battery of the laminated cell manufactured by the Example and the comparative example for 24 hours in 25 degreeC environment for 24 hours, it is charged to 4.2V by the constant current method of 0.1C in 25 degreeC environment, and is 3.0 Charging and discharging to discharge to V was performed, and initial stage _C0 was measured. Furthermore, after charging at 4.2V and storing for 7 days at 60 degreeC, it charges and discharges to 4.2V and discharges to 3.0V by 0.1C constant current method in 25 degreeC environment, and stores high temperature Capacity C ₁ after was measured. The high temperature storage characteristic was evaluated by the capacity change rate ΔC _S expressed by ΔC _S = C ₁ / C ₀ × 100 (%). The higher the value of the capacitance change rate ΔC _S, indicates the excellent high-temperature storability.

(2) high temperature cycle characteristics

After stopping the lithium ion secondary battery of the laminated cell manufactured by the Example and the comparative example for 24 hours in 25 degreeC environment for 24 hours, it is charged to 4.2V by the constant current method of 0.1C in 25 degreeC environment, and is 3.0 Charging and discharging to discharge to V was performed, and initial stage _C0 was measured. In addition, the charging and discharging operation of charging to 4.2 V and discharging to 3.0 V was repeated by a 1 C constant current method under a 60 ° C. environment, and the capacity C ₂ after 100 cycles was measured. The high temperature cycle characteristics were evaluated by the capacity change rate ΔC _C represented by ΔC _C = C ₂ / C ₀ × 100 (%). The higher the value of the capacity change rate ΔC _C, the better the high temperature cycle characteristics.

(3) pole plate expansion characteristics

After evaluation of said "(1) high temperature storage characteristic", the cell of the lithium ion secondary battery was disassembled and the thickness d1 of the negative electrode plate of the negative electrode was measured. The negative electrode plate expansion ratio (d1-d0) / d0 × 100 (%) of the negative electrode was calculated by setting the thickness of the negative electrode plate of the negative electrode before production of the cell of the lithium ion secondary battery to d0. The lower this value, the more excellent the electrode plate expansion characteristic is.

5. Low temperature output characteristics

After stopping the lithium ion secondary battery of the laminated cell produced by the Example and the comparative example for 24 hours in 25 degreeC environment, the charging operation was performed at the charging rate of 4.2V and 1C. Then, under the -10 ℃ environment, by performing an operation of a discharge in the discharge rate of 1 C, to measure the voltage V ₁₅ 15 seconds after the start of discharge. The low-temperature output characteristics were evaluated by the voltage change ΔV represented by ΔV = 4.2 V-V ₁₅ (mV). The smaller the value of the voltage change ΔV, the better the low temperature output characteristics.

6. Viscosity of 1% aqueous solution of water soluble polymer

The water-soluble polymer prepared in the Example and the comparative example was diluted with 10% ammonia water and ion-exchange water so that pH might be 8, and the 1% aqueous solution of the water-soluble polymer was prepared. The viscosity of this aqueous solution was measured with the Brookfield viscometer.

EXAMPLE 1

(1-1. Preparation of Water-Soluble Polymer)

In a 5 MPa pressure-resistant container with a stirrer, 65.5 parts of ethyl acrylate as a (meth) acrylic acid ester monomer, 30 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid monomer, and a trifluoromethyl meta as a fluorine-containing (meth) acrylic acid ester monomer 2.5 parts of methacrylate, 2 parts of 2-acrylamide-2-methylpropanesulfonic acid as the sulfonic acid group-containing monomer, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator After sufficiently stirring, the mixture was heated to 60 ° C to initiate polymerization. When the polymerization conversion ratio reached 96%, the mixture was cooled to terminate the reaction to obtain an aqueous solution containing a water-soluble polymer. 10% ammonia water was added to the aqueous solution containing the water-soluble polymer obtained in this way, it adjusted to pH 8, and the aqueous solution containing the desired water-soluble polymer was obtained. It was 12800 when the weight average molecular weight of the obtained water-soluble polymer was measured.

It was 1500 mPa * s when the viscosity of the 1% aqueous solution of a water-soluble polymer was measured using the aqueous solution containing the obtained water-soluble polymer as a sample.

(1-2. Production of Particulate Binder)

In a 5 MPa pressure vessel with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 1.5 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid monomer, 65.5 parts as styrene as an aromatic vinyl monomer, and dodecyl as an emulsifier 4 parts of sodium benzene sulfonate, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate were added as a polymerization initiator, and after fully stirring, it heated at 50 degreeC and started superposition | polymerization. When the polymerization conversion ratio reached 96%, the mixture was cooled to stop the reaction, thereby obtaining an aqueous dispersion containing a particulate binder made of a styrene butadiene copolymer (hereinafter referred to as "SBR" as appropriate). An aqueous 5% sodium hydroxide solution was added to the aqueous dispersion liquid containing the particulate-form binder obtained in this way, and after adjusting to pH 8, the unreacted monomer was removed by heat and pressure distillation. Then, it cooled to 30 degrees C or less, and obtained the aqueous dispersion liquid containing a desired particulate binder. It was 1500000 when the weight average molecular weight of the obtained particulate-form binder was measured. Moreover, the number average particle diameter of the particulate-form binder measured by the laser diffraction scattering system particle size distribution apparatus was 150 nm.

(1-3. Production of slurry composition for negative electrode)

The aqueous solution containing the water-soluble polymer obtained in step (1-1) was diluted with water and the concentration was adjusted to 5%.

In the planetary mixer with a disper, 50 parts of SiOC (volume average particle diameter: 12 μm) and 50 parts of artificial graphite (volume average particle diameter: 24.5 μm) having a specific surface area of 4 m 2 / g as the negative electrode active material, 1 part of 5% aqueous solution of a water-soluble polymer was added with solid content, respectively, and it adjusted to solid content concentration 55% with ion-exchange water, and mixed at 25 degreeC for 60 minutes. Next, after adjusting to 52% of solid content concentration with ion-exchange water, it mixed again at 25 degreeC for 15 minutes, and obtained the liquid mixture.

1 part and ion-exchange water were put into the said liquid mixture containing the particulate-form binder obtained by the process (1-2) by solid content equivalent, it was adjusted so that it might become final solid content concentration 42%, and it mixed again for 10 minutes. This was degassed under reduced pressure to obtain a slurry composition for negative electrodes having good fluidity.

About the obtained slurry composition for negative electrodes, evaluation of stability and applicability | paintability was performed. The results are shown in Table 1.

(1-4. Production of negative electrode)

The slurry composition for negative electrodes obtained at the process (1-3) was apply | coated so that the film thickness after drying might be about 150 micrometers on the copper foil of thickness 20micrometer which is an electrical power collector with a comma coater. This drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for copper foil at a speed | rate of 0.5 m / min. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the negative electrode disk. This negative electrode original fabric was rolled by roll press, and the negative electrode of 80 micrometers in thickness of the negative electrode active material layer was obtained.

Adhesive strength was evaluated about the obtained negative electrode. The results are shown in Table 1.

(1-5. Production of Positive Electrode)

As a binder for positive electrodes, the glass transition temperature Tg prepared the 40% water dispersion of the acrylate polymer whose number average particle diameter is 0.20 micrometer at -40 degreeC. Said acrylate polymer is a copolymer obtained by emulsion-polymerizing the monomer mixture containing 78 weight% of 2-ethylhexyl acrylate, 20 weight% of acrylonitrile, and 2 weight% of methacrylic acid.

100 parts of LiFePO ₄ having an olivine crystal structure with a volume average particle diameter of 0.5 μm as a positive electrode active material, and a 1% aqueous solution of carboxymethyl cellulose (“BSH-12” manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) as a dispersant were used as solid content 1 Part and 5 parts of the 40% water dispersion of the above-mentioned acrylate polymer as a solid content are mixed in solid content, and ion exchanged water is added thereto so that the total solid content concentration is 40%, and mixed by a planetary mixer, The slurry composition for positive electrodes was prepared.

The above-mentioned slurry composition for positive electrodes was apply | coated and dried so that the film thickness after drying might be about 200 micrometers on the aluminum foil of thickness 20 micrometers which is an electrical power collector with a comma coater. This drying was performed by conveying the inside of 60 degreeC oven over 2 minutes for aluminum foil at a speed | rate of 0.5 m / min. Then, it heat-processed at 120 degreeC for 2 minutes, and obtained the positive electrode disk. This positive electrode original fabric was rolled by roll press, and the positive electrode of 70 micrometers in thickness of the positive electrode active material layer was obtained.

(1-6.Preparation of Separator)

A polypropylene separator (65 mm in width, 500 mm in length, 2 micrometers in thickness, manufactured by a dry method, porosity 55%) of a single layer was prepared.

(1-7.Lithium ion secondary battery)

The aluminum wrapping material exterior was prepared as an exterior of a battery. The negative electrode obtained in the step (1-4) was cut into a rectangle of 4.2 mm x 4.2 mm. The positive electrode obtained at the process (1-5) was cut into the rectangle of 4 mm x 4 mm. The separator of process (1-6) was cut into the rectangle of 5 mm x 5 mm.

The said rectangular positive electrode was arrange | positioned so that the surface of an electrical power collector may contact an aluminum wrapping material exterior. The rectangular separator was disposed on the surface of the positive electrode active material layer of the rectangular positive electrode. Moreover, on the rectangular separator, said rectangular negative electrode was arrange | positioned so that the surface of a negative electrode active material layer may face a separator. Into an aluminum wrapping material, a mixed solvent of a LiPF ₆ solution having a concentration of 1.0 M (the solvent is EC / DEC = 1/2 (volume ratio)) was filled as an electrolytic solution. In addition, in order to seal the opening of an aluminum wrapping material, the aluminum exterior was closed by heat-sealing 150 degreeC, and the lithium ion secondary battery was produced.

About the obtained battery, high temperature storage characteristic, high temperature cycling characteristic, and electrode plate expansion characteristic were evaluated, and also low temperature output characteristic was evaluated. The results are shown in Table 1.

In addition, the capacity (initial capacity) when the obtained lithium ion secondary battery was initially charged and discharged at a charge and discharge rate of 4.2 V and 0.1 C was 50 mAh.

[Examples 2 and 3]

In the production of the water-soluble polymer of the step (1-1), styrene sulfonic acid (Example 2) or vinyl sulfonic acid (Example 3) was used as the sulfonic acid group-containing monomer instead of 2-acrylamide-2-methylpropanesulfonic acid. Others were carried out similarly to Example 1, and manufactured and evaluated the lithium ion secondary battery and its components. The results are shown in Table 1.

[Examples 4 and 5]

In the production of the water-soluble polymer of the step (1-1), as a fluorine-containing (meth) acrylic acid ester monomer, trifluoromethyl acrylate (Example 4) or perfluorooctyl meta instead of trifluoromethyl methacrylate A lithium ion secondary battery and its components were produced and evaluated in the same manner as in Example 1, except that acrylate (Example 5) was used. The results are shown in Table 1.

[Examples 6 to 12]

In manufacture of the water-soluble polymer of a process (1-1), the ratio of ethyl acrylate, methacrylic acid, trifluoromethyl methacrylate, and 2-acrylamide-2-methylpropanesulfonic acid is shown in Table 1 and Table 2. Except having changed as mentioned above, it carried out similarly to Example 1, and manufactured and evaluated the lithium ion secondary battery and its components. The results are shown in Table 1 and Table 2.

EXAMPLE 13

In the production of the slurry composition for the negative electrode of the step (1-3), a lithium ion secondary battery and its composition were prepared in the same manner as in Example 1 except that 100 parts of SiOC were used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material. Components were prepared and evaluated. The results are shown in Table 2.

EXAMPLE 14

A lithium ion secondary battery was prepared in the same manner as in Example 1, except that 100 parts of artificial graphite were used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material in the preparation of the slurry composition for the negative electrode of the step (1-3). The component was manufactured and evaluated. The results are shown in Table 2.

EXAMPLE 15

(15-1.Production of Nano Silica Active Material A)

After 200 g of silicon oxide powder (SiOx: x = 1.02) having an average particle diameter of 3 µm and a BET specific surface area of 12 m 2 / g was injected into a silicon nitride tray, the mixture was stopped still in a treatment furnace capable of maintaining the atmosphere. Next, after argon gas was introduced and argon was substituted in the treatment furnace, the temperature was raised to 1200 ° C. at a temperature increase rate of 300 ° C./hr while the argon gas was flowed in 2 NL / min, and held for 3 hours. After the end of the holding, the temperature was started, and after reaching the room temperature, the powder was recovered to obtain a Si-based active material A. The obtained Si-based active material A is a powder having an average particle diameter of 3.5 µm and a BET specific surface area of 11 m 2 / g, which is bound to Si (111) near 2θ = 28.4 ° from an X-ray diffraction pattern by Cu-Kα rays. A diffraction line was present, and it was confirmed that the silicon composite powder was 40 nm in size of crystals of silicon dispersed in silicon dioxide determined by the Scherrer method from the half width of the diffraction line.

(15-2. Fabrication and Evaluation of Lithium Ion Secondary Batteries and Their Components)

In the preparation of the slurry composition for negative electrodes of step (1-3), 5 parts of Si-based active material A obtained in step (15-1) and 95 parts of artificial graphite were used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material. Others were carried out similarly to Example 1, and manufactured and evaluated the lithium ion secondary battery and its components. The results are shown in Table 2.

[Example 16]

(16-1.Production of nano silica active material B)

The granular polycrystalline silicon produced by introducing polycrystalline silicon fine particles into a fluidized bed of 800 ° C. and feeding monosilane was pulverized using a jet mill, and then classified by a classifier to obtain polycrystalline silicon powder having a D50 = 10.2 μm. Si-type active material B was used. It was confirmed from the full width at half maximum of the X-ray diffraction line that the crystallite size of the Si-based active material B was 44 nm.

(16-2. Fabrication and Evaluation of Lithium Ion Secondary Battery and Its Components)

In the preparation of the slurry composition for negative electrodes of step (1-3), 5 parts of Si-based active material B obtained in step (16-1) and 95 parts of artificial graphite were used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material. Others were carried out similarly to Example 1, and manufactured and evaluated the lithium ion secondary battery and its components. The results are shown in Table 2.

[Comparative Examples 1-4]

In the production of the water-soluble polymer of the step (1-1), the ratio of ethyl acrylate, methacrylic acid, trifluoromethyl methacrylate, and 2-acrylamide-2-methylpropanesulfonic acid is changed as shown in Table 3. A lithium ion secondary battery and its components were produced and evaluated in the same manner as in Example 1 except for the one. The results are shown in Table 3.

The meaning of the symbol in a table | surface is as follows.

TFMMA ： Trifluoromethyl methacrylate

TFMA ： Trifluoromethyl acrylate

PFOMA ： Perfluorooctyl methacrylate

AMPS ： 2-acrylamide-2methylpropanesulfonic acid

SS: Styrene sulfonic acid

VS ： Vinyl sulfonic acid

Si-based A: Nano-silica active material A prepared in Example 15

Si-based B: Nano silica active material B prepared in Example 16

Binder ： Binder classification

EA amount ： Ethyl acrylate addition amount (part)

Fluorine monomer type ： Fluorine-containing (meth) acrylic acid ester monomer type

Amount of fluorine monomer ： Amount of fluorine-containing (meth) acrylic acid ester monomer added (part)

Type of sulfone monomer ： Type of sulfonic acid group-containing monomer

Sulfone monomer amount: Sulfonic acid group containing monomer addition amount (part)

MAA amount ： Methacrylic acid addition amount (part)

1% aqueous solution viscosity: viscosity of 1% aqueous solution of the water-soluble polymer (mPa · s)

Water-soluble polymer molecular weight ： Weight average molecular weight of the water-soluble polymer

Negative electrode active material ： Type of negative electrode active material

Active material ratio: The addition amount of each active material (part)

Adhesion strength ： Negative electrode peel strength average value (N / m)

Slurry stability: Evaluation result of viscosity change rate A: Change rate less than 10% increase, B: 10% increase or more, less than 30% increase, C: 30% increase or more

Coating property ： The number of pinholes after slurry application for negative electrode (piece)

High temperature storage characteristics ： Battery capacity change rate ΔC _S (%)

High temperature cycle characteristics ： Battery capacity change rate ΔC _C (%)

Pole plate expansion characteristics ： Pole plate expansion ratio of the negative electrode after high temperature storage characteristic evaluation (%)

Low temperature output characteristics ： Voltage change at low temperature ΔV (mV)

[Review]

As apparent from the results of Tables 1 to 3, in Examples 1 to 16 of the present application, the expansion of the negative electrode accompanying charging and discharging is suppressed compared to the comparative example which does not satisfy any of the requirements of the present invention, and also various The balance was good and good in all of the characteristics. Moreover, in Examples other than Example 8 with few addition amounts of water-soluble polymer, stability of the slurry was also excellent.

Claims (11)

As a negative electrode for secondary batteries containing a negative electrode active material, a particulate-form binder, and a water-soluble polymer,
The water-soluble polymer,
0.1 wt% to 15 wt% of a sulfonic acid group-containing monomer unit, and
The negative electrode for secondary batteries which is a copolymer containing 0.5 weight%-10 weight% of a fluorine-containing (meth) acrylic acid ester monomeric unit. The method of claim 1,
The negative electrode for secondary batteries in which the said water-soluble polymer contains an ethylenic unsaturated carboxylic monomer unit. The method of claim 2,
The negative electrode for secondary batteries whose said ethylenic unsaturated carboxylic monomer is an ethylenic unsaturated monocarboxylic acid monomer. The method of claim 1,
The negative electrode for secondary batteries which the said negative electrode active material can occlude and discharge | release lithium, and contains a metal. The method of claim 4, wherein
The negative electrode for secondary batteries whose said metal is silicon. The method of claim 1,
The negative electrode for secondary batteries in which the said particulate-form binder contains the polymer containing an aliphatic conjugated diene monomeric unit. The method of claim 6,
The negative electrode for secondary batteries whose polymer containing the said aliphatic conjugated diene monomeric unit further contains an aromatic vinyl monomeric unit. The secondary battery provided with the positive electrode, the negative electrode, electrolyte solution, and a separator, and the said negative electrode is the negative electrode for secondary batteries in any one of Claims 1-7. As a slurry composition containing a negative electrode active material, a particulate-form binder, and a water-soluble polymer,
The water-soluble polymer,
0.1 wt% to 15 wt% of a sulfonic acid group-containing monomer unit,
The slurry composition for secondary battery negative electrodes which is a copolymer containing 0.5 weight%-10 weight% of a fluorine-containing (meth) acrylic acid ester monomeric unit. The method of claim 9,
The slurry composition for secondary battery negative electrodes in which the said water-soluble polymer contains an ethylenic unsaturated carboxylic monomer unit. The manufacturing method of the negative electrode for secondary batteries containing apply | coating the slurry composition for secondary battery negative electrodes of Claim 9 or 10 on an electrical power collector, and drying.