JP2023077583A - Capacitor and method for manufacturing the same - Google Patents

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

A capacitor is known in which a solid electrolyte layer containing a conductive composite containing a π-conjugated conductive polymer and a polyanion is arranged 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 further 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, capacitors with reduced equivalent series resistance are sometimes desired regardless of the sulfide.
The present invention provides a capacitor with reduced equivalent series resistance and a manufacturing method thereof.

[1] An anode made of a porous material 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 side of the dielectric layer opposite to the anode, and a dielectric layer and a solid electrolyte layer formed between the cathode, wherein the solid electrolyte layer contains a conductive complex containing a π-conjugated conductive polymer and a polyanion, and an alkylsulfonic acid; Capacitor.
[2] The capacitor according to [1], wherein the alkylsulfonic acid is bound to the π-conjugated conductive polymer and 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] Any one of [1] to [7], wherein the π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or the polyanion is polystyrenesulfonic acid. The capacitor described in .
[9] A capacitor comprising a step of applying a conductive polymer dispersion to the surface of a dielectric layer formed on the surface of an anode made of a porous material of a valve metal and drying it to form a solid electrolyte layer. In the production method, the conductive polymer dispersion comprises a conductive composite containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium for dispersing the conductive composite. A method of manufacturing a capacitor, comprising:
[10] The method for producing a capacitor according to [9], wherein the alkylsulfonic acid is bound to the π-conjugated conductive polymer and contained in the conductive composite.

The capacitor of the present invention has a reduced equivalent series resistance 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 capacitor manufacturing method of the present invention, the above capacitor can be manufactured easily.

The present invention is considered to contribute to SDGs Goal 12 “Responsible consumption and production”.

In the present specification and claims, the lower limit and upper limit of the numerical range indicated by "-" shall be included in the numerical range.

1 is a cross-sectional view showing one embodiment of a capacitor of the present invention; FIG.

《Capacitor》
A first aspect of the present invention is a capacitor. An example of the embodiment will be described. A capacitor 10 shown in FIG. and a cathode 13 provided on the front side. Cathode 13 is provided on the opposite side of anode 11 with dielectric layer 12 and solid electrolyte layer 14 interposed therebetween.

Examples of valve metals forming the anode 11 include aluminum, tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. Among these, aluminum, tantalum and niobium are preferred.
As a specific example of the anode 11, after etching an aluminum foil to increase the surface area, the surface is oxidized, or the surface of a sintered body of tantalum particles or niobium particles is oxidized and made into pellets. mentioned. The material treated in this way becomes a porous body having 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, the surface of the metal anode 11 is anodized in an electrolytic solution such as an aqueous solution of ammonium adipate. It was formed by As with the anode 11, the dielectric layer 12 is also formed with irregularities.

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

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

<Conductive composite>
The conductive composite contained in the solid electrolyte layer will be described. The conductive composite of this embodiment contains a π-conjugated conductive polymer and a polyanion. The polyanion in the conductive composite forms a conductive composite having conductivity by doping the π-conjugated conductive polymer.
In the polyanion, only some of the anionic groups are doped into the π-conjugated conductive polymer, and there are surplus anionic groups that do not participate in the doping. Since the surplus anionic groups are hydrophilic groups, the conductive composite has water dispersibility.

(π-conjugated conductive polymer)
The π-conjugated conductive polymer may be any organic polymer having a π-conjugated main chain. molecules, polyphenylene-based conductive polymers, polyphenylene-vinylene-based conductive polymers, polyaniline-based conductive polymers, polyacene-based conductive polymers, polythiophene-vinylene-based conductive polymers, copolymers thereof, and the like. Polypyrrole-based conductive polymers, polythiophenes and polyaniline-based conductive polymers are preferable from the viewpoint of stability in air, and polythiophene-based conductive polymers are more preferable from the viewpoint of transparency.

Polythiophene-based conductive polymers include polythiophene, poly(3-methylthiophene), poly(3-ethylthiophene), poly(3-propylthiophene), poly(3-butylthiophene), and poly(3-hexylthiophene). , poly(3-heptylthiophene), poly(3-octylthiophene), poly(3-decylthiophene), poly(3-dodecylthiophene), poly(3-octadecylthiophene), poly(3-bromothiophene), poly (3-chlorothiophene), poly(3-iodothiophene), poly(3-cyanothiophene), poly(3-phenylthiophene), poly(3,4-dimethylthiophene), poly(3,4-dibutylthiophene) , poly(3-hydroxythiophene), poly(3-methoxythiophene), poly(3-ethoxythiophene), poly(3-butoxythiophene), poly(3-hexyloxythiophene), poly(3-heptyloxythiophene) , poly(3-octyloxythiophene), poly(3-decyloxythiophene), poly(3-dodecyloxythiophene), 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-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-carboxy butylthiophene).
Polypyrrole-based conductive polymers include polypyrrole, poly(N-methylpyrrole), poly(3-methylpyrrole), poly(3-ethylpyrrole), poly(3-n-propylpyrrole), poly(3-butyl pyrrole), 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), poly(3-methyl-4-hexyloxypyrrole).
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 of one type or two or more types.

(polyanion)
A polyanion is a polymer having two or more monomer units having an anionic group in its 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 anionic group of the polyanion is preferably a sulfo group or a carboxy group.
Specific examples of such polyanions include polystyrenesulfonic acid, polyvinylsulfonic acid, polyallylsulfonic 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), polymers having a sulfo group such as polyisoprene sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, Polymers having carboxy groups such as polyallylcarboxylic acid, polyacrylic acid, polymethacrylic acid, poly(2-acrylamido-2-methylpropanecarboxylic acid), polyisoprenecarboxylic acid, etc. A polyanion is a single monomer. may be a homopolymer obtained by polymerizing or a copolymer obtained by polymerizing two or more monomers.
Among these polyanions, a polymer having a sulfo group is preferable, and polystyrene sulfonic acid is more preferable, because the conductivity can be further increased.
One of the polyanions may be used alone, or two or more thereof may be used in combination.
The weight average molecular weight of the polyanion is preferably 20,000 or more and 1,000,000 or less, more preferably 100,000 or more and 500,000 or less. The mass-average molecular weight is a mass-based average molecular weight determined by pullulan conversion using gel filtration chromatography.

The content 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 with respect to 100 parts by mass of the π-conjugated conductive polymer, and 10 parts by mass or more and 700 parts by mass. It is more preferably not more than 100 parts by mass, and more preferably 100 parts by mass or more and 500 parts by mass or less. If the polyanion content is at least the above lower limit, the doping effect on the π-conjugated conductive polymer tends to be stronger, resulting in higher conductivity. On the other hand, when the polyanion content is equal to or less than the above upper limit, the π-conjugated conductive polymer can be sufficiently contained, and sufficient conductivity can be ensured.

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. . Within the above range, the equivalent series resistance of the capacitor is more likely to decrease, which is preferable.

<Alkyl sulfonic acid>
The alkylsulfonic acid contained in the solid electrolyte layer of this embodiment is a compound having a linear or branched alkane skeleton and at least one hydrogen atom bonded to the alkane substituted with a sulfonic acid group. Alkyl sulfonic acids are compounds other than the polyanions.
At least part of the alkylsulfonic acid can bind to the π-conjugated conductive polymer as a dopant, like the polyanion. When functioning as a dopant, it is believed that the sulfonic acid groups dope as anionic groups. Doping with alkylsulfonic acid is more preferable 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 doping.

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

The alkane skeleton is preferably linear. Being linear makes it easier to dope the π-conjugated conductive polymer, and as a result, the ESR of the capacitor can be further reduced.

Preferred specific examples of the alkylsulfonic acid include 1-methanesulfonic acid, 1-ethanesulfonic acid, 1-propanesulfonic acid, 1-butanesulfonic acid and the like.

One type or two or more types of alkylsulfonic acids may be contained in the solid electrolyte layer of this embodiment.
The total content of the alkylsulfonic acid contained in the solid electrolyte layer of this embodiment is preferably 10 parts by mass or more and 10000 parts by mass or less, and 50 parts by mass or more and 1000 parts by mass with respect to 100 parts by mass of the π-conjugated conductive polymer. Parts or less is more preferable, and 100 parts by mass or more and 500 parts by mass or less is even more preferable.
Within the above preferable range, the ESR of the capacitor can be further reduced.

<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.

A basic compound is one that functions as a Bronsted base that abstracts protons from the excess anionic groups of the polyanion. In order to achieve this function, the amount of the basic compound used in the present invention dissolved in water is preferably 0.001 g or more per 100 g of water at 20°C. Although the upper limit of the dissolution amount is not particularly limited, for example, even about 0.1 g can sufficiently perform the above functions.

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

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

Nitrogen-containing aromatic compounds (aromatic compounds in which at least one nitrogen atom forms a ring structure) include, for example, pyrrole, indole, imidazole, 2-methylimidazole, 2-propylimidazole, N-methylimidazole, N-propyl imidazole, 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-hydroxy benzimidazole, 2-(2-pyridyl)benzimidazole, pyridine, pyrimidine, pyrazine and alkyl-substituted products thereof (for example, substituted products with alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, propyl and butyl), Derivatives such as halogen-substituted compounds (for example, compounds substituted with halogen groups such as fluoro, chloro, and bromo) and nitrile-substituted compounds can be mentioned.
Among them, nitrogen-containing aromatic compounds are preferred, and imidazole is more preferred.

The number of basic compounds contained in the solid electrolyte layer may be one, or two or more.
The content 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, with respect to 100 parts by mass of the conductive composite. More preferably 10 parts by mass or more and 50 parts by mass or less.
Within the above preferable range, the ESR of the capacitor can be further reduced.

<Polyol compound>
In the solid electrolyte layer of this aspect, a compound having two or more hydroxy groups (hereinafter sometimes referred to as a polyol compound), which is different from the conductive composite, the polyanion, the alkylsulfonic acid, and the basic compound .) may further be included. 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 compound contained in the solid electrolyte layer is, for example, with respect to a total of 100 parts by mass of the π-conjugated conductive polymer and polyanion contained in the solid electrolyte layer (that is, 100 parts by mass of the conductive composite). , 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 even more preferably 300 parts by mass or more and 1000 parts by mass or less.
Within the above range, the ESR of the capacitor is more likely to be lowered, which is preferable.
The number of polyol compounds contained in the solid electrolyte layer may be one, or two or more.

[Electrolyte]
The capacitor of this aspect may have an electrolytic solution impregnating the solid electrolyte layer.
Solvents constituting the electrolytic solution include alcohol solvents such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol and glycerin, and lactone solvents such as γ-butyrolactone, γ-valerolactone and δ-valerolactone. Solvents, sulfur solvents such as sulfolane, dimethylsulfoxide and dimethylsulfone, amide solvents such as N-methylformamide, N,N-dimethylformamide, N-methylacetamide and N-methylpyrrolidinone, acetonitrile, 3-methoxypropionitrile and nitrile solvents such as water.
Examples of electrolytes constituting the electrolytic solution include 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, decanedicarboxylic acid such as 5,6-decanedicarboxylic acid, octanedicarboxylic acid such as 1,7-octanedicarboxylic acid, organic acid such as azelaic acid, sebacic acid; or boric acid, boric acid and polyhydric alcohol Obtained polyhydric alcohol complex compound of boric acid; inorganic acids such as phosphoric acid, carbonic acid, silicic acid, etc. as anion components, primary amines (methylamine, ethylamine, propylamine, butylamine, ethylenediamine, etc.), secondary amines (dimethyl amine, diethylamine, dipropylamine, methylethylamine, diphenylamine, etc.), tertiary amines (trimethylamine, triethylamine, tripropylamine, triphenylamine, 1,8-diazabicyclo(5,4,0)-undecene-7, etc.), Electrolytes containing tetraalkylammonium (tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, dimethyldiethylammonium, etc.) as cationic components;

The capacitor of this aspect is not limited to the above structure, and a separator may be provided between the dielectric layer and the cathode. A wound type capacitor is an example of a capacitor provided with a separator between a dielectric layer and a cathode.
Examples of separators 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.

<<Manufacturing Method of Capacitor>>
In the second aspect of the present invention, a conductive polymer dispersion, which will be described later, is applied to the surface of a dielectric layer formed on the surface of an anode made of a porous material of a valve metal, and dried to form a solid electrolyte layer. A method for manufacturing a capacitor, comprising steps. By the production method of this aspect, the capacitor of the first aspect can be easily produced.

The manufacturing method of this embodiment includes a step of forming a dielectric layer by oxidizing the surface of an anode made of a porous valve metal (dielectric forming step), and disposing a cathode at a position facing the dielectric layer. It is preferable to include a step (cathode forming step) and a step (film forming step) of forming a solid electrolyte layer on at least part of the surface of the dielectric layer. Each step will be described below with reference to FIG.

[Dielectric forming step]
In this step, the dielectric layer 12 is formed by oxidizing the surface of the anode 11 made of a porous material of valve metal. The method of forming the dielectric layer 12 is not particularly limited. For example, the surface of the anode 11 is anodized in an electrolytic solution for chemical conversion such as an ammonium adipate aqueous solution, an ammonium borate aqueous solution, or an ammonium phosphate aqueous solution. method.

[Cathode forming step]
In this step, the cathode 13 is arranged at a position facing the dielectric layer 12 . The method of arranging the cathode 13 is not particularly limited. For example, a method of forming the cathode 13 using a conductive paste such as carbon paste or silver paste, or a method of arranging a metal foil such as an aluminum foil so as to face the dielectric layer 12. etc.

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

As a method for applying the conductive polymer dispersion, for example, immersion (dip coating), comma coating, reverse coating, lip coating, microgravure coating, etc. can be applied. Among these methods, the method of immersing the anode 11 in the conductive polymer dispersion under reduced pressure is preferable. With the immersion method, the conductive polymer dispersion can be sufficiently applied to the inside of the porous structure on the surface of the dielectric layer 12 . After immersion, it is taken out and proceeded to the next drying treatment.

Examples of the drying method include room temperature drying, hot air drying, and far infrared drying. 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 preferably 0.2 to 1 hour, for example.
After drying, the capacitor may be assembled by a conventional method.

<Conductive polymer dispersion>
The conductive polymer dispersion used in the film-forming step of this embodiment comprises a conductive composite containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, a dispersion medium for dispersing the conductive composite, including.

The description of the conductive complex and alkylsulfonic acid contained in the conductive polymer dispersion is the same as the description of the first embodiment, so redundant description is omitted.
In the conductive polymer dispersion, the alkylsulfonic acid is preferably bound to the π-conjugated conductive polymer and 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.

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. may be

(dispersion medium)
The dispersion medium that constitutes the conductive polymer dispersion is not particularly limited as long as it is a liquid that can disperse the conductive composite, and examples thereof include water, an organic solvent, or a mixture of water and an organic solvent. mentioned. An aqueous dispersion medium is preferred because the conductive composite has surplus anionic groups derived from polyanions and is highly dispersible in water. 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. Examples thereof include alcohol-based solvents, ketone-based solvents, and ester-based solvents. The number of water-soluble organic solvents contained in the aqueous dispersion medium may be one, or two or more.

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 alcohol solvents include methanol, ethanol, isopropanol, n-butanol, t-butanol, allyl alcohol and the like.
Ketone solvents include, for example, 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 ester-based solvents include ethyl acetate, propyl acetate, and butyl acetate.

The total content of the π-conjugated conductive polymer and the polyanion (that is, the content of the conductive composite) with respect to the total mass of the conductive polymer dispersion is, 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 even more preferably 0.5% by mass or more and 2% by mass or less.
Within the above preferred range, it is possible to sufficiently reduce the ESR of the capacitor while further enhancing the dispersibility of the conductive composite in the conductive polymer dispersion.

The content of the alkylsulfonic acid contained in the conductive polymer dispersion is preferably 10 parts by mass or more and 10000 parts by mass or less, and 50 parts by mass or more and 1000 parts by mass with respect to 100 parts by mass of the π-conjugated conductive polymer. The following are more preferable, and 100 parts by mass or more and 500 parts by mass or less are even more preferable.
Within the above preferable 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, 1 mass with respect to a total of 100 parts by mass of the π-conjugated conductive polymer and polyanion (that is, 100 parts by mass of the conductive composite). 1000 parts by mass or less is preferable, 5 parts by mass or more and 100 parts by mass or less is more preferable, and 10 parts by mass or more and 50 parts by mass or less is even more preferable.
Within the above preferable 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, and 2.0 to 8.0. A content of 5.0 is more preferred, and a content of 2.0 to 3.0 is even more preferred.
Within the above preferable 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, 100 parts by mass with respect to a total of 100 parts by mass of the π-conjugated conductive polymer and polyanion (that is, 100 parts by mass of the conductive composite). 10000 mass parts or less is preferable, 200 mass parts or more and 2000 mass parts or less are more preferable, and 300 mass parts or more and 1000 mass parts or less are more preferable.
Within the above preferable range, the ESR of the capacitor can be further reduced.

The conductive polymer dispersion may contain any additive, and the content ratio thereof is appropriately determined according to the type of additive. (that is, 100 parts by mass of the conductive composite), for example, 1 to 1000 parts by mass.
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.

Optional additives include, for example, surfactants, inorganic conductive agents, antifoaming agents, coupling agents, antioxidants, ultraviolet absorbers, and the like.
Examples of surfactants include nonionic, anionic, and cationic surfactants, with nonionic surfactants being preferred from the standpoint of storage stability. Polymer surfactants such as polyvinyl alcohol and polyvinylpyrrolidone may also be added.
Examples of inorganic conductive agents include metal ions and conductive carbon. Metal ions can be generated by dissolving metal salts in water.
Antifoaming agents include silicone resins, polydimethylsiloxane, silicone oils and the like.
Examples of coupling agents include silane coupling agents having a vinyl group, an amino group, an epoxy group, or the like.
Antioxidants include phenol antioxidants, amine antioxidants, phosphorus antioxidants, sulfur antioxidants, sugars and the like.
UV absorbers include benzotriazole UV absorbers, benzophenone UV absorbers, salicylate UV absorbers, cyanoacrylate UV absorbers, oxanilide UV absorbers, hindered amine UV absorbers, and benzoate UV absorbers. are mentioned.

<Method for producing conductive polymer dispersion>
The conductive polymer dispersion is preferably produced by the following method. That is, by polymerizing a monomer forming a π-conjugated conductive polymer in a reaction solution containing an alkylsulfonic acid, a polyanion, and a dispersion medium, a conductive polymer containing the π-conjugated conductive polymer and the polyanion is polymerized. The manufacturing method includes a step (polymerization step) of obtaining a conductive polymer dispersion containing the complex, the alkylsulfonic acid, and the dispersion medium.

Synthesis of the conductive composite in the reaction solution can be carried out in the same manner as the conventional synthesis of the conductive composite, except that alkylsulfonic acid is contained in the reaction solution.

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

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 catalysts include transition metal compounds such as ferric chloride, ferric sulfate, ferric nitrate, and cupric chloride. Examples of the oxidizing agent include persulfates such as ammonium persulfate, sodium persulfate and potassium persulfate.

The content of the alkylsulfonic acid relative to the total mass of the reaction solution 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 0.3% by mass. Above 1% by mass or less is more preferable.
Within the above preferable range, it becomes easy to adjust the content ratio of the conductive composite and the alkylsulfonic acid in the target conductive polymer dispersion to the above-described preferable range.

The content of the monomer with respect to the total mass of the reaction solution immediately before the start of the polymerization reaction 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 0.1% by mass or more. 3 mass % or more and 1 mass % or less is more preferable.
The content of the polyanion with respect 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 1% by mass. % or more and 3 mass % or less is more preferable.
By setting the concentration within the above preferred range, a conductive polymer dispersion having the concentration of the conductive composite in the preferred content described above can be easily obtained.

In the conductive composite formed by the polymerization reaction, from the viewpoint of adjusting the content ratio of the π-conjugated conductive polymer and the polyanion to the above-mentioned suitable ratio, the monomer contained in the reaction solution immediately before the polymerization reaction is started. The content ratio of the polyanion is preferably 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 10 parts by mass or more and 700 parts by mass or less, and 100 parts by mass or more and 500 parts by mass or less. Ranges are more preferred.

A target conductive polymer dispersion can be obtained by synthesizing a π-conjugated conductive polymer by chemical oxidation polymerization of the monomers.

It is preferable to remove the catalyst and oxidizing agent added to the reaction solution from the conductive polymer dispersion after the chemical oxidative polymerization of the monomer.
As a method for removing, for example, a method of contacting the conductive polymer dispersion with an ion exchange resin to adsorb the catalyst and the oxidizing agent to the ion exchange resin, a method of ultrafiltrating the conductive polymer dispersion to remove the dispersion medium A method of removing with replacement of is mentioned. Among these, the method of using an ion exchange resin is preferable because it is simple. The ion exchange resin is preferably a combination of a cation exchange resin and an anion exchange resin.

The conductive polymer dispersion used in the capacitor manufacturing method of this embodiment can also be obtained by other methods. For example, there is a method of adding an appropriate amount of alkylsulfonic acid to a conductive composite dispersion containing a commercially available π-conjugated conductive polymer and a polyanion. However, even if the alkylsulfonic acid is added in a state where the conductive composite is already completed, the alkylsulfonic acid may be difficult to bond to the π-conjugated conductive polymer.
On the other hand, when produced by the above-described method, alkylsulfonic acid is present during the chemical oxidation polymerization of the π-conjugated conductive polymer, so the alkylsulfonic acid and the polyanion are easily bound to the π-conjugated conductive polymer. As a result, it is possible to reliably obtain a conductive polymer dispersion capable of further reducing the ESR of the capacitor.

A basic compound, a polyol compound, an optional additive, and the like 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 1.14 g of an ammonium persulfate oxidizing agent solution previously dissolved in 10 ml of water was added while stirring at 80°C. After adding dropwise for 20 minutes, the solution was stirred for 12 hours.
1000 ml of sulfuric acid diluted to 10% by mass was added to the resulting sodium polystyrenesulfonate-containing solution, and about 1000 ml of the solvent in the obtained polystyrenesulfonic acid-containing solution was removed by ultrafiltration. Next, 2000 ml of ion-exchanged water was added to the residual liquid, about 2000 ml of the solvent was removed by ultrafiltration, and the polystyrene sulfonic acid was washed with water. This washing operation was repeated three times.
Water in the obtained solution was removed under reduced pressure to obtain a colorless solid polystyrene sulfonic acid.

(Production Example 2) Production of Capacitor Element After connecting an anode lead terminal to an etched aluminum foil (anode foil), a voltage of 130 V was applied in a 10% by mass ammonium adipate aqueous solution to chemically (oxidize) the foil. , dielectric layers were formed on both sides of an aluminum foil to obtain an anode foil.
Next, opposing aluminum cathode foils to which cathode lead terminals were welded were laminated on both sides of the anode foil with a separator made of cellulose interposed therebetween, and wound 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 deionized water was mixed at 20°C. Next, 5 g of a 10 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 stirred while adding a catalyst solution of 0.03 g of ferric sulfate dissolved in 4.97 g of ion-exchanged water and 1.1 g of ammonium persulfate to 8.9 g of ions. A solution of an oxidizing agent dissolved in exchanged water was slowly added, and the resulting reaction solution was stirred for 24 hours to react.
By the above reaction, a conductive composite (PEDOT-PSS) containing poly(3,4-ethylenedioxythiophene), which is a π-conjugated conductive polymer, and polystyrene sulfonic acid, and the π-conjugated conductive polymer A conductive polymer dispersion containing bound methanesulfonic acid and water as a dispersion medium was obtained.
13.2 g of Duolite C255LFH (manufactured by Sumika Chemtex Co., Ltd., cation exchange resin) and 13.2 g of Duolite A368S (manufactured by Sumika Chemtex Co., Ltd., anion exchange resin) were added to this conductive polymer dispersion and filtered. Then, the ion exchange resin was removed, and a conductive polymer dispersion liquid from which the oxidizing agent and the catalyst were removed was obtained.

Next, water was distilled off from the resulting conductive polymer dispersion using an evaporator under reduced pressure to make the solid content 1.6% by mass. Imidazole was added to 100 g of the resulting 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% by 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 conductive polymer dispersion under reduced pressure, and then dried for 30 minutes in a hot air dryer at 125°C to form a conductive film on the surface of the dielectric layer. A solid electrolyte layer containing the composite was formed.
Finally, the capacitor element having the solid electrolyte layer formed thereon was placed in an aluminum case and sealed with a sealing rubber to produce a capacitor.

(Example 2)
Conductivity was obtained in the same manner as in Example 1, except that the amount of 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. A polymer dispersion was obtained and a capacitor was produced.

(Example 3)
Conductivity was obtained in the same manner as in Example 1, except that the amount of 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. A polymer dispersion was obtained and a capacitor was produced.

(Example 4)
A conductive polymer dispersion was obtained in the same manner as in Example 1, except that 5 g of an ethanesulfonic acid aqueous solution (concentration: 10% by mass) was added instead of 5 g of the methanesulfonic acid aqueous solution (concentration: 10% by mass). was made.
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 resulting conductive polymer dispersion.

(Example 5)
Conductivity was obtained in the same manner as in Example 4, except that the amount of 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. A polymer dispersion was obtained and a capacitor was produced.

(Example 6)
Conductivity was obtained in the same manner as in Example 4, except that the amount of 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. A polymer dispersion was obtained and a capacitor was produced.

(Comparative example 1)
A conductive polymer dispersion was obtained 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, and a capacitor was produced. bottom.

(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 (10% by mass concentration) was added instead of 5 g of an aqueous methanesulfonic acid solution (10% by mass concentration), and a capacitor was produced. bottom.

(Comparative Example 3)
A conductive polymer was prepared in the same manner as in Comparative Example 2, except that the amount of sulfuric 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. A dispersion was obtained and a capacitor was produced.

(Comparative Example 4)
A conductive polymer was prepared in the same manner as in Comparative Example 2, except that the amount of sulfuric 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. A dispersion was obtained and a capacitor was produced.

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

(Comparative Example 6)
Conductivity was performed in the same manner as in Comparative Example 5, except that the amount of paratoluenesulfonic 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. A flexible polymer dispersion was obtained and a capacitor was produced.

(Comparative Example 7)
Conductivity was carried out in the same manner as in Comparative Example 5, except that the amount of paratoluenesulfonic 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. A flexible polymer dispersion was obtained and a capacitor was produced.

(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, but a blue solid believed to be a π-conjugated conductive polymer (PEDOT) was precipitated, and ions Stopped because all the blue solid was filtered off along with the exchange resin.

(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, but a blue solid believed to be a π-conjugated conductive polymer (PEDOT) was precipitated, and ions Stopped because all the blue solid was filtered off along with the exchange resin.

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

<Evaluation>
[Capacitance/Equivalent series resistance]
For the capacitor 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.). Table 1 shows the measurement results.

The capacitors of each example having a conductive composite to which alkylsulfonic acid was bound had a capacitance equal to or greater than that of the capacitors of the comparative examples, and their equivalent series resistances were significantly reduced.

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

Claims (10)

an anode made of a porous material of a valve metal; a dielectric layer made of an oxide of the valve metal; a cathode made of a conductive material provided on a side of the dielectric layer opposite to the anode; and the dielectric layer. and a solid electrolyte layer formed between the cathodes,
A capacitor, 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 claim 1, wherein said alkylsulfonic acid is bound to said [pi]-conjugated conductive polymer and contained in said conductive composite. 3. A capacitor according to claim 1 or 2, wherein said alkylsulfonic acid is methanesulfonic acid or ethanesulfonic acid. The capacitor according to any one of claims 1 to 3, wherein said solid electrolyte layer further contains a basic compound. 5. The capacitor of claim 4, wherein said basic compound is a nitrogen-containing aromatic 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. 7. The capacitor of claim 6, wherein said polyol compound is diethylene glycol. 8. The capacitor according to claim 1, wherein said π-conjugated conductive polymer is poly(3,4-ethylenedioxythiophene), or said polyanion is polystyrenesulfonic acid. A method for producing a capacitor, comprising a step of applying a conductive polymer dispersion to the surface of a dielectric layer formed on the surface of an anode made of a porous material of a valve metal and drying it to form a solid electrolyte layer. There is
A method for producing a capacitor, wherein the conductive polymer dispersion contains a conductive composite containing a π-conjugated conductive polymer and a polyanion, an alkylsulfonic acid, and a dispersion medium in which the conductive composite is dispersed. . 10. The method of manufacturing a capacitor according to claim 9, wherein said alkylsulfonic acid is bound to said [pi]-conjugated conductive polymer and contained in said conductive composite.

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