JP6544150B2 - Slurry for positive electrode, power storage device positive electrode, method of manufacturing power storage device positive electrode, power storage device, and method of manufacturing power storage device - Google Patents

Description

  The present invention relates to a positive electrode slurry, a storage device positive electrode, a method of manufacturing a storage device positive electrode, a storage device, and a method of manufacturing a storage device.

  As a highly safe positive electrode active material, a lithium-containing phosphoric acid compound (olivine-type lithium-containing phosphoric acid compound) having an olivine structure has attracted attention. The olivine-type lithium-containing phosphoric acid compound has high thermal stability due to the covalent bond of phosphorus and oxygen, and does not release oxygen even at high temperature.

  The olivine-type lithium-containing phosphate compound has a low output voltage because the lithium ion storage / release voltage is around 3.4 V. In order to compensate for the defect, attempts have been made to improve the characteristics of peripheral materials such as electrode binders and electrolytes (see Patent Documents 1 to 3).

JP 2007-294323 A WO 2010/113940 JP, 2012-216322, A

  However, with the techniques disclosed in Patent Documents 1 to 3, it has been difficult to sufficiently improve the charge / discharge characteristics of a power storage device provided with a positive electrode using an olivine-type lithium-containing phosphoric acid compound as a positive electrode active material. The present invention has been made in view of the above points, and it is an object of the present invention to provide a positive electrode slurry, an electrical storage device positive electrode, a method of manufacturing an electrical storage device positive electrode, an electrical storage device, and a method of manufacturing an electrical storage device. I assume.

  The slurry for positive electrode of the present invention contains (A) polymer, (B) olivine type lithium containing phosphoric acid compound, and (C) liquid medium, and the (A) polymer is unsaturated carboxylic acid. And (B) an olivine-type lithium-containing phosphoric acid containing a diene polymer having a repeating unit Mc derived from a conjugated unit, a repeating unit Md derived from a conjugated diene compound, and a repeating unit Me derived from an aromatic vinyl The content of the polymer (A) is in the range of 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the content of the compound.

By using the slurry for positive electrode of the present invention to manufacture an electrical storage device positive electrode and an electrical storage device provided with the electrical storage device positive electrode, excellent charge / discharge characteristics can be exhibited.
The method of manufacturing a storage device positive electrode according to the present invention is characterized in that the above-described positive electrode slurry is applied and dried on the surface of a current collector to form a layer. If an electricity storage device is manufactured using the electricity storage device positive electrode manufactured according to the present invention, excellent charge and discharge characteristics can be exhibited.

  The storage device positive electrode of the present invention comprises a current collector and a layer formed on the surface of the current collector, wherein the layer is (A) a polymer, and (B) an olivine-type lithium-containing phosphoric acid The polymer (A) contains a compound, and the polymer (A) has a repeating unit Mc derived from an unsaturated carboxylic acid, a repeating unit Md derived from a conjugated diene compound, and a repeating unit Me derived from an aromatic vinyl The range of 0.5 to 1.5 parts by mass of the content of the polymer (A) with respect to the content of 100 parts by mass of the (B) olivine-type lithium-containing phosphate compound containing a diene polymer It is characterized by being. If an electricity storage device is manufactured using this electricity storage device positive electrode, excellent charge and discharge characteristics can be exhibited.

An electricity storage device of the present invention includes the above-described electricity storage device positive electrode. The electricity storage device of the present invention can exhibit excellent charge and discharge characteristics.
A method of manufacturing a power storage device according to the present invention is characterized in that a power storage device positive electrode is manufactured by the above-described manufacturing method. The electricity storage device manufactured according to the present invention can exhibit excellent charge and discharge characteristics.

  An embodiment of the present invention will be described. It is to be understood that the present invention is not limited to only the embodiments described below, but also includes various modifications implemented within the scope of the present invention.

  In addition, "(meth) acrylic acid ~" in the present specification is a concept encompassing both "acrylic acid ~" and "methacrylic acid ~". Moreover, "-(meth) acrylate" is the concept which includes both "-acrylate" and "-methacrylate."

  In addition, it is clear from experience that the quality of the performance is almost proportional to the bonding ability of the positive electrode active materials (binding ability) and the adhesion ability of the positive electrode active material layer to the current collector (adhesiveness). It has become. Therefore, in the present specification, hereinafter, they may be collectively referred to using the term "binding".

1. Slurry for Positive Electrode The slurry for positive electrode according to the present embodiment means a composition used to form a layer (positive electrode active material layer) containing a positive electrode active material on the surface of a current collector. The positive electrode active material layer can be formed on the surface of the current collector by, for example, applying and drying the positive electrode slurry on the surface of the current collector.

  The slurry for positive electrode according to the present embodiment includes (A) polymer (hereinafter, also referred to as “component (A)”) and (B) olivine-type lithium-containing phosphoric acid compound (hereinafter, “component (B)”). And a liquid medium (hereinafter, also referred to as "component (C)"). Hereinafter, the positive electrode slurry according to the present embodiment will be described in detail.

1.1. Component (A) The component (A) is a diene polymer having a repeating unit Mc derived from an unsaturated carboxylic acid, a repeating unit Md derived from a conjugated diene compound, and a repeating unit Me derived from an aromatic vinyl. contains.

  In the slurry for positive electrode, the component (A) may be, for example, polymer particles or a water-soluble polymer (for example, a water-soluble binder). When the component (A) is a polymer particle, for example, the component (A) is dispersed in the form of a latex in a liquid medium (C). By dispersing in a latex form, the stability of the slurry for the positive electrode becomes good, and the coatability of the slurry for the positive electrode on the current collector becomes good.

  When the component (A) is a polymer particle, the average particle diameter of the component (A) is preferably in the range of 90 to 170 nm, and more preferably in the range of 100 to 165 nm. When the average particle diameter of the component (A) is in the above range, the component (A) can be sufficiently adsorbed on the surface of the component (B). As a result, the migration of the component (A) can be suppressed, and an optimum distribution of the component (A) with less uneven distribution in the positive electrode structure can be realized. As a result, sufficient adhesion between the positive electrode active material layer and the current collector can be exhibited, and deterioration of the electrical characteristics of the power storage device can be suppressed.

  The average particle size of the component (A) is determined by measuring the particle size distribution using a particle size distribution measuring device based on the light scattering method as the measurement principle, and in the particle size distribution, accumulating the number of particles in order from the smaller particle size. It is the value of the particle diameter (number average particle diameter, D50) when the cumulative frequency of the number of particles is 50% of the total number of particles.

  As such a particle size distribution measuring apparatus, Coulter LS230, LS100, LS13320 (above, Beckman Coulter. Inc make), FPAR-1000 (made by Otsuka Electronics Co., Ltd.) etc. can be mentioned. Further, in the above-mentioned measurement method, the aqueous dispersion (latex) of the component (A) is used as a sample.

  In addition, these particle size distribution measuring apparatuses do not evaluate only the primary particle of a polymer particle in evaluation object, and can evaluate the secondary particle which primary particle aggregated and formed. Therefore, the particle size distribution measured by these particle size distribution measuring devices can also be used as an indicator of the dispersion state of the component (A) contained in the slurry for positive electrode.

The content of the component (A) is in the range of 0.5 to 1.5 parts by mass and in the range of 1 to 1.5 parts by mass with respect to 100 parts by mass of the content of the component (B). More preferable.
When the positive electrode slurry is applied to the surface of the current collector and dried to form a positive electrode active material layer, the positive electrode active material layer contains the (A) component and the (B) component. Here, since the component (A) has lower electron conductivity than the component (B), the component (A) generally has an electrical property that inhibits the flow of electrons from the component (B) to the current collector. It tends to be a resistance component. When the content of the component (A) is within the above range relative to 100 parts by weight of the component (B), the adhesion between the current collector and the positive electrode active material layer is unlikely to be impaired, and electrical resistance can be suppressed. . As a result, it is possible to produce a positive electrode in which good electrical characteristics and adhesiveness are compatible.

1.1.1. Component (A) of the diene-based polymer The diene-based polymer is contained in component (A). The diene polymer has a repeating unit Mc derived from an unsaturated carboxylic acid, a repeating unit Md derived from a conjugated diene compound, and a repeating unit Me derived from an aromatic vinyl.

1.1.1.1. Repeating unit Mc derived from unsaturated carboxylic acid
When the diene polymer has the repeating unit Mc derived from the unsaturated carboxylic acid, the stability of the slurry for positive electrode is improved.

  Specific examples of the unsaturated carboxylic acid include one or more selected from mono- or dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid. In particular, one or more selected from acrylic acid, methacrylic acid and itaconic acid is preferable.

  The content ratio of the repeating unit Mc derived from the unsaturated carboxylic acid is preferably 30 parts by mass or less, and 0.3 to 25 parts by mass, based on 100 parts by mass of all the repeating units of the diene polymer. Is more preferred. When the content ratio of the repeating unit Mc is in the above range, since the dispersion stability of the component (A) is excellent at the time of preparation of the slurry for positive electrode, aggregates are hardly generated. Moreover, the rise of the slurry viscosity over time can also be suppressed.

1.1.1.2. Repeating unit Md derived from a conjugated diene compound
When the diene polymer has the repeating unit Md derived from the conjugated diene compound, the binding power of the diene polymer becomes strong. Therefore, the binding property between the positive electrode active material layer and the current collector is improved. In addition, when the diene polymer has a repeating unit Md derived from a conjugated diene compound, rubber elasticity is imparted to the diene polymer. Therefore, the positive electrode active material layer can follow changes in volume contraction, expansion, and the like of the current collector. As a result, the charge and discharge characteristics of the power storage device can be maintained for a long time.

  The conjugated diene compound is selected, for example, from 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene and the like. One or more may be mentioned. As a conjugated diene compound, 1,3-butadiene is particularly preferable.

  The content ratio of the repeating unit Md derived from the conjugated diene compound is preferably 30 to 60 parts by mass, and more preferably 40 to 55 parts by mass, based on 100 parts by mass of all the repeating units. When the content ratio of the repeating unit Md is in the above range, the binding property between the positive electrode active material layer and the current collector is further improved.

1.1.1.3. Repeat unit Me derived from aromatic vinyl
When the slurry for a positive electrode contains a conductivity imparting agent by having the diene polymer having a repeating unit Me derived from aromatic vinyl, the affinity between the component (A) and the conductivity imparting agent can be further improved. it can.

  Specific examples of the aromatic vinyl include one or more selected from styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, divinylbenzene and the like. As the aromatic vinyl, styrene is particularly preferable among the above-mentioned specific examples.

  The content ratio of the repeating unit Me derived from aromatic vinyl is preferably 10 to 55 parts by mass, and more preferably 15 to 50 parts by mass, based on 100 parts by mass of all the repeating units. When the content ratio of the repeating unit Me is in the above range, the component (A) has a suitable binding property to the component (B). In addition, the flexibility of the obtained positive electrode active material layer and the binding property of the positive electrode active material layer to the current collector become good.

1.1.1.4. Other Repeating Units The diene polymer may have other repeating units. As a repeating unit other than the above, the repeating unit Mb derived from unsaturated carboxylic acid ester is mentioned, for example.

  When the diene polymer has a repeating unit Mb derived from an unsaturated carboxylic acid ester, the affinity between the diene polymer and the electrolytic solution becomes better, and the diene polymer becomes an electrical resistance component in the electricity storage device. It is possible to suppress an increase in internal resistance due to Further, it is possible to more effectively suppress the decrease in the binding property between the positive electrode active material layer and the current collector, which is caused by the diene polymer excessively absorbing the electrolyte solution.

  The unsaturated carboxylic acid ester is preferably a (meth) acrylic acid ester. Specific examples of (meth) acrylic acid esters include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n (meth) acrylate -Butyl, i-butyl (meth) acrylate, n-amyl (meth) acrylate, i-amyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2 (meth) acrylate -Ethylhexyl, n-octyl (meth) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxybutyl (meth) acrylate, Ethylene glycol (meth) acrylate, ethylene glycol di (meth) acrylate, di (meth) acrylate Selected from propylene glycol acid, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, allyl (meth) acrylate and ethylene di (meth) acrylate One or more of the following may be mentioned.

  Among these, one or more selected from methyl (meth) acrylate, ethyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate It is particularly preferable that it is at least one selected from methyl (meth) acrylate, hydroxymethyl (meth) acrylate and hydroxyethyl (meth) acrylate.

  The content ratio of the repeating unit Mb derived from the unsaturated carboxylic acid ester in the diene polymer is preferably 0 to 40 parts by mass, and 10 to 30 parts by mass, based on 100 parts by mass of all the repeating units. Is more preferred.

Moreover, as another repeating unit, the repeating unit derived from the (alpha), (beta)-unsaturated nitrile compound is mentioned, for example.
Specific examples of the α, β-unsaturated nitrile compound include one or more selected from acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile, vinylidene cyanide and the like. Among these, one or more selected from acrylonitrile and methacrylonitrile is preferable, and acrylonitrile is more preferable.

  Moreover, the diene polymer may further have a repeating unit derived from the compound shown below. Examples of the compound include alkylamides of ethylenically unsaturated carboxylic acids such as (meth) acrylamide and N-methylolacrylamide; vinyl esters of carboxylic acids such as vinyl acetate and vinyl propionate; and acid anhydrides of ethylenically unsaturated dicarboxylic acids Monoalkyl ester; Monoamide; One or more kinds selected from aminoalkylamides of ethylenically unsaturated carboxylic acids such as aminoethyl acrylamide, dimethylaminomethyl methacrylamide, methylaminopropyl methacrylamide and the like.

1.1.2. Synthesis Method of Diene-Based Polymer The synthesis method of the diene-based polymer is not particularly limited, and can be easily synthesized, for example, by a known emulsion polymerization step or a step obtained by appropriately combining these. For example, a diene polymer can be easily synthesized by using the method described in Japanese Patent No. 4957932 or the like.

1.1.3. Physical properties of diene polymer 1.1.3.1. Counter ion To improve the stability of slurry for positive electrode, ammonia, alkali metal (lithium, sodium, potassium, rubidium, cesium etc.) hydroxide, inorganic ammonium compound (ammonium chloride etc.), organic amine compound (ethanolamine) It is preferable to adjust the pH of the diene polymer by adding an aqueous solution such as diethylamine or the like.

  In particular, it is preferable to neutralize the repeating unit Mc derived from the unsaturated carboxylic acid which is a constituent unit of the diene polymer by using at least one cation selected from ammonium ion and sodium ion to form a salt. The binding property between the current collector and the positive electrode active material layer can be improved by previously neutralizing the diene polymer and adjusting the pH of the slurry for positive electrode to a range of 5 to 13, preferably 6 to 12. .

1.1.3.2. Tetrahydrofuran (THF) Insoluble Component The THF insoluble component of the diene polymer is preferably 80% or more, and more preferably 90% or more. The THF insoluble matter is estimated to be approximately proportional to the insoluble matter amount in the electrolyte used in the electricity storage device. For this reason, if the THF insoluble matter is in the above-mentioned range, the storage device can be manufactured, and elution of the diene polymer in the electrolytic solution can be suppressed even when charge and discharge are repeated for a long time.

1.1.3.3. Transition Temperature The transition temperature of the diene polymer can be measured by differential scanning calorimetry (DSC) according to JIS K7121. The diene polymer is preferably one having only one endothermic peak in the temperature range of -50 to 5 ° C.

1.2. (B) Component The component (B) contained in the slurry for positive electrode according to the present embodiment is, for example, a lithium atom-containing oxide represented by the following general formula (1) and having an olivine type crystal structure (olivine type 1 or more types selected from lithium containing phosphoric acid compounds are mentioned.

Li _1-x M ¹ _x (XO ₄ ) (1)
In the formula (1), M ¹ is at least one selected from the group consisting of Mg, Ti, V, Nb, Ta, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al, Ga, Ge and Sn It is an ion of one kind of metal, X is at least one kind selected from the group consisting of Si, S, P and V, and x is a number satisfying the relation of 0 <x <1).
In addition, the value of x in the said General formula (1) is selected according to the valence of M ¹ and X so that the valence of the said General formula (1) may become zero valence.

The electrode potential of the olivine-type lithium-containing phosphate compound represented by the general formula (1) varies depending on the type of the metal element M ¹ . Therefore, the electrode voltage can be appropriately set by selecting the type of the metal element M ¹ .

Representative examples of olivine-type lithium-containing phosphoric acid compounds 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. Be Among these, LiFePO ₄ (lithium iron phosphate) is particularly preferable because it is easy to obtain an iron compound as a raw material and is inexpensive.

  In addition, a compound in which Fe ion in the compound as a typical example described above is substituted by Co ion, Ni ion or Mn ion also has the same crystal structure as the compound before substitution, so the same effect as a positive electrode active material Have.

  In the slurry for positive electrode, the component (B) may be provided with various substances such as a conductive substance on the particle surface. An example of a typical conductive material is carbon. Such component (B) can be produced by a known method such as JP-A-2009-09670.

The average particle diameter of the component (B) is preferably in the range of 1 to 30 μm, more preferably in the range of 1 to 25 μm, and particularly preferably in the range of 1 to 20 μm.
In the process of applying the slurry for the positive electrode on the surface of the current collector and drying it to form the coating (positive electrode active material layer), the component (A) and / or the component (B) It may move along the thickness direction of the coating film (hereinafter, also referred to as "migration"). Specifically, the component (A) and / or the component (B) tends to move to the interface (gas-solid interface) opposite to the current collector in the coating.

  As a result, since the distribution of the component (A) and / or the component (B) becomes uneven in the thickness direction of the coating film, the electrode characteristics deteriorate or the binding between the current collector and the positive electrode active material layer Problems such as loss may occur.

  For example, the component (A) acting as a binder bleeds (transfers) to the gas-solid interface side of the positive electrode active material layer, and the amount of the component (A) at the interface between the current collector and the positive electrode active material layer is relative. If the amount is less than the above range, the permeation of the electrolytic solution into the positive electrode active material layer is inhibited, and the electrical characteristics of the positive electrode tend to be degraded. Further, in this case, the binding property between the current collector and the positive electrode active material layer is lowered, and the positive electrode active material layer tends to be easily peeled from the current collector. Furthermore, in this case, the smoothness of the surface of the positive electrode active material layer tends to be impaired by bleeding of the component (A).

  However, when the average particle size of the component (A) is in the above-mentioned range (range of 90 to 170 nm) and the average particle size of the component (B) is in the above-mentioned range, the occurrence of the above problem is suppressed. Thus, it becomes possible to produce a positive electrode having both better electrical characteristics and binding properties.

Moreover, when the average particle diameter of (A) component and (B) component exists in the said range, adsorption of (A) component to (B) component becomes still stronger, and the powdering off property mentioned later improves further .
Here, with the average particle size of the component (B), the particle size distribution is measured using a particle size distribution measuring device having a laser diffraction method as a measurement principle, and the particle numbers are accumulated sequentially from the particle size smaller in the particle size distribution. It is the value of the particle diameter (number average particle diameter, D50) when the cumulative frequency of the number of particles is 50% of the total number of particles.

  As a particle size distribution measuring apparatus which makes such a laser diffraction method a measurement principle, HORIBA LA-300 series, HORIBA LA-920 series (above, Horiba, Ltd. make) etc. can be mentioned, for example. Moreover, the sample used by the said measuring method is what remove | eliminated the supernatant liquid, after centrifuging the slurry for positive electrodes and settling (B) component.

  The above-described particle size distribution measuring apparatus does not evaluate only primary particles of the component (B), but also evaluates secondary particles formed by aggregation of primary particles. Therefore, the average particle diameter obtained by this particle size distribution measuring device can be used as an indicator of the dispersed state of the component (B) contained in the slurry for positive electrode.

1.3. (C) Component The positive electrode slurry according to the present embodiment contains (C) a liquid medium. The liquid medium (C) is preferably an aqueous medium containing water. The aqueous medium may be water, or may contain water and a non-aqueous medium other than water. Examples of the non-aqueous medium include one or more selected from an amide compound, a hydrocarbon, an alcohol, a ketone, an ester, an amine compound, a lactone, a sulfoxide, a sulfone compound, and the like.

  When the liquid medium (C) contains water and a non-aqueous medium other than water, 90% by mass or more is preferably water, and 98% by mass or more in 100% by mass of the total amount of the liquid medium (C). More preferably, it is water.

  Further, the content ratio of the non-aqueous medium contained in the aqueous medium is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, with respect to 100 parts by mass of the aqueous medium, substantially containing Not particularly preferred.

  Here, “does not substantially contain” means (C) that the non-aqueous medium is not intentionally added to the liquid medium, and it is unavoidably mixed in the preparation of the positive electrode slurry. An aqueous medium or a non-aqueous medium produced after the production of a slurry for positive electrode may be included.

By using an aqueous medium as the liquid medium (C), the positive electrode slurry according to the present embodiment is unlikely to adversely affect the environment, and the safety of the handling worker is also enhanced.
1.4. Other Components The slurry for positive electrode according to the present embodiment can contain components other than the components described above as needed. Such components include, for example, conductivity imparting agents, non-aqueous media, thickeners, preservatives and the like.

1.4.1. Conductive agent As a specific example of the conductive agent, carbon etc. may be mentioned. Carbon is suitable when using the slurry for positive electrodes for a lithium ion secondary battery (an example of an electrical storage device). Examples of carbon include graphite, activated carbon, acetylene black, furnace black, graphite, carbon fiber, fullerene and the like. Among these, acetylene black or furnace black is preferable. 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 component (B).

1.4.2. Nonaqueous Medium The slurry for positive electrode according to the present embodiment can contain, for example, a nonaqueous medium having a standard boiling point of 80 to 350 ° C. from the viewpoint of improving the coating property. Specific examples of such non-aqueous media include amide compounds such as N-methyl pyrrolidone, dimethylformamide, N, N-dimethyl acetamide and the like; hydrocarbons such as toluene, xylene, n-dodecane, tetralin and the like; 2-ethyl-1 Alcohols such as hexanol, 1-nonanol, lauryl alcohol; Ketones such as methyl ethyl ketone, cyclohexanone, phorone, acetophenone, isophorone; benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate, butyl lactate etc. o-toluidine, m- One or more selected from amine compounds such as toluidine and p-toluidine; lactones such as γ-butyrolactone and δ-butyrolactone; and sulfoxide-sulfone compounds such as dimethylsulfoxide and sulfolane. Among these, it is preferable to use N-methylpyrrolidone from the viewpoint of the stability of the component (A) and the workability at the time of applying the slurry for the positive electrode.

1.4.3. Thickener The slurry for positive electrode according to the present embodiment can contain a thickener from the viewpoint of improving its coatability. Specific examples of the thickener include cellulose compounds such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose; ammonium salts or alkali metal salts of the above-mentioned cellulose compounds; polys such as poly (meth) acrylic acid and modified poly (meth) acrylic acid Carboxylic acids; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer and the like; (meth) acrylic acid, maleic acid and fumaric acid etc Examples thereof include water-soluble polymers such as saponified products of copolymers of unsaturated carboxylic acids and vinyl esters. Among these, alkali metal salts of carboxymethylcellulose, poly (meth) acrylic acid and alkali metal salts thereof are preferable.

  As a commercial item of a thickener, the alkali metal salt of carboxymethylcelluloses, such as CMC1120, CMC1150, CMC2200, CMC2280, CMC2450 (above, Daicel Chemical Industries, Ltd. make), can be mentioned, for example.

  When the slurry for the positive electrode contains a thickener, the usage ratio of the thickener is preferably 20% by mass or less, more preferably 0.1 to 15, based on 100% by mass of the total solid content of the slurry for the positive electrode. % By mass, particularly preferably 0.5 to 10% by mass.

1.4.4. Preservative The slurry for positive electrode according to the present embodiment can contain a preservative. By containing the preservative, it is possible to suppress the growth of bacteria, sputum, and the like and the generation of foreign matter when the slurry for positive electrode is stored. In addition, since deterioration of the binder is suppressed at the time of charge and discharge of the electricity storage device manufactured using the slurry for positive electrode, it is possible to suppress a decrease in charge and discharge characteristics of the electricity storage device. The effects described above are particularly remarkable when the isothiazoline compound is contained as a preservative.

  Specific examples of the preservative include 1,2-benzoisothiazolin-3-one, 2-methyl-4,5-trimethylene-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 5 -Chloro-2-methyl-4-isothiazolin-3-one, Nn-butyl-1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 4,5- One or more selected from dichloro-2-n-octyl-4-isothiazolin-3-one and the like can be mentioned.

  Among these, 2-methyl-4-isothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 1,2- One or more selected from benzisothiazolin-3-one and the like are preferable.

1.5. Method for Producing Slurry for Positive Electrode The slurry for positive electrode according to the present embodiment comprises the component (A), the component (B), the component (C), and other components used as needed. It can be produced by mixing. The order of mixing can be set appropriately. The components can be mixed by a known stirring method, and can be mixed using, for example, a stirrer, a defoamer, a bead mill, a high pressure homogenizer, and the like.

At least a part of the steps in the production of the positive electrode slurry (mixing operation of each component) is preferably performed under reduced pressure. In this case, generation of air bubbles in the positive electrode obtained using the positive electrode slurry can be suppressed. The degree of pressure reduction is preferably about 5.0 × 10 ^{3 to} 5.0 × 10 ⁵ Pa as an absolute pressure.

  In mixing and stirring for producing the positive electrode slurry, selecting a mixer capable of stirring to such an extent that aggregates of the component (B) do not remain in the positive electrode slurry and necessary and sufficient dispersion conditions desirable.

  The degree of dispersion can be measured by means of a particle gauge. It is preferable to mix and agitate so that aggregates larger than at least 100 μm are present in the positive electrode slurry. Examples of mixers suitable for such conditions include a ball mill, sand mill, pigment disperser, grinder, ultrasonic disperser, homogenizer, planetary mixer, Hobart mixer and the like.

  The solid content concentration in the slurry for positive electrode according to the present embodiment (the ratio of the total mass of components other than the solvent in the slurry for positive electrode to the total mass of the slurry for positive electrode) is 20 to 80 mass% Preferably, it is 30 to 75% by mass.

1.6. Characteristics of Slurry for Positive Electrode The spinelability of the positive electrode slurry according to the present embodiment is preferably 30 to 80%, and more preferably 33 to 79%. When the spinnability is in the above range, sufficient leveling ability can be easily obtained when the positive electrode slurry is applied onto the current collector to form a positive electrode active material layer. In this case, a positive electrode active material layer having a uniform thickness can be formed. When a positive electrode having a uniform thickness of the positive electrode active material layer is used, in-plane variation of charge and discharge reactions can be suppressed, and thus, it becomes easy to exhibit stable electric storage device characteristics.

The “stringiness” can be measured as follows. First, a Zahn cup (Zarn Bisco City cup No. 5 manufactured by Taiyo Kikai Co., Ltd.) having an opening of diameter 5.2 mm at the bottom is prepared. With the opening of the Zahn cup closed, 40 g of the positive electrode slurry is poured into the Zahn cup. Thereafter, when the opening is opened, the slurry for the positive electrode flows out from the opening. Here, when the time when the opening is opened is T ₀ , the time when the spinning of the positive electrode slurry ends is T _A , and the time when the outflow of the positive electrode slurry ends is T _B , “stringiness” is It can be determined from the following equation (2).

Spinnability _{(%) = ((T A} -T 0) / (T B -T 0)) × 100 ····· (2)
2. Power Storage Device Positive Electrode The power storage device positive electrode according to the present embodiment includes a current collector and a layer (positive electrode active material layer) formed on the surface of the current collector. The layer contains (A) a polymer and (B) an olivine-type lithium-containing phosphoric acid compound. The (A) polymer and the (B) olivine-type lithium-containing phosphoric acid compound can be, for example, those described in the section “1. Slurry for positive electrode”.

The layer is, for example, a layer formed by applying and drying the above-described positive electrode slurry on the surface of a current collector. Moreover, the layer may be formed by another method.
In this storage device positive electrode, the binding between the current collector and the positive electrode active material layer is excellent. In addition, if an electricity storage device is manufactured using this electricity storage device positive electrode, the charge / discharge rate characteristic which is one of the electricity storage device characteristics is improved.

  The current collector is not particularly limited as long as it is made of a conductive material. When the storage device positive electrode is used for a lithium ion secondary battery, for example, a current collector made of metal such as iron, copper, aluminum, nickel, stainless steel can be used, and in particular, the current collector made of aluminum, copper is preferable.

  When the storage device positive electrode is used for a nickel hydrogen secondary battery, for example, a current collector made of a punching metal, an expanded metal, a wire mesh, a foam metal, a reticulated metal fiber sintered body, a metal plating resin plate, etc. can be used .

Although the shape and thickness of the current collector are not particularly limited, for example, a sheet-like current collector having a thickness of about 0.001 to 0.5 mm is preferable.
When the positive electrode slurry is applied to the surface of the current collector, the application method is not particularly limited. As a coating method, for example, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, an immersion method, a brush coating method and the like can be used as appropriate.

  The application amount of the positive electrode slurry is not particularly limited. The thickness of the positive electrode active material layer formed after applying the positive electrode slurry and removing the liquid medium (which is a concept including both water and an optionally used non-aqueous medium) is 0.005 to about A coating amount of 5 mm is preferable, and a coating amount of 0.01 to 2 mm is more preferable.

  When the thickness of the positive electrode active material layer is in the above range, the electrolytic solution can be effectively impregnated into the positive electrode active material layer. As a result, since metal ions are easily exchanged during charge / discharge of the positive electrode active material in the positive electrode active material layer and the electrolytic solution, the internal resistance of the positive electrode can be further reduced.

  In addition, when the thickness of the positive electrode active material layer is in the above range, the adhesion between the positive electrode active material layer and the current collector is good even when the positive electrode is processed by folding or winding. And the positive electrode active material layer is difficult to peel off from the current collector. That is, a flexible storage device positive electrode can be obtained.

  There are no particular limitations on the method of drying the coating formed by applying the positive electrode slurry (a method of removing water and the non-aqueous medium that is optionally used). For example, methods such as drying by warm air, hot air, low humidity air; vacuum drying; drying by irradiation with (far) infrared rays, electron beams and the like can be used.

  The drying speed when drying the coating film formed by applying the slurry for positive electrode is, for example, under the condition that the positive electrode active material layer does not crack or the positive electrode active material layer peels off from the current collector due to stress concentration. In order to remove the liquid medium as soon as possible, it can be set appropriately.

  After drying the coating film formed by applying the slurry for positive electrode, the density of the positive electrode active material layer is increased by pressing the electric storage device positive electrode, and the density and the porosity in the positive electrode active material layer are adjusted to the ranges shown below. Is preferred.

The density of the positive electrode active material layer after the press is preferably 1.5~2.5g / cm ^3, more preferably 1.6~2.4g / cm ^3, 1.7~2. more preferably from 2 g / cm ^3, particularly preferably 1.8~2.1g / cm ^3.

  Assuming that the density of the positive electrode active material layer is in the above range, the binding property between the current collector and the positive electrode active material layer is good, the powder removal property is excellent, and the electric storage device positive electrode is also excellent. You can get

  The porosity of the positive electrode active material layer after pressing is preferably 10 to 50%, more preferably 15 to 45%, and particularly preferably 20 to 40%. When the porosity of the positive electrode active material layer is in the above range, the binding property between the current collector and the positive electrode active material layer is good, the powder removal property is excellent, and the electric storage device is also excellent. A positive electrode can be obtained.

  In addition, when the porosity of the positive electrode active material layer is in the above range, the electrolytic solution can be sufficiently impregnated into the positive electrode active material layer, and the surface of the positive electrode active material and the electrolytic solution are sufficiently in contact. As a result, transfer of lithium ions is facilitated between the positive electrode active material and the electrolyte solution, and good charge / discharge characteristics can be exhibited.

  As a press method, methods, such as a die press and a roll press, are mentioned, for example. The conditions of the pressing can be appropriately set according to the type of pressing device to be used, the desired value of the porosity and the density of the positive electrode active material layer, and the like. The conditions of the press can be easily set by a few preliminary experiments by those skilled in the art.

The press conditions in the case of using a roll press method can be, for example, as follows.
Line pressure of the roll press: 0.1 to 10 (t / cm), preferably 0.5 to 5 (t / cm).

Roll temperature: 20 to 100 ° C.
Feeding speed (rotational speed of roll) of storage device positive electrode: 1 to 80 m / min, preferably 5 to 50 m / min.

3. Power Storage Device The power storage device according to the present embodiment includes the above-described power storage device positive electrode, and further includes, for example, an electrolytic solution, and components such as a separator and a power storage device negative electrode. As an electrical storage device, a secondary battery etc. are mentioned, for example. An electrical storage device can be manufactured according to a conventional method.

  As a specific manufacturing method, for example, the electricity storage device negative electrode and the electricity storage device positive electrode are stacked via a separator, and this is wound or folded according to the shape of the battery (an example of the electricity storage device) And a method of injecting an electrolyte solution into a battery container and sealing it. The shape of the battery can be set as appropriate, such as coin type, button type, sheet type, cylindrical type, square shape, flat type and the like.

  The electrolytic solution is a solution in which the electrolyte is dissolved in a suitable solvent. The electrolytic solution may be liquid or gel. The electrolytic solution may be selected from known electrolytic solutions used for the storage device according to the type of the positive electrode active material, which can effectively exhibit the function as the storage device.

As said electrolyte, it can select suitably from well-known electrolytes in the technical field of an electrical storage device. When the storage device is a lithium ion secondary battery, conventionally known lithium salts can be appropriately selected and used as an electrolyte, and specific examples thereof include 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 _{3) 2} ) ₂ N, lower fatty acid carboxylate lithium and the like.

  The solvent contained in the electrolyte is not particularly limited. As the solvent, for example, 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; trimethoxymethane, 1,2-dimethoxyethane, One or more selected from ether compounds such as diethyl ether, 2-ethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran and the like; sulfoxide compounds such as dimethyl sulfoxide and the like. 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.

  The negative electrode included in the power storage device according to the present embodiment includes, for example, a current collector and a negative electrode active material layer formed on the surface thereof. The negative electrode active material layer contains a negative electrode active material. The above-mentioned negative electrode can be manufactured, for example, by including a negative electrode active material and applying and drying the negative electrode slurry used in the negative electrode production on the surface of the current collector to form a negative electrode active material layer.

  The negative electrode active material is not particularly limited, and an appropriate negative electrode active material can be appropriately selected depending on the type of the intended power storage device. Examples of the negative electrode active material include carbon materials, silicon materials, oxides containing a lithium atom, lead compounds, tin compounds, arsenic compounds, antimony compounds, aluminum compounds and the like.

  Examples of the carbon material include those known as negative electrode active materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads (MCMB), pitch carbon fibers, and the like.

  Examples of the silicon material include those known as negative electrode active materials, such as silicon simple substance, silicon oxide, silicon alloy and the like. Moreover, when using a silicon material as an active material, it is preferable to use together active materials other than a silicon material, and since the volume change accompanying insertion and extraction of lithium is small, it is preferable to use a carbon material together.

The slurry for the negative electrode can contain, in addition to the negative electrode active material, the binder component described in the above “1. Slurry for positive electrode”, a liquid medium, a conductivity imparting agent, a thickener, a preservative, and the like.
Example 1
EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Unless otherwise indicated, "part" and "%" in an Example and a comparative example are mass references.

(1) Preparation of aqueous dispersion S1 In a temperature-controllable autoclave equipped with a stirrer, 200 parts by mass of water, 0.9 parts by mass of sodium dodecylbenzene sulfonate, 1.0 parts by mass of potassium persulfate, 0 parts of sodium bisulfite .5 parts by mass, 0.2 parts by mass of .alpha.-methylstyrene dimer, 0.2 parts by mass of dodecyl mercaptan, and the first-stage polymerization components shown in the column of "S1" in Table 1 are collectively charged, and the temperature is raised to 70.degree. The polymerization reaction was allowed to proceed for 2 hours.

なお、表１及び後述する表２における各成分の略称は、それぞれ以下の意味である。
・ＭＭＡ：メタクリル酸メチル
・ＨＥＭＡ：メタクリル酸２−ヒドロキシエチル
・ＡＡ：アクリル酸
・ＴＡ：イタコン酸
・ＡＮ：アクリロニトリル
・ＢＤ：１，３−ブタジエン
・ＳＴ：スチレン
ここで、ＡＡ、及びＴＡは不飽和カルボン酸に由来する繰り返し単位Ｍｃの一例であり、ＢＤは共役ジエン化合物に由来する繰り返し単位Ｍｄの一例であり、ＳＴは芳香族ビニルに由来する繰り返し単位Ｍｅの一例である。ＭＭＡ、ＨＥＭＡ、及びＡＮはその他の繰り返し単位の一例である。

In addition, the abbreviation of each component in Table 1 and Table 2 mentioned later has the following meanings, respectively.
MMA: methyl methacrylate HEMA: methacrylic acid 2-hydroxyethyl AA: acrylic acid TA: itaconic acid AN: acrylonitrile BD: 1,3-butadiene ST: styrene Here, AA and TA are not BD is an example of a repeating unit Mc derived from a saturated carboxylic acid, BD is an example of a repeating unit Md derived from a conjugated diene compound, and ST is an example of a repeating unit Me derived from an aromatic vinyl. MMA, HEMA, and AN are examples of other repeating units.

  After confirming that the polymerization addition rate was 80% or more, the second stage polymerization component shown in the column of "S1" in Table 1 was added over 6 hours while maintaining the reaction temperature at 70 ° C. Three hours after the start of the addition of the second-stage polymerization component, 1.0 part by mass of α-methylstyrene dimer and 0.3 parts by mass of dodecyl mercaptan were added.

  After completion of the second stage polymerization component addition, the temperature was raised to 80 ° C., and the reaction was further performed for 2 hours. After completion of the polymerization reaction, 5 parts by mass (in terms of solid content) of sodium tripolyphosphate was added to adjust the pH of the latex to 7.5. At this time, acrylic acid and itaconic acid (an example of the repeating unit Mc derived from unsaturated carboxylic acid) become a sodium salt.

  Thereafter, the residual monomer was treated by steam distillation and concentrated to a solid content of 50% under reduced pressure to obtain an aqueous dispersion S1 containing 50% of the polymer (A). The polymer (A) has an aspect of polymer particles. The (A) polymer contained in the aqueous dispersion S1 has the composition shown in the column of S1 in Table 2.

水系分散体Ｓ１に含まれる（Ａ）重合体について、平均粒子径と、ＴＨＦ不溶分と、転移温度（Ｔｇ）とを測定した。平均粒子径の測定においては、水系分散体Ｓ１を測定試料とした。測定結果を表２に示す。

The average particle size, the THF insoluble matter, and the transition temperature (Tg) of the polymer (A) contained in the aqueous dispersion S1 were measured. In the measurement of the average particle size, the aqueous dispersion S1 was used as a measurement sample. The measurement results are shown in Table 2.

(2) Preparation of Slurry for Positive Electrode and Preparation of Storage Device Positive Electrode A thickener (trade name “CMC1120”, Daicel) to a twin-screw type planetary mixer (manufactured by Primix, Inc., trade name “TK Hibis Mix 2P-03”) Chemical substance Co., Ltd. 1 part by mass (in terms of solid content), 100 parts by mass of lithium iron phosphate (LiFePO ₄ ) manufactured by Hosen Co., Ltd., 5 parts by mass of acetylene black, and 68 parts by mass of water are charged. Stirring was performed for a time. The lithium iron phosphate is crushed in an agate mortar and classified using a sieve to make the average particle size (D50 value) 10 μm. The lithium iron phosphate is an example of a positive electrode active material.

  Next, dispersion S1 and 5-chloro-2-methyl-4-isothiazolin-3-one which is a preservative were charged. The amount of dispersion S1 was 1 part by mass of the polymer (A). The amount of preservative added was such that the concentration of preservative in the total amount of positive electrode slurry was 100 ppm.

Then, it stirred for 1 hour and obtained the paste. After adding water to the obtained paste to adjust the solid content concentration to 50%, using a stirring and defoaming machine (made by Shinky Co., Ltd., trade name "Awatori Neritaro"), 200 rpm for 2 minutes, 1 The slurry for the positive electrode was prepared by stirring and mixing for 5 minutes at 800 rpm, and further for 1.5 minutes at 1,800 rpm under vacuum (about 5.0 × 10 ³ Pa). This positive electrode slurry has the composition shown in the column of “Example 1” in Table 3.

次に、厚み３０μｍのアルミニウム箔からなる集電体の表面に、前記のように調製した正極用スラリーを、乾燥後の膜厚が１００μｍとなるように、ドクターブレード法によって均一に塗布し、１２０℃で２０分間乾燥した。その後、形成された膜（正極活物質層）の密度が１．９ｇ／ｃｍ^３になるように、ロールプレス機を用いてプレス加工することにより、蓄電デバイス正極を得た。

Next, the positive electrode slurry prepared as described above is uniformly coated by the doctor blade method on the surface of a current collector made of an aluminum foil with a thickness of 30 μm so that the film thickness after drying becomes 100 μm, 120 It dried at 20 degreeC for 20 minutes. After that, pressing was performed using a roll press so that the density of the formed film (positive electrode active material layer) was 1.9 g / cm ³ , to obtain a positive electrode for an electricity storage device.

(3) Preparation of slurry for negative electrode and preparation of negative electrode for electricity storage device In a twin-screw type planetary mixer (manufactured by Primix, Inc., trade name "TK Hibis Mix 2P-03"), a thickener (trade name "CMC 2200", Daicel 1 part by mass (solid content conversion) manufactured by Chemical Industry Co., Ltd., 100 parts by mass (solid content conversion) as a negative electrode active material, and 68 parts by mass of water were charged, and stirring was performed at 60 rpm for 1 hour.

  Next, 2 mass parts (solid content conversion) of water-based dispersion S1 was added, and also it stirred for 1 hour, and obtained the paste. Water is added to the obtained paste to adjust the solid content to 50%, and then, using a stirring and defoaming machine (made by Shinky Co., Ltd., trade name "Bubble Neritaro"), 200 rpm for 2 minutes, 1800 rpm The slurry for the negative electrode was prepared by stirring and mixing for 5 minutes and further at 1800 rpm for 1.5 minutes under vacuum.

Next, the slurry for the negative electrode prepared as described above is uniformly coated by the doctor blade method on the surface of a current collector made of copper foil having a thickness of 20 μm so that the film thickness after drying becomes 80 μm, 120 It was dried at 20 ° C for 20 minutes. Thereafter, pressing was performed using a roll press so that the density of the formed film (negative electrode active material layer) was 1.9 g / cm ³ , to obtain a negative electrode of a storage device.

(4) Assembly of lithium ion battery In the glove box which is Ar-substituted so that the dew point is −80 ° C. or less, the electricity storage device negative electrode manufactured as described above is punched and formed into a circle having a diameter of 15.95 mm. It was placed on a polar-type coin cell (manufactured by Takasen Co., Ltd., trade name "HS flat cell").

  Next, a separator (a product of Celgard Co., Ltd., trade name “Celgard # 2400”) made of a porous film made of polypropylene punched into a circle having a diameter of 24 mm was stacked and mounted on the storage device negative electrode.

Furthermore, 500 μL of an electrolytic solution is injected so that air does not enter, and then the storage device positive electrode manufactured as described above is punched and formed into a circle having a diameter of 16.16 mm, stacked on a separator and placed. A lithium ion battery cell (an example of an electricity storage device) was assembled by screwing and sealing the exterior body of a two-pole coin cell. The electrolytic solution used here is a solution in which LiPF ₆ is dissolved at a concentration of 1 mol / L in a solvent of ethylene carbonate / ethyl methyl carbonate = 1/1 (mass ratio).

(5) Evaluation (5-1) Evaluation of Coating Property (Smoothness) A test piece of 12 cm wide x 12 cm long was cut out from the positive electrode of the electricity storage device produced in (2). This test piece is divided into 36 squares having dimensions of 2 cm × 2 cm of each mass, and the film thickness of the positive electrode active material layer in each mass is measured using a film thickness meter (DIGIMATIC MICROMETER IP65 made by Mitutoyo), The ratio (smoothness) of the standard deviation to the average value of the film thickness was calculated.

  In addition, when the ratio of the standard deviation with respect to an average value exceeds 2%, it means that the slurry for positive electrodes is not apply | coated uniformly. In such a case, in the case of a positive electrode prepared by applying a positive electrode slurry to a large area, the smoothness of the positive electrode active material layer formed on the surface of the current collector is impaired. Therefore, the electrical characteristics do not become uniform on the positive electrode surface, and stable electrical characteristics can not be exhibited particularly when mass-produced.

  On the other hand, when the ratio of the standard deviation to the average value is 2% or less, it means that the slurry for positive electrode is uniformly applied. In such a case, in the case of a positive electrode prepared by applying a positive electrode slurry to a large area, the smoothness of the positive electrode active material layer formed on the surface of the current collector is good. Therefore, the electrical characteristics become uniform on the positive electrode surface, and stable electrical characteristics can be exhibited particularly when mass-produced. From these reasons, the evaluation criteria for the coatability of the positive electrode slurry were determined as follows. The evaluation results of smoothness according to the evaluation criteria are shown in Table 3.

○: The smoothness is 2% or less and good.
X: The smoothness exceeds 2% and is poor.
(5-2) Evaluation of powder removal property From the electric storage device positive electrode prepared in (2), five 10 cm × 5 cm samples were cut out and overlapped. A commercially available high quality paper was placed on the test bench, and a 100 mesh stainless steel mesh was placed thereon. The five stacked samples were cut with scissors above the mesh. The cutting was performed along the short side direction of the sample, and was cut nine times at 1 cm intervals. And the state of the positive electrode active material powder which passed the stainless steel mesh in the case of a cutting | disconnection, and was dropped on the high quality paper was observed. The dusting properties were evaluated as follows based on the observation results. The evaluation results are shown in Table 3.

○: no powdering at all, or powdering slightly observed. Good.
X: A large amount of powdering is observed. Bad.
(5-3) Evaluation of Binding Properties Five samples of 10 cm square were cut out from the storage device positive electrode prepared in the above (2), and compressed and molded for 5 minutes with a 120 ° C. heat press. The surface of each sample was cut using a knife to a depth reaching the current collector. The cuts were made six in length and width at intervals of 2 mm. As a result, on each sample, 25 squares divided in a grid by cutting were formed.

  The adhesive tape was affixed on the part which made the notch | incision among the surfaces of each sample, and it peeled off immediately, and counted the number of the mass which the positive electrode active material layer peeled from copper foil. The above process is carried out once for one sample (one side) to count the number of squares from which the positive electrode active material layer has peeled out of a total of 125 squares in five samples, and the number of bonds is as follows according to this number The sex was evaluated. The evaluation results are shown in Table 3.

Good: 0 to 20 pieces of mass from which the positive electrode active material layer fell off, and good binding property.
X: The mass from which the positive electrode active material layer fell off is 21 or more, and the binding property is poor.
(5-4) Evaluation of Capacity Maintenance Rate With respect to the lithium ion secondary battery assembled in (4), charging was started at a constant current (1 C) and continued until the voltage became 4.2V. After the voltage reached 4.2, charging was continued at a constant voltage (4.2 V), and charging completed (cut-off) was performed when the current value reached 0.01C.

  Thereafter, the discharge was started at a constant current (1 C), and when the voltage reached 3.0 V, the discharge was completed (cut off), and the discharge capacity at the first cycle was calculated. Thus, charge and discharge were repeated 50 times, and the discharge capacity at the 50th cycle was calculated. A value obtained by dividing the discharge capacity at the 50th cycle measured in this manner by the discharge capacity at the first cycle is shown in Table 3 as a discharge capacity retention rate (%). When the discharge capacity retention rate is 80% or more, it can be judged as good.

(5-5) Evaluation of charge and discharge rate characteristics With respect to the lithium ion secondary battery assembled in the above (4), charging was started at a constant current (0.2 C) and continued until the voltage reached 4.2 V . After the voltage reaches 4.2 V, charging is continued at a constant voltage (4.2 V), and when the current value reaches 0.01 C, charging is completed (cut off) at 0.2 C. The charge capacity was measured. Thereafter, the 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, for the same lithium ion secondary battery, charging was started at a constant current (3 C) and continued until the voltage reached 4.2 V. After the voltage reaches 4.2 V, charging is continued at a constant voltage (4.2 V), and when the current value reaches 0.01 C, the charge capacity at 3 C is regarded as charge completion (cutoff). Was measured. Thereafter, discharge was started at a constant current (3 C), and when the voltage reached 2.7 V, the discharge was completed (cut off), and the discharge capacity at 3 C was measured.

  Then, the ratio (%) of the discharge capacity at 3 C to the discharge capacity at 0.2 C was calculated, and the discharge rate characteristics (%) were calculated. Moreover, the ratio (%) of the charge capacity at 3 C to the charge capacity at 0.2 C was calculated, and the charge rate characteristic (%) was calculated.

The discharge rate characteristics and the charge rate characteristics were evaluated according to the following criteria. The evaluation results are shown in Table 3.
○: Good at 80% or more of discharge rate characteristics and charge rate characteristics.

X: Defective if the discharge rate characteristic or the charge rate characteristic is less than 80%.
In addition, on the measurement conditions of a present Example, "1 C" shows the electric current value which discharges the cell which has a fixed electric capacity by a constant current, and discharge ends in 1 hour. For example, "0.1 C" is a current value at which discharge ends over 10 hours, and "10 C" is a current value at discharge completion for 0.1 hours.

(5-6) Evaluation of spinnability The spinnability of the positive electrode slurry prepared in (2) was evaluated. The evaluation results are shown in Table 3.
(Examples 2 to 10, Comparative Examples 1 to 6)
Aqueous dispersions S2 to S13 were prepared basically in the same manner as the aqueous dispersion S1 in Example 1. However, in the preparation of the aqueous dispersions S2 to S13, the type and preparation amount of the first-stage polymerizable component, and the kind and preparation amount of the second-stage polymerizable component are as shown in Table 1, and are included in the component (A). The types and amounts of monomers were as shown in Table 2.

  In addition, in the preparation of the aqueous dispersion described as “K” in the “neutralization ion” row in Table 2, by adding the same amount of potassium hydroxide instead of 5 parts by mass of sodium tripolyphosphate The pH of the latex was adjusted to 7.5. In this case, the repeating unit Mc derived from the unsaturated carboxylic acid contained in the component (A) is a potassium salt.

In addition, in the preparation of the aqueous dispersion described as “NH ₄ ” in the “neutralization ion” row in Table 2, the same amount of ammonia is added instead of 5 parts by mass of sodium tripolyphosphate, The pH of the latex was adjusted to 7.5. In this case, the repeating unit Mc derived from the unsaturated carboxylic acid contained in the component (A) is an ammonium salt.

The average particle diameter, the THF insoluble matter, and the transition temperature (Tg) of the polymer (A) contained in the aqueous dispersions S2 to S13 were measured. The results are shown in Table 2.
Also, basically in the same manner as in Example 1, a slurry for positive electrode, a storage battery positive electrode, a slurry for negative electrode, and a storage battery negative electrode were prepared, and a lithium ion battery was assembled.

  However, in Examples 2 to 10 and Comparative Examples 1 to 6, the type and amount of the component (A) in the slurry for positive electrode, the type and amount of the component (B), the average particle size of the component (B), (C The kind of the component, the kind and the addition amount of the other components are as shown in Table 3. Moreover, in Examples 2 to 10 and Comparative Examples 1 to 6, the component (A) in the slurry for the negative electrode is described in Table 3. That is, in each of Examples 2 to 10 and Comparative Examples 1 to 6, the component (A) used for the positive electrode slurry and the negative electrode slurry is the same.

  Further, in Example 9, the method for preparing the positive electrode slurry was the following method. In aqueous dispersion S13, residual monomers were removed by steam distillation and the pH was adjusted to 7 with sodium hydroxide. Next, three times the weight of the obtained latex was added N-methylpyrrolidone (NMP), and the water content was evaporated by an evaporator to obtain an NMP dispersion binder composition having a solid content concentration of 8% by mass.

Next, an NMP dispersion binder composition in an amount such that the binder solid content is 1 part by mass (solid content conversion) in a twin-screw type planetary mixer (manufactured by Primix, Inc., trade name "TK Hibismix 2P-03") 100 parts by mass of lithium iron phosphate (LiFePO ₄ ) manufactured by Hosen Co., Ltd., 3 parts by mass of acetylene black, and 68 parts by mass of NMP were charged, and the mixture was stirred at 60 rpm for 1 hour to obtain a paste.

  The lithium iron phosphate is previously crushed in an agate mortar and classified using a sieve to set the average particle diameter (D50 value) to 10 μm. The lithium iron phosphate is an example of a positive electrode active material.

Thereafter, NMP is added to the obtained paste to adjust the solid content concentration to 50% by mass, and then using a stirring and defoaming machine (made by Shinky Co., Ltd., trade name "Awatori Neritaro"), 2 at 200 rpm The slurry for positive electrodes was prepared by stirring and mixing for 5 minutes at 1,800 rpm and further at 1,800 rpm for 1.5 minutes under vacuum (about 5.0 × 10 ³ Pa).

  Further, in Example 10, the method for preparing the positive electrode slurry was the following method. A polymer was precipitated by gradually adding 400 parts of a 10% aqueous solution of sodium carbonate to the aqueous dispersion S13. After the precipitated polymer was washed with methanol, it was further washed with water until the pH of the wash water became 8.0 or less. The washed polymer was vacuum dried at 50 ° C. for 1 day to obtain a dry polymer. In a separable flask, 80 parts by mass of the obtained dried polymer and 920 parts by mass of NMP were charged, and stirred at 50 ° C. for 2 hours to dissolve the dried polymer to obtain a polymer solution.

Next, a twin screw type planetary mixer (manufactured by PRIMIX CO., LTD., Trade name "TK HIBIS MIX 2P-03"), a polymer solution in an amount such that the polymer solid content is 1 part by mass, iron phosphate phosphate manufactured by Takasen Co., Ltd. 100 parts by mass of lithium (LiFePO ₄ ), 3 parts by mass of acetylene black, and 68 parts by mass of NMP were added, and the mixture was stirred at 60 rpm for 1 hour to obtain a paste. The lithium iron phosphate is previously crushed in an agate mortar and classified using a sieve to set the average particle diameter (D50 value) to 10 μm. The lithium iron phosphate is an example of a positive electrode active material.

Thereafter, NMP is added to the obtained paste to adjust the solid content concentration to 50%, and then using a stirring and defoaming machine (made by Shinky Co., Ltd., trade name "Awatori Neritaro"), at 200 rpm for 2 minutes The slurry for positive electrode 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.

Also in Examples 2 to 10 and Comparative Examples 1 to 6, evaluation was made in the same manner as in Example 1. The results are shown in Table 3.
(Evaluation results of each example and each comparative example)
As apparent from the contents of Table 3, when using the positive electrode slurry in Examples 1 to 10, the spinnability, the positive electrode characteristics (the coatability, the powdering ability, the binding ability), and the electricity storage device characteristics It turned out to be excellent.

  On the other hand, when the slurry for positive electrodes in Comparative Examples 1 to 6 is used, the slurry for positive electrodes of Examples 1 to 10 is used in at least one of the spinnability, positive electrode characteristics, and storage device characteristics. It turned out to be inferior.

Claims (6)

(A) a polymer,
(B) with lithium iron phosphate ,
(C) water ,
Contains
The (A) polymer is
A repeating unit Mc derived from an unsaturated carboxylic acid,
A repeating unit Md derived from a conjugated diene compound,
A repeating unit Me derived from aromatic vinyl,
Containing a diene polymer having
The slurry for a positive electrode, wherein the content of the polymer (A) is in the range of 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the lithium iron phosphate (B). The slurry for positive electrode according to claim 1 , wherein the repeating unit Mc derived from the unsaturated carboxylic acid is a salt of at least one cation selected from a sodium ion and a potassium ion. Method for manufacturing a power storage device positive electrode and forming a layer by coating and drying a positive electrode slurry according to claim 1 or 2 on the surface of the current collector. A current collector, and a layer formed on the surface of the current collector;
Equipped with
The layer contains (A) a polymer and (B) lithium iron phosphate ,
The (A) polymer is
A repeating unit Mc derived from an unsaturated carboxylic acid,
A repeating unit Md derived from a conjugated diene compound,
A repeating unit Me derived from aromatic vinyl,
Containing a diene polymer having
A storage device positive electrode characterized in that the content of the polymer (A) is in the range of 0.5 to 1.5 parts by mass with respect to 100 parts by mass of the lithium iron phosphate (B). An electricity storage device comprising the electricity storage device positive electrode according to claim 4 . A method of manufacturing a power storage device, comprising: manufacturing a power storage device positive electrode by the manufacturing method according to claim 3 .