JP2002270473A - Electrolytic capacitor and electrolytic solution therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolytic solution of an electrolytic capacitor which has good high-temperature life characteristics and an electrolytic capacitor which uses the electrolytic solution. SOLUTION: The electrolytic solution is obtained by dissolving class-3 amine salt of carboxylic acid in a solvent containing water and ether glycol, so a high-temperature life test of the electrolytic solution and the electrolytic capacitor using the electrolytic solution has excellent stability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution for an electrolytic capacitor and an electrolytic capacitor using the same, and more particularly to an electrolytic solution having good high-temperature life characteristics and an electrolytic capacitor using the same.

[0002]

2. Description of the Related Art An electrolytic capacitor generally has the following configuration. In other words, the high-purity aluminum foil formed in a belt shape is chemically or electrochemically etched to enlarge the surface, and the expanded aluminum foil is subjected to a chemical conversion treatment in a chemical solution such as an ammonium borate aqueous solution. By doing so, a capacitor element is formed by winding an anode foil having an oxide film layer formed on the surface of an aluminum foil and a cathode foil having a high-purity aluminum foil subjected to a surface-expansion treatment via a separator. The capacitor element is impregnated with a driving electrolyte, and is housed in a metal bottomed cylindrical outer case. Further, a sealing body made of elastic rubber is housed at the opening end of the outer case, and the opening end of the outer case is sealed by drawing to form an electrolytic capacitor.

[0003] Conventionally, as an electrolytic solution impregnated in a capacitor element of a small-sized, low-pressure electrolytic capacitor, ethylene glycol as a main solvent, adipic acid,
Known are those in which an ammonium salt such as benzoic acid is used as a solute, and those in which γ-butyrolactone is used as a main solvent and a quaternized cyclic amidinium salt such as phthalic acid or maleic acid is used as a solute.

[0004]

However, in recent years,
In the field of in-vehicle applications and the like, demands for electrolytic capacitors having high-temperature and long-life characteristics have been increasing, but the electrolytic solution for electrolytic capacitors has not been able to satisfy this requirement.

An object of the present invention is to provide an electrolytic solution for an electrolytic capacitor having good high-temperature life characteristics and an electrolytic capacitor using the same.

[0006]

The electrolytic solution for an electrolytic capacitor according to the present invention is characterized in that a secondary amine or tertiary amine salt of a carboxylic acid is dissolved in a solvent containing water and ethylene glycol.

Further, in the electrolytic solution for an electrolytic capacitor, the water content is 5 to 70 wt%.

Further, the carboxylic acid is benzoic acid, phthalic acid or isophthalic acid.

Further, the secondary amine is diethylamine, and the tertiary amine is triethylamine or dimethylethylamine.

The electrolytic capacitor of the present invention is characterized by using these electrolytic solutions for electrolytic capacitors.

Further, in the above electrolytic capacitor,
It is characterized by using an electrode foil subjected to a phosphoric acid bath treatment.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrolytic solution for an electrolytic capacitor of the present invention contains ethylene glycol and water and has a tertiary amine salt of a carboxylic acid dissolved therein. The electrolytic solution for an electrolytic capacitor has low specific resistance because it contains water, and has good stability in a high-temperature life test despite containing water. Therefore, by using the electrolytic solution for an electrolytic capacitor, it is possible to obtain an electrolytic capacitor having good high-temperature long-life characteristics.

The water content is 5 to 70 wt%, preferably 10 to 50 wt%. Normally, when a high-temperature life test is performed using an electrolytic solution for electrolytic capacitors containing such a large amount of water, the characteristics of the electrolytic capacitors are degraded due to deterioration of the hydration of the electrode foil. Swelling and opening of the safety valve occur. However, in the electrolytic solution for an electrolytic capacitor of the present invention, such a problem does not occur.

As described above, the electrolytic solution for an electrolytic capacitor of the present invention uses a solvent containing water and ethylene glycol. Other solvents include a protic polar solvent, an aprotic solvent, and a solvent such as these. Mixtures can be used. Examples of the protic polar solvent include monohydric alcohols (methanol, ethanol, propanol, butanol, hexanol, cyclohexanol, cyclopentanol, benzyl alcohol, etc.), polyhydric alcohols and oxyalcohol compounds (ethylene glycol,
Propylene glycol, glycerin, methyl cellosolve, ethyl cellosolve, 1,3-butanediol, methoxypropylene glycol, etc.). Examples of the aprotic solvent include amides (N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-dimethylformamide, N-methylacetamide, hexamethylphosphoramide, etc.),
Lactones (such as γ-valerolactone and δ-valerolactone), cyclic amides (such as N-methyl-2-pyrrolidone), carbonates (such as ethylene carbonate and propylene carbonate), nitriles (such as acetonitrile) and oxides (dimethyl) Sulfoxide) and the like. In addition, even lactones, γ-
When butyrolactone is used as a mixed solvent with ethylene glycol, the specific resistance of the electrolytic solution for electrolytic capacitors increases during the life test, which is not preferable.

The carboxylic acids used in the present invention include adipic acid, formic acid, benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, maleic acid, benzoic acid, azelaic acid, sebacic acid, citraconic acid and the like. it can. Among these, benzoic acid, phthalic acid and isophthalic acid are preferred.

The secondary amine includes dimethylamine, diethylamine, dipropylamine, diisopropylamine, N-methylethylamine, N-ethylisobutylamine, and the like. The tertiary amine includes trimethylamine, Triethylamine, dimethylethylamine, N, N-dimethylpropylamine, N
-Ethyl-N-methylbutylamine and the like. Of these, diethylamine, dimethylethylamine and triethylamine are preferred.

Further, the withstand voltage can be improved by adding boric acid, mannitol, nonionic surfactant, colloidal silica, polyethoxyethylene glycerin and the like to the electrolytic solution for electrolytic capacitors of the present invention.

According to the present invention, when an electrolytic capacitor using an electrolytic solution containing water and degraded after being left for a long time was analyzed, the pH of the electrolytic solution was high, and the solute It was found that the anion component of was attached. From this, aluminum on the surface of the electrode foil reacts with the anion component of the solute and adheres to the electrode foil, and further, the aluminum is dissolved to form a hydroxide or the like, and a part of the aluminum reacts with the anion component of the solute. Generates hydrogen gas. It became clear that this reaction was repeated and the pH increased, leading to deterioration of the electrode foil and valve opening.

However, in the electrolytic solution for an electrolytic capacitor of the present invention, a secondary amine or tertiary amine salt of a carboxylic acid is dissolved in a solvent containing water and ethylene glycol. It is thought that it does not rise, but the high-temperature life characteristics are good.

Here, when the electrode foil treated with the phosphoric acid bath is used, the high-temperature life characteristics are further improved. What is phosphate bath treatment?
Cathode foil in phosphoric acid bath, such as phosphate conversion, phosphoric acid immersion treatment,
That is, a process of loading or unloading the anode foil.

The electrolytic solution for an electrolytic capacitor of the present invention and the electrolytic capacitor using the same have good high-temperature life characteristics.

[0022]

Next, the present invention will be described in detail with reference to embodiments. The capacitor element is formed by winding an anode foil and a cathode foil via a separator. The anode electrode foil has a purity of 9
After 9.9% of aluminum foil is chemically or electrochemically etched in an acidic solution and subjected to surface expansion treatment, a chemical conversion treatment is performed in an aqueous solution of ammonium adipate, and then phosphoric acid is added to the surface. One having an anodic oxide film layer formed thereon is used. As the cathode foil, a foil immersed in a phosphoric acid aqueous solution after etching an aluminum foil having a purity of 99.9% to perform surface enlargement treatment was used.

In the capacitor element configured as described above,
An electrolytic solution for driving an electrolytic capacitor is impregnated. The capacitor element impregnated with this electrolytic solution is housed in a bottomed cylindrical aluminum outer case, a butyl rubber sealing body is inserted into the open end of the outer case, and the end of the outer case is drawn. To seal the electrolytic capacitor.

The composition and characteristics of the electrolyte used here are shown in Table 1. Further, as a comparative example, an electrolytic solution for an electrolytic capacitor was used in which 25 parts of water, 65 parts of ethylene glycol, and 10 parts of ammonium benzoate were used. Specific resistance is 106Ωcm
Met.

A high temperature life test of the electrolytic capacitor constructed as described above was conducted. The rating of the electrolytic capacitor is 50W
V-820 μF. The test conditions are 105 ° C., no load, and 1000 hours. Each result (Table 2)
Shown in

[0026]

[Table 1]

[0027]

[Table 2] (Note) Cap: capacitance (μF), tan δ: tangent of dielectric loss, LC: leakage current (μA), ΔCap: capacitance change rate (%)

As is clear from Tables 1 and 2,
In the comparative example, although the water content was 25 wt%, the valve was opened after the test. In contrast, in the embodiment of the present invention, the water content was 5 to 50 wt%.
Despite this, the characteristics after 105 ° C. and 1000 hours hardly changed compared to the initial characteristics, indicating that the stability in the high-temperature life test was excellent.

[0029]

According to the present invention, the tertiary amine salt of a carboxylic acid is dissolved in a solvent containing water and ethylene glycol in an electrolytic solution for an electrolytic capacitor. An electrolyte and an electrolytic capacitor can be provided.

Claims (6)

[Claims] 1. A solvent containing water and ethylene glycol,
An electrolytic solution for an electrolytic capacitor in which a secondary or tertiary amine salt of a carboxylic acid is dissolved. 2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the water content is 5 to 70 wt%. 3. The electrolytic solution according to claim 1, wherein the carboxylic acid is benzoic acid, phthalic acid or isophthalic acid. 4. The secondary amine is diethylamine,
2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the tertiary amine is triethylamine or dimethylethylamine. 5. An electrolytic capacitor using the electrolytic solution for an electrolytic capacitor according to claim 1. 6. The electrolytic capacitor according to claim 5, wherein a phosphoric acid bath-treated electrode foil is used.