Electrolytic capacitor

Abstract

An electrolytic capacitor according to the present disclosure comprises a capacitor element and a liquid component. The capacitor element comprises: an anode foil; a cathode foil; a separator that is interposed between the anode foil and the cathode foil; and a conductive polymer layer that is in contact with the separator. The anode foil is provided with an etching layer, and the etching layer has a dielectric layer. The etching layer sequentially comprises, from the surface of the anode foil toward the center part thereof in the order of, a first etching region that includes a plurality of first pores each of which is ranged in the thickness direction or in the plane direction, and a second etching region that includes a plurality of second pores which extend in a tunnel shape in the thickness direction. The average pore diameter of the first pores is smaller than the average pore diameter of the second pores. The conductive polymer layer is formed in the first etching region, and the second etching region is impregnated with the liquid component.

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] It has been known for some time that the equivalent series resistance (ESR) of an electrolytic capacitor can be reduced by using a conductive polymer layer (solid electrolyte layer) formed from a conductive polymer instead of a liquid component (such as an electrolytic solution) (see, for example, Patent Document 1 below). In an electrolytic capacitor, an etching layer is typically formed on the surface of an anode substrate, and a dielectric oxide film is formed on this etching layer. The conductive polymer layer is then formed on the dielectric oxide film.

[0003] Patent Document 1 below describes an etching layer formed by stacking two etching regions with different structures in the thickness direction. Specifically, the etching layer is formed to include, in this order from the surface toward the center of the anode substrate, a first region formed in a sponge-like shape with a plurality of cubic pits and a second region formed by a plurality of tunnel pits penetrating along the thickness direction. Patent Document 1 below also describes that by configuring the etching layer in this manner, an electrolytic capacitor can be obtained that can ensure high capacitance and reduce equivalent series resistance (ESR).

[0004] Hybrid electrolytic capacitors that include both a liquid component and a conductive polymer layer are also known (see, for example, Patent Document 2 below). Hybrid electrolytic capacitors have the advantages of being able to reduce equivalent series resistance (ESR) through the conductive polymer layer and being able to improve the repairability of the dielectric oxide film through the liquid component.

[0005] JP 6-168855 A JP 2017-69390 A

[0006] Hybrid electrolytic capacitors also typically use an anode body (anode foil) with an etching layer formed on the surface. Although hybrid electrolytic capacitors are also expected to have an etching layer structure that ensures both high capacitance and low equivalent series resistance (ESR), this has not yet been fully explored. In other words, no adequate study has yet been conducted on an etching layer structure that can optimally achieve both high capacitance and low equivalent series resistance (ESR) using both a liquid component and a conductive polymer layer.

[0007] Therefore, the present disclosure provides an electrolytic capacitor that includes both a conductive polymer layer and a liquid component, and that can ensure both high capacitance and low equivalent series resistance (ESR).

[0008] an etching layer formed on the anode foil from a surface toward a center thereof, the etching layer having a dielectric layer; and a second etching region having a plurality of second pores extending in a tunnel shape along the thickness direction, the first pores having a first etching region and a second etching region having a plurality of first pores extending in a thickness direction and a surface direction, the second etching region being disposed in this order from the surface toward the center of the anode foil; an average pore diameter of the first pores being smaller than the average pore diameter of the second pores; the conductive polymer layer formed in the first etching region; and the liquid component impregnated in at least the second etching region.

[0009] According to the present disclosure, it is possible to provide an electrolytic capacitor that includes both a conductive polymer layer and a liquid component, and that can simultaneously ensure high capacitance and reduce equivalent series resistance (ESR).

[0010] 3 is a schematic cross-sectional view of an anode foil, an electron microscope photograph corresponding to portion A in FIG. 1, a schematic cross-sectional view of an electrolytic capacitor according to an embodiment of the present disclosure, and 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, a cathode foil facing the anode foil, 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, an etching layer is formed on the anode foil from the surface toward the center, and the etching layer includes a dielectric layer. In the electrolytic capacitor according to an embodiment of the present disclosure, the etching layer includes, in this order, a first etching region including a plurality of first pores extending in the thickness direction and the surface direction, and a second etching region including a plurality of second pores extending in a tunnel-like manner along the thickness direction, from the surface toward the center of the anode foil. The first pores refer to pores having an aspect ratio (length / width) of 0.5 or more and 2 or less, and the second pores refer to pores having an aspect ratio (length / width) of 15 or more and 100 or less. The aspect ratio of the pores can be obtained by observing the cross section of the etched layer of the anode foil. Cross-sectional observation can be performed, for example, by observing the cross section of the anode foil (more specifically, the cross section of the etched layer of the anode foil) at a magnification of 100x to 500x using a scanning electron microscope (SEM). The cross section is taken along the thickness direction of the anode foil. The anode foil may be removed from a disassembled electrolytic capacitor. The cross section of the anode foil may also be obtained using a cross-section polisher (CP). In the electrolytic capacitor according to the embodiment of the present disclosure, the average pore diameter of the first pores is smaller than the average pore diameter of the second pores. In the electrolytic capacitor according to the embodiment of the present disclosure, a conductive polymer layer is formed in the first etched region, and a liquid component is impregnated into at least the second etched region.

[0015] As described above, the electrolytic capacitor according to this embodiment includes a liquid component. The liquid component is contained in the voids within the capacitor element. It is sufficient for the liquid component to fill at least a portion of the voids within the capacitor element. The liquid component is preferably impregnated within the etching layer. The liquid component is preferably primarily impregnated within the second etching region. By primarily impregnating the second etching region with the liquid component, the liquid component can be sufficiently introduced into each of the multiple second pores extending in a tunnel-like manner within the second etching region. This allows sufficient capacitance to be extracted from the second etching region and allows a sufficient conductive path to be formed via the liquid component. Furthermore, as described below, a conductive path is formed between the first etching region, the separator, and the cathode foil via the conductive polymer layer. Therefore, by having the liquid component sufficiently introduced within the second etching region, a more sufficient conductive path can be formed between the etching layer and the cathode foil via the liquid component and the conductive polymer layer. As a result, the electrolytic capacitor according to this embodiment exhibits a low equivalent series resistance (ESR) and a high capacitance.

[0016] The liquid component may be impregnated in the first etching region. When the total mass of the liquid component impregnated in the etching layer is taken as 100%, the liquid component is preferably impregnated in the second etching region at 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The liquid component may be impregnated in the second etching region at 99% by mass or less, 97% by mass or less, 95% by mass or less, or 93% by mass or less. The liquid component is preferably impregnated in the first etching region at 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. The liquid component may be impregnated in the first etching region at 1% by mass or more, 3% by mass or more, 5% by mass or more, or 7% by mass or more. The impregnation ratio of the liquid component in the first etching region and the impregnation ratio of the liquid component in the second etching region can be determined by energy dispersive X-ray spectroscopy (EDX). For example, a cross section of the etching layer along the thickness direction can be observed using a scanning electron microscope (SEM), and the impregnation ratio of the liquid component in the first etching region and the impregnation ratio of the liquid component in the second etching region can be determined by EDX using an SEM image of the cross section. That is, they can be determined by SEM-EDX. Observation of the cross section of the etching layer using an SEM can be performed in the same manner as described above.

[0017] Desirable measurement conditions for SEM-EDX analysis are as follows: Measurement device (SEM): Hitachi SU8220 (field emission scanning electron microscope) Measurement device (EDX): BRUKER XFlash5060FQ / XFlash6 Combined System Acceleration voltage: 5 kV Emission: 25 μm Probe current: High Condenser lens: 1.0

[0018] <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. The nonaqueous solvent and the solute can be any nonaqueous solvent and solute used in various known electrolytic capacitors. The liquid component may be a component that is liquid at room temperature (25°C) or at the temperature at which the electrolytic capacitor is used.

[0019] The non-aqueous solvent may be an organic solvent or an ionic liquid.

[0020] 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.

[0021] 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.

[0022] 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 preferably account for more than 50 mass%, more preferably 60 mass% or more, and preferably 70 mass% or more of the organic solvents. 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.

[0023] The liquid component preferably contains at least one organic solvent selected from the group consisting of glycol compounds, sulfone compounds, and lactone compounds. 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 carried out efficiently. 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. When the liquid component contains a lactone compound, the electrolytic capacitor can exhibit excellent dielectric properties. Furthermore, glycol compounds, sulfone compounds, and lactone 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 can be made 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), the sulfone compound preferably contains sulfolane (SL), and the lactone compound preferably contains γ-butyrolactone.

[0024] When the liquid component contains at least one organic solvent selected from the group consisting of glycol compounds, sulfone compounds, and lactone compounds, the proportion of the glycol compounds in the liquid component is preferably 40% by mass to 80% by mass, the proportion of the sulfone compounds in the liquid component is preferably 20% by mass to 60% by mass, and the proportion of the lactone compounds in the liquid component is preferably 40% by mass to 80% by mass. By including the glycol compounds, sulfone compounds, and lactone compounds in the above-mentioned ranges, the re-chemical conversion of the dielectric layer by the acid component contained in the liquid component can be more efficiently carried out. Furthermore, the proton donating ability to the conductive polymer can be further improved, and the resistance of the liquid component to acid and base components can be further improved. Furthermore, the electrolytic capacitor can exhibit more excellent dielectric properties.

[0025] 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.

[0026] 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 (for example, when used at 145°C), 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.

[0027] The solute may contain 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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. The organic salt may be an amine salt of a long-chain dibasic carboxylic acid. An example of an amine salt of a long-chain dibasic carboxylic acid is diethylamine 2-butyloctanedioate (2BA).

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] The liquid component may contain a polymer compound. Examples of the polymer compound include polyalkylene glycol, polyalkylene glycol derivatives, 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 (PEG), 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.

[0041] 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.

[0042] 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).

[0043] In the electrolytic capacitor according to the embodiment of the present disclosure, the mass average molecular weight Mw of the polymer compound may be 200 or more, 300 or more, 400 or more, or 500 or more. The mass average molecular weight Mw of the polymer compound may be 5000 or less, 4000 or less, 3000 or less, 2000 or less, or 1000 or less.

[0044] The mass average molecular weight Mw of a polymer compound is a polystyrene-equivalent value 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.

[0045] 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.

[0046] In the electrolytic capacitor according to the embodiment of the present disclosure, the liquid component preferably contains a polymeric compound, a sulfone compound, and an amine salt of a long-chain dibasic carboxylic acid. The polymeric compound preferably contains a polyalkylene glycol, and the polyalkylene glycol preferably contains polyethylene glycol (PEG). The sulfone compound preferably contains sulfolane (SL). The amine salt of the long-chain dibasic carboxylic acid preferably contains 2-butyloctanedioic acid diethylamine (2BA). When the liquid component contains a polymeric compound, a sulfone compound, and an amine salt of a long-chain dibasic carboxylic acid, the content of the polymeric compound is preferably 20% by mass or more and 60% by mass or less, and more preferably 40% by mass or more and 50% by mass or less. The content of the sulfone compound is preferably 20% by mass or more and 60% by mass or less, and more preferably 40% by mass or more and 50% by mass or less. The content of the amine salt of the long-chain dibasic carboxylic acid is preferably 5% by mass or more and 30% by mass or less, and more preferably 10% by mass or more and 20% by mass or less. When the liquid component contains the polymer compound, the sulfone compound, and the amine salt of the long-chain dibasic carboxylic acid in the above-mentioned ranges, a conductive path can be more sufficiently formed inside the second etching region via the liquid component.

[0047] <Capacitor Element> As described above, the electrolytic capacitor according to the embodiment of the present disclosure includes, in addition to the liquid component, a capacitor element including an anode foil, a cathode foil facing the anode foil, 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.

[0048] (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.

[0049] As described above, in the electrolytic capacitor according to the embodiment of the present disclosure, an etching layer is formed on the anode foil from the surface toward the center. Hereinafter, the anode foil on which the etching layer is formed will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic cross-sectional view of the anode foil 11, and FIG. 2 is an electron microscope photograph of the etching layer corresponding to portion A in FIG. 1. Note that the dimensions and shapes of the components in FIG. 1 do not necessarily correspond to the actual objects.

[0050] As shown in FIG. 1 , the anode foil 11 includes two etching layers 11b formed from each of the two surfaces (main surfaces) toward the center, and a foil core 11a interposed between the two etching layers 11b. The etching layer 11b includes a first etching region 11b1 including a plurality of first pores 11b11 extending in the thickness direction and the surface direction, and a second etching region 11b2 including a plurality of second pores 11b21 extending in a tunnel-like manner along the thickness direction, in this order from each of the two surfaces (main surfaces) toward the center of the anode foil 11. The foil core 11a is the remaining portion of a valve metal foil (e.g., aluminum foil) after etching. The first etching region 11b1 is, for example, configured like a sponge. Adjacent first pores 11b11 in the thickness direction and the surface direction of the first etching region 11b1 may or may not be connected to each other. That is, adjacent first pores 11b11 may or may not be in communication with each other. The second pores 11b21 may penetrate the second etching region 11b2 in the thickness direction.

[0051] The first etching region 11b1 can be formed, for example, by applying a direct current to a metal foil made of a valve metal (e.g., aluminum foil) in a solution containing chloride ions. That is, the first etching region can be formed by direct current electrolysis. The second etching region 11b2 can be formed, for example, by applying an alternating current to a metal foil made of a valve metal on which the first etching region has been formed in a solution containing chloride ions and sulfate ions. That is, the second etching region can be formed by alternating current electrolysis. DC electrolysis and AC electrolysis can be performed by appropriately selecting various known conditions.

[0052] In the electrolytic capacitor according to the embodiment of the present disclosure, a dielectric layer (not shown) is formed on the etching layer 11b. That is, the etching layer 11b has the dielectric layer. The dielectric layer may be formed by chemical conversion treatment of the anode foil 11. In this case, the chemical conversion coating formed by the chemical conversion treatment serves as the dielectric layer. The chemical conversion treatment may be performed by applying a predetermined chemical conversion voltage to the anode foil 11 while the anode foil 11 is immersed in an acidic solution (hereinafter also referred to as a chemical conversion solution), or by heat-treating the anode foil 11 at a predetermined temperature while the anode foil 11 is immersed in the chemical conversion solution. Furthermore, when the dielectric layer is formed by chemical conversion treatment as described above, the dielectric layer (chemical conversion coating) may contain an oxide of a valve metal (e.g., aluminum oxide). The dielectric layer may be formed of any dielectric other than an oxide of a valve metal as long as it functions as a dielectric. The dielectric layer may be formed in at least the first etching region 11b1 of the first etching region 11b1 and the second etching region 11b2 that constitute the etching layer 11b. Alternatively, the dielectric layer may be formed in both the first etching region 11b1 and the second etching region 11b2.

[0053] In the electrolytic capacitor, a conductive polymer layer does not have to be formed on the end faces (side faces) of the anode foil 11. On the other hand, it is preferable that a dielectric layer is formed on the end faces (side faces) of the anode foil 11. Taking a wound electrolytic capacitor (see FIGS. 3 and 4) as an example, in the wound capacitor element 10 shown in FIG. 4, a conductive polymer layer is formed in the circumferential direction, but it does not have to be formed on the upper and lower end faces.

[0054] In the electrolytic capacitor according to the embodiment of the present disclosure, the average pore diameter P ｄ１ is the average pore diameter P of the second pores 11b21 ｄ２ It is important that the average pore diameter P ｄ１ and average pore diameter P ｄ２By satisfying this relationship, when a conductive polymer layer is formed using conductive polymer particles on the surface of the dielectric layer formed on the etching layer, the conductive polymer particles are prevented from passing through the first pores 11b11 and reaching the second etching region 11b2. This makes it easier to selectively form a conductive polymer layer on the surface of the dielectric layer formed in the first etching region 11b1. Furthermore, even if the conductive polymer particles pass through the first pores 11b11 and enter the second pores 11b21, the large diameter of the second pores 11b21 prevents the second pores 11b21 from being blocked by the conductive polymer particles. This allows the liquid component to sufficiently enter the second pores 11b21 even when the etching layer 11b is immersed in a liquid component after the conductive polymer layer is formed. In other words, the liquid component can be sufficiently retained in the second etching region 11b2. Note that the average pore diameter P ｄ１ and P ｄ２ can be determined by measuring the pore size distribution of the first etching region 11b1 and the second etching region 11b2 using a mercury porosimeter. Specifically, the pore size (mode diameter) corresponding to the apex of a peak (the maximum peak when multiple peaks exist) that appears on the pore distribution curve (vertical axis: log differential pore volume, horizontal axis: pore size) obtained by the measurement is determined as the average pore size. ｄ１ can be obtained from the pore distribution curve of the first etching region 11b1, and the average pore diameter P ｄ２ can be obtained from the pore distribution curve of the second etching region 11b2. As the measuring device, for example, an AutoPore V series manufactured by Micromeritics Corporation can be used.

[0055] The ratio (L2 / L1) of the thickness L2 of the second etched region 11b2 to the thickness L1 of the first etched region 11b1 is preferably 5 or greater, more preferably 8 or greater, and even more preferably 12 or greater. L2 / L1 is preferably 20 or less, more preferably 18 or less, and even more preferably 16 or less. By ensuring that L2 / L1 is within the above range, a more sufficient conductive path can be formed between the etched layer and the cathode foil via the liquid component and the conductive polymer layer. As a result, the electrolytic capacitor according to this embodiment exhibits higher capacitance. The thicknesses L1 and L2 can be measured by observing a cross section of the anode foil along the thickness direction using a scanning electron microscope (SEM). Observation of the cross section of the anode foil using an SEM can be performed in the same manner as described above. L2 can be calculated by selecting five locations on the cross section of the anode foil where the second pores penetrate the second etched region 11b2 from the top to the bottom, measuring the length of each location, and then arithmetically averaging the measurements at the five locations. L1 can be calculated by measuring the length from the surface of the anode foil to the top end of the second etching region 11b2 at any five points on the cross section of the anode foil and arithmetically averaging the measured values. Note that L2 / L1 can be adjusted by changing the magnitude of the etching current or the length of the etching time.

[0056] Average pore diameter P of the first pores 11b11 ｄ１ is preferably 0.1 μm or more, more preferably 0.2 μm or more, and even more preferably 0.3 μm or more. ｄ１ is preferably 1.0 μm or less, more preferably 0.8 μm or less, and even more preferably 0.5 μm or less. ｄ２ is preferably 0.2 μm or more, more preferably 0.4 μm or more, and even more preferably 0.6 μm or more. ｄ２is preferably 1.2 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. The conductive polymer particles usually have an average particle diameter D of 0.1 μm (100 nm) to 0.5 μm (500 nm). ｃｐ Since it has an average pore diameter P ｄ１ and average pore diameter P ｄ２ When the thickness of the conductive polymer particles is within the above range, it becomes easier to selectively form a conductive polymer layer on the surface of the dielectric layer formed in the first etching region 11b1. Also, it is possible to more sufficiently prevent the second pores 11b21 from being blocked by the conductive polymer particles.

[0057] (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 formed with an etching layer, as with the anode foil, or with a dielectric layer, as necessary. That is, the surface of the cathode foil may be roughened or subjected to a chemical conversion treatment as necessary.

[0058] 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 terms of emphasizing low cost and low resistance, the coating layer may include at least one of nickel and titanium.

[0059] 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.

[0060] (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 materials for the separator include cellulose, polyethylene terephthalate, polybutylene terephthalate, polyphenyl sulfide, vinylon, nylon, aromatic polyamide, polyimide, polyamideimide, polyetherimide, rayon, and glass.

[0061] (Conductive Polymer Layer) The conductive polymer layer is formed from a conductive polymer. In the electrolytic capacitor according to the embodiment of the present disclosure, the conductive polymer layer is preferably formed from conductive polymer particles. 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).

[0062] The conductive polymer may contain a dopant. The dopant can be selected appropriately 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. An example of a conductive polymer is poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS). In the electrolytic capacitor according to the embodiment of the present disclosure, the conductive polymer layer is preferably formed from particles of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with polystyrenesulfonic acid (PSS) (hereinafter also referred to as PEDOT / PSS).

[0063] The conductive polymer layer preferably contacts the anode foil 11, the cathode foil, and the separator over a sufficiently large contact area, thereby forming a sufficient conductive path between the anode foil 11 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.

[0064] The conductive polymer layer is preferably formed on at least one selected from the surface of the dielectric layer of the anode foil 11 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 a stronger conductive path to be formed between the anode foil 11 and the cathode foil by the conductive polymer layer. The conductive polymer layer is preferably formed at least on the surface of the dielectric layer of the anode foil 11, and more preferably on both the surface of the dielectric layer and the surface of the cathode foil, and further on 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.

[0065] When the conductive polymer layer is formed of conductive polymer particles, the average particle diameter D of the conductive polymer particles ｃｐis the average pore diameter P of the second pores 11b21 extending in a tunnel shape along the thickness direction of the second etching region 11b2. ｄ２ It is preferable that D ｃｐ and P ｄ２ That is, D ｃｐ >P ｄ２ It is preferable that the relationship be satisfied. By satisfying this relationship, when forming a conductive polymer layer on the dielectric layer of the anode foil 11, the conductive polymer particles can be prevented from penetrating into the second pores 11b21. This prevents the conductive polymer layer from being formed in a state where the conductive polymer particles have excessively penetrated into the anode foil 11, thereby preventing insufficient contact between the conductive polymer layer and the cathode foil. As a result, the conductive polymer layer can be formed to ensure a sufficient contact area between the anode foil 11, the cathode foil, and the separator. In other words, the conductive polymer layer forms a more sufficient conductive path between the anode foil 11 and the cathode foil, thereby further reducing the equivalent series resistance (ESR) of the electrolytic capacitor. As a result, the reliability of the electrolytic capacitor can be improved. Note that the average particle diameter D ｃｐ is determined from the volume-based particle size distribution of the conductive polymer particles. The volume-based particle size distribution of the conductive polymer particles is measured using a particle size distribution measuring device that uses dynamic light scattering. As a particle size distribution measuring device that uses dynamic light scattering, for example, a DLS-8000 light scattering spectrometer manufactured by Otsuka Electronics Co., Ltd. is used.

[0066] A dispersion containing conductive polymer particles is used to measure the volumetric particle size distribution of conductive polymer particles. The dispersion can be prepared, for example, by dispersing conductive polymer particles in a liquid dispersion medium using a dispersant. As the dispersion medium, for example, an organic medium that is liquid at room temperature (e.g., 20°C to 35°C) is used. The type and concentration of the dispersant, the type of dispersion medium, and the concentration of the conductive polymer particles in the dispersion can be selected within ranges that allow the preparation of a dispersion suitable for measuring the particle size distribution.

[0067] A specific configuration of an electrolytic capacitor according to an embodiment of the present disclosure will be described below with reference to Figures 3 and 4. Figure 3 is a cross-sectional view that schematically illustrates an electrolytic capacitor 100 according to an embodiment of the present disclosure, and Figure 4 is a schematic view that includes a portion of a capacitor element 10 included in the electrolytic capacitor 100.

[0068] 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. 3, 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.

[0069] The sealing member 102 is formed of an elastic material containing a rubber component. Examples of the rubber component include 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, and fluororubber. The sealing member 102 may contain fillers such as carbon black and silica.

[0070] Capacitor element 10 is configured as, for example, a wound body as shown in FIG. 4. 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. 3 includes capacitor element 10 shown in FIG. 4, and is therefore referred to as a wound-type electrolytic capacitor.

[0071] 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. 4 shows the wound body in a partially unfolded state before the outermost periphery is fixed with the stop tape 14.

[0072] 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.

[0073] 3 and 4 illustrate a wound electrolytic capacitor, the electrolytic capacitor according to the embodiment of the present disclosure is not limited to this, and may be a chip electrolytic capacitor or a stacked electrolytic capacitor.

[0074] [Method for Manufacturing Electrolytic Capacitor] An example of a method for manufacturing an electrolytic capacitor according to an embodiment of the present disclosure includes the steps of: (a) preparing an anode foil, a cathode foil, and a separator, each having an etching layer including a first etching region and a second etching region, and a dielectric layer formed on the etching layer; (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 to voids in the separator; (c) forming a conductive polymer layer on the one surface and in the voids in 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 for manufacturing an electrolytic capacitor according to an embodiment of the present disclosure, the steps (a) to (e) are preferably performed in this order.

[0075] <Step (a)> In the step of preparing an anode foil, the etching layer including the first etching region and the second etching region, and the dielectric layer can be formed as described above. The step of preparing a cathode foil and a separator is not particularly limited. The materials of the cathode foil and the separator are also not particularly limited. The cathode foil and the separator can be those described above.

[0076] <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.

[0077] 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.

[0078] <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.

[0079] In addition, when the electrolytic capacitor is a wound-type electrolytic capacitor 100 as shown in FIG. 3, a conductive polymer layer can be formed by impregnating a capacitor element 10 configured as a wound body as shown in FIG. 4 with a polymer dispersion, and then heating the capacitor element 10 at a predetermined temperature.

[0080] <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.

[0081] The method for forming the capacitor element is not particularly limited. The capacitor element may be formed by any of various known methods. The capacitor element may be a wound body as shown in FIG. 4. In the wound body as shown in FIG. 4, the anode foil, the cathode foil, and the separator are stacked in the radial direction of the wound body.

[0082] 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.

[0083] <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.

[0084] 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.

[0085] 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.

[0086] (Additional Note) The above description discloses the following technology: (Technology 1) An electrolytic capacitor comprising a capacitor element and a liquid component, wherein the capacitor element comprises: an anode foil, a cathode foil arranged opposite the anode foil, 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 an etching layer is formed on the anode foil from the surface to the center, the etching layer having a dielectric layer, the etching layer comprising: a first etching region including a plurality of first pores connected in the thickness direction and the surface direction, and a second etching region including a plurality of second pores extending in a tunnel shape along the thickness direction, in this order from the surface to the center of the anode foil, wherein the average pore diameter of the first pores is smaller than the average pore diameter of the second pores, the conductive polymer layer is formed in the first etching region, and the liquid component is impregnated in at least the second etching region. (Technology 2) The electrolytic capacitor according to Technology 1, wherein the conductive polymer layer is formed from conductive polymer particles, and the average particle diameter of the conductive polymer particles is larger than the average pore diameter of the second pores. (Technology 3) The electrolytic capacitor according to Technology 1 or 2, wherein the ratio (L2 / L1) of the thickness L2 of the second etched region to the thickness L1 of the first etched region is 5 or more and 20 or less. (Technology 4) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the average pore diameter of the first pores is 0.1 μm or more and 1.0 μm or less. (Technology 5) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the average pore diameter of the second pores is 0.2 μm or more and 1.2 μm or less. (Technology 6) The electrolytic capacitor according to any one of Technology 1 to 3, wherein the average pore diameter of the first pores is 0.1 μm or more and 1.0 μm or less, and the average pore diameter of the second pores is 0.1 μm or more and 1.2 μm or less. (Technology 7) The electrolytic capacitor according to any one of Technologies 1 to 6, wherein the liquid component contains at least one solvent selected from the group consisting of lactone compounds, sulfone compounds, glycol compounds, and polyalkylene glycols.

[0087] While the present invention has been described in terms of presently preferred embodiments, such disclosure should not be interpreted as limiting. Various changes 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 changes and modifications that do not depart from the true spirit and scope of the invention.

[0088] 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.

[0089] [Example 1] (A) Preparation of Components (A-1) Anode Foil An aluminum foil (width 6 mm × foil length 195 mm × thickness 120 μm) was prepared, which had a first etching region and a second etching region in this order from both surfaces toward the center. Chemical conversion treatment was performed on both surfaces of this aluminum foil, and a dielectric layer was formed on both surfaces. In this way, an anode foil with a dielectric layer formed on both surfaces was obtained. Note that the average pore diameter P of the first pores contained in the first etching region was ｄ１ is 0.3 μm, and the average pore diameter P ｄ２ That is, the average pore diameter P ｄ１ is the average pore diameter P of the second pores ｄ２ The average pore diameter P of the first pores was smaller than ｄ１ and the average pore diameter P of the second pores ｄ２ was measured according to the method described in the embodiment section above. The thickness L1 of the first etching region was 2.5 μm, and the thickness L2 of the second etching region was 38 μm. That is, the ratio (L2 / L1) of the thickness L2 of the second etching region to the thickness L1 of the first etching region was 15.2. The thickness L1 of the first etching region and the thickness L2 of the second etching region were measured according to the method described in the embodiment section above.

[0090] (A-2) Cathode Foil Both surfaces of an aluminum foil (thickness: 50 μm) were etched to obtain a cathode foil with both surfaces roughened.

[0091] (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.

[0092] (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 monomers and excess oxidizing agent. This resulted in a polymer dispersion of poly(3,4-ethylenedioxythiophene) doped with PSS (PEDOT / PSS). In the polymer dispersion, the average particle diameter D of the PEDOT / PSS particles, which are conductive polymer particles, was ｃｐ That is, the average particle diameter D of the PEDOT / PSS particles was 0.8 μm. ｃｐ is the average pore diameter P of the second pores included in the second etching region ｄ２ The average particle diameter D ｃｐ was measured according to the method described in the embodiment section above.

[0093] (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. 4.

[0094] (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.

[0095] (E) Impregnation with Liquid Component An electrolyte solution (liquid component) containing polyethylene glycol (PEG), sulfolane (SL), and 2-butyloctanedioic acid diethylamine (2BA) in a ratio of PEG:SL:2BA = 45:40:15 was prepared, and the capacitor element was immersed in the electrolyte solution for 5 minutes in a reduced pressure atmosphere (40 kPa). This allowed the capacitor element to be impregnated with the electrolyte.

[0096] (F) Sealing of Capacitor Element The capacitor element impregnated with the electrolyte was sealed to produce an electrolytic capacitor as shown in FIG. 3 . Then, an aging treatment was performed at 95°C for 90 minutes while applying a voltage. In this way, the electrolytic capacitor according to Example 1 was obtained. An elastic material containing butyl rubber as a rubber component was used as the sealing member for sealing the capacitor element. Forty electrolytic capacitors were produced. The same applies to each of the following examples.

[0097] [Example 2] In the polymer dispersion, the average particle diameter D of the conductive polymer particles, PEDPT / PSS particles, ｃｐ was set to 0.5 μm, that is, the average particle diameter D of the PETDOT / PSS particles ｃｐ The average pore diameter P of the second pores included in the second etching region ｄ２ The electrolytic capacitor of Example 2 was obtained in the same manner as Example 1, except that the average particle diameter D ｃｐ was measured according to the method described in the embodiment section above.

[0098] [Comparative Example 1] An electrolytic capacitor according to Comparative Example 1 was obtained in the same manner as in Example 1, except that an aluminum foil (width 6 mm × foil length 195 mm × thickness 120 μm) having only second etching regions extending from both surfaces toward the center was used as the anode foil. The average pore diameter P ｄ２ The average pore diameter P of the second pores was 0.6 μm, and the thickness L2 of the second etched region was 40 μm. ｄ２ , and the thickness L2 of the second etching region were measured according to the method described in the embodiment section above.

[0099] Comparative Example 2 An electrolytic capacitor according to Comparative Example 2 was obtained in the same manner as in Example 1, except that the capacitor element was not impregnated with the liquid component (electrolytic solution).

[0100] Comparative Example 3 An electrolytic capacitor according to Comparative Example 3 was obtained in the same manner as in Example 2, except that the capacitor element was not impregnated with the liquid component (electrolytic solution).

[0101] For the electrolytic capacitors according to each example, the structure of the etching layer of the anode foil, the average particle diameter D of the conductive polymer particles, ｃｐ and the average pore diameter P of the second pores ｄ２ The relationship between the values ​​and the impregnation of the electrolyte is shown in Table 1 below.

[0102]

[0103] <Evaluation> Initial capacitance For 20 electrolytic capacitors according to each example, the initial capacitance (unit: μF) 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. The results are shown in Table 2 below.

[0104] Equivalent Series Resistance (ESR) The equivalent series resistance (ESR) was measured for 20 electrolytic capacitors according to each example. The equivalent series resistance was measured as a resistance value at 100 kHz using an LCR meter. The measured values ​​were then arithmetically averaged to obtain the average equivalent series resistance (ESR). The results are shown in Table 2 below.

[0105]

[0106] From Table 2, it can be seen that the electrolytic capacitors according to Examples 1 and 2 have a high capacitance of 9.6 μF and a low equivalent series resistance (ESR) (Example 1: 30 mΩ, Example 2: 36 mΩ). ｃｐ is the average pore diameter P of the second pores included in the second etching region ｄ２ It can be seen that Example 1, where the capacitance is greater than 10 μF, has a lower equivalent series resistance (ESR) value. In contrast, the electrolytic capacitor of Comparative Example 1 is able to secure a high capacitance of 9.6 μF, but the equivalent series resistance (ESR) is a high value of 50 mΩ. It can also be seen that the electrolytic capacitors of Comparative Examples 2 and 3 are able to reduce the equivalent series resistance (ESR) (Comparative Example 2: 30 mΩ, Comparative Example 3: 35 mΩ), but are unable to secure sufficient capacitance (Comparative Example 2: 6.2 μF, Comparative Example 3: 8.4 μF). Since the maximum capacitance (underwater capacitance) of the electrolytic capacitors of each example is 10 μF, it can be seen that the electrolytic capacitors of Examples 1 and 2 are able to extract 95% or more of their maximum capacitance.

[0107] The electrolytic capacitor according to the present disclosure can be used in applications where both high capacitance and low equivalent series resistance are required.

[0108] 10: Capacitor element 11: Anode foil 11a: Foil core, 11b: Etching layer, 11b1: First etching region, 11b2: Second etching region, 11b11: First hole, 11b21: Second hole 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; a cathode foil arranged opposite the anode foil; 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 anode foil having an etching layer formed from a surface to a center thereof, the etching layer having a dielectric layer, the etching layer comprising: a first etching region including a plurality of first pores connected in each of the thickness direction and the surface direction; and a second etching region including a plurality of second pores extending in a tunnel shape along the thickness direction, in that order from the surface to the center of the anode foil, the first pores having an average pore diameter smaller than the average pore diameter of the second pores, the conductive polymer layer being formed in the first etching region, and the liquid component being impregnated in at least the second etching region.

2. The electrolytic capacitor according to claim 1, wherein the conductive polymer layer is formed from conductive polymer particles, and an average particle diameter of the conductive polymer particles is larger than an average pore diameter of the second pores.

3. The electrolytic capacitor according to claim 1 or 2, wherein a ratio (L2 / L1) of a thickness L2 of the second etching region to a thickness L1 of the first etching region is 5 or more and 20 or less.

4. The electrolytic capacitor according to claim 1 or 2, wherein the average pore diameter of the first pores is 0.1 μm or more and 1.0 μm or less.

5. The electrolytic capacitor according to claim 1 or 2, wherein the average pore diameter of the second pores is 0.2 μm or more and 1.2 μm or less.

6. The electrolytic capacitor according to claim 1 or 2, wherein the first pores have an average pore diameter of 0.1 μm or more and 1.0 μm or less, and the second pores have an average pore diameter of 0.2 μm or more and 1.2 μm or less.

7. The electrolytic capacitor according to claim 1 or 2, wherein the liquid component contains, as a solvent, at least one selected from the group consisting of lactone compounds, sulfone compounds, glycol compounds, and polyalkylene glycols.

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