Electrolyte solution for use in vehicle-mounted hybrid-type electrolytic capacitor

Abstract

The present invention addresses the problem of providing: an electrolyte solution that is for use in a vehicle-mounted hybrid-type electrolytic capacitor which is installed in vehicle-mounted AV equipment or electrical equipment, and that is capable of maintaining low ESR at high capacitance and in high frequencies in the long term, even in harsh high-temperature environments; and a vehicle-mounted hybrid-type electrolytic capacitor that is produced using the electrolyte solution.　Provided is an electrolyte solution for use in a vehicle-mounted hybrid-type electrolytic capacitor, wherein: the vehicle-mounted hybrid-type electrolytic capacitor has, inside an outer container, a capacitor element which has a solid electrolyte layer and the electrolyte solution which is impregnated in the capacitor element; the solid electrolyte layer contains a solid electrolyte comprising a conductive polymer; the electrolyte solution contains an electrolyte, an aromatic nitro compound, and an organic solvent; the electrolyte is an acid and / or a salt; the salt comprises an acid component and a base component; the aromatic nitro compound does not have, on an aromatic ring thereof, a hydroxyl group, a carboxyl group, or an alkyl group which has an hydroxyl group; and the electrical conductivity of the electrolyte solution at 30°C is 0.05-1.0 mS / cm.

Description

Electrolyte used in automotive hybrid electrolytic capacitors

[0001] The present invention relates to an electrolyte used in high-performance automotive hybrid electrolytic capacitors that can maintain high capacitance and low equivalent series resistance (ESR) in the high-frequency range of 100 Hz to 1 MHz for long periods of time, such as 1000 hours, even in harsh high-temperature environments such as 85 to 150°C, particularly 125 to 150°C, and to an automotive hybrid electrolytic capacitor manufactured using the electrolyte.

[0002] In recent years, there has been an increasing demand for higher reliability in AV equipment and automotive electronics. This necessitates improvements in performance for electrolytic capacitors used in these applications, including miniaturization, increased capacitance, and lower ESR in the high-frequency range.

[0003] In particular, with the increasing frequency of electronic devices, there is a growing demand for high-capacity electrolytic capacitors with excellent ESR characteristics in the high-frequency range. Recently, in order to reduce ESR in such high-frequency ranges, so-called hybrid electrolytic capacitors have been commercialized that use solid electrolytes such as conductive polymers with higher electrical conductivity than conventional drive electrolytes, or a combination of solid electrolytes and liquid electrolytes. Furthermore, for automotive electrolytic capacitors, even better high-temperature characteristics are required.

[0004] Patent Document 1 describes an electrolytic solution for a medium- to high-voltage electrolytic capacitor with excellent resistance to carbon halide cleaning agents, which uses ethylene glycol as the main solvent and contains boric acid and an organic acid or its salt, and nitrobenzamide. Patent Document 2 describes an electrolytic solution for a medium- to high-voltage electrolytic capacitor with excellent resistance to carbon halide cleaning agents, which uses ethylene glycol as the main solvent and contains boric acid and an organic acid or its salt, and nitroacetophenone and / or benzamide. Patent Document 3 describes an electrolytic solution for an electrolytic capacitor with excellent resistance to carbon halide cleaning agents, which uses γ-butyrolactone as the main solvent and contains an organic carboxylic acid or its salt, and a nitro compound having no hydroxyl group and carboxyl group. Patent Document 4 describes an electrolytic solution for a hybrid electrolytic capacitor with excellent high-quality sound of sound, which comprises an electrolytic solution and a conductive polymer, uses lactone and a specific organic ester system as the solvent, and contains p-nitrobenzyl alcohol or p-nitro 0. Patent Document 5 describes an electrolytic solution for a hybrid electrolytic capacitor with excellent high-temperature durability, which comprises an electrolytic solution and a solid electrolyte, and contains polyethylene glycol and nitrophenol, nitroacetophenone, nitrobenzyl alcohol, nitrobenzoic acid, or nitrobenzaldehyde. However, none of these electrolytes can exhibit sufficient performance when used in a high-capacitance in-vehicle hybrid electrolytic capacitor mounted in in-vehicle AV equipment, electrical equipment, etc., which can maintain a high capacitance and a low ESR in the high-frequency region over a long period even in a harsh high-temperature environment.

[0005] Japanese Patent Laid-Open No. 02-015610, Japanese Patent Laid-Open No. 04-188606, Japanese Patent Laid-Open No. 08-222484, Japanese Patent Laid-Open No. 2021-40036, Japanese Patent Laid-Open No. 2024-79211

[0006] The present invention aims to provide an electrolyte for use in hybrid electrolytic capacitors mounted in automotive AV equipment and electrical equipment, which can maintain high capacitance and low ESR in the high frequency range of 100 Hz to 1 MHz for long periods of time, such as 1000 hours, even in harsh high-temperature environments such as 85 to 150°C, particularly 125 to 150°C, and an automotive hybrid electrolytic capacitor manufactured using said electrolyte.

[0007] As a result of various studies, the inventors have found that an electrolyte containing a specific electrolyte and a specific aromatic nitro compound, and having a specific electrical conductivity, can achieve the above objective.

[0008] The present invention is based on the above findings and has the following embodiments: [1] An electrolyte used in an automotive hybrid electrolytic capacitor, wherein the automotive hybrid electrolytic capacitor has a capacitor element having a solid electrolyte layer and the electrolyte impregnated in the capacitor element, all contained in an outer container, the solid electrolyte layer contains a solid electrolyte made of a conductive polymer, the electrolyte has an electrical conductivity of 0.05 to 1.0 mS / cm at 30°C and contains an electrolyte, an aromatic nitro compound, and an organic solvent, the electrolyte is an acid and / or a salt, the salt consists of an acid component and a basic component, and the aromatic nitro compound has one or more selected from the group consisting of an amide group, an alkoxy group, and an acyl group on the aromatic ring, the electrolyte. [2] The electrolyte according to [1] above, wherein the aromatic nitro compound has an amide group on the aromatic ring. [3] The electrolyte according to [1], wherein the aromatic nitro compound contains at least one selected from the group consisting of 2-nitrobenzamide, 3-nitrobenzamide, and 4-nitrobenzamide, 4-nitroanisole, and m-nitroacetophenone. [4] The electrolyte according to [1], wherein the organic solvent contains a glycol compound. [5] The electrolyte according to [1], wherein the electrolyte further contains an antioxidant. [6] The electrolyte according to [1], wherein the acid and / or the acid component contains an aromatic carboxylic acid. [7] The electrolyte according to [1], wherein the acid and / or the acid component contains at least one selected from the group consisting of phthalic acid, benzoic acid, and borodisalicylic acid. [8] The electrolyte according to [1], wherein the amount of water contained in the electrolyte is 0.1% by mass or more and 3% by mass or less. [9] The electrolyte according to [1], wherein the pH of the electrolyte is 2 to 7.

[10] A hybrid electrolytic capacitor for automotive use, comprising a capacitor element having a solid electrolyte layer and an electrolyte impregnated in the capacitor element, within an outer casing, wherein the solid electrolyte layer contains a solid electrolyte made of a conductive polymer doped with a dopant component, and the electrolyte is the electrolyte described in any one of the above items [1] to [9].

[11] The conductive polymer contains polythiophene, the automotive hybrid electrolytic capacitor according to

[10] above.

[12] The dopant component contains polystyrene sulfonic acid, the automotive hybrid electrolytic capacitor according to

[10] above.

[0009] According to the present invention, it is possible to provide an electrolyte for hybrid electrolytic capacitors to be mounted in automotive AV equipment and electrical equipment that can maintain high capacitance and low ESR in the high frequency range of 100 Hz to 1 MHz for a long period of time such as 1000 hours, even in harsh high-temperature environments such as 85 to 150°C, particularly 125 to 150°C, and an automotive hybrid electrolytic capacitor manufactured using the electrolyte.

[0010] <Electrolyte> The electrolyte of the present invention is used in automotive hybrid electrolytic capacitors. A hybrid electrolytic capacitor is an electrolytic capacitor that includes an electrolyte made of a solid conductive polymer and an electrolyte. A preferred automotive hybrid electrolytic capacitor using the electrolyte of the present invention has an anode foil having a dielectric oxide film layer on its surface, a cathode foil, a capacitor element having a solid electrolyte layer made of a conductive polymer doped with a dopant component, and the electrolyte impregnated into the capacitor element, all contained within an outer casing.

[0011] The electrolyte of the present invention contains an electrolyte, an aromatic nitro compound, and an organic solvent. The electrolyte content in the electrolyte is preferably 0.2 to 13% by mass, more preferably 0.4 to 10% by mass, and even more preferably 0.5 to 5% by mass. If the electrolyte content is less than the above range, it becomes difficult to sufficiently increase the electrical conductivity of the electrolyte, making it difficult to obtain a sufficient repair effect on the dielectric oxide film layer of the anode. If the content is higher than the above range, the electrical conductivity of the electrolyte becomes too high, making it easy for the ESR in the high-frequency range of automotive hybrid electrolytic capacitors after high-temperature, long-term loading to increase.

[0012] Furthermore, since the charge, molecular weight, and solubility of electrolytes vary greatly depending on the compounds that make up the electrolyte, it is preferable to define the preferred electrolyte content in the electrolyte solution by the electrical conductivity of the electrolyte solution at 30°C rather than by the mass percentage of the electrolyte in the electrolyte solution. Generally, in order to suppress the decrease in capacitance after high temperature and prolonged loading, a method is employed to increase the electrical conductivity by drastically increasing the concentration of the electrolyte in the electrolyte solution. However, the electrolyte solution of the present invention can suppress the decrease in capacitance after high temperature and prolonged loading without drastically increasing the concentration of the electrolyte solution.

[0013] The content of aromatic nitro compounds in the electrolyte is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less. If the content of aromatic nitro compounds is below the above range, it is difficult to obtain the effect of maintaining a sufficiently low ESR in the automotive hybrid electrolytic capacitor, and if it is higher than the above range, the ESR in the high-frequency range after high-temperature, long-term loading of the automotive hybrid electrolytic capacitor tends to increase.

[0014] Furthermore, the amount of water contained in the electrolyte is preferably 0.1% by mass or more and 3% by mass or less, and more preferably 0.5% by mass or more and 2% by mass or less. If the amount of water contained in the electrolyte is less than the above range, the effect of assisting in the repair of the dielectric oxide film of the anode of the automotive hybrid electrolytic capacitor tends to be insufficient, and if it is higher than the above range, when the automotive hybrid electrolytic capacitor is reflow soldered at 200°C or higher, the internal pressure rise due to water vapor inside the automotive hybrid electrolytic capacitor makes it more susceptible to damage.

[0015] (Electrical Conductivity of Electrolyte) In the case of a general non-hybrid electrolytic capacitor where the electrolyte consists only of an electrolyte, the higher the electrical conductivity of the electrolyte, the larger the capacitance and the higher the ESR in the high-frequency range, but it does not increase significantly after high-temperature, long-term loading. In contrast, in the case of automotive hybrid electrolytic capacitors, if the electrical conductivity of the electrolyte is too high, the capacitance increases, but the ESR, which was low in the high-frequency range, tends to increase after high-temperature, long-term loading. Therefore, the electrical conductivity of the electrolyte at 30°C is preferably 0.1 to 1 mS / cm, more preferably 0.1 to 0.8 mS / cm, and even more preferably 0.2 to 0.5 mS / cm. If the electrical conductivity of the electrolyte at 30°C is below the above range, it becomes difficult to increase and maintain high capacitance in automotive hybrid electrolytic capacitors under high-temperature, long-term environments, and if it is higher than the above range, the ESR in the high-frequency range of automotive hybrid electrolytic capacitors tends to increase. By using the electrolyte of the present invention, automotive hybrid electrolytic capacitors can maintain high capacitance and low ESR in the high-frequency range even under high-temperature, long-duration environments. Although there are various ratings depending on the type of automotive hybrid electrolytic capacitor, for example, an automotive hybrid electrolytic capacitor having a capacitance of 250 μF at 120 Hz and an ESR of 13 mΩ at 100 kHz can suppress the capacitance decrease rate to less than 3% and the ESR increase rate to less than 25% even after exposure to a high-temperature environment of 150°C for 1000 hours.

[0016] (pH of the electrolyte) Furthermore, the pH of the electrolyte is preferably 2 to 7, more preferably 3 to 6.5, and even more preferably 3.5 to 6. If the pH of the electrolyte is within the above range, the automotive hybrid electrolytic capacitor will be able to maintain a low ESR in the high-frequency range over a long period of time in a high-temperature environment.

[0017] [Electrolyte] The electrolyte contained in the electrolyte solution of the present invention preferably contains an acid and / or a salt. The salt is preferably a compound consisting of an acid component and a base component. Organic acids and / or inorganic acids can be used as the acid or acid component.

[0018] The above organic acids may be aromatic and / or aliphatic, and may have any of the following groups: carboxyl group, sulfonyl group, hydroxyl group, thiol group, enol group, etc. Specific examples of aromatic organic acids include aromatic carboxylic acids such as phthalic acid, benzoic acid, salicylic acid, and borodisalicylic acid; aromatic sulfonic acids such as benzenesulfonic acid and p-toluenesulfonic acid; phenols; and aromatic enols such as thiophenol. Specific examples of aliphatic organic acids include tartaric acid, glycolic acid, adipic acid, 2-butyloctanedioic acid, 3-tert-butylhexandioic acid, and 1,10-decanedicarboxylic acid. Among these organic acids, aromatic carboxylic acids are preferred, and among aromatic carboxylic acids, phthalic acid, benzoic acid, and borodisalicylic acid are more preferred.

[0019] Specific examples of inorganic acids include boric acid, boronic acid, phosphoric acid, phosphate monoesters, phosphate diesters, and sulfonic acids.

[0020] Furthermore, the above-mentioned organic acids and inorganic acids may be used individually or in combination of two or more to form composite compounds. Examples of composite compounds include borodisalicylic acid and borodiglycolic acid.

[0021] The acidic component of the salt can be any of the organic and / or inorganic acids mentioned above.

[0022] Examples of the basic component of the salt include ammonia, primary to quaternary amines, and amidine compounds. Among these, ammonia and primary to tertiary amines are preferred, and tertiary amines are particularly preferred. Examples of tertiary amines include trialkylamines (trimethylamine, dimethylethylamine, methyldiethylamine, triethylamine, dimethyl n-propylamine, dimethylisopropylamine, methylethyl n-propylamine, methylethylisopropylamine, diethyl n-propylamine, diethylisopropylamine, tri-n-propylamine, triisopropylamine, tri-n-butylamine, tri-tert-butylamine, etc.) and phenyl group-containing amines (dimethylphenylamine, methylethylphenylamine, diethylphenylamine, etc.).

[0023] Among tertiary amines, trialkylamines are preferred, and among trialkylamines, it is more preferable to include one or more selected from the group consisting of trimethylamine, dimethylethylamine, methyldiethylamine, and triethylamine.

[0024] As for the combination of acid and base components that constitute the above salt, a salt consisting of an acid component consisting of one or more selected from the group consisting of aromatic carboxylic acids, boric acid, phosphoric acid, phosphate monoesters, phosphate diesters, and sulfonic acids, and a base component consisting of primary to quaternary amines is preferred; a salt consisting of an acid component consisting of an aromatic carboxylic acid and a base component consisting of a tertiary amine is more preferred; and a salt consisting of an acid component consisting of one or more selected from the group consisting of phthalic acid, benzoic acid, and borodisalicylic acid, and a base component consisting of trialkylamines is even more preferred.

[0025] Specific examples of the above salts include ammonium salt of benzoic acid, dimethylamine salt of benzoic acid, dimethylethylamine salt of benzoic acid, 1,2,3,4-tetramethylimidazolinium salt of benzoic acid, ammonium salt of phthalate, dimethylamine salt of phthalate, dimethylethylamine salt of phthalate, 1,2,3,4-tetramethylimidazolinium salt of phthalate, ammonium salt of azelaic acid, dimethylamine salt of azelaic acid, and dimethylethylamine salt of azelaic acid. Examples include methylamine salts, 1,2,3,4-tetramethylimidazolinium salt of azelaic acid, ammonium salt of borogisalicylic acid, dimethylamine salt of borogisalicylic acid, dimethylethylamine salt of borogisalicylic acid, and 1,2,3,4-tetramethylimidazolinium salt of borogisalicylic acid. Among these, dimethylethylamine salt of benzoic acid, dimethylethylamine salt of phthalic acid, and dimethylethylamine salt of borogisalicylic acid are particularly preferred.

[0026] [Aromatic Nitro Compounds] The aromatic nitro compounds contained in the electrolyte of the present invention preferably have one or more selected from the group consisting of an amide group, an alkoxy group, and an acyl group on the aromatic ring. This makes it easier for automotive hybrid electrolytic capacitors to maintain high capacitance and low ESR in the high-frequency range over a long period of time in a high-temperature environment. Aromatic nitro compounds having one or more selected from the group consisting of an amide group, an alkoxy group, and an acyl group on the aromatic ring have high solubility in organic solvents, and aromatic nitro compounds having an amide group in particular have high solubility in protic solvents, making it easy to obtain a highly concentrated, homogeneous electrolyte.

[0027] Specific examples of aromatic nitro compounds having one or more groups selected from the group consisting of amide groups, alkoxy groups, and acyl groups on the aromatic ring include 2-nitrobenzamide, 3-nitrobenzamide, 4-nitrobenzamide, nitrobenzene, o-nitroanisole, m-nitroanisole, p-nitroanisole, o-nitroacetophenone, m-nitroacetophenone, and p-nitroacetophenone. Among these, 2-nitrobenzamide, 3-nitrobenzamide, 4-nitrobenzamide, 4-nitroanisole, and m-nitroacetophenone are preferred, and 2-nitrobenzamide and 3-nitrobenzamide are more preferred. Furthermore, among these, aromatic nitro compounds having an amide group on the aromatic ring are preferred, and 2-nitrobenzamide and 3-nitrobenzamide are more preferred, due to their high solubility in organic solvents and their excellent ability to increase the capacitance and reduce the ESR in the high-frequency range of automotive hybrid electrolytic capacitors. These nitrobenzamides have particularly high solubility in protic solvents, allowing for higher concentrations in the electrolyte and making it easier to achieve the effect of maintaining high capacitance and low equivalent series resistance. The electrolyte may contain at least one aromatic nitro compound selected from the above group.

[0028] Furthermore, aromatic nitro compounds having a carboxyl group on the aromatic ring have extremely low solubility in organic solvents, making it difficult to obtain an electrolyte with homogeneity and sufficient electrical conductivity. If an electrolyte contains only an aromatic nitro compound having a hydroxyl group, a carboxyl group, or an alkyl group having a hydroxyl group on the aromatic ring, automotive hybrid electrolytic capacitors are prone to degradation such as increased ESR and decreased capacitance when exposed for long periods, such as 1000 hours, to high temperatures of 85-150°C, especially 125-150°C. However, aromatic nitro compounds having a hydroxyl group, a carboxyl group, or an alkyl group having a hydroxyl group on the aromatic ring can be used as long as they dissolve sufficiently in organic solvents and maintain high capacitance and low ESR in high-temperature environments, provided that they are used in combination with aromatic nitro compounds having one or more selected from the group consisting of an amide group, an alkoxy group, and an acyl group on the aromatic ring.

[0029] [Organic solvent] The organic solvent contained in the electrolyte of the present invention may be a protic polar solvent and / or an aprotic polar solvent, and may be used alone or as a mixture of two or more types.

[0030] Specific examples of protic polar solvents include monohydric alcohols (methanol, ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc.), polyhydric alcohols and oxyalcohol compounds (ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, etc.), and polyalkylene glycols (polyethylene glycol, polypropylene glycol, etc.).

[0031] Specific examples of aprotic polar solvents include γ-butyrolactone, γ-valerolactone, amides (N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphoricamide, etc.), sulfolanes (sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc.), linear sulfones (dimethylsulfone, ethylmethylsulfone, ethylisopropylsulfone), and cyclic amides. Examples include dihydrogen compounds (such as N-methyl-2-pyrrolidone), carbonates (such as ethylene carbonate, propylene carbonate, and isobutylene carbonate), nitrile compounds (such as acetonitrile), sulfoxide compounds (such as dimethyl sulfoxide), and 2-imidazolidinone compounds [1,3-dialkyl-2-imidazolidinone (such as 1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone, 1,3-di(n-propyl)-2-imidazolidinone, etc.), 1,3,4-trialkyl-2-imidazolidinone (such as 1,3,4-trimethyl-2-imidazolidinone, etc.)].

[0032] The organic solvent used in the electrolyte is preferably one selected from the group consisting of sulfolane, γ-butyrolactone, propylene carbonate, ethylene carbonate, glycol compounds (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol), benzyl alcohol, and glycerin, as it readily dissolves the electrolyte, thereby increasing the electrical conductivity of the electrolyte and thus increasing the capacitance of the automotive hybrid electrolytic capacitor, and has a high boiling point. It is more preferably sulfolane or a glycol compound. Sulfolane is highly effective in reducing the ESR of automotive hybrid electrolytic capacitors in low-temperature environments, and glycol compounds have low volatility among the above, allowing the electrolyte volume to be maintained for a long period of time even in high-temperature environments. It is even more preferable that the glycol compound contains ethylene glycol or polyethylene glycol.

[0033] [Additives] The electrolyte of the present invention may contain compounds other than those mentioned above as additives for the purpose of suppressing the increase in ESR in the high-frequency range of automotive hybrid electrolytic capacitors over a long period of time under high-temperature environments, and improving the characteristics of automotive hybrid electrolytic capacitors such as lifespan performance and resistance performance. Such additives are not particularly limited. Examples of additives include antioxidants.

[0034] (Antioxidant) The electrolyte of the present invention may contain an antioxidant for the purpose of suppressing the rise in ESR in the high-frequency range of automotive hybrid electrolytic capacitors over a long period of time under high-temperature conditions. Specific examples of antioxidants include phenol compounds, azo compounds, silane compounds, and quinone compounds. Specific examples of the above phenol compounds include catechol, resorcinol, hydroquinone, pyrogallol, protocatechuic acid, gallic acid, methyl gallate, catechin, gallein, myricetin, tannic acid, and 2,3,3',4,4',5'-hexahydroxybenzophenone, and among these, aromatic compounds having at least two hydroxyl groups are preferred.

[0035] (Other Additives) In addition to antioxidants, the electrolyte of the present invention may contain additives consisting of various compounds for maintaining high capacity, suppressing ESR increase, and suppressing leakage current increase. Such additives are not particularly limited. Specific examples of additives include phosphorus compounds (phosphoric acid and phosphate esters such as isopropyl phosphate, butyl phosphate, diisopropyl phosphate, dibutyl phosphate, trimethyl phosphate, triethyl phosphate, triisopropyl phosphate, and tributyl phosphate), boric acid, sugar alcohols (mannitol, sorbitol, etc.), complex compounds of boric acid and sugar alcohols (mannitol, sorbitol, etc.), complex compounds of boric acid and polyhydric alcohols (ethylene glycol, glycerin, etc.), pH adjusters (urea compounds such as urea and dimethylurea, and amino acid compounds such as glycine and β-alanine, etc.).

[0036] <Hybrid Electrolytic Capacitor for Automotive Use> The hybrid electrolytic capacitor for automotive use of the present invention is a hybrid electrolytic capacitor for automotive use that uses both a solid electrolyte and an electrolyte solution, and has a capacitor element having a solid electrolyte layer and the electrolyte solution of the present invention impregnated into the capacitor element, all contained within an outer casing. Furthermore, an anode foil and a cathode foil can be used for the electrodes. The hybrid electrolytic capacitor for automotive use of the present invention is mounted in automotive AV equipment and electrical equipment that require stable performance over a long period of time in high-temperature environments, and can maintain high capacitance and low ESR in the high-frequency range of 100 Hz to 1 MHz over a long period of time, even in high-temperature environments such as 85 to 150°C, especially 125 to 150°C.

[0037] [Anode Foil and Cathode Foil] The anode and cathode used in the automotive hybrid electrolytic capacitor of the present invention preferably contain a valve metal. Specific examples of valve metals include aluminum, tantalum, niobium, and titanium, and it is preferable to include one selected from the group consisting of these, and more preferably aluminum. Furthermore, the automotive hybrid electrolytic capacitor of the present invention is classified into chip type or wound type depending on the shape of the anode and cathode used, and the valve metal is usually used in the form of a sintered body or foil, but it is preferable to use it in the form of foil, i.e., as anode foil and cathode foil. The anode foil preferably has a dielectric oxide film layer on its surface, which is made of an oxide of the valve metal.

[0038] [Solid Electrolyte Layer] The solid electrolyte layer is a layer made of a solid electrolyte that is formed on a capacitor element.

[0039] (Solid Electrolyte) The solid electrolyte preferably contains a conductive polymer, and more preferably contains a conductive polymer doped with a dopant component.

[0040] A conductive polymer doped with a dopant component can be obtained by chemically oxidatively polymerizing or electrolytically oxidatively polymerizing a monomer for the conductive polymer in the presence of the dopant component to produce the conductive polymer. Alternatively, a conductive polymer doped with a dopant component can be obtained by contacting a conductive polymer obtained by chemically oxidatively polymerizing or electrolytically oxidatively polymerizing with a dopant component. The above chemically oxidative polymerization or electrolytically oxidative polymerization may be carried out by replacing some or all of the dopant component and / or monomer for the conductive polymer with monomers having functional groups that can undergo chemical oxidation doping. The solid electrolyte dispersion may be one in which a portion of the solid electrolyte is dissolved in the solvent.

[0041] (Conductive polymer) Specific examples of conductive polymers include polypyrrole, polythiophene, polyaniline, or derivatives thereof, and it is preferable to contain at least one selected from the group consisting of these.

[0042] Specific examples of monomers for conductive polymers 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-ethylenedioxifuran, methyl-3,4-ethylenedioxifuran, ethyl-3,4-ethylenedioxifuran, propyl-3,4-ethylenedioxifuran, 3,4-propylenedioxifuran, methyl-3,4-propylenedioxifuran, ethyl-3,4-propylenedioxifuran, propyl-3,4-propylenedioxifuran, 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. The conductive polymer can be obtained by (co)polymerizing one or more of these monomers.

[0043] Among these, 3,4-ethylenedioxythiophene, methyl-3,4-ethylenedioxythiophene, and ethyl-3,4-ethylenedioxythiophene are preferred because in-vehicle hybrid electrolytic capacitors can easily obtain a low ESR.

[0044] (Dopant component) The above dopant component is preferably a compound having a functional group capable of causing chemical oxidation doping to the conductive polymer. Specific examples of such functional groups include a sulfate ester group, a phosphate ester group, a phosphoric acid group, a carboxyl group, a sulfo group, etc. Among these, a sulfate ester group, a carboxyl group, and a sulfo group are more preferred because a higher doping effect can be obtained, and a sulfo group is even more preferred.

[0045] Specific examples of such dopant components include polyvinyl sulfonic acid, polystyrene sulfonic acid, polyallyl sulfonic acid, ethyl sulfonic acid polyacrylate, butyl sulfonic acid polyacrylate, polyacryl sulfonic acid, polymethacrylate sulfonic acid, poly(2-acrylamido-2-methyl sulfonic acid), polyisoprene sulfonic acid, polyvinyl carboxylic acid, polystyrene carboxylic acid, polyallyl carboxylic acid, polyacryl sulfonic acid, polymethacrylate carboxylic acid, poly(2-acrylamido-2-methyl carboxylic acid), polyisoprene carboxylic acid, p-toluenesulfonic acid, xylene sulfonic acid, methylnaphthalene sulfonic acid, butylnaphthalene sulfonic acid, and metal salts thereof. These may be single polymers or copolymers of two or more polymers. Among these, polystyrene sulfonic acid is preferred.

[0046] Specific examples of monomers having functional groups that can undergo the above chemical oxidation doping include 6-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)hexane-1-sulfonic acid, 6-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)sodium hexane-1-sulfonate, 6-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)lithium hexane-1-sulfonate, and 6-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)hexane-1 - Potassium sulfonate, 8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)octan-1-sulfonic acid, 8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)octan-1-sulfonate sodium, 8-(2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)octan-1-sulfonate potassium, 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 sodium, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl Examples include potassium methoxy-1-methyl-1-propanesulfonate, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonic acid, 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate ammonium, and 3-[(2,3-dihydrothieno[3,4-b]-[1,4]dioxin-2-yl)methoxy]-1-methyl-1-propanesulfonate triethylammonium.

[0047] (Solvent) For the solvent used in the above conductive polymer dispersion or conductive polymer solution, 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.

[0048] The content of the organic solvent in the conductive polymer dispersion or conductive polymer solution is preferably 1 to 20% by mass, more preferably 5 to 15% by mass. When the content of the organic solvent is less than the above range, it becomes difficult to form a solid electrolyte layer with a uniform surface. When it is higher than the above range, the drying process for removing the solvent during the formation of the solid electrolyte layer requires a long time and the production efficiency tends to decrease. The total content of the organic solvent and an inorganic solvent such as water in the conductive polymer dispersion or conductive polymer solution is preferably 70% by mass or more, more preferably 80% by mass.

[0049] Further, the conductive polymer dispersion or conductive polymer solution may contain a binder resin, a surfactant, and an alkali compound in order to adjust the film-forming property and film strength.

[0050] The above conductive polymer dispersion or conductive polymer solution may contain a high-boiling organic solvent. Among high-boiling organic solvents, high-boiling organic solvents having a boiling point of 150 to 300°C are particularly preferred.

[0051] (High-boiling organic solvent) Specific examples of the above high-boiling organic solvent include N-methyl-2-pyrrolidone (boiling point 202°C), dimethyl sulfoxide (boiling point 189°C), γ-butyrolactone (boiling point 204°C), sulfolane (boiling point 285°C), dimethyl sulfone (boiling point 238°C), ethylene glycol (boiling point 197.3°C), diethylene glycol (boiling point 245°C), triethylene glycol (boiling point 285°C), etc. Among these, ethylene glycol or γ-butyrolactone is more preferred in that a solid electrolyte layer containing a conductive polymer with a uniform surface can be formed.

[0052] [Manufacturing method of in-vehicle hybrid electrolytic capacitor] The manufacturing method of the in-vehicle hybrid electrolytic capacitor of the present invention includes a step of forming a solid electrolyte layer and a step of impregnating an electrolytic solution.

[0053] (Process for forming the solid electrolyte layer) The solid electrolyte layer can be formed by contacting the capacitor element with a conductive polymer dispersion or conductive polymer solution by means of immersion, and then drying off the solvent. Alternatively, the solid electrolyte layer can be formed by immersing the capacitor element in a monomer solution for conductive polymers, then generating a conductive polymer by chemical polymerization or electrolytic polymerization, and then drying off the solvent.

[0054] (Electrolyte impregnation process) The capacitor element with a solid electrolyte layer can be impregnated with the electrolyte by bringing the electrolyte and the solid electrolyte layer into contact by means such as immersing the capacitor element with a solid electrolyte layer in the electrolyte. Alternatively, the capacitor element can be impregnated with the electrolyte by inserting the capacitor element with a solid electrolyte layer into an outer container that has been pre-filled with electrolyte.

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples, and modifications are possible within the scope of the present invention.

[0056] <Ingredients> [Electrolytes] Triethylamine borodisalicylate, triethylamine phthalate, triethylamine benzoate [Aromatic nitro compounds] 3-nitrobenzamide, 2-nitrobenzamide, 4-nitroanisole, m-nitroacetophenone, 4-nitrobenzyl alcohol, 4-nitrobenzoic acid [Organic solvent for electrolyte] Ethylene glycol, sulfolane, PEG #300: polyethylene glycol, weight-average molecular weight 300. [Additives] Urea: pH adjuster, Trimethyl phosphate: corrosion inhibitor, Pyrogallol: antioxidant

[0057] <Preparation of Conductive Polymer Dispersion> As a dopant component, 12.2 g of a 20% by mass aqueous solution of polystyrene sulfonic acid (weight-average molecular weight: 50,000) was mixed with 187.5 g of water and stirred for 10 minutes. Next, 2.04 g of 3,4-ethylenedioxythiophene was added as the monomer for the conductive polymer and stirred for a further 15 minutes to prepare a monomer solution. The obtained monomer solution was pale yellow in color. The amount of polystyrene sulfonic acid contained in the above monomer solution was 119 parts by mass per 100 parts by mass of 3,4-ethylenedioxythiophene contained in the monomer solution.

[0058] While stirring the above monomer solution, 0.012 g of iron(III) sulfate and 4.46 g of ammonium persulfate were added dropwise as oxidizing agents, and the mixture was stirred at room temperature for 15 hours to carry out chemical oxidation polymerization. During this time, the monomer solution changed from light yellow to dark blue.

[0059] Next, 50.1 g of amphoteric ion exchange resin (Organo trade name: MB-1, 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. Through the above procedure, a conductive polymer dispersion containing poly(3,4-ethylenedioxythiophene) doped with 1.3% by mass of polystyrene sulfonic acid was obtained.

[0060] <Fabrication of Capacitor Element and Solid Electrolyte Layer> An aluminum anode foil with lead terminals attached, which was formed by etching the surface and then performing a chemical conversion treatment, was wound around an aluminum cathode foil with lead terminals attached, which had its surface etched and was also etched, via a separator made of cellulose fibers (thickness 0.05 mm) to fabricate a capacitor element. The obtained capacitor element was then immersed in the conductive polymer dispersion, and after the capacitor element was removed, the solvent was evaporated to form a solid electrolyte layer made of conductive polymer on the capacitor element.

[0061] <Preparation of Electrolyte and Fabrication and Evaluation of Hybrid Aluminum Electrolytic Capacitors> [Example 1] (Preparation of Electrolyte) An electrolyte was prepared using ethylene glycol as the solvent, containing 3% by mass of borodisalicylic acid triethylamine salt as the solute and 1.0% by mass of 3-nitrobenzamide as the aromatic nitro compound.

[0062] (Fabrication of Hybrid Aluminum Electrolytic Capacitors) The capacitor element having the solid electrolyte layer fabricated above was then immersed in the electrolyte solution prepared above to impregnate it. Next, the capacitor element having the solid electrolyte layer impregnated with the electrolyte solution was inserted into a bottomed cylindrical aluminum case, a sealing rubber was attached to the open end, and it was sealed by curling. After that, it was subjected to an aging treatment at 105°C to obtain a hybrid aluminum electrolytic capacitor with a cylindrical shape having an external diameter of 10 mm and a height of 10 mm after sealing, and a rated voltage of 35 V.

[0063] [Examples 2-18, Comparative Examples 1-12] Electrolytes were prepared in the same manner as in Example 1, according to the electrolyte composition shown in Tables 1-4. Hybrid aluminum electrolytic capacitors were then fabricated and evaluated in the same manner.

[0064] <Evaluation> [Measurement of Electrical Conductivity] The electrical conductivity of the electrolyte was measured using a CM-30R type electrical conductivity meter (manufactured by Toa DKK Co., Ltd.) for an electrolyte at a liquid temperature of 30°C.

[0065] [pH Measurement] The pH of the electrolyte was measured using a pH meter HM-30R (manufactured by Toa DKK Co., Ltd.) for an electrolyte solution at a liquid temperature of 25°C.

[0066] [Measurement of Capacitance and ESR] The fabricated hybrid aluminum electrolytic capacitors were subjected to a load test at a rated voltage of 35V for 1000 hours in a 150°C environment. The capacitance at 120Hz and the ESR at 100kHz of the hybrid aluminum electrolytic capacitors were measured using a Keysight Technologies E4980A precision LCR meter.

[0067]

[0068]

[0069]

[0070]

[0071] <Summary of Evaluation Results> The electrolytes of all embodiments of the present invention showed good electrical conductivity, giving hybrid electrolytic capacitors high capacitance and low ESR, and after 1000 hours of loading in a high-temperature environment of 150°C, they gave low capacitance change rate and low ESR change rate, showing an excellent balance. On the other hand, the electrolytes of the comparative examples gave hybrid electrolytic capacitors inferior results in capacitance, capacitance change rate, ESR, or ESR change rate, or the aromatic nitro compound did not dissolve sufficiently, making it impossible to prepare the electrolyte. In detail, in Table 1, the electrolyte of Comparative Example 1, which did not contain an aromatic nitro compound, and the electrolyte of Comparative Example 3, which contained 4-nitrobenzoic acid having a carboxyl group on the aromatic ring, showed a large increase in ESR after loading of the hybrid electrolytic capacitor, while the electrolyte of Comparative Example 2, which contained 4-nitrobenzyl alcohol having an alkyl group with a hydroxyl group on the aromatic ring, showed a large decrease in capacitance after loading of the hybrid electrolytic capacitor. In Table 2, in Comparative Example 4, the 4-nitrobenzoic acid having a carboxyl group on the aromatic ring did not dissolve sufficiently, and the electrolyte could not be prepared. In Comparative Example 5, which contained 4-nitrobenzyl alcohol having a -CH2-OH group on the aromatic ring, the electrolyte showed a large decrease in capacitance after loading of the hybrid electrolytic capacitor. In Table 3, in Comparative Example 6, which did not contain an electrolyte, the electrolyte showed an excessively low electrical conductivity, resulting in a large decrease in capacitance after loading of the hybrid electrolytic capacitor. In Comparative Example 9, which contained too much electrolyte, the electrolyte showed an extremely high electrical conductivity, resulting in a large increase in ESR after loading of the hybrid electrolytic capacitor. In Table 4, in Comparative Examples 8 to 12, which contained 4-nitrobenzyl alcohol having a -CH2-OH group on the aromatic ring, the electrolyte showed a large decrease in capacitance after loading.

[0072] The electrolyte of the present invention is widely used in automotive hybrid electrolytic capacitors mounted in automotive AV equipment and electrical equipment, as well as in power supplies for consumer AV equipment, mobile phones, laptop computers, and electrolytic capacitors mounted in industrial equipment.

Claims

1. An electrolyte used in an automotive hybrid electrolytic capacitor, wherein the automotive hybrid electrolytic capacitor comprises a capacitor element having a solid electrolyte layer and the electrolyte impregnated into the capacitor element, all contained within an outer casing, the solid electrolyte layer containing a solid electrolyte made of a conductive polymer, the electrolyte having an electrical conductivity of 0.05 to 1.0 mS / cm at 30°C, and containing an electrolyte, an aromatic nitro compound, and an organic solvent, the electrolyte being an acid and / or salt, the salt consisting of an acid component and a basic component, and the aromatic nitro compound having one or more groups selected from the group consisting of an amide group, an alkoxy group, and an acyl group on an aromatic ring, the electrolyte.

2. The electrolyte according to claim 1, wherein the aromatic nitro compound has an amide group on the aromatic ring.

3. The electrolyte according to claim 1, wherein the aromatic nitro compound contains at least one selected from the group consisting of 2-nitrobenzamide, 3-nitrobenzamide, and 4-nitrobenzamide, 4-nitroanisole, and m-nitroacetophenone.

4. The electrolyte according to claim 1, wherein the organic solvent contains a glycol compound.

5. The electrolyte according to claim 1, wherein the electrolyte further contains an antioxidant.

6. The electrolyte according to claim 1, wherein the acid and / or the acid component contains an aromatic carboxylic acid.

7. The electrolyte according to claim 1, wherein the acid and / or the acid component contains at least one selected from the group consisting of phthalic acid, benzoic acid, and borodisalicylic acid.

8. The electrolyte according to claim 1, wherein the amount of water contained in the electrolyte is 0.1% by mass or more and 3% by mass or less.

9. The electrolyte according to claim 1, wherein the pH of the electrolyte is 2 to 7.

10. A hybrid electrolytic capacitor for automotive use, comprising a capacitor element having a solid electrolyte layer and an electrolyte impregnated in the capacitor element, all contained within an outer casing, wherein the solid electrolyte layer contains a solid electrolyte made of a conductive polymer doped with a dopant component, and the electrolyte is the electrolyte described in any one of claims 1 to 9.

11. The automotive hybrid electrolytic capacitor according to claim 10, wherein the conductive polymer contains polythiophene.

12. The automotive hybrid electrolytic capacitor according to claim 10, wherein the dopant component contains polystyrene sulfonic acid.

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