WO2024181509A1 - Solid electrolytic capacitor and manufacturing method - Google Patents

Abstract

Provided is a hybrid type solid electrolytic capacitor in which a high withstand voltage and excellent capacitor characteristics are realized. This solid electrolytic capacitor comprises a capacitor element. The capacitor element comprises: an anode containing a valve action metal; a cathode opposing the anode; and an electrolytic layer that is interposed between the anode and the cathode, and that includes an electrolytic solution and a solid electrolyte. The anode has, on the surface thereof, a dielectric coating film having a withstand voltage of 300V or higher. The electrolytic solution includes a solute of 0.08-0.34 mol/kg, and 1-10 wt% of water in relation to the total electrolytic solution included in the capacitor element.

Description

Solid electrolytic capacitor and manufacturing method

The present invention relates to a solid electrolytic capacitor whose electrolyte layer contains an electrolyte solution and a solid electrolyte, and a manufacturing method thereof.

Capacitors are used for a variety of purposes. For example, in the field of power electronics, power from an AC power source is converted to DC power by a converter circuit, and this DC power is then converted to the desired AC power by an inverter circuit. In this type of power supply circuit, smoothing capacitors are provided to suppress pulsations in the DC output from the converter circuit and smooth the DC before inputting it to the inverter circuit. In addition, decoupling capacitors are provided near semiconductor switching elements such as gallium nitride to ensure stable operation and remove noise from the semiconductor switching elements.

　With the recent trend towards higher power, there is a growing demand for capacitors with higher capacitance. Electrolytic capacitors are easier to achieve higher capacitance than film capacitors, and can easily meet this demand. Electrolytic capacitors have valve metals such as tantalum or aluminum as anode and cathode foils. The anode foil is enlarged by forming the valve metal into a sintered compact or etched foil, and the enlarged surface has a dielectric film formed by a process such as anodizing. An electrolyte is placed between the anode and cathode foils.

Electrolytic capacitors can increase the specific surface area by expanding the surface area of the anode foil, which gives them a large electrostatic capacitance and allows them to meet the demand for higher capacity. Among electrolytic capacitors, solid electrolytic capacitors that use solid electrolytes are attracting attention. Solid electrolytic capacitors are small and have a large capacity, and the high conductivity of the solid electrolyte results in low equivalent series resistance.

Manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known as solid electrolytes. In recent years, conductive polymers derived from monomers with π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which has a slow reaction rate and excellent adhesion to dielectric films, have rapidly become popular as solid electrolytes. Conductive polymers use acid compounds such as polyanions as dopants, and have a partial structure within the monomer molecule that acts as a dopant, resulting in high conductivity.

However, compared to liquid-type electrolytic capacitors, in which the capacitor element is impregnated with an electrolyte, solid electrolytic capacitors are poor at repairing defects in the anodized film, which acts as a dielectric, and there is a risk of increased leakage current. For this reason, so-called hybrid-type solid electrolytic capacitors have been proposed, in which a solid electrolyte layer is formed in a capacitor element in which an anode foil and a cathode foil face each other with a separator in between, and the gaps in the capacitor element are impregnated with a driving electrolyte.

JP 2017-38010 A JP 2004-128076 A

On the other hand, in some fields such as power electronics, high voltage resistance capacitors are expected. For example, smoothing capacitors with a voltage resistance of 250V are used in the inverters that drive the motors installed in electric vehicles. In hybrid-type solid electrolytic capacitors used in such high voltage fields, it is necessary to form a dielectric film with a chemical formation voltage of 300V or more on the anode foil.

Dielectric films with a formation voltage of 300V or more contain many voids and are susceptible to chemical dissolution. Therefore, in order to provide a high film repair effect and suppress leakage current, it is possible to consider methods such as increasing the solute concentration of the electrolyte contained in hybrid-type solid electrolytic capacitors or increasing the amount of water in the electrolyte.

Generally, in electrolytic capacitors for high voltage applications that contain only an electrolyte, increasing the solute concentration of the electrolyte reduces the ESR. However, as a result of intensive research by the inventors, it was found that in hybrid-type solid electrolytic capacitors that form a dielectric film with a formation voltage of 300V or more, increasing the solute concentration of the electrolyte increases the equivalent series resistance (ESR).

In addition, it was found that increasing the moisture content increases the leakage current (LC) of hybrid-type solid electrolytic capacitors with a dielectric film formed at a formation voltage of 300V or more. However, for hybrid-type solid electrolytic capacitors with a dielectric film formed at a formation voltage of 100V or less, no difference in leakage current (LC) was observed depending on the moisture content.

The present invention has been proposed to solve the above problems, and its purpose is to provide a hybrid-type solid electrolytic capacitor that has good capacitor characteristics and a high withstand voltage, and a manufacturing method thereof.

In order to solve the above problem, the solid electrolytic capacitor of this embodiment is a solid electrolytic capacitor having a capacitor element, the capacitor element having an anode body containing a valve metal, a cathode body facing the anode body, and an electrolyte layer interposed between the anode body and the cathode body and containing an electrolyte solution and a solid electrolyte, the anode body having a dielectric film on its surface with a withstand voltage of 300 V or more, the electrolyte solution containing a solute of 0.08 mol/kg or more and 0.34 mol/kg or less, and moisture of 1 wt % or more and 10 wt % or less with respect to the total amount of the electrolyte contained in the capacitor element.

The electrolyte may contain 15 wt % or more of a pressure resistance improver based on the total amount of the electrolyte.

The pressure resistance improver may be an alkylene oxide-added polyol or a derivative thereof having a molecular weight of 600 or more.

The electrolyte layer may further contain a compound having a hydroxyl group and a boiling point of 150°C or higher.

The compound may be ethylene glycol, diethylene glycol, glycerin, or two or more of these.

The anode body may have a pseudo-boehmite layer on the dielectric coating, and the amount of the pseudo-boehmite layer may be 0.1 mg/cm ² or more and 1.97 mg/cm ² or less.

In order to solve the above problem, the method for manufacturing a solid electrolytic capacitor of this embodiment is a method for manufacturing a solid electrolytic capacitor having a capacitor element composed of an anode body, a cathode body, and an electrolyte layer, and includes a chemical conversion process for forming a dielectric film having a withstand voltage of 300 V or more on the surface of the anode body, a first electrolyte layer formation process for applying and drying a conductive polymer liquid between the anode body and the cathode body or on the capacitor element, and a second electrolyte layer formation process for impregnating the capacitor element with an electrolyte, the electrolyte containing a solute of 0.08 mol/kg or more and 0.34 mol/kg or less, and adjusting the moisture content of the total amount of the electrolyte contained in the capacitor element to 1 wt% or more and 10 wt% or less.

The present invention makes it possible to achieve a high withstand voltage of 300V or more while maintaining low leakage current and low ESR.

The upper graph shows the relationship between solute concentration and ESR, and the lower graph shows the relationship between solute concentration and leakage current (LC). 1 is a graph showing the relationship between moisture content and leakage current (LC). 1 is a graph showing the relationship between a voltage resistance improver and a voltage resistance.

The solid electrolytic capacitor according to the embodiment will be described below. Note that the present invention is not limited to the embodiment described below.

(Solid electrolytic capacitor)
A solid electrolytic capacitor is a passive element that obtains capacitance by the dielectric polarization action of a dielectric film and stores and discharges electric charge. The solid electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body, a cathode body, an electrolyte layer, and a separator. A dielectric film is formed on the surface of the anode foil. The anode body and the cathode body face each other with the dielectric film in between. The electrolyte layer is interposed between the dielectric film of the anode body and the cathode body. The electrolyte layer is in close contact with the dielectric film of the anode body and functions as a true cathode, and extends between the dielectric film and the cathode body to create a conductive path.

This solid electrolytic capacitor is a so-called hybrid type that has an electrolytic solution and a solid electrolyte. The electrolyte layer contains at least an electrolytic solution and a solid electrolyte. The separator separates the anode body and the cathode body to prevent short circuits, and also holds the electrolyte layer in place. If the solid electrolyte can hold the shape of the electrolyte layer by itself and isolate the anode body and cathode body, the separator can be eliminated from the solid electrolytic capacitor.

The anode and cathode bodies are alternately stacked with an electrolyte layer between them. In this stacked type, the capacitor element may be a flat plate type that omits the exterior, or, for example, the capacitor element may be covered with a laminate film, or may be sealed by molding, dip coating, or printing a resin such as a heat-resistant resin or an insulating resin. Alternatively, the anode and cathode bodies are alternately stacked with an electrolyte layer between them and wound. In this wound type, for example, the capacitor element is housed in a cylindrical case with a bottom. The opening of the case is sealed with a sealing body by crimping.

After sealing the capacitor element, the process moves to the aging process, where a DC voltage is applied to the solid electrolytic capacitor at high temperature to repair the oxide film that was damaged during the winding and other steps of the manufacturing process of the solid electrolytic capacitor. This completes the process of forming the solid electrolytic capacitor.

(Anode body)
The anode body is a foil made of a valve metal. In the wound type, the anode body is a long strip of valve metal stretched, and in the laminated type, the anode body is a flat plate or a sintered body obtained by molding and sintering powder into a flat plate. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the anode body is preferably 99.9% or more, but impurities such as silicon, iron, copper, magnesium, and zinc may be included.

A surface expansion layer is formed on one or both sides of the anode body. The surface expansion layer is a surface layer that has been treated to increase the surface area beyond the projected area, and can be an etching layer formed by etching the foil, a sintered layer formed by attaching valve metal powder to the foil and sintering it, or a deposition layer formed by depositing valve metal particles onto the foil. In other words, the surface expansion layer has a porous structure, consisting of tunnel-shaped pits, spongy pits, or spaces between densely packed powder or particles.

Tunnel-shaped etching pits are holes dug in the foil thickness direction and may penetrate the foil body. These tunnel-shaped etching pits are typically formed by passing a direct current in an acidic aqueous solution such as hydrochloric acid, in which halogen ions are present. The tunnel-shaped etching pits are further expanded in diameter by passing a direct current in an acidic aqueous solution such as nitric acid. The spongy etching pits make the expanded surface layer into a sponge-like layer with fine gaps that are connected together in a space. These spongy etching pits are formed by passing an alternating current in an acidic aqueous solution such as hydrochloric acid, in which halogen ions are present.

The sintered layer is produced by attaching a powder of a valve action metal, which is the same or different from the foil body, to the foil body and sintering it. The powder can be obtained by a milling method, atomization method, melt spinning method, rotating disk method, rotating electrode method, etc. The powder is made into a paste using a binder or solvent, which is applied to the foil body and dried. The powder is then sintered by heating in a vacuum or reducing atmosphere, etc. The atomization method may be any of water atomization method, gas atomization method, and water gas atomization method. The vapor deposition layer is produced by, for example, a resistance heating vapor deposition method or an electron beam heating vapor deposition method. This vapor deposition layer is formed by heating and evaporating a valve action metal, which is the same or different from the foil body, using resistance heat or electron beam energy, and depositing the vapor of the valve action metal particles on the surface of the foil body.

The dielectric coating is formed on the surface of the anode body, following the unevenness of the surface expansion layer. The dielectric coating is typically an oxide coating formed by anodizing the surface of the anode body. If the anode body is aluminum foil, the dielectric coating is an aluminum oxide layer formed by oxidizing the surface of the anode body, following the unevenness of the surface expansion layer. The dielectric coating is formed by chemical conversion treatment.

In chemical conversion treatment, a voltage is applied to the anode in the conversion solution until the desired withstand voltage is reached. The conversion solution is a solution that does not contain halogen ions, and examples of such solutions include phosphoric acid-based conversion solutions such as ammonium dihydrogen phosphate, boric acid-based conversion solutions such as ammonium borate, and adipic acid-based conversion solutions such as ammonium adipate. In this solid electrolytic capacitor, a dielectric film with a withstand voltage of 300V or more is formed so that the product rated withstand voltage can be set to at least 250V. That is, while the anode is immersed in the conversion solution, a voltage is applied while a constant current is passed through it until the conversion voltage reaches 300V or more.

Voids that have been generated in the dielectric film by applying a voltage of 300V or more may be repaired by depolarization. Depolarization includes heat treatment, phosphate treatment, or both. Heat treatment involves exposing the film to a temperature environment of 450°C or more in the atmosphere, for example, to open up isolated voids inside the dielectric film. Phosphate treatment enlarges cracks and openings that lead to the voids. In this phosphate treatment, the anode body is immersed in a phosphoric acid solution or ammonium dihydrogen phosphate solution. This makes it easier for the re-chemical solution to penetrate into the voids.

It is preferable to form a pseudo-boehmite layer on the dielectric coating, i.e., on the foil surface side of the dielectric coating. The pseudo-boehmite layer contains hydrated oxide of aluminum, and is AlOOH.xH ₂ O. The dielectric coating is a layer of aluminum oxide containing γ-alumina, which is a crystalline oxide. This pseudo-boehmite layer is dense inside and deteriorates the impregnation of the conductive polymer of the solid electrolyte into the anode foil, but functions as a resistance layer to improve the withstand voltage of the solid electrolytic capacitor.

The pseudo-boehmite layer is formed by a pre-chemical treatment process, which is a process that precedes the chemical treatment and is performed after the surface enlarging process of the anode foil. In the pre-chemical treatment process, the anode foil is immersed in pure water at 80°C or higher or in boiling water. The immersion time can be determined based on the balance between the withstand voltage and the electrostatic capacitance, depending on the desired thickness of the pseudo-boehmite layer. When a pseudo-boehmite layer is formed, the chemical treatment transforms the pseudo-boehmite layer into a dielectric oxide film layer from the interface between the unoxidized aluminum foil and the pseudo-boehmite layer toward the outer surface of the pseudo-boehmite layer.

The pseudo-boehmite layer is adjusted to have an amount of 0.1 mg/ ^cm2 or more and 1.97 mg/ ^cm2 or less. By having the amount of the pseudo-boehmite layer fall within this range, the solid electrolytic capacitor can be more effectively compatible with a high withstand voltage and a low ESR. In particular, when the pseudo-boehmite layer is adjusted to have an amount of 0.1 mg/ ^cm2 or more and 1.73 mg/ ^cm2 or less, the initial ESR, that is, the ESR after aging and in a non-energized state except for inspection, becomes low.

There is no limitation on the method for keeping the amount of the pseudo-boehmite layer within the range of 0.1 mg/ ^cm2 to 1.97 mg/ ^cm2 or 0.1 mg/ ^cm2 to 1.73 mg/ ^cm2 , and various methods may be used. For example, the amount of the pseudo-boehmite layer can be changed by changing the immersion time in pure water in the pre-chemical treatment. In addition, as a post-chemical treatment step, the anode foil may be immersed in phosphoric acid or the like for a short time for acid treatment, the pseudo-boehmite layer may be dissolved from the surface, and a series of steps may be repeated to perform a repair chemical treatment. In the repair chemical treatment, the anode foil is immersed in a chemical solution and a voltage is applied. As the chemical solution, a phosphoric acid-based chemical solution such as ammonium dihydrogen phosphate, a boric acid-based chemical solution such as ammonium borate, an adipic acid-based chemical solution such as ammonium adipate, or a chemical solution in which boric acid and a dicarboxylic acid such as citric acid are mixed may be used. The applied voltage may be in accordance with the desired withstand voltage.

(Cathode body)
The cathode body is a foil made of an elongated valve metal. The purity of the cathode foil is preferably 99% or more, but impurities such as silicon, iron, copper, magnesium, and zinc may be included. The foil body is a plain foil with a flat surface, or a surface-expanding layer is formed on the surface by surface-expanding. An oxide film may be formed on the surface-expanding layer intentionally or naturally. A thin oxide film of about 1 to 10 V may be intentionally formed by chemical conversion treatment. A natural oxide film is formed by the reaction of the cathode foil with oxygen in the air.

When the solid electrolytic capacitor is a laminated type, the cathode body is preferably a laminate of a metal layer and a carbon layer. The carbon layer of the cathode body is arranged facing the anode body. The carbon layer is made into a paste form, and is formed by applying it onto the electrolyte layer after the electrolyte layer is formed on the anode body, and then curing it by heating. The metal layer is, for example, a silver layer, and is formed by applying it into a paste form on top of the carbon layer, and then curing it by heating.

The cathode body may further include a laminated conductive layer. The conductive layer contains a conductive material and is a layer with higher conductivity than the oxide film. This conductive layer is laminated on one or both sides of the cathode foil and is located as the outermost layer of the cathode body. Examples of conductive materials include titanium, zirconium, tantalum, niobium, nitrides or carbides of these, aluminum carbide, carbon materials, and composites or mixtures of these.

This conductive layer may be a laminate of multiple layers, and each layer may be of a different type. The conductive layer and the cathode body may have a pressure-welded structure. After the conductive layers are laminated, a press treatment is applied. In the pressure-welded structure, the conductive layer is pressed into the pores of the surface-expanding layer, and the conductive layer is deformed along the uneven surface of the surface-expanding layer. The pressure-welded structure improves the adhesion and fixation between the conductive layer and the cathode body, and reduces the ESR of the solid electrolytic capacitor.

(Electrolyte layer)
(Electrolyte)
The solvent of the electrolyte is a protic organic polar solvent or an aprotic organic polar solvent, and may be used alone or in combination of two or more. The electrolyte also contains water. The solute contained in the electrolyte is an organic acid or its salt, an inorganic acid or its salt, or a composite compound of an organic acid and an inorganic acid or its salt, and may be used alone or in combination of two or more. When the solute is a salt, an ionically dissociable salt is selected.

The solute is contained in the electrolyte at a ratio of 0.08 mol/kg or more and 0.34 mol/kg or less relative to the total amount of the electrolyte. If the solute is less than 0.08 mol/kg, the leakage current (LC) will be high in a hybrid-type solid electrolytic capacitor having a dielectric film with a withstand voltage of 300V or more. On the other hand, if the solute is more than 0.34 mol/kg, the ESR will rise sharply in a hybrid-type solid electrolytic capacitor having a dielectric film with a withstand voltage of 300V or more. If the solute range is 0.08 mol/kg or more and 0.34 mol/kg or less, a hybrid-type solid electrolytic capacitor having a dielectric film with a withstand voltage of 300V or more can achieve both low leakage current and low ESR.

Preferably, the solute is contained in the electrolyte at a ratio of 0.08 mol/kg or more and 0.24 mol/kg or less relative to the total amount of the electrolyte. When the solute is in the range of 0.08 mol/kg or more and 0.24 mol/kg or less, a hybrid-type solid electrolytic capacitor having a dielectric film with a withstand voltage of 300 V or more can achieve both a low leakage current and an even lower ESR.

The amount of moisture in the electrolyte is between 1 wt% and 10 wt% of the total amount of electrolyte. This amount of moisture is the percentage of the electrolyte impregnated in the solid electrolytic capacitor, and is measured by extracting the electrolyte after impregnation from the solid electrolytic capacitor by centrifugation. In other words, the moisture in the electrolyte is the sum of the moisture added to the electrolyte and the moisture mixed into the capacitor element during the manufacturing process of the solid electrolytic capacitor. Therefore, by controlling the moisture mixed in during the manufacturing process of the solid electrolytic capacitor and the moisture added to the electrolyte, the amount of moisture in the electrolyte can be adjusted to be between 1 wt% and 10 wt% of the total amount of electrolyte.

If the moisture content in the electrolyte is less than 1 wt%, the leakage current (LC) will increase sharply in a hybrid-type solid electrolytic capacitor with a dielectric film with a withstand voltage of 300V or more. If the moisture content in the electrolyte is more than 10 wt%, the leakage current (LC) will actually increase in a hybrid-type solid electrolytic capacitor with a dielectric film with a withstand voltage of 300V or more. Since there is no significant change in ESR in terms of the relationship between moisture content and ESR, low leakage current and low ESR can be achieved simultaneously if the moisture content in the electrolyte is in the range of 1 wt% to 10 wt%.

The type of solute is not particularly limited. Examples of organic acids include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedioic acid, dodecanedioic acid, and tridecanedioic acid, as well as phenols and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of composite compounds of organic and inorganic acids include borodisalicylic acid, borodioxalic acid, and borodiglycolic acid.

These salts of organic acids, salts of inorganic acids, and at least one salt of a complex compound of an organic acid and an inorganic acid include ammonium salts, quaternary ammonium salts, quaternary amidinium salts, amine salts, sodium salts, potassium salts, etc. Examples of the quaternary ammonium ions of the quaternary ammonium salts include tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Examples of the quaternary amidiniums include ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Examples of the amines of the amine salts include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, propylamine, etc., secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc., and tertiary amines include trimethylamine, triethylamine, tripropylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

Protic organic polar solvents in the solvent include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, polyglycerin, diethylene glycol, dipropylene glycol, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, and dimethoxypropanol.

Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, nitriles, and sulfoxides. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, and N,N-diethylacetamide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutaronitrile. Examples of sulfoxides include dimethyl sulfoxide.

Furthermore, the electrolyte may contain a polymer solvent as a pressure resistance improver. Examples of this polymer solvent include polyols with alkylene oxide added thereto or derivatives thereof. This pressure resistance improver may improve the voltage resistance of the solid electrolytic capacitor. This pressure resistance improver is preferably added so as to occupy 15 wt % or more of the electrolyte solvent, and particularly improves the voltage resistance of the solid electrolytic capacitor.

Polyols or derivatives thereof to which alkylene oxide has been added include polyethylene glycol, polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol triglyceryl ether, polypropylene glycol, polypropylene glycol glyceryl ether, polypropylene glycol diglyceryl ether, polypropylene glycol triglyceryl ether, polyoxyethylene glycerin, polyoxypropylene glycerin, glycols containing ethylene oxide and propylene oxide, and glycerin containing ethylene oxide and propylene oxide. Among these, polyols to which alkylene oxides having a molecular weight of 600 or more have been added are particularly preferred, as they particularly improve the withstand voltage of solid electrolytic capacitors.

Other additives can also be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, phosphate esters, colloidal silica, etc. These may be used alone or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in the solid electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, etc.

The capacitor element is immersed in the electrolyte, and the electrolyte is impregnated into the voids within the capacitor element. If necessary, a pressure reduction or pressure increase may be performed to allow the electrolyte to be impregnated into smaller voids. The electrolyte impregnation process may be repeated multiple times. For example, the pressure inside the capacitor element may be reduced, and the electrolyte may be injected into the capacitor element while pressurizing the electrolyte.

(Solid electrolyte)
The solid electrolyte contained in the electrolyte layer is preferably a conductive polymer from the viewpoint of adhesion to the dielectric film. The conductive polymer is a self-doped conjugated polymer doped with a dopant molecule in the molecule or an externally doped conjugated polymer doped with an external dopant molecule. The conjugated polymer is obtained by chemically oxidizing or electrolytically oxidizing a monomer having a π-conjugated double bond or a derivative thereof. The conductive polymer exhibits high conductivity by performing a doping reaction on the conjugated polymer. That is, the conductivity is exhibited by adding a small amount of a dopant such as an acceptor that easily accepts electrons or a donor that easily gives electrons to the conjugated polymer.

Conventional conjugated polymers can be used without any particular limitations. Examples include polypyrrole, polythiophene, polyaniline, etc. These conjugated polymers can be used alone or in combination of two or more types, or can be copolymers of two or more types of monomers.

Among the above conjugated polymers, preferred are conjugated polymers formed by polymerizing thiophene or its derivatives, and preferred are conjugated polymers formed by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxine), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene, or derivatives thereof. As the thiophene derivative, a compound selected from thiophenes having substituents at the 3rd and 4th positions is preferred, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbons at the 3rd and 4th positions. The alkyl group or alkoxy group preferably has 1 to 16 carbon atoms.

In particular, a polymer of 3,4-ethylenedioxythiophene called EDOT, i.e., poly(3,4-ethylenedioxythiophene) called PEDOT, is particularly preferred. In addition, alkylated ethylenedioxythiophene in which an alkyl group is added to 3,4-ethylenedioxythiophene may be used, such as methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine) and ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxine).

　Any known dopant can be used without any particular limitation. A single dopant may be used, or two or more dopants may be used in combination. A polymer or monomer may also be used. For example, the dopant may be an inorganic acid such as a polyanion, boric acid, nitric acid, or phosphoric acid, or an organic acid such as acetic acid, oxalic acid, citric acid, tartaric acid, squaric acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalate boric acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, or butylnaphthalenesulfonic acid.

Polyanions include, for example, substituted or unsubstituted polyalkylenes, substituted or unsubstituted polyalkenylenes, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, and include polymers consisting only of structural units having an anionic group, and polymers consisting of structural units having an anionic group and structural units not having an anionic group. Specific examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallylsulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylpropanesulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, and polymaleic acid.

The method of incorporating the conductive polymer into the electrolyte layer is not particularly limited. For example, the conductive polymer liquid may be impregnated into the capacitor element to fill the electrolyte layer. The conductive polymer liquid may be applied or ejected between the anode body and the cathode body. By applying the conductive polymer liquid between the anode body and the cathode body, the conductive polymer liquid is applied to the dielectric film of the anode body, the cathode body, the separator, or a combination of these. Before assembling the capacitor element, the conductive polymer liquid may be applied individually to the dielectric film of the anode body, the cathode body, the separator, or a combination of these.

The conductive polymer liquid is a liquid in which conductive polymer particles or powder are dispersed or dissolved. In order to promote the impregnation of the conductive polymer liquid into the capacitor element, a decompression treatment or a pressurization treatment may be performed as necessary. The impregnation process of the conductive polymer liquid may be repeated multiple times. After the capacitor element is impregnated with the conductive polymer liquid, a part of the dispersion medium or solvent is removed by a drying process.

The solvent or dispersion medium of the conductive polymer liquid may be water, an organic solvent, or a mixture of these, as long as it disperses or dissolves the conductive polymer particles or powder. Suitable examples of organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, nitrile compounds, and sulfones.

Polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, etc. Alcohols include methanol, ethanol, propanol, butanol, etc. Esters include ethyl acetate, propyl acetate, butyl acetate, etc. Hydrocarbons include hexane, heptane, benzene, toluene, xylene, etc. Carbonate compounds include ethylene carbonate, propylene carbonate, etc. Ether compounds include dioxane, diethyl ether, etc. Chain ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, polypropylene glycol dialkyl ether, etc. Heterocyclic compounds include 3-methyl-2-oxazolidinone, etc. Nitrile compounds include acetonitrile, glutarodinitrile, methoxyacetonitrile, propionitrile, benzonitrile, etc. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane.

Among these, a high-boiling point solvent having a hydroxyl group and a boiling point of 150°C or higher is preferred. This high-boiling point solvent improves the chemical conversion properties of the dielectric film and increases the voltage resistance of the solid electrolytic capacitor. Examples of high-boiling point solvents include polyhydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, glycerin, and polyglycerin, or combinations of two or more of these. High-boiling point solvents can be left in the electrolyte layer due to their high boiling point, resulting in reduced ESR and improved voltage resistance.

The pH of the conductive polymer liquid may be adjusted. Examples of pH adjusters include ammonia water, sodium hydroxide, primary amines, secondary amines, and tertiary amines. Conventional additives such as organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, and ultraviolet absorbers may also be added to the conductive polymer liquid. It is also possible to significantly reduce the ESR by adding additives to the conductive polymer liquid or by increasing the number of times the capacitor element is impregnated with the conductive polymer liquid.

(Separator)
Examples of the separator include cellulose papers such as kraft, Manila hemp, esparto, hemp, and rayon, and mixed papers thereof; polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof; polytetrafluoroethylene-based resins, polyvinylidene fluoride-based resins, vinylon-based resins, polyamide-based resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide-based resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, and polyvinyl alcohol resins. These resins can be used alone or in combination.

The solid electrolytic capacitor of the embodiment will be described in more detail below. Note that the present invention is not limited to the embodiment described below.

(Examples 1 to 5)
Solid electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 to 3 were produced. First, an anode body and a cathode body were produced using aluminum foil. The anode body was subjected to an etching process to form a surface enlargement layer consisting of tunnel-shaped etching pits. Next, the anode body was subjected to a chemical conversion process to form a dielectric film. During the chemical conversion process, the anode body was immersed in an ammonium borate aqueous solution, and a voltage was applied so that the withstand voltage of the anode body was 650 V.

The cathode body is a plain aluminum foil that has not been enlarged or chemically treated. Lead wires were connected to the anode body and cathode body, and the anode body and cathode body were wound facing each other with a cellulose-based separator in between. The wound body was immersed in an aqueous solution of ammonium borate, and a constant current of 10 mA was applied while a voltage of 550 V was applied, thereby carrying out a repair chemical treatment. It was then washed with pure water and dried at 105°C.

The wound body was immersed in a conductive polymer liquid, and a solid electrolyte was applied to the dielectric film of the anode body, the cathode body, and the separator. After immersing the wound body in the conductive polymer liquid, the wound body was dried at 110°C for 1 hour.

In the conductive polymer solution, poly(3,4-ethylenedioxythiophene) particles doped with polystyrene sulfonic acid were dispersed as the conductive polymer. The dispersion medium was a mixture of 50 wt% water and 50 wt% ethylene glycol, and a conductive polymer solution was prepared with a conductive polymer concentration of 1 wt%. 2 wt% sorbitol was added to the conductive polymer solution based on the total amount of the conductive polymer solution. The conductive polymer was dispersed using an ultrasonic homogenizer.

Furthermore, the wound body on which the conductive polymer electrolyte layer was formed was impregnated with an electrolyte. The solvent of the electrolyte was composed of ethylene glycol, which accounted for 60 wt% of the total amount of the solvent, and polyethylene glycol, which accounted for 40 wt% of the total amount of the solvent. The molecular weight of the polyethylene glycol was 1000. The solute of the electrolyte was ammonium azelaate.

The moisture content of the electrolyte was set to 5 wt% of the electrolyte contained in the solid electrolytic capacitor. The moisture content of the electrolyte was adjusted by controlling the amount of moisture added to the electrolyte and the moisture that was mixed in during the manufacturing process of the solid electrolytic capacitor. The moisture content was also measured by extracting the electrolyte from the manufactured solid electrolytic capacitor by centrifugation.

Examples 1 to 5 and Comparative Examples 1 to 3 have different solute concentrations (mol/kg) in the electrolyte, as shown in Table 1 below. In Table 1 below, the moisture content in the electrolyte is expressed as the moisture content of the electrolyte in the product.
(Table 1)

After forming an electrolyte layer with the solid electrolyte and electrolyte solution, a rubber seal was attached to the open end of the bottomed cylindrical exterior case housing the capacitor element, and the case was then sealed by crimping. Each solid electrolytic capacitor was aged by applying a voltage. The size of each solid electrolytic capacitor, including the exterior case and rubber seal, was 10 mm in diameter and 12.5 mm in height, and the rated capacitance was 5.6 μF.

(Solute concentration test)
The leakage current (LC), initial ESR, and electrolytic solution resistivity of the solid electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 to 3 were measured. The leakage current was measured as the value of an oscilloscope 20 minutes after applying 475 V in a temperature environment of 105°C. The ESR was measured under the following conditions: ambient temperature of 20°C, an LCR meter (E4980A, manufactured by Agilent Technologies), an AC current level of 1.0 Vrms, and a measurement frequency of 100 kHz. The resistivity was measured at a temperature of 30°C using an electrical conductivity meter (CM-42X, manufactured by DKK-TOA Corporation).

Table 2 below shows the measurement results of leakage current (LC), initial ESR, and resistivity of the solid electrolytic capacitors of Examples 1 to 5 and Comparative Examples 1 to 3. In addition, based on Table 2 below, a graph showing the relationship between solute concentration and ESR and a graph showing the relationship between solute concentration and leakage current (LC) were created. The upper graph in Figure 1 is a graph showing the relationship between solute concentration and ESR, and the lower graph is a graph showing the relationship between solute concentration and leakage current (LC).

(Table 2)

As shown in Table 2 and Figure 1, it can be confirmed that in Examples 1 to 5, the concentration of the solute in the electrolyte is 0.08 mol/kg or more and 0.34 mol/kg or less, thereby achieving both low leakage current (LC) and low ESR. The specific resistance of the electrolyte is the lowest in Comparative Example 3, which has the highest solute concentration, but its ESR is the highest. The difference in the specific resistance of the electrolyte between Example 1 and Example 3 is nearly two times, but it can be confirmed that both have low ESR.

(Examples 6 to 8)
Solid electrolytic capacitors of Examples 6 to 8 and Comparative Examples 4 to 6 were produced. Except for the moisture content in the electrolyte impregnated in the solid electrolytic capacitor, Examples 6 to 8 and Comparative Examples 4 to 6 were produced with the same composition, configuration, manufacturing method and manufacturing conditions as the electrolyte of the solid electrolytic capacitor of Example 2. The moisture content of the electrolyte in the product was adjusted by controlling the addition of moisture to the electrolyte and the moisture mixed in during the manufacturing process of the solid electrolytic capacitor.

The moisture contents of Examples 6 to 8 and Comparative Examples 4 to 6 are shown in Table 3 below.
(Table 3)

(Moisture content test)
The leakage current (LC), initial ESR, and specific resistance of the electrolyte were measured for the solid electrolytic capacitors of Examples 6 to 8 and Comparative Examples 4 to 6. The measurement conditions for the leakage current and ESR were the same as those of Examples 1 to 5 and Comparative Examples 1 to 3.

The measurement results of the leakage current (LC), initial ESR, and resistivity of the solid electrolytic capacitors of Examples 2 and 6 to 8 and Comparative Examples 4 to 6 are shown in Table 4 below. In addition, based on Table 4 below, a graph showing the relationship between moisture content and leakage current (LC) was created as shown in Figure 2.

(Table 4)

As shown in Table 4 and Figure 2, when the moisture content is low or high, the leakage current (LC) is high. However, it can be confirmed that when the moisture content in the electrolyte is between 1 wt% and 10 wt%, the leakage current (LC) is low.

(Examples 9 to 11)
Solid electrolytic capacitors of Examples 9 to 11, Comparative Examples 7 to 9, and Reference Examples 1 to 5 were produced. Examples 9 to 11 and Comparative Examples 7 to 9 all had the same solute concentration but different moisture contents. Examples 9 to 11 and Comparative Examples 7 to 9 had different formation voltages for the anode foil compared to Examples 2, 6 to 8, and Comparative Examples 4 to 6. In addition, Examples 9 to 11 and Comparative Examples 7 to 9 were produced with the same composition, configuration, manufacturing method, and manufacturing conditions as the electrolyte of the solid electrolytic capacitors of Examples 2, 6 to 8, and Comparative Examples 4 to 6.

The anode bodies of Examples 9 to 11 and Comparative Examples 7 to 9 were immersed in an aqueous solution of ammonium borate during chemical conversion treatment, and a voltage was applied to them. A voltage was applied to the anode bodies until the final voltage reached 360 V.

In addition, Reference Examples 1 to 5 all have the same solute concentration, but different moisture percentages. The anode bodies of Reference Examples 1 to 5 were immersed in an aqueous solution of ammonium borate during chemical conversion treatment, and voltage was applied. Voltage was applied to the anode bodies until the final voltage reached 160 V. In addition, Reference Examples 1 to 5 were produced with the same composition, configuration, manufacturing method, and manufacturing conditions as the electrolyte of the solid electrolytic capacitors of Examples 2 and 6 to 8 and Comparative Examples 4 to 6.

Then, the leakage current (LC), initial ESR, and electrolytic solution resistivity of the solid electrolytic capacitors of Examples 9 to 11, Comparative Examples 7 to 9, and Reference Examples 1 to 5 were measured. The measurement conditions for leakage current and ESR were the same as those of Examples 1 to 5 and Comparative Examples 1 to 3.

The measurement results of the leakage current (LC), initial ESR, and resistivity of the solid electrolytic capacitors of Examples 9 to 11, Comparative Examples 7 to 9, and Reference Examples 1 to 5 are shown in Tables 5 and 6 below.

(Table 5)

Table 6

As shown in Table 5, the hybrid-type solid electrolytic capacitor with a dielectric film with a withstand voltage of 360 V had high leakage current (LC) when the moisture content was low and high, just as in the case of a withstand voltage of 650 V shown in Table 4. However, it can be confirmed that a low leakage current (LC) was achieved when the moisture content in the electrolyte was between 1 wt% and 10 wt%.

On the other hand, as shown in Table 6, in the case of a hybrid-type solid electrolytic capacitor with a dielectric film having a withstand voltage of 160 V, which is lower than 300 V, there is no change in leakage current (LC) and ESR even if the moisture content changes.

From the above, in the case of a hybrid-type solid electrolytic capacitor having a dielectric film with a withstand voltage of 300V or more, the electrolyte contains a solute of 0.08 mol/kg or more and 0.34 mol/kg or less, and a water content of 1 wt% or more and 10 wt% or less of the total amount of the electrolyte, thereby achieving both low leakage current (LC) and low ESR.

(Examples 12 to 17)
Next, the solid electrolytic capacitors of Examples 12 to 17 were produced. In the solid electrolytic capacitors of Examples 12 to 17, the solvent in the electrolytic solution was composed of polyethylene glycol and ethylene glycol having a molecular weight of 1000, which are pressure resistance improvers. Otherwise, the solid electrolytic capacitors of Examples 12 to 17 were produced with the same composition, configuration, manufacturing method, and manufacturing conditions as the electrolytic solution of the solid electrolytic capacitor of Example 2.

The breakdown voltage of the solid electrolytic capacitors of Examples 12 to 17 and Example 2 was measured. The breakdown voltage was measured as follows. That is, a voltage was applied to the solid electrolytic capacitor at 105°C. The starting voltage was 200V, and the applied voltage was increased by 1V every 10 seconds. The voltage when the current flowing through the solid electrolytic capacitor reached 1mA was taken as the breakdown voltage.

(Voltage resistance measurement test)
The ratio of polyethylene glycol in the electrolyte solvent and the measurement results of the withstand voltage of the solid electrolytic capacitors of Examples 12 to 17 and Example 2 are shown in Table 7 below. Based on Table 7 below, the relationship between the withstand voltage improver and the withstand voltage is shown in FIG.
(Table 7)

As shown in Table 7 and Figure 3, it can be confirmed that the voltage resistance of solid electrolytic capacitors is improved when a polymeric voltage resistance improver is added to an electrolytic capacitor. In particular, the effect of improving voltage resistance is enhanced when the voltage resistance improver is added so that it occupies 15 wt % or more of the electrolyte solvent.

(Examples 18 to 21)
Next, solid electrolytic capacitors of Examples 18 to 21 were produced. The types of voltage resistance improvers contained in the electrolytic solution of Examples 18 to 21 were different from those of Example 2. Other than that, Examples 18 to 21 were produced with the same composition, the same configuration, and the same manufacturing method and manufacturing conditions as the electrolytic solution of the solid electrolytic capacitor of Example 2.

The solvent in the electrolyte of Examples 18 to 20 is polyethylene glycol, which is a pressure resistance improver, but the molecular weight of the polyethylene glycol is different from that of Example 2. Also, the solvent in the electrolyte of Example 21 is an alkylene oxide-added glycerin derivative, which is a pressure resistance improver. The molecular weight of the alkylene oxide-added glycerin derivative is 3000.

The breakdown voltage of the solid electrolytic capacitors of Examples 18 to 21 and Example 2 was measured. The breakdown voltage was measured as follows. That is, a voltage was applied to the solid electrolytic capacitor at 105°C. The starting voltage was 200V, and the applied voltage was increased by 1V every 10 seconds. The voltage when the current flowing through the solid electrolytic capacitor reached 1mA was taken as the breakdown voltage.

(Voltage resistance measurement test)
The types of the voltage resistance improvers contained in the electrolyte solvents of the solid electrolytic capacitors of Examples 18 to 21 and Example 2 and the measurement results of the voltage resistance are shown in Table 8 below.
Table 8

As shown in Table 8, it was confirmed that the voltage resistance improving effect was particularly high when the polymer acting as the voltage resistance improving agent was an alkylene oxide-added polyol or its derivative with a molecular weight of 600 or more.

(Examples 22 to 25)
Next, solid electrolytic capacitors of Examples 22 to 25 were produced. In Examples 22 to 25, as in Example 2, the solvent of the conductive polymer liquid used to form the solid electrolyte was composed of ethylene glycol and water. However, the amount of ethylene glycol in Examples 22 to 25 is different from that in Example 2. Other than that, Examples 22 to 25 were produced with the same composition, configuration, manufacturing method, and manufacturing conditions as the electrolytic solution of the solid electrolytic capacitor of Example 2.

The breakdown voltage of the solid electrolytic capacitors of Examples 22 to 25 and Example 2 was measured. The breakdown voltage was measured as follows. That is, a voltage was applied to the solid electrolytic capacitor at 105°C. The starting voltage was 200V, and the applied voltage was increased by 1V every 10 seconds. The voltage when the current flowing through the solid electrolytic capacitor reached 1mA was taken as the breakdown voltage.

(Voltage resistance measurement test)
The ratio of ethylene glycol in the solvent of the conductive polymer solution of Examples 22 to 25 and Example 2 and the measurement results of the withstand voltage are shown in Table 9 below.
Table 9

As shown in Table 9, it was confirmed that the voltage resistance of solid electrolytic capacitors improves when ethylene glycol is included in the conductive polymer liquid. Compounds that have a hydroxyl group and a boiling point of 150°C or higher tend to remain in the electrolyte layer, and ethylene glycol in particular contributes to improving the voltage resistance of solid electrolytic capacitors.

(Examples 26 to 28)
Next, solid electrolytic capacitors of Examples 26 to 28 were produced. Examples 26 to 28 differ from Example 2 in the solvent of the conductive polymer liquid when forming the solid electrolyte. While the solvent of the conductive polymer liquid in Example 2 is composed of water and ethylene glycol, Example 26 is composed of diethylene glycol and water, Example 27 is composed of glycerin and water, and Example 28 is composed of sulfolane and water. However, diethylene glycol and glycerin are compounds that have a hydroxyl group and a boiling point of 150°C or higher, just like ethylene glycol. Sulfolane is a compound that does not have a hydroxyl group and has a boiling point of 150°C or higher.

The composition ratio of diethylene glycol, glycerin or sulfolane to water is the same as the composition ratio of ethylene glycol to water in Example 2. In addition, Examples 26 to 28 are produced with the same composition, structure, manufacturing method and manufacturing conditions as the electrolyte of the solid electrolytic capacitor in Example 2.

The breakdown voltage of the solid electrolytic capacitors of Examples 26 to 28 and Example 2 was measured. The breakdown voltage was measured as follows. That is, a voltage was applied to the solid electrolytic capacitor at 105°C. The starting voltage was 200V, and the applied voltage was increased by 1V every 10 seconds. The voltage when the current flowing through the solid electrolytic capacitor reached 1mA was taken as the breakdown voltage.

(Voltage resistance measurement test)
The ratio of ethylene glycol in the solvent of the conductive polymer solution of Examples 26 to 28 and Example 2 and the measurement results of the withstand voltage are shown in Table 10 below.
(Table 10)

As shown in Table 10, it was confirmed that when diethylene glycol or glycerin is contained in the conductive polymer liquid, the voltage resistance of the solid electrolytic capacitor is improved, just as when ethylene glycol is contained. Taking Tables 9 and 10 together, it can be confirmed that compounds that have a hydroxyl group and a boiling point of 150°C or higher tend to remain in the electrolyte layer, contributing to improving the voltage resistance of the solid electrolytic capacitor.

(Examples 29 to 33)
The solid electrolytic capacitors of Examples 29 to 33 were produced. The solid electrolytic capacitors of Examples 2 and 29 to 33 were provided with an anode body having a pseudo-boehmite layer. That is, in Examples 2 and 29 to 33, a surface-enlarging layer made of tunnel-shaped etching pits was formed by etching, and then the chemical pretreatment step was performed.

In the chemical pretreatment process, the aluminum foil was immersed in boiled pure water to form a pseudo-boehmite layer on the surface of the aluminum foil. Taking advantage of the tendency for the amount of pseudo-boehmite to increase in proportion to the square root of the immersion time in boiled pure water, the amount of pseudo-boehmite was adjusted by adjusting the immersion time of the aluminum foil in boiled pure water. Next, the same chemical treatment as in Example 2 was performed, and the pseudo-boehmite layer was transformed into a dielectric film, leaving only the outermost layer.

(Voltage resistance and ESR test)
The amount of pseudo-boehmite is different in Example 2 and Examples 29 to 33. The ESR and withstand voltage of the solid electrolytic capacitors of Example 2 and Examples 29 to 33 with different amounts of pseudo-boehmite were measured. The initial ESR measurement conditions were an ambient temperature of 20°C, an LCR meter (Agilent Technologies, E4980A), an AC current level of 1.0 Vrms, and a measurement frequency of 100 kHz. In measuring the withstand voltage, a voltage was applied to the solid electrolytic capacitor at 105°C. The starting voltage was 200V, and the applied voltage was increased by 1V every 10 seconds. The voltage when the current flowing through the solid electrolytic capacitor reached 1 mA was taken as the withstand voltage.

The measurement results of the initial ESR and the withstand voltage of the solid electrolytic capacitors of Examples 2 and 29 to 33 are shown in Table 11 below.
Table 11

As shown in Table 11, in the solid electrolytic capacitors of Examples 2 and 29 to 33, the amount of the pseudo-boehmite layer was adjusted to 0.1 mg/ ^cm2 or more and 1.97 mg/ ^cm2 or less. As a result, the solid electrolytic capacitors of Examples 2 and 26 to 30 have high withstand voltage and low ESR. In particular, in Examples 2 and 29 to 32, in which the amount of the pseudo-boehmite layer is 1.73 mg/ ^cm2 or less, the ESR is at least half or less compared to Example 33, and the ESR is particularly low.

Claims (7)

A solid electrolytic capacitor including a capacitor element,
The capacitor element is
an anode body including a valve metal;
A cathode body facing the anode body;
an electrolyte layer interposed between the anode body and the cathode body and including an electrolytic solution and a solid electrolyte;
Equipped with
The anode body has a dielectric coating on a surface thereof, the dielectric coating having a withstand voltage of 300 V or more,
the electrolyte contains a solute of 0.08 mol/kg or more and 0.34 mol/kg or less, and a moisture content of 1 wt % or more and 10 wt % or less with respect to the total amount of the electrolyte contained in the capacitor element;
A solid electrolytic capacitor characterized by: The electrolytic solution contains a pressure resistance improver of 15 wt % or more based on the total amount of the electrolytic solution;
2. The solid electrolytic capacitor according to claim 1 . The pressure resistance improver is an alkylene oxide-added polyol or a derivative thereof having a molecular weight of 600 or more;
3. The solid electrolytic capacitor according to claim 2 . the electrolyte layer further contains a compound having a hydroxy group and a boiling point of 150° C. or higher;
3. The solid electrolytic capacitor according to claim 1 or 2. the compound is ethylene glycol, diethylene glycol, glycerin, or two or more of these;
5. The solid electrolytic capacitor according to claim 4, the anode body has a pseudo-boehmite layer on the dielectric coating,
The amount of the pseudo-boehmite layer is 0.1 mg/ ^cm2 or more and 1.97 mg/ ^cm2 or less;
3. The solid electrolytic capacitor according to claim 1 or 2. A method for manufacturing a solid electrolytic capacitor having a capacitor element including an anode body, a cathode body, and an electrolyte layer, comprising the steps of:
a chemical conversion step of forming a dielectric film having a withstand voltage of 300 V or more on the surface of the anode body;
a first electrolyte layer forming step of applying and drying a conductive polymer liquid between the anode body and the cathode body or on the capacitor element;
a second electrolyte layer forming step of impregnating the capacitor element with an electrolyte;
Including,
The electrolyte contains a solute in an amount of 0.08 mol/kg or more and 0.34 mol/kg or less,
adjusting the amount of water relative to the total amount of the electrolyte contained in the capacitor element to 1 wt % or more and 10 wt % or less;
A method for producing a solid electrolytic capacitor comprising the steps of:

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