KR102142441B1 - Slurry composition for lithium-ion secondary cell negative electrode - Google Patents

Abstract

(Task) Providing a slurry composition for a secondary battery having excellent cycle characteristics, and a negative electrode for a lithium ion secondary battery capable of obtaining a negative electrode having excellent binding properties.
(Solution) The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention is a slurry composition for a negative electrode of a lithium ion secondary battery containing a negative electrode active material (A), a water-soluble polymer (B), and water (C), wherein the water-soluble polymer ( B) Aqueous polymer (B1), which is an alkali metal salt of a polymer containing ethylenically unsaturated acid monomer units and fluorine-containing (meth)acrylic acid ester monomer units, and alkali of a polymer containing 80 mass% or more of ethylenically unsaturated acid monomer units. Water-soluble polymer (B2) which is a metal salt, and the viscosity of the 5% aqueous solution of the water-soluble polymer (B1) is 100 cp or more and 1500 cp or less, and the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) is 2000 cp or more, 20000 cp Is below.

Description

Slurry composition for lithium ion secondary battery negative electrode {SLURRY COMPOSITION FOR LITHIUM-ION SECONDARY CELL NEGATIVE ELECTRODE}

The present invention relates to a slurry composition for a lithium ion secondary battery negative electrode.

In recent years, the spread of portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) is remarkable. Nickel hydrogen secondary batteries, lithium ion secondary batteries, and the like are commonly used as secondary batteries used for power supplies for these portable terminals. The portable terminal is required to have more comfortable portability, and the miniaturization, thinning, light weight, and high performance are rapidly progressing, and as a result, the portable terminal is used in various places. In addition, the battery is required to be miniaturized, thinned, lightweight, and high-performance in the same way as for a portable terminal.

Conventionally, carbon-based active materials such as graphite have been used as a negative electrode active material in lithium ion secondary batteries. In addition, the negative electrode of a lithium ion secondary battery is produced by coating and drying a slurry composition containing the negative electrode active material, a binder composition, and a water-soluble polymer such as carboxymethylcellulose.

In recent years, in order to increase the capacity of a lithium ion secondary battery, a lithium ion secondary battery negative electrode using an alloy-based active material containing Si or the like has been developed. However, in a slurry composition containing an alloy-based active material, the alloy-based active material tends to aggregate and it is difficult to disperse uniformly. As a result, the cell resistance of the secondary battery increases, and battery characteristics such as cycle characteristics may deteriorate.

In Patent Document 1, carboxymethyl cellulose is added to improve the dispersibility of the alloy-based active material, but an increase in electron resistance or charge transfer resistance, and deterioration of cell properties (battery characteristics) associated therewith are concerned.

Further, in Patent Document 2, a water-soluble polymer containing an ethylenically unsaturated carboxylic acid monomer unit, a (meth)acrylic acid ester monomer unit, or the like is used, but the dispersibility of the alloy-based active material in the slurry composition is not sufficient. Therefore, the alloy-based active material may be unevenly distributed in the negative electrode active material layer. As a result, as the volume of the alloy-based active material expands during charging and discharging, the active material may desorb (fall off) from the negative electrode, deteriorating cycle characteristics, output characteristics, and the like of the secondary battery.

International Publication 2011/37142 International Publication 2012/26462

Conventionally, a carbon-based active material has been used as a negative electrode active material for a lithium ion secondary battery, but recently, for the purpose of further increasing the capacity of the lithium ion secondary battery, a negative electrode of a lithium ion secondary battery using an alloy active material for the negative electrode active material has been studied. However, in the slurry composition, the alloy-based active material tends to aggregate and cannot be uniformly dispersed, so that battery characteristics such as cycle characteristics may deteriorate.

Accordingly, an object of the present invention is to provide a secondary battery having excellent cycle characteristics, and a slurry composition for a lithium ion secondary battery negative electrode capable of obtaining a negative electrode having excellent binding properties.

As a result of earnest examination to solve the above problems, the present inventors found that the dispersibility of the negative electrode active material is improved by using two or more kinds of water-soluble polymers having different viscosity regions. In particular, when an alloy-based active material was used as the negative electrode active material, it was found that the volume expansion of the alloy-based active material during charging and discharging can be suppressed. Moreover, even if the number of blending parts of the water-soluble polymer is reduced, the volume expansion of the alloy-based active material during charging and discharging can be sufficiently suppressed, and accordingly, the charge transfer resistance is reduced to improve the cycle characteristics of the secondary battery (especially high-temperature cycle characteristics. ). Based on these findings, the present invention has been accomplished.

The gist of the present invention for the purpose of solving such a problem is as follows.

[1] A slurry composition for a negative electrode of a lithium ion secondary battery containing a negative electrode active material (A), a water-soluble polymer (B), and water (C),

The water-soluble polymer (B) contains 80 mass% or more of a water-soluble polymer (B1) and an ethylenically unsaturated acid monomer unit that are alkali metal salts of a polymer containing an ethylenically unsaturated acid monomer unit and a fluorine-containing (meth)acrylic acid ester monomer unit. The water-soluble polymer (B2) which is an alkali metal salt of the polymer to be contained,

The viscosity of the 5% aqueous solution of the water-soluble polymer (B1) is 100 cp or more and 1500 cp or less,

The slurry composition for a lithium ion secondary battery negative electrode whose viscosity of 5% aqueous solution of the said water-soluble polymer (B2) is 2000 cp or more and 20000 cp or less.

[2] The slurry composition for a lithium ion secondary battery negative electrode according to [1], wherein the water-soluble polymer (B) contains 0.1 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the negative electrode active material (A).

[3] The slurry composition for a lithium ion secondary battery negative electrode according to [1] or [2], wherein the weight ratio (B1/B2) of the water-soluble polymer (B1) and the water-soluble polymer (B2) is 5/95 or more and 95/5 or less. .

[4] The content ratio of the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B1) is 15% by mass or more and 50% by mass or less, and the content rate of the fluorine-containing (meth)acrylic acid ester monomer unit is 1% by mass or more. , The slurry composition for a lithium ion secondary battery negative electrode in any one of [1]-[3] which is 20 mass% or less.

[5] The slurry composition for a lithium ion secondary battery negative electrode according to any one of [1] to [4], wherein the water-soluble polymer (B1) contains (meth)acrylic acid ester monomer units of 30% by mass or more and 70% by mass or less. .

[6] The lithium ion secondary according to any one of [1] to [5], wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B1) is an ethylenically unsaturated carboxylic acid monomer and/or an ethylenically unsaturated sulfonic acid monomer. Slurry composition for battery negative electrode.

[7] The lithium ion secondary battery negative electrode according to any one of [1] to [5], wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B1) is an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer. Dragon slurry composition.

[8] The content ratio of the ethylenically unsaturated carboxylic acid monomer in the water-soluble polymer (B1) is 15 mass% or more and 50 mass% or less, and the content ratio of the ethylenically unsaturated sulfonic acid monomer is 1 mass% or more and 15 mass The lithium ion secondary battery slurry composition for negative electrodes as described in [7] which is% or less.

[9] The slurry composition for a lithium ion secondary battery negative electrode according to any one of [1] to [8], wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer.

[10] The lithium ion secondary according to any one of [1] to [8], wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer and/or an ethylenically unsaturated sulfonic acid monomer. Slurry composition for battery negative electrode.

[11] The lithium ion secondary battery negative electrode according to any one of [1] to [8], wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer. Dragon slurry composition.

[12] The content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer (B2) is 90 mass% or more, and 99 mass% or less, and the content ratio of the ethylenically unsaturated sulfonic acid monomer unit is 1 mass% or more, The slurry composition for a lithium ion secondary battery negative electrode as described in [11] which is 10 mass% or less.

[13] Preparation of a lithium ion secondary battery negative electrode comprising the step of applying and drying the slurry composition for a lithium ion secondary battery negative electrode according to any one of [1] to [12] above to a current collector to form a negative electrode active material layer. Way.

[14] a positive electrode, a negative electrode, a separator and an electrolyte,

A lithium ion secondary battery in which the negative electrode is a lithium ion secondary battery negative electrode obtained by the production method described in [13].

According to the present invention, by using two or more kinds of water-soluble polymers having different viscosity regions, the negative electrode active material is a carbon-based active material, an alloy-based active material, or a mixture thereof, and the dispersibility of the negative electrode active material is improved, and during charging and discharging The volume expansion of the negative electrode active material can be suppressed. As a result, a negative electrode excellent in binding strength can be obtained. Moreover, the charge transfer resistance is reduced, and a secondary battery excellent in high-temperature cycle characteristics can be obtained.

1 is a Nyquist plot diagram used to measure charge transfer resistance.

Below, the slurry composition for a lithium ion secondary battery negative electrode, (2) lithium ion secondary battery negative electrode, and (3) lithium ion secondary battery are demonstrated in order.

(1) Slurry composition for lithium ion secondary battery negative electrode

The slurry composition for a negative electrode of a lithium ion secondary battery according to the present invention (hereinafter, simply referred to as "a slurry composition for a negative electrode") may contain a negative electrode active material (A), a water-soluble polymer (B), and water (C). .

(A) Negative electrode active material

The negative electrode active material is a material that transfers electrons (lithium ions) in the negative electrode. As the negative electrode active material, a carbon-based active material (A1) or an alloy-based active material (A2), which will be described later, can be used, but the negative-electrode active material preferably contains a carbon-based active material and an alloy-based active material. By using a carbon-based active material and an alloy-based active material as the negative electrode active material, a lithium ion secondary battery having a larger capacity than the negative electrode obtained using only the conventional carbon-based active material (hereinafter, simply referred to as a “secondary battery”) can be obtained. In addition, problems such as a decrease in the binding strength of the lithium ion secondary battery negative electrode (hereinafter sometimes simply referred to as “negative electrode”) can be solved.

(A1) Carbon-based active material

The carbon-based active material used in the present invention refers to an active material having carbon as a main skeleton capable of intercalating lithium, and specifically, a carbonaceous material and a graphite material. The carbonaceous material generally has a low graphitization (crystallinity) in which the carbon precursor is heat-treated (carbonized) at 2000° C. or lower (the lower limit of the treatment temperature is not particularly limited, but may be, for example, 500° C. or higher). Low) carbon material, and the graphite material is obtained by heat-treating this graphitic carbon at 2000°C or higher (the upper limit of the treatment temperature is not particularly limited, but can be, for example, 5000°C or lower). Graphite materials having high crystallinity close to graphite are shown.

Examples of the carbonaceous material include digraphite carbon that easily changes the structure of carbon by heat treatment temperature, and poor graphite carbon having a structure close to the amorphous structure typified by glassy carbon.

Examples of the graphitic carbon include carbon materials based on tar pitch obtained from petroleum or coal, for example, coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolysis vapor-grown carbon fibers, and the like. Can be lifted. MCMB is carbon fine particles obtained by separating and extracting mesophase globules produced in the process of heating pitches at around 400°C. The mesophase pitch-based carbon fiber is a carbon fiber using mesophase pitch obtained by growing and coalescing the mesophase globules. Pyrolytic gas phase growth carbon fiber, (1) a method for thermally decomposing acrylic polymer fibers, (2) a method for thermally decomposing by spinning a pitch, and (3) a catalyst for gas phase pyrolysis of hydrocarbons using nanoparticles such as iron as a catalyst It is a carbon fiber obtained by the growth (catalytic CVD) method.

Examples of the non-graphitic carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo isotropic carbon, and furfuryl alcohol resin fired body (PFA).

Examples of the graphite material include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite heat-treated at 2800°C or higher, graphitized MCMB heat-treated at 2000°C or higher, and graphitized mesophase pitch-based carbon fiber heat-treated at a mesophase pitch-based carbon fiber at 2000°C or higher. Can be lifted.

Among the carbon-based active materials, graphite materials are preferred. By using a graphite material, the density of the negative electrode active material layer becomes easy to increase, and the density of the negative electrode active material layer is 1.6 g/cm 3 or more (the upper limit of the density is not particularly limited, but can be 2.2 g/cm 3 or less). The production of the negative electrode becomes easy. If the negative electrode has a negative electrode active material layer having a density in the above range, the effect of the present invention is remarkable.

The volume average particle diameter of the carbon-based active material has an upper limit of preferably 100 μm or less, more preferably 50 μm or less, particularly preferably 30 μm or less, and a lower limit thereof, preferably 0.1 μm or more, more preferably It is preferably 0.5 µm or more, particularly preferably 1 µm or more. When the volume average particle diameter of the carbon-based active material is within this range, production of a slurry composition for a lithium ion secondary battery negative electrode according to the present invention becomes easy. In addition, the volume average particle diameter in this invention can be calculated|required by measuring a particle size distribution by laser diffraction.

The specific surface area of the carbon-based active material has an upper limit of preferably 20.0 m2/g or less, more preferably 15.0 m2/g or less, particularly preferably 10.0 m2/g or less, and a lower limit thereof, preferably 3.0 M 2 /g or more, more preferably 3.5 m 2 /g or more, particularly preferably 4.0 m 2 /g or more. When the specific surface area of the carbon-based active material is in the above range, since the active point of the surface of the carbon-based active material increases, the output characteristics of the lithium ion secondary battery are excellent.

(A2) Alloy-based active material

The alloy-based active material used in the present invention contains an element capable of inserting lithium into a structure, and has a theoretical electrical capacity per weight of 500 mAh/g or more when lithium is inserted (the upper limit of the theoretical electrical capacity is particularly Although it is not limited, for example, it may be 5000 mAh/g or less) phosphorus active materials, specifically, lithium metals, simple metals forming lithium alloys and alloys thereof, and oxides, sulfides, nitrides, and silicides thereof , Carbide, phosphide, etc. are used.

As a simple metal and alloy for forming a lithium alloy, metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn or metals thereof And compounds to be included. Among them, a simple metal of silicon (Si), tin (Sn) or lead (Pb), an alloy containing these atoms, or a compound of these metals is used. Among these, a simple metal of Si capable of intercalation and deintercalation of lithium at a low potential is preferred.

The alloy-based active material used in the present invention may further contain one or more nonmetal elements. Specifically, for example, SiC, SiO _x C _y (hereinafter referred to as “SiOC”) (0 <x ≤ 3, 0 <y ≤ 5), Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x ( x = 0.01 or more and less than 2), SnO _x (0 <x ≤ 2), LiSiO, LiSnO, and the like. Among them, SiOC, SiO _x , and SiC capable of intercalation and deintercalation of lithium at low potentials are preferred, SiOC, SiO _x is more preferable. For example, SiOC can be obtained by firing a polymer material containing silicon. Among SiO _x C _y , a range of 0.8 ≤ x ≤ 3, 2 ≤ y ≤ 4 is preferably used because of the balance of capacity and cycle characteristics. Also among SiO _x, because the balance of the capacity and cycle characteristics, in a range of -0.5 ≤ x ≤ 5 is preferably used.

Examples of oxides, sulfides, nitrides, silicides, carbides, and phosphides of simple metals and alloys forming lithium alloys include oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. of elements capable of inserting lithium. Among them, oxide is particularly preferred. Specifically, a lithium-containing metal complex oxide containing a metal element selected from the group consisting of oxides such as tin oxide, manganese oxide, titanium oxide, niobium oxide, and vanadium oxide, and Si, Sn, Pb, and Ti atoms is used.

As the lithium-containing metal composite oxide, a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ (0.7 ≤ x ≤ 1.5, 1.5 ≤ y ≤ 2.3, 0 ≤ z ≤ 1.6, M is Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn and Nb). Among them, Li _4/3 Ti _5/3 O ₄ , Li ₁ Ti ₂ O ₄ , Li _4/5 Ti _{11/ 5} O ₄ is used.

Among the alloy-based active materials, a material containing silicon is preferable, and among them, SiO _x C _y , SiO _x , and SiC such as SiOC are more preferable. In this compound, insertion and desorption of Li to Si (silicon) at high potential and C (carbon) at low potential is presumed to occur, and since the expansion and contraction are suppressed than other alloy-based active materials, the effect of the present invention is obtained more easy.

The volume average particle diameter of the alloy-based active material has an upper limit of preferably 50 μm or less, more preferably 20 μm or less, particularly preferably 10 μm or less, and a lower limit thereof, preferably 0.1 μm or more, more preferably It is preferably 0.5 µm or more, particularly preferably 1 µm or more. When the volume average particle diameter of the alloy-based active material is within this range, production of the slurry composition for a lithium ion secondary battery negative electrode according to the present invention becomes easy.

The specific surface area of the alloy-based active material has an upper limit of preferably 20.0 m 2 /g or less, more preferably 15.0 m 2 /g or less, particularly preferably 10.0 m 2 /g or less, and a lower limit thereof, preferably 3.0 M 2 /g or more, more preferably 3.5 m 2 /g or more, particularly preferably 4.0 m 2 /g or more. When the specific surface area of the alloy-based active material is in the above range, the active point of the surface of the alloy-based active material increases, so that the output characteristics of the lithium ion secondary battery are excellent.

The content ratio of the alloy-based active material and the carbon-based active material is the mass ratio of the alloy-based active material/carbon-based active material, and the upper limit thereof is preferably 50/50 or less, more preferably 45/55 or less, particularly preferably 40/ It is 60 or less, and its lower limit is preferably 20/80 or more, more preferably 25/75 or more, and particularly preferably 30/70 or more. By mixing the alloy-based active material and the carbon-based active material in the above range, a battery having a larger capacity than the negative electrode obtained using only the conventional carbon-based active material can be obtained, and sufficient binding strength of the negative electrode can be obtained.

(B) water-soluble polymer

The water-soluble polymer (B) is an alkali metal salt of a polymer containing an ethylenically unsaturated acid monomer unit and a fluorine-containing (meth)acrylic acid ester monomer unit (hereinafter, simply referred to as "water-soluble polymer (B1)") And a water-soluble polymer (B2), which is an alkali metal salt of a polymer containing 80% by mass or more of an ethylenically unsaturated acid monomer unit (hereinafter sometimes simply referred to as "water-soluble polymer (B2)"). Hereinafter, the water-soluble polymer (B1) and the water-soluble polymer (B2) will be described in detail.

(B1) A water-soluble polymer that is an alkali metal salt of a polymer containing an ethylenically unsaturated acid monomer unit and a fluorine-containing (meth)acrylic acid ester monomer unit

The water-soluble polymer (B1) can exhibit good water solubility by containing an ethylenically unsaturated acid monomer unit.

In addition, the water-soluble polymer (B1) contains a fluorine-containing (meth)acrylic acid ester monomer unit, so that the binding property of the negative electrode is improved, and a negative electrode having excellent strength can be obtained. Moreover, by covering the surface of the negative electrode active material with the water-soluble polymer (B1), decomposition of the electrolytic solution on the surface of the negative electrode active material in the secondary battery is suppressed, and the durability (cycle characteristics) of the secondary battery can be improved. In addition, by coating the negative electrode active material with the water-soluble polymer (B1), it is possible to increase the affinity between the negative electrode active material and the electrolyte, improve ion conductivity, and reduce the internal resistance of the secondary battery. In addition, the generation of dendrites can be prevented. In addition, in this specification, (meth)acrylic includes both acrylic and methacrylic.

In addition, the water-soluble polymer (B1) may contain a (meth)acrylic acid ester monomer unit or a crosslinkable monomer unit in addition to the monomer units described above, and also a structure formed by polymerizing monomers having functionalities such as reactive surfactant monomers. A unit or a structural unit formed by polymerizing other copolymerizable monomers may be contained.

<Ethylenic unsaturated acid monomer unit>

The ethylenically unsaturated acid monomer unit is a structural unit formed by polymerizing an ethylenically unsaturated acid monomer.

The ethylenically unsaturated acid monomer is an ethylenically unsaturated monomer having an acid group such as a carboxyl group, sulfonic acid group or phosphinyl group, and is not limited to a specific monomer. Specific examples of the ethylenically unsaturated acid monomer are ethylenically unsaturated carboxylic acid monomer, ethylenically unsaturated sulfonic acid monomer, and ethylenically unsaturated phosphoric acid monomer.

Specific examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and its derivatives, ethylenically unsaturated dicarboxylic acid and its acid anhydride, and derivatives thereof.

Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.

Examples of derivatives of ethylenically unsaturated monocarboxylic acids include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β -Diaminoacrylic acid.

Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, and itaconic acid.

Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.

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

Specific examples of the ethylenically unsaturated sulfonic acid monomer include a sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group or a salt thereof, a monomer containing an amide group and a sulfonic acid group or a salt thereof, and a monomer containing a hydroxyl group and a sulfonic acid group or a salt thereof, etc. Can be heard.

Examples of the sulfonic acid group-containing monomer having no functional group other than the sulfonic acid group include monomers sulfonated with one of the conjugated double bonds of diene compounds such as isoprene and butadiene, vinylsulfonic acid, methylvinylsulfonic acid, styrenesulfonic acid, and allylsulfonic acid, ( And meth)acrylic sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, and sulfobutyl (meth)acrylate. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example.

As a monomer containing an amide group and a sulfonic acid group, 2-acrylamide-2-hydroxypropanesulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and the like are exemplified. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example.

As a monomer containing a hydroxyl group and a sulfonic acid group, 3-aryloxy-2-hydroxypropanesulfonic acid (HAPS) etc. are mentioned, for example. Moreover, as the salt, lithium salt, sodium salt, potassium salt, etc. are mentioned, for example.

Among these, as a monomer having a sulfonic acid group, styrene sulfonic acid, 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and a monomer containing an amide group and a sulfonic acid group or a salt thereof are preferable.

Specific examples of the ethylenically unsaturated phosphoric acid monomer include a monomer having a -OP(=O)(-ORa)-ORb group (Ra and Rb are independently hydrogen atoms or arbitrary organic groups), or a salt thereof. . Specific examples of the organic group as Ra and Rb include an aliphatic group such as octyl group, and an aromatic group such as phenyl group. Specific examples of the monomer having a phosphoric acid group include a compound containing a phosphoric acid group and an aryloxy group, and a phosphoric acid group-containing (meth)acrylic acid ester. As a compound containing a phosphoric acid group and an aryloxy group, 3-aryloxy-2-hydroxypropane phosphoric acid is mentioned, for example. As the phosphoric acid group-containing (meth)acrylic acid ester, for example, dioctyl-2-methacryloyloxyethyl phosphate, diphenyl-2-methacryloyloxyethyl phosphate, monomethyl-2-methacryloyloxyethyl Phosphate, dimethyl-2-methacryloyloxyethyl phosphate, monoethyl-2-methacryloyloxyethyl phosphate, diethyl-2-methacryloyloxyethyl phosphate, monoisopropyl-2-methacryloyl Oxyethyl phosphate, diisopropyl-2-methacryloyloxyethyl phosphate, mono n-butyl-2-methacryloyloxyethyl phosphate, din-butyl-2-methacryloyloxyethyl phosphate, mono part Methoxyethyl-2-methacryloyloxyethyl phosphate, dibutoxyethyl-2-methacryloyloxyethyl phosphate, mono(2-ethylhexyl)-2-methacryloyloxyethylphosphate, di(2-ethyl Hexyl)-2-methacryloyloxyethyl phosphate.

Moreover, alkali metal salt or ammonium salt of the said ethylenic unsaturated acid monomer can also be used. The ethylenically unsaturated acid monomers may be used alone or in combination of two or more.

Among these, from the viewpoint of expressing good water solubility in the water-soluble polymer (B1), the ethylenically unsaturated acid monomer is preferably an ethylenically unsaturated carboxylic acid monomer and/or an ethylenically unsaturated sulfonic acid monomer, more preferably ethylene. Sex unsaturated carboxylic acid monomers and ethylenically unsaturated sulfonic acid monomers.

Among the ethylenically unsaturated carboxylic acid monomers, from the viewpoint of expressing good water solubility in the water-soluble polymer (B1), it is preferably an ethylenically unsaturated monocarboxylic acid, more preferably acrylic acid or methacrylic acid, particularly preferably Methacrylic acid. Moreover, among the ethylenically unsaturated sulfonic acid monomers, from the viewpoint of expressing good water solubility in the water-soluble polymer (B1), preferably 3-sulfopropane (meth)acrylic acid ester, bis-(3-sulfopropyl) itaconic acid ester, 2- Acrylamide-2-methylpropanesulfonic acid, more preferably 2-acrylamide-2-methylpropanesulfonic acid.

The content ratio of the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B1) has an upper limit of preferably 50 mass% or less, more preferably 45 mass% or less, particularly preferably 40 mass% or less, The lower limit is preferably 15% by mass or more, more preferably 20% by mass or more, and particularly preferably 25% by mass or more.

By making the content ratio of the ethylenically unsaturated acid monomer unit within the above range, it is possible to suppress the generation of aggregates of the water-soluble polymer during production of the water-soluble polymer (B1), thereby obtaining the water-soluble polymer (B1) with good yield, and It becomes possible to express good water solubility in B1). Here, the ratio of the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B1) is generally the same as the ratio (injection ratio) of the ethylenically unsaturated acid monomer in all monomers when the water-soluble polymer (B1) is polymerized. do.

Moreover, when the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B1) is an ethylenically unsaturated carboxylic acid monomer unit and an ethylenically unsaturated sulfonic acid monomer unit, the content ratio of the ethylenically unsaturated carboxylic acid monomer unit, It is preferable that the content rate of an ethylenic unsaturated sulfonic acid monomer unit is the following range.

That is, the content ratio of the ethylenically unsaturated carboxylic acid monomer unit is preferably an upper limit of 50% by mass or less, more preferably 45% by mass or less, particularly preferably 40% by mass or less, and the lower limit thereof, Preferably it is 15 mass% or more, More preferably, it is 20 mass% or more, Especially preferably, it is 22.5 mass% or more. Moreover, the upper limit of the content ratio of the ethylenically unsaturated sulfonic acid monomer unit is preferably 15 mass% or less, more preferably 12 mass% or less, particularly preferably 10 mass% or less, and the lower limit is preferably Is 1% by mass or more, more preferably 2% by mass or more, particularly preferably 3% by mass or more.

Here, the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer (B1) is usually the ratio (injection) of the ethylenically unsaturated carboxylic acid monomer in all monomers when the water-soluble polymer (B1) is polymerized. Ratio), and the ratio of the ethylenically unsaturated sulfonic acid monomer units in the water-soluble polymer (B1) is usually the ratio (injection) of the ethylenically unsaturated sulfonic acid monomer in all monomers when the water-soluble polymer (B1) is polymerized. B) matches.

When the content ratio of the ethylenically unsaturated carboxylic acid monomer unit is within the above range, good water solubility can be expressed in the water-soluble polymer (B1). Moreover, it is suppressed that the fluidity|liquidity of the slurry composition for negative electrodes falls, and in the process of manufacturing a negative electrode mentioned later, when applying the slurry composition for negative electrodes to a current collector, coating failure with respect to a current collector can be prevented. As a result, a negative electrode excellent in binding property can be obtained. In addition, by increasing the thixotropy of the slurry composition for a negative electrode, it is possible to suppress the occurrence of coating streaks when applying the slurry composition for a negative electrode to a current collector in the process of manufacturing a negative electrode. In addition, a negative electrode excellent in surface smoothness can be obtained, and the wettability of the slurry composition for negative electrodes is improved, and as a result, a negative electrode excellent in binding property can be obtained.

When the content ratio of the ethylenically unsaturated sulfonic acid monomer unit is within the above range, good water solubility can be expressed in the water-soluble polymer (B1). Moreover, in manufacture of a water-soluble polymer (B1), generation|occurrence|production of the aggregate of the water-soluble polymer (B1) is suppressed and it shows excellent polymerization stability.

<Fluorine-containing (meth)acrylic acid ester monomer unit>

The fluorine-containing (meth)acrylic acid ester monomer unit is a structural unit formed by polymerization of a fluorine-containing (meth)acrylic acid ester monomer.

As a fluorine-containing (meth)acrylic acid ester monomer, the monomer represented by following formula (I) is mentioned, for example.

[Formula 1]

In the formula (I), R ¹ represents a hydrogen atom or a methyl group. In the formula (I), R ² represents a hydrocarbon group containing a fluorine atom. Carbon number of a hydrocarbon group is 1 or more normally, and is 18 or less normally. Moreover, the number of fluorine atoms contained in R ² may be 1, or 2 or more.

Examples of the fluorine-containing (meth)acrylic acid ester monomer represented by formula (I) include (meth)acrylic acid fluoride alkyl, (meth)acrylic acid fluoride aryl, and (meth)acrylic acid fluoride aralkyl. Especially, (meth)acrylic-acid alkyl fluoride is preferable. As a specific example of such a monomer, (meth)acrylic acid-2,2,2-trifluoroethyl, (meth)acrylic acid-β-(perfluorooctyl)ethyl, (meth)acrylic acid-2,2,3 ,3-tetrafluoropropyl, (meth)acrylic acid-2,2,3,4,4,4-hexafluorobutyl, (meth)acrylic acid-1H,1H,9H-perfluoro-1-nonyl, ( (Meth)acrylic acid-1H,1H,11H-perfluorodecyl, (meth)acrylic acid perfluorooctyl, (meth)acrylic acid-3-[4-[1-trifluoromethyl-2,2-bis[bis And (meth)acrylic acid perfluoroalkyl esters such as (trifluoromethyl)fluoromethyl]ethynyloxy]benzooxy]-2-hydroxypropyl.

As the fluorine-containing (meth)acrylic acid ester monomer, one type may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer (B1) may contain only one type of a fluorine-containing (meth)acrylic acid ester monomer unit, or may contain two or more types in combination at any ratio.

The upper limit of the content ratio of the fluorine-containing (meth)acrylic acid ester monomer unit in the water-soluble polymer (B1) is preferably 20 mass% or less, more preferably 15 mass% or less, particularly preferably 12 mass% The lower limit is preferably 1% by mass or more, more preferably 3% by mass or more, and particularly preferably 5% by mass or more.

When the proportion of the fluorine-containing (meth)acrylic acid ester monomer unit is too low, the repelling force to the electrolytic solution cannot be imparted to the water-soluble polymer (B1), and the swelling property may not be in an appropriate range. As a result, the binding strength of the negative electrode may decrease. In addition, dendrites may be generated, and ionic conductivity may decrease. When the proportion of the fluorine-containing (meth)acrylic acid ester monomer unit is too high, wettability to the electrolyte cannot be imparted to the water-soluble polymer (B1), and low-temperature cycle characteristics may be deteriorated. By setting the content ratio of the fluorine-containing (meth)acrylic acid ester monomer unit within the above range, lithium ion conductivity is improved, and a battery having excellent cycle characteristics can be obtained. Moreover, a negative electrode having excellent binding strength can be obtained. Here, the proportion of the fluorine-containing (meth)acrylic acid ester monomer unit in the water-soluble polymer (B1) is usually the proportion of the fluorine-containing (meth)acrylic acid ester monomer in all monomers when the water-soluble polymer (B1) is polymerized. (Injection cost).

Moreover, when the water-soluble polymer (B1) contains a fluorine-containing (meth)acrylic acid ester monomer unit, alkali resistance is imparted to the negative electrode active material layer. An alkaline substance may be contained in the slurry composition for forming a negative electrode, and an alkaline substance may be generated by redox by operation of a device. Such an alkaline substance corrodes the current collector and impairs device life, but corrosion of the current collector by the alkaline substance is suppressed by the negative electrode active material layer having alkali resistance.

<(meth)acrylic acid ester monomer unit>

When the water-soluble polymer (B1) contains a (meth)acrylic acid ester monomer, the wettability of the negative electrode with respect to the electrolytic solution becomes good, and the cycle characteristics of the secondary battery are improved. The (meth)acrylic acid ester monomer unit is a structural unit formed by polymerizing the (meth)acrylic acid ester monomer. However, among the (meth)acrylic acid ester monomers, those containing fluorine are distinct from the (meth)acrylic acid ester monomers as the above-described fluorine-containing (meth)acrylic acid ester monomers.

Examples of the (meth)acrylic acid ester monomers are methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, and heptyl Acrylic acid alkyl esters such as acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, and stearyl acrylate; And methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate Methacrylic acid such as acrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, etc. And alkyl esters.

As the (meth)acrylic acid ester monomer, one type may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer (B1) may contain only one type of (meth)acrylic acid ester monomer unit, or may contain two or more types in combination at any ratio.

In the water-soluble polymer (B1), the content ratio of the (meth)acrylic acid ester monomer unit is preferably an upper limit of 70 mass% or less, more preferably 65 mass% or less, particularly preferably 63 mass% or less. , The lower limit thereof is preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more.

When the content ratio of the (meth)acrylic acid ester monomer unit is within the above range, the binding property of the negative electrode active material layer to the current collector can be increased, and flexibility of the negative electrode active material layer can be increased. Here, the ratio of the (meth)acrylic acid ester monomer unit in the water-soluble polymer (B1) is usually the ratio (injection ratio) of the (meth)acrylic acid ester monomer in all monomers when polymerizing the water-soluble polymer (B1). To match.

<Crosslinkable monomer unit>

The water-soluble polymer (B1) may further contain a crosslinkable monomer unit in addition to the above-described respective structural units. The crosslinkable monomer unit is a structural unit capable of forming a crosslinked structure during or after polymerization by heating or energy irradiation. As an example of a crosslinkable monomer, the monomer which normally has heat crosslinkability is mentioned. More specifically, a monofunctional monomer having a heat crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional monomer having two or more olefinic double bonds per molecule are exemplified.

Examples of the heat crosslinkable crosslinkable group contained in the monofunctional monomer include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and combinations thereof. Among these, an epoxy group is more preferable from the viewpoint of easy control of crosslinking and crosslinking density.

Examples of the crosslinkable monomer having an epoxy group as a heat crosslinkable crosslinkable group and having an olefinic double bond are vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o- allylphenyl glycidyl Unsaturated glycidyl ethers such as ether; Butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododecadiene, etc. Monoepoxides of dienes or polyenes; Alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene and 1,2-epoxy-9-decene; And glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl And glycidyl esters of unsaturated carboxylic acids such as -3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid. Can.

Examples of the crosslinkable monomer having an N-methylolamide group and having an olefinic double bond as a heat crosslinkable crosslinkable group include (meth)acrylamides having a methylol group such as N-methylol(meth)acrylamide. Can be lifted.

Examples of the crosslinkable monomer having an oxetanyl group as a heat crosslinkable crosslinkable group and having an olefinic double bond include 3-((meth)acryloyloxymethyl)oxetane and 3-((meth)acryloyl Oxymethyl)-2-trifluoromethyloxetane, 3-((meth)acryloyloxymethyl)-2-phenyloxetane, 2-((meth)acryloyloxymethyl)oxetane, and 2- ((Meth)acryloyloxymethyl)-4-trifluoromethyl oxetane.

Examples of the crosslinkable monomer having an oxazoline group and having an olefinic double bond as a heat crosslinkable crosslinkable group include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, and 2-vinyl -5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline And 2-isopropenyl-5-ethyl-2-oxazoline.

Examples of polyfunctional monomers having two or more olefinic double bonds are allyl (meth)acrylate, ethylene di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate , Tetraethylene glycol di(meth)acrylate, trimethylolpropane-tri(meth)acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyl And oxyethane, trimethylolpropane-diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than the above, triallylamine, methylenebisacrylamide, and divinylbenzene.

As the crosslinkable monomer, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate can be preferably used.

When the crosslinkable monomer unit is contained in the water-soluble polymer (B1), the lower limit of the content ratio is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, particularly preferably 0.5% by mass or more, and The upper limit of the content ratio is preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less. By setting the content ratio of the crosslinkable monomer unit to the lower limit of the above range, it is possible to increase the weight average molecular weight of the water-soluble polymer (B1) and prevent the swelling degree from excessively increasing. On the other hand, by setting the ratio of the crosslinkable monomer units to be less than or equal to the upper limit of the above range, the solubility of the water-soluble polymer (B1) in water can be increased, and dispersibility can be improved. Therefore, by making the content rate of a crosslinkable monomer unit into the said range, both swelling degree and dispersibility can be made favorable. Here, the ratio of the crosslinkable monomer unit in the water-soluble polymer (B1) usually coincides with the ratio (injection ratio) of the crosslinkable monomer in all monomers when the water-soluble polymer (B1) is polymerized.

<Reactive surfactant monomer unit>

The water-soluble polymer (B1) may contain, in addition to each of the above monomer units, a structural unit formed by polymerizing monomers having functionalities such as reactive surfactant monomers.

The reactive surfactant monomer is a monomer having a polymerizable group capable of copolymerizing with other monomers described later, and having a surfactant (hydrophilic group and hydrophobic group).

The monomer unit obtained by polymerizing a reactive surfactant monomer is a structural unit that constitutes a part of the molecule of the water-soluble polymer (B1) and can function as a surfactant.

Usually, the reactive surfactant monomer has a polymerizable unsaturated group, and this group also functions as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group of the reactive surfactant monomer include vinyl group, allyl group, vinylidene group, propenyl group, isopropenyl group, and isobutylidene group. One kind of these polymerizable unsaturated groups may be used, or two or more kinds thereof may be used.

Moreover, a reactive surfactant monomer is a part which expresses hydrophilicity, and usually has a hydrophilic group. Reactive surfactant monomers are classified into anionic, cationic, and nonionic surfactants by type of hydrophilic group.

Examples of anionic hydrophilic groups include -SO ₃ M, -COOM, and -PO(OH) ₂ . Here, M represents a hydrogen atom or a cation. Examples of cations include alkali metal ions such as lithium, sodium, and potassium; Alkaline earth metal ions such as calcium and magnesium; Ammonium ion; Ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; And ammonium ions of alkanolamines, such as monoethanolamine, diethanolamine, and triethanolamine.

Examples of cationic hydrophilic groups include -Cl, -Br, -I, and -SO ₃ ORX. Here, RX represents an alkyl group. Examples of RX include methyl group, ethyl group, propyl group, and isopropyl group.

An example of a nonionic hydrophilic group is -OH.

As an example of a preferable reactive surfactant monomer, the compound represented by following formula (II) is mentioned.

[Formula 2]

In formula (II), R represents a divalent bonding group. Examples of R include -Si-O- groups, methylene groups and phenylene groups. In Formula (II), R ³ represents a hydrophilic group. Examples of R ³ include -SO ₃ NH ₄ . In Formula (II), n is an integer of 1 or more and 100 or less. As the reactive surfactant monomer, one type may be used alone, or two or more types may be used in combination at any ratio.

When the water-soluble polymer (B1) contains a reactive surfactant monomer unit, the upper limit of the content ratio is preferably 15% by mass or less, more preferably 10% by mass or less, particularly preferably 5% by mass or less, The lower limit of the content ratio is preferably 0.1 mass% or more, more preferably 0.5 mass% or more, and particularly preferably 1 mass% or more.

The dispersibility of the negative electrode active material (A) can be improved by setting the content ratio of the reactive surfactant monomer units to the lower limit of the above range. On the other hand, the durability of the negative electrode active material layer can be improved by setting the content ratio of the reactive surfactant monomer units to the upper limit of the above range. Here, the ratio of the reactive surfactant monomer units in the water-soluble polymer (B1) usually coincides with the ratio (injection ratio) of the reactive surfactant monomer in all monomers when polymerizing the water-soluble polymer (B1).

<Other monomer units>

As a further example of the arbitrary units that the water-soluble polymer (B1) may have, structural units obtained by polymerizing the following monomers are exemplified. That is, styrene-based monomers such as styrene, chlorostyrene, vinyltoluene, t-butylstyrene, vinylbenzoic acid, methyl vinylbenzoate, vinylnaphthalene, chloromethylstyrene, hydroxymethylstyrene, α-methylstyrene, and divinylbenzene; Amide monomers such as acrylamide and acrylamide-2-methylpropanesulfonic acid; Α,β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Olefin monomers such as ethylene and propylene; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; Vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; Vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; And structural units obtained by polymerizing 1 or more of the heterocyclic-containing vinyl compound monomers, such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole, are mentioned. The ratio of these structural units in the water-soluble polymer (B1) has an upper limit of usually 10% by mass or less, preferably 5% by mass or less, and a lower limit of it is usually 0% by mass or more.

Here, the ratio of the other monomer units in the water-soluble polymer (B1) usually coincides with the ratio (injection ratio) of other monomers in all the monomers when the water-soluble polymer (B1) is polymerized.

<Solution viscosity of water-soluble polymer (B1)>

Moreover, the solution viscosity (5% aqueous solution viscosity) at the time of adjusting the 5% aqueous solution at pH 8.5 of the water-soluble polymer (B1) is 100 cp or more and 1500 cp or less, and the upper limit is preferably 1200 cp or less, More preferably, it is 1000 cp or less, and its lower limit is preferably 120 cp or more, and more preferably 200 cp or more.

Here, the pH value when adjusting the 5% aqueous solution of the water-soluble polymer (B1) is not particularly limited as long as it is pH 7.0 or higher, and the solution viscosity (5%) is adjusted by adjusting the 5% aqueous solution at any pH value of pH 7.0 or higher. Aqueous solution viscosity). The viscosity of the measured 5% aqueous solution of the water-soluble polymer (B1) does not change significantly at any pH value as long as it is pH 7.0 or higher. Therefore, the preferable viscosity range of the 5% aqueous solution viscosity at any pH value of pH 7.0 or more of the water-soluble polymer (B1) becomes the same as the above range. When the viscosity of the 5% aqueous solution of the water-soluble polymer (B1) is too high, it becomes difficult to solubilize the water-soluble polymer (B1), and the binding property of the negative electrode active material layer to the current collector decreases. Moreover, when the viscosity of the 5% aqueous solution of the water-soluble polymer (B1) is too low, the charge transfer resistance increases due to the decrease in the adsorption property of the water-soluble polymer (B1) to the negative electrode active material (A), and the flexibility of the negative electrode active material layer This may decrease. By setting the viscosity of the 5% aqueous solution of the water-soluble polymer (B1) to the above range, a secondary battery having excellent cycle characteristics and improved binding property of the negative electrode active material layer to the current collector and flexibility of the negative electrode active material layer can be obtained.

The weight-average molecular weight of the water-soluble polymer (B1) has a lower limit of preferably 500 or more, more preferably 700 or more, particularly preferably 1000 or more, and an upper limit thereof, preferably 500000 or less, more preferably 250000 or less, particularly preferably 100000 or less. The weight average molecular weight of the water-soluble polymer (B1) is a polystyrene conversion using a solution obtained by dissolving 0.85 g/ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide as a developing solvent by gel permeation chromatography (GPC). It can be obtained as a value.

In addition, the glass transition temperature of the water-soluble polymer (B1) has a lower limit thereof, preferably 0°C or higher, more preferably 5°C or higher, and an upper limit thereof, preferably 100°C or lower, more preferably 50°C. Is below. The glass transition temperature of the water-soluble polymer (B1) can be adjusted by combining various monomers.

(B2) A water-soluble polymer that is an alkali metal salt of a polymer containing 80% by mass or more of ethylenically unsaturated acid monomer units

The water-soluble polymer (B2) expresses good water solubility by containing 80% by mass or more, preferably 83% by mass or more, and more preferably 85% by mass or more of the ethylenically unsaturated acid monomer units, and the water-soluble polymer (B2) described later. ), it becomes easy to adjust the 5% aqueous solution viscosity to a desired range. The upper limit of the content ratio of the ethylenically unsaturated acid monomer units in the water-soluble polymer (B2) is 100% by mass. Here, the ratio of the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B2) is generally the same as the ratio (injection ratio) of the ethylenically unsaturated acid monomer in all monomers when the water-soluble polymer (B2) is polymerized. do.

The ethylenically unsaturated acid monomer is as exemplified in the water-soluble polymer (B1), preferably an ethylenically unsaturated carboxylic acid monomer, and more preferably an ethylenically unsaturated carboxylic acid monomer and/or an ethylenically unsaturated sulfonic acid monomer. , And particularly preferably an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer.

Moreover, among the ethylenically unsaturated carboxylic acid monomers, it is preferably an ethylenically unsaturated monocarboxylic acid, more preferably acrylic acid or methacrylic acid, from the viewpoint of providing good thickening properties to the slurry composition for negative electrodes, Especially preferred is acrylic acid. Moreover, among the ethylenically unsaturated sulfonic acid monomers, from the viewpoint of improving the wettability of the negative electrode with respect to the electrolytic solution, it is preferably styrenesulfonic acid or 2-acrylamide-2-methylpropanesulfonic acid, more preferably 2-acrylamide-2- Methyl propane sulfonic acid.

When the ethylenically unsaturated acid monomer units in the water-soluble polymer (B2) are ethylenically unsaturated carboxylic acid monomer units and ethylenically unsaturated sulfonic acid monomer units, the content ratio of ethylenically unsaturated carboxylic acid monomer units and ethylenic It is preferable that the content rate of an unsaturated sulfonic acid monomer unit is the following range.

That is, the content ratio of the ethylenically unsaturated carboxylic acid monomer unit has an upper limit of preferably 99 mass% or less, more preferably 98.5 mass% or less, and a lower limit thereof, preferably 90 mass% or more, more It is preferably 93% by mass or more, particularly preferably 95% by mass or more. Moreover, the upper limit of the content ratio of the ethylenically unsaturated sulfonic acid monomer unit is preferably 10 mass% or less, more preferably 7 mass% or less, particularly preferably 5 mass% or less, and the lower limit is preferably Is 1% by mass or more, more preferably 1.5% by mass or more.

Here, the ratio of the ethylenically unsaturated carboxylic acid monomer units in the water-soluble polymer (B2) is usually the ratio (injection) of the ethylenically unsaturated carboxylic acid monomers in all the monomers when the water-soluble polymer (B2) is polymerized. Ratio), and the ratio of the ethylenically unsaturated sulfonic acid monomer units in the water-soluble polymer (B2) is usually the ratio (injection) of the ethylenically unsaturated sulfonic acid monomer in all monomers when the water-soluble polymer (B2) is polymerized. B) matches.

By making the content rate of an ethylenically unsaturated carboxylic monomer unit into the said range, favorable water solubility can be expressed in a water-soluble polymer (B2). Moreover, it is suppressed that the fluidity|liquidity of the slurry composition for negative electrodes falls, and in the process of manufacturing a negative electrode mentioned later, when applying the slurry composition for negative electrodes to a current collector, coating failure with respect to a current collector can be prevented. As a result, a negative electrode excellent in binding property can be obtained. In addition, by increasing the thixotropy of the slurry composition for a negative electrode, it is possible to suppress the occurrence of coating streaks when applying the slurry composition for a negative electrode to a current collector in the process of manufacturing a negative electrode. In addition, a negative electrode excellent in surface smoothness can be obtained, and the wettability of the slurry composition for negative electrodes is improved, and as a result, a negative electrode excellent in binding property can be obtained.

By setting the content ratio of the ethylenically unsaturated sulfonic acid monomer unit within the above range, the wettability of the negative electrode with respect to the electrolyte solution is improved, and expansion and contraction of the negative electrode active material can be suppressed. Moreover, in manufacture of a water-soluble polymer (B2), it shows excellent polymerization stability.

In addition, the water-soluble polymer (B2) may contain a (meth)acrylic acid ester monomer unit or a crosslinkable monomer unit in addition to the monomer units described above, and also a structure formed by polymerizing monomers having functional properties such as reactive surfactant monomers. A unit or a structural unit formed by polymerizing other copolymerizable monomers may be contained. These monomers are as exemplified in the water-soluble polymer (B1).

The content ratio of the (meth)acrylic acid ester monomer unit in the water-soluble polymer (B2) is preferably an upper limit of preferably 10.0 mass% or less, more preferably 5.0 mass% or less, and preferably a lower limit of 0.5. It is mass% or more, More preferably, it is 1.5 mass% or more.

Here, the ratio of the (meth)acrylic acid ester monomer unit in the water-soluble polymer (B2) is usually the ratio (injection ratio) of the (meth)acrylic acid ester monomer in all monomers when polymerizing the water-soluble polymer (B2). To match.

The content ratio of the crosslinkable monomer unit in the water-soluble polymer (B2) has an upper limit of preferably 2.0 mass% or less, more preferably 1.0 mass% or less, and a lower limit thereof, preferably 0.1 mass% or more. , More preferably, it is 0.2 mass% or more.

Here, the ratio of the crosslinkable monomer unit in the water-soluble polymer (B2) usually coincides with the ratio (injection ratio) of the crosslinkable monomer in all monomers when polymerizing the water-soluble polymer (B2).

The content ratio of the reactive surfactant monomer unit in the water-soluble polymer (B2) is preferably an upper limit of 10.0 mass% or less, more preferably 5.0 mass% or less, and a lower limit, preferably 0.5 mass%. Above, it is more preferably 1.0% by mass or more. Here, the ratio of the reactive surfactant unit in the water-soluble polymer (B2) usually coincides with the ratio (injection ratio) of the reactive surfactant in all monomers when polymerizing the water-soluble polymer (B2).

The content ratio of the other monomer units in the water-soluble polymer (B2) has an upper limit of preferably 5.0 mass% or less, more preferably 2.0 mass% or less, and a lower limit thereof, preferably 0.1 mass% or more, More preferably, it is 0.5 mass% or more.

Here, the ratio of the other monomer units in the water-soluble polymer (B2) usually coincides with the ratio (injection ratio) of the other monomers in all the monomers when polymerizing the water-soluble polymer (B2).

Moreover, the solution viscosity (5% aqueous solution viscosity) at the time of adjusting the 5% aqueous solution at pH 8.5 of the water-soluble polymer (B2) is 2000 cp or more and 20000 cp or less, and the upper limit is preferably 12000 cp or less, More preferably, it is 10000 cp or less, and its lower limit is preferably 2500 cp or more, and more preferably 3000 cp or more.

Here, the pH value when adjusting the 5% aqueous solution of the water-soluble polymer (B2) is not particularly limited as long as it is pH 7.0 or higher, and the solution viscosity (5%) is adjusted by adjusting the 5% aqueous solution at any pH value of pH 7.0 or higher. Aqueous solution viscosity). The viscosity of the 5% aqueous solution of the measured water-soluble polymer (B2) does not change significantly, even if it is pH 7.0 or higher. Therefore, the preferable viscosity range of the 5% aqueous solution viscosity at any pH value of pH 7.0 or more of the water-soluble polymer (B2) becomes the same as the above range. When the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) is too high, it becomes difficult to solubilize the water-soluble polymer (B2), and the binding property of the negative electrode active material layer to the current collector decreases. Moreover, the viscosity of the slurry composition for negative electrodes increases. Moreover, when the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) is too low, the charge transfer resistance increases due to the decrease in the adsorption property of the water-soluble polymer (B2) to the negative electrode active material (A), and the flexibility of the negative electrode active material layer This decreases. By setting the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) to the above range, the binding property of the negative electrode active material layer to the current collector and the flexibility of the negative electrode active material layer are improved, and the viscosity of the slurry composition for negative electrodes is maintained to be excellent. A secondary battery having cycle characteristics can be obtained. Further, by setting the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) to the above range, and by setting the 5% aqueous solution of the water-soluble polymer (B1) at the pH of 8.5 to the aforementioned range, the dispersibility of the negative electrode active material can be dramatically improved. It is possible to improve the binding property of the current collector and the negative electrode active material layer, thereby improving the cycle characteristics of the secondary battery.

The weight average molecular weight of the water-soluble polymer (B2) has an upper limit of preferably 10 million or less, and a lower limit thereof is preferably 10,000 or more, more preferably 200,000 or more, particularly preferably 400,000 or more. .

The weight average molecular weight of the water-soluble polymer (B2) can be obtained in the same manner as the weight average molecular weight of the water-soluble polymer (B1) described above.

In addition, the glass transition temperature of the water-soluble polymer (B2) has a lower limit, preferably -50°C or higher, more preferably -40°C or higher, particularly preferably -30°C or higher, and an upper limit thereof, preferably 150°C or less, more preferably 120°C or less, particularly preferably 100°C or less. The glass transition temperature of the water-soluble polymer (B2) can be adjusted by combining various monomers.

[Preparation of water-soluble polymer (B)]

Although the manufacturing method of the water-soluble polymer (B) is not particularly limited, the monomer mixture containing the monomers constituting the water-soluble polymers (B1) and (B2) is emulsified and polymerized in a dispersion medium to obtain water-dispersible polymers (B1) and (B2). , Water-dispersible polymers (B1) and (B2) are alkalized to a predetermined pH to prepare water-soluble polymers (B1) and (B2), which can be obtained by mixing them. The water-dispersible polymers (B1) and (B2) are those that are readily hydrolyzed in the presence of a base (alkali metal salt) and have at least a portion of a carboxyl or acid anhydride group present in the molecule of the water-dispersible polymer as a salt, preferably It can be said that 50 mol% or more formed salt. Potassium salt, sodium salt, lithium salt, etc. are mentioned as an alkali metal salt, From a viewpoint that it is excellent in the conductivity of lithium ion and can prevent the formation of dendrites, it is preferably a sodium salt, a lithium salt, and more It is preferably a lithium salt. The preferred pH is 4 or more, more preferably 6 or more, and particularly preferably 7.5 or more. Moreover, preferable pH is 13 or less. By making pH into the said range, dispersibility, such as a negative electrode active material (A) in a slurry composition for negative electrodes is excellent, the binding property of a collector and a negative electrode active material layer can be raised, and the cycling characteristics of a secondary battery can be improved.

The method of emulsion polymerization is not particularly limited, and a conventionally known emulsion polymerization method may be employed. The mixing method is not particularly limited, and examples thereof include a method using a mixing device such as a stirring type, shaking type, and rotating type. Moreover, the method using the dispersion kneading apparatus, such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader, is mentioned.

Examples of the polymerization initiator used in the emulsion polymerization include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, p-mentane hydroperoxide, di-t-butyl peroxide, t-butylcumyl peroxide, acetyl peroxide, isobutyryl peroxide, octanoyl peroxide, benzoyl peroxide , 3,5,5-trimethylhexanoyl peroxide, organic peroxides such as t-butyl peroxy isobutylate; And azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, and methyl azobisisobutyrate.

Among these, inorganic peroxides can be preferably used. These polymerization initiators may be used alone or in combination of two or more kinds. Moreover, a peroxide initiator can also be used as a redox-type polymerization initiator in combination with a reducing agent, such as sodium bisulfite.

The use amount of the polymerization initiator is, relative to 100 parts by mass of the total amount of the monomer mixture used for polymerization, the lower limit is usually 0.02 parts by mass or more, preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more, The upper limit is usually 2 parts by mass or less, preferably 1.5 parts by mass or less, and more preferably 0.75 parts by mass or less. By making the usage-amount of a polymerization initiator into the said range, it becomes easy to adjust the 5% aqueous solution viscosity of water-soluble polymers (B1) and (B2) to a predetermined range.

In order to control the amount of tetrahydrofuran insoluble content of the obtained polymer, a chain transfer agent may be used during emulsion polymerization. Examples of the chain transfer agent include alkyl mers such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, and n-stearyl mercaptan. Captan; Xanthogen compounds, such as dimethyl xanthogen disulfide and diisopropyl xanthogen disulfide; Thiuram-based compounds such as terpinolene, tetramethylthiuram disulfide, tetraethyl thiuram disulfide, and tetramethyl thiuram monosulfide; Phenolic compounds such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol; Allyl compounds such as allyl alcohol; Halogenated hydrocarbon compounds such as dichlormethane, dibromomethane and carbon bromide; And thioglycolic acid, thiomalic acid, 2-ethylhexylthioglycolate, diphenylethylene, and α-methylstyrene dimer.

Among these, alkyl mercaptan is preferable, and t-dodecyl mercaptan can be more preferably used. These chain transfer agents can be used alone or in combination of two or more.

The amount of the chain transfer agent used is, with respect to 100 parts by mass of the monomer mixture, the lower limit of which is usually 0.01 parts by mass or more, preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and the upper limit thereof is usually 5 It is 3 parts by mass or less, preferably 3 parts by mass or less, and more preferably 2.5 parts by mass or less. By setting the amount of the chain transfer agent to be within the above range, the viscosity of the 5% aqueous solutions of the water-soluble polymers (B1) and (B2) can be adjusted more easily.

You may use surfactant in emulsion polymerization. Surfactants, unlike the reactive surfactants that may be contained in the water-soluble polymers (B1) and (B2), are non-reactive, nonionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants It may be either. Specific examples of the anionic surfactant include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecyl sulfate, ammonium dodecyl sulfate, sodium octyl sulfate, sodium decyl sulfate, sodium tetradecyl sulfate, sodium hexa Sulfate ester salts of higher alcohols, such as decyl sulfate and sodium octadecyl sulfate; Alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, sodium laurylbenzenesulfonate, and sodium hexadecylbenzenesulfonate; Aliphatic sulfonates such as sodium lauryl sulfonate, sodium dodecyl sulfonate and sodium tetradecyl sulfonate; And the like.

Since the reactive surfactants preferably contained in the water-soluble polymers (B1) and (B2) also have the same emulsifying action, only reactive surfactants may be used, or reactive surfactants and non-reactive surfactants may be used in combination. Moreover, when a reactive surfactant is not used, emulsion polymerization is stabilized by using the said non-reactive surfactant. The use amount of the non-reactive surfactant is, relative to 100 parts by mass of the monomer mixture, the lower limit is usually 0.5 parts by mass or more, preferably 1 part by mass or more, and the upper limit is usually 10 parts by mass or less, preferably Is 5 parts by mass or less.

Moreover, at the time of emulsion polymerization, pH adjusters, such as ammonia; Various additives such as dispersants, chelating agents, oxygen scavengers, builders, and seed latex for particle size control can be suitably used. Seed latex refers to a dispersion of microparticles that become the nucleus of reaction during emulsion polymerization. Many microparticles have a particle size of 100 nm or less. The microparticles are not particularly limited, and general-purpose polymers such as diene-based polymers are used. According to the seed polymerization method, copolymer particles having a relatively constant particle size are obtained.

The polymerization temperature at the time of carrying out the polymerization reaction is not particularly limited, but its lower limit is usually 0°C or higher, preferably 40°C or higher, and its upper limit is usually 100°C or lower, preferably 80°C or lower. . Emulsion polymerization is performed in such a temperature range, and a polymerization terminator is added at a predetermined polymerization conversion rate or the polymerization system is cooled to stop the polymerization reaction. The polymerization conversion rate for stopping the polymerization reaction is preferably 93% by mass or more, and more preferably 95% by mass or more.

After the polymerization reaction is stopped, unreacted monomers are removed, if desired, and the pH or solid concentration is adjusted to obtain a dispersion of dispersed polymers (B1) and (B2) in a dispersion medium (latex). Subsequently, the water-dispersible polymers (B1) and (B2) are alkalized to pH 7 to 13 to prepare water-soluble polymers (B1) and (B2), and these are mixed to obtain a water-soluble polymer (B). Thereafter, if necessary, the dispersion medium may be substituted, or the dispersion medium may be evaporated to obtain a water-soluble polymer (B) in powder form.

Known dispersants, thickeners, anti-aging agents, antifoaming agents, preservatives, antibacterial agents, blister inhibitors, pH adjusting agents, etc. may be added to the dispersion of the resulting water-soluble polymer (B), if necessary.

The dispersion medium used in the production of the water-soluble polymer (B) can be used without particular limitations on water and various organic solvents, as long as it can uniformly disperse the components and maintain a stable dispersion state. From the viewpoint of simplification of the production process, it is preferable to directly produce a water-soluble polymer (B) without performing an operation such as solvent substitution after the above emulsion polymerization, and it is preferable to use a reaction solvent during emulsion polymerization as the dispersion medium. Do. In emulsion polymerization, water is often used as a reaction solvent, and it is particularly preferable to use water as a dispersion medium from the viewpoint of the working environment.

The blending amount of the water-soluble polymer (B) is 100 mass parts of the total amount of the negative electrode active material (A), and the total amount of the water-soluble polymers (B1) and (B2) has an upper limit, preferably 5.0 parts by mass or less, more preferably Is 3 parts by mass or less, particularly preferably 2 parts by mass or less, and the lower limit thereof is preferably 0.1 parts by mass or more, more preferably 0.25 parts by mass or more, particularly preferably 0.5 parts by mass or more.

By setting the total amount of the water-soluble polymers (B1) and (B2) to the above range, the dispersibility of the negative electrode active material (A) and the like in the slurry composition for negative electrodes is improved, and the binding property between the current collector and the negative electrode active material layer is increased, and secondary The cycle characteristics of the battery can be improved. In addition, since the internal resistance of the secondary battery can be reduced, output characteristics (especially low-temperature output characteristics) can be improved.

The weight ratio of the water-soluble polymer (B1) and the water-soluble polymer (B2) is "water-soluble polymer (B1)/water-soluble polymer (B2)", the upper limit of which is preferably 95/5 or less, more preferably 90/10 or less , Especially preferably, it is 80/20 or less, and its lower limit is preferably 5/95 or more, more preferably 10/90 or more, and particularly preferably 20/80 or more.

By setting the weight ratio of the water-soluble polymer (B1) and the water-soluble polymer (B2) within the above range, the lithium ion conductivity of the surface of the negative electrode active material is increased, whereby the output of the secondary battery can be improved. In addition, the dispersibility of the negative electrode active material (A) and the like in the slurry composition for a negative electrode can be improved, the binding property between the current collector and the negative electrode active material layer can be improved, and cycle characteristics of the secondary battery can be improved.

(C) water

Examples of the water used in the present invention include water treated with an ion exchange resin (ion exchanged water) and water treated with a reverse osmosis membrane water purification system (ultra pure water). It is preferable to use water having an electrical conductivity of 0.5 mS/m or less. When the electrical conductivity of water exceeds the above range, the dispersibility of the negative electrode active material (A) in the slurry composition for the negative electrode deteriorates due to a change in the amount of adsorption of the water-soluble polymer (B) to the negative electrode active material (A), There may be effects such as a decrease in uniformity of the negative electrode. Moreover, in this invention, if it is the range which does not inhibit the dispersion stability of a water-soluble polymer (B), you may use what mixed the hydrophilic solvent with water. Methanol, ethanol, N-methylpyrrolidone, etc. are mentioned as a hydrophilic solvent, It is preferable that it is 5 mass% or less with respect to water.

(D) Particulate binder

The slurry composition for a lithium ion secondary battery negative electrode of this invention may contain a particulate-form binder (D).

The particulate binder has a property of being dispersed in water (C). By using the particulate binder, the binding property of the current collector and the negative electrode active material layer described later can be improved, and the negative electrode strength can be improved, and the capacity of the negative electrode obtained can be reduced or deterioration due to repeated charging and discharging can be suppressed.

The particulate binder may be present in a state in which the particle shape is maintained in the negative electrode active material layer. In the present invention, the "state in which the particle state is maintained" does not need to be a state in which the particle shape is completely maintained, but may be a state in which the particle shape is maintained to some extent.

Examples of the particulate binder include those in which particles of a binder such as latex are dispersed in water, or those obtained by drying such latex. In the present invention, the particulate binder is water-insoluble. That is, it is preferable that it is not dissolved in an aqueous solvent and is dispersed in the form of particles. The non-water-soluble means that the insoluble content becomes 90% by mass or more when specifically, at 25°C, 0.5 g of the binder is dissolved in 100 g of water.

The particulate binder (D) in the present invention is not particularly limited, and examples thereof include aromatic vinyl-conjugated diene copolymers such as SBR. Hereinafter, the aromatic vinyl-conjugated diene copolymer will be described in detail.

Aromatic vinyl-conjugated diene copolymer

The aromatic vinyl-conjugated diene copolymer is a structural unit obtained by polymerizing an aromatic vinyl monomer (hereinafter, sometimes referred to as "aromatic vinyl monomer unit"), and a structural unit obtained by polymerizing a conjugated diene (hereinafter, "conjugated diene" It may be described as "a monomer unit"), preferably a copolymer containing an ethylenically unsaturated carboxylic acid monomer unit in addition to the above monomer unit. Moreover, the aromatic vinyl-conjugated diene copolymer may contain other monomer units copolymerizable with these as needed.

<Aromatic vinyl monomer unit>

The aromatic vinyl monomer unit is a structural unit obtained by polymerizing an aromatic vinyl monomer.

Examples of aromatic vinyl monomers include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. Among them, styrene is preferred. These aromatic vinyl monomers can be used alone or in combination of two or more. The content ratio of the aromatic vinyl monomer unit in the aromatic vinyl-conjugated diene copolymer has an upper limit of preferably 65 mass% or less, and a lower limit thereof, preferably 40 mass% or more, more preferably 50 mass. % Or more.

<Conjugated diene monomer unit>

The conjugated diene monomer unit is a structural unit obtained by polymerizing the conjugated diene monomer.

Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chlor-1,3-butadiene, and the like. have. These conjugated diene monomers can be used alone or in combination of two or more.

The content ratio of the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer has an upper limit of preferably 46 mass% or less, and a lower limit thereof, preferably 25 mass% or more, more preferably 31 mass. % Or more.

The ratio of the total of the aromatic vinyl monomer units and the conjugated diene monomer units in the aromatic vinyl-conjugated diene copolymer has an upper limit of preferably 96% by mass or less, and a lower limit thereof, preferably 65% by mass or more, More preferably, it is 80 mass% or more.

Here, the ratio of the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer is generally the same as the ratio (injection ratio) of the conjugated diene monomer in all the monomers when the aromatic vinyl-conjugated diene copolymer is polymerized. do.

<Ethylenic unsaturated carboxylic monomer unit>

The ethylenically unsaturated carboxylic acid monomer unit is a structural unit obtained by polymerizing an ethylenically unsaturated carboxylic acid monomer.

Examples of the ethylenically unsaturated carboxylic acid monomer are as exemplified in the water-soluble polymer (B). Among these, unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid and unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid are preferred, acrylic acid, methacrylic acid and itaconic acid are more preferred, and itaconic acid is particularly preferred. desirable. Since the dispersibility of the resulting aromatic vinyl-conjugated diene copolymer with respect to a dispersion medium such as water can be further improved, and the binding property between the current collector and the negative electrode active material layer is improved, a secondary battery having excellent cycle characteristics can be obtained. to be. By using the ethylenically unsaturated carboxylic acid monomer, an acidic functional group can be introduced into the aromatic vinyl-conjugated diene copolymer.

The content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the aromatic vinyl-conjugated diene copolymer is preferably an upper limit of 6% by mass or less, more preferably 5% by mass or less, and a lower limit of that is preferred. Preferably it is 0.1 mass% or more, More preferably, it is 0.5 mass% or more.

By setting the content ratio of the ethylenically unsaturated carboxylic acid monomer unit within the above range, the binding property between the current collector and the negative electrode active material layer can be increased, and the negative electrode strength can be improved. As a result, a negative electrode for a secondary battery having excellent cycle characteristics can be obtained.

Here, the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the aromatic vinyl-conjugated diene copolymer is usually ethylenically unsaturated carboxylic acid monomer in all monomers when polymerizing the aromatic vinyl-conjugated diene copolymer. It corresponds to the ratio (injection cost) of.

<Other monomer units>

The other monomer unit is a structural unit obtained by polymerizing another monomer copolymerizable with the monomers described above.

Other monomers constituting other monomer units include hydrocarbons such as ethylene, propylene, and isobutylene; Α,β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; Halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; Vinyl esters such as vinyl acetate, vinyl propionate, and vinyl butyrate; Vinyl ethers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; Vinyl ketones such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; And heterocyclic ring-containing vinyl compounds such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole.

The content ratio of the other monomer units in the aromatic vinyl-conjugated diene copolymer has an upper limit of preferably 35 mass% or less, more preferably 20 mass% or less, and a lower limit, preferably 0 mass%. Above, it is more preferably 4% by mass or more.

Here, the ratio of the other monomer units in the aromatic vinyl-conjugated diene copolymer generally corresponds to the ratio (injection ratio) of other monomers in the total monomers when the aromatic vinyl-conjugated diene copolymer is polymerized.

The upper limit of the glass transition temperature (Tg) of the aromatic vinyl-conjugated diene copolymer is preferably 70° C. or less, more preferably 60° C. or less, particularly preferably 50° C. or less, and preferably its lower limit, Is -50°C or higher, more preferably -40°C or higher, and particularly preferably -30°C or higher.

When the glass transition temperature of the aromatic vinyl-conjugated diene copolymer is too low, it is difficult to suppress the expansion and contraction of the negative electrode active material, and the cycle characteristics of the secondary battery are lowered. Moreover, when the glass transition temperature of the aromatic vinyl-conjugated diene copolymer is too high, the binding property with the current collector is insufficient, and the cycle characteristics of the secondary battery are lowered.

The volume average particle diameter of the aromatic vinyl-conjugated diene copolymer is not particularly limited, but its upper limit is preferably 500 nm or less, more preferably 400 nm or less, particularly preferably 300 nm or less, and the lower limit is preferable. Preferably it is 10 nm or more, More preferably, it is 20 nm or more, Especially preferably, it is 30 nm or more. When the number average particle diameter of the aromatic vinyl-conjugated diene copolymer is in this range, excellent binding strength can be imparted to the negative electrode active material layer even with a small amount.

The number average particle diameter in the present invention is a number average particle diameter calculated by measuring the diameter of 100 randomly selected polymer particles by a transmission electron micrograph and calculating the arithmetic average value.

The shape of the particles may be spherical, heterogeneous, or both. These aromatic vinyl-conjugated diene copolymers may be used alone or in combination of two or more.

The blending amount of the particulate binder (D) is, relative to the total amount of 100 parts by mass of the negative electrode active material, the upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, particularly preferably 2 parts by mass or less, The lower limit is preferably 0.1 parts by mass or more, more preferably 0.25 parts by mass or more, and particularly preferably 0.5 parts by mass or more.

By setting the compounding amount of the particulate binder (D) within the above range, the expansion and contraction of the negative electrode active material can be suppressed, the binding strength of the negative electrode can be improved, and the internal resistance of the negative electrode can be reduced. A secondary battery can be obtained.

[Production of particulate binder (D)]

Although the manufacturing method of a particulate-form binder (D) is not specifically limited, It can be obtained by emulsion-polymerizing the monomer mixture containing the monomer which comprises a particulate-form binder (D). It does not specifically limit as a method of emulsion polymerization, It is the same as that of the water-soluble polymer (B) mentioned above.

(E) Water-soluble polymer other than water-soluble polymer (B)

In the slurry composition for a lithium ion secondary battery negative electrode of this invention, you may contain the water-soluble polymer (E) other than the water-soluble polymer (B) mentioned above.

Examples of the water-soluble polymer (E) include cellulose-based polymers such as carboxymethylcellulose (hereinafter sometimes referred to as "CMC"), methylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose, and ammonium salts and alkali metal salts thereof; (Modified) poly(meth)acrylic acid and ammonium salts and alkali metal salts thereof; (Modified) polyvinyl alcohols, such as polyvinyl alcohol, a copolymer of acrylic acid or acrylate and vinyl alcohol, and maleic anhydride or maleic acid or fumaric acid and vinyl alcohol copolymer; And polyethylene glycol, polyethylene oxide, polyvinylpyrrolidone, modified polyacrylic acid, starch oxide, starch phosphate, casein, and various modified starches. Among these, cellulose-based polymers are preferred, and CMC is particularly preferred.

The blending amount of the water-soluble polymer (E) is, relative to the total amount of 100 parts by mass of the negative electrode active material, the upper limit is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and the lower limit is preferably 0.5 mass parts Parts or more, more preferably 0.7 parts by mass or more. When the blending amount of the water-soluble polymer (E) is within the above range, the coatability becomes good, and thus the rise of the internal resistance of the secondary battery is prevented, and the binding property with the current collector is excellent.

(F) Conductive

The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention may contain a conductive agent (F). As the conductive agent, conductive carbon such as acetylene black, Ketjen black, carbon black, graphite, vapor-grown carbon fibers, and carbon nanotubes can be used. By containing a conductive agent, electrical contact between negative electrode active materials can be improved, and when used in a lithium ion secondary battery, discharge rate characteristics can be improved. The content of the conductive agent in the slurry composition for a lithium ion secondary battery negative electrode is, as for the total amount of 100 parts by mass of the negative electrode active material, the upper limit is usually 20 parts by mass or less, preferably 10 parts by mass or less, and the lower limit thereof , Preferably 1 part by mass or more.

(G) optional ingredients

The slurry composition for a lithium ion secondary battery negative electrode may further contain arbitrary components in addition to the above components. Examples of the optional components include reinforcing materials, leveling agents, and electrolyte additives having functions such as inhibiting electrolyte decomposition. Moreover, arbitrary components may be contained in the secondary battery negative electrode mentioned later. It will not be specifically limited if it does not affect these battery reactions.

As the reinforcing material, various inorganic and organic spherical, plate-shaped, rod-shaped, or fibrous fillers can be used. By using a reinforcing material, a robust and flexible negative electrode can be obtained, and excellent long-term cycling characteristics can be exhibited. The content of the reinforcing material in the slurry composition for a negative electrode is, relative to 100 parts by mass of the total amount of the negative electrode active material, the upper limit is usually 20 parts by mass or less, preferably 10 parts by mass or less, and the lower limit is usually 0.01 parts by mass Above, it is preferably 1 part by mass or more.

When the reinforcing material is included in the above-mentioned range in the slurry composition for a negative electrode, high capacity and high load characteristics can be exhibited.

As a leveling agent, surfactants, such as an alkyl type surfactant, a silicone type surfactant, a fluorine type surfactant, and a metal type surfactant, are mentioned. By mixing the leveling agent, it is possible to prevent cratering occurring during application or to improve the smoothness of the negative electrode. The content of the leveling agent in the slurry composition for a negative electrode is usually from 0.01 to 10 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material. When the leveling agent is contained in the above-mentioned range in the slurry composition for a negative electrode, it is excellent in productivity, smoothness, and battery characteristics at the time of manufacturing a negative electrode.

As the electrolyte additive, vinylene carbonate or the like used in the electrolyte can be used. The content of the electrolyte additive in the slurry composition for a negative electrode is usually from 0.01 to 10 parts by mass relative to 100 parts by mass of the total amount of the negative electrode active material. When the content of the electrolyte additive in the slurry composition for a negative electrode is within the above-mentioned range, the cycle characteristics and high temperature characteristics of the obtained secondary battery are excellent. In addition, nano fine particles, such as fumed silica and fumed alumina, are mentioned. By mixing the nano fine particles, the thixotropy of the slurry composition for a negative electrode can be controlled, and the leveling property of the negative electrode obtained thereby can be improved. The content of the nanoparticles in the slurry composition for a negative electrode is usually 0.01 to 10 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material. When the content of the nanoparticles in the slurry composition for a negative electrode is within the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

[Method for producing slurry composition for lithium ion secondary battery negative electrode]

The slurry composition for a lithium ion secondary battery negative electrode is obtained by mixing the above-mentioned negative electrode active material (A), water-soluble polymer (B), and components (D) to (G) used as necessary in water (C).

The mixing method is not particularly limited, and examples thereof include a method using a mixing device such as a stirring type, shaking type, and rotating type. Moreover, the method using the dispersion kneading apparatus, such as a homogenizer, a ball mill, a sand mill, a roll mill, and a planetary kneader, is mentioned.

(2) lithium ion secondary battery negative electrode

The lithium ion secondary battery negative electrode of this invention is made by apply|coating and drying the slurry composition for lithium ion secondary battery negative electrodes mentioned above to a collector.

[Production Method of Lithium Ion Secondary Battery Negative Electrode]

The manufacturing method of the lithium ion secondary battery negative electrode of this invention includes the process of forming the negative electrode active material layer by apply|coating and drying the said slurry composition for negative electrodes on one side or both surfaces of a collector.

The method of applying the slurry composition for negative electrodes on a current collector is not particularly limited. For example, methods such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method are mentioned.

Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 to 180°C.

When manufacturing the lithium ion secondary battery negative electrode of the present invention, after applying and drying the slurry composition for a negative electrode on a current collector, using a mold press or a roll press, the porosity of the negative electrode active material layer is lowered by pressure treatment. It is desirable to have a process to do. The upper limit of the porosity of the negative electrode active material layer is preferably 30% or less, more preferably 20% or less, and the lower limit is preferably 5% or more, more preferably 7% or more. If the porosity of the negative electrode active material layer is too high, charging efficiency and discharge efficiency may deteriorate. When the porosity is too low, it is difficult to obtain a high volumetric capacity, and the negative electrode active material layer tends to peel off from the current collector, which may easily cause defects. Moreover, when using a curable polymer as a particulate-form binder (D), it is preferable to harden.

The thickness of the negative electrode active material layer in the negative electrode of the lithium ion secondary battery of the present invention has an upper limit of usually 300 µm or less, preferably 250 µm or less, and a lower limit thereof, usually 5 µm or more, preferably 30 It is more than micrometer. When the thickness of the negative electrode active material layer is in the above range, a secondary battery having high characteristics in both load characteristics and cycle characteristics can be obtained.

In the present invention, the upper limit of the content ratio of the negative electrode active material in the negative electrode active material layer is preferably 99 mass% or less, more preferably 97 mass% or less, and the lower limit is preferably 85 mass%. Above, it is more preferably 88% by mass or more. When the content ratio of the negative electrode active material in the negative electrode active material layer is within the above range, it is possible to obtain a secondary battery exhibiting high capacity while exhibiting flexibility and binding properties.

In the present invention, the density of the negative electrode active material layer of the negative electrode of a lithium ion secondary battery is preferably an upper limit of 2.2 g/cm 3 or less, more preferably 1.85 g/cm 3 or less, and a lower limit thereof, preferably 1.6 g. /Cm 3 or more, more preferably 1.65 g/cm 3 or more. When the density of the negative electrode active material layer is within the above range, a high capacity secondary battery can be obtained.

<Current>

The current collector used in the present invention is not particularly limited as long as it has a material that is electrically conductive and electrochemically durable, but is preferably a metal material because it has heat resistance, for example, iron, copper, aluminum, nickel, and stainless steel. , Titanium, tantalum, gold, platinum, and the like. Among them, copper is particularly preferred as the current collector used for the lithium ion secondary battery negative electrode. The shape of the current collector is not particularly limited, but it is preferably a sheet having a thickness of about 0.001 to 0.5 mm. The current collector is preferably used by roughening in advance in order to increase the adhesive strength with the negative electrode active material layer. Examples of the roughening method include mechanical polishing, electrolytic polishing, and chemical polishing. In the mechanical polishing method, abrasive cloth paper, abrasive stone, emery buff, steel wire, or the like provided with abrasive particles are used. Moreover, in order to improve the adhesive strength and conductivity of the negative electrode active material layer, an intermediate layer may be formed on the surface of the current collector.

(3) Lithium ion secondary battery

The lithium ion secondary battery of the present invention is a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, and the negative electrode is the lithium ion secondary battery negative electrode.

<Positive Electrode>

The positive electrode is formed by laminating a positive electrode active material layer containing a positive electrode active material and a binder for a positive electrode on a current collector.

[Positive electrode active material]

As the positive electrode active material, an active material capable of doping and dedoping lithium ions is used, and is classified into an inorganic compound and an organic compound.

Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, transition metal sulfides, and lithium-containing composite metal oxides of lithium and transition metals. As said transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, etc. are used.

As the transition metal oxide, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O ₁₃ and the like. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferable in cycle characteristics and capacity. Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ and FeS. Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

As the lithium-containing composite metal oxide having a layered structure, lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), lithium composite oxide of Co-Ni-Mn, lithium composite oxide of Ni-Mn-Al, And lithium composite oxides of Ni-Co-Al. As the lithium-containing composite metal oxide having a spinel structure, Li[Mn _3/2 M _1/2 ]O ₄ in which lithium manganate (LiMn ₂ O ₄ ) or a part of Mn is replaced with another transition metal (where M is Cr , Fe, Co, Ni, Cu, etc.). As a lithium-containing composite metal oxide having an olivine structure, Li _X MPO ₄ (wherein M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si , And an olivine-type lithium phosphate compound represented by at least one selected from B and Mo and 0≦X≦2).

As the organic compound, for example, a conductive polymer such as polyacetylene or poly-p-phenylene may be used. The iron-based oxide having insufficient electrical conductivity may be used as an electrode active material covered with a carbon material by presenting a carbon source material during reduction firing. Moreover, these compounds may be partially substituted. The positive electrode active material for a lithium ion secondary battery may be a mixture of the above-mentioned inorganic compound and organic compound.

The average particle diameter of the positive electrode active material has an upper limit of 50 µm or less, preferably 30 µm or less, and a lower limit of the average particle size of 1 µm or more, preferably 2 µm or more. When the average particle diameter of the positive electrode active material is in the above range, the amount of the binder for the positive electrode in the positive electrode active material layer can be reduced, and a decrease in the capacity of the battery can be suppressed. Moreover, in order to form a positive electrode active material layer, a slurry containing a positive electrode active material and a binder for a positive electrode (hereinafter, sometimes referred to as "a slurry composition for a positive electrode") is prepared, but applying the slurry composition for a positive electrode It is easy to prepare with an appropriate viscosity, and a uniform positive electrode can be obtained.

The upper limit of the content ratio of the positive electrode active material in the positive electrode active material layer is preferably 99.9 mass% or less, more preferably 99 mass% or less, and the lower limit is preferably 90 mass% or more, more preferably Is 95% by mass or more. By setting the content of the positive electrode active material in the positive electrode active material layer within the above range, flexibility and binding properties can be exhibited while exhibiting a high capacity.

[Binder for positive electrode]

The binder for the positive electrode is not particularly limited and a known one can be used. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, etc. In addition, soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, and vinyl soft polymers can be used. These may be used alone, or two or more of them may be used in combination.

In addition to the above-mentioned components, the positive electrode may further contain other components, such as an electrolyte additive having functions such as suppressing electrolytic solution decomposition described above. These are not particularly limited as long as they do not affect the battery reaction.

The current collector may be a current collector used for the negative electrode of the lithium ion secondary battery described above, and is not particularly limited as long as it has a material that is electrically conductive and electrochemically durable, but aluminum is particularly useful for the positive electrode of a lithium ion secondary battery. desirable.

The upper limit of the thickness of the positive electrode active material layer is usually 300 µm or less, preferably 250 µm or less, and the lower limit is usually 5 µm or more, preferably 10 µm or more. When the thickness of the positive electrode active material layer is in the above range, both load characteristics and energy density exhibit high characteristics.

The positive electrode can be produced in the same manner as the negative electrode for a lithium ion secondary battery described above.

<Separator>

The separator is a porous substrate having pores, and the usable separators include (a) a porous separator having pores, (b) a porous separator having a polymer coat layer on one or both sides, or (c) an inorganic ceramic powder. And a porous separator having a porous resin coat layer formed thereon. Non-limiting examples of these include polypropylene-based, polyethylene-based, polyolefin-based, or aramid-based porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymer, etc. And a polymer film for a solid polymer electrolyte or a gel polymer electrolyte, a separator coated with a gelling polymer coat layer, or a separator coated with a porous membrane layer made of an inorganic filler and a dispersant for an inorganic filler.

<Electrolyte amount>

Although the electrolyte solution used for this invention is not specifically limited, For example, what melt|dissolved the lithium salt as a support electrolyte in a non-aqueous solvent can be used. Lithium salts include, 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, CF ₃ COOLi, (CF ₃ CO) ₂ And lithium salts such as NLi, (CF ₃ SO ₂ ) ₂ NLi, and (C ₂ F ₅ SO ₂ )NLi. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li, which are easily soluble in a solvent and exhibit high dissociation, are preferably used. These may be used alone or in combination of two or more. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, relative to the electrolyte. Even if the amount of the supporting electrolyte is too small or too large, the ionic conductivity decreases, and the charging and discharging characteristics of the battery decrease.

The solvent used for the electrolytic solution is not particularly limited as long as it dissolves the supporting electrolyte, but is usually dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate ( BC), and alkyl carbonates, such as methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate, and ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds such as sulfolane and dimethyl sulfoxide; Is used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because they are easy to obtain high ionic conductivity and have a wide operating temperature range. These may be used alone or in combination of two or more. Moreover, it is also possible to use an electrolyte solution containing an additive. As the additive, carbonate-based compounds such as vinylene carbonate (VC) are preferred.

Examples of the electrolyte solution other than the above include gel polymer electrolytes impregnated with polymer electrolytes such as polyethylene oxide and polyacrylonitrile, and inorganic solid electrolytes such as lithium sulfide, LiI and Li ₃ N.

[Method for manufacturing lithium ion secondary battery]

The manufacturing method of the lithium ion secondary battery of this invention is not specifically limited. For example, the above-mentioned negative electrode and positive electrode are superimposed via a separator, and wound or folded according to the shape of the battery, placed in a battery container, and sealed by injecting an electrolyte solution into the battery container. In addition, if necessary, an overcurrent preventing element such as an expanded metal, a fuse, a PTC element, a lead plate, or the like may be added to prevent pressure rise and overcharge and discharge in the battery. The shape of the battery may be any of a laminate cell type, a coin type, a button type, a sheet type, a cylindrical shape, a square shape, and a flat shape.

Example

The present invention will be described below with reference to examples, but the present invention is not limited to this. In addition, parts and% in this Example are mass basis unless otherwise specified. In Examples and Comparative Examples, various physical properties were evaluated as follows.

<(1) Dispersion stability of negative electrode active material>

The slurry viscosity of the slurry composition for negative electrodes was measured immediately after preparation of the slurry composition for negative electrodes prepared in Examples and Comparative Examples, and after standing still at 25° C. for 24 hours. The slurry viscosity was measured using a B-type viscometer at rotor numbers 4 and 6 rpm. The rate of change in viscosity was calculated from the following formula and evaluated according to the following criteria.

Viscosity change rate (%) = (Viscosity after stopping still for 24 hours [cp])/(Viscosity immediately after production [cp]) × 100

A: 80% or more to less than 120%

B: 70% or more to less than 80%, 120% or more to less than 130%

C: 60% or more to less than 70%, 130% or more to less than 140%

D: Less than 60%, 140% or more

<(2) Bonding strength of negative electrode>

The "negative electrode before vacuum drying" prepared in Examples and Comparative Examples was cut into a rectangle having a length of 100 mm and a width of 10 mm to obtain a test piece. The surface of the negative electrode active material layer was placed on this test piece, and a cellophane tape was affixed to the surface of the negative electrode active material layer. At this time, what was specified in JIS Z1522: (2009) was used as the cellophane tape. Moreover, the cellophane tape was fixed to the test stand. Thereafter, one end of the current collector was stretched vertically at a tensile speed of 50 mm/min, and the stress at the time of peeling was measured. This measurement was performed 3 times, the average value was determined, and the average value was used as the peel strength. The larger the peel strength, the greater the binding force of the negative electrode active material layer to the current collector, that is, the higher the binding strength.

A: 8.0 N/m or more

B: 5.0 N/m or more and less than 8.0 N/m

C: 3.0 N/m or more and less than 5.0 N/m

D: less than 3.0 N/m

<(3) High temperature cycle characteristics>

The lithium ion secondary battery of the laminate type cell prepared in Examples and Comparative Examples was stopped still for 24 hours in an environment of 25°C. Subsequently, the charging and discharging operation of charging to 4.2 V and discharging to 3.0 V was performed by a constant current method of 0.1 C in an environment of 25°C, and the initial capacity C ₀ was measured. Here, the charge transfer resistance described later was measured. Subsequently, under the environment of 60° C., charging and discharging of charging to 4.2 V and discharging to 3.0 V by a constant current method of 1.0 C was repeated 500 times to measure the capacity C ₁ . The high temperature cycle characteristics were evaluated by the capacity change rate ΔC _C expressed as ΔC _C =C ₁ /C ₀ ×100 (%). The higher the value of the capacity change rate ΔC _C, the better the high temperature cycle characteristics.

A: 90% or more

B: 80% or more and less than 90%

C: 70% or more and less than 80%

D: less than 70%

<(4) Suppress volume expansion of negative electrode active material>

The degree of volume expansion inhibition of the negative electrode active material was calculated from an increase in the negative electrode film thickness. The lithium ion secondary battery of the laminate-type cell after the high-temperature cycle characteristic test of (3) was disassembled, the negative electrode was taken out, and the film thickness was measured using a laser displacement gauge type film thickness meter. The volume expansion was evaluated from the ratio of "film thickness of the negative electrode after vacuum drying at the time of cell manufacturing" and "film thickness of the negative electrode after high-temperature cycle characteristic test".

Volume expansion (times) = (film thickness of the negative electrode after high temperature cycle property test [μm])/(film thickness of the negative electrode after vacuum drying during cell production [μm])

A: Less than 1.1 times

B: 1.1 times or more and less than 1.2 times

C: 1.2 times or more and less than 1.3 times

D: 1.3 times or more

<(5) Measurement of charge transfer resistance>

In evaluating the high-temperature cycle characteristics of (3), after the initial capacity C ₀ was measured, the lithium secondary battery of the target laminate cell was charged to SOC 50%. Here, SOC 50% refers to a state in which up to 50% of the initial charging capacity is 100%. Then, it was stopped still in an incubator at -10°C for 1 hour, and impedance measurement was performed. The charge transfer resistance was measured from the size of the arc of the Nyquist plot (refer to the Nyquist plot diagram (FIG. 1), the broken line portion is a plot of the actual results).

It shows that the mobility of Li ion in a battery is excellent, so that charge transfer resistance is small.

The size of the arc

A: less than 0.20 Ω

B: 0.20 Ω or more to less than 0.25 Ω

C: 0.25 Ω or more to less than 0.30 Ω

D: 0.30 Ω or more

(Example 1)

[1] Preparation of water-soluble polymer (B1)

25 parts of methacrylic acid (ethylenically unsaturated carboxylic acid monomer), 2 parts of 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth)acrylic acid ester monomer) in a 5 MPa pressure resistant container with a stirrer , Ethyl acrylate ((meth)acrylic acid ester monomer) 58.5 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) 5 parts, polyoxyalkylene alkenyl ether ammonium sulfate (reactive surfactant monomer, cao Production, trade name "Latteul PD-104") 1.5 parts, tert-dodecyl mercaptan (chain transfer agent) 0.2 parts, ion-exchanged water 150 parts, and potassium persulfate (polymerization initiator) 0.5 parts, after stirring sufficiently, The polymerization was started by warming to 50°C. When the polymerization conversion ratio reached 99.0% or more, the reaction was stopped by cooling to obtain a mixture containing a water-dispersible polymer (B1).

Next, a 10% LiOH aqueous solution was added to the mixture containing the water-dispersion type polymer (B1) until pH 8.5 to obtain a desired water-soluble polymer (B1).

The obtained water-soluble polymer (B1) was placed in a water bath at 25°C and temperature adjusted, and then a 5% aqueous solution viscosity was measured using a Brookfield viscometer (rotor number 4, 60 rpm, viscosity unit cp). Table 1 shows the results.

[2] Preparation of water-soluble polymer (B2)

In a 5 MPa pressure resistant vessel with a stirrer, 98 parts of acrylic acid (ethylenically unsaturated carboxylic acid monomer), 2 parts of 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer), 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate (polymerization initiator) was added, stirred sufficiently, and then heated to 50°C to initiate polymerization. When the polymerization conversion ratio reached 99.0% or more, the reaction was stopped by cooling to obtain a mixture containing a water-dispersible polymer (B2).

A 10% LiOH aqueous solution was added to the mixture containing the water-dispersible polymer (B2) until pH 8.5 to obtain a desired water-soluble polymer (B2).

About the obtained water-soluble polymer (B2), after adjusting the temperature in a water bath at 25°C in the same manner as the water-soluble polymer (B1), 5% using a Brookfield viscometer (rotor number 4, 60 rpm, viscosity unit cp) The aqueous solution viscosity was measured. Table 1 shows the results.

[3] Preparation of slurry composition for negative electrode

In a planetary mixer with a disper, 70 parts of artificial graphite (volume average particle diameter: 20.0 µm) as a negative electrode active material, 30 parts of SiO _x (x = 1.1, volume average particle diameter: 3.0 µm) as the above step [1] The obtained water-soluble polymer (B1) was adjusted to a solid content concentration of 60% by adding 0.9 parts (based on solid content) and ion-exchanged water, followed by mixing at 25°C for 60 minutes.

Next, the water-soluble polymer (B2) obtained in the above step [2] was adjusted to a solid content concentration of 50% by adding 0.6 parts (based on solid content) and ion-exchanged water, followed by further mixing at 25° C. for 15 minutes to perform a negative electrode. To obtain a slurry composition.

[4] Preparation of negative electrode

The slurry composition for a negative electrode obtained in the above step [3] was coated on a current collector (copper foil, 20 µm thick) with a comma coater so that the film thickness after drying was about 150 µm and dried. This drying was performed by conveying the copper foil in an oven at 90° C. over 2 minutes at a rate of 0.5 m/min. Then, it heat-treated at 120 degreeC for 2 minutes, and obtained the negative electrode. This negative electrode was rolled with a roll press to obtain a negative electrode (negative electrode before vacuum drying) having a thickness of 80 μm of the negative electrode active material layer. Here, the binding strength was measured for a part of the obtained “negative electrode before vacuum drying”. Table 1 shows the results. The remaining "negative electrode before vacuum drying" was vacuum dried at 60°C for 10 hours (gauge pressure: -0.09 Mpa or less) to obtain a negative electrode (negative electrode after vacuum drying). The film thickness was measured for such "negative electrode after vacuum drying". The measured film thickness corresponds to the "film thickness of the negative electrode after vacuum drying at the time of cell production" in the evaluation of the volume expansion inhibition of the negative electrode active material.

[5] Preparation of positive electrodes

As a binder for the positive electrode, a 40% water dispersion of an acrylate polymer having a glass transition temperature (Tg) of -40°C and a number average particle diameter of 0.20 µm was prepared. The said acrylate polymer is a copolymer obtained by emulsion-polymerizing the monomer mixture containing 78 mass% of 2-ethylhexyl acrylate, 20 mass% of acrylonitrile, and 2 mass% of methacrylic acid.

As a positive electrode active material, 100 parts of LiFePO ₄ having a volume average particle size of 0.5 µm and having an olivine crystal structure, and 1 part aqueous solution of carboxymethylcellulose ("BSH-12" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) as a dispersant, are equivalent to 1 part of solid content. And, as a binder, 5 parts of 40% water dispersion of the acrylate polymer described above was mixed with solid content, and ion-exchanged water was mixed. The amount of ion-exchanged water was set such that the total solid content concentration was 40%. These were mixed with a planetary mixer to prepare a slurry composition for a positive electrode.

The slurry composition for positive electrodes was coated on a current collector (aluminum, 20 µm thick) with a comma coater so that the film thickness after drying was about 200 µm and dried. This drying was performed by conveying the copper foil in an oven at 60° C. over 2 minutes at a rate of 0.5 m/min. Then, it heat-treated at 120 degreeC for 2 minutes, and then vacuum-dried at 60 degreeC for 10 hours (gauge pressure: -0.09 Mpa or less) to obtain a positive electrode.

[6] Preparation of separator

A single layer polypropylene separator (65 mm wide, 500 mm long, 25 µm thick, manufactured by dry method, porosity 55%) was cut into a square of 5 cm×5 cm.

[7] Preparation of lithium ion secondary batteries

An aluminum packaging material exterior was prepared as the exterior of the battery. The positive electrode obtained in the above step [5] was cut into a square of 4 cm x 4 cm, and placed so that the surface of the current collector side was in contact with the exterior of the aluminum packaging material. On the surface of the positive electrode active material layer of the positive electrode, a square separator obtained in the above step [6] was placed. Further, the negative electrode obtained in the above step [4] was cut into a square of 4.2 cm x 4.2 cm, and placed on the separator so that the surface of the negative electrode active material layer side faced the separator. Further, in order to seal the opening of the aluminum packaging material, a heat seal at 150°C was used to close the aluminum sheath to produce a lithium ion secondary battery. As the electrolyte, LiPF ₆ was dissolved at a concentration of 1 mol/liter in a mixed solvent formed by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at EC:EMC = 3:7 (volume ratio at 20°C). The solution was used.

The obtained lithium ion secondary battery was evaluated for high temperature cycle characteristics, inhibition of volume expansion of the negative electrode active material, and measurement of charge transfer resistance. Table 1 shows the results.

(Example 2)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the addition amount of the water-soluble polymer (B1) was 0.3 parts and the addition amount of the water-soluble polymer (B2) was 0.2 parts to prepare a slurry composition for a negative electrode. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 1 shows the results.

(Example 3)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 was performed except that a slurry composition for a negative electrode was prepared with the addition amount of the water-soluble polymer (B1) being 1.08 parts and the addition amount of the water-soluble polymer (B2) being 0.72 parts. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 1 shows the results.

(Example 4)

In the production of the water-soluble polymer (B1) in step [1], methacrylic acid (ethylenically unsaturated carboxylic acid monomer) is 25 parts to 18 parts, ethyl acrylate ((meth)acrylic acid ester monomer) is 58.5 parts to 65.5 A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that it was made negative. Table 1 shows the results.

(Example 5)

In the production of the water-soluble polymer (B1) in step [1], methacrylic acid (ethylenically unsaturated carboxylic acid monomer) is 25 parts to 20 parts, ethyl acrylate ((meth)acrylic acid ester monomer) is 58.5 parts to 63.5 A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that it was made negative. Table 1 shows the results.

(Example 6)

In the production of the water-soluble polymer (B1) in step [1], methacrylic acid (ethylenically unsaturated carboxylic acid monomer) is 25 parts to 45 parts, ethyl acrylate ((meth)acrylic acid ester monomer) is 58.5 parts to 38.5 A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that it was made negative. Table 1 shows the results.

(Example 7)

In the production of the water-soluble polymer (B1) in step [1], 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth)acrylic acid ester monomer) is added in 10 parts to 1 part, ethyl acrylate (( A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the (meth)acrylic acid ester monomer) was changed from 58.5 parts to 67.5 parts. Table 1 shows the results.

(Example 8)

In the production of the water-soluble polymer (B1) in step [1], 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth)acrylic acid ester monomer) is added in 10 parts to 2 parts, ethyl acrylate (( A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the (meth)acrylic acid ester monomer) was changed from 58.5 parts to 66.5 parts. Table 1 shows the results.

(Example 9)

In the production of the water-soluble polymer (B1) in the step [1], 2,2,2-trifluoroethyl methacrylate (fluorine-containing (meth)acrylic acid ester monomer) is 10 parts to 18 parts, ethyl acrylate (( A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the (meth)acrylic acid ester monomer) was 58.5 parts to 50.5 parts. Table 1 shows the results.

(Example 10)

In the production of the water-soluble polymer (B1) in step [1], 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) is added in 5 parts to 0 parts, and ethyl acrylate ((meth)acrylic acid ester monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 58.5 parts was changed to 63.5 parts. Table 1 shows the results.

(Example 11)

In the production of the water-soluble polymer (B1) in step [1], 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) is added in 5 parts to 1 part, and ethyl acrylate ((meth)acrylic acid ester monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 58.5 parts was 62.5 parts. Table 2 shows the results.

(Example 12)

In the production of the water-soluble polymer (B1) in step [1], 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) is added in 5 parts to 2 parts, and ethyl acrylate ((meth)acrylic acid ester monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 58.5 parts was changed to 61.5 parts. Table 2 shows the results.

(Example 13)

In the production of the water-soluble polymer (B1) in step [1], 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) is added in an amount of 5 to 13 parts, ethyl acrylate ((meth)acrylic acid ester monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 58.5 parts was made to 50.5 parts. Table 2 shows the results.

(Example 14)

In the production of the water-soluble polymer (B1) in step [1], methacrylic acid (ethylenically unsaturated carboxylic acid monomer) is 25 parts to 0 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) ) Was prepared in the same manner as in Example 1, except that 5 parts to 15 parts and ethyl acrylate ((meth)acrylic acid ester monomer) were 58.5 parts to 73.5 parts, to prepare a negative electrode and a lithium ion secondary battery. Table 2 shows the results.

(Example 15)

In the production of the water-soluble polymer (B1) in step [1], a negative electrode and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that tert-dodecyl mercaptan (chain transfer agent) was added in an amount of 0.2 to 0.05 parts. It was prepared. Table 2 shows the results.

(Example 16)

In the production of the water-soluble polymer (B1) in step [1], a negative electrode and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that tert-dodecyl mercaptan (chain transfer agent) was changed from 0.2 to 2.5 parts. It was prepared. Table 2 shows the results.

(Example 17)

In the production of the water-soluble polymer (B1) in step [1], a negative electrode and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that tert-dodecyl mercaptan (chain transfer agent) was added from 0.2 to 3 parts. It was prepared. Table 2 shows the results.

(Example 18)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 100 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 2 parts to 0 parts were used. Table 2 shows the results.

(Example 19)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 99.9 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 2 parts to 0.1 parts were used. Table 2 shows the results.

(Example 20)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 99.5 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 2 parts to 0.5 parts were used. Table 2 shows the results.

(Example 21)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 95 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 2 parts to 5 parts were used. Table 3 shows the results.

(Example 22)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 92.5 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 2 parts to 7.5 parts were used. Table 3 shows the results.

(Example 23)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 90 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 2 parts to 10 parts were used. Table 3 shows the results.

(Example 24)

In the production of the water-soluble polymer (B2) in step [2], acrylic acid (ethylenically unsaturated carboxylic acid monomer) is 98 parts to 0 parts, 2-acrylamide-2-methylpropanesulfonic acid (ethylenically unsaturated sulfonic acid monomer) A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 2 parts to 100 parts were used. Table 3 shows the results.

(Example 25)

In the production of the water-soluble polymer (B2) in the step [2], the same procedure as in Example 1 was carried out except that acrylic acid (ethylenically unsaturated carboxylic acid monomer) was set at 98 parts to 88 parts, and 10 parts of ethyl acrylate was newly added. Thus, a negative electrode and a lithium ion secondary battery were produced. Table 3 shows the results.

(Example 26)

In the production of the water-soluble polymer (B2) in step [2], the same procedure as in Example 1 was carried out except that acrylic acid (ethylenically unsaturated carboxylic acid monomer) was set at 98 parts to 78 parts, and 20 parts of ethyl acrylate was newly added. Thus, a negative electrode and a lithium ion secondary battery were produced. Table 3 shows the results.

(Example 27)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was made from 0.5 to 0.01 parts. Table 3 shows the results.

(Example 28)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was set to 0.5 to 0.05 parts. Table 3 shows the results.

(Example 29)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was set to 0.5 to 0.75 parts. Table 3 shows the results.

(Example 30)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was made from 0.5 to 2 parts. Table 3 shows the results.

(Example 31)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the addition amount of the water-soluble polymer (B1) was 0.11 part, and the addition amount of the water-soluble polymer (B2) was 1.39 parts, to prepare a slurry composition for a negative electrode. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 4 shows the results.

(Example 32)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the addition amount of the water-soluble polymer (B1) was 0.15 parts and the addition amount of the water-soluble polymer (B2) was 1.35 parts to prepare a slurry composition for a negative electrode. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 4 shows the results.

(Example 33)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the addition amount of the water-soluble polymer (B1) was 1.35 parts, and the addition amount of the water-soluble polymer (B2) was 0.15 parts, to prepare a slurry composition for a negative electrode. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 4 shows the results.

(Example 34)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the addition amount of the water-soluble polymer (B1) was 1.39 parts, and the addition amount of the water-soluble polymer (B2) was 0.11 part, to prepare a slurry composition for a negative electrode. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 4 shows the results.

(Example 35)

In the production of the slurry composition for a negative electrode in the step [3], Example 1 except that the slurry composition for a negative electrode was prepared with the addition amount of the water-soluble polymer (B1) being 2.1 parts and the addition amount of the water-soluble polymer (B2) being 1.4 parts. In the same manner as described above, a negative electrode and a lithium ion secondary battery were produced. Table 4 shows the results.

(Example 36)

In the production of the water-soluble polymer (B1) in step [1], the 10% LiOH aqueous solution is a 10% NaOH aqueous solution, and in the production of the water-soluble polymer (B2) in step [2], the 10% LiOH aqueous solution is a 10% NaOH aqueous solution. A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except for the above. Table 4 shows the results.

(Example 37)

In the production of the slurry composition for negative electrodes in step [3], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that 1.5 parts (in terms of solid content) of the following particulate binder was added. Table 4 shows the results.

Preparation of particulate binder

In a 5 kPa internal pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 1.8 parts of itaconic acid, 64.7 parts of styrene, 0.5 parts of t-dodecylmercaptan (TDM), 1.0 parts of sodium dodecylbenzenesulfonate as an emulsifier, ion 150 parts of exchanged water and 0.5 part of potassium persulfate as a polymerization initiator were added, stirred sufficiently, and then heated to 50°C to initiate polymerization. When the polymerization conversion ratio reached 96%, the reaction was stopped by cooling to obtain a mixture containing the polymer. After adding 5% NaOH aqueous solution to the mixture and adjusting the pH to 8, unreacted monomers were removed by heating and distillation under reduced pressure. Then, it cooled to 30 degrees C or less, and obtained the aqueous dispersion liquid containing a desired particulate binder (aromatic vinyl-conjugated diene copolymer). Further, the glass transition temperature of the aromatic vinyl-conjugated diene copolymer was +15°C.

(Example 38)

In the production of the slurry composition for negative electrodes in step [3], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 100 parts of artificial graphite was used as the negative electrode active material. Table 4 shows the results.

(Comparative Example 1)

In the production of the water-soluble polymer (B1) in step [1], a negative electrode and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that tert-dodecyl mercaptan (chain transfer agent) was changed from 0.2 to 3.5 parts. It was prepared. Table 5 shows the results.

(Comparative Example 2)

In the production of the water-soluble polymer (B1) in step [1], a negative electrode and a lithium ion secondary battery were prepared in the same manner as in Example 1, except that tert-dodecyl mercaptan (chain transfer agent) was added from 0.2 parts to 0 parts. It was prepared. Table 5 shows the results.

(Comparative Example 3)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was set to 0.5 to 2.5 parts. Table 5 shows the results.

(Comparative Example 4)

In the production of the water-soluble polymer (B2) in step [2], a negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except that potassium persulfate (polymerization initiator) was made from 0.5 to 0.01 parts. Table 5 shows the results.

(Comparative Example 5)

In the production of the water-soluble polymer (B2) in step [2], a 10% LiOH aqueous solution was not added to the mixture containing the water-dispersible polymer (B2), and the water-dispersible polymer (B2) was used as the water-soluble polymer (B2). A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except for the above.

Moreover, the water-dispersion-type polymer (B2) was pH 3. Moreover, with respect to the produced water-soluble polymer (B2), the viscosity of the 5% aqueous solution is too low, resulting in poor dispersibility of the negative electrode active material in the slurry composition for negative electrodes, and it is not possible to prepare a slurry composition for negative electrodes. A secondary battery could not be produced. Table 5 shows the results.

(Comparative Example 6)

In the production of the slurry composition for negative electrodes of step [3], the particulate binder produced in Example 37 without using the water-soluble polymer (B1) obtained in step [1] and the water-soluble polymer (B2) obtained in step [2] And 1.5 parts of carboxymethylcellulose ("BSH-12" manufactured by Daiichi Kogyo Pharmaceutical Co., Ltd.) were added to obtain a slurry composition for a negative electrode.

A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1, except that the slurry composition for negative electrodes was used. Table 5 shows the results.

(Comparative Example 7)

In the production of the water-soluble polymer (B1) in step [1], a 10% LiOH aqueous solution was not added to the mixture containing the water-dispersible polymer (B1), and the water-dispersible polymer (B1) was used as the water-soluble polymer (B1). A negative electrode and a lithium ion secondary battery were produced in the same manner as in Example 1 except for the above.

Moreover, the water dispersion type polymer (B1) was pH 3. Moreover, with respect to the produced water-soluble polymer (B1), the viscosity of the 5% aqueous solution is too low, resulting in poor dispersibility of the negative electrode active material in the slurry composition for negative electrodes, and it is not possible to prepare a slurry composition for negative electrodes, negative electrode and lithium ion A secondary battery could not be produced. Table 5 shows the results.

From the results of Tables 1 to 5, it can be seen that the negative electrode and the secondary battery using the slurry composition for negative electrodes of the present invention were excellent in the balance of each evaluation. Here, it was found that when the viscosity of the 5% aqueous solution of the water-soluble polymer (B1) was outside the preferred range described above (Comparative Examples 1 and 2), the dispersion stability of the negative electrode active material, charge transfer resistance, and the binding strength of the negative electrode deteriorated. Can. In addition, it can be seen that when the viscosity of the 5% aqueous solution of the water-soluble polymer (B2) was outside the above-mentioned preferred range (Comparative Examples 3 and 4), the dispersion stability of the negative electrode active material, and the binding strength of the negative electrode were deteriorated. In addition, when water-dispersible polymers (B1) or (B2) were used as the water-soluble polymers (B1) or (B2) (Comparative Examples 5 and 7), dispersion stability of the negative electrode active material deteriorated, and a slurry composition for negative electrodes could be prepared. It can be seen that there was not. In addition, instead of the water-soluble polymers (B1) and (B2), when the particulate binder and carboxymethylcellulose prepared in Example 37 were used (Comparative Example 6), it was found that the dispersion stability of the negative electrode active material and the charge transfer resistance deteriorated. Can be.

Claims (14)

A slurry composition for a negative electrode of a lithium ion secondary battery containing a negative electrode active material (A), a water-soluble polymer (B), and water (C),
The water-soluble polymer (B) contains 80 mass% or more of a water-soluble polymer (B1) and an ethylenically unsaturated acid monomer unit that are alkali metal salts of a polymer containing an ethylenically unsaturated acid monomer unit and a fluorine-containing (meth)acrylic acid ester monomer unit. The water-soluble polymer (B2) which is an alkali metal salt of the polymer to be contained,
The viscosity of the 5% aqueous solution of the water-soluble polymer (B1) is 100 cp or more and 1500 cp or less,
The slurry composition for a lithium ion secondary battery negative electrode whose viscosity of 5% aqueous solution of the said water-soluble polymer (B2) is 2000 cp or more and 20000 cp or less. According to claim 1,
The said water-soluble polymer (B) contains 0.1 mass part or more and 5.0 mass part or less with respect to 100 mass parts of said negative electrode active materials (A), The slurry composition for lithium ion secondary battery negative electrodes. According to claim 1,
The slurry composition for a lithium ion secondary battery negative electrode whose weight ratio (B1/B2) of the said water-soluble polymer (B1) and the said water-soluble polymer (B2) is 5/95 or more and 95/5 or less. According to claim 1,
The content ratio of the ethylenically unsaturated acid monomer unit in the water-soluble polymer (B1) is 15 mass% or more and 50 mass% or less, and the content ratio of the fluorine-containing (meth)acrylic acid ester monomer unit is 1 mass% or more, 20 mass % Or less lithium ion secondary battery slurry composition for negative electrodes. According to claim 1,
The water-soluble polymer (B1) is a lithium-ion secondary battery negative electrode further containing 30% by mass or more and 70% by mass or more of (meth)acrylic acid ester monomer units in addition to the ethylenically unsaturated acid monomer units and fluorine-containing (meth)acrylic acid ester monomer units. Dragon slurry composition. According to claim 1,
The slurry composition for negative electrode of a lithium ion secondary battery in which the ethylenically unsaturated acid monomer in the water-soluble polymer (B1) is an ethylenically unsaturated carboxylic acid monomer or an ethylenically unsaturated sulfonic acid monomer. According to claim 1,
The slurry composition for a negative electrode of a lithium ion secondary battery in which the ethylenically unsaturated acid monomer in the water-soluble polymer (B1) is an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer. The method of claim 7,
Lithium in which the content ratio of the ethylenically unsaturated carboxylic acid monomer in the water-soluble polymer (B1) is 15 mass% or more and 50 mass% or less, and the content ratio of the ethylenically unsaturated sulfonic acid monomer is 1 mass% or more and 15 mass% or less. Slurry composition for negative ion secondary battery. According to claim 1,
A slurry composition for a negative electrode for a lithium ion secondary battery, wherein the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer. According to claim 1,
The slurry composition for a negative electrode of a lithium ion secondary battery in which the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer or an ethylenically unsaturated sulfonic acid monomer. According to claim 1,
The slurry composition for a negative electrode of a lithium ion secondary battery in which the ethylenically unsaturated acid monomer in the water-soluble polymer (B2) is an ethylenically unsaturated carboxylic acid monomer and an ethylenically unsaturated sulfonic acid monomer. The method of claim 11,
The content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer (B2) is 90% by mass or more and 99% by mass or less, and the content rate of the ethylenically unsaturated sulfonic acid monomer unit is 1% by mass or more and 10% by mass The following slurry composition for lithium ion secondary battery negative electrodes. A method for producing a lithium ion secondary battery negative electrode, comprising the step of applying and drying the slurry composition for a lithium ion secondary battery negative electrode according to any one of claims 1 to 12 to a current collector to form a negative electrode active material layer. It has a positive electrode, a negative electrode, a separator and an electrolyte,
A lithium ion secondary battery in which the negative electrode is a lithium ion secondary battery negative electrode obtained by the production method according to claim 13.

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