JP6044773B2 - Secondary battery positive electrode binder composition, secondary battery positive electrode slurry composition, secondary battery positive electrode and secondary battery - Google Patents

Description

  The present invention relates to a binder composition for a secondary battery positive electrode used for forming a positive electrode used in a secondary battery such as a lithium ion secondary battery.

  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.

  As a positive electrode active material that is a constituent material of a lithium ion secondary battery, an active material containing a transition metal such as iron, manganese, cobalt, chromium, and copper is used. When secondary batteries using these active materials are repeatedly charged and discharged, transition metal ions are eluted into the electrolytic solution, resulting in a decrease in battery capacity and cycle characteristics, which is a big problem.

  Another major problem is that transition metal ions eluted from the positive electrode are reduced and deposited on the negative electrode surface to form dendritic metal precipitates, which damage the separator, thereby reducing the safety of the battery. It is said that.

  An electrode used in a lithium ion secondary battery usually has a structure in which an electrode active material layer is laminated on a current collector. In addition to the electrode active material, the electrode active material layer includes a pair of electrode active materials. In order to bind the electrode active material and the current collector, a polymer binder (hereinafter sometimes referred to as “binder”) is used. An electrode is usually a slurry composition obtained by mixing an active material and, if necessary, a conductive agent such as conductive carbon, in a binder composition in which a polymer serving as a binder is dispersed or dissolved in a liquid medium such as water or an organic liquid. The slurry composition is applied to a current collector and dried.

As the polymer binder, a fluorine-based polymer such as polyvinylidene fluoride is particularly suitable as a positive electrode polymer binder, because it is difficult to dissolve in an organic electrolyte.
However, fluorine-based polymers such as polyvinylidene fluoride have weak adhesion to the current collector, and the battery capacity decreases as the electrical connection between the electrode active material layer and the current collector deteriorates during repeated charging and discharging. There was a problem to do. Further, when the amount of the fluorine-based polymer such as polyvinylidene fluoride is increased for the purpose of increasing the adhesive force with the current collector, there is a problem that the internal resistance of the battery increases and the capacity decreases.

In addition, it has been proposed to use a fluorine-based polymer such as polyvinylidene fluoride (PVDF) and hydrogenated acrylonitrile-butadiene rubber (H-NBR) (Patent Document 1 and Patent Document 2).
According to Patent Documents 1 and 2, it is exemplified that the cycle characteristics and output characteristics of the secondary battery are improved by using a binder containing PVDF and H-NBR.

Japanese Patent Laid-Open No. 9-63590 JP 2005-123047 A

  However, according to the study by the present inventors, in Patent Document 1, the binder content in the electrode active material layer is 2% by mass in order to increase the binding force of the binder to such an extent that sufficient cycle characteristics can be obtained. I found that it was necessary. In particular, when an electrode active material having a large specific surface area and a small particle diameter is used, a larger amount of binder is required because the area bound to the binder increases. As a result, the amount of the binder, which is an insulating component, increases, so that the resistance of the electrode increases, and both the output characteristics and cycle characteristics of the battery may be deteriorated.

Further, when the binder proposed in Patent Documents 1 and 2 is used, the dispersibility of the conductive agent and the electrode active material is insufficient, and the stability of the slurry composition forming the electrode active material layer is poor. It is difficult to obtain a simple electrode.
Furthermore, in the electrode using the binder proposed in Patent Documents 1 and 2, the binder swells with respect to the electrolyte solution and the electronic network is cut off at high temperature, resulting in an increase in the internal resistance of the electrode. The battery cycle characteristics, particularly the cycle characteristics at high temperatures (hereinafter sometimes referred to as “high temperature cycle characteristics”) may be deteriorated.

  In view of the above circumstances, the object of the present invention is to provide a binder composition exhibiting excellent electrolytic solution resistance, a slurry composition exhibiting excellent stability, a positive electrode having high flexibility, smoothness and binding properties, and an excellent high-temperature cycle. An object of the present invention is to provide a secondary battery having characteristics.

The gist of the present invention aimed at solving such problems is as follows.
[1] A binder containing a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and a linear alkylene polymer unit having 4 or more carbon atoms,
The binder composition for secondary battery positive electrodes whose content rate of the said aromatic vinyl polymerization unit is 5-50 mass%.

[2] The binder composition for a secondary battery positive electrode according to [1], wherein a content ratio of the polymer unit having the hydrophilic group is 0.05 to 20% by mass.

[3] The binder composition for a secondary battery positive electrode according to [1] or [2], wherein the content of the polymer unit having a nitrile group is 2 to 50% by mass.

[4] The binder composition for a secondary battery positive electrode according to any one of [1] to [3], wherein the iodine value of the binder is 3 to 60 mg / 100 mg.

[5] The binder composition for a secondary battery positive electrode according to any one of [1] to [4], wherein the binder has a glass transition temperature of 25 ° C. or lower.

[6] A secondary battery positive electrode slurry composition comprising the secondary battery positive electrode binder composition and the positive electrode active material according to any one of [1] to [5].

[7] A secondary battery positive electrode formed by forming a positive electrode active material layer made of the slurry composition for a secondary battery positive electrode according to [6] above on a current collector.

[8] A secondary battery having a positive electrode, a negative electrode, a separator, and an electrolyte solution, wherein the positive electrode is the secondary battery positive electrode according to [7].

[9] A method for producing a secondary battery positive electrode comprising a step of applying and drying the slurry composition for a secondary battery positive electrode according to [6] above on at least one surface of a current collector.

  Since the binder composition of the present invention has an excellent electrolyte swelling degree, battery characteristics such as high-temperature cycle characteristics in a secondary battery can be improved. Moreover, the slurry composition for forming a positive electrode active material layer has the outstanding stability by using the binder composition of this invention. In addition, since the positive electrode active material is uniformly dispersed in the positive electrode active material layer, a positive electrode having high smoothness and binding property can be obtained. As a result, the secondary battery using the positive electrode is excellent in high temperature cycle characteristics.

Secondary Battery Positive Electrode Binder Composition The secondary battery positive electrode binder composition of the present invention (sometimes referred to as “positive electrode binder composition”) contains a specific binder.

(binder)
The binder contains a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and a linear alkylene polymer unit having 4 or more carbon atoms. The polymer unit having a nitrile group refers to a structural unit formed by polymerizing a monomer having a nitrile group. The aromatic vinyl polymer unit means a structural unit formed by polymerizing an aromatic vinyl monomer. The polymerized unit having a hydrophilic group refers to a structural unit formed by polymerizing a monomer having a hydrophilic group. The linear alkylene polymer unit having 4 or more carbon atoms refers to a structural unit formed by polymerizing monomers capable of forming a linear alkylene polymer unit having 4 or more carbon atoms. The structural unit formed into a linear alkylene structure by hydrogenating at least one part of the carbon-carbon double bond of the structural unit formed by superposing | polymerizing the conjugated diene monomer of several or more. Here, the ratio of each polymerized unit in the binder usually corresponds to the ratio (preparation ratio) of the above-mentioned monomers capable of forming each polymerized unit in all monomers used for the polymerization of the binder. In addition, when forming a linear alkylene polymer unit having 4 or more carbon atoms by hydrogenation of a structural unit formed by polymerizing the conjugated diene monomer, the number of carbon atoms is 4 or more due to the hydrogenation reaction rate described later. The proportion of the linear alkylene polymer units is controlled. Accordingly, the ratio of monomers capable of forming a linear alkylene polymer unit having 4 or more carbon atoms (preparation ratio) is determined as follows: a polymer unit obtained by hydrogenating a structural unit formed by polymerizing a conjugated diene monomer in a binder; It corresponds to the ratio of the total of the polymer units not added.

  A secondary battery positive electrode slurry composition for forming a positive electrode active material layer by including a polymer unit having a nitrile group in the polymer constituting the binder (hereinafter referred to as “positive electrode slurry composition”). The dispersibility of the positive electrode active material in the medium is improved, and the positive electrode slurry composition can be stored in a stable state for a long period of time. As a result, a uniform positive electrode active material layer can be easily manufactured. Moreover, since the lithium ion conductivity is good, the internal resistance in the battery can be reduced, and the output characteristics of the battery can be improved.

  The content ratio of the polymer unit having a nitrile group is preferably 2 to 50% by mass, more preferably 10 to 30% by mass, and still more preferably 10 to 25% by mass. When the polymerization unit having a nitrile group in the binder is less than 2% by mass, it is added to N-methylpyrrolidone (hereinafter sometimes referred to as “NMP”), which is a dispersion medium for the positive electrode slurry composition described below. Solubility and dispersibility of the positive electrode active material in the positive electrode slurry composition may be reduced, and a good positive electrode slurry composition may not be obtained. As a result, the obtained secondary battery positive electrode is inferior in uniformity, and the internal resistance of the secondary battery positive electrode may be increased. In addition, the high-temperature cycle characteristics of the secondary battery may be inferior. When the polymer unit having a nitrile group in the binder exceeds 50% by mass, the solubility in the electrolytic solution in the secondary battery increases, and a part of the binder is eluted, thereby reducing the high-temperature cycle characteristics of the secondary battery. There are things to do. By including a polymer unit having a nitrile group in the binder in the above range, the dispersibility of the positive electrode active material can be improved, and a highly stable positive electrode slurry composition can be obtained. Excellent in properties. Moreover, since it is excellent in the stability with respect to electrolyte solution, it is excellent in the high temperature cycling characteristic of a secondary battery.

  Further, by including a linear alkylene polymer unit having 4 or more carbon atoms in the polymer constituting the binder, the dispersibility of the conductive agent in the positive electrode slurry composition is improved, and a uniform secondary battery positive electrode can be obtained. Easy to manufacture. By uniformly dispersing the positive electrode active material and the conductive agent in the electrode, the internal resistance is reduced, and as a result, the high temperature cycle characteristics and output characteristics of a battery using this electrode are improved. Further, by introducing the linear alkylene polymer unit, the degree of swelling of the positive electrode with respect to the electrolyte is optimized, and the battery characteristics are improved.

  The linear alkylene polymer unit has 4 or more carbon atoms, preferably 4 to 16, more preferably 4 to 12.

  The content ratio of the linear alkylene polymer units is preferably 20 to 98% by mass, more preferably 20 to 80% by mass, and particularly preferably 20 to 70% by mass.

Moreover, the polymer which comprises the said binder contains the polymer unit which has a hydrophilic group. Since the positive electrode active material can be stably dispersed in the positive electrode slurry composition by including a polymerized unit having a hydrophilic group in the binder, the slurry stability of the positive electrode slurry composition is improved. The gelation of the positive electrode slurry composition can be prevented.
Further, the binder preferably contains a polymer unit having a hydrophilic group in an amount of 0.05 to 20% by mass, more preferably 0.05 to 10% by mass, still more preferably 0.1 to 8% by mass, and particularly preferably 1%. Contains 6 mass%. By making the content ratio of the polymer units having the hydrophilic group within the above range, the binding property between the positive electrode active materials and between the positive electrode active material layer and the current collector described later is improved. Causes such as breakage of the separator and short circuit between the positive electrode and the negative electrode due to part of the positive electrode active material being detached (powder falling) in a manufacturing process such as pressing can be reduced.

  The hydrophilic group in the present invention refers to a functional group that liberates protons in an aqueous solvent or a salt in which a proton in the functional group is substituted with a cation, specifically, a carboxylic acid group, a sulfonic acid group, Examples thereof include a phosphoric acid group, a hydroxyl group, and a salt thereof, and a carboxylic acid group or a sulfonic acid group is preferable.

Moreover, the polymer which comprises the said binder contains an aromatic vinyl polymer unit. By including an aromatic vinyl polymer unit in the binder, the positive electrode active material can be stably dispersed in the positive electrode slurry composition, so that a positive electrode slurry composition having excellent slurry stability can be obtained. it can.
The binder contains 5 to 50% by mass, preferably 10 to 40% by mass, and more preferably 10 to 35% by mass of an aromatic vinyl polymer unit. When the aromatic vinyl polymer unit in the binder exceeds 50% by mass, the dispersion stability of the positive electrode active material is lowered and the electrode becomes harder, so that the binding property of the electrode to the current collector is lowered. . Further, when the aromatic vinyl polymer unit in the binder is less than 5% by mass, the dispersion stability of the conductive agent in the electrode is lowered, and the stability of the electrolytic solution is also impaired. Inferior in characteristics. By including the aromatic vinyl polymerization unit in the binder in the above range, the dispersibility of the positive electrode active material is improved, and a highly stable positive electrode slurry composition can be obtained. In addition, the flexibility of the electrode is improved, peeling is less likely to occur, and the binding property to the current collector is increased, so that the high-temperature cycle characteristics of the secondary battery are excellent.

  As described above, the binder used in the present invention has a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and a linear alkylene polymer unit having 4 or more carbon atoms. Such a binder includes a monomer that can form a polymer unit having a nitrile group, a monomer that can form an aromatic vinyl polymer unit, and a monomer that can form a linear alkylene polymer unit having 4 or more carbon atoms. It is obtained by polymerizing a monomer capable of forming a polymer unit having a hydrophilic group. A linear alkylene polymer unit having 4 or more carbon atoms is obtained by obtaining a polymer having a structural unit having an unsaturated bond (a polymer unit capable of forming a conjugated diene monomer having 4 or more carbon atoms), and then hydrogenating the polymer. It can be formed by reaction.

Hereinafter, the manufacturing method of the binder used for this invention is demonstrated.
Examples of the monomer that can form a polymer unit having a nitrile group include an α, β-ethylenically unsaturated nitrile monomer. The α, β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α, β-ethylenically unsaturated compound having a nitrile group. For example, acrylonitrile; α-chloroacrylonitrile, α-bromoacrylonitrile, etc. [Alpha] -halogenoacrylonitrile; [alpha] -alkylacrylonitrile such as methacrylonitrile; and the like. Among these, acrylonitrile and methacrylonitrile are preferable. These can be used individually by 1 type or in combination of multiple types.

  Examples of the monomer capable of forming an aromatic vinyl polymer unit include aromatic vinyl monomers such as styrene, α-methylstyrene, and vinyl toluene.

  The method for introducing the linear alkylene polymer unit into the binder is not particularly limited, but a method in which a polymer unit capable of forming a conjugated diene monomer is introduced and then subjected to a hydrogenation reaction is simple and preferable.

  The conjugated diene monomer is preferably a conjugated diene having 4 or more carbon atoms, and examples thereof include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and the like. Of these, 1,3-butadiene is preferred. These can be used individually by 1 type or in combination of multiple types.

  Introduction of the hydrophilic group into the binder is carried out by polymerizing monomers having a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, and a salt thereof.

Examples of the monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof, dicarboxylic acids, and derivatives thereof.
Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid.
Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, β-diaminoacrylic acid, and the like. Can be mentioned.
Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.
Dicarboxylic acid derivatives include methyl maleic acid, dimethyl maleic acid, phenyl maleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid and the like methyl allyl maleate, diphenyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, And maleate esters such as octadecyl maleate and fluoroalkyl maleate.
Moreover, the acid anhydride which produces | generates a carboxyl group by hydrolysis can also be used.
Examples of the acid anhydride of dicarboxylic acid include maleic anhydride, acrylic anhydride, methyl maleic anhydride, and dimethyl maleic anhydride.
In addition, monoethyl maleate, diethyl maleate, monobutyl maleate, dibutyl maleate, monoethyl fumarate, diethyl fumarate, monobutyl fumarate, dibutyl fumarate, monocyclohexyl fumarate, dicyclohexyl fumarate, monoethyl itaconate, diethyl itaconate Also included are monoesters and diesters of α, β-ethylenically unsaturated polyvalent carboxylic acids such as monobutyl itaconate and dibutyl itaconate.

  Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, styrene sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methyl. Examples thereof include propanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.

  Examples of the monomer having a phosphate group include phosphoric acid-2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate. .

Examples of the monomer having a hydroxyl group include ethylenically unsaturated alcohols such as (meth) allyl alcohol, 3-buten-1-ol, 5-hexen-1-ol; 2-hydroxyethyl acrylate, acrylic acid-2 -Ethylene such as hydroxypropyl, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, di-2-hydroxyethyl maleate, di-4-hydroxybutyl maleate, di-2-hydroxypropyl itaconate alkanol esters of unsaturated carboxylic acids; formula ^{_{CH 2 = CR 1 -COO- (C}} n H 2n O) m -H (m is 2 to 9 integer, n represents 2 to 4 integer, ^{R 1} is hydrogen Or an ester of polyalkylene glycol represented by (meth) acrylic acid represented by 2-hydro; Mono (meth) acrylic acid esters of dihydroxy esters of dicarboxylic acids such as cyethyl-2 ′-(meth) acryloyloxyphthalate, 2-hydroxyethyl-2 ′-(meth) acryloyloxysuccinate; 2-hydroxyethyl vinyl ether; Vinyl ethers such as 2-hydroxypropyl vinyl ether; (meth) allyl-2-hydroxyethyl ether, (meth) allyl-2-hydroxypropyl ether, (meth) allyl-3-hydroxypropyl ether, (meth) allyl-2- Mono (meth) allyl ethers of alkylene glycols such as hydroxybutyl ether, (meth) allyl-3-hydroxybutyl ether, (meth) allyl-4-hydroxybutyl ether, (meth) allyl-6-hydroxyhexyl ether Polyoxyalkylene glycol (meth) monoallyl ethers such as diethylene glycol mono (meth) allyl ether and dipropylene glycol mono (meth) allyl ether; glycerin mono (meth) allyl ether, (meth) allyl-2-chloro Mono (meth) allyl ethers of halogen and hydroxy-substituted products of (poly) alkylene glycols such as -3-hydroxypropyl ether, (meth) allyl-2-hydroxy-3-chloropropyl ether; eugenol, isoeugenol Mono (meth) allyl ether of monohydric phenol and its halogen-substituted product; (meth) allyl of alkylene glycol such as (meth) allyl-2-hydroxyethylthioether and (meth) allyl-2-hydroxypropylthioether Thioether compounds; and the like.

  Among these, the hydrophilic group is preferably a carboxylic acid group or a sulfonic acid group because it is excellent in the binding property between the positive electrode active materials and the binding property between the positive electrode active material layer and the current collector described later. In particular, a carboxylic acid group is preferable because it efficiently captures transition metal ions that may be eluted from the positive electrode active material.

  Moreover, the binder used for this invention may contain the polymer unit copolymerizable with the monomer which forms these polymer units other than the said polymer unit. The copolymerizable polymer unit refers to a structural unit formed by polymerizing another monomer copolymerizable with the monomer forming the polymer unit. The content ratio of the copolymerizable polymer units is preferably 30% by mass or less, more preferably 20% by mass or less, and still more preferably 10% by mass or less with respect to all monomer units.

  Examples of such other copolymerizable monomers include, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t, which constitute the polymer unit of the (meth) acrylate monomer. -Acrylic acid alkyl esters such as butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate , N-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, Methacrylic acid alkyl esters such as nethyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate; fluoroethyl vinyl ether, fluoropropyl vinyl ether, Fluorine-containing vinyl compounds such as vinyl pentafluorobenzoate, difluoroethylene, and tetrafluoroethylene; Non-conjugated diene compounds such as 1,4-pentadiene, 1,4-hexadiene, vinylnorbornene, and dicyclopentadiene; ethylene, propylene, 1- Α-Olephi such as butene, 4-methyl-1-pentene, 1-hexene, 1-octene Compounds; alkoxyalkyl esters of α, β-ethylenically unsaturated carboxylic acids such as methoxyethyl (meth) acrylate, methoxypropyl (meth) acrylate, butoxyethyl (meth) acrylate; divinyl compounds such as divinylbenzene; Di (meth) acrylates such as ethylene di (meth) acrylate, diethylene glycol di (meth) acrylate, and ethylene glycol di (meth) acrylate; trimethacrylates such as trimethylolpropane tri (meth) acrylate; In addition to functional ethylenically unsaturated monomers, self-crosslinking compounds such as N-methylol (meth) acrylamide and N, N′-dimethylol (meth) acrylamide; Among them, showing the solubility in N-methylpyrrolidone (hereinafter referred to as “NMP”) preferably used as a solvent for the positive electrode slurry composition without eluting into the electrolytic solution, improving the flexibility of the positive electrode, Since the peeling of the positive electrode can be suppressed when a wound cell is produced and the characteristics (cycle characteristics, etc.) of the secondary battery using the positive electrode are excellent, an alkyl acrylate is preferable, and a non-carbonyl oxygen atom Acrylic acid alkyl ester having 2 to 12 carbon atoms of the alkyl group bonded to is more preferable, and among them, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, and lauryl acrylate are particularly preferable.

  Furthermore, the binder used for this invention may contain the monomer copolymerizable with these other than the monomer component mentioned above. Monomers copolymerizable with these include vinyl esters such as vinyl acetate, vinyl propionate and vinyl butyrate; vinyl ethers such as methyl vinyl ether, ethyl vinyl ether and butyl biether; methyl vinyl ketone, ethyl vinyl ketone and butyl And vinyl ketones such as vinyl ketone, hexyl vinyl ketone and isopropenyl vinyl ketone; and heterocyclic ring-containing vinyl compounds such as N-vinyl pyrrolidone, vinyl pyridine and vinyl imidazole. By graft-copolymerizing these monomers by an appropriate technique, the binder having the above-described structure can be obtained.

The binder used in the present invention is used in the state of a dispersion in which the binder is dispersed in a dispersion medium (water or an organic solvent) or a dissolved solution (hereinafter, these are collectively referred to as “binder dispersion”). To do.) The dispersion medium is not particularly limited as long as it can uniformly disperse or dissolve the binder. In the present invention, it is preferable to use water as a dispersion medium from the viewpoints of excellent environmental viewpoint and high drying speed. Examples of the organic solvent include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene and ethylbenzene; acetone, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, ethylcyclohexane and the like. Ketones; methylene chloride, chloroform, carbon tetrachloride and other chlor aliphatic hydrocarbons; ethyl acetate, butyl acetate, γ-butyrolactone, ε-caprolactone, and other esters; acetonitrile, propionitrile, and other acylonitriles; tetrahydrofuran , Ethers such as ethylene glycol diethyl ether: alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; N- Amides such as methylpyrrolidone and N, N-dimethylformamide can be mentioned.
These dispersion media may be used alone, or two or more of these dispersion media may be mixed and used as a mixed solvent. Among these, in particular, it is industrially used at the time of preparing a slurry composition for a positive electrode, which will be described later, is difficult to volatilize in production, and as a result, volatilization of the slurry composition can be suppressed and the smoothness of the resulting positive electrode is improved. Therefore, water, N-methylpyrrolidone, cyclohexanone, toluene and the like are preferable.

  When the binder is dispersed in the dispersion medium in the form of particles, the average particle diameter (dispersed particle diameter) of the binder dispersed in the form of particles is preferably 50 to 500 nm, more preferably 70 to 400 nm, and particularly preferably. 100-250 nm. When the average particle size of the binder is within this range, the strength and flexibility of the positive electrode obtained are good.

  When the binder is dispersed in the dispersion medium in the form of particles, the solid content concentration of the binder dispersion is usually 15 to 70% by mass, preferably 20 to 65% by mass, and more preferably 30 to 60% by mass. When the solid content concentration is within this range, workability in producing the positive electrode slurry composition described later is good.

In addition, LiPF ₆ is 1.0 mol in a mixed solvent obtained by mixing an electrolytic solution (ethylene carbonate (EC) and diethyl carbonate (DEC) so that the volume ratio at 20 ° C. becomes EC: DEC = 1: 2. The swelling degree of the binder with respect to the solution dissolved at a concentration of / L is preferably 100 to 500%, more preferably 110 to 400%, and still more preferably 120 to 300%. By setting the degree of swelling of the binder to the electrolytic solution in the above range, solubility in the electrolytic solution can be suppressed, and the high-temperature cycle characteristics of the secondary battery can be improved.

Here, as an index of the degree of swelling, LiPF _{6 is} added to a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) so that the volume ratio at 20 ° C. becomes EC: DEC = 1: 2. The degree of swelling with respect to a solution in which is dissolved at a concentration of 1.0 mol / L is employed. When the swelling degree of the binder with respect to the electrolytic solution is less than 100%, the binder may not sufficiently contain the electrolytic solution in the secondary battery positive electrode. Normally, the binder contains the electrolyte in the electrode, so that the binder itself exhibits Li conductivity. However, if the binder does not swell with respect to the electrolyte, the binder itself does not become a Li conduction path and resistance increases. As a result, the cycle characteristics and output characteristics of a secondary battery using the electrode may be deteriorated. In addition, when the swelling degree of the binder with respect to the electrolytic solution exceeds 500%, the binder is excessively swollen into the electrolytic solution in the positive electrode of the secondary battery, so that the conductive network is cut and the resistance is increased. The cycle characteristics and output characteristics of the used secondary battery may deteriorate.

  The degree of swelling of the binder can be adjusted to the above range by adjusting the type and ratio of all polymerized units constituting the binder.

The swelling degree of the binder can be adjusted to the above range by adjusting the type and ratio of all the polymerized units constituting the binder, and the binder solubility parameter (hereinafter referred to as “SP value”) is used as the index. It can also be used. For example, the solubility parameter (hereinafter referred to as “SP value”) is preferably 9.0 (cal / cm ³ ) ^1/2 or more and less than 11 (cal / cm ³ ) ^1/2 , more preferably 9 to 10.5 ( cal / cm ³ ) ^1/2 , more preferably, a method using a polymer or copolymer of 9.5 to 10 (cal / cm ³ ) ^1/2 as a binder. By setting the SP value in the above range, it is possible to impart appropriate swelling property to the electrolytic solution while maintaining the solubility of the binder in the dispersion medium and the dispersion medium for the positive electrode slurry composition described later. Thereby, the uniformity of the obtained secondary battery positive electrode is further improved, and the cycle characteristics of the secondary battery using the same can be improved.

Here, the SP value is J.P. Brandrup, E .; H. Immergut and E.M. A. It can be determined according to the method described in Grulk edition “Polymer Handbook” VII Solidity Parameter Values, p675-714 (John Wiley & Sons, 4th edition, 1999). Those not described in this publication can be determined according to the “molecular attraction constant method” proposed by Small. This method is a method for obtaining the SP value (δ) according to the following equation from the characteristic value of the functional group (atomic group) constituting the compound molecule, that is, the statistics of the molecular attractive constant (G) and the molecular volume.
δ = ΣG / V = dΣG / M
ΣG: Sum of molecular attraction constant G V: Specific volume M: Molecular weight d: Specific gravity

  The binder having the SP value in the above preferred range can be produced, for example, by adjusting the ratio of all polymerized units constituting the binder and polymerizing.

  The weight average molecular weight in terms of polystyrene by gel permeation chromatography of the binder used in the present invention is preferably 10,000 to 700,000, more preferably 50,000 to 500,000, particularly preferably 100,000 to. 300,000. By setting the weight average molecular weight of the binder in the above range, the positive electrode can be made flexible, and it is easy to adjust the viscosity to be easily applied during the production of the positive electrode slurry composition.

  The iodine value of the binder used in the present invention is preferably 3 to 60 mg / 100 mg, more preferably 3 to 20 mg / 100 mg, and still more preferably 8 to 10 mg / 100 mg. If the iodine value of the binder exceeds 60 mg / 100 mg, the stability at the oxidation potential is low due to the unsaturated bond contained in the binder, and the high-temperature cycle characteristics of the battery may be inferior. On the contrary, when the iodine value of the binder is less than 3 mg / 100 mg, the flexibility of the binder may be lowered. As a result, powder fall etc. occur and it is inferior to safety and long-term characteristics. When the iodine value of the binder is in the above range, the binder is chemically structurally stable with respect to a high potential, the electrode structure can be maintained even in a long-term cycle, and the high-temperature cycle characteristics are excellent. The iodine value is determined according to JIS K6235;

  The glass transition temperature (Tg) of the binder used in the present invention is preferably 25 ° C. or lower, more preferably 15 ° C. or lower, and particularly preferably 0 ° C. or lower. Although the minimum of Tg of a binder is not specifically limited, Preferably it is -50 degreeC or more, More preferably, it is -45 degreeC or more, Most preferably, it is -40 degreeC or more. When the Tg of the binder is in the above range, the secondary battery positive electrode of the present invention has excellent strength and flexibility, so that powder fall-off in the positive electrode manufacturing process is suppressed, and when the swivel cell is created, Peeling can be suppressed and the high-temperature cycle characteristics of a secondary battery using the positive electrode can be improved. The glass transition temperature of the binder can be adjusted by combining various monomers.

  The method for producing the binder used in the present invention is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, and living radical polymerization can be used. 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.

  The linear alkylene polymer unit is formed by introducing a polymer unit capable of forming a conjugated diene monomer having 4 or more carbon atoms and then hydrogenating it. The method for hydrogenation reaction is not particularly limited. Unsaturated polymer obtained by the above polymerization method by hydrogenation reaction (comprising a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having hydrophilicity, and a polymer unit capable of forming a conjugated diene monomer) In the polymer), only the carbon-carbon unsaturated bonds derived from the polymerized units capable of forming the conjugated diene monomer can be selectively hydrogenated to obtain the binder used in the present invention. Moreover, the iodine value of the binder used for this invention can be made into the range mentioned above by hydrogenation reaction. The binder used in the present invention is preferably a hydrogenated acrylonitrile-butadiene copolymer having a hydrophilic group (hereinafter sometimes referred to as “hydrogenated NBR”).

  As a selective hydrogenation method for selectively hydrogenating only carbon-carbon unsaturated bonds derived from polymerized units capable of forming a conjugated diene monomer in an unsaturated polymer, a publicly known method may be used. Either the hydration method or the aqueous layer hydrogenation method is possible, but the aqueous layer hydrogenation method is preferable because the content of impurities (for example, a coagulant or metal described later) is small in the obtained binder.

  When the binder used in the present invention is produced by the oil layer hydrogenation method, the following method is preferred. That is, first, a dispersion of an unsaturated polymer prepared by emulsion polymerization is coagulated by salting out, dissolved in an organic solvent through filtration and drying. Subsequently, the unsaturated polymer dissolved in the organic solvent is subjected to a hydrogenation reaction (oil layer hydrogenation method) to obtain a hydride, and the obtained hydride solution is coagulated, filtered and dried. A binder to be used is obtained.

  When an alkali metal caprate is used as an emulsifier, the caprate in the binder finally obtained in each step of coagulation, filtration and drying by salting out the dispersion of the unsaturated polymer is used. It is preferable to prepare such that the amount is 0.01 to 0.4% by mass. For example, a known coagulant such as magnesium sulfate, sodium chloride, calcium chloride, or aluminum sulfate can be used in coagulation by salting out of the dispersion, but preferably an alkali such as magnesium sulfate, magnesium chloride, or magnesium nitrate. By using an earth metal salt; or a Group 13 metal salt such as aluminum sulfate; the amount of caprate contained in the unsaturated polymer can be reduced. Therefore, it is preferable to use an alkaline earth metal salt or a Group 13 metal salt as the coagulant, more preferably an alkaline earth metal salt, and finally by controlling the amount of use and the solidification temperature, The amount of caprate in the obtained binder can be within the above range. The amount of the coagulant used is preferably 1 to 100 parts by mass, more preferably 5 to 50 parts by mass, and particularly preferably 10 to 50 parts by mass, when the amount of unsaturated polymer to be hydrogenated is 100 parts by mass. It is. The coagulation temperature is preferably 10 to 80 ° C.

  The solvent for the oil layer hydrogenation method is not particularly limited as long as it is a liquid organic compound that dissolves the unsaturated polymer, but benzene, toluene, xylene, hexane, cyclohexane, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, cyclohexanone, and acetone are preferable. used.

  As a catalyst for the oil layer hydrogenation method, any known selective hydrogenation catalyst can be used without limitation, and a palladium-based catalyst and a rhodium-based catalyst are preferable, and a palladium-based catalyst (such as palladium acetate, palladium chloride, and palladium hydroxide) is used. More preferred. Two or more of these may be used in combination, but when a rhodium catalyst and a palladium catalyst are used in combination, it is preferable to use a palladium catalyst as the main active ingredient. These catalysts are usually used by being supported on a carrier. Examples of the carrier include silica, silica-alumina, alumina, diatomaceous earth, activated carbon and the like. The amount of the catalyst used is preferably 10 to 5000 ppm, more preferably 100 to 3000 ppm, in terms of the amount of metal of the hydrogenation catalyst, relative to the amount of the unsaturated polymer to be hydrogenated.

  The hydrogenation reaction temperature in the oil layer hydrogenation method is preferably 0 to 200 ° C., more preferably 10 to 100 ° C., and the hydrogen pressure is preferably 0.1 to 30 MPa, more preferably 0.2 to 20 MPa. The reaction time is preferably 1 to 50 hours, more preferably 2 to 25 hours.

Alternatively, when the binder used in the present invention is produced by the aqueous layer hydrogenation method, the dispersion of the unsaturated polymer prepared by emulsion polymerization is diluted with water as necessary to carry out the hydrogenation reaction. Preferably it is done.
Here, in the aqueous layer hydrogenation method, hydrogen is supplied to a reaction system in the presence of a hydrogenation catalyst to hydrogenate (I) an aqueous layer direct hydrogenation method, and in the presence of an oxidizing agent, a reducing agent and an activator. There are (II) water layer indirect hydrogenation methods in which hydrogenation is carried out by reduction.

(I) In the aqueous layer direct hydrogenation method, the concentration of the unsaturated polymer in the aqueous layer (concentration in the dispersion state) is preferably 40% by mass or less in order to prevent aggregation.
The hydrogenation catalyst used is not particularly limited as long as it is a compound that is difficult to decompose with water. As specific examples of hydrogenation catalysts, palladium catalysts include palladium salts of carboxylic acids such as formic acid, propionic acid, lauric acid, succinic acid, oleic acid, and phthalic acid; palladium chloride, dichloro (cyclooctadiene) palladium, dichloro (norbornadiene) ) Palladium chloride such as palladium and ammonium hexachloropalladium (IV); Iodide such as palladium iodide; Palladium sulfate dihydrate and the like. Of these, palladium salts of carboxylic acids, dichloro (norbornadiene) palladium and ammonium hexachloropalladium (IV) are particularly preferred. The amount of the hydrogenation catalyst used may be determined as appropriate, but is preferably 5 to 6000 ppm, more preferably 10 to 4000 ppm in terms of the amount of metal of the hydrogenation catalyst with respect to the amount of the unsaturated polymer to be hydrogenated. is there.

  The reaction temperature in the aqueous layer direct hydrogenation method is preferably 0 to 300 ° C, more preferably 20 to 150 ° C, and particularly preferably 30 to 100 ° C. If the reaction temperature is too low, the reaction rate may decrease. Conversely, if the reaction temperature is too high, side reactions such as a hydrogenation reaction of a nitrile group may occur. The hydrogen pressure is preferably 0.1 to 30 MPa, more preferably 0.5 to 20 MPa. The reaction time is selected in consideration of the reaction temperature, hydrogen pressure, target hydrogenation rate, and the like.

  On the other hand, in the (II) aqueous layer indirect hydrogenation method, the concentration of the unsaturated polymer in the aqueous layer (concentration in the dispersion state) is preferably 1 to 50% by mass, more preferably 1 to 40% by mass. .

  Examples of the oxidizing agent used in the water layer indirect hydrogenation method include oxygen, air, and hydrogen peroxide. The amount of these oxidizing agents used is a molar ratio to the carbon-carbon double bond (oxidant: carbon-carbon double bond), preferably 0.1: 1 to 100: 1, more preferably 0.8: 1. It is in the range of -5: 1.

  As the reducing agent used in the aqueous layer indirect hydrogenation method, hydrazines such as hydrazine, hydrazine hydrate, hydrazine acetate, hydrazine sulfate, and hydrazine hydrochloride, or compounds that liberate hydrazine are used. The amount of these reducing agents used is a molar ratio to the carbon-carbon double bond (reducing agent: carbon-carbon double bond), preferably 0.1: 1 to 100: 1, more preferably 0.8: It is in the range of 1-5: 1.

  As the activator used in the water layer indirect hydrogenation method, ions of metals such as copper, iron, cobalt, lead, nickel, iron, tin and the like are used. These activators are used in a molar ratio to the carbon-carbon double bond (activator: carbon-carbon double bond), preferably 1: 1000 to 10: 1, more preferably 1:50 to 1: 2.

  The reaction in the aqueous layer indirect hydrogenation method is carried out by heating within the range from 0 ° C. to the reflux temperature, whereby the hydrogenation reaction is carried out. The heating range at this time is preferably 0 to 250 ° C, more preferably 20 to 100 ° C, and particularly preferably 40 to 80 ° C.

  In both the direct hydrogenation method and the indirect hydrogenation method in the aqueous layer, it is preferable to carry out solidification by salting out, filtration and drying after the hydrogenation. The salting out is performed in the same manner as the salting out of the dispersion of the unsaturated polymer in the oil layer hydrogenation method, in order to control the amount of caprate in the binder after the hydrogenation reaction. Alternatively, a Group 13 metal salt is preferably used, and an alkaline earth metal salt is particularly preferably used. Further, the filtration and drying steps subsequent to coagulation can be performed by known methods.

  Moreover, the method for producing the binder used in the present invention is particularly preferably a method in which the hydrogenation reaction is carried out in two or more stages. Even when the same amount of hydrogenation catalyst is used, the hydrogenation reaction efficiency can be increased by carrying out the hydrogenation reaction in two or more stages. That is, when the polymerization unit capable of forming a conjugated diene monomer is converted into a linear alkylene structural unit, the iodine value of the binder can be further reduced.

  When the hydrogenation reaction is performed in two or more stages, the hydrogenation reaction rate (hydrogenation ratio) (%) in the first stage should be 50% or more, more preferably 70% or more. Is preferred. That is, when the value obtained by the following formula is the hydrogenation reaction rate (%), this value is preferably 50% or more, and more preferably 70% or more.

Hydrogenation reaction rate (hydrogenation rate) (%)
= 100 × (carbon-carbon double bond amount before hydrogenation reaction−carbon-carbon double bond amount after hydrogenation reaction) / (carbon-carbon double bond amount before hydrogenation reaction)
In addition, the amount of carbon-carbon double bonds can be analyzed using NMR.

  After completion of the hydrogenation reaction, the hydrogenation reaction catalyst in the dispersion is removed. As the method, for example, an adsorbent such as activated carbon or ion exchange resin can be added to adsorb the hydrogenation reaction catalyst with stirring, and then the dispersion can be filtered or centrifuged. It is also possible to leave the hydrogenation reaction catalyst in the dispersion without removing it.

  The binder used in the present invention has a polymer unit having a hydrophilic group. The method for introducing a polymer unit having a hydrophilic group in the binder is not particularly limited, and a method for introducing a hydrophilic group into a polymer constituting the binder (having a hydrophilic group) in the above-described binder production process. A method of copolymerizing monomers), an unsaturated polymer comprising a polymer unit having the above nitrile group, a polymer unit capable of forming the above conjugated diene monomer, and an aromatic vinyl polymer unit. And a hydrogenated polymer (hereinafter sometimes referred to as “hydrogenated polymer”) is obtained, and then the hydrogenated polymer and the ethylenically unsaturated carboxylic acid or anhydride thereof are obtained. A method of mixing (a method of acid-modifying a hydrogenated polymer) may be mentioned. Among these, a method of copolymerizing a monomer having a hydrophilic group is preferable because it is simple in the process. When the binder includes a hydrophilic group, the positive electrode active material is excellent in dispersibility and a uniform positive electrode can be obtained. Moreover, the resistance in a positive electrode is reduced, As a result, the secondary battery which shows the outstanding cycling characteristics can be obtained. Furthermore, the binding property with the current collector becomes good, the positive electrode structure can be maintained even after repeated charge and discharge, and the high temperature cycle characteristics are excellent.

  In the following, a binder used in the present invention by mixing an ethylenically unsaturated carboxylic acid or its anhydride with a polymer after the hydrogenation reaction (hydrogenated polymer) (hereinafter referred to as “acid-modified binder”) The method for producing the hydrogenated polymer (method for acid-modifying the hydrogenated polymer) will be described in detail.

  The ethylenically unsaturated carboxylic acid or anhydride thereof used for producing the acid-modified binder is not particularly limited, but the ethylenically unsaturated dicarboxylic acid or anhydride thereof having 4 to 10 carbon atoms, particularly anhydrous Maleic acid is preferred.

Examples of the ethylenically unsaturated carboxylic acid include ethylenically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid:
Ethylenically unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid:
Ethylenically unsaturated dicarboxylic acid anhydrides such as maleic anhydride, itaconic anhydride and citraconic anhydride:
Monomethyl maleate, monoethyl maleate, monopropyl maleate, mono-n-butyl maleate, monoisobutyl maleate, mono-n-pentyl maleate, mono-n-hexyl maleate, mono-2-ethylhexyl maleate, Monomethyl fumarate, monoethyl fumarate, monopropyl fumarate, mono-n-butyl fumarate, monoisobutyl fumarate, mono-n-pentyl fumarate, mono-n-hexyl fumarate, mono-2-ethylhexyl fumarate, Monomethyl itaconate, monoethyl itaconate, monopropyl itaconate, mono-n-butyl itaconate, monoisobutyl itaconate, mono-n-pentyl itaconate, mono-n-hexyl itaconate, mono-2-ethylhexyl itaconate, Citraconate monomethyl, cyto Conethyl monoethyl, citraconic acid monopropyl, citraconic acid mono-n-butyl, citraconic acid monoisobutyl, citraconic acid mono-n-pentyl, citraconic acid mono-n-hexyl, citraconic acid mono-2-ethylhexyl, mesaconic acid monomethyl, Mesaconic acid monoethyl, mesaconic acid monopropyl, mesaconic acid mono-n-butyl, mesaconic acid monoisobutyl, mesaconic acid mono-n-pentyl, mesaconic acid mono-n-hexyl, mesaconic acid mono-2-ethylhexyl, glutaconic acid monomethyl, Monoethyl glutaconate, monopropyl glutaconate, mono-n-butyl glutaconate, monoisobutyl glutaconate, monoisobutyl glutaconate, mono-n-pentyl glutaconate, mono-n-hexyl glutaconate, mono-glutaconic acid mono- -Ethylhexyl, monomethyl allylmalonate, monoethyl allylmalonate, monopropyl allylmalonate, mono-n-butyl allylmalonate, monoisobutyl allylmalonate, mono-n-pentyl allylmalonate, mono-n-hexyl allylmalonate, mono-2 allylmalonate -Ethylhexyl, monomethyl teraconic acid, monoethyl teraconic acid, monopropyl teraconic acid, mono-n-butyl teraconic acid, monoisobutyl teraconic acid, mono-n-pentyl teraconic acid, mono-n-hexyl teraconic acid, mono-2 teraconic acid -Unsaturated dicarboxylic acid monoalkyl ester such as ethylhexyl.

  The acid-modified binder can be obtained, for example, by subjecting a hydrogenated polymer to an ethylenically unsaturated carboxylic acid or an anhydride thereof to an ene type addition reaction.

  The ene type addition reaction usually occurs by kneading a hydrogenated polymer and an ethylenically unsaturated carboxylic acid or an anhydride thereof at a high temperature without using a radical generator. When the radical generator is used, in addition to the generation of gel, the ethylenically unsaturated carboxylic acid or anhydride thereof and the hydrogenated polymer cause a radical type addition reaction, so that the ene type addition reaction cannot be performed.

  The amount of the ethylenically unsaturated carboxylic acid or anhydride thereof is not particularly limited, but is usually 0.05 to 10 parts by mass of the ethylenically unsaturated carboxylic acid or anhydride thereof with respect to 100 parts by mass of the hydrogenated polymer. Preferably, it is 0.2-6 mass parts.

  In an ene type addition reaction, for example, when an open type kneader such as a roll type kneader is used, molten ethylenically unsaturated carboxylic acid such as maleic anhydride or its anhydride is scattered, It may not be possible to carry out a simple addition reaction. In addition, when a continuous kneader such as a single-screw extruder, a same-direction twin-screw extruder, a different-direction rotary twin-screw extruder, etc. is used, the binder remaining at the outlet of the extruder is gelled, so that the die head In some cases, the addition reaction cannot be performed efficiently, such as clogging. Further, a large amount of unreacted ethylenically unsaturated carboxylic acid or anhydride thereof may remain in the binder.

  In the ene type addition reaction, it is preferable to use a heated closed kneader. The heat-sealed kneader can be arbitrarily selected from batch-type heat-sealed kneaders such as a pressure kneader, Banbury mixer, Brabender, etc. Among them, a pressure kneader is preferable.

  In the above production method, first, before adding the ethylenically unsaturated carboxylic acid or its anhydride to the hydrogenated polymer by the ene-type addition reaction, a specific process is performed at a temperature at which the ene-type addition reaction does not substantially occur. Specifically, at 60 to 170 ° C., preferably 100 to 150 ° C., an ethylenically unsaturated carboxylic acid or anhydride thereof and a hydrogenated polymer are pre-kneaded, and the ethylenically unsaturated carboxylic acid or anhydride thereof is washed with water. Disperse uniformly in the addition polymer. If the pre-kneading temperature is excessively low, the hydrogenated polymer may slip in the kneader and the ethylenically unsaturated carboxylic acid or its anhydride and the hydrogenated polymer may not be sufficiently mixed. On the other hand, if the pre-kneading temperature is excessively high, the ethylenically unsaturated carboxylic acid or anhydride thereof thrown into the kneader may be scattered in a large amount, and the ene type addition reaction rate may be lowered.

  Next, in order to carry out the ene type addition reaction, the temperature of the mixture of the hydrogenated polymer and the ethylenically unsaturated carboxylic acid or its anhydride during kneading is usually kept at 200 to 280 ° C, preferably 220 to 260 ° C. The method for maintaining the temperature is not particularly limited, but is usually achieved by flowing warm water or steam through the jacket of the kneader, or using shear heat generation.

When flowing warm water or steam through the jacket of the heat-sealed kneader, the jacket temperature is usually maintained at 70 to 250 ° C, preferably 130 to 200 ° C. Moreover, when utilizing shear heat_generation | fever, it is preferable to continue kneading | mixing with a kneading machine with the shear rate of 30-1000S < ^-1 >, Preferably it is 300-700S- ¹ . In particular, the use of shear heat generation is preferable because the temperature of the mixture can be easily controlled. The kneading time in the heat-sealed kneader is not particularly limited, but is usually 120 seconds to 120 minutes, preferably 180 seconds to 60 minutes.

  If the temperature of the mixture during kneading is excessively low, the ene type addition reaction may not proceed sufficiently. Moreover, when too high, generation | occurrence | production of gelation or a burnt thing etc. will occur, and as a result, gel may mix in a product. In addition, if the shear rate is excessively high, it is difficult to control the temperature of the mixture by shearing heat generation, the temperature of the mixture becomes too high, and generation of gels and burned products occurs, which is not preferable as an industrial production method. . On the other hand, if the shear rate is excessively low, the temperature of the mixture becomes too low, so that a sufficient ene-type addition reaction cannot be expected.

  In the ene type addition reaction, the gelation of the binder can be prevented by adding an anti-aging agent during kneading. Although the kind of anti-aging agent is not particularly limited, amine type, amine ketone type, phenol type, benzimidazole type and other anti-aging agents for binders can be used.

  Examples of amine-based antioxidants include phenyl-1-naphthylamine, alkylated diphenylamine, octylated diphenylamine, 4,4-bis (α, α-dimethylbenzyl) diphenylamine, p- (p-toluenesulfonylamide) diphenylamine, N, N-di-2-naphthyl-p-phenylenediamine, N, N-diphenyl-p-phenylenediamine, N-phenyl-N-isopropyl-p-phenylenediamine, N-phenyl-N- (1,3- And dimethylbutyl) -p-phenylenediamine and N-phenyl-N- (3-methacryloyloxy-2-hydroxypropyl) -p-phenylenediamine.

  Examples of amine ketone antioxidants include 2,2,4-trimethyl-1,2-dihydroquinoline, 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline, and the like.

  Examples of phenolic antioxidants include 2,6-di-tert-butyl-4-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,2-methylenebis (4-ethyl- 6-tert-butylphenol), 2,2-methylenebis (4-methyl-6-tert-butylphenol), 4,4-butylidenebis (3-methyl-6-tert-butylphenol), 4,4-thiobis (3-methyl) -6-tert-butylphenol), 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, and the like.

  Examples of the benzimidazole anti-aging agent include 2-mercaptobenzimidazole, 2-mercaptomethylbenzimidazole, metal salt of 2-mercaptomethylbenzimidazole, and the like.

  The usage-amount of these anti-aging agents is 0.01-5 mass parts normally with respect to 100 mass parts of binders, Preferably it is 0.1-2 mass parts.

  According to the production method described above, 80% or more of the charged amount of the ethylenically unsaturated carboxylic acid or anhydride used for the ene type addition reaction is usually added to the hydrogenated polymer to obtain the binder used in the present invention. In addition, the unreacted ethylenically unsaturated carboxylic acid or its anhydride remaining in the binder can be reduced to 5% or less of the charged amount. Therefore, this method is extremely useful for industrially stable production. In this invention, the binder which contains 0.05-20 mass% of polymer units which have a hydrophilic group can be obtained with the manufacturing method mentioned above.

  The binder used in the present invention is preferably obtained through a particulate metal removal step of removing particulate metal contained in the binder dispersion in the binder production step. When the content of the particulate metal component contained in the binder is 10 ppm or less, it is possible to prevent metal ion crosslinking over time between the polymers in the positive electrode slurry composition described later, and to prevent an increase in viscosity. Furthermore, there is little concern about self-discharge increase due to internal short circuit of the secondary battery or dissolution / precipitation during charging, and the cycle characteristics and safety of the battery are improved.

  The method for removing the particulate metal component from the binder dispersion in the particulate metal removal step is not particularly limited. For example, the removal method by filtration using a filtration filter, the removal method by a vibrating screen, the removal method by centrifugation. And a method of removing by magnetic force. Especially, since the removal object is a metal component, the method of removing by magnetic force is preferable. The method for removing by magnetic force is not particularly limited as long as it is a method capable of removing a metal component, but in consideration of productivity and removal efficiency, it is preferably performed by arranging a magnetic filter in the production line of the binder.

  In the production process of the binder used in the present invention, the dispersant used in the above polymerization method may be one used in ordinary synthesis, and specific examples include sodium dodecylbenzenesulfonate, sodium dodecylphenylethersulfonate, and the like. Benzene sulfonates; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecyl sulfate; sulfosuccinates such as sodium dioctyl sulfosuccinate and sodium dihexyl sulfosuccinate; fatty acid salts such as sodium laurate; polyoxyethylene lauryl ether sulfate sodium Salts, ethoxy sulfate salts such as polyoxyethylene nonyl phenyl ether sulfate sodium salt; alkane sulfonate salts; alkyl ether phosphate sodium salts; Nonionic emulsifiers such as xylethylene nonylphenyl ether, polyoxyethylene sorbitan lauryl ester, polyoxyethylene-polyoxypropylene block copolymer; gelatin, maleic anhydride-styrene copolymer, polyvinyl pyrrolidone, sodium polyacrylate, Examples thereof include water-soluble polymers such as polyvinyl alcohol having a polymerization degree of 700 or more and a saponification degree of 75% or more, and these may be used alone or in combination of two or more. Among these, benzenesulfonates such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate; alkyl sulfates such as sodium lauryl sulfate and sodium tetradodecylsulfate are preferable, and oxidation resistance is more preferable. From this point, it is a benzenesulfonate such as sodium dodecylbenzenesulfonate and sodium dodecylphenylethersulfonate. The addition amount of a dispersing agent can be set arbitrarily, and is about 0.01-10 mass parts normally with respect to 100 mass parts of monomer total amounts.

  The pH when the binder used in the present invention is dispersed in the dispersion medium is preferably 5 to 13, more preferably 5 to 12, and most preferably 10 to 12. When the pH of the binder is in the above range, the storage stability of the binder is improved, and further, the mechanical stability is improved.

  The pH adjuster for adjusting the pH of the binder is an alkali metal hydroxide such as lithium hydroxide, sodium hydroxide or potassium hydroxide, or an alkaline earth metal oxide such as calcium hydroxide, magnesium hydroxide or barium hydroxide. , Hydroxides such as hydroxides of metals belonging to group IIIA in the long periodic table such as aluminum hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate, alkaline earth metal carbonates such as magnesium carbonate, etc. Examples of organic amines include alkylamines such as ethylamine, diethylamine, and propylamine; alcohol amines such as monomethanolamine, monoethanolamine, and monopropanolamine; ammonia such as aqueous ammonia; Is mentioned. Among these, alkali metal hydroxides are preferable from the viewpoints of binding properties and operability, and sodium hydroxide, potassium hydroxide, and lithium hydroxide are particularly preferable.

  In addition to the polymer having a nitrile group-containing polymer unit, a hydrophilic group-containing polymer unit, an aromatic vinyl polymer unit, and a linear alkylene polymer unit, the binder further includes other binder components. May be included. As other binder components, various resin components can be used in combination. For example, polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid, polyacrylonitrile, polyacrylate, polymethacrylate, or the like may be used. it can. A copolymer containing 50% or more of the above resin component can also be used. For example, polyacrylic acid derivatives such as acrylic acid-styrene copolymer and acrylic acid-acrylate copolymer; acrylonitrile-styrene copolymer, acrylonitrile A polyacrylonitrile derivative such as an acrylate copolymer can also be used. Among these, it is preferable to use PVDF or a polyacrylonitrile derivative because the strength of the positive electrode and the resistance to electrolytic solution are excellent.

Furthermore, the soft polymers exemplified below can also be used as other binders.
Acrylic acid such as polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer Or an acrylic soft polymer which is a homopolymer of a methacrylic acid derivative or a copolymer with a monomer copolymerizable therewith;
Silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer, etc. Olefinic soft polymers of
Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
Epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
And other soft polymers such as natural rubber, polypeptide, protein, polyester-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer.
These soft polymers may have a cross-linked structure or may have a functional group introduced by modification. These may be used alone or in combination of two or more. Among these, a polyacrylonitrile derivative is preferable in order to improve the dispersibility of the positive electrode active material.

  The content of other binders is preferably 5 to 80% by mass, more preferably 10 to 70% by mass, based on 100% by mass of the total amount of binder (total amount of binder and other binders). %, Particularly preferably 20 to 60% by mass. When the content ratio of the other binder is within the above range, the internal resistance of the battery is not increased and high temperature cycle characteristics can be exhibited.

(Additive)
The binder composition for secondary battery positive electrode of the present invention contains the above-mentioned binder, and in addition, an additive may be added to improve the coating property of the slurry composition described later and the charge / discharge characteristics of the secondary battery. it can. These additives include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, polyacrylates such as sodium polyacrylate, polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, acrylic acid-vinyl alcohol copolymer, Examples include methacrylic acid-vinyl alcohol copolymer, maleic acid-vinyl alcohol copolymer, modified polyvinyl alcohol, polyethylene glycol, ethylene-vinyl alcohol copolymer, and partially saponified polyvinyl acetate. The use ratio of these additives is preferably less than 300% by mass, more preferably 30% by mass or more and 250% by mass or less, and particularly preferably 40% by mass or more and 200% by mass with respect to the total solid content of the binder composition. It is as follows. If it is this range, the secondary battery positive electrode excellent in smoothness can be obtained. Moreover, an isothiazoline type compound and a chelate compound can also be added as an additive. In addition to the method of adding these additives to the binder composition, these additives can also be added to the slurry composition for a secondary battery positive electrode of the present invention described later.

(Method for producing binder composition for secondary battery positive electrode)
The manufacturing method of the binder composition for secondary battery positive electrodes of this invention is not limited sometimes, It manufactures by adding an additive to the above-mentioned binder dispersion liquid as needed, and mixing. The method of mixing the additive with the binder dispersion 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.

Secondary battery positive electrode slurry composition The secondary battery positive electrode slurry composition of the present invention (hereinafter sometimes referred to as "positive electrode slurry composition") is the secondary battery positive electrode binder composition and Contains a positive electrode active material. Below, the aspect which uses the slurry composition for secondary battery positive electrodes of this invention as a slurry composition for lithium ion secondary battery positive electrodes is demonstrated.

(Positive electrode active material)
As the positive electrode active material, an active material capable of occluding and releasing lithium ions is used. The electrode active material for the positive electrode of the lithium ion secondary battery (positive electrode active material) is largely divided into an inorganic compound and an organic compound. Separated.

  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 them, MnO, V ₂ O ₅ , V ₆ O ₁₃ and TiO ₂ are preferable from the viewpoint of cycle stability and capacity of the obtained secondary battery.
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 composite oxide, lithium composite oxide of Ni—Co—Al, solid solution of LiMaO ₂ and Li ₂ MbO ₃ , xLiMaO _2. (1-x) Li ₂ MbO ₃ (0 <x <1, Ma is average And one or more transition metals having an oxidation state of 3+, and Mb is one or more transition metals having an average oxidation state of 4+). From the viewpoint of improving the cycle characteristics of the secondary battery, LiCoO ₂ is preferably used, and from the viewpoint of improving the energy density of the secondary battery, a solid solution of LiMaO ₂ and Li ₂ MbO ₃ is preferable. Further, as a solid solution of LiMaO ₂ and Li ₂ MbO ₃ , in particular, xLiMaO _2. (1-x) Li ₂ MbO ₃ (0 <x <1, Ma = Ni, Co, Mn, Fe, Ti, etc., Mb = Mn, Zr, Ti, etc.) are preferred, and xLiMaO _2. (1-x) Li ₂ MnO ₃ (0 <x <1, Ma = Ni, Co, Mn, Fe, Ti, etc.) is particularly preferred.

As the lithium-containing composite metal oxide having a spinel structure, Li _a [Mn _2−x Md _x ] O _{4 in} which a part of Mn of lithium manganate (LiMn ₂ O ₄ ) is substituted with another transition metal (here, Md includes one or more transition metals having an average oxidation state of 4+, Md = Ni, Co, Fe, Cu, Cr, etc., 0 <x <1, 0 ≦ a ≦ 1), and the like. Among them, _Li a was replaced Mn with _{Fe Fe x Mn 2-x O} 4-z (0 ≦ a ≦ 1,0 <x <1,0 ≦ z ≦ 0.1) , since the cost is inexpensive Preferably, LiNi _0.5 Mn _1.5 O ₄ or the like in which Mn is replaced with Ni can replace all of Mn ³⁺ which is considered to be a structural deterioration factor, and perform an electrochemical reaction from Ni ²⁺ to Ni ⁴⁺ . Therefore, a high operating voltage and a high capacity can be obtained, which is preferable.

Examples of the lithium-containing composite metal oxide having an olivine structure include Li _y McPO ₄ (wherein Mc is one or more transition metals having an average oxidation state of 3+, Mc = Mn, Co, etc., 0 ≦ y ≦ 2 An olivine type lithium phosphate compound represented by Mn or Co may be partially substituted with other metals, and examples of metals that can be substituted include Fe, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo. Can be mentioned.

Other examples include a positive electrode active material having a polyanion structure such as Li ₂ MeSiO ₄ (where Me is Fe, Mn), LiFeF ₃ having a perovskite structure, Li ₂ Cu ₂ O ₄ having an orthorhombic structure, and the like. .

  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 may be a mixture of the above inorganic compound and organic compound.

  The particle diameter of the positive electrode active material used in the present invention is appropriately selected in consideration of other constituent elements of the battery. From the viewpoint of improving battery characteristics such as load characteristics and cycle characteristics, the 50% volume cumulative diameter is Usually, it is 0.1-50 micrometers, Preferably it is 0.4-30 micrometers, More preferably, it is 1-20 micrometers. When the 50% volume cumulative diameter is within this range, a secondary battery having excellent output characteristics and a large charge / discharge capacity can be obtained, and a positive electrode slurry composition and a positive electrode for forming a positive electrode active material layer can be obtained. Easy to handle when manufacturing. The 50% volume cumulative diameter can be determined by measuring the particle size distribution by laser diffraction.

The BET specific surface area of the positive electrode active material is preferably 0.1 to 10 m ² / g, more preferably 0.2 to 1.0 cm ² / g. By setting the BET specific surface area of the positive electrode active material in the above range, it is easy to insert and desorb Li into the active material structure, and a stable slurry can be obtained.
In the present invention, the “BET specific surface area” refers to a BET specific surface area determined by a nitrogen adsorption method, and is a value measured according to ASTM D3037-81.

  Moreover, the positive electrode active material used in the present invention has a charge average voltage of less than 3.9 V with respect to lithium metal from the viewpoint of high structural stability during the long-term cycle of the positive electrode active material itself and oxidation stability of the electrolytic solution. It is preferable. In the present invention, the charging average voltage refers to a potential (plateau) at which the secondary battery is charged to the upper limit voltage by the constant current method and lithium is desorbed at that time. The upper limit voltage is a voltage that exceeds the voltage and may cause expansion and heat generation of the battery, which is the limit of ensuring safety.

  In the slurry composition for secondary battery positive electrode of the present invention, the total content (solid content equivalent amount) of the binder composition and the positive electrode active material is 100 parts by mass (solid content equivalent amount) of the positive electrode slurry composition. Preferably it is 10-90 mass parts, More preferably, it is 30-80 mass parts. Further, the content of the binder composition relative to the total amount of the positive electrode active material (solid content equivalent amount) is preferably 0.1 to 5 parts by mass, more preferably 0. 5 to 2 parts by mass. When the total content of the positive electrode active material and the binder composition in the positive electrode slurry composition and the content of the binder composition are in the above ranges, the viscosity of the resulting positive electrode slurry composition is optimized and the coating is smoothly performed. A sufficient adhesion strength can be obtained without increasing the resistance of the positive electrode obtained. As a result, peeling of the binder composition from the positive electrode active material in the electrode plate pressing step can be suppressed.

  The dispersion medium in the positive electrode slurry composition is not particularly limited as long as it can uniformly dissolve or disperse the binder composition, and either water or an organic solvent can be used. Examples of organic solvents include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene, xylene, and ethylbenzene; ketones such as acetone, ethylmethylketone, diisopropylketone, cyclohexanone, methylcyclohexane, and ethylcyclohexane. Chlorinated aliphatic hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; esters such as ethyl acetate, butyl acetate, γ-butyrolactone and ε-caprolactone; acylonitriles such as acetonitrile and propionitrile; tetrahydrofuran; Ethers such as ethylene glycol diethyl ether; alcohols such as methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether; N-methyl Amides such as lupyrrolidone and N, N-dimethylformamide may be mentioned.

  These dispersion media may be used alone, or two or more of these dispersion media may be mixed and used as a mixed solvent. Among these, a positive electrode active material and a conductive agent described later are excellent in dispersibility, and a solvent having a low boiling point and high volatility is preferable because it can be removed in a short time and at a low temperature. In addition to acetone, toluene, cyclohexanone, cyclopentane, tetrahydrofuran, cyclohexane, xylene, water, or N-methylpyrrolidone, cyclohexanone, toluene and the like, a mixed solvent thereof is preferable.

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

(Conductive agent)
In the slurry composition for positive electrodes, it is preferable to contain a electrically conductive agent. As the conductive agent, 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 agent, electrical contact between the positive electrode active materials can be improved, and when used in a secondary battery, the discharge rate characteristics can be improved. The content of the conductive agent in the positive electrode slurry composition is preferably 1 to 20 parts by mass, more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the positive electrode active material.

(Thickener)
In the slurry composition for positive electrodes, it is preferable to contain a thickener. Examples of thickeners include cellulosic 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; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches.

  As for the compounding quantity of a thickener, 0.5-1.5 mass parts is preferable with respect to 100 mass parts of positive 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 invention, “(modified) poly” means “unmodified poly” or “modified poly”, and “(meth) acryl” means “acryl” or “methacryl”.

(Other ingredients)
In addition to the above components, the positive electrode slurry composition may further contain other components such as a reinforcing material, a leveling agent, and an electrolytic solution additive having a function of suppressing electrolytic solution decomposition. It may be contained in the secondary battery positive electrode. 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 positive electrode can be obtained, and excellent long-term cycle characteristics can be exhibited. The content of the reinforcing material in the positive electrode slurry composition is usually 0.01 to 20 parts by mass, preferably 1 to 10 parts by mass with respect to 100 parts by mass of the total amount of the positive electrode active material. By being included in the said range, a high capacity | capacitance and a high load characteristic can be shown.

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

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

(Manufacture of slurry composition for secondary battery positive electrode)
The slurry composition for a secondary battery positive electrode is obtained by mixing the binder composition, the positive electrode active material, and a conductive agent used as necessary. The amount of the dispersion medium used when preparing the positive electrode slurry composition is such that the solid content concentration of the positive electrode slurry composition is usually in the range of 1 to 80% by mass, preferably 5 to 50% by mass. . When the solid content concentration is within this range, the binder composition is preferably dispersed uniformly.

  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.

  The viscosity of the positive electrode slurry composition is usually 10 to 50,000 mPa · s, preferably 100 to 10,000 mPa · s, at room temperature, when the positive electrode production method described later is carried out by the wet forming method (II). More preferably, it is in the range of 300 to 2,000 mPa · s. When the positive electrode production method described later is carried out by the dry molding method (III), it is usually 10 to 3,000 mPa · s, preferably 30 to 1. , 500 mPa · s, more preferably in the range of 50 to 1,000 mPa · s. When the viscosity of the positive electrode slurry composition is within this range, a uniform electrode can be obtained in the wet molding method, and the cycle characteristics of the resulting battery are also improved. In the dry molding method, the productivity of composite particles described later can be increased. Further, the higher the viscosity of the positive electrode slurry composition, the larger the spray droplets, and the larger the weight average particle diameter of the resulting composite particles. The viscosity is a value measured using a B-type viscometer at 25 ° C. and a rotation speed of 60 rpm.

Secondary Battery Positive Electrode The secondary battery positive electrode of the present invention (sometimes referred to as “positive electrode”) is formed by forming a positive electrode active material layer comprising the slurry composition for a secondary battery positive electrode of the present invention on a current collector. It becomes.

(Method for producing secondary battery positive electrode)
The manufacturing method of the secondary battery positive electrode of the present invention is not particularly limited. Specifically, (I) a method of forming the positive electrode slurry composition into a sheet, laminating the obtained sheet on a current collector to form a positive electrode active material layer (sheet forming method), (II) A method of forming a positive electrode active material layer (wet molding method) by applying and drying the positive electrode slurry composition on at least one surface, preferably both surfaces of the current collector, and (III) composite particles from the positive electrode slurry composition Examples thereof include a method (dry molding method) that is prepared, supplied onto a current collector and sheet-molded to form a positive electrode active material layer. Among these, (II) wet molding method or (III) dry molding method is preferable. (II) The wet molding method is excellent in the production efficiency of the secondary battery positive electrode, and (III) the dry molding method is excellent in that the capacity of the obtained secondary battery positive electrode can be increased and the internal resistance can be reduced.

  (II) In the wet molding method, the method for applying the positive electrode 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 30 minutes, and the drying temperature is usually 40 to 180 ° C.

  (III) The composite particles in the dry molding method refer to particles in which the binder composition, the positive electrode active material, and the like contained in the positive electrode slurry composition are integrated. By forming the positive electrode active material layer using the composite particles, the binding property of the obtained secondary battery positive electrode can be made higher and the internal resistance can be reduced.

  The composite particles suitably used in the present invention are produced by granulating the binder composition of the present invention, the positive electrode active material, and a conductive agent used as necessary.

  The granulation method of the composite particles is not particularly limited, and is spray drying granulation method, rolling bed granulation method, compression granulation method, stirring granulation method, extrusion granulation method, crushing granulation method, fluidized bed It can be produced by a known granulation method such as a granulation method, a fluidized bed multifunctional granulation method, a pulse combustion type drying method, or a melt granulation method. Among these, the spray-drying granulation method is preferable because composite particles in which the binder composition and the conductive agent are unevenly distributed near the surface can be easily obtained. When the composite particles obtained by the spray drying granulation method are used, the secondary battery positive electrode of the present invention can be obtained with high productivity. Moreover, the internal resistance of the secondary battery positive electrode can be further reduced.

In the spray drying granulation method, the slurry composition for secondary battery positive electrode of the present invention is spray dried and granulated to obtain composite particles. Spray drying is performed by spraying and drying the positive electrode slurry composition in hot air. An atomizer is mentioned as an apparatus used for spraying the slurry composition for positive electrodes.
There are two types of atomizers: a rotating disk method and a pressure method. In the rotating disk method, the positive electrode slurry composition is introduced almost at the center of the high-speed rotating disk, and the positive electrode slurry composition is released out of the disk by the centrifugal force of the disk. It is a method to form. The rotational speed of the disc depends on the size of the disc, but is usually 5,000 to 40,000 rpm, preferably 15,000 to 40,000 rpm. The lower the rotational speed of the disk, the larger the spray droplets and the larger the weight average particle diameter of the resulting composite particles. Examples of the rotating disk type atomizer include a pin type and a vane type, and a pin type atomizer is preferable. A pin-type atomizer is a type of centrifugal spraying device that uses a spraying plate, and the spraying plate has a plurality of spraying rollers removably mounted on a concentric circle along its periphery between upper and lower mounting disks. It consists of The slurry composition for the positive electrode is introduced from the center of the spray plate, adheres to the spray roller by centrifugal force, moves outward on the roller surface, and finally sprays away from the roller surface. On the other hand, the pressurization method is a method in which the positive electrode slurry composition is pressurized and sprayed from a nozzle to be dried.

  The temperature of the positive electrode slurry composition to be sprayed is usually room temperature, but may be heated to room temperature or higher. Moreover, the hot air temperature at the time of spray-drying is 80-250 degreeC normally, Preferably it is 100-200 degreeC.

  In spray drying, the method of blowing hot air is not particularly limited, for example, a method in which the hot air and the spray direction flow in the horizontal direction, a method in which the hot air is sprayed at the top of the drying tower and descends with the hot air, and the sprayed droplet and the hot air are in countercurrent contact And a system in which sprayed droplets first flow in parallel with hot air and then drop by gravity to make countercurrent contact.

The shape of the composite particles suitably used in the present invention is preferably substantially spherical. That is, the short axis diameter of the composite particles is L _s , the long axis diameter is L _l , L _a = (L _s + L _l ) / 2, and a value of (1− (L ₁ −L _s ) / L _a ) × 100 Is a sphericity (%), the sphericity is preferably 80% or more, more preferably 90% or more. Here, the minor axis diameter L _s and the major axis diameter L _l are values measured from a transmission electron micrograph image.

  The volume average particle diameter of the composite particles suitably used in the present invention is usually 5 to 500 μm, preferably 7 to 300 μm, more preferably 10 to 100 μm. The volume average particle diameter can be measured using a laser diffraction particle size distribution analyzer.

  In the present invention, the feeder used in the step of supplying the composite particles onto the current collector is not particularly limited, but is preferably a quantitative feeder capable of supplying the composite particles quantitatively. Here, being able to supply quantitatively means that composite particles are continuously supplied using such a feeder, the supply amount is measured a plurality of times at regular intervals, and the average value m of the measured values and the standard deviation σm are obtained. It means that the CV value (= σm / m × 100) is 4 or less. The quantitative feeder preferably used in the present invention has a CV value of preferably 2 or less. Specific examples of the quantitative feeder include a gravity feeder such as a table feeder and a rotary feeder, and a mechanical force feeder such as a screw feeder and a belt feeder. Of these, the rotary feeder is preferred.

  Next, the current collector and the supplied composite particles are pressurized with a pair of rolls to form a positive electrode active material layer on the current collector. In this step, the composite particles heated as necessary are formed into a sheet-like positive electrode active material layer by a pair of rolls. The temperature of the supplied composite particles is preferably 40 to 160 ° C, more preferably 70 to 140 ° C. When composite particles in this temperature range are used, there is no slip of the composite particles on the surface of the press roll, and the composite particles are continuously and uniformly supplied to the press roll. A positive electrode active material layer with little variation can be obtained.

  The temperature at the time of molding is usually 0 to 200 ° C, preferably higher than the melting point or glass transition temperature of the binder used in the present invention, and more preferably 20 ° C or higher than the melting point or glass transition temperature. The forming speed in the case of using a roll is usually larger than 0.1 m / min, preferably 35 to 70 m / min. Moreover, the press linear pressure between the rolls for a press is 0.2-30 kN / cm normally, Preferably it is 0.5-10 kN / cm.

  In the above production method, the arrangement of the pair of rolls is not particularly limited, but is preferably arranged substantially horizontally or substantially vertically. When arranged substantially horizontally, the current collector is continuously supplied between a pair of rolls, and the composite particles are supplied to at least one of the rolls so that the composite particles are supplied to the gap between the current collector and the rolls. The positive electrode active material layer can be formed by pressurization. When arranged substantially vertically, the current collector is transported in the horizontal direction, the composite particles are supplied onto the current collector, and the supplied composite particles are leveled with a blade or the like as necessary. The positive electrode active material layer can be formed by supplying between a pair of rolls and applying pressure.

  In producing the secondary battery positive electrode of the present invention, after forming a positive electrode active material layer made of the positive electrode slurry composition on the current collector, the positive electrode active material is subjected to pressure treatment using a die press or a roll press. It is preferable to have a step of reducing the porosity of the layer. 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 there arises a problem that the positive electrode active material layer easily peels off from the current collector. Further, when a curable polymer is used for the positive electrode binder composition, it is preferably cured.

  The thickness of the positive electrode active material layer in the secondary battery positive electrode of the present invention 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 high temperature cycle characteristics are high.

  In this invention, the content rate of the positive electrode active material in a positive electrode active material layer becomes like this. Preferably it is 90-99.9 mass%, More preferably, it is 95-99 mass%. By making the content rate of a positive electrode active material into the said range, a softness | flexibility and a binding property can be shown, showing a high capacity | capacitance.

(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, aluminum is particularly preferable as the current collector used for the secondary battery positive electrode. 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 positive 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. In order to increase the adhesive strength and conductivity between the positive electrode active material layer and the current collector, an intermediate layer may be formed on the surface of the current collector, and among them, it is preferable to form a conductive adhesive layer.

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 positive electrode is the secondary battery positive electrode.

(Negative electrode)
The negative electrode is formed by laminating a negative electrode active material layer including a negative electrode active material and a secondary battery negative electrode binder composition on a current collector.

(Negative electrode active material)
The negative electrode active material used in the present invention is a material that transfers electrons within the secondary battery negative electrode.
Specific examples of negative electrode active materials for lithium ion secondary batteries include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), and pitch-based carbon fibers; high conductivity such as polyacene Examples include molecules. Crystalline carbonaceous materials such as graphite, natural graphite, and mesocarbon microbeads (MCMB) are preferable. Moreover, as a negative electrode active material, metals, such as silicon, tin, zinc, manganese, iron, nickel, these alloys, the oxide or sulfate of the said metal or alloy can be used. In addition, lithium alloys such as lithium metal, Li—Al, Li—Bi—Cd, and Li—Sn—Cd, lithium transition metal nitride, silicone, and the like can also be used. The said negative electrode active material can be used individually or in combination of 2 or more types.

  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 size 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 20 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 tap density of the negative electrode active material is not particularly limited, but 0.6 g / cm ³ or more is preferably used.

  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.

In the present invention, the density of the negative electrode active material layer of the secondary battery negative electrode 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.

(Binder composition for secondary battery negative electrode)
As a binder composition for secondary battery negative electrodes, a well-known thing can be used without being restrict | limited in particular. For example, resins such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, acrylic soft heavy A soft polymer such as a polymer, a diene soft polymer, an olefin soft polymer, or a vinyl soft polymer can be used. These may be used alone or in combination of two or more.

  In addition to the above components, the negative electrode further contains other components such as the above-described conductive agent, thickener, reinforcing material, leveling agent, and electrolyte additive having functions such as electrolyte solution decomposition suppression. Also good. These are not particularly limited as long as they do not affect the battery reaction.

  As the current collector, the current collector used for the above-described positive electrode of the secondary battery can be used, and is not particularly limited as long as it is a material having electrical conductivity and electrochemical durability. Copper is particularly preferred for the battery negative electrode.

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

  The negative electrode can be produced in the same manner as the above-described secondary battery positive electrode.

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

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

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Usually, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene. Alkyl carbonates such as carbonate (BC) and methyl ethyl carbonate (MEC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane 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. As the additive, carbonate compounds such as vinylene carbonate (VC) are preferable.

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

(Method for 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 electrolytic solution is injected into the battery container and sealed. Further, if necessary, an expanded metal, an overcurrent prevention element such as a fuse or a PTC element, a lead plate and the like can be inserted to prevent an increase in pressure inside the battery and overcharge / discharge. The shape of the battery may be any of a laminated cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, a flat type, and the like.

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

<Glass transition temperature of binder>
The glass transition temperature (Tg) of the binder was measured based on JIS K 7121; 1987 using a differential scanning calorimeter (DSC6220SII manufactured by Nanotechnology).

<Iodine value of binder>
100 g of the NMP solution of the binder was coagulated with 1 liter of methanol and then vacuum dried at 60 ° C. overnight. The iodine value of the dried binder was measured according to JIS K6235;

<Battery electrolyte swelling degree>
The NMP solution of the binder was cast on a polytetrafluoroethylene sheet and dried to obtain a cast film. 4 cm ² of this cast film was cut out and weighed (weight A before immersion), and then immersed in an electrolytic solution at a temperature of 60 ° C. The soaked film was pulled up after 72 hours and wiped with towel paper, and the weight (weight B after soaking) was measured immediately. The degree of swelling of the electrolyte solution of the binder is calculated from the following formula and evaluated according to the following criteria. The lower the degree of swelling, the better the battery characteristics (high temperature cycle characteristics). As an electrolytic solution, LiPF ₆ is 1 in a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) so that the volume ratio at 20 ° C. is EC: DEC = 1: 2. A solution dissolved at a concentration of 0.0 mol / L was used.
Swelling degree (%) = B / A × 100 (%)

<Electrode flexibility>
A rod having a different diameter was placed on the positive electrode active material layer side of the positive electrode, and the positive electrode was wound around the rod to evaluate whether the positive electrode active material layer was broken. It shows that it is excellent in the winding property of a positive electrode, so that the diameter of a stick | rod is small.
When the winding property is excellent, peeling of the positive electrode active material layer can be suppressed, and thus the cycle characteristics of the secondary battery are excellent.
A: Not cracked at 1.2 mmφ B: Not cracked at 1.5 mmφ C: Not cracked at 2 mmφ D: Not cracked at 3 mmφ E: Not cracked at 4 mmφ

<High temperature cycle characteristics>
The 5-cell lithium ion secondary battery was charged to 4.2 V by a constant current method of 0.5 C in a 45 ° C. atmosphere, and charging / discharging to 3.0 V was repeated 200 cycles. The charge / discharge capacity retention ratio represented by the ratio of the electric capacity at the end of 200 cycles to the electric capacity at the end of 5 cycles (= electric capacity at the end of 200 cycles / electric capacity at the end of 5 cycles × 100) (%) Asked. It shows that it is excellent in high temperature cycling characteristics, so that this value is large.
A: 85% or more B: 80% or more and less than 85% C: 70% or more and less than 80% D: 60% or more and less than 70% E: 40% or more and less than 60% F: Less than 40%

Example 1
[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile, 10 parts of styrene and 5 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. , 3-butadiene 65 parts, ammonium persulfate 0.25 part was added, and the polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and A polymer comprising polymerized units capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 45 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. Further, 320 parts of N-methylpyrrolidone (hereinafter referred to as “NMP”) is added to 100 parts of this binder aqueous dispersion, water is evaporated under reduced pressure, and an NMP solution of the above binder is prepared as a positive electrode binder composition. Obtained. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 20% by mass (polymerized unit derived from acrylonitrile), 10% by mass aromatic vinyl polymerized unit (polymerized unit derived from styrene), 65% by mass polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the 1,3-butadiene-derived polymer units are 56.4% by mass of linear alkylene polymer units having 4 or more carbon atoms, 2.7% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. 5.9% by mass. Moreover, the glass transition temperature of the binder was less than −20 ° C. The iodine value of the binder was 13 mg / 100 mg. Furthermore, the swelling degree of the binder was 180%.

[Production of slurry composition for positive electrode and positive electrode]
100 parts of lithium cobaltate (LiCoO ₂ ) (particle diameter: 12 μm) having a layered structure as a positive electrode active material, 2.0 parts of acetylene black (HS-100: Electrochemical Industry), and NMP solid content of the binder 0 parts (solid content concentration 8.0%) and an appropriate amount of NMP were stirred with a planetary mixer to prepare a positive electrode slurry composition.

An aluminum foil with a thickness of 20 μm was prepared as a current collector. The positive electrode slurry composition is applied on an aluminum foil with a comma coater so that the film thickness after drying is about 65 μm, dried at 60 ° C. for 20 minutes, 120 ° C. for 20 minutes, and then heated at 150 ° C. for 2 hours. Thus, a positive electrode raw material was obtained. This positive electrode original fabric was rolled by a roll press to produce a positive electrode comprising a positive electrode active material layer having a density of 3.2 g / cm ³ and an aluminum foil. The positive electrode had a thickness of 70 μm. Electrode flexibility was evaluated using the produced positive electrode. The results are shown in Table 1.

[Production of slurry composition for negative electrode and 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 4 m ² / g as a negative electrode active material, and a 1% aqueous solution of carboxymethyl cellulose as a dispersant (Daiichi Kogyo Seiyaku Co., Ltd.) 1 part of “BSH-12” produced in the same manner as solid content was added, and the solid content concentration was adjusted to 55% with ion-exchanged water, and then mixed at 25 ° C. for 60 minutes. Next, the solid content concentration was adjusted to 52% with ion-exchanged water. Thereafter, the mixture was further mixed at 25 ° C. for 15 minutes to obtain a mixed solution.

  To the above mixture, 1.0 part of a 40% aqueous dispersion containing a styrene-butadiene copolymer (with a glass transition temperature of −15 ° C.) in an amount equivalent to the solid content, and ion-exchanged water are added, and the final solid content concentration Was adjusted to 50%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for a negative electrode having good fluidity.

  The slurry composition for the negative electrode was applied on a copper foil having a thickness of 20 μm, which was a current collector, with a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the copper foil in an oven at 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 having a thickness of 80 μm.

[Preparation of separator]
A single-layer polypropylene separator (width 65 mm, length 500 mm, thickness 25 μm, manufactured by dry method, porosity 55%) was cut into a square of 5 × 5 cm ² .

[Manufacture of lithium ion secondary batteries]
An aluminum packaging exterior was prepared as the battery exterior. The positive electrode obtained above 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 above was placed on the surface of the positive electrode active material layer of the positive electrode.
Furthermore, the negative electrode obtained above 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. Furthermore, a 1.0 μM LiPF ₆ solution containing 1.5% vinylene carbonate (VC) was charged. The solvent of this LiPF ₆ solution is a mixed solvent (EC / EMC = 3/7 (volume ratio)) of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). Furthermore, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior, and a lithium ion secondary battery was manufactured.
About the obtained lithium ion secondary battery, the high temperature cycling characteristic was evaluated.

(Example 2)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile, 5 parts of styrene and 5 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. , 3-butadiene 70 parts, ammonium persulfate 0.25 part was added, and the polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and A polymer comprising polymerized units capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 45 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 20% by weight (polymerized unit derived from acrylonitrile), 5% by weight aromatic vinyl polymerized unit (polymerized unit derived from styrene), 70% by weight polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the monomer unit derived from 1,3-butadiene is 60.7% by mass of linear alkylene polymer unit having 4 or more carbon atoms, 3.0% by mass of unhydrogenated butadiene polymer unit, and 1,2-addition. The polymerization unit was formed from 6.3% by mass. Moreover, the glass transition temperature of the binder was less than −20 ° C. The iodine value of the binder was 14 mg / 100 mg. Furthermore, the swelling degree of the binder was 150%.

Example 3
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile, 45 parts of styrene and 5 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. , 3-butadiene 30 parts, 0.25 part of ammonium persulfate was added and polymerization reaction was performed at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and A polymer comprising polymerized units capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 20% by mass (polymerized unit derived from acrylonitrile), 45% by mass aromatic vinyl polymerized unit (polymerized unit derived from styrene), 30% by mass polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the 1,3-butadiene-derived polymer units are 25.4% by mass of linear alkylene polymer units having 4 or more carbon atoms, 1.9% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. 2.7% by mass. The glass transition temperature of the binder was 24 ° C. The iodine value of the binder was 9 mg / 100 mg. Furthermore, the swelling degree of the binder was 415%.

Example 4
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion exchange water, 2.5 parts of sodium alkylbenzenesulfonate, 20 parts of acrylonitrile, 10 parts of styrene, 30 parts of methyl methacrylate and 5 parts of methacrylic acid are put in this order, and the inside of the bottle is filled with nitrogen. After the substitution, 35 parts of 1,3-butadiene was injected, 0.25 part of ammonium persulfate was added, and a polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a hydrophilic group A polymer comprising a polymerization unit having a polymerization unit and a polymerization unit capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 20% by mass (polymerized unit derived from acrylonitrile), 10% by mass aromatic vinyl polymerized unit (polymerized unit derived from styrene), 35% by mass polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the 1,3-butadiene-derived polymer units are 29.9% by mass of linear alkylene polymer units having 4 or more carbon atoms, 1.9% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. 3.2% by mass. The glass transition temperature of the binder was 30 ° C. The iodine value of the binder was 9 mg / 100 mg. Furthermore, the swelling degree of the binder was 415%.

(Example 5)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion exchange water, 2.5 parts of sodium alkylbenzenesulfonate, 7 parts of acrylonitrile, 15 parts of styrene, 15 parts of butyl acrylate and 5 parts of methacrylic acid are put in this order, and the inside of the bottle is filled with nitrogen. After the substitution, 58 parts of 1,3-butadiene was injected, 0.25 part of ammonium persulfate was added, and the polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a hydrophilic group A polymer comprising a polymerization unit having a polymerization unit and a polymerization unit capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 7% by mass (polymerized unit derived from acrylonitrile), 15% by mass aromatic vinyl polymerized unit (polymerized unit derived from styrene), 58% by mass polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the polymerized unit derived from 1,3-butadiene is 50.5% by mass of linear alkylene polymer unit having 4 or more carbon atoms, 2.3% by mass of unhydrogenated butadiene polymer unit, and 1,2-addition polymerized unit. It was formed from 5.2% by mass. Moreover, the glass transition temperature of the binder was less than −20 ° C. The iodine value of the binder was 11 mg / 100 mg. Furthermore, the swelling degree of the binder was 120%.

(Example 6)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzene sulfonate, 30 parts of acrylonitrile, 10 parts of styrene and 5 parts of methacrylic acid were put in this order. , 3-butadiene 55 parts, ammonium persulfate 0.25 part was added and a polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and A polymer comprising polymerized units capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 30% by weight (polymerized unit derived from acrylonitrile), 10% by weight aromatic vinyl polymerized unit (polymerized unit derived from styrene), 55% by weight polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) ) Containing 5 mass% of polymerized units (polymerized units derived from methacrylic acid). Here, the 1,3-butadiene-derived polymer units are 47.7% by mass of linear alkylene polymer units having 4 or more carbon atoms, 2.3% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. 5.0% by mass. The glass transition temperature of the binder was 18 ° C. The iodine value of the binder was 11 mg / 100 mg. Furthermore, the swelling degree of the binder was 455%.

(Comparative Example 1)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 35 parts of acrylonitrile and 5 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. 60 parts are injected, 0.25 part of ammonium persulfate is added, and a polymerization reaction is carried out at a reaction temperature of 40 ° C. to form a polymer unit having a nitrile group, a polymer unit having a hydrophilic group, and a polymer unit capable of forming a conjugated diene monomer. A polymer comprising was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 35% by mass (polymerized units derived from acrylonitrile), 60% by mass of polymerized units derived from 1,3-butadiene, and 5% by mass of polymerized units having a hydrophilic group (carboxylic acid group) (polymerized units derived from methacrylic acid). Included. Here, the 1,3-butadiene-derived polymer units are 53.1% by mass of linear alkylene polymer units having 4 or more carbon atoms, 1.5% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. 5.4% by mass. Moreover, it was less than -20 degreeC of glass transition temperature of a binder. The iodine value of the binder was 7 mg / 100 mg. Furthermore, the swelling degree of the binder was 525%.

(Comparative Example 2)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzenesulfonate, 18 parts of acrylonitrile, 70 parts of styrene and 2 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. , 3-butadiene 10 parts, 0.25 part of ammonium persulfate was added and the polymerization reaction was carried out at a reaction temperature of 40 ° C., and a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and A polymer comprising polymerized units capable of forming a conjugated diene monomer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 90 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 10 mg / 100 mg.

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 18% by weight (polymerized unit derived from acrylonitrile), 70% by weight aromatic vinyl polymerized unit (polymerized unit derived from styrene), 10% by weight polymerized unit derived from 1,3-butadiene, hydrophilic group (carboxylic acid group) 2% by mass of polymerized units (polymerized units derived from methacrylic acid). Here, the 1,3-butadiene-derived polymer units are 7.0% by mass of linear alkylene polymer units having 4 or more carbon atoms, 2.1% by mass of unhydrogenated butadiene polymer units, and 1,2-addition polymer units. It was formed from 0.9% by mass. The glass transition temperature of the binder was 45 ° C. The iodine value of the binder was 10 mg / 100 mg. Furthermore, the swelling degree of the binder was 485%.

(Comparative Example 3)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
In an autoclave equipped with a stirrer, 240 parts of ion-exchanged water, 2.5 parts of sodium alkylbenzene sulfonate, 30 parts of styrene and 2 parts of methacrylic acid were put in this order, and the inside of the bottle was replaced with nitrogen. 68 parts are injected, 0.25 part of ammonium persulfate is added, and a polymerization reaction is carried out at a reaction temperature of 40 ° C. to include an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and a polymer unit capable of forming a conjugated diene monomer. A polymer was obtained. The polymerization conversion was 85%, and the iodine value was 280 mg / 100 mg.

  A 400 milliliter (total solid content 48 grams) solution prepared by adjusting the total solid content of the polymer to 12% by mass with water was charged into a 1 liter autoclave equipped with a stirrer, and nitrogen gas was added for 10 minutes. After removing the dissolved oxygen in the polymer by flowing, 75 mg of palladium acetate as a hydrogenation reaction catalyst was dissolved in 180 ml of water to which nitric acid of 4 times moles of Pd had been added and added. After the inside of the system was replaced twice with hydrogen gas, the autoclave contents were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “first-stage hydrogenation reaction”) for 6 hours. ) At this time, the iodine value of the polymer was 35 mg / 100 mg.

  Next, the autoclave was returned to atmospheric pressure, and further, 25 mg of palladium acetate was dissolved in 60 ml of water added with 4 times moles of nitric acid with respect to Pd as a hydrogenation reaction catalyst. After the inside of the system was replaced twice with hydrogen gas, the contents of the autoclave were heated to 50 ° C. while being pressurized with hydrogen gas up to 3 MPa, and the hydrogenation reaction (referred to as “second stage hydrogenation reaction”) was performed for 6 hours. )

  Thereafter, the contents were returned to room temperature, the inside of the system was made into a nitrogen atmosphere, and then concentrated using an evaporator until the solid concentration was 40% to obtain a binder aqueous dispersion. In addition, 320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the binder as a positive electrode binder composition. After 100 g of the NMP solution was coagulated with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. As a result, the binder was an aromatic vinyl polymer unit (based on the total amount of the polymer). 30% by mass of polymer units derived from styrene), 68% by mass of polymer units derived from 1,3-butadiene, and 2% by mass of polymer units having a hydrophilic group (carboxylic acid group) (polymer units derived from methacrylic acid) It was out. Here, the polymer unit derived from butadiene is 10.8% by mass of linear alkylene polymer unit having 4 or more carbon atoms, 51.1% by mass of unhydrogenated butadiene polymer unit, and 6.1% of 1,2-addition polymer unit. % And was formed. Moreover, the glass transition temperature of the binder was less than −20 ° C. The iodine value of the binder was 240 mg / 100 mg. Furthermore, the swelling degree of the binder was 675%.

(Comparative Example 4)
Except having used the following binder composition as a positive electrode binder composition, operation similar to Example 1 was performed, the positive electrode slurry composition and the positive electrode were obtained, and the battery was produced. The results of each evaluation are shown in Table 1.

[Production of binder composition for positive electrode]
To polymerization can A, 6.8 parts of 2-ethylhexyl acrylate, 2 parts of acrylonitrile, 0.12 part of sodium lauryl sulfate and 79 parts of ion-exchanged water were added, 0.2 part of ammonium persulfate as a polymerization initiator, and 10 parts of ion-exchanged water. The mixture was heated to 60 ° C. and stirred for 90 minutes, and then, in another polymerization vessel B, 61.2 parts of 2-ethylhexyl acrylate, 18 parts of acrylonitrile, 2.0 parts of methacrylic acid, 10 parts of styrene, sodium lauryl sulfate 0.7 The emulsion prepared by adding 46 parts of ion exchange water and stirring was sequentially added from polymerization can B to polymerization can A over about 180 minutes, and then stirred for about 120 minutes, resulting in a monomer consumption of 95%. The reaction was terminated by cooling, and then the pH was adjusted with a 4% NaOH aqueous solution to obtain an aqueous dispersion of the polymer.
320 parts of NMP was added to 100 parts of this binder aqueous dispersion, and water was evaporated under reduced pressure to obtain an NMP solution of the above binder as a positive electrode binder composition. After 100 g of the NMP solution was solidified with 1 liter of methanol, it was vacuum dried overnight at 60 ° C. to obtain a dried product and analyzed by NMR. The binder was a polymer unit having a nitrile group with respect to the total amount of the polymer. 20% by mass (polymerized unit derived from acrylonitrile), 10% by mass of aromatic vinyl polymerized unit (polymerized unit derived from styrene), and a polymerized unit (polymerized unit derived from methacrylic acid) having a hydrophilic group (carboxylic acid group). 2% by mass was contained. Moreover, the glass transition temperature of the binder was less than −20 ° C. The iodine value of the binder was 0 mg / 100 mg. Furthermore, the swelling degree of the binder was 415%.

  From the results of Table 1, the secondary battery positive electrode and the secondary battery using the binder compositions of Examples 1 to 6 have a balance of evaluation of electrode flexibility and high temperature cycle characteristics as compared with Comparative Examples 1 to 4. Excellent.

Claims (8)

A binder composition for a secondary battery positive electrode comprising a binder containing a polymer unit having a nitrile group, an aromatic vinyl polymer unit, a polymer unit having a hydrophilic group, and a linear alkylene polymer unit having 4 or more carbon atoms,
Ri content ratio 5-40% by mass of the aromatic vinyl polymer units,
Secondary battery positive electrode binder composition glass transition temperature of the binder is Ru der 15 ℃ or less.   2. The binder composition for a secondary battery positive electrode according to claim 1, wherein a content ratio of the polymer units having the hydrophilic group is 0.05 to 20% by mass.   The binder composition for a secondary battery positive electrode according to claim 1 or 2, wherein a content ratio of the polymer unit having the nitrile group is 2 to 50% by mass.   The binder composition for secondary battery positive electrodes in any one of Claims 1-3 whose iodine value of the said binder is 3-60 mg / 100 mg. The slurry composition for secondary battery positive electrodes formed by containing the binder composition for secondary battery positive electrodes in any one of Claims 1-4, and a positive electrode active material. The secondary battery positive electrode formed by forming the positive electrode active material layer which consists of a slurry composition for secondary battery positive electrodes of Claim 5 on a collector. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolytic solution, wherein the positive electrode is the secondary battery positive electrode according to claim 6 . The manufacturing method of the secondary battery positive electrode which has the process of apply | coating and drying the slurry composition for secondary battery positive electrodes of Claim 5 to at least single side | surface of a collector.