JP3394068B2 - Electrolyte for electrolytic capacitors - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an electrolytic solution for an electrolytic capacitor, which contains metal oxide fine particles having a specific surface structure and is capable of maintaining high conductivity and high withstand voltage at high temperature for a long time. Regarding electrolyte solution.

[0002]

2. Description of the Related Art Generally, an electrolytic capacitor has, as an anode side electrode, an insulating oxide film such as aluminum or tantalum formed as a dielectric layer, and a cathode side electrode facing the anode side electrode. A separator holding an electrolytic solution is interposed between both electrodes.

The anode electrode is usually subjected to an etching treatment in order to increase its surface area, and the electrolytic solution is brought into close contact with this uneven surface and has a substantial function as a cathode. Therefore, the electric conductivity, temperature characteristics, etc. of the electrolytic solution are factors that determine the electrical characteristics of the electrolytic capacitor. In addition, the electrolytic solution repairs the deterioration and damage of the insulating oxide thin film, and affects the leakage current and life characteristics.

Generally, the higher the so-called spark voltage that the load voltage to the capacitor rises and the insulating oxide thin film is destroyed, the higher the withstand voltage of the capacitor is.
The spark voltage is determined by the electrolyte composition used. Therefore, the electrolytic solution is an important component that influences the characteristics of the electrolytic capacitor.

Conventionally, as an electrolytic solution for increasing the spark voltage while suppressing the decrease in the electric conductivity of the electrolytic solution,
An electrolytic solution in which metal oxide fine particles are added to a general electrolytic capacitor electrolytic solution is known, and for example, an electrolytic solution in which silica fine particles are added (Japanese Patent Laid-Open No. 4-12512),
Electrolyte solution containing alumina, zirconia, antimony oxide, tantalum oxide, titania, etc. (JP-A-4-1456)
Nos. 12 to 6) and the like.

[0006] However, in an electrolytic solution containing such a system in which fine particles are added, the colloid becomes unstable at a high temperature such as 105 ° C, so that a high withstand voltage cannot be maintained.
It had the drawback of having a short life. Further, there is a drawback that the gelation of the electrolytic solution is promoted by the water present in the electrolytic solution and the pressure resistance is lowered.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic solution for an electrolytic capacitor, which is capable of suppressing a decrease in electric conductivity, remarkably improving a withstand voltage, and maintaining a high withstand voltage for a long time even at a high temperature. To provide.

[0008]

The present invention is an electrolytic solution for an electrolytic capacitor containing an organic polar solvent, an ionic solute, and aluminosilicate-coated metal oxide fine particles.

The present invention will be described in detail below. Examples of the organic polar solvent used in the present invention include N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-ethylacetamide, N, N-dimethylacetamide, N.
An amide solvent such as methylpyrrolidone; a lactone solvent such as γ-butyrolactone, γ-valerolactone, δ-valerolactone; a carbonate solvent such as ethylene carbonate, propylene carbonate, butylene carbonate; an alcohol solvent such as ethylene glycol, glycerin, methylcellosolve Nitrile solvents such as 3-methoxypropionitrile and glutaronitrile, and phosphate ester solvents such as trimethyl phosphate and triethyl phosphate;
The solvent etc. which combined these 2 or more types can be mentioned. Of these, ethylene glycol and γ are preferable.
A solvent consisting mainly of butyrolactone.

As the ionic solute used in the present invention, known acids and salts thereof that can be used as solutes in general electrolytic solutions can be used. Examples of such acids include inorganic acids such as boric acid, phosphoric acid, silicic acid and HBF ₄ ; aliphatic monocarboxylic acids such as formic acid, acetic acid, propionic acid and enanthic acid; malonic acid, succinic acid and glutaric acid. , Adipic acid, methylmalonic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, citraconic acid and other aliphatic dicarboxylic acids; benzoic acid,
Inorganic or organic acids such as aromatic carboxylic acids such as phthalic acid, salicylic acid, toluic acid and pyromellitic acid can be mentioned. Examples of the salt include salts of the above organic acids and inorganic acids, for example, ammonium salts; monoalkylammonium salts such as methylammonium, ethylammonium, propylammonium; dialkylammonium salts such as dimethylammonium, diethylammonium, ethylmethylammonium, dibutylammonium. Trialkylammonium salts such as trimethylammonium, triethylammonium, tributylammonium; tetramethylammonium, triethylmethylammonium, tetraethylammonium, tetrabutylammonium,
Examples thereof include quaternary ammonium salts such as N, N-dimethylpyrrolidinium; phosphonium salts, arsonium salts, sulfonium salts and the like. These ionic solutes are
They can be used alone or in combination. The blending amount of the ionic solute varies depending on the required performance, but is generally preferably 1 to 25% by weight.

In the metal oxide fine particles used in the present invention, the surface of the core portion of the fine particles is coated with aluminosilicate. The core portion of the fine particles is preferably a metal oxide,
More preferably, SiO ₂ , Al ₂ O ₃ , TiO ₂ ,
ZrO ₂ , Sb ₂ O ₃ , Ta ₂ O _{5 and} other oxides and their composite oxides, most preferably SiO ₂ .

The aluminosilicate coating the surface of such a core portion has a composition formula: MAlO ₂ (Al ₂ O ₃ ) _x (SiO ₂ ) _y (wherein M represents a monovalent cation and x is 0). An aluminosilicate represented by a real number of .about.25, and y represents a real number of 1 to 200).

Examples of the monovalent cation (M) include alkali metal cations such as sodium ion, onium cations such as ammonium, secondary ammonium, tertiary ammonium and quaternary ammonium, and monovalent cations such as proton. Among them, sodium is preferable.

Al / Si in aluminosilicate
The ratio is preferably 0.02 to 1, more preferably 0.
It is 02-0.8. In order to maintain a stable colloidal state of the particles, it is necessary to create strong negative charge points on the particle surface due to the aluminosilicate structure, but if the amount of Al is too small relative to Si, the strong negative charge points decrease. Not preferable. Further, if the amount of Al is too large, the aluminosilicate structure cannot be formed, which is not preferable.

The particle size of the aluminosilicate-coated metal oxide fine particles is preferably 3 to 150 nm, more preferably 10 to 50 nm. If the particle size is too small, the association of the fine particles rapidly proceeds in the electrolyte at high temperature, and it is not possible to maintain a high withstand voltage. If the particle size is too large,
Since it becomes difficult to disperse the particles in a colloidal state in the electrolytic solution, and it is not possible to obtain a high withstand voltage improving effect,
Not preferable.

The amount of the coated fine particles added is preferably 0.1 to 20 parts by weight, more preferably 1 to 10 parts by weight, based on 100 parts by weight of the electrolytic solution. If the added amount is too small, the sufficient withstand voltage improving effect cannot be obtained, and if the added amount is too large, the decrease in the electrical conductivity becomes large, which is not preferable.

The coated fine particles used in the present invention are preferably added as a sol dispersed in a suitable solvent, and by adding as a sol, the fine particles are stably dispersed in a colloidal state in the electrolytic solution without associating the fine particles. This makes it easier to improve the pressure resistance and the stability of the electrolytic solution.

The aluminosilicate-coated metal oxide fine particle sol is prepared, for example, by simultaneously and gradually adding an aqueous solution of silicic acid and an aqueous solution of sodium aluminate to silica sol.
It can be easily prepared by growing an aluminosilicate on the surface of silica, replacing it with a suitable solvent and concentrating it.

The concentration of fine particles in the sol is preferably 1 to 50% by weight, but if it is too high, it is unstable against gelation,
If it is too low, there will be no freedom in adjusting the concentration of the electrolyte, so 1
0-40% by weight is more preferred. Examples of the solvent used for the sol include water and the organic polar solvent used for the above-described electrolytic solution.

[0020]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples. Examples 1 to 6 and Comparative Examples 1 to 6 Electrolytic solutions for electrolytic capacitors having the compositions shown in Table 1 were prepared, and the electrical conductivity and spark voltage of the electrolytic solutions were measured. The results are shown in Table 1. The aluminosilicate-coated fine particles used were silica fine particles having a core of silica and an aluminosilicate coating thickness of about 1 nm and an average particle size of 35 nm. The coated fine particles were used as an ethylene glycol sol, and the above sol was colloidally dispersed in an electrolytic solution in which each ionic solute was dissolved to prepare an electrolytic solution.

Regarding the electrolytic solution thus prepared,
Conductivity and spark voltage were measured. The conductivity was measured at 25 ° C, and the spark voltage was measured using an aluminum foil for the electrode.
The voltage at which dielectric breakdown was observed only when constant current anodic oxidation was performed at 5 ° C. and a current density of 5 mA / cm ² was used as the measured value. The results are shown in Table 1.

[0022]

[Table 1]

Example 7 and Comparative Examples 7 and 8 The electrolytic solution of Example 5 was allowed to stand at 110 ° C. for 500 hours, and then the changes in electric conductivity and spark voltage of the electrolytic solution were measured. The results are shown in Table 2. In addition, as a comparative example, Table 2 shows, as a comparative example, changes in electric conductivity and spark voltage measured in the same manner for an electrolytic solution using silica and alumina instead of the aluminosilicate-coated silica fine particles. The average particle size of silica and alumina used in the comparative example was 35 nm, and other conditions were the same as in Example 5.

[0024]

[Table 2]

[0025]

INDUSTRIAL APPLICABILITY The electrolytic solution for electrolytic capacitors of the present invention has a strong negative charge point due to the aluminosilicate structure on the surface of the aluminosilicate-coated metal oxide fine particles used, and is surrounded by electrolyte cations in the electrolytic solution to form a colloid. As a whole, it has a positive charge, and since the repulsion of positive charges keeps a stable colloidal state,
Furthermore, the aluminosilicate structure significantly improves the stability against gelation and other alterations due to water in the electrolytic solution, so it is possible to suppress alterations such as gelation of the electrolytic solution at high temperatures, and to withstand long-term resistance. The voltage improving effect can be maintained. Further, since it is possible to suppress the decrease in electric conductivity and increase the spark voltage, it is possible to obtain an electrolytic capacitor having a high withstand voltage and a long life.

─────────────────────────────────────────────────── ─── Continuation of front page (56) Reference JP-A-3-139537 (JP, A) JP-A-61-264679 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01G 9/02

Claims (4)

(57) [Claims] 1. An electrolytic solution for an electrolytic capacitor, which contains an organic polar solvent, an ionic solute, and aluminosilicate-coated metal oxide fine particles. 2. The aluminosilicate has the compositional formula: MAlO ₂ (Al ₂ O ₃ ) _x (SiO ₂ ) _y (wherein M represents a monovalent cation, x represents a real number of 0 to 25, and y Is a real number of 1 to 200), and the electrolytic solution according to claim 1. 3. The electrolytic solution according to claim 2, wherein the Al / Si ratio of the aluminosilicate is 0.02-1. 4. The electrolytic solution according to claim 1, wherein the inorganic compound in the core of the aluminosilicate-coated metal oxide fine particles is silica.