JP6152846B2 - Slurry composition for secondary battery negative electrode - Google Patents

Description

  The present invention relates to a slurry composition for a negative electrode of a secondary battery, more specifically, excellent storage stability, migration during drying is effectively prevented, and between the negative electrode active material layer and a current collector. The present invention relates to a slurry composition for a secondary battery negative electrode that can provide a negative electrode for a secondary battery excellent in adhesion and high-temperature cycle characteristics. The present invention also provides a secondary battery negative electrode and secondary battery using such a secondary battery negative electrode slurry composition, and a binder composition used for producing a secondary battery negative electrode slurry composition. Also related.

  A negative electrode constituting a lithium secondary battery such as a lithium ion secondary battery is usually obtained by applying a slurry containing a binder, a negative electrode active material, and a solvent on a current collector such as a copper foil, It is manufactured by removing.

  As a slurry for constituting such a negative electrode for a lithium secondary battery, a fluorine resin such as polyvinylidene fluoride (PVDF) or an organic solvent such as N-methyl-pyrrolidone (NMP) was used as a binder. An organic slurry is generally used.

  However, on the other hand, in the method using an organic slurry, there are a problem of cost required for recycling the organic solvent and a problem of ensuring safety by using the organic solvent. Therefore, in order to solve these problems In addition, an aqueous binder used for an aqueous slurry using water as a medium has been studied.

  For example, Patent Document 1 includes an electrode active material, at least one polymer aqueous dispersion selected from the group consisting of a styrene-butadiene copolymer latex, and an acrylic emulsion, and a compound having a cloud point of 70 ° C. or lower. A slurry composition for a secondary battery electrode is disclosed.

  Patent Document 2 discloses an electrode active material, a vinyl polymer-based thermoreversible thickener that reversibly changes hydrophilicity and hydrophobicity at a certain transition temperature, a binder composed of a water-dispersible resin, and Disclosed is a slurry composition for secondary battery electrodes containing a binder comprising a metal salt of Group I to VII of the periodic table.

  However, the slurry composition for a secondary battery electrode disclosed in Patent Document 1 is poor in storage stability because it thickens with time due to the influence of a compound having a cloud point of 70 ° C. or lower. When an electrode is formed using the composition, there has been a problem that characteristics of the obtained electrode vary. Further, in Patent Document 2, although the purpose is to suppress the migration of the binder during drying, the secondary battery electrode slurry composition disclosed in Patent Document 2 has low thermal response sensitivity, For this reason, the effect of suppressing migration at the time of drying is not sufficient, so that the obtained electrode has insufficient adhesion between the electrode active material layer and the current collector.

JP 2006-260782 A Japanese Patent No. 4280802

  The present invention provides a negative electrode for a secondary battery that has excellent storage stability, migration during drying is effectively prevented, and excellent adhesion between the negative electrode active material layer and the current collector and high-temperature cycle characteristics. It aims at providing the slurry composition for secondary battery negative electrodes which can provide. The present invention also provides a secondary battery negative electrode and secondary battery using such a secondary battery negative electrode slurry composition, and a binder composition used for producing a secondary battery negative electrode slurry composition. Also related.

  As a binder to be contained in the slurry composition for secondary battery negative electrode, the present inventors have a surface acid amount of 0.10 to 0.60 mmol / g, a conjugated diene monomer unit, and a thermoreversible increase. A binder comprising a particulate conjugated diene copolymer containing 0.5 to 40% by weight of a monomer unit for imparting viscosity and 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer unit. By using it, it discovered that the said objective could be achieved and came to complete this invention.

  That is, according to the present invention, a secondary battery negative electrode slurry composition comprising a negative electrode active material, a binder, and a water-soluble polymer, wherein the binder has a surface acid amount of 0.10 to 0. .60 mmol / g, conjugated diene monomer unit, 0.5 to 40% by weight of monomer unit imparting thermoreversible thickening and 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer unit A slurry composition for a negative electrode of a secondary battery, wherein the slurry composition is a particulate conjugated diene copolymer.

In the slurry composition for a secondary battery negative electrode of the present invention, the glass transition temperature of the conjugated diene copolymer is preferably -40 to + 50 ° C.
In the slurry composition for a secondary battery negative electrode of the present invention, the water-soluble polymer preferably contains at least 20 to 50% by weight of an ethylenically unsaturated carboxylic acid monomer unit.
In the slurry composition for secondary battery negative electrode of the present invention, a first monomer mixture containing at least a conjugated diene monomer and an ethylenically unsaturated carboxylic acid monomer is polymerized to obtain the first monomer mixture. Obtained by adding a second monomer mixture containing at least a monomer that imparts thermoreversible thickening to the polymerization system and polymerizing the polymer at a predetermined polymerization conversion rate. It is preferable that

Alternatively, according to the present invention, on the current collector, the step of applying the slurry composition for secondary battery negative electrode according to any one of the above, and the step of drying the slurry composition for secondary battery negative electrode The manufacturing method of the negative electrode for secondary batteries containing is provided.
Further, according to the present invention, a negative electrode for a secondary battery comprising a current collector and a negative electrode active material layer, wherein the negative electrode active material layer comprises a negative electrode active material, a binder, and a water-soluble polymer. The binder has a surface acid amount of 0.10 to 0.60 mmol / g, a conjugated diene monomer unit, and a monomer unit that imparts thermoreversible thickening 0.5 to 40 wt. % And a particulate conjugated diene copolymer containing 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer unit.
Moreover, according to this invention, the secondary battery provided with the negative electrode for secondary batteries as described above, a positive electrode, a separator, and electrolyte solution is provided.
Furthermore, according to the present invention, a binder composition for a secondary battery negative electrode comprising a binder and a water-soluble polymer, wherein the binder has a surface acid amount of 0.10 to 0.60 mmol / g. A conjugated diene monomer unit, 0.5 to 40% by weight of a monomer unit that imparts thermoreversible thickening, and 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer unit There is provided a binder composition for a negative electrode of a secondary battery, which is a particulate conjugated diene copolymer.

  According to the present invention, the secondary battery has excellent storage stability, migration during drying is effectively prevented, and excellent adhesion between the negative electrode active material layer and the current collector and high-temperature cycle characteristics. The slurry composition for secondary battery negative electrodes which can provide the negative electrode for batteries can be provided. Further, according to the present invention, a secondary battery negative electrode and a secondary battery using such a secondary battery negative electrode slurry composition, and a binder used for producing a secondary battery negative electrode slurry composition Compositions can also be provided.

FIG. 1 is a diagram showing an example of a hydrochloric acid amount-electric conductivity curve obtained when measuring the surface acid amount of a conjugated diene copolymer in the present invention.

  The slurry composition for a secondary battery negative electrode of the present invention includes a negative electrode active material, a binder, and a water-soluble polymer, and the binder has a surface acid amount of 0.10 to 0.60 mmol / g. Particles containing a conjugated diene monomer unit, 0.5 to 40% by weight of a monomer unit that imparts thermoreversible thickening, and 1 to 10% by weight of an ethylenically unsaturated carboxylic acid monomer unit It is characterized by being a conjugated diene copolymer.

(Negative electrode active material)
Although it does not specifically limit as a negative electrode active material used by this invention, A various active material can be used, For example, the slurry composition for secondary battery negative electrodes of this invention is formed in the negative electrode for lithium secondary batteries. Therefore, a material capable of occluding and releasing lithium is usually used as the negative electrode active material. Examples of the material that can occlude and release lithium include a metal-based active material, a carbon-based active material, and an active material that combines these materials.

  Examples of the metal active material include lithium metal, a single metal forming a lithium alloy and an alloy thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof. Examples of the single metal forming the lithium alloy include single metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, and Ti. Can be mentioned. Moreover, as a single metal alloy which forms a lithium alloy, the compound containing the said single metal is mentioned, for example. Among these, silicon (Si), tin (Sn), lead (Pb), and titanium (Ti) are preferable, and silicon, tin, and titanium are more preferable.

The metallic active material used as the negative electrode active material may further contain a nonmetallic element. For example, SiC, SiO _x C _y (0 <x ≦ 3, 0 <y ≦ 5), Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO and the like. Among them, the insertion of lithium at low potential and desorption capable _SiO x, SiC and _SiO x _{C y} is more preferred.

  Lithium metal, elemental metal forming lithium alloy and oxides, sulfides, nitrides, silicides, carbides and phosphides of the alloys include oxides, sulfides, nitrides and silicides of lithium-insertable elements Products, carbides, phosphides and the like. Of these, oxides are particularly preferable. For example, a lithium-containing metal composite oxide containing an oxide such as tin oxide, manganese oxide, titanium oxide, niobium oxide, and vanadium oxide and a metal element selected from the group consisting of Si, Sn, Pb, and Ti atoms is used. .

The lithium-containing metal composite oxide further includes 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, and M represents an element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.), Li _x Mn _y M _Examples thereof include a lithium manganese composite oxide represented by _z O ₄ (x, y, z and M are the same as defined in a lithium titanium composite oxide). Among these, Li _4/3 Ti _5/3 O ₄ , Li ₁ Ti ₂ O ₄ , Li _4/5 Ti _11/5 O ₄ , and Li _4/3 Mn _5/3 O ₄ are preferable.

  The carbon-based active material refers to an active material having carbon as a main skeleton into which lithium can be inserted, and examples thereof include a carbonaceous material and a graphite material.

  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 or coal. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fibers, pyrolytic vapor grown carbon fibers, and the like. Examples of the non-graphitizable carbon include a phenol resin fired body, polyacrylonitrile-based carbon fiber, pseudo-isotropic carbon, furfuryl alcohol resin fired body (PFA), and hard carbon.

  Examples of the graphite material include natural graphite and artificial graphite. As artificial graphite, for example, artificial graphite mainly heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated MCMB at 2000 ° C. or higher, graphitized mesophase pitch-based carbon fiber heat-treated mesophase pitch-based carbon fiber at 2000 ° C. or higher, etc. Is mentioned.

  Among the carbon-based active materials, a graphite material is preferable. By using the graphite material, the resistance of the secondary battery can be reduced, and a secondary battery with excellent input / output can be manufactured.

A negative electrode active material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.
When combining two or more types, an active material obtained by combining a metal-based active material and a carbon-based active material can be given. In this case, a combination of an active material containing silicon as a metal-based active material and a graphite material as a carbon-based active material can be mentioned as a preferred embodiment. In this case, the ratio between the metal-based active material and the graphite material can be a metal-based active material / graphite material = 5/95 to 50/50 weight ratio.

  The negative electrode active material is preferably sized in the form of particles. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding. When the negative electrode active material is a particle, the volume average particle diameter is usually 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 20 μm.

(Binder)
The binder used in the present invention is a component for binding the negative electrode active materials to each other or binding the negative electrode active material to the surface of the current collector. In the present invention, the binder has a surface acid amount of 0.10 to 0.60 mmol / g, a conjugated diene monomer unit, and a monomer unit that imparts thermoreversible thickening to 0.5 to A conjugated diene copolymer containing 40% by weight and 1 to 10% by weight of ethylenically unsaturated carboxylic acid monomer units is used.
Here, the surface acid amount of the conjugated diene copolymer refers to a contact with a negative electrode active material or a current collector as a binder when the conjugated diene copolymer exhibits the above binding action as a binder. It means the amount of acid on the surface that can. Specifically, when the binder is present in the form of particles in the slurry composition for secondary battery negative electrode, the acid present on the particle surface of the conjugated diene copolymer per 1 g of the conjugated diene copolymer. Specifically, it means an acid amount calculated by conductivity titration described later.

  The conjugated diene copolymer used as a binder in the present invention usually has a particulate shape, and its surface acid amount is 0.10 to 0.60 mmol / g, preferably 0.22. It is -0.57 mmol / g, More preferably, it is 0.25-0.55 mmol / g. In the present invention, by controlling the surface acid amount of the conjugated diene copolymer used as a binder in such a range, the storage stability of the secondary battery negative electrode slurry composition can be improved, Thereby, when forming the negative electrode for secondary batteries, applicability | paintability can be improved. As a result, the obtained negative electrode for a secondary battery can be made to have excellent adhesion between the negative electrode active material layer and the current collector. Cycle characteristics can be improved.

  On the other hand, when the surface acid amount is too small, the storage stability of the slurry composition for secondary battery negative electrode is deteriorated, and the coating property is deteriorated. The adhesion between the material layer and the current collector is poor, and as a result, the high-temperature cycle characteristics in the case of a secondary battery are deteriorated. In addition, if the surface acid amount is too large, coagulum (fine aggregate) is generated in the slurry composition for the negative electrode of the secondary battery, and when the negative electrode for the secondary battery is formed, the negative electrode active material layer and the current collector are collected. As a result, the high-temperature cycle characteristics in the case of a secondary battery are deteriorated. In the present invention, as a method for setting the surface acid amount of the conjugated diene copolymer used as the binder in the above range, for example, the kind and amount of the monomer used for producing the conjugated diene copolymer are adjusted. Examples thereof include a method and a method for adjusting polymerization conditions.

The surface acid amount of the conjugated diene copolymer can be measured, for example, as follows when the conjugated diene copolymer is in the form of latex particles using water as a dispersion medium.
That is, the aqueous dispersion of the conjugated diene copolymer was adjusted so that the solid content was 2% by weight, and then the electrical conductivity of the aqueous dispersion of the conjugated diene copolymer was 2.5 to 3.0 mS. As such, 0.1N sodium hydroxide is added, the electrical conductivity after 6 minutes is measured, and the obtained measured value is taken as the electrical conductivity at the start of measurement. Then, 0.5 ml of 0.1 N hydrochloric acid was added to the aqueous dispersion of this conjugated diene copolymer, and after 30 seconds, the electrical conductivity was measured, and 0.5 ml of 0.1 N hydrochloric acid was added again. The operation of measuring the electrical conductivity after 30 seconds is repeated at intervals of 30 seconds until the electrical conductivity becomes equal to or higher than the value at the start of measurement.
When the obtained electrical conductivity data is plotted on a graph with the vertical axis representing electrical conductivity (mS) and the horizontal axis representing the total amount of added hydrochloric acid (mmol), three inflections are obtained as shown in FIG. A hydrochloric acid quantity-electric conductivity curve with points is obtained. Three inflection point X coordinate and X-coordinate at the hydrochloric completion of the addition of, and in turn each _{P 1,} P 2, _{P 3} and _{P 4} from the smaller value, X coordinate from zero to _{P 1,} from _{P 1} to P _2, the data in the four sections from _{P 2} from to _{P 3} and _{P 3} to _{P 4,} respectively, by the least squares method obtaining an approximate straight line _{L 1,} L 2, _{L 3} and _{L 4.} The X coordinate of the intersection of L ₁ and L ₂ is A ₁ (mmol), the X coordinate of the intersection of L ₂ and L ₃ is A ₂ (mmol), and the X coordinate of the intersection of L ₃ and L ₄ is A ₃ (Mmol). And the surface acid amount per 1g of conjugated diene copolymers can be calculated | required from a following formula.
Surface acid amount per 1 g of conjugated diene copolymer = A ₂ −A ₁

In addition, the conjugated diene copolymer used as a binder in the present invention includes a conjugated diene monomer unit, 0.5 to 40% by weight of a monomer unit that imparts thermoreversible thickening, and an ethylenic copolymer. 1 to 10% by weight of a saturated carboxylic acid monomer unit.
The conjugated diene monomer unit refers to a structural unit formed by polymerizing a conjugated diene monomer. The monomer unit imparting thermoreversible thickening refers to a structural unit formed by polymerizing a monomer imparting thermoreversible thickening. An ethylenically unsaturated carboxylic acid monomer unit means a structural unit formed by polymerizing an ethylenically unsaturated carboxylic acid monomer.
Here, the ratio of each monomer unit in the conjugated diene copolymer is usually the ratio of the above monomers that can form each monomer unit in all monomers used for the polymerization of the conjugated diene copolymer. It matches (preparation ratio).

  Examples of the conjugated diene monomer forming the conjugated diene monomer unit include 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, and 2-chloro- 1,3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes. These may be used alone or in combination of two or more. Of these, 1,3-butadiene is preferred.

  The content ratio of the conjugated diene monomer unit in the conjugated diene copolymer used as the binder is preferably 10 to 75% by weight, more preferably 20 to 60% by weight, still more preferably 25 to 55% by weight. %. By making the content ratio of the conjugated diene monomer unit in such a range, while making the obtained negative electrode for a secondary battery excellent in the adhesion between the negative electrode active material layer and the current collector and the electrolyte resistance , Can improve flexibility.

  The monomer unit that imparts thermoreversible thickening is a monomer unit that can impart thermoreversible thickening to a conjugated diene copolymer used as a binder. Here, thermoreversible thickening means a property of reversibly increasing the viscosity of a system in which a conjugated diene copolymer used as a binder is blended when a predetermined temperature or higher is reached. That is, a conjugated diene copolymer used as a binder contains a monomer unit that imparts thermoreversible thickening, and is blended with the slurry composition for a secondary battery negative electrode to thereby produce the secondary battery. When the battery negative electrode slurry composition is heated to a predetermined temperature or higher, it has such a property that its viscosity is improved. Moreover, since the increase in viscosity due to thermoreversible thickening is reversible, the viscosity is lowered by cooling again after being heated.

  And in this invention, the slurry composition for secondary battery negative electrodes is applied by applying the slurry composition for secondary battery negative electrodes of this invention on a collector by utilizing such thermoreversible thickening. When the product layer is formed and dried, the viscosity of the slurry composition layer for the secondary battery negative electrode can be increased by heating during drying, whereby a conjugated diene copolymer used as a binder The migration phenomenon of moving can be suppressed. By suppressing the migration phenomenon, the obtained secondary battery negative electrode can be made excellent in adhesion between the negative electrode active material layer and the current collector and high-temperature cycle characteristics. In addition, since the migration phenomenon can be effectively suppressed, high-speed drying is possible, which contributes to improvement in productivity.

  In addition, since the monomer unit that imparts thermoreversible thickening becomes hydrophobic when heated, the removal rate of the aqueous solvent is increased when an aqueous solvent such as water is used as the solvent. Can be increased. Therefore, the migration phenomenon can be suppressed also from such a point.

Examples of monomers that impart thermoreversible thickening to form monomer units that impart thermoreversible thickening include:
N- (meth) acryloyl heterocyclic amines such as N- (meth) acryloylpyrrolidine, N- (meth) acryloylpiropazine, N-tetrahydrofurfuryl (meth) acrylamide acryloylpyrrolidine, N- (meth) acryloylmorpholine;
(Meth) acrylic acid esters of alkylene (2 to 4 carbon atoms) oxide adduct (1 to 40 moles added) of an acyclic amine such as diisopropylaminoethyl (meth) acrylate;
Nn-propyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-cyclopropyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-ethoxypropyl (meth) acrylamide, N-ethoxyethyl (meth) ) N-alkyl or alkoxyalkyl (meth) acrylamides such as acrylamide, N-isopropoxypropyl (meth) acrylamide;
N, such as N, N-diethyl (meth) acrylamide, N-methyl-N-ethyl (meth) acrylamide, N-methyl-Nn-propyl (meth) acrylamide, N-methyl-N-isopropyl (meth) acrylamide , N-di-alkyl or di-alkoxyalkyl (meth) acrylamides;
(Meth) acrylic acid esters of alkylene oxide adducts of cyclic amines such as morpholinoethyl (meth) acrylate [Note that cyclic amines include nitrogen-containing alicyclic compounds [having an aziridine ring (aziridine, 2-methylaziridine Etc.), those having a pyrrolidine ring (pyrrolidine, 2-methylpyrrolidine, 2-pyrrolidone, succinimide, etc.), those having a piperidine ring (piperidine, 2-methylpiperidine, 3,5-dimethylpiperidine, 2-ethylpiperidine, 4 -Piperidinopiperidine, 4-pyrrolidinopiperidine, ethylpipecolinate, etc.), those having a piperazine ring (1-methylpiperazine, 1-methyl-3-ethylpiperazine, etc.), those having a morpholine ring (morpholine, 2 -Methylmorpholine, 3,5- Dimethylmorpholine, thiomorpholine, etc.) and ε-caprolactam, etc.], nitrogen-containing unsaturated cyclic compounds (3-pyrroline, 2,5-dimethyl-3-pyrroline, 2-hydroxypyridine, 4-pyridylcarbinol, 2- Hydroxypyrimidine, etc.). ];
Vinyl monomers having a polyiminoethylene group such as tetraethyleneimine mono (meth) acrylamide, polyethyleneimine mono (meth) acrylamide, ethyleneimine adduct of aminostyrene, ethyleneimine adduct of allylamine;
Tetraethylene glycol monoethyl ether mono (meth) acrylate, pentaethylene glycol monobutyl ether mono (meth) acrylate, trioxypropylene tetraoxyethylene glycol monomethyl ether mono (meth) acrylate, tetrapropylene glycol ethylene oxide 6-mol adduct mono ( Poly (oxy) alkylene (alkylene group having 2 to 4 carbon atoms, degree of polymerization 3 to 40) monool or diol mono (meth) acrylate such as (meth) acrylate;
Polyoxyalkylenes such as tetraethylene glycol monomethyl ether monovinyl phenyl ether, pentaethylene glycol monoethyl ether monovinyl phenyl ether, pentaoxypropylene tetraoxyethylene glycol monomethyl ether monovinyl phenyl ether, monovinyl phenyl ether of tetramethylene glycol ethylene oxide 8 mol adduct Monovinyl phenyl ether of monool or diol;
And alkyl (carbon number 1 to 6) vinyl ether such as methyl vinyl ether;
These may be used alone or in combination of two or more.

  Among these monomers that impart thermoreversible thickening, N- (meth) acryloyl heterocyclic amines, N, N-di-alkyl or N -Alkyl or alkoxyalkyl (meth) acrylamides are preferred, N- (meth) acryloylpyrrolidine or N-isopropyl (meth) acrylamide is more preferred, N-acryloylpyrrolidine or N-isopropylacrylamide is more preferred, N-acryloyl Pyrrolidine is particularly preferred.

  In the conjugated diene copolymer used as the binder, the content of the monomer unit imparting thermoreversible thickening is 0.5 to 50% by weight, preferably 2 to 35% by weight. Preferably, it is 5 to 20% by weight. By making the content ratio of the monomer unit imparting thermoreversible thickening within such a range, the effect of suppressing the migration phenomenon can be made sufficient. If the content ratio of the monomer unit imparting thermoreversible thickening is too small, the effect of suppressing the migration phenomenon cannot be obtained, and if the content ratio is too large, the resulting slurry composition for secondary battery negative electrode The storage stability of things will deteriorate.

  Examples of the ethylenically unsaturated carboxylic acid monomer forming the ethylenically unsaturated carboxylic acid monomer unit include monocarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, Examples thereof include dicarboxylic acid, dicarboxylic acid monoester, and anhydride of dicarboxylic acid. These may be used alone or in combination of two or more. Among these, acrylic acid and itaconic acid are preferable, and itaconic acid is particularly preferable.

  The content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the conjugated diene copolymer used as the binder is 1 to 10% by weight, preferably 1 to 8% by weight, more preferably 2 to 2%. 5% by weight. By setting the content ratio of the ethylenically unsaturated carboxylic acid monomer unit within the above range, the surface acid amount of the conjugated diene copolymer can be controlled within the above-described range. The storage stability of things can be improved. If the content ratio of the ethylenically unsaturated carboxylic acid monomer unit is too small, the storage stability of the slurry composition for the secondary battery negative electrode is deteriorated. Aggregates) are generated.

  The conjugated diene copolymer used as a binder is added to the conjugated diene monomer unit, the monomer unit imparting thermoreversible thickening, and the ethylenically unsaturated carboxylic acid monomer unit. And may contain other monomer units copolymerizable therewith. The other monomer unit copolymerizable with these refers to a structural unit obtained by polymerizing other monomers copolymerizable with these, and as such other monomer units, Aromatic vinyl monomer unit, unsaturated carboxylic acid alkyl ester monomer unit, vinyl cyanide monomer unit, unsaturated monomer unit containing hydroxyalkyl group, unsaturated carboxylic acid amide monomer unit Etc.

  Specific examples of the aromatic vinyl monomer that forms the aromatic vinyl monomer unit include styrene, α-methylstyrene, vinyl toluene, and divinylbenzene. These may be used alone or in combination of two or more. Of these, styrene is preferred.

  When the aromatic vinyl monomer unit is contained, the content ratio of the aromatic vinyl monomer unit in the conjugated diene copolymer used as the binder is preferably 15 to 80% by weight, more preferably. Is 20 to 60% by weight, more preferably 30 to 60% by weight. By setting the content ratio of the aromatic vinyl monomer unit within the above range, the rupture strength and flexibility of the conjugated diene copolymer can be improved. The adhesive strength between the material layer and the current collector can be improved.

  Specific examples of the unsaturated carboxylic acid alkyl ester monomer forming the unsaturated carboxylic acid alkyl ester monomer unit include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, Examples include diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. These may be used alone or in combination of two or more. Among these, methyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate are preferable.

  When the unsaturated carboxylic acid alkyl ester monomer unit is contained, the content ratio of the unsaturated carboxylic acid alkyl ester monomer unit in the conjugated diene copolymer used as the binder is preferably 0.5 to 20% by weight, more preferably 1 to 10% by weight.

Specific examples of the vinyl cyanide monomer forming the vinyl cyanide monomer unit include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like. These may be used alone or in combination of two or more.
When the vinyl cyanide monomer unit is contained, the content ratio of the vinyl cyanide monomer unit in the conjugated diene copolymer used as the binder is preferably 0.5 to 15% by weight. Yes, more preferably 1 to 15% by weight, still more preferably 2 to 5% by weight.

Specific examples of the unsaturated monomer containing a hydroxyalkyl group forming an unsaturated monomer unit containing a hydroxyalkyl group include β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl Methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) Maleate, 2-hydroxyethyl methyl fumarate and the like can be mentioned. These may be used alone or in combination of two or more.
When the unsaturated monomer unit containing a hydroxyalkyl group is contained, the content ratio of the unsaturated monomer containing a hydroxyalkyl group in the conjugated diene copolymer used as a binder is preferably 0. 0.5 to 15% by weight, more preferably 1 to 15% by weight, still more preferably 2 to 5% by weight.

Specific examples of the unsaturated carboxylic acid amide monomer forming the unsaturated carboxylic acid amide monomer unit include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. Can be mentioned. These may be used alone or in combination of two or more.
When the unsaturated carboxylic amide monomer unit is contained, the content of the unsaturated carboxylic amide monomer in the conjugated diene copolymer used as the binder is preferably 0.5 to 15% by weight. More preferably, it is 1 to 15% by weight, and further preferably 2 to 5% by weight.

  The glass transition temperature of the conjugated diene copolymer used as the binder is preferably −40 to + 50 ° C., more preferably −30 to + 40 ° C., and further preferably −20 to + 30 ° C. By setting the glass transition temperature in such a range, the breaking strength and flexibility of the conjugated diene copolymer can be improved. As a result, in the case of a negative electrode for a secondary battery, the negative electrode active material layer and the current collector The adhesive strength between the body can be improved.

  Moreover, the weight average molecular weight of the conjugated diene copolymer used as a binder is preferably 10,000 to 1,000,000, more preferably 20,000 to 500,000. When the weight average molecular weight is in such a range, the strength of the obtained negative electrode for a secondary battery can be improved. In addition, the weight average molecular weight of a conjugated diene copolymer can be calculated | required as a value of polystyrene conversion which used tetrahydrofuran as a developing solvent by gel permeation chromatography (GPC), for example.

  The conjugated diene copolymer used as the binder is produced, for example, by polymerizing a monomer mixture containing the above-described monomers in an aqueous solvent to form polymer particles.

  The aqueous solvent is not particularly limited as long as it can disperse polymer particles obtained by polymerization, and usually has a boiling point of 80 to 350 ° C., preferably 100 to 300 ° C. at normal pressure. Things can be used.

  Specific examples of the aqueous solvent include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, ethylene glycol Glycol ethers such as libutyl ether, butyl cellosolve, 3-methoxy-3-methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl pyrether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; and 1,3-dioxolane , Ethers such as 1,4-dioxolane and tetrahydrofuran. Among these, water is particularly preferable from the viewpoint that it is not flammable and a dispersion of binder particles can be easily obtained.

  The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. Since it is easy to obtain a high molecular weight product and the polymer is obtained in a state of being dispersed in water as it is, no redispersion treatment is necessary, and it is directly used for producing the slurry composition for secondary battery negative electrode according to the present invention. Among them, the emulsion polymerization method is particularly preferable from the viewpoint of production efficiency.

   The emulsion polymerization method is usually performed by a conventional method. For example, the method is described in “Experimental Chemistry Course” Vol. 28, (Publisher: Maruzen Co., Ltd., edited by The Chemical Society of Japan). That is, water, an additive such as a dispersant, an emulsifier, a crosslinking agent, a polymerization initiator, and a monomer are added to a sealed container equipped with a stirrer and a heating device so as to have a predetermined composition. This is a method in which a product is stirred to emulsify monomers and the like in water, and the temperature is increased while stirring to initiate polymerization. Or after emulsifying the said composition, it is the method of putting into a sealed container and starting reaction similarly.

  Examples of polymerization initiators include organic compounds such as lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Peroxides; azo compounds such as α, α′-azobisisobutyronitrile; ammonium persulfate; and potassium persulfate. A polymerization initiator may be used individually by 1 type, and may be used in combination of 2 or more types.

  An emulsifier, a dispersant, a polymerization initiator, and the like are generally used in these polymerization methods, and the amount used is usually an amount generally used. The polymerization temperature and the polymerization time can be arbitrarily selected depending on the polymerization method and the kind of the polymerization initiator. Usually, the polymerization temperature is about 30 ° C. or more, and the polymerization time is about 0.5 to 30 hours.

  In the present invention, when each of the above-described monomers is polymerized, first, a first unit obtained by mixing the respective monomers excluding the monomer that imparts thermoreversible thickening. After the body mixture is polymerized and then the polymerization conversion rate of the first monomer mixture reaches a predetermined value (preferably 50% or more, more preferably 55 to 80%, still more preferably 60 to 75%), It is preferable to perform polymerization by adding a second monomer mixture containing a monomer that imparts thermoreversible thickening to the polymerization system and allowing the polymerization reaction to proceed. Thus, by adding a monomer that imparts thermoreversible thickening in the middle of the polymerization, monomer units that impart thermoreversible thickening are localized in the resulting conjugated diene copolymer. Can be materialized. That is, in the resulting conjugated diene copolymer, a segment containing a large amount of monomer units that impart thermoreversible thickening can be introduced, whereby monomer units that impart thermoreversible thickening can be introduced. Even when the content ratio of is relatively low at 0.5 to 40% by weight, the thermoreversible thickening expression effect by the monomer unit imparting thermoreversible thickening can be more efficiently exhibited. In particular, when the content ratio of the monomer unit imparting thermoreversible thickening is too large, coagulum (fine agglomerates) is generated during polymerization, or the storage stability of the slurry composition for secondary battery negative electrode is low. Since there is a problem of lowering, it is possible to sufficiently obtain the effect of adding a monomer unit that imparts thermoreversible thickening while preventing the occurrence of such a problem.

  In the present invention, it is preferable that the first monomer mixture previously subjected to the polymerization reaction does not contain a monomer that imparts thermoreversible thickening. If it is about 0.5 to 20 weight% among the monomers which give property thickening, it may be made to contain in a 1st monomer mixture and a polymerization reaction may be performed previously. Further, in the second monomer mixture added during the polymerization reaction, it is possible to contain a monomer other than the monomer that imparts thermoreversible thickening. In this case, Of the monomers other than the monomer imparting thermoreversible thickening used for polymerization, about 20 to 100% by weight may be contained in the second monomer mixture.

  The conjugated diene copolymer obtained by such a method can be usually obtained as particles of a water-insoluble polymer. Therefore, in the slurry composition for secondary battery negative electrode, the conjugated diene copolymer is not dissolved in the aqueous solvent but is dispersed as particles. In this case, the number average particle size of the conjugated diene copolymer is preferably 50 to 500 nm, and more preferably 70 to 400 nm. When the number average particle size of the conjugated diene copolymer is in such a range, the strength and flexibility of the obtained secondary battery negative electrode can be improved. The presence of particles can be easily measured by transmission electron microscopy, Coulter counter, laser diffraction scattering, or the like.

Furthermore, an aqueous dispersion of a conjugated diene copolymer obtained by such a method is used, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (for example, NH ₄ Cl, etc.) and an aqueous solution containing an organic amine compound (eg, ethanolamine, diethylamine, etc.) and the like, and the pH is usually adjusted to be in the range of 5-10, preferably 5-9. Also good. Among these, pH adjustment with an alkali metal hydroxide is preferable because adhesion between the current collector and the negative electrode active material layer can be further improved.

  The content ratio of the binder (conjugated diene copolymer) in the slurry composition for secondary battery negative electrode of the present invention is preferably 0.2 to 2.0 parts by weight with respect to 100 parts by weight of the negative electrode active material. More preferably, it is 0.5-1.5 weight part, More preferably, it is 0.8-1.2 weight part. By making the content rate of a binder (conjugated diene copolymer) into such a range, the improvement effect of storage stability and the migration inhibitory effect can be heightened especially.

(Water-soluble polymer)
The slurry composition for secondary battery negative electrode of the present invention contains a water-soluble polymer in addition to the negative electrode active material and the binder described above. Here, the polymer being water-soluble means that the insoluble content is less than 0.5% by weight when 0.5 g of the polymer is dissolved in 100 g of water at 25 ° C.

  The water-soluble polymer used in the present invention is not particularly limited as long as it is a water-soluble polymer, but preferably has an acidic functional group, for example, an acidic functional group-containing monomer, and if necessary Polymers obtained by polymerizing a monomer composition containing other copolymerizable monomers used in this manner (hereinafter sometimes referred to as “acidic functional group-containing polymer”) are suitable. . Note that carboxymethylcellulose, which is a derivative of cellulose formed by condensation polymerization of β-glucose, is not included in the acidic functional group-containing polymer suitably used in the present invention.

  The acidic functional group-containing monomer is a monomer having an acidic functional group. Specific examples thereof include a carboxyl group-containing monomer, a sulfonic acid group-containing monomer, and a phosphate group-containing monomer. In particular, a carboxyl group-containing monomer is preferable.

  As the carboxyl group-containing monomer, a monomer having a carboxyl group and a polymerizable group can be used. Specific examples of the carboxyl group-containing monomer include an ethylenically unsaturated carboxylic acid monomer. Can be mentioned.

  Examples of the ethylenically unsaturated carboxylic acid monomer include ethylenically unsaturated monocarboxylic acid and derivatives thereof, ethylenically unsaturated dicarboxylic acid and acid anhydrides thereof, and derivatives thereof.

Examples of the ethylenically unsaturated monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid.
Examples of the ethylenically 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 -Diamino acrylic acid etc. are mentioned.
Examples of the ethylenically unsaturated dicarboxylic acid include maleic acid, fumaric acid, and itaconic acid.
Examples of the acid anhydride of the ethylenically unsaturated dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
Examples of the ethylenically unsaturated dicarboxylic acid derivatives include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, and fluoromaleic acid; and diphenyl maleate, nonyl maleate, and maleic acid. Examples thereof include maleate esters such as decyl acid, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleate.
These may be used alone or in combination of two or more.
Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferred because the water-dispersible polymer obtained can be further improved in water dispersibility.

  The content ratio of the structural unit obtained by polymerizing the acidic functional group-containing monomer in the water-soluble polymer (hereinafter sometimes referred to as “acidic functional group-containing monomer unit”) is preferably 20 to. It is 50% by weight, more preferably 25 to 50% by weight, still more preferably 30 to 45% by weight. By making the content rate of an acidic functional group containing monomer unit into the said range, the viscosity of the slurry composition for secondary battery negative electrodes can be made suitable for coating.

In addition to the acidic functional group-containing monomer unit, the water-soluble polymer used in the present invention may contain a copolymerizable monomer unit. Examples of such other monomer units include a crosslinkable monomer unit, a fluorine-containing (meth) acrylate monomer unit, and a reactive surfactant unit.
Here, the ratio of each monomer unit in the water-soluble polymer is usually the ratio of the above-mentioned monomers that can form each monomer unit in all monomers used for polymerization of the water-soluble polymer (preparation). Ratio).

  As the crosslinkable monomer for forming the crosslinkable monomer unit, a monomer capable of forming a crosslinked structure upon polymerization can be used. Examples of the crosslinkable monomer include monomers having two or more reactive groups per molecule. Examples of such a monomer include a thermally crosslinkable crosslinkable group and one monomer per molecule. And monofunctional monomers having one olefinic double bond, and polyfunctional monomers having two or more olefinic double bonds per molecule. Examples of the thermally crosslinkable group contained in the monofunctional monomer include an epoxy group, an N-methylolamide group, an oxetanyl group, and an oxazoline group. 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, and o-allylphenyl. Unsaturated glycidyl ethers such as glycidyl ether; butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, 1,2-epoxy-5,9-cyclododeca Diene or polyene monoepoxides such as dienes; alkenyl epoxides such as 3,4-epoxy-1-butene, 1,2-epoxy-5-hexene, 1,2-epoxy-9-decene; glycidyl acrylate, glycidyl methacrylate, Glycidyl crotonate, glycidyl Unsaturated carboxylic acids such as -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 Glycidyl esters; and the like.

  An example of a crosslinkable monomer having an N-methylolamide group as a thermally crosslinkable group and having an olefinic double bond has a methylol group such as N-methylol (meth) acrylamide ( And (meth) acrylamides.

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

  Examples of the crosslinkable monomer having an oxazoline group as a thermally 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 Examples include ethers, allyls or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, methylenebisacrylamide, and divinylbenzene.

  In particular, ethylene dimethacrylate, allyl glycidyl ether, and glycidyl methacrylate can be preferably used as these crosslinkable monomers. These crosslinkable monomers may be used alone or in combination of two or more.

  The content ratio of the crosslinkable monomer unit in the water-soluble polymer is preferably 0.1 to 2% by weight, more preferably 0.2 to 1.5% by weight, and further preferably 0.5 to 1% by weight. %. By making the content rate of a crosslinkable monomer unit into such a range, the water solubility and dispersibility of a water-soluble polymer can be made favorable.

上記一般式（１）において、Ｒ^１は、水素原子又はメチル基を表し、Ｒ^２は、フッ素原子を含有する炭素数１〜１８の炭化水素基を表す。また、Ｒ^２が含有するフッ素原子の数は、１個でもよく、２個以上でもよい。As a fluorine-containing (meth) acrylic acid ester monomer which forms a fluorine-containing (meth) acrylic acid ester monomer, the monomer represented by following General formula (1) is mentioned, for example.

In the general formula (1), R ¹ represents a hydrogen atom or a methyl group, R ² represents a hydrocarbon group having 1 to 18 carbon atoms containing a fluorine atom. Moreover, the number of fluorine atoms contained in R ² may be one or two or more.

  Examples of the fluorine-containing (meth) acrylic acid ester monomer represented by the general formula (1) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, (meth) acrylic acid fluorine monomer. Aralkyl. Of these, alkyl fluoride (meth) acrylate is preferable.

  Specific examples of such monomers include 2,2,2-trifluoroethyl (meth) acrylate, β- (perfluorooctyl) ethyl (meth) acrylate, 2,2, (meth) acrylic acid. 3,3-tetrafluoropropyl, (meth) acrylic acid 2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid 1H, 1H, 9H-perfluoro-1-nonyl, (meth) 1H, 1H, 11H-perfluoroundecyl acrylate, perfluorooctyl (meth) acrylate, 3 [4 [1-trifluoromethyl-2,2-bis [bis (trifluoromethyl) fluoro (meth) acrylate] And (meth) acrylic acid perfluoroalkyl esters such as methyl] 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.

  The content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is preferably 1 to 20% by weight, more preferably 2 to 15% by weight, and further preferably 5 to 10% by weight. is there. By setting the content ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in such a range, the water-soluble polymer can be given wettability to the electrolytic solution, and the low-temperature output characteristics can be improved. it can.

  The reactive surfactant that forms the reactive surfactant unit has a polymerizable group that can be copolymerized with other monomers, and has a surfactant group (hydrophilic group and hydrophobic group). It is a monomer.

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

  Moreover, the reactive surfactant usually has a hydrophilic group as a portion that exhibits hydrophilicity. Reactive surfactants 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, —PO (OH) _{2 and the} like. 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 ammonium ions of alkanolamines such as ethanolamine, diethanolamine, and triethanolamine.
Examples of the cationic hydrophilic group include —Cl, —Br, —I, and —SO ₃ OR ^X. Here, R ^X represents an alkyl group. Examples of R ^X is methyl group, an ethyl group, a propyl group, and an isopropyl group.
Examples of nonionic hydrophilic groups include —OH and the like.

上記一般式（２）において、Ｒは２価の結合基を表し、Ｒの例としては、−Ｓｉ−Ｏ−基、メチレン基及びフェニレン基が挙げられる。また、上記一般式（２）において、Ｒ^３は親水性基を表し、Ｒ^３の例としては、−ＳＯ_３ＮＨ_４が挙げられる。さらに、上記一般式（２）において、ｎは１〜１００の整数である。Preferable examples of the reactive surfactant include a compound represented by the following general formula (2).

In the general formula (2), R represents a divalent linking group, and examples of R include a —Si—O— group, a methylene group, and a phenylene group. In the general formula (2), R ³ represents a hydrophilic group, and examples of R ³ include —SO ₃ NH ₄ . Furthermore, in the said General formula (2), n is an integer of 1-100.

  The content ratio of the reactive surfactant unit in the water-soluble polymer is preferably 0.1 to 15% by weight, more preferably 0.2 to 10% by weight, still more preferably 0.5 to 5% by weight. is there. The dispersibility of the slurry composition for secondary battery negative electrodes can be improved by making the content rate of a reactive surfactant unit into such a range.

  Further, the water-soluble polymer used in the present invention may further contain another monomer unit in addition to each monomer unit described above. Examples of such monomer units include (meth) acrylate monomer units other than fluorine-containing (meth) acrylate monomer units.

  Examples of the (meth) acrylate monomer constituting the (meth) acrylate monomer unit other than the fluorine-containing (meth) acrylate monomer unit include methyl acrylate, ethyl acrylate, n- Propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate Acrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate Methacrylic acid alkyl esters such as relate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate; Can be mentioned. These (meth) acrylic acid ester monomers may be used individually by 1 type, and may be used in combination of 2 or more types.

  The content ratio of (meth) acrylic acid ester monomer units other than fluorine-containing (meth) acrylic acid ester monomer units in the water-soluble polymer is preferably 30 to 70% by weight, more preferably 35 to 35% by weight. 70% by weight, more preferably 40 to 70% by weight. By setting the content ratio of the (meth) acrylic acid ester monomer unit in such a range, the obtained negative electrode for secondary battery has excellent adhesion between the negative electrode active material layer and the current collector It can be.

Further, the water-soluble polymer used in the present invention may contain units obtained by polymerizing the following monomers in addition to the units of the respective monomers described above.
That is, such monomers include styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl. Styrene monomers such as benzene; Amide monomers such as acrylamide and acrylamide-2-methylpropanesulfonic acid; α, β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Ethylene, propylene, etc. Olefin monomers; halogen atom-containing monomers such as vinyl chloride and vinylidene chloride; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; methyl vinyl ether, ethyl vinyl ether, butyl Such as vinyl ether Nyl ether monomers; vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocycle-containing vinyl such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole Compound monomer; and the like. The total content of these units in the water-soluble polymer is preferably 10% by weight or less, more preferably 5% by weight or less.

  The weight average molecular weight of the water-soluble polymer is preferably smaller than the above-mentioned binder (conjugated diene copolymer), preferably 100 to 500,000, more preferably 500 to 250,000, and even more preferably. Is 1,000 to 100,000. By setting the weight average molecular weight of the soluble polymer in such a range, the strength of the water-soluble polymer is increased, and a stable protective layer covering the negative electrode active material can be formed. The high temperature storage characteristics of the secondary battery can be improved. The weight average molecular weight of the water-soluble polymer may be determined by GPC as a value in terms of polystyrene using a solution obtained by dissolving 0.85 g / ml sodium nitrate in a 10% by volume aqueous solution of dimethylformamide.

  The glass transition temperature of the water-soluble polymer is preferably 0 to 100 ° C, more preferably 5 to 50 ° C. By setting the glass transition temperature of the water-soluble polymer in such a range, the adhesion and flexibility of the obtained negative electrode for a secondary battery can be made compatible.

The water-soluble polymer used in the present invention can be produced by any production method. For example, a monomer mixture containing an acidic functional group-containing monomer and other copolymerizable monomers used as necessary may be polymerized in an aqueous solvent to produce a water-soluble polymer. it can.
The aqueous solvent and polymerization method used for the polymerization can be the same as the binder (conjugated diene copolymer) described above, for example. A reaction solution containing a water-soluble polymer in an aqueous solvent is usually obtained by polymerization. You may take out a water-soluble polymer from the reaction liquid obtained in this way. However, usually, a slurry composition for a secondary battery negative electrode is prepared using a water-soluble polymer in a state dissolved in an aqueous solvent.

  The reaction solution containing a water-soluble polymer in an aqueous solvent is usually acidic. Therefore, it may be alkalized to pH 7 to pH 13 as necessary. Thereby, it can be made soluble in an aqueous solvent, the handling property of a reaction liquid can be improved, and the coating property of the slurry composition for secondary battery negative electrodes can be improved. Examples of the method for alkalinizing to pH 7 to pH 13 include alkali metal aqueous solutions such as lithium hydroxide aqueous solution, sodium hydroxide aqueous solution and potassium hydroxide aqueous solution; alkaline earth metal aqueous solutions such as calcium hydroxide aqueous solution and magnesium hydroxide aqueous solution; And a method of adding an alkaline aqueous solution such as an aqueous ammonia solution.

  The content ratio of the water-soluble polymer in the slurry composition for the negative electrode of the secondary battery of the present invention is preferably 0.1 to 3 parts by weight, more preferably 0.3 to 100 parts by weight with respect to 100 parts by weight of the negative electrode active material. 1 part by weight. By making the content rate of a water-soluble polymer into the said range, the viscosity of the slurry composition for secondary battery negative electrodes can be made suitable for application | coating.

(Other ingredients)
The slurry composition for secondary battery negative electrode of the present invention includes, in addition to the negative electrode active material, the binder and the water-soluble polymer, further, if necessary, a conductivity imparting material, a reinforcing material, a dispersing agent, a leveling agent, an antioxidant. Other components such as a thickener and an electrolyte additive having a function of inhibiting decomposition of the electrolyte may be contained.

  Examples of the conductivity imparting material include conductive carbon such as acetylene black, ketjen black, carbon black, and graphite, and fibers and foils of various metals. By using the conductivity imparting material, the electrical contact between the negative electrode active materials can be improved, and the discharge load characteristics in the case of a secondary battery can be improved. By containing a conductivity imparting material, the rate characteristics of the negative electrode for a secondary battery can be improved. The content of the conductivity-imparting material in the secondary battery negative electrode slurry composition is usually 0.01 to 20 parts by weight, preferably 1 to 10 parts by weight, per 100 parts by weight of the negative electrode active material.

  As the reinforcing material, various inorganic and organic spherical, plate-like, or rod-like fillers can be used. By using the reinforcing material, the obtained negative electrode for a secondary battery can be made tough and flexible, and this can further improve the high-temperature cycle characteristics. The content of the reinforcing material in the secondary battery negative electrode slurry composition is usually 0.01 to 20 parts by weight, preferably 1 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  Examples of the dispersant include an anionic compound, a cationic compound, a nonionic compound, and a polymer compound. What is necessary is just to select a dispersing agent according to the negative electrode active material and electroconductivity imparting material to be used. By containing a dispersant, the stability of the slurry composition in the case of a slurry composition for a secondary battery negative electrode can be improved, thereby improving the smoothness of the resulting secondary battery negative electrode. This makes it possible to increase the capacity. The content of the dispersant in the secondary battery negative electrode slurry composition is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, and metal surfactants. By blending a leveling agent, a secondary battery negative electrode slurry composition is obtained, and when this is coated on a current collector, it is possible to prevent the occurrence of repelling and to obtain a secondary composition obtained. The smoothness of the negative electrode for a battery can be improved. The content ratio of the leveling agent in the secondary battery negative electrode slurry composition is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  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 the weight average molecular weight is preferably 200 to 1000, more preferably 600 to 700. By containing an antioxidant, the stability of the slurry composition in the case of a slurry composition for a secondary battery negative electrode can be improved, and the battery capacity and high-temperature cycle characteristics in the case of a secondary battery can be improved. Can be improved. The content of the antioxidant in the secondary battery negative electrode slurry composition is preferably 0.01 to 10 parts by weight, more preferably 0.05 to 5 parts by weight with respect to 100 parts by weight of the negative electrode active material. is there.

  The thickener is not particularly limited as long as it can be dissolved in water and the viscosity can be adjusted. For example, cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and ammonium salts and alkali metal salts thereof. Polyvinyl alcohols such as modified or unmodified polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride, maleic acid or copolymers of fumaric acid and vinyl alcohol, polyethylene glycol, poly Examples include ethylene oxide, polyvinyl pyrrolidone, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. By containing a thickener, the coatability of the secondary battery negative electrode slurry composition can be further improved. The content of the thickener in the slurry composition for secondary battery negative electrode is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  As the electrolytic solution additive, for example, vinylene carbonate can be used. By including the electrolytic solution additive, the high-temperature cycle characteristics and the high-temperature characteristics in the case of a secondary battery can be improved. The content ratio of the electrolytic solution additive in the secondary battery negative electrode slurry composition is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.

  In addition to the above, nanoparticles such as fumed silica and fumed alumina; surfactants such as alkyl surfactants, silicon surfactants, fluorine surfactants, metal surfactants, etc. It can be included.

(Preparation of slurry composition for secondary battery negative electrode)
Although the manufacturing method of the slurry composition for secondary battery negative electrodes of this invention is not specifically limited, For example, it can manufacture by the following method. That is, first, among each component constituting the slurry composition for a secondary battery negative electrode, a binder, a water-soluble polymer, and a dispersion medium (for example, water) used as necessary are mixed. By doing so, a binder composition is obtained. In this case, the binder and the water-soluble polymer are usually blended in a state of being dispersed in a dispersion medium such as water. And the slurry composition for secondary battery negative electrodes can be obtained by adding and mixing a negative electrode active material and the other component added as needed to the obtained binder composition. In the present invention, a binder, a water-soluble polymer, a dispersion medium used as necessary, and a negative electrode active material and other components added as necessary are directly added to the secondary. A battery negative electrode slurry composition may be obtained.

  The mixing device is not particularly limited as long as it can uniformly mix the above components, and it is a bead mill, ball mill, roll mill, sand mill, pigment disperser, crusher, ultrasonic disperser, homogenizer, planetary mixer, fill mix. Among them, a ball mill, a roll mill, a pigment disperser, a crusher, and a planetary mixer can be preferably used because dispersion at a high concentration is possible.

(Anode for secondary battery)
The negative electrode for secondary battery of the present invention comprises a current collector and a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode active material and the binder constituting the slurry composition for secondary battery negative electrode of the present invention described above. It contains an adhesive and a water-soluble polymer. When the negative electrode active material, the binder, and other components added as necessary other than the water-soluble polymer are blended with the slurry composition for secondary battery negative electrode, the negative electrode active material layer Other components will also be included. The secondary battery negative electrode of the present invention is obtained, for example, by applying the above-described slurry composition for a secondary battery negative electrode of the present invention on a current collector and then drying the slurry composition for a secondary battery negative electrode. Can be manufactured.

The current collector is not particularly limited as long as it has electrical conductivity and is electrochemically durable, but a metal material is preferable because of its heat resistance. Specific examples of the material for the current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.
In order to increase the adhesive strength with the negative electrode active material layer, the current collector may be used after roughening the surface in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.

  The method for applying the slurry composition for the secondary battery negative electrode on the current collector is not particularly limited. For example, the doctor blade method, the dip method, the reverse roll method, the direct roll method, the gravure method, the extrusion method, And a brushing method. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 30 minutes, and the drying temperature is usually 40 ° C to 180 ° C.

  The negative electrode for a secondary battery according to the present invention is preferably subjected to a pressure treatment using a mold press, a roll press or the like, thereby reducing the porosity. The preferable range of the porosity is 5 to 15%, more preferably 7 to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity, which causes a problem that the negative electrode active material layer is easily peeled off and is likely to be defective.

  Although the thickness of a negative electrode active material layer is not specifically limited, Preferably it is 5-300 micrometers, More preferably, it is 30-250 micrometers. By setting the thickness of the negative electrode active material layer in such a range, the rate characteristics and the high-temperature cycle characteristics can be improved.

  The negative electrode for a secondary battery according to the present invention is preferably subjected to a pressure treatment using a mold press, a roll press or the like, thereby reducing the porosity. The preferable range of the porosity is 5 to 15%, more preferably 7 to 13%. If the porosity is too high, charging efficiency and discharging efficiency are deteriorated. When the porosity is too low, it is difficult to obtain a high volume capacity, which causes a problem that the negative electrode active material layer is easily peeled off and is likely to be defective.

(Secondary battery)
The secondary battery of the present invention includes the above-described negative electrode for a secondary battery of the present invention, a positive electrode, a separator, and an electrolytic solution.

  Secondary batteries include lithium ion secondary batteries, nickel metal hydride secondary batteries, etc., but lithium ion secondary batteries are required to improve performance such as long-term high-temperature cycle characteristics and output characteristics. Is preferred. Hereinafter, the case where the secondary battery of the present invention is a lithium ion secondary battery will be described as an example.

As the electrolytic solution of the secondary battery of the present invention, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is used. A lithium salt is used as the supporting electrolyte. The lithium salt is not particularly _{limited, LiPF 6, LiAsF 6, LiBF} 4, LiSbF 6, LiAlCl 4, LiClO 4, CF 3 SO 3 Li, C 4 F 9 SO 3 Li, CF 3 COOLi, (CF 3 CO) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and the like. Among these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable because they are easily dissolved in an organic solvent and exhibit a high degree of dissociation. Two or more of these may be used in combination. The lithium ion conductivity can be increased as the supporting electrolyte having a higher degree of dissociation is used.

  The organic solvent is not particularly limited as long as it can dissolve the supporting electrolyte. However, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate ( BC), carbonates such as methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; Preferably used. These organic solvents may be used in combination. Among these, carbonates are preferable from the viewpoint of a high dielectric constant and a wide stable potential region.

  The electrolyte solution may contain an additive, and examples of the additive include carbonate compounds such as vinylene carbonate (VC).

  The concentration of the supporting electrolyte in the electrolytic solution is usually 1 to 30% by weight, preferably 5 to 20% by weight. Further, it is usually used at a concentration of 0.5 to 2.5 mol / L depending on the type of the supporting electrolyte. If the concentration of the supporting electrolyte is too low or too high, the ionic conductivity tends to decrease.

Instead of the above-described electrolytic solution, a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, a gel polymer electrolyte impregnated with the polymer electrolyte, or an inorganic solid electrolyte such as LiI or Li ₃ N may be used.

  As the separator, known ones such as a microporous film or nonwoven fabric made of polyolefin such as polyethylene and polypropylene; a porous resin coat containing inorganic ceramic powder; Specific examples of the separator include known ones such as a microporous film or non-woven fabric containing a polyolefin resin such as polyethylene or polypropylene, or an aromatic polyamide resin; a porous resin coat containing an inorganic ceramic powder. For example, polyolefin (polyethylene, polypropylene, polybutene, polyvinyl chloride), and microporous membranes made of resins such as mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyethersulfone, polyamide, polyimide, polyimideamide, Examples thereof include a microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, and polytetrafluoroethylene, or a woven fabric of polyolefin fibers, a nonwoven fabric thereof, and an aggregate of insulating substance particles. Among these, it is possible to reduce the thickness of the entire separator, thereby increasing the active material ratio in the secondary battery and increasing the capacity per volume. A microporous membrane is preferred.

  The thickness of a separator is 0.5-40 micrometers normally, Preferably it is 1-30 micrometers, More preferably, it is 1-10 micrometers. Within this range, the resistance due to the separator in the battery is reduced, and the workability during battery production is excellent.

  As the positive electrode, it is possible to use a positive electrode active material, a binder, and a negative positive electrode active material layer including a conductivity-imparting material added as necessary, which is laminated on a current collector.

  Examples of the positive electrode active material include metal oxides capable of reversibly doping and dedoping lithium ions. Examples of the metal oxide include lithium cobaltate, lithium nickelate, lithium manganate, lithium iron phosphate, lithium manganese phosphate, lithium vanadium phosphate, lithium iron vanadate, nickel-manganese-lithium cobaltate, nickel-cobalt acid. Lithium, nickel-lithium manganate, iron-lithium manganate, iron-manganese-lithium cobaltate, lithium iron silicate, iron silicate-manganese lithium, vanadium oxide, copper vanadate, niobium oxide, titanium sulfide, molybdenum oxide, molybdenum sulfide , Etc. In addition, the positive electrode active material illustrated above may be used independently according to a use, and may be used in mixture of multiple types. Furthermore, polymers such as polyacetylene, poly-p-phenylene and polyquinone can be mentioned. Of these, it is preferable to use a lithium-containing metal oxide.

  As a binder used for a positive electrode active material layer, it does not restrict | limit but a well-known thing can be used. Examples of the binder include resins such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives; acrylics It is possible to use a soft polymer such as a polymer-based soft polymer, a diene-based soft polymer, an olefin-based soft polymer, or a vinyl-based soft polymer.

As the conductivity imparting material, for example, the same material as the slurry composition for secondary battery negative electrode of the present invention described above can be used.
Moreover, as a collector, the thing similar to the negative electrode for secondary batteries of this invention mentioned above can be used, for example.

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

  A positive electrode can be manufactured similarly to the negative electrode for secondary batteries mentioned above.

  The secondary battery of the present invention includes the above-described negative electrode for a secondary battery of the present invention and a positive electrode, which are stacked via a separator, and wound into a battery container according to the shape of the battery. It is manufactured by injecting an electrolytic solution into a container and sealing it. In order to prevent an increase in pressure inside the battery and occurrence of overcharge / discharge, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate, or the like may be provided as necessary. The shape of the secondary battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like.

  Since the secondary battery of the present invention obtained in this way is formed using the negative electrode for secondary battery obtained using the slurry composition for secondary battery negative electrode of the present invention described above, various battery characteristics, In particular, it has excellent high-temperature cycle characteristics.

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. “Part” and “%” in each example are based on weight unless otherwise specified.
In addition, the definition and evaluation method of each characteristic are as follows.

<Glass transition temperature (Tg) of conjugated diene copolymer>
The glass transition temperature (Tg) of the conjugated diene copolymer was measured using a differential scanning calorimeter (DSC) at a heating rate of 10 ° C./min.

<Surface acid amount of conjugated diene copolymer>
The surface acid amount of the conjugated diene copolymer was measured by the following method.
First, a 50 g sample of an aqueous dispersion of a conjugated diene copolymer prepared by adding distilled water and adjusting the solid content concentration to 2% is placed in a 150 ml glass container washed with distilled water, and a solution conductivity meter (Kyoto Electronics Industry Co., Ltd.). (Product: CM-117, cell type used: K-121), and stirring was started. And in the state which continued stirring, 0.1 normal sodium hydroxide was added so that the electrical conductivity of the aqueous dispersion of a conjugated diene copolymer might be 2.5-3.0 mS, and 6 minutes The electrical conductivity after the lapse of time was measured, and the obtained measured value was defined as the electrical conductivity at the start of measurement. Then, 0.5 ml of 0.1 N hydrochloric acid was added to the aqueous dispersion of this conjugated diene copolymer, and after 30 seconds, the electrical conductivity was measured, and 0.5 ml of 0.1 N hydrochloric acid was added again. The operation of measuring the electrical conductivity after 30 seconds was repeated at intervals of 30 seconds until the electrical conductivity became equal to or higher than that at the start of measurement.

The obtained electric conductivity data is plotted on a graph with the vertical axis representing electric conductivity (mS) and the horizontal axis representing the total amount of added hydrochloric acid (mmol), and three variables as shown in FIG. A hydrochloric acid amount-electric conductivity curve having a curved point is obtained, and the X coordinate of the obtained three inflection points and the X coordinate at the end of the addition of hydrochloric acid are respectively P ₁ , P ₂ , P ₃ and P _4, and the least square method is used for the data in the four sections of the X coordinate from zero to P ₁ , P ₁ to P ₂ , P ₂ to P ₃ and P ₃ to P ₄ , respectively. Thus, approximate lines L ₁ , L ₂ , L ₃ and L ₄ were obtained. Further, the X coordinate of the intersection of L ₁ and L ₂ is A ₁ (mmol), the X coordinate of the intersection of L ₂ and L ₃ is A ₂ (mmol), and the X coordinate of the intersection of L ₃ and L ₄ is A ₃ (mmol). And the surface acid amount per 1g of conjugated diene copolymers was calculated | required from the following formula.
Surface acid amount per 1 g of conjugated diene copolymer = A ₂ −A ₁

<Measurement of coarse aggregate after polymerization of conjugated diene copolymer>
500 g of an aqueous dispersion of a conjugated diene copolymer whose solid content was measured for weight concentration was filtered through a 200-mesh stainless steel wire mesh having a known weight, and dried at 120 ° C. for 60 minutes. Then, the weight of coarse agglomerates trapped on the mesh was weighed, and the weight percentage obtained by dividing the weight of the sample by the solid content was measured as 200 mesh on coagulum (coarse agglomerates) and evaluated according to the following criteria. . It can be judged that the smaller the value of 200 mesh on coagulum, the smaller the coarse aggregates.
A: 200 mesh on coagulum is less than 0.02% B: 200 mesh on coagulum is 0.02% or more and less than 0.05% C: 200 mesh on coagulum is 0.05% or more, 1 Less than 0.0% D: 200 mesh on coagulum is 1.0% or more

<Storage stability of conjugated diene copolymer>
Storage stability was evaluated using an aqueous dispersion of a conjugated diene copolymer. Specifically, the obtained aqueous dispersion of the conjugated diene copolymer was stored in an oven heated to 40 ° C. for 1 week. For the aqueous dispersion of the conjugated diene copolymer before and after storage for 1 week, the viscosity is measured with a B-type viscometer (product name “(DV-I Prime)”, manufactured by (Yamato Scientific)). The change in viscosity (%) was calculated according to the following formula, and the storage stability was evaluated according to the following criteria. In addition, it can be judged that it is excellent in storage stability, so that a viscosity change is small. Further, in this example, the storage stability of the aqueous dispersion of the conjugated diene copolymer was evaluated, but it is considered that the same result is obtained when the slurry composition for negative electrode is used.
The viscosity was measured under the conditions of 25 ° C. and 60 rpm, and the value after 60 seconds was taken as the viscosity.
Viscosity change (%) = (viscosity of aqueous dispersion of conjugated diene copolymer after storage) / (viscosity of aqueous dispersion of conjugated diene copolymer before storage) × 100
A: Change in viscosity is less than 110% B: Change in viscosity is 110% or more and less than 120% C: Change in viscosity is 120% or more and less than 130% D: Change in viscosity is 130% or more

<Thermal response of slurry composition for negative electrode>
The slurry composition for the negative electrode was heated at 90 ° C. for 1 minute, and the viscosity after the heating was measured using a B-type viscometer (product name “DV-I Prime”, manufactured by Yamato Scientific Co., Ltd.). And according to the following formula from the viscosity before heating and the viscosity after heating, the thermal responsiveness of the slurry composition for negative electrodes was calculated and evaluated according to the following criteria.
The viscosity was measured under the conditions of 25 ° C. and 60 rpm, and the value after 60 seconds was taken as the viscosity.
Thermal response of the negative electrode slurry composition = (viscosity after heating) / (viscosity before heating)
A: Thermal response value is 1.3 or more B: Thermal response value is 1.2 or more and less than 1.3 C: Thermal response value is less than 1.2

<Measurement of residual water content of negative electrode>
About the primary dried material of the negative electrode (the slurry composition for the negative electrode was dried at 90 ° C. for 3 minutes), immediately after drying, the residual moisture content was measured by the Karl Fischer method and evaluated according to the following criteria.
A: Less than 20 ppm B: 20 ppm or more

<Peel strength>
The negative electrodes produced in the examples and comparative examples were cut into rectangles having a length of 100 mm and a width of 10 mm to obtain test pieces. A cellophane tape was affixed on the surface of the negative electrode active material layer of the test piece with the surface of the negative electrode active material layer facing down. At this time, a cellophane tape defined in JIS Z1522 was used. Moreover, the cellophane tape was fixed to the test bench. Then, the stress when one end of the current collector was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. This measurement was performed 3 times, the average value was calculated | required, the said average value was made into peel strength, and the following references | standards evaluated. In addition, it shows that the binding strength to the electrical power collector of a negative electrode active material layer is so large that a peel strength is large, ie, adhesive strength is large.
A: Peel strength is 8.0 N / m or more B: Peel strength is 5.0 N / m or more and less than 8.0 N / m C: Peel strength is less than 5.0 N / m

<High temperature cycle characteristics>
The lithium ion secondary batteries of the laminate type cells produced in the examples and comparative examples were allowed to stand at room temperature for 24 hours, and then at a charge / discharge rate of 4.2 V and 0.1 C in an environment of 25 ° C. The charge / discharge operation was performed and the initial capacity _C0 was measured. Furthermore, charging / discharging was repeated 200 times in an environment of 60 ° C., and the capacity C ₂₀₀ after 200 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 ₂₀₀ / C ₀ × 100 (%). It shows that it is excellent in a high temperature cycling characteristic, so that the value of capacity | capacitance change rate (DELTA) _CC is high.
A: Capacity change rate ΔC _C is 90% or more B: Capacity change rate ΔC _C is 80% or more and less than 90% C: Capacity change rate ΔC _C is 70% or more and less than 80% D: Capacity change rate ΔC _C is 70 %Less than

Example 1
<Production of Conjugated Diene Copolymer (A-1)>
In a 5 MPa pressure vessel equipped with a stirrer, 55 parts of styrene, 32 parts of 1,3-butadiene, 3 parts of itaconic acid, 5 parts of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water, and 1 part of potassium persulfate as a polymerization initiator. The mixture was stirred sufficiently and then heated to 50 ° C. to initiate polymerization. When the polymerization conversion reached 65%, 10 parts of N-acryloylpyrrolidine was added to the reaction system, and the reaction temperature was raised to 70 ° C. When the polymerization conversion rate reached 95.0%, the reaction was stopped by cooling, and an aqueous dispersion of conjugated diene copolymer (A-1) having a solid content concentration of 40% (conjugated diene copolymer (A -1) number average particle diameter: 100 nm). The obtained conjugated diene copolymer (A-1) was measured for its polymer composition by ¹ H-NMR, as shown in Table 1.
And about the obtained conjugated diene copolymer (A-1), according to the above-mentioned method, the glass transition temperature (Tg), the surface acid amount, the coarse aggregate (coagulum), and the storage stability were measured. . The results are shown in Table 1.

<Production of water-soluble polymer (B-1)>
In a 5 MPa pressure vessel with a stirrer, 32.5 parts of methacrylic acid, 0.8 parts of ethylene dimethacrylate, 7.5 parts of 2,2,2-trifluoroethyl methacrylate, 59.2 parts of butyl acrylate, polyoxyalkylene alkenyl ether After putting 1.5 parts of ammonium sulfate (trade name “Latemul PD-104”, manufactured by Kao Corporation), 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator and stirring sufficiently, 60 ° C. To initiate polymerization. Then, when the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a water-soluble polymer. And 10% ammonia water was added to the mixture containing the obtained water-soluble polymer, and it adjusted to pH8, and obtained the aqueous solution of the desired water-soluble polymer (B-1).
About the obtained water-soluble polymer (B-1), when the polymer composition was measured by ¹ H-NMR, it was found that 32% methacrylic acid unit, 0.8% ethylene dimethacrylate unit, 2,2,2- They were 7.4% of trifluoroethyl methacrylate units, 58.3% of butyl acrylate units, and 1.5% of polyoxyalkylene alkenyl ether ammonium sulfate units.

<Manufacture of slurry composition for negative electrode>
Artificial graphite as a negative electrode active material in a planetary mixer with a disper (average particle size: 24.5 μm, graphite interlayer distance (surface distance (d value) of (002) plane by X-ray diffraction method): 0.354 nm) 100 parts, 1.0 part of an aqueous dispersion of the conjugated diene copolymer (A-1) on a solids basis, and 0.5 part of an aqueous dispersion of a water-soluble polymer (B-1) on a solids basis Then, 0.5 part of a 1% aqueous solution of carboxymethylcellulose was added on the basis of solid content, adjusted to a solid content concentration of 45% with ion-exchanged water, and then mixed for 60 minutes to obtain a slurry composition for negative electrode.
About the obtained slurry composition for negative electrodes, according to the above-mentioned method, the thermal responsiveness was measured. The results are shown in Table 1.

<Manufacture of negative electrode>
The slurry composition for negative electrode obtained above was applied on a copper foil having a thickness of 20 μm as a current collector with a comma coater so that the film thickness after drying was about 150 μm and dried. . This drying was performed by conveying the copper foil in an oven at 90 ° C. at a speed of 0.5 m / min for 3 minutes, thereby obtaining a primary dried product of the negative electrode. Thereafter, the primary dried material of the obtained negative electrode was heat-treated 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.
And about the primary dry thing of the negative electrode after drying on 90 degreeC and the conditions for 3 minutes, according to the above-mentioned method, the residual moisture content was measured immediately after drying. In addition, the peel strength of the negative electrode after rolling was measured according to the method described above. The results are shown in Table 1.

<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 size of 0.20 μm was prepared. This acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 2-ethylhexyl acrylate 78%, acrylonitrile 20%, and methacrylic acid 2%.

Then, in a planetary mixer, 100 parts of LiFePO ₄ having a volume average particle size of 0.5 μm and a olivine crystal structure as a positive electrode active material, and a 1% aqueous solution of carboxymethyl cellulose as a dispersant (trade name “BSH-12”, Daiichi Kogyo Made by Pharmaceutical Co., Ltd.) 1 part (corresponding to solid content), 5 parts of 40% aqueous dispersion of acrylate polymer prepared above as a binder (corresponding to solid content), and ion-exchanged water are mixed and mixed. A slurry composition was prepared. The amount of ion-exchanged water was such that the total solid concentration was 40%.

  Then, the positive electrode slurry composition thus obtained was applied on a 20 μm thick aluminum foil as a current collector with a comma coater so that the film thickness after drying was about 200 μm, Dried. This drying was performed by conveying the aluminum 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 positive electrode raw material. This positive electrode original fabric was rolled by a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 60 μm.

<Production of secondary battery>
An aluminum packaging exterior was prepared as the battery exterior. Then, the positive electrode obtained above was cut into a 4 cm × 4 cm square and arranged so that the surface on the current collector side was in contact with the aluminum packaging exterior. Next, a single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by a dry method, porosity 55%) is formed into a 5 cm × 5 cm square on the surface of the positive electrode active material layer side of the positive electrode. The cut out one was placed. Furthermore, the negative electrode obtained above was cut into a square of 4.2 cm × 4.2 cm, and this was placed on the separator so that the surface on the negative electrode active material layer side faces the separator. And, in order to seal the opening of the aluminum packaging material in order to seal the opening of the aluminum packaging material by sealing the opening of the aluminum packaging material by sealing the opening of the aluminum packaging material, A lithium ion secondary battery was manufactured. As the electrolyte, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) in (EC:: DEC = 1 2 ( volume ratio at 20 ° C.)), of LiPF ₆ 1 mol / liter concentration The solution dissolved in was used.
And about the obtained lithium ion secondary battery, according to the above-mentioned method, the high temperature cycling characteristic was measured. The results are shown in Table 1.

(Example 2)
When producing the slurry composition for the negative electrode, the amount of the artificial graphite was changed from 100 parts to 95 parts, and the same as in Example 1 except that 5 parts of SiO _x as an alloy-based negative electrode active material was used. Then, a negative electrode slurry and a secondary battery were prepared in the same manner as in Example 1 except that the negative electrode slurry composition was produced and the obtained negative electrode slurry composition was used. The results are shown in Table 1.

(Example 3)
<Production of Conjugated Diene Copolymer (A-2)>
A conjugated diene copolymer (A-2) was prepared in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 57 parts and the amount of itaconic acid was changed from 3 parts to 1 part. An aqueous dispersion was obtained. About the obtained conjugated diene copolymer (A-2), each measurement was performed similarly to Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-2) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

Example 4
<Production of Conjugated Diene Copolymer (A-3)>
A conjugated diene copolymer (A-3) was prepared in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 50 parts and the amount of itaconic acid was changed from 3 parts to 8 parts. An aqueous dispersion was obtained. About the obtained conjugated diene copolymer (A-3), each measurement was performed similarly to Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-3) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 5)
<Production of Conjugated Diene Copolymer (A-4)>
The amount of styrene was changed from 55 parts to 60 parts, the amount of N-acryloylpyrrolidine was changed from 10 parts to 2 parts, and the amount of 1,3-butadiene was changed from 32 parts to 35 parts. In the same manner as in Example 1, an aqueous dispersion of the conjugated diene copolymer (A-4) was obtained. About the obtained conjugated diene copolymer (A-4), each measurement was performed similarly to Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-4) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 6)
<Production of Conjugated Diene Copolymer (A-5)>
The conjugated diene copolymer (A-) was changed in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 45 parts and the amount of N-acryloylpyrrolidine was changed from 10 parts to 20 parts. An aqueous dispersion of 5) was obtained. For the obtained conjugated diene copolymer (A-5), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-5) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 7)
<Production of Conjugated Diene Copolymer (A-6)>
The amount of styrene was changed from 55 parts to 22 parts, and the amount of 1,3-butadiene was changed from 32 parts to 40 parts. Instead of 10 parts of N-acryloylpyrrolidine, N-isopropyl (meth) acrylamide was used. An aqueous dispersion of a conjugated diene copolymer (A-6) was obtained in the same manner as in Example 1 except that 35 parts were used. The obtained conjugated diene copolymer (A-6) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-6) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 8)
<Production of Conjugated Diene Copolymer (A-7)>
The amount of styrene was changed from 55 parts to 45 parts, the amount of 1,3-butadiene was changed from 32 parts to 36 parts, the amount of N-acryloylpyrrolidine was changed from 10 parts to 15 parts, and itaconic acid 4 An aqueous dispersion of a conjugated diene copolymer (A-7) was obtained in the same manner as in Example 1 except that 4 parts of acrylic acid was used instead of parts. The obtained conjugated diene copolymer (A-7) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-7) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

Example 9
<Production of Conjugated Diene Copolymer (A-8)>
The amount of styrene was changed from 55 parts to 45 parts, the amount of 1,3-butadiene was changed from 32 parts to 34 parts, the amount of N-acryloylpyrrolidine was changed from 10 parts to 15 parts, and itaconic acid 4 An aqueous dispersion of a conjugated diene copolymer (A-8) was obtained in the same manner as in Example 1 except that 6 parts of acrylic acid was used instead of parts. For the obtained conjugated diene copolymer (A-8), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-8) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 10)
<Production of Conjugated Diene Copolymer (A-9)>
A conjugated diene copolymer (A) was prepared in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 70 parts and the amount of 1,3-butadiene was changed from 32 parts to 17 parts. An aqueous dispersion of -9) was obtained. The obtained conjugated diene copolymer (A-9) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-9) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 11)
<Production of Conjugated Diene Copolymer (A-10)>
The conjugated diene copolymer (A) was changed in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 33 parts and the amount of 1,3-butadiene was changed from 32 parts to 54 parts. An aqueous dispersion of -10) was obtained. The obtained conjugated diene copolymer (A-10) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-10) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 12)
<Production of Conjugated Diene Copolymer (A-11)>
The timing at which 10 parts of N-acryloylpyrrolidine was added to the reaction system was changed from the time point when the polymerization conversion rate became 65% to the time point when the polymerization conversion rate became 55%. An aqueous dispersion of a conjugated diene copolymer (A-11) was obtained. For the obtained conjugated diene copolymer (A-11), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-11) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 13)
<Production of Conjugated Diene Copolymer (A-12)>
The timing at which 10 parts of N-acryloylpyrrolidine was added to the reaction system was changed in the same manner as in Example 1 except that the polymerization conversion rate was 65% and the polymerization conversion rate was 80%. An aqueous dispersion of a conjugated diene copolymer (A-12) was obtained. The obtained conjugated diene copolymer (A-12) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-12) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 14)
<Production of Conjugated Diene Copolymer (A-13)>
The timing at which 10 parts of N-acryloylpyrrolidine was added to the reaction system was changed in the same manner as in Example 1 except that the polymerization conversion rate was 65% and the polymerization conversion rate was 100%. An aqueous dispersion of a conjugated diene copolymer (A-13) was obtained. The obtained conjugated diene copolymer (A-13) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-13) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Example 15)
A slurry composition for a negative electrode, a negative electrode and a secondary battery were prepared in the same manner as in Example 1 except that the amount of the water-soluble polymer (B-1) was changed from 0.5 part to 3 parts in terms of solid content. It produced and evaluated similarly. The results are shown in Table 1.

(Comparative Example 1)
<Production of Conjugated Diene Copolymer (A-14)>
In the same manner as in Example 1, except that the amount of styrene was changed from 55 parts to 57.8 parts and the amount of itaconic acid was changed from 3 parts to 0.2 parts, a conjugated diene copolymer ( An aqueous dispersion of A-14) was obtained. The obtained conjugated diene copolymer (A-14) was measured in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-14) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Comparative Example 2)
<Production of Conjugated Diene Copolymer (A-15)>
A conjugated diene copolymer (A-15) was prepared in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 46 parts and the amount of itaconic acid was changed from 3 parts to 12 parts. An aqueous dispersion was obtained. For the obtained conjugated diene copolymer (A-15), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-15) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Comparative Example 3)
<Production of Conjugated Diene Copolymer (A-16)>
A conjugated diene copolymer was prepared in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 64.7 parts and the amount of N-acryloylpyrrolidine was changed from 10 parts to 0.3 parts. An aqueous dispersion of combined (A-16) was obtained. For the obtained conjugated diene copolymer (A-16), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-16) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

(Comparative Example 4)
<Production of Conjugated Diene Copolymer (A-17)>
The conjugated diene copolymer (A-) was changed in the same manner as in Example 1 except that the amount of styrene was changed from 55 parts to 20 parts and the amount of N-acryloylpyrrolidine was changed from 10 parts to 45 parts. An aqueous dispersion of 17) was obtained. For the obtained conjugated diene copolymer (A-17), each measurement was performed in the same manner as in Example 1. The results are shown in Table 1.

<Manufacture of slurry composition for negative electrode, negative electrode and secondary battery>
And except having used the conjugated diene copolymer (A-17) obtained above, it carried out similarly to Example 1, and produced the slurry composition for negative electrodes, a negative electrode, and a secondary battery, and evaluated similarly. Went. The results are shown in Table 1.

  As shown in Table 1, the conjugated diene copolymer of the present invention suppresses the generation of coarse aggregates during polymerization, and as a binder for producing a negative electrode for a secondary battery, When a predetermined conjugated diene copolymer is used, the resulting binder and slurry composition are excellent in storage stability and thermal sensitivity, and have a low residual water content after drying (even when high-speed drying is performed). The residual water content was low), and the obtained negative electrode for secondary battery was excellent in peel strength, and further, was excellent in high-temperature cycle characteristics when used as a secondary battery (Examples 1 to 15).

On the other hand, when the conjugated diene copolymer has a low content of ethylenically unsaturated carboxylic acid monomer units and the surface acid amount is too low, the resulting secondary battery negative electrode has a high peel strength. Moreover, when it was set as the secondary battery, it became inferior to a high temperature cycling characteristic (comparative example 1).
Further, as the conjugated diene copolymer, when the content of the ethylenically unsaturated carboxylic acid monomer unit is large and the surface acid amount is too high, the monomer unit imparting thermoreversible thickening is used. When the content is low and the surface acid amount is too low, coarse aggregates are generated during polymerization, and the obtained secondary battery negative electrode is inferior in peel strength. When it was set as the battery, it became inferior to the high temperature cycle characteristic (Comparative Examples 2 and 3).
Further, when a conjugated diene copolymer having too much content of monomer units imparting thermoreversible thickening is used, coarse aggregates are generated during polymerization, and are obtained. The binder and the slurry composition are inferior in storage stability, and further, the obtained negative electrode for a secondary battery is inferior in peel strength. In addition, when a secondary battery is obtained, the high-temperature cycle characteristics are inferior (comparison) Example 4).

Claims (11)

A slurry composition for a secondary battery negative electrode comprising a negative electrode active material, a binder, and a water-soluble polymer,
The binder has a surface acid amount of 0.10 to 0.60 mmol / g, conjugated diene monomer units of 17 to 54% by weight , and monomer units of 2 to 35 % that impart thermoreversible thickening. % ethylenically unsaturated carboxylic acid monomer units 1-8 wt%, and Ri particulate conjugated diene copolymer der containing 22-70 wt% aromatic vinyl monomer units,
The monomer unit that imparts thermoreversible thickening is an N- (meth) acryloylpyrrolidine unit or an N-isopropyl (meth) acrylamide unit,
The content ratio of the binder is 0.5 to 1.5 parts by weight with respect to 100 parts by weight of the negative electrode active material,
The secondary battery negative electrode slurry composition , wherein a content ratio of the water-soluble polymer is 0.3 to 3 parts by weight with respect to 100 parts by weight of the negative electrode active material .   The slurry composition for a secondary battery negative electrode according to claim 1, wherein the conjugated diene copolymer has a glass transition temperature of -40 to + 50 ° C.   The slurry composition for secondary battery negative electrodes according to claim 1 or 2, wherein the water-soluble polymer contains at least 20 to 50% by weight of an acidic functional group-containing monomer unit.   The slurry composition for secondary battery negative electrodes according to claim 3, wherein the acidic functional group-containing monomer constituting the acidic functional group-containing monomer unit is an ethylenically unsaturated carboxylic acid monomer. A method for producing a slurry composition for a secondary battery negative electrode comprising a negative electrode active material, a binder, and a water-soluble polymer,
The binder has a surface acid amount of 0.10 to 0.60 mmol / g, conjugated diene monomer units of 17 to 54% by weight , and monomer units of 2 to 35 % that impart thermoreversible thickening. % , A particulate conjugated diene copolymer containing 1 to 8 % by weight of ethylenically unsaturated carboxylic acid monomer units and 22 to 70% by weight of aromatic vinyl monomer units ,
The monomer unit that imparts thermoreversible thickening is an N- (meth) acryloylpyrrolidine unit or an N-isopropyl (meth) acrylamide unit,
The content ratio of the binder is 0.5 to 1.5 parts by weight with respect to 100 parts by weight of the negative electrode active material, and the content ratio of the water-soluble polymer is 100 parts by weight of the negative electrode active material. In contrast, 0.3 to 3 parts by weight,
When the first monomer mixture containing at least the conjugated diene monomer and the ethylenically unsaturated carboxylic acid monomer is polymerized, and the polymerization conversion rate of the first monomer mixture becomes 50% or more A secondary battery negative electrode comprising a step of obtaining a conjugated diene copolymer by adding a second monomer mixture containing at least a monomer imparting thermoreversible thickening to a polymerization system and polymerizing the mixture. A method for producing a slurry composition. Applying a slurry composition for a secondary battery negative electrode according to any one of claims 1 to 4 on a current collector;
Drying the slurry composition for secondary battery negative electrode. A method for producing a negative electrode for secondary battery. A negative electrode for a secondary battery comprising a current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode active material, a binder, and a water-soluble polymer,
The binder has a surface acid amount of 0.10 to 0.60 mmol / g, conjugated diene monomer units of 17 to 54% by weight , and monomer units of 2 to 35 % that impart thermoreversible thickening. % ethylenically unsaturated carboxylic acid monomer units 1-8 wt%, and Ri particulate conjugated diene copolymer der containing 22-70 wt% aromatic vinyl monomer units, wherein the thermoreversible The monomer unit imparting thickening is an N- (meth) acryloylpyrrolidine unit or an N-isopropyl (meth) acrylamide unit,
The content ratio of the binder is 0.5 to 1.5 parts by weight with respect to 100 parts by weight of the negative electrode active material,
The negative electrode for a secondary battery , wherein a content ratio of the water-soluble polymer is 0.3 to 3 parts by weight with respect to 100 parts by weight of the negative electrode active material . A secondary battery comprising the secondary battery negative electrode according to claim 7 , a positive electrode, a separator, and an electrolytic solution. A binder composition for a secondary battery negative electrode comprising a binder and a water-soluble polymer, wherein the binder has a surface acid amount of 0.10 to 0.60 mmol / g, and is a conjugated diene monomer 17 to 54% by weight unit, 2 to 35 % by weight monomer unit for imparting thermoreversible thickening, 1 to 8 % by weight ethylenically unsaturated carboxylic acid monomer unit , and 22 aromatic vinyl monomer units Ri particulate conjugated diene copolymer der containing 70 wt%,
The binder composition for a secondary battery negative electrode, wherein the monomer unit imparting thermoreversible thickening is an N- (meth) acryloylpyrrolidine unit or an N-isopropyl (meth) acrylamide unit . The binder composition for secondary battery negative electrodes according to claim 9 , wherein the water-soluble polymer contains at least 20 to 50% by weight of acidic functional group-containing monomer units. The binder composition for secondary battery negative electrode according to claim 10 , wherein the acidic functional group-containing monomer constituting the acidic functional group-containing monomer unit is an ethylenically unsaturated carboxylic acid monomer.

Images