JPH0628220B2 - Electrolytic solution for electrolytic capacitors - Google Patents

Description

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

[Conventional technology]

Electrolytic capacitors are made of aluminum, tantalum, titanium,
A valve metal on which an insulative oxide film such as niobium is formed is used for at least the electrode on the anode side, and an insulative oxide film to be a dielectric layer is formed on the surface of the valve metal by an operation such as anodizing treatment. An electrolyte layer is formed on the outer surface of the oxide film, and a means for extracting the cathode is provided on the outer surface.

The electrolytic solution that constitutes the electrolyte layer is a solution of an organic acid, an inorganic acid, or a salt thereof dissolved in various solvents, contacts the insulating anodic oxide film layer on the above-mentioned anode-side electrode surface, and serves as a true cathode. Function. Therefore, the characteristics of the electrolytic solution are important factors that directly affect the characteristics of the electrolytic capacitor.

2. Description of the Related Art In recent years, it has been required to improve various characteristics such as electric characteristics and operating temperature range of electrolytic capacitors in response to higher performance electronic devices. In particular, the specific resistance of the electrolytic solution itself has a large effect on the electrical characteristics such as loss and impedance characteristics of the electrolytic capacitor.

[Problems to be Solved by the Invention]

Conventionally, in order to reduce the specific resistance of the electrolytic solution, for example, in the electrolytic solution using a polyhydric alcohol such as ethylene glycol as a solvent, the specific resistance was reduced by adding water, but the presence of water If it is used in a high temperature range exceeding 100 ° C, water in the electrolytic solution will vaporize and the internal pressure of the electrolytic capacitor will rise, causing accidents such as destruction of the sealing part. Further, even in a low temperature region, the presence of water deteriorates the characteristics, so that it can only be used up to -25 ° C and cannot be used at all in applications requiring use in a wide temperature range.

Further, as a low-resistivity electrolytic solution, a solution of a triethylamine salt of malinic acid dissolved in an acid amide such as N, N-methylformamide has a specific resistance of about 100 Ω · cm at 30 ° C. It is often generated and difficult to put into practical use. Furthermore, with an electrolytic solution in which the ammonium salt of formic acid is dissolved in N-methylformamide, it is possible to reduce the specific resistance to around 70 to 80 Ωcm, but when it is used as an electrolytic capacitor for a long time, gas is generated and it is practically used. Not relevant.

In recent years, the dicarboxylic acid salt or monocarboxylic acid of tetraalkylammonium as a solute, an electrolytic solution obtained by dissolving it in an aprotic solvent such as γ-butyrolactone is an electrolytic solution containing essentially no water, and with a low specific resistance value. Therefore, it is attracting attention as an electrolytic solution that can obtain a wide operating temperature range and excellent electrical characteristics.

Attempts have been made to dissolve the tetraalkylammonium carboxylate-based electrolyte in a single solvent containing only γ-butyrolactone or a single solvent containing only acetonitrile. However, in the case of an electrolytic solution using such a single solvent, for example, when a solvent that obtains a low specific resistance value is selected, the operating temperature range is limited, or conversely, when a solvent having a wide operating temperature range is selected, the specific resistance is reduced. There was a defect that the value increased.

The present invention is an improvement over the conventional drawbacks described above.
It is an object of the present invention to provide an electrolytic solution suitable for an electrolytic capacitor used for an electric device that requires excellent electric characteristics and a wide operating temperature range.

[Means for Solving the Problems] The electrolytic solution for an electrolytic capacitor of the present invention uses a mixed solvent of γ-butyrolactone and acetonitrile as a solvent, and a tetracarboxylic ammonium monocarboxylic acid salt or a solute in the mixed solvent. It contains one or more selected from dicarboxylic acid salts.

The electrolysis of the present invention is characterized in that a monocarboxylic acid or dicarboxylic acid salt of tetraalkylammonium is contained as a solute in a mixed solvent of γ-butyrolactone and acetonitrile in an amount of 10 to 50% by weight based on the total amount of the electrolytic solution. I am trying.

Furthermore, the electrolytic solution for an electrolytic capacitor of the present invention has a mixing ratio of γ-butyrolactone as a solvent and acetonitrile,
It is characterized in that acetonitrile is in the range of 98 to 2% by weight with respect to 2 to 98% by weight of γ-butyrolactone, and the amount of acetonitrile is 82% by weight or less of the total amount of the electrolytic solution.

[Work]

The electrolytic solution of the present invention uses a mixed solvent of γ-butyrolactone and acetonitrile as a solvent, and has a composition in which a monocarboxylic acid salt or a dicarboxylic acid salt of tetraalkylammonium is dissolved in a solute. The usage area can be expanded to the temperature range.

Solutes that can be used in the present invention are tetraalkylammonium monocarboxylates or dicarboxylates. Specific examples of solutes include tetrabutylammonium formate, tetraethylammonium acetate, tetramethylammonium propionate, tetrabutylammonium butyrate, tetramethylammonium azide, tetraethylammonium succinate, tetraethylammonium maleate,
Examples thereof include, but are not limited to, tetrabutylammonium itaconate, tetramethylammonium salicylate, and tetramethylammonium benzoate. Moreover, you may use these solutes in combination of 2 or more types.

The specific resistance value of the solute does not become so low when the dissolution amount is small, and the specific resistance value tends to decrease as the dissolution amount increases. However, the specific resistance value increases again as the dissolved amount approaches the saturated state. Also, if the amount of dissolution is large, solute may be deposited at low temperature, and the characteristics of the electrolytic capacitor may be significantly impaired.

FIG. 3 shows the amount of solute dissolved in the mixed solvent of the present invention,
The relationship with the specific resistance is shown, and as can be seen from this graph, the preferable dissolved concentration of the solute is in the range of 10 to 50% by weight. More preferably, it is in the range of 20 to 40% by weight.

γ-butyrolactone has a melting point of −43.5 ° C., and acetonitrile has a melting point of −44.9 ° C. There is no significant difference between the two, but due to the solubility of the solute, etc.
At low temperatures such as 55 ° C, solutes precipitate and cannot be used. On the other hand, γ-butyrolactone has excellent properties at low temperatures.
However, regarding the specific resistance, a desired low specific resistance value cannot be obtained only with γ-butyrolactone, and the specific resistance value becomes lower when acetonitrile is used as a solvent. Therefore, by mixing the two, an electrolytic solution having excellent low-temperature characteristics and a small specific resistance value can be obtained.

The mixing ratio of γ-butyrolactone and acetonitrile is
Mixing as described above compensates for both drawbacks and meets the purpose of the invention. However, as shown in the graph of Figure 1, as far as the specific resistance value is concerned,
It is better to increase the proportion of acetonitrile, but if acetonitrile exceeds 82% by weight of the total amount of electrolyte, disadvantages such as precipitation will occur almost uniformly at -55 ° C in any solute, and the low temperature characteristics as electrolyte will Can't be maintained. The graph ends with the amount of acetonitrile up to 82% by weight,
This is because the solute could not be dissolved at a concentration higher than this. Therefore, for electrolytic capacitors intended for use at temperatures as low as -55 ° C, the mixing ratio of acetonitrile should be 82% by weight or less of the total amount of electrolyte.

Further, the mixing ratio of acetonitrile and γ-butyrolactone (in the ratio between the solvents) is such that at least one of the solvents is 2% by weight or more in order to exhibit the characteristics of both solvents.
More preferably, it should be contained in an amount of 5% by weight or more.

〔Example〕

The present invention will be described in more detail based on the following examples.

FIG. 1 is a graph showing the relationship between the specific resistance of an electrolytic solution prepared by dissolving various tetraalkylammonium carboxylates in a mixed solvent of γ-butyrolactone and acetonitrile and the mixing ratio of the solvent.

This graph shows the relationship of the specific resistance value of the electrolytic solution to the mixing ratio of γ-butyrolactone and acetonitrile, the solute used, tetramethyl ammonium succinate (○), tetramethyl ammonium phthalate (x), Tetraethylammonium maleate (●),
They are tetraethylammonium salicylate (Δ) and tetrabutylammonium acetate (▲) (the symbols in parentheses correspond to the symbols in the graph).

15% by weight of these solutes were dissolved in solvents with different mixing ratios, and the specific resistance value (Ω · cm / 30 ° C) was determined. Therefore, the amount of the mixed solvent with respect to the total amount of the electrolytic solution is 85% by weight in this case. The content of acetonitrile on the horizontal axis of the graph is based on the total amount of the electrolytic solution.

As is clear from this graph, the absolute value varies depending on the solute used, but in any case, only γ-butyrolactone (0% by weight of acetonitrile and 85% of γ-butyrolactone was used).
It can be seen that the specific resistance value in the case of (% by weight) is high, and the specific resistance value decreases as the mixing ratio of acetonitrile increases. However, the reduction of the specific resistance value hardly changes when the mixing ratio of acetonitrile exceeds 50% by weight.

Further, when the mixing ratio of acetonitrile exceeds 82% by weight (γ-butyrolactone is 3% by weight), the solubility decreases at −55 ° C., solute precipitation and solidification start, and the electrolyte cannot be used as an electrolyte. Therefore, as the mixed solvent, acetonitrile is a preferable range of the present invention up to 82% by weight with respect to the total amount of the electrolytic solution.

Next, an electrolytic capacitor was manufactured using these electrolytic solutions, and its characteristics were examined.

The manufactured electrolytic capacitor has a rated voltage of 10 V and an electrostatic capacity of 22.
0 μF, a strip-shaped aluminum anode foil is wound together with a separator and a cathode foil to form a cylindrical capacitor element, which is impregnated with various electrolytic solutions, then housed in a metal case and sealed with a sealing rubber. It was done.

The graph of FIG. 2 shows the characteristics of this electrolytic capacitor, and shows the relationship between the equivalent series resistance value (ESR) of the electrolytic capacitor at −5 ° C. and the solvent mixing ratio.

The solute used in this graph is the same as the solute used in the craft of FIG. 1 and is given the same reference numeral.

As is clear from this graph, the characteristic (ESR) of the electrolytic capacitor at low temperature also shows the same tendency as the specific resistance value of the electrolytic solution itself, and by using a mixed solvent,
It can be seen that a low ESR value is obtained even at a low temperature of ° C.

FIG. 3 is a graph showing the relationship between the amount of solute dissolved in the solvent and the specific resistance value.

This graph shows specific resistance values when tetraethylammonium maleate (●) and tetramethylammonium phthalate (×) were dissolved in a solvent in which γ-butyrolactone and acetonitrile were mixed in equal amounts at 30 ° C. As can be seen from this graph, as the amount of solute was increased, the specific resistance value first decreased, and then the specific resistance value increased, and then tetraethyl maleate, when the solute concentration exceeded 50% by weight, and again tetramethylphthalate. In about 70% by weight, it became saturated and became insoluble. This tendency was the same with other solutes that can be used in the present invention. From this, it is understood that the preferred solute concentration is in the range of 10 to 50% by weight, more preferably 20 to 40% by weight.

〔The invention's effect〕

According to the present invention, since the mixed solvent of γ-butyrolactone and acetonitrile is used as the solvent of the electrolytic solution, it is possible to obtain a low specific resistance value which cannot be obtained with the electrolytic solution containing only γ-butyrolactone as a solvent. Further, an electrolytic solution using only acetonitrile as a solvent can be used even at a low temperature of −55 ° C. which could not be used conventionally, and an electrolytic capacitor having both excellent electric characteristics and a wide operating temperature range can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the mixing ratio of the solvent of the electrolytic solution of the present invention and the specific resistance value, and FIG. 2 is a graph of an electrolytic capacitor using the electrolytic solution of the present invention. FIG. 3 is a graph showing the relationship between the equivalent series resistance value at 55 ° C. and the electrolytic solution, and FIG. 3 is a graph showing the relationship between the dissolved concentration of the solute and the specific resistance value.

Claims (3)

[Claims] 1. A mixed solvent comprising γ-butyrolactone and acetonitrile is used as a solvent, and in the mixed solvent,
An electrolytic solution for an electrolytic capacitor, which contains, as a solute, one or more selected from monocarboxylic acid salts or dicarboxylic acid salts of tetraalkylammonium. 2. The electrolytic solution for an electrolytic capacitor according to claim 1, wherein the monocarboxylic acid or dicarboxylic acid salt of tetraalkylammonium is contained in an amount of 10 to 50% by weight based on the total amount of the electrolytic solution. 3. The mixing ratio of γ-butyrolactone and acetonitrile is in the range of 98 to 2% by weight with respect to 2 to 98% by weight of γ-butyrolactone, and the amount of acetonitrile is 82% by weight or less of the total amount of the electrolytic solution. An electrolytic solution for an electrolytic capacitor, characterized in that a certain solvent contains, as a solute, one or more selected from monocarboxylic acid salts or dicarboxylic acid salts of tetraalkylammonium.