JP2021158125A - Slurry for lithium ion battery negative electrode and production method thereof, negative electrode for lithium ion battery, and lithium ion battery - Google Patents

Abstract

To provide a slurry for a lithium ion battery negative electrode and a production method thereof, a negative electrode for a lithium ion battery, and a lithium ion battery.SOLUTION: A slurry for a lithium ion battery negative electrode comprises: a negative electrode active material (A) including 20 mass% or more of silicon particles (a1) of 0.1-2 μm in median diameter (D50); a poly(meth)acrylamide (B1) consisting of a radical copolymer of a group of monomers including (meth)acrylamide skeleton-containing monomer (b1) and a sulfonate group-substituted unsaturated hydrocarbon group-containing monomer (b2), and having B-type viscosity of 10,000-70,000 mPa s in the state of an aqueous solution of 15 mass% in solid content at 25°C; and water.SELECTED DRAWING: None

Description

The present invention relates to a slurry for a negative electrode of a lithium ion battery and a method for producing the same, a negative electrode for a lithium ion battery, and a lithium ion battery.

Lithium-ion batteries are small and lightweight, have high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, in recent years, improvement of battery members such as electrodes has been studied for the purpose of further improving the performance of lithium ion batteries.

For both the positive electrode and the negative electrode of a lithium ion battery, a slurry obtained by dispersing an active material and a binder resin in a solvent is applied on both sides of a current collector (for example, a metal foil), and the solvent is dried and removed to remove an electrode layer. After forming the above, it is produced by compression molding with a roll press machine or the like.

By the way, in recent years, as a negative electrode for a lithium ion battery, a silicon-based negative electrode active material has been proposed as a negative electrode active material from the viewpoint of increasing the battery capacity. However, the negative electrode active material including the silicon-based negative electrode active material tends to expand and contract with charging and discharging. In that case, the negative electrode for the lithium ion battery undergoes a volume change from the initial stage of repeated charging and discharging. As a result, electrical characteristics such as cycle characteristics of lithium-ion batteries tend to deteriorate.

Therefore, in the art, studies have been made to solve the above problems with a binder resin, and for example, polyimide (Patent Document 1) and polyacrylic acid (Patent Document 2) are known. Further, Patent Document 3 discloses a negative electrode slurry containing polyacrylamide and an active material having a predetermined average particle size, and it is said that a silicon material such as silicon or silicon oxide is preferable as the active material.

Japanese Unexamined Patent Publication No. 2013-08437 Japanese Unexamined Patent Publication No. 2005-216502 Japanese Unexamined Patent Publication No. 2015-106488

However, the polyimide described in Patent Document 1 is obtained by dissolving a polyamic acid as a precursor in a solvent containing an organic solvent such as N-methyl-2-pyrrolidone (NMP) to obtain a binder resin slurry. The use of an organic solvent such as NMP has an extremely large environmental load during coating and drying as compared with the case of using an aqueous solvent in mass production due to an increase in demand in the future.

Further, the polyacrylic acid described in Patent Document 2 has a problem that the initial discharge capacity is lowered because the lithium ion occluded in the active material is taken into the carboxyl group thereof at the time of charging.

Further, in the slurry described in Patent Document 3, since the average particle size of silicon, which is a negative electrode active material, is relatively large, the volume change during charging and discharging becomes particularly large, and it is difficult to form a conductive path between the active materials. become. In this respect, when silicon particles having a small average particle size are used, there is a problem that the dispersibility of the slurry is deteriorated and the cycle characteristics are deteriorated.

Therefore, the problem to be solved by the present invention is to provide a negative electrode having good flexibility, and a slurry for a negative electrode for a lithium ion battery which can manufacture a lithium ion battery having good electrical characteristics and springback resistance and has good dispersibility. I will do it.

Further, a further problem to be solved by the present invention is to provide a method for producing a slurry for a negative electrode of a lithium ion battery, a negative electrode for a lithium ion battery, and a lithium ion battery.

As a result of diligent studies to solve the above problems, the present inventors have used silicon particles having a relatively small average particle size as a negative electrode active material, and a predetermined unsaturated monomer as a dispersant thereof as a constituent component. , It has been found that a slurry capable of solving the above-mentioned problems can be obtained by using poly (meth) acrylamide having predetermined physical properties, and the present invention has been completed.

The disclosure provides the following items:
(Item 1)
A negative electrode active material (A) containing 20% by mass or more of silicon particles (a1) having a median diameter (D50) of 0.1 to 2 μm.
(Meta) A radical copolymer of a group of monomers containing an acrylamide skeleton-containing monomer (b1) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2), and in an aqueous state with a solid content of 15% by mass at 25 ° C. In poly (meth) acrylamide (B1), which has a B-type viscosity of 10,000 to 70,000 mPa · s,
Slurry for negative electrode of lithium ion battery containing water.
(Item 2)
The slurry for a negative electrode of a lithium ion battery according to the above item, wherein the content of the component (b2) in the monomer group is 0.01 to 1 mol%.
(Item 3)
The method for producing a slurry for a negative electrode of a lithium ion battery according to any one of the above items, which comprises a step of mixing the negative electrode active material (A), the poly (meth) acrylamide (B1), and water.
(Item 4)
The step of obtaining powdered poly (meth) acrylamide (B2) by spray-drying the poly (meth) acrylamide (B1), the negative electrode active material (A), and the poly (meth) acrylamide (B2). , The method for producing a slurry for a negative electrode of a lithium ion battery according to any one of the above items, which comprises a step of mixing with water.
(Item 5)
A current collector is a lithium ion battery negative electrode slurry obtained by the method for producing a lithium ion battery negative electrode slurry according to any one of the above items or a lithium ion battery negative electrode slurry according to any one of the above items. Negative electrode for lithium-ion batteries, obtained by applying to and drying.
(Item 6)
A lithium ion battery including the negative electrode for a lithium ion battery described in the above item.

By using the slurry of the present invention, it is possible to manufacture a battery having good output characteristics and cycle characteristics (capacity retention rate) of the lithium ion battery. Further, it is known that the volume expansion of the silicon-based negative electrode active material is suppressed as the capacity retention rate is improved. As described above, the lithium ion battery obtained by using the slurry of the present invention has good cycle characteristics (capacity retention rate), so that the battery expands in volume due to charging and discharging even when the battery capacity is increased. Is suppressed. Further, since the slurry for the negative electrode of the lithium ion battery according to the present invention has good dispersibility, the flexibility of the electrode produced by using the above slurry is good.

(1. Lithium-ion battery negative electrode slurry)
The slurry of the present invention is a composition containing a predetermined negative electrode active material (A) (hereinafter, also referred to as (A) component), poly (meth) acrylamide (B1) (hereinafter, also referred to as (B1) component), and water. Is. In the present disclosure, "slurry" means a suspension of liquid and solid particles.

In one aspect, the present disclosure discloses a negative electrode active material (A) containing 20% by mass or more of silicon particles (a1) having a median diameter (D50) of 0.1 to 2 μm, and a (meth) acrylamide skeleton-containing monomer (b1). ) And a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2). A slurry for a negative electrode of a lithium ion battery containing poly (meth) acrylamide (B1) and water at 70,000 mPa · s is provided.

(Negative electrode active material (A) (component (A))
The component (A) contains a predetermined amount of silicon particles (a1) having a predetermined median diameter (D50).

(Silicon particles (a1) (also referred to as (a1) component)
Examples of the upper limit of the median diameter (D50) of the component (a1) are 2, 1.9, 1.6, 1.5, 1.4, 1.0, 0.9, 0.6, 0.5. , 0.4, 0.2, etc., and examples of the lower limit are 1.9, 1.6, 1.5, 1.4, 1.0, 0.9, 0.6, 0.5. , 0.4, 0.2, 0.1 and the like. The upper and lower limits of the median diameter (D50) of the component (a1) are not limited to the above values. The range of the median diameter (D50) of the component (a1) can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the median diameter (D50) of component (a1) ranges from 0.1 to 2 μm. As a result, the capacity of the lithium ion battery according to the present invention can be increased. By setting D50 in the range of 0.1 to 2 μm, battery characteristics such as cycle characteristics can be improved. On the other hand, if the same amount of silicon particles having a D50 of less than 0.1 μm is used instead of the component (a1), the dispersibility of the obtained slurry composition deteriorates, and it becomes difficult to prepare a negative electrode having a uniform active material layer. .. Further, if the same amount of silicon particles having a D50 of more than 2 μm is substituted, it becomes difficult to insert and remove lithium ions from them, and the output characteristics of the lithium ion battery tend to deteriorate. From this point of view, the D50 of the component (a1) is more preferably about 0.1 to 1.0 μm.

The D50 of the component (a1) can be measured by various known means. For example, the particle size distribution may be measured using a particle size distribution measuring device based on the light scattering method, and the particle size at which the cumulative frequency of the number of particles when accumulating particles from small particles is 50% may be set to D50. .. Examples of such a particle size distribution measuring device include Coulter LS230, LS100, LS13 320 (all manufactured by Beckman Coulter. Inc), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.) and the like.

Examples of the upper limit of the content of the component (a1) in the component (A) include 100, 90, 80, 70, 60, 50, 40, 30, 25% by mass of the negative electrode active material (A). Examples of the lower limit include 90, 80, 70, 60, 50, 40, 30, 25, 20% by mass and the like. The upper and lower limits of the component (a1) in the component (A) are not limited to the above values. The range of the content of the component (a1) in the component (A) can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the component (a1) in the component (A) is preferably 20% by mass or more, more preferably 20 to 80% by mass, still more preferably 40 to 80% by mass.

The method for producing the component (a1) is not particularly limited, and a conventionally known production method can be used. Examples of the method for producing the component (a1) include pulverization of silicon particles by a dry bead mill, a wet bead mill, an atlaser, etc., and production of silicon particles by a thermal plasma method or the like. Moreover, the method described in Japanese Patent Application Laid-Open No. 2013-203626 can be mentioned.

(Negative electrode active material other than component (a1) (component (a2)))
The component (A) may include, as a negative electrode active material other than the component (a1) (hereinafter, also referred to as the component (a2)), another negative electrode active material capable of occluding and releasing lithium. Examples of the component (a2) include carbonaceous materials containing graphite (graphite) such as artificial graphite, natural graphite, and fluoride graphite, amorphous carbon, mesocarbon microbeads, and pitch-based carbon fibers; and conductive weight such as polyacene. Combined; metals such as tin, zinc, manganese, iron, nickel and alloys thereof; oxides and sulfates of the metal or alloys; metallic lithium, Li-Al, Li-Bi-Cd, Li-Sn-Cd and the like. Lithium alloy; Lithium transition metal nitride and the like.

Examples of the upper limit of the content of the component (a2) in the component (A) include 80, 70, 60, 50, 40, 30, 25% by mass, and examples of the lower limit include 75, 70, 60. , 50, 40, 30, 25, 20% by mass and the like. (A2) The upper and lower limits of the content of the component are not limited to the above values. (A2) The range of the content of the component can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the content of the component (a2) in the component (A) is preferably about 20 to 80% by mass, more preferably about 20 to 60% by mass.

The component (a1) and the component (a2) (excluding the above-mentioned carbonaceous material) can be used in a mode in which a conductive agent is attached to their surfaces by a mechanical modification method. As the conductive agent, the carbonaceous material is preferable, and graphite is particularly preferable.

The content of the component (A) 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 (A) with respect to 100% by mass of the slurry of the present invention include 60, 55, 50, 45, 40, 35% by mass, and examples of the lower limit include 55, 50, 45, 40, 35, 30% by mass and the like can be mentioned. The upper and lower limits of the content of the component (A) with respect to 100% by mass of the slurry of the present invention are not limited to the above values. The range of the content of the component (A) 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). In one embodiment, the content of the component (A) with respect to 100% by mass of the slurry of the present invention is preferably 30 to 60% by mass.

(Poly (meth) acrylamide (B1) ((B1) component))
The component (B1) is a monomer containing a (meth) acrylamide skeleton-containing monomer (b1) (hereinafter, also referred to as (b1) component) and a sulfonic acid group-containing unsaturated monomer (b2) (hereinafter, also referred to as (b2) component). A group of radical copolymers. 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。）
により表される。 ((Meta) acrylamide skeleton-containing monomer (b1) ((b1) 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 N-monosubstituted (meth) acrylamide skeleton-containing monomers include N-isopropyl (meth) acrylamide, N-methylol (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide t-butylsulfonic acid and the like. Be done.
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 reduction resistance of the component (B1) becomes high.

Examples of the upper limit of the component (b1) in 100 mol% of the monomer group giving the component (B1) include 99.99, 99, 98, 95, 90, 80, 70, 60, 50, 40, 35 mol% and the like. Examples of the lower limit include 98, 95, 90, 80, 70, 60, 50, 40, 35, 30 mol% and the like. (B1) The upper and lower limits of the components are not limited to the above values. The range of the component (b1) can be appropriately set (for example, selected from the above upper and lower limit values). The component (B1) containing the structural unit derived from the (meth) acrylamide skeleton-containing monomer has a high interaction with the active material, and enhances the dispersibility of the slurry and the binding property between the active materials inside the electrode. In one embodiment, from the above viewpoint, the amount of the component (b1) used is preferably about 30 to 99 mol%, more preferably about 50 to 90 mol% of the monomer group giving the component (B1).

As an example of the upper limit of the component (b1) in 100% by mass of the monomer group giving the component (B1), 99.99, 99, 98, 95, 90, 80, 70, 60, 50, 40, 35% by mass and the like. Examples of the lower limit include 98, 95, 90, 80, 70, 60, 50, 40, 35, 30% by mass and the like. (B1) The upper and lower limits of the amount of the component used are not limited to the above values. The range of the component (b1) can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the amount of the component (b1) used is generally preferably about 30 to 99% by mass, more preferably about 50 to 90% by mass in the monomer group giving the component (B1).

(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 an 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 (b2) used is not particularly limited, but examples of the upper limit of the component (b2) in 100 mol% of the monomer group giving the component (B1) are 1, 0.9, 0.8, and 0. 7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 mol% and the like, and examples of the lower limit are 0.9, 0.8, Examples thereof include 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05, 0.01 mol% and the like. (B2) The upper and lower limits of the component are not limited to the above values. (B2) The range of the components can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the component (b2) 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 (B1). Is good. By doing so, the molecular weight and water solubility can be controlled without impairing the oxidation resistance of the component (B1).

In one embodiment, examples of the upper limit of the component (b2) in 100% by mass of the monomer group giving the component (B1) are 1, 0.9, 0.8, 0.7, 0.6, 0. .5, 0.4, 0.3, 0.2, 0.1, 0.05% by 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. (B2) The upper and lower limits of the component 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 (b2) 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 (B1). Is good. By doing so, the molecular weight and water solubility can be controlled without impairing the oxidation resistance of the component (B1).

(Copolymerization component other than (b1) component and (b2) component ((b3) component))
The monomer group may include a component (b1) and another copolymerization component capable of copolymerizing with the component (b2) (hereinafter, also referred to as a component (b3)). Examples of the component (b3) include unsaturated carboxylic acids, unsaturated carboxylic acid esters, α, β-unsaturated nitrile compounds, conjugated diene compounds, aromatic vinyl compounds and the like. Two or more of these can be used together. The amount of the component (b3) used is not particularly limited, but in one embodiment, the amount of the component (b3) used is less than 50 mol% (for example, 40, 30, among 100 mol% of the monomer group giving the component (B1)). 20, 20, 9, 5, 4, 1, less than 0.1 mol%, 0 mol%). In yet another embodiment, the amount of the component (b3) used is less than 50% by mass (for example, 40, 30, 20, 20, 9, 5, 4, 1, among 100% by mass of the monomer group giving the component (B1)). It is preferably less than 0.1% by mass and 0% by mass).

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and the like. Two or more of these can be used together. The amount of the unsaturated carboxylic acid used is not particularly limited. Considering the flexibility of the negative electrode of the present invention, the cycle characteristics of the lithium ion battery of the present invention, and the like in one embodiment, less than 10 mol% (for example, 9, 5, It is preferably 1, less than 0.1 mol%, 0 mol%), and 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. ) Is preferable.

As the unsaturated carboxylic acid ester, a (meth) acrylic acid ester is preferable. Examples of (meth) acrylic acid esters are methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, n-butyl (meth) acrylate, n-butyl (meth) acrylate. Linear chain of amyl, n-hexyl (meth) acrylate, n-heptyl (meth) acrylate, n-octyl (meth) acrylate, n-nonyl (meth) acrylate, n-decyl (meth) acrylate, etc. (Meta) acrylic acid ester;
Branched (meth) acrylic acid esters such as (meth) i-propyl acrylate, (meth) i-butyl acrylate, (meth) i-amyl acrylate, 2-ethylhexyl (meth) acrylate;
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 considering the flexibility of the negative electrode of the present invention, the cycle characteristics of the lithium ion battery of the present invention, and the like, 10 out of 100 mol% of the monomer group giving the component (B1). It is preferably less than mol% (for example, less than 9, 5, 1, 0.1 mol%, 0 mol%), and less than 10% by mass (for example, 9, 5, 1, 0. It is preferably less than 1% by mass and 0% by mass).

The α, β-unsaturated nitrile compound can be suitably used for the purpose of imparting flexibility to the negative electrode of the present invention. Examples of α, β-unsaturated nitrile compounds include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide, and the like, and two or more of them can be used in combination. 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, 39, 30, 20, 10, 5, 1,) of 100 mol% of the monomer group giving the component (B1). It is preferably less than 0.1 mol%, 0 mol%), and less than 50% by mass (for example, 40, 39, 30, 20, 10, 5, 1, 0.1% by mass) out of 100% by mass of the monomer group. Less than, 0% by mass) is preferable. By setting the above value, each coating film becomes uniform while maintaining the solubility of the component (B1) 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 conjugate. Examples thereof include pentadiene, substitution and side chain conjugated hexadiene. The amount of the conjugated diene compound used is not particularly limited, but from the viewpoint of the cycle characteristics of the lithium ion battery according to the present invention, less than 10 mol% (for example, 39, 30, 20) of the 100 mol% of the monomer group giving the component (B1) is used. 10, 5, 1, less than 0.1 mol%), more preferably 0 mol%. Further, it is preferably less than 10% by mass (for example, 39, 30, 20, 10, 5, 1, less than 0.1% by mass, 0% by mass) out of 100% by mass of the monomer group.

Examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. Two or more of these can be used together. The amount of the aromatic vinyl compound used is not particularly limited, but from the viewpoint of the cycle characteristics of the lithium ion battery according to the present invention, less than 10 mol% (for example, 9, 5, 1, 0.1 mol%) is preferable, and 0 mol% is more preferable. Further, less than 10% by mass (for example, less than 9, 5, 1, 0.1% by mass) is preferable, and 0% by mass is more preferable, out of 100% by mass of the monomer group.

((B1) Ingredient manufacturing method)
The component (B1) can be synthesized by various known radical polymerization 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 (b1) and (b2) and, if necessary, the component (b3), 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.

As the radical polymerization initiator, various known ones can be used without particular limitation. Examples of radical polymerization initiators include persulfates such as potassium persulfate and ammonium persulfate; redox-based polymerization initiators in which the persulfates are combined with reducing agents such as sodium bisulfite; 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 (B1). In this case, the polymerization reaction proceeds sufficiently, and the component (B1) 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 (B1) component 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. It is also possible to use EDTA, which is a metal ion encapsulant, or a salt thereof, for the same purpose.

(Physical characteristics)
The weight average molecular weight (Mw) of the component (B1) 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 the lower limit 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 appropriately set (for example, selected from the upper and lower limit values). In one embodiment, the weight average molecular weight (Mw) of the component (B1) 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 (B1) 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, and 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 appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the number average molecular weight (Mn) of the component (B1) 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 conversion 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 (B1) 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 (B1) 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 in the aqueous solution state of the component (B1) at 25 ° C. and a solid content of 15% by mass 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., and 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, etc. Can be mentioned. The upper and lower limits of the B-type viscosity are not limited to the above values. The range of the B-type viscosity of the component (B1) in an aqueous solution state at 25 ° C. and a solid content of 15% by mass 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 solvent in the aqueous solution. In one embodiment, the component (B1) needs to have a B-type viscosity in the range of 10,000 to 70,000 mPa · s in an aqueous solution having a solid content of 15% by mass at 25 ° C. When the viscosity is less than 10,000 mPa · s, the amount of the component (B1) in the slurry of the present invention becomes relatively large, which causes a decrease in the battery capacity of the lithium ion battery obtained by using the slurry. In addition, 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 slurry of the present invention, and defects and voids tend to increase in the electrode. Further, as will be described later, when the aqueous solution of the component (B1) is pulverized by spray drying, it tends to become fibrous without being pulverized.

(Manufacturing method of slurry for negative electrode of lithium ion battery)
The method for producing a slurry of the present invention includes an embodiment in which the component (B1) is used as an aqueous solution (hereinafter, also referred to as the first embodiment) and a powdered version of the same (hereinafter, powder poly (meth) acrylamide (hereinafter, powder poly (meth) acrylamide). Examples thereof include a mode (hereinafter, also referred to as a second mode) when used as the components B2) and (B2).

The production method of the first aspect is a method including a step of mixing the negative electrode active material (A), poly (meth) acrylamide (B1), and water, and is the simplest. In this case, water may be added as needed.

The production method of the second aspect is a step of obtaining powder poly (meth) acrylamide (B2) by spray-drying poly (meth) acrylamide (B1), and a negative electrode active material (A) and poly (meth). It is a method including a step of mixing acrylamide (B2) and water.

Examples of the mixing means in the first and second aspects include a ball mill, a sand mill, a pigment disperser, a grinder, an ultrasonic disperser, a homogenizer, a planetary mixer, a hovert mixer and the like.

(Powder poly (meth) acrylamide (B2))
The component (B2) is a powder of the component (B1) by various known methods, and for example, a known spray-drying method (spray-drying granulation method) or kneading granulation method can be used. In particular, the spray-drying method is preferable because the particle size of the component (B2) is uniform and the resolubility in water is good. For example, the method described in JP-A-2016-091904 can be mentioned.

The content of the component (B1) and / or the component (B2) in the slurry of the present invention is not particularly limited. As an example of the upper limit of the content (solid content mass) of the component (B1) and / or the component (B2) in the slurry of the present invention, 15, 14, 10, 9, 5 with respect to 100 parts by mass of the component (A). , 4 parts by mass and the like, and examples of the lower limit include 14, 10, 9, 5, 4, 2, 1 part by mass and the like. The upper and lower limits of the content (solid content mass) are not limited to the above values. The range of the content (solid content mass) of the component (B1) and / or the component (B2) in the slurry of the present invention can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the range is preferably about 1 to 15 parts by mass with respect to 100 parts by mass of the component (A).

(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. Black: Fine powder of Cu, Ni, Al, Si or an alloy thereof having an average particle size of 10 μm or less can be mentioned. The amount of the conductive auxiliary agent used is not particularly limited, but is preferably about 0 to 20% by mass, and more preferably about 0.5 to 15% by mass with respect to the component (A).

(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 include amides such as N-methylpyrrolidone, dimethylformamide, N, N-dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane, tetralin; 2-ethyl-1-hexanol, 1- Alcohols such as nonanol and lauryl alcohol; ketones such as methyl ethyl ketone, cyclohexanone, holon, acetophenone and isophorone; esters such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate and butyl lactate; o-toluidine, m-toluidine, p-toluidine Amide compounds such as γ-butyrolactone, lactones such as δ-butyrolactone; sulfoxide sulfones such as dimethyl sulfoxide and sulfolane. Among these, N-methylpyrrolidone 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 parts by mass with respect to the slurry of the present invention.

(Additive)
The slurry of the present invention contains as an additive an agent other than the component (A), the component (B1), the component (B2), the component (b1), the component (b2), water, a conductive auxiliary agent, and a non-aqueous medium. Can be done. Examples of additives include dispersants, leveling agents, antioxidants, thickeners and the like. The amount of the additive used is not particularly limited, but is, for example, about 0 to 10% by mass with respect to 100% by mass (solid content equivalent) of the (B1) component or 100% by mass of the (B2) component, less than 5% by mass, and 1% by mass. %, Less than 0.1% by mass, less than 0.01% by mass, 0% by mass, etc., and 0 to 5% by mass, less than 1% by mass, less than 0.1% by mass with respect to 100% by mass of the slurry. , Less than 0.01% by mass, 0% by mass and the like.

The dispersant can be selected according to the electrode active material and the conductive agent to be used, 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 the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, a polymer type phenol compound 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 or more, more preferably 600 or more, preferably 1000 or less, and more preferably 700 or less is preferable. 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 such as polyvinyl alcohol, acrylic acid or a polymer of acrylic acid salt and vinyl alcohol, maleic anhydride or maleic acid or a polymer of fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, etc. Examples thereof include modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride and the like.

(2. Negative electrode for lithium-ion battery)
The negative electrode for a lithium ion battery of the present invention (hereinafter, negative electrode) is a cured product obtained by applying the slurry according to 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 is not particularly limited, and for example, a metal material such as copper, iron, nickel, stainless steel, or nickel-plated steel, or a carbon material such as carbon cloth or carbon paper is used. The form of the current collector is also not particularly limited, and in the case of a metal material, a metal foil, a metal cylinder, a metal coil, a metal plate and the like can be mentioned, and in the case of a carbon material, a carbon plate, a carbon thin film, a carbon cylinder and the like can be mentioned. Above all, 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, preferably about 10 μm to 250 μm. Within such a range, it becomes easy to obtain a sufficient function of storing and releasing Li with respect to a high-density current value.

The content of the component (B1) (solid content) or the component (B2) in the negative electrode of the present invention is not particularly limited. Examples of the upper limit of the content of the component (B1) (solid content) or the component (B2) in the negative electrode of the present invention are 15, 14, 11, 10, 9, 6, 5, 4, 2, 1, 0. 5% by mass and the like can be mentioned, and examples of the lower limit include 14, 11, 10, 9, 6, 5, 4, 2, 1, 0.5.0.1% by mass and the like. The upper and lower limits of the content are not limited to the above values. The range of the content of the component (B1) (solid content) or the component (B2) in the negative electrode of the present invention can be appropriately set (for example, selected from the above upper and lower limit values). In one embodiment, the content range of the component (B1) (solid content) or the component (B2) in the negative electrode of the present invention is preferably about 0.1 to 15% by mass, more preferably about 1 to 10% by mass. Is. Within the above range, the capacity and energy density at the time of high output can be suitably improved.

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

(Electrolyte solution)
Examples of the electrolyte solution include a non-aqueous electrolyte solution in which a supporting electrolyte is dissolved in a non-aqueous solvent. 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. Examples of non-aqueous solvents include 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, Cyclic ethers such as 2-methyltetrahydrofuran, sulfolane and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate and methyl propionate; cyclic esters such as γ-butyrolactone and γ-valerolactone; acetonitrile and the like can be mentioned. .. 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 can be used without particular limitation of various known, for _{example, LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, Examples thereof include CF ₃ COOLi, (CF ₃ CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ ) NLi. _{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 substances can be used without particular limitation. For example, carbonate compounds such as vinylene carbonate, vinylethylene carbonate, vinylethyl carbonate, methylphenyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, ethylene sulfide, and propylene can be used. Examples thereof include alkene sulfides such as sulfide; sulton compounds such as 1,3-propane sulton and 1,4-butane sulton; acid anhydrides such as maleic anhydride and succinic anhydride. 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. Within the above range, 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.

(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 above-mentioned 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 preferable.

(Positive electrode)
As the positive electrode, various known ones can be used without particular limitation. For example, a slurry is prepared by mixing a positive electrode active material, a binder, and the above-mentioned conductive auxiliary agent with an organic solvent, and the prepared slurry is used as a positive electrode current collector. Obtained by coating, drying and pressing.

The positive electrode active material 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 transition metal 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 substance to be present at the time of reduction firing. Further, these compounds may be partially elementally substituted. Among these, in terms of practicality, electrical characteristics, and long life, 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.} 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.

Examples of positive electrode binders include fluororesins (vinylidene fluoride, polytetrafluoroethylene, etc.), polyolefins (polyethylene, polypropylene, etc.), polymers having unsaturated bonds (styrene-butadiene rubber, isoprene rubber, butadiene rubber, etc.). ), Acrylic acid-based polymers (acrylic acid copolymers, methacrylic acid copolymers, etc.) and the like, and two or more of them may be used in combination.

Examples of the positive electrode current collector include aluminum foil, stainless steel foil, and the like.

The form of the lithium ion battery of the present invention is not particularly limited. Examples of the form of the lithium ion battery 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, and a coin type in which the pellet electrode and the separator are laminated. 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 procedure for assembling the lithium ion battery of the present invention is not particularly limited, and the lithium ion battery of the present invention may be assembled by an appropriate procedure according to the structure of the battery. Examples include the methods described in Japanese Patent Application Laid-Open No. 2013-08934. A negative electrode can be placed on the outer case, an electrolytic solution and a separator can be provided on the negative electrode, and a positive electrode can be placed so as to face the negative electrode and fixed by a gasket and a sealing plate to form a battery.

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.).
In the case of viscosity of 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. (B1) Production of component Production example 1
In a reactor equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas introduction tube, 2300 g of ion-exchanged water, 400 g of acrylamide (5.63 mol), and 9.0 g of sodium methallyl sulfonate (0.057 mol) were placed. 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 obtain a poly (meth) having a solid content of 15.0% and a viscosity (25 ° C.) of 35,000 mPa · s. An aqueous solution containing acrylamide (B1) was obtained.

Production Examples 2-4 and 1'-4'
In Production Example 1, an aqueous solution containing poly (meth) acrylamide (B1) was prepared in the same manner as in Example 1 except that the monomer composition and the amount of the initiator were changed to those shown in Table 1 and numerical values.

・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
・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 metharylsulfonic acid ・ MAS: Metallylsulfonic acid ・ AA: Acrylic acid ・ EA: Ethyl acrylate ・ HEMA: Methacrylic 2-Hydroxyethyl acid-AN: Acrylonitrile-MPA: 3-Mercaptopropionic acid

2. (B2) Production of component Production example 5
The aqueous solution of poly (meth) acrylamide (B1) of Production Example 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.

3. 3. Production and Evaluation of Slurry for Negative Electrodes Example 1-1
Using a commercially available rotation / revolution mixer (product name "Awatori Rentaro", manufactured by Shinky Co., Ltd.), an aqueous solution of poly (meth) acrylamide (B1) of Production Example 1 in terms of solid content is placed in a container dedicated to the mixer. 10 parts, 75 parts of silicon particles having a D50 of 1.94 μm, and 15 parts of acetylene black (trade name: Denka Black, manufactured by Denka Co., Ltd.) were mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 40%, 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 negative electrode.

Example 1-2
10 parts of the aqueous solution of poly (meth) acrylamide (B1) of Production Example 2 in terms of solid content, 75 parts of silicon particles having a D50 of 0.13 μm, and 15 parts of the acetylene black were mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 40%, and the mixture was kneaded at 2000 rpm for 10 minutes using the rotation / revolution mixer and then defoamed for 1 minute to obtain a slurry for a negative electrode.

Example 1-3
10 parts of the aqueous solution of poly (meth) acrylamide (B1) of Production Example 3 in terms of solid content, 50 parts of silicon particles with a D50 of 0.85 μm, and natural graphite (manufactured by Ito Graphite Industry Co., Ltd. Product name “Z-” 25 parts of "5F") and 15 parts of the acetylene black were mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 40%, and the mixture was kneaded at 2000 rpm for 10 minutes using the rotation / revolution mixer and then defoamed for 1 minute to obtain a slurry for a negative electrode.

Example 1-4
10 parts of poly (meth) acrylamide (B1) of Production Example 4 in terms of solid content, 25 parts of silicon particles having a D50 of 1.46 μm, 50 parts of Z-5F, and 15 parts of the acetylene black. Mixed. Ion-exchanged water was added thereto so as to have a solid content concentration of 40%, and the mixture was kneaded at 2000 rpm for 10 minutes using the rotation / revolution mixer and then defoamed for 1 minute to obtain a slurry for a negative electrode.

Examples 1-5, Comparative Examples 1-1-1-6
In Example 1-1, a slurry for a negative electrode was obtained in the same manner except that the aqueous solution of poly (meth) acrylamide (B1) and the D50 of the silicon particles were 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 agglutination is 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.

4. Manufacture and Evaluation of Negative Electrode of Lithium Ion Battery Example 2-1
The negative electrode slurry prepared in Example 1-1 was uniformly applied to the surface of the current collector made of copper foil by the doctor blade method so that the film thickness after drying was 15 μm, and dried at 60 ° C. for 30 minutes. Then, the electrode was obtained by heat treatment at 150 ° C./vacuum for 120 minutes. Then, a negative electrode was obtained by press working with a roll press machine so that the density of the film (active material layer) was 1.5 g / cm ^3.

<Flexibility>
The electrode according to Example 2-1 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. It was evaluated according to the criteria of.
⊚: 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: Cracks were observed in the active material layer bound on the current collector, and more peeling occurred than Δ.

Examples 2-2-2-5, Comparative Examples 2-1-2-6
A lithium ion battery negative electrode was obtained in the same manner as in Example 2-1 except that the lithium ion battery negative electrode slurry was changed as shown in Table 2 in Example 2-1. The flexibility of the electrodes was evaluated, and the results are also shown in Table 2.

5. Assembly and Evaluation of Lithium Ion Battery Half Cell Example 3-1 Preparation of Lithium Ion Battery Half Cell (1) Assembly of Lithium Ion Battery Half Cell The negative electrode manufactured in Example 6 is punched to a diameter of 16 mm in an argon-substituted glove box. The battery was 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 foil 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 / ethylmethyl carbonate = 1/1 (mass ratio) at a concentration of 1 mol / L.

(2) Measurement of initial charge / discharge Coulomb efficiency and capacity retention rate Put the lithium-ion battery half cell manufactured above in a constant temperature bath at 25 ° C, start charging at a constant current (0.1C), and the voltage is 0.01V. When it became, charging was completed (cutoff). Next, discharging was started at a constant current (0.1C), and charging / discharging was repeated 30 times with the time when the voltage reached 1.0 V as the discharge completion (cutoff). The ratio of the discharge capacity of the first cycle to the charge capacity of the first cycle was expressed as a percentage, and this was taken as the initial charge / discharge coulomb efficiency. Further, the ratio of the discharge capacity in the 30th cycle to the discharge 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 3-2-3-5, Comparative Examples 3-1-3-5 Preparation of Lithium Ion Battery Half Cell Examples of Examples 3-1 except that the negative electrode of the lithium ion battery was changed as shown in Table 2. A lithium ion battery cell was obtained in the same manner as in 3-1. The measurements of the initial charge / discharge Coulomb efficiency and the residual capacity ratio were measured, and the results are also shown in Table 2.

As is clear from Table 2, all of the slurries for negative electrodes of Examples 1-1 to 1-5 had a good evaluation of slurry dispersibility. All of the negative electrodes of Examples 2-1 to 2-5 using these negative electrode slurries had a good evaluation of electrode flexibility. All of the half cells for lithium ion batteries of Examples 3-1 to 3-5 using these negative electrodes had good initial charge / discharge coulombic efficiency and capacity retention rate.

On the other hand, a lithium ion battery negative electrode slurry (Comparative Examples 1-1, 1-3) prepared using poly (meth) acrylamide having a low B-type viscosity in an aqueous state at 25 ° C. and a solid content of 15% by mass, 25. It was produced without using the components (Comparative Example 1-2) and (b2) for the negative electrode of a lithium ion battery prepared by using poly (meth) acrylamide having a high B-type viscosity in an aqueous solution state having a solid content of 15% by mass at ° C. In the case of a lithium ion battery negative electrode slurry prepared using poly (meth) acrylamide (Comparative Example 1-4) and a negative electrode slurry having a large average particle diameter of silicon particles (Comparative Example 1-5), a negative electrode slurry The dispersibility of the above, the electrode flexibility evaluation of the negative electrode produced using these, the initial charge / discharge Coulomb efficiency and the capacity retention rate of the lithium ion battery half cell were inferior.

6. Preparation of Laminated Lithium Ion Battery A laminated lithium ion battery was prepared from the slurry of Example 1 as follows.
(1) Preparation of Negative Electrode The lithium ion battery negative electrode slurry according to Example 6 was placed on a current collector made of copper foil and applied in a film form using a doctor blade. A lithium-ion battery negative electrode slurry coated on a current collector was dried at 80 ° C. for 20 minutes to volatilize and remove water, and then closely bonded 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 2 hours in a vacuum dryer and cut into a predetermined shape (26 mm × 31 mm rectangular shape) to obtain a negative electrode having a negative electrode active material layer having a thickness of 15 μm.

(2) Preparation of positive electrode LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as the positive electrode active material, acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as the binder were 88 parts by mass and 6 by mass, respectively. A parts by mass and 6 parts by mass were mixed, and this mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry for a positive electrode of a lithium ion battery. Next, an aluminum foil was prepared as a current collector for the positive electrode, a slurry for the positive electrode of the lithium ion battery was placed on the aluminum 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 positive electrode active material layer was set to 3.2 g / cm ² . The bonded product 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 positive electrode having a positive 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. This group of plates was 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 (3)

(Meta) A radical copolymer of a group of monomers containing an acrylamide skeleton-containing monomer (b1) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2), and in an aqueous state with a solid content of 15% by mass at 25 ° C. In poly (meth) acrylamide (B1), which has a B-type viscosity of 10,000 to 70,000 mPa · s,
The B-type viscosity contains water, and the B-type viscosity is measured at 25 ° C. using a B-type viscometer (product name "B-type viscometer model BM" manufactured by Toki Sangyo Co., Ltd.).
In the case of viscosity of 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
A binder aqueous solution for the negative electrode of a lithium ion battery, which is measured under the conditions. The binder aqueous solution for a negative electrode of a lithium ion battery according to claim 1, wherein the content of the component (b2) in the monomer group is 0.01 to 1 mol%. The binder aqueous solution for a negative electrode of a lithium ion battery according to claim 1 or 2, which is used together with a negative electrode active material (A) containing 20% by mass or more of silicon particles (a1) having a median diameter (D50) of 0.1 to 2 μm. ..