TW202414467A - Solid electrolytic capacitor and manufacturing method - Google Patents

Abstract

The purpose of the present invention is to provide a solid electrolytic capacitor that achieves both low ESR and high withstand voltage. The solid electrolytic capacitor comprises a positive electrode foil, a negative electrode body, and a capacitor element having an electrolyte. In the positive electrode foil, the surface is enlarged with tunnel-shaped etching pits, and there is a dielectric film on the surface. The negative electrode body faces the positive electrode foil. The electrolyte includes a solid electrolyte layer that contains a conductive polymer. This solid electrolyte layer has a weight of 250 mg/cm3 or less per unit volume of the capacitor element.

Description

Solid electrolytic capacitor and manufacturing method

The present invention relates to a solid electrolytic capacitor using a solid electrolyte layer or a solid electrolyte layer and a liquid component as an electrolyte and a manufacturing method thereof.

Electrolytic capacitors include valve metals such as tantalum or aluminum as anode foil and cathode foil. The anode foil is expanded by forming the valve metal into a sintered body or an etched foil, and the expanded surface is treated by anodic oxidation to have a dielectric film. An electrolyte is interposed between the anode foil and the cathode foil.

This electrolytic capacitor can increase the specific surface area by expanding the anode foil, and has the advantage of easily obtaining a large electrostatic capacitance compared to other types of capacitors. Electrolytic capacitors include electrolytes in the form of electrolytes. The contact area between the electrolyte and the dielectric film of the anode foil increases. Therefore, the electrostatic capacitance of the electrolytic capacitor is more likely to increase. However, the electrolyte evaporates to the outside over time, and the electrolytic capacitor causes a decrease in electrostatic capacitance or an increase in dielectric loss tangent over time, leading to drying.

Therefore, among electrolytic capacitors, solid electrolytic capacitors using solid electrolytes have attracted much attention. As solid electrolytes, manganese dioxide or 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known. In recent years, conductive polymers derived from monomers having π-conjugated double bonds, such as poly(3,4-ethylenedioxythiophene) (PEDOT), which have 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, or have a partial structure in the monomer molecule that functions as a dopant, and thus exhibit high conductivity. Therefore, solid electrolytic capacitors have the advantage of lowering the equivalent series resistance (ESR).

Among them, solid electrolytic capacitors lack the ability to repair defects in the anodic oxide film as a dielectric, compared to liquid electrolytic capacitors in which an electrolyte is impregnated in the capacitor element, and there is a risk of increased leakage current. Therefore, so-called hybrid solid electrolytic capacitors have also been proposed. Hybrid solid electrolytic capacitors include a driving electrolyte impregnated in the gaps of a capacitor element formed with a solid electrolyte layer. [Prior art literature] [Patent literature]

[Patent document 1] Japanese Patent Publication No. 2008-109068 [Patent document 2] Japanese Patent Publication No. 4536625

[The problem that the invention wants to solve]

Capacitors are used in various applications. For example, in the field of power electronics technology, in a power supply circuit that converts the power of an AC power source into DC power using a converter circuit and converts the DC power into the desired AC power using an inverter circuit, a smoothing capacitor is provided to suppress and smooth the DC pulse output from the converter circuit before inputting it into the inverter circuit. In addition, in order to stabilize the operation of semiconductor switching elements such as gallium nitride or remove noise, a decoupling capacitor is provided near the semiconductor switching element.

As power increases in the field of power electronics, higher withstand voltages are required for solid electrolytic capacitors. For example, depending on the field of power electronics, capacitors with a withstand voltage of at least 200 V are expected. However, it is not easy to achieve a high withstand voltage while maintaining the low ESR that is the advantage of solid electrolytic capacitors.

The present invention is proposed to solve the above-mentioned problem, and its purpose is to provide a solid electrolytic capacitor and a manufacturing method having both low ESR and high withstand voltage. [Means for solving the problem]

To solve the above-mentioned problem, the solid electrolytic capacitor of the present embodiment includes a capacitor element having an anode foil, a cathode and an electrolyte. The anode foil has a surface that is expanded by means of tunnel-shaped etching pits and has a dielectric film on the surface. The cathode faces the anode foil. The electrolyte includes a solid electrolyte layer containing a conductive polymer. The solid electrolyte layer has a weight of less than 250 mg/ ^cm3 per unit volume of the capacitor element.

Alternatively, the solid electrolyte layer includes the conductive polymer, a solvent for a conductive polymer liquid in which the conductive polymer is dispersed or dissolved, and an additive added to the conductive polymer liquid, and the total weight of the conductive polymer, the solvent, and the additive is less than 250 mg/ ^cm3 per unit volume of the capacitor element.

Alternatively, the electrolyte may include only the solid electrolyte layer, and the solid electrolyte layer may have a weight of 120 mg/cm ³ or more and 150 mg/cm ³ or less per unit volume of the capacitor element.

The electrolyte may include a liquid component filled in gaps in the capacitor element.

The electrolyte may include a liquid component that fills gaps in the capacitor element, and the solid electrolyte layer may have a weight of 15 mg/cm ³ or more and 250 mg/cm ³ or less per unit volume of the capacitor element.

The electrolyte may include a liquid component that fills gaps in the capacitor element, and the solid electrolyte layer may have a weight of 60 mg/cm ³ or more and 180 mg/cm ³ or less per unit volume of the capacitor element.

The solid electrolyte layer may contain a compound having a hydroxyl group. The compound having a hydroxyl group may be one or more selected from the group consisting of ethylene glycol, butanediol, diethylene glycol, and glycerol.

In addition, in order to solve the above-mentioned problem, the manufacturing method of the solid electrolytic capacitor of the present embodiment is a method for manufacturing a solid electrolytic capacitor having an anode foil, a cathode body and a solid electrolyte layer, comprising: an anode foil forming step, forming a tunnel-shaped etching pit on the surface of the anode foil, and then forming a dielectric film on the surface; an element forming step, forming a capacitor element in which the cathode body and the anode foil face each other; and an electrolyte layer forming step, dispersing or dissolving a conductive polymer. The conductive polymer liquid is attached between the anode foil and the cathode to form the solid electrolyte layer, and the solid electrolyte layer includes the conductive polymer, a solvent for dispersing or dissolving the conductive polymer, and an additive added to the conductive polymer liquid. In the electrolyte layer forming step, the total weight of the conductive polymer, the solvent and the additive is contained in a manner of 250 mg/cm3 or ^less per unit volume of the capacitor element. [Effect of the Invention]

According to the present invention, a solid electrolytic capacitor has both low ESR and high withstand voltage.

(Solid electrolytic capacitor) Solid electrolytic capacitor has a pair of electrodes and an electrolyte layer. One of the electrodes is an anode foil with a dielectric film formed on the foil surface. The other electrode is a cathode. The cathode and the anode foil are arranged facing each other. The pair of electrodes are arranged facing each other with the electrolyte layer sandwiched between them. The assembly composed of the pair of electrodes and the electrolyte layer is called a capacitor element.

Capacitor elements sometimes include a separator. The separator is interposed between a pair of electrodes, thereby isolating the anode foil from the cathode, preventing short circuits, and maintaining the electrolyte layer. In the case where the shape of the electrolyte layer can be maintained by itself and the pair of electrodes can be isolated by the electrolyte layer, the separator can be omitted from the capacitor element.

The anode lead is connected to the anode foil, and the cathode lead is connected to the cathode. The solid electrolytic capacitor is electrically connected to the mounting circuit via the anode lead and the cathode lead. By being connected to the mounting circuit, the solid electrolytic capacitor becomes a passive element that obtains electrostatic capacitance through the dielectric polarization of the dielectric film and performs charge storage and discharge.

An example of the manufacturing method of the solid electrolytic capacitor is roughly as follows. First, the anode foil is expanded by the anode foil forming step, and then a dielectric film is formed. Then, the anode foil and the cathode body are made to face each other to form a capacitor element. The capacitor element is subjected to a repair chemical conversion.

Next, the electrolyte layer forming step is performed by impregnating the space between the anode foil and the cathode with a conductive polymer liquid in which conductive polymer particles or powder are dispersed or dissolved to form an electrolyte layer. Then, after the opening end of the case into which the capacitor element is inserted is sealed with a sealing body, aging is performed to form a solid electrolytic capacitor.

(Electrode) In this type of solid electrolytic capacitor, the electrode is a foil made of valve metal. In the wound type, the valve metal is mostly extended into a long strip shape, and in the flat type, the valve metal is mostly extended into a flat plate. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, tungsten, bismuth, zirconium, zinc, tungsten, bismuth, and antimony. Regarding purity, the anode foil is ideally 99.9% or more, and the cathode is ideally 99% or more, and may also contain impurities such as silicon, iron, copper, magnesium, and zinc.

A diffusion layer is formed on one or both sides of the anode foil. The diffusion layer is an etching layer having a plurality of tunnel-shaped etching pits. The tunnel-shaped etching pits are holes dug in the thickness direction of the foil. The tunnel-shaped pits may penetrate the foil or may be of a length such that the deepest part remains inside the foil. Tunnel-shaped etching pits are typically formed by passing a direct current through an acidic aqueous solution such as hydrochloric acid in which halogen ions exist. The tunnel-shaped etching pits are further expanded by passing a direct current through an acidic aqueous solution such as nitric acid.

As the cathode body, for example, a cathode foil in foil form may be used. In addition, the cathode body may be a laminate of a metal layer such as silver and a carbon layer. A diffusion layer may be formed on one or both sides of the cathode foil. A flat foil without a diffusion layer may also be used as the cathode foil. The diffusion layer of the cathode foil is an etched layer, a sintered layer formed by sintering valve metal powder, or a vaporized layer formed by vaporizing valve metal particles on the foil. That is, the diffusion layer of the cathode foil contains tunnel-shaped pits, sponge-shaped pits, or dense powders or gaps between particles.

The dielectric film is formed on the uneven surface of the diffusion layer. The dielectric film is typically an oxide film formed on the surface of the anode foil. If the anode foil is an aluminum foil, it is an aluminum oxide layer that oxidizes the surface of the diffusion layer. In the chemical conversion treatment for forming the dielectric film, a voltage is applied to the anode foil in a chemical conversion liquid with the desired withstand voltage as the target. The chemical conversion liquid is a solution without halogen ions, for example, a phosphoric acid-based chemical conversion liquid such as ammonium dihydrogen phosphate, a boric acid-based chemical conversion liquid such as ammonium borate, and an adipic acid-based chemical conversion liquid such as ammonium adipate.

The cathode may have a natural oxide film or a thin oxide film (about 1 V to 10 V) formed by chemical conversion. The natural oxide film is formed by the reaction of the cathode with oxygen in the air.

(Electrolyte layer) The electrolyte layer is attached to at least a portion of the dielectric film of the anode foil and becomes the true cathode of the solid electrolytic capacitor. Preferably, the electrolyte layer is in close contact with the entire area of the dielectric film and is connected to the surface of the cathode foil. The electrolyte layer is a solid electrolyte layer, or includes a solid electrolyte layer and a liquid component. The solid electrolyte layer contains a conductive polymer. The liquid component is a driving electrolyte or a solvent portion of the electrolyte impregnated in the gap of the capacitor element formed with the solid electrolyte layer.

(Solid electrolyte layer) Conductive polymers are self-doped polymers doped with dopant molecules inside the molecule or conjugated polymers doped with external dopant molecules. Conjugated polymers are obtained by chemical oxidation polymerization or electrolytic oxidation polymerization of monomers or derivatives having π conjugated double bonds. Doped conjugated polymers exhibit high electrical conductivity. That is, electrical conductivity is exhibited by adding a small amount of dopant such as an acceptor that easily accepts electrons or a donor that easily donates electrons to the conjugated polymer.

The solid electrolyte layer is formed using a conductive polymer liquid. The conductive polymer liquid is a liquid in which particles or powders of a conductive polymer are dispersed or dissolved. Additives are added to the conductive polymer liquid as needed. At least the anode foil, a pair of electrodes, and each of the separators or the capacitor element are immersed in the conductive polymer liquid, and then dried after immersion. In addition to immersion, the conductive polymer liquid can also be applied by dripping or spraying. In this way, part or all of the solvent remaining in the conductive polymer liquid that has not been volatilized is attached to the conductive polymer and the additive to form a solid electrolyte layer.

The solid electrolyte layer has a weight of 250 mg/cm ³ or less per unit volume of the capacitor element. In other words, in the electrolyte formation step, the conductive polymer liquid is impregnated and dried so that the total weight of the conductive polymer, the residual solvent of the conductive polymer liquid, and the additives remain in the capacitor element at a ratio of 250 mg/cm ³ or less per unit volume of the capacitor element. If it is 250 mg/cm ³ or less per unit volume of the capacitor element, both low ESR and high withstand voltage are achieved. On the other hand, if the weight per unit volume of the capacitor element exceeds 301 mg/cm ³ , the ESR deteriorates.

Furthermore, the weight adjustment of the solid electrolyte layer is not limited. For example, the weight of the solid electrolyte layer can be adjusted by changing the type and amount of components evaporated from the solid electrolyte layer by setting the drying temperature, drying time and pressure after immersion in the conductive polymer liquid as variables.

Solid electrolytic capacitors are not hybrid type but non-hybrid type. When the electrolyte layer has only a solid electrolyte layer and does not contain a liquid compound, the solid electrolyte layer is preferably 120 mg/ ^cm3 or more and 150 mg/ ^cm3 or less per unit volume of the capacitor element. If the non-hybrid solid electrolyte layer is within this range, the ESR becomes particularly low and minimized, and the withstand voltage becomes particularly high and maximized. If it deviates from this range, although it is low ESR and high withstand voltage as an absolute value, the ESR increases compared to this range, and the withstand voltage decreases compared to this range.

When the solid electrolytic capacitor is a hybrid type, and the gaps of the capacitor element are impregnated with a liquid component and the electrolyte layer includes a solid electrolyte layer and a liquid component, the solid electrolyte layer is preferably 15 mg/ ^cm3 or more and 250 mg/ ^cm3 or less per unit volume of the capacitor element. In other words, it is preferable to impregnate and dry the conductive polymer liquid so that the total weight of the conductive polymer, the solvent of the conductive polymer, and the additive remains in the capacitor element at a ratio of 15 mg/ ^cm3 or more and 250 mg/ ^cm3 or less per unit volume of the capacitor element. If the hybrid type solid electrolyte layer is within this range, the ESR becomes particularly low and the withstand voltage becomes particularly high. If it deviates from this range, the ESR is low and the withstand voltage is high as absolute values, but the ESR is higher than that in this range, and the withstand voltage is lower than that in this range.

In the case of a hybrid solid electrolytic capacitor, the solid electrolyte layer is particularly preferably 60 mg/cm ³ or more and 180 mg/cm ³ or less per unit volume of the capacitor element. Within this range, the ESR is further reduced and minimized, and the withstand voltage is further increased and maximized.

In such a solid electrolyte layer, known conjugated polymers can be used without particular limitation. Examples thereof include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene vinylene, polyacene, polythiophene vinylene, etc. These conjugated polymers can be used alone or in combination of two or more, and can also be copolymers of two or more monomers.

Among the conjugated polymers, preferably, a conjugated polymer obtained by polymerizing thiophene or its derivatives is preferred, preferably, a conjugated polymer obtained by polymerizing 3,4-ethylenedioxythiophene (i.e., 2,3-dihydrothieno[3,4-b][1,4]dioxin), 3-alkylthiophene, 3-alkoxythiophene, 3-alkyl-4-alkoxythiophene, 3,4-alkylthiophene, 3,4-alkoxythiophene or their derivatives. As the thiophene derivative, preferably, 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 can form a ring together with the carbons at the 3rd and 4th positions. The carbon number of the alkyl or alkoxy group is preferably 1 to 16.

In particular, a polymer of 3,4-ethylenedioxythiophene called EDOT, that is, poly(3,4-ethylenedioxythiophene) called PEDOT is particularly preferred. In addition, a substituent may be added to 3,4-ethylenedioxythiophene. For example, an alkylated ethylenedioxythiophene to which an alkyl group having 1 to 5 carbon atoms is added as a substituent may be used. Examples of the alkylated ethylenedioxythiophene include methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydro-thieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

As dopants, known ones can be used without particular limitation. Dopants can be used alone or in combination of two or more. In addition, polymers or monomers can also be used. For example, as dopants, there can be listed: inorganic acids such as polyanions, boric acid, nitric acid, and phosphoric acid; organic acids 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, bis(oxalylboric acid), sulfonylimide, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

The polyanion is, for example, a substituted or unsubstituted polyalkylene group, a substituted or unsubstituted polyalkenylene group, a substituted or unsubstituted polyimide, a substituted or unsubstituted polyamide, a substituted or unsubstituted polyester, and may include a polymer containing only a structural unit having an anion group, a polymer containing a structural unit having an anion group and a structural unit not having an anion group. Specifically, as the polyanion, there may be exemplified: polyethylene sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacrylic acid sulfonic acid, polymethacrylic acid sulfonic acid, poly(2-acrylamide-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylic acid, polymaleic acid, and the like.

The solvent of the conductive polymer liquid, i.e., the residual solvent in the solid electrolyte layer, can be any solvent that disperses or dissolves the conductive polymer, and is preferably water or a mixture of water and an organic solvent. Examples of the organic solvent include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, and nitrile compounds.

As polar solvents, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, etc. can be listed. As alcohols, methanol, ethanol, propanol, butanol, etc. can be listed. As esters, ethyl acetate, propyl acetate, butyl acetate, etc. can be listed. As hydrocarbons, hexane, heptane, benzene, toluene, xylene, etc. can be listed. As carbonate compounds, ethyl carbonate, propyl carbonate, etc. can be listed. As ether compounds, dioxane, diethyl ether, etc. can be listed. As chain ethers, ethylene glycol dialkyl ethers, propylene glycol dialkyl ethers, polyethylene glycol dialkyl ethers, polypropylene glycol dialkyl ethers, etc. can be listed. As heterocyclic compounds, 3-methyl-2-oxazolidinone, etc. can be listed. Examples of the nitrile compound include acetonitrile, glutaronitrile, methoxyacetonitrile, propionitrile, and benzonitrile.

The additives added to the conductive polymer liquid include: polyols, organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, ultraviolet absorbers, etc. As polyols, there are: sorbitol, ethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, heptanediol, octanediol, diethylene glycol, triethylene glycol, polyoxyalkylene glycol, glycerol, polyglycerol, polyoxyalkylene glycerol, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, cyclobutane sulfonate, methylcyclobutane sulfonate, or a combination of two or more thereof.

As the solvent, additive or both constituting such a conductive polymer liquid, a compound having a hydrophilic group or a hydrophilic molecule such as a hydroxyl group is preferred. Examples of compounds having a hydroxyl group include polyols such as ethylene glycol, butanediol, diethylene glycol and glycerol. The compounds having a hydroxyl group cause changes in the higher-order structure of the conductive polymer, thereby achieving an effect of reducing the ESR of the solid electrolytic capacitor or improving the withstand voltage. In addition, polyols have a high boiling point and remain in the electrolyte layer, making it easy to constitute a solid electrolyte layer.

In addition, as a solvent, an additive, or both constituting such a conductive polymer liquid, butanediol, diethylene glycol, polyoxyethylene glycol, glycerol, and cyclobutanesulfonate are particularly preferred. Although it is a guess, the boiling points of these butanediol, diethylene glycol, polyoxyethylene glycol, glycerol, and cyclobutanesulfonate are high, for example, above 200°C. Therefore, it is believed that when the conductive polymer liquid is immersed and dried, the flexibility of the conductive polymer is increased. The conductive polymer with increased flexibility is easy to be in close contact with the electrode. If the close contact between the conductive polymer and the electrode is improved, a low ESR can be maintained even with a small amount of solid electrolyte layer.

(Liquid component) The liquid component is the driving electrolyte or the solvent part of the driving electrolyte. As the solvent of the driving electrolyte, there can be exemplified protic organic polar solvents or aprotic organic polar solvents, which can be used alone or in combination of two or more.

Examples of protic organic solvents as solvents include monohydric alcohols, polyhydric alcohols, and oxyhydric alcohol compounds. Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyhydric alcohol compounds include ethylene glycol, diethylene glycol, propylene glycol, glycerol, methyl solvent, ethyl solvent, methoxypropylene glycol, dimethoxypropylene glycol, polyglycerol, polyethylene glycol, polyoxyethylene glycerol, polypropylene glycol, and other polyhydric alcohol alkylene oxide adducts.

Representative examples of non-protic organic polar solvents as solvents include sulfones, amides, lactones, cyclic amides, nitrile, and sulfide. Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, cyclobutane sulfone, 3-methylcyclobutane sulfone, and 2,4-dimethylcyclobutane sulfone. 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, ethyl carbonate, propyl carbonate, butyl carbonate, isobutyl carbonate, etc. Examples of nitrile series include acetonitrile, 3-methoxypropionitrile, glutaronitrile, etc. Examples of sulfoxide series include dimethyl sulfoxide, etc.

When the solute of the driving electrolyte is added to the liquid component, the solute is an anion component and a cation component. The solute is typically a salt of an organic acid, a salt of an inorganic acid, or a salt of a complex compound of an organic acid and an inorganic acid, and can be used alone or in combination of two or more. An acid as an anion and a base as a cation can also be added to the solvent separately.

Organic acids that serve as solutes and become anionic components include: 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, heptanoic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, tert-butyladipic acid, 11-vinyl-8-octadecenedicarboxylic acid, resorcinic acid, pyrogallol acid, gallic acid, gentianic acid, protocatechuic acid, catecholcarboxylic acid, trimellitic acid, pyromellitic acid and other carboxylic acids, or phenols and sulfonic acids.

In addition, examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic acids and inorganic acids include boron disalicylic acid, boron dioxalic acid, boron diglycolic acid, boron dimalonic acid, boron disuccinic acid, boron diadipic acid, boron diazelaic acid, boron dibenzoic acid, boron dimaleic acid, boron dilactic acid, boron dimalic acid, boron ditartaric acid, boron dicitric acid, boron diphthalic acid, boron di(2-hydroxy) isobutyric acid, boron diresorcinolic acid, boron dimethylsalicylic acid, boron dinaphthoic acid, boron dimandelic acid, and boron di(3-hydroxy) propionic acid.

In addition, as at least one salt of an organic acid, an inorganic acid, and a complex compound of an organic acid and an inorganic acid, for example, ammonium salts, quaternary ammonium salts, quaternary amidinium salts, amine salts, sodium salts, potassium salts, etc. As quaternary ammonium ions of quaternary ammonium salts, tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. are exemplified. As quaternary amidinium, ethyldimethylimidazolinium, tetramethylimidazolinium, etc. are exemplified. As amine salts, salts of primary amines, secondary amines, and tertiary amines are exemplified. Examples of the primary amines include methylamine, ethylamine, and propylamine, examples of the secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine, and examples of the tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

Furthermore, other additives may be added to the electrolyte. Examples of additives include: epoxide adducts of polyols such as polyethylene glycol or polyoxyethylene glycerol, complex compounds of boric acid and polysaccharides (mannitol, sorbitol, etc.), complex compounds of boric acid and polyols, boric acid esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.), phosphate esters, etc. These may be used alone or in combination of two or more.

(Partition) The partition may be made of kraft paper, Manila hemp, esparto, hemp, rayon and other cellulose and mixed paper thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and derivatives thereof, polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, aliphatic polyamide, semi-aromatic polyamide, wholly aromatic polyamide and other polyamide resins, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, polyvinyl alcohol resins and the like, and these resins may be used alone or in combination. [Implementation example]

Hereinafter, the present invention will be described in more detail based on the embodiments. Furthermore, the present invention is not limited to the following embodiments.

(Example 1-Example 7) The solid electrolytic capacitors of Examples 1 to 7 and Comparative Example 1 were prepared as follows. The solid electrolytic capacitors of Examples 1 to 7 and Comparative Example 1 are non-mixed types, and the electrolyte layer does not contain liquid components.

First, the two electrodes are made of long strip-shaped aluminum foil. Tunnel-shaped pits are formed on both sides of the anode foil by direct current etching. In addition, a dielectric film is formed on the anode foil by chemical conversion treatment. During the chemical conversion treatment, the applied voltage is made to reach 650 V. As for the cathode foil, pits are formed on both sides by alternating current etching, and an oxide film is formed by chemical conversion treatment with a chemical conversion voltage of 3 Vfs. Leads are connected to the two electrodes, and the two electrodes are wound facing each other with a separator made of Manila hemp in between. Then, repair chemical conversion is carried out using an aqueous solution of ammonium borate.

Next, after the capacitor element is immersed in the conductive polymer liquid and the conductive polymer liquid is impregnated in the capacitor element, the capacitor element is dried. Polyethylene dioxythiophene (PEDOT/polystyrene sulfonic acid (PSS)) doped with polystyrene sulfonic acid as a conductive polymer is dispersed in the conductive polymer liquid. The solvent of the conductive polymer liquid is a mixed liquid of water and ethylene glycol. Sorbitol is added to the conductive polymer liquid. In the conductive polymer liquid, water accounts for 48.5 wt%, ethylene glycol accounts for 48.5 wt%, PEDOT/PSS accounts for 1 wt%, and sorbitol accounts for 2 wt%.

Thereby, a solid electrolyte layer is formed in the capacitor element. Here, the weight of the solid electrolyte layer is different in Examples 1 to 7 and Comparative Example 1. The weight of the solid electrolyte layer is the weight per unit volume of the capacitor element, and is hereinafter referred to as the solid electrolyte layer weight. The solid electrolyte layer weight is adjusted by drying the capacitor element impregnated with the conductive polymer liquid at 110°C and increasing or decreasing the drying time.

Thus, the solid electrolytic capacitors of Examples 1 to 7 and Comparative Example 1 are manufactured under the same structure, composition, manufacturing method and manufacturing conditions except for the weight of the solid electrolyte layer.

(Withstand voltage and ESR) The withstand voltage of the solid electrolytic capacitors of Examples 1 to 7 and Comparative Example 1 was measured. The withstand voltage measurement method is as follows. That is, a voltage is applied to the solid electrolytic capacitor at 105°C. The initial voltage is 200 V, and the applied voltage is increased by 1 V every 10 seconds. Then, the voltage when the current flowing into the solid electrolytic capacitor reaches 1 mA is taken as the withstand voltage.

In addition, the ESR of the solid electrolytic capacitors of Examples 1 to 7 and Comparative Example 1 was measured. The method for measuring the withstand voltage is as follows. The ESR was measured at room temperature using an LCR meter manufactured by NF CORPORATION. The measurement frequency was 100 kHz and the AC amplitude was a sine wave of 0.5 Vms.

The results of withstand voltage and ESR measurements are shown in Table 1 below together with the solid electrolyte layer weights of Examples 1 to 7 and Comparative Example 1. In Table 1, the solid electrolyte layer weight is expressed as the solid electrolyte mass per unit volume of the device. (Table 1) Solid electrolyte mass (electrolyte layer: solid electrolyte layer only) Embodiment 1 Embodiment 2 Embodiment 3 Embodiment 4 Embodiment 5 Embodiment 6 Embodiment 7 Comparison Example 1 Solid electrolyte mass per unit volume of the device [mg/cm ³ ] 18 30 60 120 150 180 250 301 Withstand voltage [V] 206 363 464 570 570 358 356 353 ESR[Ω/100 kHz] 0.826 0.659 0.289 0.109 0.109 0.110 0.313 8.635

As shown in Table 1, the weight of the solid electrolyte layer is converted into the weight per unit volume of the capacitor element (mg/cm ³ ), and varies from 18 mg/cm ³ to 301 mg/cm ³ , taking the inherent value of Examples 1 to 7 and Comparative Example 1. In addition, the weight of each solid electrolyte layer is calculated by subtracting the weight of the capacitor element before immersion from the weight of the capacitor element after immersion in the conductive polymer liquid and drying.

Based on Table 1, the relationship between the solid electrolyte layer weight and the withstand voltage, and the relationship between the solid electrolyte layer weight and the ESR are shown in the graph of Figure 1. In Figure 1, the square mark plot is the withstand voltage, and the circle mark plot is the ESR. In addition, ESR is expressed in logarithms.

As shown in Table 1 and Figure 1, when the solid electrolyte layer weight is 18 mg/cm ³ , the withstand voltage exceeds 200 V. As the solid electrolyte layer weight increases from 18 mg/cm ³ to 120 mg/cm ³ , the withstand voltage increases significantly. Then, from 120 mg/cm ³ to 150 mg/cm ³ , the withstand voltage increases to a maximum. When it reaches 180 mg/cm ³ , although the withstand voltage value is much higher than 200 V, it drops sharply compared to 150 mg/cm ^3. There is no change in the withstand voltage after 180 mg/cm ³ .

On the other hand, as the solid electrolyte layer weight increases from 18 mg/cm ³ to 120 mg/cm ³ , the ESR decreases rapidly. Then, from 120 mg/cm ³ to 180 mg/cm ³ , the ESR is minimized. From 250 mg/cm ³ , the ESR begins to increase. The ESR after 301 mg/cm ³ reaches about 28 times the ESR of 250 mg/cm ³ .

Thus, if the solid electrolyte layer weight is 250 mg/ ^cm3 or less, the solid electrolytic capacitor has both low ESR and high withstand voltage. In addition, if the solid electrolyte layer weight is 120 mg/ ^cm3 or more and 150 mg/ ^cm3 or less, the non-hybrid solid electrolytic capacitor can obtain both maximized withstand voltage and minimized ESR.

(Example 8-Example 14) Furthermore, the solid electrolytic capacitors of Examples 8 to 14 and Comparative Example 2 were prepared. The solid electrolytic capacitors of Examples 8 to 14 and Comparative Example 2 are hybrid types, and the electrolyte layer includes a solid electrolyte layer and a liquid component. The liquid component is composed of 59.4 wt% of ethylene glycol, 39.6 wt% of polyethylene glycol, and 1 wt% of ammonium azelaic acid. The average molecular weight of polyethylene glycol is 1000. The liquid component is impregnated in the capacitor element. Except for the weight of the solid electrolyte layer, the other structures, compositions, manufacturing methods and manufacturing conditions are the same as those of Examples 1 to 7 and Comparative Example 1.

(Withstand voltage and ESR) The withstand voltage of the solid electrolytic capacitors of Examples 8 to 14 and Comparative Example 2 was measured. The method and conditions for measuring the withstand voltage and ESR were the same as those of Examples 1 to 7 and Comparative Example 1. The method for confirming the weight of each solid electrolyte layer was also the same as that of Examples 1 to 7 and Comparative Example 1.

The results of withstand voltage and ESR measurements are shown in Table 2 below together with the solid electrolyte layer weights of Examples 8 to 14 and Comparative Example 2. In Table 2, the solid electrolyte layer weight is expressed as the solid electrolyte mass per unit volume of the device. (Table 2) Solid electrolyte mass (electrolyte layer: solid electrolyte layer + liquid component) Embodiment 8 Embodiment 9 Embodiment 10 Embodiment 11 Embodiment 12 Embodiment 13 Embodiment 14 Comparison Example 2 Solid electrolyte mass per unit volume of the device [mg/cm ³ ] 18 30 60 120 150 180 250 301 Withstand voltage [V] 376 479 570 570 570 570 510 465 ESR[Ω/100 kHz] 0.155 0.147 0.121 0.114 0.140 0.164 0.305 3.381

As shown in Table 2, the solid electrolyte layer weight is converted into the weight per unit volume of the capacitor element (mg/cm ³ ), and changes from 18 mg/cm ³ to 301 mg/cm ³ in a manner that takes an inherent value in Examples 8 to 14 and Comparative Example 2. Based on Table 2, the relationship between the solid electrolyte layer weight and the withstand voltage, and the relationship between the solid electrolyte layer weight and the ESR are shown in the graph of Figure 2. In Figure 2, the square mark plot is the withstand voltage, and the circle mark plot is the ESR. In addition, ESR is expressed in logarithm.

As shown in Table 2 and Figure 2, if the solid electrolyte layer weight is 18 mg/cm ³ , the withstand voltage is much higher than 200 V. As the solid electrolyte layer weight increases from 18 mg/cm ³ to 120 mg/cm ³ , the withstand voltage increases significantly. Then, from 60 mg/cm ³ to 180 mg/cm ³ , the withstand voltage is maximized. After 180 mg/cm ³ , the withstand voltage decreases as the solid electrolyte layer weight increases. However, even when the solid electrolyte layer weight is 301 mg/cm ³ , the withstand voltage is much higher than 200 V.

On the other hand, from 18 mg/cm ³ to 250 mg/cm ³ , the ESR remains low regardless of the solid electrolyte layer weight. However, after 301 mg/cm ³ , the ESR deteriorates significantly, reaching about 11 times the ESR of 250 mg/cm ³ .

Thus, solid electrolytic capacitors, whether hybrid or non-hybrid, have both low ESR and high withstand voltage if the solid electrolyte layer weight is 250 mg/ ^cm3 or less. In particular, hybrid solid electrolytic capacitors can achieve both a maximized withstand voltage and a particularly low ESR if the solid electrolyte layer weight is 60 mg/ ^cm3 or more and 150 mg/cm3 or ^less .

(Example 15-Example 18) Furthermore, the solid electrolytic capacitors of Examples 15 to 18 were prepared. The solid electrolytic capacitors of Examples 15 to 18 are the same as those of Example 4 and are non-mixed, and the solvent of the conductive polymer liquid is different from that of Example 4. Except for the difference in the solvent of the conductive polymer liquid, the solid electrolytic capacitors of Examples 15 to 18 are prepared in the same structure, composition, manufacturing method and manufacturing conditions as those of Example 4.

(Withstand voltage and ESR) The withstand voltage of the solid electrolytic capacitors of Examples 15 to 18 was measured. The method and conditions for measuring the withstand voltage and ESR were the same as those of Example 4. The method for confirming the weight of each solid electrolyte layer was also the same as that of Example 4.

The results of withstand voltage and ESR measurements are shown in Table 3 below together with the solid electrolyte layer weights of Examples 15 to 18 and Example 4. In Table 3, the solid electrolyte layer weight is expressed as the solid electrolyte mass per unit volume of the device. (Table 3) Embodiment 4 Embodiment 15 Embodiment 16 Embodiment 17 Embodiment 18 Conductive polymer liquid solvent type Ethylene glycol Butanediol Diethylene glycol glycerin Ring Ding Solid electrolyte mass per unit volume of the device [mg/cm ³ ] 120 120 120 120 120 Withstand voltage [V] 570 567 553 510 301 ESR[Ω/100 kHz] 0.109 0.276 0.172 0.129 3.040

As shown in Table 3, the solvent of the conductive polymer liquid of Example 4 is ethylene glycol, whereas that of Example 15 is set to butanediol, that of Example 16 is set to diethylene glycol, that of Example 17 is set to glycerol, and that of Example 18 is set to cyclobutanesulfonate. That is, ethylene glycol is included as a compound having a hydroxyl group in the solid electrolyte layer of Example 4. Butanediol is included as a compound having a hydroxyl group in the solid electrolyte layer of Example 15. Diethylene glycol is included as a compound having a hydroxyl group in the solid electrolyte layer of Example 16. Glycerol is included as a compound having a hydroxyl group in the solid electrolyte layer of Example 17. Cyclobutanesulfonate is included as a high boiling point solvent in the solid electrolyte layer of Example 18.

As shown in Table 3, it was confirmed that regardless of the type of solvent in the solid electrolyte layer, if the weight of the solid electrolyte layer is 250 mg/ ^cm3 or less per unit volume of the capacitor element, both high withstand voltage and low ESR can be obtained. In addition, it was confirmed that if the solvent in the solid electrolyte layer is a compound having a hydroxyl group and is ethylene glycol, butanediol, diethylene glycol or glycerol, the withstand voltage can be particularly improved and the ESR can be particularly reduced.

without

FIG. 1 is a graph showing the relationship between the weight of the solid electrolyte layer and the withstand voltage, and the relationship between the weight of the solid electrolyte layer and the ESR of Examples 1 to 7. FIG. 2 is a graph showing the relationship between the weight of the solid electrolyte layer and the withstand voltage, and the relationship between the weight of the solid electrolyte layer and the ESR of Examples 8 to 14.

Claims (9)

A solid electrolytic capacitor is characterized in that it includes a capacitor element having an anode foil, a cathode and an electrolyte, wherein the anode foil has a surface that is expanded by tunnel-shaped etching pits and has a dielectric film on the surface, the cathode and the anode foil face each other, and the electrolyte includes a solid electrolyte layer containing a conductive polymer, and the solid electrolyte layer has a weight of less than 250 mg/ ^cm3 per unit volume of the capacitor element. A solid electrolytic capacitor as described in claim 1, wherein the solid electrolyte layer comprises the conductive polymer, a solvent for a conductive polymer liquid in which the conductive polymer is dispersed or dissolved, and an additive added to the conductive polymer liquid, and the total weight of the conductive polymer, the solvent and the additive is less than 250 mg/ ^cm3 per unit volume of the capacitor element. A solid electrolytic capacitor as described in claim 1 or 2, wherein the electrolyte has only the solid electrolyte layer, and the solid electrolyte layer has a weight of 120 mg/ ^cm3 or more and 150 mg/ ^cm3 or less per unit volume of the capacitor element. A solid electrolytic capacitor as described in claim 1 or 2, wherein the electrolyte includes a liquid component filled in the gaps of the capacitor element. A solid electrolytic capacitor as described in claim 4, wherein the solid electrolyte layer has a weight of 15 mg/ ^cm3 or more and 250 mg/ ^cm3 or less per unit volume of the capacitor element. A solid electrolytic capacitor as described in claim 5, wherein the solid electrolyte layer has a weight of 60 mg/ ^cm3 or more and 180 mg/ ^cm3 or less per unit volume of the capacitor element. A solid electrolytic capacitor as described in claim 1 or 2, wherein the solid electrolyte layer contains a compound having a hydroxyl group. A solid electrolytic capacitor as described in claim 7, wherein the compound having a hydroxyl group is one or more selected from the group consisting of ethylene glycol, butanediol, diethylene glycol and glycerol. A method for manufacturing a solid electrolytic capacitor is a method for manufacturing a solid electrolytic capacitor having an anode foil, a cathode and a solid electrolyte layer, and is characterized in that it includes: an anode foil forming step, forming a tunnel-shaped etching pit on the surface of the anode foil, and then forming a dielectric film on the surface; an element forming step, forming a capacitor element in which the cathode and the anode foil face each other; and an electrolyte layer forming step, making a conductive polymer liquid in which a conductive polymer is dispersed or dissolved adhere between the anode foil and the cathode to form the solid electrolyte layer, wherein the solid electrolyte layer includes the conductive polymer, a solvent for the conductive polymer liquid in which the conductive polymer is dispersed or dissolved, and an additive added to the conductive polymer liquid. In the electrolyte layer forming step, the conductive polymer, the solvent, and the additive are contained in an amount of 250 mg/cm ³ or less per unit volume of the capacitor element.

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