JP2011009314A - Solid electrolytic capacitor, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a solid electrolytic capacitor which is high in electrostatic capacity, is low in ESR, is less in leakage current and has high breakdown voltage, and to provide a method of manufacturing the solid electrolytic capacitor.SOLUTION: The solid electrolytic capacitor includes a polymer of at least one compound, selected from a group of compounds represented by general formula [1], as a solid electrolyte. Especially, a solid electrolytic capacitor which includes a polymer having an alkyl group with C3-5 as a solid electrolyte has a small leakage current and a high breakdown voltage.

Description

  The present invention relates to a solid electrolytic capacitor having a solid electrolyte layer, and more particularly, to a solid electrolytic capacitor having a conductive polymer layer exhibiting high conductivity as a solid electrolyte layer and having excellent electrical characteristics, and a method for manufacturing the same.

Solid electrolyte forming materials used for solid electrolytic capacitors include inorganic conductive materials such as manganese dioxide, and organic conductive materials such as 7,7,8,8-tetracyanoquinodimethane (TCNQ) complex. It has been known.
Furthermore, solid electrolytic capacitors using a conductive polymer material, which is more excellent in electrical conductivity than those solid electrolyte forming materials, as a solid electrolyte have been widely put into practical use.

As this conductive polymer material, a conductive polymer obtained by polymerizing 3,4-ethylenedioxythiophene (hereinafter abbreviated as “EDOT”) as a monomer is widely known.
This EDOT is useful as a solid electrolyte layer forming material for a solid electrolytic capacitor because it has a moderate polymerization reaction rate and can form a conductive polymer layer having excellent adhesion to the dielectric oxide film of the anode.

However, in recent years, electronic devices are required to support more power saving and higher frequency, and in solid electrolytic capacitors used for such electronic devices, a smaller and larger capacity and a lower equivalent series resistance (hereinafter, It is abbreviated as “ESR.”) Further improvement in electrical characteristics is demanded.
The electrical characteristics of the solid electrolytic capacitor greatly depend on the type of solid electrolyte forming material used and the forming method, but the development of an excellent conductive polymer monomer that surpasses the conventionally known 3,4-ethylenedioxythiophene, There are expectations for a method for forming a solid electrolyte layer.

  In such a background, Patent Document 1 discloses a solid electrolytic capacitor in which a polymer of 3-alkyl-4-alkoxythiophene is a solid electrolyte, and by using the polymer, it is excellent even in a high frequency region. It is disclosed that a solid electrolytic capacitor having excellent electrical characteristics can be obtained.

Patent Document 2 discloses a solid electrolytic capacitor in which an alkylenedioxythiophene derivative polymer having a site substituted with an alkoxy group is a solid electrolyte.
It has been disclosed that by employing the polymer, crystallization of the polymerization oxidant remaining in the polymer can be suppressed, and the leakage current of the obtained solid electrolytic capacitor can be reduced.

JP 2001-332453 A JP 2004-096098 A

  However, even with the polymers disclosed in the above documents, it is still difficult to obtain sufficient electric characteristics, and further improvement of the electric characteristics of the solid electrolytic capacitor is desired.

  An object of the present invention is to provide an excellent solid electrolytic capacitor having excellent electrical characteristics such as capacitance and equivalent series resistance, a small leakage current, and high withstand voltage characteristics, and a method for manufacturing the same.

As a result of intensive studies, the present inventors have found that a solid electrolytic capacitor containing a polymer of at least one compound represented by the following general formula [1] as a solid electrolyte can solve the above-mentioned problems, and has completed the present invention. It was.
That is, the present invention is as follows.

  The first invention is a solid electrolytic capacitor comprising a polymer of at least one compound selected from the group consisting of compounds represented by the following general formula [1] as a solid electrolyte.

  In the above formula, R represents a linear or branched alkyl group having 3 to 5 carbon atoms. Z represents an oxygen atom or a sulfur atom which may be the same or different.

  According to a second aspect of the present invention, there is provided a polymer of at least one compound selected from the group consisting of compounds represented by the above general formula [1] on a valve action metal on which a dielectric oxide film is formed. It is the manufacturing method of the solid electrolytic capacitor which has the process formed on the formed valve action metal.

  According to a third aspect of the present invention, at least one compound selected from the group consisting of compounds represented by the above general formula [1], wherein the step of forming the polymer on the valve action metal on which the dielectric oxide film is formed, A second aspect of the invention is characterized in that polymerization is performed by bringing a dopant and an oxidizing agent into contact with each other in a liquid phase, and the polymer is formed on a valve action metal on which a dielectric oxide film is formed. It is a manufacturing method of the described solid electrolytic capacitor.

  4th invention is using the solution of the compound which is a dopant and oxidizing agent, It is a manufacturing method of the solid electrolytic capacitor as described in 3rd invention characterized by the above-mentioned.

In a fifth aspect of the invention, a solution of the compound that is the dopant and oxidant is
The method for producing a solid electrolytic capacitor according to the fourth invention, wherein the organic sulfonic acid ferric salt is a solution dissolved in an organic solvent in the range of 20 to 90% by weight.

  According to the present invention, it is possible to obtain a solid electrolytic capacitor having a high electrostatic capacity, a low ESR, a particularly small leakage current, and an extremely high withstand voltage.

The present invention is described in detail below.
The present invention is a solid electrolytic capacitor comprising a polymer of at least one compound selected from the group consisting of compounds represented by the following general formula [1] as a solid electrolyte.

  In the formula [1], R represents a linear or branched alkyl group having 3 to 5 carbon atoms. Z represents an oxygen atom or a sulfur atom, which may be the same.

  Specific examples of the linear or branched alkyl group having 3 to 5 carbon atoms include n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, t -Butyl group, n-pentyl group, i-pentyl group, 1-methylbutyl group, 1,2-dimethylpropyl group, 1,1-dimethylpropyl group, neopentyl group, and the like, more preferably from the viewpoint of polymerizability. N-propyl group, n-butyl group and n-pentyl group.

  [1] In the formula, Z is preferably an oxygen atom.

As the compound represented by the general formula [1], more preferably,
2-propyl-2,3-dihydrothieno [3,4-b] -1,4-dioxin (2-propyl-EDOT),
2-isopropyl-2,3-dihydrothieno [3,4-b] -1,4-dioxin (2-isopropyl-EDOT),
2-butyl-2,3-dihydrothieno [3,4-b] -1,4-dioxin (2-butyl-EDOT),
2-pentyl-2,3-dihydrothieno [3,4-b] -1,4-dioxin (2-pentyl-EDOT),
Is mentioned.

The polymer of at least one compound selected from the group consisting of the compound represented by the general formula [1] exhibits high conductivity and is excellent in thermal stability.
The monomer used in the present invention has an improved polymerization rate as compared with known conductive polymer monomers such as EDOT.
That is, although the polymerization rate is lower than that of EDOT, it has high polymerizability, so that it can penetrate and polymerize deeply into the hole of the porous metal having a complicated shape.
Therefore, the monomer polymer used in the present invention is a conductive polymer material particularly suitable for the solid electrolyte of the solid electrolytic capacitor.

  When the compound represented by [1] is used in the above monomer, a solid electrolytic capacitor exhibiting particularly low leakage current characteristics and a high withstand voltage can be obtained.

  A polymer of at least one monomer selected from the group consisting of the compound represented by the general formula [1] can be obtained by the polymerization method shown below. For example, a polymer can be obtained by chemical oxidative polymerization of the monomer compound using an oxidizing agent, and a polymer can also be obtained by electrochemical oxidative polymerization.

  As the oxidizing agent in chemical oxidative polymerization, halides such as iodine, bromine, bromine iodide, chlorine dioxide, iodic acid, periodic acid, chlorous acid, antimony pentafluoride, phosphorus phosphorus pentachloride, phosphorus phosphorus fluoride, Metal halides such as aluminum chloride and molybdenum chloride, or high valent state transition metal ions such as permanganate, dichromate, chromic anhydride, ferric salt, and cupric salt or salts thereof, sulfuric acid, Protic acids such as nitric acid and trifluoromethane sulfate, oxygen compounds such as sulfur trioxide and nitrogen dioxide, hydrogen peroxide, ammonium persulfate, peroxo acids and salts such as sodium perborate, molybdophosphoric acid, tungstophosphoric acid, tungstomolyb And heteropolyacids and salts such as doric acid.

  In addition, as the electrochemical oxidative polymerization, a polymer is obtained by electrolytic oxidation in an electrolytic solution in which a compound represented by the above formula [1] and a supporting electrolyte capable of releasing a dopant are dissolved in a solvent. Can be obtained.

  Examples of the dopant include halogen ions such as iodine, bromine and chlorine, halide ions such as hexafluorolin, hexafluoroarsenic, hexafluoroantimony, tetrafluoroboron and perchloric acid, or methanesulfonic acid and dodecylsulfonic acid. Alkyl-substituted organic sulfonate ions, cyclic sulfonate ions such as camphor sulfonate ions, or alkyl-substituted or unsubstituted benzene mono- or disulfones such as benzene sulfonic acid, para-toluene sulfonic acid, dodecyl benzene sulfonic acid, benzene disulfonic acid Alkyl ion or unsubstituted ion of naphthalenesulfonic acid substituted with 1 to 4 sulfonic acid groups such as acid ion, 2-naphthalenesulfonic acid, 1,7-naphthalenedisulfonic acid, anthracenesulfonic acid ion, Alkyl-substituted or unsubstituted biphenyl sulfonate ions such as traquinone sulfonate ion, alkylbiphenyl sulfonate, biphenyl disulfonate, polymer sulfonate ions such as polystyrene sulfonate, naphthalene sulfonate formalin condensate, etc., or molybdophosphate, Examples thereof include heteropoly acid ions such as tungstophosphoric acid and tungstomolybdophosphoric acid, and these various salts can be used as the supporting electrolyte.

Examples of the solvent include water, ethers such as tetrahydrofuran (THF), dioxane, and diethyl ether; ketones such as acetone and methyl ethyl ketone; dimethylformamide (DMF), acetonitrile, benzonitrile, N-methylpyrrolidone (NMP), and dimethyl. Aprotic solvents such as sulfoxide (DMSO), γ-butyrolactone (GBL), propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and esters such as ethyl acetate and butyl acetate Non-aromatic chlorine compounds such as chloroform and methylene chloride, nitro compounds such as nitromethane, nitroethane, and nitrobenzene, or alcohols such as methanol, ethanol, and propanol It can be exemplified Lumpur acids or formic acid and acetic acid, acid anhydrides of an organic acid or organic acids such as acetic acid and propionic acid, the (such as acetic anhydride).
The above solvents can be used alone or as a mixed solvent in which a plurality of the above-mentioned solvents are mixed.

  As an electrochemical polymerization method, a polymer can be formed on the anode by electrolytic oxidation in the electrolytic solution.

The solid electrolytic capacitor of the present invention includes a solid electrolyte layer containing a polymer of at least one compound selected from the group consisting of compounds represented by the general formula [1], has a high capacitance, and a low ESR. Excellent electrical properties.
Further, the leakage current is remarkably reduced as compared with a solid electrolytic capacitor using a conventional PEDOT as a solid electrolyte layer. The reason why the leakage current is reduced is not clear, but the polymer used in the present invention is excellent in self-repairing ability, and the hydrophobicity is increased by substitution of the alkyl group. It is thought that damage to the film is suppressed.

Next, the manufacturing method of the solid electrolytic capacitor of this invention is demonstrated.
The method for producing the solid electrolytic capacitor of the present invention includes:
On the valve action metal on which the dielectric oxide film is formed,
A method for producing a solid electrolytic capacitor comprising a step of forming a polymer of at least one compound selected from the group consisting of compounds represented by the general formula [1].

As the valve action metal, for example, aluminum, tantalum, titanium, niobium, or an alloy thereof can be used, and aluminum, tantalum, and niobium are more preferable.
As the form of the valve action metal, a metal foil or a sintered body of a powder containing these as a main component can be preferably used.

The step of forming the polymer may be the above-described chemical oxidative polymerization method or electrolytic oxidative polymerization method.
From the viewpoint of electrical characteristics of the obtained solid electrolytic capacitor and a simpler manufacturing process, a process of forming a polymer by chemical oxidative polymerization is preferable.

  As a preferred step of forming a polymer by chemical oxidative polymerization, a valve action is obtained by contacting at least one compound selected from the group consisting of the monomer compounds represented by the above [1], a dopant and an oxidizing agent in a liquid phase. This is a method of forming a polymer on a metal.

As a method of bringing the monomer compound into contact with the dopant and the oxidizing agent in the liquid phase,
1. A method of preparing a polymer by preparing a solution obtained by mixing the monomer represented by [1] above and a solution containing a dopant and an oxidizing agent, and contacting the solution with a valve action metal by coating or dipping.
2. Prepare the monomer solution, separately prepare a solution containing a dopant and an oxidant, and apply or immerse the valve action metal impregnated and held in the monomer solution in the oxidant solution to bring it into contact with the polymer. How to get.
3. A method of obtaining a polymer by applying or immersing the monomer solution in a valve action metal that has been applied or impregnated and held with a solution containing a dopant and an oxidant, and contacting them.
Is mentioned.
These methods are not particularly limited.

As a method of forming a polymer on the valve action metal, it can be formed by holding a liquid containing a monomer, a dopant and an oxidant held on the valve action metal at a predetermined temperature for a predetermined time.
Here, the predetermined temperature can be arbitrarily selected in the range of 0 ° C. to 150 ° C., and the predetermined time can be arbitrarily selected in the range of 1 minute to 24 hours.

As a more preferable form in the method for producing a solid electrolytic capacitor of the present invention, a solution of a compound that is a dopant and an oxidizing agent can be used.
The compound that is a dopant and oxidant is an oxidant compound containing an anionic component that becomes a dopant of the conductive polymer. By using such a compound, the anionic component is converted into a conductive polymer during chemical polymerization. Can be formed into a conductive polymer which functions as a dopant and has improved conductivity.
Preferable anion components include organic acid ions such as organic sulfonate ions and carboxylate ions, inorganic acid ions such as boron compound ions, phosphate compound ions, and perchlorate ions.
Particularly suitable as an oxidizing agent containing such anionic components are iron (III) salts of inorganic acids such as ferric chloride and ferric perchlorate, ferric benzenesulfonate and paratoluenesulfonic acid. An iron (III) salt of an organic acid such as a ferric salt or a ferric alkylnaphthalenesulfonic acid salt can be mentioned, and an organic sulfonic acid ferric salt can be mentioned as the most preferable one.

As the solvent for the dopant and oxidizing agent, alcohol solvents such as methanol, ethanol, n-propanol, iso-propanol, and n-butanol are preferable.
Among these, particularly preferred is iron (III) of the organic sulfonic acid in the alcohol solvent, 20% to 90% by weight, more preferably 40% to 80% by weight, and still more preferably 50% by weight. % To 70% by weight.
By using the dopant and oxidizing agent dissolved in such a concentration, it becomes possible to densely form a polymer having excellent conductivity and durability on a valve metal having a complicated shape.

  Hereinafter, the manufacturing method of the solid electrolytic capacitor of the present invention will be described by taking a method of manufacturing an aluminum wound capacitor as a specific example.

  First, the surface of the aluminum foil serving as the anode is roughened by etching, and then an anode lead is connected, followed by chemical conversion treatment in an aqueous solution of diammonium adipate or the like to form a dielectric oxide film. In practicing the present invention, it is preferable to use a foil having a large etching magnification, whereby a capacitor having a large capacitance can be obtained.

  Separately, a separator such as manila paper is sandwiched between the facing cathode aluminum foil to which the cathode lead is connected and the anode aluminum foil, wound up in a cylindrical shape, and then carbonized by heat treatment, and the winding type capacitor. Prepare the device.

  Next, a solid electrolyte layer made of a conductive polymer is formed on the anode foil of the capacitor element. As a method of forming the solid electrolyte layer, the capacitor element is impregnated with a monomer solution containing a compound represented by the general formula [1], which is a conductive polymer monomer, by a method such as immersion, coating, or spraying, and then impregnation. A polymerization reaction is caused by bringing the monomer into contact with an oxidizing agent to form a solid electrolyte layer. In addition, the method of impregnating with an oxidizing agent first and then polymerizing by contacting the monomer, and the method of impregnating and polymerizing a solution mixed with the monomer and the oxidizing agent at a time can be applied, and are not particularly limited. The chemical oxidative polymerization is performed at a temperature of 0 to 150 ° C., preferably in a liquid phase. If it is less than 0 ° C., the polymerization reaction hardly occurs, and if it exceeds 150 ° C., the capacitor characteristics may be deteriorated.

  The impregnation and heating steps may be repeated a plurality of times.

  By the above process, a solid electrolyte layer in which the conductive polymer layer is sufficiently filled in the fine etching holes of the anode aluminum foil can be formed.

  Next, an epoxy resin or the like is used to seal the capacitor case, and voltage is applied to perform aging to complete the solid electrolytic capacitor of the present invention.

  Hereinafter, the present invention will be described in detail based on experimental examples, but the present invention is not limited to the experimental examples. In the experimental examples, “%” represents “% by mass”, capacitance (C) and dielectric loss (tan δ) were measured at a frequency of 120 Hz, and equivalent series resistance (ESR) was measured at a frequency of 100 kHz. The capacity impregnation ratio is a percentage of the capacitance of the obtained solid electrolytic capacitor with respect to the capacitance measured in a 15% ammonium adipate aqueous solution before the formation of the solid electrolyte layer. . Further, the leakage current was a value of 60 seconds after flowing a current of 4.0V.

  Furthermore, the withstand voltage of the obtained solid electrolytic capacitor element was measured by the following method. That is, the applied voltage is stepped up in steps of 0.5V from 0V, the leakage current after holding at each voltage for 1 minute is measured, and the maximum voltage at which the leakage current of the capacitor is 100 mA or less is taken as the withstand voltage. evaluated.

Experimental Example 1 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -2-propyl-1,4-dioxin (2-propyl-EDOT)]
After the surface of the aluminum foil is roughened by etching, the anode lead is connected by caulking, followed by chemical conversion treatment at a voltage of 4 V in a 10% diammonium adipate aqueous solution, and a dielectric oxide film on the surface Formed.

  Next, a 50 μm-thick manila paper is sandwiched as a separator between the anode foil and the counter cathode aluminum foil in which the cathode lead is connected by resistance welding, and wound into a cylindrical shape. The capacitor element was prepared by heat treating for a minute to carbonize the Manila paper. The capacitance of the obtained capacitor element in a 15% diammonium adipate aqueous solution was 650 μF.

  Next, 2,3-dihydrothieno [3,4-b] -2-propyl-1,4-dioxin (2-propyl-EDOT) as a monomer and 50% p-toluenesulfonic acid second as an oxidizing agent An iron / n-butanol solution was prepared, and the capacitor element was immersed in a solution prepared by mixing the weight ratio of the two at 1: 2.5 for 120 seconds, then at 45 ° C. for 2 hours, at 105 ° C. for 35 minutes, and at 125 ° C. By heating for 1 hour, chemical oxidative polymerization was performed to form poly-2-propyl-EDOT in the capacitor element.

  Next, the capacitor case was sealed with an epoxy resin, and aging was performed by applying a voltage of 4 V to both electrodes to complete a solid electrolytic capacitor.

  Experimental Example 2 [Method for Manufacturing Solid Electrolytic Capacitor Using 2,3-Dihydrothieno [3,4-b] -2-butyl-1,4-dioxin (2-butyl-EDOT)]

  The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and 2,3-dihydrothieno [3,4-b] -2-butyl-1,4-dioxin (2-butyl-EDOT) was used as a monomer. A solid electrolytic capacitor was produced by performing the same treatment as in Experimental Example 1 except for the above.

Experimental Example 3 [Production Method of Solid Electrolytic Capacitor Using 2,3-Dihydrothieno [3,4-b] -2-pentyl-1,4-dioxin (2-pentyl-EDOT)]

  The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and 2,3-dihydrothieno [3,4-b] -2-pentyl-1,4-dioxin (2-pentyl-EDOT) was used as a monomer. A solid electrolytic capacitor was produced by performing the same treatment as in Experimental Example 1 except for the above.

Experimental Example 4 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -2-hexyl-1,4-dioxin (2-hexyl-EDOT)]

  The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and 2,3-dihydrothieno [3,4-b] -2-hexyl-1,4-dioxin (2-hexyl-EDOT) was used as a monomer. A solid electrolytic capacitor was produced by performing the same treatment as in Experimental Example 1 except for the above.

  Experimental Example 5 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -2-methyl-1,4-dioxin (2-methyl-EDOT)]

  The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and 2,3-dihydrothieno [3,4-b] -2-methyl-1,4-dioxin (2-methyl-EDOT) was used as a monomer. A solid electrolytic capacitor was produced by performing the same treatment as in Experimental Example 1 except for the above.

  Experimental Example 6 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -2-ethyl-1,4-dioxin (2-ethyl-EDOT)]

  The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and 2,3-dihydrothieno [3,4-b] -2-ethyl-1,4-dioxin (2-ethyl-EDOT) was used as a monomer. A solid electrolytic capacitor was produced by performing the same treatment as in Experimental Example 1 except for the above.

Experimental Example 7 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -2-hydroxymethyl-1,4-dioxin (2-ethoxy-EDOT)]
The same prepolymerized capacitor element as in Experimental Example 1 was prepared, and Experimental Example 1 was used except that 2,3-dihydrothieno [3,4-b] -2-hydroxymethyl-1,4-dioxin was used as the monomer. Processing was performed in the same manner to produce a solid electrolytic capacitor.

  Experimental Example 8 [Method for producing solid electrolytic capacitor using 2,3-dihydrothieno [3,4-b] -1,4-dioxin (EDOT)]

  The same method as in Experimental Example 1 except that a pre-polymerized capacitor element similar to Experimental Example 1 was prepared and the monomer was changed to 2,3-dihydrothieno [3,4-b] -1,4-dioxin (EDOT). The solid electrolytic capacitor was manufactured by processing.

  Table 1 shows the initial electrical characteristics and the electrical characteristics of the capacity impregnation rate of the solid electrolytic capacitors obtained in Experimental Examples 1 to 8, respectively.

As shown in Table 1, as a result of comparing various monomers, the solid electrolytic capacitors obtained in Experimental Examples 1 to 6 have higher withstand voltage than the solid electrolytic capacitor using EDOT in Experimental Example 8. I understood.
In particular, it was found that the solid electrolytic capacitor obtained in Experimental Example 1-3 is a solid electrolytic capacitor that exhibits low ESR, low leakage current, and high withstand voltage and has extremely excellent electrical characteristics.
In addition, the solid electrolytic capacitor using the alkoxy group having the alkoxy group of Experimental Example 7 as a substituent had a poor capacity impregnation rate and a large ESR.
From these facts, it has been clarified that the solid electrolytic capacitor of the present invention has excellent electrical characteristics, unlike the conventionally known solid electrolytic layer.

Claims (5)

The following general formula [1],

(In the above formula [1], R represents a linear or branched alkyl group having 3 to 5 carbon atoms. Z represents an oxygen atom or a sulfur atom which may be the same or different.)
A solid electrolytic capacitor comprising, as a solid electrolyte, a polymer of at least one compound selected from the group consisting of compounds represented by: On the valve action metal on which the dielectric oxide film is formed, the following general formula [1],

(In the formula [1], R represents a linear or branched alkyl group having 3 to 5 carbon atoms. Z represents an oxygen atom or a sulfur atom which may be the same or different.)
A method for producing a solid electrolytic capacitor, comprising a step of forming a polymer of at least one compound selected from the group consisting of compounds represented by the formula (1) on a valve action metal on which a dielectric oxide film is formed. The step of forming the polymer on the valve action metal on which the dielectric oxide film is formed,
Polymerization is performed by bringing at least one compound selected from the group consisting of the compounds represented by the general formula [1], a dopant, and an oxidizing agent into contact with each other in a liquid phase, and a dielectric oxide film is formed on the polymer. The method for producing a solid electrolytic capacitor according to claim 2, wherein the method is a step of forming a valve action metal.   The method for producing a solid electrolytic capacitor according to claim 3, wherein a solution of a compound that is a dopant and an oxidizing agent is used. A solution of the compound that is the dopant and oxidizing agent is
5. The method for producing a solid electrolytic capacitor according to claim 4, wherein the organic sulfonic acid ferric salt is a solution dissolved in an organic solvent in an amount of 20 to 90% by weight.