JPH0760780B2 - Electrolytic solution for aluminum electrolytic capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention According to the present invention, an excellent electrolytic solution for an aluminum electrolytic capacitor having high electrical conductivity (hereinafter sometimes simply referred to as electrolytic solution) can be obtained.

2. Description of the Related Art Although the characteristics of capacitors are determined by various factors, the characteristics of the electrolytic solution that is housed in the outer case together with the capacitor element can greatly affect the impedance or equivalent series resistance (ESR). It's known.

For example, an electrolytic solution in which boric acid or its ammonium salt is dissolved in an ethylene glycol solvent is used for medium- and high-voltage electrolytic capacitors, but it has the drawbacks of low electrical conductivity and high equivalent series resistance. ing.

Therefore, it cannot be used for smoothing of a switching regulator which has been frequently used in recent years, such as one for which low equivalent series resistance is required even in a high frequency region.

In addition, since the viscosity of the ethylene glycol solvent used in this electrolyte is high and the freezing point is relatively high, the conductivity of the electrolyte is significantly reduced at low temperatures, and the low temperature characteristics of the electrolytic capacitor are poor. There is a drawback that the operating temperature range is narrow, such that it cannot be used in electrolytic capacitors exceeding 100 ° C due to the large amount of water generated by the esterification reaction between carboxylic acid and boric acid.

Means for Solving the Problems The present inventor has conducted diligent studies to solve the drawbacks of the boric acid-based electrolytic solution, and the conventional ammonium salt of boric acid was not dissolved γ-butyrolactone N, N-dimethylformamide, etc. It was found that the aliphatic quaternary ammonium salt of boric acid was dissolved in the aprotic solvent (1) and showed high conductivity, and the present invention was completed.

That is, the present invention provides an electrolytic solution for an aluminum electrolytic capacitor, which uses an aliphatic quaternary ammonium salt of boric acid as a solute.

Detailed Description of the Invention As the quaternary ammonium salt in the quaternary ammonium salt of boric acid used as a solute in the present invention, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, methyltriethylammonium, methyltripropylammonium, methyltributylammonium, Aliphatic quaternary ammonium salts such as dimethyldiethylammonium, dimethyldipropylammonium, dimethyldibutylammonium, ethyltripropylammonium, ethyltributylammonium, N,
N-dimethylpyrrolidinium can be illustrated.

As a solvent for dissolving the quaternary ammonium salt of boric acid of the present invention, N-methylformamide, N-ethylformamide, N, N-dimethylformamide, N, N-diethylformamide, N-methylacetamide, N-ethylacetamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylpyrrolidinone and other amide solvents,
lactone solvents such as γ-butyrolactone, γ-valerolactone and δ-parerolactone, carbonate solvents such as ethylene carbonate, propylene carbonate and butylene carbonate, alcohol solvents such as ethylene glycol, glycerin and methyl cellosolve, and 3-methoxypropionitrile. Examples thereof include nitrile solvents and phosphoric acid ester solvents such as trimethyl phosphate alone or in a mixed solvent.

The amount of the quaternary ammonium salt of boric acid dissolved in the solvent is not more than the saturation concentration, preferably 1 to 40% by weight.

The dissolved salt in the electrolytic solution may be a neutral salt or an acidic salt.

The electrolytic solution of the present invention essentially consists of a quaternary ammonium salt of boric acid and a solvent, but prevents electrolytic corrosion, reduces leakage current, etc.
Small amounts of co-solutes can be added for various purposes.

EFFECT OF THE INVENTION The quaternary ammonium salt of boric acid used as a solute in the present invention has good solubility in a solvent, and its electrolytic solution exhibits a high electric conductivity, and is used in combination with a solvent having a wide range of freezing point to boiling point to obtain a working temperature. It is an electrolytic solution for a wide range of aluminum electrolytic capacitors.

Experimental Example The present invention will be described more specifically with reference to Examples and Comparative Examples below.

Example 1 An electrolyte solution was obtained by dissolving 10% by weight of tetraethylammonium salt of boric acid in a γ-butyrolactone solvent. The electroconductivity of this electrolyte at 25 ° C. was 4.9 mS / cm, and the spark generation voltage was 330 V when a constant current of 4 mA / cm ² was applied to the + and −− sets of aluminum smooth foil. The temperature change of the electric conductivity of this electrolytic solution is shown in FIG.

Examples 2 to 4 Conductivity of an electrolytic solution when a γ-butyrolactone solvent N, N-dimethylformamide (Example 2), propylene carbonate (Example 3), and ethylene glycol (Example 4) in Example 1 were used. Is shown in Table 1.

Comparative Examples 1 to 4 Table 1 shows the results when the solute was changed to conventional ammonium borate using the solvents used in Examples 1 to 4.
The temperature change of the electric conductivity of the electrolytic solution of Comparative Example 4 is shown in FIG. 1 (■).

The following abbreviations were used in the first method.

GBL: γ-butyrolactone DMF: N, N-dimethylformamide PC: Propylene carbonate EG: Ethylene glycol

[Brief description of drawings]

FIG. 1 is a diagram showing the temperature change of the electric conductivity of the electrolytic solutions obtained in Example 1 (□) and Comparative Example 4 (■).

Claims (1)

[Claims] 1. An electrolytic solution for an aluminum electrolytic capacitor, characterized in that a quaternary ammonium salt of boric acid is used as a solute.