JP7156449B2 - Binder aqueous solution for lithium ion battery negative electrode - Google Patents

Description

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

Lithium-ion batteries are small, 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, improvements in battery members such as electrodes have 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, an active material and a binder resin are dispersed in a solvent to form a slurry, which is coated on both sides of a current collector (for example, a metal foil), and the solvent is removed by drying to form an electrode layer. is formed, and then compression-molded by a roll press machine or the like.

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

Therefore, in the art, studies have been made to solve the above problems with binder resins. 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 the active material is preferably a silicon material such as silicon or silicon oxide.

JP 2013-089437 A JP-A-2005-216502 JP 2015-106488 A

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

In addition, the polyacrylic acid described in Patent Document 2 has a problem in that the initial discharge capacity decreases because the lithium ions occluded by the active material are taken into the carboxyl groups during charging.

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

Therefore, the problem to be solved by the present invention is to provide a slurry for a negative electrode for a lithium ion battery that can produce a negative electrode with good flexibility and a lithium ion battery with good electrical characteristics and springback resistance, and has good dispersibility. It is assumed that

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

As a result of intensive studies by the present inventors to solve the above problems, the inventors have found that silicon particles having a relatively small average particle size are used as a negative electrode active material, and a predetermined unsaturated monomer is used as a dispersant for the negative electrode active material, and have found that a slurry that can solve the above problems can be obtained by using poly(meth)acrylamide having predetermined physical properties, and have completed the present invention.

The following items are provided by this disclosure.
(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;
It is a radical copolymer of a monomer group containing a (meth)acrylamide skeleton-containing monomer (b1) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2), and is in an aqueous solution state with a solid content of 15% by mass at 25 ° C. A poly(meth)acrylamide (B1) having a B-type viscosity of 10,000 to 70,000 mPa s at
A slurry for a lithium ion battery negative electrode, comprising water.
(Item 2)
The slurry for a lithium ion battery negative electrode according to the above items, wherein the content of the component (b2) in the monomer group is 0.01 to 1 mol%.
(Item 3)
The method for producing slurry for a lithium ion battery negative electrode according to any one of the above items, comprising mixing the negative electrode active material (A), the poly(meth)acrylamide (B1), and water.
(Item 4)
a step of obtaining powdery poly(meth)acrylamide (B2) by spray-drying the poly(meth)acrylamide (B1), and the negative electrode active material (A) and the poly(meth)acrylamide (B2); and water.
(Item 5)
The lithium ion battery negative electrode slurry according to any one of the above items or the lithium ion battery negative electrode slurry obtained by the method for producing the lithium ion battery negative electrode slurry according to any one of the above items is used as a current collector. A negative electrode for a lithium ion battery obtained by coating and drying.
(Item 6)
A lithium ion battery comprising the negative electrode for a lithium ion battery as described above.

By using the slurry of the present invention, it is possible to manufacture a lithium ion battery with good output characteristics and cycle characteristics (capacity retention rate). Further, it is known that as the capacity retention rate improves, the volume expansion of the silicon-based negative electrode active material is suppressed. As described above, the lithium ion battery obtained using the slurry of the present invention has good cycle characteristics (capacity retention rate). is suppressed. Moreover, since the slurry for a lithium ion battery negative electrode according to the present invention has good dispersibility, the electrode produced using the slurry has good flexibility.

(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 component (A)), poly(meth)acrylamide (B1) (hereinafter also referred to as component (B1)), and water. is. By "slurry" in this disclosure is meant a suspension of liquid and solid particles.

In one aspect, the present disclosure provides 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), which is a radical copolymer of a monomer group and has a B-type viscosity of 10,000 to 10,000 in an aqueous solution with a solid content of 15% by mass at 25 ° C. Provided is a slurry for a lithium ion battery negative electrode, comprising poly(meth)acrylamide (B1) having a viscosity of 70,000 mPa·s and water.

(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 component (a1) are 2, 1.9, 1.6, 1.5, 1.4, 1.0, 0.9, 0.6, and 0.5. , 0.4, 0.2, etc. Examples of lower limits include 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 component (a1) are not limited to the above values. The range of the median diameter (D50) of component (a1) can be appropriately set (for example, selected from the above upper and lower limits). In one embodiment, the median diameter (D50) of component (a1) ranges from 0.1 to 2 μm. As a result, it becomes possible to increase the capacity of the lithium ion battery according to the present invention. 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 in place of the component (a1), the dispersibility of the obtained slurry composition deteriorates, making it difficult to produce a negative electrode having a uniform active material layer. . Also, if the same amount of silicon particles with a D50 exceeding 2 μm is used as a substitute, it becomes difficult to intercalate and deintercalate lithium ions into and out of them, and the output characteristics of the lithium ion battery tend to deteriorate. From this point of view, the D50 of component (a1) is more preferably about 0.1 to 1.0 μm.

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

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

The method for producing component (a1) is not particularly limited, and conventionally known production methods can be used. Examples of the method for producing the component (a1) include pulverization of silicon particles by a dry bead mill, wet bead mill, Atlastar, etc., and production of silicon particles by a thermal plasma method, etc. In addition, the method described in JP-A-2013-203626 and the like are included.

(Negative electrode active material other than component (a1) (component (a2)))
The component (A) may contain other negative electrode active materials capable of intercalating and deintercalating lithium as negative electrode active materials other than the component (a1) (hereinafter also referred to as component (a2)). Examples of the component (a2) include graphite such as artificial graphite, natural graphite, and graphite fluoride; carbonaceous materials including amorphous carbon, mesocarbon microbeads, pitch-based carbon fibers; Coalescence; metals such as tin, zinc, manganese, iron, nickel, and alloys thereof; oxides and sulfates of the metals or alloys; metallic lithium, Li—Al, Li—Bi—Cd, Li—Sn—Cd, etc. lithium alloys; lithium transition metal nitrides;

Examples of the upper limit of the content of component (a2) in 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. The upper and lower limits of the content of component (a2) are not limited to the above values. The range of the content of component (a2) can be appropriately set (for example, by selecting from the above upper and lower limits). In one embodiment, the content of component (a2) in component (A) is preferably about 20 to 80% by mass, more preferably about 20 to 60% by mass.

The components (a1) and (a2) (excluding the above carbonaceous material) can be used in a manner in which a conductive agent is adhered 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 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 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 are 55, 50, 45, 40, 35, 30% by mass and the like. The upper and lower limits of the content of 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 component (A) with respect to 100% by mass of the slurry of the present invention can be appropriately set (for example, by selecting from the above upper and lower limits). In one embodiment, the content of 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) (component (B1)))
Component (B1) is a monomer containing a (meth)acrylamide skeleton-containing monomer (b1) (hereinafter also referred to as component (b1)) and a sulfonic acid group-containing unsaturated monomer (b2) (hereinafter also referred to as component (b2)). It is a radical copolymer of the group. In the present disclosure, "(meth)acryl" means "at least one selected from the group consisting of acryl and methacryl". The term "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。 ((Meth)acrylamide skeleton-containing monomer (b1) (component (b1)))
In the present disclosure, "(meth)acrylamide skeleton-containing monomer" means (meth)acrylamide skeleton

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

(wherein R ¹ is hydrogen or a methyl group, R ² and R ³ are each independently hydrogen, a substituted or unsubstituted alkyl group, or an acetyl group, or R ² and R ³ are R ⁴ and R ⁵ are each independently hydrogen, a substituted or unsubstituted alkyl group, a carboxyl group, a hydroxy group, an amino group (-NR ^a R ^b (R ^a and R ^b are each independently hydrogen or a substituted or unsubstituted alkyl group (hereinafter the same), acetyl group, sulfonic acid group Examples of substituents of substituted alkyl groups include hydroxy group, amino group , acetyl group, etc. Examples of groups in which R ² and R ³ together form a ring structure include morpholyl group, etc.)
is represented by

Examples of (meth)acrylamide skeleton-containing monomers include N-unsubstituted (meth)acrylamide skeleton-containing monomers, N-monosubstituted (meth)acrylamide skeleton-containing monomers, N,N-disubstituted (meth)acrylamide skeleton-containing monomers, and the like. is mentioned. Two or more kinds of (meth)acrylamide skeleton-containing monomers can be used in combination.
Examples of N-unsubstituted (meth)acrylamide skeleton-containing monomers include (meth)acrylamide and maleic acid amide.
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, particularly acrylamide, is used, the reduction resistance of the component (B1) is enhanced.

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

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

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

As the component (b2), various known compounds can be used without particular limitation as long as they are compounds in which hydrogen atoms of unsaturated hydrocarbon groups are substituted with sulfonic acid groups or salts thereof. Examples of component (b2) include vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, and salts thereof, and two or more of them can be used in combination. Examples of salts include organic salts such as organic amine salts; metal salts including alkali metal salts such as potassium salts and sodium salts; and inorganic salts including ammonium salts. Among these, methallyl sulfonate, particularly sodium methallyl sulfonate, which acts as a chain transfer agent for controlling the molecular weight and water solubility of component (B1) is preferred.

The amount of component (b2) to be used is not particularly limited, but examples of the upper limit of component (b2) in 100 mol % of the monomer group that provides component (B1) are 1, 0.9, 0.8, 0.3%, 7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1, 0.05 mol%, etc., and examples of lower limits 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. The upper and lower limits of component (b2) are not limited to the above values. The range of component (b2) can be appropriately set (for example, by selecting from the above upper and lower limits). In one embodiment, component (b2) is preferably about 0.01 to 1 mol%, more preferably about 0.05 to 1 mol% of 100 mol% of the monomer group that provides component (B1). It's 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 providing the component (B1) are 1, 0.9, 0.8, 0.7, 0.6, 0 0.5, 0.4, 0.3, 0.2, 0.1, 0.05% by mass, etc., and examples of lower limits 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. The upper and lower limits of component (b2) are not limited to the above values. The range of component (b) can be appropriately set (for example, selected from the above upper and lower limits). In one embodiment, component (b2) is preferably about 0.01 to 1% by mass, more preferably about 0.05 to 1% by mass of 100% by mass of the monomer group that provides component (B1). It's good. By doing so, the molecular weight and water solubility can be controlled without impairing the oxidation resistance of the component (B1).

(Copolymerized components other than components (b1) and (b2) (component (b3)))
The monomer group may include another copolymerizable component (hereinafter also referred to as component (b3)) that can be copolymerized with components (b1) and (b2). Examples of component (b3) include unsaturated carboxylic acids, unsaturated carboxylic acid esters, α,β-unsaturated nitrile compounds, conjugated diene compounds, and aromatic vinyl compounds. These can be used in combination of two or more. The amount of component (b3) used is not particularly limited, but in one embodiment, the amount of component (b3) used is less than 50 mol% (e.g., 40, 30, 20, 20, 9, 5, 4, 1, less than 0.1 mol %, 0 mol %). In yet another embodiment, the amount of component (b3) used is less than 50% by mass (e.g., 40, 30, 20, 20, 9, 5, 4, 1, 40, 30, 20, 20, 9, 5, 4, 1, less than 0.1% by mass, 0% by mass).

Examples of unsaturated carboxylic acids include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. These can be used in combination of two or more. The amount of unsaturated carboxylic acid used is not particularly limited. In one embodiment, considering the flexibility of the negative electrode of the present invention and the cycle characteristics of the lithium ion battery of the present invention, less than 10 mol% of 100 mol% of the monomer group that provides the component (B1) (for example, 9, 5, 1, less than 0.1 mol%, 0 mol%), and less than 10% by mass (e.g., 9, 5, 1, less than 0.1% by mass, 0% by mass) of 100% by mass of the monomer group ) is preferred.

As 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, n-(meth) acrylate, Linear chains such as amyl, n-hexyl (meth)acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-nonyl (meth)acrylate, and n-decyl (meth)acrylate (meth)acrylic acid ester;
branched (meth)acrylates such as i-propyl (meth)acrylate, i-butyl (meth)acrylate, i-amyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate;
Alicyclic (meth)acrylic acid esters such as cyclohexyl (meth)acrylate;
Glycidyl (meth)acrylate, hydroxymethyl (meth)acrylate, hydroxyethyl (meth)acrylate, ethylene glycol (meth)acrylate, ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, tri Substituted (meth)acrylic acids such as trimethylolpropane (meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol hexa(meth)acrylate, allyl (meth)acrylate, and ethylene di(meth)acrylate Ester etc. are mentioned. These can be used in combination of two or more. The amount of unsaturated carboxylic acid ester used is not particularly limited, but considering the flexibility of the negative electrode of the present invention and the cycle characteristics of the lithium ion battery of the present invention, 10% of 100 mol% of the monomer group that provides component (B1) It is preferably less than 9, 5, 1, 0.1 mol%, 0 mol%, and less than 10% by mass (eg, 9, 5, 1, 0.1% by mass) of 100% by mass of the monomer group. less than 1% by mass, 0% by mass).

An 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. Among these, acrylonitrile and/or methacrylonitrile are preferred, and acrylonitrile is particularly preferred. The amount of the α,β-unsaturated nitrile compound to be used is not particularly limited, but less than 50 mol% (for example, 40, 39, 30, 20, 10, 5, 1, less than 0.1 mol%, 0 mol%), and less than 50% by mass (e.g., 40, 39, 30, 20, 10, 5, 1, 0.1% by mass) of 100% by mass of the monomer group less than 0% by mass). By setting it to the above value, while maintaining the solubility of the component (B1) in water, each of the coating films becomes uniform, making it easier to exhibit the flexibility.

Examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, substituted linear conjugated Examples include pentadienes, substituted and side chain conjugated hexadienes, and the like. 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% (e.g., 39, 30, 20 , 10, 5, 1, less than 0.1 mol %), and more preferably 0 mol %. Moreover, it is preferably less than 10 mass % (for example, 39, 30, 20, 10, 5, 1, less than 0.1 mass %, 0 mass %) in 100 mass % of the monomer group.

Examples of aromatic vinyl compounds include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. These can be used in combination of two or more. 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% (e.g., 9, 5, 1, less than 0.1 mol%) is preferred, and 0 mol% is more preferred. Moreover, it is preferably less than 10% by mass (for example, less than 9, 5, 1, or less than 0.1% by mass), more preferably 0% by mass, out of 100% by mass of the monomer group.

(Method for producing component (B1))
The (B1) component can be synthesized by various known radical polymerization methods. An aqueous solution radical polymerization method is preferred. Specifically, a radical polymerization initiator and, if necessary, other polymerization reagents are added to a monomer mixed solution containing the components (b1) and (b2), and optionally the component (b3), while stirring. 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 polymerization initiators in which the persulfates are combined with reducing agents such as sodium hydrogen sulfite; azo initiators; be done. The amount of the radical polymerization initiator to be used is not particularly limited, but it 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 that provides component (B1). In this case, the polymerization reaction proceeds sufficiently to increase the molecular weight of the component (B1).

Before the radical polymerization reaction or when water-solubilizing the obtained component (B1), for the purpose of improving the production stability, common solvents such as ammonia, organic amines, potassium hydroxide, sodium hydroxide, lithium hydroxide, etc. A neutralizing agent may be used to adjust the pH. In that case, it is preferable to adjust the pH in the range of about 5 to 11. For the same purpose, it is also possible to use EDTA or a salt thereof, which is a metal ion sealant.

(physical properties)
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, 3 million , 2.5 million, 2 million, 1.5 million, 1 million, 950 thousand, 900 thousand, 850 thousand, 800 thousand, 750 thousand, 700 thousand, 650 thousand, 600 thousand, 550 thousand, 500 thousand, 450 thousand, 400 thousand, etc. Examples of lower limits include 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. 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 limits described above). In one embodiment, the weight average molecular weight (Mw) of component (B1) is preferably 300,000 to 6,000,000 from the viewpoint of dispersion stability of the electrode slurry.

Examples of the upper limit of the number average molecular weight (Mn) of 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 include 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 . 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 upper and lower limits above). In one embodiment, the number average molecular weight (Mn) of component (B1) is preferably 10,000 or more from the viewpoint of the dispersion stability of the electrode slurry.

The weight average molecular weight and 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) by gel permeation chromatography (GPC), for example. can be

Examples of the upper limit of the molecular weight distribution (Mw/Mn) of component (B1) include 7, 6, 5, 4, 3, 2, etc., and examples of the lower limit include 6, 5, 4, 3, 2. , 1 and the like. 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 limits described above). In one embodiment, the molecular weight distribution (Mw/Mn) of component (B1) is preferably 1 to 7 from the viewpoint of the dispersion stability of the electrode slurry.

Examples of the upper limits of the B-type viscosity of the component (B1) in an aqueous solution having a solid content of 15% by mass at 25°C are 70,000, 65,000, 60,000, 55,000, 50,000, and 45,000. , 40,000, 35,000, 30,000, 25,000, 20,000, 15,000, 11,000 mPa s, etc. Examples of lower limits include 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 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 of 15% by mass of solids at 25° C. can be appropriately set (for example, by selecting from the above upper and lower limits). The B-type viscosity can be adjusted by the amount of solvent in the aqueous solution. In one embodiment, component (B1) should 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. If the viscosity is less than 10,000 mPa·s, the amount of component (B1) in the slurry of the present invention is relatively large, resulting in a decrease in battery capacity of a lithium ion battery obtained using the slurry. Moreover, the adhesion between the coating film made of the slurry and the metal foil as the current collector tends to decrease. On the other hand, if the viscosity exceeds 70,000 mPa·s, the slurry of the present invention tends to form a gel-like substance, which tends to increase defects and voids in the electrode. As will be described later, when the aqueous solution of component (B1) is powdered by spray drying, it tends to become fibrous without being powdered.

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

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

Examples of mixing means in the first and second aspects include ball mills, sand mills, pigment dispersers, crushers, ultrasonic dispersers, homogenizers, planetary mixers, Hobart mixers, and the like.

(Powder poly(meth)acrylamide (B2))
Component (B2) is obtained by pulverizing component (B1) by various known methods. 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, resulting in good re-solubility in water.

The content of component (B1) and/or component (B2) in the slurry of the present invention is not particularly limited. Examples 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 are 15, 14, 10, 9, 5 per 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 and 1 parts by mass. The upper and lower limits of the above 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 limits). In one embodiment, the range of about 1 to 15 parts by weight per 100 parts by weight of component (A) is preferred.

(Conductivity aid)
The slurry of the present invention may contain a conductive aid depending on the purpose. Examples of conductive aids include fibrous carbon such as vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), carbon nanofiber (CNF), graphite particles, carbon such as acetylene black, ketjen black, and furnace black. Black; Fine powders of Cu, Ni, Al, Si or alloys thereof having an average particle size of 10 μm or less. The amount of the conductive aid used is not particularly limited, but is preferably about 0 to 20% by mass, more preferably about 0.5 to 15% by mass, based on component (A).

(Non-aqueous medium)
The slurry of the present invention may contain a non-aqueous medium having a normal 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 and N,N-dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane and tetralin; alcohols such as nonanol and lauryl alcohol; ketones such as methyl ethyl ketone, cyclohexanone, phorone, acetophenone, and isophorone; esters such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate, and butyl lactate; o-toluidine, m-toluidine, p-toluidine amine compounds such as γ-butyrolactone and δ-butyrolactone; sulfoxides and sulfones such as dimethylsulfoxide 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 relative to the slurry of the present invention.

(Additive)
The slurry of the present invention may contain, as additives, agents other than (A) component, (B1) component, (B2) component, (b1) component, (b2) component, water, conductive aid, and 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 for example, about 0 to 10% by mass, less than 5% by mass, and 1% by mass relative to 100% by mass of component (B1) (in terms of solid content) or 100% by mass of component (B2) %, 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 conductive agent used, and examples thereof include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds.

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

Examples of antioxidants include phenolic compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, polymeric phenolic compounds, and the like. The polymer-type phenol compound is a polymer having a phenol structure in the molecule, and preferably has a weight-average molecular weight of 200 or more, more preferably 600 or more, preferably 1000 or less, more preferably 700 or less. Used.

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

(2. Negative electrode for lithium ion battery)
The negative electrode for a lithium ion battery of the present invention (hereinafter referred to as negative electrode) is a cured product obtained by coating the slurry of the present invention on a current collector and drying, that is, the cured product of the slurry of 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, metal materials such as copper, iron, nickel, stainless steel, and nickel-plated steel, and carbon materials such as carbon cloth and carbon paper are used. The form of the current collector is not particularly limited, and examples thereof include metal foil, metal cylinder, metal coil, and metal plate in the case of metal materials, and carbon plates, carbon thin films, carbon cylinders, and the like in the case of carbon materials. Among them, metal foil is preferable because it is currently used in industrialized products.

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

Although the thickness of the electrode (cured coating film) is not particularly limited, it is preferably about 5 μm to 300 μm, more preferably about 10 μm to 250 μm. By setting the content in such a range, it becomes easy to obtain a sufficient Li intercalation/deintercalation function for a high-density current value.

The content of component (B1) (solid content) or component (B2) in the negative electrode of the present invention is not particularly limited. Examples of the upper limit of the content of component (B1) (solid content) or 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, 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 above content are not limited to the above values. The content range of component (B1) (solid content) or component (B2) in the negative electrode of the present invention can be appropriately set (for example, by selecting from the above upper and lower limits). In one embodiment, the content range of component (B1) (solid content) or 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 high output can be favorably improved.

(3. Lithium ion battery)
A lithium ion battery of the present invention is an article comprising the negative electrode of the present invention. Other members in the battery, ie, electrolyte solution, separator, positive electrode, and packaging material, are not particularly limited.

(electrolyte solution)
Examples of electrolyte solutions include non-aqueous electrolyte solutions in which a supporting electrolyte is dissolved in a non-aqueous solvent. In addition, the non-aqueous electrolytic solution may contain a film-forming agent.

As the non-aqueous solvent, various known solvents 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; 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; . One of these non-aqueous solvents may be used alone, or two or more of them may be mixed and used, but a mixed solvent combination containing a cyclic carbonate and a chain carbonate is preferable.

A lithium salt is used as the supporting electrolyte. _{As the lithium salt , various known ones can} be used without _{particular limitation} . _CF3COOLi , _{( CF3CO} ) _2NLi , _{( CF3SO2} ) _2NLi , _{( C2F5SO2} )NLi and the like. Among them, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and exhibit a high degree of dissociation, are preferable. These may be used in combination of two or more. Since the lithium ion conductivity increases with the use of a supporting electrolyte having a higher degree of dissociation, 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 any particular limitation. Alkene sulfides such as sulfide; sultone compounds such as 1,3-propanesultone and 1,4-butanesultone; 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 this order. When the amount is within the above range, the advantages of the film-forming agent, such as suppression of initial irreversible capacity and improvement of low-temperature characteristics and rate characteristics, can be easily obtained.

(separator)
A separator is an article interposed between a positive electrode and a negative electrode, and is used to prevent a short circuit between the electrodes. Specifically, porous separators such as porous membranes and non-woven fabrics can be preferably used, and they are impregnated with the non-aqueous electrolytic solution. As a material for the separator, polyolefin such as polyethylene and polypropylene, polyethersulfone, and the like are used, and polyolefin is 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-described conductive aid with an organic solvent, and the prepared slurry is applied to a positive electrode current collector. Obtained by coating, drying and pressing.

Positive electrode active materials are roughly classified into active materials containing inorganic compounds and active materials containing organic compounds. Examples of inorganic compounds contained in the positive electrode active material include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metals include Fe, Co, Ni, Mn, Al and the like. Examples of inorganic compounds used for the positive electrode active material include 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 and LiFeVO ₄ ; transitions such as TiS ₂ , TiS ₃ and amorphous MoS ₂ 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 and V ₆ O ₁₃ ; 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 exist during reduction firing. Also, these compounds may be partially element-substituted. Among these, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiNi _1/2 Mn _3/2 O ₄ , and LiCo _1/3 are preferable in terms of practicality, electrical properties, and long life. _{Ni1 / 3Mn1 / 3O2} , Li[ _{Li0.1Al0.1Mn1.9} ] _O4 are used as positive electrode active materials.

Examples of positive electrode binders include fluorine-based resins (polyvinylidene 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.), etc., and two or more of them may be used in combination.

Examples of positive electrode current collectors include aluminum foil and stainless steel foil.

The form of the lithium ion battery of the present invention is not particularly limited. Examples of the form of lithium ion batteries include a cylinder type in which a sheet electrode and a separator are spirally formed, a cylinder type with an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are laminated, and the like. Moreover, by housing the batteries of these forms in an arbitrary exterior case, they can be used in arbitrary shapes such as coin-shaped, cylindrical, and rectangular.

The procedure for assembling the lithium-ion battery of the present invention is also not particularly limited, and may be assembled according to an appropriate procedure according to the structure of the battery. Examples include the method described in JP-A-2013-089437. A battery can be made by placing a negative electrode on an exterior case, placing an electrolytic solution and a separator thereon, placing a positive electrode so as to face the negative electrode, and fixing them with a gasket and a sealing plate.

EXAMPLES The method of the present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these. In the examples, "%" means "% by mass" and "parts" means "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
If the viscosity is less than 20,000 mPa·s: No. 3 rotors used, rotation speed 6 rpm

1. Production of component (B1) Production Example 1
2300 g of ion-exchanged water, 400 g (5.63 mol) of acrylamide, and 9.0 g (0.057 mol) of sodium methallylsulfonate were placed in a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet 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 Nippo Chemical Co., Ltd.) and 30 g of ion-exchanged water were added thereto, and the temperature was raised to 80° C. The reaction was carried out for 0.5 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) with 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 above, 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 initiator were changed to those shown in Table 1.

・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 methallylsulfonate ・MAS: methallylsulfonic acid ・AA: acrylic acid ・EA: ethyl acrylate ・HEMA: methacryl Acid 2-hydroxyethyl AN: acrylonitrile MPA: 3-mercaptopropionic acid

2. Production of component (B2) 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 dry air flow rate: 0.45 m ³ /min, inlet temperature: 180°C, outlet temperature: 80°C, spray pressure: 1.0 kgf/cm ² , solution supply rate: 500 mL/hour. The obtained powder was added to a columnar glass container containing ion-exchanged water while being stirred with a flat spring so as to be 15% by mass, and dissolved.

3. Production and Evaluation of Negative Electrode Slurry Example 1-1
Using a commercially available rotation-revolution mixer (product name “Awatori Mixer”, manufactured by Thinky Co., Ltd.), an aqueous solution of poly(meth)acrylamide (B1) of Production Example 1 was added in a solid content conversion to 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 KK) were mixed. Ion-exchanged water was added thereto so that the solid content concentration was 40%, and the container was set in the mixer. Next, after kneading at 2000 rpm for 10 minutes, defoaming was performed for 1 minute to obtain a negative electrode slurry.

Example 1-2
10 parts of the aqueous solution of the 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 negative electrode slurry.

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 having a D50 of 0.85 μm, and natural graphite (product name “Z- 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 negative electrode slurry.

Examples 1-4
10 parts of the 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 negative electrode slurry.

Example 1-5, Comparative Examples 1-1 to 1-6
A negative electrode slurry was obtained in the same manner as in Example 1-1, except that the D50 values of the poly(meth)acrylamide (B1) aqueous solution and silicon particles were changed as shown in Table 2.

<Slurry dispersibility evaluation>
The dispersibility immediately after preparation of the slurry was visually evaluated according to the following criteria.
⊚: Whole is in the form of a homogeneous paste, no liquid separation is observed, and no aggregates are observed.
◯: The whole is a substantially homogeneous paste, and slight liquid separation is observed, but no aggregates are observed.
Δ: A small amount of aggregates and a slightly large amount of liquid separation are observed at the bottom of the container.
x: A large number of clay-like aggregates are observed at the bottom of the container, and a large amount of liquid separation is also observed.

4. Production and evaluation of lithium ion battery negative electrode Example 2-1
The negative electrode slurry prepared in Example 1-1 was uniformly applied to the surface of a current collector made of copper foil by a doctor blade method so that the film thickness after drying was 15 μm, and dried at 60° C. for 30 minutes. After that, heat treatment was performed at 150° C./vacuum for 120 minutes to obtain an electrode. Thereafter, the negative electrode was obtained by pressing with a roll press machine so that the film (active material layer) had a density of 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 with a diameter of 6 mm, with the active material layer facing outward, and the state of the surface of the active material layer was observed. was evaluated according to the criteria of
⊚: No cracking or peeling occurred in the active material layer bound on the current collector.
◯: Cracks are observed in the active material layer bound on the current collector, but peeling is not observed.
Δ: Cracks are observed in the active material layer bound on the current collector, and peeling is also partially observed.
×: Cracks were observed in the active material layer bound on the current collector, and peeling occurred more frequently than Δ.

Examples 2-2 to 2-5, Comparative Examples 2-1 to 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 in Example 2-1 was changed as shown in Table 2. The flexibility of the electrode was evaluated, and the results are shown in Table 2 together.

5. Assembly and Evaluation of Lithium-ion Battery Half-cell Example 3-1 Production of Lithium-ion Battery Half-cell (1) Assembly of Lithium-ion Battery Half-cell The negative electrode produced in Example 6 was punched into a diameter of 16 mm in an argon-filled glove box. This was placed on a bipolar 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 (manufactured by CS TECH CO., LTD, trade name “Selion P2010”) was placed, and 500 μL of an electrolytic solution was injected so as not to enter air. A lithium ion battery cell was assembled by placing a commercially available metal lithium foil punched into a size of 16 mm and sealing the exterior body of the bipolar coin cell with screws. The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol/L in a solvent of ethylene carbonate/ethyl methyl carbonate=1/1 (mass ratio).

(2) Measurement of initial charge/discharge coulombic efficiency and capacity retention rate Put the lithium-ion battery half-cell produced above in a 25 ° C. thermostat, start charging at a constant current (0.1 C), and the voltage is 0.01 V Charging was completed (cutoff) when Then, discharge was started at a constant current (0.1 C), and charge/discharge was repeated 30 times, with discharge being completed (cutoff) when the voltage reached 1.0V. The ratio of the discharge capacity in the first cycle to the charge capacity in the first cycle was expressed as a percentage, and was defined as the initial charge/discharge coulombic efficiency. Also, the ratio of the discharge capacity at the 30th cycle to the discharge capacity at the 1st cycle was expressed as a percentage, which was taken as the capacity retention rate. The results are also shown in Table 2.

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

Examples 3-2 to 3-5 and Comparative Examples 3-1 to 3-5 Production of Lithium-ion Battery Half Cells Examples except that the lithium-ion battery negative electrode was changed as shown in Table 2 in Example 3-1 above. A lithium ion battery cell was obtained in the same manner as in 3-1. The initial charge/discharge coulombic efficiency and residual capacity ratio were measured, and the results are shown in Table 2 together.

As is clear from Table 2, all of the negative electrode slurries of Examples 1-1 to 1-5 were evaluated to have good slurry dispersibility. All of the negative electrodes of Examples 2-1 to 2-5 using these negative electrode slurries were evaluated for 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 coulomb efficiency and capacity retention rate.

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

6. Production of Laminated Lithium Ion Battery A laminated lithium ion battery was produced from the slurry of Example 1 as follows.
(1) Fabrication of Negative Electrode The lithium ion battery negative electrode slurry described in Example 6 was put on a current collector made of copper foil and coated in a film using a doctor blade. The current collector coated with the lithium ion battery negative electrode slurry was dried at 80° C. for 20 minutes to volatilize and remove water, and then closely bonded by a roll press. At this time, the density of the negative electrode active material layer was set to 1.5 g/cm ² . The bonded product was heated at 120° C. for 2 hours in a vacuum dryer and cut into a predetermined shape (rectangular shape of 26 mm×31 mm) to obtain a negative electrode having a negative electrode active material layer with a thickness of 15 μm.

(2) Preparation of positive electrode 88 parts by mass of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder, respectively. 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 slurry for lithium ion battery positive electrode. Next, an aluminum foil was prepared as a current collector for the positive electrode, and the lithium ion battery positive electrode slurry was placed on the aluminum foil and coated with a doctor blade to form a film. The aluminum foil coated with the lithium ion battery positive electrode slurry was dried at 80° C. for 20 minutes to volatilize and remove NMP, and then closely bonded by a roll press. 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 (rectangular shape of 25 mm×30 mm) to obtain a positive electrode having a positive electrode active material layer with a thickness of about 45 μm.

(3) Production of Laminated Lithium Ion Battery A laminated lithium ion secondary battery was produced using the positive and negative electrodes described above. Specifically, a rectangular sheet (27×32 mm, thickness 25 μm) of a separator made of a polypropylene porous film (manufactured by CS TECH CO., LTD, trade name “Selion P2010”) was sandwiched between the positive electrode and the negative electrode. was used as an electrode plate group. This electrode plate assembly was covered with a pair of laminate films, and after three sides were sealed, an electrolytic solution was injected into the bag-shaped laminate film. As an electrolytic solution, a solution in which LiPF ₆ was dissolved at a concentration of 1 mol/L in a solvent of ethylene carbonate/ethyl methyl carbonate=1/1 (mass ratio) was used. After that, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were airtightly sealed and the electrode plate group and the electrolytic solution were sealed. In addition, the positive electrode and the negative electrode have tabs that can be electrically connected to the outside, and a part of the tabs extends outside the laminate type lithium ion secondary battery. When the laminate-type lithium ion battery manufactured by the above steps was energized, no problem occurred in operation.

Claims (2)

It is a radical copolymer of a monomer group containing a (meth)acrylamide skeleton-containing monomer (b1) and a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (b2), and is in an aqueous solution state with a solid content of 15% by mass at 25 ° C. A poly(meth)acrylamide (B1) having a B-type viscosity of 10,000 to 70,000 mPa s at
and water, and the B-type viscosity is measured 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
If the viscosity is less than 20,000 mPa·s: No. 3 rotors used, rotation speed 6 rpm
A binder aqueous solution for a lithium ion battery negative electrode, which is used 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 . 2. The aqueous binder solution for a lithium ion battery negative electrode according to claim 1, wherein the content of said component (b2) in said monomer group is 0.01 to 1 mol %.