JP2013030447A - Slurry for positive electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slurry for a positive electrode, having high oxidation resistance for being resistant to oxidation of positive electrode reaction and allowing manufacture of a positive electrode excellent in adhesion and also electrical characteristics.SOLUTION: The slurry for a positive electrode is a slurry for a positive electrode of an electricity storage device and contains at least (A) a polymer particle having a repeating unit from a monomer having a fluorine atom, (B) an active material particle comprising a lithium atom-containing oxide and (C) a liquid medium. A ratio (Da/Db) of an average particle diameter (Da) of the (A) polymer particle to an average particle diameter (Db) of the (B) active material particle is 0.01 to 1.0 and the slurry has a spinnability of 30 to 80%.

Description

  The present invention relates to a slurry for a positive electrode containing polymer particles and active material particles.

In recent years, a power storage device having a high voltage and a high energy density is required as a power source for driving electronic equipment. In particular, lithium ion batteries, lithium ion capacitors, and the like are expected as power storage devices with high voltage and high energy density.
The electrode used for such an electricity storage device is usually produced by applying and drying a mixture of active material particles and polymer particles functioning as an electrode binder onto the current collector surface. The properties required for the polymer particles used for the electrode include the binding ability between the active material particles and the binding ability between the active material particles and the current collector, the abrasion resistance in the step of winding the electrode, Examples thereof include resistance to falling off, in which fine powder of the active material is not generated from the electrode composition layer (hereinafter also simply referred to as “active material layer”) applied by cutting or the like. When the polymer particles satisfy these various required characteristics, the degree of freedom in designing the structure of the electricity storage device, such as the method of folding the obtained electrode and setting the winding radius, is increased, and the miniaturization of the device is achieved. Can do. In addition, it has been empirically clarified that the quality of the active material particles is substantially proportional to the ability to bind the active material particles, the binding ability between the active material particles and the current collector, and the powder-off resistance. . Therefore, in the present specification, hereinafter, the term “adhesiveness” may be used in a comprehensive manner.

Since the polymer particles used for the active material layer are generally non-conductive, they tend to hinder the movement of electrons. For this reason, reducing the use ratio of the polymer particles is effective in improving the electrical characteristics of the electricity storage device. However, if the use ratio of the polymer particles is reduced, the above-mentioned adhesion is insufficient, and the workability is greatly impaired, which is not practical. For this reason, there is a limit in reducing the use ratio of the polymer particles, and there is a trade-off relationship between improvement of electrical characteristics.
For example, Patent Document 1 describes a technique for controlling the particle diameter of polymer particles in order to improve the electrical characteristics and adhesion of the electricity storage device at the same time. Patent Document 2 describes a technique for improving adhesion by controlling the ratio between the average particle diameter of polymer particles used as an electrode binder and the average particle diameter of active material particles.
The above-mentioned problems are particularly noticeable in the positive electrode slurry. In other words, when polymer particles made of organic substances are applied to the positive electrode, a high degree of oxidation resistance that can withstand the oxidation of the positive electrode reaction is required, and therefore it is necessary to use a fluorine-containing organic polymer. It is advantageous. However, since organic polymers containing fluorine atoms generally have poor adhesion, it is more difficult to ensure the mechanical strength and durability of the resulting electrode. Therefore, the techniques described in the above patent documents are not yet at a level applicable to the positive electrode.

Recently, in consideration of the environment and the like, the use of an electrode slurry containing water as a dispersion medium (hereinafter also simply referred to as “aqueous slurry”) instead of a conventional organic medium has begun to be studied. After this aqueous slurry is applied to the surface of the current collector, the active material layer can be formed on the surface of the current collector by circulating hot air in the dryer or spraying it to evaporate water. However, according to this method, there is a problem that when the water evaporates, the polymer particles contained in the aqueous slurry are localized and immobilized. For example, when the proportion of polymer particles at the interface between the current collector and the active material layer is relatively reduced, the adhesion between the current collector and the active material layer is significantly reduced. In addition, if the polymer particles are unevenly distributed on the side of the active material layer opposite to the surface in contact with the current collector, the penetration of the electrolytic solution into the active material layer is hindered.
Thus, when the active material layer in which the polymer particles contained in the aqueous slurry are localized and immobilized is formed, not only the above-described adhesion is remarkably lowered, but also the electrical characteristics of the electricity storage device are sufficiently improved. It cannot be demonstrated. Accordingly, there is a need for a positive electrode slurry in which localization of polymer particles is suppressed when forming a positive electrode in an aqueous positive electrode slurry.

Japanese Patent Laid-Open No. 2003-1000029 JP-A-11-297313

The present invention has been made in view of the above circumstances, and its first object is to have a high degree of oxidation resistance capable of withstanding the oxidation property of the positive electrode reaction, excellent adhesion, and electrical characteristics. The object is to provide a positive electrode slurry capable of producing an excellent positive electrode.
A second object of the present invention is to provide a positive electrode slurry in which localization of polymer particles during formation of the positive electrode is suppressed even when used as an aqueous slurry.

The above objects and advantages of the present invention are as follows:
Polymer particles having at least (A) a repeating unit derived from a monomer having a fluorine atom,
(B) An active material particle comprising a lithium atom-containing oxide, and (C) a slurry for a positive electrode of an electricity storage device containing a liquid medium,
The ratio (Da / Db) of the average particle diameter (Da) of the (A) polymer particles to the average particle diameter (Db) of the (B) active material particles is 0.01 to 1.0, and the slurry This is achieved by the positive electrode slurry, characterized in that the spinnability is 30 to 80%.

According to the positive electrode slurry of the present invention, it is possible to produce a positive electrode having excellent oxidation resistance, high adhesion, and excellent electrical characteristics. Even when the slurry for positive electrode of the present invention is used as an aqueous slurry, a positive electrode in which localization of polymer particles is suppressed can be formed.
An electricity storage device including a positive electrode manufactured using the positive electrode slurry of the present invention has extremely good charge / discharge rate characteristics, which is one of electrical characteristics.

2 is a DSC chart of polymer particles obtained in Example 3. 6 is a DSC chart of polymer particles obtained in Comparative Example 2. 6 is a DSC chart of polymer particles obtained in Comparative Example 6. 6 is a DSC chart of polymer particles obtained in Synthesis Example 4.

Hereinafter, preferred embodiments of the present invention will be described in detail. It should be understood that the present invention is not limited only to the embodiments described below, and includes various modified examples that are implemented without departing from the scope of the present invention.
1. Each component contained in the positive electrode slurry The positive electrode slurry of the present invention is as described above.
Polymer particles having at least (A) a repeating unit derived from a monomer having a fluorine atom,
(B) The active material particle which consists of a lithium atom containing oxide, and (C) liquid medium are contained.

1.1 (A) Polymer Particle The (A) polymer particle contained in the positive electrode slurry of the present invention has a repeating unit derived from a monomer having a fluorine atom.
Examples of the monomer having a fluorine atom include an olefin compound having a fluorine atom and a (meth) acrylic acid ester having a fluorine atom. Examples of the olefin compound having a fluorine atom include vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, trifluorochloroethylene, and perfluoroalkyl vinyl ether. Examples of the (meth) acrylic acid ester having a fluorine atom include a compound represented by the following general formula (1), (meth) acrylic acid 3 [4 [1-trifluoromethyl-2,2-bis [bis (tri Fluoromethyl) fluoromethyl] ethynyloxy] benzooxy] 2-hydroxypropyl and the like.

(In the general formula (1), R ¹ is a hydrogen atom or a methyl group, and R ² is a C 1-18 hydrocarbon group containing a fluorine atom.)
Examples of R ² in the general formula (1) include a fluorinated alkyl group having 1 to 12 carbon atoms, a fluorinated aryl group having 6 to 16 carbon atoms, and a fluorinated aralkyl group having 7 to 18 carbon atoms. It is preferably a fluorinated alkyl group having 1 to 12 carbon atoms. Preferable specific examples of R ^{2 in} the general formula (1) include, for example, 2,2,2-trifluoroethyl group, 2,2,3,3,3-pentafluoropropyl group, 1,1,1, 3,3,3-hexafluoropropan-2-yl group, β- (perfluorooctyl) ethyl group, 2,2,3,3-tetrafluoropropyl group, 2,2,3,4,4,4- Hexafluorobutyl group, 1H, 1H, 5H-octafluoropentyl group, 1H, 1H, 9H-perfluoro-1-nonyl group, 1H, 1H, 11H-perfluoroundecyl group, perfluorooctyl group, etc. Can do. Among these, the monomer having a fluorine atom is preferably an olefin compound having a fluorine atom, particularly preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene. .
The monomer having a fluorine atom may be used alone or in combination of two or more.

The polymer particles (A) contained in the positive electrode slurry of the present invention may have only a repeating unit derived from a monomer having a fluorine atom, or a repetition derived from a monomer having a fluorine atom. In addition to the unit, a repeating unit derived from another monomer may be included.
Examples of other monomers that can be used here include alkyl esters of unsaturated carboxylic acids, cycloalkyl esters of unsaturated carboxylic acids, hydrophilic monomers, crosslinkable monomers, α-olefins, and aromatics. Group vinyl compounds (excluding those corresponding to the aforementioned hydrophilic monomers and crosslinkable monomers; the same shall apply hereinafter), etc., and one or more selected from these may be used. be able to.
Examples of the alkyl ester of the unsaturated carboxylic acid include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, and (meth) acrylic acid n. -Butyl, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, (meth) acryl N-octyl acid, nonyl (meth) acrylate, decyl (meth) acrylate, etc .;
Examples of the alkyl ester of the unsaturated carboxylic acid may include cyclohexyl (meth) acrylate, and one or more selected from these may be used.

Examples of the hydrophilic monomer include unsaturated carboxylic acids, hydroxyalkyl esters of unsaturated carboxylic acids, polyhydric alcohol esters of unsaturated carboxylic acids, α, β-unsaturated nitrile compounds, and aromatic vinyl compounds having a hydroxyl group. And so on. Specific examples thereof include, for example, (meth) acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid and the like as the unsaturated carboxylic acid;
Examples of the hydroxyalkyl ester of the unsaturated carboxylic acid include hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate;
Examples of the polyhydric alcohol ester of the unsaturated carboxylic acid include ethylene glycol (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, tri (Meth) acrylic acid trimethylolpropane, tetra (meth) acrylic acid pentaerythritol, hexa (meth) acrylic acid dipentaerythritol, etc .;
Examples of the α, β-unsaturated nitrile compound include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like;
Examples of the aromatic vinyl compound having a hydroxyl group include p-hydroxystyrene, and one or more selected from these can be used.
(A) It is preferable at the point which the stability of the slurry for positive electrodes using the binder composition for positive electrodes of this invention improves because a polymer particle has the structural unit derived from unsaturated carboxylic acid among the above. Moreover, the swelling property with respect to the electrolyte solution of a polymer alloy particle can be improved more because (A) polymer particles have a repeating unit derived from an α, β-unsaturated nitrile compound. That is, the presence of the nitrile group makes it easier for the solvent (medium) to enter the network structure composed of polymer chains and the network interval is widened, so that the solvated lithium ions can easily move through the network structure. Thereby, it is thought that the diffusibility of lithium ion improves, As a result, electrode resistance falls and it is preferable at the point which can implement | achieve more favorable charge / discharge characteristics.

The crosslinkable monomer is a monomer having two or more polymerizable double bonds, such as an alkenyl ester of an unsaturated carboxylic acid, a vinyl ester of an unsaturated carboxylic acid, a conjugated diene, and a carbon-carbon double bond. The aromatic compound which has two can be mentioned. Specific examples of such alkenyl esters of unsaturated carboxylic acids include, for example, allyl (meth) acrylate, ethylene di (meth) acrylate, and the like;
Examples of the vinyl ester of the unsaturated carboxylic acid include vinyl acetate and vinyl propionate;
Examples of the conjugated diene include butadiene, isoprene, chloroprene and the like;
Examples of the aromatic compound having two carbon-carbon double bonds include divinylbenzene, and one or more selected from these can be used.
(A) When a polymer particle has the structural unit derived from the conjugated diene compound among the above, it becomes easy to manufacture the binder composition for positive electrodes excellent in viscoelastic property and strong. That is, when a polymer having a structural unit derived from a conjugated diene compound is used, it becomes a polymer particle having a cross-linked structure while having a low Tg, so that it easily functions as a binder having a balance between elongation and strength. As a result, the adhesiveness can be further improved, which is preferable.

Furthermore, examples of the α-olefin include ethylene and propylene;
Examples of the aromatic vinyl compound include styrene, α-methylstyrene, p-methylstyrene, chlorostyrene, and the like, and one or more selected from these can be used. (A) When the polymer particle has a structural unit derived from an aromatic vinyl compound, when the positive electrode slurry contains a conductivity-imparting agent, it is preferable in that the affinity for this can be improved.
In the present specification, “(meth) acrylic acid” is a concept encompassing both “acrylic acid” and “methacrylic acid”.

The preferable content ratio of the repeating unit derived from each monomer in the (A) polymer particles contained in the binder composition for an electrode of the present invention is as follows based on the total mass of the (A) polymer particles. It is as follows.
Repeating unit derived from a monomer having a fluorine atom: preferably 3% by mass or more, more preferably 5 to 50% by mass, still more preferably 15 to 40% by mass, particularly preferably 20 to 30% by mass;
Repeating units derived from at least one selected from the group consisting of alkyl esters of unsaturated carboxylic acids and cycloalkyl esters of unsaturated carboxylic acids: preferably 95% by mass or less, more preferably 30 to 90% by mass, and even more preferably Is 40 to 85% by mass;
Repeating unit derived from a hydrophilic monomer: preferably 15% by mass or less, more preferably 2-12% by mass, still more preferably 4-8% by mass;
Repeating unit derived from a crosslinkable monomer: preferably 2% by mass or less, more preferably 1% by mass or less; and a repeating unit derived from at least one selected from the group consisting of α-olefins and aromatic vinyl compounds : Preferably it is 10 mass% or less, More preferably, it is 5 mass% or less, and it is still more preferable not to contain this.
The polymer particles (A) contained in the electrode binder composition of the present invention are the above-described monomer having a fluorine atom, an alkyl ester of an unsaturated carboxylic acid, a cycloalkyl ester of an unsaturated carboxylic acid, a hydrophilic It is preferable not to contain a repeating unit derived from a monomer other than a polymerizable monomer, a crosslinkable monomer, an α-olefin, and an aromatic vinyl compound.

1.1.1 Polymer Alloy Particles As (A) polymer particles contained in the positive electrode slurry of the present invention, polymer particles having a repeating unit derived from a monomer having a fluorine atom as described above are used as they are. You may use
A polymer A having a repeating unit derived from a monomer having a fluorine atom;
It is a polymer alloy particle containing at least one polymer unit B having a repeating unit derived from at least one selected from the group consisting of an alkyl ester and a cycloalkyl ester of an unsaturated carboxylic acid. And the adhesiveness can be expressed at the same time.
“Polymer alloy” is a “generic name for multi-component polymers obtained by mixing or chemical bonding of two or more components” according to the definition in “Iwanami Physical and Chemical Dictionary 5th edition. Iwanami Shoten”. “Polymer blends physically mixed with different polymers, block and graft copolymers in which different polymer components are covalently bonded, polymer complexes in which different polymers are associated by intermolecular forces, and different polymers entangled with each other IPN (Interpenetrating Polymer Network, etc.). However, the polymer alloy particles contained in the positive electrode binder composition of the present invention are preferably particles made of IPN among the “polymer alloys in which different types of polymer components are not bonded by covalent bonds”.

The polymer A constituting the polymer alloy particle is excellent in ionic conductivity, and the hard segment of the crystalline resin is aggregated to give the main chain a pseudo-crosslinking point such as C—H—F—C. it is conceivable that. For this reason, when the polymer A is used alone as the binder resin, its ionic conductivity and oxidation resistance are good, but the adhesion and flexibility are insufficient, and therefore the adhesion is low. On the other hand, although the polymer B constituting the polymer alloy particle is excellent in adhesion and flexibility, it has low oxidation resistance. Therefore, when this is used alone as a binder resin for a positive electrode, charge and discharge are repeated. Therefore, good charge / discharge characteristics cannot be obtained.
However, by using the polymer alloy particles containing the polymer A and the polymer B, it is possible to simultaneously exhibit ionic conductivity, oxidation resistance, and adhesion, and a positive electrode having good charge / discharge characteristics. It became possible to manufacture. When the polymer alloy particles are composed only of the polymer A and the polymer B, the oxidation resistance can be further improved, which is preferable.
The polymer alloy particles preferably have only one endothermic peak in the temperature range of −50 to 250 ° C. when measured by differential scanning calorimetry (DSC) according to JIS K7121. The temperature of this endothermic peak is more preferably in the range of -30 to + 30 ° C.
When the polymer A constituting the polymer alloy particles is present alone, it generally has an endothermic peak (melting temperature) at −50 to 250 ° C. In addition, the polymer B constituting the polymer alloy particles generally has an endothermic peak (glass transition temperature) different from that of the polymer A. For this reason, when the polymer A and the polymer B in the particles are present in phase separation as in, for example, a core-shell structure, two endothermic peaks should be observed at −50 to 250 ° C. However, when there is only one endothermic peak at −50 to 250 ° C., it can be estimated that the particles are polymer alloy particles.
Furthermore, when the temperature of only one endothermic peak of the polymer alloy particles is in the range of −30 to + 30 ° C., the particles can impart better flexibility and tackiness to the active material layer. Therefore, the adhesiveness can be further improved, which is preferable.

1.1.2 Polymer A
The polymer alloy particles preferably contained in the positive electrode slurry of the present invention contain a polymer A having a repeating unit derived from a monomer having a fluorine atom. As described above, the monomer having a fluorine atom is preferably at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene, and propylene hexafluoride.
The polymer A may further have a repeating unit derived from another unsaturated monomer in addition to the repeating unit derived from the monomer having a fluorine atom. Here, as the other unsaturated monomer, the unsaturated carboxylic acid alkyl ester, unsaturated carboxylic acid cycloalkyl ester, hydrophilic monomer, crosslinkable monomer, α-olefin, and Aromatic vinyl compounds can be used.
The content ratio of the repeating unit derived from the monomer having a fluorine atom in the polymer A is preferably 80% by mass or more, more preferably 90% by mass or more with respect to the total mass of the polymer A. is there. In this case, the monomer having a fluorine atom is preferably at least one selected from vinylidene fluoride, ethylene tetrafluoride and propylene hexafluoride. The preferable content ratio of the repeating unit derived from each monomer in the polymer A of the repeating unit derived from these monomers is as follows based on the total mass of the polymer A.
Repeating units derived from vinylidene fluoride in the polymer A: preferably 50 to 99% by mass, more preferably 80 to 98% by mass;
Repeating units derived from tetrafluoroethylene: preferably 50% by weight, more preferably 1-30% by weight, even more preferably 2-20% by weight; and repeating units derived from hexafluoropropylene: preferably 50% by weight Hereinafter, more preferably 1 to 30% by mass, and still more preferably 2 to 25% by mass.
The polymer A is most preferably composed of only a repeating unit derived from at least one selected from the group consisting of vinylidene fluoride, tetrafluoroethylene and hexafluoropropylene.

1.1.3 Polymer B
The polymer particle (A) which is a polymer alloy preferably contained in the electrode binder composition of the present invention is a repeating unit derived from another copolymerizable unsaturated monomer other than a monomer having a fluorine atom. Have. Other unsaturated compounds include the above-described unsaturated carboxylic acid alkyl esters, unsaturated carboxylic acid cycloalkyl esters, hydrophilic monomers, crosslinkable monomers, α-olefins and aromatic vinyl compounds. Can be used.
In general, a component such as polymer B has good adhesion, but is considered to have poor ionic conductivity and oxidation resistance, and has not been used for positive electrodes. However, in the present invention, by using such a polymer B as a polymer alloy particle together with the polymer A, it has succeeded in developing sufficient ionic conductivity and oxidation resistance while maintaining good adhesion. It is a thing.
The content ratio of the repeating unit derived from each monomer in the polymer B is as follows. The following are values when the mass of the polymer B is 100% by mass.
Repeating units derived from at least one selected from the group consisting of alkyl esters of unsaturated carboxylic acids and cycloalkyl esters of unsaturated carboxylic acids: preferably 50% by mass or more, more preferably 60 to 95% by mass;
Repeating units derived from hydrophilic monomers: preferably 50% by mass or less, more preferably 5-40% by mass;
Repeating unit derived from a crosslinkable monomer: preferably 3% by mass or less, more preferably 2% by mass or less; and a repeating unit derived from at least one selected from the group consisting of α-olefins and aromatic vinyl compounds : Preferably it is 20 mass% or less, More preferably, it is 10 mass% or less, and it is still more preferable not to contain this.
The polymer B is a monomer other than the alkyl ester of the unsaturated carboxylic acid exemplified above, the cycloalkyl ester of the unsaturated carboxylic acid, the hydrophilic monomer, the crosslinkable monomer, the α-olefin, and the aromatic vinyl compound. It is preferable not to contain a repeating unit derived from the body.

1.1.4 Preparation of Polymer Alloy Particles The polymer alloy particles preferably contained in the positive electrode slurry of the present invention are not particularly limited as long as they have the above-described configuration. It can be easily synthesized by an emulsion polymerization step or a combination thereof.
For example, first, a polymer A having a repeating unit derived from a monomer having a fluorine atom is synthesized by a known method, and then a monomer for constituting the polymer B is added to the polymer A. After the monomer is sufficiently absorbed in the stitch structure of the polymer particles made of the polymer A, the absorbed monomer is polymerized in the stitch structure of the polymer A to obtain the polymer B. The polymer alloy can be easily produced by the synthesis method. When producing a polymer alloy by such a method, it is essential for the polymer A to sufficiently absorb the monomer of the polymer B. When the absorption temperature is too low or the absorption time is too short, only a core-shell type polymer or a part of the surface layer becomes a polymer having an IPN type structure, and the polymer alloy in the present invention may not be obtained. Many. However, if the absorption temperature is too high, the pressure of the polymerization system becomes too high, which is disadvantageous in terms of reaction system handling and reaction control, and even if the absorption time is excessively long, further advantageous results are not obtained. .

From the above viewpoint, the absorption temperature is preferably 30 to 100 ° C, more preferably 40 to 80 ° C;
The absorption time is preferably 1 to 12 hours, and more preferably 2 to 8 hours. At this time, it is preferable to lengthen the absorption time when the absorption temperature is low, and a short absorption time is sufficient when the absorption temperature is high. The conditions are such that the value obtained by multiplying the absorption temperature (° C.) and the absorption time (h) is generally in the range of 120 to 300 (° C. · h), preferably 150 to 250 (° C. · h).
The operation of absorbing the monomer of the polymer B in the network structure of the polymer A is preferably performed in a known medium used for emulsion polymerization, for example, in water.
The content of the polymer A in the polymer alloy is preferably 3 to 60% by mass, more preferably 5 to 55% by mass, and 10 to 50% by mass in 100% by mass of the polymer alloy. Is more preferable, and 20 to 40% by mass is particularly preferable. When the polymer alloy contains the polymer A in the above range, the balance between the ionic conductivity and the oxidation resistance and the adhesion becomes better. Moreover, when the polymer B in which the content ratio of the repeating unit derived from each monomer is in the above preferred range is used, the polymer alloy contains the polymer A in the above range, so that the entire polymer alloy It is possible to set the content ratio of each repeating unit in the above-mentioned preferable range, and this ensures that the charge / discharge characteristics of the electricity storage device are good.

1.1.5 Production method of polymer (emulsion polymerization conditions)
Production of polymer particles in the present invention, that is,
The polymerization when a polymer having a repeating unit derived from a monomer having a fluorine atom is synthesized by one-step polymerization;
The polymerization of the polymer A and the polymerization of the polymer B in the presence of the polymer A can be performed in the presence of a known emulsifier (surfactant), a polymerization initiator, a molecular weight modifier, and the like, respectively.
Examples of the emulsifier include sulfate esters of higher alcohols, alkylbenzene sulfonates, alkyl diphenyl ether disulfonates, aliphatic sulfonates, aliphatic carboxylates, dehydroabietic acid salts, naphthalene sulfonic acid / formalin condensates, Anionic surfactants such as sulfate salts of ionic surfactants;
Nonionic surfactants such as alkyl esters of polyethylene glycol, alkyl phenyl ethers of polyethylene glycol, alkyl ethers of polyethylene glycol;
Fluorosurfactants such as perfluorobutyl sulfonate, perfluoroalkyl group-containing phosphate ester, perfluoroalkyl group-containing carboxylate, and perfluoroalkylethylene oxide adducts can be mentioned, and selected from these More than one kind can be used.
The proportion of the emulsifier used is the sum of the monomers used ((A) the sum of the monomers used when the polymer particles are synthesized by one-step polymerization, and the polymer A is derived in the production of the polymer A. In the case of polymerizing the polymer B in the presence of the polymer A in the presence of the polymer A, the sum of the monomers leading to the polymer B. The same shall apply hereinafter.) 0.01 to 10 masses per 100 mass parts Part, preferably 0.02 to 5 parts by mass.

Examples of the polymerization initiator include water-soluble polymerization initiators such as lithium persulfate, potassium persulfate, sodium persulfate, and ammonium persulfate;
Cumene hydroperoxide, benzoyl peroxide, t-butyl hydroperoxide, acetyl peroxide, diisopropylbenzene hydroperoxide, 1,1,3,3-tetramethylbutyl hydroperoxide, azobisisobutyronitrile, 1, Oil-soluble polymerization initiators such as 1′-azobis (cyclohexanecarbonitrile) can be appropriately selected and used. Of these, potassium persulfate, sodium persulfate, cumene hydroperoxide or t-butyl hydroperoxide is particularly preferably used. The ratio of the polymerization initiator used is not particularly limited, but is appropriately set in consideration of the monomer composition, the pH of the polymerization reaction system, a combination of other additives and the like.
The use ratio of the polymerization initiator is preferably 0.3 to 3 parts by mass with respect to 100 parts by mass in total of the monomers used.

Examples of the molecular weight modifier include alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan;
Xanthogen compounds such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide;
Thiuram compounds such as terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetramethylthiuram monosulfide;
Phenolic compounds such as 2,6-di-tert-butyl-4-methylphenol and styrenated phenol;
Allyl compounds such as allyl alcohol;
Halogenated hydrocarbon compounds such as dichloromethane, dibromomethane, carbon tetrabromide;
In addition to vinyl ether compounds such as α-benzyloxystyrene, α-benzyloxyacrylonitrile, α-benzyloxyacrylamide,
Examples include triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid, thiomalic acid, 2-ethylhexyl thioglycolate, α-methylstyrene dimer, and one or more selected from these are used. can do.
The use ratio of the molecular weight regulator is preferably 5 parts by mass or less with respect to 100 parts by mass in total of the monomers used.
The emulsion polymerization is preferably carried out in a suitable aqueous medium, particularly preferably in water. The total content of the monomers in the aqueous medium can be 10 to 50% by mass, and preferably 20 to 40% by mass.
The conditions for emulsion polymerization are preferably a polymerization time of 2 to 24 hours at a polymerization temperature of 40 to 85 ° C, and more preferably a polymerization time of 3 to 20 hours at a polymerization temperature of 50 to 80 ° C.

1.1.6 (A) Other characteristics of polymer particles (A) The average particle diameter (Da) of the polymer particles is preferably in the range of 50 to 400 nm, and preferably in the range of 100 to 250 nm. More preferred. When the average particle diameter of the polymer particles is within the above range, (A) the polymer particles can be sufficiently adsorbed to the surface of the active material particles (B). Can follow and move. As a result, since only one of the particles can be prevented from migrating alone, deterioration of electrical characteristics can be suppressed. When the average particle diameter of the polymer particles is less than the above range, the electrical characteristics deteriorate due to the migration of the particles, which is not preferable. On the other hand, when the average particle diameter of the polymer particles exceeds the above range, the ratio of the surface area to the addition amount of the polymer particles becomes low, so that good binder characteristics cannot be expressed. As a result, the adhesiveness is lowered, which is not preferable.
(A) The average particle diameter of a polymer particle is performed using the particle size distribution measuring apparatus which makes a light scattering method a measurement principle. Examples of such a particle size distribution measuring apparatus include Coulter LS230, LS100, LS13320 (above, manufactured by Beckman Coulter. Inc.), FPAR-1000 (manufactured by Otsuka Electronics Co., Ltd.), and the like. These particle size distribution measuring devices are not intended to evaluate only the primary particles of the polymer particles, but can also evaluate the secondary particles formed by aggregation of the primary particles. Therefore, the particle size distribution measured by these particle size distribution measuring devices can be used as an indicator of the dispersion state of the polymer particles contained in the positive electrode slurry. The average particle diameter of the polymer particles can also be measured by a method of centrifuging the positive electrode slurry to precipitate the active material particles and measuring the supernatant with the above particle size distribution measuring apparatus.
The use ratio of (A) polymer particles in the positive electrode slurry of the present invention is preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of (B) active material particles described later, 0.5 to More preferably 5 parts by mass.

1.2 (B) Active Material Particles The material constituting the (B) active material particles contained in the positive electrode slurry is a lithium atom-containing oxide. “Oxide” in the present specification is a concept that means a compound or salt composed of oxygen and an element having an electronegativity smaller than that of oxygen. In addition to metal oxides, metal phosphates and nitrates , Halogen oxo acid salts, sulfonic acid salts and the like.
As a material constituting the active material particles (B) in the present invention, the following general formula (B-1)
Li _{1 + x} M ¹ _y M ² _z O ₂ (B-1)
(In Formula (B-1), M ¹ is at least one metal atom selected from the group consisting of Co, Ni and Mn;
M ² is at least one metal atom selected from the group consisting of Al and Sn;
O is an oxygen atom;
x, y and z are numbers in the range of 0.10 ≧ x ≧ 0, 4.00 ≧ y ≧ 0.85 and 2.00 ≧ z ≧ 0, respectively. )
A composite metal oxide represented by the following general formula (B-2)
Li _1-x M _x (XO ₄ ) (B-2)
(In the formula (B-2), M is a metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, A1, Ga, Ge, and Sn. At least one kind of ions;
X is at least one selected from the group consisting of Si, S, P and V; and x is a number and satisfies the relationship 0 <x <1. )
And a compound having an olivine type crystal structure, and it is preferable to use one or more selected from the group consisting of these. The value of x in the general formula (B-2) is selected according to the valences of M and X so that the valence of the entire formula (1) becomes zero.

Examples of the composite metal oxide represented by the general formula (B-1) include LiCoO ₂ , LiNiO ₂ , LiNi _y Co _1-y O ₂ (y = 0.01 to 0.99), LiMnO ₂ , LiMn. ₂ O ₄ , LiCo _x Mn _y Ni _z O ₂ (x + y + z = 1) and the like can be used, and one or more selected from these can be used. Among these, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, and LiNi _0.33 Mn _0.33 Co _0.33 O ₂ have a high electrode potential and high efficiency, and therefore have a high voltage and high energy density. Can be obtained. Li _{1 + x} M ¹ _y M ² _z O ₂ is particularly preferable in that the Li diffusion rate in the solid is high and the charge / discharge rate is excellent.
The compound represented by the general formula (B-2) and having an olivine structure has a positive electrode potential that varies depending on the type of the metal element M. Therefore, the battery voltage can be arbitrarily set by selecting the type of the metal element M. Typical examples of the lithium atom-containing oxide having an olivine structure include LiFePO ₄ , LiCoPO ₄ , Li _0.90 Ti _0.05 Nb _0.05 Fe _0.30 Co _0.30 Mn _0.30 PO _{4, and the} like. Can be mentioned. Among these, LiFePO ₄ is particularly preferable because it is easy to obtain an iron compound as a raw material and is inexpensive. In addition, compounds obtained by substituting Fe ions in the above compounds with Co ions, Ni ions, or Mn ions have the same olivine type crystal structure as each of the above compounds, and thus have the same effect as the positive electrode active material.

(B) The average particle diameter (Db) of the active material particles is the average particle diameter (Da) of the polymer particles (A) and (B) the average particle diameter (Db) of the active material particles contained in the positive electrode slurry. The ratio (Da / Db) is selected to be 0.01 to 1.0. This value is preferably selected to be 0.05 to 0.5. By setting the values of the average particle diameter (Db) and the ratio (Da / Db) within the above ranges, the area in which the polymer particles and the active material particles are in contact with each other becomes an appropriate value. The migration of the active material particles can be more reliably suppressed.
(B) The average particle diameter (Db) of the active material particles is such that the ratio (Da / Db) is within the above range, and the average particle diameter (Db) of the active material particles is 0.1 to 25 μm. The thickness is preferably 0.4 to 23 μm, more preferably 0.5 to 20 μm.
(B) When the active material particles are a composite metal oxide represented by the general formula (B-1), the average particle diameter (Db) of the active material particles is preferably 0.5 to 25 μm, It is more preferably 1 to 23 μm, and particularly preferably 2 to 20 μm.
(B) When the active material particles are a compound represented by the above general formula (B-2) and having an olivine type crystal structure, the average particle diameter (Db) of the active material particles is 0.1 to 10 μm. It is preferable that it is 0.4-8 micrometers, and it is especially preferable that it is 0.5-7 micrometers.

When the average particle diameter of the active material particles is within the above range, the diffusion distance of lithium in the active material particles is shortened, so that the resistance accompanying lithium desorption during charging and discharging can be reduced, and as a result The charge / discharge characteristics are further improved. Furthermore, when the positive electrode slurry contains a conductivity-imparting agent described later, the contact area between the active material particles and the conductivity-imparting agent can be sufficiently ensured by the average particle diameter of the active material particles being within the above range. As a result, the electronic conductivity of the positive electrode is improved and the positive electrode resistance is further reduced.
Here, the average particle diameter (Db) of the active material particles is a particle diameter (measured by using a particle size distribution measuring apparatus based on a laser diffraction method) and a cumulative frequency of 50% in terms of volume percentage ( D50). Examples of such a laser diffraction particle size distribution measuring apparatus include HORIBA LA-300 series and HORIBA LA-920 series (manufactured by Horiba, Ltd.). This particle size distribution measuring apparatus does not only evaluate the primary particles of the active material particles, but also evaluates secondary particles formed by aggregation of the primary particles. Therefore, the average particle diameter (Db) obtained by this particle size distribution measuring apparatus can be used as an indicator of the dispersion state of the active material particles contained in the positive electrode slurry.
The average particle diameter (Db) of the active material particles is obtained by centrifuging the positive electrode slurry to settle the active material particles, then removing the supernatant, and measuring the precipitated active material particles by the above method. Can also be measured.

1.3 (C) Liquid Medium The positive electrode slurry of the present invention further contains (C) a liquid medium. This (C) liquid state body can be an aqueous medium or a non-aqueous medium.
The positive electrode slurry of the present invention is preferably in the form of a slurry or latex in which the above (A) polymer particles and (B) active material particles are dispersed in a liquid medium.
The aqueous medium contains water. The aqueous medium can contain a small amount of a non-aqueous medium in addition to water. Examples of such a non-aqueous medium include amide compounds, hydrocarbons, alcohols, ketones, esters, amine compounds, lactones, sulfoxides, sulfone compounds, and the like, and one or more selected from these are used. can do. The content ratio of such a non-aqueous medium is preferably 10% by mass or less, more preferably 5% by mass or less, based on the entire aqueous medium.

The non-aqueous medium can be suitably used as long as it can stably disperse (A) polymer particles and (B) active material particles. Specific examples of the non-aqueous medium include aliphatic hydrocarbons such as n-octane, isooctane, nonane, decane, decalin, pinene, and chlorododecane;
Cycloaliphatic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, methylcyclopentane;
Aromatic hydrocarbons such as chlorobenzene, chlorotoluene, ethylbenzene, diisopropylbenzene, cumene;
Alcohols such as methanol, ethanol, propanol, isopropanol, butanol, benzyl alcohol, glycerin;
Ketones such as acetone, methyl ethyl ketone, cyclopentanone, isophorone;
Ethers such as methyl ethyl ether, diethyl ether, tetrahydrofuran, dioxane;
lactones such as γ-butyrolactone and δ-butyrolactone;
lactams such as β-lactams;
Linear or cyclic amide compounds such as dimethylformamide, N-methylpyrrolidone, N, N-dimethylacetamide;
Compounds having a nitrile group, such as methylene cyanohydrin, ethylene cyanohydrin, 3,3′-thiodipropionitrile, acetonitrile;
Nitrogen-containing heterocyclic compounds such as pyridine and pyrrole;
Glycol compounds such as ethylene glycol and propylene glycol;
Diethylene glycol or derivatives such as diethylene glycol, diethylene glycol monoethyl ether, diethylene glycol ethyl butyl ether;
Examples thereof include esters such as ethyl formate, ethyl lactate, propyl lactate, methyl benzoate, methyl acetate, and methyl acrylate, and one or more selected from these can be used.

  As the (C) liquid medium in the present invention, an aqueous medium is preferably used. (C) When the liquid medium contains water, the positive electrode slurry of the present invention has good stability, and the positive electrode can be produced with good reproducibility. Water has a higher evaporation rate than a high boiling point solvent (for example, N-methylpyrrolidone, etc.) generally used in a positive electrode slurry. We can expect suppression. As the liquid medium (C) in the present invention, it is most preferable to use a medium containing only water without containing a non-aqueous medium.

1.4 Other Components The positive electrode slurry of the present invention can contain other components as necessary in addition to the components described above. Examples of such other components include a conductivity-imparting agent and a non-aqueous system. A medium, a thickener, etc. can be mentioned.

1.4.1 Conductivity-imparting agent Specific examples of the conductivity-imparting agent include carbon in a lithium ion secondary battery;
In nickel-metal hydride secondary batteries, cobalt oxide is the positive electrode:
For the negative electrode, nickel powder, cobalt oxide, titanium oxide, carbon and the like are used. In both the batteries, examples of carbon include graphite, activated carbon, acetylene black, furnace black, graphite, carbon fiber, and fullerene. Among these, acetylene black or furnace black can be preferably used. The use ratio of the conductivity-imparting agent is preferably 20 parts by mass or less, more preferably 1 to 15 parts by mass, and particularly preferably 2 to 10 parts by mass with respect to 100 parts by mass of the active material particles.

1.4.2 Thickener The positive electrode slurry may contain a thickener from the viewpoint of improving the coating property. Specific examples of the thickener include cellulose compounds such as carboxymethylcellulose, methylcellulose, and hydroxypropylcellulose;
An ammonium salt or an alkali metal salt of the cellulose compound;
Polycarboxylic acids such as poly (meth) acrylic acid, modified poly (meth) acrylic acid;
An alkali metal salt of the polycarboxylic acid;
Polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymer;
Examples thereof include water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid and fumaric acid and vinyl esters. Among these, particularly preferred thickeners include alkali metal salts of carboxymethyl cellulose and alkali metal salts of poly (meth) acrylic acid.
Examples of commercially available products of these thickeners include CMC1120, CMC1150, CMC2200, CMC2280, and CMC2450 (above, manufactured by Daicel Chemical Industries, Ltd.) as alkali metal salts of carboxymethylcellulose.

When the positive electrode slurry contains a thickener, the use ratio of the thickener is preferably less than 15% by mass, more preferably less than 15% by mass with respect to 100 parts by mass of the active material particles contained in the positive electrode slurry. It is 0.1-10 mass%, More preferably, it is 0.5-7.5 mass%, It is especially preferable that it is 1-5 mass%.
When the active material particle (B) used for the positive electrode slurry is a composite metal oxide represented by the above general formula (B-1), the active material contained in the positive electrode slurry may be used as a proportion of the thickener used. Preferably it is less than 15 mass% with respect to 100 mass parts of particle | grains, More preferably, it is 0.05-10 mass%, More preferably, it is 0.1-7.5 mass%, Especially 0.2- It is preferably 5% by mass.
When the active material particle (B) used for the positive electrode slurry is a compound represented by the general formula (B-2) and having an olivine type crystal structure, the use ratio of the thickener is contained in the positive electrode slurry. Preferably, it is less than 15% by weight, more preferably 0.1 to 10% by weight, still more preferably 0.5 to 7.5% by weight, based on 100 parts by weight of the active material particles. It is preferable that it is 1-5 mass%.

2. 2. Slurry for positive electrode 2.1 Method for producing slurry for positive electrode The slurry for positive electrode of the present invention may be produced by any method as long as it contains the above-mentioned components.
However, from the viewpoint of more efficiently and cheaply producing a positive electrode slurry having better dispersibility and stability, the positive electrode slurry is a latex containing (A) polymer particles in an emulsified state in an aqueous medium. A binder composition can be prepared first, and then it can be produced by mixing (B) active material particles, (C) a liquid medium, and additives used as necessary.

2.1.1 Positive electrode binder composition As the above binder composition, (A) the polymerization reaction mixture after the synthesis (polymerization) of the polymer particles is adjusted as necessary, and then this is used as it is. Can be used. Therefore, the binder composition for positive electrodes may contain other components such as an emulsifier, a polymerization initiator or a residue thereof, a surfactant, and a neutralizer in addition to the polymer particles as described above. The content ratio of these other components is preferably 3% by weight or less, more preferably 2% by weight or less as a ratio of the total weight of the other components to the solid content weight of the composition.
The solid content concentration of the binder composition for the positive electrode (the ratio of the weight of components other than the aqueous medium in the composition to the total weight of the composition) is preferably 30 to 50% by weight. More preferably, it is 45% by weight.
The liquid property of the positive electrode binder composition is preferably near neutral, more preferably pH 6.0 to 8.5, and particularly preferably pH 7.0 to 8.0. For adjusting the liquidity of the composition, a known water-soluble acid or base can be used. Examples of the acid include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like;
Examples of the base include sodium hydroxide, potassium hydroxide, lithium hydroxide, and aqueous ammonia.

2.1.2 Mixing of the positive electrode binder composition and other components In order to mix the positive electrode binder composition and other components as described above, it can be carried out by stirring by a known method, for example, A stirrer, a defoamer, a bead mill, a high-pressure homogenizer, etc. can be used.
The preparation of the positive electrode slurry (mixing operation of each component) is preferably performed at least part of the process under reduced pressure. Thereby, it can prevent that a bubble arises in the positive electrode layer obtained. The degree of pressure reduction is preferably about 5.0 × 10 ^{4 to} 5.0 × 10 ⁵ Pa as an absolute pressure.
As mixing and stirring for producing the positive electrode slurry, it is necessary to select a mixer that can stir to such an extent that no agglomerates of active material particles remain in the slurry and sufficient dispersion conditions as necessary. The degree of dispersion can be measured by a particle gauge, but it is preferable to mix and disperse so that aggregates larger than at least 100 μm are eliminated. Examples of the mixer that meets such conditions include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, a planetary mixer, and a Hobart mixer.

2.2 Characteristics of positive electrode slurry In the step of drying the formed coating film after applying the positive electrode slurry containing water as a dispersion medium to the surface of the current collector, At least one of them has been confirmed to migrate. That is, the particles move along the thickness direction of the coating film by receiving the action of surface tension. More specifically, at least one of the polymer particles and the active material particles moves to the side of the coating film surface opposite to the surface in contact with the current collector, that is, the gas-solid interface side where water evaporates. To do. When such migration occurs, the distribution of polymer particles and active material particles becomes non-uniform in the thickness direction of the coating film, causing problems such as deterioration of positive electrode characteristics and loss of adhesion. For example, when polymer particles functioning as a binder bleed (migrate) to the gas-solid interface side of the active material layer, and the amount of polymer particles at the interface between the current collector and the active material layer is relatively small, When the penetration of the electrolyte solution into the material layer is hindered, sufficient electrical characteristics cannot be obtained, and the binding property between the current collector and the active material layer is insufficient and the material layer is peeled off. Furthermore, the smoothness of the surface of the active material layer is impaired by bleeding of the polymer particles.
However, the ratio (Da / Db) of the average particle diameter (Da) of (A) polymer particles contained in the positive electrode slurry and the average particle diameter (Db) of (B) active material particles is 0.01 to 1. 0.0 and the spinnability of the slurry is in the range of 30-80%,
Occurrence of the problems as described above can be suppressed, and a positive electrode having both good electrical characteristics and binding properties can be easily manufactured.
The technical significance of the value of the ratio (Da / Db) has been described in the above section “1.2 (B) Active material particles”.

The positive electrode slurry of the present invention has a spinnability in the range of 30 to 80%. This value is preferably 33 to 79%, and more preferably 35 to 78%. When the spinnability is less than the above range, the leveling property is insufficient when the positive electrode slurry is applied onto the current collector, and it may be difficult to obtain the uniformity of the positive electrode thickness. When such a positive electrode having a non-uniform thickness is used, an in-plane distribution of charge / discharge reaction occurs, making it difficult to achieve stable battery performance. On the other hand, if the spinnability exceeds the above range, dripping tends to occur when the positive electrode slurry is applied onto the current collector, and it is difficult to obtain a positive electrode with stable quality. Therefore, by setting the spinnability within the above range, the occurrence of these problems can be suppressed, and it becomes easy to produce a positive electrode that achieves both good electrical characteristics and adhesion. .
The “threadability” in the present specification is measured as follows.
First, a Zahn cup (made by Dazai Equipment Co., Ltd., Zaan Biscocity Cup No. 5) having an opening with a diameter of 5.2 mm at the bottom is prepared. With this opening closed, 40 g of positive electrode slurry is poured into the Zahn cup. Thereafter, when the opening is opened, the positive electrode slurry flows out from the opening. Here, T ₀ when opening the _opening, the T _A when the thread of the positive electrode slurry is _completed, when the outflow of the positive electrode slurry is completed when the T _B, "hauls herein "Thread property" can be obtained from the following mathematical formula (1).
Spinnability (%) = ((T _A −T ₀ ) / (T _B −T ₀ )) × 100 (1)
The positive electrode slurry of the present invention preferably has a solid content concentration (the ratio of the total weight of components other than the medium in the slurry to the total weight of the slurry) of 20 to 85% by weight, and 20 to 80% by weight. %, More preferably 30 to 75% by weight.

When the active material particle (B) used for the positive electrode slurry is a composite metal oxide represented by the general formula (B-1), the solid content concentration (the total weight of components other than the medium in the slurry is The proportion of the total weight) is preferably 20 to 85% by weight, and more preferably 30 to 80% by weight.
When the active material particles (B) used for the positive electrode slurry are compounds represented by the above general formula (B-2) and having an olivine type crystal structure, the solid content concentration (total of components other than the medium in the slurry) The ratio of the weight to the total weight of the slurry is preferably 20 to 80% by weight, and more preferably 30 to 75% by weight.

3. Positive electrode The positive electrode can be produced by applying the positive electrode slurry of the present invention on the surface of an appropriate current collector such as a metal foil to form a coating film, and then drying the coating film. The positive electrode produced for this purpose is formed by binding an active material layer containing the above-described polymer particles and active material particles, and optionally added optional components, on a current collector. . Such a positive electrode having a layer formed from the above-described positive electrode slurry on the surface of the current collector has excellent binding properties between the current collector and the active material layer, and is a charge that is one of the electrical characteristics. Discharge rate characteristics are good. Such a positive electrode is suitable as a positive electrode of an electricity storage device.
The current collector is not particularly limited as long as it is made of a conductive material. In a lithium ion secondary battery, a current collector made of metal such as iron, copper, aluminum, nickel, and stainless steel is used. In particular, when aluminum is used for the positive electrode and copper is used for the negative electrode, it is used for the positive electrode of the present invention. The effect of the slurry is most apparent. As the current collector in the nickel metal hydride secondary battery, a punching metal, an expanded metal, a wire mesh, a foam metal, a mesh metal fiber sintered body, a metal plated resin plate, or the like is used.
The shape and thickness of the current collector are not particularly limited, but it is preferable that the current collector has a sheet shape with a thickness of about 0.001 to 0.5 mm.

There is no particular limitation on the method of applying the positive electrode slurry to the current collector. The coating can be performed by an appropriate method such as a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a dipping method, or a brush coating method. The coating amount of the positive electrode slurry is not particularly limited, but the thickness of the active material layer formed after removing the liquid medium (a concept including both water and a non-aqueous medium that is optionally used) is not limited. The amount is preferably 0.005 to 5 mm, and more preferably 0.01 to 2 mm.
There is no particular limitation on the drying method (liquid medium removing method) from the coated film after coating, for example, drying with warm air, hot air or low-humidity air; vacuum drying; Can be. The drying speed is appropriately set so that the liquid medium can be removed as quickly as possible within a speed range in which the active material layer does not crack due to stress concentration or the active material layer does not peel from the current collector. be able to.

Furthermore, it is preferable to increase the density of the active material layer and adjust the porosity by pressing the current collector after drying. Examples of the pressing method include a mold press and a roll press.
The porosity of the active material layer after pressing is preferably 10 to 50%. This value is more preferably 15 to 45%, and further preferably 20 to 40%.
When the porosity of the active material layer is in the above range, the binding property between the current collector and the active material layer is improved, and a positive electrode having excellent powder falling properties and excellent electrical characteristics can be obtained. It will be. Furthermore, when the porosity of the active material layer is within the above range, the electrolytic solution can be sufficiently infiltrated into the active material layer, and the surface of the active material particles and the electrolytic solution can be sufficiently in contact with each other. As a result, transfer of lithium ions of the active material and the electrolytic solution becomes easy, and good charge / discharge characteristics can be achieved.

In the present invention, the “porosity of the active material layer” refers to the volume of the pores (the amount excluding the volume occupied by the solid content (active material, conductive additive, binder, etc.) from the volume of the active material layer). In the positive electrode having an active material layer with an area C (cm ² ) and a thickness D (μm) on one side of the current collector, the mass of the active material layer is B ( g) When the pore volume measured by mercury porosimetry is V (cm ³ / g), it is a value defined by the following mathematical formula (2).
Porosity (%) of active material layer = (V (cm ³ / g) × B (g)) / (C (cm ² ) × D (μm) × 10 ⁻⁴ ) × 100 (2)
The pore volume can be measured, for example, by a mercury intrusion method using a mercury porosimeter. As the mercury porosimeter, for example, a product name “PoreMaster” manufactured by Quantachrome, a product name “Autopore IV” manufactured by Shimadzu Corporation can be used.
The density of the active material layer after pressing is preferably 1.5 to 5.0 g / cm ³ .

When the active material particle (B) contained in the positive electrode slurry of the present invention is a composite metal oxide represented by the general formula (B-1), the density of the active material layer is 2.0 to 4. is preferably set to 5 g / cm ^3, more preferably to 2.5~4.0g / cm ^3, and most preferably a 3.0~3.5g / cm ^3.
(B) When the active material particles are a compound represented by the above general formula (B-2) and having an olivine type crystal structure, the density of the active material layer is 1.5 g / cm ³ or more and 2.5 g / cm ^3. and is preferably less than, more preferably 1.6~2.4g / cm ^3, more preferably from 1.7~2.2g / cm ^3, 1.8~2.1g / cm ³ is most preferred.
When the density of the active material layer is within the above range, the binding property between the current collector and the active material layer is improved, and a positive electrode having excellent powdering properties and electrical characteristics can be obtained. It becomes. When the density of the active material layer is less than the above range, the (A) polymer particles in the active material layer do not sufficiently function as a binder, and the powder fallen property is deteriorated due to aggregation and peeling of the active material layer. When the density of the active material layer exceeds the above range, the binder function of the polymer in the active material layer is too strong and the adhesion between the active materials becomes too strong. As a result, the active material layer cannot follow the flexibility of the current collector, and the interface between the current collector and the active material layer may peel off, which is not preferable.

However, when the polymer particle (A) contained in the active material layer is a polymer alloy particle, the flexibility of the active material layer becomes more excellent. The effect of the present invention can be expressed. When the polymer particles (A) contained in the active material layer are polymer alloy particles, the density of the active material layer can be 1.5 to 4.0 g / cm ^3, and 1.6 to ³ . 8 g / cm ³ is preferable.
The “density of the active material layer” in the present invention is a value indicating the bulk density of the active material layer, and can be known from the following measurement method. That is, in a positive electrode having an active material layer with an area C (cm ² ) and a thickness D (μm) on one side of the current collector, the mass of the current collector is A (g), and the mass of the positive electrode for an electricity storage device is B ( In the case of g), the density of the active material layer is defined by the following mathematical formula (3).
Active material layer density (g / cm ³ ) = (B (g) −A (g)) / (C (cm ² ) × D (μm) × 10 ⁻⁴ ) (3)

4). Electric storage device An electric storage device can be manufactured using the positive electrode as described above.
The electricity storage device includes the above-described positive electrode, further contains an electrolytic solution, and can be manufactured according to a conventional method using components such as a separator. As a specific manufacturing method, for example, a negative electrode and a positive electrode are overlapped via a separator, and this is wound into a battery container according to a battery shape, put into a battery container, an electrolyte is injected into the battery container, and sealing is performed. The method of doing is mentioned. The shape of the battery can be an appropriate shape such as a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, or a flat shape.
The electrolyte solution may be liquid or gel, and the one that effectively expresses the function as a battery is selected from the known electrolyte solutions used for the electricity storage device according to the type of the negative electrode active material and the positive electrode active material. That's fine.
The electrolytic solution can be a solution in which an electrolyte is dissolved in a suitable solvent.

As the electrolyte, in the lithium ion secondary battery, any conventionally known lithium salt can be used, and specific examples thereof include, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ CO ₂ , LiAsF. ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiB (C ₂ H ₅ ) ₄ , LiCF ₃ SO ₃ , LiCH ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lithium of lower fatty acid carboxylate etc. can be illustrated. In a nickel metal hydride secondary battery, for example, an aqueous potassium hydroxide solution having a conventionally known concentration of 5 mol / liter or more can be used.
The solvent for dissolving the electrolyte is not particularly limited, and specific examples thereof include carbonate compounds such as propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate;
Lactone compounds such as γ-butyl lactone;
Ether compounds such as trimethoxymethane, 1,2-dimethoxyethane, diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran;
Examples thereof include sulfoxide compounds such as dimethyl sulfoxide, and one or more selected from these can be used.
The concentration of the electrolyte in the electrolytic solution is preferably 0.5 to 3.0 mol / L, more preferably 0.7 to 2.0 mol / L.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples.
“Parts” and “%” in Examples and Comparative Examples are based on weight unless otherwise specified.

Synthesis example 1
<Synthesis of cellulose derivative>
Put 5,730 mL of 88% 2-propanol aqueous solution into a Werner type crusher, put 191 g of pulp pieces cut into about 2 cm square as an absolute dry mass and crush them while stirring at high speed. The slurry was sufficiently stirred until there was no pulp left. After cooling the obtained slurry to room temperature, 28 g of sodium hydroxide was added to the crusher, and the mixture was cooled to 10 ° C. or lower again as alkali cellulose. 67 g of monochloroacetic acid was added to the ice-cooled slurry containing alkali cellulose, stirred for 1 minute, cooled to 5 ° C., and allowed to stand for 1.5 hours. Thereafter, the slurry was put into a three-necked flask equipped with a stirrer and a reflux condenser, heated in a hot water bath to boil, and reacted at the boiling point for 3 hours. After completion of the reaction, the reaction solution was cooled to room temperature, washed with 80% aqueous methanol and filtered several times to remove chloride ions. At this time, a part of the filtrate was taken, and silver nitrate was added dropwise thereto to examine the presence or absence of silver chloride precipitation, and the removal of chlorine ions was confirmed by the fact that no precipitation occurred. And the sodium salt type carboxymethylcellulose (CMC-A) was obtained by drying a reaction product.

Synthesis Examples 2 and 3
In Synthesis Example 1, the same as in Synthesis Example 1 except that the addition amount of sodium hydroxide and monochloroacetic acid and the reaction time at the boiling point after addition, stirring, cooling, and standing of monochloroacetic acid were as shown in Table 1. Thus, carboxymethyl cellulose (CMC-B and C) was obtained.

Example 1
<Preparation of binder composition>
(1) Synthesis of Polymer A The interior of an autoclave having an internal volume of about 6 L equipped with an electromagnetic stirrer was sufficiently purged with nitrogen, and then charged with 2.5 L of deoxygenated pure water and 25 g of ammonium perfluorodecanoate as an emulsifier. The temperature was raised to 60 ° C. while stirring at 350 rpm. Next, a mixed gas composed of 70% of vinylidene fluoride (VDF) as a monomer and 30% of propylene hexafluoride (HFP) was charged until the internal pressure reached 20 kg / cm ² . 25 g of Freon 113 solution containing 20% of diisopropyl peroxydicarbonate as a polymerization initiator was injected using nitrogen gas to initiate polymerization. During the polymerization, a mixed gas composed of 60.2% VDF and 39.8% HFP was sequentially injected so that the internal pressure was maintained at 20 kg / cm ² to maintain the pressure at 20 kg / cm ² . Further, since the polymerization rate decreased as the polymerization progressed, the same amount of the same polymerization initiator solution as that described above was injected using nitrogen gas after 3 hours, and the reaction was continued for 3 hours. Thereafter, the reaction liquid was cooled and the stirring was stopped at the same time. After the unreacted monomer was released, the reaction was stopped to obtain an aqueous dispersion containing 40% of polymer A fine particles.
As a result of analyzing the obtained polymer by ¹⁹ F-NMR, the mass composition ratio of each monomer was VDF / HFP = 21/4.

(2) Synthesis of polymer alloy particles (polymerization of polymer B)
After fully replacing the inside of the 7 L separable flask with nitrogen, 1,600 g of an aqueous dispersion containing the fine particles of the polymer A obtained in the above (1) (corresponding to 25 parts in terms of the polymer A), Emulsifier “ADEKA rear soap SR1025” (trade name, manufactured by ADEKA Corporation) 0.5 part, methyl methacrylate (MMA) 30 parts, 2-ethylhexyl acrylate (EHA) 40 parts and methacrylic acid (MAA) 5 parts; 130 parts of water was sequentially added and stirred at 70 ° C. for 3 hours to allow the polymer A to absorb the monomer. Next, 20 mL of a tetrahydrofuran (THF) solution containing 0.5 part of azobisisobutyronitrile as an oil-soluble polymerization initiator was added, the temperature was raised to 75 ° C., and the reaction was performed for 3 hours, and further at 85 ° C. for 2 hours. Reaction was performed. Then, after cooling, the reaction was stopped, and the aqueous dispersion (binder composition) containing 40% polymer particles was obtained by adjusting the pH to 7 with a 2.5N aqueous sodium hydroxide solution.
For the obtained aqueous dispersion, the particle size distribution is measured using a particle size distribution measuring apparatus (manufactured by Otsuka Electronics Co., Ltd., type “FPAR-1000”) based on the dynamic light scattering method. When the mode particle size was determined, the number average particle size was 330 nm.

Further, about 10 g of the obtained aqueous dispersion was taken into a Teflon (registered trademark) petri dish having a diameter of 8 cm and dried at 120 ° C. for 1 hour to form a film. 1 g of the obtained membrane (polymer) was accurately weighed, immersed in 400 mL of THF, and shaken at 50 ° C. for 3 hours. Next, the THF phase was filtered through a 300-mesh wire mesh to separate the insoluble matter, and the weight of the residue (Y (g)) obtained by evaporating and removing the dissolved THF was measured. When the THF-insoluble content was determined according to 4), the THF-insoluble content of the polymer particles was 85%.
THF insoluble matter (%) = {(1-Y) / 1} × 100 (4)
Furthermore, when the obtained fine particles were measured with a differential scanning calorimeter (DSC), the melting temperature Tm was not observed, and a single glass transition temperature Tg was observed at -2 ° C. The particles are considered to be polymer alloy particles.

<Preparation of active material particles>
Commercially available lithium iron phosphate (LiFePO ₄ ) was pulverized in an agate mortar and classified using a sieve to prepare active material particles having a particle diameter (D50 value) of 0.5 μm.

<Preparation of slurry for positive electrode>
Biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Co., Ltd.) and cellulose derivative (product name “CMC1120”, carboxymethyl cellulose, manufactured by Daicel Chemical Industries, Ltd.) as a thickener. 1 part (in terms of solid content), 100 parts by mass of the active material particles prepared in “Preparation of active material particles”, 5 parts of acetylene black, and 68 parts of water were added, and the mixture was stirred at 60 rpm for 1 hour. Next, the binder composition prepared in the above “Preparation of binder composition” is added so that the polymer particles contained in the composition are in the amount (parts) described in Table 2, and further stirred for 1 hour. To obtain a paste. After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring defoamer (manufactured by Shinkey Co., Ltd., trade name “Awatori Netaro”) at 200 rpm for 2 minutes, A positive electrode slurry was prepared by stirring and mixing at 1,800 rpm for 5 minutes and further under vacuum (about 5.0 × 10 ³ Pa) at 1,800 rpm for 1.5 minutes.
The ratio (Da / Db) of the average particle size (Da) of (A) polymer particles to the average particle size (Db) of (B) active material particles in this positive electrode slurry is 0.7.
-Measurement of spinnability of positive electrode slurry-
The spinnability of this positive electrode slurry was measured as follows.
First, a Zaan cup (Daisen Equipment Co., Ltd., Zaan Biscocity Cup No. 5) having an opening with a diameter of 5.2 mm at the bottom of the container was prepared. With the opening of the Zahn cup closed, 40 g of the positive electrode slurry prepared above was poured. When the opening was opened, the slurry flowed out. In this case, the time instant of opening the opening and T _0, the time continued to flow out so as to draw the yarn when the slurry flows measured visually, the time was T _A. Moreover, to continue the measurement from no longer attracted yarn was measured time T _B to the slurry for the positive electrode not flow out. The measured values T ₀ , T _A and T _B were substituted into the above formula (1) to obtain the spinnability.

<Manufacture and evaluation of positive electrode and electricity storage device>
(1) Production of positive electrode The positive electrode slurry prepared above was uniformly applied to the surface of a current collector made of aluminum foil by a doctor blade method so that the film thickness after drying was 100 μm. Dried for minutes. Then, the positive electrode was obtained by pressing with a roll press so that the density of a film | membrane (active material layer) might become the value as described in Table 3.
(2) Evaluation of porosity of active material layer For the positive electrode manufactured in “(1) Manufacturing of positive electrode”, the pore volume V (cm ³ / g) was measured by mercury intrusion using Quantachrome's PoreMaster. The positive electrode has a mass of B (g), an area of C (cm ² ), and a thickness of D (μm). By substituting these values into the above formula (2), the pores of the active material layer The rate was calculated.
(3) Evaluation of the crack rate of the positive electrode This positive electrode was cut into a 2 cm wide × 10 cm long electrode plate, and the positive electrode plate was repeatedly bent at 100 times along a round bar having a diameter of 2 mm in the width direction. It was. The size of the crack along the round bar was visually observed and measured, and the crack rate was measured. The crack rate was defined by the following mathematical formula (5).
Crack rate (%) = {length with crack (mm) ÷ total length of electrode plate (mm)} × 100 (5)
Here, the electrode plate excellent in flexibility and adhesion has a low crack rate. The crack rate is preferably 0%. However, when the electrode plate group is manufactured by winding the positive electrode plate and the negative electrode plate in a spiral shape through a separator, the crack rate is allowed to be up to 20%. However, if the crack rate is larger than 20%, the positive electrode plate is easily cut and it becomes impossible to manufacture the electrode plate group, and the productivity of the electrode plate group is lowered. From this, it is considered that a good range is up to 20% as the threshold of the crack rate.
The measurement results of the crack rate are shown in Table 3.

(4) Manufacture of negative electrode As a negative electrode active material, a biaxial planetary mixer (product name "TK Hibismix 2P-03", manufactured by PRIMIX Corporation), 4 parts of polyvinylidene fluoride (PVDF) (solid content conversion), 100 parts of graphite (in terms of solid content) and 80 parts of N-methylpyrrolidone (NMP) were added and stirred at 60 rpm for 1 hour. Then, after further adding 20 parts of NMP, using a stirring defoaming machine (product name “Netaro Awatori” manufactured by Shinky Co., Ltd.) for 2 minutes at 200 rpm, then 5 minutes at 1,800 rpm and further vacuuming Below, the slurry for negative electrodes was prepared by stirring and mixing for 1.5 minutes at 1,800 rpm.
The negative electrode slurry prepared above was uniformly applied to the surface of the current collector made of copper foil by the doctor blade method so that the film thickness after drying was 150 μm, and dried at 120 ° C. for 20 minutes. Then, the negative electrode was obtained by pressing using a roll-press machine so that the density of a film | membrane may be 1.5 g / cm < ³ >.

(5) Assembly of lithium ion battery cell In a glove box substituted with Ar so that the dew point is -80 ° C. or lower, the negative electrode manufactured in “(2) Manufacturing of negative electrode” above is punched and molded to a diameter of 16.16 mm Was placed on a bipolar coin cell (trade name “HS Flat Cell” manufactured by Hosen Co., Ltd.). Next, a separator made of a polypropylene porous membrane punched to a diameter of 24 mm (product name “Celguard # 2400”, manufactured by Celgard Co., Ltd.) was placed, and after injecting 500 μL of electrolytic solution so that air did not enter, A lithium ion battery is manufactured by placing the positive electrode manufactured in the above-mentioned “(1) Manufacturing of positive electrode” by punching and molding the positive electrode to a diameter of 15.95 mm, and sealing the outer body of the two-pole coin cell with a screw. A cell (electric storage device) was assembled.
The electrolytic solution used here is a solution obtained by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

(6) Evaluation of electricity storage device (Evaluation of charge / discharge rate characteristics)
About the electrical storage device manufactured above, charging is started at a constant current (0.2 C), and when the voltage reaches 4.2 V, charging is continued at a constant voltage (4.2 V). The charge capacity at 0.2C was measured with the time when the temperature reached 0.01C being regarded as completion of charge (cutoff). Next, discharge was started at a constant current (0.2 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 0.2 C was measured.
Next, charging is started at a constant current (3C) for the same cell, and when the voltage reaches 4.2V, charging is continued at a constant voltage (4.2V). The charging capacity at 3C was measured with the time point of becoming the completion of charging (cutoff). Next, discharge was started at a constant current (3C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 3C was measured.
Using the above measured value, the charge rate (%) is calculated by calculating the ratio (percent%) of the charge capacity at 3C to the charge capacity at 0.2C.
The discharge rate (%) was calculated respectively by calculating the ratio (percent%) of the discharge capacity at 3C to the discharge capacity at 0.2C.
When both the charge rate and the discharge rate are 80% or more, it can be evaluated that the charge / discharge rate characteristics are good.
The measured charge rate and discharge rate values are shown in Table 3, respectively.
In the measurement conditions, “1C” indicates a current value at which discharge is completed in one hour after constant current discharge of a cell having a certain electric capacity. For example, “0.1 C” is a current value at which discharge is completed over 10 hours, and 10 C is a current value at which discharge is completed over 0.1 hours.

Examples 2-14 and Comparative Examples 1-4
<Preparation of binder composition>
A polymer having the composition shown in Table 2 in the same manner as in Example 1 except that the composition of the monomer gas and the amount of emulsifier were appropriately changed in “(1) Synthesis of Polymer A” in Example 1 above. An aqueous dispersion containing fine particles of A was prepared, and water was removed under reduced pressure or added according to the solid content concentration of the aqueous dispersion to obtain an aqueous dispersion having a solid content concentration of 40%.
Next, in “(2) Synthesis of polymer alloy particles” in Example 1, the above-mentioned aqueous dispersion was used in the amount shown in Table 2 in terms of solid content, and the monomer charge (parts) and polymer A were used. A water system containing polymer particles having the particle diameters shown in Table 2 by changing the temperature and time when the monomer is absorbed into each of them as shown in Table 2 and further varying the amount of emulsifier used as appropriate. A dispersion (binder composition) was obtained. Here, for Example 12 and Comparative Example 2, the monomer for synthesizing the polymer B in the aqueous dispersion containing the fine particles of the polymer A without causing the polymer A to absorb the monomer was used. Immediately after the addition, a THF solution of a polymerization initiator was added, and the temperature was raised via polymerization.
The results of the THF insoluble matter measurement and DSC measurement (glass transition temperature Tg, melting temperature Tm, and polymer alloy or not) performed on the obtained fine particles are shown in Table 2 together.

<Preparation of active material particles>
In “Preparation of active material particles” in Example 1 above, active material particles having the particle diameters (D50 values) shown in Table 2 were prepared by appropriately changing the sieve openings used.
<Preparation of slurry for positive electrode>
As the binder composition and active material particles, those prepared above are used in the amounts shown in Table 2, and the thickeners of the type and amount shown in Table 2 are used in <Preparation of slurry for positive electrode>. The positive electrode slurry was prepared in the same manner as in “Preparation of positive electrode slurry” in Example 1, and the spinnability was measured. The values of the spinnability are shown in Table 2. The ratio (Da / Db) between the average particle diameter (Da) of the polymer particles (Da) and the average particle diameter (Db) of the active material particles (Da / Db) in this positive electrode slurry is also shown in Table 2. Indicated.
<Manufacture and evaluation of positive electrode and electricity storage device>
A positive electrode and an electricity storage device were produced and evaluated in the same manner as in Example 1 except that each material obtained above was used.
The evaluation results are shown in Table 3.

Example 15 and Comparative Example 5
<Preparation of binder composition>
The fine particles of polymer A having the composition shown in Table 2 were the same as in Example 1 except that the composition of the monomer gas was changed appropriately in “(1) Synthesis of Polymer A” in Example 1 above. An aqueous dispersion containing was obtained.
Next, in “(2) Synthesis of polymer alloy particles” in Example 1, the above-mentioned aqueous dispersion was used in the amount shown in Table 2 in terms of solid content, and the charged amount of monomer of polymer (B) ( Part) was as shown in Table 2, and the amount of emulsifier used was further varied to obtain an aqueous dispersion containing polymer particles having the particle sizes shown in Table 2.
Furthermore, the binder composition was obtained by performing solvent substitution using N-methylpyrrolidone (NMP) as a solvent.
In this binder composition of Comparative Example 8, the polymer was dissolved in the solvent (thus, the value of the ratio (Da / Db) is 0).

<Preparation of active material particles>
In “Preparation of active material particles” in Example 1 above, active material particles having particle diameters (D50 values) shown in Table 2 were prepared by changing the openings of the sieves used.
<Preparation of slurry for positive electrode and production and evaluation of positive electrode and power storage device>
Biaxial planetary mixer (product name “TK Hibismix 2P-03” manufactured by PRIMIX Co., Ltd.) and cellulose derivative (product name “CMC1150”, carboxymethyl cellulose, manufactured by Daicel Chemical Industries, Ltd.) 10 parts (in terms of solid content), 100 parts by mass of active material particles prepared in the above “Preparation of active material particles”, 5 parts of acetylene black, 4 parts of binder composition prepared in “Preparation of binder composition” (solid content) Conversion) and 68 parts of NMP were added and stirred at 60 rpm for 2 hours to obtain a paste. After adding NMP to the obtained paste to adjust the solid content concentration to 45%, using a stirring defoaming machine (manufactured by Shinky Co., Ltd., trade name “Awatori Netaro”), at 200 rpm for 2 minutes, A positive electrode slurry was prepared by stirring and mixing at 1,800 rpm for 5 minutes and further under vacuum at 1,800 rpm for 1.5 minutes.
A positive electrode and an electricity storage device were produced and evaluated in the same manner as in “Production and evaluation of positive electrode and electricity storage device” in Example 1, except that the above slurry for positive electrode was used.
The evaluation results are shown in Table 3.

Example 16
<Preparation of binder composition>
In a 7-liter separable flask, 150 parts of water and 0.2 part of sodium dodecylbenzenesulfonate were charged, and the inside of the separable flask was sufficiently purged with nitrogen.
On the other hand, in another container, 60 parts of water, ether sulfate type emulsifier (trade name “Adekaria Soap SR1025”, manufactured by ADEKA Co., Ltd.) as an emulsifier, 0.8 parts in terms of solid content, and 2,2 , 2-trifluoroethyl methacrylate (TFEMA) 20 parts, acrylonitrile (AN) 10 parts, methyl methacrylate (MMA) 25 parts, 2-ethylhexyl acrylate (EHA) 40 parts and acrylic acid 5 parts, and stirred well A monomer emulsion containing a mixture of the above monomers was prepared.
Thereafter, the temperature inside the separable flask was started, and when the temperature inside the separable flask reached 60 ° C., 0.5 part of ammonium persulfate was added as a polymerization initiator. Then, when the temperature inside the separable flask reaches 70 ° C., the addition of the monomer emulsion prepared above is started, and the monomer emulsion is added while maintaining the temperature inside the separable flask at 70 ° C. Slowly added over time. Thereafter, the temperature inside the separable flask was raised to 85 ° C., and this temperature was maintained for 3 hours to carry out the polymerization reaction. After 3 hours, the separable flask was cooled to stop the reaction, and then the aqueous dispersion (binder composition) containing 30% polymer particles was prepared by adding ammonium water to adjust the pH to 7.6. Obtained.
When the aqueous dispersion obtained above was evaluated in the same manner as in Example 1, the number average particle diameter was 110 nm. Only one glass transition temperature was observed at -2 ° C.

<Preparation of active material particles>
In “Preparation of active material particles” in Example 1 above, active material particles having the particle diameters (D50 values) shown in Table 2 were prepared by appropriately changing the sieve openings used.
<Preparation of slurry for positive electrode and production and evaluation of positive electrode and power storage device>
A positive electrode slurry in the same manner as in “Preparation of positive electrode slurry” and “Preparation and evaluation of positive electrode and electricity storage device” in Example 1, except that the binder composition and the active material particles were each prepared above. Was prepared, and a positive electrode and an electricity storage device were produced and evaluated using the same.
The ratio (Da / Db) is shown in Table 2, and the evaluation results are shown in Table 3.

Examples 17 and 18 and Comparative Example 6
<Preparation of binder composition>
It contains polymer particles having the number average particle size described in Table 2 in the same manner as in Example 16 except that the type and amount (parts) of each monomer are as shown in Table 2. An aqueous dispersion (binder composition) was obtained.
<Preparation of active material particles>
In “Preparation of active material particles” in Example 1 above, active material particles having the particle diameters (D50 values) shown in Table 2 were prepared by appropriately changing the sieve openings used.
<Preparation of slurry for positive electrode>
A positive electrode slurry was prepared in the same manner as in “Preparation of positive electrode slurry” in Example 1, except that the binder composition and the active material particles were each prepared in the above amounts in the amounts shown in Table 2. .
<Manufacture and evaluation of positive electrode and electricity storage device>
A positive electrode and an electricity storage device were produced and evaluated in the same manner as in Example 1 except that each material obtained above was used.
The evaluation results are shown in Table 3.
The polymer particles synthesized in <Preparation of Binder Composition> in Examples 16 to 18 are not the “polymer B” but the polymer according to the present invention. It was described in the column of “Polymer B”.

Abbreviations of each component in Table 2 have the following meanings.
[Monomer of Polymer A]
VDF: vinylidene fluoride HFP: propylene hexafluoride TFE: tetrafluoroethylene [monomer of polymer B]
-(Meth) acrylic acid alkyl ester-
MMA: Methyl methacrylate EHA: 2-ethylhexyl acrylate-hydrophilic monomer-
AN: Acrylonitrile AA: Acrylic acid MAA: Methacrylic acid HEMA: Acrylic acid-2-hydroxyethyl-polyfunctional monomer-
DVB: divinylbenzene TMPTMA: trimethylolpropane trimethacrylate AMA: allyl methacrylate-fluorinated monomer-
TFEMA: 2,2,2-trifluoroethyl methacrylate TFEA: 2,2,2-trifluoroethyl acrylate HFIPA: 1,1,1,3,3,3-hexafluoroisopropyl acrylate [solvent]
NMP: N-methylpyrrolidone

[Is it a polymer alloy or not? ]
A: A polymer alloy.
X: Not a polymer alloy.
[Active material]
LiFeP: LiFePO ₄
LiCoO: LiCoO ₂
LiNiO: LiNiO ₂
LiMnO: LiMn ₂ O ₄
LNMCO: LiNi _0.33 Mn _0.33 Co _0.33 O ₂
[Thickener]
CMC1120, CMC1150, CMC2200, CMC2280 and CMC2450 are all trade names of products of Daicel Chemical Industries, Ltd., and are cellulose derivatives composed of an alkali metal salt of carboxymethylcellulose.
CMC-A, CMC-B, and CMC-C are sodium salt type carboxymethyl cellulose obtained in Synthesis Examples 1 to 3, respectively.
The notation “-” in Table 2 indicates that the corresponding component was not used or the corresponding operation was not performed.

As is apparent from Tables 2 and 3 above, the positive electrode slurry prepared using the binder composition of the present invention shown in Examples 1 to 18 is between the current collector and the active material layer. A positive electrode having good binding properties, low crack rate, and excellent adhesion was obtained. Moreover, the electrical storage device (lithium ion battery) provided with these positive electrodes had favorable charge / discharge rate characteristics.
On the other hand, a positive electrode having good adhesion was not obtained from the binder compositions of Comparative Examples 1, 3, and 4, and a positive electrode having a poor crack rate was not formed. The positive electrodes formed from the binder compositions of Comparative Examples 2 and 6 had good adhesion, but no electricity storage device showing good charge / discharge characteristics was obtained. Comparative Example 5 is an example in which a non-aqueous dispersion medium was used, but the polymer particles were dissolved, so that both the adhesion of the positive electrode and the charge / discharge rate characteristics of the electricity storage device were poor.

As described above, it was estimated from the DSC chart that the polymer particles in the present invention are polymer alloys.
DSC charts of the polymer particles obtained in Example 3, Comparative Example 2 and Comparative Example 6 are shown in FIGS. 1, 2 and 3, respectively.
Moreover, the DSC chart of the polymer particle synthesize | combined in the following synthesis example 4 was shown in FIG.

Synthesis example 4
80% of structural units derived from vinylidene fluoride (VDF) in the same manner as in Example 1 except that the composition of the monomer gas was changed in “(1) Synthesis of Polymer A” in Example 1 above. An aqueous dispersion containing fine particles of polymer A composed of 20% of a structural unit derived from hexafluoropropylene (HFP) was obtained (the subsequent “(2) synthesis of polymer alloy particles” was not performed. .)

FIG. 2 shows a mixture of polymer A and polymer B.
FIG. 3 shows the case of polymer B only.
FIG. 4 shows the case of polymer A only.
1 corresponds to the polymer alloy particles composed of the polymer A and the polymer B, respectively.
In FIG. 3, the glass transition temperature Tg of the polymer B was observed, and in FIG. 4, the melting temperature Tm of the polymer A was observed.
In FIG. 2 (when polymer A does not absorb the monomer of polymer B), both melting temperature Tm of polymer A and glass transition temperature Tg of polymer B were observed. Whereas the coalesced particles are considered to be a mixture of polymer A and polymer B,
Referring to FIG. 1, neither the melting temperature Tm of polymer A nor the glass transition temperature Tg of polymer B is observed, and a single new glass transition at a temperature different from the Tm of polymer A and the Tg of polymer B. Since the temperature Tg is generated, this polymer particle is considered to be a polymer alloy.

  The present invention is not limited to the above embodiment, and various modifications can be made. The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). The present invention also includes a configuration in which a non-essential part of the configuration described in the above embodiment is replaced with another configuration. Furthermore, the present invention includes a configuration that achieves the same effects as the configuration described in the above embodiment or a configuration that can achieve the same object. Furthermore, the present invention includes a configuration obtained by adding a known technique to the configuration described in the above embodiment.

Claims (6)

Polymer particles having at least (A) a repeating unit derived from a monomer having a fluorine atom,
(B) An active material particle comprising a lithium atom-containing oxide, and (C) a slurry for a positive electrode of an electricity storage device containing a liquid medium,
The ratio (Da / Db) of the average particle diameter (Da) of the (A) polymer particles to the average particle diameter (Db) of the (B) active material particles is 0.01 to 1.0, and the slurry The positive electrode slurry is characterized by having a spinnability of 30 to 80%.   The slurry for positive electrodes of Claim 1 whose average particle diameter of the said (B) active material particle is 0.1-25 micrometers. The positive electrode slurry according to claim 1 or 2, wherein the (B) active material particles are a composite metal oxide represented by the following general formula (B-1).
Li _{1 + x} M ¹ _y M ² _z O ₂ (B-1)
(In Formula (B-1), M ¹ is at least one metal atom selected from the group consisting of Co, Ni and Mn;
M ² is at least one metal atom selected from the group consisting of Al and Sn;
O is an oxygen atom;
x, y and z are numbers in the range of 0.10 ≧ x ≧ 0, 4.00 ≧ y ≧ 0.85 and 2.00 ≧ z ≧ 0, respectively. ) The positive electrode slurry according to claim 1 or 2, wherein the (B) active material particles are a compound represented by the following general formula (B-2) and having an olivine type crystal structure.
Li _1-x M _x (XO ₄ ) (B-2)
(In the formula (B-2), M is a metal selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, A1, Ga, Ge, and Sn. At least one kind of ions;
X is at least one selected from the group consisting of Si, S, P and V; and x is a number and satisfies the relationship 0 <x <1. )   It has an electrical power collector and the active material layer formed using the slurry for positive electrodes as described in any one of Claims 1-3, The positive electrode of the electrical storage device characterized by the above-mentioned.   An electrical storage device comprising the positive electrode according to claim 5.

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