WO2014014006A1

WO2014014006A1 - Negative electrode for secondary cell, and secondary cell

Info

Publication number: WO2014014006A1
Application number: PCT/JP2013/069372
Authority: WO
Inventors: 徳一山本; 園部　健矢; 智一佐々木
Original assignee: 日本ゼオン株式会社
Priority date: 2012-07-17
Filing date: 2013-07-17
Publication date: 2014-01-23
Also published as: JPWO2014014006A1; KR102157157B1; CN104247110A; KR20150035515A; JP6245173B2

Abstract

[Problem] To provide a secondary-cell negative electrode capable of yielding a secondary cell having exceptional cycle characteristics and output characteristics. [Solution] This secondary-cell negative electrode comprises a current collector and a negative-electrode active substance layer layered on the current collector, the negative-electrode active substance layer containing a negative-electrode active substance (A), a particulate binder (B), a hydroxyl-group-containing aqueous polymer (C), and an aqueous polymer (D) containing 0.5-20 mass% of a fluorine-containing (meth)acrylic acid ester monomer unit, the particulate binder (B) containing an aromatic vinyl-conjugated diene copolymer (b1) having a glass transition temperature of -30-20°C and containing an unsaturated carboxylic acid monomer unit, and an aromatic vinyl-conjugated diene copolymer (b2) having a glass transition temperature of 30-80°C and containing an unsaturated carboxylic acid monomer unit.

Description

Negative electrode for secondary battery and secondary battery

The present invention relates to a negative electrode used for a secondary battery such as a lithium ion secondary battery.

In recent years, portable terminals such as notebook personal computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. As a secondary battery used for the power source of these portable terminals, a nickel hydrogen secondary battery, a lithium ion secondary battery, and the like are frequently used. Mobile terminals are required to have more comfortable portability, and are rapidly becoming smaller, thinner, lighter, and higher in performance. As a result, mobile terminals are used in various places. In addition, the battery is required to be smaller, thinner, lighter, and higher in performance as in the case of the portable terminal.

Conventionally, a carbon-based active material such as graphite is used as a negative electrode active material in a lithium ion secondary battery. For example, Patent Document 1 describes a negative electrode for a lithium ion secondary battery containing a carbon-based active material and a binder composed of two types of carboxy-modified styrene-butadiene copolymers having different glass transition temperatures.

Also, for the purpose of increasing the capacity of lithium ion secondary batteries, a negative electrode for lithium ion secondary batteries using an alloy-based active material containing Si or the like has been developed (for example, Patent Document 2).

JP 2011-108373 A Patent No. 4025995

As a result of investigations by the present inventors, the negative electrode described in Patent Document 1 has insufficient dispersibility of the negative electrode active material and lithium ion conductivity, so that it is difficult to obtain a secondary battery having excellent cycle characteristics and output characteristics. It turns out that.

In addition, when an alloy-based active material is used as the negative electrode active material, when lithium ions are doped / dedoped, the volume of the negative electrode active material expands / contracts greatly. It has been found that detachment (powder falling) occurs and battery characteristics such as cycle characteristics and output characteristics may be deteriorated.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a secondary battery negative electrode capable of obtaining a secondary battery having excellent cycle characteristics and output characteristics.

As a result of intensive studies to solve the above problems, the present inventors have improved the dispersibility and lithium ion conductivity of the negative electrode active material in the negative electrode by using a specific particulate binder and a specific water-soluble polymer. As a result, it was found that a secondary battery having excellent cycle characteristics and output characteristics can be obtained, and the present invention has been completed.

That is, the gist of the present invention aimed at solving such problems is as follows.

(1) A current collector and a negative electrode active material layer laminated on the current collector,
The negative electrode active material layer comprises a negative electrode active material (A), a particulate binder (B), a hydroxyl group-containing water-soluble polymer (C), and a fluorine-containing (meth) acrylate monomer unit of 0.5 to Including a water-soluble polymer (D) containing 20% by mass,
The particulate binder (B) has a glass transition temperature of −30 to 20 ° C., an aromatic vinyl-conjugated diene copolymer (b1) comprising an unsaturated carboxylic acid monomer unit, and a glass transition temperature. And an aromatic vinyl-conjugated diene copolymer (b2) having an unsaturated carboxylic acid monomer unit at 30 to 80 ° C.

(2) The negative electrode for a secondary battery according to (1), wherein the negative electrode active material (A) includes a carbon-based active material (a1) and an alloy-based active material (a2).

(3) The negative electrode for a secondary battery according to (2), comprising 1 to 50 parts by mass of the alloy-based active material (a2) with respect to 100 parts by mass of the carbon-based active material (a1).

(4) The negative electrode for a secondary battery according to (2) or (3), wherein the alloy-based active material (a2) is Si, SiO _x (x = 0.01 or more and less than 2), or SiOC.

(5) The content ratio of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) in terms of mass ratio is the aromatic vinyl-conjugated diene copolymer (b1). ) / Aromatic vinyl-conjugated diene copolymer (b2) = the negative electrode for a secondary battery according to any one of (1) to (4), wherein 80/20 to 30/70.

(6) Each of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) has a tetrahydrofuran-insoluble content of 70 to 98% (1) to (5) The negative electrode for secondary batteries in any one of.

(7) A secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator,
A secondary battery, wherein the negative electrode is a negative electrode for a secondary battery according to any one of (1) to (6).

Since the negative electrode for secondary batteries of the present invention contains a specific particulate binder and a specific water-soluble polymer, the negative electrode active material is excellent in dispersibility and lithium ion conductivity. As a result, a secondary battery having excellent cycle characteristics (particularly high-temperature cycle characteristics) and output characteristics (particularly low-temperature output characteristics) can be obtained.
Further, according to the present invention, even when an alloy-based active material having a large volume expansion / contraction during lithium ion doping / dedoping is used as the negative electrode active material, the negative electrode active material can be expanded from the electrode plate swell or from the electrode. Occurrence of substance detachment (powder falling) can be suppressed. As a result, the cycle characteristics and output characteristics of the secondary battery can be improved.

[Anode for secondary battery]
The negative electrode for a secondary battery of the present invention (hereinafter sometimes simply referred to as “negative electrode”) includes a current collector and a negative electrode active material layer laminated on the current collector. The negative electrode active material layer contains the following components (A) to (D), and may contain other components (E) added as necessary. The negative electrode for secondary batteries of the present invention can be used for lithium ion secondary batteries, nickel metal hydride secondary batteries, and the like. Among these, a lithium ion secondary battery is preferable as a use because the long-term cycle characteristics and output characteristics are most demanded. Below, each component is explained in full detail about the case where it uses for a lithium ion secondary battery.

(A) Negative electrode active material The negative electrode active material is a substance that delivers 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) 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 battery having a larger capacity than a negative electrode obtained using only a conventional carbon-based active material can be obtained, and the adhesion strength of the negative electrode It is possible to solve problems such as lowering of cycle and cycle characteristics.

(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 into which lithium can be inserted, and specifically includes a carbonaceous material and a graphite material. The carbonaceous material is generally low in graphitization in which a carbon precursor is heat-treated (carbonized) at 2000 ° C. or less (the lower limit of the treatment temperature is not particularly limited, but can be, for example, 500 ° C. or more). A carbon material (low crystallinity) is shown, and a graphitic material is a heat treatment of graphitizable carbon at 2000 ° C. or higher (the upper limit of the processing temperature is not particularly limited, but can be, for example, 5000 ° C. or lower). The graphite material which has high crystallinity close to the graphite obtained by this is shown.

Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon.
Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum and coal, such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Is mentioned. MCMB is carbon fine particles obtained by separating and extracting mesophase spherules produced in the process of heating pitches at around 400 ° C. The mesophase pitch-based carbon fiber is a carbon fiber using as a raw material mesophase pitch obtained by growing and coalescing the mesophase microspheres. Pyrolytic vapor-grown carbon fibers are: (1) a method for pyrolyzing acrylic polymer fibers and the like, (2) a method for pyrolyzing by spinning a pitch, and (3) using nanoparticles such as iron as a catalyst It is a carbon fiber obtained by a catalytic vapor deposition (catalytic CVD) method in which hydrocarbon is vapor-phase pyrolyzed.
Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, and furfuryl alcohol resin fired bodies (PFA).

Graphite materials 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, graphitized mesophase pitch carbon fiber heat-treated at 2000 ° C or higher. It is done.

Of the carbon-based active materials, a graphite material is preferable. By using the graphite material, it becomes easy to increase the density of the negative electrode active material layer, 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 2.2 g / cm ³⁾ or less.) Can be easily produced. 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 remarkably exhibited.

The volume average particle diameter of the carbon-based active material is preferably 0.1 to 100 μm, more preferably 0.5 to 50 μm, and particularly preferably 1 to 30 μm. When the volume average particle diameter of the carbon-based active material is within this range, it becomes easy to prepare a slurry composition used for manufacturing the negative electrode. 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, preferably 3.0 ~ 20.0m ² / g, more preferably 3.5 ~ 15.0m ² / g, particularly preferably 4.0 ~ 10.0m ² / g is there. When the specific surface area of the carbon-based active material is in the above range, the active points on the surface of the carbon-based active material are increased, so that 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 includes an element into which lithium can be inserted and has a theoretical electric capacity per unit weight of 500 mAh / g or more when lithium is inserted (the theory The upper limit of the electric capacity is not particularly limited, but can be, for example, 5000 mAh / g or less.) Specifically, lithium metal, a single metal that forms a lithium alloy, and an alloy thereof, and Those oxides, sulfides, nitrides, silicides, carbides, phosphides and the like are used.

Examples of simple metals and alloys that form lithium alloys include Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. The compound to contain is mentioned. Among these, silicon (Si), tin (Sn) or lead (Pb) simple metals, alloys containing these atoms, or compounds of these metals are used. Among these, a simple substance of Si capable of inserting and extracting lithium at a low potential is preferable.
The alloy-based active material used in the present invention may further contain one or more nonmetallic 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 that can insert and desorb lithium at a low potential are preferable, and SiOC SiO _x is more preferred. For example, SiOC can be obtained by firing a polymer material containing silicon. Among SiOC, the range of 0.8 ≦ x ≦ 3 and 2 ≦ y ≦ 4 is preferably used in view of the balance between capacity and cycle characteristics.

Examples of oxides, sulfides, nitrides, silicides, carbides, and phosphides include oxides, sulfides, nitrides, silicides, carbides, and phosphides of elements into which lithium can be inserted. Oxides are particularly preferred. Specifically, an oxide such as tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide, or a lithium-containing metal composite oxide containing a metal element selected from the group consisting of 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 includes Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb), among which Li _4/3 Ti _5/3 O ₄ , Li ₁ Ti ₂ O ₄ and Li _4/5 Ti _11/5 O ₄ are used.

Among these, a material containing silicon is preferable, and SiO _x C _y such as SiOC, SiO _x , and SiC are more preferable. In this compound, it is presumed that insertion / extraction of Li to / from Si (silicon) occurs at a high potential, and C (carbon) occurs at a low potential, and expansion / contraction is suppressed as compared with other alloy-based active materials. It is easier to obtain the effect.

The volume average particle diameter of the alloy-based active material is preferably 0.1 to 50 μm, more preferably 0.5 to 20 μm, and particularly preferably 1 to 10 μm. When the volume average particle diameter of the alloy-based active material is within this range, the slurry composition used for producing the negative electrode can be easily produced.

The specific surface area of alloy-formable active material is preferably 3.0 ~ 20.0m ² / g, more preferably 3.5 ~ 15.0m ² / g, particularly preferably 4.0 ~ 10.0m ² / g is there. When the specific surface area of the alloy-based active material is in the above range, the active points on the surface of the alloy-based active material are increased, so that the output characteristics of the lithium ion secondary battery are excellent.

The method for mixing the alloy-based active material and the carbon-based active material is not particularly limited, and conventionally known dry mixing and wet mixing may be mentioned.

In the negative electrode active material (A) in the present invention, the alloy-based active material (a2) is preferably contained in an amount of 1 to 50 parts by mass with respect to 100 parts by mass of the carbon-based active material (a1). 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 the adhesion strength of the negative electrode can be increased. It is possible to prevent deterioration and cycle characteristics.

(B) Particulate binder The particulate binder has the property of being dispersed in a dispersion medium described below. By using the particulate binder, it is possible to improve the binding property between the current collector and the negative electrode active material layer, which will be described later, to improve the negative electrode strength, and to suppress the decrease in capacity of the obtained negative electrode and the deterioration due to repeated charge and discharge. .
The particulate binder only needs to be present in a state where 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 have to be a state in which the particle shape is completely maintained, and may be in a state in which the particle shape is maintained to some extent.
Examples of the particulate binder include those in which binder particles such as latex are dispersed in water, and powders obtained by drying such a dispersion.
In the present invention, the particulate binder is insoluble in water. That is, it is preferably dispersed in the form of particles without being dissolved in an aqueous solvent. Specifically, being water-insoluble means that when 0.5 g of the binder is dissolved in 100 g of water at 25 ° C., the insoluble content becomes 90% by mass or more.
The particulate binder (B) in the present invention has an aromatic vinyl-conjugated diene copolymer (b1) (hereinafter, referred to as “a”) having a glass transition temperature of −30 to 20 ° C. and comprising an unsaturated carboxylic acid monomer unit. Simply referred to as “aromatic vinyl-conjugated diene copolymer (b1)”), a glass transition temperature of 30 to 80 ° C., and an aromatic carboxylic acid monomer unit. Vinyl-conjugated diene copolymer (b2) (hereinafter sometimes simply referred to as “aromatic vinyl-conjugated diene copolymer (b2)”).

(B1) Aromatic vinyl-conjugated diene copolymer The aromatic vinyl-conjugated diene copolymer (b1) used in the present invention is a structural unit obtained by polymerizing an aromatic vinyl monomer (hereinafter referred to as “aromatics”). Vinyl monomer units ”), structural units obtained by polymerizing conjugated dienes (hereinafter, sometimes referred to as“ conjugated diene monomer units ”), and unsaturated carboxylic acid monomer It is a copolymer containing a body unit. In addition, the aromatic vinyl-conjugated diene copolymer (b1) may contain other monomer units copolymerizable therewith as necessary.
The ratio of the monomer units constituting the aromatic vinyl-conjugated diene copolymer (b1) matches the charging ratio of the monomers at the time of polymerization. Thereafter, unless otherwise specified, the ratio of the monomer units constituting the polymer corresponds to the charging ratio of the monomers at the time of polymerization.

<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-methyl styrene, vinyl toluene, and divinyl benzene. Of these, styrene is preferred. These aromatic vinyl monomers can be used alone or in combination of two or more. The content of aromatic vinyl monomer units in the aromatic vinyl-conjugated diene copolymer (b1) is preferably 40% by mass or more, more preferably 50 to 65% by mass.

<Conjugated diene monomer unit>
The conjugated diene monomer unit is a structural unit obtained by polymerizing a conjugated diene monomer.
Examples of conjugated diene monomers include 1,3-butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like Is mentioned. These conjugated diene monomers can be used alone or in combination of two or more.
The content of the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer (b1) is preferably 25% by mass or more, more preferably 31 to 46% by mass.
The total proportion of the aromatic vinyl monomer unit and the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer (b1) is preferably 65% by mass or more, more preferably 80 to 96% by mass. It is.
Hereinafter, the unsaturated carboxylic acid monomer unit and other monomer units will be described in detail.

<Unsaturated carboxylic acid monomer unit>
An unsaturated carboxylic acid monomer unit is a structural unit obtained by polymerizing an unsaturated carboxylic acid monomer. Examples of the unsaturated carboxylic acid monomer include unsaturated monocarboxylic acid and its derivative, unsaturated dicarboxylic acid and its acid anhydride, and derivatives thereof. Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of unsaturated monocarboxylic acid derivatives 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 unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of unsaturated dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of unsaturated dicarboxylic acids include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, methylallyl maleate; and diphenyl maleate, nonyl maleate, maleate Examples thereof include maleate esters such as decyl acid, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.
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 preferable, acrylic acid, methacrylic acid, and itaconic acid are more preferable, and itaconic acid is particularly preferable. preferable. The dispersibility of the resulting aromatic vinyl-conjugated diene copolymer (b1) in 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. This is because a secondary battery having cycle characteristics can be obtained. By using the unsaturated carboxylic acid monomer, an acidic functional group can be introduced into the aromatic vinyl-conjugated diene copolymer (b1).

The content of the unsaturated carboxylic acid monomer unit in the aromatic vinyl-conjugated diene copolymer (b1) is preferably 0.1 to 6% by mass, more preferably 0.5 to 5% by mass. By making the content rate of an unsaturated carboxylic acid monomer unit into the said range, the binding property of a collector and a negative electrode active material layer can be improved, and negative electrode intensity | strength can be improved. As a result, a negative electrode for a secondary battery having excellent cycle characteristics can be obtained.

<Other monomer units>
The other monomer unit is a structural unit obtained by polymerizing another monomer copolymerizable with the above-mentioned monomer.
Other monomers constituting other monomer units include hydrocarbons such as ethylene, propylene and isobutylene; α, β-unsaturated nitrile compounds such as acrylonitrile and methacrylonitrile; vinyl chloride and vinylidene chloride Halogen atom-containing monomers; 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; methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone and hexyl vinyl ketone And vinyl ketones such as isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole.
The ratio of the other monomer units in the aromatic vinyl-conjugated diene copolymer (b1) is preferably 1 to 35% by mass, more preferably 4 to 20% by mass.

The glass transition temperature (Tg) of the aromatic vinyl-conjugated diene copolymer (b1) is −30 to 20 ° C., preferably −20 to 20 ° C., more preferably −10 to 15 ° C. If the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) is too low, it will be difficult to suppress the expansion and contraction of the negative electrode active material, and the cycle characteristics of the secondary battery will deteriorate. If the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) is too high, the binding property with the current collector becomes insufficient, and the cycle characteristics of the secondary battery are deteriorated.
When the aromatic vinyl monomer unit constituting the aromatic vinyl-conjugated diene copolymer (b1) is increased, the glass transition temperature tends to increase, and when the conjugated diene monomer unit is increased, the glass transition temperature is increased. Tend to be low. The ratio of each monomer unit is adjusted based on the ratio of unsaturated carboxylic acid monomer units and other monomer units in the polymer so that the glass transition temperature is in the above range.

The number average particle diameter of the aromatic vinyl-conjugated diene copolymer (b1) is not particularly limited, but is usually 80 to 250 nm, preferably 100 to 200 nm, more preferably 120 to 180 nm. When the number average particle diameter of the aromatic vinyl-conjugated diene copolymer (b1) is within this range, an excellent binding force can be imparted to the negative electrode active material layer even with a small amount of use. The number average particle diameter in the present invention is a number average particle diameter calculated as an arithmetic average value obtained by measuring the diameter of 100 polymer particles randomly selected in a transmission electron micrograph. The shape of the particles can be either spherical or irregular. These aromatic vinyl-conjugated diene copolymers (b1) can be used alone or in combination of two or more.

(B2) Aromatic vinyl-conjugated diene copolymer The aromatic vinyl-conjugated diene copolymer (b2) used in the present invention is similar to the aromatic vinyl-conjugated diene copolymer (b1). A copolymer comprising a monomer unit, a conjugated diene monomer unit, and an unsaturated carboxylic acid monomer unit. Further, the aromatic vinyl-conjugated diene copolymer (b2) may contain other monomer units copolymerizable therewith as necessary. The aromatic vinyl monomer, conjugated diene monomer, unsaturated carboxylic acid monomer and other monomers copolymerizable therewith are as exemplified in the aromatic vinyl-conjugated diene copolymer (b1). It is.

The ratio of the aromatic vinyl monomer unit in the aromatic vinyl-conjugated diene copolymer (b2) is preferably 55% by mass or more, more preferably 68-80% by mass.
The ratio of the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer (b2) is preferably 10% by mass or more, more preferably 16 to 28% by mass.
The total proportion of the aromatic vinyl monomer unit and the conjugated diene monomer unit in the aromatic vinyl-conjugated diene copolymer (b2) is preferably 65% by mass or more, more preferably 84 to 98% by mass. It is.
The ratio of the unsaturated carboxylic acid monomer unit in the aromatic vinyl-conjugated diene copolymer (b2) is preferably 0.1 to 6% by mass, more preferably 0.5 to 5% by mass. By making the content rate of an unsaturated carboxylic acid monomer into the said range, the binding property of a collector and a negative electrode active material layer can be improved, and negative electrode intensity | strength can be improved. As a result, a negative electrode for a secondary battery having excellent cycle characteristics can be obtained.
The ratio of the other monomer units in the aromatic vinyl-conjugated diene copolymer (b2) is preferably 1 to 35% by mass, more preferably 2 to 16% by mass.

The glass transition temperature (Tg) of the aromatic vinyl-conjugated diene copolymer (b2) is 30 to 80 ° C., preferably 30 to 70 ° C., more preferably 35 to 60 ° C. If the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) is too low, it becomes difficult to suppress the expansion and contraction of the negative electrode active material, and the cycle characteristics of the secondary battery deteriorate. In addition, if the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) is too high, the flexibility of the aromatic vinyl-conjugated diene copolymer (b2) is reduced and the expansion and contraction of the negative electrode active material is suppressed. As a result, the negative electrode is cracked.
The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) can be adjusted to the above range in the same manner as in the case of the aromatic vinyl-conjugated diene copolymer (b1).

The number average particle size of the aromatic vinyl-conjugated diene copolymer (b2) is not particularly limited, but is usually 80 to 250 nm, preferably 100 to 200 nm, more preferably 120 to 180 nm. When the number average particle diameter of the aromatic vinyl-conjugated diene copolymer (b2) is within this range, an excellent binding force can be imparted to the negative electrode active material layer even with a small amount of use. These aromatic vinyl-conjugated diene copolymers (b2) can be used alone or in combination of two or more.

The content ratio (mass ratio) of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) in the negative electrode for secondary battery according to the present invention is the aromatic vinyl-conjugated diene. Copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b2) = 80/20 to 30/70 is preferable, and 70/30 to 40/60 is more preferable. By setting the content ratio of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) in the above range, the expansion and shrinkage of the negative electrode active material is suppressed, The binding property with the negative electrode active material layer can be improved, and the negative electrode strength can be improved.

The difference between the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) and the glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) is preferably 10 to 90 ° C., more preferably 20 to 70 ° C. If the difference in glass transition temperature is too large, the electrode strength is weakened and the cycle characteristics may be deteriorated. Further, if the difference in glass transition temperature is too small, the electrode plate may easily swell.

The tetrahydrofuran-insoluble content of each of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) is preferably 70 to 98%, more preferably 90 to 93%. It is. By making the tetrahydrofuran-insoluble content of the aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) in the above range, the binding force between the negative electrode active materials is increased, and the secondary battery Cycle characteristics are improved. Here, the tetrahydrofuran-insoluble component represents the mass ratio of the components insoluble in tetrahydrofuran among the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2). Value. Tetrahydrofuran insolubles can be measured by the method described in the examples described later.

The compounding amount of the particulate binder (B) is preferably 0.7 to 2 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material. By adjusting the blending amount of the particulate binder (B) within the above range, it is possible to suppress the expansion / contraction of the negative electrode active material and reduce the internal resistance of the electrode. Therefore, a secondary battery having excellent cycle characteristics and output characteristics can be obtained. Obtainable.

[Production of particulate binder (B)]
The method for producing the particulate binder (B) is not particularly limited. As described above, the monomer mixture containing the monomers constituting each copolymer is emulsion-polymerized to obtain an aromatic vinyl-conjugated diene. Copolymers (b1) and (b2) can be obtained and mixed. The method for 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 apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

Examples of the polymerization initiator used for emulsion polymerization include inorganic peroxides such as sodium persulfate, potassium persulfate, ammonium persulfate, potassium perphosphate, and hydrogen peroxide; t-butyl peroxide, cumene hydroperoxide, p-menthane 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 oxide and t-butylperoxyisobutyrate; azo compounds such as azobisisobutyronitrile, azobis-2,4-dimethylvaleronitrile, azobiscyclohexanecarbonitrile, methyl azobisisobutyrate, etc. Et That.

Of these, inorganic peroxides can be preferably used. These polymerization initiators can be used alone or in combination of two or more. The peroxide initiator can also be used as a redox polymerization initiator in combination with a reducing agent such as sodium bisulfite.

The amount of the polymerization initiator used is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 2 parts by mass with respect to 100 parts by mass of the total amount of the monomer mixture used for the polymerization.

It is preferable to use a chain transfer agent during emulsion polymerization in order to adjust the amount of insoluble tetrahydrofuran in the resulting copolymer. By increasing the amount of the chain transfer agent used, the amount of insoluble tetrahydrofuran is decreased, and by decreasing the amount of the chain transfer agent used, the amount of the tetrahydrofuran insoluble component tends to increase. The amount can be controlled within a range. Examples of the chain transfer agent include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan; dimethylxanthogen disulfide, diisopropylxanthogendi Xanthogen compounds such as sulfide; thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide; phenols such as 2,6-di-t-butyl-4-methylphenol and styrenated phenol Compounds; allyl compounds such as allyl alcohol; halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide; thioglycolic acid, Oringo acid, 2-ethylhexyl thioglycolate, diphenylethylene, etc. α- methylstyrene dimer.

Of these, alkyl mercaptans are 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 preferably 0.05 to 2 parts by mass, more preferably 0.1 to 1 part by mass with respect to 100 parts by mass of the monomer mixture.

A surfactant may be used during emulsion polymerization. Unlike the reactive surfactant preferably contained in the water-soluble polymer (D) described later, the surfactant is non-reactive, and is an anionic surfactant, a nonionic surfactant, a cationic surfactant, Any of amphoteric surfactants may be used. 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 hexadecyl sulfate, sodium octadecyl sulfate and the like. Sulfuric acid ester salts of higher alcohols; alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, sodium lauryl benzene sulfonate, sodium hexadecyl benzene sulfonate; fats such as sodium lauryl sulfonate, sodium dodecyl sulfonate, sodium tetradecyl sulfonate Group sulfonates; and the like.

Since the reactive surfactant described later has the same emulsifying action, only the reactive surfactant may be used, or the reactive surfactant and the non-reactive surfactant may be used in combination. Furthermore, when a reactive surfactant is not used, emulsion polymerization is stabilized by using the non-reactive surfactant. The amount of the surfactant used (including the reactive surfactant) is preferably 0.5 to 10 parts by mass, more preferably 1 to 5 parts by mass with respect to 100 parts by mass of the monomer mixture.

Further, in the emulsion polymerization, various additives such as a pH adjusting agent such as sodium hydroxide and ammonia; a dispersing agent, a chelating agent, an oxygen scavenger, a builder, and a seed latex for adjusting the particle size can be appropriately used. . Seed latex refers to a dispersion of fine particles that becomes the nucleus of the reaction during emulsion polymerization. The fine particles often have a particle size of 100 nm or less. The fine particles are not particularly limited, and general-purpose polymers such as diene polymers are used. According to the seed polymerization method, copolymer particles having a relatively uniform particle diameter can be obtained.

The polymerization temperature for carrying out the polymerization reaction is not particularly limited, but is usually 0 to 100 ° C., preferably 40 to 80 ° C. Emulsion polymerization is performed in such a temperature range, and the polymerization reaction is stopped at a predetermined polymerization conversion rate by adding a polymerization terminator or cooling the polymerization system. The polymerization conversion rate for stopping the polymerization reaction is preferably 93% by mass or more, more preferably 95% by mass or more.

After stopping the polymerization reaction, if necessary, the unreacted monomer is removed, the pH and the solid content concentration are adjusted, and the aromatic vinyl in a form (latex) in which the particulate copolymer is dispersed in the dispersion medium Conjugated diene copolymers (b1) and (b2) are obtained. Thereafter, if necessary, the dispersion medium may be replaced, or the dispersion medium may be evaporated to obtain a particulate copolymer in powder form.

A known dispersant, thickener, anti-aging agent, antifoaming agent, antiseptic, antibacterial agent, anti-blistering agent, pH adjuster, etc. are added to the resulting latex of the particulate copolymer as necessary. You can also.

(C) Hydroxyl group-containing water-soluble polymer A hydroxyl group-containing water-soluble polymer is a polymer containing a hydroxyl group and having water solubility. The hydroxyl group-containing water-soluble polymer is a polymer different from the water-soluble polymer (D) described later, that is, a water-soluble polymer containing a hydroxyl group and not containing a fluorine-containing (meth) acrylate monomer unit.
The hydroxyl group-containing water-soluble polymer (C) (hereinafter sometimes simply referred to as “water-soluble polymer (C)”) is used by being dissolved in a slurry composition for producing a negative electrode for a secondary battery. And negative electrode active material (A) and the like have a function of uniformly dispersing in the slurry composition. Therefore, a uniform secondary battery negative electrode can be obtained by using the water-soluble polymer (C).

Examples of the hydroxyl group-containing water-soluble polymer (C) include cellulose polymers such as carboxymethylcellulose, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxypropylmethylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic Acids and their ammonium salts and alkali metal salts; (modified) polyvinyl alcohol, acrylic acid or copolymers of acrylate and vinyl alcohol, maleic anhydride or maleic anhydride or copolymers of fumaric acid and vinyl alcohol, etc. Alcohols: polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, various modified products Pung, chitin, such as chitosan derivatives, and the like. Among these, a cellulose polymer is preferable and carboxymethyl cellulose is particularly preferable.

When the water-soluble polymer (C) is used, the 1% aqueous solution viscosity is preferably 100 to 3000 mPa · s, more preferably 500 to 2500 mPa · s, and particularly preferably 1000 to 2000 mPa · s. When the viscosity of the 1% aqueous solution of the water-soluble polymer (C) is within the above range, the viscosity of the slurry composition used for producing the negative electrode can be made suitable for coating, and the drying time of the slurry composition is shortened. Therefore, the productivity of the secondary battery is excellent. Moreover, a negative electrode with favorable binding properties can be obtained. The aqueous solution viscosity can be adjusted by the average degree of polymerization of the water-soluble polymer (C). When the average degree of polymerization is high, the aqueous solution viscosity tends to increase. The average degree of polymerization of the water-soluble polymer (C) is preferably 100 to 1500, more preferably 300 to 1200, and particularly preferably 500 to 1000. If the average degree of polymerization of the water-soluble polymer (C) is in the above range, the 1% aqueous solution viscosity can be set in the above range, and thereby the above-described effects are exhibited.
The 1% aqueous solution viscosity is a value measured by a single cylindrical rotational viscometer (25 ° C., rotational speed = 60 rpm, spindle shape: 1) according to JIS Z8803;

In the present invention, the degree of etherification of the cellulosic polymer suitable as the water-soluble polymer (C) is preferably 0.6 to 1.5, more preferably 0.7 to 1.2, and particularly preferably 0.8 to 1.0. The degree of etherification of the cellulosic polymer is in the above range, thereby reducing the affinity with the negative electrode active material, preventing the water-soluble polymer (C) from being unevenly distributed on the surface of the negative electrode active material, and the negative electrode active material in the negative electrode The binding property between the layer and the current collector can be maintained, and the binding property of the negative electrode is significantly improved. Here, the degree of etherification refers to the degree of substitution of carboxymethyl groups or the like to hydroxyl groups (three) per anhydroglucose unit in cellulose. Theoretically, values from 0 to 3 can be taken. It shows that as the degree of etherification increases, the ratio of hydroxyl groups in cellulose decreases and the ratio of substituted substances increases, and as the degree of etherification decreases, hydroxyl groups in cellulose increase and substituents decrease. The degree of etherification (degree of substitution) is determined by the following method and formula.

First, weigh 0.5-0.7g of sample precisely and incinerate in a magnetic crucible. After cooling, the resulting incinerated product is transferred to a 500 ml beaker, and about 250 ml of water and 35 ml of N / 10 sulfuric acid are added with a pipette and boiled for 30 minutes. This is cooled, phenolphthalein indicator is added, excess acid is back titrated with N / 10 potassium hydroxide, and the degree of substitution is calculated from the following formulas (I) and (II).

In the above formulas (I) and (II), A is the amount (ml) of N / 10 sulfuric acid consumed by the bound alkali metal ions in 1 g of the sample. a is the amount (ml) of N / 10 sulfuric acid used. f is the titer coefficient of N / 10 sulfuric acid. b is the titration amount (ml) of N / 10 potassium hydroxide. f ¹ is the titer coefficient of N / 10 potassium hydroxide. M is the weight average molecular weight of the sample.

The blending amount of the water-soluble polymer (C) is preferably 1 to 3 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material. When the blending amount of the water-soluble polymer (C) is in the above range, the coating property is improved, so that the increase in internal resistance of the secondary battery is prevented and the binding property with the current collector is excellent. Further, since the expansion / contraction of the negative electrode active material can be suppressed, the cycle characteristics of the secondary battery are improved.

(D) Water-soluble polymer containing 0.5 to 20% by mass of fluorine-containing (meth) acrylate monomer unit 0.5 to 20% of fluorine-containing (meth) acrylate monomer unit used in the present invention % Water-soluble polymer (D) (hereinafter sometimes simply referred to as “water-soluble polymer (D)”) is 0.5 to 20% by mass of fluorine-containing (meth) acrylate monomer units. The copolymer is preferably 2 to 15% by mass, more preferably 3 to 12% by mass. The copolymer may further contain an unsaturated carboxylic acid monomer unit, a (meth) acrylic acid ester monomer unit, a crosslinkable monomer unit, and a reactive surfactant alone. A structural unit obtained by polymerizing a functional monomer such as a polymer, or a structural unit obtained by polymerizing other copolymerizable monomers may be included.
In the present specification, (meth) acryl includes both acrylic and methacrylic.
By using such a water-soluble polymer (D), the binding property between the current collector and the negative electrode active material layer can be improved, and the negative electrode strength can be improved. In addition, by covering the surface of the negative electrode active material with the water-soluble polymer (D), the decomposition of the electrolyte solution by the negative electrode active material is suppressed in the secondary battery, and the durability (cycle characteristics) of the secondary battery is improved. it can. Furthermore, since the negative electrode active material is coated with the water-soluble polymer (D), the affinity between the negative electrode active material and the electrolytic solution can be improved, the ionic conductivity can be improved, and the internal resistance of the secondary battery can be reduced.

<Fluorine-containing (meth) acrylic acid ester monomer unit>
The fluorine-containing (meth) acrylic acid ester monomer unit is a structural unit formed by polymerizing a fluorine-containing (meth) acrylic acid ester monomer.
Examples of the fluorine-containing (meth) acrylic acid ester monomer include monomers represented by the following formula (I).

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

Examples of fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, and (meth) acrylic acid fluoride. Aralkyl is mentioned. Of these, alkyl fluoride (meth) acrylate is preferable. Specific examples of such a monomer include (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-perfluoroundecyl, perfluorooctyl (meth) acrylate, (meth) acrylic acid-3- [4- [1-trifluoromethyl-2,2- And (meth) acrylic acid perfluoroalkyl esters such as bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] -2-hydroxypropyl.

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

The content ratio of the fluorine-containing (meth) acrylate monomer unit in the water-soluble polymer (D) is 0.5 to 20% by mass, preferably 2 to 15% by mass, more preferably 3 to 12% by mass. is there. If the ratio of the fluorine-containing (meth) acrylic acid ester monomer unit is too low, the water-soluble polymer (D) cannot be given a repulsive force against the electrolytic solution, and the swellability cannot be adjusted to an appropriate range. Moreover, when the ratio of a fluorine-containing (meth) acrylic acid ester monomer unit is too high, the wettability with respect to electrolyte solution cannot be provided to water-soluble polymer (D), and low temperature cycling characteristics will fall.

When the water-soluble polymer (D) contains a fluorine-containing (meth) acrylic acid ester monomer unit, alkali resistance is imparted to the negative electrode active material layer. The slurry composition for forming the negative electrode may contain an alkaline substance, and the alkaline substance may be generated by oxidation / reduction due to the operation of the element. Such an alkaline substance corrodes the current collector and impairs the device life, but the negative electrode active material layer has alkali resistance, so that corrosion of the current collector due to the alkaline substance is suppressed.

<Unsaturated carboxylic acid monomer unit>
An unsaturated carboxylic acid monomer unit is a structural unit formed by polymerizing an unsaturated carboxylic acid monomer. The unsaturated carboxylic acid monomer is the same as the unsaturated carboxylic acid monomer detailed in the particulate binder (B).
Among unsaturated carboxylic acid monomers, 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, and unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferred. Carboxylic acid is more preferred. It is because the dispersibility with respect to the water of the obtained water-soluble polymer (D) can be improved more.

The content of the unsaturated carboxylic acid monomer unit in the water-soluble polymer (D) is preferably 1 to 40% by mass, more preferably 5 to 30% by mass. By making the content rate of an unsaturated carboxylic acid monomer into the said range, the binding property of a collector and a negative electrode active material layer can be improved, and negative electrode intensity | strength can be improved. Moreover, since the dispersibility of water-soluble polymer (D) can be improved, a uniform negative electrode slurry composition can be obtained. As a result, a secondary battery having excellent cycle characteristics can be obtained.

<(Meth) acrylic acid ester monomer unit>
A (meth) acrylic acid ester monomer unit is a structural unit obtained by polymerizing a (meth) acrylic acid ester monomer. However, among the (meth) acrylate monomers, those containing fluorine are distinguished from (meth) acrylate monomers as the above-mentioned fluorine-containing (meth) acrylate monomers.

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

(Meth) acrylic acid ester monomer may be used alone or in combination of two or more at any ratio. Therefore, the water-soluble polymer (D) 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 (D), the content ratio of the (meth) acrylic acid ester monomer unit is preferably 30% by mass or more, more preferably 35% by mass or more, and particularly preferably 40% by mass or more. Preferably it is 75 mass% or less, More preferably, it is 70 mass% or less, Most preferably, it is 65 mass% or less. By making the content ratio of the (meth) acrylate monomer unit more than the lower limit of the above range, the binding property of the negative electrode active material layer to the current collector can be increased, and the upper limit of the above range or less By doing so, the flexibility of the negative electrode active material layer can be increased.

<Crosslinkable monomer unit>
The water-soluble polymer (D) may further contain a crosslinkable monomer unit in addition to the above 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 the crosslinkable monomer, a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

Examples of thermally crosslinkable groups contained in the monofunctional monomer include epoxy groups, N-methylolamide groups, oxetanyl groups, oxazoline groups, and combinations thereof. Among these, an epoxy group is more preferable in terms of easy adjustment of crosslinking and crosslinking density.

Examples of the crosslinkable monomer having an epoxy group as a thermally crosslinkable group and having an olefinic double bond include vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, 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 Monoepoxides of dienes or polyenes such as; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; and glycidyl acrylate, glycidyl methacrylate Glycidyl crotonate Unsaturated carboxylic acids such as glycidyl-4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl-4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexene carboxylic acid, glycidyl ester of 4-methyl-3-cyclohexene carboxylic acid Examples include glycidyl esters of acids.

Examples of the crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond have a methylol group such as N-methylol (meth) acrylamide (meta ) Acrylamides.

Examples of the crosslinkable monomer having an oxetanyl group as a thermally crosslinkable group and having an olefinic double bond include 3-((meth) acryloyloxymethyl) oxetane, 3-((meth) Acryloyloxymethyl) -2-trifluoromethyloxetane, 3-((meth) acryloyloxymethyl) -2-phenyloxetane, 2-((meth) acryloyloxymethyl) oxetane, and 2-((meth) acryloyloxymethyl) ) -4-Trifluoromethyloxetane.

Examples of the crosslinkable monomer having an oxazoline group as a heat crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2- Oxazoline, 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 multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, 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, tetraallyloxyethane, trimethylolpropane-diallyl Ethers, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylene bisacrylamide, and divinylbenzene.

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

When the water-soluble polymer (D) contains a crosslinkable monomer unit, the content ratio is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and particularly preferably 0.5% by mass. Or more, preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less. By making the content rate of a crosslinkable monomer unit more than the lower limit of the said range, the weight average molecular weight of water-soluble polymer (D) can be raised and it can prevent that a swelling degree rises too much. On the other hand, by setting the ratio of the crosslinkable monomer units to be equal to or less than the upper limit of the above range, the water-soluble polymer (D) can be improved in water solubility and the dispersibility can be improved. Therefore, by setting the content ratio of the crosslinkable monomer unit within the above range, both the degree of swelling and the dispersibility can be improved.

<Reactive surfactant monomer unit>
The water-soluble polymer (D) may contain a structural unit obtained by polymerizing a functional monomer such as a reactive surfactant monomer in addition to the above monomer units. .

The reactive surfactant monomer is a monomer having a polymerizable group that can be copolymerized with other monomers described later, and having a surfactant group (hydrophilic group and hydrophobic group). is there. The monomer unit obtained by polymerizing the reactive surfactant monomer is a structural unit that constitutes part of the molecule of the water-soluble polymer (D) and can function as a surfactant.

Usually, the reactive surfactant monomer has a polymerizable unsaturated group, and this group also acts as a hydrophobic group after polymerization. Examples of the polymerizable unsaturated group that the reactive surfactant monomer has include a vinyl group, an allyl group, a vinylidene group, a propenyl group, an isopropenyl group, and an isobutylidene group. The type of the polymerizable unsaturated group may be one type or two or more types.

Also, the reactive surfactant monomer usually has a hydrophilic group as a portion that exhibits hydrophilicity. Reactive surfactant monomers are classified into anionic, cationic and nonionic surfactants depending on the type of hydrophilic group.

Examples of the anionic hydrophilic group 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 ions; ammonium ions of alkylamines such as monomethylamine, dimethylamine, monoethylamine and triethylamine; and Examples include ammonium ions of alkanolamines such as monoethanolamine, diethanolamine, and triethanolamine.

Examples of the cationic hydrophilic group 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.

Examples of suitable reactive surfactant monomers include compounds represented by the following formula (II).

In the formula (II), R represents a divalent linking group. Examples of R include —Si—O— group, methylene group and phenylene group. In the formula (II), R ³ represents a hydrophilic group. An example of R ³ includes —SO ₃ NH ₄ . In the formula (II), n is an integer of 1 or more and 100 or less. A reactive surfactant monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

When the water-soluble polymer (D) contains a reactive surfactant monomer unit, the ratio is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, particularly preferably 1 to It is in the range of 5% by mass. The dispersibility of the negative electrode active material (A) and the particulate binder (B) can be improved by setting the ratio of the reactive surfactant monomer unit to the lower limit value or more of the above range. On the other hand, the durability of the negative electrode active material layer can be improved by setting the ratio of the reactive surfactant monomer unit to be equal to or less than the upper limit of the above range.

<Other monomer units>
Further examples of the arbitrary unit that the water-soluble polymer (D) may have include a structural unit obtained by polymerizing the following monomers. That is, styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene and divinyl benzene; 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; Vinyl chloride , Halogen atom-containing monomers such as 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; Methyl Vinyl ketone monomers such as nyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, isopropenyl vinyl ketone; and one or more of heterocyclic compound-containing vinyl compound monomers such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole The structural unit obtained by polymerizing is mentioned. The proportion of these structural units in the water-soluble polymer (D) is preferably 0 to 10% by mass, more preferably 0 to 5% by mass.

The water-soluble polymer in this specification refers to a polymer having a 1% aqueous solution viscosity of 0.1 to 100,000 mPa · s at pH 8.

The solution viscosity of the water-soluble polymer (D) at the time of adjusting a 1% aqueous solution at pH 8 is preferably 0.1 to 20000 mPa · s, more preferably 1 to 10000 mPa · s, and particularly preferably 10 to 5000 mPa. -It is in the range of s. If the solution viscosity is too high, the binding property of the negative electrode active material layer to the current collector may be reduced, and if it is too low, the flexibility of the negative electrode active material layer may be reduced.

The weight average molecular weight of the water-soluble polymer (D) is usually smaller than the polymer (aromatic vinyl-conjugated diene copolymers (b1) and (b2)) serving as a binder, preferably 100 or more, more preferably 500. As described above, it is particularly preferably 1000 or more, preferably 500,000 or less, more preferably 250,000 or less, and particularly preferably 100,000 or less. The weight average molecular weight of the water-soluble polymer (D) is converted to polystyrene by gel permeation chromatography (GPC) using a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide. Can be obtained as the value of.

Furthermore, the glass transition temperature of the water-soluble polymer (D) is usually 0 ° C. or higher, preferably 5 ° C. or higher, and is usually 100 ° C. or lower, preferably 50 ° C. or lower. The glass transition temperature of the water-soluble polymer (D) can be adjusted by combining various monomers.

The blending amount of the water-soluble polymer (D) is preferably determined according to the blending amount of the water-soluble polymer (C), and the water-soluble polymer (C) and (D) with respect to 100 parts by mass of the total amount of the negative electrode active material. ) Is preferably 0.5 to 5 parts by mass, more preferably 0.7 to 3 parts by mass. By setting the total amount of the water-soluble polymers (C) and (D) within the above range, the binding property between the current collector and the negative electrode active material layer can be improved, and the cycle characteristics of the secondary battery can be improved. Moreover, since the internal resistance of the secondary battery can be reduced, output characteristics (particularly low temperature output characteristics) can be improved.

The weight ratio of the water-soluble polymer (D) and the water-soluble polymer (C) is “water-soluble polymer (C) / water-soluble polymer (D)”, preferably 99/1 to 70/30, more preferably 99 / 1 to 85/15, particularly preferably 99/1 to 90/10. By setting the weight ratio of the water-soluble polymer (D) and the water-soluble polymer (C) within the above range, the lithium ion conductivity on the surface of the negative electrode active material is increased, thereby improving the output of the secondary battery.

[Production of water-soluble polymer (D)]
As a method for producing the water-soluble polymer (D), a monomer mixture containing monomers constituting the water-soluble polymer (D) is polymerized in a dispersion medium to obtain a water-dispersed polymer, and the pH is 7 to 13. The method of alkalizing is mentioned. About the polymerization method, it is the same as that of the above-mentioned particulate binder.

The method for alkalinizing to pH 7 to 13 is not particularly limited, but alkaline earth solutions such as an aqueous alkali metal solution such as an aqueous lithium hydroxide solution, an aqueous sodium hydroxide solution, and an aqueous potassium hydroxide solution, an aqueous calcium hydroxide solution, and an aqueous magnesium hydroxide solution. Examples include a method of adding an aqueous metal solution or an aqueous alkali solution such as an aqueous ammonia solution.

In the dispersion medium used for the production of the particulate binder (B) and the water-soluble polymer (D), water and various organic solvents are particularly limited as long as the above-described components can be uniformly dispersed and can be stably dispersed. Can be used without From the viewpoint of simplification of the production process, it is preferable to produce the particulate binder (B) or the water-soluble polymer (D) directly without performing operations such as solvent substitution after the emulsion polymerization. It is desirable to use a reaction solvent for emulsion polymerization. During 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 working environment.

(E) Other components In addition to the above components, the other components of the negative electrode active material layer include other components such as a conductive agent, a reinforcing material, a leveling agent, an antioxidant, and an electrolyte additive having a function of inhibiting decomposition of the electrolyte. May be included. These are not particularly limited as long as they do not affect the battery reaction.

As the conductive agent, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor growth carbon fiber, and carbon nanotube can be used. By containing a conductive agent, electrical contact between the negative electrode active materials can be improved, and when used in a lithium ion secondary battery, the discharge rate characteristics can be improved. The content of the conductive agent is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the negative electrode active material.

As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible negative electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The content of the reinforcing material in the negative electrode active material layer is usually 0.01 to 20 parts by mass, preferably 1 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 reinforcing material is in the above range, a secondary battery exhibiting high capacity and high load characteristics can be obtained.

Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the leveling agent, the repelling that occurs during coating can be prevented and the smoothness of the negative electrode can be improved. The content of the leveling agent in the negative electrode active material layer is preferably 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 content is in the above range, the productivity, smoothness, and battery characteristics during the production of the negative electrode are excellent.

Examples of the antioxidant include a phenol compound, a hydroquinone compound, an organic phosphorus compound, a sulfur compound, a phenylenediamine compound, and a polymer type phenol compound. The polymer type phenol compound is a polymer having a phenol structure in the molecule, and a polymer type phenol compound having a weight average molecular weight of 200 to 1000, preferably 600 to 700 is preferably used. The content of the antioxidant in the negative electrode active material layer is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass. When the content ratio of the antioxidant is within the above range, the slurry composition used for producing the negative electrode is excellent in stability, battery capacity and cycle characteristics of the obtained secondary battery.

As the electrolytic solution additive, vinylene carbonate used in the electrolytic solution can be used. The content of the electrolyte solution additive in the negative electrode active material layer is preferably 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 electrolytic solution additive is in the above range, the high temperature cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the slurry composition can be controlled, and the leveling property of the negative electrode obtained thereby can be improved. The content of the nanoparticles in the negative electrode active material layer is preferably 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 is in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

In addition to the above, an isothiazoline compound or a chelate compound can be added as an additive.

Current collector The current collector used in the present invention is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but is preferably a metal material because of its heat resistance, such as iron, Examples include copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among these, copper is particularly preferable as the current collector used for the negative electrode for the secondary battery. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. The current collector may be used after roughening in advance in order to increase the adhesive strength with the negative electrode active material layer. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. In order to increase the adhesive strength and conductivity between the negative electrode active material layer and the current collector, an intermediate layer may be formed on the surface of the current collector, and among these, a conductive adhesive layer is preferably formed.

[Method for producing secondary battery negative electrode]
As a method for producing the negative electrode for a secondary battery of the present invention, any method may be used as long as the negative electrode active material layer is bound in layers on at least one surface of the current collector. For example, a negative electrode slurry composition for a secondary battery, which will be described later (hereinafter sometimes referred to as “negative electrode slurry composition”), is applied to a current collector, dried, and then 1 at 120 ° C. or higher as necessary. A negative electrode is formed by heat treatment for more than an hour. The method for applying the negative electrode slurry composition to the current collector is not particularly limited. Examples thereof include a doctor blade method, a zip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. 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 50 minutes, and the drying temperature is usually 40 to 180 ° C.

In producing the negative electrode for a secondary battery of the present invention, after forming a negative electrode active material layer comprising a negative electrode slurry composition on a current collector, the negative electrode active material layer is subjected to pressure treatment using a mold press or a roll press. It is preferable to have a step of lowering the porosity. The porosity of the negative electrode active material layer is preferably 5 to 30%, more preferably 7 to 20%. If the porosity is too high, charging efficiency and discharging efficiency may deteriorate. When the porosity is too low, it may be difficult to obtain a high volume capacity, and the negative electrode active material layer may be easily peeled off from the current collector and may be defective. Further, when a curable polymer is used for the particulate binder (B), it is preferably cured.

In the present invention, the density of the negative electrode active material layer of the negative electrode for a secondary battery is preferably 1.6 ~ 2.2g / cm ^3, more preferably 1.65 ~ 1.85g / cm ^3. When the density of the negative electrode active material layer is within the above range, a high-capacity secondary battery can be obtained.

The thickness of the negative electrode active material layer in the negative electrode of the lithium ion secondary battery of the present invention is usually 5 to 300 μm, preferably 30 to 250 μm. When the thickness of the negative electrode active material layer is in the above range, it is possible to obtain a secondary battery that exhibits high load characteristics and cycle characteristics.

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

(Negative electrode slurry composition for secondary battery)
The negative electrode slurry composition for a secondary battery contains the above-mentioned components (A) to (D), other components (E) added as necessary, and a dispersion medium.

The dispersion medium is not particularly limited as long as the above components can be uniformly dispersed or dissolved. In the present invention, the dispersion medium exemplified as the dispersion medium used for the production of the particulate binder (B) and the water-soluble polymer (D) can be used.

The solid content concentration of the negative electrode slurry composition is not particularly limited as long as it can be applied and immersed and has a fluid viscosity, but is generally about 10 to 80% by mass.

[Production of negative electrode slurry composition for secondary battery]
The negative electrode slurry composition for a secondary battery is obtained by mixing each of the above components (A) to (D), another component (E) added as necessary, and a dispersion medium. The amount of the dispersion medium used when preparing the negative electrode slurry composition is such that the solid content concentration of the negative electrode slurry composition is usually 40 to 80% by mass, preferably 60 to 80% by mass, more preferably 72 to 80% by mass. This is an amount that falls within the range. When the solid content concentration of the negative electrode slurry composition is within this range, each of the above components can be uniformly dispersed. Furthermore, since the thickness change before and behind drying of a negative electrode slurry composition can be made small, the residual stress which remains in a negative electrode inside can be reduced. Thereby, the suppression of the crack in a negative electrode and a binding property can be improved.

In the present invention, by using the above components, a negative electrode slurry composition in which the above components are highly dispersed can be obtained regardless of the mixing method and the mixing order. The mixing device is not particularly limited as long as it can uniformly mix the above-mentioned components. Bead mill, ball mill, roll mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, fill mix, etc. Among them, it is particularly preferable to use a ball mill, a roll mill, a pigment disperser, a crusher, or a planetary mixer because dispersion at a high concentration is possible.

The viscosity of the negative electrode slurry composition is preferably 10 to 100,000 mPa · s, more preferably 100 to 50,000 mPa · s, from the viewpoints of uniform coatability and slurry aging stability. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

[Secondary battery]
The secondary battery of this invention is a secondary battery provided with a positive electrode, a negative electrode, electrolyte solution, and a separator, Comprising: The said negative electrode is the above-mentioned negative electrode for secondary batteries.

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

Cathode Active Material Cathode active materials use active materials that can be doped and dedoped with lithium ions, and are broadly classified into those composed of inorganic compounds and those composed of organic compounds.

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

Transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O. ₅ , V ₆ O _{13 and the} like. Among them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle characteristics and capacity. The transition metal _sulfide, TiS _2, TiS _{_3,} amorphous _MoS 2, FeS, and the like. 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 ), Co—Ni—Mn lithium composite oxide, Ni—Mn—Al lithium Examples thereof include composite oxides and lithium composite oxides of Ni—Co—Al. Examples of the lithium-containing composite metal oxide having a spinel structure include lithium manganate (LiMn ₂ O ₄ ) and Li [Mn _3/2 M _1/2 ] O _{4 in} which a part of Mn is substituted with another transition metal (wherein M may be Cr, Fe, Co, Ni, Cu or the like. Li _X MPO ₄ (wherein, M is Mn, Fe, Co, Ni, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Li _X MPO ₄ as the lithium-containing composite metal oxide having an olivine structure) An olivine type lithium phosphate compound represented by at least one selected from Si, B, and Mo, 0 ≦ X ≦ 2) may be mentioned.

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

The average particle diameter of the positive electrode active material is usually 1 to 50 μm, preferably 2 to 30 μm. When the average particle diameter of the positive electrode active material is in the above range, the amount of the positive electrode binder in the positive electrode active material layer can be reduced, and the decrease in battery capacity can be suppressed. In order to form a positive electrode active material layer, a slurry containing a positive electrode active material and a positive electrode binder (hereinafter sometimes referred to as “positive electrode slurry composition”) is usually prepared. It becomes easy to prepare the composition at a viscosity appropriate for application, and a uniform positive electrode can be obtained.

The content ratio of the positive electrode active material in the positive electrode active material layer is preferably 90 to 99.9% by mass, more preferably 95 to 99% by mass. 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 high capacity.

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

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

As the current collector, the current collector used in the above-described negative electrode for a secondary battery can be used, and there is no particular limitation as long as the material has electrical conductivity and is electrochemically durable. Aluminum is particularly preferable for the positive electrode of the secondary battery.

The thickness of the positive electrode active material layer is usually 5 to 300 μm, preferably 10 to 250 μm. When the thickness of the positive electrode active material layer is in the above range, both load characteristics and energy density are high.

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

(separator)
The separator is a porous substrate having pores, and usable separators include (a) a porous separator having pores, and (b) a porous separator in which a polymer coat layer is formed on one or both sides. Or (c) a porous separator in which a porous resin coat layer containing an inorganic ceramic powder is formed. Non-limiting examples of these include solids such as polypropylene, polyethylene, polyolefin, or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride hexafluoropropylene copolymers. There are polymer films for polymer electrolytes or gel polymer electrolytes, separators coated with gelled polymer coating layers, or separators coated with porous membrane layers made of inorganic fillers and dispersants for inorganic fillers. .

(Electrolyte)
The electrolytic solution used in the present invention is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used alone or in admixture 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, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the battery are degraded.

The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane; tetrahydrofuran; sulfolane and dimethyl sulfoxide Sulfur-containing compounds are used. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferable because high ion conductivity is easily obtained and the use temperature range is wide. These can be used alone or in admixture of two or more. Moreover, it is also possible to use an electrolyte containing an additive. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution, and an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N.

[Method for producing secondary battery]
The manufacturing method of the secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and positive electrode are overlapped via a separator, and this is wound or folded according to the shape of the battery and placed in the battery container, and the electrolytic solution is injected into the battery container and sealed. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto. In addition, unless otherwise indicated, the part and% in a present Example are a mass reference | standard. In the examples and comparative examples, various physical properties were evaluated as follows.

<Glass transition temperature>
The glass transition temperature (Tg) of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) was measured using a differential scanning calorimeter (DSC6220SII manufactured by Nanotechnology). It measured based on JISK7121; 1987. In the measurement using a differential scanning calorimeter, when two or more peaks appeared, the peak on the high temperature side was defined as Tg.

<Tetrahydrofuran insoluble matter>
Prepare an aqueous dispersion containing the copolymer, put the aqueous dispersion in an aluminum dish, and dry it in an environment of 50% humidity and 23 to 25 ° C. for 48 hours to form a film having a thickness of 3 ± 0.3 mm. A film was formed. The film formed was cut into 1 mm square, and 1 g was precisely weighed. The mass of the film piece obtained by this cutting is defined as W0. This film piece was immersed in 100 g of tetrahydrofuran (THF) at 25 ° C. for 24 hours. Then, the film piece pulled up from THF was vacuum-dried at 105 degreeC for 3 hours, and the mass W1 of insoluble matter was measured. And the ratio (%) of tetrahydrofuran insoluble content was computed according to the following formula.
Tetrahydrofuran insoluble matter (%) = W1 / W0 × 100

<High temperature cycle characteristics>
The lithium-ion secondary battery of the laminate type cell manufactured in Examples and Comparative Examples was allowed to stand for 24 hours in an environment at 25 ° C., and then charged at 4.2 V and 0.1 C in an environment at 25 ° C. The charge / discharge operation was performed at a discharge of 3.0 V and 0.1 C, and the initial capacity C ₀ was measured. Furthermore, charge / discharge was repeated under an environment of 45 ° C., and the capacity C ₂ after 100 cycles was measured.
The high-temperature cycle characteristics were evaluated based on the following criteria by calculating a capacity change rate ΔC _C represented by ΔC _C = C ₂ / C ₀ × 100 (%). It shows that it is excellent in high temperature cycling characteristics, so that the value of this capacity change rate (DELTA) _CC is high.
A: 93% or more B: 88% or more and less than 93% C: 83% or more and less than 88% D: Less than 83%

<Plate swelling characteristics>
After the evaluation of the “high temperature cycle characteristic”, the cell of the lithium ion secondary battery was disassembled, and the thickness d ₁ of the negative electrode plate was measured. The negative electrode plate swell ratio (d ₁ -d ₀ ) / d ₀ was calculated with the thickness of the negative electrode plate before production of the cell of the lithium ion secondary battery as d ₀ , and evaluated according to the following criteria. It shows that it is excellent in the electrode plate swelling characteristic, so that this value is low. In the case where only graphite was used as the negative electrode active material (Example 12), the evaluation was made according to the criteria in parentheses.
A: Less than 30% (less than 20%)
B: 30% or more and less than 38% (20% or more and less than 29%)
C: 38% or more and less than 45% (29% or more and less than 36%)
D: 45% or more (36% or more)

<Low temperature output characteristics>
The lithium ion secondary batteries of the laminate type cells produced in the examples and comparative examples were allowed to stand for 24 hours in an environment at 25 ° C., and then at a charge rate of 4.2 V and 1 C in an environment at 25 ° C. The charging operation was performed. Thereafter, a discharge operation was performed at a discharge rate of 1 C under an environment of −10 ° C., and a voltage V ₁₀ 10 seconds after the start of discharge was measured. The low temperature output characteristic was evaluated based on the following criteria by calculating a voltage change ΔV represented by ΔV = 4.2 V−V ₁₀ . It shows that it is excellent in low temperature output characteristics, so that the value of this voltage change (DELTA) V is small.
A: Less than 1.1V B: 1.1V or more and less than 1.3V C: 1.3V or more and less than 1.6V D: 1.6V or more

<Initial capacity>
A negative electrode is cut out into a disk shape with a diameter of 15 mm, and a separator made of a polypropylene porous film having a disk shape with a diameter of 18 mm and a thickness of 25 μm, a metal lithium counter electrode, and an expanded metal are sequentially laminated on the negative electrode active material layer side. It was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm) provided with a packing made of steel.
The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A half cell of 20 mm and a thickness of about 2 mm was produced.
As an electrolytic solution, LiPF ₆ was added at 1 mol / liter to a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at EC: EMC = 3: 7 (volume ratio at 20 ° C.). A solution dissolved at a concentration of was used.
Using this coin-type battery, constant current-constant voltage charging was performed at 0.05 C to confirm the initial capacity.
The case where the initial capacity was 420 mAh / g or more was evaluated as “good”, and the case where it was less than 420 mAh / g was evaluated as “bad”.

(Example 1)
(1) Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 46 parts of 1,3-butadiene, 4 parts of itaconic acid, 50 parts of styrene, t-dodecyl mercaptan (TDM) 0. 3 parts, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator are stirred sufficiently, and then heated to 50 ° C. for polymerization. Started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −10 ° C.

(2) Similarly to the production of the aromatic vinyl-conjugated diene copolymer (b2), in a 5 MPa pressure vessel equipped with a stirrer, 21 parts of 1,3-butadiene, 4 parts of itaconic acid, 75 parts of styrene, t-dodecyl mercaptan (TDM) ) 0.25 parts, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were stirred sufficiently and heated to 50 ° C. The polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 45 ° C.

(3) An aqueous dispersion containing the aromatic vinyl-conjugated diene copolymer (b1) obtained in the production step (1) of the particulate binder (B) and the aromatic vinyl obtained in the step (2) The aqueous dispersion containing the conjugated diene copolymer (b2) is solid-corresponding to the aromatic vinyl-conjugated diene copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b2) = 50/50. To obtain an aqueous dispersion of the particulate binder (B).

(4) Production of water-soluble polymer (D) In a 5 MPa pressure vessel equipped with a stirrer, 30 parts of methacrylic acid (unsaturated carboxylic acid monomer), 0.8 part of ethylene dimethacrylate (crosslinkable monomer), 2, 2 , 2-trifluoroethyl methacrylate (fluorine-containing (meth) acrylate monomer) 7.5 parts, butyl acrylate ((meth) acrylate monomer) 60.5 parts, polyoxyalkylene alkenyl ether ammonium sulfate ( Reactive surfactant monomer, manufactured by Kao, trade name “Latemul PD-104” 1.2 parts, 0.6 parts t-dodecyl mercaptan, 150 parts ion-exchanged water, and potassium persulfate (polymerization initiator) After adding 0.5 part and stirring sufficiently, it heated at 60 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a water-dispersed polymer. 10% aqueous ammonia was added to the mixture containing the water-dispersed polymer to adjust the pH to 8, and an aqueous solution containing the desired water-soluble polymer (D) was obtained.

(5) Production of negative electrode slurry composition In a planetary mixer with a disper, 90 parts of artificial graphite (specific surface area: 4 m ² / g, volume average particle size: 24.5 μm) as a negative electrode active material (A), and SiO x ( x = 1.1, volume average particle size: 10 μm) 10 parts, 1% aqueous solution of carboxymethylcellulose (“BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as the hydroxyl group-containing water-soluble polymer (C) Was added in an amount of 1 part, and an aqueous solution containing the water-soluble polymer (D) synthesized in the above step (4) was added in an amount of 0.03 part in terms of solid content.
These mixtures were adjusted to a solids concentration of 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting the solid content concentration to 52% with ion-exchanged water, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.

Next, 1 part of the aqueous dispersion of the particulate binder (B) obtained in the above step (3) and ion-exchanged water are added to the mixed liquid, and the final solid content concentration is 42%. And mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition.

(6) Manufacture of negative electrode The negative electrode slurry composition obtained in the above step (5) is dried with a comma coater on a copper foil having a thickness of 20 μm that is a current collector. And then dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material. This negative electrode original fabric was rolled with a roll press to obtain a negative electrode having a negative electrode active material layer thickness of 80 μm.

(7) Production of Positive Electrode As a positive electrode binder, a 40% aqueous 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 acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 78% by mass of 2-ethylhexyl acrylate, 20% by mass of acrylonitrile, and 2% by mass of methacrylic acid.
100 parts of LiFePO ₄ having a volume average particle size of 0.5 μm and having an olivine crystal structure as a positive electrode active material and a 1% aqueous solution of carboxymethyl cellulose (“BSH-12” manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a dispersant 1 part at a time and a 40% aqueous dispersion of the above acrylate polymer as a binder are mixed with 5 parts at a solid content, and ion-exchanged water is added to this so that the total solid content concentration is 40%. The positive electrode slurry composition was prepared by mixing with a planetary mixer.
The positive electrode slurry composition was applied onto a current collector of 20 μm thick aluminum with a comma coater so that the film thickness after drying was about 200 μm and dried. This drying was performed by conveying aluminum in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the positive electrode.

(8) Preparation of Separator A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by a dry method, porosity 55%) was cut into a square of 5 cm × 5 cm.

(9) An aluminum packaging exterior was prepared as the exterior of the laminated cell manufacturing battery of the lithium ion secondary battery . The positive electrode obtained in the step (7) was cut into a 4 cm × 4 cm square and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. On the surface of the positive electrode active material layer of the positive electrode, the separator prepared in the above step (8) was disposed. Furthermore, on the separator, the negative electrode obtained in the above step (6) was cut into a square of 4.2 cm × 4.2 cm, and arranged so that the surface on the negative electrode active material layer side faced the separator. Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. As an electrolytic solution, 1 mol / liter of LiPF ₆ was mixed in a mixed solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at EC: EMC = 3: 7 (volume ratio at 20 ° C.). A solution dissolved at a concentration was used.
Each evaluation other than the initial capacity confirmation was performed on the obtained laminated lithium ion secondary battery. The results are shown in Table 1.

(10) Manufacture of coin cell of lithium ion secondary battery The negative electrode obtained in the above step (6) is cut into a disk shape with a diameter of 16 mm to be used as a positive electrode. The same separator as used in step (8) above was cut into a disk shape having a diameter of 18 mm and a thickness of 25 μm, and lithium metal used as the negative electrode and expanded metal were laminated in this order on this positive electrode, and a polypropylene packing was installed. Was stored in a stainless steel coin-type outer container (diameter 20 mm, height 1.8 mm, stainless steel thickness 0.25 mm). The electrolyte is poured into the container so that no air remains, and the outer container is fixed with a 0.2 mm thick stainless steel cap through a polypropylene packing, and the battery can is sealed, and the diameter is A lithium ion coin battery (half cell) having a thickness of 20 mm and a thickness of about 2 mm was produced. As the electrolyte, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) EC: EMC = 3 : 7 to LiPF ₆ 1 mixed in a mixed solvent comprising at (20 ° C. volume ratio in) mol / A solution dissolved at a concentration of 1 liter was used.
The initial capacity of the obtained coin-type lithium ion secondary battery was confirmed. The results are shown in Table 1.

(Example 2)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) were used. Manufactured. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 47.5 parts of 1,3-butadiene, 0.3 part of itaconic acid, 52.2 parts of styrene, t-dodecyl mercaptan (TDM) ) 0.3 parts, 4 parts of sodium dodecylbenzenesulfonate as emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were stirred sufficiently, and then heated to 50 ° C. The polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −10 ° C.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 22.5 parts of 1,3-butadiene, 0.3 part of itaconic acid, 77.2 parts of styrene, t-dodecyl mercaptan (TDM) ) 0.25 parts, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were stirred sufficiently and heated to 50 ° C. The polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 45 ° C.

(Example 3)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) were used. Manufactured. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 44.5 parts of 1,3-butadiene, 5.5 parts of itaconic acid, 50 parts of styrene, t-dodecyl mercaptan (TDM) 0 .3 parts, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were stirred sufficiently and then heated to 50 ° C. for polymerization. Started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −10 ° C.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 21.5 parts of 1,3-butadiene, 5.5 parts of itaconic acid, 73 parts of styrene, t-dodecyl mercaptan (TDM) 0 .25 parts, sodium dodecylbenzenesulfonate 4 parts as an emulsifier, ion exchanged water 150 parts, and potassium persulfate 0.5 part as a polymerization initiator, stirred sufficiently, heated to 50 ° C. and polymerized Started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 45 ° C.

Example 4
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) were used. Manufactured. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 50 parts of 1,3-butadiene, 4 parts of itaconic acid, 46 parts of styrene, 0.3 part of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −18 ° C.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 17 parts of 1,3-butadiene, 4 parts of itaconic acid, 79 parts of styrene, 0.25 parts of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 55 ° C.

(Example 5)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) were used. Manufactured. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 32 parts of 1,3-butadiene, 4 parts of itaconic acid, 64 parts of styrene, 0.3 part of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was 18 ° C.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 26 parts of 1,3-butadiene, 4 parts of itaconic acid, 70 parts of styrene, 0.25 parts of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 33 ° C.

(Example 6)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) was used. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 46 parts of 1,3-butadiene, 4 parts of itaconic acid, 50 parts of styrene, 0.48 parts of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −10 ° C.

(Example 7)
In the production of the particulate binder (B) in the step (3), an aqueous dispersion containing the aromatic vinyl-conjugated diene copolymer (b1) and an aqueous dispersion containing the aromatic vinyl-conjugated diene copolymer (b2) The liquid was mixed so that the aromatic vinyl-conjugated diene copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b2) = 80/20 corresponding to the solid content, and the particulate binder (B The lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the aqueous dispersion was obtained. Each evaluation result is shown in Table 1.

(Example 8)
In the production of the particulate binder (B) in the step (3), an aqueous dispersion containing the aromatic vinyl-conjugated diene copolymer (b1) and an aqueous dispersion containing the aromatic vinyl-conjugated diene copolymer (b2) The liquid was mixed so that the aromatic vinyl-conjugated diene copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b2) = 30/70 corresponding to the solid content, and the particulate binder (B The lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the aqueous dispersion was obtained. Each evaluation result is shown in Table 1.

Example 9
In the production of the negative electrode slurry composition in the step (5), the same operation as in Example 1 was performed except that the amount of the aqueous dispersion of the particulate binder (B) was 2 parts corresponding to the solid content, A lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Example 10)
In the production of the negative electrode slurry composition in the step (5), the addition amount of the aqueous solution containing the water-soluble polymer (D) was the same as in Example 1 except that the amount corresponding to the solid content was 0.14 parts. Then, a lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Example 11)
Except for using 90 parts of artificial graphite (specific surface area: 4 m ² / g, volume average particle diameter: 24.5 μm) and 10 parts of SiOC (volume average particle diameter: 10 μm) as the negative electrode active material (A), The same operation as in Example 1 was performed to manufacture a lithium ion secondary battery. Each evaluation result is shown in Table 1.

Example 12
The same operation as in Example 1 was performed except that 100 parts of artificial graphite (specific surface area: 4 m ² / g, volume average particle diameter: 24.5 μm) was used as the negative electrode active material (A). A secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Example 13)
In the production of the water-soluble polymer (D) in step (4), except that 7.5 parts of 2,2,2-trifluoroethyl methacrylate is 1.0 part and 60.5 parts of butyl acrylate is 67.0 parts Performed the same operation as Example 1, and manufactured the lithium ion secondary battery. Each evaluation result is shown in Table 1.

(Example 14)
In the production of the water-soluble polymer (D) in step (4), except that 7.5 parts of 2,2,2-trifluoroethyl methacrylate is 15.0 parts and 60.5 parts of butyl acrylate is 53.0 parts Performed the same operation as Example 1, and manufactured the lithium ion secondary battery. Each evaluation result is shown in Table 1.

(Example 15)
In the production of the aromatic vinyl-conjugated diene copolymer (b2) in the step (2), the same operation as in Example 1 was conducted except that 0.25 part of t-dodecyl mercaptan (TDM) was changed to 0.38 part. The lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Example 16)
In the production of the aromatic vinyl-conjugated diene copolymer (b2) in the step (2), the same operation as in Example 1 was carried out except that 0.25 part of t-dodecyl mercaptan (TDM) was changed to 0.19 part. The lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Comparative Example 1)
A lithium ion secondary battery was prepared in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) and aromatic vinyl-conjugated diene copolymer (b2) were used. Manufactured. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 48 parts of 1,3-butadiene, 52 parts of styrene, 0.3 part of t-dodecyl mercaptan (TDM), dodecylbenzenesulfone as an emulsifier 4 parts of sodium acid, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was −10 ° C.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 23 parts of 1,3-butadiene, 77 parts of styrene, 0.25 part of t-dodecyl mercaptan (TDM), dodecylbenzenesulfone as an emulsifier 4 parts of sodium acid, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 45 ° C.

(Comparative Example 2)
The same operation as in Example 1 except that the particulate vinyl binder (B) was produced only with the aromatic vinyl-conjugated diene copolymer (b1) without using the aromatic vinyl-conjugated diene copolymer (b2). The lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Comparative Example 3)
The same operation as in Example 1 except that the particulate vinyl binder (B) was produced only with the aromatic vinyl-conjugated diene copolymer (b2) without using the aromatic vinyl-conjugated diene copolymer (b1). The lithium ion secondary battery was manufactured. Each evaluation result is shown in Table 1.

(Comparative Example 4)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b1) was used. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b1) In a 5 MPa pressure vessel equipped with a stirrer, 29 parts of 1,3-butadiene, 4 parts of itaconic acid, 67 parts of styrene, 0.3 part of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b1). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b1) was 23 ° C.

(Comparative Example 5)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the following aromatic vinyl-conjugated diene copolymer (b2) was used. Each evaluation result is shown in Table 1.

Production of aromatic vinyl-conjugated diene copolymer (b2) In a 5 MPa pressure vessel equipped with a stirrer, 27 parts of 1,3-butadiene, 4 parts of itaconic acid, 69 parts of styrene, 0.3 part of t-dodecyl mercaptan (TDM), 4 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water as an emulsifier and 0.5 part of potassium persulfate as a polymerization initiator were added and stirred sufficiently, and then the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a polymer. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust to pH 8, and then unreacted monomers were removed by heating under reduced pressure. Thereafter, the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired aromatic vinyl-conjugated diene copolymer (b2). The glass transition temperature of the aromatic vinyl-conjugated diene copolymer (b2) was 27 ° C.

(Comparative Example 6)
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the water-soluble polymer (D) was not used. Each evaluation result is shown in Table 1.

As shown in the results of Table 1, the lithium ion secondary batteries using the secondary battery electrodes of Examples 1 to 16 are excellent in the balance of each evaluation as compared with Comparative Examples 1 to 6.

Claims

A current collector, and a negative electrode active material layer laminated on the current collector,
The negative electrode active material layer comprises a negative electrode active material (A), a particulate binder (B), a hydroxyl group-containing water-soluble polymer (C), and a fluorine-containing (meth) acrylate monomer unit of 0.5 to Including a water-soluble polymer (D) containing 20% by mass,
The particulate binder (B) is
An aromatic vinyl-conjugated diene copolymer (b1) having a glass transition temperature of −30 to 20 ° C. and comprising an unsaturated carboxylic acid monomer unit;
An aromatic vinyl-conjugated diene copolymer (b2) having a glass transition temperature of 30 to 80 ° C. and comprising an unsaturated carboxylic acid monomer unit,
Negative electrode for secondary battery.
The negative electrode for a secondary battery according to claim 1, wherein the negative electrode active material (A) includes a carbon-based active material (a1) and an alloy-based active material (a2).
The negative electrode for a secondary battery according to claim 2, comprising 1 to 50 parts by mass of the alloy-based active material (a2) with respect to 100 parts by mass of the carbon-based active material (a1).
The negative electrode for a secondary battery according to claim 2 or 3, wherein the alloy-based active material (a2) is Si, SiO x (x = 0.01 or more and less than 2), or SiOC.
The aromatic vinyl-conjugated diene copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b1) / aromatic vinyl-conjugated diene copolymer (b2) / aromatic vinyl-conjugated diene copolymer (b2) / aromatic The negative electrode for a secondary battery according to any one of claims 1 to 4, wherein the group vinyl-conjugated diene copolymer (b2) = 80/20 to 30/70.
The tetrahydrofuran-insoluble content of each of the aromatic vinyl-conjugated diene copolymer (b1) and the aromatic vinyl-conjugated diene copolymer (b2) is 70 to 98%. Negative electrode for secondary battery.
A secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator,
A secondary battery, wherein the negative electrode is a negative electrode for a secondary battery according to any one of claims 1 to 6.