Electrolyte for hybrid electrolytic capacitors and hybrid electrolytic capacitors

Abstract

To provide an electrolyte for hybrid electrolytic capacitors that, when used in hybrid electrolytic capacitors, exhibits high capacitance even in high-temperature environments and suppresses the rise in ESR. [Solution] The molecule has 2 to 6 ester groups and a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm³). 3 ) 0.5 A hybrid electrolytic capacitor is formed from an electrolyte for a hybrid electrolytic capacitor containing a liquid ester compound (A) and a carboxylic acid (B) or a salt of carboxylic acid (B) having a molecular weight of 250 or less, and a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (C) in contact with the dielectric layer of the anode foil, wherein the capacitor element is impregnated with the electrolyte for a hybrid electrolytic capacitor of the present invention, and the solid electrolyte (C) contains a conductive polymer.

Description

[Technical Field]

[0001] The present invention relates to an electrolyte for hybrid electrolytic capacitors, and to a hybrid electrolytic capacitor equipped with a capacitor element impregnated with the electrolyte for hybrid electrolytic capacitors. [Background technology]

[0002] Hybrid electrolytic capacitors are widely used in various electrical and electronic products, with diverse applications including charge storage, noise reduction, and phase adjustment. In recent years, there has been a growing demand for higher reliability, particularly in AV equipment and automotive electronics, and various improvements are being attempted.

[0003] For example, Patent Document 1 discloses a technique for improving the ESR (equivalent series resistance) of a capacitor by using a high-boiling point solvent consisting of polyalkylene glycol or a derivative thereof as the electrolyte. Furthermore, Patent Document 2 discloses a technique for improving the short-circuit resistance and ESR (equivalent series resistance) of a capacitor by using a high-boiling point solvent containing glycerin and polyalkylene glycol as the electrolyte.

[0004] However, the electrolytic capacitors described in Patent Documents 1 and 2 do not exhibit sufficient capacitance or ESR characteristics after high-temperature long-term testing, and improvements in these areas are desired. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2014-195116 [Patent Document 2] Patent No. 7486210 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide an electrolyte for hybrid electrolytic capacitors that, when used in hybrid electrolytic capacitors, exhibits high capacitance even in high-temperature environments and suppresses the rise in ESR. [Means for solving the problem]

[0007] The inventors of this invention arrived at this present invention as a result of diligent research to solve the above problems. In other words, the present invention provides a molecule having 2 to 6 ester groups and a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm³). 3 ) 0.5 This invention relates to an electrolyte for a hybrid electrolytic capacitor containing a liquid ester compound (A) and a carboxylic acid (B) or a salt of carboxylic acid (B) having a molecular weight of 250 or less.

[0008] Furthermore, the present invention relates to a hybrid electrolytic capacitor formed from a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (C) in contact with the dielectric layer of the anode foil, wherein the capacitor element is impregnated with the electrolyte for hybrid electrolytic capacitors of the present invention, and the solid electrolyte (C) contains a conductive polymer. [Effects of the Invention]

[0009] By using the electrolyte for hybrid electrolytic capacitors of the present invention, it is possible to provide a hybrid electrolytic capacitor that has a large capacitance even in high-temperature environments and can suppress the rise in ESR. [Modes for carrying out the invention]

[0010] The electrolyte for hybrid electrolytic capacitors of the present invention has 2 to 6 ester groups in its molecule and a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm³). 3 ) 0.5The present invention is characterized by containing a liquid ester compound (A) and a carboxylic acid (B) or a salt of carboxylic acid (B) having a molecular weight of 250 or less. In this invention, a liquid ester compound refers to an ester compound that is fluid at room temperature (25°C).

[0011] A liquid ester compound (A) having 2 to 6 ester groups in its molecule has a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm³). 3 ) 0.5 Therefore, there are no particular limitations, and examples include ester compounds of di- to hexavalent carboxylic acids and 1- to divalent alcohols, and ester compounds of di- to hexavalent alcohols and 1- to divalent carboxylic acids. The SP value in this invention is calculated using the method described in Fedors' method (Polymer Engineering and Science, February, 1974, Vol. 14, No. 2, pp. 147-154).

[0012] Examples of divalent to hexavalent carboxylic acids include divalent carboxylic acids (oxalic acid, phthalic acid, isophthalic acid, terephthalic acid, malonic acid, and succinic acid, etc.), trivalent carboxylic acids (trimellitic acid, citric acid, acetylated citrate, etc.), tetravalent carboxylic acids (pyromellitic acid, etc.), pentavalent carboxylic acids (benzenepentacarboxylic acid, etc.), and hexavalent carboxylic acids (mellitic acid, etc.), which have 2 to 20 carbon atoms. The above carboxylic acids may also be anhydrides.

[0013] Examples of monohydric and dihydric alcohols include monools (ethanol, propanol, butanol, pentanol, hexanol, 2-ethylhexanol, heptanol, octanol, nonanol, decanol, dodecanol, and tetradecanol, etc.) and diols (alkylene glycols having 2 to 10 carbon atoms and polyalkylene glycols having 2 to 6 carbon atoms and oxyethylene units, etc.).

[0014] Examples of 2-6 valent alcohols include diols, triols, and 4-6 valent alcohols.

[0015] Examples of the diol include alkylene glycols having 2 to 10 carbon atoms and polyalkylene glycols having 2 to 6 oxyalkylene units.

[0016] Examples of the alkylene glycol having 2 to 10 carbon atoms include ethylene glycol, propylene glycol, 1,4 - butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, and decanediol. Examples of the polyalkylene glycol having 2 to 6 oxyalkylene units include polyethylene glycol, polypropylene glycol, polybutylene glycol, and polytetramethylene glycol. The number of oxyalkylene units of the above polyalkylene glycol is not particularly limited, but is, for example, 2 or more. The number - average molecular weight of the above polyalkylene glycol is not particularly limited, but from the viewpoints of withstand voltage and solubility, it is preferably 2000 or less, more preferably 1000 or less.

[0017] Examples of the triol include glycerin and trimethylolpropane.

[0018] Examples of the tetra - to hexa - valent alcohol include pentaerythritol, dipentaerythritol, diglycerin, triglycerin, sorbitol, and sucrose.

[0019] Examples of the monovalent or divalent carboxylic acids include monocarboxylic acids {saturated aliphatic monocarboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, 2,2-dimethylheptanoic acid, lauric acid, myristic acid, etc.), unsaturated aliphatic monocarboxylic acids [(meth)acrylic acid, crotonic acid, hexenoic acid, etc.], and aromatic monocarboxylic acids (benzoic acid, cinnamic acid, naphthoic acid, toluic acid, etc.)}, and dicarboxylic acids {saturated aliphatic dicarboxylic acids (oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, 2-methylazelaic acid, sebacic acid, 1,5-octanedicarboxylic acid, 4,5-octanedicarboxylic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, methylmalonic acid, ethylmalonic acid, propylmalonic acid, butylmalonic acid, methylsuccinic acid, ethylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyl-3-ethylglutaric acid, 3,3-diethylglutaric acid, 3,3-dimethylglutaric acid, 3-methyladipic acid, etc.), unsaturated aliphatic dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, citraconic acid, etc.), and aromatic dicarboxylic acids (phthalic acid, isophthalic acid, terephthalic acid, etc.)}.

[0020] As combinations of the above divalent to hexavalent carboxylic acids and monovalent to divalent alcohols, ester compounds of divalent carboxylic acids and diols, and ester compounds of trivalent carboxylic acids and monohydric alcohols are preferred. As ester compounds of divalent to hexavalent alcohols and monovalent to divalent carboxylic acids, ester compounds of trihydric alcohols and monocarboxylic acids are preferred.

[0021] Specific examples of liquid ester compounds (A) having 2 to 6 ester groups in the molecule include triethyl citrate (SP value: 11.5, viscosity at 25°C: 26 mPa·s), tributyl citrate (SP value: 10.7, viscosity at 25°C: 30 mPa·s), triacetin (SP value: 10.2, viscosity at 25°C: 16 mPa·s), and triethyl acetyl citrate (SP value: 10.2, viscosity at 25°C: 39 mPa·s). Examples include tributyl acetylcitrate (SP value: 9.8, viscosity at 25°C: 42 mPa·s), tributyl trimellitate (SP value: 10.2, viscosity at 25°C: 100 mPa·s), tri(2-ethylhexyl) trimellitate (SP value: 9.5, viscosity at 25°C: 180 mPa·s), and bis(2-hydroxyethyl) phthalate (SP value: 14.3, viscosity at 25°C: 85 mPa·s).

[0022] From the viewpoint of electrolyte impregnation, the viscosity of ester compound (A) at 25°C is preferably 200 mPa·s or less. The viscosity of ester compound (A) at 25°C can be measured, for example, using an E-type viscometer (TVE-25L, manufactured by Toki Sangyo Co., Ltd.).

[0023] The weight percentage of ester compound (A) is preferably 20 to 95% by weight, more preferably 20 to 90% by weight, and particularly preferably 70 to 90% by weight, based on the weight of the electrolyte for the hybrid electrolytic capacitor of the present invention, from the viewpoint of voltage resistance and suppression of ESR increase in high-temperature environments.

[0024] The electrolyte for the hybrid electrolytic capacitor of the present invention contains a carboxylic acid (B) or a salt of carboxylic acid (B) having a molecular weight of 250 or less. Examples of carboxylic acid (B) having a molecular weight of 250 or less include monocarboxylic acids and dicarboxylic acids having a molecular weight of 250 or less. Dicarboxylic acids with a molecular weight of 250 or less include saturated aliphatic dicarboxylic acids (oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, 2-methylazelaic acid, sebacic acid, 1,5-octanedicarboxylic acid, 4,5-octanedicarboxylic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,6-decanedicarboxylic acid, 5,6-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, methylmalonic acid, ethylmalonic acid, pro Examples include pyrmalonic acid, butylmalonic acid, methylsuccinic acid, ethylsuccinic acid, 2,2-dimethylsuccinic acid, 2,3-dimethylsuccinic acid, 2-methylglutaric acid, 3-methylglutaric acid, 3-methyl-3-ethylglutaric acid, 3,3-diethylglutaric acid, 3,3-dimethylglutaric acid, and 3-methyladipic acid, etc.), unsaturated aliphatic dicarboxylic acids (maleic acid, fumaric acid, itaconic acid, and citraconic acid, etc.), and aromatic dicarboxylic acids (phthalic acid, isophthalic acid, and terephthalic acid, etc.). Monocarboxylic acids with a molecular weight of 250 or less include saturated aliphatic monocarboxylic acids (formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, 2,2-dimethylheptanoic acid, lauric acid, myristic acid, etc.), unsaturated aliphatic monocarboxylic acids [(meth)acrylic acid, crotonic acid and hexenoic acid, etc.], aromatic monocarboxylic acids (benzoic acid, cinnamic acid, naphthoic acid, toluic acid, ethylbenzoic acid, propylbenzoic acid, isopropylbenzoic acid, butylbenzoic acid, isobutylbenzoic acid, sec-butylbenzoic acid, tert-butylbenzoic acid, Examples include hydroxybenzoic acid, ethoxybenzoic acid, propoxybenzoic acid, isopropoxybenzoic acid, butoxybenzoic acid, isobutoxybenzoic acid, sec-butoxybenzoic acid, tert-butoxybenzoic acid, aminobenzoic acid, N-methylaminobenzoic acid, N-ethylaminobenzoic acid, N-propylaminobenzoic acid, N-isopropylaminobenzoic acid, N-butylaminobenzoic acid, N-isobutylaminobenzoic acid, N-sec-butylaminobenzoic acid, N-tert-butylaminobenzoic acid, N,N-dimethylaminobenzoic acid, and N,N-diethylaminobenzoic acid, etc.

[0025] Of the carboxylic acids (B) with a molecular weight of 250 or less, saturated aliphatic dicarboxylic acids, aromatic dicarboxylic acids, and aromatic monocarboxylic acids are preferred from the viewpoint of dielectric strength and suppression of ESR increase in high-temperature environments, more preferably aromatic dicarboxylic acids and aromatic monocarboxylic acids, and particularly preferably phthalic acid, isophthalic acid, terephthalic acid, and benzoic acid.

[0026] In the electrolyte for the hybrid electrolytic capacitor of the present invention, the salt of carboxylic acid (B) is a salt of carboxylic acid (B) and a base, and is a salt formed from an anion derived from carboxylic acid (B) and its counter cation. Examples of counter cations include ammonium ions, primary ammonium cations, secondary ammonium cations, tertiary ammonium cations, and amidinium cations. Examples of ammonium cations, primary ammonium cations, secondary ammonium cations, and tertiary ammonium cations include cations produced from bases such as ammonia, primary amines, secondary amines, and tertiary amines, respectively. Examples of these amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, N,N-diisopropylethylamine, tetramethylethylenediamine, hexamethylenediamine, spermidine, spermine, amantadine, aniline, phenethylamine, toluidine, pyrrolidine, piperidine, piperazine, morpholine, ethylmorpholine, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, 4-dimethylaminopyridine, and trimethanolamine. Examples of amidinium cations include 1,2,3,4-tetramethylimidazolinium cation, 1,3-dimethylimidazolium cation, 1,3-diisopropylimidazolium cation, 1,3-dibutylimidazolium cation, 1-methyl-3-propylimidazolium cation, 1-ethyl-3-methylimidazolium cation, 1-ethyl-2,3-dimethylimidazolium cation, 1-butyl-3-methylimidazolium cation, and 1-benzyl-3-methylimidazolium cation. The countercation may be used alone or in combination of two or more types.

[0027] From the viewpoint of suppressing an increase in ESR, the countercation that forms the salt of the above carboxylic acid (B) is preferably at least one selected from the group consisting of ammonium cations, secondary ammonium cations, and tertiary ammonium cations, and more preferably a tertiary ammonium cation.

[0028] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains a salt of a liquid ester compound (A) and a carboxylic acid (B), the content of a base that generates a countercation (ammonia, primary amine, secondary amine, tertiary amine, etc.) is not particularly limited, but from the viewpoint of dielectric strength and suppression of ESR increase in high-temperature environments, it is preferably 0.1 to 20% by weight, more preferably 1.0 to 10% by weight, and even more preferably 2.0 to 5.0% by weight.

[0029] The electrolyte for the hybrid electrolytic capacitor of the present invention may further contain a solvent in addition to the liquid ester compound (A) and carboxylic acid (B). Examples of solvents include water, alcohol solvents (methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, ethylene glycol, ethylene glycol monobutyl ether, and polyethylene glycol, etc.), amide solvents (N-methylformamide, N-ethylformamide, and N,N-dimethylformamide, etc.), lactone solvents (α-acetyl-γ-butyrolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, and δ-valerolactone, etc.), nitrile solvents (acetonitrile, propionitrile, butyronitrile, acrylonitrile, methacrylatenitrile, and benzonitrile, etc.), sulfoxide solvents (dimethyl sulfoxide, methyl ethyl sulfoxide, and diethyl sulfoxide), and sulfone solvents (sulfolane and ethylmethyl sulfone, etc.). From the viewpoint of suppressing the increase in ESR, the above solvent is preferably water, an alcohol solvent, a lactone solvent, or a sulfone solvent, and more preferably water or an alcohol solvent. The above solvents may be used individually or in combination of two or more.

[0030] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains water as a solvent, the water content in the electrolyte for the hybrid electrolytic capacitor of the present invention is preferably 0.05 to 4% by weight, and more preferably 0.1 to 1.0% by weight, based on the weight of the electrolyte, from the viewpoint of dielectric strength.

[0031] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains a solvent other than water, the content of the solvent other than water in the electrolyte for the hybrid electrolytic capacitor of the present invention is preferably 10 to 80% by weight, and more preferably 15 to 70% by weight, based on the weight of the electrolyte, from the viewpoint of dielectric strength.

[0032] The pH of the electrolyte for the hybrid electrolytic capacitor of the present invention at 25°C is not particularly limited, but from the viewpoint of suppressing the rise in ESR and withstanding voltage, it is preferably 4 to 7, more preferably 4 to 6.5, and even more preferably 4 to 6. In this specification, the pH of the electrolyte for the hybrid electrolytic capacitor of the present invention at 25°C is the value measured directly with a pH meter.

[0033] The hybrid electrolytic capacitor of the present invention is formed from a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (C) in contact with the dielectric layer of the anode foil, wherein the capacitor element is impregnated with the electrolyte for hybrid electrolytic capacitors of the present invention, and the solid electrolyte (C) contains a conductive polymer. In one embodiment, the hybrid electrolytic capacitor of the present invention may have, in addition to the capacitor element, a pair of lead wires and an outer casing. One end of each of the pair of lead wires is connected to the capacitor element. The outer casing encloses the capacitor element with the other end of the lead wires leading out to the outside. The outer casing consists of a cylindrical case, a drawn portion provided on the outer surface of the case, and a sealing body having through holes for inserting lead wires. The case houses a capacitor element impregnated with the electrolyte for the hybrid electrolytic capacitor of the present invention. Lead wires, one end of which is connected to the capacitor element, are each inserted through the through holes in the sealing body and sealed by compression in the drawn portion.

[0034] Anode foil having a dielectric layer on its surface can be formed, for example, by roughening an aluminum foil by etching and then chemically converting it to an anodic oxide film, which is a dielectric. A capacitor element comprises an anode foil, a dielectric layer formed on the surface of the anode foil, and a layer of solid electrolyte (C) in contact with the dielectric layer. The layer of solid electrolyte (C) contains a conductive polymer. Typically, in addition to the anode foil and the layer of solid electrolyte (C), the capacitor element further comprises a cathode foil and a separator. In one embodiment, the capacitor element has a wound structure in which a laminate is formed by sequentially stacking an anode foil, a dielectric layer formed on the surface of the anode foil, a layer of solid electrolyte (C) containing a conductive polymer, a separator, and a cathode foil. The solid electrolyte (C) containing a conductive polymer may be impregnated into the separator. The method for forming the layer of solid electrolyte (C) containing a conductive polymer is not particularly limited and known methods can be used, such as a method of impregnating the solid electrolyte (C) in a conductive polymer solution and then drying it, or a method of electrolytically polymerizing a conductive polymer to form a solid electrolyte (C). In the hybrid electrolytic capacitor of the present invention, the capacitor element is impregnated with the electrolyte solution for the hybrid electrolytic capacitor of the present invention. Specifically, the electrolyte solution for the hybrid electrolytic capacitor of the present invention is impregnated into the gaps in the solid electrolyte (C) layer formed within the capacitor element.

[0035] The shape and size of the hybrid electrolytic capacitor of the present invention are not particularly limited. The structure of the hybrid electrolytic capacitor of the present invention is also not particularly limited. Examples include wound-type hybrid electrolytic capacitors, that is, hybrid electrolytic capacitors having a structure in which an anode foil (aluminum oxide foil, etc.) having a dielectric layer (aluminum oxide layer, etc.) on its surface and a cathode foil (aluminum foil, etc.) are wound with a separator interposed between them. The method for manufacturing the hybrid electrolytic capacitor of the present invention is not particularly limited, and conventionally known methods can be employed. For example, one method involves impregnating a separator (such as kraft paper or Manila paper) with the electrolyte for the hybrid electrolytic capacitor of the present invention as a driving electrolyte, interposing it between the anode foil and the cathode foil, winding it up, housing it in a bottomed cylindrical aluminum case, and then sealing the opening of the aluminum case with sealing rubber (such as butyl rubber or silicone rubber).

[0036] In the hybrid electrolytic capacitor of the present invention, the solid electrolyte (C) layer contains a conductive polymer. Examples of conductive polymers include (co)polymers comprising thiophene, 3,4-ethylenedioxythiophene, alkylated ethylenedioxythiophene, alkoxylated ethylenedioxythiophene, pyrrole, and aniline as constituent monomers. However, it is preferable to use a (co)polymer comprising 3,4-ethylenedioxythiophene as a constituent monomer, and it is more preferable to use poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid. The conductive polymer may be used alone or in combination of two or more types.

[0037] The hybrid electrolytic capacitor of the present invention is superior in that it not only reduces the initial ESR but also suppresses the rise in ESR at high temperatures, because it comprises a capacitor element impregnated with the electrolyte for hybrid electrolytic capacitors of the present invention. Although the mechanism by which the rise in ESR at high temperatures is suppressed is not yet clear, it is presumed to be as follows. The performance degradation (such as a decrease in the ESR maintenance rate) of the conventional electrolytic solution for a hybrid-type electrolytic capacitor is considered to be caused by the oxidative degradation and dedoping of the conductive polymer constituting the solid electrolyte. The electrolytic solution for a hybrid-type electrolytic capacitor of the present invention has 2 to 6 ester groups in the molecule and a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm 3 ) 0.5 and contains a liquid ester compound (A) and a carboxylic acid (B) having a molecular weight of 250 or less. Therefore, acid generation occurs reversibly by transesterification of the ester compound during the test, and the pH at 25°C is maintained within the range of 4 to 7. It is considered that oxidative degradation and dedoping of the conductive polymer contained in the layer of the solid electrolyte (C) are suppressed.

[0038] <Others> The following matters are disclosed in this specification. <1> An electrolytic solution for a hybrid-type electrolytic capacitor containing a liquid ester compound (A) having 2 to 6 ester groups in the molecule and a solubility parameter (SP value) of 9.0 to 15.0 (cal / cm 3 ) 0.5 and a carboxylic acid (B) having a molecular weight of 250 or less or a salt of the carboxylic acid (B). <2> The electrolytic solution for a hybrid-type electrolytic capacitor according to <1>, wherein the viscosity of the ester compound (A) at 25°C is 200 mPa·s or less. <3> The electrolytic solution for a hybrid-type electrolytic capacitor according to <1> or <2>, wherein the weight ratio of the ester compound (A) based on the weight of the electrolytic solution is 20 to 95% by weight. <4> The electrolytic solution for a hybrid-type electrolytic capacitor according to any one of <1> to <3>, wherein the pH of the electrolytic solution at 25°C is 4 to 7. <5> The electrolytic solution for a hybrid-type electrolytic capacitor according to any one of <1> to <4>, wherein the water content is 0.05 to 4% by weight based on the weight of the electrolytic solution. <6> A hybrid electrolytic capacitor is formed from a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (C) in contact with the dielectric layer of the anode foil, wherein the capacitor element includes <1> ~ <5> A hybrid electrolytic capacitor in which an electrolyte for hybrid electrolytic capacitors described in any of the above is impregnated, and the solid electrolyte (C) contains a conductive polymer. [Examples]

[0039] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0040] <Method for measuring the viscosity of ester compound (A) at 25°C> The viscosity at 25°C was measured using an E-type viscometer (TVE-25L, manufactured by Toki Sangyo Co., Ltd.).

[0041] Table 1 shows the number of intramolecular ester groups, SP value, and viscosity at 25°C for the ester compounds (A1) to (A8) used in Examples 1 to 14 and Comparative Examples 1 to 4. (A1) to (A7) were purchased as reagents from Tokyo Chemical Industry Co., Ltd., while (A8) was synthesized in Production Example 1 below.

[0042] <Manufacturing Example 1> 70 parts by weight (1 mol equivalent) of phthalic anhydride, 30 parts by weight (2 mol equivalent) of ethylene glycol, and 0.7 parts by weight of p-toluenesulfonic acid were added and a condensation reaction was carried out at 150°C. Then sodium carbonate and water were added and the mixture was washed with water to neutralize it, and the salt and water were removed to obtain (A8).

[0043] [Table 1]

[0044] <Examples 1-14 and Comparative Examples 1-4> <Preparation of electrolyte for hybrid electrolytic capacitors> The components were mixed according to the composition (parts by weight) shown in Table 2, and carbon dioxide was removed by vacuum degassing as necessary to prepare the electrolytes for hybrid electrolytic capacitors (Y-1) to (Y-14) of the present invention (Examples) and the electrolytes for hybrid electrolytic capacitors (Y'-1) to (Y'-4) of the comparative examples. For the electrolyte for hybrid electrolytic capacitors (Y-9) of the present invention, 10.4 parts by weight of 1,2,3,4-tetramethylimidazolinium / methyl carbonate and 5.0 parts by weight of phthalic acid were mixed, and the generated carbon dioxide and methanol were removed under reduced pressure at 100°C. After cooling to room temperature, 70.0 parts by weight of triethyl citrate, 16.2 parts by weight of sulfolane and 0.5 parts of water were mixed to obtain (Y-9). Furthermore, the PEG200 solvent shown in Table 2 refers to polyethylene glycol with a number-average molecular weight of 200.

[0045] [Table 2]

[0046] <Fabrication of Hybrid Electrolytic Capacitors> An element was obtained by connecting electrode tabs to an anode foil (pre-formed aluminum foil: manufactured by Nippon Energy Storage Industry Co., Ltd., 115HD-658Vf) having a dielectric layer on its surface and a cathode foil (unformed aluminum foil: manufactured by Nippon Energy Storage Industry Co., Ltd., 30CB), and placing them opposite each other with kraft paper as a separator. To repair the cut surfaces and defects, the element was subjected to a repair chemical formation process at a voltage of 500V in an aqueous ammonium borate solution to obtain a capacitor element (theoretical capacitance: 10.0μF). Next, a capacitor element was vacuum-impregnated for 1 minute (vacuum level: 2.7 kPa) with a PEDOT / PSS aqueous dispersion (containing a polymer with 3,4-ethylenedioxythiophene as a constituent monomer and polystyrene sulfonic acid) (Heraeus, Clevios PH500) and dried at 150°C for 30 minutes to obtain a capacitor element in which a solid electrolyte (C) layer was formed on the surface of the dielectric layer. Subsequently, the capacitor element with the layer of solid electrolyte (C) formed on the surface of the dielectric layer was impregnated with the electrolytic solution for hybrid electrolytic capacitors obtained in Examples 1 to 14 and Comparative Examples 1 to 4 at 50°C for 1 minute under vacuum (vacuum degree: 2.7 kPa). Finally, the capacitor element having a solid electrolyte layer and impregnated with the electrolytic solution for hybrid electrolytic capacitors was stored in a case and caulked. A load was applied by the constant current method (2 mA) using a constant voltage and constant current DC power supply device (manufactured by Takasago Seisakusho Co., Ltd., GP0650-05R) at 85°C, and aging was performed up to 35 V to obtain a hybrid electrolytic capacitor.

[0047] For the obtained hybrid electrolytic capacitors, the "ESR" and "capacitance" before (initial) and after the high-temperature test were evaluated by the following methods. Also, the capacitance retention rate and ESR retention rate after the high-temperature test were calculated by the following methods. The results are shown in Table 3.

[0048] <ESR evaluation method> For the hybrid electrolytic capacitor, the ESR value at 100 kHz was measured using an LCR meter (manufactured by Hioki Electric Co., Ltd., LCR HiTESTER 3532-50). It indicates that the lower the ESR value, the better the stability of the operation of the capacitor. <Capacitance evaluation method> For the hybrid electrolytic capacitor, the capacitance at 120 Hz was measured using an LCR meter (manufactured by Hioki Electric Co., Ltd., LCR HiTESTER 3532-50). <Evaluation of ESR and capacitance after high-temperature test> The hybrid electrolytic capacitor was left in a thermostat set at 125°C for 500 hours. Thereafter, for each hybrid electrolytic capacitor, the ESR and capacitance were evaluated by the above method. <Calculation method of capacitance retention rate and ESR retention rate> The capacitance retention rate and ESR retention rate were calculated by the following formulas, respectively. The closer the ESR retention rate is to 100, the more the increase in ESR is suppressed. Capacitance retention rate (%) = (Capacitance after high-temperature test) × 100 / (Initial capacitance) ESR retention rate (%) = (ESR value after high-temperature test) × 100 / (initial ESR value)

[0049] [Table 3]

[0050] The electrolytes for hybrid electrolytic capacitors in Examples 1 to 14 showed high voltage withstand capability both in the initial and after high-temperature testing. Furthermore, the hybrid electrolytic capacitors using the electrolytes in Examples 1 to 14 exhibited good initial characteristics (capacitance and ESR), and maintained good capacitance and ESR even after high-temperature testing. On the other hand, in Comparative Examples 1-4, one or more items were insufficient. [Industrial applicability]

[0051] The hybrid electrolytic capacitor using the electrolyte for hybrid electrolytic capacitors of the present invention suppresses the rise in ESR in high-temperature environments, making it suitable for use as a component in electrical and electronic products that can handle high currents. The electrolyte for hybrid electrolytic capacitors of the present invention is suitable as an electrolyte for hybrid electrolytic capacitors in mobile applications such as laptop computers, which are susceptible to ambient temperature changes and tend to become hot during operation, and especially for automotive applications.

Claims

1. It has 2 to 6 ester groups in its molecule, and its solubility parameter (SP value) is 9.0 to 15.0 (cal / cm³). ３ ) ０．５ An electrolyte for hybrid electrolytic capacitors containing a liquid ester compound (A) and a carboxylic acid (B) with a molecular weight of 250 or less, or a salt of carboxylic acid (B).

2. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein the viscosity of the ester compound (A) at 25°C is 200 mPa·s or less.

3. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein the weight percentage of the ester compound (A) is 20 to 95% by weight based on the weight of the electrolyte.

4. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein the pH of the electrolyte at 25°C is 4 to 7.

5. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein the water content is 0.05 to 4% by weight based on the weight of the electrolyte.

6. A hybrid electrolytic capacitor formed from a capacitor element having an anode foil having a dielectric layer on its surface and a layer of solid electrolyte (C) in contact with the dielectric layer of the anode foil, wherein the capacitor element is impregnated with the electrolyte for hybrid electrolytic capacitors described in any one of claims 1 to 5, and the solid electrolyte (C) contains a conductive polymer.

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