Capacitor and method for manufacturing the same

Abstract

To provide a capacitor with reduced equivalent series resistance and a method for manufacturing the same.SOLUTION: A capacitor (10) includes: an anode (11) made of a porous body of a valve metal; a dielectric layer (12) made of an oxide of the valve metal; a cathode (13) made of a conductive material provided on a side opposite to the anode of the dielectric layer; and a solid electrolyte layer (14) formed between the dielectric layer and the cathode. The solid electrolyte layer includes a conductive composite including a π-conjugated conductive polymer and a polyanion, and alkylsulfonic acid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a capacitor provided with a solid electrolyte layer containing a π-conjugated conductive polymer and a method for manufacturing the same.

Background Art

[0002] A capacitor is known in which a solid electrolyte layer containing a conductive composite containing a π-conjugated conductive polymer and a polyanion is disposed between a dielectric layer and a cathode (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The solid electrolyte layer of the capacitor of Patent Document 1 contains a sulfide represented by a specific chemical formula in addition to the conductive composite, so that the equivalent series resistance (ESR) is reduced and the heat resistance is also improved. On the other hand, there may be a demand for a capacitor in which the equivalent series resistance is reduced regardless of the above sulfide. The present invention provides a capacitor with reduced equivalent series resistance and a method for manufacturing the same.

Means for Solving the Problems

[0005] [1] A capacitor comprising an anode made of a porous body of valve metal, a dielectric layer made of an oxide of the valve metal, a cathode made of a conductive material provided on the opposite side of the dielectric layer from the anode, and a solid electrolyte layer formed between the dielectric layer and the cathode, wherein the solid electrolyte layer contains a conductive composite containing a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid. [2] The capacitor according to [1], wherein the alkylsulfonic acid is bonded to the π-conjugated conductive polymer and is contained in the conductive composite. [3] The capacitor according to [1] or [2], wherein the alkylsulfonic acid is methanesulfonic acid or ethanesulfonic acid. [4] The capacitor according to any one of [1] to [3], wherein the solid electrolyte layer further contains a basic compound. [5] The capacitor according to [4], wherein the basic compound is a nitrogen-containing aromatic compound. [6] The capacitor according to any one of [1] to [5], wherein the solid electrolyte layer further contains a polyol compound containing two or more hydroxyl groups. [7] The capacitor according to [6], wherein the polyol compound is diethylene glycol. [8] The capacitor according to any one of [1] to [7], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) or the polyanion is polystyrenesulfonic acid. [9] A method for manufacturing a capacitor, comprising a step of applying a conductive polymer dispersion liquid onto the surface of a dielectric layer formed on the surface of an anode made of a porous body of valve metal and drying to form a solid electrolyte layer, wherein the conductive polymer dispersion liquid includes a conductive composite containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium for dispersing the conductive composite.

[10] The method for manufacturing a capacitor according to [9], wherein the alkylsulfonic acid is bonded to the π-conjugated conductive polymer and is contained in the conductive composite. [Effects of the Invention]

[0006] In the capacitor of the present invention, the equivalent series resistance is reduced because the solid electrolyte layer contains a conductive composite containing a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid. According to the method for manufacturing the capacitor of the present invention, the above capacitor can be easily manufactured.

[0007] The present invention is considered to contribute to SDGs Goal 12, "Responsibility for Production and Consumption."

[0008] In this specification and the claims, the lower and upper limit values of the numerical range indicated by "~" are included in the numerical range.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] 《Capacitor》 The first aspect of the present invention is a capacitor. Examples of its embodiments will be described. The capacitor 10 shown in FIG. 1 includes an anode 11 made of a porous body of valve metal, a dielectric layer 12 made of an oxide of valve metal, a solid electrolyte layer 14 formed on the surface of the dielectric layer 12, and a cathode 13 provided on the outermost side. The cathode 13 is provided on the opposite side of the anode 11 with the dielectric layer 12 and the solid electrolyte layer 14 interposed therebetween.

[0011] Examples of the valve metal constituting the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, antimony, etc. Among these, aluminum, tantalum, and niobium are preferred. Specific examples of the anode 11 include those obtained by etching an aluminum foil to increase the surface area and then subjecting the surface to an oxidation treatment, and those obtained by subjecting the surface of a sintered body of tantalum particles or niobium particles to an oxidation treatment to form pellets. Those treated in this way become a porous body with unevenness formed on the surface.

[0012] The dielectric layer 12 in the present embodiment is a layer formed by oxidizing the surface of the anode 11, and is formed, for example, by anodizing the surface of the metal anode 11 in an electrolytic solution such as an ammonium adipate aqueous solution. Like the anode 11, the dielectric layer 12 also has unevenness formed on its surface.

[0013] As the cathode 13 in the present embodiment, a metal layer made of a conductive material such as a conductive layer formed from a conductive paste or an aluminum foil can be used.

[0014] The solid electrolyte layer 14 in the present embodiment is formed on the surface of the dielectric layer 12. The solid electrolyte layer 14 covers at least a part 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 be constant or not constant, and for example, a thickness of 1 μm or more and 100 μm or less can be mentioned.

[0015] <Conductive composite> The conductive composite contained in the solid electrolyte layer will be described. The conductive composite of the present aspect contains a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive composite dopes the π-conjugated conductive polymer to form a conductive composite having conductivity. In the polyanion, only some of the anion groups are doped into the π-conjugated conductive polymer, and it has surplus anion groups that do not participate in the doping. Since the surplus anion groups are hydrophilic groups, the conductive composite has water dispersibility.

[0016] (π-conjugated conductive polymer) The π-conjugated conductive polymer may be an organic polymer whose main chain is composed of a π-conjugated system. For example, 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 can be mentioned. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferable, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferable.

[0017] 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-hydroxy-thiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene), poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), poly(3-octadecyloxythiophene), poly(3,4-dihydroxy-thiophene), 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-didodecyloxythiophene), 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), 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 π-conjugated conductive polymer contained in the conductive composite may be one type or two or more types.

[0018] (Polyanion) A polyanion is a polymer having two or more monomer units having an anion group in the molecule. The anion group of this polyanion functions as a dopant for the π-conjugated conductive polymer and improves the conductivity of the π-conjugated conductive polymer. The anion group of the polyanion is preferably a sulfo group or a carboxy group. Specific examples of such polyanions include polystyrene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyacrylic acid esters having a sulfo group, polymethacrylic acid esters having a sulfo group (for example, poly(4-sulfobutyl methacrylate), polysulfoethyl methacrylate, polymethacryloyloxybenzene sulfonic acid), polymers having a sulfo group such as poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, etc., and polymers having a carboxy group such as polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropane carboxylic acid), polyisoprene carboxylic acid, etc. The polyanion may be a homopolymer obtained by polymerizing a single monomer, or may be a copolymer obtained by polymerizing two or more monomers. Among these polyanions, polymers having a sulfo group are preferred and polystyrene sulfonic acid is more preferred because the conductivity can be made higher. The polyanion may be used alone or in combination of two or more. The mass average molecular weight of the polyanion is preferably 20,000 or more and 1,000,000 or less, and more preferably 100,000 or more and 500,000 or less. The mass average molecular weight is the average molecular weight on a mass basis measured using gel permeation chromatography and determined in terms of pullulan.

[0019] The content ratio of the polyanion in the conductive composite is preferably in the range of, for example, 1 part by mass or more and 1000 parts by mass or less, more preferably 10 parts by mass or more and 700 parts by mass or less, and even more preferably 100 parts by mass or more and 500 parts by mass or less, based on 100 parts by mass of the π-conjugated conductive polymer. If the content ratio of the polyanion is at least the above lower limit value, the doping effect on the π-conjugated conductive polymer tends to be stronger and the conductivity becomes higher. On the other hand, if the content of the polyanion is at most the above upper limit value, the π-conjugated conductive polymer can be sufficiently contained, so that sufficient conductivity can be ensured.

[0020] The content of the conductive composite with respect to the total mass of the solid electrolyte layer is preferably 1% by mass or more and 99% by mass or less, more preferably 50% by mass or more and 98% by mass or less, and even more preferably 70% by mass or more and 97% by mass or less. When it is within the above range, it is preferable because the equivalent series resistance of the capacitor is more likely to decrease.

[0021] <Alkyl sulfonic acid> The alkyl sulfonic acid contained in the solid electrolyte layer of this embodiment is a compound in which at least one of the hydrogen atoms bonded to the alkane is substituted with a sulfonic acid group, with a linear or branched alkane as the backbone. The alkyl sulfonic acid is a compound other than the above polyanion. At least a part of the alkyl sulfonic acid can be bonded as a dopant to the π-conjugated conductive polymer in the same manner as the polyanion. When functioning as a dopant, it is considered that the sulfonic acid group dopes as an anion group. It is more preferable from the viewpoint of reducing the ESR of the capacitor that the alkyl sulfonic acid dopes, but it is considered that the ESR of the capacitor can be reduced to some extent even if it is simply contained in the solid electrolyte layer as an additive without doping.

[0022] The number of carbon atoms in the alkane backbone is preferably 1 to 20, more preferably 1 to 10, even more preferably 1 to 6, and particularly preferably 1 to 4. When the number of carbon atoms is within the above preferable range, the alkyl sulfonic acid is more likely to dope the π-conjugated conductive polymer, and as a result, the ESR of the capacitor can be further reduced.

[0023] The alkane backbone is preferably linear. By being linear, doping to the π-conjugated conductive polymer becomes easier, and as a result, the ESR of the capacitor can be further reduced.

[0024] Preferable specific examples of the alkyl sulfonic acid include, for example, 1-methanesulfonic acid, 1-ethanesulfonic acid, 1-propanesulfonic acid, 1-butanesulfonic acid, and the like.

[0025] The alkylsulfonic acid contained in the solid electrolyte layer of this aspect may be one type or two or more types. The total content of the alkylsulfonic acid contained in the solid electrolyte layer of this aspect is preferably 10 parts by mass or more and 10,000 parts by mass or less, more preferably 50 parts by mass or more and 1,000 parts by mass or less, and even more preferably 100 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the π-conjugated system conductive polymer. When it is within the above-mentioned preferred range, the ESR of the capacitor can be further reduced.

[0026] <Basic compound> The solid electrolyte layer of this aspect may further contain a basic compound different from the conductive composite, the polyanion, and the alkylsulfonic acid. By containing a basic compound, the ESR of the capacitor can be further reduced.

[0027] The basic compound functions as a Bronsted base that extracts protons from the excess anion groups of the polyanion. In order to fulfill this function, the amount of the basic compound used in the present invention dissolved in water is preferably 0.001 g or more with respect to 100 g of water at 20°C. The upper limit value of the dissolution amount is not particularly limited, but for example, even if it is about 0.1 g, the above function can be sufficiently fulfilled.

[0028] As the basic compound, an organic or inorganic basic compound containing nitrogen, a hydroxide of an alkali metal or an alkaline earth metal, various carbonates and bicarbonates, etc. can be used. For example, hydroxides of alkali metals, quaternary ammonium hydroxides or their salts, ammonia, amines, etc. can be mentioned. Specific examples of the hydroxide of an alkali metal include potassium hydroxide, sodium hydroxide, etc. Specific examples of the carbonate or bicarbonate include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, etc. Specific examples of the quaternary ammonium hydroxide or its salt include tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and the like.

[0029] 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, trinaphthylamine, and the like.

[0030] Examples of the nitrogen-containing aromatic compound (aromatic compound in which at least one nitrogen atom forms a ring structure) include, for example, 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, 1-cyanoethyl-2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 1-acetylimidazole, 2-aminobenzimidazole, 2-amino-1-methylbenzimidazole, 2-hydroxybenzimidazole, 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine, and their alkyl-substituted products (for example, substituted products with alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, propyl, butyl, etc.), halogen-substituted products (for example, substituted products with halogen groups such as fluoro, chloro, bromo, etc.), and derivatives such as nitrile-substituted products. Among them, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

[0031] The basic compound contained in the solid electrolyte layer may be one kind or two or more kinds. The content ratio of the basic compound contained in the solid electrolyte layer is preferably, for example, 1 part by mass or more and 1000 parts by mass or less, more preferably 5 parts by mass or more and 100 parts by mass or less, and still more preferably 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the conductive composite. When it is within the above-mentioned preferred range, the ESR of the capacitor can be further reduced.

[0032] <Polyol compound> The solid electrolyte layer of this embodiment may further contain one or more compounds having two or more hydroxy groups (hereinafter sometimes referred to as polyol compounds), which are different from the conductive composite, the polyanion, the alkylsulfonic acid, and the basic compound. By containing a polyol compound, the ESR of the capacitor can be further reduced.

[0033] Examples of the polyol compound include one or more selected from ethylene glycol, diethylene glycol, propylene glycol, 1,4 - butanediol, glycerin, pentaerythritol, trimethylolpropane, and trimethylolethane.

[0034] The total content of the polyol compound contained in the solid electrolyte layer is preferably, for example, 100 parts by mass or more and 10000 parts by mass or less, more preferably 200 parts by mass or more and 2000 parts by mass or less, and still more preferably 300 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass in total of the π - conjugated conductive polymer and the polyanion contained in the solid electrolyte layer (that is, 100 parts by mass of the conductive composite). When it is within the above range, it is preferable because the ESR of the capacitor is more likely to decrease. The type of the polyol compound contained in the solid electrolyte layer may be one type or two or more types.

[0035] [Electrolyte solution] The capacitor of this embodiment may have an electrolyte solution that impregnates the solid electrolyte layer. Examples of the solvent constituting the electrolyte include alcohol solvents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, and glycerin; lactone solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone; sulfur solvents such as sulfolane, dimethyl sulfoxide, and dimethyl sulfone; amide solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide, and N-methylpyrrolidinone; nitrile solvents such as acetonitrile and 3-methoxypropionitrile; and water. Examples of the electrolyte constituting the electrolyte include decanedicarboxylic 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, 1,6-decanedicarboxylic acid, and 5,6-decanedicarboxylic acid; octanedicarboxylic acids such as 1,7-octanedicarboxylic acid; organic acids such as azelaic acid and sebacic acid; or boric acid, a polyhydric alcohol complex compound of boric acid obtained from boric acid and a polyhydric alcohol; inorganic acids such as phosphoric acid, carbonic acid, and silicic acid, etc. as the anion component, 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 the cation component; and the like.

[0036] The capacitor of this aspect is not limited to the above configuration, and a separator may be provided between the dielectric layer and the cathode. Examples of the capacitor having a separator provided between the dielectric layer and the cathode include a wound capacitor. Examples of the separator include a sheet (including nonwoven fabric) made of, for example, cellulose, polyvinyl alcohol, polyester, polyethylene, polystyrene, polypropylene, polyimide, polyamide, polyvinylidene fluoride, etc., and a nonwoven fabric of glass fiber. The density of the separator is, for example, 0.1 g / cm 3 or more and 1.0 g / cm 3 or less. When providing a separator, a method of impregnating the separator with carbon paste or silver paste to form a cathode can also be applied.

[0037] 《Method for Manufacturing a Capacitor》 A second aspect of the present invention is a method for manufacturing a capacitor, which includes a step of applying a conductive polymer dispersion liquid described below to the surface of a dielectric layer formed on the surface of an anode made of a porous body of valve metal, and drying to form a solid electrolyte layer. By the manufacturing method of this aspect, the capacitor of the first aspect can be easily manufactured.

[0038] The manufacturing method of this aspect preferably includes a step of oxidizing the surface of an anode 11 made of a porous body of valve metal to form a dielectric layer (dielectric formation step), a step of arranging a cathode at a position facing the dielectric layer (cathode formation step), and a step of forming a solid electrolyte layer on at least a part of the surface of the dielectric layer (film formation step). Hereinafter, each step will be described with reference to FIG. 1.

[0039] [Dielectric Formation Step] In this step, the surface of the anode 11 made of a porous body of valve metal is oxidized to form a dielectric layer 12. The method for forming the dielectric layer 12 is not particularly limited, and examples thereof include a method of anodizing the surface of the anode 11 in an electrolytic solution for forming treatment such as an ammonium adipate aqueous solution, an ammonium borate aqueous solution, or an ammonium phosphate aqueous solution.

[0040] [Cathode Formation Step] In this project, the cathode 13 is arranged at a position facing the dielectric layer 12. The arrangement method of the cathode 13 is not particularly limited. For example, there are methods of forming the cathode 13 using a conductive paste such as carbon paste or silver paste, and methods of arranging a metal foil such as aluminum foil facing the dielectric layer 12, etc.

[0041] [Film Formation Process] In this process, a solid electrolyte layer 14 is formed by applying a conductive polymer dispersion liquid described later to at least a part of the surface of the dielectric layer 12 and drying it.

[0042] As the application method of the conductive polymer dispersion liquid, for example, dipping (dip coating), comma coating, reverse coating, lip coating, microgravure coating, etc. can be applied. Among these, the method of dipping the anode 11 into the conductive polymer dispersion liquid under reduced pressure is preferable. In the case of the dipping method, the conductive polymer dispersion liquid can be sufficiently applied to the inside of the porous structure on the surface of the dielectric layer 12. After dipping, it is taken out and the next drying treatment is carried out.

[0043] As the drying method, for example, room temperature drying, hot air drying, far-infrared drying, etc. can be mentioned. Among these, hot air drying is preferable. As the drying temperature, for example, 100 to 180 °C is preferable, and 120 to 150 °C is more preferable. As the drying time, for example, 0.2 to 1 hour is preferable. After the drying treatment, the capacitor may be assembled by a conventional method.

[0044] <Conductive Polymer Dispersion Liquid> The conductive polymer dispersion liquid used in the film formation process of this embodiment includes a conductive composite containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium for dispersing the conductive composite.

[0045] The description of the conductive composite and alkylsulfonic acid contained in the conductive polymer dispersion liquid is the same as that in the description of the first embodiment, so the overlapping description is omitted. In the conductive polymer dispersion, it is preferable that the alkylsulfonic acid is bonded to the π-conjugated conductive polymer and is contained in the conductive composite. The conductive polymer dispersion may contain at least one of the basic compound and the polyol compound described in the first aspect.

[0046] Each component (π-conjugated conductive polymer, polyanion, alkylsulfonic acid, basic compound, polyol compound) that can be contained in the conductive polymer dispersion may be of one type or two or more types.

[0047] (Dispersion medium) The dispersion medium constituting the conductive polymer dispersion is not particularly limited as long as it is a liquid capable of dispersing the conductive composite. Examples include water, an organic solvent, or a mixture of water and an organic solvent. Since the conductive composite has an excess anion group derived from the polyanion and has high dispersibility in water, an aqueous dispersion medium is preferable. Here, the aqueous dispersion medium is water or a mixture of water and a water-soluble organic solvent. The water-soluble organic solvent is an organic solvent having a solubility of 1 g or more in 100 g of water at 20°C, and examples include alcohol solvents, ketone solvents, and ester solvents. The water-soluble organic solvent contained in the aqueous dispersion medium may be of one type or two or more types.

[0048] The water content with respect to the total mass of the aqueous dispersion medium is 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and may be 100% by mass.

[0049] Examples of the alcohol solvent include methanol, ethanol, isopropanol, n-butanol, t-butanol, allyl alcohol, and the like. Examples of the ketone solvent include diethyl ketone, methyl propyl ketone, methyl butyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, methyl amyl ketone, diisopropyl ketone, methyl ethyl ketone, acetone, diacetone alcohol, and the like. Examples of the ester solvents include ethyl acetate, propyl acetate, butyl acetate and the like.

[0050] The total content of the π-conjugated conductive polymer and the polyanion (i.e., the content of the conductive composite) relative to the total mass of the conductive polymer dispersion is preferably, for example, 0.1% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less, and still more preferably 0.5% by mass or more and 2% by mass or less. Within the above preferred range, the dispersibility of the conductive composite in the conductive polymer dispersion can be further enhanced while sufficiently reducing the ESR of the capacitor.

[0051] The content of the alkylsulfonic acid contained in the conductive polymer dispersion is preferably 10 parts by mass or more and 10,000 parts by mass or less, more preferably 50 parts by mass or more and 1,000 parts by mass or less, and still more preferably 100 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the π-conjugated conductive polymer. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0052] The content of the basic compound contained in the conductive polymer dispersion is preferably, for example, 1 part by mass or more and 1,000 parts by mass or less, more preferably 5 parts by mass or more and 100 parts by mass or less, and still more preferably 10 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive composite). Within the above preferred range, the ESR of the capacitor can be further reduced.

[0053] The content of the basic compound contained in the conductive polymer dispersion is preferably such that the pH of the conductive polymer dispersion (25 °C) is 2.0 to 8.0, more preferably 2.0 to 5.0, and still more preferably 2.0 to 3.0. Within the above preferred range, the ESR of the capacitor can be further reduced.

[0054] The content of the polyol compound contained in the conductive polymer dispersion is preferably, for example, 100 parts by mass or more and 10,000 parts by mass or less, more preferably 200 parts by mass or more and 2,000 parts by mass or less, and even more preferably 300 parts by mass or more and 1,000 parts by mass or less, based on 100 parts by mass in total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive composite). When it is within the above-mentioned preferred range, the ESR of the capacitor can be further reduced.

[0055] The conductive polymer dispersion may contain an arbitrary additive, and the content ratio thereof can be appropriately determined according to the type of the additive. For example, it can be 1 to 1,000 parts by mass based on 100 parts by mass in total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive composite). Here, the arbitrary additive is a compound other than the conductive composite, the alkylsulfonic acid, the basic compound, the polyol compound, and the dispersion medium.

[0056] Examples of the arbitrary additive include a surfactant, an inorganic conductive agent, an antifoaming agent, a coupling agent, an antioxidant, an ultraviolet absorber, and the like. Examples of the surfactant include nonionic, anionic, and cationic surfactants, and nonionic surfactants are preferred from the viewpoint of storage stability. Also, polymer surfactants such as polyvinyl alcohol and polyvinylpyrrolidone may be added. Examples of the inorganic conductive agent include metal ions and conductive carbon. Metal ions can be generated by dissolving a metal salt in water. Examples of the antifoaming agent include silicone resin, polydimethylsiloxane, silicone oil, and the like. Examples of the coupling agent include silane coupling agents having a vinyl group, an amino group, an epoxy group, and the like. Examples of the antioxidant include phenolic antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, saccharides, and the like. 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, benzoate-based ultraviolet absorbers, and the like.

[0057] <Method for producing conductive polymer dispersion> The conductive polymer dispersion is preferably produced by the following method. That is, in a reaction solution containing an alkylsulfonic acid, a polyanion, and a dispersion medium, a monomer that forms a π-conjugated conductive polymer is polymerized to obtain a conductive polymer dispersion containing the π-conjugated conductive polymer and the polyanion, the alkylsulfonic acid, and the dispersion medium (polymerization step).

[0058] The synthesis of the conductive complex in the reaction solution can be carried out in the same manner as the synthesis of the conventional conductive complex except that the reaction solution contains an alkylsulfonic acid.

[0059] The dispersion medium contained in the reaction solution is preferably the aqueous dispersion medium, more preferably water. When the dispersion medium contains water, the polymerization reaction of the monomer proceeds stably, and the obtained conductive complex is obtained in a state of being stably dispersed in the dispersion medium.

[0060] The monomers can be polymerized by chemically oxidizing the monomers. Chemical oxidative polymerization can be carried out using known catalysts and oxidizing agents. Examples of the catalyst include transition metal compounds such as ferric chloride, ferrous sulfate, ferric nitrate, and cupric chloride. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate, and potassium persulfate.

[0061] The content of the alkylsulfonic acid relative to the total mass of the reaction solution is preferably, for example, 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 2% by mass or less, and even more preferably 0.3% by mass or more and 1% by mass or less. When within the above-mentioned preferred range, in the target conductive polymer dispersion liquid, it becomes easy to adjust the content ratio of the conductive complex and the alkylsulfonic acid to the above-mentioned preferred range.

[0062] The content of the monomer with respect to the total mass of the reaction liquid immediately before the start of the polymerization reaction is preferably, for example, 0.01% by mass or more and 5% by mass or less, more preferably 0.1% by mass or more and 2% by mass or less, and even more preferably 0.3% by mass or more and 1% by mass or less. The content of the polyanion with respect to the total mass of the reaction liquid immediately before the start of the polymerization reaction is preferably, for example, 0.02% by mass or more and 10% by mass or less, more preferably 0.3% by mass or more and 5% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less. By setting it within the above-mentioned preferred range, a conductive polymer dispersion liquid in which the concentration of the conductive complex is the above-mentioned preferred content can be easily obtained.

[0063] In the conductive complex formed by the polymerization reaction, from the viewpoint of making the content ratio of the π-conjugated conductive polymer and the polyanion the above-mentioned preferred ratio, the content ratio of the monomer and the polyanion contained in the reaction liquid immediately before the start of the polymerization reaction is preferably in the range of 1 part by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the monomer, more preferably in the range of 10 parts by mass or more and 700 parts by mass or less, and even more preferably in the range of 100 parts by mass or more and 500 parts by mass or less.

[0064] By synthesizing a π-conjugated conductive polymer by chemical oxidative polymerization of the monomer, the target conductive polymer dispersion liquid can be obtained.

[0065] It is preferable to remove the catalyst and the oxidant added to the reaction liquid from the conductive polymer dispersion liquid after the chemical oxidative polymerization of the monomer. As a method of removal, for example, there are a method of bringing the conductive polymer dispersion into contact with an ion exchange resin to adsorb the catalyst and the oxidizing agent onto the ion exchange resin, a method of removing the conductive polymer dispersion by ultrafiltration to replace and remove the dispersion medium, and the like. Among these, the method using an ion exchange resin is preferable because it is simple. It is preferable to use a cation exchange resin and an anion exchange resin in combination as the ion exchange resin.

[0066] The conductive polymer dispersion used in the method for manufacturing the capacitor of this embodiment can also be obtained by other methods. For example, there is a method of adding an appropriate amount of an alkylsulfonic acid to a dispersion of a commercially available conductive composite containing a π-conjugated conductive polymer and a polyanion. However, even when an alkylsulfonic acid is added in a state where the conductive composite has already been completed, the alkylsulfonic acid may be difficult to bind to the π-conjugated conductive polymer. On the other hand, when manufactured by the above method, since an alkylsulfonic acid is present during the chemical oxidative polymerization of the π-conjugated conductive polymer, the alkylsulfonic acid easily binds to the π-conjugated conductive polymer together with the polyanion. As a result, a conductive polymer dispersion capable of further reducing the ESR of the capacitor can be surely obtained.

[0067] A basic compound, a polyol compound, an arbitrary additive, etc. can be further added to the conductive polymer dispersion obtained above.

Example

[0068] (Production Example 1) Production of polystyrene sulfonic acid 206 g of sodium styrene sulfonate was dissolved in 1000 ml of ion-exchanged water, and while stirring at 80°C, a 1.14 g ammonium persulfate oxidizing agent solution previously dissolved in 10 ml of water was added dropwise over 20 minutes, and this solution was stirred for 12 hours. To the obtained sodium polystyrene sulfonate-containing solution, 1000 ml of sulfuric acid diluted to 10% by mass was added, and approximately 1000 ml of the solvent of the obtained polystyrene sulfonic acid-containing solution was removed by ultrafiltration. Next, 2000 ml of ion-exchanged water was added to the remaining liquid, and approximately 2000 ml of the solvent was removed by ultrafiltration to wash the polystyrene sulfonic acid with water. This water-washing operation was repeated three times. The water in the obtained solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid.

[0069] (Production Example 2) Preparation of an element for a capacitor After connecting an anode lead terminal to an etched aluminum foil (anode foil), a voltage of 130 V was applied in an aqueous solution of 10% by mass of ammonium adipate for formation (oxidation treatment) to form a dielectric layer on both sides of the aluminum foil to obtain an anode foil. Next, a counter aluminum cathode foil with a cathode lead terminal welded thereto was laminated on both sides of the anode foil via a separator made of cellulose, and this was wound into a cylindrical shape to obtain an element for a capacitor.

[0070] (Example 1) A solution prepared by dissolving 0.5 g of 3,4-ethylenedioxythiophene and 1.5 g of polystyrene sulfonic acid in 15.0 g of ion-exchanged water was mixed at 20°C. Next, 5 g of a 10% by mass aqueous solution of methanesulfonic acid and 84.5 g of ion-exchanged water were added. While maintaining the obtained mixed solution at 20°C and stirring, a catalyst solution prepared by dissolving 0.03 g of ferric sulfate in 4.97 g of ion-exchanged water and an oxidizing agent solution prepared by dissolving 1.1 g of ammonium persulfate in 8.9 g of ion-exchanged water were slowly added, and the obtained reaction solution was stirred for 24 hours to cause a reaction. By the above reaction, a conductive polymer dispersion containing a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene), which is a π-conjugated conductive polymer, and polystyrene sulfonic acid, methanesulfonic acid bonded to the π-conjugated conductive polymer, and water as a dispersion medium was obtained. To this conductive polymer dispersion, 13.2 g of Duolite C255LFH (manufactured by Sumika Chemtex Corporation, cation exchange resin) and 13.2 g of Duolite A368S (manufactured by Sumika Chemtex Corporation, anion exchange resin) were added, and the mixture was filtered to remove the ion exchange resin, obtaining a conductive polymer dispersion from which the oxidizing agent and the catalyst had been removed.

[0071] Next, water was distilled off under reduced pressure using an evaporator from the obtained conductive polymer dispersion to make the solid content 1.6 mass%. To 100 g of the obtained conductive polymer dispersion, imidazole was added to adjust the pH to 2.5, 8 g of diethylene glycol was added, and the solid content was made 1.635 mass%. Table 1 shows the results of measuring the mass and pH of the solid content (non-volatile component) of the obtained conductive polymer dispersion. Subsequently, the capacitor element obtained in Production Example 2 was immersed in the above conductive polymer dispersion under reduced pressure, and then dried for 30 minutes using a hot air dryer at 125 °C to form a solid electrolyte layer containing a conductive composite on the surface of the dielectric layer. Finally, the capacitor element having the above solid electrolyte layer formed thereon was loaded into an aluminum case and sealed with a sealing rubber to fabricate a capacitor.

[0072] (Example 2) A conductive polymer dispersion was obtained in the same manner as in Example 1 except that the addition amount of the methanesulfonic acid aqueous solution (concentration 10 mass%) was changed from 5 g to 10 g and the addition amount of ion-exchanged water was changed from 84.5 g to 79.5 g, and a capacitor was fabricated.

[0073] (Example 3) A conductive polymer dispersion was obtained in the same manner as in Example 1 except that the addition amount of the methanesulfonic acid aqueous solution (concentration 10 mass%) was changed from 5 g to 15 g and the addition amount of ion-exchanged water was changed from 84.5 g to 74.5 g, and a capacitor was fabricated.

[0074] (Example 4) Instead of adding 5 g of an aqueous methanesulfonic acid solution (concentration: 10% by mass), 5 g of an aqueous ethanesulfonic acid solution (concentration: 10% by mass) was added, and a conductive polymer dispersion was obtained in the same manner as in Example 1, and a capacitor was fabricated. The conductive polymer dispersion obtained here contains PEDOT-PSS and ethanesulfonic acid bonded to PEDOT. Table 1 shows the results of measuring the solid content and pH of the obtained conductive polymer dispersion.

[0075] (Example 5) A conductive polymer dispersion was obtained in the same manner as in Example 4, except that the addition amount of the aqueous ethanesulfonic acid solution (concentration: 10% by mass) was changed from 5 g to 10 g, and the addition amount of ion-exchanged water was changed from 84.5 g to 79.5 g, and a capacitor was fabricated.

[0076] (Example 6) A conductive polymer dispersion was obtained in the same manner as in Example 4, except that the addition amount of the aqueous ethanesulfonic acid solution (concentration: 10% by mass) was changed from 5 g to 15 g, and the addition amount of ion-exchanged water was changed from 84.5 g to 74.5 g, and a capacitor was fabricated.

[0077] (Comparative Example 1) A conductive polymer dispersion was obtained in the same manner as in Example 1, except that 5 g of the aqueous methanesulfonic acid solution was not added and the addition amount of ion-exchanged water was changed from 84.5 g to 89.5 g, and a capacitor was fabricated.

[0078] (Comparative Example 2) A conductive polymer dispersion was obtained in the same manner as in Example 1, except that 5 g of an aqueous sulfuric acid solution (concentration: 10% by mass) was added instead of 5 g of the aqueous methanesulfonic acid solution, and a capacitor was fabricated.

[0079] (Comparative Example 3) A conductive polymer dispersion was obtained in the same manner as in Comparative Example 2, except that the addition amount of the aqueous sulfuric acid solution (concentration: 10% by mass) was changed from 5 g to 10 g, and the addition amount of ion-exchanged water was changed from 84.5 g to 79.5 g, and a capacitor was fabricated.

[0080] (Comparative Example 4) A conductive polymer dispersion was obtained and a capacitor was fabricated in the same manner as in Comparative Example 2, except that the addition amount of the sulfuric acid aqueous solution (concentration: 10% by mass) was changed from 5 g to 15 g, and the addition amount of the ion-exchanged water was changed from 84.5 g to 74.5 g.

[0081] (Comparative Example 5) A conductive polymer dispersion was obtained and a capacitor was fabricated in the same manner as in Example 1, except that 5 g of an aqueous solution of p-toluenesulfonic acid (concentration: 10% by mass) was added instead of 5 g of the aqueous solution of methanesulfonic acid (concentration: 10% by mass).

[0082] (Comparative Example 6) A conductive polymer dispersion was obtained and a capacitor was fabricated in the same manner as in Comparative Example 5, except that the addition amount of the aqueous solution of p-toluenesulfonic acid (concentration: 10% by mass) was changed from 5 g to 10 g, and the addition amount of the ion-exchanged water was changed from 84.5 g to 79.5 g.

[0083] (Comparative Example 7) A conductive polymer dispersion was obtained and a capacitor was fabricated in the same manner as in Comparative Example 5, except that the addition amount of the aqueous solution of p-toluenesulfonic acid (concentration: 10% by mass) was changed from 5 g to 15 g, and the addition amount of the ion-exchanged water was changed from 84.5 g to 74.5 g.

[0084] (Comparative Example 8) The reaction was carried out in the same manner as in Example 3, except that polystyrene sulfonic acid was not added in Example 3. However, a blue solid considered to be a π-conjugated conductive polymer (PEDOT) precipitated, and all of the blue solid together with the ion-exchange resin was filtered off, so the reaction was terminated.

[0085] (Comparative Example 9) The reaction was carried out in the same manner as in Example 6, except that polystyrene sulfonic acid was not added in Example 6. However, a blue solid considered to be a π-conjugated conductive polymer (PEDOT) precipitated, and all of the blue solid together with the ion-exchange resin was filtered off, so the reaction was terminated.

[0086] [Measurement of pH] For the conductive polymer dispersions prepared in each example, the pH at 25°C was measured by a conventional method using a commercially available pH meter.

[0087] <Evaluation> [Capacitance · Equivalent Series Resistance] For the capacitors of each example, the capacitance (C) at 120 Hz and the equivalent series resistance (ESR) at 100 kHz were measured using an LCR meter ZM2376 (manufactured by NF Circuit Design Block Co., Ltd.). The measurement results are shown in Table 1.

[0088]

Table 1

[0089] The capacitors of each example having a conductive composite bonded with an alkylsulfonic acid had a capacitance equal to or greater than that of the capacitors of the comparative example, and the equivalent series resistance decreased significantly.

Explanation of Symbols

[0090] 10 Capacitor 11 Anode 12 Dielectric Layer 13 Cathode 14 Solid Electrolyte Layer

Claims

1. An anode made of a porous body of valve metal, a dielectric layer made of an oxide of the valve metal, a cathode made of a conductive material provided on the side opposite to the anode of the dielectric layer, and a solid electrolyte layer formed between the dielectric layer and the cathode, The solid electrolyte layer contains a conductive composite including a π-conjugated conductive polymer and a polyanion, and contains an alkylsulfonic acid, The content of the alkylsulfonic acid contained in the solid electrolyte layer is 50 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the π-conjugated conductive polymer, a capacitor.

2. The content ratio of the polyanion in the conductive composite is 100 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the π-conjugated conductive polymer, the capacitor according to Claim 1.

3. The alkylsulfonic acid is bonded to the π-conjugated conductive polymer and is contained in the conductive composite, the capacitor according to Claim 1 or 2.

4. The alkylsulfonic acid is methanesulfonic acid or ethanesulfonic acid, the capacitor according to any one of Claims 1 to 3.

5. The solid electrolyte layer further contains a basic compound, the capacitor according to any one of Claims 1 to 4.

6. The solid electrolyte layer further contains a polyol compound containing two or more hydroxyl groups, the capacitor according to any one of Claims 1 to 5.

7. The polyol compound is diethylene glycol, the capacitor according to Claim 6.

8. The π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrenesulfonic acid, the capacitor according to any one of Claims 1 to 7.

9. A method for manufacturing a capacitor, comprising a step of applying a conductive polymer dispersion liquid onto the surface of a dielectric layer formed on the surface of an anode made of a porous body of valve metal and drying the applied liquid to form a solid electrolyte layer. The conductive polymer dispersion liquid contains a conductive composite including a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium for dispersing the conductive composite. A method for manufacturing a capacitor, wherein the content of the alkylsulfonic acid contained in the conductive polymer dispersion liquid is 50 parts by mass or more and 1000 parts by mass or less with respect to 100 parts by mass of the π-conjugated conductive polymer.

10. The method for manufacturing a capacitor according to claim 9, wherein the alkylsulfonic acid is bonded to the π-conjugated conductive polymer and is contained in the conductive composite.

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