Electrolyte for electrolytic capacitors, electrolytic capacitors, and method for manufacturing electrolytic capacitors

Abstract

The present invention provides an electrolyte for electrolytic capacitors that can suppress the increase in leakage current in high-temperature environments without worsening yield, an electrolytic capacitor using this electrolyte, and a method for manufacturing an electrolytic capacitor. [Solution] The electrolyte for the electrolytic capacitor contains inorganic oxide colloidal particles, phosphoric acid in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of the electrolyte for the electrolytic capacitor, and diethylene glycol in an amount of 14 wt% or more relative to the total amount of the solvent. The electrolytic capacitor comprises an anode body having a dielectric film formed on the surface of a foil made of a valve metal as a base material, and a cathode body, with the electrolyte for the electrolytic capacitor interposed between the anode body and the cathode body. The electrolyte for the electrolytic capacitor is prepared in advance in the electrolyte preparation step and impregnated into the element consisting of the anode body and cathode body in the impregnation step.

Description

Technical Field

[0001] The present invention relates to an electrolytic solution for an electrolytic capacitor, an electrolytic capacitor, and a method for manufacturing an electrolytic capacitor.

Background Art

[0002] An electrolytic capacitor includes valve action metals such as tantalum or aluminum as an anode body and a cathode body. The anode body is enlarged in surface area by forming the valve action metal into a sintered body or an etched foil shape, etc., and has a dielectric film on the enlarged surface. An electrolytic solution for an electrolytic capacitor is interposed between the anode body and the cathode body. The electrolytic solution for an electrolytic capacitor closely adheres to the uneven surface of the anode body and functions as a true cathode.

[0003] The electrolytic solution for an electrolytic capacitor is interposed between the dielectric film of the anode body and the cathode body. Therefore, the electrical conductivity, temperature characteristics, etc. of the electrolytic solution for an electrolytic capacitor have a great influence on the electrical characteristics of the electrolytic capacitor such as impedance, dielectric loss (tanδ), and equivalent series resistance (ESR). Further, the electrolytic solution for an electrolytic capacitor has a forming property for repairing deterioration parts such as deterioration and damage of the dielectric film formed on the anode body, and affects the leakage current (LC) and life characteristics of the electrolytic capacitor.

[0004] Therefore, at least an electrolytic solution for an electrolytic capacitor with high electrical conductivity is suitable for an electrolytic capacitor. However, when the electrical conductivity of the electrolytic solution for an electrolytic capacitor is increased, the spark voltage tends to decrease, and there is a risk that the withstand voltage characteristics of the electrolytic capacitor will be impaired. From the viewpoint of safety, it is desirable to have a high withstand voltage so that short circuits and ignition do not occur even under severe conditions where an abnormal voltage exceeding the rated voltage is applied to the electrolytic capacitor.

[0005] Attempts have been made to improve voltage resistance while maintaining high electrical conductivity by adding alkylene oxide adducts of 3- to 8-valent polyhydric alcohols to the electrolyte for electrolytic capacitors (see, for example, Patent Document 1). However, these alkylene oxide adducts are water-soluble polymers. When water-soluble polymers are used as voltage-reducing agents, the capacitance of the electrolytic capacitor deteriorates when used in low-temperature environments such as -40°C.

[0006] Therefore, attempts have been made to add various inorganic oxide colloidal particles instead of water-soluble polymers (see Patent Document 2). Inorganic oxide colloidal particles are typically silica colloidal particles, but other materials such as zirconia, titania, aluminosilicate, and aluminosilicate-coated silica have also been proposed. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2016 / 143535 [Patent Document 2] Japanese Patent Application Publication No. 1-232713 [Overview of the project] [Problems that the invention aims to solve]

[0008] Electrolytic capacitors can contain moisture. Moisture can be intentionally included in the electrolyte solution used for electrolytic capacitors, or it can be introduced during the manufacturing process. The valve metal of the anode deteriorates due to hydration. This deterioration of the anode's valve metal can, for example, lead to an increase in the leakage current of the electrolytic capacitor.

[0009] The valve metal of the anode is usually covered with a dielectric film. However, inorganic oxide colloidal particles can dissolve the dielectric film in high-temperature environments, such as 105°C. When the dielectric film of the anode dissolves, the valve metal is exposed and inevitably deteriorates due to hydration reactions, leading to an increase in the leakage current of the electrolytic capacitor. In other words, when using an electrolyte for electrolytic capacitors that contains inorganic oxide colloidal particles, the low-temperature characteristics are good, but there are areas that need improvement in the high-temperature characteristics.

[0010] Furthermore, when improving high-temperature characteristics, it is preferable to take measures to avoid worsening the yield of electrolytic capacitors.

[0011] The present invention was proposed to solve the above problems, and its objective is to provide an electrolyte for electrolytic capacitors that can suppress the increase in leakage current in a high-temperature environment without worsening the yield, an electrolytic capacitor using this electrolyte, and a method for manufacturing an electrolytic capacitor. [Means for solving the problem]

[0012] It is hypothesized that hydroxyl groups on the surface of inorganic oxide colloid particles present near the dielectric film of the anode attract moisture from the electrolyte of the electrolytic capacitor, and that this attracted moisture dissolves the dielectric film, passes through the dielectric film to the valve metal, and causes hydration degradation of the valve metal.

[0013] In contrast, phosphorus oxoacids form a coating film that covers the dielectric film of the anode, and even if inorganic oxide colloid particles attract moisture, the moisture is prevented from approaching the dielectric film by the coating film. However, the acid component itself dissolves the dielectric film, creating a pathway for moisture to reach the valve metal. Through diligent research, the inventors have found that among phosphorus oxoacids, phosphoric acid and hypophosphorous acid have a small dissolving effect on the dielectric film.

[0014] Simultaneously, through diligent research, the inventors discovered that the larger the total amount of electric current in the spike current during the aging process of an electrolytic capacitor, the higher the likelihood of a short circuit occurring during the aging process. In other words, reducing the total amount of electric current in the spike current improves the yield of electrolytic capacitors. Furthermore, the inventors found that, among the oxoacids of phosphorus, phosphoric acid alone, when combined with diethylene glycol, reduces the total amount of electric current in the spike current.

[0015] This embodiment is based on these findings, and in order to achieve the above objective, the electrolyte for electrolytic capacitors according to this embodiment contains inorganic oxide colloidal particles, phosphoric acid in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of the electrolyte for electrolytic capacitors, and diethylene glycol in an amount of 14 wt% or more relative to the total amount of the solvent.

[0016] The material may contain an organic acid, and the organic acid may contain 25 mol% or more of 1,6-decanedicarboxylic acid relative to the total amount of the organic acid.

[0017] The solvent may contain 14 wt% to 62 wt% of diethylene glycol relative to the total amount of solvent.

[0018] Furthermore, in order to achieve the above objective, the electrolytic capacitor according to this embodiment comprises an anode body having a dielectric film formed on the surface of a foil made of a valve metal as a base material, a cathode body, and an electrolyte interposed between the anode body and the cathode body, wherein the electrolyte contains inorganic oxide colloidal particles, phosphoric acid in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of the electrolyte, and diethylene glycol in an amount of 14 wt% or more relative to the total amount of the solvent.

[0019] In addition, in order to achieve the above object, a method for manufacturing an electrolytic capacitor according to the present embodiment includes an anodic formation step of forming an anode body having a dielectric film formed on the surface of a foil made of a valve action metal as a base material, a cathode formation step of forming a cathode body, an electrolytic solution preparation step of preparing an electrolytic solution to be interposed between the anode body and the cathode body, an element formation step of forming an element in which the anode body and the cathode body face each other, and an electrolytic solution impregnation step of impregnating the element with the electrolytic solution. The electrolytic solution contains inorganic oxide colloid particles, phosphoric acid contained in an amount of more than 0.1 wt% and not more than 0.3 wt% based on the total amount of the electrolytic solution, and diethylene glycol contained in an amount of 14 wt% or more based on the total amount of the solvent.

Advantages of the Invention

[0020] According to the present invention, an increase in leakage current can be suppressed in a high-temperature environment, and the yield of the electrolytic capacitor can be improved.

Brief Description of the Drawings

[0021] [Figure 1] These are graphs showing the relationship between various acid components and leakage current. [Figure 2] These are graphs showing the relationship between various acid components and the total amount of spike current during the aging process. [Figure 3] This is a graph showing the relationship between various addition amounts of phosphoric acid and the total amount of spike current during the aging process. [Figure 4] This is a graph showing the relationship between various addition amounts of diethylene glycol and the total amount of spike current during the aging process. <00,00093>This is a graph showing the relationship between various addition amounts of 1,6-decanedicarboxylic acid and the total amount of spike current during the aging process.

Embodiments for Carrying Out the Invention

[0022] The following describes the electrolyte for electrolytic capacitors, electrolytic capacitors, and methods for manufacturing electrolytic capacitors according to embodiments of the present invention. However, the present invention is not limited to the embodiments described below.

[0023] (Overall configuration of electrolytic capacitors) An electrolytic capacitor is a passive element that stores and discharges electric charge by obtaining capacitance through the dielectric polarization effect of a dielectric film. An electrolytic capacitor comprises an anode and a cathode, both having dielectric films formed on their surfaces. The anode and cathode are positioned opposite each other. An electrolytic electrolyte is filled between the dielectric film of the anode and the cathode. The electrolyte is in close contact with the dielectric film, forming the true cathode. The anode and cathode are positioned opposite each other with a separator in between. The separator prevents short circuits between the anode and cathode and also holds the electrolytic electrolyte.

[0024] An example of the manufacturing method for this electrolytic capacitor is outlined below. First, the anode and cathode bodies formed in the anode formation and cathode formation processes are stacked via a separator in the element formation process to form a capacitor element. Next, the electrolyte for electrolytic capacitors, prepared in the electrolyte preparation process, is impregnated into the capacitor element in the electrolyte impregnation process. Then, the capacitor element is packaged by sealing the open end of the case with a sealing body in the packaging process, and a voltage is applied in the aging process to repair any defects that have occurred in the dielectric film.

[0025] (Electrolyte for electrolytic capacitors) The electrolyte for electrolytic capacitors is a mixture in which a solute is dissolved in a solvent, and additives are added to the solvent. At a minimum, inorganic oxide colloidal particles are added as additives.

[0026] Examples of inorganic oxide colloidal particles include silica, alumina, titania, zirconia, antimony oxide, aluminosilicate, silica-zirconia, titania-zirconia, silica coated with aluminosilicate, silica coated with silica-zirconia, or mixtures thereof. Among these inorganic oxide colloidal particles, silica, aluminosilicate, or silica coated with aluminosilicate are particularly preferred from the viewpoint of ease of silylation treatment, stability of colloidal particles, and improvement of dielectric strength.

[0027] The inorganic oxide colloid particles are preferably present in an amount of 1 wt% to 17 wt% relative to the electrolyte for the electrolytic capacitor. A concentration of 1 wt% or more results in a better voltage-bearing effect from the inorganic oxide colloid particles. On the other hand, a concentration of 17 wt% or less results in a lower resistivity of the electrolyte for the electrolytic capacitor. Furthermore, the average particle size of the inorganic oxide colloid particles is preferably between 5 nm and 50 nm. A particle size of 5 nm or more results in a smaller rate of change in voltage after the heat resistance test. A particle size of 50 nm or less results in a higher initial voltage-bearing effect.

[0028] However, exposure of the dielectric film of the anode to inorganic oxide colloidal particles affects the dissolution of the dielectric film. This is a hypothesis and not limited to this mechanism, but the dissolution of the dielectric film of the anode is thought to be due to the following reason: The hydroxyl groups on the surface of the inorganic oxide colloidal particles attract water from the electrolyte of the electrolytic capacitor. Therefore, when inorganic oxide colloidal particles are present near the dielectric film of the anode, the water attracted by the hydroxyl groups on the surface of the inorganic oxide colloidal particles easily approaches the dielectric film of the anode, dissolves the dielectric film, passes through the dielectric film to the valve metal, and causes hydration degradation of the valve metal.

[0029] Therefore, the electrolyte for electrolytic capacitors contains phosphoric acid, hypophosphorous acid, or both as the acidic solute component. The phosphoric acid or hypophosphorous acid forms a coating film that covers the dielectric film of the anode. This coating film acts as a barrier, making it difficult for the hydroxyl groups of inorganic oxide colloid particles and the moisture attracted to these hydroxyl groups to approach the dielectric film. As a result, the dissolution of the dielectric film is suppressed.

[0030] However, generally speaking, the acid component itself dissolves the dielectric film, creating a pathway for moisture to reach the valve metal. However, among the oxoacids of phosphorus, phosphoric acid and hypophosphorous acid have a small dissolving effect on the dielectric film. Therefore, by including phosphoric acid or hypophosphorous acid as the acid component of the solute in the electrolyte for electrolytic capacitors, the dielectric strength of the electrolytic capacitor is increased by the inorganic oxide colloid particles, and the increase in leakage current of the electrolytic capacitor is suppressed even when exposed to high-temperature environments.

[0031] The acid component of the solute in the electrolyte for electrolytic capacitors is particularly preferably phosphoric acid. Among the oxoacids of phosphorus, phosphoric acid, when combined with diethylene glycol, reduces the risk of short circuits that may occur during the aging of electrolytic capacitors and improves the yield of electrolytic capacitors.

[0032] While this is a hypothesis and not limited to this, it is thought that the larger the total amount of electrical current in the spike current during the aging process of an electrolytic capacitor, the higher the likelihood of a short circuit occurring during the aging process. On the other hand, when an electrolyte for electrolytic capacitors is prepared by combining phosphoric acid and diethylene glycol, the total amount of electrical current in the spike current during the aging process becomes smaller.

[0033] More preferably, the electrolyte for the electrolytic capacitor contains 1,6-decanedicarboxylic acid as a solute. By preparing the electrolyte for the electrolytic capacitor by combining phosphoric acid, diethylene glycol, and 1,6-decanedicarboxylic acid, the total amount of electric current in the spike current during the aging process is further reduced.

[0034] The total electrical charge of the spike current during the aging process should be measured as follows. First, the spike current is defined as the leakage current region where the difference between the measured leakage current and the 5-point moving average of the leakage current is +0.02mA or more. The leakage current measurement interval should be 200msec. The total electrical charge of the spike current is the integrated value of the spike currents. Note that +0.02mA is the threshold for noise rejection.

[0035] The components of the electrolyte for electrolytic capacitors will be explained in more detail. First, the inorganic oxide colloidal particles may have their surface modified with organic matter. Inorganic oxide colloidal particles with organic matter surface modification suppress the gelation of the electrolyte and the aggregation of colloidal particles, thereby maintaining the voltage withstand capability of the electrolytic capacitor.

[0036] Organic substances substitute for the surface hydroxyl groups of inorganic oxide colloid particles, suppressing aggregation between the inorganic oxide colloid particles. Examples include silylation agents, silane coupling agents, titanate coupling agents, aluminum coupling agents, alcohols, latex, and various polymer compounds. Silylation agents or silane coupling agents are represented by the following general formula (Chemical Formula 1). [ka] [In the formula, X1 is a hydrocarbon group (-R) having 1 to 20 carbon atoms, which may be a carboxyl group, ester group, amide group, cyano group, ketone group, formyl group, ether group, hydroxyl group, amino group, mercapto group, sulfide group, sulfoxide group, sulfone group, isocyanate group, ureido group, or epoxy group, with X2 to X4 being acetoxy groups, alkoxy groups having 1 to 5 carbon atoms, or alkyl groups, and at least two of X2 to X4 being alkoxy groups.]

[0037] Specific examples of X1 include alkyl groups such as methyl, ethyl, propyl, butyl, decyl, and octadecyl groups; alkenyl groups such as vinyl and allyl groups; aryl groups such as phenyl, naphthyl, and styryl groups; hydrocarbon groups such as benzyl and phenethyl groups; oxy hydrocarbon groups or hydroxyl groups such as methoxy, ethoxy, propoxy, butoxy, vinyloxy, phenoxy, and benzyloxy groups. Furthermore, examples of groups having substituents include acrylic groups such as 3-methacryloxypropyl and 3-acryloxypropyl; epoxy groups such as 3-glycidoxypropyl and 2-(3,4-epoxycyclohexyl)ethyl; amino groups such as 3-aminopropyl, N-phenyl-3-aminopropyl, and N-2-(aminoethyl)-3-aminopropyl; mercapto groups such as 3-mercaptopropyl; isocyanate groups such as 3-isocyanatetopropyl; and ureido groups such as 3-ureidopropyl.Specific examples of X2 to X4 include alkoxy groups such as methoxy, ethoxy, propoxy, and butoxy; alkyl groups such as methyl, ethyl, propyl, butyl, decyl, and octadecyl; and acetoxy groups, where at least two of X2 to X4 are alkoxy groups.

[0038] Among these combinations are methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyl Preference candidates include 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-ureidopropyltrialkoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatetopropyltriethoxysilane, and p-styryltrimethoxysilane.

[0039] Specific examples of titanate coupling agents include isopropyltriisostearoyl titanate, isopropyltridodecylbenzenesulfonyl titanate, isopropyltris(dioctyl pyrophosphate) titanate, tetraisopropylbis(dioctyl phosphite) titanate, tetraoctylbis(ditridecyl phosphite) titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(ditridecyl)phosphite titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, isopropyltrioctanoyl titanate, isopropyldimethacroylisostearoyl titanate, isopropyltri(dioctyl phosphate) titanate, isopropyltricumylphenyl titanate, and isopropyltri(N-aminoethylaminoethyl) titanate.

[0040] Specific examples of aluminum-based coupling agents include aluminum ethyl acetacetate diisopropylate, aluminum tris(ethyl acetate), aluminum tris(acetylacetonate), and aluminum bis(ethyl acetate) monoacetylacetonate. Specific examples of alcohols include methanol, ethanol, n-propanol, iso-propanol, n-butanol, amyl alcohol, 4-methyl-2-pentanol, n-heptanol, n-octanol, 2-ethylhexanol, nonanol, decanol, tridecanol, 2-methoxyethanol, 2-ethoxyethanol, 2-butoxyethanol, 3-methoxybutanol, 3-methyl-3-methoxybutanol, and polyvinyl alcohol.

[0041] These organic substances used for surface modification, such as silylation agents, silane coupling agents, titanate coupling agents, aluminum coupling agents, alcohols, and various polymer compounds, can be used individually or in combination.

[0042] The phosphoric acid should be included in a proportion of more than 0.1 wt% and less than or equal to 0.3 wt% of the total amount of electrolyte for the electrolytic capacitor. Diethylene glycol should be included in a proportion of 14 wt% or more of the total amount of solvent in the electrolyte for the electrolytic capacitor. When the content of phosphoric acid and diethylene glycol are within these ranges, the total electrical charge of the spike current during the aging process is significantly reduced, suppressing the short-circuit rate of the electrolytic capacitor. If either phosphoric acid or diethylene glycol deviates from these ranges, the total electrical charge of the spike current during the aging process increases, and the short-circuit rate of the electrolytic capacitor cannot be suppressed.

[0043] Particularly preferable is to include diethylene glycol in a proportion of 18.7 wt% or more relative to the total amount of solvent in the electrolyte for the electrolytic capacitor. This further reduces the total amount of electrical current in the spike current during the aging process.

[0044] There are no particular limitations on other solvents, and any known solvent may be used. For example, in addition to diethylene glycol, a protic organic polar solvent or an aprotic organic polar solvent can be added as the solvent for the electrolyte of an electrolytic capacitor. Representative examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Representative examples of aprotic organic polar solvents include sulfones, amides, lactones, cyclic amides, and nitriles.

[0045] Examples of monohydric alcohols include ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, and benzyl alcohol. Examples of polyhydric alcohols and oxyalcohol compounds include ethylene glycol, propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, methoxypropylene glycol, dimethoxypropanol, polyglycerin, and alkylene oxide adducts of polyhydric alcohols such as polyethylene glycol, polyoxyethylene glycerin, and polypropylene glycol.

[0046] Examples of sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, and N,N-diethylacetamide. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethylene carbonate, propylene carbonate, butylene carbonate, and isobutylene carbonate. Examples of nitriles include acetonitrile, 3-methoxypropionitrile, and glutalonitrile.

[0047] When adding organic acids to the electrolyte for electrolytic capacitors, 1,6-decanedicarboxylic acid should be included in a proportion of 25 mol% or more relative to the total amount of organic acids. By including 25 mol% or more, the effect of further reducing the total electrical amount of spike current during the aging process can be obtained by combining phosphoric acid, diethylene glycol, and 1,6-decanedicarboxylic acid.

[0048] There are no particular limitations on organic acids other than 1,6-decanedicarboxylic acid; any known organic acid may be used. For example, examples of organic acids include carboxylic acids such as oxalic acid, succinic acid, glutaric acid, pimelic acid, suberic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, enanthic acid, malonic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanediic acid, dodecanediic acid, tridecanediic acid, t-butyladipic acid, 11-vinyl-8-octadecenediic acid, resorcinic acid, phloroglucic acid, gallic acid, gentisic acid, protocatechuic acid, pyrocatechuic acid, trimellitic acid, pyromellitic acid, phenols, and sulfonic acids.

[0049] The electrolyte for electrolytic capacitors may contain not only acidic components but also basic components as solutes. Acids and bases may be added separately as solute components to the electrolyte for electrolytic capacitors. Furthermore, salts of organic acids, salts of phosphoric acid, or composite compounds of organic acids and phosphoric acid, or ionic dissociable salts thereof, may be added to the electrolyte for electrolytic capacitors.

[0050] Basic components include ammonium, quaternary ammonium, amidinium quaternary, amines, sodium, potassium, etc. Examples of quaternary ammonium include tetramethylammonium, triethylmethylammonium, and tetraethylammonium. Examples of amidinium quaternary include ethyldimethylimidazolinium and tetramethylimidazolinium. Examples of amines include primary amines, secondary amines, and tertiary amines. Examples of primary amines include methylamine, ethylamine, and propylamine; examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, and dibutylamine; and examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, and ethyldiisopropylamine.

[0051] Other additives include complex compounds of boric acid and polysaccharides (such as mannitol and sorbitol), complex compounds of boric acid and polyhydric alcohols, boric acid esters, and nitro compounds. These may be used individually or in combination of two or more. Nitro compounds act as gas absorbers, suppressing the generation of hydrogen gas within the electrolytic capacitor. Examples of nitro compounds include o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, o-nitrobenzyl alcohol, m-nitrobenzyl alcohol, p-nitrobenzyl alcohol, o-nitroacetophenone, m-nitroacetophenone, and p-nitroacetophenone. Examples of pressure-resistant agents include polyethylene glycol, polypropylene glycol, and polyoxyethylene glycerin. These pressure-resistant agents may be added in amounts that do not degrade the properties in low-temperature environments such as -40°C.

[0052] Next, we will describe in more detail the electrolytic capacitor equipped with this electrolyte. The anode and cathode are foil bodies made of valve metal. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, hafnium, zirconium, zinc, tungsten, bismuth, and antimony. The purity is preferably 99.9% or higher for the anode and 99% or higher for the cathode, but impurities such as silicon, iron, copper, magnesium, and zinc may be present.

[0053] The anode and cathode bodies are formed by creating molded foils from valve metal powder, sintered foils from sintered molded bodies, etched foils from rolled foils that have been etched, or sintered or vapor-deposited foils from rolled foils with valve metal powder formed and sintered or vapor-deposited on the surface. The surface is then expanded. Specifically, the expanded layer consists of tunnel-shaped pits, spongy pits, or voids between densely packed powder particles.

[0054] Tunnel-shaped etching pits are holes carved in the thickness direction of the foil. These tunnel-shaped etching pits are typically formed in the anode formation and cathode formation processes by passing a direct current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid. The tunnel-shaped etching pits are further expanded by passing a direct current through an acidic aqueous solution containing nitric acid, etc. Sponge-like etching pits cause the expanded layer to become a sponge-like layer with a series of fine voids that spread out in a spatial manner. These sponge-like etching pits are formed by passing an alternating current through an acidic aqueous solution containing halogen ions, such as hydrochloric acid.

[0055] Sintered foil is produced by anode formation and cathode formation processes in which powder of the same or different valve metal as the foil body is pasteurized with a binder and solvent, applied to the foil body and dried, and then heated and sintered in a vacuum or reducing atmosphere. Vapor-deposited foil is produced in anode formation and cathode formation processes, for example, by resistance heating vapor deposition or electron beam heating vapor deposition. This vapor-deposited foil is produced by heating the same or different valve metal as the foil body with resistance heat or electron beam energy to evaporate it, and depositing the vapor of valve metal particles onto the surface of the foil body to form a film.

[0056] The dielectric film is typically an oxide film formed on the surface of the anode, and if the anode is made of aluminum, it is an aluminum oxide layer formed by oxidizing the porous structure. An oxide film is also formed on the foil surface of the cathode. The oxide film on the cathode may be formed intentionally or naturally. These dielectric and oxide films are formed in the anode formation process and the cathode formation process by a chemical conversion treatment in which a voltage is applied in a halogen-free solution such as an acid such as ammonium borate, ammonium phosphate, or ammonium adipate, or an aqueous solution of these acids. The oxide film intentionally formed on the foil surface of the cathode is preferably thin, about 1 to 10 Vfs. The naturally occurring oxide film is formed by the reaction of the cathode foil with oxygen in the air.

[0057] External terminals are connected to both the anode and cathode. These external terminals are electrically and mechanically connected to the anode and cathode by methods such as stitching, cold welding, ultrasonic welding, or laser welding. The external terminals protrude from the capacitor element and act as conductors, electrically connecting the electrolytic capacitor to the mounting board.

[0058] Examples of separators include cellulose and mixed papers such as kraft, Manila hemp, esparto, hemp, and rayon; polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and their derivatives; polyamide resins such as polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins; polyamide resins such as aliphatic polyamides, semi-aromatic polyamides, and fully aromatic polyamides; polyimide resins; polyethylene resins; polypropylene resins; trimethylpentene resins; polyphenylene sulfide resins; acrylic resins; and polyvinyl alcohol resins. These resins can be used individually or in combination.

[0059] Capacitor elements include wound and multilayer types. In a wound capacitor element, the anode, cathode, and separator are long, and the wound capacitor element is a wound body. In a wound electrolytic capacitor, the anode and cathode are superimposed with a separator in between during the element formation process. The separator is superimposed so that one end extends beyond one end of the anode and cathode. The core of the wound body is created by first winding the protruding separator so that the core of the wound body follows the short sides of the anode and cathode. Then, using this core as the winding axis, the long sides of the anode and cathode are wound together. The wound body is then formed into a cylindrical shape by winding the stack of anode, cathode, and separator in multiple spiral layers.

[0060] In multilayer capacitor elements, the anode, cathode, and separator have a flat plate shape. In multilayer electrolytic capacitors, during the element formation process, flat anodes and cathodes are stacked with a separator in between.

[0061] After the element formation process, a repair chemical conversion step may be provided to repair defects in the exposed base metal portion of the valve acting metal when the anode and cathode are cut to a desired width, or defects formed in the dielectric film of the anode and oxide film of the cathode due to physical stress. In the repair chemical conversion step, the wound body or laminate is immersed in a conversion solution and a voltage is applied.

[0062] As the chemical conversion solution, a phosphate-based solution such as ammonium dihydrogen phosphate, a boric acid-based solution such as ammonium borate, or an adipic acid-based solution such as ammonium adipate is used. As for the voltage application method during the repair chemical conversion, a method of applying a constant voltage from the start of the repair chemical conversion or a method of gradually increasing the applied voltage at regular intervals can be appropriately selected.

[0063] The process then moves to the electrolyte impregnation step, where the capacitor elements are immersed in the electrolyte solution prepared in advance during the electrolyte preparation step, allowing the electrolyte solution to penetrate the voids within the capacitor elements. Depressurization or pressurization may be performed as needed to ensure the electrolyte solution penetrates even finer voids. The electrolyte impregnation step may be repeated multiple times. For example, the inside of the winding or laminated body may be depressurized, and the electrolyte solution may be injected into the capacitor elements while pressurizing the electrolyte solution.

[0064] After the impregnation process, the manufactured capacitor elements are packaged in an outer casing during the packaging process. The outer casing consists of a case with a closed bottom at one end and an open end at the other, and a sealing body. The capacitor elements are housed in the case, and the opening of the case is sealed with the sealing body. Through crimping, the opening of the case is folded inward and crushed, and the sealing body is tightly sealed. After the capacitor elements are sealed, the electrolytic capacitor is manufactured after an aging process.

[0065] The outer casing may be a laminate film. Alternatively, the outer casing may be a resin such as a heat-resistant resin or an insulating resin, and may be molded around the capacitor element or formed as a thin film using methods such as dip coating or printing. [Examples]

[0066] The present invention will be described in more detail below based on the following examples. However, the present invention is not limited to the following examples.

[0067] (Example 1) An electrolyte for electrolytic capacitors was prepared according to Example 1. The composition of the electrolyte for electrolytic capacitors in Example 1 is as follows: The composition of the electrolyte for electrolytic capacitors is, relative to the total weight of the electrolyte for electrolytic capacitors, 8.5 wt% water, 58.33 wt% ethylene glycol, 15.4 wt% diethylene glycol, 4.4 wt% azelaic acid, 2.0 wt% 1,6-decanedicarboxylic acid, 0.17 wt% phosphoric acid, 6.0 wt% inorganic oxide colloidal particles, 2.0 wt% paranitrobenzyl alcohol, and 3.2 wt% diethylamine. As the inorganic oxide colloidal particles, silica whose surface was modified with 3-glycidoxypropyltrimethoxysilane was used.

[0068] In this Example 1, the electrolyte for the electrolytic capacitor contains 18.7 wt% diethylene glycol relative to the total amount of water, ethylene glycol, and diethylene glycol used as solvents. Therefore, the electrolyte for the electrolytic capacitor in Example 1 contains inorganic oxide colloidal particles, 0.17 wt% phosphoric acid relative to the total amount of the electrolyte for the electrolytic capacitor, and 18.7 wt% diethylene glycol relative to the total amount of solvent.

[0069] (Comparative Example 1) Comparative Example 1 electrolytic capacitor electrolyte was prepared. Comparative Example 1 electrolytic capacitor electrolyte does not contain phosphoric acid. The ethylene glycol content was increased by an amount equivalent to the phosphoric acid content of Example 1. The electrolytic capacitor electrolyte of Comparative Example 1 is identical in composition to the electrolytic capacitor electrolyte of Example 1, except that the difference in phosphoric acid was adjusted with ethylene glycol.

[0070] Therefore, the electrolyte for the electrolytic capacitor of Comparative Example 1 contains 18.7 wt% diethylene glycol relative to the total amount of inorganic oxide colloid particles and solvent, but does not contain phosphoric acid.

[0071] (Comparative Example 2) Comparative Example 2 electrolytic capacitor electrolyte was prepared. In Comparative Example 2, instead of phosphoric acid, 0.11 wt% hypophosphorous acid was added to the total amount of electrolytic capacitor electrolyte. The difference in the amount of phosphoric acid in Example 1 and hypophosphorous acid in Comparative Example 2 was adjusted by the amount of ethylene glycol. The electrolytic capacitor electrolyte of Comparative Example 2 is identical in composition to the electrolytic capacitor electrolyte of Example 1, except that hypophosphorous acid is used instead of phosphoric acid and the amount is adjusted with ethylene glycol.

[0072] Therefore, the electrolyte for the electrolytic capacitor of Comparative Example 2 contains inorganic oxide colloidal particles, 0.11 wt% hypophosphorous acid relative to the total amount of the electrolyte for the electrolytic capacitor, and 18.7 wt% diethylene glycol relative to the total amount of solvent, but does not contain phosphoric acid.

[0073] (Comparative Example 3) Comparative Example 3 electrolytic capacitor electrolyte was prepared. In Comparative Example 3, instead of phosphoric acid, 0.14 wt% of phosphorous acid was added to the total amount of the electrolytic capacitor electrolyte. The difference in the amount of phosphoric acid in Example 1 and the amount of phosphorous acid in Comparative Example 3 was adjusted by the amount of ethylene glycol. The electrolytic capacitor electrolyte of Comparative Example 3 is identical in composition to the electrolytic capacitor electrolyte of Example 1, except that phosphorous acid is used instead of phosphoric acid and the amount is adjusted with ethylene glycol.

[0074] Therefore, the electrolyte for the electrolytic capacitor of Comparative Example 3 contains inorganic oxide colloidal particles, 0.14 wt% phosphorous acid relative to the total amount of the electrolyte for the electrolytic capacitor, and 18.7 wt% diethylene glycol relative to the total amount of the solvent, but does not contain phosphoric acid.

[0075] (Fabrication of electrolytic capacitors) Electrolytic capacitors impregnated with the electrolytes for electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 were fabricated.

[0076] In the fabrication of the electrolytic capacitor, first, a pair of electrodes were made using aluminum foil in the anode formation process and the cathode formation process. The aluminum foil that would become the anode was enlarged by DC etching to form an enlarged surface layer. In the DC etching process, a DC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid, forming tunnel-shaped etching pits in the anode aluminum foil. The aluminum foil that would become the cathode was enlarged by AC etching to form an enlarged surface layer. In the AC etching process, an AC current was passed through the aluminum foil in an aqueous solution containing hydrochloric acid, forming sponge-like etching pits in the aluminum foil that would become the cathode.

[0077] The aluminum foil serving as the anode had a dielectric film formed on its surface by a chemical conversion treatment. In the chemical conversion treatment process, the aluminum foil with the expanded surface layer was subjected to the chemical conversion treatment, forming a dielectric film with a conversion voltage of 771V on the surface of the aluminum foil.

[0078] The aluminum foil used as the cathode had an oxide film formed on its surface by a chemical conversion treatment. In the chemical conversion treatment process, the aluminum foil, which had a widened surface layer formed on it, was subjected to the chemical conversion treatment, and an oxide film with a conversion voltage of 3V was formed on the surface of the aluminum foil.

[0079] Lead wires were attached to each of these anodes and cathodes using stitch connections. Next, the process moved to the element formation stage, where the anodes and cathodes were wound together with a kraft fiber separator in between.

[0080] The process then moved to the electrolyte impregnation step, in which the winding was impregnated with the electrolyte for electrolytic capacitors. The winding was immersed in the electrolyte for electrolytic capacitors at room temperature, the pressure of the winding was reduced to 0.002 MPa, and the pressure of the electrolyte for electrolytic capacitors was increased to 0.2 MPa, allowing the electrolyte for electrolytic capacitors to be impregnated into the winding every 60 minutes. The electrolyte impregnation step was performed a total of two times.

[0081] The capacitor element, consisting of an anode, cathode, separator, and electrolytic electrolyte, was housed in an aluminum outer casing with a closed bottom at one end and an open end at the other. A sealing body was press-fitted into the opening of the outer casing and crimped to create a tight seal. The electrolytic capacitor had a diameter of 10 mm and a height of 25 mm. The rated voltage of the electrolytic capacitor was 450 WV, and the rated capacitance was 6 μF.

[0082] (Aging test) The electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 were subjected to an aging process. The leakage current during this aging process was measured over time. In the aging process, the electrolytic capacitors were first subjected to a voltage of 500V for 1 hour at room temperature, and then to a voltage of 475V for 2 hours at a temperature of 85°C.

[0083] Leakage current was measured every 200 msec. A base chart was created by calculating a 5-point moving average of the leakage current. Then, leakage currents with a difference of 0.02 mA or more from the base chart were extracted as spike currents, and the total electrical charge was calculated by integrating all spike currents.

[0084] (LC test) After the aging process, the electrolytic capacitors of Example 1 and Comparative Examples 1 to 3 were left in a 105°C environment for 1000 hours, and the leakage current was measured. The leakage current was measured using a digital oscilloscope when a voltage of 450V was applied at 20°C for 5 minutes.

[0085] (Test results) Table 1 below shows the measurement results of the total charge and leakage current of the electrolytic capacitors in Example 1 and Comparative Examples 1 to 3.

[0086] (Table 1) TIFF2026095167000003.tif108161

[0087] Based on Table 1 above, Figure 1 shows graphs illustrating the relationship between various acid components and leakage current, and Figure 2 shows graphs illustrating the relationship between various acid components and the total amount of electricity in the spike current during the aging process.

[0088] As shown in Table 1 and Figure 1, Comparative Example 3, which contains phosphorous acid, exhibits the same leakage current as Comparative Example 1, which does not contain phosphoric acid, indicating that it is not able to suppress the degradation of the anode body due to moisture attracted by inorganic oxide colloidal particles. In contrast, Comparative Example 2, which contains hypophosphorous acid, and Example 1, which contains phosphoric acid, exhibit lower leakage currents than Comparative Example 1, which does not contain phosphoric acid, indicating that they suppress the degradation of the anode body due to moisture attracted by inorganic oxide colloidal particles.

[0089] In particular, the leakage current of Example 1, which contains phosphoric acid, is less than half that of Comparative Example 1, which does not contain phosphoric acid, etc., demonstrating that degradation of the anode due to moisture attracted by inorganic oxide colloidal particles is effectively suppressed.

[0090] Next, as shown in Table 1 and Figure 2, regarding the total amount of electrical current in the spike current during the aging process, Comparative Example 3, which contains hypophosphorous acid, was the same as Comparative Example 1, which did not contain phosphoric acid, and the risk of short-circuiting the electrolytic capacitor was not reduced. The total amount of electrical current in the spike current during the aging process in Comparative Example 2, which contains hypophosphorous acid, was lower than that of Comparative Example 1, which did not contain phosphoric acid. However, the results for Comparative Example 2 did not significantly reduce the risk of short-circuiting the electrolytic capacitor.

[0091] In contrast, the total amount of electric current in the spike current during the aging process in Example 1, which contains phosphoric acid, is less than half that of Comparative Example 1, which does not contain phosphoric acid. The results of Example 1 demonstrate a significant reduction in short circuits in electrolytic capacitors.

[0092] In other words, by combining phosphoric acid and diethylene glycol to prepare an electrolyte for electrolytic capacitors, the risk of short circuits in electrolytic capacitors is reduced, while the deterioration of the anode due to moisture attracted by inorganic oxide colloidal particles is effectively suppressed.

[0093] (Examples 2 and 3) Electrolytic solutions for electrolytic capacitors were prepared for Examples 2 and 3 and Comparative Examples 4 to 6. The electrolytic solutions for electrolytic capacitors in Examples 2 and 3 and Comparative Examples 4 to 6 contain a combination of phosphoric acid and diethylene glycol, following the example of Example 1. However, the phosphoric acid content differs in the electrolytic solutions for electrolytic capacitors in Examples 2 and 3 and Comparative Examples 4 to 6. The difference in phosphoric acid content is adjusted by the ethylene glycol content. In other words, the electrolytic solutions for electrolytic capacitors in Examples 2 and 3 and Comparative Examples 4 to 6 are identical in composition to the electrolytic solution for electrolytic capacitors in Example 1, except for the difference in the amount of phosphoric acid.

[0094] Specifically, Example 1 contains 0.17 wt% phosphoric acid relative to the total amount of electrolyte for electrolytic capacitors, whereas Comparative Example 1 did not contain any added phosphoric acid. In contrast, Comparative Example 4 contains 0.05 wt% phosphoric acid relative to the total amount of electrolyte for electrolytic capacitors. Comparative Example 5 contains 0.1 wt% phosphoric acid relative to the total amount of electrolyte for electrolytic capacitors.

[0095] Furthermore, Example 2 contains 0.25 wt% phosphoric acid relative to the total amount of electrolyte for the electrolytic capacitor. Example 3 contains 0.3 wt% phosphoric acid relative to the total amount of electrolyte for the electrolytic capacitor. Comparative Example 6 contains 0.34 wt% phosphoric acid relative to the total amount of electrolyte for the electrolytic capacitor.

[0096] (Aging test) Electrolytic capacitors impregnated with the electrolytes for electrolytic capacitors of Examples 2 and 3 and Comparative Examples 4 to 6 were manufactured. The configuration of the electrolytic capacitors, the manufacturing method of the electrolytic capacitors, and the manufacturing conditions were the same as those of Example 1 and Comparative Example 1.

[0097] Then, under the same conditions as in Example 1 and Comparative Example 1, the electrolytic capacitors of Examples 2 and 3 and Comparative Examples 4 to 6 were subjected to an aging process, and the total amount of electric current during the aging process was measured. The leakage current during this aging process was measured over time.

[0098] (Test results) Table 2 below shows the measurement results of the total electrical charge of the electrolytic capacitors in Examples 1 to 3 and Comparative Examples 1, 4 to 6. Furthermore, Figure 3 shows a graph based on Table 2 illustrating the relationship between various phosphoric acid addition amounts and the total electrical charge of the spike current during the aging process.

[0099] (Table 2) TIFF2026095167000004.tif68163

[0100] As shown in Table 2 and Figure 3 above, the total amount of electric spike current during the aging process in Comparative Examples 4 to 6 was no different from that of Comparative Example 1, and worse than that of Comparative Example 2, which contained hypophosphorous acid. In Comparative Examples 4 and 5, although a combination of phosphoric acid and diethylene glycol was included in the electrolyte for electrolytic capacitors, the phosphoric acid content was 0.1 wt% or less. In Comparative Example 6, although a combination of phosphoric acid and diethylene glycol was included in the electrolyte for electrolytic capacitors, the phosphoric acid content was more than 0.3 wt%.

[0101] In contrast, the total electrical energy of the spike current during the aging process in Examples 1 to 3 is less than half that of Comparative Example 1. Compared with Comparative Examples 4 to 6, the total electrical energy of the spike current during the aging process in Examples 1 to 3 is significantly smaller.

[0102] This confirmed that by preparing an electrolyte for electrolytic capacitors with a phosphoric acid content in the range of more than 0.1 wt% and less than or equal to 0.3 wt% of the total amount of electrolyte in the electrolytic capacitor, the risk of short circuits in the electrolytic capacitor is reduced while effectively suppressing the deterioration of the anode body due to moisture attracted by inorganic oxide colloid particles.

[0103] (Examples 4 to 6) Electrolytic solutions for electrolytic capacitors were prepared for Examples 4 to 6 and Comparative Example 7. The electrolytic solutions for electrolytic capacitors in Examples 4 to 6 and Comparative Example 7 contain a combination of phosphoric acid and diethylene glycol, following the example of Example 1. Furthermore, the electrolytic solutions for electrolytic capacitors in Examples 4 to 6 and Comparative Example 7 contain phosphoric acid in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of electrolyte in the electrolytic capacitor.

[0104] However, the electrolytes for electrolytic capacitors in Examples 4 to 6 and Comparative Example 7 differ in their diethylene glycol content. The difference in diethylene glycol content is adjusted by the ethylene glycol content. In other words, the electrolytes for electrolytic capacitors in Examples 4 to 6 and Comparative Example 7 are identical in composition to the electrolyte for electrolytic capacitors in Example 1, except for the amount of phosphoric acid.

[0105] Specifically, Example 1 contains 15.4 wt% diethylene glycol relative to the total amount of electrolyte for the electrolytic capacitor. Converted to a solvent content, the diethylene glycol content of Example 1 is 18.7 wt% relative to the total amount of solvent.

[0106] In contrast, Comparative Example 7 contains 5 wt% diethylene glycol relative to the total amount of electrolyte for the electrolytic capacitor. Converted to a content relative to the solvent, the diethylene glycol content of Comparative Example 7 is 6.1 wt% relative to the total amount of solvent.

[0107] Example 4 contains 11.6 wt% diethylene glycol relative to the total amount of electrolyte for the electrolytic capacitor. When converted to a percentage of the solvent, the diethylene glycol content in Example 4 is 14.1 wt% relative to the total amount of solvent.

[0108] Example 5 contains 30 wt% diethylene glycol relative to the total amount of electrolyte for the electrolytic capacitor. When converted to a percentage of the solvent, the diethylene glycol content in Example 5 is 36.5 wt% relative to the total amount of solvent.

[0109] Example 6 contains 50.53 wt% diethylene glycol relative to the total amount of electrolyte for the electrolytic capacitor. Converted to a solvent content, the diethylene glycol content of Example 6 is 61.4 wt% relative to the total amount of solvent.

[0110] (Aging test and LC test) Electrolytic capacitors impregnated with the electrolytes for electrolytic capacitors of Examples 4 to 6 and Comparative Example 7 were manufactured. The configuration of the electrolytic capacitors, the manufacturing method of the electrolytic capacitors, and the manufacturing conditions were the same as those of Example 1 and Comparative Example 1.

[0111] Then, under the same conditions as in Example 1 and Comparative Example 1, the electrolytic capacitors of Examples 4 to 6 and Comparative Example 7 were subjected to an aging process, and the total amount of electric current during the aging process was measured. The leakage current during this aging process was measured over time. Furthermore, under the same conditions as in Example 1 and Comparative Example 1, the leakage current of the electrolytic capacitors of Examples 4 to 6 and Comparative Example 7 was measured after being left in a high-temperature environment for a long period of time following the aging process.

[0112] (Test results) Table 3 below shows the measurement results of the total charge and leakage current of the electrolytic capacitors in Examples 4 to 6 and Comparative Example 7. Furthermore, based on Table 3, Figure 4 shows a graph illustrating the relationship between various diethylene glycol addition amounts and the total charge of the spike current during the aging process.

[0113] (Table 3) TIFF2026095167000005.tif95161

[0114] First, as shown in Table 3 above, regardless of the diethylene glycol content, Comparative Example 7, Example 1, and Examples 4 to 6 exhibited low leakage currents, effectively suppressing the degradation of the anode due to moisture attracted by inorganic oxide colloidal particles.

[0115] However, as shown in Table 3 and Figure 4 above, the total amount of electric spike current during the aging process in Comparative Example 7 deteriorated to the same extent as in Comparative Example 2, which contained hypophosphorous acid. In Comparative Example 7, a combination of phosphoric acid and diethylene glycol was included in the electrolyte for electrolytic capacitors, and although the phosphoric acid content was in the range of more than 0.1 wt% and 0.3 wt% or less of the total amount of electrolyte for electrolytic capacitors, the diethylene glycol content was reduced.

[0116] In contrast, the total electrical energy of the spike current during the aging process in Examples 1 and 4 to 6, where the diethylene glycol content relative to the total solvent is 14.1 wt% or more, is lower than that of Comparative Examples 1 and 2. In particular, the total electrical energy of the spike current during the aging process in Examples 1, 5, and 6, where the diethylene glycol content relative to the total solvent is 18.7 wt% or more, is remarkably low.

[0117] In general, it was confirmed that by preparing an electrolyte for electrolytic capacitors by combining phosphoric acid and diethylene glycol, with the phosphoric acid content being in the range of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of electrolyte for electrolytic capacitors, and the diethylene glycol content being 14 wt% or more relative to the total amount of solvent, the risk of short circuits in electrolytic capacitors is reduced, while the deterioration of the anode body due to moisture attracted by inorganic oxide colloidal particles is effectively suppressed.

[0118] (Examples 7 to 11) Electrolytic solutions for electrolytic capacitors were prepared in Examples 7 to 11. The electrolytic solutions for electrolytic capacitors in Examples 7 to 11 have the same composition as the electrolytic solution for electrolytic capacitors in Example 1, but differ in the content of azelaic acid and 1,6-decanedicarboxylic acid.

[0119] Specifically, Example 7 contains 7.36 wt% of 1,6-decanedicarboxylic acid relative to the total amount of electrolyte for the electrolytic capacitor, and no azelaic acid is added. When converted to mol% relative to the total amount of organic acids, which is the sum of azelaic acid and 1,6-decanedicarboxylic acid, the content of 1,6-decanedicarboxylic acid in Example 7 is 100 mol% relative to the total amount of organic acids.

[0120] Example 8 contains 5.52 wt% 1,6-decanedicarboxylic acid and 1.50 wt% azelaic acid relative to the total amount of electrolyte for electrolytic capacitors. When converted to mol% relative to the total amount of organic acids, the 1,6-decanedicarboxylic acid content in Example 8 is 75 mol% relative to the total amount of organic acids.

[0121] Example 9 contains 3.68 wt% of 1,6-decanedicarboxylic acid and 3.00 wt% of azelaic acid relative to the total amount of electrolyte for electrolytic capacitors. When converted to mol% relative to the total amount of organic acids, the 1,6-decanedicarboxylic acid content in Example 9 is 50 mol% relative to the total amount of organic acids.

[0122] Example 10 contains 1.84 wt% of 1,6-decanedicarboxylic acid and 4.50 wt% of azelaic acid relative to the total amount of electrolyte for electrolytic capacitors. When converted to mol% relative to the total amount of organic acids, the 1,6-decanedicarboxylic acid content in Example 10 is 25 mol% relative to the total amount of organic acids.

[0123] Example 11 contains 6.00 wt% azelaic acid relative to the total amount of electrolyte for electrolytic capacitors, and no 1,6-decanedicarboxylic acid is added. When converted to a mol% content relative to the total amount of organic acids, the 1,6-decanedicarboxylic acid content in Example 11 is 0 mol% relative to the total amount of organic acids.

[0124] (Aging test and LC test) Electrolytic capacitors impregnated with the electrolytes for electrolytic capacitors of Examples 7 to 11 were manufactured. The configuration of the electrolytic capacitors, the manufacturing method of the electrolytic capacitors, and the manufacturing conditions were the same as those of Example 1 and Comparative Example 1.

[0125] Then, under the same conditions as in Example 1 and Comparative Example 1, the electrolytic capacitors of Examples 7 to 11 were subjected to an aging process, and the total amount of electrical current during the aging process was measured. The leakage current during this aging process was measured over time. Furthermore, under the same conditions as in Example 1 and Comparative Example 1, the leakage current of the electrolytic capacitors of Examples 7 to 11 was measured after being left in a high-temperature environment for a long period of time following the aging process.

[0126] (Test results) Table 4 below shows the measurement results of the total charge and leakage current of the electrolytic capacitors in Examples 7 to 11. Furthermore, based on Table 4, Figure 5 shows a graph illustrating the relationship between various amounts of 1,6-decanedicarboxylic acid added and the total charge of the spike current during the aging process.

[0127] (Table 4) TIFF2026095167000006.tif122163

[0128] First, as shown in Table 4 above, regardless of the 1,6-decanedicarboxylic acid content, Examples 7 to 11 exhibited low leakage currents, effectively suppressing the degradation of the anode body due to moisture attracted by the inorganic oxide colloid particles.

[0129] Next, as shown in Table 4 and Figure 5 above, even in Example 11, where 1,6-decanedicarboxylic acid is not added, the total amount of electric current in the spike current during the aging process is small. It can be confirmed that the total amount of electric current in the spike current during the aging process is even smaller for the electrolytic capacitors of Examples 7 to 10 compared to Example 11.

[0130] As a result, it was confirmed that by further preparing the electrolyte for electrolytic capacitors by including 25 mol% or more of 1,6-decanedicarboxylic acid relative to the total amount of electrolyte for electrolytic capacitors, the risk of short circuits in electrolytic capacitors is further reduced, while the deterioration of the anode body due to moisture attracted by inorganic oxide colloidal particles is effectively suppressed.

Claims

1. Inorganic oxide colloidal particles and Phosphoric acid contained in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of electrolyte for electrolytic capacitors, Diethylene glycol present in 14 wt% or more of the total amount of solvent, Including, An electrolyte for electrolytic capacitors characterized by the following.

2. Contains organic acids, The organic acid contains 25 mol% or more of 1,6-decanedicarboxylic acid relative to the total amount of the organic acid. The electrolyte for electrolytic capacitors according to claim 1, characterized by the above.

3. It contains 14 wt% to 62 wt% of diethylene glycol relative to the total amount of solvent. The electrolyte for electrolytic capacitors according to claim 1, characterized by the above.

4. An anode body having a dielectric film formed on the surface of a foil with a valve-acting metal as the base material, Cathode body and, An electrolyte interposed between the anode and the cathode, Equipped with, The aforementioned electrolyte is Inorganic oxide colloidal particles and Phosphoric acid in an amount of more than 0.1 wt% and 0.3 wt% or less relative to the total amount of the electrolyte, Diethylene glycol in an amount of 14 wt% or more relative to the total amount of solvent, Including, An electrolytic capacitor characterized by the following features.

5. Anode formation step in which an anode body is formed in which a dielectric film is formed on the surface of a foil with a valve metal as the base material, A cathode formation process for forming a cathode body, An electrolyte preparation step for preparing an electrolyte to be interposed between the anode and the cathode, An element formation step of forming an element in which the anode and the cathode are facing each other, An electrolyte impregnation step in which the element is impregnated with the electrolyte, Includes, The aforementioned electrolyte is Inorganic oxide colloidal particles and Phosphoric acid contained in an amount greater than 0.1 wt% and less than or equal to 0.3 wt% of the total amount of electrolyte, Diethylene glycol present in 14 wt% or more of the total amount of solvent, Including, A method for manufacturing electrolytic capacitors characterized by the following.

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