JP6922456B2 - Lithium-ion battery positive electrode binder aqueous solution, lithium-ion battery positive electrode powder binder, lithium-ion battery positive electrode slurry, lithium-ion battery positive electrode, lithium-ion battery - Google Patents

Description

The present invention relates to an aqueous binder for a positive electrode of a lithium ion battery, a powdery binder for a positive electrode of a lithium ion battery, a slurry for a positive electrode of a lithium ion battery obtained by using them, and a positive electrode for a lithium ion battery and a lithium ion battery.

A power storage device having a high voltage and a high energy density is required as a power source for driving an electronic device. In particular, lithium-ion batteries are expected as power storage devices having high voltage and high energy density, and are becoming widespread.

The positive and negative electrodes of the lithium ion battery are formed by dispersing an active material and a binder resin in a solvent to form a slurry, which is applied on both sides of a metal foil as a current collector, and the solvent is dried and removed to form an electrode layer. Later, this is produced by compression molding with a roll press machine or the like. Since higher voltage and higher energy density are desired in the future, the use of a higher potential positive electrode active material has been proposed. Therefore, it is necessary to withstand the decrease in capacity due to oxidative deterioration of the binder resin due to the increase in the potential of the active material.

As the binder resin, polyvinylidene fluoride (hereinafter abbreviated as "PVDF") is often used for both poles. Since this binder resin is a fluororesin, it is dissolved in a solvent containing an organic solvent such as N-methyl-2-pyrrolidone (NMP) and used as a binder resin slurry.

On the other hand, the use of an emulsion in which a binder resin is dispersed in water or a water-soluble binder resin is being studied. For example, Patent Documents 1 and 2 propose an aqueous binder in which a conjugated diene compound is used as a binder for a negative electrode and carboxymethyl cellulose (CMC) is used as a thickener. However, in these methods, PVDF is still widely used as a binder for the positive electrode because the double bond of the conjugated diene compound tends to be oxidatively deteriorated in the environment of the positive electrode where the oxidation reaction occurs. On the other hand, Patent Documents 3 and 4 propose water-soluble polymers containing repeating units derived from (meth) acrylamide as binders for positive electrodes and negative electrodes.

Japanese Unexamined Patent Publication No. 2014-103122 Japanese Patent No. 5077612 JP 2015-022956 JP-A-2015-106489

However, the lithium ion battery prepared by using the electrode slurry composition containing the binder described in Patent Document 3 and Patent Document 4 using poly (meth) acrylamide containing a repeating unit derived from (meth) acrylamide is a battery. There was still room for improvement in terms of further improving the characteristics, especially the output characteristics and cycle characteristics.

When the B-type viscosity of poly (meth) acrylamide is low, the viscosity of the electrode slurry is lowered, so that dripping is likely to occur when the slurry is applied, the dispersibility of the slurry is lowered, and sediment is generated. , The uniformity of the thickness of the coating film is impaired, and the flexibility of the electrode is deteriorated. On the other hand, if the B-type viscosity of poly (meth) acrylamide is too high, the water solubility of poly (meth) acrylamide decreases and it becomes a gel, so that it cannot be used as a binder. However, in the conventional method for controlling the B-type viscosity of poly (meth) acrylamide, poly (meth) acrylamide is oxidatively deteriorated, resulting in deterioration of battery characteristics such as output characteristics and cycle characteristics. Therefore, there was a trade-off between the problem of battery characteristics and the problem of B-type viscosity.

Therefore, the problem to be solved by the present invention is to solve both the problem of battery characteristics and the problem of B-type viscosity, that is, a slurry having good dispersibility, an electrode having good flexibility, and output characteristics and cycle characteristics. Provided is an aqueous binder solution for a positive electrode of a lithium ion battery capable of producing a good lithium battery.

Further, further problems to be solved by the present invention are provided as a powder binder for a positive electrode of a lithium ion battery, a slurry for a positive electrode of a lithium ion battery, a positive electrode of a lithium ion battery, and a lithium ion battery having excellent output characteristics and cycle characteristics. I will do it.

As a result of diligent studies to solve the above problems, the present inventor has solved the above problems by using a binder aqueous solution containing a predetermined unsaturated monomer as a constituent component and a poly (meth) acrylamide as a main component having predetermined physical properties. It was found that the present invention could be solved, and the present invention was completed. That is, the present invention relates to the following lithium ion battery positive electrode binder aqueous solution, lithium ion battery positive electrode powder binder, lithium ion battery positive electrode slurry, lithium ion battery positive electrode and lithium ion battery.

The disclosure provides the following items:
(Item 1)
It contains poly (meth) acrylamide (A), which is a radical copolymer of a monomer group containing a (meth) acrylamide skeleton-containing monomer (a) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b), and 25. A binder aqueous solution for a positive electrode of a lithium ion battery, which has a B-type viscosity of 10,000 to 70,000 mPa · s at ° C. and a solid content of 15% by mass.
(Item 2)
The binder aqueous solution for a positive electrode of a lithium ion battery according to any one of the above items, wherein the content of the component (b) in the monomer group is 0.01 to 1 mol%.
(Item 3)
A powdery binder for a positive electrode of a lithium ion battery obtained by spray-drying the aqueous binder solution for the positive electrode of a lithium ion battery according to any one of the above items.
(Item 4)
A slurry for a positive electrode of a lithium ion battery containing the aqueous binder solution for the positive electrode of a lithium ion battery according to any one of the above items and the positive electrode active material (B).
(Item 5)
A slurry for a positive electrode of a lithium ion battery, which comprises the powdery binder for the positive electrode of a lithium ion battery according to any one of the above items, water, and the positive electrode active material (B).
(Item 6)
The slurry for a positive electrode of a lithium ion battery according to any one of the above items, wherein the content of the poly (meth) acrylamide (A) is 1 to 8% by mass with respect to 100% by mass of the positive electrode active material (B). ..
(Item 7)
A positive electrode for a lithium ion battery obtained by applying the slurry for a positive electrode for a lithium ion battery according to any one of the above items to a current collector and drying the slurry.
(Item 8)
A lithium ion battery including the lithium ion battery positive electrode according to any one of the above items.

Since the aqueous binder solution for the positive electrode of the lithium ion battery according to the present invention is unlikely to be oxidatively deteriorated, it can be used as a binder for the positive electrode capable of sufficiently improving the output characteristics and cycle characteristics of the lithium battery. Further, from the aqueous solution of the binder for the positive electrode of the lithium ion battery, a slurry for the positive electrode of the lithium ion battery having good dispersibility can be produced. Further, since the slurry for the positive electrode of the lithium ion battery has good dispersibility, the flexibility of the positive electrode manufactured by using the slurry is good.

If the aqueous binder solution for the positive electrode of the lithium ion battery of the present invention, the powdery binder obtained by spray-drying the aqueous binder, and the slurry for the positive electrode of the lithium ion battery containing them and the active material are used, the output characteristics and cycle characteristics of the lithium battery are used. It is possible to provide a lithium ion battery positive electrode capable of sufficiently improving the above value, and a lithium ion battery having excellent output characteristics and cycle characteristics.

(1. Lithium-ion battery positive electrode binder aqueous solution (binder aqueous solution))
The aqueous binder solution for a positive electrode of a lithium ion battery of the present invention (hereinafter, also simply referred to as a binder aqueous solution) contains a (meth) acrylamide skeleton-containing monomer (a) (hereinafter, also referred to as a component (a)) and a sulfonic acid group-substituted unsaturated carbide. Poly (meth) acrylamide (A) (hereinafter, also referred to as (A) component), which is a radical copolymer of a group of monomers containing a hydrogen group-containing monomer (b) (hereinafter, also referred to as (b) component), and water. It is a composition containing. In the present disclosure, "(meth) acrylic" means "at least one selected from the group consisting of acrylic and methacryl". Further, the "radical copolymer" means a copolymer obtained by radical polymerization.

（式中、Ｒ^１は水素又はメチル基である。）
を有する化合物を意味する。１つの実施形態において、（メタ）アクリルアミド骨格含有モノマーは下記構造式

（式中、Ｒ^１は水素又はメチル基であり、Ｒ^２及びＲ^３はそれぞれ独立して、水素、置換若しくは非置換のアルキル基、又はアセチル基であるか、或いはＲ^２及びＲ^３が一緒になって環構造を形成する基であり、Ｒ^４及びＲ^５はそれぞれ独立して、水素、置換若しくは非置換のアルキル基、カルボキシル基、ヒドロキシ基、アミノ基（−ＮＲ^ａＲ^ｂ（Ｒ^ａ及びＲ^ｂはそれぞれ独立して水素又は置換若しくは非置換のアルキル基である）（以下同様））、アセチル基、スルホン酸基である。置換アルキル基の置換基の例としてはヒドロキシ基、アミノ基、アセチル基等が挙げられる。また、Ｒ^２及びＲ^３が一緒になって環構造を形成する基の例としては、モルホリル基等が挙げられる。）
により表現される。 ((Meta) acrylamide skeleton-containing monomer ((a) component))
In the present disclosure, the term "(meth) acrylamide skeleton-containing monomer" refers to a (meth) acrylamide skeleton.

(In the formula, R ¹ is a hydrogen or methyl group.)
Means a compound having. In one embodiment, the (meth) acrylamide skeleton-containing monomer has the following structural formula:

(In the formula, R ¹ is a hydrogen or methyl group, and R ² and R ³ are independently hydrogen, substituted or unsubstituted alkyl or acetyl groups, or R ² and R ³ are together. R ⁴ and R ⁵ are independently hydrogen, substituted or unsubstituted alkyl groups, carboxyl groups, hydroxy groups, and amino groups (-NR ^a R ^b (Ra ^a)). And R ^b are independently hydrogen or a substituted or unsubstituted alkyl group) (the same applies hereinafter)), an acetyl group and a sulfonic acid group. Examples of the substituent of the substituted alkyl group are a hydroxy group and an amino group. , Acetyl group and the like. Further, ^{as an example of a group in which R 2} and R ³ form a ring structure together, a morpholic group and the like can be mentioned.)
Represented by.

Examples of the (meth) acrylamide skeleton-containing monomer include an N-unsubstituted (meth) acrylamide skeleton-containing monomer, an N-unisubstituted (meth) acrylamide skeleton-containing monomer, an N, N-disubstituted (meth) acrylamide skeleton-containing monomer, and the like. Can be mentioned. Two or more types of (meth) acrylamide skeleton-containing monomers can be used in combination.
Examples of the N-unsubstituted (meth) acrylamide skeleton-containing monomer include (meth) acrylamide, maleic acid amide and the like.
Examples of the N-monosubstituted (meth) acrylamide skeleton-containing monomer include N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, diacetone (meth) acrylamide (meth) acrylamide, t-butylsulfonic acid and the like. ..
Examples of N-disubstituted (meth) acrylamide skeleton-containing monomers include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide and the like. Be done.
Among these, when (meth) acrylamide, especially acrylamide, is used, the oxidation resistance of the component (A) is increased.

The amount of the component (a) used is not particularly limited, but examples of the upper limit of the component (a) in 100 mol% of the monomer group giving the component (A) are 99.99, 99, 98, 95, 90, 80, 70, 60, 55 mol% and the like can be mentioned, and examples of the lower limit include 98, 95, 90, 80, 70, 60, 55, 50 mol% and the like. (A) The upper limit and the lower limit of the component are not limited to the above values. (A) The range of the components can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the component (A) containing (meth) acrylamide has a high interaction with the active material, and from the viewpoint of enhancing the dispersibility of the slurry and the binding property between the active materials inside the electrode, (a). The amount of the component () used is preferably about 30 to 99 mol%, more preferably about 50 to 90 mol% of the monomer group giving the component (A).

In one embodiment, as an example of the upper limit of the component (a) in 100% by mass of the monomer group giving the component (A), 99.99, 99, 98, 95, 90, 80, 70, 60, 55% by mass. Etc., and examples of the lower limit include 98, 95, 90, 80, 70, 60, 55, 50% by mass and the like. (A) The upper limit and the lower limit of the component are not limited to the above values. (A) The range of the components can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the component (A) containing (meth) acrylamide has a high interaction with the active material, and from the viewpoint of enhancing the dispersibility of the slurry and the binding property between the active materials inside the electrode, (a). The amount of the component () used is preferably about 30 to 99% by mass, and more preferably about 50 to 90% by mass in the monomer group giving the component (A).

(Sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2) ((b2) component))
In the present disclosure, the "sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer" means a compound in which the hydrogen of the unsaturated hydrocarbon group is substituted with a sulfonic acid group or a salt thereof. In one embodiment, the sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer is represented by the following general formula R-SO ₃ H
(In the formula, R is an unsaturated hydrocarbon group. Examples of the unsaturated hydrocarbon group include an alkenyl group such as a vinyl group, an allyl group and a 2-methylpropenyl group, an alkynyl group such as an ethynyl group and a propynyl group, and the like. Is mentioned.)
A compound represented by (for example, an organic salt such as an organic amine salt, a metal salt containing an alkali metal salt such as a potassium salt or a sodium salt, an inorganic salt containing an ammonium salt or the like).

As the component (b2), any known compound can be used without particular limitation as long as it is a compound in which hydrogen of an unsaturated hydrocarbon group is substituted with a sulfonic acid group or a salt thereof. Examples of the component (b2) include vinyl sulfonic acid, allyl sulfonic acid, metallic sulfonic acid, and salts thereof, and two or more of them can be used in combination. Examples of the salt include an organic salt such as an organic amine salt; a metal salt containing an alkali metal salt such as a potassium salt and a sodium salt, an inorganic salt containing an ammonium salt and the like. Among these, methallyl sulfonate, which acts as a chain transfer agent for controlling the molecular weight and water solubility of the component (B1), particularly sodium methallyl sulfonate is preferable.

The amount of the component (b) used is not particularly limited, but examples of the upper limit of the component (b) in 100 mol% of the monomer group giving the component (A) are 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 mol% and the like can be mentioned, and examples of the lower limit are 0.9, 0.8, 0. 7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.01 mol% and the like can be mentioned. (B) The upper and lower limits of the components are not limited to the above values. (B) The range of components can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the component (b) is preferably about 0.01 to 1 mol%, more preferably about 0.05 to 1 mol%, out of 100 mol% of the monomer group giving the component (A). good. By doing so, the molecular weight and water solubility can be controlled without impairing the oxidation resistance of the component (A).

In one embodiment, examples of the upper limit of the component (b) in 100% by mass of the monomer group giving the component (A) are 1, 0.9, 0.8, 0.7, 0.6, 0.5. , 0.4, 0.3, 0.2, 0.1, 0.05 mass%, etc., and examples of the lower limit are 0.9, 0.8, 0.7, 0.6, 0. .5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.01% by mass and the like can be mentioned. (B) The upper and lower limits of the components are not limited to the above values. (B) The range of components can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the component (b) is preferably about 0.01 to 1% by mass, more preferably about 0.05 to 1% by mass, out of 100% by mass of the monomer group giving the component (A). good. By doing so, the molecular weight and water solubility can be controlled without impairing the oxidation resistance of the component (A).

(Copolymerization component other than (a) component and (b) component ((c) component))
The monomer group may include a component (a) and another copolymerization component (c) that can be copolymerized with the component (b) (hereinafter, also referred to as a component (c)). Examples of the component (c) include unsaturated carboxylic acids, unsaturated carboxylic acid esters, α, β-unsaturated nitrile compounds, conjugated diene compounds, aromatic vinyl compounds, and the like, and two or more of them can be used in combination. The amount of the component (c) used is not particularly limited, but in one embodiment, the amount of the component (c) used is less than 50 mol% (for example, 40, 30, etc.) out of 100 mol% of the monomer group giving the component (A). 20, 20, 10, 9, 5, 1, less than 0.1 mol%, 0 mol%). In yet another embodiment, the amount of the component (c) used is less than 50% by mass (for example, 40, 30, 20, 20, 15, 10, 9, 5,) out of 100% by mass of the monomer group giving the component (A). 1, less than 0.1% by mass, 0% by mass) is preferable.

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and the like. The amount of the unsaturated carboxylic acid used is not particularly limited, but is less than 10 mol% (for example, 9, 5, 1, less than 0.1 mol%, 0 mol%) out of 100 mol% of the monomer group giving the component (A). It is preferable that it is less than 10% by mass (for example, 9, 5, 1, less than 0.1% by mass, 0% by mass) out of 100% by mass of the monomer group giving the component (A). By doing so, the oxidation resistance of the component (A) is enhanced, and a high-potential active material can be combined.

As an example of the unsaturated carboxylic acid ester, a (meth) acrylic acid ester is preferable. Examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, and n-butyl (meth) acrylate. Linear (meth) acrylate esters such as amyl, hexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate;
Branched (meth) acrylic acid esters such as (meth) acrylic acid i-propyl, (meth) acrylic acid i-butyl, (meth) acrylic acid i-amyl, and (meth) acrylic acid 2-ethylhexyl;
Alicyclic (meth) acrylic acid ester such as cyclohexyl (meth) acrylic acid;
Glycidyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, ethylene glycol (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, tri Substitution (meth) acrylic acid such as trimethylolpropane (meth) acrylic acid, pentaerythritol tetra (meth) acrylic acid, dipentaerythritol hexa (meth) acrylic acid, allyl (meth) acrylic acid, ethylene di (meth) acrylic acid, etc. Examples include ester. Two or more of these can be used together. The amount of the unsaturated carboxylic acid ester used is not particularly limited, but is less than 10 mol% (for example, 9, 5, 1, less than 0.1 mol%, 0 mol%) out of 100 mol% of the monomer group giving the component (A). It is preferable that it is less than 10% by mass (for example, 9, 5, 1, less than 0.1% by mass, 0% by mass) out of 100% by mass of the monomer group giving the component (A). By doing so, the oxidation resistance of the component (A) is enhanced, and a high-potential active material can be combined.

The α, β-unsaturated nitrile compound can be suitably used for the purpose of imparting flexibility to the coating film obtained from the binder aqueous solution or powdery binder of the present invention, or the coating film obtained from the slurry of the present invention. Examples of α, β-unsaturated nitrile compounds include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like. Two or more of these can be used together. Of these, acrylonitrile and / or methacrylonitrile are preferred, and acrylonitrile is particularly preferred. The amount of the α, β-unsaturated nitrile compound used is not particularly limited, but is less than 50 mol% (for example, 40, 30, 20, 20, 9, 5, 1,) of 100 mol% of the monomer group giving the component (A). It is preferably less than 0.1 mol%, 0 mol%), and less than 50% by mass (for example, 40, 30, 20, 20, 9, 5, 1,) out of 100% by mass of the monomer group giving the component (A). It is preferably less than 0.1% by mass and 0% by mass). By doing so, each of the coating films becomes uniform while maintaining the solubility of the component (A) in water, and it becomes easy to exert the flexibility.

Examples of conjugated diene compounds are 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, substituted linear conjugates. Examples include pentadiene, substitution and side chain conjugated hexadiene. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. Two or more of these can be used together. The amount of these used is not particularly limited, but it is less than 10 mol% (for example, 9, 5, 1, less than 0.1 mol%, 0 mol%) out of 100 mol% of the monomer group giving the component (A). preferable. Since the positive electrode binder is exposed to a high voltage, it is preferable that the component (A) has a high oxidation potential, and less than 10% by mass (for example, 9, 5) of the 100% by mass of the monomer group giving the component (A). 1, less than 0.1% by mass, 0% by mass) is preferable. However, conjugated diene compounds and aromatic vinyl compounds tend to lower the oxidation potential of component (A). Therefore, it is preferable not to use them.

The content of the component (A) with respect to 100% by mass of the aqueous solution of the present invention is not particularly limited. Examples of the upper limit of the content of the component (A) with respect to 100% by mass of the aqueous solution of the present invention include 20, 19, 16, 15, 13, 11% by mass, and examples of the lower limit are 19, 16, 15, 13 , 11, 10% by mass and the like. The upper and lower limits of the component (A) are not limited to the above values. The range of the content of the component (A) with respect to 100% by mass of the aqueous solution of the present invention can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the content of the component (A) with respect to 100% by mass of the aqueous solution of the present invention is preferably 10 to 20% by mass.

(Method for manufacturing component (A))
The component (A) can be synthesized by a radical polymerization method by various known methods. An aqueous solution radical polymerization method is preferable. Specifically, a radical polymerization initiator and, if necessary, another polymerization reagent are added to the monomer mixture containing the components (a) and (b) and, if necessary, the component (c), and the mixture is stirred. The polymerization reaction may be carried out at a reaction temperature of about 50 to 100 ° C. The reaction time is not particularly limited, and is preferably about 1 to 10 hours. The aqueous solution containing the component (A) thus obtained can be used as it is as the binder aqueous solution of the present invention.

As the radical polymerization initiator, various known ones can be used without particular limitation. Examples of the radical polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; redox-based polymerization initiators in which the above-mentioned persulfates and reducing agents such as sodium bisulfite are combined; and azo-based initiators. Be done. The amount of the radical polymerization initiator used is not particularly limited, but is about 0.05 to 2% by mass, preferably about 0.1 to 1.5% by mass, based on the total mass of the monomer group giving the component (A). In this case, the polymerization reaction proceeds sufficiently, and the component (A) can be made high molecular weight.

Ammonia, organic amines, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. are commonly used before the radical polymerization reaction or when the obtained component (A) is solubilized in water for the purpose of improving production stability. The pH may be adjusted with a neutralizing agent. In that case, the pH is preferably adjusted to the range of about 5 to 11. Further, for the same purpose, EDTA, which is a metal ion encapsulant, or a salt thereof or the like can be used.

Examples of other polymerization reagents include chain transfer agents and the like. Examples of the chain transfer agent include thiol-based chain transfer agents, amine-based chain transfer agents, alcohol-based chain transfer agents, and the like, which are known as general chain transfer agents. From the viewpoint of deterioration of output characteristics and cycle characteristics, the amount of the chain transfer agent used is preferably about 0.1 to 1.5% by mass, more preferably 0% by mass, based on the total mass of the monomer group giving the component (A). preferable.

(Physical characteristics)
The weight average molecular weight (Mw) of the component (A) is not particularly limited, but examples of the upper limit of the weight average molecular weight (Mw) are 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, and 3 million. , 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, etc. Examples of lower limits are 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.9 million, 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000. , 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000 and the like. The upper and lower limits of the weight average molecular weight (Mw) are not limited to the above values. The range of the weight average molecular weight (Mw) can be set as appropriate (for example, by selecting from the upper and lower limit values). In one embodiment, the weight average molecular weight (Mw) of the component (A) is preferably 300,000 to 6 million from the viewpoint of dispersion stability of the electrode slurry.

Examples of the upper limit of the number average molecular weight (Mn) of the component (A) are 6 million, 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.5 million, 2 million, 1.5 million, 1 million. , 950,000, 900,000, 850,000, 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 300,000, 200,000, 100,000, 50,000, etc. Examples of lower limits are 5.5 million, 5 million, 4.5 million, 4 million, 3.5 million, 3 million, 2.9 million, 2.5 million, 2 million, 1.5 million, 1 million, 950,000, 900,000, 850,000. , 800,000, 750,000, 700,000, 650,000, 600,000, 550,000, 500,000, 450,000, 400,000, 350,000, 300,000, 200,000, 100,000, 10,000, etc. The upper and lower limits of the number average molecular weight (Mn) are not limited to the above values. The range of the number average molecular weight (Mn) can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the number average molecular weight (Mn) of the component (A) is preferably 10,000 or more from the viewpoint of dispersion stability of the electrode slurry.

The weight average molecular weight and the number average molecular weight are calculated as polyacrylic acid equivalent values measured under 0.2 M phosphate buffer / acetonitrile solution (90/10, PH 8.0), for example, by gel permeation chromatography (GPC). Can be done.

Examples of the upper limit of the molecular weight distribution (Mw / Mn) of the component (A) include 7, 6, 5, 4, 3, 2, and the like, and examples of the lower limit include 6, 5, 4, 3, 2. 1st grade can be mentioned. The upper and lower limits of the molecular weight distribution (Mw / Mn) are not limited to the above values. The range of the molecular weight distribution (Mw / Mn) can be appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the molecular weight distribution (Mw / Mn) of the component (A) is preferably 1 to 7 from the viewpoint of dispersion stability of the electrode slurry.

Examples of the upper limit of the B-type viscosity at 25 ° C. and 15% by mass of the solid content of the binder aqueous solution are 70,000, 65,000, 60,000, 55,000, 50,000, 45,000, 40,000. , 35,000, 30,000, 25,000, 20,000, 15,000, 11,000 mPa · s, etc. Examples of the lower limit are 69,000, 65,000, 60,000, 55. 000, 50,000, 45,000, 40,000, 35,000, 30,000, 25,000, 20,000, 15,000, 11,000, 10,000 mPa · s and the like. The upper and lower limits of the B-type viscosity are not limited to the above values. The range of the B-type viscosity at 25 ° C. and 15% by mass of the solid content of the binder aqueous solution can be appropriately set (for example, selected from the above upper and lower limit values). The B-type viscosity can be adjusted by the amount of the solvent of the aqueous solution containing the component (A). In one embodiment, the B-type viscosity of the aqueous binder solution at 25 ° C. and 15% by mass of solid content is 10,000 to 70,000 mPa · s from the viewpoint of reducing the capacity of the lithium ion battery. When the viscosity is less than 10,000 mPa · s, the amount of the component (1) in the slurry is relatively large in order to set the viscosity of the slurry obtained by using the binder in an appropriate range. It causes a decrease in the capacity of the lithium ion battery obtained by using the slurry. Further, in this case, the adhesion between the coating film made of the slurry and the metal foil which is a current collector tends to decrease. On the other hand, when the viscosity exceeds 70,000 mPa · s, a gel-like substance is likely to be generated in the binder aqueous solution and the slurry, and defects and voids tend to increase in the electrode. Further, when the aqueous binder solution is spray-dried to be powdered, it tends to be in the form of fibers without being powdered.

(Additive)
The aqueous binder solution for a lithium ion battery can contain an agent other than the component (a), the component (b), the component (A), and water as additives. Examples of additives include dispersants, leveling agents, antioxidants, thickeners, dispersions (emulsions) and the like. Examples of the content of the additive are 0 to 10% by mass, less than 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, based on 100% by mass of the component (A). 0% by mass and the like, and 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, 0% by mass and the like with respect to 100% by mass of the aqueous solution.

The dispersant can be selected according to the type of the positive electrode active material and the conductive agent, and examples thereof include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds.

Examples of the leveling agent include alkyl-based surfactants, silicon-based surfactants, fluorine-based surfactants, and surfactants such as metal-based surfactants. By using a surfactant, it is possible to prevent repelling generated during coating and improve the smoothness of the electrode.

Examples of antioxidants include phenol compounds, hydroquinone compounds, organophosphorus compounds, sulfur compounds, phenylenediamine compounds, polymer-type phenol compounds and the like. The polymer-type phenol compound is a polymer having a phenol structure in the molecule, and a polymer-type phenol compound having a weight average molecular weight of preferably 200 to 1000, more preferably 600 to 700 is used.

Examples of thickeners include cellulose-based polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose and their ammonium salts and alkali metal salts; (modified) poly (meth) acrylic acid and these ammonium salts and alkali metal salts; (Modified) Polyvinyl alcohol, acrylic acid or a polymer of acrylic acid and vinyl alcohol, polyvinyl alcohol such as maleic anhydride or a polymer of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, Examples thereof include modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydrogenated additives and the like.

(2. Powdery binder for positive electrode of lithium ion battery)
The powdery binder for a positive electrode of a lithium ion battery of the present invention (hereinafter, also referred to as a powdery binder) is a powder obtained by spray-drying an aqueous binder solution of the present invention. By doing so, long-term storage becomes possible, which is advantageous in terms of transportation costs.

The spray-drying method is not particularly limited, and various known methods can be adopted. Examples of the spray-drying method include a spray-drying granulation method and a kneading granulation method. Further, as the former method, for example, the method described in Japanese Patent Application Laid-Open No. 2016-091904 can be mentioned. According to the spray-drying method, a powdery binder having a uniform particle size can be obtained. Further, since the powdery binder is easily redissolved in water, a uniform binder aqueous solution is provided.

(3. Lithium-ion battery positive electrode slurry)
The first aspect of the lithium ion battery positive electrode slurry (hereinafter, also referred to as slurry) of the present invention is a composition containing the binder aqueous solution and the cathode active material (B) (hereinafter, also referred to as (B) component) according to the present invention. The second aspect is a composition containing the powdery binder, water, and the positive electrode active material (B) according to the present invention. In the present disclosure, "slurry" means a suspension of liquid and solid particles.

(Positive electrode active material (B) (hereinafter, also referred to as component (B)))
The component (B) is roughly classified into an active material containing an inorganic compound and an active material containing an organic compound. Examples of the inorganic compound contained in the positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals, transition metal sulfides, and the like. Examples of the above transition metals include Fe, Co, Ni, Mn, Al and the like. Examples of inorganic compounds used for positive electrode active materials are LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _1/2 Mn _3/2 O ₄ , LiCo _1/3 Ni _1/3. Lithium-containing composite metal oxides such as Mn _1/3 O ₂ , Li [Li _0.1 Al _0.1 Mn _1.9 ] O ₄ , LiFeVO ₄ ; transitions of _{TiS 2} , TiS ₃ , amorphous MoS _{2, etc.} Metal sulfides; transition metal oxides such as _{Cu 2} V ₂ O ₃ , amorphous V ₂ O-P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _{13 and the like.} These compounds may be partially elementally substituted. Examples of the organic compound contained in the positive electrode active material include conductive polymers such as polyacetylene and poly-p-phenylene. An iron-based oxide having poor electrical conductivity may be used as an electrode active material covered with a carbon material by allowing a carbon source material to be present at the time of reduction firing. Further, these compounds may be partially elementally substituted. _{Among these, LiCoO 2} , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _1/2 Mn _3/2 O ₄ , LiCo _1/3 are preferable in terms of practicality, electrical characteristics, and long life. Ni _1/3 Mn _1/3 O ₂ and Li [Li _0.1 Al _0.1 Mn _1.9 ] O ₄ are used as the positive electrode active material.

The content of the component (A) in the slurry of the present invention is not particularly limited, but examples of the upper limit of the component (A) with respect to 100% by mass of the component (B) are 8, 7, 6, 5, 4, 3, 2. Mass% and the like can be mentioned, and examples of the lower limit include 7, 6, 5, 4, 3, 2, 1 mass% and the like. The upper and lower limits of the component (A) are not limited to the above values. The range of the content of the component (A) in the slurry can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the content of the component (A) is preferably about 1 to 8% by mass, and more preferably about 1 to 5% by mass with respect to 100% by mass of the component (B). Within the above range, the dispersibility of the component (B) in the slurry of the present invention is improved, and the adhesion between the active material layer and the current collector in the positive electrode obtained from the slurry of the present invention tends to be improved. It is in.

The content of the component (B) with respect to 100% by mass of the slurry of the present invention is not particularly limited. Examples of the upper limit of the content of the component (B) with respect to 100% by mass of the slurry of the present invention include 65, 60, 55, 50, 45% by mass, and examples of the lower limit include 60, 55, 50, and so on. 45, 40% by mass and the like can be mentioned. The upper and lower limits of the component (B) are not limited to the above values. The range of the content of the component (B) with respect to 100% by mass of the slurry of the present invention can be appropriately set (for example, selected from the above upper and lower limit values). The content of the component (B) with respect to 100% by mass of the slurry of the present invention is preferably 40 to 65% by mass.

The content of water in the slurry of the present invention is also not particularly limited. Examples of the upper limit of the solid content concentration of the slurry include 60, 55, 50, 45, 40% by mass and the like, and examples of the lower limit include 55, 50, 45, 40, 35% by mass and the like. Be done. The upper and lower limits of the solid content concentration are not limited to the above values. The range of solid content concentration can be set as appropriate (for example, by selecting from the above upper and lower limit values). In one embodiment, the solid content concentration range of the slurry is preferably 35-60% by mass.

(Conductive aid)
The slurry of the present invention may contain a conductive auxiliary agent depending on the purpose. Examples of conductive auxiliaries include fibrous carbon such as vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), and carbon nanofiber (CNF), graphite particles, carbon such as acetylene black, ketjen black, and furnace black. Examples thereof include black, fine powder made of Cu, Ni, Al, Si having an average particle size of 10 μm or less, or an alloy thereof. The amount of the conductive auxiliary agent used is not particularly limited, but is preferably 0 to 10% by mass, more preferably 0.5 to 6% by mass, based on the component (B).

(Non-aqueous medium)
The slurry of the present invention may contain a non-aqueous medium having a standard boiling point of 80 to 350 ° C. for the purpose of improving coating workability. Examples of non-aqueous media having a standard boiling point of 80 to 350 ° C. include amide media such as N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide; toluene, xylene, etc. Carboxide medium such as n-dodecane, tetralin; alcohol medium such as 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol; ketone medium such as methyl ethyl ketone, cyclohexanone, holone, acetphenone, isophorone; benzyl acetate, isopentyl butyrate, etc. Ester media such as methyl lactate, ethyl lactate, butyl lactate; amine media such as o-toluidine, m-toluidine, p-toluidine; lactone media such as γ-butyrolactone and δ-butyrolactone; The medium and the like can be mentioned. Among these, N-methyl-2-pyrrolidone (NMP) is preferable from the viewpoint of coating workability. The amount of the non-aqueous medium used is not particularly limited, but is preferably about 0 to 10% by mass with respect to the slurry of the present invention.

In the slurry of the present invention, a component (A), a component (B), a component (a), a component (b), water, a conductive auxiliary agent, an agent other than a non-aqueous medium (dispersant, leveling agent, antioxidant, Thickener, etc.) may be included as an additive. The amount of the additive used is not particularly limited, but is about 0 to 10% by mass with respect to 100% by mass of the component (A), less than 5% by mass, less than 1% by mass, less than 0.1% by mass, 0.01% by mass. Less than 1% by mass, less than 5% by mass, less than 1% by mass, less than 0.1% by mass, less than 0.01% by mass, etc. with respect to 100% by mass of the slurry.

(4. Positive electrode for lithium-ion batteries)
The positive electrode for a lithium ion battery of the present invention (hereinafter, also referred to as a positive electrode) is a cured product obtained by applying the slurry of the present invention to a current collector and drying it, that is, a cured product of the slurry according to the present invention.

As the current collector, various known ones can be used without particular limitation. The material of the current collector is not particularly limited, and examples thereof include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, and carbon materials such as carbon cloth and carbon paper. Of these, metal materials are preferable, and aluminum is particularly preferable. The form of the current collector is also not particularly limited, and in the case of a metal material, a metal foil, a metal column, a metal coil, a metal plate, an expanded metal, a punch metal, a foam metal, etc., and in the case of a carbon material, a carbon plate, a carbon thin film, etc. Examples include carbon cylinders. Of these, metal leaf is preferable because it is currently used in industrialized products.

The coating means is not particularly limited, and examples thereof include conventionally known coating devices such as a comma coater, a gravure coater, a micro gravure coater, a die coater, and a bar coater.

The drying means is not particularly limited, and the temperature is preferably about 60 ° C. to 200 ° C., more preferably about 100 ° C. to 195 ° C., and the atmosphere may be dry air or an inert atmosphere.

The thickness of the electrode (cured coating film) is not particularly limited, but is preferably about 5 μm to 300 μm, and more preferably about 10 μm to 250 μm. Within the above range, it becomes easy to obtain a sufficient function of storing and releasing Li with respect to a high-density current value while ensuring the smoothness of the coating film.

The content of the component (A) in the positive electrode of the present invention is not particularly limited, but is preferably about 0.1 to 8% by mass, more preferably about 0.5 to 5% by mass in terms of solid content. Within the above range, the capacity and energy density at the time of high output can be suitably improved.

(5. Lithium-ion battery)
The lithium ion battery of the present invention is an article containing the positive electrode of the present invention. The other members of the battery, that is, the electrolyte solution, the negative electrode, the separator, and the packaging material are not particularly limited.

(Electrolyte solution)
As the electrolyte solution, a non-aqueous electrolyte solution in which the supporting electrolyte is dissolved in a non-aqueous solvent is used. Further, the film-forming agent may be included in the non-aqueous electrolyte solution.

As the non-aqueous solvent, various known ones can be used without particular limitation. For example, chain carbonates such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate; chain ethers such as 1,2-dimethoxyethane; tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane and the like. , 1,3-Dioxolane and other cyclic ethers; chain esters such as methyl formate, methyl acetate and methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone; acetonitrile and the like. Any one of these non-aqueous solvents may be used alone, or two or more thereof may be mixed and used, but a combination of a mixed solvent containing a cyclic carbonate and a chain carbonate is preferable.

A lithium salt is used as the supporting electrolyte. The lithium salt is not particularly limited, but LiPF ₆ , _{LiAsF 6} , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF _3). CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi and the like can be mentioned. _{Of these, LiPF 6} , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and show a high degree of dissociation, are preferable. These may be used in combination of two or more. Since the lithium ion conductivity becomes higher as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

As the film forming agent, various known ones can be used without particular limitation. Specifically, carbonate compounds such as vinylene carbonate, vinylethylene carbonate, vinylethyl carbonate, methylphenyl carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; alkene sulfides such as ethylene sulfide and propylene sulfide; 1,3-propane sulton, 1 , 4-Butane sulton and other sulton compounds; examples thereof include maleic acid anhydride, succinic acid anhydride and other acid anhydrides. The amount of the film-forming agent used in the electrolyte solution is not particularly limited, but is preferably 10% by mass or less, 8% by mass or less, 5% by mass or less, and 2% by mass or less in that order. By setting the amount to be used as described above, it becomes easy to obtain the advantages of the film forming agent, such as suppression of initial irreversible capacity and improvement of low temperature characteristics and rate characteristics.

(Negative electrode)
As the negative electrode, various known ones can be used without particular limitation. For example, a slurry is prepared by mixing a negative electrode active material, a conductive auxiliary agent, and a binder with an organic solvent, and the prepared slurry is applied to a current collector, dried, and pressed.

Examples of negative electrode active materials include silicon particles, artificial graphite, natural graphite, graphite such as graphite fluoride, and carbonaceous materials including amorphous carbon, mesocarbon microbeads, pitch-based carbon fibers, etc .; conductivity such as polyacene. Sex polymer; metals such as tin, zinc, manganese, iron, nickel or alloys thereof; oxides and sulfates of the above metals or alloys; metallic lithium, Li-Al, Li-Bi-Cd, Li-Sn- Lithium alloys such as Cd; lithium transition metal nitrides and the like can be mentioned.

(Separator)
The separator is an article interposed between the positive electrode and the negative electrode, and is used to prevent a short circuit between the electrodes. Specifically, a porous separator such as a porous membrane or a non-woven fabric can be preferably used, and they are impregnated with the non-aqueous electrolyte solution and used. As the material of the separator, polyolefins such as polyethylene and polypropylene, polyether sulfone and the like are used, and polyolefins are preferably used.

The shape of the lithium ion battery of the present invention is also not particularly limited, and examples thereof include a square type, a cylindrical type, and a pouch type. Specific examples include a cylinder type in which the sheet electrode and the separator are spirally formed, a cylinder type having an inside-out structure in which the pellet electrode and the separator are combined, a coin type in which the pellet electrode and the separator are laminated, and the like. Further, by storing the batteries of these forms in an arbitrary outer case, they can be used in any shape such as a coin type, a cylindrical type, and a square type.

The method for manufacturing the lithium ion battery of the present invention is not particularly limited, and the lithium ion battery may be assembled by an appropriate procedure according to the structure of the battery. For example, a negative electrode can be placed on an outer case, an electrolytic solution and a separator can be provided on the negative electrode, a positive electrode can be placed so as to face the negative electrode, and the battery can be fixed by a gasket and a sealing plate.

Hereinafter, the method of the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In the examples, “%” indicates “mass%” and “parts” indicates “parts by mass” unless otherwise specified.

(1) B-type viscosity The viscosity of each aqueous binder solution was measured at 25 ° C. under the following conditions using a B-type viscometer (product name "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.).
When the viscosity is 100,000 to 20,000 mPa · s: No. 4 rotors used, rotation speed 6 rpm
When the viscosity is less than 20,000 mPa · s: No. 3 rotors used, rotation speed 6 rpm

1.1. Preparation of Binder Aqueous Solution Example 1-1
2300 g of ion-exchanged water, 400 g of acrylamide (5.63 mol), and 9.0 g of sodium metharylsulfonate (0.057 mol) were placed in a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube. After removing oxygen in the reaction system through nitrogen gas, the temperature was raised to 50 ° C. 4.0 g of 2,2'-azobis-2-amidinopropane dihydrochloride (product name "NC-32" manufactured by Nippoh Chemicals, Inc.) and 30 g of ion-exchanged water were added thereto, and the temperature was raised to 80 ° C. 1 The reaction was carried out for 5 hours. Next, 4.0 g of NC-32 and 30 g of ion-exchanged water were added and reacted at 80 ° C. for 1.5 hours to contain poly (meth) acrylamide (A) at 25 ° C. and a solid content of 15.0% by mass. A binder aqueous solution having a B-type viscosity of 35,000 mPa · s was obtained.

Examples 1-2-1-6, Comparative Examples 1-1-1-5
In the above Example 1-1, an aqueous solution containing poly (meth) acrylamide (A) was prepared in the same manner as in Example 1-1 except that the monomer composition and the amount of the initiator were changed to those shown in Table 1 and numerical values. Prepared.

・ＡＭ：アクリルアミド
・ＮＭＡＭ：Ｎ−メチロールアクリルアミド
・ＡＴＢＳ：アクリルアミドｔ−ブチルスルホン酸
・ＳＭＡＳ：メタリルスルホン酸ナトリウム
・ＭＡＳ：メタリルスルホン酸
・ＶＳ：ビニルスルホン酸
・ＡＡ：アクリル酸
・ＥＡ：アクリル酸エチル
・ＨＥＭＡ：メタクリル酸２−ヒドロキシエチル
・ＡＮ：アクリロニトリル
・ＭＰＡ：３−メルカプトプロピオン酸

・ AM: Acrylamide ・ NMAM: N-methylolacrylamide ・ ATBS: Acrylamide t-butylsulfonic acid ・ SMAS: Sodium methacrylic sulfonic acid ・ MAS: Metallyl sulfonic acid ・ VS: Vinyl sulfonic acid ・ AA: Acrylic acid ・ EA: Acrylic Ethyl acrylate, HEMA: 2-hydroxyethyl methacrylate, AN: acrylonitrile, MPA: 3-mercaptopropionic acid

1.2. Production Example 1-7 of Powdery Binder
The aqueous solution of poly (meth) acrylamide (A) of Example 1-1 was pulverized using a spray dryer (Pulvis GB22 manufactured by Yamato Scientific Co., Ltd.). The drying conditions were a dry air flow rate: 0.45 m ³ / min, an inlet temperature: 180 ° C., an outlet temperature: 80 ° C., a spray pressure: 1.0 kgf / cm ² , and a solution supply amount: 500 mL / hour. The obtained powder was added to a cylindrical glass container containing ion-exchanged water in an amount of 15% by mass while stirring with a flat spring to dissolve the powder.

2. Production and Evaluation of Slurry for Positive Electrode Example 2-1
Using a commercially available rotating and revolving mixer (product name "Awatori Rentaro", manufactured by Shinky Co., Ltd.), put 3 parts of the binder aqueous solution of Example 1 in terms of solid content in a container dedicated to the mixer, and use it as an electrode active material. 91 parts of lithium nickel manganate (Li [Ni _1/2 Mn _3/2 ] O ₄ , median diameter D50: 3.7 μm) and 6 parts of acetylene black were mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 50%, and the container was set in the mixer. Then, after kneading at 2000 rpm for 10 minutes, defoaming was performed for 1 minute to obtain a slurry for a positive electrode.

Examples 2-2-2-7, Comparative Examples 2-1-2-5
A slurry for a positive electrode was obtained in the same manner as in Example 2-1 except that the aqueous binder solution was changed as shown in Table 2.
<Slurry dispersibility evaluation>
The dispersibility immediately after the slurry was prepared was visually evaluated according to the following criteria.
⊚: The whole is a homogeneous paste, there is no liquid separation, and no agglomerates are observed.
◯: The whole is a substantially homogeneous paste, and slight liquid separation is observed, but no agglomerates are observed.
Δ: A small amount of agglomerates and a slightly large amount of liquid separation were observed at the bottom of the container.
X: Many clay-like aggregates are observed at the bottom of the container, and many liquid separations are also observed.

3. 3. Production and Evaluation of Positive Electrodes Example 3-1 Preparation of Positive Electrodes for Lithium Ion Batteries On the surface of a current collector made of aluminum foil, the slurry for positive electrodes prepared in Example 2-1 above was dried to a thickness of 110 μm. The electrodes were uniformly applied by the doctor blade method, dried at 60 ° C. for 30 minutes, and then heat-treated at 150 ° C./vacuum for 120 minutes to obtain electrodes. Then, a positive electrode was obtained by press working with a roll press machine so that the density of the film (active material layer) was 3.0 g / cm ^3. The flexibility of the electrodes was evaluated, and the results are also shown in Table 2.

<Flexibility>
The electrode was cut into a width of 10 mm and a length of 70 mm, wound around a Teflon (registered trademark) rod having a diameter of 6 mmφ with the active material layer on the outside, and the state of the surface of the active material layer was observed and evaluated according to the following criteria.
⊚: No cracks or peeling occurred in the active material layer bonded on the current collector.
◯: Cracks are seen in the active material layer bonded on the current collector, but no peeling is observed.
Δ: Cracks are observed in the active material layer bonded on the current collector, and some peeling is also observed.
X: The active material layer bound on the current collector was cracked and peeled off more than Δ.

Examples 3-2-3-7, Comparative Examples 3-1-3-5
In Example 3-1 above, a lithium ion battery positive electrode was obtained in the same manner as in Example 3-1 except that the slurry for the positive electrode of the lithium ion battery was changed as shown in Table 2. The flexibility of the electrodes was evaluated, and the results are also shown in Table 2.

4. Assembly and Evaluation of Lithium Ion Battery Cell Example 4-1 Preparation of Lithium Ion Battery (1) Assembly of Lithium Ion Battery Cell In a glove box substituted with argon, the positive electrode manufactured above is punched and molded to a diameter of 16 mm. , Placed on a 2-pole coin cell (manufactured by Hosen Co., Ltd., trade name "HS flat cell"). Next, a separator made of a polypropylene porous film punched to a diameter of 24 mm (CS TECH CO., Made by LTD, trade name "Selion P2010") was placed, and further, 500 μL of an electrolytic solution was injected so as not to allow air to enter. A lithium ion battery cell was assembled by placing a commercially available metallic lithium negative electrode punched and molded to 16 mm and sealing the exterior body of the bipolar coin cell with a screw. _{The electrolytic solution used here is a solution in which LiPF 6} is dissolved in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio) at a concentration of 1 mol / L.

(2) Measurement of initial discharge capacity and residual capacity ratio The lithium-ion battery cell manufactured above was placed in a constant temperature bath at 25 ° C., charging was started at a constant current (0.5C), and the voltage became 5.0V. At that point, charging was completed (cutoff). Next, discharging is started at a constant current (0.5C), and charging / discharging is repeated 50 times to complete the discharge (cutoff) when the voltage reaches 3.0 V, and the battery capacity of the first cycle and 50 cycles are repeated. The battery capacity of the eye was measured. The battery capacity of the first cycle was used as the initial capacity. Further, the ratio of the battery capacity in the 50th cycle to the battery capacity in the 1st cycle was expressed as a percentage, and this was taken as the capacity retention rate. The results are also shown in Table 2.

In the above measurement conditions, "1C" indicates a current value at which a cell having a certain electric capacity is discharged with a constant current and the discharge is completed in 1 hour. For example, "0.1C" is a current value at which the discharge is completed over 10 hours, and "10C" is a current value at which the discharge is completed over 0.1 hours.

Examples 4-2-4-7, Comparative Examples 4-1 to 4-5 Preparation of Lithium Ion Battery Example 4 except that the positive electrode of the lithium ion battery was changed as shown in Table 2 in Example 4-1 above. A lithium ion battery cell was obtained in the same manner as in -1. The measurement of the initial discharge capacity and the remaining capacity ratio was measured, and the results are also shown in Table 2.

As is clear from Table 2, all of the slurry solutions for positive electrodes of Examples 1-1 to 1-7 had a good evaluation of slurry dispersibility. All of the positive electrodes of Examples 2-1 to 2-7 using these slurry solutions for positive electrodes had a good evaluation of electrode flexibility. All of the cells for lithium ion batteries of Examples 3-1 to 3-7 using these positive electrodes had good initial discharge capacity and capacity retention rate.

On the other hand, (b) a lithium ion battery positive electrode binder aqueous solution having a large amount of components (Comparative Examples 1-1, 1-3, 1-4) and (b) a thium ion battery positive electrode binder aqueous solution having a small amount of components (Comparative Example 1-). In the cases of 2 and 1-5), the dispersibility of the positive electrode slurry produced using these, the evaluation of the electrode flexibility of the positive electrode, the initial discharge capacity of the lithium ion battery cell, and the capacity retention rate were inferior.

5. Preparation of Laminated Lithium Ion Battery A laminated lithium ion battery was prepared as follows using the slurry of Example 2-1.
(1) Preparation of Positive Electrode The positive electrode slurry prepared in Example 2-1 above is uniformly applied to the surface of a current collector made of aluminum foil by a doctor blade method so that the film thickness after drying is 110 μm. Then, after drying at 60 ° C. for 30 minutes, heat treatment was performed at 150 ° C./vacuum for 120 minutes to obtain an electrode. Then, a positive electrode was obtained by press working with a roll press machine so that the density of the film (active material layer) was 3.0 g / cm ^3.

(2) Preparation of negative electrode 88 parts by mass of natural graphite (product name "Z-5F" manufactured by Ito Graphite Industry Co., Ltd.) as the negative electrode active material and 6 parts by mass of polyvinylidene fluoride (product name "HSV900") of polyvinylidene fluoride as a binder , And this mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry for the negative electrode of a lithium ion battery. Next, a copper foil was prepared as a current collector for the negative electrode, a slurry for the negative electrode of a lithium ion battery was placed on the copper foil, and the slurry was applied so as to form a film using a doctor blade. The aluminum foil after applying the lithium ion battery positive electrode slurry was dried at 80 ° C. for 20 minutes to volatilize and remove the NMP, and then closely joined by a roll press machine. At this time, the density of the negative electrode active material layer was set to 1.5 g / cm ² . The bonded material was heated at 120 ° C. for 6 hours in a vacuum dryer and cut into a predetermined shape (25 mm × 30 mm rectangular shape) to obtain a negative electrode having a negative electrode active material layer having a thickness of about 45 μm.

(3) Production of Laminated Lithium Ion Battery A laminated lithium ion secondary battery was produced using the above positive and negative electrodes. Specifically, a rectangular sheet (27 x 32 mm, thickness 25 μm) of a separator (CS TECH CO., Made by LTD, trade name “Selion P2010”) made of a polypropylene porous film is sandwiched between the positive electrode and the negative electrode. It was made into a group of electrode plates. The electrode plates were covered with a set of two laminated films, the three sides were sealed, and then the electrolytic solution was injected into the bag-shaped laminated film. _{As the electrolytic solution, a solution prepared by dissolving LiPF 6} at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio) was used. Then, by sealing the remaining one side, a laminated lithium ion secondary battery was obtained in which the four sides were hermetically sealed and the electrode plate group and the electrolytic solution were sealed. The positive electrode and the negative electrode are provided with tabs that can be electrically connected to the outside, and a part of the tabs extends to the outside of the laminated lithium ion secondary battery. When the laminated lithium-ion battery produced in the above steps was energized, no operational problem occurred.

Claims (8)

It contains poly (meth) acrylamide (A), which is a radical copolymer of a monomer group containing a (meth) acrylamide skeleton-containing monomer (a) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b), and 25. ° C., wherein the poly (meth) acrylamides (a) and the measured B-type viscosity the aqueous solution of solid content of 15 wt% consisting of water Ri 10,000~70,000mPa · s der, the B-type viscosity,
Using a B-type viscometer (product name "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.), at 25 ° C.
When the viscosity is 100,000 to 20,000 mPa · s: No. 4 rotors used, rotation speed 6 rpm
When the viscosity is less than 20,000 mPa · s: No. 3 rotors used, rotation speed 6 rpm
Binder aqueous solution for positive electrode of lithium ion battery measured under the condition. The content of the component (b) in the monomer group is 0.01 to 1 . The binder aqueous solution for a positive electrode of a lithium ion battery according to claim 1, which is 0 mol%. A powdery binder for a positive electrode of a lithium ion battery obtained by spray-drying the aqueous binder solution for the positive electrode of a lithium ion battery according to claim 1 or 2. A slurry for a positive electrode of a lithium ion battery containing the aqueous binder solution for the positive electrode of a lithium ion battery according to claim 1 or 2 and the positive electrode active material (B). A slurry for a positive electrode of a lithium ion battery, which comprises the powdery binder for the positive electrode of a lithium ion battery according to claim 3, water, and the positive electrode active material (B). The slurry for a positive electrode of a lithium ion battery according to claim 4 or 5, wherein the content of the poly (meth) acrylamide (A) is 1 to 8 parts by mass with respect to 100 parts by mass of the positive electrode active material (B). A positive electrode for a lithium ion battery obtained by applying the slurry for a positive electrode for a lithium ion battery according to any one of claims 4 to 6 to a current collector and drying the slurry. A lithium ion battery including the lithium ion battery positive electrode according to claim 7.