JP6111895B2 - Slurry composition for negative electrode of lithium ion secondary battery, negative electrode for secondary battery and secondary battery - Google Patents

Description

  The present invention relates to a slurry composition for a negative electrode of a lithium ion secondary battery, and the present invention relates to a negative electrode formed using the slurry composition for a negative electrode of a lithium ion secondary battery and a secondary battery including the negative electrode.

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

  In the lithium ion secondary battery, a polymer (hereinafter sometimes referred to as “polymer binder”) is used as a binder for shape retention of the electrode active material layer and adhesion to the current collector.

  This polymer binder is required to have adhesiveness with an electrode active material, resistance to a polar solvent used as an electrolytic solution, and stability in an electrochemical environment. From such required characteristics, fluorine-based polymers such as polyvinylidene fluoride are used. However, the fluorine-based polymer has problems such as inhibiting ion conductivity when an electrode active material layer is formed and insufficient adhesion strength between the current collector and the electrode active material layer. Furthermore, when a fluorine-based polymer is used for the negative electrode which is a reducing condition, there are problems that the stability is not sufficient and the cycle characteristics of the secondary battery are deteriorated.

  In order to form an electrode active material layer, a mixture of an active material, a binder and, if necessary, a conductive additive, a dispersant, a thickener, etc., is slurried with an appropriate solvent or dispersion medium, and this electrode slurry is collected. The electrode active material layer is formed by coating and drying the electric body. When a fluorine-based polymer such as polyvinylidene fluoride (PVdF) is used as a binder, an organic solvent such as N-methylpyrrolidone (NMP) is used as a solvent because the binder is insoluble in water. However, even when NMP is used, the dissolved concentration of PVdF is not high and is generally used at a concentration of 10% or less, and it is difficult to increase the solid content concentration. In addition, from the viewpoint of work environment sanitation, there is a demand for switching from organic solvent systems to water systems. Furthermore, in order to control the viscosity of the electrode slurry within a range suitable for coating, a thickener such as carboxymethyl cellulose (CMC) is often added. However, a slurry containing CMC often increases with time, and it is difficult to uniformly apply the slurry, making it difficult to make the quality uniform.

  As a binder used in an aqueous electrode slurry, Patent Document 1 (Japanese Patent Application Laid-Open No. 2011-119192) discloses an unsaturated polyalkylene glycol ether monomer unit and an ethylenically unsaturated carboxylic acid such as acrylic acid. Polymers containing monomeric units have been proposed.

JP 2011-119192 A

  According to the description in Patent Document 1, the strength of the electrode film is improved by using the binder. However, secondary batteries are constantly required to have higher functionality and longer life. Specifically, it is required to improve cycle characteristics, output characteristics, etc., and to improve adhesion between the current collector after charging and discharging and the electrode active material layer.

  As a polymer binder used for the negative electrode active material layer, the present inventors have continued intensive studies to solve the above problems, and as an unsaturated polyalkylene glycol ether monomer unit and an ethylenically unsaturated carboxylic acid monomer. In addition to the unit, the use of a specific polymer containing a fluorine-containing (meth) acrylate monomer unit further suppresses thickening of the slurry over time, improves coatability, and provides an electrode. In, the adhesion between the current collector after charging and discharging and the electrode active material layer and the ion conductivity are improved, and as a result, a secondary battery with improved cycle characteristics and output characteristics can be obtained. As a result, the present invention has been completed.

That is, the gist of the present invention aimed at solving the above problems is as follows.
(1) A slurry composition for a negative electrode of a lithium ion secondary battery comprising a negative electrode active material, a water-soluble polymer and water,
The water-soluble polymer is composed of an ethylenically unsaturated carboxylic acid monomer unit 20 to 50% by mass, a fluorine-containing (meth) acrylic acid ester monomer unit 0.1 to 30% by mass, and an unsaturated polyalkylene glycol ether type. It is a polymer containing 1 to 20% by mass of monomer units.
A slurry composition for a negative electrode of a lithium ion secondary battery.

(2) The slurry composition for a negative electrode of a lithium ion secondary battery according to (1), wherein the 1% aqueous solution viscosity of the water-soluble polymer is 10 to 10,000 mPa · s.

(3) The lithium ion secondary battery negative electrode according to (1) or (2), wherein the ethylenically unsaturated carboxylic acid monomer unit of the water-soluble polymer is an ethylenically unsaturated monocarboxylic acid monomer unit. Slurry composition.

(4) The lithium ion secondary battery negative electrode according to any one of (1) to (3), wherein a content ratio of the water-soluble polymer is 0.1 to 20 parts by mass with respect to 100 parts by mass of the negative electrode active material. Slurry composition.

(5) The slurry composition for a lithium ion secondary battery negative electrode according to any one of (1) to (4), further comprising a particulate binder.

(6) A negative electrode for a lithium ion secondary battery obtained by applying the slurry composition for a lithium ion secondary battery negative electrode according to any one of (1) to (5) above on a current collector and drying.

(7) A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to (6) above, a positive electrode, an electrolytic solution, and a separator.

  In the present invention, an electrode slurry can be obtained in an aqueous system by using a specific water-soluble polymer instead of the binder in the slurry composition for the negative electrode of a lithium ion secondary battery, and the viscosity of the slurry over time can be increased. It is suppressed and coatability is improved. The polymer is considered to have a function as a thickener in addition to a function as a binder. In the slurry composition for a negative electrode of a lithium ion secondary battery of the present invention, a thickener such as CMC is not used. The slurry viscosity can be adjusted to an appropriate range. As a result, it is considered that thickening with time due to the thickener hardly occurs, and the above-described effect is exhibited.

Further, in the electrode obtained using the slurry, since the swelling of the electrode during charging and discharging is suppressed, high adhesion between the current collector and the electrode active material layer even after repeated charging and discharging Sex is maintained. Moreover, the ion conductivity of an electrode active material layer improves by including a fluorine-containing (meth) acrylic acid ester monomer unit. As a result, a secondary battery with improved cycle characteristics and output characteristics can be obtained.

  Hereinafter, (1) a slurry composition for a lithium ion secondary battery negative electrode, (2) a lithium ion secondary battery negative electrode, and (3) a lithium ion secondary battery will be described in this order.

(1) Slurry composition for negative electrode of lithium ion secondary battery The slurry composition for negative electrode of lithium ion secondary battery of the present invention (hereinafter sometimes simply referred to as “slurry” or “slurry composition”) It contains substances, water-soluble polymers, and water, and includes a particulate binder, a conductive aid, and the like as necessary.

(Water-soluble polymer)
The water-soluble polymer is a polymer containing an ethylenically unsaturated carboxylic acid monomer unit, a fluorine-containing (meth) acrylic acid ester monomer unit, and an unsaturated polyalkylene glycol ether monomer unit, and further necessary (Meth) acrylic acid ester monomer unit, a crosslinkable monomer unit may be included, and a structure derived from a functional monomer such as a reactive surfactant monomer A structural unit derived from a unit or another copolymerizable monomer may be contained.

Ethylenically unsaturated carboxylic acid monomer The ethylenically unsaturated carboxylic acid monomer unit is a structural unit formed by polymerization of an ethylenically unsaturated carboxylic acid monomer. 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 ethylenically unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of 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-diaminoacrylic acid. Examples of ethylenically unsaturated dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of acid anhydrides of ethylenically unsaturated dicarboxylic acids include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride. Examples of derivatives of ethylenically unsaturated dicarboxylic acids include methyl maleate such as methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid; and diphenyl maleate, nonyl maleate And maleate esters such as decyl maleate, dodecyl maleate, octadecyl maleate and fluoroalkyl maleate. Among these, ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid are preferable. This is because the dispersibility of the obtained water-soluble polymer in water can be further improved. Further, one type of ethylenically unsaturated carboxylic acid monomer may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer may contain only one type of ethylenically unsaturated carboxylic acid monomer unit, or may contain two or more types in combination at any ratio.

  The ratio of the ethylenically unsaturated carboxylic acid monomer unit in the water-soluble polymer is 20 to 50% by mass, preferably 25 to 45% by mass, more preferably 30 to 40% by mass in 100% by mass of the water-soluble polymer. It is. By containing the ethylenically unsaturated carboxylic acid monomer unit in the above range, the water-soluble polymer exhibits excellent adhesion to the electrode active material and the current collector, and the solubility in water is improved. . If the ratio of the ethylenically unsaturated carboxylic acid monomer unit is too small, adhesion and water solubility may be reduced, and the coating property of the slurry may be impaired, or the swelling of the electrode during charge / discharge The electrode active material may fall off and the output characteristics may be impaired. Further, if the ratio of the ethylenically unsaturated carboxylic acid monomer unit is excessive, the durability is impaired, and in particular, the high temperature cycle characteristics and the high temperature holding characteristics may be deteriorated.

Fluorine-containing (meth) acrylic acid ester monomer The fluorine-containing (meth) acrylic acid ester monomer unit is a structural unit formed by polymerizing a fluorine-containing (meth) acrylic acid ester monomer.
Examples of the fluorine-containing (meth) acrylic acid ester monomer include monomers represented by the following formula (I). In the present specification, (meth) acryl includes both acrylic and methacryl.

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

  Examples of fluorine-containing (meth) acrylic acid ester monomers represented by formula (I) include (meth) acrylic acid alkyl fluoride, (meth) acrylic acid fluoride aryl, and (meth) acrylic acid fluoride. Aralkyl is mentioned. Of these, alkyl fluoride (meth) acrylate is preferable. Specific examples of such a monomer include (meth) acrylic acid-2,2,2-trifluoroethyl, (meth) acrylic acid-β- (perfluorooctyl) ethyl, (meth) acrylic acid-2. , 2,3,3-tetrafluoropropyl, (meth) acrylic acid-2,2,3,4,4,4-hexafluorobutyl, (meth) acrylic acid-1H, 1H, 9H-perfluoro-1- Nonyl, (meth) acrylic acid-1H, 1H, 11H-perfluoroundecyl, perfluorooctyl (meth) acrylate, (meth) acrylic acid-3- [4- [1-trifluoromethyl-2,2- And (meth) acrylic acid perfluoroalkyl esters such as bis [bis (trifluoromethyl) fluoromethyl] ethynyloxy] benzooxy] -2-hydroxypropyl. Among them, (meth) acrylic acid-2,2,2-trifluoroethyl is particularly preferable because it has high wettability with an electrolytic solution and improves low-temperature characteristics.

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

  The ratio of the fluorine-containing (meth) acrylic acid ester monomer unit in the water-soluble polymer is 0.1 to 30% by mass, preferably 0.2 to 25% by mass, more preferably 0.5 to 20% by mass. is there. By containing the fluorine-containing (meth) acrylic acid ester monomer unit in the above range, the water-soluble polymer is improved in dispersion stability with respect to water. In addition, the adhesion between the electrode active materials is improved, the adhesion between the electrode active material layer and the current collector is improved, and particularly high temperature cycle characteristics and high temperature holding characteristics are excellent. Furthermore, by including a fluorine-containing (meth) acrylic acid ester monomer unit, ion conductivity is improved and output characteristics are also excellent. When the ratio of the fluorine-containing (meth) acrylic acid ester monomer unit is too small, the ionic conductivity may be lowered and the output characteristics may be deteriorated. On the other hand, if the ratio of the fluorine-containing (meth) acrylic acid ester monomer unit is excessive, the solubility in water is lowered, and uniform coating of the slurry may be difficult.

  Furthermore, alkali resistance is provided to the electrode active material layer by including the fluorine-containing (meth) acrylic acid ester monomer unit. The electrode forming slurry may contain an alkaline substance, and the alkaline substance may be generated by oxidation-reduction due to the operation of the element. Such an alkaline substance corrodes the current collector and impairs the device life. However, the electrode active material layer has alkali resistance, so that corrosion of the current collector due to the alkaline substance is suppressed.

Unsaturated polyalkylene glycol ether monomer An unsaturated polyalkylene glycol ether monomer unit is a structural unit formed by polymerization of an unsaturated polyalkylene glycol ether monomer.
The unsaturated polyalkylene glycol ether monomer is not particularly limited as long as it has a polymerizable ethylene group and a polyalkylene glycol chain, but the following general formula (II);

^(Wherein, R 1, ^{R 2} and ^{R 3} are the same or different, .R ⁴ represents a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, a hydrogen atom or a straight, Represents ^a branched or cyclic hydrocarbon group, R ^a is the same or different and represents an alkylene group having 2 to 10 carbon atoms, X is a divalent alkylene group having 1 to 5 carbon atoms, or a direct bond M represents the average added mole number of the oxyalkylene group represented by R ^a O, and is preferably an integer of 2 to 200.

R ¹ , R ² and R ³ are the same or different and are a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, and the alkyl group is any of linear, branched or cyclic. Also good. As an alkyl group, a C1-C8 thing is preferable. More preferably, it is a C1-C6 alkyl group, More preferably, it is a C1-C4 alkyl group. Moreover, it is preferable that the said unsaturated polyalkylene glycol ether-type monomer is a C2-C10 alkenyl group. More preferably, it has a C3-C8 alkenyl group, More preferably, it has a C3-C6 alkenyl group. R ¹ , R ² and R ³ are preferably set appropriately so as to have such a preferable structure.

In the above general formula (II), when R ⁴ is a linear, branched or cyclic hydrocarbon group having 1 to 20 carbon atoms, R ⁴ may be methyl, ethyl, n-propyl, isopropyl, n- C 1-20 aliphatic or alicyclic alkyl groups such as butyl, isobutyl, sec-butyl, tert-butyl, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, etc .; phenyl, naphthyl, anthryl, phenanthryl, etc. An aryl group having 6 to 20 carbon atoms; an aryl group substituted with an alkyl group such as o-, m- or p-tolyl, 2,3- or 2,4-xylyl, and mesityl; an (alkyl) such as biphenylyl Aryl groups substituted with phenyl groups; alkyl groups substituted with aryl groups such as benzyl, phenethyl, benzhydryl, trityl, etc. The Among these, R ⁴ is preferably a hydrocarbon group or hydrogen atom having 10 or less carbon atoms, more preferably a hydrocarbon group or hydrogen atom having 3 or less carbon atoms, and still more preferably 2 or less carbon atoms. A saturated alkyl group, an unsaturated alkyl group, or a hydrogen atom. R ⁴ is particularly preferably a hydrogen atom, methyl, ethyl, or vinyl, and most preferably a hydrogen atom or methyl.

In the general formula (II), R ^a represents an alkylene group having 2 to 10 carbon atoms. The alkylene group may be linear or branched. The oxyalkylene groups represented by R ^a O may be the same or different. Among these, an alkylene group having 2 to 5 carbon atoms is preferable. More preferably, it is a C2-C3 alkylene group.

Specific examples of the ^Ra include ethylene (—CH ₂ CH ₂ —), trimethylene (—CH ₂ CH ₂ CH ₂ —), tetramethylene (—CH ₂ CH ₂ CH ₂ CH ₂ —), pentamethylene, A linear alkylene group such as xamethylene; ethylidene [—CH (CH ₃ ) —], propylene [—CH (CH ₃ ) CH ₂ —], propylidene [—CH (CH ₃ CH ₂ ) —], isopropylidene [ Branched chain alkylene groups such as —C (CH ₃ ) ₂ —] and the like. Among these, those having 2 to 5 carbon atoms such as ethylene, trimethylene, tetramethylene, pentamethylene, ethylidene, propylene, and isopropylidene are preferable, ethylene and propylene are more preferable, and ethylene is most preferable. That is, as the oxyalkylene group represented by R ^a O, those composed of such preferable R ^a are preferable.

In the unsaturated polyalkylene glycol ether monomer, the oxyalkylene group represented by R ^a O in the general formula (II) is composed of only one kind of oxyalkylene group. Although it may be composed of two or more different oxyalkylene groups, it is preferable that 50 to 100 mol% of the total oxyalkylene groups are composed of the above preferred oxyalkylene groups. If the oxyalkylene group is such, it will ensure solubility in water and contribute to flexibility. The ratio of the preferable oxyalkylene group in the entire oxyalkylene group is more preferably 70 to 100 mol%, and still more preferably 80 to 100 mol%.

In the general formula (II), when X is a divalent alkylene group having 1 to 5 carbon atoms, examples of X include methylene (—CH ₂ —), ethylene (—CH ₂ CH ₂ —), trimethylene. _{(-CH 2 CH 2 CH 2 -} ), tetramethylene _{(-CH 2 CH 2 CH 2 CH} 2 -), propylene _{[-CH (CH 3) CH 2} -] , and the like. Among these, X is preferably methylene or ethylene, and particularly preferably ethylene.

In the said general formula (II), m represents the average addition mole number of the oxyalkylene group represented by R ^<a> O, and is the number of 2-200. When the oxyalkylene group represented by R ^a O has two or more different oxyalkylene groups, the addition of the oxyalkylene group may be any addition form such as random addition, block addition, and alternate addition. Good. The average number of moles added means the average number of moles of oxyalkylene groups added in 1 mole of monomer.

  When the above m exceeds 200, the polymerizability of the monomer is lowered. On the other hand, if m is less than 2, the resulting polymer does not have sufficient flexibility and may not be suitable for use as a binder. As a range of m, 2-150 are preferable and 10-100 are more preferable.

  One type of unsaturated polyalkylene glycol ether monomer may be used alone, or two or more types may be used in combination at any ratio. Therefore, the water-soluble polymer may contain only one type of unsaturated polyalkylene glycol ether monomer, or may contain two or more types in combination at any ratio.

  The unsaturated polyalkylene glycol ether monomer is preferably one having an alkenyl group and a polyalkylene glycol chain, and an unsaturated alcohol polyalkylene glycol adduct having an alkenyl group is preferred. The monomer may be a compound having a structure in which a polyalkylene glycol chain is added to an unsaturated alcohol having an alkenyl group, and an alkenyl group having 2 to 10 carbon atoms, preferably 3 to 8 carbon atoms. In addition, the average added mole number of the oxyalkylene group having 2 to 10 carbon atoms is preferably 2 to 200. Specifically, vinyl alcohol alkylene oxide adduct, (meth) allyl alcohol alkylene oxide adduct, 3-buten-1-ol alkylene oxide adduct, isoprenol (3-methyl-3-buten-1-ol) alkylene oxide Adduct, 3-methyl-2-buten-1-ol alkylene oxide adduct, 2-methyl-3-buten-2-ol alkylene oxide adduct, 2-methyl-2-buten-1-ol alkylene oxide adduct 2-methyl-3-buten-1-ol alkylene oxide adduct is more preferable, more preferably isoprenol (3-methyl-3-butene-1-ol obtained by adding alkylene oxide to 3-methyl-3-buten-1-ol. Buten-1-ol) alkylene oxide adduct, particularly preferably 3-methyl- - butene-1-ol 1 mol and the alkylene oxide is an average 2 to 200 mols isoprenol (3-methyl-3-buten-1-ol) alkylene oxide adducts.

  The ratio of the unsaturated polyalkylene glycol ether monomer unit in the water-soluble polymer is 1 to 20% by mass, preferably 1.5 to 18% by mass, and more preferably 2 to 15% by mass. By containing the unsaturated polyalkylene glycol ether monomer unit in the above range, the water-soluble polymer has improved water dispersion stability. Further, the adhesion between the electrode active materials and the adhesion between the electrode active material layer and the current collector are improved, and in particular, the high temperature cycle characteristics and the high temperature holding characteristics are excellent. When the ratio of the unsaturated polyalkylene glycol ether monomer unit is too small, the solubility in water is lowered, and uniform application of the slurry may be difficult. If the ratio of unsaturated polyalkylene glycol ether monomer units is excessive, the dispersion stability in water may decrease, and the electrode active material may fall off due to swelling of the electrode during charge and discharge, resulting in output characteristics. May be damaged.

  The water-soluble polymer may further contain a (meth) acrylic acid ester monomer unit or a crosslinkable monomer unit, if necessary, and has functionality such as a reactive surfactant monomer. The structural unit derived from the monomer which it has, and the structural unit derived from the other copolymerizable monomer may be contained.

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

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

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

  In the water-soluble polymer, when the (meth) acrylic acid ester monomer unit is contained, the ratio is preferably 30 to 70% by mass, more preferably 35 to 65% by mass, and particularly preferably 40 to 60% by mass. It is. By containing the (meth) acrylic acid ester monomer unit, the adhesion of the electrode active material layer containing the water-soluble polymer to the current collector can be increased, and the flexibility of the electrode active material layer can be increased. Can be increased.

The crosslinkable monomer water-soluble polymer may further contain a crosslinkable monomer unit in addition to the above structural units. The crosslinkable monomer unit is a structural unit capable of forming a crosslinked structure during or after polymerization by heating or energy irradiation of the crosslinkable monomer. As an example of the crosslinkable monomer, a monomer having thermal crosslinkability can be usually mentioned. More specifically, a monofunctional monomer having a heat-crosslinkable crosslinkable group and one olefinic double bond per molecule, and a polyfunctional having two or more olefinic double bonds per molecule. Ionic monomers.

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

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

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

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

  Examples of the crosslinkable monomer having an oxazoline group as a 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 is mentioned.

  Examples of multifunctional monomers having two or more olefinic double bonds include allyl (meth) acrylate, ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, Tetraethylene glycol di (meth) acrylate, trimethylolpropane-tri (meth) acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl Ethers, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylene bisacrylamide, and divinylbenzene.

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

  When the water-soluble polymer contains a crosslinkable monomer unit, the ratio is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and particularly preferably 0.5% by mass or more. , Preferably 5% by mass or less, more preferably 4% by mass or less, and particularly preferably 2% by mass or less. By setting the ratio of the crosslinkable monomer unit to the lower limit value or more of the above range, it is possible to increase the molecular weight of the water-soluble polymer and prevent the degree of swelling from excessively increasing. On the other hand, by setting the ratio of the crosslinkable monomer unit to be equal to or less than the upper limit of the above range, the solubility of the water-soluble polymer in water can be enhanced and the dispersibility can be improved. Therefore, by setting the ratio of the crosslinkable monomer unit within the above range, both the degree of swelling and dispersibility can be improved.

Other monomer units Water-soluble polymers include structural units derived from functional monomers such as reactive surfactant monomers and other copolymers in addition to the above monomer units. Structural units derived from possible monomers may be included.

  The reactive surfactant monomer is a monomer having a polymerizable group that can be copolymerized with another monomer and having a surface active group (hydrophilic group and hydrophobic group). The reactive surfactant unit obtained by polymerizing the reactive surfactant monomer constitutes a part of the molecule of the water-soluble polymer and is a structural unit that can function as a surfactant.

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

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

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

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

  -OH is mentioned as an example of a nonionic hydrophilic group.

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

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

  When the water-soluble polymer contains a reactive surfactant unit, the ratio is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.5% by mass or more, and usually 15%. It is at most 10% by mass, preferably at most 10% by mass, more preferably at most 5% by mass. The dispersibility of the negative electrode slurry composition can be improved by setting the ratio of the reactive surfactant unit to the lower limit value or more of the above range. On the other hand, the durability of the negative electrode active material layer can be improved by setting the ratio of the reactive surfactant unit to the upper limit of the above range.

  Further examples of arbitrary units that the water-soluble polymer may have include units obtained by polymerizing the following monomers. That is, styrene monomers such as styrene, chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, and divinyl benzene; Amide monomers such as acrylamide and acrylamide-2-methylpropanesulfonic acid; α, β-unsaturated nitrile compound monomers such as acrylonitrile and methacrylonitrile; Olefin monomers such as ethylene and propylene; Vinyl chloride , Halogen atom-containing monomers such as vinylidene chloride; vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether and butyl vinyl ether; Methyl Vinyl ketone monomers such as nil ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; and one or more of heterocyclic compound-containing vinyl compound monomers such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole The unit obtained by polymerizing is mentioned. The proportion of these units in the water-soluble polymer is preferably 0% by mass to 10% by mass, more preferably 0% by mass to 5% by mass.

  The 1% aqueous solution viscosity of the water-soluble polymer is preferably 10 to 10,000 mPa · s. Here, the 1% aqueous solution viscosity of the water-soluble polymer refers to a viscosity measured at 23 ° C. and pH 8.

  Moreover, the solution viscosity when adjusting a 1% aqueous solution of a water-soluble polymer at pH 8 is more preferably 10 to 10,000 mPa · s, more preferably 20 to 8,000 mPa · s, and particularly preferably 30 to. It is in the range of 5,000 mPa · s. If the solution viscosity is too high, the adhesion of the negative electrode active material layer to the current collector may be reduced, and if it is too low, the flexibility of the negative electrode active material layer may be reduced.

  The weight average molecular weight of the water-soluble polymer is preferably 100 or more, more preferably 500 or more, particularly preferably 1000 or more, preferably 500,000 or less, more preferably 250,000 or less, and particularly preferably 100,000 or less. The weight average molecular weight of the water-soluble polymer is 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 by gel permeation chromatography (GPC). As long as you ask.

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

Production of water-soluble polymer As a method for producing a water-soluble polymer, a monomer mixture containing the monomers constituting the water-soluble polymer in a predetermined ratio is polymerized in an aqueous solvent to obtain a polymer. The method of alkalizing to pH 7-13 is mentioned.

  The aqueous solvent is not particularly limited as long as it can dissolve or disperse the monomer mixture and the resulting water-soluble polymer, and usually has a boiling point of 80 to 350 ° C. at normal pressure such as water. Preferably, it is selected from a dispersion medium at 100 to 300 ° C. In addition, the number in parentheses after the name of the following exemplified dispersion medium is the boiling point (unit: ° C) at normal pressure, and the value after the decimal point is rounded off or rounded down. For example, diacetone alcohol (169), γ-butyrolactone (204) as ketones; ethyl alcohol (78), isopropyl alcohol (82), normal propyl alcohol (97) as alcohols; ethylene as glycols Glycol (193), propylene glycol (188), diethylene glycol (244); glycol ethers include propylene glycol monomethyl ether (120), methyl cellosolve (124), ethyl cellosolve (136), ethylene glycol tertiary butyl ether (152) , Butyl cellosolve (171), 3-methoxy-3-methyl-1-butanol (174), ethylene glycol monopropyl ether (150), diethylene glycol monobutyl pyrute (230), triethylene glycol monobutyl ether (271), dipropylene glycol monomethyl ether (188); ethers include 1,3-dioxolane (75), 1,4-dioxolane (101), and tetrahydrofuran (66) Can be mentioned. Among these, water is most preferable because it is not flammable and the polymer-containing aqueous solution can be used for slurry production without solvent substitution after the production of the water-soluble polymer. In addition, water may be used as the main solvent, and an aqueous solvent other than the above-described water may be mixed and used within a range in which the dissolved state of the water-soluble polymer can be ensured.

  The polymerization method is an emulsion polymerization method, and examples of the polymerization reaction include ionic polymerization, radical polymerization, and living radical polymerization. In the emulsion polymerization method, for example, water, an additive such as a dispersant and an emulsifier, an 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, and the temperature is increased while stirring. This is a method for initiating polymerization.

  An emulsifier, a dispersant, a polymerization initiator, and the like are generally used in these polymerization methods, and the amount used may be a generally used amount.

The polymerization temperature and polymerization time can be arbitrarily selected depending on the polymerization method and the type of polymerization initiator used, but the polymerization temperature is usually about 30 ° C. or higher and the polymerization time is about 0.5 to 30 hours. Additives such as amines can also be used as polymerization aids. Further, the polymer solution obtained by these methods is added to alkali metal (Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium compound (NH ₄ Cl, etc.), organic amine compound (ethanolamine, diethylamine). Etc.) can be adjusted by adding a basic aqueous solution in which pH is 5 to 10, preferably 5 to 9. The pH adjustment with the alkali metal hydroxide is preferable because the binding property (peel strength) between the current collector and the active material is improved by the water-soluble polymer.

  The water-soluble polymer described above may be a mixture of two or more types of polymers. The polymer mixture can also be obtained by a method (two-stage polymerization method) in which at least one monomer component is polymerized by a conventional method, and then at least one other monomer component is added and polymerized by a conventional method. it can.

  Examples of the polymerization initiator used for polymerization include lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butyl peroxypivalate, 3,3,5-trimethylhexanoyl peroxide, and the like. Organic peroxides, azo compounds such as α, α′-azobisisobutyronitrile, ammonium persulfate, potassium persulfate, and the like.

  In the polymerization, a chain transfer agent may be added. The chain transfer agent is preferably an alkyl mercaptan, specifically, n-butyl mercaptan, t-butyl mercaptan, n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan. , N-stearyl mercaptan. Among these, n-octyl mercaptan and t-dodecyl mercaptan are preferable from the viewpoint of good polymerization stability.

  In addition, other chain transfer agents may be used in combination with the alkyl mercaptan. Examples of chain transfer agents that may be used in combination include terpinolene, allyl alcohol, allylamine, sodium allyl sulfonate (potassium), and sodium methallyl sulfonate (potassium). The amount of the chain transfer agent used is not particularly limited as long as the effect of the present invention is not hindered.

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

Content of water-soluble polymer The content of the water-soluble polymer in the slurry composition for a negative electrode of the lithium ion secondary battery of the present invention is not particularly limited, but is preferably 0 with respect to 100 parts by mass of the negative electrode active material described later. 0.1 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, and particularly preferably 1 to 10 parts by mass. If the ratio of the water-soluble polymer is too small, the adhesion between the current collector and the negative electrode active material layer will be reduced, and the negative electrode active material will fall off due to expansion and contraction of the negative electrode active material layer during charge and discharge, resulting in output characteristics. May be damaged. On the other hand, when the ratio of the water-soluble polymer is excessive, the amount of the negative electrode active material in the negative electrode active material layer is relatively decreased, and the output characteristics may be deteriorated.

(Negative electrode active material)
The slurry composition for a negative electrode of a lithium ion secondary battery of the present invention comprises a negative electrode active material in addition to the water-soluble polymer and water as a solvent or a dispersion medium. The negative electrode active material is a material that transfers electrons in the negative electrode for a secondary battery. Examples of the negative electrode active material include a carbon material-based active material and an alloy-based active material.

  The carbon material-based active material refers to an active material having carbon as a main skeleton into which lithium can be inserted, and specifically includes a carbonaceous material and a graphite material. The carbonaceous material generally indicates a carbon material having a low graphitization (low crystallinity) obtained by heat-treating (carbonizing) a carbon precursor at 2000 ° C. or less, and the graphitic material is a graphitizable carbon at 2000 ° C. A graphitic material having high crystallinity close to that of the graphite obtained by heat treatment as described above will be shown.

  Examples of the carbonaceous material include graphitizable carbon that easily changes the carbon structure depending on the heat treatment temperature, and non-graphitic carbon having a structure close to an amorphous structure typified by glassy carbon.

  Examples of graphitizable carbon include carbon materials made from tar pitch obtained from petroleum and coal, such as coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, pyrolytic vapor-grown carbon fibers, etc. Is mentioned. MCMB is a carbon fine particle obtained by separating and extracting mesophase spherules produced in the process of heating pitches at around 400 ° C., and mesophase pitch-based carbon fiber is a mesophase pitch obtained by growing and coalescing the mesophase spherules. Is a carbon fiber made from a raw material.

  Examples of the non-graphitizable carbon include phenol resin fired bodies, polyacrylonitrile-based carbon fibers, pseudo-isotropic carbon, and furfuryl alcohol resin fired bodies (PFA).

Examples of the graphite material include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite heat-treated at 2800 ° C. or higher, graphitized MCMB heat-treated MCMB at 2000 ° C. or higher, and graphitized mesophase pitch carbon fiber heat-treated at 2000 ° C. or higher. It is done.
Among these carbon-based active materials, a graphite material is preferable.

  The alloy-based active material refers to an active material that contains an element into which lithium can be inserted and has a theoretical electric capacity per mass of 500 mAh / g or more when lithium is inserted. A single metal forming a lithium alloy and an alloy thereof, and oxides, sulfides, nitrides, silicides, carbides, phosphides, and the like thereof are used.

  Examples of single metals and alloys forming lithium alloys include compounds containing metals such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, and Zn. Is mentioned. Among these, silicon (Si), tin (Sn) or lead (Pb) simple metals, alloys containing these atoms, or compounds of these metals are used.

The alloy-based active material may further contain one or more nonmetallic elements. Specifically, for example, SiC, SiO _x C _y (hereinafter referred to as “Si—O—C”) (0 <x ≦ 3, 0 <y ≦ 5), Si ₃ N ₄ , Si ₂ N ₂ O, Examples thereof include SiO _x (0 <x ≦ 2), SnO _x (0 <x ≦ 2), LiSiO, LiSnO, etc. Among them, SiO _x C _y capable of inserting and releasing lithium at a low potential is preferable. For example, SiO _x C _y can be obtained by firing a polymer material containing silicon. Among SiO _x C _y , the range of 0.8 ≦ x ≦ 3 and 2 ≦ y ≦ 4 is preferably used in view of the balance between capacity and cycle characteristics.

  Examples of oxides, sulfides, nitrides, silicides, carbides, and phosphides include oxides, sulfides, nitrides, silicides, carbides, and phosphides of elements into which lithium can be inserted. Oxides are particularly preferred. Specifically, an oxide such as tin oxide, manganese oxide, titanium oxide, niobium oxide, vanadium oxide, or a lithium-containing metal composite oxide material containing a metal element selected from the group consisting of Si, Sn, Pb, and Ti atoms is used. It has been. Examples of the silicon oxide include materials such as silicon carbide (Si—O—C).

As the lithium-containing metal composite oxide, a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ (0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, 0 ≦ z ≦ 1.6, M includes Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb), among which Li _4/3 Ti _5/3 O ₄ , Li1Ti ₂ O ₄ and Li _4/5 Ti _11/5 O ₄ are used.

Among these, a material containing silicon is preferable, and SiC, SiO _x (0 <x ≦ 2), and Si—O—C are more preferable. In this compound, it is presumed that insertion / extraction of Li to / from Si (silicon) occurs at a high potential and C (carbon) at a low potential, and expansion / contraction is suppressed as compared with other alloy-based active materials.

  In the present invention, carbon materials and silicon-containing materials are preferable, and graphite materials and Si—O—C are particularly preferable. In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together. The shape of the negative electrode active material is preferably a granulated particle. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.

  In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together. When used in combination, a combination of a graphite material and a silicon-containing material is preferred. The blending ratio (graphitic material / silicon-containing material) is preferably 99/1 to 40/60, more preferably 95/5 to 45/55, by weight. The shape of the negative electrode active material is preferably a granulated particle. When the shape of the particles is spherical, a higher density electrode can be formed during electrode molding.

  The volume average particle diameter of the negative electrode active material is appropriately selected in consideration of other constituent requirements of the battery, but is usually 0.1 to 100 μm, preferably 1 to 50 μm, more preferably 5 to 40 μm. Further, the 50% volume cumulative diameter of the negative electrode active material is usually 1 to 50 μm, preferably 15 to 30 μm, from the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and cycle characteristics. The volume average particle diameter is determined by measuring the particle size distribution by laser diffraction. The 50% volume cumulative diameter is a 50% volume average particle diameter calculated by measuring with a laser diffraction particle size distribution analyzer (SALD-3100; manufactured by Shimadzu Corporation).

The tap density of the negative electrode active material is not particularly limited, but 0.6 g / cm ³ or more is preferably used.

The BET specific surface area of the negative electrode active material is preferably 3 to 20 m ² / g, more preferably 3 to 15 m ² / g, and particularly preferably 3 to 10 m ² / g. When the BET specific surface area of the negative electrode active material is in the above range, the active points on the surface of the negative electrode active material are increased, so that the low-temperature output characteristics of the secondary battery are excellent.

(Dispersion medium)
In the present invention, water is used as a dispersion medium for the slurry. In the present invention, a hydrophilic solvent may be mixed with water as a dispersion medium as long as the dispersion stability of the slurry composition is not impaired and the working environment hygiene is not adversely affected. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and the amount is preferably 5% by mass or less based on water.

  The slurry composition for a lithium ion secondary battery negative electrode of the present invention may contain a binder, a conductive material, a thickener, and other additives in addition to the above components as long as the object of the present invention is not impaired. Good.

(binder)
The binder is not particularly limited as long as it is a compound that can bind the negative electrode active materials to each other and has adhesion to the current collector, but is preferably a particulate binder. The binder has the property of binding the negative electrode active materials to each other in the negative electrode active material layer, or binding the negative electrode active material and the current collector. Among them, the negative electrode active material can be obtained by using a particulate binder. Thus, the adhesion of the negative electrode active material layer to the current collector can be enhanced. Further, by using the particulate binder, particles other than the negative electrode active material contained in the negative electrode active material layer can be bound, and the role of maintaining the strength of the negative electrode active material layer can also be achieved.

  The particulate binder is not particularly limited as long as it is present in a state in which the particle shape is maintained in the slurry, but the negative electrode active material layer is preferably one that can be present in a state in which the particle shape is retained. In the present invention, the “state in which the particle state is maintained” does not have to be a state in which the particle shape is completely maintained, and may be in a state in which the particle shape is maintained to some extent.

  Usually, the polymer forming the particulate binder is water-insoluble. Therefore, the particulate binder is usually in the form of particles in the slurry composition for producing the electrode, and is contained in the secondary battery electrode while maintaining the particle shape.

  Examples of the particulate binder include those in which polymer particles of the binder such as latex are dispersed in water, and powders obtained by drying such a dispersion.

  The particulate binder is preferably water-insoluble, that is, dispersed in a particulate form without being dissolved in an aqueous solvent. Specifically, being water-insoluble means that when 0.5 g of the binder is dissolved in 100 g of water at 25 ° C., the insoluble content becomes 90% by mass or more.

  Examples of the polymer constituting the binder include polymer compounds such as fluoropolymers, diene polymers, acrylate polymers, polyimides, polyamides, polyurethane polymers, and fluorine polymers, diene polymers, or acrylate polymers. A diene polymer or an acrylate polymer is more preferable.

  The diene polymer is a polymer containing a structural unit obtained by polymerizing a conjugated diene monomer (hereinafter sometimes referred to as “conjugated diene monomer unit”). A homopolymer or a copolymer obtained by polymerizing a monomer mixture containing a conjugated diene monomer, or a hydrogenated product thereof.

  Examples of the conjugated diene monomer include 1,3-butadiene, isoprene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like. . These conjugated dienes can be used alone or in combination of two or more. The ratio of the conjugated diene monomer unit in the diene polymer is preferably 20% by mass to 60% by mass, and preferably 30% by mass to 55% by mass.

  The diene polymer may contain other monomer units copolymerizable with the conjugated diene monomer.

  Other monomers constituting other monomer units include ethylenically unsaturated carboxylic acid monomers, aromatic vinyl monomers, vinyl cyanide monomers, unsaturated carboxylic acid alkyl ester monomers And unsaturated monomers containing a hydroxyalkyl group, unsaturated carboxylic acid amide monomers, and the like. These other monomers can be used alone or in combination of two or more. Among these, an ethylenically unsaturated carboxylic acid monomer, an aromatic vinyl monomer, and a vinyl cyanide monomer are preferable.

Examples of ethylenically unsaturated carboxylic acid monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, and anhydrides thereof. And so on. Among these, an ethylenically unsaturated dicarboxylic acid monomer is preferable, and itaconic acid is particularly preferable.
The content ratio of the ethylenically unsaturated carboxylic acid monomer unit in the diene polymer is preferably 0.5% by mass or more, more preferably 2% by mass or more, particularly preferably 3% by mass or more, preferably 10%. It is not more than mass%, more preferably not more than 7.5 mass%, particularly preferably not more than 5.0 mass%.

  Examples of the aromatic vinyl monomer include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. Of these, styrene is preferred.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, Examples include monomethyl fumarate, monoethyl fumarate, and 2-ethylhexyl acrylate.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, and N, N-dimethylacrylamide.

  Examples of the unsaturated monomer containing a hydroxyalkyl group include hydroxyalkyl acrylates such as 2-hydroxyethyl acrylate, 2-hydroxy methacrylate, and 2-hydroxypropyl acrylate.

  The total content of other copolymerizable monomers in the diene polymer is preferably 40% by mass to 80% by mass, and preferably 45% by mass to 70% by mass.

  The acrylate polymer is a polymer containing a structural unit obtained by polymerizing a (meth) acrylic acid ester monomer (hereinafter sometimes referred to as “(meth) acrylic acid ester monomer unit”). . Specifically, it is a copolymer obtained by polymerizing a homopolymer of a (meth) acrylate monomer or a monomer mixture containing a (meth) acrylate monomer. In the present invention, (meth) acrylic acid ester refers to acrylic acid ester and / or methacrylic acid ester.

  Examples of acrylic acid ester monomers include ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-amyl acrylate, isoamyl acrylate, and n-acrylate. -Hexyl, 2-ethylhexyl acrylate, hexyl acrylate, nonyl acrylate, lauryl acrylate, stearyl acrylate and the like. Examples of methacrylic acid esters include ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-amyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, Examples include 2-ethylhexyl methacrylate, octyl methacrylate, isodecyl methacrylate, lauryl methacrylate, tridecyl methacrylate, stearyl methacrylate, and the like. Among these, acrylic acid esters are preferable, and n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferable in that the strength of the obtained electrode can be improved. The content ratio of the (meth) acrylic acid ester monomer unit in the acrylate polymer is preferably 50% by mass or more, more preferably 60% by mass or more, preferably 95% by mass or less, more preferably 90% by mass. It is as follows. When the content ratio of the (meth) acrylic acid ester monomer unit in the acrylate polymer is in the above range, the heat resistance is high, and the internal resistance of the obtained electrode can be reduced.

The acrylate polymer may contain other monomer units copolymerizable with the (meth) acrylic acid ester monomer.
Examples of other monomers constituting other monomer units include ethylenically unsaturated carboxylic acid monomers and vinyl cyanide monomers.

  Examples of ethylenically unsaturated carboxylic acid monomers include ethylenically unsaturated monocarboxylic acids such as acrylic acid, methacrylic acid, and crotonic acid; ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, and itaconic acid, and anhydrides thereof. And so on. Of these, acrylic acid, methacrylic acid, and itaconic acid are particularly preferable.

  The content of the ethylenically unsaturated carboxylic acid monomer unit in the acrylate polymer is preferably 0.1% by mass or more, more preferably 0.5% by mass or more, and particularly preferably 1% by mass or more. Is 50% by mass or less, more preferably 20% by mass or less, and particularly preferably 10% by mass or less. When the ratio of the ethylenically unsaturated carboxylic acid monomer unit in the acrylate polymer is within this range, the binding property can be improved and the electrode strength can be improved.

Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, and α-ethylacrylonitrile.
The content ratio of the vinyl cyanide monomer unit in the acrylate polymer is preferably 3% by mass or more, more preferably 5% by mass or more, preferably 40% by mass or less, more preferably 30% by mass or less.

  Furthermore, the acrylate polymer may contain an arbitrary structural unit other than those described above. These arbitrary structural units are structural units obtained by polymerizing a monomer copolymerizable with the above-described monomer. Monomers copolymerizable with the above-mentioned monomers include carboxylic acid esters having two or more carbon-carbon double bonds such as ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, and trimethylolpropane triacrylate; styrene Aromatic vinyl monomers such as chlorostyrene, vinyl toluene, t-butyl styrene, vinyl benzoic acid, methyl vinyl benzoate, vinyl naphthalene, chloromethyl styrene, hydroxymethyl styrene, α-methyl styrene, divinyl benzene; Unsaturated carboxylic acid amide monomers such as N-methylolacrylamide and acrylamide-2-methylpropanesulfonic acid; olefins such as ethylene and propylene; diene monomers such as butadiene and isoprene; vinyl chloride and salts Monomers containing halogen atoms such as vinylidene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl butyrate and vinyl benzoate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl biether; methyl vinyl ketone and ethyl vinyl ketone , Vinyl ketones such as butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine, and vinyl imidazole. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the arbitrary structural unit in the acrylate polymer is limited to a range in which the amount of the (meth) acrylic acid ester monomer unit in the acrylate polymer is usually 50% by mass or more, preferably 60% by mass or more. It is desirable.

  The glass transition temperature (Tg) of the binder is preferably 50 ° C. or lower, more preferably −40 to 0 ° C. When the glass transition temperature (Tg) of the binder is within this range, the binding property is excellent with a small amount of use, the binding property between the current collector and the negative electrode active material layer is excellent, the electrode strength is strong, and the flexibility is achieved. It is rich, and the electrode density can be easily increased by a pressing process during electrode formation.

  When the binder is in the form of particles, the number average particle diameter is not particularly limited, but is usually 0.01 to 1 μm, preferably 0.03 to 0.8 μm, more preferably 0.05 to 0. .5 μm. When the number average particle diameter is in this range when the binder is in the form of particles, an excellent binding force can be imparted to the negative electrode active material layer even with a small amount of use. Here, the number average particle diameter is a number average particle diameter calculated as an arithmetic average value obtained by measuring the diameter of 100 binder particles randomly selected in a transmission electron micrograph. The shape of the particles can be either spherical or irregular. These binders can be used alone or in combination of two or more.

  The production method of the binder is not particularly limited, but can be obtained by emulsion polymerization of monomer mixtures containing monomers constituting each copolymer. The method for emulsion polymerization is not particularly limited, and a conventionally known emulsion polymerization method may be employed.

  The dispersion medium, the polymerization initiator, the chain transfer agent, the surfactant, the emulsifier, and the like used for the emulsion polymerization are generally used in these polymerization methods, and the amount used may be a generally used amount.

  When a binder is added to the slurry composition for a negative electrode of a lithium ion secondary battery, the content ratio is not particularly limited, but is preferably 0.1 to 10 parts by weight, more preferably 100 parts by weight of the negative electrode active material. The range is 0.2 to 8 parts by mass, particularly preferably 0.5 to 5 parts by mass. When the blending amount of the binder is excessive, the binding property is improved, but the ratio of the water-soluble polymer is relatively decreased, and the effect of the present invention may be impaired.

  In the slurry composition for secondary battery negative electrode of the present invention, the total content of the negative electrode active material, the water-soluble polymer, and the binder used as necessary is preferably 10 with respect to 100 parts by mass of the slurry composition. It is -90 mass parts, More preferably, it is 30-80 mass parts. Further, the content of the water-soluble polymer and the binder (solid content equivalent amount) relative to the total amount of the negative electrode active material is preferably 0.1 to 20 parts by mass, more preferably 100 parts by mass of the total amount of the negative electrode active material. Is 0.5 to 15 parts by mass. When the content of the negative electrode active material, the water-soluble polymer, and the binder in the slurry composition is within the above range, the viscosity of the obtained secondary battery negative electrode slurry composition is optimized so that the coating can be performed smoothly. In addition, sufficient adhesion strength can be obtained without increasing the resistance of the obtained negative electrode. As a result, peeling of the negative electrode active material layer from the current collector in the electrode plate pressing step can be suppressed.

(Other ingredients)
(Conductive material)
The slurry composition of the present invention preferably contains a conductive material. As the conductive material, conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube can be used. By containing a conductive material, electrical contact between the negative electrode active materials can be improved, and when used in a secondary battery, the discharge rate characteristics can be improved. When mix | blending a electrically conductive material, content of the electrically conductive material in a slurry composition becomes like this. Preferably it is 1-20 mass parts with respect to 100 mass parts of negative electrode active materials, More preferably, it is 1-10 mass parts.

(Thickener)
In the slurry composition for a secondary battery negative electrode of the present invention, a viscosity of the slurry may be adjusted by blending a thickener separately from the water-soluble polymer. Examples of thickeners include cellulose polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof;
(Modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof;
(Modified) Polyvinyl alcohols such as polyvinyl alcohol, a copolymer of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or a copolymer of maleic acid or fumaric acid and vinyl alcohol;
Examples include polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches.

  When using a thickener, the compounding quantity has preferable 0.5-1.5 mass parts with respect to 100 mass parts of negative electrode active materials. When the blending amount of the thickener is within the above range, the coating property and the adhesion with the current collector are good. In the present specification, “(modified) poly” means “unmodified poly” or “modified poly”.

  In addition to the above components, the slurry composition for secondary battery negative electrode may further contain other components such as a reinforcing material, a leveling agent, and an electrolyte additive having a function of inhibiting electrolyte decomposition, It may be contained in a negative electrode for a secondary battery described later. These are not particularly limited as long as they do not affect the battery reaction.

  As the reinforcing material, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible negative electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. Content of the reinforcing material in a slurry composition is 0.01-20 mass parts normally with respect to 100 mass parts of negative electrode active materials, Preferably it is 1-10 mass parts. By being included in the above range, high capacity and high load characteristics are exhibited.

  Examples of the leveling agent include surfactants such as alkyl surfactants, silicone surfactants, fluorine surfactants, and metal surfactants. By mixing the leveling agent, the repelling that occurs during coating can be prevented and the smoothness of the negative electrode can be improved. The content of the leveling agent in the slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the leveling agent is in the above range, the productivity, smoothness, and battery characteristics during the production of the negative electrode are excellent. By containing the surfactant, the dispersibility of the negative electrode active material and the like in the slurry composition can be improved, and the smoothness of the negative electrode can be improved.

  As the electrolytic solution additive used in the slurry composition and the electrolytic solution, vinylene carbonate or the like can be used. The content of the electrolytic solution additive in the slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the electrolytic solution additive is in the above range, the cycle characteristics and the high temperature characteristics are excellent. Other examples include nanoparticles such as fumed silica and fumed alumina. By mixing the nanoparticles, the thixotropy of the slurry composition can be controlled, and the leveling property of the negative electrode can be improved. The content of the nanoparticles in the slurry composition is preferably 0.01 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material. When the nanoparticles are in the above range, the slurry stability and productivity are excellent, and high battery characteristics are exhibited.

  Furthermore, the slurry composition may contain additives such as anti-aging agents and preservatives. Examples of the antioxidant include amine-based antioxidants, phenol-based antioxidants, quinone-based antioxidants, organic phosphorus-based antioxidants, sulfur-based antioxidants, and phenothiazine-based antioxidants. Examples of the preservative include isothiazoline compounds and pyrithione compounds. When the slurry composition contains these components, the solid content concentration of these components in the composition is not particularly limited, but about 0.001 to 1% by mass is appropriate. Furthermore, the slurry composition may contain various dispersants used in preparing the water-soluble polymer and the binder.

(Production of slurry composition for secondary battery negative electrode)
The slurry composition for a secondary battery negative electrode is prepared by mixing the water-soluble polymer, water as a solvent or a dispersion medium, a negative electrode active material, and a binder used as necessary so as to have a predetermined solid content ratio. can get.

  The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

(2) Negative electrode for secondary battery The negative electrode for a secondary battery of the present invention comprises the above-described negative electrode active material, a water-soluble polymer, a binder used as necessary, and the like. The slurry composition for secondary battery negative electrode is obtained by applying and drying on a current collector.

(Method for producing secondary battery negative electrode)
Although the manufacturing method of the negative electrode for secondary batteries of this invention is not specifically limited, For example, the method of apply | coating and drying the said slurry composition to at least one surface of a collector, and forming a negative electrode active material layer is mentioned.

  The method for applying the slurry composition onto the current collector is not particularly limited. Examples of the method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is usually 5 to 50 minutes, and the drying temperature is usually 40 to 180 ° C.

  In producing the negative electrode for secondary battery of the present invention, the porosity of the negative electrode active material layer is lowered by pressure treatment using a die press or a roll press after applying and drying the slurry composition on the current collector. It is preferable to have the process to do. The preferable range of the porosity is 5 to 30%, more preferably 7 to 20%. 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, and the negative electrode active material layer is liable to be peeled off from the current collector, resulting in a defect.

  The thickness of the negative electrode active material layer in the negative electrode for secondary battery is usually 5 to 300 μm, preferably 30 to 250 μm. When the thickness of the negative electrode active material layer is in the above range, both load characteristics and cycle characteristics are high.

  The content ratio of the negative electrode active material in the negative electrode active material layer is preferably 85 to 99% by mass, more preferably 88 to 97% by mass. By making the content rate of a negative electrode active material into the said range, a softness | flexibility and a binding property can be shown, showing a high capacity | capacitance.

The density of the negative electrode active material layer of the negative electrode for a secondary battery is preferably 1.6 to 1.9 g / cm ³ , more preferably 1.65 to 1.85 g / cm ³ . When the density of the negative electrode active material layer is in the above range, a high-capacity battery can be obtained.

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

(3) Secondary battery The secondary battery of the present invention is a secondary battery comprising a positive electrode, a negative electrode, a separator and an electrolytic solution, and the negative electrode is the negative electrode for a secondary battery.

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

(Positive electrode active material)
As the positive electrode active material, an active material that can be doped and dedoped with lithium ions is used, and the positive electrode active material is roughly classified into an inorganic compound and an organic compound.

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

Examples of transition metal oxides include MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O. ₅ , V ₆ O _{13 and the} like,
Among these, MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ are preferable from the viewpoint of cycle stability and capacity. The transition metal _sulfide, TiS _2, TiS _3, amorphous _MoS 2, FeS, and the like. Examples of the lithium-containing composite metal oxide include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

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

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

  The volume average particle diameter of the positive electrode active material is usually 0.01 to 50 μm, preferably 0.05 to 30 μm. When the volume average particle diameter is in the above range, the amount of the binder composition for the positive electrode when preparing the slurry composition for the positive electrode described later can be reduced, the decrease in the capacity of the battery can be suppressed, and for the positive electrode It becomes easy to prepare the slurry composition to have a viscosity suitable for application, and a uniform electrode can be obtained.

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

(Binder composition for secondary battery positive electrode)
The binder composition for a lithium secondary battery positive electrode is not particularly limited and a known one can be used. For example, resins such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, secondary battery negative electrodes A polymer such as an acrylic polymer or a diene polymer, which is preferably used as a particulate binder in the slurry composition for use, can be used. These may be used alone or in combination of two or more.

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

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

The thickness of the positive electrode active material layer is usually 5 to 300 μm, preferably 10 to 250 μm. When the thickness of the positive electrode active material layer is in the above range, both load characteristics and energy density are high.
The positive electrode can be produced in the same manner as the above-described negative electrode for secondary battery.

(Separator)
The separator is a porous substrate having pores, and usable separators include (a) a porous separator having pores, and (b) a porous separator having a polymer coating layer formed on one or both sides. Or (c) a porous separator in which a porous resin coat layer containing an inorganic ceramic powder is formed. These non-limiting examples include polypropylene, polyethylene, polyolefin or aramid porous separators, polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile or polyvinylidene fluoride hexafluoropropylene copolymers. Examples include a separator having a molecular film and a coat layer, or a separator coated with a porous film layer made of an inorganic filler or a dispersant for inorganic filler.

(Electrolyte)
The electrolytic solution used in the present invention is not particularly limited. For example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. These can be used alone or in admixture of two or more. The amount of the supporting electrolyte is usually 1% by mass or more, preferably 5% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the battery are degraded.

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

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

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

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

(1) Method for Measuring Viscosity of 1% Aqueous Solution of Water-Soluble Polymer A water-soluble polymer produced in Examples and Comparative Examples was prepared by using a 10% sodium hydroxide aqueous solution and ion-exchanged water, pH 8) was prepared. The viscosity of this aqueous solution at 25 ° C. and 60 rpm was measured with a B-type viscometer.

(2) Adhesiveness Negative electrodes manufactured in 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, and the said average value was made into peel strength (N / m). The higher the peel strength, the greater the binding force of the negative electrode active material layer to the current collector, that is, the higher the adhesion strength.

(3) Dispersion stability The slurry compositions for negative electrodes produced in Examples and Comparative Examples were measured for a viscosity η0 of 60 rpm at room temperature (25 ° C) using a B-type viscometer, and the slurry composition was measured at room temperature (25 C.) for 72 hours, and the viscosity η1 at 60 rpm after storage was measured at room temperature (25 ° C.). Δη (%) = η1 / η0 × 100 is calculated, and the smaller this value, the better the dispersion stability.

(4) Coatability The negative electrode slurry composition produced in Examples and Comparative Examples was applied on a 20 μm thick copper foil as a current collector so that the film thickness after drying was about 150 μm. , Dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode. The obtained negative electrode was cut out with a size of 100 cm × 100 cm, and the number of pinholes having a diameter of 0.1 mm or more was visually measured. The smaller the number of pinholes, the better the coatability.

(5) 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 for 24 hours in an environment at 25 ° C, and then 4.2 V in an environment at 25 ° C. The charge / discharge operation was performed at a charge rate of 1 C, a discharge rate of 3.0 V, and 1 C, and the initial capacity C0 was measured. Furthermore, in a 60 ° C. environment, charging and discharging were repeated with one cycle from charging to discharging under the above conditions, and the capacity C2 after 1000 cycles was measured. The high temperature cycle characteristics are evaluated by a capacity retention ratio represented by ΔC = C2 / C0 × 100 (%), and the higher this value, the better the high temperature cycle characteristics.

(6) High-temperature storage characteristics After the lithium-ion secondary battery of the laminate type cell produced in the examples and comparative examples was allowed to stand for 24 hours in an environment at 25 ° C, 4.2V under an environment at 25 ° C, The charge / discharge operation was performed at a charge rate of 0.1 C, a discharge rate of 3.0 V, and 0.1 C, and the initial capacity C0 was measured. Furthermore, after charging to 4.2V in a 25 ° C. environment and storing it in a 60 ° C. environment for 30 days, the charge / discharge operation was performed at a discharge rate of 3.0V and 0.1C in a 25 ° C. environment. The capacity C1 after high temperature storage was measured. The high temperature storage characteristics are evaluated by a capacity retention ratio represented by ΔC = C1 / C0 × 100 (%), and the higher this value, the better the high temperature storage characteristics.

(7) Output characteristics After the lithium ion secondary battery of the laminate type cell produced in the Example and the comparative example was allowed to stand for 24 hours in an environment of 25 ° C, 4.2V, 1C in an environment of 25 ° C The charging operation was performed at a charging rate of. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., and the voltage V 15 seconds after the start of discharge was measured. The output characteristic is evaluated by a voltage change represented by ΔV = 4.2 V−V, and the smaller this value is, the better the output characteristic is.

Example 1
(1-1. Production of water-soluble polymer)
In a 5 MPa pressure vessel with a stirrer, 35 parts of methacrylic acid (ethylenically unsaturated carboxylic acid monomer), 0.8 part of ethylene dimethacrylate (crosslinkable monomer), 2,2,2-trifluoroethyl methacrylate (fluorine) Containing (meth) acrylic acid ester monomer) 10 parts, 10 parts of an unsaturated polyalkylene glycol ether monomer obtained by adding an average of 50 moles of ethylene oxide to 3-methyl-3-buten-1-ol, ethyl acrylate ( 45 parts of other monomers), 0.6 parts of sodium dodecylbenzenesulfonate as a surfactant, 0.6 parts of t-dodecyl mercaptan, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate (polymerization initiator) A portion was added and stirred sufficiently, and then heated to 60 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a water-soluble polymer. 10% aqueous ammonia was added to the mixture containing the water-soluble polymer to adjust the pH to 8 to obtain an aqueous solution containing the desired water-soluble polymer. A 1% aqueous solution (pH 8) of the water-soluble polymer was prepared from the obtained aqueous solution containing the water-soluble polymer using a 10% aqueous sodium hydroxide solution and ion-exchanged water, and the viscosity was measured. The results are shown in Table 1.

(1-2. Production of particulate binder)
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63 parts of styrene, 4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and persulfuric acid as a polymerization initiator After adding 0.5 part of potassium and stirring sufficiently, it heated to 50 degreeC and superposition | polymerization was started. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate binder (SBR). After adding 5% aqueous sodium hydroxide solution to the mixture containing the particulate binder and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C. or lower to obtain a desired content. An aqueous dispersion containing a particulate binder was obtained.

(1-3. Production of slurry composition for negative electrode)
100 parts of artificial graphite (average particle size: 24.5 μm) having a specific surface area of 5.5 m ² / g as a negative electrode active material in a planetary mixer with a disper, 1 of the water-soluble polymer produced in (1-1) above 3 parts of an aqueous solution corresponding to a solid content was added, and the solid content concentration was adjusted to 65% with ion-exchanged water, followed by mixing at 25 ° C. for 60 minutes. Next, after adjusting to 60% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the liquid mixture was obtained.

  To the above mixed liquid, 1.0 part of the aqueous dispersion containing the particulate binder obtained in (1-2) above in an amount corresponding to the solid content and ion-exchanged water are added so that the final solid content concentration becomes 56%. And mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for negative electrode having good fluidity. The dispersion stability and coating property of the obtained negative electrode slurry were evaluated. The results are shown in Table 1.

(1-4. Production of negative electrode)
The slurry composition for negative electrode obtained in (1-3) above was applied on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying was about 150 μm. , Dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, the negative electrode original fabric was obtained by heat-processing at 120 degreeC for 2 minute (s). 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.
The adhesion strength of the obtained negative electrode was measured. The results are shown in Table 1.

(1-5. Production of positive electrode)
As a binder for the positive electrode, 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. The acrylate polymer is a copolymer obtained by emulsion polymerization of a monomer mixture containing 78% by mass of 2-ethylhexyl acrylate, 20% by mass of acrylonitrile, and 2% by mass of methacrylic acid.

100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as a positive electrode active material, ₂ parts of carbon black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and 1% aqueous solution of carboxymethyl cellulose as a dispersant ( Daiichi Kogyo Seiyaku Co., Ltd. “BSH-12”) mixed with 1 part of solid content, 5 parts of 40% aqueous dispersion of the above acrylate polymer as a binder, and ion-exchanged water did. The amount of ion-exchanged water was such that the total solid concentration was 40%. These were mixed by a planetary mixer to prepare a positive electrode slurry composition.

  The above slurry composition for positive electrode was applied with a comma coater onto an aluminum foil having a thickness of 20 μm as a current collector so that the film thickness after drying was about 200 μm and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. 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 raw material was rolled with a roll press to obtain a positive electrode having a positive electrode active material layer thickness of 90 μm.

(1-6. Preparation of separator)
A single-layer polypropylene separator (Celgard 2500, manufactured by Celgard) was cut into a 5 × 5 cm ² square.

(1-7. Lithium ion secondary battery)
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained in the above (1-5) was cut into a square of 4 × 4 cm ² and arranged so that the current collector-side surface was in contact with the aluminum packaging exterior. The square separator obtained in (1-6) above was placed on the surface of the positive electrode active material layer of the positive electrode. Furthermore, the negative electrode obtained in the above (1-4) was cut into a square of 4.2 × 4.2 cm ² and arranged on the separator so that the surface on the negative electrode active material layer side faces the separator. An electrolyte solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF6 at a concentration of 1 M) is injected so that no air remains, and the opening of the aluminum packaging material is sealed. For this purpose, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured. Using the obtained lithium ion secondary battery, high-temperature cycle characteristics, high-temperature storage characteristics, and output characteristics were evaluated. The results are shown in Table 1.

(Examples 2 to 5 and 9, 10)
In Example 1-1 (1-1. Production of water-soluble polymer), ethylenically unsaturated carboxylic acid monomer, fluorine-containing (meth) acrylic acid ester monomer, unsaturated polyalkylene glycol ether monomer The same procedure as in Example 1 was conducted except that the blending amount of ethyl acrylate was changed as shown in Table 1. The results are shown in Table 1.

(Example 6)
Example 1 (1-1. Production of water-soluble polymer) was the same as Example 1 except that perfluorooctyl methacrylate was used instead of 2,2,2-trifluoroethyl methacrylate. The results are shown in Table 1.

(Example 7)
In Example 1-1 (1-1. Production of water-soluble polymer), instead of an unsaturated polyalkylene glycol ether monomer obtained by adding an average of 50 moles of ethylene oxide to 3-methyl-3-buten-1-ol. Then, the same procedure as in Example 1 was conducted except that an unsaturated polyalkylene glycol ether monomer obtained by adding an average of 25 moles of ethylene oxide to 3-methyl-3-buten-1-ol was used. The results are shown in Table 1.

(Example 8)
In Example 1-1 (1-1. Production of water-soluble polymer), instead of an unsaturated polyalkylene glycol ether monomer obtained by adding an average of 50 moles of ethylene oxide to 3-methyl-3-buten-1-ol. The same procedure as in Example 1 was conducted, except that an unsaturated polyalkylene glycol ether monomer obtained by adding an average of 75 moles of ethylene oxide to 3-methyl-3-buten-1-ol was used. The results are shown in Table 1.

(Examples 11 and 12)
In Example 1 (1-3. Production of slurry composition for negative electrode), the same procedure as in Example 1 was conducted, except that 0.3 part or 18 parts of water-soluble polymer was added corresponding to the solid content. The results are shown in Table 1.

(Example 13)
90 parts of natural graphite (average particle diameter: 24.5 μm) having a BET specific surface area of 5.5 m ² / g and 10 parts of SiOC (average particle diameter: 10 μm) having a BET specific surface area of 6.5 m ² / g as the negative electrode active material The procedure was the same as in Example 1 except that it was used. The results are shown in Table 1.

(Example 14)
Example 1 was the same as Example 1 except that the particulate binder was not used. The results are shown in Table 1.

(Comparative Example 1)
(Production of slurry composition for negative electrode)
In a planetary mixer with a disper, 100 parts of artificial graphite (average particle size: 24.5 μm) having a specific surface area of 5.5 m ² / g as a negative electrode active material, 1% aqueous solution of carboxymethyl cellulose (manufactured by Nippon Paper Chemicals Co., Ltd., MAC350HC) One part was added in an amount corresponding to the solid content, and the solid content concentration was adjusted to 65% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, after adjusting to 60% of solid content concentration with ion-exchange water, it mixed for 15 minutes at 25 degreeC, and the liquid mixture was obtained.

  To the above mixed liquid, 1.0 part of the aqueous dispersion containing the particulate binder obtained in (1-2) above in an amount corresponding to the solid content and ion-exchanged water are added so that the final solid content concentration becomes 56%. And mixed for another 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode slurry composition.

  The procedure was the same as Example 1 except that the above negative electrode slurry composition was used. The results are shown in Table 1.

(Comparative Example 2)
In Example 1-1 (Production of water-soluble polymer), blending amount of unsaturated polyalkylene glycol ether monomer and ethyl acrylate without using fluorine-containing (meth) acrylate monomer Were changed as shown in Table 1 to obtain a water-soluble polymer.

  The procedure was the same as Example 1 except that the water-soluble polymer obtained above was used and no particulate binder was used. The results are shown in Table 1.

(Comparative Example 3)
The same procedure as in Example 1 was performed except that the water-soluble polymer obtained in Comparative Example 2 was used as the water-soluble polymer. The results are shown in Table 1.

(Comparative Example 4)
In Example 1-1 (1-1. Production of water-soluble polymer), the blending amounts of the unsaturated polyalkylene glycol ether monomer and ethyl acrylate were changed without using the fluorine-containing (meth) acrylate monomer. The water-soluble polymer was obtained by changing as shown in Table 1.

  The procedure was the same as Example 1 except that the water-soluble polymer obtained above was used. The results are shown in Table 1.

(Comparative Example 5)
In Example 1-1 (1-1. Production of water-soluble polymer), the blending amounts of the fluorine-containing (meth) acrylic acid ester monomer and ethyl acrylate were changed as shown in Table 1 to obtain a water-soluble polymer. It was.

  The procedure was the same as Example 1 except that the water-soluble polymer obtained above was used. The results are shown in Table 1.

  As can be seen from Table 1, according to the examples, it is possible to obtain a slurry having superior dispersion stability as compared with the comparative example, whereby the electrode obtained using the slurry is excellent in coatability and current collection. High adhesion between the body and the electrode active material layer is maintained. Furthermore, it was confirmed that the secondary battery using the electrode is excellent in durability and output characteristics.

Claims (7)

A slurry composition for a negative electrode of a lithium ion secondary battery comprising a negative electrode active material, a water-soluble polymer and water,
The water-soluble polymer is composed of an ethylenically unsaturated carboxylic acid monomer unit 20 to 50% by mass, a fluorine-containing (meth) acrylic acid ester monomer unit 0.1 to 30% by mass, and an unsaturated polyalkylene glycol ether type. It is a polymer containing 1 to 20% by mass of monomer units.
A slurry composition for a negative electrode of a lithium ion secondary battery.   The slurry composition for lithium ion secondary battery negative electrodes of Claim 1 whose 1-% aqueous solution viscosity of the said water-soluble polymer is 10-10000 mPa * s.   The slurry composition for a lithium ion secondary battery negative electrode according to claim 1 or 2, wherein the ethylenically unsaturated carboxylic acid monomer unit of the water-soluble polymer is an ethylenically unsaturated monocarboxylic acid monomer unit.   The slurry composition for a negative electrode of a lithium ion secondary battery according to any one of claims 1 to 3, wherein a content ratio of the water-soluble polymer is 0.1 to 20 parts by mass with respect to 100 parts by mass of the negative electrode active material.   Furthermore, the slurry composition for lithium ion secondary battery negative electrodes in any one of Claims 1-4 containing a particulate-form binder.   The negative electrode for lithium ion secondary batteries formed by apply | coating the slurry composition for lithium ion secondary battery negative electrodes in any one of Claims 1-5 on a collector, and drying.   The lithium ion secondary battery which consists of a negative electrode for lithium ion secondary batteries of Claim 6, a positive electrode, electrolyte solution, and a separator.