Electrolyte for electrolytic capacitor and electrolytic capacitor

Abstract

To provide an electrolytic solution for an electrolytic capacitor that is capable of maintaining high performance over a long period of time even in severe environments, and an electrolytic capacitor using this electrolytic solution.SOLUTION: There is provided an electrolytic solution for an electrolytic capacitor, the electrolytic capacitor including: a capacitor element having an anode foil that has a dielectric oxide film layer on a surface thereof, a cathode foil, and a solid electrolyte layer; and an electrolytic solution impregnated into the capacitor element. The electrolytic solution comprises an organic solvent containing the following compound (a) and / or (b): (a) an aromatic carboxylic acid having a sulfo group and a hydroxy group, and a boron compound; and (b) a composite compound of an aromatic carboxylic acid having a sulfo group and a hydroxy group, and a boron compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to an electrolytic solution for an electrolytic capacitor capable of maintaining high performance such as a low ESR over a long period even under harsh environments, and an electrolytic capacitor using the same electrolytic solution.

Background Art

[0002] In recent years, in AV equipment, in-vehicle electrical equipment, etc., the demand for higher reliability has been increasing. Therefore, even in electrolytic capacitors used therein, it has become necessary to improve performance such as small size, large capacitance, and equivalent series resistance (hereinafter also referred to as ESR) in the high-frequency region.

[0003] In particular, with the increase in the operating frequency of electronic devices, there has been a demand for large-capacitance electrolytic capacitors having excellent equivalent series resistance (hereinafter referred to as ESR) characteristics in the high-frequency region. Recently, in order to reduce the ESR in such a high-frequency region, electrolytic capacitors provided with a solid electrolyte such as a conductive polymer having a higher electrical conductivity than a conventional driving electrolytic solution as an electrolyte or a solid electrolyte and an electrolytic solution have been studied and commercialized.

[0004] Specifically, an electrolytic capacitor containing an electrolytic solution composed of an organic solvent such as γ-butyrolactone, γ-valerolactone, ethylene glycol, etc., together with a solid electrolyte composed of a conductive polymer such as polypyrrole, polythiophene, polyaniline, etc., and ammonium salts, amine salts such as phthalic acid, maleic acid, adipic acid, salicylic acid, etc., and ammonium and amine salts of borodisalicylate which is a composite compound of salicylic acid and boric acid is used. Such an electrolytic capacitor is known as an electrolytic capacitor having high characteristics because it has a large capacitance and a small leakage current (see Patent Documents 1 to 3).

[0005] In addition, Patent Document 4 discloses an electrolytic capacitor including a solid electrolyte layer and an electrolytic solution. The solid electrolyte layer contains a π-conjugated conductive polymer and a first sulfonic acid, and the electrolytic solution contains a solvent and an acid component containing a second sulfonic acid. It is disclosed that the acid component of this electrolytic capacitor may contain a third component such as a carboxylic acid, boric acid, or phosphonic acid together with the second sulfonic acid in order to suppress corrosion of the electrode and stabilize the ESR, and it is described that a carboxylic acid is preferable as this third component.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] In recent years, in electrolytic capacitors used in in-vehicle electrical equipment and the like, characteristics capable of maintaining high performance such as a low ESR over a long period of time in a harsh high-temperature environment where the maximum operating temperature is 85 to 150°C have been demanded. In particular, the present invention aims to provide an electrolytic solution for an electrolytic capacitor that can maintain a low ESR over a long period of time even in a harsh high-temperature environment where the maximum operating temperature is 85 to 150°C, such as in in-vehicle AV equipment and electrical equipment, and an electrolytic capacitor using this electrolytic solution.

Means for Solving the Problems

[0008] As a result of various studies, the inventors of the present invention have found that an electrolytic capacitor including a solid electrolyte layer and an electrolytic solution can achieve the above object of maintaining a low ESR even in a harsh high-temperature environment when the electrolytic solution contains the following compound (a) and / or (b). (a) An aromatic carboxylic acid having a sulfo group and a hydroxy group, and a boron compound. (b) A composite compound of an aromatic carboxylic acid having a sulfo group and a hydroxy group and a boron compound. On the other hand, even when an electrolytic solution contains an aromatic carboxylic acid having a sulfo group and a hydroxy group, an electrolytic solution containing a carboxylic acid compound instead of the boron compound, or even when an electrolytic solution contains a boron compound, and contains an aromatic carboxylic acid having only a sulfo group without a hydroxy group instead of the aromatic carboxylic acid having a sulfo group and a hydroxy group, it is unexpected that the above results are obtained because the above object is hardly achieved.

[0009] The present invention is based on the above findings and has the following aspects. (1) An electrolytic solution for an electrolytic capacitor, comprising an anode foil having a dielectric oxide film layer on a surface thereof, a cathode foil, and a capacitor element having a solid electrolyte layer, and an electrolytic solution impregnated in the capacitor element, wherein the electrolytic solution is composed of an organic solvent containing the following compound (a) and / or (b). An electrolytic solution for an electrolytic capacitor characterized by this. (a) An aromatic carboxylic acid having a sulfo group and a hydroxy group, and a boron compound (b) A composite compound of an aromatic carboxylic acid having a sulfo group and a hydroxy group and a boron compound

[0010] (2) The electrolytic solution for an electrolytic capacitor according to (1) above, wherein the aromatic carboxylic acid having a sulfo group and a hydroxy group is 5-sulfosalicylic acid. (3) The electrolytic solution for an electrolytic capacitor according to (1) or (2) above, wherein the boron compound is boric acid. (4) Further, an electrolytic solution for an electrolytic capacitor according to any one of (1) to (3) above, containing ammonia or a primary to quaternary amine. (5) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (4) above, wherein the organic solvent is polyalkylene glycol, γ-butyrolactone, γ-valerolactone, ethylene glycol, diethylene glycol, triethylene glycol or benzyl alcohol.

[0011] (6) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (5) above, wherein the content of the aromatic carboxylic acid having a sulfo group and a hydroxy group is 0.1 part by mass or more. (7) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (6) above, wherein the content of the boron compound is 0.1 mol or more per 1 mol of the aromatic carboxylic acid having a sulfo group and a hydroxy group. (8) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (7) above, wherein the content of the composite compound of the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound is 0.05 part by mass or more. (9) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (8) above, having a water content of 0.5% by mass or less. (10) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (9) above, having a pH of 2 to 6. (11) Further, an electrolytic solution for an electrolytic capacitor according to any one of (1) to (10) above, containing an additive composed of a nitro compound.

[0012] (12) The electrolytic solution for an electrolytic capacitor according to any one of (1) to (11) above, wherein the solid electrolyte layer is a layer of polythiophene, polypyrrole, polyaniline or a derivative thereof. (13) An electrolytic capacitor using the electrolytic solution according to any one of (1) to (12) above.

Advantages of the Invention

[0013] According to the electrolytic solution of the present invention, an electrolytic solution for an electrolytic capacitor can be provided that can maintain a large capacitance and a low ESR over a long period even in a harsh high-temperature environment where the maximum operating temperature is 85 to 150°C.

Embodiments for Carrying Out the Invention

[0014] <Electrolytic Capacitor> The electrolytic solution of the present invention is used in an electrolytic capacitor having an anode and a cathode having a dielectric oxide film layer on the surface, a capacitor element having a solid electrolyte, and an electrolytic solution impregnated in the capacitor element. The solid electrolyte used in the present invention is a conductive polymer doped with a dopant component. As the conductive polymer, polypyrrole, polythiophene, polyaniline, or their derivatives are used.

[0015] The solid electrolyte layer used in the present invention can be obtained by chemically oxidizing and polymerizing or electrolytically oxidizing and polymerizing the monomer of the conductive polymer in the presence of the above dopant component. Alternatively, it can be obtained by bringing into contact a dispersion or a solution in which the conductive polymer formed in fine particle form by chemical oxidation polymerization is dispersed or dissolved in a solvent such as water. Further, in the above chemical oxidation polymerization or electrolytic oxidation polymerization, a part or all of the above dopant component and the monomer of the conductive polymer may be replaced with a monomer having a functional group capable of causing chemical oxidation doping.

[0016] The monomers of the conductive polymer specifically include 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, propyl-3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, methyl-3,4-propylenedioxythiophene, ethyl-3,4-propylenedioxythiophene, propyl-3,4-propylenedioxythiophene, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, ethyl-3,4-ethylenedioxythiophene, propyl-3,4-ethylenedioxythiophene, 3,4-propylenedioxythiophene, methyl-3,4-propylenedioxythiophene, ethyl-3,4-propylenedioxythiophene, propyl-3,4-propylenedioxythiophene, 3,4-ethylenedithiotiophene, methyl-3,4-ethylenedithiotiophene, ethyl-3,4-ethylenedithiotiophene, propyl-3,4-ethylenedithiotiophene, 3,4-propylenedithiotiophene, methyl-3,4-propylenedithiotiophene, ethyl-3,4-propylenedithiotiophene, propyl-3,4-propylenedithiotiophene, etc. Among them, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, and ethyl-3,4-ethylenedioxythiophene are particularly preferred because of their excellent low ESR of the electrolytic capacitor.

[0017] The above dopant component only needs to have a functional group capable of causing chemical oxidation doping to the polymer, and a sulfate group, a phosphate group, a phosphoric acid group, a carboxyl group, a sulfo group, etc. are preferred. Among these, from the viewpoint of the doping effect, a sulfate group, a carboxyl group, and a sulfo group are more preferred, and a sulfo group is particularly preferred. As the dopant component, specifically, polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, polyethyl acrylate sulfonic acid, polybutyl acrylate sulfonic acid, polyacrylic sulfonic acid, polymethacrylic sulfonic acid, poly(2-acrylamido-2-methylsulfonic acid), polyisoprene sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacrylic sulfonic acid, polymethacrylic carboxylic acid, poly(2-acrylamido-2-methylcarboxylic acid), polyisoprene carboxylic acid, p-toluenesulfonic acid, xylene sulfonic acid, methylnaphthalene sulfonic acid, butylnaphthalene sulfonic acid, or metal salts thereof, etc. may be mentioned. These may be single polymers or copolymers of two or more types. Among these, polystyrene sulfonic acid is particularly preferred.

[0018] Examples of monomers having functional groups capable of undergoing the above chemical acid doping include 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, sodium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, lithium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, potassium 6-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonate, 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonic acid, sodium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonate, potassium 8-(2,3-dihydro-thieno[3,4-b][1,4]dioxin-2-yl)octane-1-sulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-ethyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-propyl-1-propanesulfonate, sodium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, potassium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, ammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, triethylammonium 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate, and the like.

[0019] As the dispersion medium, water or an organic solvent can be used. As the organic solvent, alcohols, ketones, esters, ethers, cellosolves, aromatic hydrocarbons, aliphatic hydrocarbons, etc. can be used.

[0020] The conductive polymer dispersion or solution of the present invention may contain a high-boiling organic solvent. Among the high-boiling organic solvents, a high-boiling organic solvent having a boiling point of 150 to 250 °C is particularly preferable. Specific examples of the high-boiling organic solvent include N-methyl-2-pyrrolidone, dimethyl sulfoxide, γ-butyrolactone, sulfolane, dimethyl sulfone, ethylene glycol, diethylene glycol, triethylene glycol, etc. Among these, ethylene glycol or γ-butyrolactone is more preferable in that it can form a solid electrolyte layer containing a conductive polymer with a uniform surface.

[0021] The content of the organic solvent in the conductive polymer dispersion or solution is preferably 1 to 20% by mass, and particularly preferably 5 to 15% by mass. When the content of the organic solvent is less than 1% by mass, there is a problem that the effect of forming a solid electrolyte layer containing a conductive polymer with a uniform surface is slightly inferior, and when it exceeds 20% by mass, there is a problem that the drying process takes time. In addition, the conductive polymer dispersion or solution may contain a binder resin, a surfactant, and an alkali compound in order to adjust the film-forming property and film strength. The conductive polymer dispersion is one in which the conductive polymer is dispersed in the dispersion medium, and a part of the conductive polymer may be dissolved in the dispersion medium.

[0022] As the anode and cathode used in the electrolytic capacitor, valve metal is preferable. Specifically, one selected from the group consisting of aluminum, tantalum, niobium, and titanium can be mentioned, and among them, aluminum is preferable. The valve metal is usually used in the form of a sintered body or a foil. The electrolytic capacitor can be of a chip type or a wound type depending on the shapes of the anode and cathode used.

[0023] In the electrolytic capacitor of the present invention, the solid electrolyte may be formed by bringing the capacitor element into contact with a dispersion or solution of a conductive polymer by means such as immersion, and drying the solvent, or by immersing the capacitor element in a monomer solution of the conductive polymer and then forming it by chemical polymerization or electrolytic polymerization.

[0024] (Electrolyte solution) The electrolyte solution in the present invention contains an electrolyte and an organic solvent, and the electrolyte contains the following (a) and / or (b). (a) An aromatic carboxylic acid having a sulfo group and a hydroxy group, and a boron compound (b) A composite compound of an aromatic carboxylic acid having a sulfo group and a hydroxy group and a boron compound. Examples of the aromatic carboxylic acid having a sulfo group and a hydroxy group preferably include compounds having a sulfo group and a hydroxy group in the aromatic ring of an aromatic carboxylic acid having 1 to 4, more preferably 1 or 2, and particularly preferably 1 ring structure. The number of sulfo groups and hydroxy groups in the aromatic ring is each independently preferably 1 to 4, more preferably 1 or 2, and particularly preferably 1.

[0025] Preferable specific examples of the aromatic carboxylic acid having a sulfo group and a hydroxy group include 5-sulfosalicylic acid, 4-sulfosalicylic acid, 3-sulfosalicylic acid, 6-sulfosalicylic acid, 3-hydroxy-4-sulfobenzoic acid, 3-hydroxy-5-sulfobenzoic acid, 2,4-dihydroxy-5-sulfobenzoic acid, 2-hydroxy-4-methyl-5-sulfobenzoic acid, 2-hydroxy-4-methoxy-5-sulfobenzoic acid, 3-hydroxy-7-sulfo-2-naphthalenecarboxylic acid, 3-hydroxy-6-sulfo-2-naphthalenecarboxylic acid, 3-hydroxy-5-sulfo-2-naphthalenecarboxylic acid, 3-hydroxy-8-sulfo-2-naphthalenecarboxylic acid, 1-hydroxy-4-sulfo-2-naphthalenecarboxylic acid, 1-hydroxy-6-sulfo-2-naphthalenecarboxylic acid, 1-hydroxy-7-sulfo-2-naphthalenecarboxylic acid, 2-hydroxy-4-sulfo-1-naphthalenecarboxylic acid, 2-hydroxy-6-sulfo-1-naphthalenecarboxylic acid, 2-hydroxy-7-sulfo-1-naphthalenecarboxylic acid, and the like. Among them, 5-sulfosalicylic acid is preferable.

[0026] Examples of the boron compound contained in the electrolytic solution in the present invention include boric acid, boronic acids (such as methylboronic acid, ethylboronic acid, butylboronic acid, isobutylboronic acid, cyclopentylboronic acid, cyclohexylboronic acid, phenylboronic acid, 4-tert-butylphenylboronic acid, 4-ethoxyphenylboronic acid, 2-naphthaleneboronic acid, 2-anthraceneboronic acid, etc.), borate esters (such as trimethyl borate, triethyl borate, tripropyl borate, tributyl borate, triphenyl borate, etc.), boronic esters (such as allylboronic acid pinacol, etc.). Among them, boric acid having excellent properties is preferable.

[0027] In addition to the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound, the electrolytic solution in the present invention preferably contains ammonia, or a primary to quaternary amine, or an amidine compound. As such a primary to quaternary amine, a tertiary amine is preferable. Examples of the tertiary amine include trialkylamines (such as trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl n-propylamine, dimethyl isopropylamine, methylethyl n-propylamine, methylethyl isopropylamine, diethyl n-propylamine, diethyl isopropylamine, tri n-propylamine, triisopropylamine, tri n-butylamine, tri tert-butylamine, etc.), and phenyl group-containing amines (such as dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.).

[0028] Among them, it is a trialkylamine, and more preferably, it contains one or more selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine.

[0029] As the organic solvent used in the electrolytic solution, a protic polar solvent or an aprotic polar solvent can be used, and it can be used alone or in a mixture of two or more. Examples of the protic polar solvent include monohydric alcohols (such as methanol, ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols, and oxyalcohol compounds (such as ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.), polyalkylene glycols (such as polyethylene glycol, polypropylene glycol, etc.).

[0030] Examples of aprotic polar solvents include γ-butyrolactone, γ-valerolactone, amide solvents (N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphoric triamide, etc.), sulfolane solvents (sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc.), chain sulfone solvents (dimethyl sulfone, ethyl methyl sulfone, ethyl isopropyl sulfone), cyclic amide solvents (N-methyl-2-pyrrolidone, etc.), carbonates (ethylene carbonate, propylene carbonate, isobutylene carbonate, etc.), nitrile solvents (acetonitrile, etc.), sulfoxide solvents (dimethyl sulfoxide, etc.), 2-imidazolidinone solvents [1,3-dialkyl-2-imidazolidinone (1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di(n-propyl)-2-imidazolidinone, etc.), 1,3,4-trialkyl-2-imidazolidinone (1,3,4-trimethyl-2-imidazolidinone, etc.)], and the like.

[0031] Among the above, the organic solvent used in the electrolytic solution is preferably at least one selected from the group consisting of sulfolane, γ-butyrolactone, propylene carbonate, ethylene carbonate, ethylene glycol, diethylene glycol, triethylene glycol, benzyl alcohol, and glycerin because the capacitance of the capacitor is high. In particular, γ-butyrolactone, ethylene glycol, or polyethylene glycol is preferred.

[0032] The content of the aromatic carboxylic acid having a sulfo group and a hydroxy group in the electrolytic solution of the present invention is preferably 0.1 to 40% by mass, more preferably 1 to 20% by mass, and particularly preferably 3 to 10% by mass. When the content is less than 0.1% by mass, it is difficult to obtain sufficient electrical characteristics. On the other hand, when the content exceeds 40% by mass, the maintenance rate of low ESR deteriorates in a high-temperature environment. In addition, the content of the boron compound is preferably at a ratio of 0.1 mol or more, more preferably 0.25 to 1 mol, and particularly preferably 0.4 to 0.6 mol, per 1 mol of the aromatic carboxylic acid having a sulfo group and a hydroxy group. When the content is less than 0.1 mol per 1 mol of the carboxylic acid, it is difficult to obtain sufficient electrical properties. On the other hand, when it exceeds 1 mol, it is difficult to obtain a high maintenance rate of low ESR in a high-temperature environment.

[0033] The electrolytic solution of the present invention is produced by simultaneously or sequentially adding an aromatic carboxylic acid having a sulfo group and a hydroxy group, a boron compound, preferably further ammonia or a primary to quaternary amine, so that each has the above-described content, to the above-described organic solvent. When adding these, it can be carried out while stirring and, if necessary, while heating. These stirring and heating can be carried out under appropriate conditions. For example, heating can be carried out at 35 to 120°C.

[0034] In addition, the electrolytic solution of the present invention can also be produced by previously reacting an aromatic carboxylic acid having a sulfo group and a hydroxy group with a boron compound and adding the reaction product to the above-described organic solvent, and further by previously reacting an aromatic carboxylic acid having a sulfo group and a hydroxy group with a boron compound and ammonia or a primary to quaternary amine and adding the reaction product to the above-described organic solvent.

[0035] When the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound are added without previously reacting them, or in any of the cases where they are previously reacted and then added, since the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound are reactive with each other, the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound react with each other, and a composite compound formed by the reaction of the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound can be formed in the electrolytic solution. For example, when the aromatic carboxylic acid has a hydroxy group and a carboxyl group at adjacent positions on the aromatic ring, and the boron compound is boric acid, when the two react, a composite compound having an anion structure represented by the following formula is at least temporarily or partially formed in the obtained electrolytic solution.

[0036]

Chemical formula

[0037] When the electrolytic solution of the present invention contains a composite compound of an aromatic carboxylic acid having a sulfo group and a hydroxy group and a boron compound, the content of such a composite compound is preferably 0.05 to 40% by mass, more preferably 0.5 to 20% by mass, and particularly preferably 1.5 to 10% by mass. When the content is less than 0.05% by mass, it is difficult to obtain sufficient electrical characteristics. On the other hand, when it exceeds 40% by mass, the maintenance rate of low ESR deteriorates under a high-temperature environment.

[0038] In the electrolytic solution of the present invention, when the water content contained therein is preferably 1% by mass or less, excellent characteristics can be obtained in that the internal pressure rise can be suppressed even when heat of 200 °C or higher is applied, such as in the case of reflow soldering. The contained water content is more preferably 0.5% by mass or less, and particularly preferably 0.3% by mass or less. Furthermore, it has been found that the electrolytic solution of the present invention has excellent characteristics in that a low ESR can be maintained when the pH thereof is preferably 2 to 6. The reason is not clear, but the pH is more preferably 2.5 to 5.5, and particularly preferably 3 to 5.

[0039] <Other contained substances> In the electrolytic solution of the present invention, substances other than those described above can be added for the purpose of improving characteristics such as the life performance and resistance performance of the electrolytic capacitor. Such additives are not particularly limited. For example, the following can be mentioned. Phosphorus-based compounds (such as phosphate esters), polysaccharides (such as mannitol, sorbitol), complex compounds of boric acid and polysaccharides (such as mannitol, sorbitol), complex compounds of boric acid and polyhydric alcohols (such as ethylene glycol, glycerin), nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, p-nitrobenzyl alcohol, etc.) can be mentioned.

[0040] In addition, an antioxidant can be added to the electrolytic solution, and examples of the antioxidant include phenolic compounds, amine compounds, azo compounds, silane compounds, quinone compounds, carboxylic acid compounds, etc.

Examples

[0041] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to these examples, and modifications within the scope of the present invention are possible. (Preparation of conductive polymer dispersion) 12.2 g of a 20% by mass aqueous solution of polystyrene sulfonic acid (weight average molecular weight: 50,000), which is a dopant component, was mixed with 187.5 g of water and stirred for 10 minutes. Next, 2.04 g of 3,4-ethylenedioxythiophene as a monomer was added and stirred for another 15 minutes to prepare a monomer solution. The obtained monomer solution exhibited a pale yellow color.

[0042] The amount of polystyrene sulfonic acid contained in the monomer solution was 119 parts by mass with respect to 100 parts by mass of 3,4-ethylenedioxythiophene contained in the monomer solution. While stirring the monomer solution, 0.012 g of iron(III) sulfate as an oxidizing agent and 4.46 g of ammonium persulfate were added dropwise, and the mixture was stirred at room temperature for 15 hours to perform chemical oxidative polymerization. At this time, the monomer solution changed from light yellow to dark blue. Next, 50.1 g of an amphoteric ion exchange resin (trade name: MB-1, manufactured by Organo Corporation, ion exchange form: -H, -OH) was added to the obtained reaction solution and stirred for 2 hours. As a result, the pH of the reaction solution changed from 1.15 to 1.83. Thereby, a conductive polymer dispersion containing poly(3,4-ethylenedioxythiophene) doped with 1.3% by mass of polystyrene sulfonic acid was prepared.

[0043] (Fabrication of Capacitor Element) After the surface was subjected to an etching treatment, a chemical conversion treatment was performed to form an oxide film layer, and an aluminum anode foil with lead terminals attached and an aluminum cathode foil with the surface etched and lead terminals attached were wound through a separator (thickness 0.05 mm) made of cellulose fiber to fabricate a capacitor element.

[0044] (Example 1) The capacitor element obtained above was immersed in the above conductive polymer dispersion, and after pulling up the capacitor element, the solvent was evaporated to form a solid electrolyte layer made of a conductive polymer. Next, each component in the amount described in Table 1 was mixed while stirring at 50 °C to produce an electrolytic solution, and this electrolytic solution was impregnated into this capacitor element. Next, the capacitor element was inserted into a bottomed cylindrical aluminum case, a sealing rubber was attached to the open end portion, and it was sealed by curling. Thereafter, an aging treatment was performed under the condition of 105 °C to fabricate an aluminum electrolytic capacitor. The rated voltage of this electrolytic capacitor was 35 V, and the outer dimensions after sealing were cylindrical with a diameter of 10 mm and a height of 10 mm.

[0045] (Examples 2 to 7, Comparative Examples 1 to 4) Electrolytic capacitors of Examples 2 to 7 and Comparative Examples 1 to 6 were produced in the same manner as in Example 1, except that an electrolytic solution obtained by mixing each component in the amounts shown in Table 1 while stirring at 95 °C was used. Table 1 shows the pH and water content of the electrolytic solutions used in each of the electrolytic capacitors of Examples 1 to 7 and Comparative Examples 1 to 6.

[0046] (Capacitor Test) The produced electrolytic capacitors were subjected to a load test at the rated voltage in an atmosphere of 150 °C, and the ESR (100 kHz) was measured. The results are shown in Table 2.

[0047]

Table 1

[0048]

Table 2

[0049] When the electrolytic solutions of the above Examples 1 to 7 and Comparative Examples 1 to 4 were analyzed by liquid chromatography-mass spectrometry (LC-MS), the compounds detected in each electrolytic solution were as follows. In the following, 5-sulfosalicylic acid is denoted as 5-Ssa, 4-sulfosalicylic acid as 4-Ssa, sulfophthalic acid as Spa, salicylic acid as Sa, phthalic acid as Pa, and 4-nitrophenol as Np, respectively. <lc-ms> Column: Silica C18M 4E, manufactured by Showa Denko KK Mobile phase: 5 mM ammonium formate aqueous solution / acetonitrile = 80 / 20 (V / V) Detector: ACQUITY QDa detector, manufactured by Waters Japan KK Ionization method: ESI Negative

[0050] Electrolyte of Example 1 m / z: 217 (5-Ssa - H) - , 221 (2(5-Ssa) + B(OH)3 - 3H2O - 2H) 2- , 443 (2(5-Ssa) + B(OH)3 - 3H2O - H) - Electrolyte of Example 2 m / z: 217 (5-Ssa - H) - , 221 (2(5-Ssa) + B(OH)3 - 3H2O - 2H) 2- , 443 (2(5-Ssa) + B(OH)3 - 3H2O - H) - Electrolyte of Example 3 m / z: 217 (5-Ssa - H) - , 221 (2(5-Ssa) + B(OH)3 - 3H2O - 2H) 2- , 443 (2(5-Ssa) + B(OH)3 - 3H2O - H) - Electrolyte of Example 4 m / z: 217 (5-Ssa - H) - , 221 (2(5-Ssa) + B(OH)3 - 3H2O - 2H) 2- , 443 (2(5-Ssa) + B(OH)3 - 3H2O - H) - Electrolyte of Example 5 m / z: 138 (Np - H) - , 217 (5-Ssa - H) - , 221 (2(5-Ssa) + B(OH)3 - 3H2O - 2H) 2- , 443 (2(5-Ssa) + B(OH)3 - 3H2O - H) - Electrolyte of Example 6 m / z: 217 (4‐Ssa - H) - ,221(2(4-Ssa) + B(OH)3- 3H2O - 2H) 2- ,443(2(4-Ssa) + B(OH)3- 3H2O - H) -

[0051] Electrolyte of Comparative Example 1 m / z: 217 (5‐Ssa - H) - Electrolyte of Comparative Example 2 No detection Electrolyte of Comparative Example 3 m / z: 217 (5‐Ssa - H) - Electrolyte of Comparative Example 4 m / z: 137(Sa - H) - ,283(2Sa + B(OH)3- 3H2O - H) - Electrolyte of Comparative Example 5 m / z: 245 (Spa - H) - Electrolyte of Comparative Example 6 m / z: 165(Pa - H) - ,217(5‐Ssa - H) -

[0052] As can be seen from Tables 1 and 2, the electrolytic capacitors of Examples 1 to 7 are superior to the electrolytic capacitors of Comparative Examples 1 to 3 in that they can maintain a low ESR even at a high temperature of 150° C. On the other hand, it can be seen that none of Comparative Example 4, which used an aromatic carboxylic acid without a sulfo group instead of an aromatic carboxylic acid having a sulfo group and a hydroxy group, Comparative Example 5, which used 4-sulfophthalic acid without a hydroxy group, and Comparative Example 6, which used phthalic acid instead of a boron compound, were able to maintain a low ESR. Furthermore, the above LC-MS results suggest that in the electrolyte solutions of Examples 1 to 7, at least a portion of the aromatic carboxylic acid having a sulfo group and a hydroxy group and the boron compound contained in the electrolyte solution form a complex compound.

Industrial Applicability

[0053] The electrolytic solution of the present invention is widely used as an electrolytic solution in electrolytic capacitors that are frequently used in power supplies for various consumer devices such as AV devices, mobile phones, and notebook computers, in-vehicle electrical equipment, and industrial equipment. In addition, the entire contents of the specification, claims, drawings, and abstract of Japanese Patent Application No. 2019-109812 filed on June 12, 2019 are hereby incorporated by reference and made a part of the disclosure of the specification of the present invention.

Claims

1. An electrolytic solution for an electrolytic capacitor, comprising: a capacitor element having an anode foil, a cathode foil, and a solid electrolyte layer on its surface; and an electrolytic solution impregnated in the capacitor element. The electrolytic solution is composed of an organic solvent containing the following compound (a) and / or (b), and the content of the following boric acid is 0.1 to 1 mol with respect to 1 mol of the following 5-sulfosalicylic acid or 4-sulfosalicylic acid. An electrolytic solution for an electrolytic capacitor, characterized in that. (a) 5-sulfosalicylic acid or 4-sulfosalicylic acid, and boric acid (b) A composite compound of 5-sulfosalicylic acid or 4-sulfosalicylic acid, and boric acid

2. The electrolytic solution for an electrolytic capacitor according to claim 1, further containing ammonia or a primary to quaternary amine.

3. The electrolytic solution for an electrolytic capacitor according to claim 1 or 2, wherein the organic solvent is polyalkylene glycol, γ-butyrolactone, γ-valerolactone, ethylene glycol, diethylene glycol, triethylene glycol, or benzyl alcohol.

4. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 3, wherein the content of the 5-sulfosalicylic acid or 4-sulfosalicylic acid is 0.1 part by mass or more.

5. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 4, wherein the content of the boric acid is 0.1 mol or more with respect to 1 mol of the 5-sulfosalicylic acid or 4-sulfosalicylic acid.

6. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 5, wherein the content of the composite compound of the 5-sulfosalicylic acid or 4-sulfosalicylic acid and boric acid is 0.05 part by mass or more.

7. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 6, having a water content of 0.5% by mass or less.

8. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 7, having a pH of 2 to 6.

9. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 8, further containing an additive composed of a nitro compound.

10. The electrolytic solution for an electrolytic capacitor according to any one of claims 1 to 9, wherein the solid electrolyte layer is a layer of polythiophene, polypyrrole, polyaniline, or a derivative thereof.

11. An electrolytic capacitor using the electrolytic solution according to any one of claims 1 to 10.

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