Conductive particle and method for producing the same

Abstract

To provide conductive particles which have good conductivity and are easy to handle as powder, and to provide a method for producing the same.SOLUTION: (1) A conductive particle comprising an inorganic particle containing silicon dioxide or a metal oxide, a polythiophene-based conductive polymer, and a sulfonic acid group-containing compound having a molecular weight of less than 500. (2) A method for producing a conductive particle, comprising a step of polymerizing, in a slurry containing an inorganic particle containing silicon dioxide or a metal oxide, a sulfonic acid group-containing compound having a molecular weight of less than 500, a monomer for forming a polythiophene-based conductive polymer, and water, the monomer to form the polythiophene-based conductive polymer doped with the sulfonic acid group-containing compound, followed by filtration, thereby obtaining a conductive particle in which a part or all of the surface of the inorganic particle is coated with the polythiophene-based conductive polymer and the sulfonic acid group-containing compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to conductive particles and a method for producing the same. [Background technology]

[0002] Although π-conjugated conductive polymers, whose main chains are composed of π-conjugated systems, are poorly soluble in water, they are known to become water-dispersible when they form complexes with polyanions that have hydrophilic anionic groups. A typical example is the complex of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonic acid (PEDOT-PSS).

[0003] On the other hand, a method has been disclosed in which, when the compounding ratio of PEDOT:PSS during the formation of the conductive complex is controlled to be greater than (1:0) but less than (1:1), a powder of conductive particles that is difficult to dissolve in water can be obtained while still obtaining the conductivity-enhancing effect of PSS doping (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-052249 Summary of the Invention [Problem to be solved by the invention]

[0005] The conductive particles of Patent Document 1 require a large amount of the π-conjugated conductive polymer itself because the π-conjugated conductive polymer forms the particle body. The present inventors have studied ways to reduce the amount of the π-conjugated conductive polymer used and thereby reduce production costs, and have completed the present invention.

[0006] The present invention provides conductive particles that have good conductivity and can be easily handled as powder, and a method for producing the same. [Means for solving the problem]

[0007] [1] Conductive particles containing inorganic particles containing silicon dioxide or metal oxide, a polythiophene-based conductive polymer, and a sulfonic acid group-containing compound with a molecular weight of less than 500. [2] The conductive particles according to [1], wherein the sulfonic acid group-containing compound includes sulfuric acid or an aromatic sulfonic acid compound. [3] The conductive particles according to [1] or [2], wherein the aromatic sulfonic acid compound comprises at least one selected from the group consisting of benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, benzenedisulfonic acid, naphthalenesulfonic acid, and naphthalenedisulfonic acid. [4] The conductive particles according to any one of [1] to [3], wherein the inorganic particles contain at least one selected from the group consisting of silica, alumina, titania, zirconia, and ceria. [5] The conductive particles according to any one of [1] to [4], wherein the polythiophene-based conductive polymer covers a part or the whole of the surface of the inorganic particles. [6] The conductive particles according to any one of [1] to [5], which contain 10 to 1000 parts by weight of the inorganic particles per 100 parts by weight of the polythiophene-based conductive polymer. [7] The conductive particles according to any one of [1] to [6], wherein the polythiophene-based conductive polymer is poly(3,4-ethylenedioxythiophene). [8] The conductive particles according to any one of [1] to [6], wherein the inorganic particles have an average primary particle size of 1 to 500 μm as measured by image analysis using an electron microscope. [9] A method for producing conductive particles, comprising the steps of: polymerizing the monomer in a slurry containing inorganic particles containing silicon dioxide or a metal oxide, a sulfonic acid group-containing compound having a molecular weight of less than 500, a monomer for forming a polythiophene-based conductive polymer, and water; forming the polythiophene-based conductive polymer doped with the sulfonic acid group-containing compound; and filtering the polymer to obtain conductive particles in which the polythiophene-based conductive polymer and the sulfonic acid group-containing compound coat part or all of the surfaces of the inorganic particles.

[10] The method for producing conductive particles according to [9], further comprising the step of suspending the conductive particles in a cleaning solution and filtering the same again to wash the conductive particles. [Effects of the Invention]

[0008] The conductive particles of the present invention contain inorganic particles, making them easy to handle as powder. Furthermore, the inorganic particles can also contribute to increasing the conductivity of the conductive particles. Furthermore, since the inorganic particles constitute a portion of the conductive particles, the content of the π-conjugated conductive polymer is lower than when the particles are composed solely of a π-conjugated conductive polymer. As a result, manufacturing costs can be reduced. The conductive particles of the present invention can be pressure-molded into, for example, a tablet. Furthermore, since the particles contain inorganic particles, the molded body can have good mechanical strength.

[0009] According to the method for producing conductive particles of the present invention, a π-conjugated conductive polymer is synthesized in a slurry containing a sulfonic acid group-containing compound as a low-molecular-weight dopant, inorganic particles, and water. This makes it easy for the doped π-conjugated conductive polymer to coat at least a portion of the surface of the inorganic particles. Furthermore, the use of inorganic particles provides excellent filterability. Therefore, the slurry of conductive particles after synthesis of the π-conjugated conductive polymer can be easily filtered to remove water and impurities from the slurry. The conductive particles obtained after filtration can also be easily suspended in a cleaning solution and filtered again, resulting in efficient repeated washing of the conductive particles. As a result, conductive particles with excellent conductivity and free of impurities can be produced.

[0010] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

[0011] In this specification and claims, the lower and upper limits of numerical ranges indicated with "to" are included in the numerical range. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Conductive particles> A first aspect of the present invention is a conductive particle containing inorganic particles containing silicon dioxide or a metal oxide, a polythiophene-based conductive polymer, and a sulfonic acid group-containing compound having a molecular weight of less than 500.

[0013] [Conductive polythiophene polymers] The polythiophene-based conductive polymer of this embodiment is a conductive organic polymer whose main chain is composed of a π-conjugated system, and is known to have excellent transparency among various π-conjugated conductive polymers.

[0014] Specific 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), poly(3- iodothiophene), 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-dodecathiophene), siloxythiophene), 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- Examples of suitable thiophenes include 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). Among these π-conjugated conductive polymers, poly(3,4-ethylenedioxythiophene) is particularly preferred because of its excellent conductivity, transparency, and heat resistance. The polythiophene-based conductive polymer constituting the conductive particles of this embodiment may be one type or two or more types.

[0015] [Sulfonic acid group-containing compounds] The sulfonic acid group-containing compound of this embodiment (hereinafter sometimes referred to as "low-molecular dopant") is a low-molecular compound having a molecular weight of less than 500 and having one or more sulfonic acid groups (-SO2-OH). The number of sulfonic acid groups is preferably 1 to 5, more preferably 1 to 2. The low-molecular dopant may be an inorganic compound or an organic compound. The sulfonic acid group is an anionic functional group that is doped into a polythiophene-based conductive polymer. Because the molecular weight is less than 500 and the molecular structure is small, steric hindrance is unlikely to occur when doping a polythiophene-based conductive polymer. Furthermore, polythiophene-based conductive polymers inherently have low solubility in water, even after doping with a low-molecular-weight dopant. Therefore, the polythiophene-based conductive polymer formed by polymerization in the presence of water easily adheres to the surface of inorganic particles, easily covering part or all of the surface of the inorganic particles. In the present invention, sulfuric acid (H2SO4) is a compound that corresponds to a sulfonic acid group-containing compound.

[0016] Examples of sulfonic acid group-containing compounds include sulfuric acid and aromatic sulfonic acid compounds. Aromatic sulfonic acid compounds are compounds in which one or more of the hydrogen atoms of an aromatic compound are substituted with a sulfonic acid group. The aromatic compound is not particularly limited, and known aromatic compounds can be used. Specific examples of aromatic sulfonic acid compounds that are preferred include benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, benzenedisulfonic acid, naphthalenesulfonic acid, and naphthalenedisulfonic acid. These preferred compounds make it easier to achieve the above-mentioned effects.

[0017] [Inorganic particles] The inorganic particles contained in the conductive particles of this embodiment contain silicon dioxide or a metal oxide. Materials other than silicon dioxide and a metal oxide may also be contained, but the content of silicon dioxide or a metal oxide in the total mass of the inorganic particles is preferably 50 mass% or more, more preferably 75 mass% or more, and even more preferably 90 mass% or more, and may even be 100 mass%.

[0018] The shape of the inorganic particles is not particularly limited, but from the viewpoint of improving the handling and filterability of the powder, it is preferable that the inorganic particles be spherical or approximately spherical. Here, approximately spherical refers to a shape without corners, protrusions, or flat surfaces, and is a concept that includes shapes that are not perfect spheres, such as potatoes. The inorganic particles may have a structure having voids in some parts of the interior (for example, a porous structure), or may have a dense interior.

[0019] The average particle size of the primary particles of the inorganic particles is not particularly limited, and examples thereof include particle sizes that can be used as materials for batteries or electrodes, such as ranges of 1 to 500 μm, 10 to 400 μm, 20 to 300 μm, and 30 to 200 μm. The average particle size can be measured by image analysis using an electron microscope, for example, as the average diameter or major axis of primary particles of 10 to 100 inorganic particles.

[0020] Examples of inorganic particles made of silicon dioxide include particles made of silica gel. Examples of inorganic particles made of metal oxides include particles made of alumina, titania, zirconia, ceria, and the like.

[0021] <Content ratio> In the conductive particles of this embodiment, the content of the inorganic particles per 100 parts by mass (parts by weight) of the π-conjugated conductive polymer is preferably 10 to 2000 parts by mass, more preferably 50 to 1500 parts by mass, and even more preferably 80 to 1200 parts by mass. Examples of this preferred range include 100 to 1000 parts by mass, 150 to 750 parts by mass, 200 to 600 parts by mass, and 250 to 450 parts by mass. When the content is at least as large as the lower limit of the above range, the mechanical strength of the conductive particles is improved, the particles are easy to handle as powder, filterability is improved, and molding by pressure is also easier. When the content is equal to or less than the upper limit of the above range, the relative content of the π-conjugated conductive polymer increases, and therefore the conductivity, as expressed by the conductivity, tends to increase.

[0022] In the conductive particles of this embodiment, the content of the sulfonic acid group-containing compound (low-molecular dopant) per 100 parts by mass (parts by weight) of the π-conjugated conductive polymer is preferably 0.1 to 500 parts by mass, more preferably 1 to 200 parts by mass, and even more preferably 2 to 100 parts by mass. Within this preferred range, for example, ranges of 3 to 80 parts by mass, 5 to 60 parts by mass, 8 to 40 parts by mass, and 10 to 20 parts by mass can also be mentioned. Within the preferred range, the conductivity, which is expressed as the electrical conductivity of the π-conjugated conductive polymer, is further improved.

[0023] The conductive particles of this embodiment may contain other components in addition to the inorganic particles, the π-conjugated conductive polymer, and the sulfonic acid group-containing compound. However, from the viewpoint of fully obtaining the effects of the present invention, the content of the other components is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less, relative to the total mass of the conductive particles.

[0024] <Method for manufacturing conductive particles> A second aspect of the present invention is a method for producing conductive particles, comprising the steps of polymerizing the monomer in a slurry containing inorganic particles containing silicon dioxide or a metal oxide, a sulfonic acid group-containing compound having a molecular weight of less than 500, a monomer for forming a polythiophene-based conductive polymer, and water, to form the polythiophene-based conductive polymer doped with the sulfonic acid group-containing compound, and then filtering the polymer to obtain conductive particles in which the polythiophene-based conductive polymer and the sulfonic acid group-containing compound coat part or all of the surfaces of the inorganic particles. The conductive particles of the first embodiment can be produced by the production method of this embodiment.

[0025] A reaction solution containing the inorganic particles, the monomer, the sulfonic acid group-containing compound (low-molecular-weight dopant), and water is prepared, and the monomer is polymerized to form a π-conjugated conductive polymer. In the reaction solution, the low-molecular-weight dopant spontaneously dopes into the π-conjugated conductive polymer, forming a conductive composite consisting of the π-conjugated conductive polymer and the low-molecular-weight dopant. In this case, the sulfonic acid groups of the low-molecular-weight dopant can be doped into the π-conjugated conductive polymer in the same way as conventional polyanions (organic compounds having a large number of anionic groups, for example, 10 or more) and anionic groups of other dopants.

[0026] The synthesis of the π-conjugated conductive polymer in the reaction solution can be carried out in the same manner as conventional synthesis of π-conjugated conductive polymers, except that the inorganic particles and a low-molecular-weight dopant are added to the reaction solution. However, it is preferable not to add a polyanion to the reaction solution. If a polyanion is added to the reaction solution and the monomer is polymerized in the presence of the polyanion, the polyanion will dope the formed π-conjugated conductive polymer, forming a water-dispersible (water-soluble) conductive composite, which may reduce adhesion to the inorganic particles and reduce the yield of the desired conductive particles.

[0027] Since the reaction liquid contains water, the π-conjugated conductive polymer formed by the polymerization reaction of the monomer and doped with the low-molecular-weight dopant cannot maintain a stably dispersed state in water, but becomes attached to the inorganic particles, making it possible to recover it by filtration.

[0028] The reaction liquid may contain a dispersion medium other than water. The dispersion medium other than water is not required to inhibit polymerization, and a water-soluble organic solvent is preferred. The water-soluble organic solvent is an organic solvent that dissolves in an amount of 1 g or more in 100 g of water at 20°C, and examples thereof include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The water-soluble organic solvent contained as the dispersion medium may be one type or two or more types. The content of water relative to the total mass of the aqueous dispersion medium is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and may be 100% by mass.

[0029] It is preferable to add a known catalyst and oxidizing agent to the reaction solution to promote chemical oxidation of the monomer. Examples of the catalyst include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0030] The amount of catalyst to be blended relative to the total mass of the reaction solution containing the catalyst and the oxidizing agent (excluding the mass of the inorganic particles) is, from the viewpoint of obtaining a high-yield and stable polymerization reaction, preferably from 0.10 mass% to 2.50 mass%, more preferably from 0.50 mass% to 2.0 mass%, and even more preferably from 1.0 mass% to 1.6 mass%.

[0031] The amount of the oxidizing agent to be blended relative to the total mass of the reaction solution containing the catalyst and the oxidizing agent (excluding the mass of the inorganic particles) is, from the viewpoint of obtaining a high-yield and stable polymerization reaction, preferably from 1.0 mass% to 10.0 mass%, more preferably from 2.0 mass% to 8.0 mass%, and even more preferably from 3.0 mass% to 6.0 mass%.

[0032] The amount of the monomer relative to the total mass of the reaction solution (excluding the mass of the inorganic particles) is preferably, for example, 0.1% by mass to 5.0% by mass in order to achieve a high-yield, stable polymerization reaction. Within this range, the amount may be, for example, 0.5% by mass to 4.0% by mass, 1.0% by mass to 3.0% by mass, 1.5% by mass to 3.0% by mass, or 2.0% by mass to 3.0% by mass.

[0033] The amount of the low-molecular-weight dopant added to the reaction solution is, for example, preferably 0.5 to 5.0 mol, more preferably 1.0 to 4.0 mol, and even more preferably 1.5 to 3.0 mol, relative to 1 mol of the monomer added to the reaction solution. The remaining low-molecular-weight dopant that has been added to the reaction solution and not used for doping can be washed away in a washing step after the polymerization reaction. Therefore, it is preferable to add an excess amount of low-molecular-weight dopant to the monomer in order to ensure sufficient doping at the polymerization stage.

[0034] The reaction temperature in the reaction solution can be, for example, 15 to 35°C. At the reaction temperature, the polymerization reaction is usually completed within about 4 to 24 hours. The completion of the polymerization reaction can be determined by measuring the amount of unreacted monomer in the reaction solution using high performance liquid chromatography, gas chromatography, or the like.

[0035] The conductive particles formed in the reaction liquid are difficult to dissolve in water. Examples of methods for separating (recovering) the conductive particles formed in the reaction liquid include a method in which the conductive particles are allowed to settle naturally 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.

[0036] The conductive particles immediately after being separated from the reaction solution are preferably washed with a washing solution because the reaction solution containing the catalyst, decomposition products of the oxidizing agent, etc. is attached to the conductive particles. Specific washing methods include, for example, a method of pouring a washing solution made of water or an organic solvent onto the conductive particles, a method of adding the conductive particles to the washing solution, stirring the mixture, and then separating the conductive particles again as a solid content, etc. The organic solvent is preferably water or an alcohol such as isopropyl alcohol or methanol, for example, because it does not easily dissolve the conductive particles and has excellent cleaning power.

[0037] The conductive particles obtained in this embodiment can be dried to form a dry powder that is easy to handle. The drying method is not particularly limited, and any known method for drying powder can be used.

[0038] The conductive particles obtained in this embodiment may be pulverized to a desired particle size. The pulverization method is not particularly limited, and examples thereof include a method of grinding and pulverizing using a mortar and a method of pulverizing using a pulverizer. Examples of the pulverizer include a homogenizer, a ball mill, a bead mill, a roller mill, a jet mill, and a hammer mill.

[0039] ≪Electrode≫ A third aspect of the present invention is an electrode comprising the conductive particles of the first aspect. The shape of the electrode is not particularly limited, and examples thereof include known electrode shapes such as plate, sheet, film, rod, and column. The average thickness of the plate-, sheet-, and film-like electrodes is, for example, preferably 0.01 μm or more and 1000 μm or less, more preferably 0.1 μm or more and 100 μm or less, from the viewpoint of achieving both reduced electrical resistance and thinning of the electrodes. The average thickness of plate-, sheet-, and film-shaped electrodes is the average value of thickness measurements taken at five or more randomly selected locations on the cross section of the electrode observed using a magnifying observation means such as a measuring microscope. The electrode of this embodiment may be supported by a substrate such as a film or a substrate, or may be an independent electrode. When the electrode of this embodiment is used as an electrode for a battery such as a lithium ion secondary battery, it may be either a positive electrode or a negative electrode.

[0040] The electrode of this embodiment may be an electrode consisting of only the conductive particles of the first embodiment, or may be an electrode containing a binder and a conductive additive.

[0041] When the electrode of this embodiment consists only of the conductive particles of the first embodiment, its conductivity (unit: S / cm) is preferably 10 or more, more preferably 15 or more, even more preferably 20 or more, particularly preferably 30 or more, and most preferably 40 or more. Higher conductivity is preferable because it increases the conductivity of the electrode. The upper limit of the conductivity is not particularly limited, and 500 is an example of a guideline. The above examples of electrical conductivity were measured using a molded product (pressure molded product) obtained by compressing the powder of the conductive particles of the first embodiment as a sample.

[0042] (binder) The binder is a resin other than the π-conjugated conductive polymer, which is capable of binding the conductive particles together. The binder contained as an optional component in the electrode of this embodiment may be one type or two or more types. Examples of binders include binder resins that are added to electrode active materials in known lithium ion secondary batteries, such as fluorine-containing resins, polyolefins, conjugated diene polymers, acrylic resins, polyvinyl alcohol resins, cellulose resins, latexes, and other resins.

[0043] Examples of fluorine-containing resins include polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and ethylene-tetrafluoroethylene copolymer. Examples of polyolefins include polyethylene, polypropylene, ethylene propylene rubber, and modified products thereof. Examples of conjugated diene polymers include styrene-butadiene copolymers and hydrogenated products thereof, acrylonitrile-butadiene copolymers and hydrogenated products thereof, and acrylonitrile-butadiene-styrene copolymers and hydrogenated products thereof. Examples of acrylic resins include polyacrylic acid, polyacrylic acid ester, polymethacrylic acid ester, methacrylic acid ester-acrylate copolymer, styrene-acrylate copolymer, and acrylonitrile-acrylate copolymer. Examples of polyvinyl alcohol resins include polyvinyl alcohol and polyvinyl acetate. Examples of the cellulose-based resin include ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and carboxymethyl cellulose. Examples of latexes include styrene-butadiene latex, acrylic latex, acrylonitrile-butadiene latex, fluorine-based latex, and silicone-based latex.

[0044] The content of the binder in the electrode of this embodiment is, for example, 10 parts by mass or more and 10,000 parts by mass or less per 100 parts by mass of the conductive particles.

[0045] (Conductive additive) The electrode of this embodiment may contain one or more types of conductive additives as optional components. Examples of conductive additives include known conductive additives added to electrode active materials of lithium ion secondary batteries. Specific examples include carbon materials and metal particles. Examples of carbon materials include carbon black, graphite, vapor-grown carbon fiber, carbon nanofiber, and carbon nanotube. Examples of metal particles include silver particles, copper particles, gold particles, and aluminum particles.

[0046] The content of the conductive auxiliary agent in the electrode of this embodiment is, for example, 0.1 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the conductive particles.

[0047] <Electrode manufacturing method> A fourth aspect of the present invention is a method for producing an electrode, which includes obtaining an electrode using the conductive particles of the first aspect as a material. The electrode of the third aspect can be obtained by the production method of this aspect. The electrode production method of this aspect may also include a step of producing the conductive particles of the second aspect.

[0048] Examples of methods for producing an electrode of this embodiment include a method of molding the conductive particles of the first embodiment into an electrode of a desired shape, and a method of applying a coating material containing the conductive particles of the first embodiment to a desired substrate and drying it to form an electrode layer (conductive layer) containing the conductive particles of the first embodiment on the surface of the substrate.

[0049] The method of forming the conductive particles of the first aspect into an electrode of a desired shape is not particularly limited. For example, a composition obtained by kneading the binder and the conductive particles may be obtained, and this composition may be molded using a mold or the like, or may be extrusion-molded. Alternatively, the conductive particles may be filled into a mold and pressed to form a three-dimensional electrode reflecting the shape of the mold.

[0050] As the base material for applying the coating material, a base material that supports a known electrode active material layer of a battery can be applied, and examples thereof include metal materials such as metal foils and metal plates. For example, copper foils, aluminum foils, stainless steel plates, etc. can be mentioned. Further, known resin films or resin plates may be used as the base material. The coating method is not particularly limited, and a conventional method may be applied.

[0051] The coating material contains a dispersion medium for becoming liquid, and may contain the binder and the conductive assistant as necessary. The dispersion medium may be any of water, an organic solvent, or a mixed liquid of water and an organic solvent.

[0052] <Battery> According to the present invention, a battery or a capacitor provided with the electrode of the third aspect can also be manufactured. The battery may be a primary battery or a secondary battery. The form of the battery is not particularly limited, and examples thereof include known battery forms such as dry batteries, electrode laminated type laminated batteries, button batteries, etc. The battery usually has a positive electrode, a negative electrode, and an electrolyte. The electrode of the third aspect may be a positive electrode or a negative electrode. It is preferable that the positive electrode and the negative electrode in the battery are insulated by a separator such as a non-woven fabric. The battery may be, for example, a lithium ion secondary battery.

Examples

[0053] [Preparation of thiophene-based compound] Commercially available 3,4-ethylenedioxythiophene (manufactured by Tokyo Chemical Industry Co., Ltd.) was purchased and purified by vacuum distillation before use in the reaction.

[0054] [Preparation of aqueous sodium peroxodisulfate solution] Sodium peroxodisulfate (manufactured by Junsei Chemical Co., Ltd.) was dissolved in ion-exchanged water at room temperature to adjust the concentration to 10 wt %.

[0055] [Example 1] A 1000 ml three-neck flask was charged with 5.67 g (14.2 mmol) of ferric sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 168 g of ion-exchanged water, and 30.0 g of silica gel particles (Wakogel C-500HG, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average particle size of primary particles: 20 μm), and the mixture was bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes. The mixture was then stirred for a further 50 minutes under a nitrogen atmosphere, and the liquid temperature was maintained at 25°C. To this solution, 10.0 g (102 mmol) of sulfuric acid (molecular weight 98, Fujifilm Wako Pure Chemical Industries, Ltd.) and 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene were added and stirred for an additional 10 minutes. To this solution, 185 g of a 10 wt% aqueous solution of sodium peroxodisulfate (Fujifilm Wako Pure Chemical Industries, Ltd., 77.7 mmol as sodium peroxodisulfate) was added dropwise over 60 minutes. After stirring for 3 hours, the conversion of 3,4-ethylenedioxythiophene to PEDOT was 98%. The reaction solution was filtered under suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a black solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 38.5 g of black conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 306 parts by weight of silica gel for every 100 parts by weight of PEDOT. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the particles contained 8.3 parts by weight of sulfuric acid, the dopant, for every 100 parts by weight of PEDOT. The obtained conductive particles were pulverized using a ball mill, then tableted under a pressure of 50 MPa, and the conductivity was measured (automatic powder resistivity measuring system MCP-PD600, manufactured by Nitto Seiko Analytech Co., Ltd.). The conductivity of the conductive particles was found to be 12 S / cm.

[0056] [Example 2] Sodium 1-naphthalenesulfonate (Tokyo Chemical Industry Co., Ltd.) was dissolved in ion-exchanged water to a concentration of 15 wt%. This aqueous solution was treated with a cation exchange resin to adjust the concentration, and a 10 wt% aqueous solution of 1-naphthalenesulfonic acid was prepared. A 1000 ml three-neck flask was charged with 300 g of an aqueous 1-naphthalenesulfonic acid solution (10 wt %, molecular weight 208, 144 mmol as 1-naphthalenesulfonic acid), 5.67 g (14.2 mmol) of ferric sulfate, and 30.0 g of titanium dioxide particles (rutile type, manufactured by Tokyo Chemical Industry Co., Ltd., average particle size of primary particles: 2 μm), and the mixture was bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes. The mixture was then stirred for a further 50 minutes under a nitrogen atmosphere, and the liquid temperature was maintained at 25°C. To this solution, 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene was added and stirred for an additional 10 minutes. To this solution, 185 g of an aqueous solution of sodium peroxodisulfate (77.7 mmol as sodium peroxodisulfate) adjusted to a concentration of 10 wt% was added dropwise over 60 minutes. After stirring for 3 hours, the conversion of 3,4-ethylenedioxythiophene to PEDOT was 100%. This reaction solution was filtered by suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 39.6 g of dark blue conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 300 parts by weight of titanium dioxide per 100 parts by weight of PEDOT. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the particles contained 11.2 parts by weight of the dopant 1-naphthalenesulfonic acid per 100 parts by weight of PEDOT. The resulting conductive particles had a conductivity of 38 S / cm.

[0057] [Example 3] Sodium 2-naphthalenesulfonate (Tokyo Chemical Industry Co., Ltd.) was dissolved in ion-exchanged water to a concentration of 15 wt%. This aqueous solution was treated with a cation exchange resin to adjust the concentration, and a 10 wt% aqueous solution of 2-naphthalenesulfonic acid was prepared. A 1000 ml three-neck flask was charged with 300 g of an aqueous solution of 2-naphthalenesulfonic acid (10 wt %, molecular weight 208, 144 mmol as 2-naphthalenesulfonic acid), 5.67 g (14.2 mmol) of ferric sulfate, and 10.0 g of aluminum oxide particles (α-alumina, Fujifilm Wako Pure Chemical Industries, Ltd., average particle size of primary particles: 2 μm). The mixture was then bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes, and further stirred for 50 minutes under a nitrogen atmosphere while maintaining the liquid temperature at 25°C. To this solution, 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene was added and stirred for an additional 10 minutes. To this solution, 185 g of an aqueous solution of sodium peroxodisulfate (77.7 mmol as sodium peroxodisulfate) adjusted to a concentration of 10 wt% was added dropwise over 60 minutes. After stirring for 6 hours, the conversion rate of 3,4-ethylenedioxythiophene to PEDOT was 96%. The reaction solution was filtered under suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a black solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 19.2 g of black conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 104 parts by weight of aluminum oxide per 100 parts by weight of PEDOT. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the particles contained 10.4 parts by weight of the dopant 2-naphthalenesulfonic acid per 100 parts by weight of PEDOT. The resulting conductive particles had a conductivity of 16 S / cm.

[0058] [Example 4] 5.67 g (14.2 mmol) of ferric sulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 168 g of ion-exchanged water, and 20.0 g of cerium (IV) oxide particles (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average particle size of primary particles: 1 μm) were added to a 1000 ml three-neck flask, and the mixture was bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes, and then stirred for an additional 50 minutes under a nitrogen atmosphere, maintaining the liquid temperature at 35°C. To this solution, 17.7 g (93.2 mmol) of p-toluenesulfonic acid monohydrate (molecular weight 190, Fujifilm Wako Pure Chemical Industries, Ltd.) and 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene were added and stirred for an additional 10 minutes. To this solution, 185 g of a 10 wt% aqueous solution of sodium peroxodisulfate (Fujifilm Wako Pure Chemical Industries, Ltd., 77.7 mmol as sodium peroxodisulfate) was added dropwise over 60 minutes. After stirring for 16 hours at 35°C, the conversion of 3,4-ethylenedioxythiophene to PEDOT was 94%. The reaction solution was filtered under suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a black solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 38.5 g of black conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 210 parts by weight of cerium oxide per 100 parts by weight of PEDOT. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the particles contained 15.7 parts by weight of the dopant p-toluenesulfonic acid per 100 parts by weight of PEDOT. The resulting conductive particles had a conductivity of 26 S / cm.

[0059] [Example 5] 19.6 g of black conductive particles were obtained in the same manner as in Example 3, except that the aluminum oxide was changed to zirconium (IV) oxide particles (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average particle size of primary particles: 5 μm). The reaction conversion rate to PEDOT was 98%, and it was calculated that the zirconium oxide content was 102 parts by weight per 100 parts by weight of PEDOT. Elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the dopant 2-naphthalenesulfonic acid was 12.6 parts by weight per 100 parts by weight of PEDOT. The resulting conductive particles had a conductivity of 42 S / cm.

[0060] [Example 6] A 1000 ml three-neck flask was charged with 300 g of an aqueous solution of 2-naphthalenesulfonic acid (10 wt %, molecular weight 208, 144 mmol as 2-naphthalenesulfonic acid), 5.67 g (14.2 mmol) of ferric sulfate, and 80.0 g of titanium dioxide particles (average particle size of primary particles: 2 μm), and the mixture was bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes. The mixture was then stirred for a further 50 minutes under a nitrogen atmosphere, and the liquid temperature was maintained at 25°C. To this solution, 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene was added and stirred for an additional 10 minutes. To this solution, 185 g of an aqueous solution of sodium peroxodisulfate (77.7 mmol as sodium peroxodisulfate) adjusted to a concentration of 10 wt% was added dropwise over 60 minutes. After stirring for 6 hours, the conversion of 3,4-ethylenedioxythiophene to PEDOT was 100%. This reaction solution was filtered by suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 89.4 g of bluish-white conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 800 parts by weight of titanium dioxide per 100 parts by weight of PEDOT. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the particles contained 14.1 parts by weight of the dopant 2-naphthalenesulfonic acid per 100 parts by weight of PEDOT. The resulting conductive particles had a conductivity of 28 S / cm.

[0061] [Comparative Example 1] An example that does not contain a low molecular weight sulfonic acid group-containing compound will be given below. 3.84 g (14.2 mmol) of ferrous chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), 168 g of ion-exchanged water, and 30.0 g of silica gel particles (average particle size of primary particles: 2 μm) were added to a 1000 ml three-neck flask, and the mixture was bubbled with nitrogen at a flow rate of 1 L / min for 10 minutes. The mixture was then stirred for an additional 50 minutes under a nitrogen atmosphere, and the liquid temperature was maintained at 25°C. To this solution, 10.0 g (70.4 mmol) of distilled and purified 3,4-ethylenedioxythiophene was added and stirred for an additional 10 minutes. To this solution, 123 g of a 10 wt% potassium permanganate aqueous solution (Fujifilm Wako Pure Chemical Industries, Ltd., 77.8 mmol as potassium permanganate) was added dropwise over 60 minutes. After stirring for 3 hours, the conversion of 3,4-ethylenedioxythiophene to PEDOT was 100%. The reaction solution was filtered under suction using quantitative filter paper (Advantec, No. 5C quantitative filter paper) to obtain a black solid. The solid was washed with ion-exchanged water and dried using a vacuum dryer until the loss on drying was 1% or less, yielding 37.8 g of black conductive particles. Based on the ratio of raw materials used in the reaction and the reaction conversion rate, it was calculated that these conductive particles contained 100 parts by weight of PEDOT and 300 parts by weight of silica gel. Furthermore, elemental analysis of sulfur using X-ray photoelectron spectroscopy did not detect any sulfur components other than polythiophene. The resulting conductive particles had a conductivity of 0.9 S / cm.

[0062] Comparative Example 2 An example that does not contain metal oxide particles will be given. The reaction was carried out in the same manner as in Example 1, except that silica gel was not used, to obtain 9.12 g of a black powder. However, because the filterability of the powder was poor, the number of washings was three times as many as in Example 1. Elemental analysis of sulfur using X-ray photoelectron spectroscopy revealed that the powder contained 4.7 parts by weight of sulfuric acid as a dopant for 100 parts by weight of PEDOT. The conductivity of this conductive powder was 6.2 S / cm.

[0063] [Table 1]

[0064] <Result> The conductive particles of the examples contained inorganic particles, and therefore, cleaning treatment during production was carried out efficiently, resulting in excellent conductivity.

Claims

1. Conductive particles comprising inorganic particles containing silicon dioxide or a metal oxide, a polythiophene-based conductive polymer, and a sulfonic acid group-containing compound having a molecular weight of less than 500.

2. The conductive particles according to claim 1 , wherein the sulfonic acid group-containing compound comprises sulfuric acid or an aromatic sulfonic acid compound.

3. The conductive particle according to claim 2, wherein the aromatic sulfonic acid compound comprises at least one selected from the group consisting of benzenesulfonic acid, toluenesulfonic acid, xylenesulfonic acid, benzenedisulfonic acid, naphthalenesulfonic acid, and naphthalenedisulfonic acid.

4. The conductive particles according to claim 1 , wherein the inorganic particles contain at least one selected from the group consisting of silica, alumina, titania, zirconia, and ceria.

5. The conductive particles according to claim 1 , wherein the polythiophene-based conductive polymer coats a part or the whole of the surface of the inorganic particles.

6. 2. The conductive particles according to claim 1, wherein the inorganic particles are contained in an amount of 10 to 1000 parts by weight per 100 parts by weight of the polythiophene-based conductive polymer.

7. 2. The conductive particle according to claim 1, wherein the polythiophene-based conductive polymer is poly(3,4-ethylenedioxythiophene).

8. 7. The conductive particles according to claim 6, wherein the inorganic particles have an average primary particle size of 1 to 500 μm as measured by image analysis using an electron microscope.

9. In a slurry containing inorganic particles containing silicon dioxide or a metal oxide, a sulfonic acid group-containing compound having a molecular weight of less than 500, a monomer for forming a polythiophene-based conductive polymer, and water, the monomer is polymerized to form the polythiophene-based conductive polymer doped with the sulfonic acid group-containing compound, and the resulting polymer is then filtered, a step of obtaining conductive particles in which the polythiophene-based conductive polymer and the sulfonic acid group-containing compound cover part or all of the surfaces of the inorganic particles, A method for producing conductive particles.

10. The method for producing conductive particles according to claim 9 , further comprising the step of suspending the conductive particles in a cleaning solution and filtering the same again to wash the conductive particles.

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