JP7696282B2 - Capacitor and manufacturing method thereof - Google Patents

Description

The present invention relates to a capacitor having a solid electrolyte layer containing a π-conjugated conductive polymer and a method for manufacturing the same.

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

JP 2020-100744 A

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, thereby reducing the equivalent series resistance (ESR) and improving the heat resistance. On the other hand, there is a demand for a capacitor with reduced equivalent series resistance without relying on the sulfide.
The present invention provides a capacitor with reduced equivalent series resistance and a method for manufacturing the same.

[1] 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 contains a conductive complex including a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid.
[2] The capacitor according to [1], wherein the alkylsulfonic acid is bound 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 the steps of applying a conductive polymer dispersion onto a surface of a dielectric layer formed on a surface of an anode made of a porous valve metal, and drying the applied conductive polymer dispersion to form a solid electrolyte layer, wherein the conductive polymer dispersion contains a conductive complex containing a π-conjugated conductive polymer and a polyanion, alkylsulfonic acid, and a dispersion medium for dispersing the conductive complex.
[10] The method for producing a capacitor according to [9], wherein the alkylsulfonic acid is bound to the π-conjugated conductive polymer and is contained in the conductive composite.

The capacitor of the present invention has a reduced equivalent series resistance due to the inclusion of a conductive complex containing a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid in the solid electrolyte layer. The capacitor can be easily manufactured by the method of manufacturing the capacitor of the present invention.

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

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

1 is a cross-sectional view showing an embodiment of a capacitor of the present invention.

Capacitor
A first aspect of the present invention is a capacitor. An example of an embodiment of the capacitor will be described. A capacitor 10 shown in Fig. 1 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 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 to the anode 11, with the dielectric layer 12 and the solid electrolyte layer 14 sandwiched therebetween.

Examples of the valve metal constituting the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Among these, aluminum, tantalum, and niobium are preferable.
Specific examples of the anode 11 include an aluminum foil that has been etched to increase its surface area and then oxidized, and a sintered body of tantalum particles or niobium particles that has been oxidized and formed into pellets. Such a treatment results in a porous body with irregularities formed on the surface.

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. As with the anode 11, the dielectric layer 12 also has projections and recesses.

In this embodiment, the cathode 13 can be a conductive layer formed from a conductive paste or a metal layer made of a conductive material, such as aluminum foil.

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 be constant or may not be constant, and may be, for example, 1 μm or more and 100 μm or less.

<Conductive composite>
The conductive complex contained in the solid electrolyte layer will be described. The conductive complex of this embodiment contains a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive complex is doped into the π-conjugated conductive polymer to form a conductive complex having electrical conductivity.
In the polyanion, only a part 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. Since the excess anionic groups are hydrophilic groups, the conductive composite has water dispersibility.

(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, polyphenylenevinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophenevinylene-based conductive polymers, and copolymers thereof. From the viewpoint of stability in air, polypyrrole-based conductive polymers, polythiophenes, and polyaniline-based conductive polymers are preferred, and from the viewpoint of transparency, polythiophene-based conductive polymers are more preferred.

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

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

The content of the polyanion in the conductive complex is preferably, for example, in the range of 1 part by mass to 1000 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, and the conductivity becomes higher. On the other hand, if the content of the polyanion is equal to or less than the upper limit, the π-conjugated conductive polymer can be sufficiently contained, so that sufficient conductivity can be ensured.

The content of the conductive complex relative 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. The above ranges are preferable because they make it easier for the equivalent series resistance of the capacitor to decrease.

<Alkyl sulfonic acid>
The alkylsulfonic acid contained in the solid electrolyte layer of this embodiment is a compound in which a linear or branched alkane is used as a skeleton, and at least one hydrogen atom bonded to the alkane is substituted with a sulfonic acid group. The alkylsulfonic acid is a compound other than the polyanion.
At least a part of the alkylsulfonic acid can be bonded to the π-conjugated conductive polymer as a dopant, similar to the polyanion. When it functions as a dopant, it is considered that the sulfonic acid group is doped as an anion group. It is more preferable to dope the alkylsulfonic acid from the viewpoint of reducing the ESR of the capacitor, 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 being doped.

The alkane skeleton preferably has 1 to 20 carbon atoms, more preferably 1 to 10 carbon atoms, further preferably 1 to 6 carbon atoms, and particularly preferably 1 to 4 carbon atoms.
When the number of carbon atoms is within the above preferred range, the alkylsulfonic acid can be easily doped into the π-conjugated conductive polymer, and as a result, the ESR of the capacitor can be further reduced.

The alkane skeleton is preferably linear. This makes it easier to dope the π-conjugated conductive polymer, resulting in a further reduction in the ESR of the capacitor.

Specific examples of suitable alkylsulfonic acids include 1-methanesulfonic acid, 1-ethanesulfonic acid, 1-propanesulfonic acid, and 1-butanesulfonic acid.

The solid electrolyte layer of this embodiment may contain one type of alkylsulfonic acid or two or more types of alkylsulfonic acids.
The total content of alkylsulfonic acid contained in the solid electrolyte layer of this embodiment 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, relative 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.

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

The basic compound functions as a Bronsted base that extracts protons from excess anion groups of the polyanion. To achieve this function, the amount of the basic compound used in the present invention that dissolves 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 of dissolution, but even if it is about 0.1 g, for example, the above function can be sufficiently achieved.

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, amines, etc.
Specific examples of the alkali metal hydroxide 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, and sodium carbonate.
Specific examples of the quaternary ammonium hydroxide or a salt thereof include tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.

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.

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, 1-cyanoethyl-2-ethyl-4-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole. Examples of the compound include 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine, and derivatives thereof such as alkyl-substituted products (e.g., those substituted with an alkyl group having 1 to 4 carbon atoms, such as methyl, ethyl, propyl, butyl, etc.), halogen-substituted products (e.g., those substituted with a halogen group, such as fluoro, chloro, bromine, etc.), and nitrile-substituted products.
Of these, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

The basic compound contained in the solid electrolyte layer may be one type or two or more types.
The content ratio of the basic compound in the solid electrolyte layer is, for example, preferably 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 even more preferably 10 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass of the conductive composite.
Within the above preferred range, the ESR of the capacitor can be further reduced.

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

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

The total content of the polyol compounds contained in the solid electrolyte layer is, for example, preferably 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, relative to 100 parts by mass in total of the π-conjugated conductive polymer and polyanion contained in the solid electrolyte layer (i.e., 100 parts by mass of the conductive composite).
The above range is preferable because it is easier to reduce the ESR of the capacitor.
The type of polyol compound contained in the solid electrolyte layer may be one type, or two or more types.

[Electrolyte]
The capacitor of this embodiment may have an electrolyte that impregnates the solid electrolyte layer.
Examples of the solvent constituting 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, 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 as anion components, 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.

The capacitor of this embodiment 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 or more and 1.0 g/cm ³ or less.
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.

<<Method of manufacturing a capacitor>>
A second aspect of the present invention is a method for producing a capacitor, comprising the steps 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 valve metal body, and drying the applied conductive polymer dispersion liquid to form a solid electrolyte layer. The method for producing the capacitor of the first aspect can be easily used.

The manufacturing method of this embodiment preferably includes a step of oxidizing the surface of an anode made of a porous valve metal to form a dielectric layer (dielectric formation step), a step of arranging a cathode in a position opposite the dielectric layer (cathode formation step), and a step of forming a solid electrolyte layer on at least a portion of the surface of the dielectric layer (film formation step). Each step will be described below with reference to FIG. 1.

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

[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.

[Film forming process]
In this step, a conductive polymer dispersion liquid, which will be described later, 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.

Methods for applying the conductive polymer dispersion include, for example, immersion (dip coating), comma coating, reverse coating, lip coating, and microgravure coating. Of these, a method in which the anode 11 is immersed in the conductive polymer dispersion under reduced pressure is preferred. With the immersion method, the conductive polymer dispersion can be applied sufficiently to the inside of the porous structure on the surface of the dielectric layer 12. After immersion, the anode is removed and the next drying process is performed.

Examples of the drying method include 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 drying, the capacitor can be assembled in the usual manner.

<Conductive polymer dispersion>
The conductive polymer dispersion used in the film formation step of this embodiment contains a conductive complex containing a π-conjugated conductive polymer and a polyanion, alkylsulfonic acid, and a dispersion medium for dispersing the conductive complex.

The conductive complex and alkylsulfonic acid contained in the conductive polymer dispersion liquid are similar to those in the first embodiment, and therefore will not be described again.
In the conductive polymer dispersion, the alkylsulfonic acid is preferably bound to the π-conjugated conductive polymer and contained in the conductive complex.
The conductive polymer dispersion may contain at least one of the basic compound and the polyol compound described in the first embodiment.

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

(Dispersion medium)
The dispersion medium constituting the conductive polymer dispersion liquid is not particularly limited as long as it is a liquid capable of dispersing the conductive complex, and examples thereof include water, an organic solvent, or a mixture of water and an organic solvent. The conductive complex has an excess of anionic groups derived from polyanions and has high dispersibility in water, so an aqueous dispersion medium is preferred. 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 dissolution 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 in the aqueous dispersion medium may be one type or two or more types.

The water content relative 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.

Examples of the alcohol solvent include methanol, ethanol, isopropanol, n-butanol, t-butanol, and allyl alcohol.
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, and diacetone alcohol.
Examples of the ester solvent include ethyl acetate, propyl acetate, and butyl acetate.

The total content of the π-conjugated conductive polymer and the polyanion (i.e., the content of the conductive complex) relative to the total mass of the conductive polymer dispersion is, for example, preferably 0.1 mass % or more and 10 mass % or less, more preferably 0.3 mass % or more and 5 mass % or less, and even more preferably 0.5 mass % or more and 2 mass % or less.
When the content is within the above preferred range, the dispersibility of the conductive composite in the conductive polymer dispersion can be further improved, while the ESR of the capacitor can be sufficiently reduced.

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 even more preferably 100 parts by mass or more and 500 parts by mass or less, relative 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.

The content of the basic compound contained in the conductive polymer dispersion is, for example, preferably 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 even more preferably 10 parts by mass or more and 50 parts by mass or less, relative to 100 parts by mass in total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive complex).
Within the above preferred range, the ESR of the capacitor can be further reduced.

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 even more preferably 2.0 to 3.0.
Within the above preferred range, the ESR of the capacitor can be further reduced.

The content of the polyol compound contained in the conductive polymer dispersion is, for example, preferably 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, relative to 100 parts by mass in total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive complex).
Within the above preferred range, the ESR of the capacitor can be further reduced.

The conductive polymer dispersion may contain any additive. The content ratio of the additive is appropriately determined depending on the type of additive, but can be, for example, 1 to 1,000 parts by mass with respect to 100 parts by mass in total of the π-conjugated conductive polymer and the polyanion (i.e., 100 parts by mass of the conductive complex).
Here, the optional additive is a compound other than the conductive complex, the alkylsulfonic acid, the basic compound, the polyol compound, and the dispersion medium.

Examples of the optional additives include a surfactant, an inorganic conductive agent, an antifoaming agent, a coupling agent, an antioxidant, and an ultraviolet absorbing agent.
The surfactant may be a nonionic, anionic or cationic surfactant, with the nonionic surfactant being preferred from the standpoint of storage stability. Polymer surfactants such as polyvinyl alcohol and polyvinylpyrrolidone may also be added.
Examples of the inorganic conductive agent include metal ions, conductive carbon, etc. Metal ions can be generated by dissolving a metal salt in water.
The antifoaming agent includes silicone resin, polydimethylsiloxane, silicone oil, and the like.
The coupling agent may be a silane coupling agent 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.

<Method of producing conductive polymer dispersion>
The conductive polymer dispersion is preferably produced by the following method: That is, the production method includes a step (polymerization step) of polymerizing a monomer that forms a π-conjugated conductive polymer in a reaction solution containing an alkylsulfonic acid, a polyanion, and a dispersion medium to obtain a conductive polymer dispersion containing a conductive complex containing the π-conjugated conductive polymer and the polyanion, and the alkylsulfonic acid and the dispersion medium.

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

The dispersion medium contained in the reaction liquid is preferably an aqueous dispersion medium, and more preferably water.
When the dispersion medium contains water, the polymerization reaction of the monomers proceeds stably, and the resulting conductive composite is obtained in a state where it is stably dispersed in the dispersion medium.

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

The content of the alkylsulfonic acid relative to the total mass of the reaction liquid is, for example, preferably 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 the content is within the above preferred range, it becomes easy to adjust the content ratio of the conductive complex and the alkylsulfonic acid in the target conductive polymer dispersion liquid to the above preferred range.

The content of the monomer relative to the total mass of the reaction liquid immediately before the start of the polymerization reaction is, for example, preferably 0.01 mass % or more and 5 mass % or less, more preferably 0.1 mass % or more and 2 mass % or less, and even more preferably 0.3 mass % or more and 1 mass % or less.
The content of the polyanion relative to the total mass of the reaction solution immediately before the start of the polymerization reaction is, for example, preferably 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 the content within the above preferred range, a conductive polymer dispersion having the conductive complex concentration in the above preferred content can be easily obtained.

From the viewpoint of making the content ratio of the π-conjugated conductive polymer and the polyanion in the conductive complex formed by the polymerization reaction the preferred ratio described above, the content ratio of the monomer and the polyanion contained in the reaction solution immediately before the start of the polymerization reaction is 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, per 100 parts by mass of the monomer.

The desired conductive polymer dispersion can be obtained by synthesizing a π-conjugated conductive polymer through chemical oxidative polymerization of the monomer.

The catalyst and oxidizing agent added to the reaction liquid are preferably removed from the conductive polymer dispersion after the chemical oxidative polymerization of the monomer.
Examples of the removal method include a method of contacting the conductive polymer dispersion with an ion exchange resin to adsorb the catalyst and oxidizing agent to the ion exchange resin, and a method of ultrafiltrating the conductive polymer dispersion to replace the dispersion medium and remove the catalyst and oxidizing agent. 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.

The conductive polymer dispersion used in the capacitor manufacturing method of this embodiment can also be obtained by other methods. For example, a method of adding an appropriate amount of alkylsulfonic acid to a dispersion of a conductive complex containing a commercially available π-conjugated conductive polymer and a polyanion can be mentioned. However, even if alkylsulfonic acid is added to a conductive complex that has already been completed, it may be difficult for the alkylsulfonic acid to bond to the π-conjugated conductive polymer.
On the other hand, when produced by the above-mentioned method, the alkylsulfonic acid is present during the chemical oxidative polymerization of the π-conjugated conductive polymer, and the alkylsulfonic acid is easily bonded 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 reliably obtained.

A basic compound, a polyol compound, any additives, etc. can be further added to the conductive polymer dispersion obtained above.

(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., 1.14 g of an oxidizing agent solution of ammonium persulfate previously dissolved in 10 ml of water was added dropwise over 20 minutes, and the solution was stirred for 12 hours.
1000ml of sulfuric acid diluted to 10% by mass was added to the obtained sodium polystyrene sulfonate-containing solution, and about 1000ml of the solvent was removed from the obtained polystyrene sulfonic acid-containing solution by ultrafiltration. Next, 2000ml of ion-exchanged water was added to the remaining liquid, and about 2000ml of the solvent was removed by ultrafiltration to wash the polystyrene sulfonic acid with water. This water washing operation was repeated three times.
Water in the resulting solution was removed under reduced pressure to obtain colorless solid polystyrene sulfonic acid.

(Production Example 2) Preparation of Capacitor Element An anode lead terminal was connected to an etched aluminum foil (anode foil), and then a voltage of 130 V was applied in a 10 mass % aqueous solution of ammonium adipate to perform chemical conversion (oxidation treatment). A dielectric layer was formed on both sides of the aluminum foil, thereby obtaining an anode foil.
Next, opposing aluminum cathode foils with cathode lead terminals welded thereto were laminated on both sides of the anode foil via a cellulose separator, and the resultant was rolled up into a cylindrical shape to obtain a capacitor element.

Example 1
A solution of 0.5 g of 3,4-ethylenedioxythiophene and 1.5 g of polystyrenesulfonic acid dissolved 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.
The resulting mixed solution was kept at 20° C., and while stirring, a catalyst solution prepared by dissolving 0.03 g of ferric sulfate in 4.97 g of ion-exchanged water and an oxidant solution prepared by dissolving 1.1 g of ammonium persulfate in 8.9 g of ion-exchanged water were slowly added, and the resulting reaction solution was stirred for 24 hours to cause a reaction.
By the above reaction, a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene) and polystyrenesulfonic acid, which are π-conjugated conductive polymers, and a conductive polymer dispersion containing methanesulfonic acid bonded to the π-conjugated conductive polymer and water as a dispersion medium were obtained.
To this conductive polymer dispersion, 13.2 g of Duolite C255LFH (a cation exchange resin manufactured by Sumika Chemtex Corporation) and 13.2 g of Duolite A368S (anion exchange resin manufactured by Sumika Chemtex Corporation) were added, and the ion exchange resin was removed by filtration, thereby obtaining a conductive polymer dispersion from which the oxidant and the catalyst had been removed.

Next, water was distilled off under reduced pressure from the obtained conductive polymer dispersion using an evaporator to adjust the solid content to 1.6 mass%. Imidazole was added to 100 g of the obtained conductive polymer dispersion to adjust the pH to 2.5, and 8 g of diethylene glycol was added to adjust the solid content to 1.635 mass%. The mass of the solid content (non-volatile components) and pH of the obtained conductive polymer dispersion were measured, and the results are shown in Table 1.
Next, the capacitor element obtained in Production Example 2 was immersed in the above-mentioned conductive polymer dispersion liquid under reduced pressure, and then dried for 30 minutes with 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-mentioned solid electrolyte layer formed thereon was loaded into an aluminum case, and the case was sealed with a sealing rubber to prepare a capacitor.

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

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

Example 4
A conductive polymer dispersion was obtained and a capacitor was produced in the same manner as in Example 1, except that 5 g of an aqueous solution of ethanesulfonic acid (concentration: 10% by mass) was added instead of 5 g of the aqueous solution of methanesulfonic acid (concentration: 10% by mass).
The conductive polymer dispersion thus obtained contained PEDOT-PSS and ethanesulfonic acid bonded to PEDOT. The solid content and pH of the conductive polymer dispersion thus obtained were measured, and the results are shown in Table 1.

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

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

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

(Comparative Example 2)
A conductive polymer dispersion was obtained and a capacitor was produced 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 an aqueous methanesulfonic acid solution (concentration: 10% by mass).

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

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

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

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

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

(Comparative Example 8)
The reaction was carried out in the same manner as in Example 3 except that polystyrene sulfonic acid was not added. However, a blue solid which was thought to be a π-conjugated conductive polymer (PEDOT) precipitated, and the blue solid was entirely filtered off together with the ion exchange resin, and therefore the reaction was discontinued.

(Comparative Example 9)
The reaction was carried out in the same manner as in Example 6, except that polystyrene sulfonic acid was not added. However, a blue solid which was thought to be a π-conjugated conductive polymer (PEDOT) precipitated, and the blue solid was entirely filtered off together with the ion exchange resin, and therefore the reaction was discontinued.

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

<Evaluation>
[Capacitance/Equivalent Series Resistance]
The capacitance (C) at 120 Hz and the equivalent series resistance (ESR) at 100 kHz of each capacitor were measured using an LCR meter ZM2376 (manufactured by NF Corporation). The measurement results are shown in Table 1.

The capacitors of each example having a conductive complex bonded with alkylsulfonic acid had a capacitance equal to or greater than that of the comparative example capacitor, and the equivalent series resistance was significantly reduced.

10 Capacitor 11 Anode 12 Dielectric layer 13 Cathode 14 Solid electrolyte layer

Claims (10)

The present invention relates to a valve metal porous body, and a cathode made of a conductive material and provided on the dielectric layer opposite to the anode.
the solid electrolyte layer contains a conductive complex including a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid;
A capacitor , wherein the content of the alkylsulfonic acid 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 . 2. The capacitor according to claim 1, wherein a content ratio of the polyanion in the conductive complex 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 or 2 , wherein the alkylsulfonic acid is bound to the π-conjugated conductive polymer and is contained in the conductive composite. The capacitor according to claim 1 , wherein the alkylsulfonic acid is methanesulfonic acid or ethanesulfonic acid. The capacitor according to claim 1 , wherein the solid electrolyte layer further contains a basic compound. The capacitor according to any one of claims 1 to 5, wherein the solid electrolyte layer further contains a polyol compound containing two or more hydroxyl groups. The capacitor of claim 6, wherein the polyol compound is diethylene glycol. The capacitor according to any one of claims 1 to 7, wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene) or the polyanion is polystyrenesulfonic acid. 1. A method for manufacturing a capacitor, comprising the steps of: applying a conductive polymer dispersion onto a surface of a dielectric layer formed on a surface of an anode made of a porous valve metal; and drying the applied conductive polymer dispersion to form a solid electrolyte layer,
The conductive polymer dispersion includes a conductive complex containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium for dispersing the conductive complex,
A method for producing a capacitor , wherein a content of the alkylsulfonic acid contained in the conductive polymer dispersion 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 . The method for producing a capacitor according to claim 9, wherein the alkylsulfonic acid is bound to the π-conjugated conductive polymer and is contained in the conductive composite.

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