Conductive composite dispersion and capacitor

Abstract

A high-performance capacitor and a conductive composite dispersion suitable for producing the same are provided. [Solution] A conductive complex dispersion containing a conductive complex containing a π-conjugated conductive polymer and a polyanion, water, and a water-soluble compound, wherein the water-soluble compound is any one of the following (1) to (3): (1) one or two types of cyclodextrins, (2) two types of sugar alcohols having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule, and (3) one type of sugar alcohol having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule and one type of cyclodextrin.

Description

[Technical Field]

[0001] The present invention relates to a conductive composite dispersion containing a π-conjugated conductive polymer and a polyanion, and to a capacitor. [Background technology]

[0002] A π-conjugated conductive polymer whose main chain is composed of a π-conjugated system forms a conductive complex by doping with a polyanion having an anionic group, and becomes dispersible in water. A method for producing a capacitor has been disclosed (for example, Patent Document 1), in which a coating material made from a conductive composite dispersion liquid containing a conductive composite is applied to a dielectric layer provided on the surface of an anode made of a valve metal, the coating material is dried to form a solid electrolyte layer, and a cathode is placed opposite the solid electrolyte layer. According to this disclosure, the capacitor performance is improved by including a specific unsaturated aliphatic alcohol compound in the paint. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-071400 Summary of the Invention [Problem to be solved by the invention]

[0004] A capacitor with a solid electrolyte layer is required to have a low equivalent series resistance (ESR). In addition, it is desirable for the capacitor's ESR to change little before and after heating tests, assuming that the capacitor will be used in a high-temperature environment.

[0005] The present invention provides a high-performance capacitor and a conductive composite dispersion suitable for producing the same. [Means for solving the problem]

[0006] [1] A conductive composite dispersion comprising a conductive composite containing a π-conjugated conductive polymer and a polyanion, water, and a water-soluble compound, wherein the water-soluble compound contains any one of the following (1) to (3): (1) One or two types of cyclodextrin (2) Two types of sugar alcohols with 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule (3) A sugar alcohol having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule, and a cyclodextrin. [2] The conductive composite dispersion according to [1], which contains the water-soluble compound (1). [3] The conductive composite dispersion according to [1], which contains the water-soluble compound (2). [4] The conductive composite dispersion according to [1], which contains the water-soluble compound (3). [5] The conductive complex dispersion liquid according to any one of [1] to [4], wherein the sugar alcohol is sorbitol, mannitol, erythritol, myo-inositol, or pentaerythritol. [6] The conductive composite dispersion liquid according to any one of [1] to [5], wherein the content of the water relative to the total mass of the conductive composite dispersion liquid is 70 mass % or more and 99 mass % or less. [7] The conductive composite dispersion liquid according to any one of [1] to [6], further containing an organic solvent having a boiling point of 150° C. or higher at 1 atmosphere. [8] The conductive composite dispersion according to any one of [1] to [7], further comprising a neutralizing agent. [9] The conductive composite dispersion liquid according to any one of [1] to [8], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrenesulfonic acid, or the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) and the polyanion is polystyrenesulfonic acid.

[10] A capacitor comprising: an anode made of a porous body of a valve metal; a dielectric layer made of an oxide of the valve metal; a cathode made of a conductive material provided on the dielectric layer opposite the anode; and a solid electrolyte layer formed between the dielectric layer and the cathode, wherein the solid electrolyte layer is a cured product of the conductive composite dispersion liquid according to any one of [1] to [9]. [Effects of the Invention]

[0007] Since the conductive composite dispersion of the present invention contains a specific water-soluble compound, a capacitor having a solid electrolyte layer made of a cured product thereof has a low ESR and improved heat resistance.

[0008] This invention is believed to contribute to SDG Goal 12, "Responsible Consumption and Production."

[0009] In this specification and claims, the lower and upper limits of numerical ranges indicated with "to" are included in the numerical range. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view illustrating one embodiment of a capacitor. DETAILED DESCRIPTION OF THE INVENTION

[0011] <<Conductive composite dispersion>> The conductive composite dispersion liquid of the first aspect of the present invention is a conductive composite dispersion liquid containing a conductive composite containing a π-conjugated conductive polymer and a polyanion, water, and a water-soluble compound. The conductive composite dispersion liquid of the first embodiment contains any one of the following (1) to (3) as the water-soluble compound. (1) One or two types of cyclodextrin (2) Two types of sugar alcohols with 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule (3) A sugar alcohol having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule, and a cyclodextrin.

[0012] <Conductive composite> The conductive composite of this embodiment includes a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive composite is doped into the π-conjugated conductive polymer to form a conductive composite having electrical conductivity. In the polyanion, only a portion of the anionic groups is doped into the π-conjugated conductive polymer, and there are excess anionic groups that are not involved in the doping. Because the excess anionic groups are hydrophilic groups, the conductive composite has water dispersibility.

[0013] (π-conjugated conductive polymer) The π-conjugated conductive polymer may be an 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, polyphenylene vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene vinylene-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.

[0014] 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 preferred because of its excellent conductivity, transparency, and heat resistance. The conductive composite may contain one type of π-conjugated conductive polymer, or two or more types of polymers.

[0015] (polyanion) A polyanion is a polymer having two or more monomer units with an anionic group in the molecule. The anionic group of this polyanion functions as a dopant for a π-conjugated conductive polymer, improving the conductivity of the π-conjugated conductive polymer. The anionic group of the polyanion is preferably a sulfo group or a carboxy group. Specific examples of such polyanions include polymers having sulfo groups, such as polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having sulfo groups, polymethacrylic acid esters having sulfo groups (for example, poly(4-sulfobutyl methacrylate, polysulfoethyl methacrylate, polymethacryloyloxybenzenesulfonic acid), poly(2-acrylamido-2-methylpropanesulfonic acid), and polyisoprene sulfonic acid; and polymers having carboxy groups, 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 formed by polymerizing a single monomer, or a copolymer formed by polymerizing two or more types of monomers. Among these polyanions, polymers having sulfo groups are preferred, and polystyrene sulfonic acid is more preferred, since they can further increase the conductivity.

[0016] The weight average molecular weight Mw of the polyanion is not particularly limited, and is, for example, preferably from 10,000 to 1,000,000, more preferably from 50,000 to 800,000, and even more preferably from 100,000 to 600,000. When the weight average molecular weight Mw of the polyanion is within the above range, the viscosity of the conductive composite dispersion of this embodiment becomes appropriately low, and a capacitor with a low ESR can be easily produced. The weight average molecular weight Mw of the polyanion is measured by gel filtration chromatography and is the average molecular weight based on mass calculated as pullulan.

[0017] The content of the polyanion contained in the conductive composite dispersion of this embodiment is, for example, preferably in the range of 1 part by mass to 1,000 parts by mass, more preferably 10 parts by mass to 700 parts by mass, and even more preferably 100 parts by mass to 500 parts by mass, relative to 100 parts by mass of the π-conjugated conductive polymer. If the content of the polyanion is equal to or greater than the lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, if the content of the polyanion is equal to or less than the upper limit, a sufficient amount of the π-conjugated conductive polymer can be contained, thereby ensuring sufficient conductivity.

[0018] The content of the conductive complex in the conductive complex dispersion liquid of this embodiment is preferably 0.1 parts by mass or more and 3.0 parts by mass or less, more preferably 0.5 parts by mass or more and 2.5 parts by mass or less, still more preferably 1.0 parts by mass or more and 2.3 parts by mass or less, and most preferably 1.3 parts by mass or more and 2.0 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion) and water combined. When the content is at least as large as the lower limit of the above range, the conductivity of the cured product of the conductive composite dispersion is further increased. When the content is equal to or less than the upper limit of the above range, the dispersibility of the conductive composite is improved.

[0019] The content of the conductive complex (total content of the π-conjugated conductive polymer and the polyanion) relative to the total mass of the conductive complex dispersion of this embodiment is, for example, preferably 0.1 mass% or more and 3.0 mass% or less, more preferably 0.5 mass% or more and 2.5 mass% or less, and even more preferably 1.0 mass% or more and 2.0 mass% or less. When the content is at least as large as the lower limit of the above range, the conductivity of the cured product of the conductive composite dispersion is further increased. When the content is equal to or less than the upper limit of the above range, the dispersibility of the conductive composite is improved.

[0020] <Water-soluble compounds> The conductive composite dispersion of this embodiment contains any one of the following (1) to (3) as a water-soluble compound. (1) One or two types of cyclodextrin (2) Two types of sugar alcohols with 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule (3) A sugar alcohol having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule, and a cyclodextrin.

[0021] In a capacitor using the conductive composite dispersion liquid of this embodiment, the inclusion of the water-soluble compound makes it possible to reduce the ESR and also to reduce changes in the ESR due to heating.

[0022] When the sugar alcohols contain two types, a first sugar alcohol and a second sugar alcohol, the ratio of the two is not particularly limited, and for example, the mass ratio of first sugar alcohol:second sugar alcohol is preferably 9:1 to 1:9, and may also be 8:2 to 2:8, 7:3 to 3:7, 6:4 to 4:6, or 5:5.

[0023] The sugar alcohol preferably has 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the sugar alcohol molecule, and has an acyclic structure, and is more preferably one or more selected from pentaerythritol, sorbitol, mannitol, myo-inositol, and erythritol.

[0024] Cyclodextrin is a compound in which multiple D-glucose molecules are bonded via α-1,4 glycosidic bonds to form a cyclic structure. The number of glucose molecules constituting cyclodextrin is, for example, 5 to 8. Specific examples include α-, β-, and γ-cyclodextrin. One or more hydroxyl groups of cyclodextrin may be chemically modified. For example, the hydrogen atoms of the hydroxyl groups of cyclodextrin may be substituted with alkyl groups to form alkyl ether groups. Furthermore, one or more hydrogen atoms constituting the alkyl group may be substituted with hydroxyl groups. By including cyclodextrin in the conductive composite dispersion liquid of this embodiment, the rate at which the ESR of the solid electrolyte layer made of the cured product increases after heating compared to before heating (rate of change) can be reduced, thereby improving the heat resistance of the capacitor.

[0025] The total content of the water-soluble compounds in the conductive composite dispersion liquid of this embodiment is preferably 10 parts by mass or more and 3000 parts by mass or less, more preferably 100 parts by mass or more and 2000 parts by mass or less, even more preferably 200 parts by mass or more and 1000 parts by mass or less, and most preferably 300 parts by mass or more and 800 parts by mass or less, relative to 100 parts by mass of the conductive composite (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the conductivity of the solid electrolyte layer is increased, resulting in a further reduction in the ESR of the capacitor and an improvement in heat resistance.

[0026] The total content of the sugar alcohols in the conductive complex dispersion liquid of this embodiment is preferably 10 parts by mass or more and 3000 parts by mass or less, more preferably 100 parts by mass or more and 2000 parts by mass or less, and even more preferably 200 parts by mass or more and 1000 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the conductivity of the solid electrolyte layer is increased, resulting in a further reduction in the ESR of the capacitor and an improvement in heat resistance.

[0027] The total content of the cyclodextrin in the conductive composite dispersion liquid of this embodiment is preferably 10 parts by mass or more and 2000 parts by mass or less, more preferably 100 parts by mass or more and 1000 parts by mass or less, and even more preferably 200 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conductive composite (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the ESR can be prevented from increasing after heating, and the heat resistance of the capacitor can be improved.

[0028] <Dispersion medium> The dispersion medium contained in the conductive composite dispersion liquid is preferably an aqueous dispersion medium containing water because the conductive composite is hydrophilic. Alternatively, a dispersion medium other than water may be contained. The dispersion medium other than water is not particularly limited as long as it does not significantly impair the dispersibility of the conductive composite. Since the conductive composite has excess anionic groups derived from the polyanion and has high dispersibility in water, the dispersion medium other than water is preferably a water-soluble organic solvent. Here, 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. Note that the water-insoluble organic solvent is an organic solvent that dissolves in an amount of less than 1 g.

[0029] The water content relative to the total mass of the conductive composite dispersion is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more. It is also preferably 99% by mass or less. When the water content is equal to or greater than the lower limit, the dispersibility of the conductive composite contained in the conductive composite dispersion is improved, and the performance of a capacitor having a solid electrolyte layer formed from the conductive composite dispersion can be further improved. Furthermore, the conductivity of the conductive layer formed from the conductive composite dispersion can be further improved.

[0030] <Neutralizer> The conductive complex dispersion of this embodiment may further contain one or more neutralizing agents. When the polyanion has an acid group, the conductive complex dispersion tends to become strongly acidic, but this can be neutralized with a neutralizing agent. Examples of the neutralizing agent include basic compounds. The basic compound functions as a Bronsted base that accepts protons from excess anion groups of the polyanion. To fulfill this function, the amount of the basic compound dissolved in water is preferably 0.001 g or more per 100 g of water at 20° C. There is no particular upper limit to the amount dissolved, but even an amount of about 0.1 g can fully fulfill the above function.

[0031] Examples of the basic compound that can be used include organic or inorganic basic compounds containing nitrogen, hydroxides of alkali metals or Group 2 metals, various carbonates and hydrogen carbonates, etc. Examples include hydroxides of alkali metals, quaternary ammonium hydroxides or salts thereof, ammonia, and amines. Specific examples of alkali metal hydroxides include potassium hydroxide and sodium hydroxide. Specific examples of carbonates or hydrogen carbonates include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, and the like. Specific examples of quaternary ammonium hydroxides or salts thereof include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.

[0032] Examples of the amine include aliphatic tertiary amines and nitrogen-containing aromatic compounds. Examples of the aliphatic tertiary amine include triethanolamine, trimethylamine, triethylamine, tripropylamine, tributylamine, trihexylamine, trioctylamine, triphenylamine, tribenzylamine, and trinaphthylamine.

[0033] Examples of nitrogen-containing aromatic compounds (aromatic compounds in which at least one nitrogen atom forms a ring structure) include pyrrole, indole, imidazole, 2-methylimidazole, 2-propylimidazole, N-methylimidazole, N-propylimidazole, N-butylimidazole, 1-(2-hydroxyethyl)imidazole, 2-ethyl-4-methylimidazole, 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole, 1-cyanoethyl-2-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole. Examples of suitable hydroxybenzoates include benzotriazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, 2-aminobenzimidazole, 2-amino-1-methylbenzimidazole, 2-hydroxybenzimidazole, 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine, and derivatives thereof such as alkyl-substituted products thereof (e.g., products substituted with an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, or butyl), halogen-substituted products thereof (e.g., products substituted with a halogen group, such as fluoro, chloro, or bromine), and nitrile-substituted products. Of these, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

[0034] The content of the basic compound contained in the conductive complex dispersion is, for example, preferably 1 part by mass or more and 100 parts by mass or less, more preferably 5 parts by mass or more and 60 parts by mass or less, and even more preferably 10 parts by mass or more and 30 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the acidity of the conductive complex dispersion is weakened, the corrosiveness to the substrate is reduced, and the ESR of the capacitor can be further reduced.

[0035] The content of the basic compound contained in the conductive composite dispersion is preferably such that the pH of the conductive composite dispersion (25°C) is 2.0 to 8.0, more preferably 2.0 to 5.0, and even more preferably 2.0 to 3.0. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0036] <High boiling point solvent> The conductive composite dispersion of this embodiment may further contain one or more organic solvents (high boiling point solvents) having a boiling point of 150° C. or higher at 1 atmosphere (101,325 Pascals). The boiling point is preferably 250° C. or lower. The inclusion of a high boiling point solvent can provide effects such as improved conductivity of a cured product of the conductive composite dispersion.

[0037] Examples of high-boiling point solvents include water-soluble organic solvents and water-insoluble organic solvents, where the definitions of water-soluble organic solvents and water-insoluble organic solvents are the same as those described above.

[0038] Examples of high-boiling water-soluble organic solvents include alcohol-based solvents, ether-based solvents, ketone-based solvents, nitrogen-atom-containing solvents, and sulfur-atom-containing solvents. Examples of alcohol-based solvents include polyhydric alcohols such as ethylene glycol (boiling point 198°C), 1,2-propanediol (also known as propylene glycol, boiling point 188°C), 1,3-propanediol (boiling point 214°C), 1,2-butanediol (boiling point 194°C), 1,3-butanediol (boiling point 207°C), 1,4-butanediol (boiling point 228°C), dipropylene glycol (boiling point 232°C, mixture of isomers), and diethylene glycol (boiling point 245°C). Examples of ether solvents include diethylene glycol dimethyl ether (boiling point 162°C) and diethylene glycol diethyl ether (boiling point 188°C). Examples of ketone solvents include methyl amyl ketone (boiling point 151°C) and diacetone alcohol (boiling point 168°C). Examples of nitrogen atom-containing solvents include N-methylpyrrolidone (boiling point 202°C), N-methylacetamide (boiling point 206°C), dimethylacetamide (boiling point 165°C), and N,N-dimethylformamide (boiling point 153°C). An example of the sulfur atom-containing solvent is dimethyl sulfoxide (boiling point: 189° C.).

[0039] Examples of the high-boiling point water-insoluble organic solvent include hydrocarbon solvents, etc. Examples of the hydrocarbon solvent include aliphatic hydrocarbon solvents and aromatic hydrocarbon solvents. Examples of the aliphatic hydrocarbon solvent include nonane (boiling point 151° C.), decane (boiling point 174° C.), and dodecane (boiling point 216° C.). Examples of aromatic hydrocarbon solvents include propylbenzene (boiling point 159°C) and isopropylbenzene (boiling point 152°C).

[0040] Among the above examples, alcohol-based high-boiling point solvents are preferred because they provide a greater effect of improving conductivity. Among alcohol-based high-boiling point solvents, ethylene glycol (boiling point 198°C), 1,2-propanediol (boiling point 188°C), 1,3-propanediol (boiling point 214°C), diethylene glycol (boiling point 245°C), and dimethyl sulfoxide (boiling point 189°C) are preferred because of their excellent effects in improving conductivity, etc.

[0041] The content of the high-boiling point solvent contained in the conductive composite dispersion is, for example, preferably 10 parts by mass or more and 2000 parts by mass or less, more preferably 100 parts by mass or more and 1000 parts by mass or less, and even more preferably 400 parts by mass or more and 800 parts by mass or less, relative to 100 parts by mass of the conductive composite (total of the π-conjugated conductive polymer and the polyanion). Within the above range, the ESR of a capacitor having a solid electrolyte layer formed from the conductive composite dispersion can be further reduced, and the conductivity of the solid electrolyte layer formed from the conductive composite dispersion can be further increased.

[0042] The content of the high-boiling point solvent relative to the total mass of the conductive polymer-containing liquid of this embodiment is, for example, preferably 0.1 mass % or more and 20 mass % or less, more preferably 1.0 mass % or more and 18.0 mass % or less, even more preferably 3.0 mass % or more and 15.0 mass % or less, and most preferably 6.0 mass % or more and 12.0 mass % or less. When the content is at least the lower limit of the above range, the ESR and electrical conductivity can be further improved. When the content is equal to or less than the upper limit of the above range, an increase in viscosity of the conductive composite dispersion can be suppressed.

[0043] <Optional additives> The conductive composite dispersion may contain other optional additives. The content ratio of the additives is determined appropriately depending on the type of additive, but can be, for example, 1 to 1,000 parts by mass per 100 parts by mass of the π-conjugated conductive polymer and polyanion combined. Here, the optional additives are compounds other than the basic compound, high-boiling point solvent, sugar alcohol, cyclodextrin, and dispersion medium.

[0044] Examples of optional additives include surfactants, inorganic conductive agents, antifoaming agents, coupling agents, antioxidants, and ultraviolet absorbers. The surfactant may be a nonionic, anionic, or cationic surfactant, with the nonionic surfactant being preferred from the standpoint of storage stability. A polymer surfactant such as polyvinyl alcohol may also be added. Examples of inorganic conductive agents include metal ions, conductive carbon, etc. Metal ions can be generated by dissolving a metal salt in water. Examples of the antifoaming agent include silicone resin, polydimethylsiloxane, and silicone oil. Examples of the coupling agent include silane coupling agents having a vinyl group, an amino group, an epoxy group, or the like. Examples of the antioxidant include phenol-based antioxidants, amine-based antioxidants, phosphorus-based antioxidants, sulfur-based antioxidants, and sugars. Examples of the ultraviolet absorber include benzotriazole-based ultraviolet absorbers, benzophenone-based ultraviolet absorbers, salicylate-based ultraviolet absorbers, cyanoacrylate-based ultraviolet absorbers, oxanilide-based ultraviolet absorbers, hindered amine-based ultraviolet absorbers, and benzoate-based ultraviolet absorbers.

[0045] <Method for producing conductive composite dispersion> As a method for producing the conductive composite dispersion of the first aspect of the present invention, for example, a method of adding the water-soluble compound and, if necessary, a neutralizing agent and a high-boiling point solvent to an aqueous dispersion of a conductive composite can be mentioned. The blending of each component can be as desired, and it is preferable to blend them so that the blending ratio falls within the above-mentioned preferred range. The aqueous dispersion of the conductive complex may be obtained by chemically oxidatively polymerizing a monomer that forms a π-conjugated conductive polymer in an aqueous solution of polyanion by a known method, or a commercially available product may be used.

[0046] <Capacitor manufacturing method> A capacitor can be produced by a production method including a step of applying the conductive composite dispersion of the first embodiment to the surface of a dielectric layer formed on the surface of an anode made of a porous valve metal, and drying the applied conductive composite dispersion to form a solid electrolyte layer.

[0047] The method for manufacturing a capacitor preferably includes the steps of: oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric forming step), arranging a cathode in a position opposite to the dielectric layer (cathode forming step), and forming a solid electrolyte layer on at least a part of the surface of the dielectric layer (film forming step). Each step will be described below with reference to FIG.

[0048] [Dielectric formation process] In this step, the surface of anode 11 made of a porous valve metal is oxidized to form dielectric layer 12. The method for forming dielectric layer 12 is not particularly limited, and examples thereof include a method of anodizing the surface of anode 11 in a chemical conversion treatment electrolyte such as an aqueous solution of ammonium adipate, an aqueous solution of ammonium borate, or an aqueous solution of ammonium phosphate.

[0049] [Cathode formation process] In this step, the cathode 13 is disposed at a position facing the dielectric layer 12. The method for disposing the cathode 13 is not particularly limited, and examples thereof include a method of forming the cathode 13 using a conductive paste such as a carbon paste or a silver paste, and a method of disposing a metal foil such as an aluminum foil facing the dielectric layer 12.

[0050] [Film forming process] In this step, the conductive composite dispersion liquid is applied to at least a portion of the surface of the dielectric layer 12 and then dried to form the solid electrolyte layer 14.

[0051] Examples of methods that can be used to apply the conductive composite dispersion include immersion (dip coating), comma coating, reverse coating, lip coating, and microgravure coating. Among these, a method in which the anode 11 is immersed in the conductive composite dispersion under reduced pressure is preferred. The immersion method allows the conductive composite dispersion to be sufficiently applied even to the interior of the porous structure on the surface of the dielectric layer 12. After immersion, the anode is removed and then subjected to the next drying process.

[0052] Drying methods include, for example, room temperature drying, hot air drying, far infrared drying, etc. Among these, hot air drying is preferred. The drying temperature is, for example, preferably 100 to 180° C., more preferably 120 to 150° C. The drying time is, for example, preferably 0.2 to 1 hour. After the drying process, the capacitor can be assembled in the usual manner.

[0053] The composition of the components contained in the solid electrolyte layer 14 reflects the composition of the applied conductive composite dispersion liquid. The total content of the water-soluble compounds relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion) contained in the solid electrolyte layer 14 is preferably 10 parts by mass or more and 3000 parts by mass or less, more preferably 100 parts by mass or more and 2000 parts by mass or less, even more preferably 200 parts by mass or more and 1000 parts by mass or less, and most preferably 300 parts by mass or more and 800 parts by mass or less. Within the above preferred range, the conductivity of the solid electrolyte layer is increased, resulting in a further reduction in the ESR of the capacitor and an improvement in heat resistance.

[0054] The total content of the sugar alcohols relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion) contained in the solid electrolyte layer 14 is preferably 10 parts by mass or more and 3000 parts by mass or less, more preferably 100 parts by mass or more and 2000 parts by mass or less, and even more preferably 200 parts by mass or more and 1000 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the conductivity of the solid electrolyte layer is increased, resulting in a further reduction in the ESR of the capacitor and an improvement in heat resistance.

[0055] The total content of the cyclodextrins relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion) contained in the solid electrolyte layer 14 is preferably 10 parts by mass or more and 2000 parts by mass or less, more preferably 100 parts by mass or more and 1000 parts by mass or less, and even more preferably 200 parts by mass or more and 500 parts by mass or less, relative to 100 parts by mass of the conductive complex (total of the π-conjugated conductive polymer and the polyanion). Within the above preferred range, the ESR can be prevented from increasing after heating, and the heat resistance of the capacitor can be improved.

[0056] <Capacitor> The capacitor comprises an anode made of a porous body of a valve metal, a dielectric layer made of an oxide of the valve metal, a cathode made of a conductive material provided on the dielectric layer opposite the anode, and a solid electrolyte layer formed between the dielectric layer and the cathode, and the solid electrolyte layer contains a cured product of the conductive composite dispersion of the first aspect.

[0057] An example of an embodiment of the capacitor will be described with reference to Fig. 1. Capacitor 10 shown in Fig. 1 includes an anode 11 made of a porous valve metal, a dielectric layer 12 made of an oxide of the valve metal, a solid electrolyte layer 14 formed on the surface of dielectric layer 12, and a cathode 13 provided on the outermost side. Cathode 13 is provided on the opposite side of anode 11, with dielectric layer 12 and solid electrolyte layer 14 sandwiched therebetween.

[0058] Examples of valve metals that can be used to form the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Of these, aluminum, tantalum, and niobium are preferred. Specific examples of the anode 11 include an aluminum foil that has been etched to increase its surface area and then oxidized, and a tantalum or niobium particle sintered body whose surface has been oxidized and then pelletized. Such a processed body becomes a porous body with irregularities formed on the surface.

[0059] The dielectric layer 12 in this embodiment is a layer formed by oxidizing the surface of the anode 11, for example, by anodizing the surface of the metallic anode 11 in an electrolyte such as an aqueous solution of ammonium adipate. Similar to the anode 11, the dielectric layer 12 also has projections and recesses.

[0060] The cathode 13 in this embodiment may be a conductive layer formed from a conductive paste or a metal layer made of a conductive material such as aluminum foil.

[0061] The solid electrolyte layer 14 in this embodiment is formed on the surface of the dielectric layer 12. The solid electrolyte layer 14 covers at least a portion of the surface of the dielectric layer 12, and may cover the entire surface of the dielectric layer 12. The thickness of the solid electrolyte layer 14 may or may not be constant, and may be, for example, 1 μm or more and 100 μm or less.

[0062] [Electrolyte] The capacitor may have an electrolyte solution impregnating the solid electrolyte layer. Examples of the solvent that constitutes the electrolytic solution include alcohol-based solvents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, and glycerin; lactone-based solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; sulfur-based solvents such as sulfolane, dimethyl sulfoxide, and dimethyl sulfone; amide-based solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, and N-methylpyrrolidinone; nitrile-based solvents such as acetonitrile and 3-methoxypropionitrile; and water. Examples of the electrolyte constituting the electrolytic solution include organic acids such as adipic acid, glutaric acid, succinic acid, benzoic acid, isophthalic acid, phthalic acid, terephthalic acid, maleic acid, toluic acid, enanthic acid, malonic acid, formic acid, decanedicarboxylic acids such as 1,6-decanedicarboxylic acid and 5,6-decanedicarboxylic acid, octanedicarboxylic acids such as 1,7-octanedicarboxylic acid, azelaic acid, and sebacic acid; or boric acid, polyhydric alcohol complex compounds of boric acid obtained from boric acid and polyhydric alcohols; inorganic acids such as phosphoric acid, carbonic acid, and silicic acid; and primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, etc.), secondary amines (dimethylamine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo(5,4,0)-undecene-7, etc.), tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.), etc. as a cationic component;

[0063] The capacitor is not limited to the above configuration, and a separator may be provided between the dielectric layer and the cathode. An example of a capacitor having a separator provided between the dielectric layer and the cathode is a wound capacitor. Examples of the separator include sheets (including nonwoven fabrics) made of cellulose, polyvinyl alcohol, polyester, polyethylene, polystyrene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, etc., and nonwoven fabrics of glass fibers. The density of the separator is, for example, 0.1 g / cm 3 More than 1.0g / cm 3 The following are included: When a separator is provided, a method of forming a cathode by impregnating the separator with carbon paste or silver paste can also be applied. [Example]

[0064] (Production Example 1) 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, which had been dissolved in 10 ml of water in advance, was added dropwise over 20 minutes, and the solution was stirred for 12 hours. To the resulting sodium polystyrene sulfonate solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent from the resulting polystyrene sulfonic acid solution was removed by ultrafiltration. Next, 2000 ml of ion-exchanged water was added to the remaining solution, and approximately 2000 ml of the solvent was removed by ultrafiltration, and the polystyrene sulfonic acid was washed with water. This water washing procedure was repeated three times. Water in the resulting solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid (PSS).

[0065] (Production Example 2) Production of PEDOT-PSS aqueous dispersion 14.2 g of 3,4-ethylenedioxythiophene and a solution prepared by dissolving 36.7 g of polystyrene sulfonic acid in 2000 ml of ion-exchanged water were mixed at 20°C. The resulting mixed solution was kept at 20°C and, while stirring, an oxidation catalyst solution of 29.64 g of ammonium persulfate and 8.0 g of ferric sulfate dissolved in 200 ml of ion-exchanged water was slowly added, followed by stirring for 3 hours to allow the reaction to proceed. To the resulting reaction solution, 2000 ml of ion-exchanged water was added, and about 2000 ml of the solvent was removed by ultrafiltration. This procedure was repeated three times. Then, 200 ml of sulfuric acid diluted to 10% by mass and 2000 ml of ion-exchanged water were added to the obtained solution, and about 2000 ml of the solvent was removed by ultrafiltration. 2000 ml of ion-exchanged water was added to the remaining liquid, and about 2000 ml of the solution was removed by ultrafiltration. This procedure was repeated three times. 2000 ml of ion-exchanged water was added to the resulting solution, and approximately 2000 ml of solvent was removed by ultrafiltration. This procedure was repeated five times to obtain a 1.2% by weight polystyrene sulfonate-doped poly(3,4-ethylenedioxythiophene) (PEDOT-PSS aqueous dispersion). Further ultrafiltration yielded a 2% by weight PEDOT-PSS aqueous dispersion.

[0066] (Manufacturing Example 3) Preparation of capacitor element After connecting an anode lead terminal to the etched aluminum foil (anode foil), a voltage of 40 V was applied in a 10% by mass aqueous solution of ammonium adipate to perform chemical conversion (oxidation treatment), forming a dielectric layer on both sides of the aluminum foil to obtain an anode foil. Next, opposing aluminum cathode foils with cathode lead terminals welded thereto were laminated on both sides of the anode foil with a cellulose separator interposed therebetween, and the resultant was rolled up into a cylindrical shape to obtain a capacitor element.

[0067] Example 1 To 100 g of the PEDOT-PSS aqueous dispersion obtained in Production Example 2, 0.44 g of imidazole, 10 g of diethylene glycol, and 10 g of α-cyclodextrin were added and stirred for 30 minutes to obtain a conductive composite dispersion (hereinafter referred to as a coating composition). The pH of the coating composition was 2.5. Next, the capacitor element obtained in Production Example 3 was immersed in the coating composition under reduced pressure, and then dried in a hot air dryer at 125°C for 30 minutes, thereby forming a solid electrolyte layer containing a conductive composite on the surface of the dielectric layer, thereby obtaining a capacitor element. Finally, the capacitor element having the solid electrolyte layer formed thereon was placed in an aluminum case and sealed with a sealing rubber to prepare a capacitor.

[0068] Example 2 A capacitor was fabricated in the same manner as in Example 1, except that α-cyclodextrin was changed to hydroxypropyl-β-cyclodextrin.

[0069] Example 3 A capacitor was fabricated in the same manner as in Example 1, except that 10 g of α-cyclodextrin was replaced with 5 g of sorbitol and 5 g of mannitol.

[0070] Example 4 A capacitor was produced in the same manner as in Example 3, except that mannitol was changed to erythritol.

[0071] Example 5 A capacitor was produced in the same manner as in Example 3, except that mannitol was replaced with α-cyclodextrin.

[0072] Example 6 A capacitor was fabricated in the same manner as in Example 4, except that sorbitol was changed to mannitol.

[0073] Example 7 A capacitor was fabricated in the same manner as in Example 5, except that sorbitol was changed to erythritol.

[0074] Example 8 A capacitor was fabricated in the same manner as in Example 7, except that erythritol was changed to pentaerythritol.

[0075] Example 9 A capacitor was fabricated in the same manner as in Example 8, except that α-cyclodextrin was changed to hydroxypropyl-β-cyclodextrin.

[0076] Example 10 A capacitor was fabricated in the same manner as in Example 8, except that pentaerythritol was changed to myo-inositol.

[0077] Example 11 A capacitor was fabricated in the same manner as in Example 9, except that pentaerythritol was changed to myo-inositol.

[0078] Example 12 A capacitor was fabricated in the same manner as in Example 8, except that pentaerythritol was replaced with hydroxypropyl-β-cyclodextrin.

[0079] (Comparative Example 1) A capacitor was fabricated in the same manner as in Example 1, except that 10 g of α-cyclodextrin was replaced with 10 g of ion-exchanged water.

[0080] (Comparative Example 2) A capacitor was fabricated in the same manner as in Example 3, except that 5 g of sorbitol was changed to 10 g of sorbitol and no mannitol was added.

[0081] [pH measurement] The pH was measured at 25°C by a conventional method using a commercially available pH meter.

[0082] [Measurement of equivalent series resistance] For the capacitors fabricated using the conductive composite dispersions of each example, the equivalent series resistance (ESR) (unit: mΩ) at 100 kHz was measured using an LCR meter ZM2376 (NF Corporation). After measuring the initial ESR (before testing), the capacitors were placed in a temperature cycle tester (ETAC Corp., gas-phase thermal shock tester NT550A), and 100 cycles were performed, with one cycle consisting of 145°C for 10 minutes and then 0°C for 10 minutes. The ESR (after testing) was then measured again. The measurement results are shown in Table 1.

[0083] [Table 1]

[0084] From the above, since the conductive composite dispersion liquid prepared in the examples according to the present invention contains a specific water-soluble compound, the performance of the prepared capacitor is excellent. Since Examples 1, 2, and 12 contain one or two types of cyclodextrin, the ESR is lower than that of Comparative Examples 1 and 2, and the heat resistance is also improved. Since Examples 3, 4, and 6 contain two types of sugar alcohols, the ESR is reduced and the heat resistance is improved compared to Comparative Example 2, which contains only one type of sugar alcohol. Examples 5, 7 to 11 contain one type of sugar alcohol and one type of cyclodextrin, and therefore have a lower ESR and improved heat resistance than Comparative Example 2, which contains only one type of sugar alcohol. [Explanation of symbols]

[0085] 10 Capacitors 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims

1. A conductive complex dispersion liquid containing a conductive complex containing a π-conjugated conductive polymer and a polyanion, water, and a water-soluble compound, A conductive composite dispersion comprising, as the water-soluble compound, any one of the following (1) to (3): (1) One or two types of cyclodextrin (2) Two types of sugar alcohols with 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule. (3) One type of sugar alcohol having 4 to 7 carbon atoms and 3 to 7 hydroxyl groups in the molecule, and one type of cyclodextrin

2. The conductive composite dispersion according to claim 1 , wherein the water-soluble compound comprises (1).

3. The conductive composite dispersion according to claim 1 , wherein the water-soluble compound comprises (2).

4. The conductive composite dispersion according to claim 1 , wherein the water-soluble compound comprises (3).

5. 5. The conductive complex dispersion according to claim 3, wherein the sugar alcohol is sorbitol, mannitol, erythritol, myo-inositol, or pentaerythritol.

6. The conductive complex dispersion according to claim 1 , wherein the content of the water relative to the total mass of the conductive complex dispersion is 70% by mass or more and 99% by mass or less.

7. The conductive composite dispersion according to claim 6 , further comprising an organic solvent having a boiling point of 150° C. or higher at 1 atmosphere.

8. The conductive composite dispersion according to claim 7 , further comprising a neutralizing agent.

9. The π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrene sulfonic acid, or 2. The conductive composite dispersion according to claim 1, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) and the polyanion is polystyrenesulfonic acid.

10. a cathode made of a conductive material and provided on the dielectric layer opposite to the anode; and a solid electrolyte layer formed between the dielectric layer and the cathode. A capacitor, wherein the solid electrolyte layer is a cured product of the conductive composite dispersion liquid according to any one of claims 1 to 4.

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