阅读说明：本技术 二次电池正极用粘结剂组合物、二次电池正极用浆料组合物及其制造方法、二次电池用正极以及二次电池 (Binder composition for secondary battery positive electrode, slurry composition for secondary battery positive electrode, method for producing same, secondary battery positive electrode, and secondary) 是由 园部健矢 小黑宽树 召田麻贵 于 2018-12-14 设计创作，主要内容包括：一种二次电池正极用粘结剂组合物,包含聚合物,该聚合物含有含腈基单体单元、芳香族乙烯基单体单元、含亲水性基单体单元、共轭二烯单体单元和碳原子数为4以上的直链亚烷基结构单元。在此,芳香族乙烯基单体单元在聚合物中的含有百分比为30.0质量％以上且60.0质量％以下。此外,聚合物的碘值为60mg/100mg以上且150mg/100mg以下。(A binder composition for a secondary battery positive electrode, comprising a polymer containing a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and a linear alkylene structural unit having 4 or more carbon atoms. Here, the content percentage of the aromatic vinyl monomer unit in the polymer is 30.0 mass% or more and 60.0 mass% or less. The iodine value of the polymer is 60mg/100mg or more and 150mg/100mg or less.)

1. A binder composition for a positive electrode of a secondary battery, comprising a polymer,

the polymer contains nitrile group-containing monomer units, aromatic vinyl monomer units, hydrophilic group-containing monomer units, conjugated diene monomer units and linear alkylene structural units with the carbon number of more than 4,

the content percentage of the aromatic vinyl monomer unit in the polymer is 30.0 mass% or more and 60.0 mass% or less,

the iodine value of the polymer is 60mg/100mg or more and 150mg/100mg or less.

2. The binder composition for a secondary battery positive electrode according to claim 1, wherein,

the total content of the conjugated diene monomer unit and the linear alkylene structural unit having 4 or more carbon atoms in the polymer is defined as A mass%,

The content percentage of the aromatic vinyl monomer unit in the polymer is defined as B mass%,

When the value of the iodine value of the polymer is IV and the unit of the iodine value is mg/100mg, the relationship of { A/(A + B) } X IV < 90 is satisfied.

3. The binder composition for a secondary battery positive electrode according to claim 1 or 2, wherein,

the polymer contains an acidic group-containing monomer unit as the hydrophilic group-containing monomer unit in a percentage of 0.1 to 20.0 mass%.

4. The binder composition for a secondary battery positive electrode according to any one of claims 1 to 3, wherein the polymer further contains a (meth) acrylate monomer unit.

5. The binder composition for a secondary battery positive electrode according to claim 4, wherein the polymer contains the (meth) acrylate monomer unit in a percentage of 1.0 mass% or more and 20.0 mass% or less.

6. A slurry composition for a secondary battery positive electrode, comprising a positive electrode active material, a solvent, and the binder composition for a secondary battery positive electrode according to any one of claims 1 to 5.

7. A positive electrode for a secondary battery, comprising a positive electrode composite material layer formed using the slurry composition for a positive electrode for a secondary battery according to claim 6.

8. A secondary battery comprising the positive electrode for a secondary battery according to claim 7, a negative electrode, an electrolytic solution, and a separator.

9. A method for producing a slurry composition for a secondary battery positive electrode, comprising the following steps in this order:

a step of mixing a positive electrode active material and a conductive material to obtain a positive electrode active material-conductive material mixture;

a step of adding the binder composition for a secondary battery positive electrode according to any one of claims 1 to 5 to the positive electrode active material-conductive material mixture to obtain a positive electrode active material-conductive material-binder mixture; and

and a step of adding a solvent to the positive electrode active material-conductive material-binder mixture and mixing the mixture.

Technical Field

The present invention relates to a binder composition for a secondary battery positive electrode, a slurry composition for a secondary battery positive electrode, a method for producing the same, a secondary battery positive electrode, and a secondary battery.

Background

Secondary batteries such as lithium ion secondary batteries have characteristics of being small and light, having high energy density, and being capable of being repeatedly charged and discharged, and have been used in a wide range of applications. Therefore, in recent years, for further improvement in performance of secondary batteries, improvement of battery members such as electrodes has been studied.

Here, a positive electrode used for a secondary battery such as a lithium ion secondary battery generally has a current collector and an electrode composite material layer (positive electrode composite material layer) formed on the current collector. The positive electrode composite material layer is formed using a slurry composition in which, for example, a positive electrode active material, a binder composition containing a binder, and the like are dispersed in a dispersion medium.

Therefore, in recent years, in order to achieve further improvement in performance of secondary batteries, attempts have been made to improve a binder composition used for formation of a positive electrode composite layer.

Specifically, for example, patent document 1 proposes a binder composition for a secondary battery positive electrode, which is a binder containing a polymerization unit having a nitrile group, an aromatic vinyl polymerization unit, a polymerization unit having a hydrophilic group, and a linear alkylene polymerization unit having 4 or more carbon atoms, wherein the content percentage of the aromatic vinyl polymerization unit is 5 to 50% by mass. By using the binder composition, a secondary battery having excellent cycle characteristics and the like can be provided.

Disclosure of Invention

Problems to be solved by the invention

Here, there is room for further improvement in the output characteristics and cycle characteristics of the secondary battery formed using the binder composition for a positive electrode of the above-described conventional technique.

Accordingly, an object of the present invention is to provide a binder composition for a secondary battery positive electrode and a slurry composition for a secondary battery positive electrode, which can be used for forming a secondary battery having excellent output characteristics and cycle characteristics, and a method for producing the slurry composition.

It is another object of the present invention to provide a positive electrode capable of improving the output characteristics and cycle characteristics of the obtained secondary battery, and a secondary battery having excellent output characteristics and cycle characteristics.

Means for solving the problems

The present inventors have conducted intensive studies in order to solve the above problems. Then, the present inventors have found that when a polymer containing a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and a linear alkylene structural unit having 4 or more carbon atoms, wherein the content percentage of the aromatic vinyl monomer unit and the iodine value are within a predetermined range, is contained in a positive electrode of a secondary battery, both the output characteristics and the cycle characteristics of the secondary battery can be improved in a balanced manner, and have completed the present invention.

That is, the present invention is directed to solving the above problems, and an adhesive composition for a secondary battery positive electrode according to the present invention is characterized by comprising a polymer containing a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and a linear alkylene structural unit having 4 or more carbon atoms, wherein the content percentage of the aromatic vinyl monomer unit in the polymer is 30.0 mass% or more and 60.0 mass% or less, and the iodine value of the polymer is 60mg/100mg or more and 150mg/100mg or less. If the percentage of the aromatic vinyl monomer unit contained in the polymer and the iodine value of the polymer are adjusted to be within the above ranges, a secondary battery having excellent output characteristics and cycle characteristics can be formed using the binder composition for a secondary battery positive electrode comprising the polymer.

The term "comprising a monomer unit" as used herein means that a polymer obtained using a monomer contains a structural unit derived from the monomer. Further, "containing a linear alkylene structural unit having 4 or more carbon atoms" means that the polymer contains a structural unit represented by the general formula: -C_nH_2n- [ wherein n is an integer of 4 or more]The straight chain alkylene structure represented by the formula (I). Further still, the percentage of monomer units contained in the polymer can be determined by, for example¹H-NMR was measured. Further, the "iodine value" of the polymer can be measured in accordance with JIS K6235 (2006).

In the binder composition for a secondary battery positive electrode of the present invention, it is preferable that the relationship of { A/(A + B) } × IV ≦ 10 when the total content percentage of the conjugated diene monomer unit and the linear alkylene structural unit having 4 or more carbon atoms in the polymer is defined as A mass%, the content percentage of the aromatic vinyl monomer unit in the polymer is defined as B mass%, and the value of the iodine value of the polymer is defined as IV (mg/100 mg). If the polymer satisfies the above-mentioned relationship, the output characteristics and cycle characteristics of the secondary battery obtained using the binder composition can be further improved.

Further, in the binder composition for a secondary battery positive electrode according to the present invention, it is preferable that the polymer contains an acidic group-containing monomer unit as the hydrophilic group-containing monomer unit in a percentage of 0.1 mass% to 20.0 mass%. When the content percentage of the acid group-containing monomer unit in the polymer is in the range of 0.1 mass% to 20.0 mass%, the output characteristics and cycle characteristics of the secondary battery obtained using the binder composition can be further improved.

In the binder composition for a secondary battery positive electrode according to the present invention, the polymer preferably further contains a (meth) acrylate monomer unit. When the polymer further contains a (meth) acrylate monomer unit, the cycle characteristics of a secondary battery obtained using the binder composition can be further improved. In the present specification, "(meth) acrylic acid" means acrylic acid and/or methacrylic acid.

In the binder composition for a secondary battery positive electrode according to the present invention, the polymer preferably contains the (meth) acrylate monomer unit in a percentage of 1.0 mass% or more and 20.0 mass% or less. When the content percentage of the (meth) acrylate monomer unit in the polymer is in the range of 1.0 mass% to 20.0 mass%, the output characteristics and cycle characteristics of the secondary battery obtained using the binder composition can be further improved.

The present invention is also directed to advantageously solve the above problems, and a slurry composition for a secondary battery positive electrode according to the present invention is characterized by containing a positive electrode active material, a solvent, and any one of the above binder compositions for a secondary battery positive electrode. According to the slurry composition for a secondary battery positive electrode of the present invention, a secondary battery having excellent output characteristics and cycle characteristics can be formed.

Further, the present invention is directed to advantageously solve the above problems, and a positive electrode for a secondary battery according to the present invention is characterized by having a positive electrode composite layer formed using the slurry composition for a positive electrode for a secondary battery. By using the slurry composition for a secondary battery positive electrode as described above, a secondary battery positive electrode capable of improving the output characteristics and cycle characteristics of the obtained secondary battery can be obtained.

Further, the present invention is directed to advantageously solve the above problems, and a secondary battery of the present invention is characterized by having the above-described positive electrode for a secondary battery, negative electrode, electrolyte solution, and separator. When the above-described positive electrode for a secondary battery is used in this manner, the output characteristics and cycle characteristics of the secondary battery can be improved.

Further, the present invention is directed to advantageously solve the above problems, and a method for producing a slurry composition for a positive electrode of a secondary battery according to the present invention includes the following steps in order: a step of mixing a positive electrode active material and a conductive material to obtain a positive electrode active material-conductive material mixture; a step of adding any one of the binder compositions for a secondary battery positive electrode to the positive electrode active material-conductive material mixture to obtain a positive electrode active material-conductive material-binder mixture; and a step of adding a solvent to the positive electrode active material-conductive material-binder mixture and mixing the mixture. According to such a production method, a slurry composition for a positive electrode of a secondary battery having excellent dispersibility of a conductive material can be obtained.

Effects of the invention

According to the present invention, a binder composition for a secondary battery positive electrode and a slurry composition for a secondary battery positive electrode, which can be used for forming a secondary battery having excellent output characteristics and cycle characteristics, and a method for producing the slurry composition can be provided.

Further, according to the present invention, it is possible to provide a positive electrode capable of improving the output characteristics and cycle characteristics of the obtained secondary battery, and a secondary battery excellent in the output characteristics and cycle characteristics.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail.

Here, the binder composition for a secondary battery positive electrode of the present invention can be used when preparing a slurry composition for a secondary battery positive electrode. The slurry composition for a secondary battery positive electrode prepared using the binder composition for a secondary battery positive electrode of the present invention can be used for forming a positive electrode of a secondary battery such as a lithium ion secondary battery. Further, the secondary battery of the present invention is characterized by using a secondary battery positive electrode formed using the secondary battery positive electrode slurry composition of the present invention.

(Binder composition for Secondary Battery Positive electrode)

The binder composition for a secondary battery positive electrode of the present invention contains a polymer. The polymer contains nitrile group-containing monomer units, aromatic vinyl monomer units, hydrophilic group-containing monomer units, conjugated diene monomer units and linear alkylene structural units with the carbon number of more than 4. Further, the polymer is characterized in that the content percentage of the aromatic vinyl monomer unit in the polymer is 30.0 mass% or more and 60.0 mass% or less, and the iodine value of the polymer is 60mg/100mg or more and 150mg/100mg or less.

The binder composition containing the polymer satisfying the above composition and properties can improve both the output characteristics and the cycle characteristics of the obtained secondary battery. The reason for this is not clear, but is presumed as follows. It is supposed that, particularly, since the above-mentioned polymer contains 30.0 mass% or more of an aromatic vinyl monomer unit and a synergistic effect of having an iodine value of 60mg/100mg or more, aggregation and excessive dispersion of solid components containing an electrode active material and the like in the slurry composition can be effectively suppressed at the same time. As a result, a secondary battery having low internal resistance and excellent output characteristics can be formed. The polymer has appropriate flexibility because the content percentage of the aromatic vinyl monomer unit is 60.0 mass% or less. It is presumed that this flexibility contributes to an improvement in the electrode density in the heating and pressing step in the production of the positive electrode using the binder composition, and also contributes to an improvement in the cycle characteristics of the secondary battery. Further, the iodine value of the polymer is 150mg/100mg or less, and the content of carbon-carbon double bonds is moderately low, so that the structural stability of the polymer is high, and the cycle characteristics of the secondary battery can be improved.

< polymers >

The polymer is a component that functions as a binder, and in a positive electrode manufactured by forming a positive electrode composite material layer on a current collector using a slurry composition for a secondary battery positive electrode prepared using the binder composition, the components contained in the positive electrode composite material layer are kept from being detached from the positive electrode composite material layer. The polymer is required to contain a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and a linear alkylene structural unit having 4 or more carbon atoms, and the aromatic vinyl monomer unit is required to have a content percentage of 30.0 mass% or more and 60.0 mass% or less and an iodine value of 60mg/100mg or more and 150mg/100mg or less. The polymer may optionally contain other monomer units such as (meth) acrylate monomer units as long as the effects of the present invention are not impaired. The polymer is preferably a hydrogenated polymer obtained by hydrogenating a polymer obtained by polymerizing a monomer composition containing a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and optionally other monomer units such as a (meth) acrylate monomer unit by a known method.

[ nitrile group-containing monomer units ]

The nitrile group-containing monomer unit is a repeating unit derived from a nitrile group-containing monomer. Further, since the polymer contains a nitrile group-containing monomer unit, the strength of the polymer itself is high, and therefore, it is presumed that when the positive electrode composite material layer is formed on the current collector using the binder composition, the adhesive strength between the positive electrode composite material layer and the current collector is improved, and the positive electrode composite material layer becomes less likely to fall off from the current collector (that is, the peel strength of the positive electrode becomes high). Therefore, it is estimated that the cycle characteristics of the obtained secondary battery can be improved.

Here, as the nitrile group-containing monomer capable of forming a nitrile group-containing monomer unit, an α, β -ethylenically unsaturated nitrile monomer is exemplified. Specifically, the α, β -ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α, β -ethylenically unsaturated compound having a nitrile group, and examples thereof include: acrylonitrile; α -halogenated acrylonitrile such as α -chloroacrylonitrile and α -bromoacrylonitrile; and alpha-alkylacrylonitrile such as methacrylonitrile and alpha-ethylacrylonitrile. Among these, acrylonitrile and methacrylonitrile are preferable, and acrylonitrile is more preferable as the nitrile group-containing monomer, from the viewpoint of improving the cohesive force of the polymer.

These can be used alone or in combination of 2 or more.

When the total repeating units in the polymer is defined as 100 mass%, the percentage of the nitrile group-containing monomer units in the polymer is preferably 5 mass% or more, more preferably 7 mass% or more, still more preferably 10 mass% or more, preferably 25 mass% or less, still more preferably 20 mass% or less, and still more preferably 15 mass% or less. When the content percentage of the nitrile group-containing monomer unit in the polymer is not less than the lower limit, the output characteristics and cycle characteristics of the obtained secondary battery can be further improved. It is presumed that when the content percentage of the nitrile group-containing monomer unit having high polarity is not less than the lower limit, the softening temperature of the polymer is moderately increased, and therefore, the adhesive strength of the polymer can be increased, and the peel strength of the positive electrode formed using the adhesive composition can be increased. Thus, the internal resistance of the secondary battery is reduced by increasing the adhesive strength between the positive electrode composite material layer and the current collector, and the output characteristics of the secondary battery can be further improved. Further, if the percentage of the nitrile group-containing monomer unit in the polymer is not more than the upper limit, the problem of the adhesion between the electrode composite material layer and the current collector decreasing with repeated charge and discharge can be suppressed, and the cycle characteristics of the secondary battery can be improved.

[ aromatic vinyl monomer Unit ]

The aromatic vinyl monomer unit is a repeating unit derived from an aromatic vinyl monomer. Further, since the polymer contains the aromatic vinyl monomer unit in the content percentage within the above range, when the polymer is contained in the slurry composition, the solid content can be dispersed well in the slurry composition. Further, by using the slurry composition, a high-density positive electrode can be formed satisfactorily.

Examples of the monomer capable of forming an aromatic vinyl polymerization unit include: aromatic vinyl monomers such as styrene, alpha-methylstyrene, and vinyltoluene. Among these, styrene is preferable because of good copolymerizability with other monomers and less side reactions such as branching, chain and intermolecular crosslinking of the polymer.

When the total repeating units in the polymer is defined as 100 mass%, the content percentage of the aromatic vinyl monomer unit in the polymer needs to be 30.0 mass% or more and 60.0 mass% or less, preferably 32.0 mass% or more, more preferably 40.0 mass% or more, preferably 55.0 mass% or less, more preferably 50.0 mass% or less, and still more preferably 48.0 mass% or less. When the content percentage of the aromatic vinyl monomer unit in the polymer is not less than the lower limit, the dispersibility of the solid content in the slurry composition containing the binder composition can be appropriately improved. Furthermore, if the content percentage of the aromatic vinyl monomer unit in the polymer is not more than the upper limit value, the density of the positive electrode formed using the slurry composition containing the binder composition can be increased, and as a result, the output characteristics of the secondary battery containing the positive electrode can be improved. It is presumed that when the content percentage of the aromatic vinyl monomer unit in the polymer is not more than the above upper limit, the polymer has appropriate flexibility, and therefore can be easily pressed at the time of electrode formation, and the electrode density increased by pressing is easily maintained even after pressing (i.e., so-called "springback" is not likely to occur).

Further, the "content percentage of the nitrile group-containing monomer units" and the "content percentage of the aromatic vinyl monomer units" in the polymer preferably satisfy a relationship of 0.05 or less (content percentage [ mass% ]) of the nitrile group-containing monomer units)/(content percentage [ mass% ]) of the aromatic vinyl monomer units) of 0.60 or less, and more preferably satisfy a relationship of 0.10 or less (content percentage [ mass% ]) of the nitrile group-containing monomer units)/(content percentage [ mass% ]) of the aromatic vinyl monomer units of 0.45 or less. If this relationship is satisfied, the effect of suppressing springback during electrode formation and the effect of improving the output characteristics of the obtained secondary battery can be further satisfactorily achieved at the same time.

[ hydrophilic group-containing monomer Unit ]

The hydrophilic group-containing monomer unit is a repeating unit derived from a hydrophilic group-containing monomer. Further, since the polymer contains a hydrophilic group-containing monomer unit, the cycle characteristics of the obtained secondary battery can be further improved.

Examples of the hydrophilic group-containing monomer capable of forming a hydrophilic group-containing monomer unit include: acid group-containing monomers, hydroxyl group-containing monomers, and monomers having salts thereof. Examples of the acidic group that can be contained in the acidic group-containing monomer include: carboxylic acid groups, sulfonic acid groups, and phosphoric acid groups, and the like. In addition, a unit that can belong to the above-mentioned nitrile group-containing monomer unit or aromatic vinyl monomer unit and has a hydrophilic group is included in the hydrophilic group-containing monomer unit instead of the nitrile group-containing monomer unit/aromatic vinyl monomer unit.

Examples of the monomer having a carboxylic acid group include: monocarboxylic acids and derivatives thereof; dicarboxylic acids, and their derivatives, and the like.

Examples of monocarboxylic acids include: acrylic acid, methacrylic acid, crotonic acid, and the like.

Examples of monocarboxylic acid derivatives include: 2-ethacrylic acid, isocrotonic acid, alpha-acetoxy acrylic acid, beta-trans-aryloxy acrylic acid, alpha-chloro-beta-E-methoxy acrylic acid, beta-diamino acrylic acid, and the like.

Examples of the dicarboxylic acid include: maleic acid, fumaric acid, itaconic acid, and the like.

Examples of the dicarboxylic acid derivative include: methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloro maleic acid, dichloro maleic acid, fluoro maleic acid, etc.; maleic acid esters such as methallyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.

Further, an acid anhydride which generates a carboxyl group by hydrolysis can also be used.

Examples of the acid anhydride of the dicarboxylic acid include: maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and the like.

In addition, there may be mentioned: monoesters and diesters of α, β -ethylenically unsaturated polycarboxylic acids such as monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate, monobutyl itaconate, and dibutyl itaconate.

In addition, examples of the monomer having a sulfonic acid group include: vinylsulfonic acid, methylvinylsulfonic acid, (meth) allylsulfonic acid, styrenesulfonic acid, ethyl (meth) acrylate-2-sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, and the like.

Examples of the monomer having a phosphoric acid group include: 2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, ethyl- (meth) acryloyloxyethyl phosphate, and the like.

Examples of the monomer having a hydroxyl group include: ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol and 5-hexen-1-ol; alkanol esters of ethylenically unsaturated carboxylic acids such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate and di-2-hydroxypropyl itaconate; general formula CH₂＝CR¹-COO-(C_nH_2nO)_mH (in the formula, m represents an integer of 2 to 9, n represents an integer of 2 to 4, R¹Represents hydrogen or methyl) with (meth) acrylic acid; mono (meth) acrylates of dihydroxy esters of dicarboxylic acids such as 2-hydroxyethyl-2 '- (meth) acryloyloxyphthalate and 2-hydroxyethyl-2' - (meth) acryloyloxysuccinate; vinyl ethers such as 2-hydroxyethyl vinyl ether and 2-hydroxypropyl vinyl ether; mono (meth) allyl ethers of alkylene glycols such as (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2-hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, and (meth) allyl-6-hydroxyhexyl ether; polyoxyalkylene glycol mono (meth) allyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; (Poly) alkylene glycol such as glycerol mono (meth) allyl ether, (meth) allyl-2-chloro-3-hydroxypropyl ether, and (meth) allyl-2-hydroxy-3-chloropropyl etherMono (meth) allyl ethers of halogen and hydroxy substituents; mono (meth) allyl ethers of polyhydric phenols such as eugenol and isoeugenol, and halogen-substituted compounds thereof; (meth) allyl sulfides of alkylene glycols such as (meth) allyl-2-hydroxyethyl sulfide and (meth) allyl-2-hydroxypropyl sulfide.

Among these, the hydrophilic group-containing monomer is preferably a monomer having an acidic group and having a carboxylic acid group or a sulfonic acid group, and particularly preferably a monomer having a carboxylic acid group because transition metal ions that may elute from the positive electrode active material are efficiently captured, from the viewpoint of excellent adhesion between the positive electrode active materials and adhesion between the positive electrode composite material layer and a current collector described later.

When the total repeating units in the polymer are defined as 100 mass%, the content percentage of the hydrophilic group-containing monomer unit in the polymer is preferably 0.1 mass% or more, preferably 20.0 mass% or less, more preferably 15.0 mass% or less, and still more preferably 10.0 mass% or less. When the content percentage of the hydrophilic group-containing monomer unit in the polymer is not less than the lower limit, the cycle characteristics of the obtained secondary battery can be further improved. The reason for this is not clear, and it is presumed that the hydrophilic group-containing monomer unit in the polymer improves the adhesive strength of the polymer and improves the peel strength of the positive electrode formed using the adhesive composition, as in the case of the nitrile group-containing monomer unit. Further, if the content percentage of the hydrophilic group-containing monomer unit in the polymer is not more than the upper limit value, it is possible to favorably suppress an excessive increase in the degree of swelling in the electrolyte solution of the polymer. This can further improve the output characteristics of the obtained secondary battery.

[ conjugated diene monomer Unit ]

The conjugated diene monomer unit is a repeating unit derived from a conjugated diene monomer. Further, it is supposed that the polymer contains a conjugated diene monomer, and therefore, the coagulation and excessive dispersion of solid components including an electrode active material and the like in the slurry composition can be effectively suppressed at the same time by a synergistic effect with the aromatic vinyl monomer unit. As a result, a secondary battery having low internal resistance and excellent output characteristics can be formed.

Here, examples of the conjugated diene monomer capable of forming a conjugated diene monomer unit include: conjugated diene compounds having 4 or more carbon atoms such as 1, 3-butadiene, isoprene, 2, 3-dimethyl-1, 3-butadiene, 1, 3-pentadiene and the like. 1, 3-butadiene is particularly preferred. These can be used alone or in combination of 2 or more.

[ straight-chain alkylene structural unit having 4 or more carbon atoms ]

A linear alkylene structural unit having 4 or more carbon atoms (hereinafter, also referred to simply as "alkylene structural unit") represented by the general formula: -C_nH_2n- [ wherein n is an integer of 4 or more]A repeating unit having a linear alkylene structure having 4 or more carbon atoms. Further, since the polymer has a linear alkylene structural unit having 4 or more carbon atoms, the problem that the charge/discharge polymer is likely to swell in the positive electrode can be suppressed, the adhesion between the current collector and the positive electrode composite layer can be improved, and the cycle characteristics of the secondary battery can be improved.

The method for introducing the linear alkylene structural unit having 4 or more carbon atoms into the polymer is not particularly limited, and examples thereof include the following methods (1) and (2):

(1) a method in which a polymer is prepared from a monomer composition containing a conjugated diene monomer, and the polymer is hydrogenated, thereby converting a conjugated diene monomer unit into a linear alkylene structural unit having 4 or more carbon atoms;

(2) a method for producing a polymer from a monomer composition containing a 1-olefin monomer having 4 or more carbon atoms. These conjugated diene monomers and 1-olefin monomers can be used alone or in combination of 2 or more.

Among these, the method (1) is particularly preferable because it is easy to produce a polymer.

In addition, as the conjugated diene monomer that can be used in the method of the above (1), there can be mentioned various compounds described in the item of [ conjugated diene monomer unit ], and 1, 3-butadiene is particularly preferable. That is, the linear alkylene structural unit having 4 or more carbon atoms is preferably a structural unit obtained by hydrogenating a conjugated diene monomer unit (conjugated diene hydride unit), and more preferably a structural unit obtained by hydrogenating a 1, 3-butadiene unit (1, 3-butadiene hydride unit). The selective hydrogenation of the conjugated diene monomer unit can be carried out by a known method such as an oil layer hydrogenation method or an aqueous layer hydrogenation method.

The polymer herein contains a linear alkylene structural unit having 4 or more carbon atoms and a conjugated diene monomer unit. When the total repeating units (total of the structural units and the monomer units) in the polymer is defined as 100 mass%, the total content percentage of the linear alkylene structural unit having 4 or more carbon atoms and the conjugated diene monomer unit is preferably 10.0 mass% or more, more preferably 15.0 mass% or more, preferably 60.0 mass% or less, more preferably 55.0 mass% or less, and further preferably 50.0 mass% or less. When the total content percentage is equal to or higher than the lower limit value, an excessive increase in the glass transition temperature of the polymer can be suppressed, and as a result, the density can be effectively increased in the pressing step in the production of the positive electrode. Further, when the total content percentage is equal to or higher than the lower limit, the polymer has appropriate flexibility, and the ease of pressing in the pressing step can be improved and the springback can be suppressed. On the other hand, when the total content percentage is not more than the upper limit, the dispersibility of the solid content in the slurry composition can be appropriately improved, and as a result, the internal resistance of the obtained secondary battery can be reduced. As a result, the output characteristics of the secondary battery can be improved.

In addition, in the case of hydrogenated polymer, the percentage of the linear alkylene structural unit having 4 or more carbon atoms in the polymer is not limited to¹The measurement results obtained by measuring the iodine value of the hydrogenated polymer can be used in addition to the measurement results obtained by H-NMR, if necessary.

Further, the "total content percentage of the linear alkylene structural unit having 4 or more carbon atoms and the conjugated diene monomer unit (hereinafter also simply referred to as the content percentage (A))" "in the polymer and the" content percentage of the aromatic vinyl monomer unit (hereinafter also simply referred to as the content percentage (B)) "" described above preferably satisfy a relationship of 0.2. ltoreq. in terms of the content percentage (A) [ mass% ])/(the content percentage (B) [ mass% ]. ltoreq.2.0, and more preferably satisfy a relationship of 0.3. ltoreq. in terms of the content percentage (A) [ mass% ])/(the content percentage (B) [ mass% ]. ltoreq.1.80. If this relationship is satisfied, the effect of suppressing springback during electrode formation and the effect of improving the output characteristics of the obtained secondary battery can be further satisfactorily achieved at the same time.

[ other monomer units ]

Further, as other monomers capable of forming other monomer units, there can be mentioned (meth) acrylate monomers and known monomers copolymerizable with the above monomers.

These can be used alone in 1 kind or in combination of 2 or more kinds.

Here, examples of the (meth) acrylate ester monomer include: alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, isopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; and alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, isopentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate.

The content percentage of the (meth) acrylate monomer unit in the polymer is preferably 1.0 mass% or more, preferably 20.0 mass% or less, more preferably 18.0 mass% or less, and further preferably 15.0 mass% or less. When the content percentage of the (meth) acrylate monomer unit in the polymer is not less than the lower limit, the cycle characteristics of the obtained secondary battery can be further improved. The reason for this is not clear, and it is presumed that, similarly to the case of the nitrile group-containing monomer unit and the hydrophilic group-containing monomer unit, the (meth) acrylate monomer unit in the polymer can improve the adhesive strength of the polymer and improve the peel strength of the positive electrode formed using the adhesive composition. Further, if the content percentage of the (meth) acrylate monomer unit in the polymer is not more than the upper limit value, it is possible to favorably suppress an excessive increase in the degree of swelling in the electrolyte solution of the polymer. This can further improve the output characteristics of the obtained secondary battery.

In addition, in the case where the polymer contains other monomer units than the (meth) acrylate ester monomer unit, the content percentage of the other monomer units is preferably 20% by mass or less, more preferably 10% by mass or less.

[ iodine value ]

Further, the iodine value of the polymer is required to be 60mg/100mg or more and 150mg/100mg or less, preferably 130mg/100mg or less, and more preferably 120mg/100mg or less. When the iodine value of the polymer is not less than the above lower limit, the dispersibility of the solid content in the slurry composition can be suitably improved due to a synergistic effect with the aromatic vinyl monomer unit contained in the polymer. Further, if the iodine value of the polymer is not more than the above upper limit, the structural stability of the polymer is high, and the cycle characteristics of the secondary battery can be improved. Further, it is presumed that if the iodine value of the polymer is not more than the above upper limit, the structural stability of the polymer is high, and the polymer is inhibited from easily swelling in the positive electrode with charge and discharge, whereby the cycle characteristics of the secondary battery can be improved. Further, if the iodine value of the polymer is not more than the above upper limit, the polymer has appropriate flexibility, and the ease of pressing in the pressing step can be improved and the springback can be suppressed. In addition, the iodine value of the polymer can be controlled by adjusting, for example, the composition of the polymer and, in the case where the polymer is a hydrogenated polymer, the hydrogenation rate.

[ relationship between iodine value and content percentage of each monomer Unit ]

Here, from the viewpoint of improving the output characteristics and cycle characteristics of the resulting secondary battery in a more balanced manner, the content percentages of the aromatic vinyl monomer unit, the conjugated diene monomer unit, and the linear alkylene structural unit having 4 or more carbon atoms included in the polymer and the iodine value of the polymer preferably satisfy the following relationship.

That is, when the total content percentage of the conjugated diene monomer units and the linear alkylene structural units having 4 or more carbon atoms in the polymer is defined as A mass%, the content percentage of the aromatic vinyl monomer units in the polymer is defined as B mass%, and the iodine value of the polymer is defined as IV (mg/100mg),

preferably, the relationship of 10 ≦ { A/(A + B) } × IV ≦ 90 is satisfied.

Further, the value of { a/(a + B) } × IV is preferably 20 or more, preferably 80 or less, and more preferably 75 or less.

If the value of { a/(a + B) } × IV is equal to or greater than the lower limit value, a positive electrode with high density can be obtained, and the output characteristics of the secondary battery can be further improved. If the value of { a/(a + B) } × IV is equal to or less than the upper limit value, the electrolyte swelling degree of the polymer can be suppressed from excessively increasing, and the output characteristics of the secondary battery can be further improved. Further, if the value of { a/(a + B) } × IV is equal to or less than the upper limit value, it is possible to suppress the swelling property of the charge/discharge polymer from being easily improved, and it is possible to suppress the decrease in the adhesion between the current collector and the electrode composite layer due to the charge/discharge and further improve the cycle characteristics of the secondary battery.

[ glass transition temperature ]

Further, the glass transition temperature of the polymer is preferably-50 ℃ or higher, more preferably-40 ℃ or higher, still more preferably-30 ℃ or higher, and preferably 50 ℃ or lower. When the glass transition temperature of the polymer is within the above range, the output characteristics and cycle characteristics of the obtained secondary battery can be further improved. The "glass transition temperature" of the polymer can be measured according to JIS K7121 (1987). In addition, the glass transition temperature of the polymer can be controlled by adjusting, for example, the composition of the polymer and, in the case where the polymer is a hydrogenated polymer, the hydrogenation rate.

[ Mooney viscosity ]

The polymer is preferably Mooney viscosity (ML)₁₊₄100 ℃ C. is 50 or more, more preferably 60 or more, further preferably 70 or more, preferably 200 or less, more preferably 180 or less, further preferably 170 or less. When the Mooney viscosity of the polymer is not less than the lower limit, the dispersibility of the solid content in the slurry composition can be suitably improved. On the other hand, if the Mooney viscosity of the polymer is not more than the above upper limit, the coatability of the slurry composition can be improved. Note that "Mooney viscosity" (ML) of the polymer₁₊₄100 ℃ C.) "can be measured according to JIS K6300-1 by the method described in the examples. The mooney viscosity of the polymer can be adjusted by changing, for example, the composition of the polymer, production conditions (for example, the amount of the chain transfer agent used, the polymerization temperature, and the polymerization conversion at the end of polymerization).

[ method for producing Polymer ]

The method for producing the polymer is not particularly limited, and the polymer can be produced, for example, by polymerizing a monomer composition containing the monomer in the presence of a chain transfer agent as desired to obtain a polymer, and then hydrogenating (hydrogenating) the obtained polymer.

Here, the content percentage of each monomer in the monomer composition for preparing the polymer can be determined according to the content percentage of each repeating unit in the polymer.

The polymerization method is not particularly limited, and any of solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, and the like can be used. As the polymerization reaction, any of ionic polymerization, radical polymerization, living radical polymerization, and the like can be used.

Further, the method for hydrogenating the polymer is not particularly limited, and a general method using a catalyst can be used (see, for example, international publication nos. 2012/165120 and 2013/080989, and japanese patent application laid-open publication No. 2013-8485).

[ solvent ]

The binder composition may also contain a solvent. The solvent is not particularly limited, and an organic solvent can be used. Further, examples of the organic solvent include: alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, and pentanol; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; diethyl ether, diEthers such as alkane and tetrahydrofuran; amide polar organic solvents such as N, N-dimethylformamide and N-methyl-2-pyrrolidone (NMP); and aromatic hydrocarbons such as toluene, xylene, chlorobenzene, o-dichlorobenzene, and p-dichlorobenzene. These may be used alone in 1 kind, or may be used in combination of 2 or more kinds.

As the solvent, NMP is particularly preferable.

[ other ingredients ]

The adhesive composition of the present invention may contain, in addition to the above components, a polymer having a different composition from the above polymer, and a component such as a known additive as described in Japanese patent application laid-open No. 2013-179040. These components may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio.

Examples of the polymer having a different composition from the above-mentioned polymer include: fluoropolymers such as polyvinylidene fluoride (PVDF), polyacrylonitrile, and polymethyl methacrylate. These polymers do not contain at least one of a nitrile group-containing monomer unit, an aromatic vinyl monomer unit, a hydrophilic group-containing monomer unit, a conjugated diene monomer unit, and a linear alkylene structural unit having 4 or more carbon atoms, or even if a polymer contains all of the above units, they are different from the polymers contained in the adhesive composition of the present invention in that the content percentage of the aromatic vinyl monomer unit is less than 30.0% by mass or more than 60.0% by mass. Or even if a polymer contains all of the above units, it is different from the polymer contained in the binder composition of the present invention in that the iodine value is less than 60mg/100mg or more than 150mg/100 mg. For example, even if a polymer contains 30.0 mass% to 60.0 mass% of an aromatic vinyl monomer unit and has an iodine value of 60mg/100mg to 150mg/100mg, the polymer is different from the polymer contained in the adhesive composition of the present invention in that it does not contain, for example, a linear alkylene structural unit having 4 or more carbon atoms.

The total amount of the polymer and the polymer having a different composition from the polymer is defined as 100% by mass, and the content percentage of the polymer having a different composition from the polymer in the binder composition is preferably less than 50% by mass, and more preferably less than 20% by mass.

(slurry composition for Secondary Battery cathode)

The slurry composition for a secondary battery positive electrode of the present invention contains a positive electrode active material, a solvent, and the above binder composition, and optionally contains a conductive material and/or other components. That is, the slurry composition for a secondary battery positive electrode of the present invention contains a positive electrode active material, a solvent, and the above-described polymer, and further optionally contains a conductive material and/or other components. Further, since the slurry composition for a secondary battery positive electrode of the present invention contains the above binder composition, a secondary battery having excellent output characteristics and cycle characteristics can be formed.

In the following, a case where the slurry composition for a secondary battery positive electrode is a slurry composition for a lithium ion secondary battery positive electrode will be described as an example, but the present invention is not limited to the following example.

< Positive electrode active Material >

The positive electrode active material is a material that transfers electrons to the positive electrode of the secondary battery. In addition, as a positive electrode active material for a lithium ion secondary battery, a material capable of inserting and extracting lithium is generally used.

Specifically, the positive electrode active material for a lithium ion secondary battery is not particularly limitedSpecifically, there may be mentioned: lithium-containing cobalt oxide (LiCoO)₂) Lithium manganate (LiMn)₂O₄) Lithium-containing nickel oxide (LiNiO)₂) Lithium-containing composite oxide of Co-Ni-Mn, lithium-containing composite oxide of Ni-Mn-Al, lithium-containing composite oxide of Ni-Co-Al, olivine-type lithium iron phosphate (LiFePO)₄) Olivine-type lithium manganese phosphate (LiMnPO)₄)、Li_1+xMn_2-xO₄(0<X<2) Spinel Compound with excess lithium, Li [ Ni ]_0.17Li_0.2Co_0.07Mn_0.56]O₂、LiNi_0.5Mn_1.5O₄And the like known as positive electrode active materials. Further, examples of the lithium-containing composite oxide of Co — Ni — Mn include: li (Ni)_0.5Co_0.2Mn_0.3)O₂、Li(Ni_1/3Co_1/3Mn_1/3)O₂And the like.

Among the above, from the viewpoint of improving the battery capacity of the secondary battery and the like, it is preferable to use a lithium cobalt oxide (LiCoO) as the positive electrode active material₂) Lithium-containing nickel oxide (LiNiO)₂) Lithium-containing composite oxide of Co-Ni-Mn, Li [ Ni ]_0.17Li_0.2Co_0.07Mn_0.56]O₂Or LiNi_0.5Mn_1.5O₄More preferably, a lithium-containing composite oxide of Co-Ni-Mn is used.

The amount of the positive electrode active material to be added and the particle size are not particularly limited, and can be the same as those of conventionally used positive electrode active materials.

< conductive Material >

The conductive material is used to ensure electrical contact of the positive electrode active materials with each other. Further, as the conductive material, it is possible to use: conductive carbon materials such as carbon black (e.g., acetylene black, ketjen black (registered trademark), furnace black, etc.), graphene, graphite, carbon fiber, carbon sheet, and ultra-short carbon fiber (e.g., carbon nanotube, vapor-deposited carbon fiber, etc.); fibers, foils, etc. of various metals. As the conductive material, carbon black is particularly preferable, and acetylene black is more preferable.

These can be used alone in 1 or a combination of 2 or more.

< Binder composition >

The binder composition for a secondary battery positive electrode of the present invention is used as the binder composition.

< solvent >

As the solvent, the same solvents as various solvents listed as solvents that can be contained in the binder composition for a secondary battery positive electrode of the present invention can be used.

< content ratio >

The content of the conductive material in the slurry composition is preferably 1 part by mass or more and 20 parts by mass or less, with the content of the positive electrode active material being 100 parts by mass. If the proportion of the conductive material is not less than the lower limit value, the electrical contact between the positive electrode active materials can be promoted. Further, if the amount of the conductive material added is not more than the above upper limit, the viscosity stability of the slurry composition can be improved.

The content of the polymer in the slurry composition is preferably 0.1 parts by mass or more and 3.1 parts by mass or less, with respect to 100 parts by mass of the positive electrode active material. It is considered that if the amount of the polymer added is equal to or greater than the lower limit, the adhesion between the current collector and the positive electrode composite material layer can be improved, and thus a positive electrode having low volume resistance can be formed. Further, if the amount of the polymer added is not more than the above upper limit value, it is possible to suppress the percentage of the polymer in the positive electrode composite material layer formed using the slurry composition from becoming excessively high, thereby suppressing a decrease in the capacity of the secondary battery.

< other ingredients >

The other components that can be added to the slurry composition are not particularly limited, and the same components as those that can be added to the binder composition of the present invention can be mentioned. Further, 1 kind of the other component may be used alone, or 2 or more kinds may be used in combination in an arbitrary ratio.

< method for producing slurry composition >

The slurry composition can be prepared by dissolving or dispersing the above components in a solvent such as an organic solvent. Specifically, a slurry composition can be prepared by mixing the above-described respective ingredients and a solvent using a ball mill, a sand mill, a bead mill, a pigment dispersing machine, an attritor, an ultrasonic dispersing machine, a homogenizer, a planetary mixer, a Filmix or the like mixer. In addition, as a solvent used for preparing the slurry composition, a solvent contained in the binder composition may also be used. Here, the order of addition of the components in the preparation is not particularly limited, and the components may be mixed at once or may be mixed in stages. From the viewpoint of improving the dispersibility of the conductive material, it is preferable to perform the step of mixing the positive electrode active material and the conductive material to obtain a positive electrode active material-conductive material mixture, then the step of adding the binder composition to the positive electrode active material-conductive material mixture to obtain a positive electrode active material-conductive material-binder mixture, and then the step of adding the solvent to the positive electrode active material-conductive material-binder mixture and mixing the mixture. The step of obtaining the positive electrode active material-conductive material mixture is preferably performed in the absence of a solvent.

(Positive electrode for Secondary Battery)

The positive electrode for a secondary battery of the present invention comprises a current collector and a positive electrode composite material layer formed on the current collector, wherein the positive electrode composite material layer is formed using the slurry composition for a positive electrode for a secondary battery. That is, at least the positive electrode active material and the polymer are contained in the positive electrode composite material layer. The components contained in the positive electrode composite material layer are the components contained in the slurry composition for a positive electrode of a secondary battery, and the preferred presence ratio of these components is the same as the preferred presence ratio of the components in the slurry composition.

In addition, since the positive electrode for a secondary battery of the present invention is manufactured using the slurry composition containing the binder composition for a positive electrode for a secondary battery of the present invention, the electrode density is high and the adhesive strength between the current collector and the positive electrode composite layer is high. Therefore, if this positive electrode is used, a secondary battery having excellent output characteristics and cycle characteristics can be obtained.

< method for producing Positive electrode >

The positive electrode for a secondary battery of the present invention is produced, for example, by the following steps: the method for manufacturing a positive electrode for a lithium secondary battery includes a step of coating the slurry composition on a current collector (coating step) and a step of drying the slurry composition coated on the current collector to form a positive electrode composite layer on the current collector (drying step).

[ coating Process ]

The method for applying the slurry composition to the current collector is not particularly limited, and a known method can be used. Specifically, as the coating method, a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure printing method, an extrusion method, a brush coating method, or the like can be used. In this case, 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 after coating and before drying can be appropriately set according to the thickness of the positive electrode composite material layer obtained by drying.

Here, as the current collector to which the slurry composition is applied, a material having conductivity and electrochemical durability may be used. Specifically, as the current collector, for example, a current collector formed of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used. As the current collector for the positive electrode, aluminum foil is particularly preferable. The above-mentioned materials may be used alone in 1 kind, or may be used in combination in 2 or more kinds at an arbitrary ratio.

[ drying Process ]

The method for drying the slurry composition on the current collector is not particularly limited, and known methods can be used, and examples thereof include: drying with warm air, hot air and low humidity air; vacuum drying; drying by irradiation with infrared rays, electron beams, or the like. By drying the slurry composition on the current collector in this manner, a positive electrode composite material layer can be formed on the current collector, and a positive electrode for a secondary battery having the current collector and the positive electrode composite material layer can be obtained.

After the drying step, the positive electrode composite material layer may be subjected to a pressure treatment using press molding, roll pressing, or the like. By the pressure treatment, the density of the positive electrode composite material layer can be effectively increased, and the adhesion and adhesive strength between the positive electrode composite material layer and the current collector can be improved. Further, when the positive electrode composite material layer contains a curable polymer, it is preferable to cure the polymer after the positive electrode composite material layer is formed.

The slurry composition for a secondary battery positive electrode of the present invention contains the above-mentioned predetermined polymer, and has a suitably high dispersibility of solid components. Therefore, the positive electrode can be efficiently densified by the pressure treatment, and the occurrence of springback is less likely. Therefore, if the slurry composition for a secondary battery positive electrode of the present invention is used, the battery characteristics of the secondary battery can be sufficiently improved even when the pressure treatment is performed during the production of the positive electrode.

(Secondary Battery)

The secondary battery of the present invention has a positive electrode, a negative electrode, an electrolyte solution, and a separator, and the positive electrode for the secondary battery of the present invention is used as the positive electrode. Further, the secondary battery of the present invention has excellent output characteristics and cycle characteristics because it has the positive electrode for a secondary battery of the present invention.

In the following, a case where the secondary battery is a lithium-ion secondary battery will be described as an example, but the present invention is not limited to the following example.

< negative electrode >

As the negative electrode, a known negative electrode can be used. Specifically, as the negative electrode, for example, a negative electrode formed of a thin plate of metallic lithium or a negative electrode formed by forming a negative electrode composite layer on a current collector can be used.

As the current collector, a current collector made of a metal material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, or platinum can be used. In addition, as the anode composite material layer, a layer containing an anode active material and a binder can be used. Further, the binder is not particularly limited, and any known binder can be used.

< electrolyte solution >

As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is generally used. As the supporting electrolyte of the lithium ion secondary battery, for example, a lithium salt can be used. MakingAs the lithium salt, for example, LiPF₆、LiAsF₆、LiBF₄、LiSbF₆、LiAlCl₄、LiClO₄、CF₃SO₃Li、C₄F₉SO₃Li、CF₃COOLi、(CF₃CO)₂NLi、(CF₃SO₂)₂NLi、(C₂F₅SO₂) NLi, etc. LiPF is particularly preferable because it is easily dissolved in a solvent and shows a high dissociation degree₆、LiClO₄、CF₃SO₃Li, particularly preferably LiPF₆. Further, 1 kind of electrolyte may be used alone, or 2 or more kinds may be used in combination at an arbitrary ratio. Since lithium ion conductivity tends to be higher as the support electrolyte having a higher dissociation degree is used, the lithium ion conductivity can be adjusted by the kind of the support electrolyte. The concentration of the supporting electrolyte in the electrolytic solution (25 ℃) can be, for example, 0.5mol/L to 2.0 mol/L.

The organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte, and for example: carbonates such as dimethyl carbonate (DMC), Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Butylene Carbonate (BC), and Ethyl Methyl Carbonate (EMC); esters such as γ -butyrolactone and methyl formate; ethers such as 1, 2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide, and the like. Further, a mixed solution of these solvents may also be used. Since the dielectric constant is high and the stable potential region is wide, carbonates are particularly preferably used, and a mixture of ethylene carbonate and diethyl carbonate is preferably used. In addition, additives such as Vinylene Carbonate (VC), fluoroethylene carbonate, and ethyl methanesulfonate may be added to the electrolyte solution. The addition of vinylene carbonate is particularly preferred.

< spacer >

The spacer is not particularly limited, and for example, the spacer described in japanese patent laid-open No. 2012-204303 can be used. The microporous membrane formed of a polyolefin-based (polyethylene, polypropylene, polybutylene, polyvinyl chloride) resin is particularly preferable because the thickness of the separator as a whole can be reduced, and thus the proportion of the electrode active material in the secondary battery can be increased, and the capacity per unit volume can be increased.

< method for producing Secondary Battery >

The secondary battery of the present invention can be produced, for example, by stacking a positive electrode and a negative electrode with a separator interposed therebetween, winding or folding the stacked electrodes into a battery container according to the battery shape as needed, injecting an electrolyte into the battery container, and sealing the battery container. In order to prevent the internal pressure of the secondary battery from rising and the occurrence of overcharge and discharge, overcurrent prevention elements such as fuses and PTC elements, metal meshes, guide plates, and the like may be provided as necessary. The shape of the secondary battery may be, for example, any of a coin type, a button type, a sheet type, a cylinder type, a square type, a flat type, and the like.