Electrolytic capacitor, smoothing circuit, filter circuit, and method for manufacturing an electrolytic capacitor

Abstract

This suppresses the deterioration of ESR in hybrid-type electrolytic capacitors under low-temperature conditions. [Solution] An electrolytic capacitor is used, for example, in smoothing circuits and filter circuits, and comprises an anode body on which a dielectric film is formed, a cathode body facing the anode body, and an electrolyte interposed between the anode body and the cathode body. The electrolyte contains a conductive polymer and an electrolyte solution. The electrolyte solution contains glycerin accounting for 8 wt% to 55 wt% in the solvent and a polyhydric alcohol accounting for 70 wt% or less. The electrolytic capacitor is manufactured by comprising an anode manufacturing step for producing an anode body, a cathode manufacturing step for producing a cathode body, a solid electrolyte layer formation step for adhering the conductive polymer to the dielectric film by impregnating at least a dispersion of conductive polymer into the dielectric film and drying it, an element formation step for forming a capacitor element, and an electrolyte impregnation step for impregnating the capacitor element with the electrolyte solution prepared in the electrolyte solution preparation step.

Description

Technical Field

[0001] An electrolytic capacitor includes valve action metals such as tantalum or aluminum as an anode foil and a cathode foil. The anode foil is surface-expanded by forming the valve action metal into a sintered body or an etched foil, etc., and has a dielectric film layer on the surface-expanded surface. This electrolytic capacitor can increase the specific surface area by surface-expanding the anode foil, and thus has a large capacitance, meeting the requirement of high capacitance.

[0002] An electrolyte is interposed between the anode foil and the cathode foil from the viewpoint of adhesion to the uneven surface of the anode foil. In an electrolytic capacitor, this electrolyte functions as a true cathode. Solid electrolytes have attracted attention as electrolytes. As solid electrolytes, manganese dioxide and 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes are known.

[0003] In recent years, electrolytic capacitors using conductive polymers derived from monomers having a π-conjugated double bond have been rapidly popularized (see, for example, Patent Document 1). In conductive polymers, acid compounds such as polyanions are used as external dopants, and also have a partial structure acting as a dopant within the monomer molecule, expressing high conductivity. In particular, polyanions such as organic sulfonic acids are used as dopants, and poly(3,4-ethylenedioxythiophene) (PEDOT) has a slow reaction rate and excellent adhesion to the dielectric film.

[0004] However, an electrolytic capacitor equipped with a solid electrolyte has a poor repair effect on the defective parts of the dielectric film compared with an electrolytic capacitor equipped with an electrolytic solution. Therefore, a so-called hybrid type electrolytic capacitor in which a conductive polymer is interposed between the anode foil and the cathode foil and impregnated with an electrolytic solution has also attracted attention (see, for example, Patent Document 2). That is, in addition to the solid electrolyte, an electrolytic solution is also interposed between the anode foil and the cathode foil. The electrolytic solution increases the contact area with the dielectric film of the anode foil. Therefore, the capacitance of the electrolytic capacitor can be further increased, which is suitable for the requirement of high capacitance accompanying the increase in large power in recent years.

[0005] Such electrolytic capacitors are sometimes used in automotive applications, such as in the electrical systems of electric and hybrid vehicles, and in power converters. For example, electrolytic capacitors are frequently used in filter circuits. Examples of filter circuits include low-pass filters, high-pass filters, band-pass filters, and ripple filters, also called smoothing circuits. In a power converter, a smoothing circuit is provided, and this smoothing circuit incorporates a smoothing capacitor. A power converter converts AC power into DC power using a converter circuit, and then converts this DC power back into the desired AC power using an inverter circuit. The smoothing circuit is interposed between the converter circuit and the inverter circuit, suppressing and smoothing the pulsations of the DC output from the converter circuit before inputting it to the inverter circuit.

[0006] Electrolytic capacitors used in automotive applications are expected to be used under harsh conditions. For example, electrolytic capacitors are used for long periods in high-temperature environments with a maximum operating temperature of 85 to 150°C. In such conditions, evaporation of electrolyte can occur, where the electrolyte escapes from the electrolytic capacitor over time. As a result of this evaporation, the characteristics of the electrolytic capacitor deteriorate, such as a decrease in capacitance over time or an increase in the tangent (tanδ) of the loss angle over time.

[0007] Therefore, in hybrid electrolytic capacitors, a proposal has been made to include glycerin, a non-volatile solvent, in the electrolyte to prevent the electrolyte from volatilizing and evaporating in high-temperature environments (see, for example, Patent Document 3). Glycerin is a high-viscosity solvent and therefore has high resistivity. However, in hybrid electrolytic capacitors, the electrical conductivity of the conductive polymer is orders of magnitude higher than that of the electrolyte, so the equivalent series resistance (ESR) is less affected by the electrical conductivity of the electrolyte. For this reason, glycerin can be a promising candidate as a non-volatile solvent in hybrid electrolytic capacitors. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2011-60980 [Patent Document 2] Japanese Patent Publication No. 2015-228424 [Patent Document 3] International Publication No. 2012 / 149750 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] Electrolytic capacitors used in automotive applications are sometimes operated for extended periods in extremely low-temperature environments, with minimum operating temperatures as low as -55°C. In these low-temperature environments, it has been confirmed that gelation of the electrolyte progresses due to glycerin, degrading the ESR of the electrolytic capacitor. Therefore, a hybrid type of electrolytic capacitor that exhibits good electrical characteristics in both high-temperature and low-temperature environments has yet to be proposed.

[0010] This invention was proposed to solve the above problems, and its objective is to suppress the deterioration of ESR in hybrid-type electrolytic capacitors under low-temperature conditions. [Means for solving the problem]

[0011] To solve the above problems, the electrolytic capacitor of this embodiment comprises an anode body on which a dielectric film is formed, a cathode body facing the anode body, and an electrolyte interposed between the anode body and the cathode body, wherein the electrolyte comprises a conductive polymer and an electrolyte solution, and the electrolyte solution comprises glycerin accounting for 8 wt% to 55 wt% of the solvent and a polyhydric alcohol accounting for 70 wt% or less of the solvent.

[0012] The glycerin may be present in an amount of 15 wt% to 40 wt% of the solvent.

[0013] The electrolyte may further contain 35 wt% or less of lactones in the solvent.

[0014] The polyhydric alcohol may be present in the solvent at a concentration of 50 wt% or less.

[0015] The aforementioned polyhydric alcohol may be ethylene glycol.

[0016] The aforementioned lactones may be γ-butyrolactones.

[0017] The conductive polymer may be polyethylenedioxythiophene doped with polystyrene sulfonic acid.

[0018] The present invention comprises a solid electrolyte layer made of the conductive polymer, interposed between the anode and the cathode, and the solid electrolyte layer may contain a sugar alcohol.

[0019] Furthermore, in order to solve the above-mentioned problems, the smoothing circuit provided by the electrolytic capacitor of this embodiment and the filter circuit provided by the electrolytic capacitor of this embodiment are also embodiments of the present invention.

[0020] Furthermore, in order to solve the above problems, the method for manufacturing an electrolytic capacitor of this embodiment includes an anode manufacturing step of manufacturing an anode body on which a dielectric film is formed; a cathode manufacturing step of manufacturing a cathode body opposite to the anode body; a solid electrolyte layer forming step of impregnating at least the dielectric film with a dispersion of conductive polymer and drying it to make the conductive polymer adhere to the dielectric film; an electrolyte preparation step of preparing an electrolyte by including 8 wt% to 55 wt% of glycerin and 70 wt% or less of polyhydric alcohol in the solvent; an element forming step of forming a capacitor element including the anode body, the cathode body and the solid electrolyte layer; and an electrolyte impregnation step of impregnating the capacitor element with the electrolyte. [Effects of the Invention]

[0021] According to the present invention, the deterioration of the ESR of electrolytic capacitors is suppressed even in low-temperature environments such as -55°C.

Brief Description of the Drawings

[0022] [Figure 1] It is an example of a smoothing circuit including an electrolytic capacitor. [Figure 2] It is an example of a filter circuit including an electrolytic capacitor. [Figure 3] It is a graph showing the relationship between the glycerin ratio in the solvent of the electrolytic solution and the ratio of the ESR related to -55°C with respect to 20°C. [Figure 4] It is a graph showing the relationship between the ethylene glycol ratio in the solvent of the electrolytic solution and the ratio of the ESR related to -55°C with respect to 20°C. [Figure 5] It is a graph showing the relationship between the γ-butyrolactone ratio in the solvent of the electrolytic solution and the ESR related to -55°C.

Embodiments for Carrying Out the Invention

[0023] Hereinafter, an electrolytic capacitor and a manufacturing method according to an embodiment of the present invention will be described. Note that the present invention is not limited to the embodiments described below.

[0024] (Electrolytic Capacitor) An electrolytic capacitor is a passive element that obtains capacitance by the dielectric polarization action of a dielectric film and performs charge storage and discharge. The electrolytic capacitor includes a capacitor element. The capacitor element includes an anode body, a cathode body, an electrolyte, and a separator. The anode body has a dielectric film on its surface. The anode body and the cathode body face each other with the dielectric film interposed therebetween. The electrolyte is interposed between the dielectric film of the anode body and the cathode body. The electrolyte adheres closely to 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.

[0025] This electrolytic capacitor is a so-called hybrid type, comprising both an electrolyte and a solid electrolyte layer. Specifically, the electrolyte consists of both an electrolyte and a solid electrolyte layer. The electrolyte fills the voids in the capacitor element, creating a conductive path between the anode and cathode through ion transfer. The solid electrolyte layer is made of a conductive polymer. The conductive polymer fills the voids in the capacitor element or is layered between the anode and cathode, creating a conductive path between them through charge transfer.

[0026] (conductive polymer) Conductive polymers are either self-doped conjugated polymers doped with intramolecular dopants, or conjugated polymers doped with external dopant molecules. Conjugated polymers are obtained by chemical oxidation polymerization or electrolytic oxidation polymerization of monomers or derivatives thereof having π-conjugated double bonds. Dopants or external dopant molecules are acceptors that readily accept electrons into the conjugated polymer, or donors that readily donate electrons, thereby enabling the conductive polymer to exhibit high conductivity.

[0027] Any known conjugated polymer can be used without particular limitation. Examples include polypyrrole, polythiophene, polyfuran, polyaniline, polyacetylene, polyphenylene, polyphenylenevinylene, polyacene, and polythiophenevinylene. These conjugated polymers may be used individually, in combination of two or more types, or as copolymers of two or more monomers.

[0028] Among the above-mentioned conjugated polymers, conjugated polymers formed by polymerizing thiophene or its derivatives are preferred, and conjugated polymers formed 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 derivatives thereof are preferred. As the thiophene derivative, compounds selected from thiophenes having substituents at the 3rd and 4th positions are preferred, and the substituents at the 3rd and 4th positions of the thiophene ring may form a ring together with the carbon atoms at the 3rd and 4th positions. The number of carbon atoms in the alkyl or alkoxy group is suitable to be 1 to 16.

[0029] In particular, a polymer of 3,4-ethylenedioxythiophene called EDOT, i.e., poly(3,4-ethylenedioxythiophene) called PEDOT, is preferred. Furthermore, substituents may be added to 3,4-ethylenedioxythiophene. For example, alkylated ethylenedioxythiophene, in which an alkyl group having 1 to 5 carbon atoms is added as a substituent, may be used. Examples of alkylated ethylenedioxythiophene include methylated ethylenedioxythiophene (i.e., 2-methyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), ethylated ethylenedioxythiophene (i.e., 2-ethyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), butylated ethylenedioxythiophene (i.e., 2-butyl-2,3-dihydrothieno[3,4-b][1,4]dioxin), and 2-alkyl-3,4-ethylenedioxythiophene.

[0030] Dopants can be any known substance without particular limitation. Dopants may be used alone or in combination of two or more. Polymers or monomers may also be used. Examples of dopants include polyanions, inorganic acids such as boric acid, nitric acid, and phosphoric acid, and organic acids such as acetic acid, oxalic acid, citric acid, tartaric acid, squalaneic acid, rhodizonic acid, croconic acid, salicylic acid, p-toluenesulfonic acid, 1,2-dihydroxy-3,5-benzenedisulfonic acid, methanesulfonic acid, trifluoromethanesulfonic acid, borodisalicylic acid, bisoxalateborate acid, sulfonylimide acid, dodecylbenzenesulfonic acid, propylnaphthalenesulfonic acid, and butylnaphthalenesulfonic acid.

[0031] Polyanions include, for example, substituted or unsubstituted polyalkylenes, substituted or unsubstituted polyalkenes, substituted or unsubstituted polyimides, substituted or unsubstituted polyamides, and substituted or unsubstituted polyesters, which are polymers consisting only of structural units having anionic groups, or polymers consisting of structural units having anionic groups and structural units not having anionic groups. Specifically, examples of polyanions include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyacryl sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methylpropane sulfonic acid), polyisoprene sulfonic acid, polyacrylic acid, polymethacrylate, and polymaleic acid.

[0032] Examples of conductive polymers include poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid, and hereafter this conductive polymer will be referred to as PEDOT:PSS.

[0033] (electrolyte) The electrolyte is a solution in which a solute is added to a solvent. The solute is an organic acid or its salt, an inorganic acid or its salt, or a complex compound of an organic acid and an inorganic acid or its salt, and is an ionic dissociable salt that dissociates into an anionic component and a cationic component. The solvent is used alone or in combination of two or more types.

[0034] This electrolyte contains at least glycerin and a polyhydric alcohol as solvents. Preferably, it further contains lactones as solvents. The glycerin content is 8 wt% to 55 wt% of the total solvent, preferably 15 wt% to 40 wt%. The polyhydric alcohol content is 70 wt% or less of the total solvent, preferably 50 wt% or less. If lactones are included, the lactone content is 35 wt% or less of the total solvent.

[0035] As a result, electrolytic capacitors can maintain good equivalent series resistance (ESR) even in high-temperature environments and low-temperature environments as low as -55°C. That is, although glycerin has high resistivity, the electrical conductivity of conductive polymers is orders of magnitude higher than that of the electrolyte, so in hybrid-type electrolytic capacitors, the effect of glycerin addition on ESR deterioration is minimal. On the other hand, because glycerin is a high-boiling-point solvent, it can suppress the evaporation of electrolyte in hybrid-type electrolytic capacitors, allowing the electrical characteristics to be maintained for a long period of time even in high-temperature environments.

[0036] Furthermore, polyhydric alcohols have a boiling point of 150°C or higher and contain hydroxyl groups. These polyhydric alcohols with hydroxyl groups alter the higher-order structure of the conductive polymer within the electrolyte layer, and also reorient the crystalline structure of the polymer chains, thereby improving carrier mobility and enhancing the electrical conductivity of the conductive polymer. Therefore, in hybrid electrolytic capacitors, the inclusion of both a conductive polymer and a polyhydric alcohol can reduce ESR.

[0037] Furthermore, if the glycerin content is between 8 wt% and 55 wt% of the total solvent, and the polyhydric alcohol content is 70 wt% or less of the total solvent, the deterioration of the electrolyte state can be suppressed in low-temperature environments such as -55°C, and the deterioration of the ESR of electrolytic capacitors in low-temperature environments can also be suppressed.

[0038] First, although the freezing point of polyhydric alcohols is higher than -55°C, because they are mixed with glycerin, if the polyhydric alcohol content is 70 wt% or less of the total solvent, they are less likely to solidify even in a low-temperature environment of -55°C. Therefore, the deterioration of the ESR of electrolytic capacitors is suppressed. If the polyhydric alcohol content is 50 wt% or less of the total solvent, solidification becomes even less likely, and the effect of suppressing the deterioration of the ESR of electrolytic capacitors is significant.

[0039] Furthermore, while conductive polymers form conductive paths for charge transfer through the connection of their particles, as the electrolyte gels, the gel-like portion of the electrolyte penetrates between the conductive polymer particles, resulting in many electrically disconnected conductive paths. Consequently, as the electrolyte gels, the ESR of the electrolytic capacitor deteriorates. However, if the glycerin content is 55 wt% or less of the total solvent volume, the electrolyte gels less easily, even in a low-temperature environment of -55°C.

[0040] In particular, when the glycerin content is in the range of 15 wt% to 40 wt% of the total solvent, the effect of suppressing the deterioration of ESR of electrolytic capacitors in a low-temperature environment of -55°C is remarkable.

[0041] Next, lactones, such as γ-butyrolactone, have a freezing point of around -40°C and do not solidify easily in low-temperature environments, making them preferable as solvents for electrolytes in low-temperature environments. However, while glycerin or polyhydric alcohols, for example, form hydrogen bonds with the dopants of conductive polymers, such as with the SO3H groups of polystyrene sulfonic acid, thereby improving the electrical conductivity of the conductive polymers, lactones do not exhibit this effect.

[0042] Therefore, by limiting the lactone content to 35 wt% or less of the total solvent volume and increasing the composition ratio of glycerin and ethylene glycol, the electrolyte becomes less prone to solidification, the electrical conductivity of the conductive polymer improves, and the ESR of the electrolytic capacitor at cryogenic temperatures decreases.

[0043] Examples of such polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, polyoxyethylene glycol, polyoxypropylene glycol, sorbitol, xylitol, erythritol, mannitol, dipentaerythritol, pentaerythritol, or combinations of two or more of these. Among these, ethylene glycol is particularly preferred as a polyhydric alcohol. Ethylene glycol particularly reduces the initial ESR of electrolytic capacitors.

[0044] Examples of lactones include γ-butyrolactone, γ-valerolactone, and δ-valerolactone. Among these, γ-butyrolactone is preferred as a lactone because it suppresses the dissolving effect of the dielectric oxide film caused by chloride ions.

[0045] Other solvents may be mixed with the electrolyte. The solvent may be either a protic polar solvent or an aprotic polar solvent. Examples of protic polar solvents include monohydric alcohols and oxyalcohol compounds. Examples of aprotic polar solvents include sulfones, amides, cyclic amides, nitriles, and sulfoxides.

[0046] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol.

[0047] Examples of sulfone-based compounds include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Examples of amide-based compounds include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, and hexamethylphosphoric amide. Examples of cyclic amide-based compounds include N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitrile-based compounds include acetonitrile, 3-methoxypropionitrile, and glutalonitrile. Examples of sulfoxide-based compounds include dimethyl sulfoxide.

[0048] The solute is not particularly limited and any known solute can be used. Examples of organic acids that act as anionic components as solutes 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, resorcinic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, t-butyladipic acid, and 11-vinyl-8-octadecenediic 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 complex compounds of organic and inorganic acids include borodisalicylic acid, borodisuoic acid, borodiglycolic acid, borodimalonic acid, borodisuccinic acid, borodiadipic acid, borodiazelaic acid, borodibenzoic acid, borodimaleic acid, borodilactic acid, borodimalic acid, boroditartaric acid, borodicitric acid, borodiphthalic acid, borodi(2-hydroxy)isobutyric acid, borodiresorcinic acid, borodimethylsalicylic acid, borodinafthoic acid, borodimandelic acid, and borodi(3-hydroxy)propionic acid.

[0049] Cationic components include ammonium, quaternary ammonium, amidinium quaternary, amines, sodium, potassium, etc. Quaternary ammonium includes tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. Amidinium quaternary includes ethyldimethylimidazolinium, tetramethylimidazolinium, etc. Amines include primary amines, secondary amines, and tertiary amines. Primary amines include methylamine, ethylamine, propylamine, etc. Secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

[0050] Furthermore, anions and cations may be added to the electrolyte in the form of ionically dissociable salts, or the acid that forms the anion and the base that forms the cation may be added separately to the electrolyte as solute components. Anions and cations can be used individually or in combination of two or more types.

[0051] Furthermore, other additives can be added to the electrolyte. Examples of additives include complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, nitro compounds, phosphate esters, and colloidal silica. These may be used individually or in combination of two or more. Nitro compounds suppress the generation of hydrogen gas in the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, and m-nitroacetophenone.

[0052] Furthermore, the electrolyte may contain a polymeric solvent as a voltage-breaking agent. This polymeric solvent may include a polyol with an alkylene oxide attached or a derivative thereof. This voltage-breaking agent may improve the voltage breakdown of an electrolytic capacitor containing a conductive polymer.

[0053] Examples of polyols or derivatives thereof to which alkylene oxides are 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 glycerins containing ethylene oxide and propylene oxide.

[0054] (electrolyte layer) An electrolyte layer containing an electrolyte and a conductive polymer may be manufactured as follows, for example. First, a solid electrolyte layer made of a conductive polymer may be formed using a conductive polymer solution in a solid electrolyte layer formation process. The conductive polymer solution is a dispersion or solution in which a conductive polymer is dispersed or dissolved. A capacitor element is immersed in the conductive polymer solution to impregnate it with the conductive polymer solution. Alternatively, the conductive polymer solution may be applied to the anode. The conductive polymer solution may be immersed or applied once or multiple times. The inside of the capacitor element may be depressurized, or in addition, the conductive polymer solution may be pressurized while impregnating the capacitor element with the conductive polymer solution.

[0055] The dispersion medium or solvent for the conductive polymer liquid may be any medium that disperses or dissolves the conductive polymer particles or powder. The dispersion medium or solvent for the conductive polymer liquid may be water or a mixture of water and an organic solvent. Suitable examples of organic solvents include polar solvents, alcohols, esters, hydrocarbons, carbonate compounds, ether compounds, chain ethers, heterocyclic compounds, nitrile compounds, and sulfones.

[0056] Examples of polar solvents include N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide. Examples of alcohols include methanol, ethanol, propanol, butanol, ethylene glycol, glycerin, and polyglycerin. Examples of esters include ethyl acetate, propyl acetate, and butyl acetate. Examples of hydrocarbons include hexane, heptane, benzene, toluene, and xylene. Examples of carbonate compounds include ethylene carbonate and propylene carbonate. Examples of ether compounds include dioxane and diethyl ether. Examples of linear ethers include ethylene glycol dialkyl ether, propylene glycol dialkyl ether, polyethylene glycol dialkyl ether, and polypropylene glycol dialkyl ether. Examples of heterocyclic compounds include 3-methyl-2-oxazolidinone. Examples of nitrile compounds include acetonitrile, glutalodinitrile, methoxyacetonitrile, propionitrile, and benzonitrile. Examples of sulfone compounds include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

[0057] The conductive polymer solution may contain pH adjusters and various additives as needed. The pH adjusters neutralize the dopants and improve the acidity of the conductive polymer solution so that the anode, cathode, and separator do not dissolve. Examples of pH adjusters include ammonia, water-soluble alkylamines such as ethylamine and diethylamine, water-soluble arylamines such as aniline and benzylamine, and water-soluble heterocyclic amines such as pyridine and imidazole. Other examples of pH adjusters include alkali metal or alkaline earth metal hydroxides such as sodium hydroxide and calcium hydroxide, alkali metal or alkaline earth metal carbonates such as sodium carbonate and calcium carbonate, and alkali metal or alkaline earth metal alkoxides such as sodium methoxide and calcium methoxide.

[0058] Polyhydric alcohols may be included in the solid electrolyte layer by adding them as additives to the conductive polymer solution, in addition to the electrolyte solution. Because polyhydric alcohols have a high boiling point, they remain in the electrolyte layer even after the conductive polymer solution has been impregnated into the object and dried.

[0059] Furthermore, sugar alcohols may be added to the conductive polymer solution. Sugar alcohols improve the chemical properties of the dielectric film and further increase the dielectric strength of the electrolytic capacitor. Because sugar alcohols also have a high boiling point, they remain in the electrolyte layer even after the conductive polymer solution has been impregnated into the object and dried. In other words, sugar alcohols are contained in the solid electrolyte layer of the electrolytic capacitor. Examples of sugar alcohols include mannitol, sorbitol, erythritol, and pentaerythritol.

[0060] Additives include, for example, organic binders, surfactants, dispersants, defoamers, coupling agents, antioxidants, and UV absorbers. Examples of organic binders include polyvinyl alcohol, methyl methacrylate, and hydroxypropyl methylcellulose. Examples of surfactants include sorbitan oleate, polyoxyethylene sorbitan oleate, and alkylphenol polyoxyethylene ether. Examples of dispersants include polyvinylpyrrolidone, carboxymethylcellulose, and polyoxyethylene. Examples of defoamers include silicone oil, polyglycerin laurate, and polyglycerin polyphosphate. Examples of coupling agents include silane coupling agents, polyimide coupling agents, and titanate esters. Examples of antioxidants include hydroquinone, methylhydroquinone, and 1,4-dihydroxybenzene. Examples of UV absorbers include benzophenone, octocrylene, and avobenzone.

[0061] Conductive polymers are produced by chemical oxidation polymerization or electrolytic oxidation polymerization. In chemical oxidation polymerization, a solution containing monomers that will become the monomer units of the conductive polymer is mixed with an oxidizing agent to induce a polymerization reaction. Any known compound that releases dopants can be used as the oxidizing agent, such as trivalent iron salts like iron(III) p-toluenesulfonate, iron(III) naphthalenesulfonate, iron(III) anthraquinonesulfonate, or peroxodisulfates such as peroxodisulfate, ammonium peroxodisulfate, or sodium peroxodisulfate. A single compound may be used, or two or more compounds may be used. There are no strict restrictions on the polymerization temperature, but it is generally in the range of 10 to 200°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0062] In electrolytic oxidative polymerization, monomers that form the monomer units of a conductive polymer are mixed with a supporting electrolyte and polymerized using a constant potential method, a constant current method, or a potential sweep method. The supporting electrolyte contains at least one compound selected from the group consisting of borodisalicylic acid and borodisalicylate salts. Examples of salts include alkali metal salts such as lithium salts, sodium salts, and potassium salts; alkylammonium salts such as ammonium salts, ethylammonium salts, and butylammonium salts; dialkylammonium salts such as diethylammonium salts and dibutylammonium salts; trialkylammonium salts such as triethylammonium salts and tributylammonium salts; and tetraalkylammonium salts such as tetraethylammonium salts and tetrabutylammonium salts.

[0063] For the constant potential method, a potential of 1.0 to 1.5 V relative to the reference electrode is preferable. For the constant current method, a current value of 1 to 10,000 μA / cm² is preferable. For the potential sweep method, sweeping within the range of 0 to 1.5 V relative to the reference electrode at a speed of 5 to 200 mV / second is preferable. There are no strict restrictions on the polymerization temperature, but it is generally in the range of 10 to 60°C. The polymerization time is generally in the range of 10 minutes to 30 hours.

[0064] In chemical oxidation polymerization or electrolytic oxidation polymerization, the solvent to which monomers and oxidizing agents or supporting electrolytes are added can be any solvent that can dissolve the desired amount of monomer and supporting electrolyte and does not adversely affect the electrolytic oxidation polymerization, without any particular limitations. For example, suitable solvents include water, methanol, ethanol, isopropanol, butanol, ethylene glycol, acetonitrile, butyronitrile, acetone, methyl ethyl ketone, tetrahydrofuran, 1,4-dioxane, γ-butyrolactone, methyl acetate, ethyl acetate, methyl benzoate, ethyl benzoate, ethylene carbonate, propylene carbonate, nitromethane, nitrobenzene, sulfolane, and dimethylsulfolane. These solvents may be used individually or in mixtures of two or more.

[0065] The conductive polymer solution is then prepared by purifying the solution after chemical oxidation polymerization or electrolytic oxidation polymerization by ultrafiltration, cation exchange, and anion exchange, removing residual monomers and impurities, and dispersing them in a solution.

[0066] Furthermore, the conductive polymer may be formed inside the electrolytic capacitor by immersing a wound body in a solution of monomers that will become monomer units of the conductive polymer and an oxidizing agent or supporting electrolyte, and generating it through a polymerization reaction.

[0067] The electrolyte is prepared in the electrolyte preparation step, and the capacitor element is immersed in the electrolyte to impregnate the voids within the capacitor element. To impregnate even finer voids with the electrolyte, vacuum or pressure treatment may be performed as needed. The electrolyte impregnation step may be repeated multiple times. For example, the inside of the capacitor element may be depressurized, and the electrolyte may be injected into the capacitor element while pressurizing the electrolyte.

[0068] (Other configurations) Other components of the electrolytic capacitor, namely the anode, cathode, and separator, are not particularly limited and known components can be used.

[0069] (Anode) The anode body is the anode-side electrode made of a valve metal, and is, for example, a thin plate or foil. This anode body may be formed by stretching a valve metal or by sintering a powder of a valve metal. Furthermore, the anode body may be formed by laminating powders of the same or different valve metals onto the surface of a stretched valve metal substrate by sintering or vapor deposition. Examples of valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity of the valve metal is preferably 99.9% or higher for the anode foil, and other elements such as silicon, iron, copper, manganese, magnesium, chromium, zinc, titanium, vanadium, gallium, nickel, boron, and zirconium may be included.

[0070] A widening layer is formed on one or both sides of the anode. The widening layer is an etched layer, a sintered layer, or a vapor-deposited layer, where valve metal particles are deposited onto a foil. In other words, the widening layer has a porous structure and consists of tunnel-shaped pits, spongy pits, or densely packed powder or voids between particles.

[0071] Tunnel-shaped etching pits are holes carved in the direction of the foil thickness. These tunnel-shaped etching pits are typically formed by passing a direct current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current through an acidic aqueous solution containing nitric acid, for example. Sponge-like etching pits cause the expanded layer to become a sponge-like layer with a series of fine voids. These sponge-like etching pits are formed by passing an alternating current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0072] The sintered layer is produced by pasteuring powder of the same or different valve metal as the foil body with a binder and solvent, coating and drying it on the foil body, and then heating and sintering it in a vacuum or reducing atmosphere. The vapor-deposited layer is produced, for example, by resistance heating vapor deposition or electron beam heating vapor deposition. This vapor-deposited layer is formed by heating the same or different valve metal as the foil body with resistance heat or electron beam energy to evaporate it, and depositing the vapor of valve metal particles onto the surface of the foil body.

[0073] The dielectric film is formed on one or both sides of the anode body on which the expanding layer is formed. If an expanding layer is formed, the dielectric film is formed on the surface of the expanding layer, following the irregularities of the expanding layer. Typically, the dielectric film is an oxide film formed on the surface of the anode body, and if the anode body is made of aluminum, it is an aluminum oxide layer formed by oxidizing the surface of the expanding layer.

[0074] In the conversion treatment for forming a dielectric film, a voltage is applied to the anode in the conversion solution to achieve a desired dielectric strength. Furthermore, in the conversion treatment for forming a dielectric film, it is preferable to form a dielectric film with a thickness of 0.9 to 1.5 nm in order to obtain a dielectric strength of 1 V. The conversion solution is a halogen ion-free solution, such as a phosphoric acid-based conversion solution such as ammonium dihydrogen phosphate, a boric acid-based conversion solution such as ammonium borate, or an adipic acid-based conversion solution such as ammonium adipate.

[0075] A pseudo-boehmite layer may be formed on the dielectric film. The pseudo-boehmite layer contains a hydrated aluminum oxide, such as AlOOH·xH2O or Al2O3·xH2O. On the other hand, the dielectric film is a layer of aluminum oxide containing γ-alumina, which is a crystalline oxide. This pseudo-boehmite layer is dense internally and functions as a resistive layer, improving the voltage withstand capability of the electrolytic capacitor.

[0076] (Cathole body) The cathode body is a foil made of a valve metal, or a laminate of a metal layer such as a silver layer and a carbon layer. The purity of the valve metal is preferably 99% or higher for the cathode body. The foil made of the valve metal is formed by stretching. The carbon layer of the cathode body is positioned facing the anode body. The carbon layer is formed by making it into a paste, coating it onto the electrolyte layer after the electrolyte layer has been formed on the anode body, and curing it by heating. The metal layer is, for example, a silver layer, and the metal layer is formed by making it into a paste, coating it on top of the carbon layer, and curing it by heating.

[0077] A widening layer is formed on the cathode body, similar to that of the anode body. A plain foil without a widening layer may also be used as the cathode body. The cathode body may have a thin oxide film of about 1 to 10 Vfs, formed by a native oxide film or a chemical conversion treatment. The native oxide film is formed when the cathode body reacts with oxygen in the air.

[0078] Furthermore, the cathode body may be provided with a conductive layer. The conductive layer is laminated on the cathode foil. The conductive layer may mainly contain inorganic materials or inorganic compounds. Examples of inorganic materials or inorganic compounds include titanium, zirconium, tantalum, niobium, nitrides or carbides thereof, aluminum carbide, carbon materials, and composites or mixtures thereof. Specifically, examples include a carbon layer which is a conductive layer of carbon material, a conductive layer of titanium nitride, a conductive layer of titanium carbide, a conductive layer which is a mixture of titanium and carbon material, and a conductive layer which is a composite of aluminum carbide (Al4C3) and titanium oxide (TiO2).

[0079] The carbon layer contains graphite, carbon black, or a mixture thereof as the carbon material. Examples of graphite include natural graphite, artificial graphite, and graphitized Ketjenblack. Examples of carbon black include Ketjenblack, acetylene black, channel black, and thermal black. In addition, the carbon layer may contain activated carbon, carbon nanohorns, or fibrous carbon as the carbon material. Activated carbon is made from natural plant tissues such as coconut shells, synthetic resins such as phenol, and fossil fuels such as coal, coke, and pitch. Examples of fibrous carbon include carbon nanotubes (hereinafter referred to as CNTs) and carbon nanofibers (hereinafter referred to as CNFs). Activated carbon and fibrous carbon are preferred because their pi electrons are delocalized and they have a large specific surface area.

[0080] Methods for forming a carbon layer on the cathode foil include vacuum deposition, sputtering, ion plating, CVD, coating, electroplating, and electroless plating. In the coating method, a slurry is prepared by dispersing the carbon material in a dispersion solvent, and the slurry is applied to the cathode foil and dried using methods such as slurry casting, doctor blade method, or spray atomization. In the deposition method, the carbon material is evaporated by electrically heating it in a vacuum, or by irradiating the carbon material with an electron beam in a vacuum, thereby forming a carbon film on the cathode foil. In the sputtering method, a target made of carbon material and the cathode foil are placed in a vacuum chamber, and an inert gas is introduced into the vacuum chamber and a voltage is applied to cause the plasma-generated inert gas to collide with the target, depositing the carbon material particles knocked out from the target onto the cathode foil.

[0081] (Separator) The separator is made of cellulose and mixed papers such as kraft paper, Manila hemp, esparto paper, hemp, cotton, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate and their derivatives; polytetrafluoroethylene resins; polyvinylidene fluoride resins; vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins, and these resins are used individually or in mixtures.

[0082] The separator may be fibrillated by generating thin fibers that branch out from the surface of the original fibers, such as fibrillated cellulose. Fibrillation can be achieved, for example, by beating. The fibrillated fibers intertwine using the thin fibrillated fibers, improving the strength of the separator. As a result, the separator can be made thinner. Increasing the foil thickness of the separator allows for longer anodes and cathodes per unit volume, improving the capacitance of the electrolytic capacitor.

[0083] Furthermore, in fibrillated cellulose, the electron paths formed by the conductive polymer along the thin fibers branching off from the surface of the original fibers are physically narrower. It is presumed that many of these narrow electron paths exist within the separator of fibrillated cellulose. These narrow electron paths, carried out by the conductive polymer, are easily interrupted when a large current flows through defects in the dielectric film, thereby suppressing short circuits. In other words, an improvement in the voltage withstand capability of the electrolytic capacitor can be expected. The interruption of the electron path here is achieved by the insulating effect of the conductive polymer due to Joule heating caused by the flow of current.

[0084] (Capacitor element) Capacitor elements are formed by alternately stacking anodes and cathodes with an electrolyte layer in between. Specifically, an anode with a dielectric film formed on it and a cathode facing the anode are fabricated in an anode fabrication process and a cathode fabrication process. In the anode formation process and the cathode formation process, anode leads and cathode leads are electrically and mechanically connected to the anode and cathode. The anode leads and cathode leads are electrically and mechanically connected to the anode and cathode by stitching, cold welding, ultrasonic welding, or laser welding.

[0085] Next, in the element formation process, the anode and cathode are stacked with a separator in between, and in the case of a wound type, they are wound to form a capacitor element, and the capacitor element is subjected to a repair chemical treatment. In the repair chemical treatment process, the exposed base metal portion of the valve acting metal when the anode and cathode are cut to the desired width, and defects in the anode and cathode caused by physical stress such as winding are repaired.

[0086] In the repair chemical conversion process, the wound body is immersed in a conversion solution and a voltage is applied. The conversion solution can be a phosphoric acid-based solution such as ammonium dihydrogen phosphate, a boric acid-based solution such as ammonium borate, an adipic acid-based solution such as ammonium adipate, or a solution made by mixing boric acid and dicarboxylic acids such as citric acid. The voltage is preferably, for example, 0.1 to 1.2 times the conversion voltage. Furthermore, as a method of applying the voltage during repair chemical conversion, a method of applying a constant voltage from the start of repair chemical conversion, or a method of gradually increasing the applied voltage at regular intervals can be appropriately selected.

[0087] Then, through a solid electrolyte layer formation process and an electrolyte impregnation process, an electrolyte layer is formed inside the capacitor element, and the electrolyte layer is composed of a conductive polymer solid electrolyte layer and an electrolyte. The capacitor element is housed in an outer case with a closed bottom at one end and an open end at the other, and the capacitor element is sealed to the outer case with a sealing body. The sealing body is made of an elastic insulator such as a rubber sheet, or a laminate of a rigid substrate insulating board such as a synthetic resin sheet and an elastic insulator, and is crimped from the outside of the outer case. The capacitor element may also be covered with a laminate film, or sealed by molding, dip coating, or printing a resin such as a heat-resistant resin or insulating resin.

[0088] After sealing the capacitor elements in the outer casing, the electrolytic capacitor undergoes an aging process to complete its manufacturing. During the aging process, a DC voltage is applied to the electrolytic capacitor to repair defects in the dielectric oxide film layer and other areas, and to insulate conductive polymers present in the defective areas of the dielectric film, thereby improving the reliability of the electrolytic capacitor.

[0089] (circuit) Such electrolytic capacitors are suitable for various filter circuits. Examples of filter circuits include low-pass filters, high-pass filters, band-pass filters, and ripple filters, also known as smoothing circuits.

[0090] Figure 1 is a circuit diagram showing an example of a smoothing circuit equipped with this electrolytic capacitor. This smoothing circuit 1 includes a diode 2, an electrolytic capacitor 3, and an inrush current limiting circuit 4. Diode 2 is connected in series with the circuit and allows the rectified input voltage Vin to pass through while preventing reverse connection. Electrolytic capacitor 3 is placed after diode 2 and connected in parallel with the circuit to smooth the rectified input voltage Vin.

[0091] Figure 2 is a circuit diagram showing an example of a filter circuit equipped with this electrolytic capacitor. The filter circuit 5 shown in Figure 2 includes an electrolytic capacitor 3 and an inrush current limiting circuit 4. The electrolytic capacitor 3 is connected in parallel to the circuit, and the inrush current limiting circuit 4 is connected in series to the circuit before the electrolytic capacitor 3. The inrush current limiting circuit 4 includes a resistor 41 and a switch 42 connected in parallel.

[0092] In this smoothing circuit 1 and filter circuit 5, the electrolytic capacitor's resistance is low even in low-temperature environments, resulting in a high allowable ripple current value, and the reduced resistance of resistor 41 reduces power loss. Furthermore, it is possible to reduce the number of electrolytic capacitors used, enabling the realization of even smaller smoothing circuit 1 and filter circuit 5. [Examples]

[0093] The electrolytic capacitor of the present invention will be described in more detail below based on the following examples. However, the present invention is not limited to the following examples.

[0094] (Examples 1-7) Electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 and 2 were fabricated, each having a different glycerin ratio in the electrolyte solvent. These electrolytic capacitors were common to all except the electrolyte solvent and were fabricated as follows.

[0095] Specifically, in the anode formation process, aluminum foil was used as the anode body. By etching the aluminum foil with an alternating current in an acidic solution containing halogen, an expanded surface layer containing numerous spongy etching pits was formed on the surface of the aluminum foil. A dielectric film was then formed on the expanded aluminum foil by a chemical conversion treatment. Ammonium adipate at a liquid temperature of 85°C was used as the chemical conversion solution. A constant current was applied to the aluminum foil in the chemical conversion solution until a voltage of 65V was applied.

[0096] In the cathode formation process, aluminum foil was used as the cathode body. A 3V oxide film was formed by chemical conversion treatment. In the element formation process, a strip-shaped anode body and a strip-shaped cathode body were overlapped via a cellulose separator and wound so that the longitudinal direction of the strips formed a spiral, thereby forming a capacitor element. The capacitor element underwent a repair chemical conversion by immersing it in an aqueous solution of ammonium dihydrogen phosphate of the same concentration for 10 minutes. Prior to the element formation process, lead wires were connected to both the anode body and the cathode body.

[0097] Next, a conductive polymer solution was prepared by dispersing polyethylene dioxythiophene (PEDOT / PSS) doped with polystyrene sulfonic acid as the conductive polymer. The concentration of PEDOT / PSS in the conductive polymer solution was 2 wt%. Water was used as the dispersion medium for the conductive polymer solution, and 20 wt% ethylene glycol was added to the conductive polymer solution relative to the total volume of the conductive polymer solution. The pH of the conductive polymer solution was adjusted to 4 by adding ammonia. In the solid electrolyte layer formation process, a capacitor element was immersed in this conductive polymer solution, the capacitor element was removed, and dried at 150°C for 30 minutes. This formed a solid electrolyte layer composed of conductive polymer.

[0098] Furthermore, in the electrolyte impregnation step, the capacitor element with the solid electrolyte layer was impregnated with an electrolyte. The electrolyte used in the electrolyte impregnation step contained 4 wt% triethylamine azelaate salt as the solute, and the solvent was a mixed solvent of glycerin, ethylene glycol, and γ-butyrolactone, which was common to Examples 1 to 7 and Comparative Examples 1 and 2.

[0099] However, the composition ratios of glycerin, ethylene glycol, and γ-butyrolactone in the solvent differed in Examples 1 to 7 and Comparative Examples 1 and 2. Table 1 below shows the solvent composition ratios of the electrolyte.

[0100] (Table 1) TIFF2026061688000002.tif111161

[0101] As shown in Table 1 above, Examples 1 to 7 and Comparative Examples 1 and 2 differ in the proportion of glycerin in the solvent, ranging from 8 wt% to 80 wt%. In Examples 1 to 7, the glycerin content in the electrolyte solvent is between 8 wt% and 55 wt%. In Comparative Examples 1 and 2, the glycerin content in the electrolyte solvent exceeds 55 wt%.

[0102] The capacitor elements were housed in aluminum cases of the same dimensions and shape. A sealing body was attached to the open end of the aluminum case and sealed by crimping with the same applied pressure. Lead wires extending from the capacitor elements were routed out from the sealing body to allow current to flow to the electrolytic capacitor. The electrolytic capacitor was subjected to aging treatment by applying voltage. The electrolytic capacitor has a diameter of 8 mm, a height of 10 mm, and a rating of 35 WV, 150 μF.

[0103] (ESR test) The ESR of the electrolytic capacitors in Examples 1 to 7 and Comparative Examples 1 and 2 was measured. First, the ESR was measured in a 20°C environment, and then, after being left in a -55°C environment for 63 hours, the ESR was measured again in a -55°C environment. The measurement conditions for ESR were an ambient temperature of 20°C or -55°C at the time of measurement, using an LCR meter (Agilent Technologies, E4980A), with an AC signal level of 1.0Vrms and a measurement frequency of 100kHz. The ratio of the ESR after being left in a -55°C environment to the ESR at 20°C was calculated as a percentage. The ESR ratio was calculated by dividing the ESR at -55°C by the ESR at 20°C and expressing the result as a percentage.

[0104] The results of the ESR ratio (ΔESR) are shown in Table 2 below. Based on Table 2 above, Figure 3 shows the relationship between the glycerin ratio in the electrolyte solvent and the ESR ratio (ΔESR) at -55°C relative to 20°C.

[0105] (Table 2) TIFF2026061688000003.tif111161

[0106] As shown in Table 2 and Figure 3, Examples 1 to 7 have a smaller ESR ratio at -55°C to 20°C compared to Comparative Examples 1 and 2. Examples 1 to 7 are electrolytic capacitors in which the glycerin ratio in the electrolyte solvent is within the range of 8 wt% to 55 wt%. That is, by keeping the glycerin ratio in the electrolyte solvent within the range of 8 wt% to 55 wt%, the deterioration of the ESR of the electrolytic capacitor in a -55°C temperature environment is suppressed.

[0107] Furthermore, as shown in Table 2 and Figure 3, the ESR ratio for -55°C to 20°C in Examples 2 to 4 is 120% or less, which is an even more significant reduction in ESR degradation compared to the results of Examples 1 to 7. Examples 2 to 4 are electrolytic capacitors in which the glycerin ratio in the electrolyte solvent is within the range of 15 wt% to 40 wt%. In other words, by keeping the glycerin ratio in the electrolyte solvent within the range of 15 wt% to 40 wt%, the degradation of the ESR of the electrolytic capacitor in a -55°C temperature environment is further suppressed.

[0108] (Examples 8-11) Next, electrolytic capacitors were fabricated in Examples 8 to 11 and Comparative Example 3, in which the glycerin ratio in the electrolyte solvent was the same as in Example 2, but the ethylene glycol ratio was different. In Examples 8 to 11 and Comparative Example 3, the glycerin ratio in the electrolyte solvent was 15 wt%, which is between 8 wt% and 55 wt%, similar to Example 2.

[0109] On the other hand, in Examples 8 to 11 and Comparative Example 3, the ratio of ethylene glycol in the solvent varied from 15 wt% to 85 wt%. In Examples 8 to 11, similar to Example 2, the ethylene glycol in the electrolyte solvent was kept within the range of 70 wt% or less. In Comparative Example 3, the ethylene glycol added to the electrolyte solvent exceeded 70 wt%. These electrolytic capacitors were common to all except the electrolyte solvent, had the same configuration as Example 2, and were manufactured using the same manufacturing method and conditions as Example 2.

[0110] The composition ratios of glycerin, ethylene glycol, and γ-butyrolactone in the solvent for Examples 2, 8 to 11, and Comparative Example 3 are shown in Table 3 below. (Table 3) TIFF2026061688000004.tif81161

[0111] (ESR test) The ESR of the electrolytic capacitors in Examples 2, 8 to 11, and Comparative Example 3 was measured. First, the ESR was measured at a temperature of 20°C, and then the ESR was measured after being left at a temperature of -55°C for 63 hours. The ESR measurement conditions were the same as those for Examples 1 to 7. The ratio of the ESR after being left at a temperature of -55°C to the ESR at a temperature of 20°C (ΔESR) is shown in Table 4 below. Furthermore, based on Table 4 above, Figure 4 shows the relationship between the glycerin ratio in the electrolyte solvent and the ratio of the ESR at -55°C to 20°C (ΔESR).

[0112] (Table 4) TIFF2026061688000005.tif81161

[0113] As shown in Table 4 and Figure 4, Examples 2 and 8 to 11 have an ESR ratio of 120% or less for -55°C to 20°C. However, Comparative Example 3 has a worsened ESR ratio of 140% or more for -55°C to 20°C. In Examples 2, 8 to 11, and Comparative Example 3, the glycerin ratio in the electrolyte solvent is 15 wt%. However, in Examples 2 and 8 to 11, the ethylene glycol ratio in the electrolyte solvent is within the range of 70 wt% or less, whereas in Comparative Example 3, the ethylene glycol ratio in the electrolyte solvent is 85 wt%.

[0114] This confirmed that when the glycerin ratio in the electrolyte solvent is between 8 wt% and 55 wt%, and the polyhydric alcohol ratio in the electrolyte solvent is 70 wt% or less, the deterioration of the ESR of electrolytic capacitors in low-temperature environments such as -55°C is suppressed.

[0115] Table 5 below shows the ESR measurements of the electrolytic capacitors of Examples 2 and 8 to 11, taken after leaving them in a -55°C environment for 1 hour. Figure 5 is a graph showing the relationship between the γ-butyrolactone ratio in the electrolyte solvent and the ESR at -55°C, based on Table 5 below.

[0116] (Table 5) TIFF2026061688000006.tif71161

[0117] As shown in Table 5 and Figure 5, the ESR of Examples 11 and 2 when exposed to a temperature environment of -55°C is significantly lower than that of Examples 8 and 9. In other words, it was confirmed that the deterioration of the ESR of electrolytic capacitors at a temperature environment of -55°C can be further suppressed by keeping the ratio of γ-butyrolactone in the electrolyte solvent within the range of 35 wt% or less.

Claims

1. an anode body on which a dielectric film has been formed, A cathode body facing the anode body, An electrolyte interposed between the anode and the cathode, Equipped with, The electrolyte comprises a conductive polymer and an electrolyte solution. The aforementioned electrolyte is Glycerin, which accounts for 8 wt% to 55 wt% of the solvent, Polyhydric alcohols that make up 70 wt% or less of the solvent, Including, An electrolytic capacitor characterized by the following features.

2. The glycerin shall constitute 15 wt% to 40 wt% of the solvent. The electrolytic capacitor according to claim 1, characterized by the above.

3. The electrolyte further contains 35 wt% or less of lactones in the solvent. The electrolytic capacitor according to claim 1, characterized by the above.

4. The aforementioned polyhydric alcohol is present in the solvent at a concentration of 50 wt% or less. The electrolytic capacitor according to claim 1, characterized by the above.

5. The aforementioned polyhydric alcohol is ethylene glycol. The electrolytic capacitor according to claim 1 or 3, characterized by the above.

6. The lactones are γ-butyrolactones. The electrolytic capacitor according to claim 3, characterized by the above.

7. The conductive polymer is polyethylenedioxythiophene doped with polystyrene sulfonic acid. The electrolytic capacitor according to claim 1, characterized by the above.

8. The solid electrolyte layer, which is made of the conductive polymer, is interposed between the anode and the cathode. The solid electrolyte layer contains a sugar alcohol. The electrolytic capacitor according to claim 1, characterized by the above.

9. The electrolytic capacitor is provided according to claim 1 or 2. A smoothing circuit characterized by the following.

10. The electrolytic capacitor is provided according to claim 1 or 2. A filter circuit characterized by the following.

11. Anode fabrication process for creating an anode body on which a dielectric film has been formed, A cathode manufacturing step for manufacturing a cathode body opposite to the anode body, A solid electrolyte layer formation step involves impregnating the dielectric film with a dispersion of conductive polymers and drying it to adhere the conductive polymers to the dielectric film, An electrolyte preparation step involves preparing an electrolyte by including 8 wt% to 55 wt% of glycerin in the solvent and 70 wt% or less of a polyhydric alcohol in the solvent. A device forming step for forming a capacitor element including the anode, the cathode and the solid electrolyte layer, An electrolyte impregnation step in which the capacitor element is impregnated with the electrolyte, Including, A method for manufacturing electrolytic capacitors characterized by the following.

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