JP2572021B2 - Electrolyte for electrolytic capacitors - Google Patents

Description

The present invention relates to an electrolytic solution used for an electrolytic capacitor.

[Conventional technology]

Electrolytic capacitors use the so-called valve metal, on which an insulating oxide film is formed on the surface of aluminum, tantalum, niobium, etc., as an anode, and perform an operation such as anodizing treatment on the electrode surface to form the insulating oxide which becomes a dielectric layer. Form a layer.

Next, a cathode-side collector electrode faces the anode electrode, and an electrolytic solution is interposed between the electrodes.

The electrode of the electrolytic capacitor is generally formed into a cylindrical shape by cutting a foil-shaped valve metal into a strip shape and winding it together with a separator inserted for holding the electrolyte and separating the anode and the cathode.

The electrolyte is held by the separator and comes into contact with the surface of the oxide film, which is a dielectric, to function as a true cathode. As the electrolytic solution, those obtained by dissolving an inorganic acid, an organic acid, or a salt thereof in various solvents are used.

Since the conductivity of the electrolyte directly affects the loss and impedance characteristics of the electrolytic capacitor, an electrolyte having a high conductivity is required.

As a conventional electrolytic solution having a relatively high conductivity, a solution obtained by dissolving ammonium adipate in ethylene glycol is well known.

However, in the case of such an electrolytic solution, water is added to increase the electric conductivity. But the presence of water
At a high temperature exceeding 100 ° C., water evaporates, increasing the internal pressure, damaging the sealing portion of the electrolytic capacitor, operating the explosion-proof valve, and causing the electrolytic capacitor to be defective. Further, at a low temperature, there is a drawback that water is frozen and sufficient electric characteristics cannot be obtained, so that it cannot be used at all for purposes requiring use in a wide temperature range.

In recent years, as a solution to such a drawback, an electrolytic solution that minimizes the water content and obtains a high conductivity has been studied. For such purposes,
For example, as disclosed in JP-A-59-78522, a quaternary ammonium salt of a saturated linear dicarboxylic acid is used as a solute, and as described in JP-A-62-276815, a quaternary unsaturated carboxylic dicarboxylic acid is used. There is a solution in which a quaternary ammonium salt is used as a solute and dissolved in a polar solvent. Although these conventional examples have higher conductivity and lower loss than existing electrolytes, their properties are not sufficient for the purpose of demanding higher properties, At present, the conductivity was improved by adding water.

[Problems to be solved by the invention]

An object of the present invention is to provide a novel electrolytic solution which is a substantially non-aqueous electrolytic solution and has a high electric conductivity based on such a conventional technical background.

[Means for solving the problem]

The electrolytic solution of the present invention has been found that the heterocyclic quaternary ammonium salt of itaconic acid exhibits high conductivity as a solute for an electrolytic solution for an electrolytic capacitor, and this solute is at least a solute of the electrolytic solution. It is characterized by including as.

Itaconic acid Is a dicarboxylic acid having an unsaturated bond having the structural formula:

Further, specific examples of the heterocyclic quaternary ammonium include:
N, N-dimethylpyrrolidinium, N-methylpyridolinium, N-methylquinuclidinium, N, N-diethylmorpholinium, N-methyl-N-propylpiperidinium, N-methylpyridinium, N-ethyl-2,4,6-
Trimethylpyridinium, N-methylrepidinium, N
-Methylthiardinium and the like.

An electrolyte is obtained by dissolving these quaternary ammonium salts in various solvents.

The solvent is not particularly limited as long as it has solubility in the solute of the present invention. Specific examples include N-methylformamide, N, N-dimethylformamide, N-ethylformamide, N, N-diethyl. Formamide, N-
Amides such as methylacetamide and N, N-diethylacetamide.

Lactones such as γ-butyrolactone and γ-valerolactone.

Carbonates such as ethylene carbonate, butylene carbonate and propylene carbonate;

Alcohols such as ethylene glycol, diethylene glycol, propylene glycol, ethyl cellosolve, and methyl cellosolve.

Further, various solvents such as N-methyl-2-pyrrolidone, dimethyl sulfoxide, acetonitrile and the like can be used.

These solvents may be used alone, or may be a mixed solvent obtained by combining two or more solvents.

[Action]

As a solute of the heterocyclic quaternary ammonium salt of itaconic acid of the present invention, it has high solubility in various solvents and high conductivity. Further, since it is not necessary to add water to increase the electric conductivity, the internal pressure of the electrolytic capacitor does not increase due to the use at a high temperature. In addition, freezing at low temperatures and precipitation of solutes hardly occur.

〔Example〕

Next, the present invention will be described based on examples. First, a heterocyclic quaternary ammonium of itaconic acid of the present invention,
An electrolytic solution was prepared by combining with various solvents, and the conductivity thereof was examined. For comparison, an electrolytic solution of ammonium adipate-ethylene glycol system and an electrolytic solution using a quaternary alkyl ammonium salt of itaconic acid were also tested.

The composition and conductivity are listed below. In each case, the composition ratio is% by weight, and the conductivity is mS / cm at 30 ° C.

Invention Example 1 (composition) γ-butyrolactone 80 mono-N, N-diethylpyrrolidinium itaconate 20 (conductivity) 11.5 Invention Example 2 (composition) γ-butyrolactone 60 acetonitrile 20 mono-N-itaconate, N-diethylpiperidinium 20 (conductivity) 15.4 Invention Example 3 (composition) N, N-dimethylformamide 80 mono-N, N-dimethylmorpholinium itaconate 20 (conductivity) 15.3 Invention Example 4 (conductivity) Composition) N, N-dimethylformamide 70 ethylene glycol 10 mono-N-methylquinuclidinium itaconate 20 (conductivity) 14.0 Invention Example 5 (composition) N-methylformamide 80 itaconic acid di-N, N -Dimethylpyrrolidinium 20 (conductivity) 18.2 Invention Example 6 (composition) γ-butyrolactone 60 methylcellosolve 20 mono-N-ethylquinuclidinium itaconate 20 (conductivity) 13. 3 Invention Example 7 (composition) Acetonitrile 60 ethylene glycol 20 mono-N, N-dimethylpyrrolidinium itaconate 20 (conductivity) 14.9 Comparative Example 1 (composition) ethylene glycol 78 water 10 ammonium adipate 12 (conductivity) 6.7 Comparative Example 2 (composition) Ethylene glycol 20 γ-butyrolactone 55 water 5 tetramethylammonium itaconate 20 (conductivity) 9.1 Comparative Example 3 (composition) Propylene carbonate 69 water 1 tetraethylammonium itaconate 20 itaconic acid 10 (Electrical Conductivity) 5.9 As can be seen from these compositions, it can be seen that the electrolytic solution of the present invention shows high electrical conductivity while being a non-aqueous electrolytic solution.

Next, an electrolytic capacitor was prepared using these electrolytic solutions, and the results of a life test are shown.

The created electrolytic capacitor has a rated voltage of 16 V consisting of a winding type capacitor element using aluminum foil as the anode,
It has a capacitance of 180 μF.

This capacitor element was impregnated with each of the above electrolytes, housed in a metal outer case, and the opening was sealed with elastic rubber to obtain a capacitor.

For each electrolytic capacitor, the capacitance and loss (Tan
δ) and the leakage current (binary value)
Table 2 shows the values after the high-temperature life test was performed at a load of 110 hours at 110 ° C. (applied rated voltage).
Each measurement is the average value of 10 capacitors.

As is clear from the above results, the electrolytic capacitor using the electrolytic solution of the present invention maintains stable characteristics with low loss and little change in characteristics for a long time.

〔The invention's effect〕

As described above, according to the present invention, since the electrolytic solution has a high conductivity and is a non-aqueous electrolytic solution, it is possible to obtain an electrolytic capacitor having a low loss, low impedance, and a wide operating temperature range. . In addition, even if the capacitor is used at a high temperature for a long period of time, the internal pressure does not increase, so that stable characteristics can be obtained for a long period, and a long-life and highly reliable electrolytic capacitor can be obtained.

Claims (2)

(57) [Claims] 1. An electrolytic solution for an electrolytic capacitor comprising a heterocyclic quaternary ammonium salt of itaconic acid as a solute. 2. The method according to claim 1, wherein the heterocyclic quaternary ammonium is N, N-dimethylpyrrolidinium, N-methylpyridolinium,
N-methylquinuclidinium, N, N-diethylmorpholinium, N-methyl-N-propylpiperidinium, N
The method according to claim 1, wherein the compound is one or a combination of two or more selected from -methylpyridinium, N-ethyl-2,4,6-trimethylpyridinium, N-methylrepidinium, and N-methylthiardinium. Electrolyte for electrolytic capacitors.