KR20160102399A - Binder composition for lithium ion secondary battery, slurry composition for lithium ion secondary battery, method for manufacturing electrode for secondary battery, and lithium ion secondary battery - Google Patents

Abstract

A binder composition for a lithium ion secondary battery comprising a crosslinking agent (A), a particulate binder (B) and water, and having an aqueous phase and a solid phase, wherein the crosslinking agent (A) has a functional group which reacts with a carboxylic acid, (B) contains an ethylenically unsaturated carboxylic acid group monomer unit, wherein the ratio of the surface acid amount of the particulate binder (B) to the total solid mass of the binder composition, the total solid mass of the binder composition Wherein the ratio of the amount of the acid in the aqueous phase and the amount of the surface acid / the amount of acid in the aqueous phase are within a predetermined range.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a binder composition for a lithium ion secondary battery, a slurry composition for a lithium ion secondary battery, a method for manufacturing an electrode for a secondary battery, and a lithium ion secondary battery. , AND LITHIUM ION SECONDARY BATTERY}

The present invention relates to a binder composition for a lithium ion secondary battery, a slurry composition for a lithium ion secondary battery, a method for producing an electrode for a secondary battery, and a lithium ion secondary battery.

Lithium ion secondary batteries are small and light in weight, have high energy density, and are capable of repeated charging and discharging, and are used in a wide range of applications. Lithium ion secondary batteries are required to have high cycle performance and other performance under high temperature service conditions. In recent years, improvement of battery members such as electrodes has been studied for the purpose of further enhancing the performance of secondary batteries. For example, by adding a crosslinking agent to a slurry composition used for forming an electrode active material layer of a lithium ion secondary battery in addition to an active material, a water-soluble thickener such as carboxymethyl cellulose and a particulate binder, the electrode active material layer (For example, Patent Documents 1 to 2). The cross-linking agent generally causes a cross-linking reaction in the drying step after the slurry composition is applied to the current collector to form a cross-link between the particles of the particulate binder and the like, and exhibits such action.

For the convenience of preparation of such a slurry composition, it is conceivable to prepare a slurry composition by previously preparing a binder composition containing a particulate binder and a cross-linking agent, and mixing the slurry composition with other components of the slurry composition.

Japanese Laid-Open Patent Publication No. 2011-134618 International Publication No. 2010/114119 (corresponding foreign publication: U.S. Patent Application Publication No. 2012/095131)

However, in some cases, the crosslinking agent may not be effective even when added in a large amount. In such a case, if a large amount of a crosslinking agent is added in order to exhibit the effect of the crosslinking agent, the strength (peel strength) in which the electrode active material layer adheres to the current collector is rather lowered and a desired effect such as high- .

In addition, the binder composition containing the crosslinking agent and the particulate binder deteriorates during the storage period until use after the preparation, and the desired performance may not be exhibited in some cases. For example, in a storage period after the adjustment, there is a case where undesirable crosslinking progresses, the viscosity increases, and the reactivity of the crosslinking agent decreases.

Accordingly, an object of the present invention is to provide a binder composition for a lithium ion secondary battery which has high storage stability, can impart a high peak strength to an electrode for a lithium ion secondary battery, and can impart a high temperature cycle characteristic to the lithium ion secondary battery .

A further object of the present invention is to provide a slurry composition for a lithium ion secondary battery, which can be easily produced and has high peel strength, and which can impart a high-temperature cycle characteristic to a lithium ion secondary battery.

A further object of the present invention is to provide a production method capable of easily producing an electrode for a lithium ion secondary battery capable of imparting a high-temperature cycle characteristic to a lithium ion secondary battery, .

A further object of the present invention is to provide a lithium ion secondary battery which can be easily produced and which has high high-temperature cycle characteristics.

Means for Solving the Problems The present inventors have conducted studies to achieve the above object. The present inventors have found that the effect of the crosslinking agent can be excellently expressed by setting the ratio of the surface acid amount of the particulate binder in the binder composition to the acid amount in the aqueous phase of the binder composition within a predetermined range, The present invention has been completed. That is, according to the present invention, the following [1] to [10] are provided.

[1] A binder composition for a lithium ion secondary battery comprising a crosslinking agent (A), a particulate binder (B) and water, and having an aqueous phase and a solid phase,

The crosslinking agent (A) has a functional group which reacts with a carboxylic acid,

The particulate binder (B) contains an ethylenically unsaturated carboxylic acid group monomer unit,

The ratio of the surface acid amount of the particulate binder (B) to the total mass of solids of the binder composition is not less than 0.01 mmol / g and not more than 1.0 mmol / g,

The ratio of the amount of the acid in the aqueous phase to the total mass of solids in the binder composition is 0.01 mmol / g to 1.0 mmol / g,

Wherein the value obtained by dividing the value of the ratio of the surface acid amount by the value of the ratio of the amount of acid in the aqueous phase is 1.0 or more.

[2] The binder composition for a lithium ion secondary cell according to [1], wherein the ratio of the ethylenically unsaturated carboxylic acid group monomer units in the particulate binder (B) is 0.1% by mass or more and 30% by mass or less.

[3] The lithium-ion secondary battery according to [1] or [2], wherein the particulate binder (B) further contains an ethylenically unsaturated hydroxyl group-containing monomer unit in a proportion of 0.1 mass% Binder composition.

[4] The lithium ion secondary battery according to any one of [1] to [3], wherein the crosslinking agent (A) is at least one selected from the group consisting of polyfunctional epoxy compounds, oxazoline compounds and carbodiimide compounds A binder composition for a battery.

[5] The binder composition for a lithium ion secondary cell according to any one of [1] to [4], wherein the particulate binder (B) further contains an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit.

[6] The lithium ion secondary battery according to any one of [1] to [5], wherein the amount of the crosslinking agent (A) relative to 100 parts by mass of the particulate binder (B) is 0.001 parts by mass or more and 20 parts by mass or less. Binder composition.

[7] A slurry composition for a lithium ion secondary battery comprising the binder composition for a lithium ion secondary battery according to any one of [1] to [6], an electrode active material, and a water-soluble thickener (C).

[8] The composition according to [8], wherein the water-soluble thickening agent (C) is at least one selected from the group consisting of carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, polyvinylalcohol, polycarboxylic acid, The slurry composition for a lithium ion secondary battery according to [7], wherein the slurry composition is one kind.

[9] A method for producing an electrode for a lithium ion secondary battery, which comprises applying the slurry composition for a lithium ion secondary battery according to [7] or [8] onto a collector and drying to form an electrode active material layer.

[10] A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator,

The lithium ion secondary battery according to [9], wherein the positive electrode, the negative electrode, or both of them are electrodes produced by the method for manufacturing an electrode for a lithium ion secondary battery.

INDUSTRIAL APPLICABILITY The binder composition for a lithium ion secondary battery of the present invention has a high storage stability and can impart a high peak strength to an electrode for a lithium ion secondary battery, thereby imparting a high-temperature cycle characteristic to the lithium ion secondary battery.

The slurry composition for a lithium ion secondary battery of the present invention can be easily produced and has high peel strength, so that a high-temperature cycle characteristic can be imparted to the lithium ion secondary battery.

INDUSTRIAL APPLICABILITY The method for producing a lithium ion secondary battery electrode of the present invention can produce an electrode for a lithium ion secondary battery which can be easily carried out and has high peel strength and can give a high-temperature cycle characteristic to the lithium ion secondary battery.

The lithium ion secondary battery of the present invention can be easily produced and has high high temperature cycle characteristics.

Brief Description of Drawings Fig. 1 is a graph showing the relationship between the cumulative amount (m mol) of the added hydrochloric acid and the electric conductivity (mS) in the surface acid amount of the particulate binder (B) and the amount of acid in the binder composition aqueous phase FIG.

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 can be arbitrarily changed without departing from the scope of the claims of the present invention and the equivalents thereof.

〔One. Binder composition for secondary battery]

The binder composition for a lithium ion secondary battery of the present invention comprises a crosslinking agent (A), a particulate binder (B), and water.

1.1. Crosslinking agent (A)]

The cross-linking agent (A), when coexisting with the particulate binder (B) as a component of the binder composition, is subjected to treatment such as heating at the time of forming the electrode active material layer using the slurry composition containing the binder composition, Is a component capable of forming a crosslinked structure between the other components (for example, the particulate binder (B) and the water-soluble thickener (C)). Specifically, the crosslinking agent (A) is preferably at least one of the particles of the particulate binder (B), the molecule of the water-soluble thickener (C), and the particulate binder (B) A crosslinked structure can be formed. Preferably, as the crosslinking agent (A), those capable of forming at least a crosslinked structure in the particles of the particulate binding agent (B) can be used.

The cross-linking agent (A) forms a cross-link in the electrode active material layer so that mechanical properties such as elastic modulus, tensile fracture strength and fatigue resistance, and adhesiveness to the current collector are excellent and the solubility in water is low Is excellent), an electrode active material layer having a crosslinked structure can be obtained.

Therefore, when the slurry composition containing the binder composition of the present invention is used for preparing an electrode, the formation of the crosslinked structure can suppress the swelling of the electrode accompanying repetition of charging and discharging in a high temperature use environment And high adhesiveness between the electrode active material layer and the current collector can be ensured. As a result, the high temperature cycle characteristics and the like of the secondary battery can be improved.

The amount of the crosslinking agent (A) in the binder composition of the present invention is preferably at least 0.001 part by mass, more preferably at least 0.5 part by mass, more preferably at least 0.5 part by mass, relative to 100 parts by mass of the particulate binder (B) Preferably not less than 2 parts by mass, more preferably not more than 20 parts by mass, more preferably not more than 12 parts by mass, and even more preferably not more than 8 parts by mass. By setting the ratio of the cross-linking agent (A) to the above-mentioned lower limit or more, a high degree of crosslinking can be obtained, peel strength and breaking strength can be increased, and swelling of the electrode plate can be suppressed. By reducing the ratio of the cross-linking agent (A) to the upper limit or lower, it is possible to prevent undesirable phenomena such as cracking of the electrode plate and reduction in handling easiness.

[1.1.1. Crosslinking agent (A): Structure]

The crosslinking agent (A) has a functional group which reacts with the carboxylic acid. It is possible to react effectively with the particulate binder (B) by having a functional group reacting with the carboxylic acid to effectively form the crosslinking between the particles of the particulate binder (B).

Examples of the functional group that reacts with the carboxylic acid include an epoxy group, an oxazoline group, a carbodiimide group, and a combination thereof. Accordingly, examples of the crosslinking agent (A) include compounds having an epoxy group, an oxazoline group, a carbodiimide group, and combinations thereof. Preferable examples of the cross-linking agent (A) include polyfunctional epoxy compounds, oxazoline compounds, carbodiimide compounds, and combinations thereof. Among them, a carbodiimide compound is preferable, and further, a water-soluble carbodiimide compound is preferable. By using these preferred compounds as the crosslinking agent (A), it is possible to obtain a high degree of crosslinking, to increase the peel strength and the breaking strength, to suppress the swelling of the electrode plate, and to improve the storage stability of the binder composition.

[1.1.2. Carbodiimide compound]

Examples of the carbodiimide compound as the crosslinking agent (A) include a crosslinkable compound having a carbodiimide group represented by the general formula (1): -N = C = N - (1) in the molecule. Examples of such a carbodiimide compound include compounds having two or more carbodiimide groups, specifically, a compound represented by the general formula (2): -N = C = NR ¹ - (2) ), R ¹ represents a divalent organic group), and / or a modified polycarbodiimide having a repeating unit represented by the following formula (1). In the present specification, the modified polycarbodiimide refers to a compound obtained by reacting a polycarbodiimide with a reactive compound described below.

[1.1.3. Synthesis of polycarbodiimide]

The synthesis method of the polycarbodiimide is not particularly limited. For example, by reacting the organic polyisocyanate in the presence of a catalyst for promoting the carbodiimidization reaction of the isocyanate group (hereinafter referred to as " carbodiimidization catalyst ") , And a polycarbodiimide can be synthesized. The polycarbodiimide having a repeating unit represented by the general formula (2) can also be synthesized by copolymerizing an oligomer (carbodiimide oligomer) obtained by reacting an organic polyisocyanate with a monomer copolymerizable with the oligomer.

As the organic polyisocyanate used for synthesis of the polycarbodiimide, an organic diisocyanate is preferable.

Examples of the organic diisocyanate used in the synthesis of the polycarbodiimide include those described in JP-A-2005-49370. Among them, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are particularly preferable from the viewpoint of the storage stability of the binder composition and the slurry composition. As the organic diisocyanate, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

In addition to the above-mentioned organic diisocyanate, a stoichiometric excess amount of an organic polyisocyanate having three or more isocyanate groups (trifunctional or higher functional organic polyisocyanate) or a trifunctional or higher functional polyisocyanate and a polyfunctional active hydrogen- A terminal isocyanate prepolymer obtained by the reaction of the compound (hereinafter, the above-mentioned trifunctional or higher functional polyisocyanate and the terminal isocyanate prepolymer may be referred to as "trifunctional or higher functional polyisocyanate") may be used. Examples of such trifunctional or higher organic polyisocyanates include those described in JP-A-2005-49370. As the trifunctional or more organic polyisocyanates, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. The amount of the organic polyisocyanate having three or more functional groups in the synthesis reaction of the polycarbodiimide is usually 0 to 40 parts by mass, preferably 0 to 20 parts by mass, per 100 parts by mass of the organic diisocyanate.

Further, when synthesizing the polycarbodiimide, an organic monoisocyanate may be added as needed. When the organic polyisocyanate contains an organic polyisocyanate having three or more functional groups by the addition of the organic monoisocyanate, the molecular weight of the obtained polycarbodiimide can be appropriately regulated, and by using the organic diisocyanate in combination with the organic monoisocyanate, A polycarbodiimide having a small molecular weight can be obtained. Examples of such organic monoisocyanates include those described in JP-A-2005-49370. As the organic monoisocyanate, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. The amount of the organic monoisocyanate to be used in the synthesis reaction of the polycarbodiimide varies depending on the molecular weight required for the resulting polycarbodiimide, the presence or absence of the use of the organic polyisocyanate having three or more functional groups, and the like, Usually from 0 to 40 parts by mass, and preferably from 0 to 20 parts by mass, per 100 parts by mass of the component (component (B), diisocyanate and trifunctional or higher functional polyisocyanate).

Examples of the carbodiimidization catalyst include a phospholene compound, a metal carbonyl complex, an acetylacetone complex of metal, and a phosphoric acid ester. These embodiments are respectively shown in, for example, Japanese Laid-Open Patent Publication No. 2005-49370. As the carbodiimide catalyst, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. The amount of the carbodiimidization catalyst to be used is generally 0.001 to 30 parts by mass, preferably 0.01 to 10 parts by mass, per 100 parts by mass of the total organic isocyanate (organic monoisocyanate, organic diisocyanate, and trifunctional or higher functional polyisocyanate) to be.

The carbodiimidation reaction of the organic polyisocyanate can be carried out in a solvent which is not solvent-free or in a suitable solvent. The solvent for carrying out the synthesis reaction in a solvent is not particularly limited and a solvent capable of dissolving the polycarbodiimide or carbodiimide oligomer produced by heating during the synthesis reaction can be appropriately selected. Examples of the solvent include a halogenated hydrocarbon solvent, an ether solvent, a ketone solvent, an aromatic hydrocarbon solvent, an amide solvent, an aprotic polar solvent, and an acetate solvent. These embodiments are respectively shown in, for example, Japanese Laid-Open Patent Publication No. 2005-49370. As these solvents, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. The amount of the solvent used in the synthesis reaction of the polycarbodiimide is such that the concentration of the total organic isocyanate component is usually 0.5 to 60 mass%, preferably 5 to 50 mass%. If the concentration of the entire organic isocyanate component in the solvent is excessively high, the resulting polycarbodiimide or carbodiimide oligomer may gel during the synthesis reaction, and if the concentration of the total organic isocyanate component in the solvent is too low, And the productivity may be lowered.

The temperature of the carbodiimidation reaction of the organic polyisocyanate is appropriately selected depending on the type of the organic isocyanate component or the carbodiimidization catalyst, but is usually from 20 to 200 ° C. In the carbodiimidation reaction of the organic polyisocyanate, the total amount of the organic isocyanate component may be added before the reaction, or a part or all of the organic isocyanate component may be added continuously or stepwise during the reaction. In the present invention, a compound capable of reacting with an isocyanate group is added in an appropriate reaction step from an initial stage to a late stage of the carbodiimidization reaction of the organic polyisocyanate to seal the terminal isocyanate group of the polycarbodiimide, The molecular weight of the carbodiimide can also be controlled. The molecular weight of the obtained polycarbodiimide may be regulated to a predetermined value by adding it to a later stage of the carbodiimidation reaction of the organic polyisocyanate. Examples of the compound capable of reacting with such an isocyanate group include alcohols such as methanol, ethanol, i-propanol, and cyclohexanol; And amines such as dimethylamine, diethylamine and benzylamine.

Examples of monomers copolymerizable with the carbodiimide oligomer include divalent or higher valent alcohols such as ethylene glycol and propylene glycol.

For example, a divalent alcohol having a hydroxyl group at both terminals of a molecular chain is copolymerized with a carbodiimide oligomer by a known method to synthesize a polycarbodiimide structure and a polycarbodiimide having a divalent alcohol-derived monomer unit can do. As described above, when the polycarbodiimide as the crosslinking agent (A) has a monomer unit derived from a divalent or higher alcohol, preferably a monomer unit derived from a bivalent alcohol, an electrode formed from the binder composition containing the polycarbodiimide The wettability of the electrolytic solution to the electrolytic solution is improved, and the liquidity of the electrolytic solution in the production of the secondary battery including the battery member can be improved. Further, the copolymerization of the alcohols increases the degree of water-solubility of the carbodiimide compound and increases the self-micelle formation in water, that is, the structure of covering the hydrophobic carbodiimide structure with hydrophilic ethylene glycol chains It has an excellent chemical stability.

The above-mentioned polycarbodiimide is used as a solution or as a solid separated from a solution to prepare the binder composition or slurry composition of the present invention. Examples of the method of separating the polycarbodiimide from the solution include a method in which a polycarbodiimide solution is added to a non-solvent which is inactive to the polycarbodiimide and the resulting precipitate or oil is separated by filtration or decantation · How to collect; A method of separating and collecting by spray drying; When the polycarbodiimide dissolved in the solvent is precipitated by lowering the temperature of the system immediately after synthesis, that is, when the polycarbodiimide is precipitated by lowering the temperature of the system, A method of separating and collecting the supernatant by filtration or the like from the turbid liquid, and the separation and harvesting methods may be appropriately combined. The polystyrene reduced number average molecular weight (hereinafter referred to as " Mn ") of the polycarbodiimide in the present invention determined by gel permeation chromatography (GPC) is usually 400 to 500,000, preferably 1,000 to 200,000, And preferably 2,000 to 100,000.

[1.1.4. Synthesis of Modified Polycarbodiimide]

Next, the synthesis method of the modified polycarbodiimide will be described. The modified polycarbodiimide is obtained by reacting at least one kind of reactive compound with at least one kind of polycarbodiimide having a repeating unit represented by the general formula (2) in the presence or absence of a suitable catalyst at a suitable temperature Hereinafter referred to as " denaturation reaction ").

Examples of the reactive compound used in the synthesis of the modified polycarbodiimide include compounds in which one group having a reactivity with a polycarbodiimide (hereinafter simply referred to as " reactive group ") and a compound having another functional group Compounds may be used. The reactive compound may be an aromatic compound, an aliphatic compound or an alicyclic compound, and the ring structure in an aromatic compound and an alicyclic compound may be a carbon ring or a heterocyclic ring. The reactive group in the reactive compound may be a group having an active hydrogen. Examples of the reactive group include a carboxyl group, a primary amino group and a secondary amino group. The reactive compound may further have another functional group in addition to one reactive group in the molecule. Examples of the functional group other than the reactive group contained in the reactive compound include groups having a function of promoting the crosslinking reaction of the polycarbodiimide and / or modified polycarbodiimide, (Apart from the above-mentioned reactive groups), the above-described active hydrogen-containing groups are included, and for example, a carboxyl group exemplified as a group having an active hydrogen other than a carboxylic acid anhydride group and a tertiary amino group, Secondary or tertiary amino groups, and the like. These other functional groups may have two or more identical or different groups in one molecule of the reactive compound.

Examples of the reactive compound include those described in JP-A-2005-49370. Among them, trimellitic anhydride and nicotinic acid are preferable. As the reactive compound, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The amount of the reactive compound used in the modification reaction for synthesizing the modified polycarbodiimide can be appropriately controlled depending on the kind of the polycarbodiimide or the reactive compound, the physical properties required for the obtained modified polycarbodiimide, and the like. The ratio of the reactive group in the reactive compound to 1 mole of the repeating unit represented by the general formula (2) of the polycarbodiimide is preferably 0.01 to 1 mole, more preferably 0.02 to 0.8 mole. If the ratio is less than 0.01 mol, the storage stability of the binder composition or slurry composition containing the modified polycarbodiimide may be deteriorated. On the other hand, if the ratio is more than 1 mol, the inherent properties of the polycarbodiimide may be impaired.

In the denaturation reaction, the reaction between the reactive group in the reactive compound and the repeating unit represented by the general formula (2) of the polycarbodiimide usually proceeds quantitatively, and a functional group suitable for the amount of use of the reactive compound is reacted with the modified polycarbodiimide ≪ / RTI > The denaturation reaction can be carried out without solvent, but is preferably carried out in a suitable solvent. Such a solvent is not particularly limited as long as it is inert to the polycarbodiimide and the reactive compound and can dissolve the polycarbodiimide and the reactive compound, and examples thereof include an ether-based solvent which can be used for the synthesis of the polycarbodiimide described above , Amide-based solvents, ketone-based solvents, aromatic hydrocarbon-based solvents, aprotic polar solvents, and the like. As these solvents, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio. When the solvent used in the synthesis of the polycarbodiimide can be used in the denaturation reaction, the polycarbodiimide solution obtained by the synthesis may be used as it is. The amount of the solvent used in the denaturation reaction is usually 10 to 10,000 parts by mass, preferably 50 to 5,000 parts by mass, per 100 parts by mass of the total amount of the reaction raw materials. The temperature of the modification reaction is appropriately selected depending on the kind of the polycarbodiimide or the reactive compound, but is usually 100 占 폚 or lower, preferably -10 to 80 占 폚. The Mn of the modified polycarbodiimide in the present invention is usually 500 to 1,000,000, preferably 1,000 to 400,000, and more preferably 2,000 to 200,000.

[1.1.5. Properties of carbodiimide compounds, etc.]

The compounding amount (NCN equivalent) per 1 mole of the carbodiimide group (-N═C═N-) of the carbodiimide compound is preferably 300 or more, more preferably 400 or more, and preferably 600 or less, More preferably 500 or less. By virtue of the NCN equivalent of the carbodiimide compound being 400 or more, the storage stability of the binder composition or slurry composition of the present invention can be sufficiently ensured, and when it is 600 or less, the crosslinking reaction can proceed favorably as a crosslinking agent.

The NCN equivalent of the carbodiimide compound can be determined by measuring the polystyrene reduced number average molecular weight of the carbodiimide compound using, for example, gel permeation chromatography (GPC) and by using IR (infrared spectroscopy) The number of carbodiimide groups per molecule can be quantitatively analyzed and calculated using the following equation.

NCN equivalent = (number average molecular weight in terms of polystyrene of carbodiimide compound) / (number of carbodiimide groups per one molecule of carbodiimide compound)

[1.1.6. Oxazoline compound]

Examples of the oxazoline compound as the crosslinking agent (A) include a crosslinkable compound having an oxazoline group in the molecule thereof. As such an example of the oxazoline compound, a compound having two or more oxazoline groups in the molecule is preferable. Some or all of the hydrogen atoms of the oxazoline group may be substituted by other groups. Examples of such a compound having two or more oxazoline groups in the molecule include a compound having two oxazoline groups in the molecule (divalent oxazoline compound) and a polymer containing an oxazoline group (oxazoline group-containing polymer) have.

[1.1.7. Divalent oxazoline compound]

Examples of the divalent oxazoline compound include 2,2'-bis (2-oxazoline), 2,2'-bis (4-methyl-2-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-hexyl-2-oxazoline), 2,2'-bis Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), 2,2'- . Among them, 2,2'-bis (2-oxazoline) is preferable from the viewpoint of forming a more rigid crosslinked structure.

[1.1.8. Oxazoline group-containing polymer]

In the present application, the oxazoline group-containing polymer is a compound other than a divalent oxazoline compound and is an oxazoline group-containing polymer.

The oxazoline group-containing polymer can be synthesized, for example, by polymerizing an oxazoline group-containing monomer represented by the following formula (I), or by copolymerizing a monomer composition containing the oxazoline group-containing monomer.

 [Chemical Formula 1]

(I)

(I)

In formula (I), R ¹ , R ² , R ³ and R ⁴ each independently represent a hydrogen atom, a halogen atom, an alkyl group, an aryl group which may have a substituent or an aralkyl group which may have a substituent, R ⁵ represents a non-cyclic organic group having an addition polymerizable unsaturated bond.

In the formula (I), examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Among them, a fluorine atom and a chlorine atom are preferable.

In the formula (I), examples of the alkyl group include an alkyl group having 1 to 8 carbon atoms. Among them, an alkyl group having 1 to 4 carbon atoms is preferable.

In the formula (I), examples of the aryl group which may have a substituent include an aryl group which may have a substituent such as a halogen atom. Examples of the aryl group include an aryl group having 6 to 18 carbon atoms such as a phenyl group, a tolyl group, a xylyl group, a biphenyl group, a naphthyl group, an anthryl group, and a phenanthryl group. Preferable examples of the aryl group which may have a substituent include an aryl group having 6 to 12 carbon atoms and may have a substituent.

In the formula (I), examples of the aralkyl group which may have a substituent include an aralkyl group which may have a substituent such as a halogen atom. Examples of the aralkyl group include an aralkyl group having 7 to 18 carbon atoms such as a benzyl group, a phenylethyl group, a methylbenzyl group and a naphthylmethyl group. Preferable examples of the aralkyl group which may have a substituent include an aralkyl group having 7 to 12 carbon atoms which may have a substituent.

In the formula (I), examples of the non-cyclic organic group having an addition polymerizable unsaturated bond include an alkenyl group having 2 to 8 carbon atoms such as a vinyl group, an allyl group and an isopropenyl group. Among them, a vinyl group, an allyl group and an isopropenyl group are preferable.

Examples of the oxazoline group-containing monomer represented by the formula (I) include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-oxazoline, 2-vinyl-4-propyl-2-oxazoline, 2-vinyl- 2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2 2-oxazoline, 2-isopropenyl-4-ethyl-2-oxazoline, 2-isopropenyl- 2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, 2-isopropenyl- 5-butyl-2-oxazoline. Among them, 2-isopropenyl-2-oxazoline is preferable because it is industrially easily available. As these oxazoline group-containing monomers, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The monomer composition for the synthesis of the oxazoline group-containing polymer may include a monomer other than the oxazoline group-containing polymer. As such a monomer, any monomer capable of copolymerizing with an oxazoline group-containing monomer can be used. Preferred examples of the monomers include (meth) acrylic acid monomers, (meth) acrylic acid ester monomers, and aromatic monomers. In the present specification, "(meth) acryl" means acryl and / or methacryl.

Examples of the (meth) acrylic acid monomers usable for the synthesis of the oxazoline group-containing polymer include acrylic acid; Methacrylic acid; Acrylates such as sodium acrylate and ammonium acrylate; And methacrylic acid salts such as sodium methacrylate and ammonium methacrylate. These (meth) acrylic acid monomers may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

Examples of the (meth) acrylic acid ester monomers usable in the synthesis of the oxazoline group-containing polymer include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, perfluoroalkyl ethyl acrylate, Acrylic acid esters such as 2-hydroxyethyl acrylate, 2-aminoethyl acrylate and its salts, methoxy polyethylene glycol acrylate, and monoester of acrylic acid and polyethylene glycol; And examples thereof include methyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, methoxypolyethyleneglycol methacrylate, monoester of methacrylic acid and polyethylene glycol, 2- Methacrylic acid esters such as aminoethyl and its salts. These (meth) acrylic acid ester monomers may be used singly or two or more kinds may be used in combination at an arbitrary ratio.

Examples of the aromatic monomer that can be used for the synthesis of the oxazoline group-containing polymer include styrene compounds such as styrene,? -Methylstyrene, and sodium styrenesulfonate. As these aromatic monomers, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

These monomers can be synthesized by, for example, polymerizing the monomers by the methods described in the same references at the use ratios described in, for example, JP-A-2013-72002 and JP-B-2644161. The oxazoline group-containing polymer may be synthesized, for example, by polymerizing a polymer having no oxazoline group and then partially or wholly substituting functional groups in the polymer with an oxazoline group.

[1.1.9. Properties of oxazoline compounds]

When the above-described oxazoline group-containing polymer is used as the crosslinking agent (A), the glass transition temperature (Tg) of the oxazoline group-containing polymer is preferably -50 ° C or higher, more preferably -20 ° C or higher, Preferably 60 DEG C or lower, more preferably 30 DEG C or lower.

The chemical formula (oxazoline equivalent) per 1 mole of the oxazoline group of the oxazoline compound is preferably 30 or more, more preferably 50 or more, still more preferably 100 or more, preferably 600 or less Is less than 500. This oxazoline equivalent is also referred to as oxazoline (g-solid / eq.) Per gram of oxazoline group. When the crosslinking agent (A) has an oxazoline equivalent of 70 or more, the storage stability of the binder composition or slurry composition of the present invention can be sufficiently secured. When the crosslinking agent (A) is 600 or less, the crosslinking reaction can be favorably promoted as a crosslinking agent.

The oxazoline equivalent of the crosslinking agent (A) can be calculated using the following equation.

Oxazoline equivalent = (molecular weight of oxazoline compound) / (number of oxazoline groups per molecule of oxazoline compound)

Here, when the oxazoline compound is an oxazoline group-containing polymer, the molecular weight of the oxazoline compound may be, for example, the number average molecular weight in terms of polystyrene measured by GPC (gel permeation chromatography), and the oxazoline compound The number of oxazoline groups per molecule can be quantified using, for example, IR (infrared spectroscopy).

[1.1.10. Polyfunctional epoxy compound]

Examples of the polyfunctional epoxy compound as the crosslinking agent (A) include polyfunctional glycidyl ether compounds such as aliphatic polyglycidyl ether, aromatic polyglycidyl ether and diglycidyl ether. Examples of the compound having an oxazoline group include 2,2'-bis (2-oxazoline), 2,2'-bis (4-methyl-2-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-ethyl-2-oxazoline), 2,2'- 2-oxazoline), 2,2'-bis (4-hexyl-2-oxazoline), 2,2'-bis Bis (4-phenyl-2-oxazoline), 2,2'-bis (4-cyclohexyl-2-oxazoline), and 2,2'- . Polymer types such as Epochros (trade name) manufactured by Nippon Catalysts Co., Ltd. are also exemplified.

[1.1.11. The properties of the crosslinking agent (A), etc.]

The viscosity of the 1 mass% aqueous solution of the crosslinking agent (A) is preferably 5000 mPa s or less, more preferably 700 mPa s or less, and particularly preferably 150 mPa s or less. By using a crosslinking agent having a viscosity in the range of 1% by mass of the aqueous solution of 1% by mass, adhesion between the electrode active material layer and the current collector can be improved. The viscosity of the 1 mass% aqueous solution of the crosslinking agent (A) can be measured by the same method as that of the 1 mass% aqueous solution of carboxymethyl cellulose (salt).

The cross-linking agent (A) is preferably water-soluble. Since the cross-linking agent (A) is water-soluble, the cross-linking agent (A) is prevented from being unevenly distributed in the aqueous slurry composition containing the binder composition, and the resulting electrode active material layer can form a preferable cross-linked structure. Accordingly, the adhesion strength between the electrode active material layer and the current collector in the obtained secondary battery can be ensured, the cycle characteristics can be improved, and the increase in resistance after the cycle can be suppressed. Further, the water resistance of the electrode can be improved.

In this specification, the term "water-soluble" in the present specification means that the mixture obtained by adding 1 part by mass (corresponding to solid content) of a crosslinking agent per 100 parts by mass of ion-exchanged water is stirred at a temperature of 20 to 70 ° C, (3) to (12), wherein the pH is adjusted to at least one of the following conditions: an aqueous solution of NaOH and / or an aqueous solution of HCl, and a solid Is not more than 50 mass% with respect to the solid content of the added crosslinking agent. Even when the mixture of the crosslinking agent and water is in an emulsion state separated into two phases when the mixture is allowed to stand still, if the above definition is satisfied, the crosslinking agent is defined as water-soluble. From the viewpoint of satisfactorily promoting the formation reaction of the crosslinking structure and improving the adhesion strength between the electrode active material layer and the current collector and the high temperature cycle characteristics, the mixture of the crosslinking agent and water is not separated into two phases ), That is, the cross-linking agent is more preferably one-phase water-soluble.

1.2. Particulate binder (B)]

The particulate binder (B) contained in the binder composition of the present invention is a binder capable of dispersing in the form of particles in an aqueous medium such as water, and is present in the form of particles in the binder composition and the slurry composition. Normally, when the particulate binder (B) is dissolved in 100 g of water at 25 占 폚, the particulate binder (0.5 g) has an insoluble content of 90 mass% or more.

When the electrode active material layer is formed by using the slurry composition containing the binder composition of the present invention, the particulate binder (B) is preferably such that, in the electrode active material layer, other components (for example, electrode active material) Can be maintained. The particulate binder (B) in the electrode active material layer absorbs and swells the electrolyte solution when immersed in an electrolytic solution to keep the particulate shape while binding the electrode active materials to prevent the electrode active material from falling off the current collector Function can be expressed. The particulate binder (B) can also bind particles other than the electrode active material contained in the electrode active material layer to maintain the strength of the electrode active material layer.

1.2.1. Particulate binder (B): Ethylenic unsaturated carboxylic acid group monomer unit]

The particulate binder (B) is a polymer containing an ethylenically unsaturated carboxylic acid group monomer unit. In the present application, a monomer unit is a unit having a structure obtained by polymerization of the monomer. Therefore, the ethylenically unsaturated carboxylic acid group monomer unit is a unit having a structure obtained by polymerization of an ethylenically unsaturated carboxylic acid group monomer, and the polymer containing an ethylenically unsaturated carboxylic acid group monomer unit is a polymer having a carboxylic acid group to be.

In the present invention, the monomer unit is usually obtained by the polymerization of the corresponding monomer, but is not limited to the unit itself obtained by polymerization of the monomer. For example, a carboxylic acid group can be introduced into the particulate binder by polymerizing a particulate binder having no carboxylic acid group, and replacing part or all of the functional groups in the particulate binder with a carboxylic acid group. By the operation of the substitution, an ethylenically unsaturated carboxylic acid group monomer unit may be formed in the polymer constituting the particulate binder. In this way, the particulate binder (B) may be prepared.

The particulate binder (B) can be prepared by polymerization of a monomer composition containing an ethylenically unsaturated carboxylic acid group monomer and containing any other monomers. Here, the "monomer composition" includes a material composed of only one kind of monomer for convenience of explanation, but usually it is composed of an ethylenically unsaturated carboxylic acid group monomer and any other monomers. In general, the ratio of each monomer contained in the monomer composition is the ratio of each monomer unit in the resulting polymer.

Examples of the ethylenically unsaturated carboxylic acid group monomer include monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. Among them, acrylic acid, methacrylic acid and itaconic acid are preferable as the ethylenically unsaturated carboxylic acid group monomer from the viewpoint of stability of the slurry composition containing the binder composition of the present invention, and acrylic acid and itaconic acid are particularly preferable. These may be used singly or in combination of two or more in an arbitrary ratio. By using these preferred ethylenically unsaturated carboxylic acid group monomers, the amount of carboxylic acid groups present on the surface among the carboxylic acid groups present in the whole particulate binder (B) can be increased, and as a result, the particulate binder (B) And the water-soluble thickener (C).

The ratio of the ethylenically unsaturated carboxylic acid group monomer units in the particulate binder (B) is preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and still more preferably 30% by mass or less, 10 mass% or less, and more preferably 5 mass% or less. By setting the proportion of the ethylenically unsaturated carboxylic acid group monomer units to the above-mentioned lower limit or more, it is possible to impart a sufficient amount of acid groups to the particulate binder (B), and to improve the storage stability. Also, the crosslinking between the particulate binder and the water-soluble thickener can be satisfactorily formed, and good peel strength and high-temperature cycle characteristics can be obtained. On the other hand, by setting the ratio of the ethylenically unsaturated carboxylic acid group monomer units to be not more than the upper limit, coarse particles can be prevented from being generated during the polymerization reaction, and as a result, good storage stability can be obtained.

1.2.2. Particulate binder (B): Ethylenically unsaturated hydroxyl group-containing monomer unit]

The particulate binder (B) may optionally contain an ethylenically unsaturated hydroxyl group-containing monomer unit. Such particulate binder (B) can be prepared by polymerizing a monomer composition containing an ethylenically unsaturated hydroxyl group-containing monomer. The ethylenically unsaturated hydroxyl group-containing monomer is a monomer having an ethylenic unsaturated group and further having a hydroxyl group, and therefore the polymer containing an ethylenically unsaturated hydroxyl group-containing monomer unit is a polymer having a hydroxyl group.

Examples of the ethylenically unsaturated hydroxyl group-containing monomer include hydroxyethyl acrylate such as 2-hydroxyethyl acrylate, hydroxyethyl methacrylate such as 2-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxy Hydroxyethyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, di- 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, and the like. Among them, hydroxybutyl acrylate, hydroxypropyl acrylate, and hydroxyethyl acrylate are preferable, and hydroxypropyl acrylate and hydroxyethyl acrylate are more preferable, and 2-hydroxyethyl acrylate is particularly preferable desirable. These may be used singly or in combination of two or more in an arbitrary ratio. By using these preferred ethylenically unsaturated hydroxyl group-containing monomers, the ethylenically unsaturated carboxylic acid group monomer in the aqueous phase tends to polymerize with the particles in the latex during polymerization of the polymer composition, thereby increasing the ratio of the surface acid amount to the amount of acid in the aqueous phase .

The proportion of the ethylenically unsaturated hydroxyl group-containing monomer units in the particulate binder (B) is preferably 0.1% by mass or more, more preferably 0.7% by mass or more, and further preferably 20% by mass or less, By mass or less, and more preferably 2% by mass or less. By setting the ratio of the ethylenically unsaturated hydroxyl group-containing monomer units to the above-mentioned lower limit or more, the ratio of the surface acid amount to the acid amount in the aqueous phase can be increased. On the other hand, by setting the ratio of the ethylenically unsaturated hydroxyl group-containing monomer units to be not more than the upper limit, coarse particles can be prevented from being generated during the polymerization reaction.

1.2.3. Aliphatic conjugated diene monomer unit]

The particulate binder (B) may optionally contain an aliphatic conjugated diene monomer unit. Particularly, when the binder composition of the present invention and the slurry composition of the present invention are used for forming the negative electrode active material layer, it is preferable that the particulate binder (B) contains an aliphatic conjugated diene monomer unit, . Examples of the aliphatic conjugated diene monomer capable of forming an aliphatic conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 1,3-butadiene, substituted linear conjugated pentadienes, substituted and side-chain conjugated hexadiene, and the like, among which 1,3-butadiene is preferable. 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.

In the particulate binder (B), the content of the aliphatic conjugated diene monomer unit is preferably 10% by mass or more, more preferably 20% by mass or more, and still more preferably 50% by mass or less, 40 mass% or less. By setting the content ratio of the aliphatic conjugated diene monomer unit to the lower limit or higher, flexibility of the electrode can be increased. The content of the aliphatic conjugated diene monomer unit is not more than the upper limit so that the adhesion between the electrode active material layer and the current collector can be improved and the electrolyte solution resistance of the electrode obtained using the binder composition for a secondary battery of the present invention can be improved .

1.2.4. Aromatic vinyl monomer unit]

The particulate binder (B) may optionally contain an aromatic vinyl monomer unit. Particularly, when the binder composition of the present invention and the slurry composition of the present invention are used for forming the negative electrode active material layer, it is preferable that the particulate binder (B) contains an aromatic vinyl monomer unit, Which is preferable for suppressing electrode swelling. Examples of the aromatic vinyl monomer capable of forming an aromatic vinyl monomer unit include styrene,? -Methylstyrene, vinyltoluene, divinylbenzene and the like, among which styrene is preferable. As the aromatic vinyl monomer, one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

In the particulate binder (B), the content ratio of the aromatic vinyl monomer unit is preferably 40% by mass or more, more preferably 50% by mass or more, preferably 80% by mass or less, more preferably 70% % Or less. By setting the content ratio of the aromatic vinyl monomer units to the lower limit or more, the electrolyte solution resistance of the electrode obtained using the binder composition of the present invention can be improved. By setting the content ratio of the aromatic vinyl monomer unit to be not more than the upper limit, the adhesion between the electrode active material layer and the current collector can be improved.

The particulate binder (B) is preferably a 1,3-butadiene unit as the aliphatic conjugated diene monomer unit and a styrene unit as the aromatic vinyl monomer unit (that is, a styrene-butadiene copolymer).

1.2.5. Any monomer units]

The particulate binder (B) may contain any monomer units other than those described above. These arbitrary monomer units can be prepared by using a monomer composition containing the respective monomers.

Examples of the monomer capable of forming an arbitrary monomer unit include an unsaturated monomer having a glycidyl ether group, a monomer having a thiol group, a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, and an unsaturated carboxylic acid amide monomer have. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the unsaturated monomer having a glycidyl ether group include glycidyl acrylate and glycidyl methacrylate. Among them, glycidyl methacrylate is preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the monomer having a thiol group include pentaerythritol tetrakis (3-mercaptobutyrate), trimethylolpropane tris (3-mercaptobutyrate), trimethylol ethane tris (3-mercaptobutyrate) . Among them, pentaerythritol tetrakis (3-mercaptobutyrate) is preferable. These may be used singly or in combination of two or more in an arbitrary ratio.

Examples of the vinyl cyanide monomers 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. Particularly, when the binder composition of the present invention and the slurry composition of the present invention are used for the formation of the positive electrode active material layer, the particulate binder (B) contains a vinyl cyanide monomer unit because of the improvement in affinity between the electrolyte and the binder , And is preferable for reducing the migration resistance of lithium ions.

Examples of the unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, dimethyl fumarate, diethyl fumarate, dimethyl maliate, , Dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate. Among them, methyl methacrylate is preferable. These may be used singly or in combination of two or more in an arbitrary ratio. Particularly, when the binder composition of the present invention and the slurry composition of the present invention are used for forming the positive electrode active material layer, it is preferable that the particulate binder (B) contains an unsaturated carboxylic acid alkyl ester monomer unit, It is preferable for imparting the flexibility of the electrode and for reducing the migration resistance of the lithium ion by improving the affinity between the electrolyte and the binder.

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.

The particulate binder (B) may contain units formed by monomers used in conventional emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, and the like . These may be used singly or in combination of two or more in an arbitrary ratio.

When the particulate binder (B) has an arbitrary monomer unit, its content is not particularly limited, but the upper limit is preferably 10% by mass or less, more preferably 8% by mass or less, and more preferably 5% And the lower limit is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and particularly preferably 1.5% by mass or more.

1.2.6. Preparation of particulate binder (B)]

The particulate binder (B) can be prepared, for example, by polymerizing a monomer composition containing the above-described monomer in an aqueous solvent.

Here, the content of each monomer in the monomer composition is generally the same as the content of each unit in the desired particulate binder (B).

The aqueous solvent is not particularly limited, and the particulate binder (B) that can be dispersed in a particle state can be suitably used. Usually, an aqueous solvent having a boiling point at normal pressure of usually 80 ° C or higher, preferably 100 ° C or higher, and usually 350 ° C or lower, preferably 300 ° C or lower can be selected.

Specifically, examples of the aqueous solvent include water; Ketones such as diacetone alcohol and? -Butyrolactone; Alcohols such as ethyl alcohol, isopropyl alcohol and normal propyl alcohol; Propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol Glycol ethers such as monobutyl ether, triethylene glycol monobutyl ether and dipropylene glycol monomethyl ether; 1,3-dioxolane, 1,4-dioxolane, and tetrahydrofuran; And the like. Among them, water is particularly preferable from the viewpoint that there is no flammability and a dispersion of particles of the particulate binder (B) is easily obtained. Water may be used as the main solvent and an aqueous solvent other than the above-mentioned water may be mixed in the range in which the dispersion state of the particles of the particulate binder (B) 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, and an emulsion polymerization method can be used. Examples of polymerization methods that can be used include ionic polymerization, radical polymerization, and living radical polymerization. It is possible to obtain the binder composition of the present invention and the slurry composition of the present invention without the redispersion treatment since the polymer is obtained in a state in which the polymer is dispersed in water as it is, From the viewpoint of efficiency, the emulsion polymerization method is particularly preferable. The emulsion polymerization can be carried out according to a conventional method.

A commonly used emulsifier, dispersant, polymerization initiator, polymerization assistant and the like used in the polymerization may be used, and the amount thereof may be generally used. In polymerization, seed polymerization may be carried out by employing seed particles. The polymerization conditions may also be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator.

The order of adding the respective monomers to the reaction system at the time of polymerization is not particularly limited, but from the viewpoint of increasing the ratio of the surface acid amount, the addition of the ethylenically unsaturated hydroxyl group-containing monomer is carried out at a time point when polymerization of the other monomers proceeds . When the monomer containing an ethylenically unsaturated hydroxyl group is added at the beginning of the polymerization reaction, a sufficient effect can not be obtained. However, the addition of the ethylenically unsaturated hydroxyl group-containing monomer is carried out at a time point when polymerization of the other monomer proceeds, The ratio of the surface acid amount to the acid amount in the aqueous phase can be easily increased.

Specifically, it is preferable to start polymerization of a monomer composition containing a monomer other than the ethylenically unsaturated hydroxyl group-containing monomer, and to add the ethylenically unsaturated hydroxyl group-containing monomer to the reaction system when the polymerization conversion rate reaches a predetermined value. The polymerization conversion rate at the time of adding the ethylenically unsaturated hydroxyl group-containing monomer is preferably 50% or more, more preferably 60% or more, and preferably 85% or less. The ethylenically unsaturated carboxylic acid group monomer in the aqueous phase of the reaction system is easily polymerized with the particles in the latex and the surface acid amount to the amount of the acid in the aqueous phase The ratio can be increased and generation of coarse particles during the polymerization reaction can be prevented.

Here, the aqueous dispersion of the particles of the particulate binding agent (B) obtained by the above-described polymerization method can be used as it is or after the pH adjustment and purification steps, if necessary, in the production of the binder composition of the present invention . PH of the aqueous dispersion is, for example, an alkali metal hydroxide, ammonia, inorganic ammonium compounds (e.g., Li, Na, K, Rb, Cs) (for example, NH ₄ Cl, etc.), an organic amine compound (e.g. For example, ethanolamine, diethylamine, etc.) can be used to adjust the pH to a range of usually 5 to 10, preferably 5 to 9. Among them, the pH adjustment by the alkali metal hydroxide is preferable because it improves the adhesion between the current collector and the electrode active material layer.

1.2.7. Appearance of particulate binder (B)

Normally, the particulate binder (B) is water-insoluble. Therefore, the particulate binder (B) usually becomes particulate in the binder composition and slurry composition containing water, and is contained in, for example, an electrode for a secondary battery while maintaining the particle shape.

In the binder composition and slurry composition of the present invention, the particulate binder (B) preferably has a number average particle diameter of 50 nm or more, more preferably 70 nm or more, preferably 500 nm or less, Is 400 nm or less. When the number average particle diameter is in the above range, strength and flexibility of the obtained electrode can be improved. The number average particle diameter can be easily measured by a transmission electron microscope, a Coulter counter, a laser diffraction scattering method or the like.

The gel content of the particulate binder (B) is preferably 50% by mass or more, more preferably 80% by mass or more, preferably 98% by mass or less, and more preferably 95% by mass or less. When the content of the gel in the particulate binder (B) is less than 50% by mass, the cohesive force of the particulate binder (B) decreases, and the adhesion with the current collector or the like may become insufficient. On the other hand, when the content of the gel in the particulate binder (B) is more than 98% by mass, the particulate binder (B) tends to lose its toughness and, as a result, the adhesion may be insufficient.

Particulate binder glass transition temperature of the (B) (T _g), is preferably not less than -30 ℃, more preferably not less than -20 ℃, preferably from 80 ℃ or less, and more preferably not more than 30 ℃. The glass transition temperature of the particulate binder (B) is -30 DEG C or higher, whereby the components contained in the slurry composition containing the binder composition for a secondary battery of the present invention are prevented from aggregating and settling, and the stability of the slurry composition can be ensured . Further, the swelling of the electrode can be suppressed preferably. Also, since the glass transition temperature of the particulate binder (B) is 80 占 폚 or less, the workability in applying the slurry composition containing the binder composition for a secondary battery of the present invention to the current collector or the like can be improved.

The glass transition temperature and the gel content of the particulate binder (B) can be appropriately adjusted by changing the preparation conditions of the particulate binder (B) (for example, monomers to be used, polymerization conditions, and the like).

The glass transition temperature can be adjusted by changing the kind and amount of the monomers to be used. For example, when monomers such as styrene and acrylonitrile are used, the glass transition temperature can be increased and monomers such as butyl acrylate and butadiene If used, the glass transition temperature can be lowered.

The gel content can be adjusted by changing the polymerization temperature, the kind of the polymerization initiator, the kind and amount of the molecular weight adjuster, the conversion rate at the time of stopping the reaction, and for example, by decreasing the chain transfer agent, the gel content can be increased, Increasing the amount of the transfer agent may lower the gel content.

1.3. Water and other solvents]

The binder composition of the present invention includes water. The water functions as a solvent and / or a dispersion medium in the binder composition. Usually, in the binder composition of the present invention, the cross-linking agent (A) is dissolved or dispersed in water, and the particulate binder (B) is dispersed in water.

In the binder composition of the present invention, a solvent other than water may be used in combination with water as a solvent, but from the viewpoint of avoiding reaction with the cross-linking agent (A), it is preferable that it does not substantially contain a solvent other than water.

The amount of the solvent in the binder composition of the present invention is preferably set so that the solid content concentration of the binder composition falls within a desired range suitable for the production of the slurry composition. The solid content concentration of the specific binder composition is preferably 10% by mass or more, more preferably 15% by mass or more, preferably 60% by mass or less, and more preferably 55% by mass or less. In the present application, the solid content of a composition refers to a substance that remains after drying the composition.

1.4. Other ingredients]

The binder composition of the present invention may contain a component such as a conductive agent, a reinforcing agent, a leveling agent, an electrolyte additive, and a cellulose nanofiber in addition to the above components. As these, those which do not affect the cell reaction can be appropriately selected. For example, those known in the art, specifically those described in International Publication No. 2012/115096. These components may be used singly or in combination of two or more in an arbitrary ratio.

1.5. Preparation of binder composition]

The binder composition of the present invention can be prepared by mixing the cross-linking agent (A), the particulate binder (B), water, and optionally optional components in an arbitrary order. The addition of the crosslinking agent (A) and the particulate binder (B) to the mixing system can be carried out by adding a solution or suspension containing them.

1.6. Properties of the binder composition]

The binder composition for a lithium ion secondary battery of the present invention has an aqueous phase and a solid phase. The water phase is composed of components soluble in water and water, and the solid phase is a phase of a solid which is insoluble in particulate binder (B) and other water.

In the binder composition of the present invention, the ratio of the surface acid amount of the particulate binder (B) to the total solid mass of the binder composition is not less than 0.01 mmol / g and not more than 1.0 mmol / g, The ratio of the amount of acid in the aqueous phase to the total amount is 0.01 mmol / g or more and 1.0 mmol / g, and the value obtained by dividing the value of the ratio of the surface acid amount by the value of the amount of the acid in the aqueous phase is 1.0 or more.

The ratio of the surface acid amount of the particulate binder (B) is preferably 0.05 mmol / g to 1.0 mmol / g, and more preferably 0.05 mmol / g to 0.8 mmol / g. The ratio of the amount of acid in the aqueous phase is preferably 0.05 mmol / g to 1.0 mmol / g, and more preferably 0.05 mmol / g to 0.8 mmol / g. The value obtained by dividing the value of the ratio of the surface acid amount by the value of the ratio of the acid amount in the aqueous phase is preferably 1.05 or more, more preferably 1.10 or more, preferably 10 or less, more preferably 5 or less . These values can be measured in accordance with the method described in the examples of this specification.

(B) and the other components (water-soluble thickener (C) and the like) in the slurry composition can be effectively used because a small amount of the cross-linking agent (A) Crosslinking between particles, between molecules, and / or between particles and molecules can be efficiently achieved. Further, at the time of storing the binder composition, the reaction between the crosslinking agent (A) in the aqueous phase and the acid in the aqueous phase can be reduced, and the storage stability can be improved. As a result, it is possible to provide a binder composition for a lithium ion secondary battery that has high storage stability, can impart a high peak strength to an electrode for a lithium ion secondary battery, and can impart a high temperature cycle characteristic to the lithium ion secondary battery.

Preferable examples of the method for obtaining such a binder composition in which the amount of surface acid and the amount of acid in the aqueous phase satisfy the above conditions include the above items [1.2.1.] And 1.2.2. , A polymerization reaction product in which the ratio of the surface acid amount and the surface acid amount to the acid amount in the aqueous phase is increased at the time of preparing the particulate binder (B) is obtained and used as the material of the binder composition . The method for increasing the ratio of the surface acid amount to the surface acid amount relative to the acid amount in the aqueous phase will be specifically described. The addition of the ethylenically unsaturated hydroxyl group-containing monomer during the preparation of the particulate binding agent (B) A polymerization reaction product obtained by increasing the ratio of the amount of surface acid to the amount of surface acid relative to the amount of acid in the aqueous phase is obtained at the time when polymerization of the other monomers proceeds and by using this as a material for the binder composition, Can be obtained.

The surface acid amount, and the amount of acid in the aqueous phase satisfy the above-described conditions, other methods may be employed in place of, or in addition to, the above-described methods. For example, the unreacted acid may be removed by a distillation method such as heating and reduced pressure distillation after the polymerization reaction of the preparation of the particulate binder (B). However, a polymerization reaction product obtained by raising the ratio of the surface acid amount and the surface acid amount to the acid amount in the aqueous phase is obtained by the method described in the item [1.2.1.] And the item [1.2.2.], Particularly regarding the particulate binder (B) , The carboxylic acid group can be effectively added to the surface of the particulate binder (B) by the small amount of the ethylenically unsaturated carboxylic acid group monomer, and the step of distillation can be omitted, and as a result, a good product Can be efficiently produced.

〔2. Slurry composition for secondary battery]

The slurry composition for a lithium ion secondary battery of the present invention contains the binder composition for the lithium ion secondary battery of the present invention, the electrode active material, and the water-soluble thickener (C).

2.1. Electrode active material]

When the slurry composition of the present invention is used in the production of a negative electrode, an appropriate material may be appropriately selected as the negative electrode active material. When the slurry composition of the present invention is used in the production of a positive electrode, an appropriate material may be appropriately selected as the positive electrode active material.

[2.1.1. Negative electrode active material]

As the negative electrode active material, a material which can be used as a substance to exchange electrons in the negative electrode of a lithium ion secondary battery can be appropriately selected and used.

As the negative electrode active material of the lithium ion secondary battery, a material capable of absorbing and desorbing lithium is generally used. Examples of the substance capable of occluding and releasing lithium include a carbon-based negative-electrode active material, a metal-based negative-electrode active material, and a negative electrode active material obtained by combining them.

The carbon-based negative electrode active material refers to an active material having carbon as a main skeleton capable of intercalating lithium (also referred to as " dope "), and examples of the carbon-based negative electrode active material include a carbonaceous material and a graphite material.

The carbonaceous material is a material having a low degree of graphitization (i.e., low crystallinity), obtained by carbonizing a carbon precursor at a temperature of 2000 占 폚 or lower. The lower limit of the heat treatment temperature at the time of carbonization is not particularly limited, but may be 500 deg. C or higher, for example.

Examples of the carbonaceous material include graphite-free carbon which easily changes the structure of carbon due to the heat treatment temperature and non-graphite-like carbonaceous materials having a structure close to an amorphous structure typified by glassy carbon, Carbon.

Here, as examples of graphitizable carbon, there can be mentioned a carbon material obtained by using tar pitch obtained from petroleum or coal as a raw material. Specific examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolysis-phase grown carbon fibers, and the like.

Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile carbon fibers, pseudo isotropic carbon, furfuryl alcohol resin (PFA) fired bodies, and hard carbon.

The graphite material is a material having a high crystallinity close to graphite obtained by heat-treating graphitizing carbon at 2000 ° C or higher. The upper limit of the heat treatment temperature is not particularly limited, but may be, for example, 5000 占 폚 or lower.

Examples of the graphite material include natural graphite and artificial graphite.

Examples of the artificial graphite include artificial graphite heat-treated with carbon containing graphitizing carbon at a temperature of 2800 ° C or higher, graphitized MCMB heat-treated with MCMB at a temperature of 2000 ° C or higher, and mesophase pitch- Graphitized mesophase pitch-based carbon fibers, and the like.

A metal negative electrode active material is an active material containing a metal and includes an element capable of inserting lithium in its structure and having a theoretical capacity per unit mass of 500 mAh / g or more when lithium is inserted. Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, and Ni, which can form a lithium metal or a lithium alloy, Si, Sn, Sr, Zn, Ti, etc.) and alloys thereof, and oxides, sulfides, nitrides, silicides, carbides and phosphides thereof.

Among the metal negative electrode active materials, an active material containing silicon (silicon negative electrode active material) is preferable. This is because the capacity of the lithium ion secondary battery can be increased by using the silicon negative electrode active material.

Examples of the silicon-based negative electrode active material is silicon (Si), an alloy containing silicon, SiO, SiO _x, Si-containing material and the mixture of the carbon material, the Si-containing material and a conductive carbon made by coating or compounding a Si-containing material as a conductive carbon And the like.

Examples of alloys containing silicon include alloys containing silicon, aluminum, and iron, and further containing rare earth elements such as tin and yttrium. Such an alloy can be prepared, for example, by the meltspun method. Examples of such an alloy include those described in JP-A-2013-65569.

SiO _x is a compound containing Si and at least one of SiO and SiO ₂ , and x is usually 0.01 or more and less than 2. The SiO _x can be formed using a disproportionation reaction of, for example, silicon monoxide (SiO 2). Specifically, SiO _x can be prepared by heat-treating SiO in the presence of a polymer such as polyvinyl alcohol, to produce silicon and silicon dioxide. The heat treatment can be carried out at a temperature of 900 占 폚 or higher, preferably 1000 占 폚 or higher, in an atmosphere containing SiO2 and optionally a polymer and then containing organic gas and / or steam.

Examples of the mixture of the Si-containing material and the carbon material include a mixture of a Si-containing material such as silicon or SiO _x and a carbon material such as a carbonaceous material or a graphite material optionally in the presence of a polymer such as polyvinyl alcohol . Examples of the carbonaceous material and the graphite material include materials usable as the carbon-based negative electrode active material.

Examples of the composite material of the Si-containing material and the conductive carbon include a compound obtained by heat-treating SiO and a polymer such as polyvinyl alcohol and optionally a pulverized mixture of a carbon material under an atmosphere containing, for example, an organic gas and / . A method of coating a surface of a SiO 2 particle by a chemical vapor deposition method using an organic gas or the like, a method of granulating a SiO 2 particle and graphite or artificial graphite into a composite particle by a mechanochemical method, Method can be used.

Here, when the carbon-based negative electrode active material or the metal negative electrode active material is used as the negative electrode active material, the negative electrode active material expands and shrinks with charge and discharge. Therefore, when these negative electrode active materials are used, there is a possibility that the negative electrode gradually becomes swollen due to the repeated expansion and contraction of the negative electrode active material, and the secondary battery may be deformed to deteriorate electrical characteristics such as cycle characteristics. However, in the negative electrode formed using the binder composition of the present invention, due to the crosslinking structure formed by the crosslinking agent (A), the particulate binder (B) and the water-soluble thickening agent (C) The swelling of the negative electrode can be suppressed and the cycle characteristics can be improved.

When the silicon based negative electrode active material is used, the capacity of the lithium ion secondary battery can be increased. In general, however, the silicon based negative electrode active material expands and contracts largely (for example, about 5 times) with charge and discharge. Therefore, from the viewpoint of increasing the capacity of the lithium ion secondary battery while sufficiently suppressing the swelling of the negative electrode, it is preferable to use a mixture of the carbon-based negative electrode active material and the silicon based negative electrode active material as the negative electrode active material.

When a mixture of the carbon-based negative electrode active material and the silicon based negative electrode active material is used as the negative electrode active material, it is preferable to use artificial graphite as the carbon-based negative electrode active material from the viewpoint of sufficiently sufficiently increasing the capacity of the lithium ion secondary battery while sufficiently suppressing swelling of the negative electrode It is preferable to use at least one selected from the group consisting of Si, an alloy including silicon, a mixture of SiO _x , a Si-containing material and a carbon material, and a composite material of a Si-containing material and a conductive carbon as a silicon- preferred, and a silicon-based negative electrode alloy as an active material containing silicon, and a Si-containing material and, and is more preferable to use at least one of the conductive carbon composite product of, an alloy containing silicon, and SiO _x are dispersed in a conductive carbon matrix, to the use of at least one in particular of the composite cargo (Si-SiO _x -C complex) desirable. These negative electrode active materials are capable of occluding and releasing a relatively large amount of lithium, while a volume change when inserting and discharging lithium is relatively small. Therefore, by using these negative electrode active materials, it is possible to sufficiently increase the capacity of the lithium ion secondary battery using the negative electrode for a lithium ion secondary battery formed using the slurry composition, while suppressing an increase in the volume change of the negative electrode active material during charging and discharging. Further, when an alloy containing silicon is used, the lithium ion secondary battery can be sufficiently high in capacity, and the initial coulombic efficiency and cycle characteristics can be improved.

When a mixture of the carbon-based negative electrode active material and the silicon-based negative electrode active material is used as the negative electrode active material, from the viewpoint of sufficiently sufficiently increasing the capacity of the lithium ion secondary battery while sufficiently suppressing swelling of the negative electrode, It is preferable that the silicon based negative electrode active material is contained in an amount of more than 0 parts by mass and 100 parts by mass or less, more preferably 10 parts by mass or more and 70 parts by mass or less, particularly preferably 30 parts by mass or more and 50 parts by mass or less. The lithium ion secondary battery can have a sufficiently high capacity by including the silicon negative electrode active material (that is, making the amount of the silicon negative electrode active material per 100 parts by mass of the carbonaceous negative electrode active material greater than 0 part by mass). In addition, by making the amount of the silicon-based negative electrode active material per 100 parts by mass of the carbon-based negative electrode active material 100 parts by mass or less, occurrence of swelling of the negative electrode can be sufficiently suppressed.

It is preferable that the negative electrode active material is formed into a granular 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, its volume average particle diameter is appropriately selected in balance with other constituent requirements of the secondary battery. The volume average particle diameter of the negative electrode active material particles is usually not less than 0.1 占 퐉, preferably not less than 1 占 퐉, more preferably not less than 3 占 퐉, usually not more than 100 占 퐉, preferably not more than 50 占 퐉, more preferably not more than 30 占 퐉 Or less. Here, the volume average particle diameter adopts a 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 0.3 m 2 / g or larger, preferably 0.5 m 2 / g or larger, more preferably 0.8 m 2 / g or larger and usually 20 m 2 / g or smaller, Is 10 m < 2 > / g or less, and more preferably 5 m < 2 > / g or less. The specific surface area of the negative electrode active material can be measured, for example, by the BET method.

[2.1.2. Positive electrode active material]

As the positive electrode active material, a material that can be used as a substance to exchange electrons at the positive electrode of the lithium ion secondary battery can be appropriately selected and used.

The positive electrode active material is not particularly limited and various kinds of active materials can be used. For example, a compound containing a transition metal, specifically, an oxide containing a transition metal, or a composite oxide of lithium and a transition metal can be used. Examples of such a transition metal include cobalt, manganese, nickel, iron and the like. In the present invention, a compound containing nickel, particularly, a composite oxide containing lithium and nickel is preferably used. In particular, the composite oxide containing lithium and nickel is preferable because it is in a high capacity as compared with lithium cobalt oxide (LiCoO ₂ ) which has been conventionally used as a positive electrode active material of a lithium-based secondary battery. The composite oxide containing lithium and nickel includes, for example, those represented by the following general formulas.

LiNi _1-xy Co _x M _y O ₂

(Wherein 0? X <1, 0? Y <1, x + y <1, and M is at least one element selected from B, Mn,

The positive electrode active material preferably has an average particle diameter of 0.01 to 30 mu m, more preferably 0.02 to 20 mu m. If the average particle diameter of the positive electrode active material is too small, the conductivity of the positive electrode active material decreases and the internal resistance in the case of using the secondary battery becomes large. On the other hand, if the average particle diameter of the positive electrode active material is excessively large, the dispersibility in the slurry is lowered when the slurry is formed to form the positive electrode active material layer, which makes it difficult to produce a good slurry.

2.2. Ratio of binder composition]

The proportion of the binder composition for a lithium ion secondary battery of the present invention in the slurry composition for a lithium ion secondary battery of the present invention can be suitably adjusted so as to obtain a desired battery performance. In particular, the desired composition can be obtained by appropriately adjusting the proportion of the binder composition so that the ratio of the particulate binder (B) in the binder composition to the 100 parts by mass of the electrode active material is within a desired range. The ratio of the particulate binder (B) in the binder composition to 100 parts by mass of the electrode active material is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 10 parts by mass or less Is not more than 7 parts by mass. By setting the ratio above the lower limit described above, a sufficient fill strength can be obtained, and by making the ratio lower than the upper limit, resistance increase can be prevented.

2.3. Water-soluble thickener (C)]

The water-soluble thickener (C) is a water-soluble thickener having a carboxyl group. The water-soluble thickener (C) can function as a viscosity adjuster of the slurry composition. In the electrode active material layer obtained by the slurry composition of the present invention, the physical properties of the electrode active material layer are maintained in an appropriate state, and as a result, properties such as high temperature cycle characteristics can be improved.

In the present specification, the term "water-soluble" in the present specification means that a mixture obtained by adding and stirring 1 part by mass (corresponding to solid content) of a thickener per 100 parts by mass of ion-exchanged water is stirred at a temperature of 20 to 70 ° C, To 12 (a condition in which the NaOH aqueous solution and / or the aqueous HCl solution is used for the pH adjustment), and when passing through a screen of 250 mesh, the solid content of the residue remaining on the screen without passing through the screen Means that the mass does not exceed 50 mass% with respect to the solid content of the added thickener. Even if the mixture of the thickener and water is in an emulsion state in which the mixture is separated into two phases when the mixture is allowed to stand, if the above definition is satisfied, the thickening agent is defined as water-soluble.

Examples of the water-soluble thickener (C) include, for example, carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, Methyl cellulose, polyvinyl alcohol, polycarboxylic acid, and salts thereof. Examples of the polycarboxylic acid include polyacrylic acid, polymethacrylic acid, and alginic acid. As the water-soluble thickener (C), one type may be used alone, or two or more types may be used in combination at an arbitrary ratio.

The water-soluble thickening agent (C) preferably contains carboxymethylcellulose or a salt thereof (hereinafter sometimes abbreviated as "carboxymethylcellulose (salt)"). Since the water-soluble thickener (C) contains carboxymethylcellulose (salt), the workability when the slurry composition containing the binder composition is applied to the current collector or the like can be improved.

When carboxymethylcellulose (salt) is used as the water-soluble thickener (C), the degree of etherification of the carboxymethylcellulose (salt) used is preferably 0.4 or more, more preferably 0.7 or more, and preferably 1.5 Or less, more preferably 1.0 or less. By using carboxymethylcellulose (salt) having an etherification degree of 0.4 or more, workability can be improved when the slurry composition containing the binder composition is applied to a current collector or the like. When the degree of etherification is less than 0.4, the water-soluble thickener (C) can become a gel product because the hydrogen bond between molecules and molecules in carboxymethyl cellulose (salt) is strong. Further, when preparing the slurry composition, it is difficult to obtain a thickening effect and there is a fear that the workability at the time of preparation of the slurry composition is deteriorated. Further, when the obtained slurry composition is coated on the current collector to form a crosslinked structure via the crosslinking agent (A), the reaction between the carboxymethyl cellulose (salt) and the crosslinking agent (A) becomes difficult, . Further, by using carboxymethyl cellulose having an etherification degree of 1.5 or less, the number of hydroxyl groups per one molecule of carboxymethyl cellulose (salt) becomes sufficient and the reactivity with the crosslinking agent (A) described later becomes good. Therefore, since carboxymethyl cellulose (salt) can form a good cross-linking structure via the cross-linking agent (A), as described in detail later, the binder property of the binder composition of the present invention And the cycle characteristics of the secondary battery can be made excellent.

The degree of etherification of carboxymethylcellulose (salt) refers to the average value of the number of hydroxyl groups substituted by substituents such as carboxylmethyl group per 1 unit of anhydroglucose constituting carboxymethylcellulose (salt), and a value of more than 0 and less than 3 I can take it. As the degree of etherification increases, the proportion of hydroxyl groups in one molecule of carboxymethyl cellulose (salt) decreases (that is, the proportion of substituents increases) and the proportion of hydroxyl groups in one molecule of carboxymethyl cellulose (salt) (I.e., the proportion of the substituent decreases). This degree of etherification (degree of substitution) can be determined by the method described in Japanese Patent Application Laid-Open No. 2011-34962.

The viscosity of the 1 mass% aqueous solution of carboxymethylcellulose (salt) is preferably 500 mPa · s or more, more preferably 1000 mPa · s or more, preferably 10000 mPa · s or less, 9000 mPa s or less. A slurry composition containing the binder composition can have appropriate viscosity by using carboxymethyl cellulose (salt) having an aqueous solution viscosity of 500 mPa 占 퐏 or more when it is a 1 mass% aqueous solution. Therefore, the workability in applying the slurry composition to the current collector or the like can be improved. Further, by using carboxymethylcellulose (salt) having a viscosity of 1 mass% aqueous solution of 10000 mPa.s or less, the viscosity of the slurry composition containing the binder composition is not excessively increased, and when the slurry composition is applied to the collector, The workability can be improved and the adhesion between the electrode active material layer obtained by using the slurry composition containing the binder composition and the current collector can be improved. The viscosity of a 1 mass% aqueous solution of carboxymethylcellulose (salt) is measured using a B-type viscometer at 25 占 폚 at a revolution of 60 rpm.

More preferably, the water-soluble thickener (C) includes carboxymethylcellulose (salt) and polycarboxylic acid or a salt thereof (hereinafter may be abbreviated as "polycarboxylic acid (salt)"). As described above, the combination of carboxymethyl cellulose (salt) and polycarboxylic acid (salt) as the water-soluble thickening agent (C) can improve the binding property of the binder composition, and the binder composition obtained by using the slurry composition containing the binder composition The mechanical properties such as strength of the electrode active material layer including the water-soluble thickener (C) can be improved while improving the adhesion between the electrode active material layer and the current collector. As a result, the cycle characteristics and the like of the secondary battery using the electrode can be improved. Herein, preferred examples of the polycarboxylic acid (salt) used in combination with carboxymethylcellulose (salt) include salts of alginic acid and alginic acid (hereinafter collectively referred to as "alginic acid (salt)") (Hereinafter sometimes referred to as &quot; polyacrylic acid (salt) &quot; in some cases), and polyacrylic acid (salt) is particularly preferable. That is, it is particularly preferable that the water-soluble thickener (C) comprises carboxymethylcellulose or a salt thereof and a polyacrylic acid or a salt thereof. Alginic acid or polyacrylic acid is less likely to swell excessively in an electrolyte solution of a secondary battery as compared with polymethacrylic acid or the like. By using carmethyl methyl cellulose (salt) and alginic acid (salt) or polyacrylic acid (salt) The cycle characteristics can be sufficiently improved. Since polyacrylic acid (salt) reacts well with the crosslinking agent (A) as compared with carboxymethyl cellulose (salt), the use of polyacrylic acid can promote the reaction of forming the crosslinking structure via the crosslinking agent (A) Because.

When the water-soluble thickener (C) contains carboxymethyl cellulose (salt) and polycarboxylic acid (salt) in the slurry composition of the present invention, the mixing amount of carboxymethyl cellulose (salt) and the amount of polycarboxylic acid The proportion of the total amount of the polycarboxylic acid (salt) to be incorporated is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, particularly preferably 1% by mass or more, and preferably 20% % Or less, more preferably 10 mass% or less, particularly preferably 5 mass% or less. (Salt) and the polycarboxylic acid (salt) account for 0.1% by mass or more of the total amount of the carboxymethylcellulose (salt) and the polycarboxylic acid (salt) in the total amount of the polycarboxylic acid It is possible to satisfactorily improve the binding property of the slurry composition and to improve the adhesion between the electrode active material layer obtained by using the slurry composition and the current collector . The proportion of the polycarboxylic acid (salt) to the total amount of the carboxymethyl cellulose (salt) and the polycarboxylic acid (salt) is 20% by mass or less, The electrode active material layer is not excessively hardened, and binding properties and ionic conductivity of the slurry composition can be ensured. In addition, the adhesion between the electrode active material layer obtained by using the slurry composition and the current collector can be satisfactorily improved.

The degree of polymerization of the water-soluble thickener (C) can be appropriately selected from the viewpoint of obtaining an appropriate viscosity and the like. The degree of polymerization of the water-soluble thickener (C) is preferably from 100 to 10,000, more preferably from 500 to 3,000.

The proportion of the water-soluble thickener (C) relative to 100 parts by mass of the electrode active material in the slurry composition of the present invention is preferably at least 0.1 part by mass, more preferably at least 0.5 parts by mass, still more preferably at least 1.0 part by mass More preferably not more than 10 parts by mass, more preferably not more than 5 parts by mass, and even more preferably not more than 3 parts by mass. When the blending amount of the water-soluble thickener (C) is within the above range, the viscosity of the slurry composition can be set to an appropriate size, and workability can be improved when the slurry composition is applied to the current collector or the like. By mixing the water-soluble thickener (C) per 100 parts by mass of the electrode active material in a proportion of 0.5 parts by mass or more, good cycle characteristics can be obtained. Further, by combining the water-soluble thickener (C) per 100 parts by mass of the electrode active material in a proportion of 5 parts by mass or less, the resistance of the resulting electrode can be reduced.

2.4. Water and other solvents]

The slurry composition of the present invention may contain water. The water functions as a solvent and / or a dispersion medium in the slurry composition. Usually, in the slurry composition of the present invention, the crosslinking agent (A) is dissolved or dispersed in water, the particulate binder (B) and the electrode active material are dispersed in water, the water-soluble thickener (C) have.

In the slurry composition of the present invention, a solvent other than water may be used in combination with water as a solvent. However, from the viewpoint of avoiding the reaction with the crosslinking agent (A) before forming the electrode active material layer, .

The amount of the solvent in the slurry composition of the present invention can be appropriately set so that the respective components can be uniformly dispersed or dissolved and the physical properties such as the viscosity of the slurry composition fall within a desired range suitable for use of the slurry composition. The solid content concentration of the specific slurry composition is preferably 30% by mass or more, more preferably 40% by mass or more, preferably 90% by mass or less, and more preferably 80% by mass or less.

2.5. Other ingredients]

The slurry composition for a lithium ion secondary battery of the present invention may contain components such as a conductive agent, a reinforcing agent, a leveling agent, an electrolyte additive, and a cellulose nanofiber in addition to the above components. As these, those which do not affect the cell reaction can be appropriately selected. For example, those known in the art, specifically those described in International Publication No. 2012/115096. These components may be used singly or in combination of two or more in an arbitrary ratio.

2.6. Preparation of slurry composition]

The slurry composition for a lithium ion secondary battery of the present invention can be prepared by mixing a binder composition for a lithium ion secondary battery, an electrode active material, a water-soluble thickener (C), and other arbitrary components such as water in an arbitrary order. For example, the binder composition for a lithium ion secondary battery of the present invention is added to the mixed solution by mixing the electrode active material, the water-soluble thickener (C) and water, further adjusting the solid content concentration with water, , And further optionally subjected to optional treatment such as defoaming treatment, if necessary, to obtain a slurry composition.

Alternatively, at the time of preparing the slurry composition of the present invention, the crosslinking agent (A) and the particulate binder (B), which are components of the binder composition, are simultaneously or sequentially added to the mixing system, The slurry composition of the present invention may be prepared.

Concretely, mixing of the respective components can be carried out using a mixer such as a ball mill, a sand mill, a bead mill, a pigment dispersing machine, a brain ball, an ultrasonic dispersing machine, a homogenizer, a planetary mixer and a fill mix. The mixing of the respective components can be carried out usually at room temperature to 80 ° C for 10 minutes to several hours.

When the slurry composition is prepared, unwanted acids other than the particulate binder (B) may be incorporated into the mixing system. Most of these acids are unreacted monomers remaining in the polymerization of the particulate binder (B), oligomers containing a carboxylic acid group having a low degree of polymerization produced during polymerization of the particulate binder (B) It comes from. These acids react with the crosslinking agent (A) to consume the crosslinking agent (A). Therefore, when such an acid is present in a large amount, the amount of the cross-linking agent (A) to be crosslinked, such as the particulate binder (B), which is desired to be crosslinked, is relatively reduced. In such a case, if a large amount of the crosslinking agent (A) is added in order to exhibit the effect of the crosslinking agent (A), the peel strength may be rather lowered and the properties such as cycle characteristics may be lowered. However, in the slurry composition of the present invention comprising the binder composition of the present invention, since the ratio of such acid to the particulate binder (B) can be reduced, good crosslinking can be easily obtained.

[3. Method for manufacturing electrode for secondary battery]

The method for producing an electrode for a secondary battery according to the present invention comprises coating the slurry composition for a lithium ion secondary battery of the present invention on a current collector and drying to form an electrode active material layer. Specifically, there are a step (coating step) of applying the slurry composition of the present invention onto a collector, a step of drying the slurry composition applied on the current collector to form an electrode active material layer on the current collector (drying step) , And optionally a step of further heating the electrode active material layer (heating step).

When the production method of the present invention is carried out, for example, the crosslinking reaction through the crosslinking agent (A) proceeds by the heat applied in the drying step or the heat added in the heating step. That is, a cross-linked structure in which the water-soluble thickener (C), the water-soluble thickener (C), the particulate binder (B), and / or the particulate binder (B) The cross-linking structure can suppress the blistering caused by charging and discharging, improve the adhesion between the current collector and the electrode active material layer, and further improve characteristics such as high-temperature cycle characteristics. Can be improved.

3.1. Coating process]

The method of applying the slurry composition on the current collector is not particularly limited and a known method can be used. Specific examples of the coating 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. At this time, the slurry composition may be applied to only one surface of the current collector, or may be applied to both surfaces. The thickness of the slurry film on the current collector before application and after drying can be suitably set in accordance with the thickness of the electrode active material layer obtained by drying.

As the current collector to which the slurry composition is applied, a material having electric conductivity and electrochemically durable is used. Specifically, examples of current collectors that can be used include current collectors made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, a copper foil is particularly preferable as the current collector used for the negative electrode. On the other hand, as the current collector used for the positive electrode, aluminum foil is particularly preferable. These materials may be used singly or in combination of two or more in an arbitrary ratio.

3.2. Drying process]

The method for drying the slurry composition on the current collector is not particularly limited and a known method can be used. Examples of the drying method include hot air, hot air, low-humidity air drying, vacuum drying, and drying by irradiation with infrared rays or electron beams. By drying the slurry composition on the current collector in this manner, an electrode active material layer is formed on the current collector to obtain an electrode for a lithium ion secondary battery including a current collector and an electrode active material layer. When the slurry composition is dried, the crosslinking reaction through the crosslinking agent (A) can proceed due to the applied heat.

After the drying step, the electrode active material layer may be subjected to pressure treatment using a die press or a roll press. By the pressing treatment, the adhesion between the electrode active material layer and the current collector can be improved.

Further, it is preferable that after the formation of the electrode active material layer, a heating step is carried out to proceed the crosslinking reaction to make the crosslinking structure more sufficient. The heating step is preferably performed at 80 to 160 DEG C for about 1 to 20 hours.

〔4. Secondary battery]

The lithium ion secondary battery of the present invention is an electrode comprising a positive electrode, a negative electrode, an electrolyte, and a separator, and the positive electrode, the negative electrode, or both of them are manufactured by the method for manufacturing the electrode for a lithium ion secondary battery of the present invention. Since the secondary battery of the present invention uses such an electrode, it is possible to improve the electrical characteristics and secure the adhesion between the electrode active material layer and the current collector. The secondary battery of the present invention can be suitably used for, for example, a mobile phone such as a smart phone, a tablet, a personal computer, an electric vehicle, and a stationary emergency battery.

4.1. electrode〕

When only one of the positive electrode and the negative electrode of the secondary battery is an electrode manufactured by the manufacturing method of the present invention, a known electrode can be used as the other electrode. For example, when only the negative electrode is an electrode manufactured by the manufacturing method of the present invention, the positive electrode can be a known positive electrode used as a positive electrode for a lithium ion secondary battery. Further, for example, when only the positive electrode is an electrode manufactured by the manufacturing method of the present invention, the negative electrode may be a known negative electrode used as a negative electrode for a lithium ion secondary battery.

4.2. Electrolyte solution]

As the electrolytic solution, an electrolytic solution in which an electrolyte is dissolved in a solvent can be used.

As the solvent, an organic solvent capable of dissolving an electrolyte can be used. Specifically, as the solvent, an alkyl carbonate solvent such as ethylene carbonate, propylene carbonate or? -Butyrolactone is added with an organic solvent such as 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethylmethyl carbonate, dimethyl carbonate , Methyl acetate, dimethoxyethane, dioxolane, methyl propionate, and methyl formate may be added.

As the electrolyte, a lithium salt can be used. Examples of the lithium salt include those described in JP-A-2012-204303. Of these lithium salts, in that it is easy to dissolve in an organic solvent, shows a high degree of dissociation, it is preferable that the electrolyte is _{LiPF 6, LiClO 4, CF 3} SO 3 Li.

The electrolytic solution may be a gel electrolyte containing the polymer and the electrolytic solution, or may be an intrinsic polymer electrolyte.

4.3. Separator]

As an example of the separator, those described in Japanese Laid-Open Patent Publication No. 2012-204303 can be used. Among them, polyolefin resins (polyethylene, polypropylene, polybutene, poly (ethylene terephthalate), polybutylene terephthalate, polybutylene terephthalate, Polyvinyl chloride) is preferable. It is also possible to use a separator comprising a porous film obtained by binding non-conductive particles with a binder composition for a secondary battery of the present invention as a separator.

4.4. Manufacturing Method of Secondary Battery]

In the lithium ion secondary battery of the present invention, for example, the positive electrode and the negative electrode are overlapped with each other with a separator interposed therebetween. The battery is wrapped or folded according to the shape of the battery as required, And can be manufactured by sealing. An overcurrent prevention element such as a fuse, a PTC element, an expanded metal, a lead plate, or the like may be provided as necessary in order to prevent internal pressure rise and overcharge discharge of the lithium ion secondary battery from occurring. The shape of the secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.

Example

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited thereto. In the present embodiment, parts and% are on a mass basis unless otherwise specified. The operations described below were carried out under normal temperature and normal pressure conditions unless otherwise stated.

In the Examples and Comparative Examples, the storage stability test, the surface acid amount, the acid amount measurement in the aqueous phase, and the determination of the fill strength and the high temperature cycle characteristics of the binder composition were carried out as follows.

&Lt; Storage stability test of binder composition &gt;

The viscosity (unit: mPa · s) of the binder composition was measured by a B-type viscometer and then stored in an oven heated at 40 ° C for 1 week. After storage, the viscosity was again measured with a B-type viscometer, and the change in viscosity was calculated by the following equation, and evaluated by the following evaluation criteria.

(%) = (Viscosity of the binder composition after storage) / (viscosity of the binder composition before storage) x 100

A: less than 110%

B: 110% or more and less than 120%

C: 120% or more and less than 130%

D: Over 130%

&Lt; Measurement of the surface acid amount of the particulate binder (B) and the amount of acid in the binder composition aqueous phase &

(M mol / g) of the particulate binder (B) per 1 g of the solid content of the binder composition and the amount of acid (m mol / g) in the binder composition aqueous phase per 1 g of the solid content of the binder composition Respectively.

A glass container having a capacity of 150 ml was rinsed with distilled water. 50 g of a binder composition having a solid content concentration of 4% was placed in the container, and the mixture was set in a solution conductivity meter (CM-117 manufactured by Kyoto Electronics Industry Co., Ltd., used cell type: K-121) and stirred. Thereafter, stirring was continued until the addition of hydrochloric acid was completed. 0.1 Concentration of sodium hydroxide (manufactured by Wako Pure Chemical Industries, Limited: reagent grade) was added to the binder composition so that the electrical conductivity of the binder composition was 2.5 to 3.0 (mS), and electrical conductivity was measured after 6 minutes passed. This value was defined as the electric conductivity at the start of measurement. 0.5 ml of 0.1 N hydrochloric acid (manufactured by Wako Pure Chemical Industries, Ltd., reagent grade) was added to this binder composition, and the electric conductivity was measured after 30 seconds. Immediately after the measurement, 0.5 ml of 0.1 N hydrochloric acid was added again, and the electric conductivity was measured 30 seconds later. Thus, the addition of hydrochloric acid and the measurement of the electrical conductivity after 30 seconds were repeated until the electrical conductivity of the binder composition became equal to or higher than the electrical conductivity at the start of the measurement.

Generally, such titration is carried out on the surface of the particulate binder and the binder composition in which the acid exists on both sides of the surface, and the electrical conductivity data obtained are shown in the form of a cumulative amount of hydrochloric acid (mS) m mol), a hydrochloric acid amount-electric conductivity curve having three changing points (a point at which the graph is bent) is obtained as shown in Fig. The X coordinate at the time of the three change point X coordinate, and hydrochloric acid was added end of, respectively P _1, P _2, P ₃ and P ₄ in the order from the side of the smaller values and, X coordinates are separated from 0 to P _1, from P ₁ for the identification, classification and respectively in the data in the segment from P ₃ to P ₄ from P ₂ to P ₃ to P _2, the approximate straight line by the least square method L _1, L _2, L ₃ and L ₄ was obtained. The X coordinate of the intersection of L ₁ and L ₂ is A ₁ (m mol), the X coordinate of the intersection of L ₂ and L ₃ is A ₂ (m mol), the X coordinate of the intersection of L ₃ and L ₄ is A ₃ ( m mol).

The surface acid amount of the particulate binder (B) per 1 g of the solid content of the binder composition and the amount of acid in the binder composition aqueous phase per 1 g of the solid content of the binder composition were determined from the formulas (a) and (b) m mol / g). The total amount of acid per 1 g of the solid content of the binder composition was determined from the formula (c).

(A): surface acid amount (ml / g) of the particulate binder (B) per 1 g of the solid content of the binder composition = (A ₂ - A ₁ ) / (mass of solid component

The amount of acid in the aqueous phase per 1 g of the solid content of the binder composition (m) / (g) = (A ₃ - A ₂ ) / (mass of solid component (g)

(C): total amount of the binder composition per gram of solids per gram (m mol / g) = (A ₃ - A ₁ ) / (mass of solids in the binder composition (g)

<Peel Strength>

The electrode for the secondary battery was cut into a square having a width of 1 cm and a length of 10 cm to prepare a test piece, and the surface of the electrode active material layer side was fixed and fixed. A cellophane tape was stuck to the surface of the electrode active material layer side, and the cellophane tape was peeled from one end of the test piece at a rate of 50 mm / min in the direction of 180 占 and the stress at the time of peeling was measured. The measurement was carried out ten times, and the average value was obtained, which was regarded as the peel strength. The larger this value is, the larger the adhesion strength of the electrode is. The negative electrode was evaluated by the following evaluation criteria.

A: 5 N / m or more

B: 3 N / m or more and less than 5 N / m

C: Less than 3 N / m

<High temperature cycle characteristics>

The charging and discharging operations of charging five single-layer laminate cell cells at 4.2 V under a constant current of 1.0 C under an atmosphere of 50 캜 and discharging them to 3.0 V were repeated to measure the electric capacity. The charge / discharge capacity retention ratio, which is represented by the ratio of the electric capacity at the end of the 200 cycles to the electric capacity at the end of the fifth cycle (%), was taken as a measurement value of five average values. The higher the value, the better the high-temperature cycle characteristics.

A: 80% or more

B: 60% or more and less than 80%

C: 40% or more and less than 60%

D: Less than 40%

[Example 1]

(1-1 Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 32 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 64 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(1-2 Preparation of Binder Composition)

1.5 parts (based on solid content) of the aqueous dispersion of the particulate binder (B) obtained in the step (1-1) and 20 parts by weight of the crosslinking agent (A) (polycarbodiimide, product name: (I.e., a mass ratio of 5 parts by mass of the crosslinking agent (A) to 100 parts by mass of the particulate binder (B)), 0.075 parts by mass To adjust the solid content ratio to 40% to obtain a binder composition. The storage stability of the obtained binder composition was tested, and the surface acid amount of the particulate binder (B) and the amount of acid in the binder composition aqueous phase were measured.

1-3. Preparation of Slurry Composition for Negative Electrode of Lithium Ion Secondary Battery [

Carboxymethylcellulose (abbreviated as "CMC", Daicel 2200, manufactured by Daicel Chemical Industries, Ltd.) was used as the water-soluble thickener (C). The water-soluble thickener (C) had a degree of polymerization of 1700 and an etherification degree of 0.65.

(Volume average particle diameter: 24.5 占 퐉, graphite interlayer distance (plane spacing (d value) of (002) plane by X-ray diffraction method: 0.354 nm) was used as the negative electrode active material.

100 parts of artificial graphite and 1 part (by solid content) of a 1% aqueous solution of the water-soluble thickener (C) were added to a planetary mixer with a dispenser, and the solid content concentration was adjusted to 55% C &lt; / RTI &gt; for 60 minutes. Next, the solid content was adjusted to 52% with ion-exchanged water, and further stirred at 25 캜 for 15 minutes to obtain a mixed solution.

1.575 parts (that is, 1.5 parts of particulate binder and 0.075 parts of polycarbodiimide) of the binder composition obtained in (1-2) was added to this mixed solution, and water was added to the mixture to obtain a final solid content concentration of 50% And further mixed for 10 minutes. This was degassed under reduced pressure to obtain a lithium ion secondary battery negative electrode slurry composition having excellent flowability.

(1-4. Preparation of negative electrode)

The slurry composition obtained in the step (1-3) was coated on the surface of copper foil having a thickness of 20 占 퐉 with a comma coater so that the film thickness after drying became 150 占 퐉 and dried for 2 minutes (at a rate of 0.5 m / ) And subjected to a heat treatment (120 ° C) for 2 minutes to obtain an electrode cloth. The electrode fabric was rolled by a roll press to obtain a negative electrode for a secondary battery having a negative electrode active material layer thickness of 80 mu m. The obtained negative electrode was subjected to measurement of the peel strength.

(1-5. Preparation of Slurry Composition for Positive Electrode of Lithium Ion Secondary Battery)

PVDF (polyvinylidene fluoride) as a binder for positive electrode active material layer was added to 95 parts of LiCoO ₂ having a spinel structure as a positive electrode active material, and 2 parts of acetylene black and 20 parts of N-methylpyrrolidone were added And mixed with a planetary mixer to obtain a slurry composition for positive electrode of a lithium ion secondary battery.

(1-6. Preparation of positive electrode)

The lithium ion secondary battery positive electrode slurry composition obtained in the step (1-5) was coated on an aluminum 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 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 subjected to heat treatment at 120 ° C for 2 minutes to obtain a positive electrode having a positive electrode active material.

(1-7. Preparation of lithium ion secondary battery)

An aluminum-coated sheath was prepared as an exterior of the battery.

The positive electrode obtained in the above step (1-6) was cut into a square of 4.6 x 4.6 cm &lt; 2 &gt; to obtain a square positive electrode.

The negative electrode obtained in the above step (1-4) was cut into a square of 5 × 5 cm 2 to obtain a rectangular negative electrode.

A single-layered polypropylene separator ("Cell Guide 2500" manufactured by Cell Guide) was cut into a square of 5 × 5 cm 2 to obtain a rectangular separator.

A rectangular positive electrode was placed inside the aluminum-containing sheath so that the surface of the collector side was in contact with the aluminum-covered sheath. A rectangular separator was disposed on the surface of the positive electrode active material layer side of the rectangular positive electrode. Further, the square negative electrode was disposed on a separator of a quadrangle, and the surface of the negative electrode active material layer side was facing the separator. The electrolyte (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF _{6 with a} concentration of 1 M) was injected so that no air remained. 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 obtain a single layer laminate cell type lithium ion secondary battery.

Charging and discharging of the obtained lithium ion secondary cell was repeated three times at a rate of 0.1 C to confirm that a predetermined capacity was expressed, and then the high temperature cycle characteristics were tested.

[Examples 2 to 3]

In the preparation of the binder composition of the process (1-2), a polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd.) was used in place of the polycarbodiimide ("Carbodilite (registered trademark) SV-02" , 2,2'-bis (2-oxazoline) (manufactured by Tokyo Chemical Industry Co., Ltd., oxazoline equivalents: 140, 1 (trade name), trade name: Carbodilite (registered trademark) E-02, NCN equivalent 445, emulsion, The negative electrode, and the lithium ion secondary battery were evaluated in the same manner as in Example 1, except that the positive electrode active material was used.

[Examples 4 to 5]

A binder composition, a negative electrode and a lithium ion secondary battery were obtained in the same manner as in Example 1 except that the following points were changed.

In the preparation of the binder composition of the step (1-2), 0.01 part (Example 4) or 0.15 part (Example 5) of the addition amount (based on solid content) of the cross-linking agent (A) was used.

1.51 parts (that is, 1.5 parts of particulate binder and 0.01 part of polycarbodiimide, Example 4) in the preparation of the slurry composition for a lithium ion secondary battery negative electrode in the step (1-3) , Or 1.65 parts (i.e., 1.5 parts of particulate binder and 0.15 part of polycarbodiimide, Example 5).

[Example 6]

(6-1 Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 33.8 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 0.2 part of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 65 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(6-2. Binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was obtained in the same manner as in Example 1 except that the aqueous dispersion of the particulate binder (B) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Example 7]

(7-1 Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 1 part of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 65 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(7-2. Binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1 except that the aqueous dispersion of the particulate binder (B) was obtained in the step (7-1) instead of the aqueous dispersion obtained in the step (1-1) of Example 1, (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Example 8]

(8-1 Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 30 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 7 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 62 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(8-2. Binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was replaced with the aqueous dispersion of the particulate binder (B) obtained in the above step (8-1) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Example 9]

(9-1) Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 32.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 64 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 0.5 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(9-2. Binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) used in Example (1) was replaced by the aqueous dispersion of the particulate binder (B) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Example 10]

(Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 30 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 62 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 5 parts of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(10-2. Binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was replaced with the aqueous dispersion of the particulate binder (B) obtained in the above step (10-1) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Examples 11 to 13]

In the preparation of the particulate binder (B) in the step (1-1), the timing of adding 2-hydroxyethyl acrylate was changed from 60% (Example 11) to 60% , A negative electrode and a lithium ion secondary battery were obtained in the same manner as in Example 1 except that the polymerization conversion rate was 85% (Example 13).

[Example 14]

(Preparation of particulate binder (B)

To the polymerizable can A were added 74 parts of ion-exchanged water, 0.2 part of polyoxyethylene lauryl ether sodium sulfate (polyoxyethylene lauryl ether sulfate sodium salt), 0.3 part of ammonium persulfate and 9.7 parts of ion-exchanged water, The mixture was warmed and stirred for 30 minutes. Subsequently, 32 parts of 2-ethylhexyl acrylate, 64 parts of acrylonitrile, 3 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, and 0.3 part of sodium polyoxyethylene lauryl ether sulfate were charged into the polymerization cans B separate from the above And 74 parts of ion-exchanged water were added and stirred to prepare an emulsion. The emulsion thus prepared was added sequentially from the polymerization can B to the polymerization can A over a period of about 200 minutes, and then 1 part of 2-hydroxyethyl acrylate was added at the time when the polymerization conversion rate reached 70%. The mixture was stirred for about 180 minutes, cooled at the point when the monomer consumption became 97% or more, and the reaction was terminated. Thus, an aqueous dispersion liquid of the particulate binder (B) was obtained.

(14-2 Preparation of Binder Composition)

1.5 parts (based on solid content) of the aqueous dispersion of the particulate binder (B) obtained in the step (14-1) and 20 parts by weight of the crosslinking agent (A) (polycarbodiimide, product name: &quot; Carbodilite (registered trademark) SV (I.e., a mass ratio of 8 parts by mass of the crosslinking agent (A) to 100 parts by mass of the particulate binder (B)), 0.12 parts by mass The solids content ratio was adjusted to 40% to obtain a binder composition. The storage stability of the obtained binder composition was tested, and the surface acid amount of the particulate binder (B) and the amount of acid in the binder composition aqueous phase were measured.

(14-3 Preparation of Slurry Composition for Positive Electrode of Lithium Ion Secondary Battery)

98 parts of Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ , ₂ parts of acetylene black (Denka Black HS-100, manufactured by Denki Kagaku Kogyo K.K.) as the conductive material and 2 parts of the water-soluble thickener (C ) (1 part (the same as that prepared in the step (1-3) of Example 1) of solid content of 80% by weight was added thereto, Lt; / RTI &gt; Next, the solid content concentration was adjusted to 70% with ion-exchanged water and further stirred at 25 캜 for 15 minutes to obtain a mixed solution.

To this mixed solution, 1.62 parts (namely, 1.5 parts of particulate binder and 0.12 parts of polycarbodiimide) of the binder composition obtained in (14-2) was added, and water was added thereto so that the final solid content concentration became 50% And further mixed for 10 minutes. This was degassed under a reduced pressure to obtain a lithium ion secondary battery positive electrode slurry composition having excellent flowability.

(14-4 Production of positive electrode)

The slurry composition obtained in the step (14-3) was coated on the surface of an aluminum foil having a thickness of 20 占 퐉 by a comma coater so that the film thickness after drying was 80 占 퐉 and dried for 2 minutes (at a rate of 0.5 m / ° C.), and subjected to a heat treatment (120 ° C.) for 2 minutes to obtain an electrode cloth. The electrode fabric was rolled by a roll press to obtain a positive electrode for a lithium ion secondary battery having a thickness of the positive electrode active material layer of 50 m. The peel strength was measured for the obtained positive electrode, and the peel strength was 30 N / m.

(14-5 Production of Negative Electrode)

Except that the addition amount of the particulate binder (B) was changed to 1.575 parts (solid basis) without adding the cross-linking agent (A) in the preparation of the binder composition of the step (1-2) In the same manner as in 1-1) to (1-4), a lithium ion secondary negative electrode was obtained.

(14-6 Production of Lithium Ion Secondary Battery)

Except for using the positive electrode obtained in the step (1-6) as the positive electrode and the negative electrode and the one obtained in the step (14-4) and the step (14-5) in place of the negative electrode obtained in the step (1-4) In the same manner as in the step (1-7), a lithium ion secondary battery was obtained and evaluated.

[Comparative Example 1]

(C1-1. Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 32.5 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 64.5 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 0.09 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(C1-2 binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was replaced with the aqueous dispersion of the particulate binder (B) obtained in the above step (C1-1) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Comparative Example 2]

(C2-1. Preparation of particulate binder (B)

In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 0.05 part of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 66 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(C2-2 binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was replaced with the aqueous dispersion of the particulate binder (B) obtained in the above step (C2-1) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Comparative Example 3]

(C3-1. Preparation of particulate binder (B)

20 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 32 parts of itaconic acid as an ethylenically unsaturated carboxylic acid group monomer, 47 parts of styrene as an aromatic vinyl monomer, 4 parts of sodium silbenzenesulfonate, 150 parts of ion exchanged water, 0.4 part of t-dodecylmercaptan as a chain transfer agent and 0.5 part of potassium persulfate as a polymerization initiator were put into the flask and sufficiently stirred. . When the polymerization conversion rate reached 70%, 1 part of 2-hydroxyethyl acrylate was added. When the polymerization conversion rate reached 96%, the reaction was terminated by cooling to obtain an aqueous dispersion of the particulate binder (B).

(C3-2 binder composition, negative electrode and lithium ion secondary battery)

(1-2) of Example 1, except that the aqueous dispersion of the particulate binder (B) was replaced with the aqueous dispersion of the particulate binder (B) obtained in the above step (C3-1) (1-7), a binder composition, a negative electrode, and a lithium ion secondary battery were evaluated.

[Comparative Examples 4 to 5]

In the preparation of the particulate binder (B) in the step (1-1), the timing of addition of 2-hydroxyethyl acrylate was changed from the time when the polymerization conversion rate was 0% (i.e., , Or when the polymerization conversion rate was 40% (Comparative Example 5), the binder composition, the negative electrode, and the lithium ion secondary battery were evaluated in the same manner as in Example 1.

[Comparative Example 6]

The procedure of Example 16 was repeated except that the addition amount of the particulate binder (B) was changed to 1.62 parts (based on solid content) without adding the crosslinking agent (A) in the preparation of the binder composition of the step (16-2) , And the binder composition was evaluated. The positive electrode and the lithium ion secondary battery were also evaluated. The peel strength was measured with respect to the obtained positive electrode, and the peel strength was found to be 8 N / m.

Table 1 to Table 3 summarize the operations of the examples and comparative examples and the evaluation results.

The abbreviations in the table indicate the following.

Use (A): Crosslinking agent (A) used. SV-02: polycarbodiimide, product name "Carbodilite (registered trademark) SV-02", manufactured by Nisshinbo Chemical Co., Ltd., NCN equivalent 429, single phase water solubility. E-02: polycarbodiimide, product name "Carbodilite (registered trademark) E-02", manufactured by Nisshinbo Chemical Co., NCN equivalent 445, emulsion. Oxazoline: 2,2'-bis (2-oxazoline), manufactured by Tokyo Chemical Industry Co., oxazoline equivalent 140, single phase water solubility.

(A) Addition amount: Amount of addition of crosslinking agent (A). (Parts) to 100 parts by mass of the particulate binder (B)

Surface acid amount: Surface acid amount (ml / g) of particulate binder (B)

Acid amount in water: amount of acid in aqueous phase of binder composition (mmol / g)

(Amount of Surface Acid in Particulate Binder (B) (m mol / g)) / (Amount of Acid in Water of Binder Composition (m mol / g))

Itaconic acid amount: amount of itaconic acid used in the preparation of the particulate binder (B) (part)

2HEA Amount: Amount (parts) of 2-hydroxyethyl acrylate used for preparing particulate binder (B)

Conversion rate when 2HEA was added: polymerization conversion rate (%) of other monomers at the time of adding 2-hydroxyethyl acrylate

St: Amount (part) of styrene used for preparing particulate binder (B)

Amount of Bd: Amount (parts) of 1,3-butadiene used for preparing particulate binder (B)

Storage stability: Evaluation results of storage stability test

Peel Strength: Evaluation results of peel strength

Cycle characteristics: Evaluation results of cycle characteristics

As is clear from the results of Tables 1 to 3, the present examples using the binder composition having the surface acid amount, the acid amount in water, and the acid amount ratio within the range specified in the present invention are excellent in both storage stability, And a high performance in which a balance is obtained.

From Table 1, it can be seen that Examples 2 and 3, in which the type of crosslinking agent (A) was changed to be different from that of Example 1 within the scope of the present invention, are also excellent in storage stability, peel strength and cycle characteristics.

Examples 4 and 5 in which the amount of the cross-linking agent (A) was adjusted to a value different from that in Example 1 within the range of the present invention also showed high performance in balance in terms of storage stability, fill strength and cycle characteristics. .

Examples 6 to 10 in which the surface acid amount of the particulate binder (B) and the acid amount in the aqueous layer were adjusted to values different from those in Example 1 within the range of the present invention also showed high performance in terms of storage stability, peel strength and cycle characteristics . On the other hand, in Comparative Examples 2 and 3 in which the surface acid amount of the particulate binder (B) and the acid amount in the water layer were outside the range defined in the present application, the storage stability, peel strength and cycle characteristics were inferior.

Examples 11 to 13 in which the ratios of the surface acid amount and the aqueous acid amount ratio of the particulate binder (B) to the particulate binder (B) were adjusted to values different from those in Example 1 were also found to have high performance in terms of storage stability, . &Lt; / RTI &gt; On the other hand, in Comparative Examples 1, 4 and 5 in which the ratio of the surface acid amount and the amount of water-receiving acid of the particulate binder (B) is outside the range defined in the present application, the storage stability, peel strength and cycle characteristics are inferior.

It can be seen from the comparison between Example 14 and Comparative Example 6 in which the binder composition of the present invention is applied to the positive electrode that a beneficial effect is obtained in the peel strength and cycle characteristics even when the binder composition of the present invention is applied to the positive electrode.

Claims (10)

A binder composition for a lithium ion secondary battery comprising a crosslinking agent (A), a particulate binder (B) and water, and having an aqueous phase and a solid phase,
The crosslinking agent (A) has a functional group which reacts with a carboxylic acid,
The particulate binder (B) contains an ethylenically unsaturated carboxylic acid group monomer unit,
The ratio of the surface acid amount of the particulate binder (B) to the total mass of solids of the binder composition is not less than 0.01 mmol / g and not more than 1.0 mmol / g,
The ratio of the amount of the acid in the aqueous phase to the total mass of solids in the binder composition is 0.01 mmol / g to 1.0 mmol / g,
Wherein the value obtained by dividing the value of the ratio of the surface acid amount by the value of the ratio of the amount of acid in the aqueous phase is 1.0 or more. The method according to claim 1,
Wherein the proportion of the ethylenically unsaturated carboxylic acid group monomer units in the particulate binder (B) is 0.1% by mass or more and 30% by mass or less. 3. The method according to claim 1 or 2,
Wherein the particulate binder (B) further contains 0.1% by mass or more and 20% by mass or less of the ethylenically unsaturated hydroxyl group-containing monomer unit. 4. The method according to any one of claims 1 to 3,
Wherein the crosslinking agent (A) is at least one selected from the group consisting of a polyfunctional epoxy compound, an oxazoline compound, and a carbodiimide compound. 5. The method according to any one of claims 1 to 4,
The particulate binder (B) further contains an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit. 6. The method according to any one of claims 1 to 5,
Wherein the amount of the crosslinking agent (A) relative to 100 parts by mass of the particulate binder (B) is 0.001 parts by mass or more and 20 parts by mass or less. A slurry composition for a lithium ion secondary battery, comprising the binder composition for a lithium ion secondary battery according to any one of claims 1 to 6, an electrode active material, and a water-soluble thickener (C). 8. The method of claim 7,
Wherein the water-soluble thickening agent (C) is at least one selected from the group consisting of carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, polyvinylalcohol, polycarboxylic acid, A slurry composition for a lithium ion secondary battery. A method for producing an electrode for a lithium ion secondary battery, which comprises applying the slurry composition for a lithium ion secondary battery according to claim 7 or 8 onto a current collector and drying the electrode active material layer to form an electrode active material layer. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte, and a separator,
The lithium ion secondary battery according to claim 9, wherein the positive electrode, the negative electrode, or both are electrodes produced by the method for manufacturing an electrode for a lithium ion secondary battery according to claim 9.

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