Electrolyte for hybrid electrolytic capacitor and hybrid electrolytic capacitor

Abstract

The present invention relates to an electrolyte solution for a hybrid electrolytic capacitor, which contains an aromatic carboxylic acid (A) having a substituent having 2 or more carbon atoms, and which is characterized in that the acid dissociation constant (pKa) of the carboxylic acid (A) as determined by the following measurement method is 1.0-4.5. The measurement method comprises the following steps: dropwise adding 0.1 mol / L methanol potassium hydroxide solution into a solution consisting of 1 part by weight of carboxylic acid (A) and 99 parts by weight of methanol at 25 DEG C, and taking the point with the minimum dropwise adding amount among inflection points of an obtained titration curve as a neutralization point. And the pH at half of the dropping amount of the neutralization point is used as the acid dissociation constant (pKa) of the carboxylic acid (A).

Description

Technical Field

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

[0002] Hybrid electrolytic capacitors are widely used in various electrical and electronic products for purposes such as charge accumulation, noise removal, and phase adjustment. In recent years, their use in automotive applications has increased, leading to a greater demand for higher voltage withstand capabilities and prompting various improvements to be made.

[0003] For example, Patent Document 1 discloses a technique for increasing the voltage resistance of capacitors by using a complex compound of aliphatic carboxylic acids, inorganic acids and organic acids as anions of the electrolyte.

[0004] In addition, Patent Document 2 discloses a technique for improving the ESR (Equivalent Series Resistance) of capacitors used in high-voltage applications by using aliphatic ammonium carboxylate salts in the electrolyte.

[0005] However, although the electrolytic capacitors described in Patent Documents 1 and 2 can achieve high voltage withstand capability, their voltage withstand capability is insufficient, and their ESR characteristics under high temperature conditions are also insufficient.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2015-165550

[0009] Patent Document 2: Japanese Patent Application Publication No. 2017-38010 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] The objective of this invention is to provide an electrolyte for hybrid electrolytic capacitors, which is a high-voltage-resistant electrolyte for hybrid electrolytic capacitors. When used in hybrid electrolytic capacitors, it exhibits large capacitance even at high temperatures and can suppress the rise of ESR.

[0012] Methods for solving problems

[0013] In order to solve the above-mentioned problems, the inventors conducted in-depth research and completed this invention.

[0014] That is, the present invention relates to an electrolyte for a mixed electrolytic capacitor, which is an electrolyte for a mixed electrolytic capacitor containing an aromatic carboxylic acid (A) having two or more carbon atoms as a substituent, wherein the acid dissociation constant (pKa) of the carboxylic acid (A) determined by the following determination method is 1.0 to 4.5.

[0015] Determination method: At 25°C, 0.1 mol / L methanolic potassium hydroxide solution was added dropwise to a solution consisting of 1 part by weight of the above carboxylic acid (A) and 99 parts by weight of methanol. The point with the smallest amount of added solution in the inflection point of the resulting titration curve was taken as the neutralization point. The pH at which half the amount of added solution was added at the neutralization point was taken as the acid dissociation constant (pKa) of the above carboxylic acid (A).

[0016] In addition, the present invention relates to a hybrid electrolytic capacitor, which is a hybrid electrolytic capacitor having a capacitor element having 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, wherein the capacitor element is impregnated with the electrolyte for the hybrid electrolytic capacitor of the present invention, and the layer of solid electrolyte (C) comprises a conductive polymer.

[0017] The effects of the invention

[0018] The electrolyte for the hybrid electrolytic capacitor of the present invention has high voltage resistance, and is therefore suitable for use in hybrid electrolytic capacitors.

[0019] The hybrid electrolytic capacitor of the present invention contains the electrolyte of the hybrid electrolytic capacitor of the present invention, thus having a large capacitance at high temperatures and suppressing the rise of ESR. Detailed Implementation

[0020] The electrolyte for the hybrid electrolytic capacitor of the present invention is an electrolyte for the hybrid electrolytic capacitor containing an aromatic carboxylic acid (A) having two or more carbon atoms as a substituent, characterized in that the acid dissociation constant (pKa) of the carboxylic acid (A) determined by the following determination method is 1.0 to 4.5.

[0021] Determination method: At 25°C, 0.1 mol / L methanolic potassium hydroxide solution was added dropwise to a solution consisting of 1 part by weight of the above carboxylic acid (A) and 99 parts by weight of methanol. The point with the smallest amount of added solution in the inflection point of the resulting titration curve was taken as the neutralization point. The pH at which half the amount of added solution was added at the neutralization point was taken as the acid dissociation constant (pKa) of the above carboxylic acid (A).

[0022] The aromatic carboxylic acid (A) having two or more carbon atoms (hereinafter referred to as carboxylic acid (A)) is not particularly limited, and compounds having an aromatic ring, a carboxyl group, and two or more carbon atoms can be cited as examples. From the viewpoint of voltage resistance, the carboxylic acid (A) preferably has at least one bond selected from the group consisting of ester bond, amide bond, imide bond, ether bond, carbamate bond, and urea bond, and more preferably has an ester bond.

[0023] Examples of the above-mentioned carboxylic acids (A) having ester bonds include aromatic carboxylic acids having aromatic ester groups. In this specification, an aromatic ester group refers to a group in which the carbon atom constituting the aromatic ring is directly bonded to the carbon atom of the ester group.

[0024] As an aromatic carboxylic acid having an aromatic ester group, an ester compound of an aromatic carboxylic acid (a1) and an alcohol (a2) can be used.

[0025] Examples of aromatic carboxylic acids (a1) include aromatic dicarboxylic acids, aromatic tricarboxylic acids, aromatic tetracarboxylic acids, aromatic pentacarboxylic acids, and aromatic hexacarboxylic acids.

[0026] Examples of aromatic dicarboxylic acids include phthalic acid (including phthalic anhydride), isophthalic acid, and terephthalic acid.

[0027] Examples of aromatic tricarboxylic acids include trimellitic acid (including trimellitic anhydride), 1,2,3-benzenetricarboxylic acid (including anhydride), and 1,3,5-tricarboxylic acid.

[0028] Examples of aromatic tetracarboxylic acids include pyromellitic acid (including pyromellitic anhydride).

[0029] Examples of aromatic pentacarboxylic acids include benzopentacarboxylic acid (including its anhydride).

[0030] Examples of aromatic hexacarboxylic acids include benzohexacarboxylic acid (including benzohexacarboxylic anhydride).

[0031] Among these aromatic carboxylic acids (a1), from the viewpoint of suppressing the increase of ESR under high temperature conditions and solubility in solvents described later, phthalic acid (including phthalic anhydride), terephthalic acid, trimellitic acid (including trimellitic anhydride), pyromellitic acid (including pyromellitic anhydride) and hexacarboxylic acid (including hexacarboxylic anhydride) are preferred, more preferably phthalic acid (including phthalic anhydride), trimellitic acid (including trimellitic anhydride) and pyromellitic acid (including pyromellitic anhydride), and even more preferably phthalic acid (including phthalic anhydride).

[0032] Aromatic carboxylic acids (a1) can be used alone or in combination of two or more.

[0033] As alcohols (a2), examples include monohydric alcohols, dihydric alcohols, trihydric alcohols, and alcohols with four or more hydroxyl groups.

[0034] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, and tetradecanol. The monohydric alcohol is preferably a monohydric alcohol with 2 to 10 carbon atoms. More specifically, the monohydric alcohol is preferably at least one selected from the group consisting of ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol.

[0035] Furthermore, monohydric alcohols may have substituents. Examples of monohydric alcohols with substituents include monohydric alcohols in which one or more hydrogen atoms are replaced by substituents. Examples of substituents include halogen atoms (fluorine atoms, chlorine atoms, and bromine atoms, etc.) and alkoxy groups having 1 to 4 carbon atoms.

[0036] Examples of diols include alkylene glycols with 2 to 10 carbon atoms and polyalkylene glycols having 2 to 6 oxoalkylene units.

[0037] Examples of alkylene glycols with 2 to 10 carbon atoms include ethylene glycol, propylene glycol, 1,4-butanediol, 1,10-butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, and decanediol.

[0038] Examples of polyalkylene glycols having 2 to 6 carbon atoms include polyethylene glycol, polypropylene glycol, polybutane glycol, and polytetramethylene glycol.

[0039] The number of alkylene units in the aforementioned polyalkylene glycol is not particularly limited, but may be, for example, 2 or more. The number average molecular weight of the aforementioned polyalkylene glycol is not particularly limited, but from the viewpoint of voltage resistance and solubility, it is preferably 2000 or less, more preferably 1000 or less.

[0040] Examples of triols include glycerol and trimethylolpropane.

[0041] Examples of alcohols with four or more ions include pentaerythritol, dipentaerythritol, diglycerol, triglycerides, sorbitol, and sucrose.

[0042] From the viewpoint of voltage resistance and solubility in solvents described later, alcohol (a2) is preferably a diol, more preferably at least one selected from the group consisting of ethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol and polytetramethylene glycol, and even more preferably at least one selected from the group consisting of ethylene glycol, polyethylene glycol and polypropylene glycol.

[0043] Alcohols (a2) can be used alone or in combination of two or more.

[0044] There are no particular limitations on the methods and conditions for reacting aromatic carboxylic acids (a1) with alcohols (a2), and existing known methods and conditions can be used. Furthermore, in order to precipitate a solid after the condensation reaction of aromatic carboxylic acids (a1) with alcohols (a2), ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, toluene, etc., can be added to the resulting reaction solution.

[0045] As a preferred embodiment of an aromatic carboxylic acid having an aromatic ester group, an aromatic carboxylic acid having one aromatic ester group (aromatic carboxylic acid monoester) can be cited. In addition, as a preferred embodiment of an aromatic carboxylic acid monoester, a carboxylic acid represented by the following general formula (1) can be cited.

[0046] [Chemistry 1]

[0047] ,

[0048] In general formula (1), R 1 This refers to a residue after removing a hydroxyl group from a monohydric alcohol with or without substituents, a residue after removing one hydroxyl group from an alkylene glycol with 2 to 10 carbon atoms, a residue after removing one hydroxyl group from a polyalkylene glycol with 2 to 6 carbon atoms, or a residue after removing one hydroxyl group from glycerol.

[0049] Examples of monohydric alcohols with 2 to 10 carbon atoms include ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, and decanol. Monohydric alcohols with 2 to 10 carbon atoms may have substituents. Examples of monohydric alcohols with 2 to 10 carbon atoms that have substituents include those in which one or more hydrogen atoms are substituted.

[0050] Examples of substituents include halogen atoms (fluorine, chlorine, and bromine atoms, etc.) and alkoxy groups with 1 to 4 carbon atoms.

[0051] Examples of alkylene glycols with 2 to 10 carbon atoms include ethylene glycol, propylene glycol, 1,4-butanediol, 1,10-butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, and decanediol.

[0052] Examples of polyalkylene glycols having 2 to 6 carbon alkylene units include polyethylene glycol, polypropylene glycol, polybutane glycol, and polytetramethylene glycol. The number of alkylene units in these polyalkylene glycols is not particularly limited, but may be 2 or more. The number average molecular weight of these polyalkylene glycols is not particularly limited, but from the viewpoint of voltage resistance and solubility, it is preferably 2000 or less, more preferably 1000 or less.

[0053] There is no particular limitation as long as n is an integer from 1 to 5. From the viewpoint of voltage resistance, it is preferred to be an integer from 1 to 3, and more preferably 1 or 2.

[0054] Specific examples of aromatic carboxylic acids having aromatic ester groups include decyl phthalate, ethylene glycol phthalate, polyethylene glycol phthalate, polypropylene glycol phthalate, glyceryl phthalate, decyl terephthalate, ethylene glycol terephthalate, polyethylene glycol terephthalate, polypropylene glycol terephthalate, glyceryl terephthalate, and decyl trimellitate. Ethylene trimellitate monoester, polyethylene trimellitate monoester, polyethylene trimellitate monoester, glyceryl trimellitate monoester, decyl pyromellitic acid monoester, ethylene glycol pyromellitic acid monoester, polyethylene glycol pyromellitic acid monoester, polyethylene glycol pyromellitic acid monoester, glyceryl pyromellitic acid monoester, decyl hexacarboxylate monoester, ethylene glycol pyromellitic acid monoester, polyethylene glycol pyromellitic acid monoester, polyethylene glycol pyromellitic acid monoester, and glyceryl hexacarboxylate monoester, etc.

[0055] From the viewpoint of balancing ESR rise suppression and voltage resistance under high temperature conditions, the above-mentioned carboxylic acid (A) is preferably an aromatic carboxylic acid having an aromatic ester group, more preferably an aromatic carboxylic acid having one aromatic ester group (aromatic carboxylic acid monoester), and even more preferably a carboxylic acid represented by the above general formula (1).

[0056] The above-mentioned carboxylic acid (A) can be used alone or in combination with two or more types.

[0057] The acid dissociation constant (pKa) of the carboxylic acid (A) obtained by the above-described measurement method is not particularly limited as long as it is between 1.0 and 4.5, but is preferably between 1.5 and 4.0, more preferably between 2.0 and 4.0. If the pKa of the carboxylic acid (A) is less than 1.0, the oxide film on the anode of the hybrid electrolytic capacitor will dissolve, and the oxide film cannot be repaired, sometimes resulting in a decrease in the initial spark voltage (withstand voltage). On the other hand, if the pKa exceeds 4.5, the effect of inhibiting the oxidation and deterioration of the conductive polymer becomes insufficient, and the capacitance and ESR at high-temperature environments may sometimes deteriorate.

[0058] The pKa of the above carboxylic acid (A) will be explained. The pKa is represented by the following formula.

[0059] pKa=-log 10 (([(A) anion][proton]) / [(A)])

[0060] [(A) anion]: Concentration (mol / L) of the above carboxylic acid (A) anion

[0061] [Protons]: Proton concentration (mol / L)

[0062] [(A)]: Concentration of carboxylic acid (A) (mol / L)

[0063] Furthermore, based on the relationship between pKa and the hydrogen ion concentration pH, the pH of the liquid is equal to the pKa when 0.5 mol equivalent of a strong base is added relative to the acid.

[0064] In this specification, the pKa of the above-mentioned carboxylic acid (A) can be determined, for example, using an automatic titration apparatus under the following conditions.

[0065] Apparatus (example): Automatic titration apparatus COM-A19 (manufactured by HIRANUMA Co., Ltd.)

[0066] Electrode (example): Glass electrode GE-101B (manufactured by HIRANUMA Co., Ltd.)

[0067] Measurement temperature: 25℃

[0068] At 25°C, a 0.1 mol / L methanolic potassium hydroxide solution was added dropwise to a solution consisting of 1 part by weight of the above carboxylic acid (A) and 99 parts by weight of methanol. The point with the smallest amount of added solution was taken as the neutralization point. The pH at which half the amount of added solution was added was taken as the acid dissociation constant (pKa) of the above carboxylic acid (A).

[0069] The pKa of the aforementioned carboxylic acid (A) can be adjusted, for example, by selecting substituents with two or more carbon atoms. For instance, as substituents with two or more carbon atoms, introducing an electron-withdrawing group can lower the pKa, while introducing an electron-donating group can increase the pKa.

[0070] The content of the above-mentioned carboxylic acid (A) in the electrolyte of the hybrid electrolytic capacitor of the present invention is not particularly limited. From the viewpoint of voltage resistance and suppressing the rise of ESR under high temperature environment, it is preferably 0.05 to 40% by weight, more preferably 1 to 30% by weight, and even more preferably 1 to 20% by weight.

[0071] In the electrolyte for the hybrid electrolytic capacitor of the present invention, the content of the carboxylic acid (A) is not particularly limited. Based on the total weight of the acid components (the total weight of the carboxylic acid (A) and the acid components (A') other than the carboxylic acid (A) described below), from the viewpoint of voltage resistance and suppressing the rise of ESR under high temperature conditions, it is preferably 50 to 100% by weight, more preferably 60 to 100% by weight, and even more preferably 70 to 100% by weight.

[0072] From the viewpoint of suppressing the increase of ESR under high temperature conditions, the electrolyte for the hybrid electrolytic capacitor of the present invention preferably further contains alcohol (B).

[0073] Examples of the alcohols (B) mentioned above include ethylene glycol, propylene glycol, 1,4-butanediol, 1,10-butanediol, pentanediol, hexanediol, heptanediol, octanediol, nonanediol, n-decyl alcohol, 1,10-decanediol, glycerol, and polyalkylene glycols having 2 to 6 carbon atoms.

[0074] Examples of polyalkylene glycols having 2 to 6 carbon atoms include polyethylene glycol, polypropylene glycol, polybutane glycol, and polytetramethylene glycol.

[0075] The number of alkylene units in the aforementioned polyalkylene glycol is not particularly limited, but may be, for example, 2 or more. The number average molecular weight of the aforementioned polyalkylene glycol is not particularly limited, but from the viewpoint of voltage resistance, it is preferably 2000 or less, more preferably 1000 or less.

[0076] From the viewpoint of voltage resistance, the alcohol (B) is preferably selected from at least one of the group consisting of ethylene glycol, polyethylene glycol, polypropylene glycol, polybutylene glycol and polytetramethylene glycol, and more preferably from at least one of the group consisting of ethylene glycol, polyethylene glycol and polypropylene glycol.

[0077] The above alcohol (B) can be used alone or in combination with two or more.

[0078] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains the above-mentioned alcohol (B), the content of the above-mentioned alcohol (B) in the electrolyte for the hybrid electrolytic capacitor of the present invention is not particularly limited, but from the viewpoint of voltage resistance and suppressing the rise of ESR under high temperature environment, it is preferably 40 to 99% by weight, more preferably 60 to 90% by weight, and even more preferably 75 to 90% by weight.

[0079] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains the above-mentioned alcohol (B), the weight ratio ((B) / (A)) of the above-mentioned alcohol (B) to the above-mentioned carboxylic acid (A) in the electrolyte for the hybrid electrolytic capacitor of the present invention is not particularly limited, but from the viewpoint of voltage resistance, it is preferably 1 to 500, more preferably 1 to 200, and even more preferably 2 to 20.

[0080] The electrolyte for the hybrid electrolytic capacitor of the present invention may also contain acid components (A') other than the above-mentioned carboxylic acid (A).

[0081] Examples of acid components (A') other than the aforementioned carboxylic acid (A) include aliphatic carboxylic acids and other acid components having aliphatic ester groups. In this specification, an aliphatic ester group refers to a group in which the carbon atom constituting the non-aromatic hydrocarbon group is directly bonded to the carbon atom of the ester group. The non-aromatic hydrocarbon group can be acyclic (straight-chain or branched) or cyclic.

[0082] As an aliphatic carboxylic acid having the aforementioned aliphatic ester group, an ester compound of an aliphatic carboxylic acid (a'1) and an alcohol (a2) can be used. As the aforementioned alcohol (a2), the same alcohol (a2) used in the aforementioned aromatic carboxylic acid having an aromatic ester group can be used.

[0083] Examples of aliphatic carboxylic acids (a'1) include aliphatic dicarboxylic acids, aliphatic tricarboxylic acids, and aliphatic tetracarboxylic acids.

[0084] Examples of aliphatic dicarboxylic acids mentioned above include malonic acid, succinic acid (including succinic anhydride), malic acid, fumaric acid, adipic acid, sebacic acid, etc.

[0085] Examples of aliphatic tricarboxylic acids mentioned above include citric acid, isocitric acid, and propane-1,2,3-tricarboxylic acid.

[0086] Examples of aliphatic tetracarboxylic acids mentioned above include cyclobutanetetracarboxylic acid (including anhydride) and 1,2,3,4-butanetetracarboxylic acid (including anhydride).

[0087] There are no particular limitations on the methods and conditions for reacting aliphatic carboxylic acids (a'1) with alcohols (a2), and existing known methods and conditions can be used. Additionally, to induce the precipitation of a solid after the condensation reaction of aliphatic carboxylic acids (a'1) with alcohols (a2), ethyl acetate, butyl acetate, acetone, methyl ethyl ketone, toluene, etc., can be added to the resulting reaction solution.

[0088] Examples of other acid components mentioned above include aromatic carboxylic acids such as benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, 1,2-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 2,3-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, acetylsalicylic acid, trimellitic acid, and pyromellitic acid; aliphatic carboxylic acids such as adipic acid, sebacic acid, azelaic acid, 1,6-decanedicarboxylic acid, 2-furanic acid, 3-furanic acid, and 2,5-furanic acid; and acids such as phosphoric acid (phosphoric acid, diphosphite, phosphate ester) and boric acid (boric acid, borate ester, borosalicylic acid). Additionally, ester compounds of monocarboxylic acids with sulfonates and alcohols (a2) can also be used as other acid components mentioned above. Examples of monocarboxylic acids with sulfonates include m-sulfobenzoic acid and o-sulfobenzoic acid. As the alcohol (a2) mentioned above, the same alcohol as the alcohol (a2) used in the aromatic carboxylic acids having aromatic ester groups mentioned above can be used.

[0089] From the viewpoint of suppressing the increase of ESR under high temperature conditions, the acid component (A') other than the above-mentioned carboxylic acid (A) is preferably selected from at least one of the group consisting of benzoic acid, phthalic acid and 2,5-furan dicarboxylic acid, and more preferably phthalic acid.

[0090] From the viewpoint of high voltage resistance, the acid component (A') other than the carboxylic acid (A) is preferably selected from at least one of the group consisting of aliphatic carboxylic acids having aliphatic ester groups, aromatic carboxylic acids and boric acid, more preferably aromatic carboxylic acids and boric acid, and even more preferably boric acid.

[0091] The acid component (A') other than the carboxylic acid (A) mentioned above can be used alone or in combination with two or more.

[0092] When the electrolyte for the hybrid electrolytic capacitor of the present invention contains an acid component (A') other than the above-mentioned carboxylic acid (A), the content of the acid component (A') other than the above-mentioned carboxylic acid (A) in the electrolyte for the hybrid electrolytic capacitor of the present invention is not particularly limited. From the viewpoint of suppressing the increase of ESR under high temperature environment, it is preferably 10% by weight or less, more preferably 5% by weight or less, and even more preferably 1% by weight or less.

[0093] In the electrolyte for the hybrid electrolytic capacitor of the present invention, the above-mentioned carboxylic acid (A) and the above-mentioned acid component (A') may be contained in the form of acid or may be contained in the form of anion by ionization.

[0094] Examples of counter cations to anions include ammonium, primary ammonium, secondary ammonium, tertiary ammonium, and amidonium. Examples of ammonium, primary ammonium, secondary ammonium, and tertiary ammonium include ammonium formed from ammonia, primary amines, secondary amines, and tertiary amines, respectively.

[0095] Examples of these amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, N,N-diisopropylethylamine, tetramethylethylenediamine, hexamethylenediamine, spermidine, spermine, adamantane, aniline, phenethylamine, toluidine, pyrrolidine, piperidine, piperazine, morpholine, ethylmorpholine, imidazole, pyridine, pyridazine, pyrimidine, pyrazine, 4-dimethylaminopyridine, and triethanolamine.

[0096] Examples of amidonium include 1,2,3,4-tetramethylimidazoline, 1,3-dimethylimidazoline, 1,3-diisopropylimidazoline, 1,3-dibutylimidazoline, 1-methyl-3-propylimidazoline, 1-ethyl-3-methylimidazoline, 1-ethyl-2,3-dimethylimidazoline, 1-butyl-3-methylimidazoline, and 1-benzyl-3-methylimidazoline.

[0097] Anions can be countered by one type of cation alone, or by a combination of two or more types.

[0098] From the viewpoint of suppressing the rise of ESR, the counter cation of the above-mentioned anion is preferably selected from at least one of the group consisting of ammonium, primary ammonium and tertiary ammonium, and more preferably tertiary ammonium.

[0099] In the case where the electrolyte for the hybrid electrolytic capacitor of the present invention contains, in addition to the above-mentioned carboxylic acid (A), the counter cation of the above-mentioned anion, the content of the substance that generates the counter cation of the above-mentioned anion (ammonia, primary amine, secondary amine and tertiary amine) is not particularly limited. From the viewpoint of voltage resistance and suppressing the rise of ESR under high temperature conditions, 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.

[0100] In addition to the alcohol (B) mentioned above, the electrolyte for the hybrid electrolytic capacitor of the present invention may further contain a solvent.

[0101] Examples of solvents include water, alcohol solvents other than the alcohols mentioned above (B) (such as methanol, ethanol, propanol, butanol, and ethylene glycol monobutyl ether), amide solvents (such as N-methylformamide, N-ethylformamide, and N,N-dimethylformamide), lactone solvents (such as α-acetyl-γ-butyrolactone, β-butyrolactone, γ-butyrolactone, γ-valerolactone, and δ-valerolactone), nitrile solvents (such as acetonitrile, propionitrile, butyronitrile, acrylonitrile, methacrylonitrile, and benzonitrile), sulfoxide solvents (such as dimethyl sulfoxide, methyl ethyl sulfoxide, and diethyl sulfoxide), and sulfone solvents (such as sulfolane and methyl ethyl sulfone).

[0102] From the viewpoint of suppressing the rise of ESR, the above-mentioned solvents are preferably lactone solvents and sulfone solvents, more preferably sulfone solvents, and even more preferably sulfolane.

[0103] The above solvents can be used alone or in combination of two or more.

[0104] 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 not particularly limited, but from the viewpoint of voltage resistance, it is preferably 0.05 to 40% by weight, more preferably 0.5 to 3.0% by weight.

[0105] The electrolyte for the hybrid electrolytic capacitor of the present invention is not particularly limited in pH at 25°C, but from the viewpoint of suppressing the rise of ESR and voltage withstand capability, it is preferably 4 to 6, more preferably 4 to 5.5, and even more preferably 4 to 5.

[0106] In this specification, the pH of the electrolyte for the hybrid electrolytic capacitor of the present invention at 25°C is a value directly measured using a pH meter.

[0107] The hybrid electrolytic capacitor of the present invention is a hybrid electrolytic capacitor having a capacitor element, wherein the capacitor element has 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, wherein the capacitor element is impregnated with the electrolyte of the hybrid electrolytic capacitor of the present invention, and the solid electrolyte (C) comprises a conductive polymer.

[0108] In one embodiment, the hybrid electrolytic capacitor of the present invention may have a pair of leads and an outer casing together with the aforementioned capacitor element. One end of each pair of leads is connected to the capacitor element. The outer casing encapsulates the capacitor element such that the other ends of the leads are led to the outside.

[0109] The outer casing comprises a cylindrical shell, a deep-drawn section disposed on the outer peripheral surface of the shell, and a sealing body having through holes for inserting leads. A capacitor element impregnated with the electrolyte for a hybrid electrolytic capacitor of the present invention is housed within the shell. Leads, one end of which is connected to the capacitor element, are inserted into the through holes of the sealing body and compressed in the deep-drawn section to be sealed.

[0110] An anode foil having a dielectric layer on its surface is formed, for example, by roughening an aluminum foil using an etching process and then performing a chemical conversion treatment on its surface to form an anodized film that serves as a dielectric.

[0111] A capacitor element has 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. In addition to the anode foil and the layer of solid electrolyte (C), the capacitor element typically has a cathode foil and a separator. In one embodiment, the capacitor element has a structure formed by winding a laminate of 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 in sequence. The solid electrolyte (C) containing the conductive polymer can be impregnated in the separator. The method for forming the layer of solid electrolyte (C) containing the conductive polymer is not particularly limited; known methods can be used, such as methods that impregnate the solid electrolyte (C) with a conductive polymer solution and then dry it, or methods that electrolytically polymerize conductive polymers to form the solid electrolyte (C).

[0112] In the hybrid electrolytic capacitor of the present invention, the electrolyte for the hybrid electrolytic capacitor of the present invention is impregnated into the capacitor element. Specifically, the electrolyte for the hybrid electrolytic capacitor of the present invention is impregnated in the gaps between the layers of solid electrolyte (C) formed within the capacitor element.

[0113] 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, and examples include, for instance, a wound hybrid electrolytic capacitor, i.e., a hybrid electrolytic capacitor having a structure in which a separator is sandwiched between an anode foil (alumina foil, etc.) having a dielectric layer (alumina layer, etc.) on its surface and a cathode foil (aluminum foil, etc.).

[0114] The manufacturing method of the hybrid electrolytic capacitor of the present invention is not particularly limited, and existing known methods can be used. For example, a method can be described in which the hybrid electrolytic capacitor of the present invention is impregnated with an electrolyte as the driving electrolyte in a separator (such as kraft paper or Manila paper) between the anode foil and the cathode foil, and then wound and housed in a bottomed cylindrical aluminum shell, and the opening of the aluminum shell is sealed with sealing rubber (such as butyl rubber or silicone rubber).

[0115] In the hybrid electrolytic capacitor of the present invention, the solid electrolyte (C) layer comprises a conductive polymer.

[0116] Examples of conductive polymers include (co)polymers with thiophene, 3,4-ethylenedioxythiophene, alkylated ethylenedioxythiophene, alkoxylated ethylenedioxythiophene, pyrrole, and aniline as monomers. Copolymers with 3,4-ethylenedioxythiophene as monomer are preferred, and poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid is more preferred.

[0117] Conductive polymers can be used alone or in combination of two or more.

[0118] The hybrid electrolytic capacitor of the present invention comprises a capacitor element impregnated with the electrolyte for hybrid electrolytic capacitors of the present invention. Therefore, it is excellent not only in reducing the initial ESR, but also in suppressing the rise of ESR at high temperatures. Although the mechanism for suppressing the rise of ESR at high temperatures is not yet clear, it is speculated as follows.

[0119] The performance degradation (such as decreased ESR retention) of electrolytes in existing hybrid electrolytic capacitors is considered to be caused by oxidative degradation and dedoping of the conductive polymers constituting the solid electrolyte. The electrolyte for hybrid electrolytic capacitors of the present invention contains an aromatic carboxylic acid (A) with substituents having two or more carbon atoms. The acid dissociation constant (pKa) of the carboxylic acid (A), determined by the aforementioned method, is 1.0 to 4.5. Therefore, it is believed that by maintaining the pH in the range of 4 to 6 at 25°C, oxidative degradation and dedoping of the conductive polymers contained in the solid electrolyte (C) layer can be suppressed.

[0120] <Other>

[0121] The following information is disclosed in this specification.

[0122] <1> An electrolyte for a hybrid electrolytic capacitor is an electrolyte containing an aromatic carboxylic acid (A) having two or more carbon atoms, wherein the acid dissociation constant (pKa) of the carboxylic acid (A) determined by the following method is 1.0 to 4.5.

[0123] Determination method: At 25°C, 0.1 mol / L methanolic potassium hydroxide solution was added dropwise to a solution consisting of 1 part by weight of the above carboxylic acid (A) and 99 parts by weight of methanol. The point with the smallest amount of added solution in the inflection point of the resulting titration curve was taken as the neutralization point. The pH at which half the amount of added solution was added at the neutralization point was taken as the acid dissociation constant (pKa) of the above carboxylic acid (A).

[0124] <2> according to <1> The electrolyte for the hybrid electrolytic capacitor, wherein the carboxylic acid (A) has at least one bond selected from the group consisting of ester bond, amide bond, imide bond, ether bond, carbamate bond and urea bond.

[0125] <3> according to <1> or <2> The electrolyte for the hybrid electrolytic capacitor, wherein the carboxylic acid (A) has an ester bond.

[0126] <4> according to <1> ~ <3> The electrolyte for a hybrid electrolytic capacitor according to any one of the following methods, wherein the content of the above-mentioned carboxylic acid (A) is 50 to 100% by weight based on the total weight of the acid components.

[0127] <5> according to <1> ~ <4> The electrolyte for the hybrid electrolytic capacitor described in any one of the following methods further contains an alcohol (B), wherein the weight ratio of the alcohol (B) to the carboxylic acid (A) ((B) / (A)) is 1 to 200.

[0128] <6> according to <1> ~ <5> The electrolyte for a hybrid electrolytic capacitor according to any one of the following methods, wherein the carboxylic acid (A) contains a carboxylic acid represented by general formula (1).

[0129] [Chemistry 2]

[0130] .

[0131] In general formula (1), R 1 This refers to a residue obtained by removing a hydroxyl group from a monohydric alcohol with 2 to 10 carbon atoms (with or without substituents), a residue obtained by removing one hydroxyl group from an alkylene glycol with 2 to 10 carbon atoms, a residue obtained by removing one hydroxyl group from a polyalkylene glycol with 2 to 6 carbon atoms, or a residue obtained by removing one hydroxyl group from glycerol. n represents an integer from 1 to 5.

[0132] <7> A hybrid electrolytic capacitor is a hybrid electrolytic capacitor comprising a capacitor element, wherein the capacitor element has 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, wherein the capacitor element is impregnated with... <1> ~ <6> The electrolyte for a hybrid electrolytic capacitor according to any one of the following methods, wherein the layer of the solid electrolyte (C) comprises a conductive polymer.

[0133] Example

[0134] The present invention will be specifically described below through embodiments, but the present invention is not limited to these embodiments.

[0135] <Method for determining the acid dissociation constant (pKa) of carboxylic acid (A)>

[0136] At 25°C, 99 parts by weight of methanol were added to 1 part by weight of carboxylic acid (A), and the mixture was shaken until completely dissolved. A 0.1 mol / L methanolic potassium hydroxide solution was then added dropwise to the resulting methanol solution of carboxylic acid (A), and the point on the titration curve with the smallest amount of added solution was taken as the neutralization point. The pH value at half the amount added at the neutralization point was recorded on the titration curve, and this pH value was taken as the acid dissociation constant (pKa) of the carboxylic acid (A).

[0137] It should be noted that the pKa of the acid component (A') was determined in the same manner as that of the carboxylic acid (A).

[0138] pKa=-log 10 (([(A) anion][proton]) / [(A)])

[0139] [(A) anion]: Concentration (mol / L) of carboxylic acid (A) anion

[0140] [Protons]: Proton concentration (mol / L)

[0141] [(A)]: Concentration of carboxylic acid (A) (mol / L)

[0142] <Measurement Conditions>

[0143] Apparatus: Automatic titration apparatus COM-A19 (manufactured by HIRANUMA Co., Ltd.)

[0144] Electrode: Glass electrode GE-101B (manufactured by HIRANUMA Co., Ltd.)

[0145] Measurement temperature: 25℃

[0146] <Manufacturing Example 1>

[0147] 21.0 parts by weight (1 mol equivalent) of phthalic anhydride were added to a flask (Kolben), followed by the dropwise addition of 79.0 parts by weight (9.0 mol equivalent) of ethylene glycol to initiate a condensation reaction (esterification reaction), yielding a reaction solution. 50.0 parts by weight of ethyl acetate were added to the resulting reaction solution, and the mixture was cooled to -5°C to allow a solid to precipitate. The precipitated solid was separated by filtration and dried to obtain 29.8 parts by weight of ethylene glycol monophthalate (Al). The acid dissociation constant (pKa) of ethylene glycol monophthalate (Al) was determined using the above method, and the result was 3.8.

[0148] <Manufacturing Example 2>

[0149] 14.7 parts by weight (1 mol equivalent) of terephthalic acid and 85.3 parts by weight (15.5 mol equivalent) of ethylene glycol were added to a flask (Kolben), and the mixture was heated to 140°C and maintained for 3 hours to carry out a condensation reaction (esterification reaction). Then, unreacted ethylene glycol was removed under reduced pressure (0.5 kPa) at 120°C to obtain 20 parts by weight of a mixture (A2) of ethylene glycol monoterephthalate and ethylene glycol diterephthalate. The acid dissociation constant (pKa) of the mixture (A2) of ethylene glycol monoterephthalate and ethylene glycol diterephthalate was determined using the above method, and the result was 4.1.

[0150] <Manufacturing Example 3>

[0151] In Manufacturing Example 1, phthalic anhydride was replaced with trimellitic anhydride at 22.2 parts by weight (1 mol equivalent), and the weight of ethylene glycol was changed to 77.8 parts by weight (11.8 mol equivalent). Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 28.8 parts by weight of trimellitic acid ethylene glycol monoester (A3). The acid dissociation constant (pKa) of trimellitic acid ethylene glycol monoester (A3) was determined using the above-described method, and the result was 3.4.

[0152] <Manufacturing Example 4>

[0153] In Manufacturing Example 1, 15.9 parts by weight (1 mol equivalent) of phthalic anhydride were replaced with trimellitic anhydride, and 84.1 parts by weight (5.6 mol equivalent) of PEG200 (polyethylene glycol, number average molecular weight 200, manufactured by Sanyo Chemical Industry Co., Ltd.) were replaced with PEG200. Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 28.8 parts by weight of trimellitic acid polyethylene glycol monoester (A4). The acid dissociation constant (pKa) of trimellitic acid polyethylene glycol monoester (A4) was determined using the above-described method, and the result was 3.6.

[0154] <Manufacturing Example 5>

[0155] In Manufacturing Example 1, phthalic anhydride was replaced with 26.1 parts by weight (1 mol equivalent) of pyromellitic anhydride, and ethylene glycol was replaced with 73.9 parts by weight (11.6 mol equivalent). Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 32.4 parts by weight of pyromellitic ethylene glycol monoester (A5). The acid dissociation constant (pKa) of pyromellitic ethylene glycol monoester (A5) was determined using the above-described method, and the result was 2.6.

[0156] <Manufacturing Example 6>

[0157] In Manufacturing Example 1, 11.6 parts by weight (1 mol equivalent) of phthalic anhydride were replaced with pyromellitic anhydride, and 88.4 parts by weight (9.7 mol equivalent) of PEG200 (polyethylene glycol, number average molecular weight 200, manufactured by Sanyo Chemical Industry Co., Ltd.) were replaced with PEG200. Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 20.6 parts by weight of pyromellitic polyethylene glycol monoester (A6). The acid dissociation constant (pKa) of pyromellitic polyethylene glycol monoester (A6) was determined using the above-described method, and the result was 2.9.

[0158] <Manufacturing Example 7>

[0159] In Manufacturing Example 1, phthalic anhydride was replaced with 24.5 parts by weight (1 mol equivalent) of hexacarboxylic anhydride, and ethylene glycol was replaced with 75.5 parts by weight (14.3 mol equivalent). Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1 to obtain 29.8 parts by weight of ethylene glycol hexacarboxylate monoester (A7). The acid dissociation constant (pKa) of ethylene glycol hexacarboxylate monoester (A7) was determined using the above-described method, and the result was 1.7.

[0160] <Manufacturing Example 8>

[0161] In Manufacturing Example 1, the phthalic anhydride was changed to 5.1 parts by weight (1 mol equivalent), and the ethylene glycol was changed to 94.9 parts by weight (7.0 mol equivalent) of SANNIX PP-400 (polypropylene glycol, number average molecular weight 400, manufactured by Sanyo Chemical Industry Co., Ltd.). Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 18.7 parts by weight of polypropylene glycol phthalate monoester (A8). The acid dissociation constant (pKa) of polypropylene glycol phthalate monoester (A8) was determined using the above-described method, and the result was 3.9.

[0162] <Manufacturing Example 9>

[0163] In Manufacturing Example 1, the phthalic anhydride was changed to 2.5 parts by weight (1 mol equivalent), and the ethylene glycol was changed to 97.5 parts by weight (5.8 mol equivalent) of PEG1000 (polyethylene glycol, number average molecular weight 1000, manufactured by Sanyo Chemical Industry Co., Ltd.). Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 19.2 parts by weight of polyethylene glycol phthalate monoester (A9). The acid dissociation constant (pKa) of polyethylene glycol phthalate monoester (A9) was determined using the above-described method, and the result was 4.2.

[0164] <Manufacturing Example 10>

[0165] In Manufacturing Example 1, the phthalic anhydride was changed to 13.2 parts by weight (1 mol equivalent), and the ethylene glycol was changed to 86.8 parts by weight (6.2 mol equivalent) of n-decanol. Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 27.2 parts by weight of n-decanol phthalate monoester (A10). The acid dissociation constant (pKa) of n-decanol phthalate monoester (A10) was determined using the above-described method, and the result was 3.9.

[0166] <Manufacturing Example 11>

[0167] In Manufacturing Example 1, the phthalic anhydride was changed to 12.9 parts by weight (1 mol equivalent), and the ethylene glycol was changed to 87.1 parts by weight (5.7 mol equivalent) of 1,10-decanediol. Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 28.1 parts by weight of 1,10-decanediol phthalate monoester (A11). The acid dissociation constant (pKa) of 1,10-decanediol phthalate monoester (A11) was determined using the above-described method, and the result was 4.0.

[0168] <Manufacturing Example 12>

[0169] In Manufacturing Example 1, the phthalic anhydride was changed to 13.1 parts by weight (1 mol equivalent), and the ethylene glycol was changed to 86.9 parts by weight (10.6 mol equivalent) of glycerol. Otherwise, the reaction was carried out in the same manner as in Manufacturing Example 1, yielding 21.3 parts by weight of phthalic acid monoester (A12). The acid dissociation constant (pKa) of phthalic acid monoester (A12) was determined using the above-described method, and the result was 3.7.

[0170] <Manufacturing Example 13>

[0171] In Manufacturing Example 1, phthalic anhydride was replaced with 18.4 parts by weight (1 mol equivalent) of succinic anhydride, and the weight of ethylene glycol was changed to 81.6 parts by weight (7.2 mol equivalent). Otherwise, the process was the same as in Manufacturing Example 1, yielding 29.8 parts by weight of ethylene glycol succinate monoester (A'1). The acid dissociation constant (pKa) of ethylene glycol succinate monoester (A'1) was determined using the above-described method, and the result was 6.5.

[0172] <Manufacturing Example 14>

[0173] In Manufacturing Example 1, phthalic anhydride was replaced with 20.7 parts by weight (1 mol equivalent) of m-sulfobenzoic acid, and the weight of ethylene glycol was changed to 79.3 parts by weight (12.5 mol equivalent). Otherwise, the process was the same as in Manufacturing Example 1, yielding 27.0 parts by weight of ethylene glycol monoester m-sulfobenzoate (A'2). The acid dissociation constant (pKa) of ethylene glycol monoester m-sulfobenzoate (A'2) was determined using the above-described method, and the result was 0.9.

[0174] Table 1 shows the acid dissociation constants (pKa) of the compounds used in each manufacturing example and the resulting carboxylic acids (A).

[0175]

[0176] <Examples 1-17 and Comparative Examples 1-6>

[0177] <Preparation of Electrolyte for Hybrid Electrolytic Capacitors>

[0178] The components were mixed according to the composition (parts by weight) shown in Table 2, and carbonic acid was removed by degassing under reduced pressure as needed to prepare the electrolytes for hybrid electrolytic capacitors of the present invention (Examples) (Y-1) to (Y-17) and the electrolytes for hybrid electrolytic capacitors of comparative examples (Y'-1) to (Y'-6). It should be noted that, regarding the electrolyte for hybrid electrolytic capacitors of the present invention (Y-2), an electrolyte was used after removing carbonic acid generated by the reaction of 1,2,3,4-tetramethylimidazoline onion / methyl carbonate with acid by degassing under reduced pressure. Therefore, the parts by weight after removing carbonic acid are shown in Table 2.

[0179]

[0180] For the electrolytes used in the hybrid electrolytic capacitors obtained in Examples 1-17 and Comparative Examples 1-6, the "spark voltage" before (initial) and after the high-temperature test was evaluated using the following method. The results are shown in Table 3.

[0181] <Evaluation Methods for Spark Voltage>

[0182] In the electrolyte for hybrid electrolytic capacitors, a surface layer of 5cm is formed.2 The dielectric layer consists of an anode foil (aluminum foil that has undergone chemical conversion, manufactured by Nippon Electric Industrial Co., Ltd., 115HD-658Vf) and a cathode foil (5cm). 2 A flat aluminum foil was placed opposite the sample, and a constant voltage / constant current DC power supply (manufactured by Takasago Manufacturing Co., Ltd., GP0650-05R) was used to apply a load (2mA) at 85°C, and the voltage was measured. A graph was plotted with time on the horizontal axis and voltage on the vertical axis, and the voltage rise curve over time was observed. The voltage at the moment when the rise curve first deforms due to a spark or flash is taken as the spark voltage. The higher the spark voltage, the higher the withstand voltage.

[0183] <Evaluation Method for Spark Voltage After High Temperature Test>

[0184] The electrolytes used in the hybrid electrolytic capacitors obtained in Examples 1-17 and Comparative Examples 1-6 were sealed in a closed container and placed in a constant temperature bath set at 125°C for 500 hours. Afterwards, the spark voltage of each hybrid electrolytic capacitor electrolyte was evaluated using the method described above. It should be noted that in Comparative Example 3, the voltage could not be increased during the spark voltage evaluation, therefore the spark voltage could not be measured.

[0185]

[0186] <Fabrication of Hybrid Electrolytic Capacitors>

[0187] Electrode tabs are connected to an anode foil (chemically converted aluminum foil: manufactured by Nippon Electric Industrial Co., Ltd., 115HD-658Vf) and a cathode foil (unchemically converted aluminum foil: manufactured by Nippon Electric Industrial Co., Ltd., 30CB) with a dielectric layer on their surface, and they are placed opposite each other with kraft paper as a separator to obtain an element. In order to repair the cut surface and the defect, the above element is subjected to repair chemical conversion in an ammonium borate aqueous solution at a voltage of 500V to obtain a capacitor element (theoretical capacitance: 10.0μF).

[0188] Next, a PEDOT / PSS aqueous dispersion (containing a polymer with 3,4-ethylenedioxythiophene as a monomer and polystyrene sulfonic acid) (Heraeus, Clevios PH500) was vacuum impregnated into the capacitor element (vacuum degree: 20 mmHg) for 1 minute, and then dried at 150°C for 30 minutes, thereby obtaining a capacitor element with a solid electrolyte (C) layer formed on the surface of the dielectric layer.

[0189] Next, the electrolyte of the hybrid electrolytic capacitors obtained in Examples 1-17 and Comparative Examples 1-6 was vacuum impregnated (vacuum degree: 20 mmHg) for 1 minute at 50°C in a capacitor element in which a layer of solid electrolyte (C) was formed on the surface of the dielectric layer.

[0190] Finally, a capacitor element having a solid electrolyte layer and impregnated with the electrolyte for a hybrid electrolytic capacitor was housed in a case and riveted. A load was applied at 85 °C by a constant voltage / constant current DC power supply device (manufactured by Takasago Seisakusho Co., Ltd., GP0650-05R) by the constant current method (2 mA) until 35 V, and a hybrid electrolytic capacitor was obtained.

[0191] For the obtained hybrid electrolytic capacitor, “ESR” and “capacitance” before (initial) and after the high-temperature test were evaluated by the following methods. In addition, 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 4. Note that in Comparative Example 3, it was broken during aging, and a hybrid electrolytic capacitor could not be manufactured, so neither ESR nor capacitance could be measured.

[0192] <Method for evaluating ESR>

[0193] 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).

[0194] The lower the ESR value, the more excellent the operating stability of the capacitor.

[0195] <Method for evaluating capacitance>

[0196] 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).

[0197] <Evaluation of ESR and capacitance after high-temperature test>

[0198] The hybrid electrolytic capacitor was placed in a thermostat set at 125 °C for 500 hours. After that, for each hybrid electrolytic capacitor, ESR and capacitance were evaluated by the above methods.

[0199] <Method for calculating capacitance retention rate and ESR retention rate>

[0200] The capacitance retention rate and ESR retention rate were calculated by the following formulas, respectively.

[0201] Capacitance retention rate (%) = (capacitance after high-temperature test) × 100 / (initial capacitance)

[0202] ESR retention rate (%) = (ESR value after high-temperature test) × 100 / (initial ESR value)

[0203]

[0204] The electrolytes for hybrid electrolytic capacitors in Examples 1-17 all exhibited high withstand voltage after initial and high-temperature testing. Furthermore, the hybrid electrolytic capacitors using the electrolytes from Examples 1-17 showed good initial characteristics (capacitance and ESR), and maintained good capacitance and ESR even after high-temperature testing.

[0205] On the other hand, in Comparative Examples 1 and 2, carboxylic acid (A) was not included, but a pKa exceeding 4.5 (A'1) was used. Therefore, the effect of inhibiting the oxidative degradation of conductive polymers became insufficient, resulting in a significant deterioration in the capacitance and ESR of the hybrid electrolytic capacitor after the high-temperature test. In Comparative Example 3, carboxylic acid (A) was not included, but a pKa less than 1.0 (A'2) was used. Therefore, the oxide film on the anode could not be repaired, the spark voltage evaluation failed, and the capacitor cracked during aging, making it impossible to manufacture a hybrid electrolytic capacitor. Comparative Examples 4 and 5 did not contain carboxylic acid (A) but used acetylsalicylic acid (pKa=4.7) or azelaic acid (pKa=6.7) with a pKa exceeding 4.5. Therefore, the effect of inhibiting the oxidative degradation of conductive polymers became insufficient, resulting in a significant deterioration in the capacitance and ESR after the high-temperature test. Comparative Example 6 did not contain carboxylic acid (A) but used phthalic acid, therefore the spark voltage (withstand voltage) was insufficient.

[0206] Industrial applicability

[0207] The hybrid electrolytic capacitor using the electrolyte of the present invention suppresses the rise of ESR in high-temperature environments, and is therefore suitable for use as a component in electrical and electronic products that can handle high current.

[0208] The electrolyte for hybrid electrolytic capacitors of the present invention is suitable as an electrolyte for hybrid electrolytic capacitors used in mobile applications such as laptops, especially automotive applications, where the capacitors are easily affected by external temperature and tend to reach high temperatures during operation.

Claims

1. An electrolyte for a hybrid electrolytic capacitor, comprising an aromatic carboxylic acid (A) having two or more carbon atoms, wherein... The acid dissociation constant pKa of the carboxylic acid (A), determined by the following method, is 1.0–4.

5. Determination method: At 25°C, 0.1 mol / L methanolic potassium hydroxide solution was added dropwise to a solution consisting of 1 part by weight of carboxylic acid (A) and 99 parts by weight of methanol. The point with the smallest amount of added solution in the inflection point of the obtained titration curve was taken as the neutralization point. The pH at half the amount of added solution at the neutralization point was taken as the acid dissociation constant pKa of carboxylic acid (A).

2. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein, The carboxylic acid (A) has at least one bond selected from the group consisting of ester bond, amide bond, imide bond, ether bond, carbamate bond and urea bond.

3. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein, The carboxylic acid (A) has an ester bond.

4. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein, The content of the carboxylic acid (A) is 50% to 100% by weight based on the total weight of the acid components.

5. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein, It also contains an alcohol (B), wherein the weight ratio of the alcohol (B) to the carboxylic acid (A) is 1 to 200.

6. The electrolyte for a hybrid electrolytic capacitor according to claim 1, wherein, The carboxylic acid (A) contains the carboxylic acid represented by general formula (1). [Chemistry 1] ， In general formula (1), R 1 The residue is the residue after removing a hydroxyl group from a monohydric alcohol with or without a substituent, the residue after removing one hydroxyl group from an alkylene glycol with 2 to 10 carbon atoms, the residue after removing one hydroxyl group from a polyalkylene glycol with 2 to 6 carbon atoms, or the residue after removing one hydroxyl group from glycerol; n represents an integer from 1 to 5.

7. A hybrid electrolytic capacitor comprising a capacitor element having 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, wherein, The capacitor element is impregnated with the electrolyte for a hybrid electrolytic capacitor as described in any one of claims 1 to 6, and the layer of the solid electrolyte (C) comprises a conductive polymer.

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