阅读说明：本技术 组合物、正极用粘合剂组合物 (Composition and binder composition for positive electrode ) 是由 中西崇一朗 成富拓也 井上享一 铃木茂 渡边淳 于 2018-06-13 设计创作，主要内容包括：提供一种具有柔软性的组合物。一种组合物,其含有接枝共聚物,所述接枝共聚物是将具有聚乙烯醇的主链聚合物与以(甲基)丙烯腈及(甲基)丙烯酸酯为主成分的单体接枝共聚而成的,所述聚乙烯醇的皂化度为50～100摩尔％,所述聚乙烯醇的含量为5～50质量％,所述(甲基)丙烯腈单体单元及所述(甲基)丙烯酸酯单体单元的总量为50～95质量％,所述(甲基)丙烯腈单体单元及所述(甲基)丙烯酸酯单体单元的共计100质量％中的所述(甲基)丙烯腈单体单元的含量为20～95质量％,所述(甲基)丙烯腈单体单元及所述(甲基)丙烯酸酯单体单元的共计100质量％中的(甲基)丙烯酸酯单体单元的含量为5～80质量％,所述(甲基)丙烯酸酯是仅由所述(甲基)丙烯酸酯构成的聚(甲基)丙烯酸酯均聚物的玻璃化转变温度为150～300K的单体。(A composition having flexibility is provided. A composition comprising a graft copolymer obtained by graft-copolymerizing a backbone polymer having polyvinyl alcohol with a monomer mainly comprising (meth) acrylonitrile and (meth) acrylic acid ester, wherein the polyvinyl alcohol has a degree of saponification of 50 to 100 mol%, the polyvinyl alcohol is contained in an amount of 5 to 50 mass%, the total amount of the (meth) acrylonitrile monomer units and the (meth) acrylic acid ester monomer units is 50 to 95 mass%, the amount of the (meth) acrylonitrile monomer units is 20 to 95 mass% based on 100 mass% of the total of the (meth) acrylonitrile monomer units and the (meth) acrylic acid ester monomer units, and the amount of the (meth) acrylic acid ester monomer units is 5 to 80 mass% based on 100 mass% of the total of the (meth) acrylonitrile monomer units and the (meth) acrylic acid ester monomer units, the (meth) acrylate is a monomer having a glass transition temperature of 150 to 300K, the monomer being a poly (meth) acrylate homopolymer consisting of only the (meth) acrylate.)

1. A composition comprising a graft copolymer obtained by graft-copolymerizing a main chain polymer having polyvinyl alcohol with a monomer mainly comprising (meth) acrylonitrile and (meth) acrylic acid ester,

the polyvinyl alcohol has a saponification degree of 50 to 100 mol%,

the content of the polyvinyl alcohol is 5 to 50 mass%,

the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit is 50 to 95 mass%,

the content of the (meth) acrylonitrile monomer unit in 100 mass% in total of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit is 20 to 95 mass%,

the content of the (meth) acrylate monomer unit in 100 mass% in total of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit is 5 to 80 mass%,

the (meth) acrylate is a monomer having a glass transition temperature of 150 to 300K, the monomer being a poly (meth) acrylate homopolymer consisting of only the (meth) acrylate.

2. The composition according to claim 1, wherein the composition,

the adhesive contains at least one of a (meth) acrylonitrile- (meth) acrylate-based non-graft copolymer and a non-graft polymer having polyvinyl alcohol.

3. The composition according to claim 1, wherein the composition,

the (meth) acrylate has 1 or more structures selected from linear alkyl groups, branched alkyl groups, linear or branched polyethers, cyclic ethers, and fluoroalkyl groups.

4. The composition according to any one of claims 1 to 3,

the graft rate of the graft copolymer is 150-1900%.

5. The composition according to any one of claims 1 to 4,

the average polymerization degree of the polyvinyl alcohol is 300-3000.

6. A binder composition for a positive electrode, comprising the composition according to any one of claims 1 to 5.

7. A positive electrode slurry comprising the binder composition for positive electrodes according to claim 6 and a conductive auxiliary agent.

8. A positive electrode slurry comprising the binder composition for a positive electrode according to claim 6, a positive electrode active material, and a conductive auxiliary agent.

9. The slurry for a positive electrode according to claim 7 or 8,

the conductive additive is selected from 1 or more of (i) fibrous carbon, (ii) carbon black, and (iii) a carbon composite in which fibrous carbon and carbon black are connected to each other.

10. The slurry for a positive electrode according to any one of claims 7 to 9,

the binder composition for positive electrodes has a solid content of 0.01 to 20 mass% based on the total solid content of the slurry for positive electrodes.

11. The slurry for a positive electrode according to claim 8,

the positive active material is selected from LiNi_XMn_(2-X)O₄(however, 0)<X<2) Or Li (Co)_XNi_YMn_Z)O₂(however, 0)<X<1,0<Y<1,0<Z<1, and X + Y + Z is 1) or more.

12. A positive electrode comprising a metal foil and a coating film of the slurry for a positive electrode according to any one of claims 7 to 11 formed on the metal foil.

13. A lithium ion secondary battery comprising the positive electrode according to claim 12.

14. A method for producing the composition according to any one of claims 1 to 5,

the graft copolymer is obtained by graft copolymerization of the polyvinyl alcohol, the (meth) acrylonitrile, and the (meth) acrylic acid ester.

[ technical field ] A method for producing a semiconductor device

The present invention relates to a composition, a binder composition for a positive electrode, a positive electrode slurry using the binder composition, and a positive electrode and a lithium ion secondary battery using the positive electrode slurry.

[ background of the invention ]

In recent years, secondary batteries have been used as power sources for electronic devices such as notebook computers and cellular phones, and hybrid vehicles and electric vehicles using secondary batteries as power sources have been developed for the purpose of reducing environmental loads. These power sources require secondary batteries having high energy density, high voltage, and high durability. Lithium ion secondary batteries have attracted attention as secondary batteries capable of achieving high voltage and high energy density.

The lithium ion secondary battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, wherein the positive electrode comprises a positive electrode active material, a conductive auxiliary agent, a metal foil and a binder. As the binder, a fluorine-based resin such as polyvinylidene fluoride or polytetrafluoroethylene, a styrene-butadiene-based copolymer, or an acrylic copolymer is used (for example, see patent documents 1 to 3).

As a positive electrode binder for a lithium ion secondary battery, a binder (graft copolymer) containing polyvinyl alcohol and polyacrylonitrile as main components and having high adhesion and oxidation resistance is disclosed (see patent document 4).

However, patent documents 1 to 4 do not describe the glass transition temperature of (meth) acrylic acid esters.

[ Prior art documents ]

[ patent document ]

[ patent document 1] Japanese patent application laid-open No. 2013-98123

[ patent document 2] Japanese patent laid-open No. 2013-84351

[ patent document 3] Japanese patent laid-open No. 6-172452

[ patent document 4] International publication No. 2015/053224

[ summary of the invention ]

[ problem to be solved by the invention ]

In view of the above problems, an object of the present invention is to provide a composition having flexibility.

[ MEANS FOR SOLVING PROBLEMS ] to solve the problems

The present inventors have conducted extensive studies to achieve the above object and have found that a composition using a specific (meth) acrylate has flexibility.

Namely, the present invention provides a binder composition for a positive electrode as described below.

(1) A composition comprising a graft copolymer obtained by graft-copolymerizing a main chain polymer having polyvinyl alcohol with a monomer mainly comprising (meth) acrylonitrile and (meth) acrylic acid ester, wherein the polyvinyl alcohol has a saponification degree of 50 to 100 mol%, the polyvinyl alcohol is contained in an amount of 5 to 50% by mass, the total amount of the (meth) acrylonitrile monomer units and the (meth) acrylic acid ester monomer units is 50 to 95% by mass, the (meth) acrylonitrile monomer units and the (meth) acrylic acid ester monomer units together comprise 100% by mass, the (meth) acrylonitrile monomer units together with the (meth) acrylic acid ester monomer units together comprise 20 to 95% by mass, and the (meth) acrylic acid ester monomer units together comprise 100% by mass, the (meth) acrylonitrile monomer units together with the (meth) acrylic acid ester monomer units together comprise 5 to 80% by mass, the (meth) acrylate is a monomer having a glass transition temperature of 150 to 300K, the monomer being a poly (meth) acrylate homopolymer consisting of only the (meth) acrylate.

(2) The composition according to (1), which contains at least one of a (meth) acrylonitrile- (meth) acrylate-based non-graft copolymer and a non-graft polymer having polyvinyl alcohol.

(3) The composition according to (1), wherein the (meth) acrylate has 1 or more structures selected from the group consisting of a linear alkyl group, a branched alkyl group, a linear or branched polyether, a cyclic ether, and a fluoroalkyl group.

(4) The composition as described in any one of (1) to (3), wherein the graft ratio of the graft copolymer is 150 to 1900%.

(5) The composition according to any one of (1) to (4), wherein the polyvinyl alcohol has an average polymerization degree of 300 to 3000.

(6) A binder composition for a positive electrode, comprising the composition according to any one of (1) to (5).

(7) A positive electrode slurry comprising the binder composition for positive electrodes according to (6) and a conductive auxiliary agent.

(8) A positive electrode slurry comprising the binder composition for positive electrodes according to (6), a positive electrode active material, and a conductive auxiliary agent.

(9) The slurry for a positive electrode according to (7) or (8), wherein the conductive auxiliary agent is at least 1 selected from the group consisting of (i) fibrous carbon, (ii) carbon black, and (iii) a carbon composite in which fibrous carbon and carbon black are connected to each other.

(10) The positive electrode slurry according to any one of (7) to (9), wherein the binder composition for positive electrodes has a solid content of 0.01 to 20% by mass based on the total solid content in the positive electrode slurry.

(11) The slurry for positive electrode according to (8), wherein the positive electrode active material is LiNi_XMn_(2-X)O₄(however, 0)<X<2) Or Li (Co)_XNi_YMn_Z)O₂(however, 0)<X<1,0<Y<1,0<Z<1, and X + Y + Z is 1) or more.

(12) A positive electrode comprising a metal foil and a coating film of the positive electrode slurry according to any one of (7) to (11) formed on the metal foil.

(13) A lithium ion secondary battery comprising the positive electrode described in (12).

(14) A method for producing a composition according to any one of (1) to (5), wherein the graft copolymer is obtained by graft copolymerization of the polyvinyl alcohol, the (meth) acrylonitrile, and the (meth) acrylic acid ester.

[ Effect of the invention ]

The present invention can provide a composition having flexibility.

[ detailed description ] embodiments

Hereinafter, embodiments of the present invention will be described in detail. The present invention is not limited to the embodiments described below.

< composition (Binder composition for Positive electrode) >

The composition according to the embodiment of the present invention contains a graft copolymer obtained by graft-copolymerizing a main chain polymer mainly composed of polyvinyl alcohol (hereinafter, also referred to as PVA) and a monomer mainly composed of (meth) acrylonitrile (hereinafter, also referred to as poly (meth) acrylonitrile or PAN) and (meth) acrylate (hereinafter, also referred to as poly (meth) acrylate or PAK) as a side chain polymer. The graft copolymer is a copolymer produced by copolymerizing a main chain having polyvinyl alcohol with a monomer containing (meth) acrylonitrile and (meth) acrylate as main components, and a (meth) acrylonitrile- (meth) acrylate copolymer is produced as a side chain.

The composition of the present embodiment may contain a non-graft polymer that does not participate in graft copolymerization, in addition to the graft copolymer, that is, a non-graft polymer having a (meth) acrylonitrile- (meth) acrylate copolymer (hereinafter, also referred to as "non-graft copolymer", "meth) acrylonitrile- (meth) acrylate non-graft copolymer") and/or polyvinyl alcohol that is not covalently bonded to the graft copolymer and is present in a free state, in the composition. Here, "no covalent bond is formed" means, for example, that copolymerization is not performed.

Accordingly, the composition of the present embodiment may contain, as a resin component (polymer component), a non-graft polymer having a (meth) acrylonitrile- (meth) acrylate-based non-graft copolymer and/or polyvinyl alcohol, in addition to the graft copolymer.

The non-graft polymer having a main chain polymer mainly composed of polyvinyl alcohol and polyvinyl alcohol is preferably a polyvinyl alcohol homopolymer.

Further, not only the (meth) acrylonitrile- (meth) acrylate-based copolymer, but also the "non-graft copolymer" may include a homopolymer of each monomer that does not form a covalent bond with the graft copolymer.

The (meth) acrylate among the monomers grafted to the backbone polymer having polyvinyl alcohol is 1 kind of the monomer to be graft-copolymerized.

The (meth) acrylate of the present embodiment is preferably copolymerizable with (meth) acrylonitrile. As the (meth) acrylate, a homopolymer of a (meth) acrylate composed only of the (meth) acrylate, that is, a monomer having a glass transition temperature of 150 to 300K of a poly (meth) acrylate homopolymer can be used.

Examples of the (meth) acrylate having a homopolymer glass transition temperature of 150 to 300K include benzyl acrylate (279K), butyl acrylate (219K), 4-cyanobutyl acrylate (233K), cyclohexyl acrylate (292K), dodecyl acrylate (270K), (2- (2-ethoxy) ethyl acrylate (223K), 2-ethylhexyl acrylate (223K), 1H-heptafluoroacrylate (243K), 1H, 3H-butylacrylate (251K), 2,2, 2-trifluoroethyl acrylate (263K), methyl fluoroacrylate (288K), hexyl acrylate (216K), isobutyl acrylate (249K), 2-methoxyethyl acrylate (223K), dodecyl methacrylate (208K), Hexyl methacrylate (268K), octyl acrylate (208K), octadecyl methacrylate (173K), phenyl methacrylate (268K), n-octyl acrylate (208K), and the like. The (meth) acrylate having a functional group such as a nitro group, a halogenated alkane, an alkylamine, a thioether, an alcohol, a cyano group or the like may be used as long as the oxidation resistance is not impaired. These may be used in 1 or more kinds.

The ester group of the (meth) acrylate is preferably an ester group having 1 or more structures selected from a linear alkyl group, a branched alkyl group, a linear or branched polyether group, a cyclic ether group, and a fluoroalkyl group, more preferably an ester group having 1 or more structures selected from a branched alkyl group, a linear alkyl group, and a linear or branched polyether group, and most preferably an ester group having 1 or more structures selected from a linear alkyl group, a linear or branched polyether group.

The glass transition here means a change in which a substance such as glass which is liquid at a high temperature has its viscosity sharply increased within a certain temperature range due to a decrease in temperature, almost loses fluidity, and becomes an amorphous solid. The method for measuring the glass transition temperature is not particularly limited, and generally means the glass transition temperature calculated by a thermogravimetry method, a differential scanning calorimetry method, a differential thermal analysis method, or a dynamic viscoelasticity measurement method. Among them, dynamic viscoelasticity measurement is preferable.

Glass transition temperatures of homopolymers of (meth) acrylates are described in J.org.Brandrup, E.M.H.Immergut, Polymer Handbook,2nd Ed., J.Wiley, New York 1975, Handbook of photohardening technology data (Technenet Books Co., Ltd.), and the like.

The (meth) acrylonitrile among the monomers grafted to the backbone polymer having polyvinyl alcohol is 1 kind of the monomer graft-copolymerized.

In the monomer units in the composition, the ratio of the (meth) acrylonitrile monomer unit to the (meth) acrylate monomer unit may be limited to 100 mass% or less. The composition of the monomeric units in the composition may consist of¹H-NMR (proton nuclear magnetic resonance spectroscopy).

The PVA has a saponification degree of 50 to 100 mol% from the viewpoint of oxidation resistance. From the viewpoint of improving coverage with living matter, it is preferably 80 mol% or more, and more preferably 95 mol% or more. The degree of saponification of PVA as referred to herein is a value measured according to JIS K6726.

The average degree of polymerization of PVA is preferably 300 to 3000 from the viewpoints of solubility, adhesiveness, and viscosity of the composition solution for a positive electrode. The average polymerization degree of the PVA is preferably 320 to 2950, more preferably 500 to 2500, and most preferably 500 to 1800. When the average polymerization degree of PVA is less than 300, the adhesive property between the binder and the active material and the conductive auxiliary agent may be reduced, and the durability may be reduced. When the average polymerization degree of PVA exceeds 3000, the solubility decreases and the viscosity increases, making it difficult to produce a slurry for a positive electrode. The average degree of polymerization of PVA referred to herein is a value measured according to JIS K6726.

The graft ratio of the graft copolymer is preferably 150 to 1900%, more preferably 155 to 1800%, most preferably 200 to 1500%, and further preferably 200 to 900% from the viewpoint of improving the coverage of living matter. If the graft ratio is less than 150%, the oxidation resistance may be lowered. If the graft ratio exceeds 900%, the adhesion may be lowered.

In the case of producing a graft copolymer (in the case of graft copolymerization), since there is a possibility that a copolymer (hereinafter, also referred to as "non-graft copolymer" or "meth) acrylonitrile- (meth) acrylate-based non-graft copolymer") obtained by copolymerization of monomers including (meth) acrylonitrile and (meth) acrylate is produced without participating in the graft copolymerization, that is, in a free state in which no covalent bond is formed with the graft copolymer, a step of separating the non-graft copolymer from a composition containing the graft copolymer and the non-graft copolymer is required in order to calculate the graft ratio. The non-graft copolymer is dissolved in dimethylformamide (hereinafter, may also be referred to as DMF), but PVA or graft-copolymerized (meth) acrylonitrile or (meth) acrylate is not dissolved in DMF. By utilizing this difference in solubility, the non-graft copolymer can be separated by an operation such as centrifugation.

Specifically, a composition having a known content of (meth) acrylonitrile monomer units and (meth) acrylate monomer units is immersed in a predetermined amount of DMF, and the non-graft copolymer is eluted in the DMF. The impregnated liquid was then separated by centrifugation into a DMF soluble fraction and a DMF insoluble fraction.

Here, if provided

A: the amount of graft composition used for the determination,

B: the mass% of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit in the graft composition used for the measurement,

C: the amount of the DMF insoluble fraction is,

the graft ratio can be determined by the following formula (1).

Graft rate [ C-A X (100-B). times.0.01 ]/[ A X (100-B). times.0.01 ]. times.100 (%). cndot. (1)

The weight average molecular weight of the non-grafted copolymer is preferably 30000 to 250000, more preferably 80000 to 150000. The weight average molecular weight of the non-graft copolymer is preferably 250000 or less, more preferably 190000 or less, and most preferably 150000 or less, from the viewpoint of suppressing an increase in viscosity of the non-graft copolymer and allowing easy production of a slurry for a positive electrode. The weight average molecular weight of the non-graft copolymer can be determined by GPC (gel permeation chromatography).

The amount of PVA in the composition is 5 to 50% by mass, preferably 5 to 40% by mass, and more preferably 5 to 20% by mass. If the content is less than 5% by mass, the adhesiveness may be lowered. If the amount exceeds 40 mass%, the oxidation resistance and flexibility may be reduced.

In the present embodiment, the amount of PVA in the composition refers to the total amount of the graft copolymer, the non-graft copolymer, and the homopolymer of PVA in terms of mass, and is preferably the total amount of the PVA in the graft copolymer and the PVA in the non-graft polymer having polyvinyl alcohol in the composition.

The total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit in the composition is 50 to 95% by mass, preferably 60 to 90% by mass. If the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate ester monomer unit in the composition is less than 50% by mass, it may result in a decrease in oxidation resistance. If the content exceeds 95% by mass, the adhesiveness may be lowered.

When the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate ester monomer unit in the composition is 50 mass% or more, the specific reason is not clear, but it is confirmed that the amount of Mn or Ni eluted from the positive electrode active material to the negative electrode of the lithium ion secondary battery decreases.

The total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate ester monomer unit in the composition is a ratio of the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylate ester monomer unit contained in the graft copolymer, the non-graft copolymer, and the non-graft polymer having polyvinyl alcohol, in terms of mass, to the composition. That is, the ratio (% by mass) of the total amount of the (meth) acrylonitrile monomer unit amount and the (meth) acrylate monomer unit amount in the graft-copolymerized (meth) acrylonitrile- (meth) acrylate based non-graft copolymer (non-graft copolymer) to the total mass of the composition, in terms of mass, and the total amount of the (meth) acrylonitrile monomer unit amount and the (meth) acrylate monomer unit amount in the graft-copolymerized (meth) acrylonitrile- (meth) acrylate based non-graft copolymer (non-graft copolymer).

The amount of the (meth) acrylonitrile monomer unit in the total 100 mass% of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit in the composition is 20 to 95 mass%, more preferably 30 to 80 mass%, and still more preferably 40 to 70 mass%.

The amount of the (meth) acrylate monomer unit in the total 100 mass% of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit in the composition is 5 to 80 mass%, more preferably 20 to 70 mass%, and still more preferably 30 to 60 mass%.

The composition ratio of the resin components in the composition can be calculated from the reaction rate (polymerization rate) of the monomer for polymerization and the composition of the addition amount of each component for polymerization.

The mass ratio of the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester in the polymer produced by copolymerization, that is, the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit graft-copolymerized with PVA (polymer having polyvinyl alcohol) and the non-graft copolymer, can be calculated from the polymerization rate of (meth) acrylonitrile or (meth) acrylic acid ester and the mass of (meth) acrylonitrile or (meth) acrylic acid ester added. By taking the ratio of the mass of the (meth) acrylonitrile and the (meth) acrylate to the mass of the PVA added, the mass ratio of the PVA to the (meth) acrylonitrile monomer units to the (meth) acrylate monomer units can be calculated.

Specifically, the total mass% of the (meth) acrylonitrile monomer units or (meth) acrylate monomer units in the composition can be determined by the following formula (2). Here, the monomer means (meth) acrylonitrile or (meth) acrylate.

Here, if provided

D: the polymerization rate (%) of the monomer used for polymerization,

E: the mass (amount) of the monomers used for the graft copolymerization,

F: the quality (amount added) of PVA used for graft copolymerization,

the total mass% of the (meth) acrylonitrile monomer units and the (meth) acrylate ester monomer units in the composition may be made of

Dx0.01 xE/(F + Dx0.01 xE). times.100 (%). cndot.2.

The polymerization rate (D) of the monomer may be determined by¹H-NMR in the present application is a numerical value obtained by the following formula (3).

Here, the notation is as follows.

G: quality of PVA for polymerization

H: mass of monomer used for polymerization

I: quality of the obtained product

D:＝[I－G]/H×100(％)····(3)

The composition ratio of the (meth) acrylonitrile monomer unit and the (meth) acrylate monomer unit in the composition of the resin component may be set by¹H-NMR.¹The measurement of H-NMR can be carried out, for example, under the following conditions: the solvent was measured using a product name "ALPHA 500" manufactured by Nippon electronic Co., Ltd.:dimethyl sulfoxide, measurement tube: 5 mm. phi., sample concentration: 50mg/1ml, measurement temperature: at 30 ℃.

The method for producing the composition of the present embodiment is not particularly limited, and a method in which after polyvinyl acetate is polymerized and saponified to obtain PVA, the PVA is graft-copolymerized with a monomer containing (meth) acrylonitrile and (meth) acrylic acid ester as main components is preferable.

The method for obtaining polyvinyl acetate by polymerizing vinyl acetate may be any known method such as bulk polymerization or solution polymerization.

Examples of the initiator used for the synthesis of polyvinyl acetate include azo initiators such as azobisisobutyronitrile, and organic peroxides such as benzoyl peroxide and bis (4-t-butylcyclohexyl) peroxydicarbonate.

The saponification reaction of polyvinyl acetate can be carried out, for example, by a method of saponifying in an organic solvent in the presence of a saponification catalyst.

Examples of the organic solvent include methanol, ethanol, propanol, ethylene glycol, methyl acetate, ethyl acetate, acetone, methyl ethyl ketone, benzene, and toluene. These may be used in 1 or more kinds. Among them, methanol is preferred.

Examples of the saponification catalyst include basic catalysts such as sodium hydroxide, potassium hydroxide, and sodium alkoxide, and acidic catalysts such as sulfuric acid and hydrochloric acid. Among them, sodium hydroxide is preferable from the viewpoint of the saponification rate.

The method of graft-copolymerizing polyvinyl alcohol (polymer having polyvinyl alcohol) and a monomer containing (meth) acrylonitrile or (meth) acrylate as a main component can be carried out by any polymerization method such as solution polymerization, emulsion polymerization, suspension polymerization, and the like. Examples of the solvent used in the solution polymerization or suspension polymerization include dimethyl sulfoxide, N-methylpyrrolidone, and the like.

As the initiator used for graft copolymerization, organic peroxides such as benzoyl peroxide, azo compounds such as azobisisobutyronitrile, potassium peroxodisulfate, ammonium peroxodisulfate, and the like can be used.

The composition of the present embodiment can be used by dissolving it in a solvent. Examples of the solvent include dimethyl sulfoxide, N-methylpyrrolidone, and DMF. These solvents are preferably included in the adhesive composition. It is sufficient that 1 or more of these solvents are contained.

When the composition is dissolved in a solvent, the content of the composition in the solution is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, and most preferably 3to 10% by mass, based on the solid content.

The composition of the present embodiment described above contains the above graft copolymer, and therefore has high flexibility, good adhesion to a positive electrode active material or a metal foil, and covers the positive electrode active material. Therefore, the composition of the present embodiment can be used as an adhesive composition. The binder composition of the present embodiment can be used as a binder composition for a positive electrode. The slurry for a positive electrode containing the binder composition for a positive electrode has cycle characteristics and rate characteristics of a positive electrode active material using a high potential, suppresses the OCV (storage characteristics) degradation during high-temperature storage, and can provide a lithium ion secondary battery having excellent electrode flexibility, and an electrode (positive electrode) of such a lithium ion secondary battery. Therefore, the binder composition for a positive electrode of the present embodiment is suitably used for a lithium ion secondary battery.

< slurry for positive electrode >

The positive electrode slurry of the present embodiment contains the above-described binder composition for a positive electrode, a conductive auxiliary agent, and, if necessary, a positive electrode active material.

(conductive auxiliary agent)

The positive electrode slurry of the present embodiment may contain a conductive assistant. The conductive additive is preferably at least 1 or more selected from the group consisting of (i) fibrous carbon, (ii) carbon black, and (iii) a carbon composite in which fibrous carbon and carbon black are connected to each other.

Examples of the fibrous carbon include vapor grown carbon fibers, carbon nanotubes, and carbon nanofibers. Examples of the carbon Black include acetylene Black, furnace Black, and Ketjen Black (registered trademark). These conductive aids may be used alone or in combination of 2 or more. Among them, from the viewpoint of having a high effect of improving the dispersibility of the conductive auxiliary, 1 or more selected from acetylene black, carbon nanotubes and carbon nanofibers is preferable.

(Positive electrode active material)

The positive electrode slurry of the present embodiment may contain a positive electrode active material. The positive electrode active material used for the positive electrode is not particularly limited, and is preferably at least one selected from the group consisting of a composite oxide containing lithium and a transition metal (lithium-transition metal composite oxide) and a phosphate of lithium and a transition metal (lithium-transition metal phosphate). More specifically, LiCoO is preferably used as the positive electrode active material₂、LiNiO₂、Li(Co_XNi_YMn_Z)O₂(0<X<1,0<Y<1,0<Z<1, and X + Y + Z ═ 1), Li (Ni)_XAl_YCo_Z)O₂(0<X<1,0<Y<1,0<Z<1, and X + Y + Z ═ 1), LiMn₂O₄And LiNi_XMn_(2-X)O₄(0<X<2) And the like, or a combination of 1 or more selected from these. Among these positive electrode active materials, the positive electrode active material is preferably selected from the group consisting of LiNi in which the positive electrode voltage at the time of charging is 4.5V or more in the charge-discharge curve of the positive electrode of the lithium ion secondary battery_XMn_(2－X)O₄(0 < X < 2) and Li (Co)_XNi_YMn_Z)O₂At least 1 or more kinds of positive electrode active materials of high potential system (0 < X < 1, 0 < Y < 1, 0 < Z < 1, and X + Y + Z ═ 1).

From the viewpoint of high potential, the positive electrode active material is preferably a positive electrode active material in which the positive electrode voltage at the time of charging is 4.5V or more in the charge-discharge curve of the positive electrode of the lithium ion secondary battery.

The positive electrode slurry of the present embodiment may contain a plurality of kinds of conductive aids or a carbon composite to which the positive electrode active material is bonded, in order to improve the conductivity imparting ability and conductivity of the conductive aid and the positive electrode active material. Examples of the slurry for lithium ion secondary battery electrodes include a carbon composite in which fibrous carbon and carbon black are connected to each other, a composite in which a positive electrode active material coated with carbon is combined and integrated with fibrous carbon and carbon black, and the like. The carbon composite in which the fibrous carbon and the carbon black are connected to each other can be obtained, for example, by calcining a mixture of the fibrous carbon and the carbon black. The mixture of the carbon composite and the positive electrode active material may be calcined to form a carbon composite.

In the slurry for a positive electrode according to the present embodiment, the content of the binder composition for a positive electrode, the conductive auxiliary agent, and the positive electrode active material used as needed is not particularly limited, but the following ranges are preferable from the viewpoint of improving the adhesiveness and from the viewpoint of providing good characteristics to a lithium ion secondary battery when manufacturing the battery.

The content of the binder composition is preferably 0.01 to 20% by mass, more preferably 0.1 to 10% by mass, even more preferably 0.5 to 5% by mass, and most preferably 1 to 3% by mass, based on the total solid content of the positive electrode slurry.

In the slurry for a positive electrode, the content of the positive electrode active material is preferably 50 to 99.8 mass%, more preferably 80 to 99.5 mass%, and still more preferably 95 to 99.0 mass%.

In the positive electrode slurry, the content of the conductive auxiliary is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass, and most preferably 0.5 to 3% by mass.

Here, the solid content of the positive electrode slurry is the total amount of the positive electrode composition, the conductive auxiliary agent, and the positive electrode active material used as needed.

By setting the content of the conductive auxiliary agent to 0.01 mass% or more, the high-speed charging property and high-output characteristics of the lithium ion secondary battery are improved. When the amount is 10 mass% or less, a higher density positive electrode can be obtained, and therefore, the charge/discharge capacity of the battery becomes good.

< Positive electrode >

The positive electrode of the present embodiment is produced using the positive electrode slurry. The positive electrode is preferably produced from a metal foil and the positive electrode slurry provided on the metal foil. The positive electrode is preferably used for a lithium ion secondary battery electrode.

(Positive electrode)

The positive electrode of the present embodiment is preferably produced by coating the slurry for a positive electrode on a metal foil and drying the coating to form a coating film. As the metal foil, foil-like aluminum is preferably used. The thickness of the metal foil is preferably 5 to 30 μm from the viewpoint of workability.

(method for producing Positive electrode)

As a method of applying the slurry for a positive electrode to the metal foil, a known method can be used. Examples thereof include a reverse roll method, a forward roll method, a blade method, a doctor blade method, an extrusion method, a curtain coating method, a gravure printing method, a bar coating method, a dipping method, and an extrusion method. Among them, the doctor blade method (Comma roll or die cutting), the blade method and the extrusion method are preferable. In this case, the coating method is selected according to the solution properties and the drying properties of the binder, and a good surface state of the coating layer can be obtained. The coating may be performed on one side or both sides, and when performed on both sides, the coating may be performed on one side sequentially or both sides simultaneously. The coating may be continuous, batch, or stripe. The size of the battery may be determined as appropriate depending on the coating thickness, length, and width of the positive electrode slurry. For example, the thickness of the positive electrode plate including the coating thickness of the positive electrode slurry may be in the range of 10 to 500 μm.

The method for drying the slurry for a positive electrode can be a commonly used method. It is particularly preferable to use hot air, vacuum, infrared rays, far infrared rays, electron beams, and low-temperature air singly or in combination.

The positive electrode may be pressed as needed. The pressing method may be a commonly used method, and a die pressing method, a roll press method (cold roll or hot roll) is particularly preferable. The pressing pressure is not particularly limited, but is preferably 0.1 to 3 ton/cm.

< lithium ion secondary battery >

The lithium ion secondary battery of the present embodiment is preferably manufactured using the positive electrode, and preferably includes the positive electrode, the negative electrode, a separator, and an electrolytic solution (electrolyte and electrolytic solution).

(cathode)

The negative electrode used in the lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced using a negative electrode slurry containing a negative electrode active material. For example, the negative electrode can be produced using a metal foil for a negative electrode and a slurry for a negative electrode provided on the metal foil. The negative electrode slurry preferably contains a negative electrode binder, a negative electrode active material, and the conductive auxiliary agent. The binder for the negative electrode is not particularly limited, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene copolymers, and acrylic copolymers. The binder for the negative electrode is preferably a fluorine-based resin, more preferably polyvinylidene fluoride or polytetrafluoroethylene, and most preferably polyvinylidene fluoride.

Examples of the negative electrode active material used for the negative electrode include carbon materials such as graphite, polyacene, carbon nanotube, and carbon nanofiber, alloy materials such as tin and silicon, and oxide materials such as tin oxide, silicon oxide, and lithium titanate. These may be used in 1 or more kinds.

The metal foil for the negative electrode is preferably foil-shaped copper, and the thickness is preferably 5 to 30 μm from the viewpoint of workability. The negative electrode can be produced using the slurry for the negative electrode and the metal foil for the negative electrode according to the above-described method for producing the positive electrode.

(diaphragm)

The separator may be a separator having sufficient strength such as an electrically insulating porous film, a net, or a nonwoven fabric. In particular, the use of the electrolyte solution is low in ion migration resistance and the solution can be kept excellent. The material is not particularly limited, and examples thereof include inorganic fibers such as glass fibers, organic fibers, synthetic resins such as polyethylene, polypropylene, polyester, polytetrafluoroethylene resin (polyflon), and layered composites thereof. Among them, polyethylene, polypropylene, or a layered composite of these are preferable from the viewpoint of adhesiveness and safety.

(electrolyte)

As the electrolyte, any lithium salt can be used, and for example, LiClO can be mentioned₄、LiBF₄、LiBF₆、LiPF₆、LiCF₃SO₃、LiCF₃CO₂、LiAsF₆、LiSbF₆、LiB₁₀Cl₁₀、LiAlCl₄、LiCl、LiBr、LiI、LiB(C₂H₅)₄、LiCF₃SO₃、LiCH₃SO₃、LiCF₃SO₃、LiC₄F₉SO₃、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂、LiC(CF₃SO₂)₃And lithium lower aliphatic carboxylates.

(electrolyte)

The electrolyte solution for dissolving the electrolyte is not particularly limited. Examples of the electrolyte solution include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, lactones such as γ -butyrolactone, ethers such as trimethoxymethane, 1, 2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran and 2-methyltetrahydrofuran, sulfoxides such as dimethyl sulfoxide, propylene oxides such as 1, 3-dioxolane and 4-methyl-1, 3-dioxolane, nitrogen-containing compounds such as acetonitrile, nitromethane and N-methyl-2-pyrrolidone, esters such as methyl formate, methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate and phosphoric triester, inorganic acid esters such as sulfuric acid esters, nitric acid esters and hydrochloric acid esters, amides such as dimethylformamide and dimethylacetamide, and the like, Glymes such as diglyme, triglyme and tetraglyme, ketones such as acetone, diethyl ketone, methyl ethyl ketone and methyl isobutyl ketone, sulfolanes such as sulfolane, oxazolidinones such as 3-methyl-2-oxazolidinone, and sultones such as 1, 3-propane sultone, 4-butane sultone and naphthalene sultone. More than 1 kind selected from these electrolytic solutions can be used.

Among the above electrolytes and electrolytic solutions, LiPF is preferable₆Dissolved in a solution of carbonates. The concentration of the electrolyte in the solution varies depending on the electrode and the electrolyte used, and is preferably 0.5 to 3 mol/L.