KR20150044839A - Negative electrode for secondary cell, secondary cell, slurry composition, and manufacturing method - Google Patents

Abstract

A negative electrode for a secondary battery comprising a negative electrode active material, a particulate binder and a water-soluble polymer, wherein the water-soluble polymer contains 0.1 to 15% by weight of a sulfonic acid group-containing monomer unit and 0.5 to 10% by weight of a fluorine-containing (meth) A negative electrode for a secondary battery, which is a copolymer containing hydrogen peroxide, and a secondary battery including the negative electrode.

Description

TECHNICAL FIELD [0001] The present invention relates to a negative electrode for a secondary battery, a secondary battery, a slurry composition, and a method for manufacturing the negative electrode,

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

2. Description of the Related Art In recent years, portable terminals such as a notebook computer, a mobile phone, and a PDA (Personal Digital Assistant) have become popular. As a secondary battery used as a power source for these portable terminals, for example, a nickel hydrogen secondary battery, a lithium ion secondary battery, and the like have been used. Portable terminals are demanded to be more comfortable to carry, and miniaturization, thinning, weight reduction, and high performance are progressing rapidly, and as a result, portable terminals are used in various places. Also, as with the portable terminal, the secondary battery is required to be downsized, thinned, lightweight, and high in performance.

In order to improve the performance of the secondary battery, improvement of electrodes, electrolyte, and other battery members has been studied. Of these, the electrode is usually prepared by mixing an electrode active material and a conductive agent such as a conductive carbon, if necessary, into a liquid composition obtained by dispersing or dissolving a polymer serving as a binder (binder) in a solvent such as water or an organic solvent Obtaining a slurry composition, applying the slurry composition to a current collector, and drying the slurry composition. As for the electrode, in addition to the examination of the electrode active material and the current collector itself, a binder for binding the electrode active material to the current collector and various additives have been studied (see, for example, Patent Documents 1 to 4).

For example, Patent Document 1 and Patent Document 2 describe a negative electrode slurry for a nonaqueous secondary battery containing a carbonaceous active material and a binder composed of an aqueous dispersion emulsion resin and a water-soluble polymer compound. Examples of the water-soluble polymer compound include polyvinyl alcohol, carboxymethylcellulose, sodium polyacrylate, and the like. According to this, it is described that the coating film strength and the coating film density of the battery are improved.

Patent Document 3 discloses a fluorine-containing copolymer containing 0.02 to 13 wt% of a fluorine-containing unsaturated monomer, 10 to 38 wt% of an aliphatic conjugated diene monomer, 0.1 to 10 wt% of an ethylenically unsaturated carboxylic acid monomer, and 49 to 88.88 wt% There is disclosed a binder for a secondary battery electrode comprising a copolymer latex obtained by emulsion polymerization of a monomer composition to be constituted. According to this, it is disclosed that the compounding stability, the blocking resistance, the resistance to dropping dust and the binding force are excellent.

Patent Document 4 discloses a binder for a secondary battery electrode comprising a polymer having a monomer unit derived from a fluorine atom-containing monomer such as alkyl (meth) acrylate. It is described that cellulose-based polymers, polyacrylic acid salts and the like can be added in order to improve the coating property and improve the charge-discharge characteristics. According to this, it is described that an electrode having a good bondability with the active material is continuously obtained.

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

In the secondary battery, the particles of the electrode active material contained in the negative electrode may expand and shrink in accordance with charging and discharging. When 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 a technique capable of suppressing the expansion of the negative electrode as described above is desired.

In addition, the capacity of the conventional secondary battery is deteriorated when it is stored in a high temperature environment of, for example, 60 占 폚. Therefore, even if the secondary battery is stored in a high-temperature environment, development of a technique capable of suppressing the deterioration of the capacity of the secondary battery is also desired.

Also, in the secondary battery, it is required that the characteristics such as the cycle characteristics and the output characteristics are good in both the high-temperature environment and the low-temperature environment.

Disclosure of the Invention The present invention was conceived in view of the above-described problems, and it is an object of the present invention to provide a negative electrode capable of suppressing expansion of a negative electrode accompanied with charge and discharge, A negative electrode for a secondary battery capable of realizing a secondary battery having excellent characteristics, a slurry composition for a negative electrode capable of producing the negative electrode for the secondary battery, a method for producing the negative electrode for a secondary battery, And to provide a secondary battery.

As a result of intensive studies to solve the above problems, the present inventors have found that a water-soluble polymer containing a sulfonic acid group-containing monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit in a specific ratio, It is possible to suppress the expansion of the negative electrode accompanied by charge and discharge and to make it difficult to lower the capacity 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-

0.1 to 15% by weight of sulfonic acid group-containing monomer units, and

And 0.5 to 10% by weight of a fluorine-containing (meth) acrylic acid ester monomer unit.

[2] The negative electrode for a secondary battery according to [1], wherein the water-soluble polymer contains an ethylenically unsaturated carboxylic acid monomer unit.

[3] The negative electrode for a secondary battery according to [2], wherein the ethylenically unsaturated carboxylic acid monomer is an ethylenically unsaturated monocarboxylic acid monomer.

[4] The negative electrode for a secondary battery according to any one of [1] to [3], wherein the negative electrode active material is capable of absorbing and desorbing lithium and contains a metal.

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

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

[7] The negative electrode for a secondary battery according to [6], wherein the polymer containing the aliphatic conjugated diene monomer unit further contains an aromatic vinyl monomer unit.

[8] A secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode for a 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-

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

And 0.5 to 10% by weight of a fluorine-containing (meth) acrylic acid ester monomer unit.

[10] The negative electrode slurry composition according to [9], wherein the water-soluble polymer contains an ethylenically unsaturated carboxylic acid monomer unit.

[11] A method for producing a negative electrode for a secondary battery, which comprises applying the slurry composition for a secondary battery anode according to [9] or [10] onto a current collector and drying.

According to the negative electrode for a secondary battery of the present invention, it is possible to suppress the expansion of the negative electrode accompanied by charging and discharging, and it is difficult to lower the capacity even when it is stored in a high temperature environment, and in both of high temperature environment and low temperature environment, A secondary battery can be realized.

The secondary battery of the present invention can suppress the expansion of the negative electrode accompanied by charging and discharging, and it is difficult to lower the capacity even when it is stored in a high temperature environment, and the characteristics are good in both the high temperature environment and the low temperature environment.

When the negative electrode slurry composition of the present invention is used, the negative electrode for a secondary battery of the present invention can be produced. Further, since the negative electrode slurry composition of the present invention has high stability, it can be stored for a long time and is easy to use.

According to the method for producing a negative electrode for a secondary battery of the present invention, the negative electrode for a secondary battery of the present invention can be produced.

Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and may be arbitrarily changed without departing from the scope of the claims of the present invention and the equivalents thereof.

In the following description, (meth) acrylic acid means acrylic acid and methacrylic acid. In the following description, "water-soluble" means that when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C., the content of insolubles is less than 0.5% by weight. The term "water-insoluble" means that the insoluble matter is not less than 90% by weight at 25 ° C. when 0.5 g of the substance is dissolved in 100 g of water.

[One. Negative electrode for secondary battery]

The negative electrode for a secondary battery of the present invention (hereinafter referred to as "negative electrode of the present invention" as appropriate) contains a negative electrode active material, a particulate binder, and a water-soluble polymer. Typically, the negative electrode of the present invention has a current collector and a negative electrode active material layer formed on the surface of the current collector, and the negative electrode active material layer contains the above negative electrode active material, particulate binder, and water-soluble polymer.

[1-1. Negative electrode active material]

The negative electrode active material is an electrode active material for the negative electrode, and is a substance that exchanges electrons with the negative electrode of the secondary battery.

For example, when the secondary battery of the present invention is a lithium ion secondary battery, a material capable of occluding and releasing lithium is generally used as the negative electrode active material.

An example of a preferable negative electrode active material is carbon. Examples of the carbon include natural graphite, artificial graphite and carbon black. Of these, natural graphite is preferably used.

Another example of a preferable negative electrode active material is a material containing a metal. 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 them, a negative electrode active material containing silicon is preferable. By using a negative electrode active material containing silicon, the electric capacity of the lithium ion secondary battery can be increased. In general, the negative electrode active material containing silicon expands and contracts largely (for example, about 5 times) with charge and discharge. In the negative electrode of the present invention, however, the negative electrode active material containing silicon Deterioration of performance can be suppressed.

Examples of the silicon-containing active material include an active material made of a metal silicon, an active material made of a compound of silicon and another element (hereinafter sometimes referred to as a "silicon-based active material"), an active material made of a metal silicon, . ≪ / RTI >

The negative electrode active material may be used singly or in combination of two or more in an arbitrary ratio. Therefore, two or more kinds of negative electrode active materials may be used in combination. Among them, it is preferable to use a negative electrode active material containing a combination of carbon and an active material containing silicon. When a combination of carbon and silicon-containing active material is used as the negative electrode active material, insertion and desorption of Li into one or both of metal silicon and silicon-based active material occur at a high electric potential, Is expected to occur. Therefore, expansion and contraction are suppressed, so that the cycle characteristics of the lithium ion secondary battery can be improved.

Examples of the silicon-based active material include SiO ₂ , SiO ₂ , SiO _x (0.01 ≦ x <2), SiC and SiOC, and SiO _x , SiC and SiOC are preferable. Among them, it is particularly preferable to use SiO _x as the silicon-based active material since expansion of the negative electrode active material itself is suppressed. SiO _x is a compound which can be formed from one or both of SiO and SiO ₂ and metal silicon. This SiO _x can be produced, for example, by cooling and precipitating silicon monoxide gas produced by heating a mixture of SiO ₂ and metal silicon.

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

Examples of the composite method include a method of forming a composite by coating a silicon-containing active material with carbon, and a method of forming a composite by assembling a mixture containing an electrically conductive carbon and an active material containing silicon.

When a negative electrode active material containing a combination of carbon and an active material containing silicon is used, it is preferable that the amount of silicon atoms is 0.1 to 50 parts by weight based on 100 parts by weight of the total amount of carbon atoms in the negative electrode active material. As a result, the conductive path can be well formed, and the conductivity of the negative electrode can be improved.

In the case of using a negative electrode active material containing a combination of carbon and silicon-containing active material, 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 higher, more preferably 70/30 or higher, preferably 97/3 or lower, more preferably 90/10 or lower. Thus, the cycle characteristics of the secondary battery can be improved.

(Shape of negative electrode active material)

It is preferable that the negative electrode active material is formed into a particle shape. When the shape of the particles is spherical, a higher density electrode can be formed at the time of electrode formation.

When the negative electrode active material is a particle, the volume average particle diameter thereof is suitably selected from a 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, But is usually 100 μm or less, preferably 50 μm or less, and more preferably 30 μm or less. Here, the volume average particle diameter adopts the particle diameter in which 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 not less than 2 m 2 / g, preferably not less than 3 m 2 / g, more preferably not less than 5 m 2 / g, usually not more than 20 m 2 / g, Preferably 15 m &lt; 2 &gt; / g or less, and more preferably 10 m &lt; 2 &gt; / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

[1-2. Particulate binder]

The particulate binder is a component that binds the electrode active material to the surface of the current collector in the 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 by binding the particulate binder to the negative electrode active material. The particulate binder also binds particles other than the negative electrode active material contained in the negative electrode active material layer, and also achieves a role of maintaining the strength of the negative electrode active material layer.

As the particulate binder, it is preferable to use one having a high ability of holding the negative electrode active material and having high adhesion to the current collector. Normally, a particulate binder containing a polymer is used, and in particular, those substantially consisting of a polymer 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. The aliphatic conjugated diene monomer unit is a low rigid and flexible repeating unit. Therefore, by using a polymer containing an aliphatic conjugated diene monomer unit as a particulate binder, sufficient adhesion between the negative electrode active material layer and the current collector can be obtained.

The aliphatic conjugated diene monomer unit is a repeating unit obtained by polymerizing an aliphatic conjugated diene monomer. Examples of the aliphatic conjugated diene monomer include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, Conjugated pentadiene, substituted and side-chain conjugated hexadiene, and the like. Of these, 1,3-butadiene is preferred.

One kind of the aliphatic conjugated diene monomer may be used alone, or two or more kinds thereof may be used in combination at an arbitrary ratio. Therefore, the polymer of the particulate binder may contain only one kind of the aliphatic conjugated diene monomer unit, or two or more kinds may be combined in an arbitrary ratio.

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% Particularly preferably 55% by weight or less. By setting the ratio of the aliphatic conjugated diene monomer unit to the lower limit value or more in the above range, the flexibility of the negative electrode can be enhanced. When the ratio is less than the upper limit value, sufficient adhesion between the negative electrode active material layer and the current collector can be obtained, .

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

The aromatic vinyl monomer unit is a repeating unit obtained by polymerizing an aromatic vinyl monomer. Examples of the aromatic vinyl monomer include styrene,? -Methylstyrene, vinyltoluene, divinylbenzene, and the like. Among them, styrene is preferable. The polymer of the particulate binder preferably contains an aromatic vinyl monomer unit, and as already described, the polymer of the particulate binder preferably contains an aliphatic conjugated diene monomer unit such as butadiene. Therefore, the polymer of the particulate binder is preferably a polymer containing an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit, and for example, a styrene-butadiene copolymer is preferable.

One kind of the aromatic vinyl monomer may be used alone, or two or more kinds thereof may be used in combination at an arbitrary ratio. Therefore, the polymer of the particulate binder may contain only one type of aromatic vinyl monomer, or two or more types may be combined in an arbitrary ratio.

When an aromatic vinyl monomer is used, the polymer of the particulate binder may contain unreacted aliphatic conjugated diene monomer and unreacted aromatic vinyl monomer as the 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 particulate binder polymer is Preferably 1000 ppm or less, and more preferably 200 ppm or less. When the amount of the aliphatic conjugated diene monomer contained in the polymer of the particulate binder is controlled within the above range, when the negative electrode slurry composition according to the present invention is applied to the surface of the current collector and dried to produce the negative electrode, It is possible to prevent the occurrence of roughing due to the odor, or the environmental load caused by the odor. When the amount of the aromatic vinyl monomer contained in the polymer of the particulate binder is controlled within the above range, the environmental load caused by the drying conditions and the roughness of the surface of the negative electrode can be suppressed, and further, the electrolyte resistance of the polymer of the particulate binder .

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 setting the ratio of the aromatic vinyl monomer units to the lower limit value or more in the above range, the electrolyte solution resistance of the negative electrode for a secondary battery of the present invention can be enhanced and by setting the ratio to be not more than the upper limit value, the negative electrode slurry composition according to the present invention Sufficient adhesion between the negative electrode active material layer and the current collector can be obtained.

The polymer of the particulate binder preferably contains an ethylenically unsaturated carboxylic acid monomer unit. Since the ethylenically unsaturated carboxylic acid monomer unit contains a carboxyl group (-COOH group) which enhances adsorption to the negative electrode active material and the current collector and is a repeating unit having high strength, it is possible to stably prevent the negative active material from being desorbed from the negative electrode active material layer And the strength of the negative electrode can be improved.

The ethylenically unsaturated carboxylic acid monomer unit is a repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer. Examples of the ethylenically unsaturated carboxylic acid monomer include monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and their anhydrides. Among them, monomers selected from the group consisting of acrylic acid, methacrylic acid and itaconic acid are preferably used singly or in combination from the viewpoint of stability of the negative electrode slurry composition according to the present invention.

The ethylenically unsaturated carboxylic acid monomer may be used singly or in combination of two or more kinds in any ratio. Therefore, the polymer of the particulate binder may contain only one ethylenic unsaturated carboxylic acid monomer unit, or may contain two or more kinds of the ethylenically unsaturated carboxylic acid monomer units in combination at an arbitrary ratio.

In the polymer of the particulate binder, the proportion of the ethylenically unsaturated carboxylic acid monomer unit is preferably 0.5% by weight or more, more preferably 1% by weight or more, particularly preferably 2% by weight or more, % Or less, more preferably 8 wt% or less, particularly preferably 7 wt% or less. The stability of the negative electrode slurry composition according to the present invention can be enhanced by setting the ratio of the ethylenically unsaturated carboxylic acid monomer units to the lower limit value or more within the above range and by setting the ratio to the upper limit value or less, Can be prevented from becoming excessively high and can be easily handled.

The polymer of the particulate binder may contain an arbitrary repeating unit other than those described above, so far as the effect of the present invention is not significantly impaired. Examples of the monomer corresponding to any of the above repeating units include unsaturated carboxylic acid amide monomers and vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers, hydroxyalkyl groups, and unsaturated carboxylic acid amide monomers. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile,? -Chlor acrylonitrile,? -Ethyl acrylonitrile, and the like. Of these, acrylonitrile and methacrylonitrile are preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the unsaturated carboxylic acid alkyl ester monomers include 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, and 2-ethylhexyl acrylate. Of these, methyl methacrylate, ethyl acrylate, and butyl acrylate are preferred. These may be used singly or in combination of two or more in an arbitrary ratio.

As the unsaturated monomer containing a hydroxyalkyl group, for example,? -Hydroxyethyl acrylate,? -Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, Hydroxyethyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis -Hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. Among them,? -Hydroxyethyl acrylate is preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide and N, N-dimethylacrylamide. Among them, acrylamide and methacrylamide are preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

As the monomer constituting the polymer of the particulate binder, for example, monomers used in conventional emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride and vinylidene chloride may be used. These may be used singly or in combination of two or more in an arbitrary ratio.

The weight average molecular weight of the polymer of the particulate binder is preferably 10000 or more, more preferably 20000 or more, preferably 2000000 or less, and more preferably 500000 or less. When the weight average molecular weight of the polymer of the particulate binder is within the above range, the strength of the negative electrode of the present invention and the dispersibility of the negative electrode active material are easily improved. The weight average molecular weight of the polymer of the particulate binder can be determined by gel permeation chromatography (GPC) as a value in terms of polystyrene using tetrahydrofuran as a developing solvent.

The glass transition temperature of the particulate binder is preferably -75 ° C or more, more preferably -55 ° C or more, particularly preferably -35 ° C or more, preferably 40 ° C or less, preferably 30 ° C or less 20 DEG C or less, particularly preferably 15 DEG C or less. When the glass transition temperature of the particulate binder is in the above range, the properties such as the flexibility of the negative electrode, the binding property and the winding property, and the adhesion property between the negative electrode active material layer and the collector are highly balanced.

Normally, the particulate binder becomes a water-insoluble polymer. Therefore, in the negative electrode slurry composition of the present invention, the particulate binder is dispersed as particles without being dissolved in water as a solvent. In the case where the particulate binder is dissolved in water and an organic solvent (for example, N-methyl-2-pyrrolidone), the binder is adsorbed on the negative electrode active material and the resulting output characteristics of the secondary battery are deteriorated. When the particulate binder is a water-insoluble polymer, the above problems can be avoided. In the negative electrode slurry composition, the particulate binder is preferably dispersed in water in particulate form. When the binder used as the negative electrode slurry composition is dissolved in an organic solvent such as NMP (N-methyl-2-pyrrolidone) and does not maintain the shape of particles, the binder is adsorbed on the surface of the negative electrode active material, The characteristics 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. When the number average particle diameter of the particulate binder is in the above range, the strength and flexibility of the resulting negative electrode can be improved. The presence of the particles can be easily measured by a transmission electron microscope, a Coulter counter, a laser diffraction scattering method or the like.

The particulate binder is produced, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent.

The proportion of each monomer in the monomer composition is usually determined by the ratio of the repeating unit (e.g., an aliphatic conjugated diene monomer unit, an aromatic vinyl monomer unit, an ethylenically unsaturated carboxylic acid monomer unit, etc.) in the polymer of the particulate binder, The same.

The aqueous solvent is not particularly limited as long as it is capable of dispersing particles of the particulate binder, and usually has a boiling point at normal pressure of usually not lower than 80 캜, preferably not lower than 100 캜, usually not higher than 350 캜, Is selected from an aqueous solvent of 300 DEG C or lower. Hereinafter, examples of the aqueous solvent will be given. In the following examples, the numeral in parentheses after the solvent name is the boiling point (unit DEG C) at normal pressure, and the fractional part is the value rounded or truncated.

Examples of the water-based solvent include water (100), ketones such as diacetone alcohol (169) and gamma -butyrolactone (204), ethyl alcohol (78), isopropyl alcohol (82), n-propyl alcohol ), Propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152), butyl cellosolve (171) (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl ether (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188), and ethers such as 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66). Among them, water is not particularly flammable, and it is particularly preferable from the viewpoint that a dispersion of particles of the particulate binder is easy to be easily obtained. Water may be used as a main solvent and an aqueous solvent other than the above-described water may be mixed in a range in which the dispersion state of the particles of the particulate binder can be ensured.

The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsion polymerization method and the like can be used. As the polymerization method, any methods such as ion polymerization, radical polymerization, and living radical polymerization can be used. A high molecular weight material is easily obtained and a polymer is obtained in a state in which the polymer is dispersed in water as it is. Therefore, it is unnecessary to carry out redispersion treatment and can be provided for production of a negative electrode slurry composition according to the present invention. Among them, the emulsion polymerization method is particularly preferable.

The emulsion polymerization method is usually carried out by a conventional method. For example, the method described in &quot; Experimental Chemistry Lecture &quot; vol. 28, (published by Maruzen Co., Ltd., Japan Chemical Society). That is, an additive such as water, a dispersing agent, an emulsifying agent, a crosslinking agent, etc., a polymerization initiator and a monomer are added to a closed container with a stirrer and a heating device so as to have a predetermined composition and the composition in the container is stirred to emulsify the monomer or the like into water , And the temperature is raised while stirring to initiate polymerization. Alternatively, the composition is emulsified and then placed in a sealed container to initiate the reaction in the same manner.

Examples of the polymerization initiator include, for example, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide Organic peroxides such as?,? '-Azobisisobutyronitrile, and the like; ammonium persulfate; and potassium persulfate. One type of polymerization initiator may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The emulsifier, the dispersant, the polymerization initiator and the like are generally used in these polymerization methods, and the amount of the emulsifier, the dispersant, and the polymerization initiator is generally used. In the polymerization, seed polymerization may be carried out by employing seed particles.

The polymerization temperature and the polymerization time may be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator, and usually the polymerization temperature is about 30 캜 or higher and the polymerization time is about 0.5 to 30 hours.

In addition, additives such as amines may be used as polymerization auxiliary agents.

The aqueous dispersion of the particles of the particulate binder obtained by these methods can also be used in the form of aqueous solutions of hydroxides of alkali metals (for example, Li, Na, K, Rb and Cs), ammonia, inorganic ammonium compounds ₄ Cl and the like), an organic amine compound (for example, ethanolamine, diethylamine, etc.), etc., and adjusting the pH to be in the range of usually 5 to 10, preferably 5 to 9 do. Among them, the pH adjustment by the alkali metal hydroxide is preferable because it improves the binding property (fill strength) between the current collector and the negative electrode active material.

The particle of the particulate binder described above may be a composite polymer particle composed of two or more kinds of polymers. The composite polymer particles can be obtained also by a method of polymerizing at least one monomer component by a conventional method and subsequently polymerizing at least one other monomer component by a conventional method (two-step polymerization method). By stepwise polymerizing the monomers in this manner, particles of a core shell structure having a core layer present inside the particles and a shell layer covering the 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 or less based on 100 parts by weight of the negative electrode active material 2 parts by weight or less. By setting the amount of the particulate binder within the above-mentioned range, the viscosity of the negative electrode slurry composition according to the present invention becomes appropriate, and the application to the current collector can be performed smoothly. Further, sufficient adhesion strength between the current collector and the negative electrode active material layer can be obtained without increasing the resistance with respect to the negative electrode of the present invention. As a result, peeling of the particulate binder from the negative electrode active material layer in the step of applying the positive 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 predetermined proportion of a sulfonic acid group-containing monomer unit and a fluorine-containing (meth) acrylic acid ester monomer unit in a predetermined ratio. The negative electrode of the present invention contains a water-soluble polymer, so that expansion of the negative electrode accompanied by charging and discharging can be suppressed, and a secondary battery in which the capacity is hardly lowered even when it is stored in a high temperature environment can be realized. By using such a water-soluble polymer, the coating property when the negative electrode slurry composition of the present invention is applied to the current collector and the adhesion property to the current collector of the negative electrode active material layer in the secondary battery of the present invention, In addition, high-temperature cycle characteristics and low-temperature output characteristics are usually excellent.

Since the water-soluble polymer contains the sulfonic acid group-containing monomer unit, the dispersion stability of the negative electrode active material can be improved, the negative electrode active material can be prevented from being separated from the negative electrode active material layer, or the chemical change of the negative electrode active material itself can be suppressed. The high-temperature storage characteristics and the low-temperature output characteristics of the battery can be improved. Further, the water-soluble polymer contains the fluorine-containing (meth) acrylic acid ester monomer unit, whereby the swelling property of the water-soluble polymer to water (the degree of swelling of the water-soluble polymer by absorbing water when the water- Further, the water-soluble polymer can be elastically deformed, and as a result, the properties of the slurry are improved, and the performance of the battery is further improved. It is considered that the above-described effects are exerted by combining these actions.

Specifically, when the negative electrode active material expands or shrinks in the negative electrode, the water-soluble polymer can elastically deform following the expansion or contraction of the negative electrode active material, so that expansion of the negative electrode accompanying charge and discharge can be suppressed. Conventionally, when the negative electrode active material repeatedly expands and shrinks, the particulate binder can not be brought into close contact with the negative electrode active material, and a gap is created between the negative electrode active materials or between the negative electrode active material and the conductive agent, There is a case where the electrical connection of the electrodes is impeded. If the above electrical connection is impeded, there is a possibility that the electric capacity of the secondary battery is lowered. However, if the water-soluble polymer can undergo elastic deformation following the expansion or contraction of the negative electrode active material, generation of the gap can be suppressed and electrical connection can be maintained, thereby improving cycle characteristics.

In the negative electrode, the water-soluble polymer may be adsorbed on the surface of the negative electrode active material to cover the negative electrode active material to form a protective layer. With this protective layer, decomposition of the electrolytic solution in a high temperature environment and decomposition of the electrolytic solution accompanying charge and discharge can be suppressed. When the electrolytic solution is decomposed, bubbles are formed around the negative electrode active material, and this bubble inhibits the transfer of electrons, which may lower the electric capacity of the secondary battery. However, if the decomposition of the electrolytic solution can be suppressed by the water-soluble polymer, the lowering of the electric capacity as described above can be suppressed, and the high temperature storage characteristics and the high temperature cycle characteristics can be improved.

In addition, the protective layer formed of the water-soluble polymer has higher ionic conductivity than the protective layer formed by the conventional additives such as carboxymethylcellulose (hereinafter referred to as &quot; CMC &quot; This is presumably because the water-soluble polymer has swelling property with respect to the electrolytic solution (when the water-soluble polymer is immersed in the electrolytic solution, the water-soluble polymer swells by absorbing the electrolytic solution). Since the ionic conductivity is high, the diffusion resistance (that is, the resistance that interrupts the diffusion of ions) is lowered, so that the secondary battery of the present invention has a high output characteristic and particularly a low temperature output characteristic. Since the solvent of the electrolytic solution can swell to such an extent that the protective layer can not easily permeate, even if it has the swelling property to the electrolytic solution, the action of suppressing the decomposition of the electrolytic solution as described above is sufficiently exhibited.

In addition, the water-soluble polymer has high solubility in water and can be easily adsorbed to the negative electrode active material. Therefore, in the whole of the negative electrode slurry composition of the present invention, the water-soluble polymer covers the surface of the particles of the negative electrode active material, and the dispersibility of the particles of the negative electrode active material can be increased. Therefore, since a negative electrode active material is hardly formed during application of the negative electrode slurry composition, a coating film having a uniform film thickness and composition can be easily formed. In addition, in the negative electrode active material layer obtained from the coating film thus formed, the negative electrode active material is well dispersed, so that the electric capacity of the secondary battery can be improved.

Further, the water-soluble polymer is highly flexible and flexible, so that the water-soluble polymer is easily adhered to the surface of the current collector and the surface of the negative electrode active material without gaps. For this reason, the water-soluble polymer can improve the adhesion by supplementing binding to the current collector and the negative electrode active material by the particulate binder. Therefore, it is possible to improve the adhesion of the negative electrode active material layer to the current collector.

(Sulfonic acid group-containing monomer unit)

The 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 sulfonic acid group-containing monomers or salts thereof having no functional group other than the sulfonic acid group, monomers or salts thereof containing an amide group and a sulfonic acid group, and monomers or salts thereof containing a hydroxyl group and a sulfonic acid group . These may be used singly or in combination of two or more in an arbitrary ratio. Therefore, the water-soluble polymer may contain only one kind of the sulfonic acid group-containing monomer unit, or may contain two or more kinds in combination at an arbitrary ratio.

Examples of the sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group include sulfonic acid group-containing monomers such as isoprene and butadiene, , Sulfopropyl methacrylate, sulfobutyl methacrylate, and the like. Examples of the salt include a lithium salt, a sodium salt, and a potassium salt. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the monomer containing an amide group and a sulfonic acid group include 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and the like. Examples of the salt include a lithium salt, a sodium salt, and a potassium salt. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the monomer containing a hydroxyl group and a sulfonic acid group include 3-aryloxy-2-hydroxypropanesulfonic acid (HAPS) and the like. Examples of the salt include a lithium salt, a sodium salt, and a potassium salt. These may be used singly or in combination of two or more in an arbitrary ratio.

Of these, styrene sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid (AMPS) and other amide groups and sulfonic acid group-containing monomers and their salts are preferable.

The proportion of the sulfonic acid group-containing monomer units in the water-soluble polymer is 0.1% by weight or more, preferably 1% by weight or more, and 15% by weight or less, preferably 10% by weight or less. When the density of sulfonic acid groups present in the water-soluble polymer is increased, the dispersibility of the slurry for the negative electrode is improved. Further, since a sulfonic acid group usually causes a cross-linking reaction when the negative electrode of the present invention is produced, a cross-linked structure is formed by a sulfonic acid group in the negative electrode active material layer. In this case, since the water-soluble polymer has a sufficient amount of sulfonic acid groups, the number of crosslinked structures can be increased to strengthen the strength of the negative electrode active material layer, and the high temperature storage characteristics and low temperature output characteristics of the secondary battery can be improved. Therefore, the water-soluble polymer preferably contains a large number of sulfonic acid group-containing monomer units as described above. However, when the number of the sulfonic acid group-containing monomer units is too large, the other monomer units may be reduced and the water-soluble polymer may have a low adsorptivity and strength with respect to the negative electrode active material. .

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

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

Examples of the fluorine-containing (meth) acrylic acid ester monomers include monomers represented by the following formula (I).

[Chemical Formula 1]

In the above formula (I), R ¹ represents a hydrogen atom or a methyl group.

In the above formula (I), R ² represents a hydrocarbon group containing a fluorine atom. The number of carbon atoms in the hydrocarbon group is usually 1 or more, and usually 18 or less. The number of fluorine atoms contained in R ² may be one or two or more.

Examples of the fluorine-containing (meth) acrylic acid ester monomer represented by the formula (I) include alkyl (meth) acrylate, aryl fluoride (meth) acrylate and aralkyl fluoride (meth) acrylate. Among them, alkyl (meth) acrylate is preferred. Specific examples of such monomers include (meth) acrylic acid trifluoromethyl, 2,2,2-trifluoroethyl (meth) acrylate,? - (perfluorooctyl) , 2,3,3-tetrafluoropropyl, 2,2,3,4,4,4-hexafluorobutyl (meth) acrylate, 1H, 1H, 9H-perfluoro-1-nonyl Perfluorooctyl (meth) acrylate, 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri (meth) Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like, and the like.

The fluorine-containing (meth) acrylic acid ester monomers may be used alone or in combination of two or more at any ratio. Therefore, the water-soluble polymer may contain only one fluorine-containing (meth) acrylic acid ester monomer unit, or may contain two or more kinds of fluorine-containing (meth) acrylic acid ester monomer units in combination at an arbitrary ratio.

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. By setting the amount of the fluorine-containing (meth) acrylic acid ester monomer unit to be not less than the lower limit of the above range, the low temperature output characteristic of the secondary battery can be improved. When the amount is less than the upper limit, the water-soluble polymer is excessively softened and the durability of the negative electrode can be prevented from being lowered.

(Arbitrary unit)

The water-soluble polymer may contain a repeating unit other than the above-described sulfonic acid group-containing monomer unit and fluorine-containing (meth) acrylic acid ester monomer unit, so long as the effect of the present invention is not significantly impaired. Such a repeating unit may be a repeating unit obtained by polymerizing a monomer copolymerizable with a sulfonic acid group-containing monomer and a fluorine-containing (meth) acrylic acid ester monomer.

(Arbitrary unit: ethylenically unsaturated carboxylic acid monomer unit)

For example, the water soluble polymer may contain ethylenically unsaturated carboxylic acid monomer units. The ethylenically unsaturated carboxylic acid monomer unit is a repeating unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer.

Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acids and derivatives thereof, ethylenically unsaturated dicarboxylic acids and acid anhydrides thereof, and derivatives thereof. Of these, the ethylenically unsaturated monocarboxylic acid is preferable because the dispersibility of the resulting water-soluble polymer to water can be further increased.

Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid and crotonic acid. Examples of the derivative of the ethylenically unsaturated monocarboxylic acid include 2-ethyl acrylic acid, isocrotonic acid,? -Acetoxy acrylic acid,? -Trans-aryloxy acrylic acid,? -Chloro-? -E-methoxy acrylic acid, And amino acrylic acid. Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, itaconic acid, and the like. Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic acid anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of the derivative of the ethylenically unsaturated dicarboxylic acid include maleic acid substituted with a hydrocarbon group such as methylmaleic acid, dimethylmaleic acid, and phenylmaleic acid; halogenated maleic acid such as chloromaleic acid, dichloromaleic acid, and fluoromaleic acid; Maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride, maleic anhydride and maleic anhydride; and maleic acid esters such as maleic acid diphenyl maleate, maleic anhydride, maleic acid decyl, maleic acid octadecyl and maleic acid fluoroalkyl. Of these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. The dispersibility of the obtained water-soluble polymer to water can be further increased.

The ethylenically unsaturated carboxylic acid monomer may be used singly or in combination of two or more kinds in any ratio. Therefore, the water-soluble polymer may contain only one type of ethylenically unsaturated carboxylic acid monomer unit, or may contain two or more kinds in combination at an arbitrary ratio.

In the water-soluble polymer, the proportion of the ethylenically unsaturated carboxylic acid monomer unit is preferably 5% by weight or more, more preferably 10% by weight or more, preferably 35% by weight or less, more preferably 30% to be. By setting the amount of the ethylenically unsaturated carboxylic acid monomer unit to be not less than the lower limit of the above range, the water-soluble polymer can be increased in adsorption to the negative electrode active material, and the dispersibility of the negative electrode active material and the adhesion to the current collector can be increased. In addition, since the flexibility of the water-soluble polymer can be increased by lowering it to the upper limit value, the flexibility of the negative electrode can be improved to prevent the negative electrode from being lost or cracked, and the durability can be improved.

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

Also, for example, the water-soluble polymer may contain (meth) acrylic acid ester monomer units. The (meth) acrylic acid ester monomer unit is a repeating unit obtained by polymerizing a (meth) acrylic acid ester monomer. Among the (meth) acrylic acid ester monomers, those corresponding to the above-mentioned sulfonic acid group-containing monomers or fluorine-containing (meth) acrylic acid ester monomers are included in the sulfonic acid group-containing monomer or the fluorine-containing (meth) acrylic acid ester monomer , (Meth) acrylic acid ester monomers. For example, fluorine-containing (meth) acrylic acid ester monomers are distinguished from (meth) acrylic acid ester monomers as fluorine-containing (meth) acrylic acid ester monomers.

Examples of the (meth) acrylic acid ester monomers include monomers such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, , Alkyl acrylate esters such as heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; , Ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl 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 monomers may be used singly or in a combination of two or more. Therefore, the water-soluble polymer may contain only one type of (meth) acrylic acid ester monomer unit, or may contain two or more kinds in combination at an arbitrary ratio.

The proportion of (meth) acrylic acid ester monomer units in the water-soluble polymer is preferably 30% by weight or more, more preferably 35% by weight or more, particularly preferably 40% by weight or more, and preferably 70% Or less. By making the amount of the (meth) acrylic acid ester monomer unit be not more than the upper limit of the above range, the adhesion of the negative electrode active material to the current collector can be increased, and the flexibility of the negative electrode can be increased by setting it to the lower limit.

(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 energy irradiation of the crosslinkable monomer. By containing the crosslinkable monomer unit, the water-soluble polymer can be crosslinked, so that the strength and stability of the film formed of the water-soluble polymer can be enhanced.

As the crosslinkable monomer, a monomer capable of forming a crosslinked structure upon polymerization can be used. Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. More specifically, there can be mentioned a monofunctional monomer having a thermally crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional monomer having at least two olefinic double bonds per molecule.

Examples of the thermally crosslinkable crosslinkable group contained in the monofunctional monomer include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and a combination thereof. Among them, an epoxy group is more preferable in that the crosslinking and crosslinking density can be easily controlled.

Examples of the crosslinkable monomer having an epoxy group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include vinyl glycidyl 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- Monoepoxide of a diene or a polyene such as 9-cyclododecadiene, alkenyl such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2- Epoxides and glycidyl acrylates such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl Methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, 4-methyl-3-cyclohexenecarboxylic acid 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 thermally crosslinkable crosslinkable group and having an olefinic double bond include (meth) acrylamides having a methylol group such as N-methylol (meth) acrylamide and the like .

Examples of the crosslinkable monomer having an oxetanyl group as the thermally crosslinkable crosslinkable group and having an olefinic double bond include 3 - ((meth) acryloyloxymethyl) oxetane, 3 - ((meth) acryloyloxy (Meth) acryloyloxymethyl) oxetane, 2- ((meth) acryloyloxymethyl) oxetane, 2- (Meth) acryloyloxymethyl) -4-trifluoromethyl oxetane, and the like.

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

Examples of the polyfunctional monomer having two or more olefinic double bonds include allyl (meth) acrylate, ethylenedi (meth) acrylate, diethyleneglycol di (meth) acrylate, triethyleneglycol di (meth) (Meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diaryl ether, tetraallyloxy (meth) acrylate, tetraethylene glycol di Ethane, trimethylolpropane-diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylenebisacrylamide, and divinylbenzene.

Among them, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate are preferable as the crosslinkable monomer.

In the water-soluble polymer, the content 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% Is not more than 1.5% by weight, particularly preferably not more than 1% by weight. When the content of the crosslinkable monomer unit is within the above range, the swelling degree can be suppressed and the durability of the electrode can be enhanced. Here, the ratio of the cross-linkable monomer units in the water-soluble polymer is generally the same as the ratio (injection ratio) of the cross-linkable monomer in the total monomers of the water-soluble polymer.

(Arbitrary unit: reactive surfactant monomer unit)

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

The reactive surfactant monomer is a monomer having a polymerizable group capable of copolymerizing with another monomer and also having a surfactant (a hydrophilic group and a hydrophobic group). Typically, the reactive surfactant monomer has a polymerizable unsaturated group, which group also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group contained in the reactive surfactant monomer include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group. One kind of such polymerizable unsaturated group may be used alone, or two or more kinds may be used in combination at an arbitrary ratio.

The reactive surfactant monomer is a moiety that exhibits hydrophilicity, and usually has a hydrophilic group. The reactive surfactant monomers are classified into anionic, cationic, and nonionic surfactants depending on the kind of the hydrophilic group.

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

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

An example of a nonionic system hydrophilic group is -OH.

Examples of preferred reactive surfactant monomers include compounds represented by the following formula (II).

(2)

In formula (II), R represents a divalent linking group. Examples of R include a -Si-O- group, a methylene group and a phenylene group.

In the formula (II), R ³ represents a hydrophilic group. An example of R ³ is -SO ₃ NH ₄ .

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

As another example of a preferable reactive surfactant, there may be mentioned an alkenyl group having a structural unit having a structure formed by polymerizing ethylene oxide and a structure having a structure formed by polymerization of butylene oxide, Compounds having SO ₃ NH ₄ (for example, trade names: "Latemer PD-104" and "Latemer PD-105", manufactured by Kao Corporation).

The reactive surfactant monomers may be used singly or in combination of two or more at any desired ratio.

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, particularly preferably 2% by weight or less. The dispersibility of the slurry composition can be improved by setting the content ratio of the reactive surfactant unit to be equal to or lower than the lower limit of the above range. In addition, by setting it to be not more than the upper limit value, the durability of the electrode can be improved.

(Arbitrary units: other units)

Examples of the optional units that the water-soluble polymer may contain include repeating units obtained by polymerizing various kinds of optional copolymerizable monomers in addition to those exemplified above. Examples of such a copolymerizable monomer include a carboxylic acid ester monomer having at least two carbon-carbon double bonds, such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; Styrene monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene,? -Methylstyrene and divinylbenzene; acrylamide, N Amide-based monomers such as methylol acrylamide,?,? -Unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile, olefin monomers such as ethylene and propylene, monomers such as vinyl chloride and vinylidene chloride, Containing monomer (other than the (meth) acrylic acid ester-containing monomer), vinyl acetate, vinyl propionate , Vinyl butyrate, and vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, butyl vinyl ether and the like; vinyl monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl Vinyl ketone monomers such as vinyl ketone; heterocyclic vinyl compound monomers such as N-vinylpyrrolidone, vinylpyridine and vinylimidazole; and the like.

These copolymerizable monomers may be used singly or in combination of two or more at any ratio. Therefore, the water-soluble polymer may contain only one type of unit based on such a copolymerizable monomer, or may contain two or more kinds in combination at an arbitrary ratio. In the water-soluble polymer, the proportion of units based on such a copolymerizable monomer is preferably 0% by weight to 10% by weight, more preferably 0% by weight to 5% by weight.

(Properties of Water-Soluble Polymer)

The weight average molecular weight of the water-soluble polymer is usually smaller than that of 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, And particularly preferably 100000 or less. By setting the weight average molecular weight of the water-soluble polymer to a value lower than 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. For example, the dispersibility of the negative electrode active material and the high- And the like can be improved. The water-soluble polymer can be made flexible by setting it to be not more than the upper limit of the above range, for example, suppressing the expansion of the negative electrode and improving the adhesion of the negative electrode active material layer to the current collector. The weight average molecular weight of the water-soluble polymer can be determined as a value in terms of polystyrene using a solution in which 0.85 g / ml of sodium nitrate is dissolved in a 10% by volume aqueous solution of dimethylformamide by GPC as a developing solvent.

The glass transition temperature of the water-soluble polymer is preferably 0 占 폚 or higher, more preferably 5 占 폚 or higher, preferably 100 占 폚 or lower, more preferably 50 占 폚 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 water-soluble polymer preferably has a viscosity of not less than 0.1 mPa · s, preferably not less than 1 mPa · s, more preferably not less than 10 mPa · s, usually not more than 20000 mPa · s, Is not more than 10000 mPa s, more preferably not more than 5000 mPa s. By setting the viscosity above the lower limit of the above range, the strength of the water-soluble polymer can be enhanced to improve the durability of the negative electrode. By making the viscosity lower than the upper limit, the applicability of the negative electrode slurry composition can be improved, The adhesion strength of the layer can be improved. The above viscosity can be adjusted, for example, by the molecular weight of the water-soluble polymer. The above viscosity is a value measured at 25 캜 and a rotation number of 60 rpm using a B-type viscometer.

(Method for producing water-soluble polymer)

The water-soluble polymer can be produced, for example, by polymerizing a monomer composition containing the above-mentioned sulfonic acid group-containing monomer, the fluorine-containing (meth) acrylic acid ester monomer and, if necessary, an optional monomer in an aqueous solvent . The aqueous solvent and the polymerization method may be the same as, for example, the preparation of the particulate binder. 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 can be taken out from the aqueous solution thus obtained, a negative electrode slurry composition is usually prepared using a water-soluble polymer dissolved in an aqueous solvent, and the negative electrode is prepared using the negative electrode slurry composition.

The above aqueous solution containing a water-soluble polymer in an aqueous solvent is usually acidic, and therefore may be alkalized to pH 7 to pH 13, if necessary. As a result, the handling properties of the aqueous solution can be improved, and the applicability of the negative electrode slurry composition can be improved. Examples of a method for alkalizing the solution to pH 7 to pH 13 include an aqueous solution of an alkali metal such as an aqueous solution of lithium hydroxide, an aqueous solution of sodium hydroxide and an aqueous solution of potassium hydroxide, an alkaline earth metal aqueous solution such as an aqueous calcium hydroxide solution or an aqueous magnesium hydroxide solution, Are mixed with each other. The above-mentioned alkali aqueous solution may be used singly or in combination of two or more in an arbitrary ratio.

(Amount of water-soluble polymer)

The amount of the water-soluble polymer is preferably at least 0.1 part by weight, more preferably at least 0.5 part by weight, particularly preferably at least 1 part by weight, preferably at most 10 parts by weight, more preferably at most 10 parts by weight, based on 100 parts by weight of the negative electrode active material Is not more than 5 parts by weight. By controlling the amount of the water-soluble polymer in the above range, it is possible to suppress the expansion of the negative electrode accompanied by charging and discharging, to improve the high temperature storage characteristics, the high temperature cycle characteristics and the low temperature output characteristics of the secondary battery; The above-described effects such as improvement in coating property at the time of coating and improvement in adhesion of the negative electrode active material layer to the current collector can be stably exhibited.

[1-4. Optional component of 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 optional components include a viscosity adjusting agent, a conductive agent, a reinforcing agent, a leveling agent, and an electrolyte additive. These are not particularly limited as long as they do not affect the cell reaction. These components may be used singly or in combination of two or more in an arbitrary ratio.

The viscosity adjuster is a component used for adjusting the viscosity of the negative electrode slurry composition of the present invention to improve the dispersibility and coatability of the negative electrode slurry composition. Normally, the viscosity adjuster contained in the negative electrode slurry composition remains in the negative electrode active material layer.

As the viscosity adjusting agent, it is preferable to use a water-soluble polysaccharide. Examples of polysaccharides include natural polymer compounds and cellulose-based semisynthetic polymer compounds. The viscosity modifiers may be used alone, or two or more of them may be used in combination at an arbitrary ratio.

Examples of natural macromolecule compounds include polysaccharides and proteins derived from plants or animals. In addition, a natural high molecular compound having undergone fermentation treatment with a microorganism or the like, treatment with heat or the like may be exemplified. These natural polymer compounds can be classified as plant-based natural polymeric compounds, animal-based natural polymeric compounds, and microbial natural-based polymeric compounds.

Examples of the vegetable natural macromolecule compound include gum arabic, tragacanth gum, galactan, guar gum, carab gum, karaya gum, carrageenan, pectin, agar, queen seed (quince seed), algae colloid Starch (derived from rice, corn, potato, wheat and the like), glycyrrhizin and the like. Examples of animal-based natural high-molecular compounds include collagen, casein, albumin, and gelatin. Examples of the microbial natural polymer include xanthan gum, dextran, succinoglucan, pullulan, and the like.

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

Examples of the nonionic cellulosic semi-synthetic polymeric compound include alkylcelluloses such as methylcellulose, methylethylcellulose, ethylcellulose, microcrystalline cellulose and the like; hydroxyalkylcelluloses such as hydroxyethylcellulose, hydroxybutylmethylcellulose, hydroxypropylcellulose, Hydroxyalkylcelluloses such as hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose stearoxyether, carboxymethylhydroxyethylcellulose, alkylhydroxyethylcellulose, and nonoxynylhydroxyethylcellulose, and the like can be used. .

Examples of the anionic cellulose-based semisynthetic polymer compound include alkylcellulose in which the above nonionic cellulosic semi-synthetic polymer compound is substituted by various induction groups, and sodium salts and ammonium salts thereof. Specific examples thereof include sodium cellulose sulfate, methylcellulose, methylethylcellulose, ethylcellulose, carboxymethylcellulose (CMC) and salts thereof.

Examples of the cationic cellulose based semisynthetic polymer compound include low nitrogen hydroxyethyl cellulose dimethyldiallylammonium chloride (polyquaternium-4), chlorinated O- [2-hydroxy-3- (trimethylammonio) propyl Hydroxyethyl cellulose (polyquaternium-10), chlorinated O- [2-hydroxy-3- (lauryldimethylammonio) propyl] hydroxyethyl cellulose (polyquaternium-24) and the like.

Of these, cellulose-based semisynthetic polymer compounds, sodium salts thereof and ammonium salts thereof are preferable in that cationic, anionic and positive characteristics can be taken. In particular, from the viewpoint of dispersibility of the negative electrode active material, anionic cellulose based semisynthetic polymer compound is particularly preferable.

The degree of etherification of the cellulose based semisynthetic polymer compound is preferably 0.5 or more, more preferably 0.6 or more, preferably 1.0 or less, more preferably 0.8 or less. Here, the degree of etherification refers to the substitution degree of a hydroxyl group (3) per one anhydroglucose unit in cellulose with respect to a substituent to a carboxymethyl group and the like. The degree of etherification can theoretically take a value of 0 to 3. When the degree of etherification is in the above range, the cellulosic semisynthetic polymeric compound is adsorbed on the surface of the negative electrode active material and shows good compatibility with water. Thus, the dispersibility is excellent and the negative electrode active material is finely dispersed to the primary particle level .

When a polymer compound is used as the viscosity modifier, the average degree of polymerization of the viscosity modifier calculated from the intrinsic viscosity determined from the Uberode viscometer is preferably 500 or more, more preferably 1000 or more, and preferably 2500 or less, More preferably 2000 or less, and particularly preferably 1500 or less. The average degree of polymerization of the viscosity modifier may affect the fluidity of the negative electrode slurry composition of the present invention, the film uniformity of the negative electrode active material layer, and the process in the process. By setting the average polymerization degree to the above range, the time-course stability of the negative electrode slurry composition of the present invention can be improved, and coating without aggregation and thickness irregularity becomes possible.

The amount of the viscosity adjusting agent is preferably 0 parts by weight or more, and preferably 0.5 parts by weight or less, based on 100 parts by weight of the negative electrode active material. By adjusting the amount of the viscosity adjusting agent within the above range, the viscosity of the negative electrode slurry composition of the present invention can be set within a preferable range which is easy to handle.

The conductive agent is a component that improves the electrical contact between the negative electrode active materials. By containing the conductive agent, the discharge rate characteristic of the secondary battery of the present 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. The conductive agent may be used alone, or two or more conductive agents may be used in combination at an arbitrary ratio.

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, rod-like or fibrous fillers can be used, for example. One type of reinforcing material may be used alone, or two or more kinds of reinforcing materials may be used in combination at an arbitrary ratio. By using the reinforcing material, it is possible to obtain a strong and flexible negative electrode and realize a secondary battery exhibiting excellent long-term cycle characteristics.

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, and 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 within the above range, the secondary battery can exhibit high capacity and high load characteristics.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorinated surfactants, and metal surfactants. One type of leveling agent may be used alone, or two or more types may be used in combination at an arbitrary ratio. By using the leveling agent, it is possible to prevent the occurrence of cratering during application of the negative electrode slurry composition and to improve the smoothness of the negative electrode.

The amount of the leveling agent is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. Since the leveling agent is in the above range, productivity, smoothness and battery characteristics at the time of negative electrode production are excellent. In addition, by containing a surfactant, dispersibility of the negative electrode active material and the like in the negative electrode slurry composition can be improved, and the smoothness of the negative electrode obtained thereby can be improved.

Examples of the electrolyte additive include vinylene carbonate and the like. The electrolyte additive may be used alone or in combination of two or more in an arbitrary ratio. By using the electrolyte additive, for example, decomposition of the electrolyte can be suppressed.

The amount of the electrolyte additive is preferably 0.01 to 10 parts by weight based on 100 parts by weight of the negative electrode active material. By setting the amount of the electrolyte additive within the above range, it is possible to realize a secondary battery excellent in cycle characteristics and high temperature characteristics.

The negative electrode active material layer may contain nanoparticles such as fumed silica or fumed alumina. The nanoparticles may be used singly or in combination of two or more in an arbitrary ratio. In the case of containing nanoparticles, it is possible to adjust the plasticity of the negative electrode slurry composition, so that the leveling property of the negative electrode of the present invention obtained thereby can be improved.

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

[1-5. Collector and negative electrode active material layer]

The negative electrode of the present invention usually contains a current collector and a negative electrode active material layer formed on the surface of the current collector. The negative electrode active material layer contains a negative electrode active material, a particulate 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 surface of the sheet-like current collector, but it is preferably formed on both surfaces.

The collector for the negative electrode has electrical conductivity and is not particularly limited as long as it is an electrochemically durable material, but a metal material is preferable because it has heat resistance. Examples of the material of the current collector for the negative electrode include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, copper is particularly preferable as the current collector used for the secondary battery negative electrode. The above-mentioned materials may be used singly or in combination of two or more in an arbitrary ratio.

The shape of the current collector is not particularly limited, but it is preferable that the sheet is in the form of a sheet having a thickness of about 0.001 mm to 0.5 mm.

The collector may be subjected to a surface roughening treatment beforehand in order to increase the bonding strength with the negative electrode active material layer. Examples of the roughening method include mechanical roughening, electrolytic roughening, chemical roughening, and the like. In mechanical polishing, a wire brush with polishing abrasive grains fixed to abrasive particles, a grinding stone, an emery buff, a steel wire, or the like is usually used. An intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the negative electrode active material layer.

The thickness of the negative electrode active material layer formed on the surface of the current collector is usually 5 占 퐉 or more, preferably 30 占 퐉 or more, and usually 300 占 퐉 or less, preferably 250 占 퐉 or less. When the thickness of the negative electrode active material layer is in the above range, load characteristics and cycle characteristics can be improved.

The content of the negative electrode active material in the negative electrode active material layer is preferably 85 wt% or more, more preferably 88 wt% or more, preferably 99 wt% or less, more preferably 97 wt% or less. By setting the content ratio of the negative electrode active material within the above range, it is possible to realize a negative electrode exhibiting flexibility and binding property while exhibiting a high capacity.

[2. &Lt; / RTI &gt; a slurry composition for negative electrode and a method for producing negative electrode)

The negative electrode for a secondary battery of the present invention can be produced by an arbitrary production method, but it is preferable that the negative electrode slurry composition of the present invention (hereinafter referred to as &quot; negative electrode slurry composition of the present invention &quot; (Hereinafter referred to as &quot; method for producing a negative electrode of the present invention &quot;, as appropriate) of the present invention described below.

[2-1. Slurry composition for negative electrode]

The negative electrode slurry composition of the present invention is a slurry-like composition containing a negative electrode active material, a particulate binder, and a water-soluble polymer.

The negative electrode slurry composition of the present invention usually further contains a solvent. 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.

The water functions as a solvent or a dispersant in the negative electrode slurry composition, and the negative electrode active material may be dispersed, the particulate binder may be dispersed in particulate form, or the water-soluble polymer may be dissolved. When the particulate binder and the liquid for dissolving the water-soluble polymer are combined, the particulate binder and the water-soluble polymer are adsorbed on the surface of the negative electrode active material, thereby stabilizing the dispersion of the negative electrode active material.

The kind of liquid to be combined with water is preferably selected from the viewpoint of drying speed and environment. Preferred examples thereof 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, gamma -butyrolactone , and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl And amides such as N-methylpyrrolidone and N, N-dimethylformamide. Of these, N-methylpyrrolidone (NMP) is preferable. These liquids may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

The amount of the solvent in the negative electrode slurry composition is preferably adjusted so that the viscosity of the negative electrode slurry composition of the present invention becomes a preferable viscosity for application. Concretely, the solid content of the negative electrode slurry composition of the present invention is preferably 30% by weight or more, more preferably 40% by weight or more, preferably 90% by weight or less, more preferably 80% To be used in the present invention.

The negative electrode slurry composition may contain optional components other than the negative electrode active material, the particulate binder, the water-soluble polymer and the solvent, if necessary. The amount of the optional component is usually made equal to the amount of any component contained in the negative electrode active material layer. In such a negative electrode slurry composition of the present invention, a part of the water-soluble polymer is dissolved in water, but a part of the water-soluble polymer is adsorbed on the surface of the negative electrode active material so that the negative electrode active material is covered with a stable layer of the water- The dispersibility of the negative electrode active material in the solvent is improved. For this reason, the negative electrode slurry composition of the present invention has good applicability when applied to a current collector.

The method for preparing the negative electrode slurry composition of the present invention is not particularly limited and may be produced by mixing a negative electrode active material, a particulate binder, a water-soluble polymer, a solvent, and optional components as required. The mixing method is not particularly limited, and examples thereof include a method using a mixing device such as a stirring type, shaking type, and rotary type. In addition, a method using a dispersion kneading apparatus such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer and a planetary kneader may be used.

[2-2. Manufacturing method of negative electrode]

The negative electrode of the present invention can be produced by applying the negative electrode slurry composition of the present invention to the surface of the current collector and drying as required to form a negative electrode active material layer on the surface of the current collector.

The method of applying the negative electrode slurry composition of the present invention to the surface of the current collector is not particularly limited. Examples of the method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

Examples of the drying method include, for example, hot air, hot air, low-humidity air drying, vacuum drying, and drying by irradiation with (circle) infrared rays or electron beams. The drying time is usually from 1 minute to 40 minutes, and the drying temperature is usually from 40 ° C to 180 ° C.

It is also preferable that the negative electrode active material layer is subjected to a pressing treatment, for example, by using a die press or a roll press, if necessary after coating and drying the negative electrode slurry composition on the surface of the current collector. By the pressure treatment, the porosity of the negative electrode active material layer can be lowered. The porosity is preferably 5% or more, more preferably 7% or more, preferably 30% or less, and more preferably 20% or less. By setting the porosity to the lower limit of the above range, a high volume capacity is easily obtained, the negative electrode active material layer can be made difficult to peel off from the current collector, and if it is not more than the upper limit value, high charging efficiency and discharge efficiency can be obtained.

When the negative electrode active material layer contains a curable polymer, it is preferable to cure the polymer after formation of the negative electrode active material layer.

[3. Secondary battery]

The secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte, and a separator, and the negative electrode is the negative electrode of the present invention.

Since the secondary battery of the present invention is provided with the negative electrode of the present invention, expansion of the negative electrode accompanying charge and discharge can be suppressed, or capacity can be made less difficult to be stored even in a high temperature environment. It is also possible to improve the high-temperature cycle characteristics and low-temperature output characteristics of the secondary battery of the present invention, or to improve the adhesion of the negative-electrode active material layer to the current collector.

[3-1. Positive]

The positive electrode usually has a positive electrode active material layer containing a positive electrode active material and a binder for a positive electrode, which are formed on the surfaces 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 the collector of the positive electrode, for example, a collector used for the negative electrode of the present invention may be used. Among them, aluminum is particularly preferable.

As the positive electrode active material, for example, when the secondary battery of the present invention is a lithium ion secondary battery, a material capable of inserting and desorbing lithium ions is used. Such a positive electrode active material is roughly classified into an inorganic compound and an organic compound.

Examples of the positive electrode active material composed of an inorganic compound include transition metal oxides, transition metal sulfides, lithium-containing composite metal oxides with lithium and transition metals, and the like.

Examples of the transition metal include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Mo.

Examples of transition metal oxides include 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 , V ₆ O _13, etc. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable in terms of cycle stability and capacity.

Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , FeS, and the like.

The lithium-containing composite metal oxide includes, for example, a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

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, lithium of Ni-Mn- Complex oxides, and lithium composite oxides of Ni-Co-Al.

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 is Cr, Fe, Co, Ni, Cu, etc.).

As the lithium-containing composite metal oxide having an olivine structure, for example, Li _X MPO ₄ (where M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Al, Si, B and Mo, and X represents a number satisfying 0 &amp;le; X &amp;le; 2).

Examples of the positive electrode active material composed of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.

Further, a positive electrode active material composed of a composite material in which an inorganic compound and an organic compound are combined may be used. For example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. The iron-based oxide tends to lack electrical conductivity, but by using the composite material as described above, it can be used as a high-performance positive electrode active material.

Further, the above-mentioned compound may be partially substituted with an element to use as a positive electrode active material. A mixture of the inorganic compound and the organic compound may be used as the positive electrode active material.

The positive electrode active material may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

The volume average particle diameter of the particles of the positive electrode active material is usually 1 占 퐉 or more, preferably 2 占 퐉 or more, and usually 50 占 퐉 or less, preferably 30 占 퐉 or less. By setting the volume average particle diameter of the particles of the positive electrode active material within the above range, it is possible to reduce the amount of the binder when preparing the positive electrode active material layer, thereby suppressing the capacity of the secondary battery from being lowered. In order to form the positive electrode active material layer, a positive electrode slurry composition containing a positive electrode active material and a binder is usually prepared. However, it is easy to adjust the viscosity of the positive electrode slurry composition to a suitable viscosity, One positive electrode can be obtained.

The content of the positive electrode active material in the positive electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, preferably 99.9% by weight or less, more preferably 99% by weight or less. By setting the content of the positive electrode active material within the above range, the capacity of the secondary battery can be increased, and flexibility of the positive electrode and adhesion of the current collector and the positive electrode active material layer can be improved.

Examples of the binder for the positive electrode include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, A soft polymer such as an acrylic soft polymer, a diene soft polymer, an olefin soft polymer, and a vinyl soft polymer can be used. The binder may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

The positive electrode active material layer may contain components other than the positive electrode active material and the binder, if necessary. Examples thereof include a viscosity adjusting agent, a conductive agent, a reinforcing agent, a leveling agent, and an electrolyte additive. These components may be used singly or in combination of two or more in an arbitrary ratio.

The thickness of the positive electrode active material layer is usually not less than 5 占 퐉, preferably not less than 10 占 퐉, and usually not more than 300 占 퐉, preferably not more than 250 占 퐉. When the thickness of the positive electrode active material layer is in the above range, high characteristics in both the load characteristic and the energy density can be realized.

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

[3-2. Electrolyte]

As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a nonaqueous solvent can be used. As the lithium salt, _{e.g., 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 NLi, (CF ₃ SO ₂₎ can be cited lithium salts such as _{2 NLi, (C 2 F 5} SO 2) NLi. _{LiPF 6, LiClO 4, CF 3} SO 3 Li , particularly exhibiting a high degree of dissociation easily soluble in the solvent is preferably used. These may be used singly or in combination of two or more in an arbitrary ratio.

The amount of the supporting electrolyte is usually not less than 1% by weight, preferably not less than 5% by weight, and usually not more than 30% by weight, preferably not more than 20% by weight, based on the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ion conductivity may be lowered and the charging characteristics and the discharging characteristics of the secondary battery may be deteriorated.

The solvent used for the electrolytic solution is not particularly limited as far as it dissolves the supporting electrolyte. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate ; Ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur compounds such as sulfolane and dimethylsulfoxide; and the like. Particularly, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. One solvent may be used alone, or two or more solvents may be used in combination at an arbitrary ratio.

The electrolytic solution may contain an additive if necessary. As the additive, for example, a carbonate-based compound such as vinylene carbonate (VC) is preferable. The additives may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the electrolytic solution other than the above include gelated polymer electrolytes in which a polymer electrolyte such as polyethylene oxide or polyacrylonitrile is impregnated with an electrolytic solution, inorganic solid electrolytes such as lithium sulfide, LiI and Li ₃ N, and the like .

[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 side or both sides thereof, (c) a porous separator formed with a porous resin coat layer containing inorganic ceramic powder, etc. . Examples thereof include a solid polymer electrolyte such as a polypropylene-based, polyethylene-based, polyolefin-based or aramid-based porous separator, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer A separator coated with a porous film layer made of an inorganic filler and a dispersant for an inorganic filler, and the like.

[3-4. Manufacturing Method of Secondary Battery]

The production method of the secondary battery of the present invention is not particularly limited. For example, the negative electrode and the positive electrode described above are superimposed with a separator interposed therebetween, and the secondary battery is manufactured by winding or bending the negative electrode and the positive electrode through a separator, inserting an electrolyte solution into the battery container, . If necessary, an overcurrent prevention element such as an X-fund metal, a fuse, or a PTC element, or a lead plate may be inserted to prevent pressure rise and overcharge discharge inside the battery. The shape of the battery may be, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, or a flat type.

Example

Hereinafter, the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following embodiments, and may be arbitrarily changed without departing from the scope of the claims of the present invention and its equivalents.

In the following description, &quot;% &quot; and &quot; part &quot; representing amounts are based on weight unless otherwise specified. The operations described below were carried out under normal temperature and normal pressure conditions unless otherwise specified. In particular, the evaluation operation of the battery was carried out at 25 占 폚 unless otherwise specified.

[Assessment Methods]

The properties of Examples and Comparative Examples were evaluated as follows.

1. Adhesion strength

The negative electrode prepared in Examples and Comparative Examples was cut into a rectangular shape having a length of 100 mm and a width of 10 mm to prepare test pieces. The test piece was attached with a cellophane tape on the surface of the negative electrode active material layer with the surface of the negative electrode active material layer facing downward. At this time, the cellophane tape specified in JIS Z1522 was used. The cellophane tape was fixed to a horizontal test stand. Thereafter, the stress at the time when one end of the current collector was pulled up vertically at a tensile speed of 50 mm / min was measured. This measurement was carried out three times, and the average value was obtained, and the average value was determined as the peel strength (N / m). The larger the fill strength, the larger the binding force of the negative electrode active material layer to the current collector, i.e., the larger the adhesion strength.

2. Slurry stability

With respect to the negative electrode slurry composition prepared in Examples and Comparative Examples, a viscosity? 0 at 25 占 폚 and a rotation number of 60 rpm was measured by a B-type viscometer.

Thereafter, the slurry composition for negative electrode was stopped still at 5 deg. C for 72 hours, then returned to 25 deg. C, and the viscosity? 1 was measured again as described above. If the viscosity change rate (= (η1 - η0) / η0 × 100) is less than 10% increase, A, 10% increase to 30% increase, and B .

3. Coating property

The slurry composition for negative electrode prepared in Examples and Comparative Examples was coated on a copper foil having a thickness of 20 mu m as a current collector so that the film thickness after drying was about 150 mu m and dried. This drying was carried out by conveying the copper foil in an oven at 60 캜 for 2 minutes at a speed of 0.5 m / min. Thereafter, it was heat-treated at 120 ° C for 2 minutes to obtain a negative electrode. The obtained negative electrode was cut into a size of 10 10 cm, and the number of pinholes having a diameter of 0.1 mm or more was visually observed. The smaller the number of pinholes, the better the applicability.

4. Durability

(1) High-temperature storage characteristics

The lithium ion secondary batteries of the laminate type cells prepared in the examples and the comparative examples were stopped at 25 캜 for 24 hours and charged to 4.2 V at a constant current of 0.1 C under an environment of 25 캜 to give 3.0 V was carried out to measure the initial capacity C ₀ . The battery was charged at 4.2 V, stored at 60 캜 for 7 days, charged at 4.2 V by a constant current method of 0.1 C under a 25 캜 environment, and discharged to 3.0 V, And the capacity C ₁ after the measurement was measured. The high-temperature storage characteristics were evaluated by the capacity change rate? C _S expressed by? C _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

The lithium ion secondary batteries of the laminate type cells prepared in the examples and the comparative examples were stopped at 25 캜 for 24 hours and charged to 4.2 V at a constant current of 0.1 C under an environment of 25 캜 to give 3.0 V was carried out to measure the initial capacity C ₀ . The charging and discharging operation of discharging to 4.2 V and discharging to 3.0 V by the constant current method of 1 C under the environment of 60 캜 was repeated to measure the capacity C ₂ after 100 cycles. High-temperature cycle characteristic was evaluated by the capacity change rate ΔC _C represented by _{ΔC C = C 2 / C 0} × 100 (%). The higher the value of the capacitance change rate? _{C C,} the better the high-temperature cycle characteristics.

(3) Expansion characteristics of plate

After the above evaluation of &quot; (1) high temperature storage characteristics &quot;, the cell of the lithium ion secondary battery was disassembled and the thickness d1 of the electrode plate of the negative electrode was measured. (D1 - d0) / d0 x 100 (%) of the negative electrode was calculated by taking the thickness of the negative electrode plate as d0 before manufacturing the cell of the lithium ion secondary battery. The lower this value is, the better the expansion property of the electrode plate is.

5. Low Temperature Output Characteristics

The lithium ion secondary batteries of the laminate type cells prepared in Examples and Comparative Examples were stopped for 24 hours under the environment of 25 캜 and then charged at a charging rate of 4.2 V and 1 C. Thereafter, discharge operation was performed at a discharge rate of 1 C under an environment of -10 캜, and a voltage V ₁₅ after 15 seconds from the start of discharge was measured. The low-temperature output characteristic was evaluated by a voltage change? V expressed by? V = 4.2 V - V ₁₅ (mV). The smaller the value of the voltage change? V, the better the low-temperature output characteristic.

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

The water-soluble polymers prepared in Examples and Comparative Examples were diluted with 10% ammonia water and ion-exchange water so as to have a pH of 8 to prepare a 1% aqueous solution of a water-soluble polymer. The viscosity of this aqueous solution was measured by a B-type viscometer.

[Example 1]

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

In a pressure vessel of 5 MPa equipped with a stirrer, 65.5 parts of ethyl acrylate as the (meth) acrylic acid ester monomer, 30 parts of methacrylic acid as the ethylenically unsaturated carboxylic acid monomer, 30.0 parts of trifluoromethylmethacrylate as the fluorine-containing (meth) Acrylate-2-methylpropanesulfonic acid 2 parts as a sulfonic acid group-containing monomer, 1.0 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator After sufficiently stirring, the mixture was heated to 60 DEG C to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous solution containing a water-soluble polymer. To the aqueous solution containing the water-soluble polymer thus obtained, 10% ammonia water was added to adjust the pH to 8 to obtain an aqueous solution containing the desired water-soluble polymer. The weight average molecular weight of the obtained water-soluble polymer was measured and found to be 12800.

The aqueous solution containing the water-soluble polymer thus obtained was used as a sample, and the viscosity of a 1% aqueous solution of the water-soluble polymer was measured and found to be 1,500 mPa · s.

(1-2. Preparation of particulate binder)

In a 5 MPa pressure vessel equipped 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 of styrene as an aromatic vinyl monomer, 4 parts of sodium benzenesulfonate, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred, followed by heating to 50 캜 to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain an aqueous dispersion containing particulate binder made of styrene butadiene copolymer (hereinafter referred to as "SBR" as appropriate). A 5% aqueous sodium hydroxide solution was added to the aqueous dispersion containing the particulate binder thus obtained to adjust the pH to 8, and the unreacted monomers were removed by distillation under reduced pressure by heating. Thereafter, the mixture was cooled to 30 DEG C or lower to obtain an aqueous dispersion containing a desired particulate binder. The weight average molecular weight of the obtained particulate binder was measured and found to be 1500000. The number average particle diameter of the particulate binder measured by the laser diffraction scattering type particle size distribution analyzer was 150 nm.

(1-3) Preparation of Slurry Composition for Negative Electrode [

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

50 parts of SiOC (volume average particle diameter: 12 mu m) and 50 parts of artificial graphite having a specific surface area of 4 m &lt; 2 &gt; / g (volume average particle diameter: 24.5 mu m) as a negative electrode active material, 1 part of a 5% aqueous solution of the water-soluble polymer corresponding to the solid content was added, and the solid content concentration was adjusted to 55% by ion-exchanged water, followed by mixing at 25 캜 for 60 minutes. Next, the solid content was adjusted to 52% with ion-exchanged water, and then mixed again at 25 캜 for 15 minutes to obtain a mixed solution.

To the mixed solution, 1 part of the aqueous dispersion containing the particulate binder obtained in the step (1-2) in an amount corresponding to the solid content, and ion-exchanged water were added to adjust the final solid content concentration to 42%, and mixed again for 10 minutes. This was degassed under reduced pressure to obtain a negative electrode slurry composition having good flowability.

The stability and applicability of the obtained negative electrode slurry composition were evaluated. The results are shown in Table 1.

(1-4. Preparation of negative electrode)

The slurry composition for negative electrode obtained in the step (1-3) was coated on a copper foil having a thickness of 20 mu m as a current collector with a comma coater so that the film thickness after drying was about 150 mu m and dried. This drying was carried out by conveying the copper foil in an oven at 60 캜 for 2 minutes at a speed of 0.5 m / min. Thereafter, the substrate was subjected to heat treatment at 120 캜 for 2 minutes to obtain a negative electrode disc. This negative electrode disc was rolled by a roll press to obtain a negative electrode having a thickness of the negative electrode active material layer of 80 mu m.

The obtained negative electrode was evaluated for adhesion strength. The results are shown in Table 1.

(1-5. Preparation of positive electrode)

A 40% aqueous dispersion of an acrylate polymer having a glass transition temperature Tg of -40 캜 and a number average particle diameter of 0.20 탆 was prepared as a positive electrode binder. The above acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 78% by weight of 2-ethylhexyl acrylate, 20% by weight of acrylonitrile, and 2% by 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 1% aqueous solution of carboxymethylcellulose ("BSH-12" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) And 5 parts of a 40% aqueous dispersion of the acrylate polymer corresponding to the solid content as a binder were mixed and ion-exchanged water was added thereto so that the total solid content concentration was 40%. The mixture was mixed by a planetary mixer, To prepare a positive electrode slurry composition.

The above-described slurry composition for positive electrode was applied on a 20 mu m thick aluminum foil as a current collector with a comma coater so that the film thickness after drying was about 200 mu m and dried. This drying was carried out by conveying the aluminum foil in an oven at 60 ° C for 2 minutes at a rate of 0.5 m / min. Thereafter, it was heat-treated at 120 DEG C for 2 minutes to obtain a positive electrode plate. The original plate of the positive electrode was rolled by a roll press to obtain a positive electrode having a thickness of the positive electrode active material layer of 70 mu m.

(1-6 Preparation of Separator)

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

(1-7. Lithium ion secondary battery)

An aluminum foil sheathing was prepared as the outer surface of the 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 in the step (1-5) was cut into a rectangle of 4 mm x 4 mm. The separator of step (1-6) was cut into a rectangle of 5 mm x 5 mm.

The rectangular positive electrode was disposed so that the surface of the current collector was in contact with the aluminum-containing sheath. On the surface of the positive electrode active material layer of the rectangular positive electrode, a rectangular separator was disposed. Further, on the rectangular separator, the rectangular negative electrode was arranged so that the surface of the negative electrode active material layer was directed to the separator. A mixed solvent of a 1.0 M LiPF ₆ solution (solvent: EC / DEC = 1/2 (volume ratio)) was filled as an electrolyte in the aluminum foil. Further, in order to seal the openings of the aluminum foil, a heat seal of 150 DEG C was carried out, and the aluminum sheath was closed to prepare a lithium ion secondary battery.

The obtained battery was evaluated for high-temperature storage characteristics, high temperature cycle characteristics, and extreme plate expansion characteristics, and the low temperature output characteristics were evaluated. The results are shown in Table 1.

The capacity (initial capacity) when the obtained lithium ion secondary battery was first charged and discharged at a charging and discharging 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 in place of 2-acrylamide-2-methylpropane sulfonic acid as a sulfonic acid group- , A lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1. [ The results are shown in Table 1.

[Examples 4 and 5]

In the preparation of the water-soluble polymer of the step (1-1), the fluorine-containing (meth) acrylic acid ester monomer was replaced by trifluoromethyl acrylate (Example 4) or perfluorooctyl methacrylate Lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1, except that the above-prepared lithium ion secondary battery (Example 5) was used. The results are shown in Table 1.

[Examples 6 to 12]

In the preparation of the water-soluble polymer of the step (1-1), the ratios of ethyl acrylate, methacrylic acid, trifluoromethyl methacrylate, and 2-acrylamido-2-methylpropanesulfonic acid are shown in Tables 1 and 2 A lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1, The results are shown in Tables 1 and 2.

[Example 13]

In the same manner as in Example 1 except that 100 parts of SiOC was used instead of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material in the production of the negative electrode slurry composition of the step (1-3) The components were manufactured and evaluated. The results are shown in Table 2.

[Example 14]

In the same manner as in Example 1 except that 100 parts of artificial graphite was used in place of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material in the production of the negative electrode slurry composition of the step (1-3) The components were manufactured and evaluated. The results are shown in Table 2.

[Example 15]

(Production of Nanosilica Active Material A)

200 g of a silicon oxide powder (SiOx: x = 1.02) having an average particle diameter of 3 占 퐉 and a BET specific surface area of 12 m &lt; 2 &gt; / g was introduced into a tray made of silicon nitride and then quenched in a treatment furnace capable of maintaining the atmosphere. Subsequently, argon gas was introduced, the inside of the furnace was replaced with argon, and the temperature was raised to 1200 DEG C at a heating rate of 300 DEG C / hr while flowing argon gas at 2 NL / min, and the furnace was maintained for 3 hours. After the end of the holding, the temperature was started to decrease. After reaching the room temperature, the powder was recovered to obtain a Si-based active material A. The obtained Si-based active material A had an average particle diameter of 3.5 mu m and a BET specific surface area of 11 m &lt; 2 &gt; / g. From the X-ray diffraction pattern of the Cu- , And it was confirmed from the half value width of this diffraction line that the silicon crystal powder dispersed in the silicon dioxide obtained by the Scherrer method had a crystal size of 40 nm.

(15-2 Production and Evaluation of Lithium Ion Secondary Battery and Its Components)

In the production of the negative electrode slurry composition of the step (1-3), 5 parts of the Si-based active material A obtained in the step (15-1) and 95 parts of artificial graphite were used in place of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material , A lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1. [ The results are shown in Table 2.

[Example 16]

(Production of Nanosilica Active Material B)

The granular polycrystalline silicon produced by introducing the polycrystalline silicon fine particles into the fluidized bed at an internal temperature of 800 DEG C and feeding the monosilane was crushed using a jet mill and classified with a classifier to obtain a polycrystalline silicon powder having a D50 of 10.2 mu m, Si-based active material B. It was confirmed from the half-width total width of the X-ray diffraction line that the crystallite size of the Si-based active material B was 44 nm by the Scherrer method.

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

In the production of the negative electrode slurry composition of the step (1-3), 5 parts of the Si-based active material B obtained in the step (16-1) and 95 parts of artificial graphite were used in place of 50 parts of SiOC and 50 parts of artificial graphite as the negative electrode active material , A lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1. [ The results are shown in Table 2.

[Comparative Examples 1 to 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 was changed , A lithium ion secondary battery and its components were manufactured and evaluated in the same manner as in Example 1. [ The results are shown in Table 3.

The meanings of the abbreviations in the table are as follows.

TFMMA: Trifluoromethyl methacrylate

TFMA: Trifluoromethyl acrylate

PFOMA: Perfluorooctyl methacrylate

AMPS: 2-acrylamide-2-methylpropanesulfonic acid

SS: Styrene sulfonic acid

VS: vinylsulfonic acid

Si system A: The nanosilica active material A prepared in Example 15

Si system B: The nanosilica active material B prepared in Example 16

Binder: Type of binder

EA amount: Ethyl acrylate added amount (parts)

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 (parts)

Sulfone monomer type: Sulfonic acid group-containing monomer type

Sulfone monomer amount: Sulfonic acid group-containing monomer Addition amount (parts)

MAA amount: methacrylic acid addition amount (parts)

1% aqueous solution viscosity: viscosity (mPa · s) of a 1% aqueous solution of a water-

Water-Soluble Polymer Molecular Weight: The weight average molecular weight

Negative electrode active material: negative electrode active material type

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

Adhesion strength: Average value of negative electrode fill strength (N / m)

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

Coating property: Number of pinholes after application of slurry for negative electrode (pieces)

High-Temperature Storage Characteristics: Capacity Change Rate ΔC _S (%)

High-temperature cycle characteristics: rate of change of capacity of battery? _{C C} (%)

Expansion characteristics of polar plate: Expansion rate of polar plate of negative electrode after evaluation of high temperature storage property (%)

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

[Review]

As is apparent from the results of Tables 1 to 3, in Examples 1 to 16 of the present invention, compared with Comparative Examples which did not satisfy any of the requirements of the present invention, expansion of the negative electrode accompanying charge and discharge was suppressed, It was well balanced and good for any of the characteristics. In addition, in Examples other than Example 8 in which the addition amount of the water-soluble polymer was small, the stability of the slurry was excellent.

Claims (11)

A negative electrode for a secondary battery comprising a negative electrode active material, a particulate binder and a water-soluble polymer,
The water-
0.1 to 15% by weight of sulfonic acid group-containing monomer units, and
And 0.5 to 10% by weight of a fluorine-containing (meth) acrylic acid ester monomer unit. The method according to claim 1,
Wherein the water-soluble polymer contains an ethylenically unsaturated carboxylic acid monomer unit. 3. The method of claim 2,
Wherein the ethylenically unsaturated carboxylic acid monomer is an ethylenically unsaturated monocarboxylic acid monomer. 4. The method according to any one of claims 1 to 3,
Wherein the negative electrode active material is capable of absorbing and desorbing lithium and contains a metal. 5. The method of claim 4,
Wherein the metal is silicon. 6. The method according to any one of claims 1 to 5,
Wherein the particulate binder contains a polymer containing an aliphatic conjugated diene monomer unit. The method according to claim 6,
Wherein the polymer containing the aliphatic conjugated diene monomer unit further contains an aromatic vinyl monomer unit. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the negative electrode is the negative electrode for a secondary battery according to any one of claims 1 to 7. A slurry composition comprising a negative electrode active material, a particulate binder and a water-soluble polymer,
The water-
0.1 to 15% by weight of a sulfonic acid group-containing monomer unit,
And 0.5 to 10% by weight of a fluorine-containing (meth) acrylic acid ester monomer unit. 10. The method of claim 9,
Wherein the water-soluble polymer contains an ethylenically unsaturated carboxylic acid monomer unit. A method for producing a negative electrode for a secondary battery, which comprises applying the slurry composition for a secondary battery negative electrode according to claim 9 or 10 onto a current collector and drying.