TWI838391B - Electrolyte for electrolytic capacitor and electrolytic capacitor - Google Patents

Abstract

The present invention provides an electrolyte for an electrolytic capacitor and an electrolytic capacitor that improves the withstand voltage and maintains the withstand voltage effect for a long time, and suppresses the characteristic change of the electrolytic capacitor by suppressing the dissolution of the dielectric oxide film, thereby making the life characteristics good. The electrolyte contains a solute, inorganic oxide colloid particles whose surface is modified by an organic substance, and a silane coupling agent or a silylating agent. The electrolytic capacitor is formed by impregnating the electrolyte into a capacitor element, and the silane coupling agent or the silylating agent is adsorbed on the surface of the electrode foil, and the silane coupling agent or the silylating agent is interposed between the inorganic oxide colloid particles whose surface is modified by an organic substance, so that the colloid particles are stably dispersed.

Description

Electrolyte for electrolytic capacitor and electrolytic capacitor

The present invention relates to an electrolyte for an electrolytic capacitor and an electrolytic capacitor.

The electrolytic capacitor includes a valve metal such as tantalum or aluminum as an anode foil and a cathode foil. The anode foil is expanded by making the valve metal into a sintered body or an etched foil, and has a dielectric oxide film layer on the expanded surface. An electrolyte is interposed between the anode foil and the cathode foil. The electrolyte is in close contact with the concave and convex surface of the anode foil and functions as a true cathode.

The electrolyte is interposed between the dielectric oxide film layer of the anode foil and the cathode foil, and electrons are transferred between the anode foil and the cathode foil. Therefore, the conductivity and temperature characteristics of the electrolyte have a great influence on the electrical characteristics of the electrolytic capacitor, such as impedance, dielectric loss (tanδ) and equivalent series resistance (ESR). In addition, the electrolyte has the chemical property of repairing the deteriorated parts such as deterioration or damage of the dielectric oxide film formed on the anode foil, which affects the leakage current (LC) or life characteristics of the electrolytic capacitor.

Therefore, an electrolyte with at least high conductivity is appropriate for an electrolytic capacitor. If the conductivity of the electrolyte is increased, the spark voltage tends to decrease, which may damage the withstand voltage characteristics of the electrolytic capacitor. From the perspective of safety, it is ideal that the electrolytic capacitor has a high withstand voltage even under severe conditions such as an abnormal voltage exceeding the rated voltage, so as not to cause a short circuit or fire.

Therefore, in order to maintain high conductivity and improve withstand voltage, attempts have been made to add various inorganic oxide colloid particles to the electrolyte (see Patent Document 1). Inorganic oxide colloid particles are typically silica colloid particles, and in addition to silica, zirconium oxide, titanium oxide, aluminum silicate, aluminum silicate coated with silica, etc. have also been proposed.

[Prior art literature]

[Patent Literature]

[Patent document 1] Japanese Patent Publication No. 10-241999

However, in an electrolyte containing inorganic oxide colloid particles, the inorganic oxide colloid particles precipitate or aggregate over time, and gelation of the electrolyte is confirmed. Moreover, a decrease in withstand voltage is confirmed along with this phenomenon. That is, inhibiting the gelation or precipitation of the inorganic oxide colloid particles and stably maintaining the colloidal state has become a problem for improving the withstand voltage. In particular, it is confirmed that inorganic oxide colloid particles whose surfaces are modified by organic substances are difficult to cause gelation or precipitation, but even when ethylene glycol is selected as the solvent of the electrolyte, it is expected that the stable colloidal state will last for a longer time. In addition, according to the research of the inventors and others, it has been confirmed that when the electrolyte contains inorganic oxide colloid particles whose surface is modified by organic matter, the dielectric oxide film dissolves. If the dielectric oxide film dissolves, it will affect the various characteristics and life characteristics of the electrolytic capacitor after a long time.

The present invention is proposed to solve the above-mentioned problem, and its purpose is to provide an electrolyte for an electrolytic capacitor and an electrolytic capacitor that improves the withstand voltage and makes the withstand voltage last for a long time. Furthermore, by suppressing the dissolution of the dielectric oxide film of the electrode foil, the characteristic change of the electrolytic capacitor is suppressed, and the life characteristics are improved.

In order to achieve the above-mentioned purpose, the electrolyte for the electrolytic capacitor of the present invention is characterized by comprising: a solvent, a solute, inorganic oxide colloid particles whose surface is modified by organic matter, and a silane coupling agent or a silylating agent.

The silylating agent or the silane coupling agent can be represented by the following general formula (Chemical 1).

[In the formula, _X1 is an alkyl group, alkenyl group, aryl group or aralkyl group having 1 to 20 carbon atoms, and is a hydrocarbon group (-R) whose hydrogen atoms may be partially substituted by a carboxyl group, an ester group, an amide group, a cyano group, a keto group, a formyl group, an ether group, a hydroxyl group, an amine group, an oxirane group, a sulfide group, a sulfonate group, an isocyanate group, a urea group or an epoxy group; _X2 to _X4 are acetyloxy groups, alkoxy groups or alkyl groups having 1 to 5 carbon atoms, and at least two of _X2 to _X4 are alkoxy groups]

The silylating agent or silane coupling agent represented by the general formula (1) may be one or more selected from the group consisting of 3-glycidyloxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, vinyltrimethoxysilane, p-phenylenediyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropylmethyldiethoxysilane.

The inorganic oxide colloid particles may be silicon dioxide.

The amount of the silane coupling agent or the silylating agent added relative to the solvent may be greater than 0.05 mol/kg and less than 0.40 mol/kg.

The amount of the silylating agent or silane coupling agent added may be 0.76×10 ^-3 mol or more based on 1 g of the inorganic oxide colloid particles whose surfaces are modified with organic matter.

The solvent may mainly contain ethylene glycol.

In addition, an electrolytic capacitor including the electrolyte for the electrolytic capacitor is also an aspect of the present invention. The electrolytic capacitor may include a pair of electrode foils, a portion of the silylating agent or the silane coupling agent may exist on the surface of the electrode foil, and a portion of the inorganic oxide colloid particles surface-modified by an organic substance may approach the electrode foil via the silylating agent or the silane coupling agent existing on the surface of the electrode foil.

According to the present invention, the colloidal state can be maintained stably for a long time, and a high withstand voltage can be maintained for a long time. Furthermore, the dissolution of the dielectric oxide film of the electrode foil is suppressed, and the hydration degradation reaction is suppressed, thereby suppressing the change of various characteristics of the electrolytic capacitor and achieving a long life.

Figure 1 is a graph showing the results of withstand voltage measurement of the dielectric oxide film of the cathode foil.

Figure 2 is a graph showing the withstand voltage test results of the dielectric oxide film of the anode foil.

Figure 3(a) to Figure 3(c) are scanning electron microscope (SEM) images of anode foil.

Figure 4(a) and Figure 4(b) are graphs showing the temporal variation of the electrostatic capacitance of an electrolytic capacitor.

FIG5 is a graph showing the temporal variation of the electrostatic capacitance of an electrolytic capacitor.

The electrolyte and electrolytic capacitor of the embodiment of the present invention are described. The electrolytic capacitor is a passive element that stores and discharges electric charge by electrostatic capacitance. The electrolytic capacitor has a capacitor element in which the anode foil and the cathode foil are facing each other through a spacer, and the capacitor element is impregnated with an electrolyte. The anode foil and the cathode foil have a porous structure on the surface, and a dielectric oxide film layer is formed at least on the porous structure portion of the anode foil. The electrolyte medium exists between the anode foil and the cathode foil, and is in close contact with the dielectric oxide film layer of the anode foil, becoming a true cathode that transmits the electric field of the foil. The spacer prevents the short circuit between the anode foil and the cathode foil, and also retains the electrolyte.

Anode foil and cathode foil are long foils made of valve metals. Valve metals include aluminum, tantalum, niobium, niobium oxide, titanium, uranium, zirconium, zinc, tungsten, bismuth and antimony. For anode foil, the ideal purity is about 99.9% or more, and for cathode foil, the ideal purity is about 99% or more. It may also contain impurities such as silicon, iron, copper, magnesium and zinc.

Anode foil and cathode foil are sintered bodies formed by sintering valve metal powder, or etched foil formed by etching stretched foil. The porous structure is formed by channel-shaped pits, sponge-shaped pits, or gaps between dense powders. Typically, the porous structure is formed by applying direct current or alternating current etching or alternating current etching in an acidic aqueous solution containing halogen ions such as hydrochloric acid, or by evaporating or sintering metal particles in the core. Compared with anode foil, cathode foil has less influence on the surface area of the electrostatic capacitance of the electrolytic capacitor, so the surface roughness of the porous structure can also be small.

Typically, the dielectric oxide film layer is an oxide film formed on the surface of the anode foil. If the anode foil is made of aluminum, it is an aluminum oxide layer formed by oxidizing the porous structure. The dielectric oxide film layer is formed by applying a voltage to a solution without halogen ions such as an acid such as ammonium borate, ammonium phosphate, ammonium adipate, or an aqueous solution of these acids. The dielectric oxide film layer can also be provided on the cathode foil.

The spacers include: kraft paper, Manila hemp (Musa textilis), thatch (Esparto), hemp (hemp), rayon and other cellulose and mixed papers thereof, polyester resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, and derivatives thereof, polytetrafluoroethylene resins, polyvinylidene fluoride resins, vinylon resins, aliphatic polyamide, semi-aromatic polyamide, fully aromatic polyamide and other polyamide resins, polyimide resins, polyethylene resins, polypropylene resins, trimethylpentene resins, polyphenylene sulfide resins, acrylic resins, etc. These resins can be used alone or in combination.

The electrolyte is a mixed solution in which a solute is dissolved in a solvent and an additive is added to the solvent. As additives, at least inorganic oxide colloid particles whose surfaces are modified by organic matter (hereinafter referred to as organic modified colloid particles) and a silane coupling agent or a silylating agent (hereinafter collectively referred to as a silane coupling agent) are added to the electrolyte.

As inorganic oxide colloid particles, there can be listed: silicon dioxide, aluminum oxide, titanium oxide, zirconia, antimony oxide, aluminum silicate, silica zirconia, titanium oxide zirconia, silicon dioxide coated with aluminum silicate, silicon dioxide coated with silica zirconia, etc., or mixtures thereof. Among these inorganic oxide colloid particles, silicon dioxide, aluminum silicate, or silicon dioxide coated with aluminum silicate is particularly preferred from the viewpoint of the ease of silylation treatment, the stability of the colloid particles, and the effect of improving the withstand voltage.

The organic substance used to modify the surface of the inorganic oxide colloid particles is an organic substance that replaces the surface hydroxyl groups of the inorganic oxide colloid particles to inhibit the aggregation of the inorganic oxide colloid particles, such as silylating agents, silane coupling agents, titanium ester coupling agents, aluminum coupling agents, alcohols, latex and other polymer compounds. The silylating agent or silane coupling agent is represented by the following general formula (Chemical 2).

[Chemistry 2]

[In the formula, _X1 is an alkyl group, alkenyl group, aryl group or aralkyl group having 1 to 20 carbon atoms, and is a hydrocarbon group (-R) whose hydrogen atoms may be partially substituted by a carboxyl group, an ester group, an amide group, a cyano group, a keto group, a formyl group, an ether group, a hydroxyl group, an amine group, an oxirane group, a sulfide group, a sulfonate group, an isocyanate group, a urea group or an epoxy group; _X2 to _X4 are acetyloxy groups, alkoxy groups or alkyl groups having 1 to 5 carbon atoms, and at least two of _X2 to _X4 are alkoxy groups]

Specific examples of _X1 include alkyl groups such as methyl, ethyl, propyl, butyl, decyl, and octadecyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl, naphthyl, and styryl; alkyl groups such as aralkyl groups such as benzyl and phenethyl; and oxyalkyl or hydroxyl groups such as methoxy, ethoxy, propoxy, butoxy, vinyloxy, phenoxy, and benzyloxy. Furthermore, examples of the case where there is a substituent include: acrylic groups such as 3-methacryloxypropyl and 3-acryloxypropyl; epoxy groups such as 3-glycidyloxypropyl and 2-(3,4-epoxycyclohexyl)ethyl; amino groups such as 3-aminopropyl, N-phenyl-3-aminopropyl and N-2-(aminoethyl)-3-aminopropyl; alkoxy groups such as 3-butylpropyl; isocyanate groups such as 3-isocyanatepropyl; urea groups such as 3-ureidopropyl, etc. Specific examples of X ₂ to X ₄ include: alkoxy groups such as methoxy, ethoxy, propoxy and butoxy; alkyl groups such as methyl, ethyl, propyl, butyl, decyl and octadecyl; acetyloxy, and at least two of X ₂ to X ₄ are alkoxy groups.

Among these combinations, the preferred ones are: methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, isobutyltrimethoxysilane, isobutyltriethoxysilane, decyltrimethoxysilane, decyltriethoxysilane, vinyltrimethoxysilane, Methoxysilane, vinyl triethoxysilane, 3-methacryloyloxypropyl trimethoxysilane, 3-methacryloyloxypropyl triethoxysilane, 3-glycidyloxypropyl trimethoxysilane, 3-glycidyloxypropyl triethoxysilane, 3-glycidyloxypropyl methyl dimethoxysilane, 3-glycidyloxypropyl methyl diethoxysilane, 2-(3,4 -(3,4-Epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-Epoxycyclohexyl)ethyltriethoxysilane, 3-ureidopropyltrialkoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, N-phenyl-3-aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropyl N-2-(aminoethyl)-3-aminopropyl triethoxysilane, N-2-(aminoethyl)-3-aminopropyl methyldimethoxysilane, 3-butylenepropyl trimethoxysilane, 3-butylenepropyl triethoxysilane, 3-acryloyloxypropyl trimethoxysilane, 3-isocyanate propyl triethoxysilane, p-phenylenetrimethoxysilane, etc.

Specific examples of titanium ester coupling agents include isopropyl triisostearate titanium ester, isopropyl tri-dodecylbenzenesulfonyl titanium ester, isopropyl tri(dioctyl pyrophosphate) titanium ester, tetraisopropyl di(dioctyl phosphite) titanium ester, tetraoctyl di(di-tridecanthyl phosphite) titanium ester, tetra(2,2-diallyloxymethyl-1- butyl)bis(di-tridecyl)phosphite titanium ester, bis(dioctyl pyrophosphate)oxyacetate titanium ester, isopropyl trioctyl titanium ester, isopropyl dimethacryloyl isostearyl titanium ester, isopropyl tri(dioctyl phosphate) titanium ester, isopropyl tricumylphenyl titanium ester, isopropyl tri(N-aminoethylaminoethyl) titanium ester, etc.

Specific examples of aluminum coupling agents include: ethyl acetate diisopropyl aluminum, tri(ethyl acetate) aluminum, tri(acetylacetone) aluminum, bis(ethyl acetate) monoacetylacetone aluminum, etc. Specific examples of alcohols include: methanol, ethanol, n-propanol, isopropanol, 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, polyvinyl alcohol, etc.

These organic substances used in surface modification such as silylating agents, silane coupling agents, titanium ester coupling agents, aluminum coupling agents, alcohols, various polymer compounds, etc. can be used alone or in combination.

The silane coupling agent added to the electrolyte together with the organic modified colloid particles is also represented by the general formula (Chemical 2). The organic substance and the silane coupling agent for modifying the surface of the inorganic oxide colloid particles may be the same compound or different compounds. The organic modified colloid particles and the silane coupling agent inhibit the gelation of the electrolyte and the aggregation of the colloid particles, and maintain the withstand voltage of the electrolytic capacitor increased by adding the organic modified colloid particles. The amount of the silane coupling agent added relative to 1 kg of the solvent is preferably greater than 0.05 mol/kg and less than 0.40 mol/kg. If it is within this range, the gelation of the electrolyte or the aggregation of the colloid particles can be suppressed for a long time, and the organic modified colloid particles can be stably dispersed for a long time. If the amount of silane coupling agent added is too large, although gelation and aggregation can be suppressed, the effect is reduced. Therefore, when adding 0.40 mol/kg or more, it is better to consider the balance with other characteristics of the electrolytic capacitor.

The reason for suppressing aggregation and maintaining the withstand voltage is not limited to this mechanism, and can be inferred as follows. First, the organic modified colloidal particles have higher dispersion stability than the inorganic oxide colloidal particles whose surfaces are not modified by organic substances, thereby suppressing the gelation of the electrolyte. Therefore, the withstand voltage improved by adding the organic modified colloidal particles can be maintained for a long time. Furthermore, in the present application, not only the organic modified colloidal particles are used, but also the silane coupling agent is used at the same time. By using the silane coupling agent in combination with the organic modified colloidal particles, and the silane coupling agent is present between the organic modified colloidal particles, the aggregation suppression effect of the organic modified colloidal particles can be further improved. Therefore, by adding both organic modified colloidal particles and silane coupling agents to the electrolyte, the gelation of the electrolyte and the aggregation of the colloidal particles can be suppressed, and a high withstand voltage can be maintained.

In addition, the inventors have made intensive research and have obtained the following insights: organic modified colloidal particles affect the dissolution of dielectric oxide films of anode foil and cathode foil. Furthermore, the inventors have obtained the following insights: if both organic modified colloidal particles and silane coupling agents are added to the electrolyte, the dissolution of dielectric oxide films of anode foil and cathode foil can be suppressed, and the change of electrostatic capacitance can be suppressed. From the viewpoint of suppressing the change of electrostatic capacitance, the addition amount of silane coupling agent relative to 1g of organic modified colloidal particles is preferably 0.76×10 ^-3 mol or more, and if it is 2.27×10 ^-3 mol or more, it is particularly preferred that the addition amount is greatly improved. Furthermore, when the concentration is 7.57×10 ^-3 mol or more, the change in electrostatic capacitance can be suppressed to the same level as that in the state where the organic modified colloidal particles are not added.

This is also speculation, and is not limited to this mechanism. It is believed that the effects of suppressing dissolution and suppressing changes in electrostatic capacitance are based on the following reasons. That is, it is believed that there are residual hydroxyl groups on the surface of the organic modified colloidal particles. The hydroxyl groups on the surface of the organic modified colloidal particles attract moisture in the electrolyte. Therefore, if the organic modified colloidal particles exist near the electrode foil, the moisture attracted by the hydroxyl groups on the surface of the organic modified colloidal particles easily approaches the dielectric oxide film, dissolves the dielectric oxide film, and reaches the valve metal through the dielectric oxide film, causing the valve metal to hydrate and deteriorate. However, silane coupling agent is adsorbed on the dielectric oxide film of the electrolytic capacitor. Therefore, a certain distance can be maintained between the organic modified colloidal particles and the electrode foil, and the hydroxyl groups on the surface of the organic modified colloidal particles or the water attracted by them are difficult to approach the electrode foil, which can inhibit hydration degradation.

As described above, the electrolytic capacitor of the present application suppresses the dissolution of the dielectric oxide film by adsorbing the silane coupling agent on the electrode foil and existing on the surface of the electrode foil, and further improves the withstand voltage by bringing the organic modified colloid particles close to the electrode foil through the silane coupling agent adsorbed on the electrode foil. In addition, the silane coupling agent exists between the organic modified colloid particles to suppress the aggregation of the organic modified colloid particles.

The solvent used together with the organic modified colloidal particles and the silane coupling agent can be any of a protic organic polar solvent or an aprotic organic polar solvent. Representative examples of protic organic polar solvents include monohydric alcohols, polyhydric alcohols, and oxyalcohol compounds. Representative examples of aprotic organic polar solvents include sulfonates, amides, lactones, cyclic amides, nitrile, and oxides.

As monohydric alcohols, there are ethanol, propanol, butanol, pentanol, hexanol, cyclobutanol, cyclopentanol, cyclohexanol, benzyl alcohol, etc. As polyols and oxy alcohol compounds, there are ethylene glycol, propylene glycol, glycerol, methyl sulfoxide, ethyl sulfoxide, methoxy propylene glycol, dimethoxy propylene glycol, etc. As sulfones, there are dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, cyclobutane sulfone, 3-methylcyclobutane sulfone, 2,4-dimethylcyclobutane sulfone, etc. Examples of amides include N-methylformamide, N,N-dimethylformamide, N-ethylformamide, N,N-diethylformamide, N-methylacetamide, N,N-dimethylacetamide, N-ethylacetamide, N,N-diethylacetamide, hexamethylphosphatamide, etc. Examples of lactones and cyclic amides include γ-butyrolactone, γ-valerolactone, δ-valerolactone, N-methyl-2-pyrrolidone, ethyl carbonate, propyl carbonate, butyl carbonate, isobutyl carbonate, etc. Examples of nitrile series include acetonitrile, 3-methoxypropionitrile, glutaronitrile, etc. Examples of oxide series include dimethyl sulfoxide, etc. As a solvent, these may be used alone or in combination of two or more. In addition, the solvent may also contain water.

In particular, when using ethylene glycol or a solvent composed mainly of ethylene glycol and mixed with other solvents, if the organic modified colloid particles and the silane coupling agent are added, the effects of inhibiting gelation and agglomeration are very high, and it is an appropriate combination.

As the solute contained in the electrolyte, at least one salt of organic acid, inorganic acid, and complex compound of organic acid and inorganic acid used in the electrolyte for electrolytic capacitors can be listed. These can be used alone or in combination of two or more.

Examples of organic acids include phthalic acid, isophthalic acid, terephthalic acid, maleic acid, adipic acid, benzoic acid, toluic acid, heptanoic acid, malonic acid, 1,6-decanedicarboxylic acid, 1,7-octanedicarboxylic acid, azelaic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, and other carboxylic acids, phenols, and sulfonic acids. Examples of inorganic acids include boric acid, phosphoric acid, phosphorous acid, hypophosphorous acid, carbonic acid, and silicic acid. Examples of complex compounds of organic and inorganic acids include borodisalicylic acid, boro dioxalic acid, and borodiglycolic acid.

In addition, as at least one salt of an organic acid, an inorganic acid, and a complex compound of an organic acid and an inorganic acid, ammonium salts, quaternary ammonium salts, quaternary amidinium salts, amine salts, sodium salts, potassium salts, etc., can be cited. As quaternary ammonium of the quaternary ammonium salt, tetramethylammonium, triethylmethylammonium, tetraethylammonium, etc. can be cited. As quaternary amidinium, ethyldimethylimidazolium, tetramethylimidazolium, etc. can be cited. As amines of the amine salts, primary amines, secondary amines, and tertiary amines can be cited. Examples of primary amines include methylamine, ethylamine, propylamine, etc. Examples of secondary amines include dimethylamine, diethylamine, ethylmethylamine, dibutylamine, etc. Examples of tertiary amines include trimethylamine, triethylamine, tributylamine, ethyldimethylamine, ethyldiisopropylamine, etc.

Particularly preferred are ammonium salts and amine salts. Ammonium salts can reduce the specific resistance of the electrolyte, thereby achieving low ESR of the electrolytic capacitor. If amine salts are used, the hydration inhibition effect is obtained by the amine salts, thereby extending the life of the electrolytic capacitor. Furthermore, among amine salts, diamines with excellent balance between withstand voltage and specific resistance are particularly preferred.

In addition, compounds other than organic modified colloid particles, silylating agents or silane coupling agents may be further added to the electrolyte as other additives. For example, polyalkylene glycol, boric acid, ester compounds of boric acid and polysaccharides (mannite, sorbitol, etc.), ester compounds of boric acid and polyols (ethylene glycol, mannitol, sorbitol), boric acid compounds such as borate esters, nitro compounds (o-nitrobenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, o-nitrophenol, m-nitrophenol, p-nitrophenol, m-nitroacetophenone, p-nitrobenzyl alcohol, etc.), phosphoric acid, phosphoric acid esters and other phosphorus compounds.

[Implementation example]

The present invention is described in more detail below based on the embodiments. Furthermore, the present invention is not limited to the following embodiments.

(Gelative evaluation 1)

As shown in Table 1 below, the electrolyte solutions of Comparative Examples 1 to 3 and Examples 1 to 7 were prepared.

The solvent of the electrolyte is a mixture of ethylene glycol and water, the solute is ammonium azelaic acid, and p-nitrobenzyl alcohol is added as an additive. The composition of the electrolyte of Comparative Example 1 is as described above, but silica as inorganic oxide colloid particles is further added to the electrolyte of Comparative Example 2. In the electrolytes of Comparative Example 3 and Examples 1 to 7, organic modified silica is added as organic modified colloid particles. The organic modified silica is formed by modifying the surface of silica with 3-glyceryloxypropyltrimethoxysilane. Furthermore, in the electrolytes of Examples 1 to 7, 3-glyceryloxypropylmethyldimethoxysilane (KBM-402 manufactured by Shin-Etsu Silicones) is added as a silane coupling agent. The composition ratios are in weight % and are shown in Table 1. In addition, the amount of silane coupling agent added relative to 1 kg of solvent and the amount of silane coupling agent added relative to 1 g of organic modified silica are also shown in Table 1. Here, the solvent is the total amount of ethylene glycol and water.

The specific resistance of the prepared electrolyte is shown in Table 1. The specific resistance was measured at 30°C.

For the electrolytes of Comparative Examples 1 to 3 and Examples 1 to 7, a placement test was conducted to confirm the state of gelation. The results are also shown in Table 1. In the placement test, the time until each electrolyte gelled was measured. Each electrolyte was placed in an ampoule tube and maintained at 125°C. During a maximum period of 2300 hours, it was visually confirmed whether gelation occurred within each measurement time. The state in which the contents did not flow even if the ampoule tube containing the electrolyte was tilted was considered to be gelled. The times recorded in Table 1 are the times when gelation was confirmed, not the times when gelation occurred. In addition, the hyphen (-) mark indicates the case where gelation was not observed after 2300 hours.

The capacitor element is then impregnated with each electrolyte, and then placed in a bottomed cylindrical outer casing and sealed with a sealing rubber. The anode foil is expanded by etching, and then a dielectric oxide film layer is formed by chemical conversion. In addition, the aluminum foil is expanded by etching to produce an aluminum cathode foil. The electrode lead-out parts are connected to the produced anode foil and cathode foil, and a cellulose spacer is interposed and wound to produce a capacitor element. In this way, a wound electrolytic capacitor with a capacitor element size of 10 mm in diameter and 25 mm in length is obtained. The electrolytic capacitors of Comparative Examples 1 to 3 and Examples 1 to 7 were subjected to a withstand voltage test. The results are also shown in Table 1. In the withstand voltage test, the withstand voltage was measured at 125°C.

As shown in Table 1, if the main solvent is ethylene glycol, the electrolyte of Comparative Example 2 with added silica gelates within 2 hours. Regarding the electrolyte of Comparative Example 3, the main solvent is ethylene glycol, and organic modified silica is added. Compared with Comparative Example 2, the gelation time becomes longer, but even so, it still gelates within 250 hours.

On the other hand, as shown in Table 1, even if the main solvent is ethylene glycol, the time for the electrolytes of Examples 1 to 7 to which organic modified silica and silane coupling agents are added to reach gelation is also prolonged. In particular, the electrolytes of Examples 1 to 4 and 6, in which the amount of silane coupling agents added is suppressed to less than 0.40 mol/kg relative to the solvent, did not reach gelation during the observation for 2300 hours. That is, it was confirmed that the gelation of the electrolytes to which organic modified silica and silane coupling agents are added is suppressed, and in particular, it was confirmed that the gelation can be suppressed dramatically if the amount of silane coupling agents is less than 0.40 mol/kg relative to the total amount of the solvent.

Secondly, as shown in Table 1, it was confirmed that even when the main solvent was ethylene glycol, the withstand voltage of the electrolytic capacitor was improved when organic modified silica was added. Therefore, it was confirmed that the withstand voltage was improved by adding organic modified silica to the electrolyte, and the gelation of the electrolyte was suppressed by adding a silane coupling agent.

(Gelative evaluation 2)

As shown in Table 2 below, electrolytes of Comparative Examples 4 to 7 and Examples 8 to 9 were prepared. As in Table 1, the results of the placement test to confirm the gelation state and the withstand voltage measured at 125°C are shown.

Comparative Example 4, Comparative Example 5, and Example 8 are the same as Comparative Example 1, Comparative Example 3, and Example 1, respectively, except that diethylamine azelaic acid is used as the solute. Comparative Example 6, Comparative Example 7, and Example 9 are the same as Comparative Example 1, Comparative Example 3, and Example 1, respectively, except that triethylamine azelaic acid is used as the solute.

According to the results in Table 2, when diethylamine or triethylamine is used as the alkaline component of the solute, the time to gelation of the electrolyte of Examples 8 to 9 to which organic modified silica and silane coupling agent are added is also prolonged. In addition, it is also confirmed that the withstand voltage of the electrolytic capacitor is improved by adding organic modified silica.

If the specific resistance of Example 1 and Examples 8 to 9 is compared, it is confirmed that the specific resistance of Example 1 is the smallest. By using ammonia as the alkaline component, the specific resistance becomes smaller, and as a result, the ESR of the electrolytic capacitor is expected to become smaller.

When the withstand voltages of Example 1 and Examples 8 to 9 are compared, it is confirmed that Example 1 has the highest withstand voltage, and the withstand voltage becomes higher by using ammonia as the alkaline component. In addition, it is confirmed that although the withstand voltages of Examples 8 and 9 are of the same level, the specific resistance is smaller in Example 8. Based on this, it is known that among amine salts, diethylamine, which is a diamine, excels in the balance between withstand voltage and specific resistance.

(Gelative evaluation 3)

As shown in Table 3 below, the electrolyte solutions of Examples 10 to 12 were prepared. Similar to Table 1, the results of the placement test to confirm the gelation state and the withstand voltage measured at 125°C are also shown.

In Examples 10 to 12, the amount of silane coupling agent added relative to 1 g of organic modified silica is set to the same level as in Example 2, and the type of silane coupling agent is changed. Example 10 uses 3-glyceryloxypropyl trimethoxysilane (KBM-403 manufactured by Shin-Etsu Silicone), Example 11 uses 2-(3,4-epoxyhexyl)ethyl trimethoxysilane (KBM-303 manufactured by Shin-Etsu Silicone), and Example 12 uses N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane (KBM-602 manufactured by Shin-Etsu Silicone).

According to Examples 10 to 12, it was confirmed that even if the silane coupling agent was changed, the withstand voltage was good and the electrolyte did not gel. It was confirmed that if the balance between the specific resistance and the withstand voltage of Examples 2 and 10 to 12 was considered, the preferred silane coupling agents were 3-glyceryloxypropylmethyldimethoxysilane, 3-glyceryloxypropyltrimethoxysilane, and 2-(3,4-epoxyhexyl)ethyltrimethoxysilane, and particularly preferred were 3-glyceryloxypropylmethyldimethoxysilane and 3-glyceryloxypropyltrimethoxysilane.

(Evaluation of electrostatic capacitor)

First, the electrolytic capacitors of Comparative Example 1, Comparative Example 3 and Example 1 were placed in a high temperature environment of 150°C for 300 hours without load. The electrolytic capacitors were disassembled, the cathode foil and the anode foil were washed with water, and the withstand voltage of each dielectric oxide film was measured. The results are shown in Figures 1 and 2. In Figure 1, the vertical axis is the withstand voltage of the dielectric oxide film (V vs. Pt), and in Figure 2, the vertical axis is the withstand voltage of the dielectric oxide film (V). In both figures, the horizontal axis is time. Figure 1 shows the results of the cathode foil, and Figure 2 shows the results of the anode foil.

As shown in Figure 1, the cathode foil of Example 3 has a higher rise voltage than the cathode foil of Comparative Example 3. Here, Comparative Example 1 without organic modified silica and silane coupling agent shows a rise voltage of about 0.1V vs. Pt, but the rise voltage of Comparative Example 3 containing only organic modified silica drops to about -0.5V vs. Pt, and the dissolution of the dielectric oxide film is observed at about 0.6V compared to Comparative Example 1. On the other hand, it is known that Example 3 is -0.35V vs. Pt, and the film has a voltage resistance characteristic compared to Comparative Example 3, and the dissolution of the dielectric oxide film is suppressed.

In addition, as shown in FIG. 2 , the voltage of the anode foil of Comparative Example 3 rises slowly compared to the anode foil of Example 3, and the anode foil of Example 3 behaves in the same manner as the anode foil of Comparative Example 1. The reason for this is that the dielectric oxide film of the anode foil of Comparative Example 3 containing only organic modified silica is dissolved, and the voltage rises slowly. On the other hand, it is believed that the dissolution of the dielectric oxide film of the anode foil of Example 3 to which organic modified silica and a silane coupling agent are added is suppressed, and the anode foil behaves in the same manner as the anode foil of Comparative Example 1 not containing organic modified silica and a silane coupling agent.

In order to verify the dissolution of the dielectric oxide film layer, the leakage current (LC) of the electrolytic capacitors of Comparative Example 1, Comparative Example 3 and Example 3 was measured. The leakage current was measured at the initial stage of the electrolytic capacitor production and after a high temperature test at 150°C, 300 hours and without load. The applied voltage was 200V, and the leakage current value was measured after 30 seconds. The results are shown in Table 4 below.

As shown in Table 4, the initial leakage currents of the electrolytic capacitors of Comparative Example 1, Comparative Example 3, and Example 3 are all of the same level. However, the leakage current after the high temperature test is the largest in Comparative Example 3. This is believed to be because the dielectric oxide film of the anode foil of Comparative Example 3 is dissolved by the high temperature test, so the leakage current becomes larger. On the other hand, the leakage current of Example 3 after the high temperature test is suppressed to about half of that of Comparative Example 3, thereby confirming that the dissolution of the dielectric oxide film is suppressed by using organic modified silica and silane coupling agent.

In addition, the electrolytic capacitors of Comparative Example 1, Comparative Example 3 and Example 3 were placed in a high temperature environment of 150°C for 300 hours without load. The electrolytic capacitors were disassembled, and the surface state of the anode foil after washing with water was observed at 5,000 times using a scanning electron microscope (hereinafter referred to as SEM. JSM-7800F Prime, manufactured by JEOL Ltd.). The photos taken during the SEM observation are shown in Figures 3(a) to 3(c). Figure 3(a) is a photo of Comparative Example 1, Figure 3(b) is a photo of Comparative Example 3, and Figure 3(c) is a photo of Example 3.

As shown in Figures 3(a) to 3(c), the anode foil of Comparative Example 3 has more parts where no etching pits are seen. On the other hand, the anode foil of Example 3 has a surface state close to that of the anode foil of Comparative Example 1, and the etching pits remain clearly. This result indicates that the dielectric oxide film layer of the anode foil of Comparative Example 3 is dissolved or some substance is deposited on the dielectric oxide film.

In order to further verify the dissolution of the dielectric oxide film layer and the accumulation of substances, elemental analysis was performed on the surface of the anode foil of Comparative Example 1, Comparative Example 3 and Example 3 observed by SEM. The elemental analysis was performed using an energy dispersive X-ray spectrometer (EDS). The results are shown in Table 5. In Table 5, each value represents the existence ratio (mass %) of each element.

As shown in Table 5, the amount of silicon detected on the surface of the anode foil of Comparative Example 1 and Example 3 is a trace amount, while a large amount of silicon is detected in the anode foil of Comparative Example 3. That is, it is confirmed that if only organic modified silica is added to the electrolyte, the silicon compound adheres to the surface of the anode foil. Based on the above, it is found that the organic modified colloidal particles have a certain effect on the anode foil. In contrast, by using organic modified silica and silane coupling agent together, the effect of organic modified silica on the dielectric oxide film of the anode foil can be suppressed, and the change of the surface state of the anode foil can be suppressed.

Based on the confirmation that the organic modified colloidal particles affect the dissolution of the dielectric oxide film, the initial electrostatic capacitance (Cap) of the electrolytic capacitors of Comparative Example 1, Comparative Example 3 and Examples 1 to 7 was measured, and then placed without load in a temperature environment of 150°C, and the electrostatic capacitance was measured after each time and the time change of the electrostatic capacitance was calculated. The time change of the electrostatic capacitance is shown in Table 6, Figure 4 (a), and Figure 4 (b). Table 6 is a table showing the change rate (△Cap (%) relative to the initial electrostatic capacitance after each time, and Figure 4 (a) and Figure 4 (b) are graphs with △Cap as the vertical axis and time as the horizontal axis, respectively. Furthermore, △Cap is calculated by the following formula 1. In formula 1, the electrostatic capacitance after time refers to the electrostatic capacitance after 110 hours, 200 hours, and 300 hours.

As shown in Table 6, Figure 4(a), and Figure 4(b), the electrolytic capacitor of Comparative Example 3, which only added organic modified silica, had a larger change in electrostatic capacitance than the electrolytic capacitor of Comparative Example 1, which did not add organic modified silica and silane coupling agent. However, compared with Comparative Example 3, the change in electrostatic capacitance was suppressed in the electrolytic capacitors of Examples 1 to 7, which also added silane coupling agent.

In addition, compared with Example 1 in which the amount of silane coupling agent added was 0.76× ^10-3 mol per 1g of organic modified silica, the ΔCap of Example 2 in which the amount of silane coupling agent added was 2.27× ^10-3 mol was suppressed to about 66% (calculated from the value after 300 hours in Table 5), and the suppression effect increased as the amount of addition increased. Moreover, in the electrolytic capacitor of Example 5 in which the amount of silane coupling agent added was 7.57× ^10-3 mol per 1g of organic modified silica, the change in electrostatic capacitance was suppressed to the same level as that of Comparative Example 1.

Thus, it was confirmed that the change in electrostatic capacitance can be suppressed by adding both organic modified colloidal particles and silane coupling agent. It was confirmed that the change in electrostatic capacitance can be suppressed when the amount of silane coupling agent added is 0.76× ^10-3 mol or more relative to 1g of organic modified colloidal particles, and the change in electrostatic capacitance can be suppressed dramatically when the amount of silane coupling agent added is 2.27× ^10-3 mol or more relative to 1g of organic modified colloidal particles. Furthermore, it was confirmed that the change in electrostatic capacitance can be suppressed to the same level as the case where no organic modified colloidal particles are added when the amount of silane coupling agent added is 7.57× ^10-3 mol or more relative to 1g of organic modified colloidal particles.

Next, after measuring the initial electrostatic capacitance (Cap) of the electrolytic capacitors of Comparative Examples 4 to Comparative Examples 7 and Examples 8 to 9, they were placed without load in a temperature environment of 150°C, and the electrostatic capacitance was measured after each time, and the time change of the electrostatic capacitance was calculated. The time change of the electrostatic capacitance is shown in Table 7 and Figure 5. Table 7 is a table showing the change rate (ΔCap (%) relative to the initial electrostatic capacitance after each time, and Figure 5 is a graph with Δcap as the vertical axis and time as the horizontal axis. In addition, ΔCap is calculated using the following formula 2. In formula 2, the electrostatic capacitance after time refers to the electrostatic capacitance after 110 hours, 200 hours, and 300 hours.

According to Table 7, it is confirmed that: even when diethylamine or triethylamine is used as the alkaline component of the solute, Examples 8 to 9 using organic modified silica and silane coupling agent together also suppress the change of electrostatic capacitance in the same way as Example 1. In addition, when Example 1 and Examples 8 to 9 are compared, the △Cap value after 300 hours is 24.7% for Example 1, 4.3% for Example 8, and 4.3% for Example 9. According to this result, it is known that: compared with the use of ammonium salt as the solute, the change rate of electrostatic capacitance when using amine salts such as diethylamine salt or triethylamine salt as the solute is small, and the life characteristics are good.

Claims (7)

An electrolyte for an electrolytic capacitor, characterized by comprising: a solvent, a solute, inorganic oxide colloid particles whose surface is modified by an organic substance, and a silane coupling agent or a silylating agent, wherein the amount of the silane coupling agent or the silylating agent added relative to the solvent is 0.05 mol/kg or more and 0.40 mol/kg or less, and the amount of the silane coupling agent or the silylating agent added relative to 1 g of the inorganic oxide colloid particles whose surface is modified by an organic substance is 0.76×10 ^-3 mol or more. The electrolyte for an electrolytic capacitor as described in item 1 of the patent application, wherein the silane coupling agent or the silylating agent is represented by the following general formula (1):

In the formula, _X1 is an alkyl group, alkenyl group, aryl group or aralkyl group having 1 to 20 carbon atoms, and is a hydrocarbon group (-R) whose hydrogen atoms may be partially substituted by a carboxyl group, an ester group, an amide group, a cyano group, a keto group, a formyl group, an ether group, a hydroxyl group, an amine group, an oxirane group, a sulfide group, a sulfonate group, an isocyanate group, a urea group or an epoxy group; _X2 to _X4 are acetyloxy groups, alkoxy groups or alkyl groups having 1 to 5 carbon atoms, and at least two of _X2 to _X4 are alkoxy groups. The electrolyte for electrolytic capacitors as described in item 2 of the patent application, wherein the silylating agent or silane coupling agent represented by the general formula (Chemical 1) is one or more selected from the group consisting of 3-glycidyloxypropylmethyldimethoxysilane, 3-methacryloxypropyltriethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, vinyltrimethoxysilane, p-phenylenediyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropylmethyldiethoxysilane. The electrolyte for electrolytic capacitors as described in item 1 or 2 of the patent application, wherein the inorganic oxide colloid particles are silicon dioxide. The electrolyte for electrolytic capacitors as described in item 1 or 2 of the patent application, wherein the solvent mainly contains ethylene glycol. An electrolytic capacitor, characterized by comprising: an electrolyte for an electrolytic capacitor as described in any one of items 1 to 5 of the patent application scope. The electrolytic capacitor as described in Item 6 of the patent application scope includes a pair of electrode foils, and a portion of the silane coupling agent or the silylating agent exists on the surface of the electrode foils, and a portion of the inorganic oxide colloid particles surface-modified by organic matter approaches the electrode foils through the silane coupling agent or the silylating agent existing on the surface of the electrode foils.