JP7535898B2 - Powder composition, electrode paint and electrode - Google Patents

Description

The present invention relates to a powder composition containing a π-conjugated conductive polymer, a paint for electrodes, and an electrode.

π-conjugated conductive polymers, whose main chains are composed of π-conjugated systems, are basically poorly soluble in water, but a method is known in which a water-dispersible conductive complex is made by forming a complex with a polyanion having a hydrophilic anionic group. The formation of this conductive complex increases the conductivity. In addition, a method is known in which the water-dispersible anionic group of the conductive complex is reacted with an amine compound or an epoxy compound to hydrophobize it, thereby dispersing it in an organic solvent (see Patent Documents 1 and 2).

JP 2011-032382 A International Publication No. 2014/125827

However, there has been little research into the use of conductive composites as electrode materials for lithium-ion secondary batteries (LiBs).

The present invention provides a powder composition, electrode paint, and electrodes that are useful as electrode materials for energy devices such as LiBs.

[1] A powder composition comprising a Li-containing compound, conductive particles having the following structure (A) or (B), and a binder:
(A) Conductive particles made of a π-conjugated conductive polymer.
(B) A conductive particle comprising a conductive complex having a π-conjugated conductive polymer and a dopant.
[2] The conductive particles have the structure (B), and the content ratio of the π-conjugated conductive polymer:the dopant is, on a mass basis, greater than (1:0) and less than or equal to (1:1). The powder composition according to [1].
[3] The powder composition according to [1] or [2], wherein the π-conjugated conductive polymer contains poly(3,4-ethylenedioxythiophene).
[4] The powder composition according to any one of [1] to [3], wherein the dopant comprises one or more selected from the group consisting of polystyrene sulfonic acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, paratoluenesulfonic acid, and hydroxybenzenesulfonic acid.
[5] The powder composition according to any one of [1] to [4], wherein the content ratio of the Li-containing compound: the conductive particles: the binder is 8: (0.5 to 1.5): 1 on a mass basis.
[6] The powder composition according to any one of [1] to [5], wherein the binder contains polyvinylidene fluoride, polytetrafluoroethylene, polyester, or polyvinyl alcohol.
[7] The powder composition according to any one of [1] to [6], wherein the Li-containing compound includes _LiFePO4 .
[8] A coating material for an electrode, comprising the powder composition according to any one of [1] to [7] and a solvent.
[9] The electrode coating material according to [8], wherein the solvent is N-methyl-2-pyrrolidone.
[10] An electrode comprising the powder composition according to any one of [1] to [7].

Electrodes made using the powder composition and electrode paint of the present invention can improve the battery characteristics of LiB.

This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

In this specification and claims, the lower and upper limits of the numerical ranges indicated with "~" are considered to be included in the numerical range.

<Powder composition>
A first aspect of the present invention is a powder composition including a Li (lithium)-containing compound, the following conductive particles, and a binder.

<Conductive particles>
The conductive particles contained in the powder composition of this embodiment have the following configuration (A) or (B).
(A) Conductive particles made of a π-conjugated conductive polymer.
(B) A conductive particle comprising a conductive complex having a π-conjugated conductive polymer and a dopant.

[π-conjugated conductive polymer]
The π-conjugated conductive polymer of (A) or (B) may be any conductive organic polymer whose main chain is composed of a π-conjugated system, and examples thereof include polypyrrole-based conductive polymers, polythiophene-based conductive polymers, polyacetylene-based conductive polymers, polyphenylene-based conductive polymers, polyphenylenevinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophenevinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferred, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferred.

Examples of polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene), poly(3-propylthiophene), poly(3-butylthiophene), poly(3-hexylthiophene), poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly(3-chlorothiophene), and poly(3-iodothiophene). thiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene), poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), oxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxythiophene), poly(3,4-dimethoxythiophene), poly(3,4-diethoxythiophene), poly(3,4-dipropoxythiophene), poly(3,4-dibutoxythiophene), poly(3,4-dihexyloxythiophene), poly(3,4-diheptyloxythiophene), poly(3,4-dioctyloxythiophene), poly(3,4-didecyloxythiophene), poly(3,4-di dodecyloxythiophene), poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), poly(3,4-butylenedioxythiophene), poly(3-methyl-4-methoxythiophene), poly(3-methyl-4-ethoxythiophene), poly(3-carboxythiophene), poly(3-methyl-4-carboxythiophene), poly(3-methyl-4-carboxyethylthiophene), and poly(3-methyl-4-carboxybutylthiophene).
Examples of polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butylpyrrole), poly(3-octylpyrrole), poly(3-decylpyrrole), poly(3-dodecylpyrrole), poly(3,4-dimethylpyrrole), poly(3,4-dibutylpyrrole), poly(3-carboxypyrrole), poly(3-methyl-4-carboxypyrrole), poly(3-methyl-4-carboxyethylpyrrole), poly(3-methyl-4-carboxybutylpyrrole), poly(3-hydroxypyrrole), poly(3-methoxypyrrole), poly(3-ethoxypyrrole), poly(3-butoxypyrrole), poly(3-hexyloxypyrrole), and poly(3-methyl-4-hexyloxypyrrole).
Examples of polyaniline-based conductive polymers include polyaniline, poly(2-methylaniline), poly(3-isobutylaniline), poly(2-anilinesulfonic acid), and poly(3-anilinesulfonic acid).
Among these π-conjugated conductive polymers, poly(3,4-ethylenedioxythiophene) is particularly preferable from the viewpoints of conductivity, transparency, and heat resistance.
The conductive particles may contain one type of π-conjugated conductive polymer, or two or more types of polymers.

When the conductive particles have the configuration (B) described above, the dopant in the conductive complex is doped into the π-conjugated conductive polymer to form a conductive complex having electrical conductivity.

The content ratio of the π-conjugated conductive polymer:the dopant in the conductive composite is, on a mass basis, preferably greater than (1:0) and equal to or less than (1:1), more preferably from (1:0.1) to (1:1), more preferably from (1:0.3) to (1:1), even more preferably from (1:0.5) to (1:1), particularly preferably from (1:0.7) to (1:0.99), and most preferably from (1:0.8) to (1:0.98).
When the content is more than or equal to or greater than the lower limit of the above range, the doping effect of the dopant is sufficiently exhibited, and the conductivity of the conductive particles is further improved.
When the content is equal to or less than the upper limit of the above range, the conductive particles have low dispersibility in water and can be easily precipitated in water while obtaining the doping effect of the dopant.

[Dopant]
The dopant used in this embodiment is preferably an anion, more preferably an anionic compound having an anionic group, and further preferably a polyanion having a plurality of anionic groups.

The low molecular weight dopant is preferably at least one selected from the group consisting of sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, paratoluenesulfonic acid, and hydroxybenzenesulfonic acid. It is believed that the anion portion of these dopants dopes the π-conjugated conductive polymer.
Powder compositions containing conductive particles having these dopants can form electrodes that exhibit excellent battery characteristics.

(Polyanion)
A polyanion is a polymer having two or more monomer units each having an anionic group in the molecule. The anionic group of the polyanion functions as a dopant for a π-conjugated conductive polymer, thereby improving the conductivity of the π-conjugated conductive polymer.
The anion group of the polyanion is preferably a sulfo group or a carboxy group.
Specific examples of such polyanions include polymers having a sulfo group, such as polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having a sulfo group, polymethacrylic acid esters having a sulfo group (e.g., poly(4-sulfobutyl methacrylate, polysulfoethyl methacrylate, polymethacryloyloxybenzenesulfonic acid), poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid; and polymers having a carboxy group, such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanecarboxylic acid), and polyisoprene carboxylic acid. The polyanion may be a homopolymer in which a single monomer is polymerized, or a copolymer in which two or more monomers are polymerized.
Among these polyanions, polymers having a sulfo group are preferred, and polystyrene sulfonic acid is more preferred, since they can provide higher electrical conductivity.
The polyanions may be used alone or in combination of two or more kinds.
The mass average molecular weight of the polyanion is preferably from 20,000 to 1,000,000, and more preferably from 100,000 to 500,000. The mass average molecular weight is the average molecular weight based on mass measured by gel permeation chromatography and calculated in terms of polystyrene.

In the polyanion in the conductive composite of this embodiment, most or almost all of the anion groups are doped into the π-conjugated conductive polymer, and it is preferable that there are few or almost no excess anion groups that are not involved in the doping. By setting the content ratio of π-conjugated conductive polymer:polyanion within the above-mentioned suitable range of π-conjugated conductive polymer:dopant, the excess anion groups can be reduced or almost eliminated.
Since the conductive particles have few or almost no excess anionic groups, they are hydrophobic enough to easily precipitate in water. Furthermore, a powder composition containing conductive particles including the conductive complex can form an electrode that exhibits excellent battery characteristics.

The electrical conductivity (unit: S/cm) of the conductive particles of this embodiment is preferably 0.1 to 100, more preferably 0.3 to 100, even more preferably 1 to 100, particularly preferably 2 to 100, and most preferably 3 to 100.
A higher electrical conductivity is preferable since the conductive particles have a higher electrical conductivity.
The upper limit of the electrical conductivity is not particularly limited, and the above range of 100 or less is merely a guideline.
The electrical conductivity of the conductive particles of this embodiment was measured using a molded sample obtained by compressing powder of the conductive particles.

The number average particle size of the conductive particles in this embodiment is preferably 0.1 μm or more and 100 μm or less, more preferably 0.5 μm or more and 50 μm or less, and even more preferably 1 μm or more and 10 μm or less.
When the content is at least the lower limit of the above range, handling as a powder becomes easier.
When it is equal to or less than the upper limit of the above range, the dispersibility in the powder composition is further improved.
The number average particle size of the conductive particles in this embodiment is a number-based average particle size measured using a dynamic light scattering particle size distribution measuring device.

The conductive particles of this embodiment may contain Fe (iron) atoms. The Fe content relative to the total mass of the conductive particles is, for example, preferably 0.5 mass% or less, more preferably 0.2 mass% or less, and even more preferably 0.1 mass% or less. The Fe content is most preferably substantially 0 mass%.
When the content is equal to or less than the upper limit of the above range, the impurity Fe is small, and therefore the powder composition containing the conductive particles can form an electrode that exhibits excellent battery characteristics.
The Fe content in the conductive particles is a value measured by fluorescent X-ray analysis.

The conductive particles of this embodiment may contain water together with the conductive complex, but the smaller the water content, the more preferable. The water content relative to the total mass of the conductive particles is, for example, preferably 20 mass% or less, more preferably 10 mass% or less, and even more preferably 5 mass% or less. The water content is most preferably substantially 0 mass%.
When the content is equal to or less than the upper limit of the above range, aggregation of the conductive particles can be suppressed when the conductive particles are mixed with a non-aqueous material, such as a binder resin.
The water content in the conductive particles is a value measured by the Karl Fischer method.

The content of the conductive particles in the powder composition of this embodiment is, for example, preferably 1 mass % or more and 30 mass % or less, more preferably 3 mass % or more and 20 mass % or less, and even more preferably 5 mass % or more and 15 mass % or less, when the total mass of the Li-containing compound, the conductive particles, and the binder is 100 mass %.
When the content is at least the lower limit of the above range, when used as an electrode material, an electrode having excellent electrical conductivity and battery characteristics can be formed.
When the content is equal to or less than the upper limit of the above range, the Li-containing compound and the binder can be contained sufficiently, and when used as an electrode material, an electrode having excellent electrical conductivity and battery characteristics can be formed.

<Method of manufacturing conductive particles>
The conductive particles used in this embodiment can be produced, for example, by the following method.
That is, the method for producing conductive particles includes the steps of: polymerizing the monomer in an aqueous solution containing at least the monomer among a monomer, a polyanion, and a catalyst that form a π-conjugated conductive polymer after polymerization, and having a content ratio of the monomer:the polyanion in a range of (1:0) to (1:1) on a mass basis (polymerization step); precipitating conductive particles in the aqueous solution after polymerization of the monomer (precipitation step); and recovering the precipitated conductive particles from the aqueous solution (recovery step).

(Polymerization process)
In this step, an aqueous solution (reaction solution) containing the monomer and the optional polyanion at a specific content ratio is prepared, and the monomer is polymerized in the aqueous solution to form a π-conjugated conductive polymer. When the aqueous solution contains the polyanion, the polyanion is naturally doped into the π-conjugated conductive polymer, and a conductive complex consisting of the π-conjugated conductive polymer and the polyanion is formed. The content ratio (mass basis) of the π-conjugated conductive polymer:polyanion contained in the formed conductive complex is the same as the ratio of the content of the monomer contained in the aqueous solution immediately before the start of polymerization to the content of the polyanion. In other words, the content ratio of the monomer and the polyanion blended in the aqueous solution is reflected in the content ratio of the π-conjugated conductive polymer and the polyanion in the formed conductive complex and the conductive particles obtained in the latter stage. When the aqueous solution does not contain a polyanion, a conductive particle consisting of a π-conjugated conductive polymer is obtained.

In this step, the catalyst contained in the aqueous solution is not particularly limited as long as it polymerizes the monomer, and examples thereof include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride.
It is preferable to contain an oxidizing agent together with the catalyst. The oxidizing agent can return the reduced catalyst to its original oxidized state. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.
When a catalyst containing Fe (iron) is used as the catalyst, the conductive particles may contain Fe derived from the catalyst.

The content of the monomer contained in the aqueous solution immediately before the start of polymerization is, for example, preferably 0.1 mass % or more and 20 mass % or less, more preferably 0.5 mass % or more and 15 mass % or less, and even more preferably 1 mass % or more and 10 mass % or less, relative to the total mass of the aqueous solution.
When the content is at least the lower limit of the above range, the conductive particles formed can be easily precipitated.
When the content is equal to or less than the upper limit of the above range, the polymerization reaction can be stably carried out, so that the formation of a complex with an optional polyanion present in the reaction system can be stably carried out, and high-quality conductive particles with high conductivity can be easily obtained.

It is preferable that the content of the polyanion contained in the aqueous solution immediately before the start of polymerization is set based on the content ratio to the monomer.

The content ratio of the monomer to the polyanion in the aqueous solution immediately before the start of polymerization is, on a mass basis, preferably more than (1:0) and not more than (1:1), more preferably from (1:0.1) to (1:1), even more preferably from (1:0.3) to (1:1), still more preferably from (1:0.5) to (1:1), particularly preferably from (1:0.7) to (1:0.99), and most preferably from (1:0.8) to (1:0.98).
When the content is at least the lower limit of the above range, the doping effect of the polyanion is sufficiently exhibited, and conductive particles having better conductivity can be obtained.
When the content is equal to or less than the upper limit of the above range, it is possible to obtain the doping effect of the polyanion while forming conductive particles that have low dispersibility in water and can be easily precipitated.

The content of the catalyst in the aqueous solution immediately before the start of polymerization is, for example, preferably 0.01% by mass to 1% by mass, and more preferably 0.1% by mass to 0.5% by mass, relative to the total mass of the aqueous solution.
When the content is at least the lower limit of the above range, the conductive particles can be easily formed.
When the content is equal to or less than the upper limit of the above range, the polymerization reaction can be stably carried out, so that the formation of a complex with a polyanion optionally present in the reaction system can be stably carried out, and high-quality conductive particles with high conductivity can be easily obtained.

In order to promote the polymerization reaction, the reaction liquid may be heated and stirred to cause the reaction. The heating temperature of the reaction liquid may be, for example, 60 to 100° C.
When the content is equal to or more than the lower limit of the above range, the polymerization reaction can be sufficiently promoted.
When the content is equal to or less than the upper limit of the above range, deterioration of the π-conjugated conductive polymer due to heat can be suppressed.
The reaction time at the heating temperature in the above range can be, for example, about 1 to 10 hours.

(Precipitation process)
In this step, the method for precipitating the conductive particles in the aqueous solution (reaction solution) after the polymerization reaction of the monomer is not particularly limited, and examples thereof include a method of leaving the reaction solution after the reaction at rest, a method of slowly stirring the reaction solution after the reaction, a method of cooling the reaction solution after the reaction to about −20° C. to 4° C., etc. In any method, the conductive particles can be naturally precipitated due to their property of being difficult to dissolve in water.

(Recovery process)
In this process, examples of methods for recovering the conductive particles precipitated in the aqueous solution (reaction liquid) include a method in which the conductive particles are allowed to naturally settle at the bottom of a container containing the reaction liquid and the supernatant liquid is removed, a method in which the reaction liquid is filtered to obtain conductive particles on a filter, a method in which a pellet of conductive particles is formed at the bottom of a container containing the reaction liquid by centrifugation, and a method in which the reaction liquid is sprayed into a gas and dried to obtain dried conductive particles.
Among these recovery methods, the method of recovering by natural precipitation is preferred because it is easy to obtain conductive particles that have few impurities, are excellent in conductivity, and can become a powder with excellent flowability.

Since the conductive particles immediately after being collected from the reaction solution still have the reaction solution containing the catalyst and oxidant attached thereto, it is preferable to wash the conductive particles with water or an organic solvent. Specifically, for example, the conductive particles are added to a washing solution made of water or an organic solvent, stirred, and then precipitated again, so that the conductive particles are collected from the washing solution.
The organic solvent is preferably at least one selected from isopropyl alcohol, methanol, and acetone, because, for example, it is difficult for the conductive particles to dissolve therein and the organic solvent has excellent cleaning power.

The conductive particles obtained in this process can be dried to form a dry powder that is easy to handle. There are no particular limitations on the drying method, and any known method for drying powder can be used.

The conductive particles obtained in this process may be pulverized to the desired particle size. The pulverization method is not particularly limited, and examples include a method of grinding and pulverizing using a mortar, a method of grinding using a pulverizer, etc. Examples of pulverizers include a homogenizer, a ball mill, a bead mill, a roller mill, a jet mill, and a hammer mill.

The method for grinding the conductive particles may be a wet method in which the conductive particles are ground in a dispersion medium, or a dry method in which the conductive particles are ground without a dispersion medium. The wet method is preferred in that it can easily produce conductive particles having a number average particle size in the range of 0.1 μm to 100 μm. When the wet method is used, the conductive particles are obtained in a state where they are dispersed in the dispersion medium. The dispersion medium used for wet grinding preferably contains one or more selected from isopropyl alcohol, methanol, and acetone. By using these preferred dispersion media, conductive particles having a number average particle size in the range of 0.1 μm to 100 μm can be more easily produced without impairing the conductivity of the conductive particles.

By using the steps described above, the conductive particles contained in the powder composition of this embodiment can be easily produced.

[Binder]
The binder contained in the powder composition of this embodiment is a resin other than the π-conjugated conductive polymer and the dopant. The binder is a resin that binds the Li-containing compound and the conductive particles together. As the binder used in this embodiment, a binder that constitutes a known LiB positive electrode or positive electrode active material is suitable.

Specific examples of binders include fluorine-containing resins, polyolefins, conjugated diene polymers, acrylic resins, polyvinyl alcohol resins, cellulose resins, latexes, and other resins.

Examples of fluorine-containing resins include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, etc.

Examples of polyolefins include polyethylene, polypropylene, ethylene propylene rubber, and modified versions of these.

Examples of conjugated diene polymers include styrene-butadiene copolymers and their hydrogenated products, acrylonitrile-butadiene copolymers and their hydrogenated products, and acrylonitrile-butadiene-styrene copolymers and their hydrogenated products.

Examples of acrylic resins include methacrylate-acrylate copolymers, styrene-acrylate copolymers, and acrylonitrile-acrylate copolymers.

Examples of polyvinyl alcohol-based resins include polyvinyl alcohol and polyvinyl acetate.

Examples of cellulose-based resins include ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose.

Examples of latexes include copolymers of unsaturated carboxylic acid monomers and other monomers that can be copolymerized with them. Here, examples of aliphatic conjugated diene monomers include butadiene and isoprene, examples of unsaturated carboxylic acid monomers include (meth)acrylic acid, and examples of other monomers include styrene. Such copolymers can be produced, for example, by known emulsion polymerization. Specific examples include styrene-butadiene latex, acrylic latex, acrylonitrile-butadiene latex, fluorine-based latex, silicone-based latex, etc.

Examples of other resins include resins having a melting point and/or glass transition temperature of 180° C. or higher, and polymers having no melting point but a decomposition temperature of 200° C. or higher. Specific examples include polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester, etc.
The binder included in this embodiment may be one type or two or more types.

The content of the binder in the powder composition of this embodiment is, for example, preferably 2 mass% or more and 20 mass% or less, more preferably 5 mass% or more and 15 mass% or less, and even more preferably 8 mass% or more and 12 mass% or less, when the total mass of the Li-containing compound, the conductive particles, and the binder is 100 mass%.
When the content is at least as much as the lower limit of the above range, the binder can sufficiently bind the Li-containing compound and the conductive particles.
When the content is equal to or less than the upper limit of the above range, when used as an electrode material, an electrode having excellent electrical conductivity and battery characteristics can be formed.

[Li-containing compound]
The Li-containing compound contained in the powder composition of this embodiment is preferably a Li-containing compound used in known LiB positive electrode active materials.Specific examples of the Li-containing composite oxides include _LiCoO2 , _LiNiO2 , spinel type _LiMnO4 , and olivine type _{LiFePO4.Among} them, the powder composition containing the olivine type Li-containing composite oxide can form an electrode that exhibits excellent battery characteristics.

In general, the olivine type Li-containing composite oxide is represented by the chemical formula Li _x α _y δ _z PO ₄ (wherein α is at least one selected from Co, Mn, Ni, Fe, Cu and Cr, δ is at least one selected from Mg, Ca, Sr, Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc and Y, and 0.9<x<1.1, 0<y≦1, 0≦z<1, 0.9<y+z<1.1).

From the viewpoint of improving battery characteristics such as capacity and cycle characteristics of a LiB having an electrode formed from the powder composition of this embodiment, α is preferably Co, Mn, Ni, or Fe, and δ is preferably Mg, Ca, Sr, Ba, Ti, Zn, or Al.
The Li-containing compound included in this embodiment may be one type or two or more types.

The content of the Li-containing compound in the powder composition of this embodiment is, for example, preferably 60% by mass or more and 95% by mass or less, more preferably 70% by mass or more and 90% by mass or less, and even more preferably 75% by mass or more and 85% by mass or less, when the total mass of the Li-containing compound, the conductive particles, and the binder is 100% by mass.
When the content is equal to or greater than the lower limit of the above range, when the material is used as an electrode material, particularly as an electrode material for LiB, an electrode having excellent electrical conductivity and battery characteristics can be formed.
When the content is equal to or less than the upper limit of the above range, the conductive particles and the binder can be contained sufficiently, and when used as an electrode material, an electrode having excellent conductivity and battery characteristics can be formed.

The Li-containing compound included in this embodiment preferably contains LiFePO ₄ from the viewpoint of improving the battery characteristics of the electrode to be formed.

<Content ratio of each component>
The content ratio of the Li-containing compound: the conductive particles: the binder is preferably 8:(0.5 to 1.5):1 on a mass basis.
Within the above range, when used as an electrode material, particularly as an electrode material for LiB, an electrode having excellent electrical conductivity and battery characteristics can be formed.

The total mass of the Li-containing compound, the conductive particles, and the binder relative to the total mass of the powder composition of this embodiment is preferably 60 mass% or more and 100 mass% or less, more preferably 70 mass% or more and 100 mass% or less, and even more preferably 80 mass% or more and 100 mass% or less.
Within the above range, when used as an electrode material, particularly as an electrode material for LiB, an electrode having excellent electrical conductivity and battery characteristics can be formed.

[Conductive assistant]
The powder composition of this embodiment may contain a conductive assistant other than the conductive particles and the Li-containing compound described above.
Examples of the conductive assistant include known conductive assistants added to electrode active materials for LiB. Specific examples of the conductive assistant include carbon materials and metal particles.
Examples of the carbon material include carbon black, graphite, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotube.
Examples of the metal particles include silver particles, copper particles, gold particles, and aluminum particles.
The conductive assistant included in this embodiment may be one type or two or more types.

The content of the conductive assistant relative to the total mass of the powder composition of this embodiment can be, for example, 0% by mass or more and 10% by mass or less.

(Other optional ingredients)
The powder composition of this embodiment may contain any component other than the conductive particles, the Li-containing compound, and the conductive assistant described above. Specific examples of the optional components include inorganic compounds (excluding carbon materials and metal particles).
Examples of inorganic compounds include silica, silica-alumina, glass, calcium carbonate, calcium hydroxide, talc, alumina, titania, zirconia, magnesium hydroxide, aluminum hydroxide, hydrotalcite, and mica.

The content of the other optional components relative to the total mass of the powder composition of this embodiment can be, for example, 0% by mass or more and 10% by mass or less.

The powder composition of this embodiment is preferably in the form of a paste or a slurry. In such a relatively high viscosity state, it becomes easier to mold the powder composition of this embodiment into a desired shape.

<Method of producing powder composition>
A powder composition can be obtained by mixing the Li-containing compound, conductive particles, a binder, and, if necessary, other optional components in a desired ratio.
The mixing method is not particularly limited, and any known method for mixing materials constituting a known powder composition may be used.

<Electrode paint>
A second aspect of the present invention is a coating material for an electrode, comprising the powder composition of the first aspect and a solvent.

The solvent contained in the electrode paint of this embodiment is not particularly limited as long as it dilutes or disperses the powder composition of the first embodiment so that the powder composition of the first embodiment can be applied to a substrate, and a solvent that dilutes or disperses known LiB electrode materials can be used.
Specific examples of the solvent include amine-based solvents such as N,N-dimethylaminopropylamine and diethylenetriamine; ether-based solvents such as tetrahydrofuran; ketone-based solvents such as methyl ethyl ketone; ester-based solvents such as methyl acetate; and amide-based solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (NMP).
The solvent included in this embodiment may be one type or two or more types.

The method for mixing the powder composition of the first embodiment with the solvent is not particularly limited, and examples of the method include mixing methods using a ball mill, a sand mill, a planetary mixer, a paint shaker, a homogenizer, etc.

The viscosity of the electrode paint of this embodiment is not particularly limited, as long as it has a viscosity that allows it to be applied to a substrate with sufficient fluidity.

The content of the powder composition of the first embodiment relative to the total mass of the electrode paint of this embodiment may be set taking into consideration the viscosity of the electrode paint, and may be, for example, 20% by mass or more and 80% by mass or less.

Methods for applying the electrode coating material of this embodiment to a substrate include, for example, slit die coating, screen coating, curtain coating, knife coating, gravure coating, and electrostatic spraying.

The electrode paint of this embodiment is applied to an electrode current collector, the coating film formed is dried, and if necessary, pressure is applied to bond the film to the electrode current collector, thereby obtaining an electrode in which an electrode layer is formed on the electrode current collector.

Electrodes
A third aspect of the present invention is an electrode comprising the powder composition of the first aspect.
The shape of the electrode is not particularly limited, and examples thereof include known electrode shapes such as a plate, sheet, film, rod, and column.
The average thickness of the plate-, sheet- or film-like electrode is, for example, preferably 0.01 μm or more and 1000 μm or less, and more preferably 0.1 μm or more and 100 μm or less, from the viewpoint of achieving both a reduction in electrical resistance and a reduction in the thickness of the electrode.
The average thickness of a plate-, sheet-, or film-like electrode is determined by observing the cross section of the electrode using a magnifying observation means such as a measuring microscope and measuring the thickness at 10 or more randomly selected locations, and averaging the measured values.
The electrode of this embodiment may be supported by a base material such as a film or substrate, or may be an independent electrode.
When the electrode of this embodiment is used as an electrode for LiB, it may be a positive electrode or a negative electrode, but is preferably a positive electrode.

<Electrode manufacturing method>
Examples of methods for producing the electrode of this embodiment include a method of forming the powder composition of the first embodiment into an electrode of a desired shape, and a method of applying the electrode coating material of the second embodiment to a desired substrate and drying it to form an electrode layer made of the powder composition of the first embodiment on the surface of the substrate.
The method for molding the powder composition of the first embodiment is not particularly limited, and well-mixed pellets may be molded by hand, may be molded using a mold, or may be extrusion molded.
As the substrate to which the electrode coating material of the second embodiment is applied, a known substrate supporting an electrode active material layer of LiB can be applied, and examples thereof include metal materials such as metal foils and metal plates. Examples thereof include copper foils, aluminum foils, and stainless steel plates.

<Batteries>
It is also possible to manufacture a battery or a capacitor equipped with the electrode of this embodiment.
The battery may be a primary battery or a secondary battery. The form of the battery is not particularly limited, and examples of the battery include known battery forms such as a dry battery, an electrode-stacked laminate battery, and a button battery.
The battery generally has a positive electrode, a negative electrode, and an electrolyte. The electrode in this embodiment may be a positive electrode or a negative electrode. The positive electrode and the negative electrode in the battery are preferably insulated from each other by a separator such as a nonwoven fabric.
The battery is preferably a lithium ion secondary battery.

<Production of polystyrene sulfonic acid>
206 g of sodium styrenesulfonate was dissolved in 1000 ml of ion-exchanged water, and while stirring at 80° C., 1.14 g of an oxidizing agent solution of ammonium persulfate previously dissolved in 10 ml of water was added dropwise over 20 minutes, and the solution was stirred for 12 hours.
1000ml of sulfuric acid diluted to 10% by mass was added to the obtained sodium polystyrene sulfonate-containing solution, and about 1000ml of the solvent was removed from the obtained polystyrene sulfonic acid-containing solution by ultrafiltration. Next, 2000ml of ion-exchanged water was added to the remaining liquid, and about 2000ml of the solvent was removed by ultrafiltration to wash the polystyrene sulfonic acid with water. This water washing operation was repeated three times.
Water in the resulting solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid.
The weight average molecular weight was measured to be 300,000. The weight average molecular weight was measured using an HPLC (high performance liquid chromatography) system with a GPC (gel permeation chromatography) column, with polystyrene as the standard substance.

<Production of Conductive Particles 1>
To 285 g of water, 50 g of an aqueous solution of polystyrene sulfonic acid having a solid content of 10% and 5 g of 3,4-ethylenedioxythiophene were added, and the mixture was stirred at 30° C. for 1 hour.
While stirring the resulting aqueous solution, 11 g of ammonium persulfate and 0.3 g of an oxidation catalyst solution of ferric sulfate dissolved in 100 ml of ion-exchanged water were slowly added, and the mixture was stirred for 6 hours to cause a reaction.
When the aqueous solution was left to stand after the reaction, a blue powder precipitated. This solution was filtered and dried to obtain a powder of an aggregate of conductive particles (PEDOT:PSS=5g:5g).
The number average particle size of the obtained conductive particles was 2.0 μm.
The content of Fe contained in the obtained conductive particles was 0.15 mass % based on the total mass of the conductive particles.
The content of water in the obtained conductive particles was 1.7 mass % based on the total mass of the conductive particles.
The resulting conductive particles had an electrical conductivity of 3.4 S/cm.

<Production of Conductive Particles 2>
To 50 g of water, 50 g of a 10% aqueous sulfuric acid solution and 5 g of 3,4-ethylenedioxythiophene were added, and the mixture was stirred at 30° C. for 1 hour.
While stirring the resulting aqueous solution, 11 g of ammonium persulfate and 0.3 g of an oxidation catalyst solution of ferric sulfate dissolved in 100 ml of ion-exchanged water were slowly added, and the mixture was stirred for 6 hours to cause a reaction.
When the aqueous solution was allowed to stand after the reaction, a blue powder precipitated. This solution was filtered and dried to obtain a powder that was an aggregate of conductive particles.
The number average particle size of the obtained conductive particles was 1.2 μm.
The content of Fe contained in the obtained conductive particles was 0.13 mass % based on the total mass of the conductive particles.
The content of water in the obtained conductive particles was 1.3 mass % based on the total mass of the conductive particles.
The resulting conductive particles had an electrical conductivity of 1.9 S/cm.

(Reference Example 1)
To 235 g of water, 100 g of an aqueous solution of polystyrene sulfonic acid having a solid content of 10% and 5 g of 3,4-ethylenedioxythiophene were added, and the mixture was stirred at 30° C. for 1 hour.
While stirring the resulting aqueous solution, 11 g of ammonium persulfate and 0.3 g of an oxidation catalyst solution of ferric sulfate dissolved in 100 ml of ion-exchanged water were slowly added, and the mixture was stirred for 6 hours to cause a reaction.
After the reaction, the aqueous solution was allowed to stand, but no precipitation occurred and PEDOT-PSS remained dispersed in water.

[Measurement of number average particle size]
The number average particle size of the conductive particles obtained in each example was measured by the following method.
The conductive particles were dissolved in water to give a 0.1% by mass aqueous solution, and the number average particle size was measured using a dynamic light scattering particle size distribution measuring device (ELSZ-2000, manufactured by Otsuka Electronics Co., Ltd.).

[Measurement of Fe content]
The Fe content in the conductive particles obtained in each example was quantified using an X-ray fluorescence analyzer.

[Measurement of Water Content]
The water content in the conductive particles obtained in each example was measured by the following method.
The conductive particles were dissolved in methanol to give a 1% by mass solution, and the water content was measured using a Karl Fischer moisture meter (KF-31, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

<Production of Powder Composition>
Example 1
The three materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 : conductive particles 1 obtained above: polytetrafluoroethylene (PTFE) = 8:0.5:1

Example 2
The three materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 : conductive particles 1 obtained above: polytetrafluoroethylene (PTFE) = 8:1:1

Example 3
The three materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 : conductive particles 1 obtained above: polytetrafluoroethylene (PTFE) = 8: 1.5: 1

Example 4
The three materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 : conductive particles 2 obtained above: polytetrafluoroethylene (PTFE) = 8: 1.5: 1

Example 5
The three materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 : conductive particles 1 obtained above: polytetrafluoroethylene (PTFE) = 8: 1.5: 1
Further, 2.2 g of N-methyl-2-pyrrolidone (NMP) was added to 0.5 g of the pellets to prepare an electrode coating material, which was then applied to an aluminum foil to obtain an electrode sheet having an electrode layer with a thickness of about 20 μm.

(Comparative Example 1)
The two materials were mixed in the mass ratio shown below to obtain pellets of a powder composition.
_LiFePO4 :polytetrafluoroethylene (PTFE)=8:1

[Battery fabrication and characterization]
The pellets obtained in Examples 1 to 4 and Comparative Example 1 were each formed into a sheet (thickness: about 50 μm) and dried at 120° C. The electrode sheet obtained in Example 5 (thickness of electrode layer: about 20 μm) was also dried at 120° C. These were punched out into a circular shape of Φ16 mm to form a positive electrode. Next, in a glove box, the circular positive electrode, a glass filter paper separator of Φ16 mm, and a circular Li metal foil negative electrode of Φ16 mm were laminated in this order in a stainless steel exterior for a 2032-type coin cell, and an ethylene carbonate/diethyl carbonate mixed solution (mixed volume ratio 1/1) containing LiPF ₆ electrolyte salt was poured as an electrolyte. Finally, a stainless steel exterior was placed as a lid and sealed to prepare a coin battery.
The capacity of the produced battery was evaluated as follows: Using an automatic battery evaluation device, the battery was charged and discharged in a thermostatic chamber at 30° C. under a current density of 30 mA/g with a cutoff voltage of 4 V for charging and 2.8 V for discharging, and the capacity of the battery was measured.
The capacity was measured using an automatic battery evaluation device (1024B-7V 0.1A-4) manufactured by Electrofield.

<Results>
As shown in Examples 1 to 5, it was found that the initial capacity and cycle characteristics improved as the content of conductive particles in the positive electrode of the lithium ion secondary battery increased. Furthermore, although the positive electrodes of Examples 1 to 4 did not have aluminum foil, they showed a battery capacity exceeding that of Example 5, which had a positive electrode with aluminum foil.
The positive electrode of Comparative Example 1 did not contain conductive particles and had poor battery capacity.
It should be noted that Example 4 is a reference example.

Claims (9)

A powder composition comprising: a Li-containing compound; conductive particles including a conductive complex having a π-conjugated conductive polymer and a dopant; and a binder;
The powder composition , wherein a content ratio of the π-conjugated conductive polymer to the dopant in the conductive composite is, on a mass basis, greater than (1:0) and less than or equal to 1:1 . The powder composition according to claim 1 , wherein the π-conjugated conductive polymer comprises poly(3,4-ethylenedioxythiophene). 3. The powder composition according to claim 1 , wherein the dopant comprises at least one selected from the group consisting of polystyrene sulfonic acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, paratoluenesulfonic acid, and hydroxybenzenesulfonic acid. The powder composition according to any one of claims 1 to 3 , wherein a content ratio of the Li-containing compound:the conductive particles:the binder is 8:(0.5 to 1.5):1 on a mass basis. The powder composition according to claim 1 , wherein the binder comprises polyvinylidene fluoride, polytetrafluoroethylene, polyester, or polyvinyl alcohol. The powder composition according to any one of claims 1 to 5 , wherein the Li-containing compound comprises _LiFePO4 . A coating material for electrodes, comprising the powder composition according to any one of claims 1 to 6 and a solvent. The electrode coating material according to claim 7 , wherein the solvent is N-methyl-2-pyrrolidone. An electrode comprising the powder composition according to any one of claims 1 to 6 .