Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present disclosure includes a capacitor element and a liquid component. The capacitor element includes: an anode foil that has a dielectric layer; a cathode foil that is disposed so as to face the dielectric layer; a separator that is interposed between the anode foil and the cathode foil; and a conductive polymer layer that is interposed between the anode foil and the cathode foil, and is in contact with the separator. The liquid component includes a polymer compound. The polymer compound includes a first component that has a mass average molecular weight Mw of 200 or more but 2,000 or less and a polydispersity (Mw / Mn) of 1.35 or less, the polydispersity being the ratio of the mass average molecular weight Mw to the number average molecular weight Mn.

Description

electrolytic capacitor

[0001] The present invention relates to an electrolytic capacitor, and more particularly to an electrolytic capacitor including a liquid component and a conductive polymer layer.

[0002] BACKGROUND ART Conventionally, electrolytic capacitors have been known that have a capacitor element formed by winding an anode electrode foil and a cathode electrode foil, each having a dielectric oxide film formed thereon, with a separator interposed therebetween.

[0003] Known examples of such electrolytic capacitors include hybrid electrolytic capacitors that include both a conductive polymer layer and a liquid component (such as an electrolyte solution) (see, for example, Patent Document 1 below). Hybrid electrolytic capacitors have the advantages of being able to reduce the equivalent series resistance (ESR) (low ESR) through the conductive polymer layer and being able to enhance the repairability of the dielectric oxide film through the liquid component.

[0004] In recent years, various studies have been conducted to improve the characteristics of hybrid electrolytic capacitors. For example, Patent Document 1 below proposes a hybrid electrolytic capacitor using an electrolyte containing a first solvent selected from gamma-valerolactone, gamma-butyrolactone, delta-valerolactone, and alpha-methyl-gamma-butyrolactone; a second solvent selected from polyalkylene glycols and their derivatives having a number-average molecular weight of 100 to 250; and a third solvent selected from polyalkylene glycols and their derivatives having a number-average molecular weight of 500 to 2000. Specifically, a hybrid electrolytic capacitor has been proposed that uses an electrolyte containing a first solvent that is a volatile solvent (low-viscosity solvent) and second and third solvents that are low-volatility solvents. It also describes that a hybrid electrolytic capacitor using such an electrolyte can achieve both a small capacitance change rate (the rate of capacitance reduction at low temperatures relative to the capacitance at 25°C) at low temperatures (specifically, −55°C) and a low ESR at high temperatures (e.g., 135°C).

[0005] JP 2017-69390 A

[0006] As described above, electrolytic capacitors containing a polymer compound such as polyalkylene glycol as a liquid component (e.g., electrolyte) can exhibit variations in characteristics among multiple electrolytic capacitors. In particular, when multiple electrolytic capacitors are used at high temperatures (e.g., after 1,000 hours at 145°C), significant variations in capacitance can occur among the multiple electrolytic capacitors. Such large variations in capacitance among multiple electrolytic capacitors are undesirable from the perspective of quality assurance. However, it cannot be said that sufficient research has yet been conducted into reducing variations in capacitance among multiple electrolytic capacitors using a liquid component containing a polymer compound.

[0007] Therefore, the present disclosure provides an electrolytic capacitor that can reduce variations in capacitance even when a liquid component containing a polymer compound is used.

[0008] One aspect of the present invention relates to an electrolytic capacitor including a capacitor element and a liquid component, wherein the capacitor element includes an anode foil having a dielectric layer, a cathode foil arranged so as to face the dielectric layer, a separator interposed between the anode foil and the cathode foil, and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator, wherein the liquid component includes a polymer compound, and the polymer compound includes a first component having a mass average molecular weight Mw of 200 or more and 2000 or less, and a polydispersity (Mw / Mn), which is the ratio of the mass average molecular weight Mw to the number average molecular weight Mn, of 1.35 or less.

[0009] According to the present disclosure, it is possible to provide an electrolytic capacitor that can reduce variations in capacitance even when a liquid component containing a polymer compound is used.

[0010] 1 is a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure; FIG. 2 is a schematic exploded view of a portion of a capacitor element included in the electrolytic capacitor of FIG.

[0011] Below, embodiments of the present disclosure will be described using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values, materials, etc. may be applied as long as the effects of the present disclosure are obtained. Note that known components may be applied to components characteristic of the present disclosure. In this specification, when a "range from numerical value A to numerical value B" is mentioned, the range includes numerical value A and numerical value B.

[0012] In the following description, when lower and upper limits of numerical values ​​relating to specific physical properties, conditions, etc. are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not equal to or greater than the upper limit. When multiple materials are exemplified, one of them can be selected and used alone, or two or more can be used in combination, unless otherwise specified.

[0013] The present disclosure also encompasses combinations of two or more features arbitrarily selected from the appended claims, i.e., two or more features arbitrarily selected from the appended claims can be combined unless a technical contradiction arises.

[0014] [Electrolytic Capacitor] An electrolytic capacitor according to an embodiment of the present disclosure includes a capacitor element and a liquid component. In the electrolytic capacitor according to an embodiment of the present disclosure, the capacitor element includes an anode foil having a dielectric layer, a cathode foil disposed opposite the dielectric layer, a separator interposed between the anode foil and the cathode foil, and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator. In the electrolytic capacitor according to an embodiment of the present disclosure, the liquid component includes a polymer compound, and the polymer compound includes a first component having a mass-average molecular weight Mw of 200 to 2000 and a polydispersity (Mw / Mn), which is the ratio of the mass-average molecular weight Mw to the number-average molecular weight Mn, of 1.35 or less.

[0015] As described above, the electrolytic capacitor according to this embodiment includes a liquid component. The liquid component is contained in the voids in the capacitor element. The liquid component may be filled in at least a portion of the voids in the capacitor element.

[0016] <Liquid Component> The liquid component includes a nonaqueous solvent and an electrolytic solution. As the electrolytic solution, a nonaqueous electrolytic solution containing a nonaqueous solvent and a solute dissolved in the nonaqueous solvent can be used. As the nonaqueous solvent and the solute, nonaqueous solvents and solutes used in various known electrolytic capacitors can be used. The liquid component may be a component that is liquid at room temperature (25°C) or may be a component that is liquid at the temperature at which the electrolytic capacitor is used.

[0017] The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0018] Examples of organic solvents include glycol compounds, sulfone compounds, and lactone compounds. Examples of glycol compounds include ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TEG), and propylene glycol (PG). Examples of sulfone compounds include sulfolane (SL), dimethyl sulfoxide (DMSO), and diethyl sulfoxide (DESO). Examples of lactone compounds include γ-butyrolactone (GBL), γ-valerolactone (GVL), and the like.

[0019] Examples of the organic solvent include carbonate compounds and monohydric, trihydric or higher alcohols. Examples of the carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and fluoroethylene carbonate (FEC). Examples of the monohydric, trihydric or higher alcohol include glycerin and polyglycerin. These may be used alone or in combination of two or more.

[0020] Regarding organic solvents, if a group consisting of glycol compounds, sulfone compounds, and lactone compounds is defined as Group 1, and a group consisting of carbonate compounds and monohydric or trihydric or higher alcohols is defined as Group 2, the organic solvents belonging to Group 1 are preferably contained in the organic solvent in an amount of more than 50 mass%, more preferably 60 mass% or more, and even more preferably 70 mass% or more. All of the organic solvents may be organic solvents belonging to Group 1. That is, the organic solvents belonging to Group 1 may be the main solvent, and the organic solvents belonging to Group 2 may be the auxiliary solvent.

[0021] The liquid component preferably contains at least one of a glycol compound and a sulfone compound as an organic solvent. When the liquid component contains at least one of these compounds, the re-chemical conversion of the dielectric layer by the acid component contained in the liquid component can be efficiently carried out. Furthermore, since the liquid component contains a glycol compound, protons (H ＋ ) (specifically, the proton (H ＋ ) can be easily provided. This makes it particularly easy to swell the conductive polymer layer. When the liquid component contains a sulfone compound, the liquid component has high resistance to acidic and basic components. Furthermore, glycol compounds and sulfone compounds generally have high boiling points (specifically, boiling points of 180°C or higher). Therefore, when the liquid component contains these compounds, the liquid component is less likely to volatilize even when the electrolytic capacitor is used at high temperatures (e.g., at temperatures of 145°C). The glycol compound preferably contains ethylene glycol (EG), and the sulfone compound preferably contains sulfolane (SL).

[0022] When the liquid component contains a glycol compound and a sulfone compound as organic solvents, the proportion of the glycol compound in the liquid component is preferably 10% by mass or more and 60% by mass or less, and the proportion of the sulfone compound in the liquid component is preferably 20% by mass or more and 70% by mass or less. By including the glycol compound and the sulfone compound in the above-mentioned ranges, the re-chemical conversion of the dielectric layer by the acid component contained in the liquid component can be carried out more efficiently. Furthermore, the proton donating ability to the conductive polymer can be further improved, and the resistance of the liquid component to acid components and base components can be further improved.

[0023] From the viewpoint of donating protons to the conductive polymer, the liquid component may contain compounds other than glycol compounds, such as glycerin and polyglycerin.

[0024] The liquid component may contain water. The water content in the liquid component may be 0.1% by mass or more and 6.0% by mass or less, 0.2% by mass or more and 4.0% by mass or less, or 0.5% by mass or more and 2.0% by mass or less. By containing water in the liquid component within the above range, the repairability of the dielectric layer by the liquid component can be improved. Furthermore, when the electrolytic capacitor is used at high temperatures (e.g., when used at 145°C for 1000 hours), fluctuations in the equivalent series resistance (ESR) value can be suppressed. Note that sulfone compounds have excellent hydrolysis resistance, and therefore, when the liquid component contains a sulfone compound as described above, the hydrolysis resistance of the liquid component can be improved.

[0025] The solute contains at least one of an acid component (acid) and a base component (base). When the liquid component contains a solute, the proportion of the solute in the liquid component is preferably 70% by mass or less, and more preferably 50% by mass or less.

[0026] Polycarboxylic acids and monocarboxylic acids can be used as the acid component. Examples of polycarboxylic acids include aliphatic polycarboxylic acids, aromatic polycarboxylic acids, and alicyclic polycarboxylic acids. Examples of aliphatic polycarboxylic acids include saturated polycarboxylic acids and unsaturated polycarboxylic acids. Examples of saturated polycarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,6-decanedicarboxylic acid, and 5,6-decanecarboxylic acid. Examples of unsaturated polycarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of aromatic polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, and pyromellitic acid. Examples of alicyclic polycarboxylic acids include cyclohexane-1,2-dicarboxylic acid and cyclohexene-1,2-dicarboxylic acid.

[0027] Examples of monocarboxylic acids include aliphatic monocarboxylic acids, aromatic monocarboxylic acids, and oxycarboxylic acids. Examples of aliphatic monocarboxylic acids include saturated monocarboxylic acids and unsaturated monocarboxylic acids. Examples of saturated monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, lauric acid, myristic acid, stearic acid, and behenic acid. Examples of unsaturated monocarboxylic acids include acrylic acid, methacrylic acid, and oleic acid. Examples of aromatic monocarboxylic acids include benzoic acid, cinnamic acid, and naphthoic acid. Examples of oxycarboxylic acids include salicylic acid, mandelic acid, and resorcylic acid.

[0028] An inorganic acid may be used as the acid component. Examples of inorganic acids include phosphoric acid, phosphorous acid, hypophosphorous acid, alkyl phosphate esters, boric acid, fluoroboric acid, tetrafluoroboric acid, hexafluorophosphoric acid, benzenesulfonic acid, and naphthalenesulfonic acid. Alternatively, a composite compound of an organic acid and an inorganic acid may be used as the acid component. Examples of such composite compounds include dicarboxylic acid derivatives such as borodiglycolic acid, borodisalic acid, and borodisalicylic acid.

[0029] The base component may be a compound having an alkyl-substituted amidine group, such as an imidazole compound, a benzimidazole compound, or an alicyclic amidine compound (a pyrimidine compound, an imidazoline compound). Specifically, 1,8-diazabicyclo[5,4,0]undecene-7; 1,5-diazabicyclo[4,3,0]nonene-5; 1,2-dimethylimidazolinium; 1,2,4-trimethylimidazoline; 1-methyl-2-ethylimidazoline; 1,4-dimethyl-2-ethylimidazoline; 1-methyl-2-heptylimidazoline; 1-methyl-2-(3'heptyl)imidazoline; 1-methyl-2-dodecylimidazoline; 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine; 1-methylimidazole; or 1-methylbenzimidazole is preferred. By using these, the electrolytic capacitor can be made to have excellent impedance characteristics.

[0030] The base component may be a quaternary salt of a compound having an alkyl-substituted amidine group, such as an imidazole compound, a benzimidazole compound, or an alicyclic amidine compound (a pyrimidine compound, an imidazoline compound) quaternized with an alkyl group or an arylalkyl group having 1 to 11 carbon atoms. Specifically, 1-methyl-1,8-diazabicyclo [5,4,0] undecene-7; 1-methyl-1,5-diazabicyclo [4,3,0] nonene-5; 1,2,3-trimethylimidazolinium; 1,2,3,4-tetramethylimidazolinium; 1,2-dimethyl-3-ethyl-imidazolinium; 1,3,4-trimethyl-2-ethylimidazolinium; 1,3-dimethyl-2-heptylimidazolinium; 1,3-dimethyl-2- (3' heptyl) imidazolinium, 1,3-dimethyl-2-dodecylimidazolinium; 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium; 1,3-dimethylimidazolium; 1-methyl-3-ethylimidazolium; 1,3-dimethylbenzimidazolium is preferred. By using these materials, the electrolytic capacitor can be made to have excellent impedance characteristics.

[0031] Tertiary amines may be used as the base component. Examples of tertiary amines include trialkylamines and phenyl group-containing amines. Examples of trialkylamines include trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl-n-propylamine, dimethylisopropylamine, methylethyl-n-propylamine, methylethylisopropylamine, diethyl-n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, and tri-tert-butylamine. Examples of phenyl group-containing amines include dimethylphenylamine, methylethylphenylamine, and diethylphenylamine. From the viewpoint of increasing conductivity, trialkylamines are preferably used, and among trialkylamines, it is preferable to use at least one selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine. Examples of the base component may include secondary amines such as dialkylamines, primary amines such as monoalkylamines, and ammonia.

[0032] A heterocyclic amine may be used as the base component. Examples of the heterocyclic amine include morpholines, and examples of the morpholines include morpholine and morpholine derivatives. Specific examples include morpholine, N-alkylmorpholine, and N-hydroxyalkylmorpholine, and examples of the N-alkylmorpholine include N-methylmorpholine, N-butylmorpholine, and 4-isobutylmorpholine.

[0033] The liquid component may contain a salt of an acid component and a base component. The salt may be an inorganic salt or an organic salt. An organic salt is a salt in which at least one of the anion and the cation contains an organic substance. Examples of organic salts include trimethylamine maleate, triethylamine borodisalicylate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-2-ethylimidazolinium phthalate.

[0034] In the electrolytic capacitor according to the embodiment of the present disclosure, when the liquid component contains at least one of a glycol compound and a sulfone compound as an organic solvent, the liquid component preferably contains at least one of a dicarboxylate and a dicarboxylic acid derivative as a solute. By including the above-mentioned components in the liquid component, the acid component contained in the liquid component can sufficiently promote the re-chemical conversion of the derivative layer. Furthermore, the pH of the liquid component can be maintained low, thereby suppressing deterioration of the conductive polymer layer. Examples of dicarboxylates include the above-mentioned triethylamine maleate, ethyldimethylamine phthalate, mono-1,2,3,4-tetramethylimidazolinium phthalate, and mono-1,3-dimethyl-ethylimidazolinium phthalate. Examples of dicarboxylic acid derivatives include the above-mentioned borodiglycolic acid, borodisalic acid, and borodisalicylic acid.

[0035] The ionic liquid is synonymous with a salt in a molten state (molten salt), and is an ionic substance that is liquid at, for example, 25°C.

[0036] Examples of cations that constitute ionic liquids include cations of nitrogen-containing heterocycles (imidazolium, pyrrolidinium, piperidinium, pyridinium, morpholinium, etc.), ammonium, phosphonium, sulfonium, and derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group). The cation may also be an organic cation.

[0037] The anions that constitute the ionic liquid include hydrogen sulfate ions (HSO ４ － ), sulfate ions (SO ４ ２－ , -SO ４ － ), carboxylate anion (-COO － ), nitrate anion, sulfonate anion (-SO ３ － ), phosphonate anion (PO ３ ２－ , -HPO ３ －) and the like. Acids capable of generating these anions include sulfuric acid, sulfuric acid monoesters (methyl sulfate, etc.), carboxylic acids (acetic acid, lactic acid, benzoic acid, trifluoromethane acetic acid, etc.), nitric acid, sulfonic acids (methanesulfonic acid, trifluoromethanesulfonic acid, bis(trifluoromethylsulfonyl)imide anion, etc.), phosphonic acids (diethylphosphonic acid, etc.), or derivatives thereof (e.g., substituted compounds having a substituent such as an alkyl group, a halogenated alkyl group, or a halogen atom). The anion may contain a fluorine atom. Examples of fluorine atom-containing anions include the above-mentioned trifluoromethane acetic acid, trifluoromethanesulfonic acid, bis(trifluoromethylsulfonyl)imide anion, and derivatives thereof.

[0038] Specific examples of ionic liquids include 1-butyl-3-methylimidazolium hydrogen sulfate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-ethyl-3-methylimidazolium diethylphosphonate.

[0039] The liquid component contains a polymer compound. Examples of the polymer compound include polyalkylene glycol, polyalkylene glycol derivatives (polyalkylene glycol monoethers, polyalkylene glycol diethers, polyalkylene glycol monoesters, polyalkylene glycol diesters, etc.), and compounds in which at least one hydroxyl group of a polyhydric alcohol is substituted with polyalkylene glycol (including derivatives). Specific examples include polyethylene glycol, polyethylene glycol glyceryl ether, polyethylene glycol diglyceryl ether, polyethylene glycol sorbitol ether, polypropylene glycol, polypropylene glycol diglyceryl ether, polypropylene glycol sorbitol ether, and polybutylene glycol.

[0040] The polyalkylene glycol may be a copolymer (random copolymer, block copolymer, random block copolymer, or the like), such as a copolymer of ethylene glycol and propylene glycol, a copolymer of ethylene glycol and butylene glycol, or a copolymer of propylene glycol and butylene glycol.

[0041] The polymer compound may be a copolymer having ethylene oxide (EO) units and propylene oxide (PO) units. The copolymer includes a copolymer of EO and PO (EO-PO copolymer) and a derivative thereof. These may be used alone or in combination of two or more. The copolymer may be crosslinked with a crosslinking agent. The derivative may be a copolymer obtained by converting a hydroxyl group (—OH) that an EO-PO copolymer normally has at its terminal into an acrylic group (O—CO—CH═CH ２ ) or the like. When the entire EO-PO copolymer is taken as 1 mole, the molar ratio of EO units to PO units is preferably EO:PO=0.9:0.1 to 0.5:0.5. That is, the EO-PO copolymer preferably contains the same amount of EO units as the PO units. This makes it possible to prevent the EO-PO copolymer contained in the liquid component from permeating through the sealing member in an electrolytic capacitor in which a capacitor element is housed in a bottomed case and the opening of the bottomed case is sealed with a sealing member (such as sealing rubber).

[0042] In the electrolytic capacitor according to the embodiment of the present disclosure, it is important that the polymer compound contains a first component having a mass average molecular weight Mw of 200 or more and 2000 or less, and a polydispersity (Mw / Mn), which is the ratio of the mass average molecular weight Mw to the number average molecular weight Mn, of 1.35 or less.

[0043] A polymer compound with a polydispersity index (Mw / Mn) of 1.35 or less refers to a polymer compound with a relatively narrow distribution of mass-average molecular weight Mw, i.e., a polymer compound with a relatively small variation in mass-average molecular weight Mw. Therefore, by using a polymer compound containing a first component with a relatively small variation in mass-average molecular weight Mw as the polymer compound contained in the liquid component, the quality variation of the liquid component can be relatively reduced among multiple electrolytic capacitors. For example, the quality variation of the liquid component can be relatively reduced among multiple electrolytic capacitors manufactured to contain polymer compounds with the same lot number (more specifically, multiple electrolytic capacitors with the same lot number). Furthermore, the quality variation of the liquid component can be relatively reduced among multiple electrolytic capacitors manufactured to contain polymer compounds with different lot numbers (more specifically, multiple electrolytic capacitors with different lot numbers). This reduces the variation in product characteristics of electrolytic capacitors within the same lot and between different lots. Although the polydispersity (Mw / Mn) often increases as the mass-average molecular weight Mw increases, the effect of the mass-average molecular weight Mw on the polydispersity (Mw / Mn) can be reduced by using a polymer compound containing a first component having a mass-average molecular weight Mw of 200 to 2000 as the liquid component, thereby suppressing variations in capacitance among a plurality of electrolytic capacitors.

[0044] The above-mentioned polymer compounds can be obtained by fractionating polymer compounds having various mass-average molecular weights Mw and polydispersities (Mw / Mn) by various known methods such as microfiltration, reverse osmosis, or ultrafiltration.

[0045] The number-average molecular weight Mn and mass-average molecular weight Mw of a polymer compound are polystyrene-equivalent values ​​measured by gel permeation chromatography (GPC). GPC measurement is usually performed using a polystyrene gel column and water / methanol (volume ratio 8 / 2) as the mobile phase.

[0046] Measurement by GPC is carried out using, for example, a column consisting of two connected Shodex OHpak SB804HQ and SB8025HQ columns, with 50 mM NaNO ３ The analysis can be carried out using an aqueous solution as an eluent, an RI detector, a column temperature of 40° C., a flow rate of the eluent of 0.7 mL / min, and an analysis time of 40 min.

[0047] The polydispersity (Mw / Mn) may be 1.25 or less, 1.20 or less, or 1.10 or less. When the polymer compound contains the first component within the above numerical range, the variation in capacitance between multiple electrolytic capacitors can be further reduced. In particular, when multiple electrolytic capacitors are used at high temperatures (e.g., when used at 145°C for 1,000 hours), the variation in capacitance between multiple electrolytic capacitors can be further reduced. The theoretical lower limit of the polydispersity (Mw / Mn) is 1.00. The polydispersity (Mw / Mn) is preferably 1.05 or more. A polydispersity (Mw / Mn) of 1.05 or more can reduce the effort required for fractionation to obtain the first component. Furthermore, since the effort required for fractionation can be reduced, the associated increase in production costs can be suppressed.

[0048] The polymer compound may contain a second component other than the first component. The second component refers to a polymer compound having at least one of a mass average molecular weight Mw and a polydispersity index (Mw / Mn) outside the above-mentioned ranges. For example, the second component refers to a polymer compound having a mass average molecular weight Mw of 4000 or a polydispersity index (Mw / Mn) of 1.5.

[0049] In the electrolytic capacitor according to the embodiment of the present disclosure, the proportion of the first component in the polymer compound is preferably greater than 50% by mass, more preferably 70% by mass or more, and even more preferably 90% by mass or more. The entire polymer compound may be the first component. That is, the proportion of the first component in the polymer compound may be 100% by mass.

[0050] In the electrolytic capacitor according to the embodiment of the present disclosure, the liquid component preferably contains the first component in a range of 5% by mass to 30% by mass. By including the first component in the liquid component in the above range, the liquid component has a moderate viscosity. Therefore, even when the electrolytic capacitor according to the embodiment is used at high temperatures (e.g., after 1,000 hours at 145°C), the liquid component is less likely to volatilize from the inside to the outside of the electrolytic capacitor. Furthermore, the moderate viscosity of the liquid component allows the acid component contained in the liquid component to sufficiently promote re-chemical conversion of the derivative layer. Furthermore, the electrolytic capacitor according to the embodiment of the present disclosure includes a conductive polymer layer. Therefore, even when the first component is contained in the liquid component at a high concentration of up to 30% by mass, the conductive polymer layer ensures sufficient electrical conductivity. The lower limit of the proportion of the first component may be 10% by mass or more, or 15% by mass or more. The upper limit of the proportion of the first component may be 25% by mass or less, or 20% by mass or less.

[0051] <Capacitor Element> As described above, an electrolytic capacitor according to an embodiment of the present disclosure includes a liquid component and a capacitor element. The capacitor element includes an anode foil having a dielectric layer, a cathode foil disposed opposite the dielectric layer, a separator interposed between the anode foil and the cathode foil, and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator.

[0052] (Anode foil) Examples of the anode foil include metal foils containing at least one valve metal such as titanium, tantalum, aluminum, and niobium. The anode foil may be a metal foil of a valve metal (e.g., aluminum foil). The anode foil may contain the valve metal in the form of an alloy containing the valve metal or a compound containing the valve metal. The thickness of the anode foil may be 15 μm or more and 300 μm or less. The surface of the anode foil may be roughened by etching or the like.

[0053] A dielectric layer is formed on the surface (main surface) of the anode foil. The dielectric layer may be formed by chemical conversion of the anode foil. In this case, the chemical conversion coating formed by the chemical conversion serves as the dielectric layer. The chemical conversion may be performed by applying a predetermined chemical conversion voltage to the anode foil while the anode foil is immersed in an acidic aqueous solution (hereinafter also referred to as a chemical conversion solution), or by heat-treating the anode foil at a predetermined temperature while the anode foil is immersed in the chemical conversion solution. Furthermore, when the dielectric layer is formed by chemical conversion as described above, the dielectric layer (chemical conversion coating) may contain an oxide of a valve metal (e.g., aluminum oxide). Note that the dielectric layer may be formed of a dielectric other than an oxide of a valve metal as long as it functions as a dielectric.

[0054] In an electrolytic capacitor, a conductive polymer layer does not need to be formed on the end face (side face) of the anode foil. On the other hand, a dielectric layer is preferably formed on the end face (side face) of the anode foil. Taking a wound electrolytic capacitor (see FIGS. 1 and 2 ) as an example, in the wound capacitor element 10 shown in FIG. 2 , the conductive polymer is formed in the circumferential direction, but does not need to be formed on the upper and lower end faces.

[0055] (Cathode foil) The cathode foil is not particularly limited as long as it functions as a cathode. Examples of the cathode foil include metal foil (e.g., aluminum foil). The type of metal contained in the metal foil is not particularly limited. The metal may be a valve metal or an alloy containing a valve metal. The thickness of the cathode foil may be 15 μm or more and 300 μm or less. The surface of the cathode foil may be roughened or chemically treated as necessary.

[0056] The cathode foil may include a conductive coating layer. When the metal foil includes a valve metal, the coating layer may include at least one of carbon and a metal having a lower ionization tendency than the valve metal. This facilitates improving the acid resistance of the metal foil. When the metal foil includes aluminum, the coating layer may include at least one selected from the group consisting of carbon, nickel, titanium, tantalum, and zirconium. In order to achieve low cost and low resistance, the coating layer may include at least one of nickel and titanium.

[0057] The thickness of the coating layer may be 5 nm or more, or 10 nm or more. The thickness of the coating layer may be 200 nm or less. The coating layer may be formed by vapor deposition or sputtering the metal on the metal foil. Alternatively, the coating layer may be formed by vapor deposition of a conductive carbon material on the metal foil or by applying a carbon paste containing a conductive carbon material. Examples of conductive carbon materials include graphite, hard carbon, soft carbon, and carbon black.

[0058] (Separator) A porous sheet can be used for the separator. Examples of porous sheets include woven fabric, nonwoven fabric, and microporous membrane. The thickness of the separator is not particularly limited and may be in the range of 10 μm to 300 μm. Examples of separator materials include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0059] (Conductive polymer layer) The conductive polymer layer is formed from a conductive polymer. Examples of conductive polymers include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The conductive polymer may be used alone or in combination of two or more types. The conductive polymer may be a copolymer of two or more types of monomers. Note that a derivative of a conductive polymer refers to a polymer having a conductive polymer as a basic skeleton. For example, a derivative of polythiophene includes poly(3,4-ethylenedioxythiophene).

[0060] The conductive polymer may contain a dopant. The dopant can be appropriately selected depending on the type of conductive polymer. Various known dopants may be used as the dopant. Examples of dopants include naphthalenesulfonic acid, p-toluenesulfonic acid, polystyrenesulfonic acid, and salts thereof. A specific example of a conductive polymer containing a dopant is a polymer in which poly(3,4-ethylenedioxythiophene) (PEDOT) is doped with polystyrenesulfonic acid (PSS).

[0061] The conductive polymer layer preferably contacts the anode foil, cathode foil, and separator over a sufficiently large contact area, thereby forming a sufficient conductive path between the anode foil and the cathode foil. As a result, the equivalent series resistance (ESR) of the electrolytic capacitor can be reduced, thereby improving the reliability of the electrolytic capacitor.

[0062] The conductive polymer layer is preferably formed on at least one of the surface of the dielectric layer of the anode foil and the surface of the cathode foil. The conductive polymer layer may also be formed within the voids of the separator (i.e., on the surface of the separator's constituent material surrounding the voids of the separator). This allows for the formation of a stronger conductive path between the anode foil and the cathode foil via the conductive polymer layer. The conductive polymer layer is preferably formed on at least the surface of the dielectric layer of the anode foil, and more preferably on both the surface of the dielectric layer and the surface of the cathode foil, and furthermore, within the voids of the separator. The conductive polymer layer is preferably formed so as to continuously connect the surface of the dielectric layer and the surface of the cathode foil. The continuous connection between the surface of the dielectric layer and the surface of the cathode foil allows for an even stronger conductive path to be formed between the anode foil and the cathode foil.

[0063] The conductive polymer layer can be formed by applying a polymer dispersion, in which a conductive polymer and a dopant are dispersed in a liquid medium, to a dielectric layer, and then removing at least a portion of the liquid medium. Alternatively, the conductive polymer layer can be formed by impregnating a dielectric layer with a monomer dispersion containing a monomer that forms a constituent unit of the conductive polymer and a dopant, and then chemically or electrolytically polymerizing the monomer in the dielectric layer in the presence of the dopant. In order to ensure that the electrolytic capacitor exhibits excellent voltage resistance characteristics, it is preferable that the conductive polymer layer be formed using a polymer dispersion.

[0064] A specific configuration of an electrolytic capacitor according to an embodiment of the present disclosure will be described below with reference to Figures 1 and 2. Figure 1 is a cross-sectional view that schematically illustrates an electrolytic capacitor 100 according to an embodiment of the present disclosure, and Figure 2 is a schematic view of a portion of a capacitor element 10 included in the electrolytic capacitor 100, in which the portion is expanded.

[0065] Electrolytic capacitor 100 includes capacitor element 10, bottomed case 101 that houses capacitor element 10, sealing member 102 (e.g., a sealing rubber) that closes the opening of bottomed case 101, seat plate 103 that covers sealing member 102, seat plate 103 that is disposed outside bottomed case 101 so as to cover sealing member 102 from the open side of bottomed case 101, a pair of lead wires 104A, 104B that extend from sealing member 102 and pass through seat plate 103, and a pair of lead tabs 105A, 105B that connect each of the pair of lead wires 104A, 104B to electrodes of the capacitor element (e.g., an anode foil 11 and a cathode foil 12, which will be described later). The vicinity of the open end of bottomed case 101 is drawn to be recessed inward, and the open end of bottomed case 101 is curled to be crimped to sealing member 102. In the example shown in FIG. 1, lead wire 104A is connected to an electrode of the capacitor element via lead tab 105A, and lead wire 104B is connected to an electrode of the capacitor element via lead tab 105B.

[0066] The sealing member 102 is made of an elastic material containing a rubber component, such as butyl rubber (IIR), nitrile rubber (NBR), ethylene propylene rubber, ethylene propylene diene rubber (EPDM), chloroprene rubber (CR), isoprene rubber (IR), Hypalon (trademark) rubber, silicone rubber, or fluororubber. The sealing member 102 may contain fillers such as carbon black or silica.

[0067] Capacitor element 10 is configured as, for example, a wound body as shown in FIG. 2. The wound body includes anode foil 11 connected to lead tab 105A, cathode foil 12 connected to lead tab 105B, and separator 13. Capacitor element 10 includes a conductive polymer layer (not shown). Note that electrolytic capacitor 100 shown in FIG. 1 includes capacitor element 10 shown in FIG. 2, and is therefore referred to as a wound-type electrolytic capacitor.

[0068] The anode foil 11 and the cathode foil 12 are wound with a separator 13 interposed therebetween to form a wound body. The outermost periphery of this wound body is fixed with a stop tape 14. Note that Fig. 2 shows the wound body in a partially unfolded state before the outermost periphery is fixed with the stop tape 14.

[0069] The electrolytic capacitor according to the present disclosure may include at least one capacitor element, or may include multiple capacitor elements, with the number of capacitor elements being determined appropriately depending on the intended use.

[0070] 1 and 2 illustrate a wound-type electrolytic capacitor, but the electrolytic capacitor according to the embodiment of the present disclosure is not limited to this and may be a chip-type electrolytic capacitor or a stacked-type electrolytic capacitor.

[0071] [Method of Manufacturing Electrolytic Capacitor] An example of a method of manufacturing an electrolytic capacitor according to an embodiment of the present disclosure includes the steps of: (a) preparing an anode foil having a dielectric layer, a cathode foil, and a separator; (b) applying a polymer dispersion, in which a conductive polymer and a dopant are dispersed in a liquid medium, to at least one surface of the dielectric layer and the cathode foil and into the voids of the separator; (c) forming a conductive polymer layer on the one surface and in the voids of the separator by removing at least a portion of the liquid medium from the polymer dispersion; (d) forming a capacitor element by disposing a separator between the anode foil and the cathode foil; and (e) filling the voids in the capacitor element with a liquid component. In the method of manufacturing an electrolytic capacitor according to an embodiment of the present disclosure, the steps (a) to (e) are preferably performed in this order.

[0072] <Step (a)> The step of preparing an anode foil having a dielectric layer, a cathode foil, and a separator is not particularly limited. The materials of the anode foil, the cathode foil, and the separator are also not particularly limited. The anode foil, the cathode foil, and the separator may be the same as those described above.

[0073] <Step (b)> In step (b), the polymer dispersion may be applied to the surface of the dielectric layer and the separator, or to the surface of the cathode foil and the separator. Alternatively, the polymer dispersion may be applied to the surface of the dielectric layer, the surface of the cathode foil, and the separator. When dielectric layers are formed on both sides of the anode foil, the polymer dispersion may be applied to the surfaces of the dielectric layers formed on both sides of the dielectric layer. Alternatively, the polymer dispersion may be applied to both sides of the cathode foil. A conductive polymer layer is formed at the location where the polymer dispersion is applied.

[0074] Examples of methods for applying the polymer dispersion include coating. Coating can be carried out by various known methods. Examples of coating include coating using a coater, spray coating, and coating by immersing the object to be coated in the polymer dispersion. Examples of coating using a coater include gravure coating and die coating. Note that an example of the liquid medium is water.

[0075] <Step (c)> In step (c), the method for removing at least a portion of the liquid medium from the polymer dispersion is not particularly limited. The liquid medium is preferably removed by at least heating. The liquid medium may be removed by heating under reduced pressure. When the liquid medium is water, the liquid medium is preferably removed by heating the liquid medium to 100°C or higher.

[0076] In addition, when the electrolytic capacitor is a wound-type electrolytic capacitor 100 as shown in FIG. 1, a conductive polymer layer can be formed by impregnating a capacitor element 10 configured as a wound body as shown in FIG. 2 with a polymer dispersion, and then heating the capacitor element 10 at a predetermined temperature.

[0077] <Step (d)> In step (d), a conductive polymer layer is formed on the separator and on at least one surface of the dielectric layer and the cathode foil, and then the separator is disposed between the anode foil and the cathode foil to form a capacitor element (specifically, a capacitor element including a conductive polymer layer). This step is also a step in which the anode foil and the cathode foil are laminated with the separator interposed therebetween.

[0078] The method for forming the capacitor element is not particularly limited. The capacitor element may be formed by any known method. The capacitor element may be a wound body as shown in Fig. 2. In the wound body as shown in Fig. 2, the anode foil, the cathode foil, and the separator are stacked in the radial direction of the wound body.

[0079] A capacitor element may be formed by stacking flat anode foils, flat cathode foils, and flat separators in one direction. For example, a capacitor element may be formed by stacking multiple anode foils, multiple cathode foils, and multiple separators in one direction. An electrolytic capacitor including such a stacked capacitor element is called a stacked electrolytic capacitor. In a typical example of a stack, the anode foils and cathode foils are arranged alternately, with separators disposed between the anode foils and cathode foils.

[0080] <Step (e)> The method for filling the voids in the capacitor element with the liquid component is not particularly limited. For example, the voids in the capacitor element may be filled with the liquid component by impregnating at least a portion of the capacitor element with the liquid component.

[0081] As described above, by carrying out steps (a) to (e), a capacitor element including a conductive polymer layer and a liquid component is formed. Thereafter, if necessary, the capacitor element is encapsulated in an exterior body (case). In this manner, an electrolytic capacitor according to an embodiment of the present disclosure is manufactured.

[0082] Although the above describes an example in which a conductive polymer layer is formed on the separator and on at least one surface of the dielectric layer and the cathode foil before laminating the anode foil and the cathode foil with the separator interposed therebetween, the example in which a conductive polymer layer is formed is not limited to this. The conductive polymer layer may be formed after laminating the anode foil and the cathode foil with the separator interposed therebetween. For example, after obtaining a wound body in which the anode foil and the cathode foil are laminated with the separator interposed therebetween, the wound body may be immersed in a polymer dispersion to form a conductive polymer layer on the separator and on at least one surface of the dielectric layer and the cathode foil.

[0083] (Additional Notes) The above description discloses the following technologies. (Technology 1) An electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises: an anode foil having a dielectric layer; a cathode foil arranged so as to face the dielectric layer; a separator interposed between the anode foil and the cathode foil; and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator, wherein the liquid component contains a polymer compound, and the polymer compound includes a first component having a mass average molecular weight Mw of 200 to 2000 and a polydispersity (Mw / Mn) of 1.35 or less, which is the ratio of the mass average molecular weight Mw to the number average molecular weight Mn. (Technology 2) The electrolytic capacitor according to Technology 1, wherein the first component is a polyalkylene glycol. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the liquid component contains 5% by mass to 30% by mass of the first component. (Technology 4) The electrolytic capacitor according to any one of Technologies 1 to 3, wherein the liquid component contains at least one of a glycol compound and a sulfone compound as a solvent, and at least one of a dicarboxylate and a dicarboxylic acid derivative as a solute. (Technology 5) The electrolytic capacitor according to any one of Technologies 1 to 4, wherein the liquid component contains a glycol compound and a sulfone compound as solvents, a proportion of the glycol compound in the liquid component is 10% by mass or more and 60% by mass or less, and a proportion of the sulfone compound in the liquid component is 20% by mass or more and 70% by mass or less.

[0084] While the present invention has been described with respect to presently preferred embodiments, such disclosure should not be interpreted as limiting. Various variations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all variations and modifications that do not depart from the true spirit and scope of the invention.

[0085] Hereinafter, the present disclosure will be specifically described based on examples and comparative examples, but the present disclosure is not limited to the following examples.

[0086] (Example 1) (A) Preparation of Components (A-1) Anode Foil Both surfaces of an aluminum foil (thickness 100 μm) were subjected to an etching treatment to roughen the surfaces. Both surfaces of the roughened aluminum foil were subjected to a chemical conversion treatment to form a dielectric layer on both surfaces. In this way, an anode foil having a dielectric layer formed on both surfaces was obtained.

[0087] (A-2) Cathode Foil Both surfaces of an aluminum foil (thickness: 50 μm) were etched to obtain a cathode foil with both surfaces roughened.

[0088] (A-3) Separator A nonwoven fabric (thickness: 50 μm) was prepared as a separator. The nonwoven fabric was composed of 50% by mass of synthetic fibers (25% by mass of polyester fibers and 25% by mass of aramid fibers) and 50% by mass of cellulose, and contained polyacrylamide as a paper strength agent. The density of the nonwoven fabric was 0.35 g / cm ３ It was.

[0089] (B) Preparation of Polymer Dispersion 3,4-ethylenedioxythiophene and poly(4-styrenesulfonic acid) (PSS, mass-average molecular weight Mw 100,000; dopant) were dissolved in ion-exchanged water to prepare a mixed solution. Next, while stirring the mixed solution, an oxidizing agent (iron(III) sulfate and ammonium persulfate) dissolved in ion-exchanged water was added to the mixed solution to carry out a polymerization reaction. After the polymerization reaction, the resulting reaction solution was dialyzed to remove unreacted monomer and excess oxidizing agent. This resulted in a polymer dispersion, poly(3,4-ethylenedioxythiophene) doped with PSS (PEDOT / PSS).

[0090] (C) Fabrication of a wound body The anode foil, cathode foil, and separator were each cut to have predetermined planar dimensions. An anode lead tab was connected to the anode foil, and a cathode lead tab was connected to the cathode foil. Next, the anode foil and cathode foil were wound with the separator interposed therebetween to obtain a wound body. At this time, the ends of the outer surface of the wound body were fixed with winding tape. An anode lead wire was connected to the end of the anode lead tab, and a cathode lead wire was connected to the end of the cathode lead tab. The fabricated wound body was again subjected to chemical conversion treatment to form a dielectric layer on the end surface of the anode foil. Specifically, dielectric layers were formed on the upper and lower end surfaces of the wound body as shown in FIG. 2.

[0091] (D) Formation of Conductive Polymer Layer The wound body was immersed in a polymer dispersion contained in a container in a reduced pressure atmosphere (40 kPa) for 5 minutes, and then removed from the polymer dispersion. The wound body impregnated with the polymer dispersion was then dried in a drying oven at 150°C for 20 minutes to form a conductive polymer layer so as to cover at least a portion of the dielectric layer, thereby obtaining a capacitor element.

[0092] (E) Impregnation with Liquid Component An electrolyte solution (liquid component) containing ethylene glycol (EG), sulfolane (SL), and polyethylene glycol (PEG; mass average molecular weight Mw: 300, polydispersity (Mw / Mn): 1.05) was prepared in the proportions shown in Table 1, and then the capacitor element was immersed in the electrolyte solution for 5 minutes in a reduced pressure atmosphere (40 kPa). In this way, the capacitor element was impregnated with the electrolyte. The mass average molecular weight Mw and polydispersity (Mw / Mn) were measured according to the method described in the embodiment section above. The same applies to the following examples.

[0093] (F) Sealing of Capacitor Element The capacitor element impregnated with the electrolyte was sealed to produce an electrolytic capacitor as shown in FIG. 1 . Then, an aging treatment was performed at 95°C for 90 minutes while applying a voltage. In this manner, the electrolytic capacitor according to Example 1 was obtained. Note that an elastic material containing butyl rubber as a rubber component was used as the sealing member for sealing the capacitor element. Note that a total of 40 electrolytic capacitors according to Example 1 were produced. The same number of electrolytic capacitors was produced in each of the following examples.

[0094] Example 2 An electrolytic capacitor according to Example 2 was obtained in the same manner as in Example 1, except that PEG with a polydispersity (Mw / Mn) of 1.11 was used in the electrolyte solution (liquid component).

[0095] Example 3 An electrolytic capacitor according to Example 3 was obtained in the same manner as in Example 1, except that PEG with a polydispersity (Mw / Mn) of 1.23 was used in the electrolyte solution (liquid component).

[0096] Example 4 An electrolytic capacitor according to Example 4 was obtained in the same manner as in Example 1, except that PEG with a polydispersity (Mw / Mn) of 1.31 was used in the electrolyte solution (liquid component).

[0097] Example 5 An electrolytic capacitor according to Example 5 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 200 and a polydispersity (Mw / Mn) of 1.13 was used in the electrolyte solution (liquid component).

[0098] Example 6 An electrolytic capacitor according to Example 6 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 400 and a polydispersity index (Mw / Mn) of 1.14 was used in the electrolyte solution (liquid component).

[0099] Example 7 An electrolytic capacitor according to Example 7 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 600 and a polydispersity index (Mw / Mn) of 1.15 was used in the electrolyte solution (liquid component).

[0100] Example 8 An electrolytic capacitor according to Example 8 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 1,000 and a polydispersity (Mw / Mn) of 1.06 was used in the electrolyte solution (liquid component).

[0101] Example 9 An electrolytic capacitor according to Example 9 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 1,000 and a polydispersity (Mw / Mn) of 1.17 was used in the electrolyte solution (liquid component).

[0102] Example 10 An electrolytic capacitor according to Example 10 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 1,000 and a polydispersity (Mw / Mn) of 1.30 was used in the electrolyte solution (liquid component).

[0103] Example 11 An electrolytic capacitor according to Example 11 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 2000 and a polydispersity (Mw / Mn) of 1.15 was used in the electrolytic solution (liquid component).

[0104] Example 12 An electrolytic capacitor according to Example 12 was obtained in the same manner as in Example 1, except that a copolymer of ethylene oxide (EO) and propylene oxide (PO) (EO-PO copolymer) having a mass average molecular weight Mw of 200 and a polydispersity index (Mw / Mn) of 1.08 was used in the electrolyte solution (liquid component). When the entire EO-PO copolymer is taken as 1 mole, the molar ratio of EO units to PO units was EO:PO=0.8:0.2.

[0105] Example 13 An electrolytic capacitor according to Example 13 was obtained in the same manner as in Example 1, except that an EO-PO copolymer (EO:PO=0.8:0.2) having a mass average molecular weight Mw of 2000 and a polydispersity (Mw / Mn) of 1.15 was used in the electrolytic solution (liquid component).

[0106] Example 14 An electrolytic capacitor according to Example 14 was obtained in the same manner as in Example 3, except that the proportions of EG, SL, and PEG in the electrolyte solution (liquid component) were changed as shown in Table 1.

[0107] Example 15 An electrolytic capacitor according to Example 15 was obtained in the same manner as in Example 3, except that the proportions of EG, SL, and PEG in the electrolytic solution (liquid component) were changed as shown in Table 1.

[0108] Example 16 An electrolytic capacitor according to Example 16 was obtained in the same manner as in Example 3, except that the proportions of EG, SL, and PEG in the electrolyte solution (liquid component) were changed as shown in Table 1.

[0109] Example 17 An electrolytic capacitor according to Example 17 was obtained in the same manner as in Example 3, except that the proportions of EG, SL, and PEG in the electrolyte solution (liquid component) were changed as shown in Table 1.

[0110] Example 18 An electrolytic capacitor according to Example 18 was obtained in the same manner as in Example 1, except that a combination of two types of PEG (PEGa: mass average molecular weight Mw 200, polydispersity (Mw / Mn) 1.13, and PEGb: mass average molecular weight Mw 300, polydispersity (Mw / Mn) 1.23) was used in the electrolyte solution (liquid component). PEGa and PEGb were mixed in a mass ratio of PEGa:PEGb = 50:50.

[0111] Example 19 An electrolytic capacitor according to Example 19 was obtained in the same manner as in Example 18, except that PEGc (mass average molecular weight Mw: 300, polydispersity index (Mw / Mn): 1.23) and PEGd (mass average molecular weight Mw: 400, polydispersity index (Mw / Mn): 1.14) were combined as the two types of PEG.

[0112] Example 20 An electrolytic capacitor according to Example 20 was obtained in the same manner as in Example 18, except that PEGe (mass average molecular weight Mw: 400, polydispersity index (Mw / Mn): 1.14) and PEGf (mass average molecular weight Mw: 600, polydispersity index (Mw / Mn): 1.15) were combined as the two types of PEG.

[0113] Comparative Example 1 An electrolytic capacitor according to Comparative Example 1 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 300 and a polydispersity index (Mw / Mn) of 1.42 was used.

[0114] Comparative Example 2 An electrolytic capacitor according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the electrolyte solution (liquid component) did not contain a polymer compound such as PEG or EO-PO copolymer, and the proportions of EG and SL were changed as shown in Table 1.

[0115] Comparative Example 3 An electrolytic capacitor according to Comparative Example 3 was obtained in the same manner as in Example 1, except that PEG having a mass average molecular weight Mw of 4000 and a polydispersity (Mw / Mn) of 1.25 was used in the electrolyte solution.

[0116]

[0117] <Evaluation> Initial Capacitance The initial capacitance (unit: μF) of 20 electrolytic capacitors according to each example was measured at a temperature of 20°C and a frequency of 120 Hz. The initial capacitance was measured using an LCR meter. The measured values ​​were then arithmetically averaged to determine the average initial capacitance (average capacitance). The standard deviation of the initial capacitance was also calculated for the 20 electrolytic capacitors according to each example. The results are shown in Table 2 below.

[0118] Capacitance after high-temperature load test: A high-temperature load test was conducted on 20 electrolytic capacitors according to each example. The high-temperature load test was conducted by applying a rated voltage of 25 V to the electrolytic capacitors according to each example for 1,000 hours at a temperature of 145°C. The average capacitance (average capacitance) was calculated for the electrolytic capacitors according to each example after the high-temperature load test. In addition, the standard deviation of the capacitance was calculated for the 20 electrolytic capacitors according to each example. The average capacitance and standard deviation were calculated in the same manner as for the initial capacitance above. The results are shown in Table 2 below.

[0119]

[0120] From Table 2, it can be seen that, initially, the electrolytic capacitors according to the examples and comparative examples all exhibited a high average capacitance of 300 μF or more and a low standard deviation of up to 1.41, indicating that there was no significant variation in capacitance between multiple electrolytic capacitors.

[0121] On the other hand, after the high-temperature load test, all of the electrolytic capacitors according to the examples exhibited a relatively high average capacitance of 250 μF or more and a relatively small standard deviation of up to 3.21. However, the electrolytic capacitor according to Comparative Example 1, which contained PEG (polymer compound) with a polydispersity of 1.42, exhibited a high standard deviation of 6.08, and the electrolytic capacitor according to Comparative Example 3, which contained PEG (polymer compound) with a mass-average molecular weight Mw of 4000, exhibited a high standard deviation of 11.33. In other words, it can be seen that there was a large variation in capacitance between multiple electrolytic capacitors after the high-temperature load test. Furthermore, the electrolytic capacitor according to Comparative Example 2, which did not contain a polymer compound such as PEG or EO-PO copolymer, exhibited a significant decrease in average capacitance of 201 μF after the high-temperature load test.

[0122] The electrolytic capacitor according to the present disclosure can be used in applications where small variations in capacitance are required.

[0123] 10: Capacitor element 11: Anode foil 12: Cathode foil 13: Separator 14: Winding tape 100: Electrolytic capacitor 101: Bottomed case 102: Sealing member 103: Seat plate 104A, 104B: Lead wire 105A, 105B: Lead tab

Claims

1. An electrolytic capacitor comprising: a capacitor element; and a liquid component, the capacitor element comprising: an anode foil having a dielectric layer; a cathode foil arranged so as to face the dielectric layer; a separator interposed between the anode foil and the cathode foil; and a conductive polymer layer interposed between the anode foil and the cathode foil and in contact with the separator, the liquid component comprising a polymer compound, the polymer compound comprising a first component having a mass average molecular weight Mw of 200 or more and 2000 or less, and a polydispersity (Mw / Mn), which is the ratio of the mass average molecular weight Mw to the number average molecular weight Mn, of 1.35 or less.

2. The electrolytic capacitor according to claim 1, wherein the first component is a polyalkylene glycol.

3. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component contains the first component in an amount of 5 mass % or more and 30 mass % or less.

4. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component contains at least one of a glycol compound and a sulfone compound as a solvent, and at least one of a dicarboxylate and a dicarboxylate derivative as a solute.

5. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component contains a glycol compound and a sulfone compound as a solvent, the proportion of the glycol compound in the liquid component is 10% by mass or more and 60% by mass or less, and the proportion of the sulfone compound in the liquid component is 20% by mass or more and 70% by mass or less.

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