JPH06196366A - Electrolytic solution for electrolytic capacitors - Google Patents

Abstract

(57) [Abstract] [Purpose] At least 5 mS / c in quaternary ammonium salt of benzoic acid / gamma-butyrolactone electrolyte
Provided is an electrolytic solution capable of maintaining an electric conductivity of m (25 ° C.) or more and a withstand voltage of 100 V (105 ° C.) or more at a high temperature such as 105 ° C. for a long time. [Structure] Phosphoric acid having two saturated alkyl groups having 8 to 18 carbon atoms per 100 parts by weight of a solution containing a quaternary ammonium salt of benzoic acid as a main solute and a complex solvent containing gamma-butyrolactone and ethylene glycol as a main solvent. High electrical conductivity in which silica fine particles containing 1 to 8 parts by weight of dialkyl ester and 0.5 to 10 parts by weight of colloidal silica are stably colloid-dispersed to prevent deterioration such as hydrolysis and gelation of the electrolytic solution at high temperature. High-conductivity electrolyte that can maintain high voltage and high withstand voltage at high temperature for a long time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrolytic solution used for an electrolytic capacitor, and more particularly to an electrolytic solution capable of maintaining high conductivity and high withstand voltage at high temperature for a long period of time.

[0002]

2. Description of the Related Art An electrolytic capacitor has an anode formed by forming an insulating oxide film thin film as a dielectric layer on the surface of a so-called valve metal on which an insulating oxide film layer such as aluminum or tantalum can be formed by anodizing. Used for the side electrode. A cathode side electrode is arranged so as to face the anode side electrode, a separator is interposed between the anode side electrode and the cathode side electrode, and an electrolytic solution is held in this separator to form an electrolytic capacitor. The anode-side electrode is usually subjected to etching treatment to increase the surface area, and the electrolytic solution comes into close contact with this uneven surface and has a substantial function as a cathode. Therefore, the electric conductivity and temperature characteristics 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. As described above, the electrolytic solution is an important component that influences the characteristics of the electrolytic capacitor.

Among the characteristics of the electrolytic solution, the conductivity is directly related to the dielectric loss and impedance characteristics of the electrolytic capacitor, so that the electrolytic solution having a high conductivity has been actively developed in recent years. Among these, organic acids, particularly those obtained by dissolving a solute of a quaternary ammonium salt having various carboxylic acids as anions, dissolved in an aprotic solvent such as gamma-butyrolactone, are attracting attention because they can obtain high conductivity. (See, for example, JP-A-62-145713 and JP-A-62-145715). However, such a high-conductivity electrolytic solution generally has a low withstand voltage of the electrolytic solution itself, and has been used in a range where the rated voltage is 50 V or less.

Therefore, it has been attempted to add a chemical agent to the high-conductivity electrolytic solution to improve the withstand voltage while suppressing the decrease in the electric conductivity. For example, quaternary ammonium such as phthalic acid or maleic acid. A system in which an alkyl phosphate ester is added to a salt / gamma-butyrolactone-based electrolytic solution (JP-A-63-261820, JP-A-63-2618).
22 and JP-A-3-209810), a system in which silica colloid particles are added to a quaternary ammonium salt of phthalic acid or maleic acid / gamma-butyrolactone-based electrolytic solution (JP-A-4-58512), and maleic acid A system in which titania colloid particles are added to a quaternary ammonium salt / gamma-butyrolactone-based electrolytic solution (JP-A-4-3110).
No. 20), a system in which colloidal particles of titania or silica, hexites, and boric acid are added to a quaternary ammonium salt of phthalic acid / gamma-butyrolactone-based electrolytic solution (Japanese Patent Laid-Open No. Hei 4).
313210) and the like.

However, in the electrolytic solution system using the above quaternary ammonium salt of phthalic acid or maleic acid, 10
At a high temperature such as 5 ° C., high conductivity and withstand voltage cannot be maintained, and there is a problem that the life is short.

[0006]

DISCLOSURE OF THE INVENTION The present invention is an improvement over the above-mentioned drawbacks of the high-conductivity electrolyte, and in the quaternary ammonium salt of benzoic acid / gamma-butyrolactone-based electrolyte,
Conductivity of at least 5 mS / cm (25 ° C) or higher, 10
It is an object of the present invention to provide an electrolytic solution capable of maintaining a withstand voltage of 0 V (105 ° C) or higher at a high temperature such as 105 ° C for a long time.

[0007]

According to the present invention, 100 parts by weight of a solution containing a quaternary ammonium salt of benzoic acid as a main solute and a complex solvent containing gamma-butyrolactone and ethylene glycol as a main solvent has 8 to 8 carbon atoms. High conductivity which contains 1 to 8 parts by weight of a phosphoric acid dialkyl ester having two 18 saturated alkyl groups and 0.5 to 10 parts by weight of colloidal silica and which can maintain high conductivity and high withstand voltage at high temperature for a long time. To provide an electrolytic solution.

The electrolytic solution for an electrolytic capacitor of the present invention comprises a quaternary ammonium salt of benzoic acid as a main solute and a solution in which a complex solvent composed of gamma-butyrolactone and ethylene glycol is dissolved as a basic electrolytic solution. .

The anion component of the solute of the basic electrolytic solution is benzoic acid, but the quaternary ammonium as the cation component is preferably a tetraalkylammonium salt, and particularly, the total carbon number of the alkyl group is 8 or less. Tetraalkylammonium salts are preferred because of their high conductivity. Specific examples include tetramethylammonium, trimethylethylammonium, dimethyldiethylammonium,
Examples thereof include triethylmethylammonium salt, tetraethylammonium salt, N, N-dimethylpyrrolidinium and the like.

The concentration of the quaternary ammonium salt of benzoic acid in the basic electrolyte is 15 to 25 in order to obtain high conductivity.
A weight% range is preferred.

The mixed solvent consisting of gamma-butyrolactone and ethylene glycol in the basic electrolytic solution has a weight ratio of ethylene glycol to gamma-butyrolactone of 0.1 to 0.1 in order to maintain high conductivity at high temperature.
It is preferably in the range of 4.

The phosphoric acid dialkyl ester used in the electrolytic solution of the present invention can be represented by the following general formula (1).

[0013]

[Chemical 1]

(In the formula, the alkyl groups R ¹ and R ² are linear or non-linear saturated alkyl groups having 8 to 18 carbon atoms.) In the above formula, R ¹ and R ² are not necessarily the same. It is not necessary, but usually the same. Specific examples of the phosphoric acid dialkyl ester include di-n-octyl phosphate, di (2-ethylhexyl) phosphate, dinonyl phosphate, and di-n-phosphate.
Examples thereof include decyl, diisodecyl phosphate, dilauryl phosphate, ditridecyl phosphate, dimyristyl phosphate, dipalmityl phosphate, distearyl phosphate and diisostearyl phosphate. Among these, those in which the saturated alkyl groups R ¹ and R ² have 8 to 12 carbon atoms are preferable because they have good solubility and high pressure resistance increasing effect. These dialkyl phosphates can maintain the pressure resistance improving effect at high temperature for a long time, as compared with dibutyl phosphate having a lower alkyl group.

Since the dialkyl phosphoric acid ester which is usually available contains a monoalkyl phosphoric acid ester as a by-product due to its production method, it is necessary to use a purified product. Content of monoalkyl phosphate is 10% by weight
The following are preferable. Two or more kinds of phosphoric acid dialkyl esters may be used in combination, but the total addition amount is in the range of 1 to 8 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the basic electrolytic solution. If the amount of addition is small, the effect of improving the pressure resistance is not sufficient, and if it is too large, the electrical conductivity decreases, which is not preferable.

The silica used in the electrolytic solution of the present invention is preferably fine particles having a particle size of 20 to 50 nm. Particle size is 10-2
Although 0 nm is a general-purpose product industrially, if the particle size is too small, the association of silica fine particles will proceed in the electrolytic solution at high temperature, and eventually gelation will occur, so that the pressure resistance improving effect can be maintained. Can not. On the other hand, if the particle size is too large, the number of particles is small even with the same weight, and therefore it is necessary to add a large amount in order to obtain a predetermined improvement in withstand voltage, which leads to a decrease in electrical conductivity, which is not preferable. Further, in order to maintain a stable colloidal state, silicon atoms on the particle surface are replaced with aluminum atoms to strengthen the negative charge, and the amount of aluminum in the vicinity of the surface is 0.01 to 0.1% by weight based on the whole particles. The range is preferable.

The method for producing silica fine particles is roughly classified into a method in which sodium silicate (water glass) is dealkalized with a hydrogen type cation exchange resin and the obtained silicic acid solution is polymerized in an alkaline atmosphere (ion exchange method). , A method in which water glass is neutralized with an acid to form a gel, and then the salt is washed away with water to peptize the gel in an autoclave (peptization method), and silica obtained by hydrolyzing ethyl silicate with an acid There are wet methods such as a method of heating and aging a liquid (sol-gel method) and dry methods such as a method of hydrolyzing chlorosilane and the like in oxyhydrogen flame at high temperature (combustion method), but silica produced by a wet method Fine particles are preferred. The addition of silica fine particles to the basic electrolytic solution is a method of adding in the form of an organosilica sol in which the water solvent of silica hydrosol produced by a wet method is replaced with an organic solvent, without associating the silica fine particles into the electrolytic solution. This is because it is easy to stably disperse it in a colloidal form, and the pressure resistance improving effect is great.

As the organic solvent used in the organosilica sol, alcohol solvents such as methanol, propanol, isopropanol, butanol, methoxyethanol and ethylene glycol, N-methylformamide,
Amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidone, lactone solvents such as gamma-butyrolactone, carbonate solvents such as propylene carbonate, carbamate solvents such as N-methyloxazolidone, N, N- Urea solvent such as dimethyl imidazolidone, nitrile solvent such as acetonitrile, phosphate ester solvent such as trimethyl phosphate,
Although polar solvents such as sulfur-containing solvents such as dimethylsulfoxide, 3-methylsulfolane and ethylene sulfite can be used, ethylene glycol or gamma-butyrolactone used in the basic electrolytic solution is preferable for the preparation of the electrolytic solution. Especially, ethylene glycol is more preferable because it has excellent dispersibility of silica fine particles. When the solvent used for the organosilica sol is a low boiling point solvent, it is preferable to add the organosilica sol to the electrolytic solution and then remove the solvent from the electrolytic solution by distillation or the like. If the silica concentration in the organosilica sol is too high, it is unstable against gelation, and if it is too low, the degree of freedom in adjusting the concentration of the electrolytic solution is lost. Therefore, the silica concentration is 1 to 50% by weight, preferably 10%.
-40% by weight.

The amount of silica fine particles added is 100
0.5 to 10 parts by weight, preferably 2 to 8 parts by weight
The range is parts by weight. If the amount of addition is small, the effect of improving the pressure resistance is not sufficient, and if it is too large, the electrical conductivity is too low, and the effect of improving the pressure resistance is reduced due to association and gelation at high temperatures, which is not preferable.

When the electrolytic solution of the present invention has a large amount of water, hydrolysis of dialkyl phosphate ester and association of silica fine particles,
It is preferable to keep it at 3% by weight or less because it promotes gelation and reduces the pressure resistance improving effect. Therefore, in preparing the electrolytic solution, it is preferable that the water content of the organosilica sol obtained by substituting the water solvent of the silica hydrosol with the organic solvent is low.

[0021]

The phosphoric acid dialkyl ester having a lower alkyl group such as dimethyl phosphate, diethyl phosphate, dipropyl phosphate, and dibutyl phosphate, which has been conventionally used as a pressure resistance improver, is hydrolyzed by water in the electrolytic solution at high temperature, Since the phosphoric acid monoalkyl ester or phosphoric acid is produced, not only the pressure resistance improving effect is gradually lowered, but also gelation of silica fine particles is promoted and the pressure resistance improving effect is further lowered. Further, the phosphoric acid dialkyl ester having a lower alkyl group is generally low in purity because it is difficult to separate the phosphoric acid monoester produced as a by-product in the production method, and there is a problem in stability.

The electrolytic solution of the present invention uses a hydrolysis-resistant dialkyester having a higher alkyl group and has a stable colloidal dispersion of silica fine particles, whereby the electrolytic solution is hydrolyzed or gelled at a high temperature. Prevent the deterioration of
It is possible to maintain the withstand voltage improving effect for a long period of time.

[0023]

EXPERIMENTAL EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples. Example 1. Benzoic acid triethylmethyl ammonium salt 2
Gamma-butyrolactone solution in which 5% by weight is dissolved, di (2-ethylhexyl) phosphate having a purity of 95%, a particle size of 25 nm produced by an ion exchange method, and silica having a content of aluminum near the surface of 0.02% by weight of the entire particle. Fine particles 30
20% by weight of triethylmethylammonium benzoate salt, 64% by weight of gamma-butyrolactone, using organosilica sol in which weight% is dispersed in ethylene glycol, gamma-butyrolactone and ethylene glycol,
2 parts by weight of di (2-ethylhexyl) phosphate per 100 parts by weight of a solution consisting of 16% by weight of ethylene glycol,
An electrolytic solution containing 6 parts by weight of silica fine particles was prepared, and the water content in the electrolytic solution was adjusted to 1% by weight.

After aging this electrolyte at 110 ° C. for 1 hour, the conductivity and the withstand voltage were measured. The electrical conductivity at 25 ° C. was 5.6 mS / cm. The withstand voltage was the scintillation start voltage observed when an electrolytic capacitor having a rated voltage of 200 V and a capacitance of 68 μF was produced and a constant current of 5 mA was applied at 110 ° C.
Met. Further, the electrolytic solution was sealed in a closed glass container and stored at 110 ° C. for 500 hours, and then the electric conductivity and the withstand voltage were measured by the same method.
cm and 185V.

Comparative Example 1. In Example 1, diphosphoric acid (2
-Ethylhexyl), an electrolytic solution was prepared in the same manner as in Example 1 except that dibutyl phosphate having a purity of 95% was used, and an experiment was conducted. Initial conductivity and withstand voltage are 5.4 mS each
/ Cm, 165V, the electric conductivity and withstand voltage after storage for 500 hours at 110 ℃ 4.3mS / c
m, 130 V, and the withstand voltage was significantly reduced.

Example 2. An electrolyte solution was prepared and tested in the same manner as in Example 1 except that the particle size of the silica fine particles in Example 1 was changed to 12 nm. The initial conductivity and withstand voltage were 5.4 mS / cm and 200 V, respectively.

Comparative Example 2. In Example 2, diphosphate (2
-Ethylhexyl), an electrolytic solution was prepared and tested in the same manner as in Example 2 except that diphenyl phosphate having a purity of 99% was used. Initial conductivity and withstand voltage are respectively 5.
It was 6 mS / cm and 90 V, and the withstand voltage improving effect was low.

Example 3. An electrolyte solution was prepared and an experiment was performed in the same manner as in Example 1 except that the particle size of the silica fine particles in Example 1 was changed to 45 nm. The initial conductivity and withstand voltage are 5.7 mS / cm and 150 V, respectively.
The electrical conductivity and withstand voltage after storage at 500 ° C. for 500 hours were 4.6 mS / cm and 185 V, respectively.

Example 4. In Example 1, diphosphoric acid (2
-Ethylhexyl) was added in the same manner as in Example 1 except that the amount added was changed as shown in Table 1, and the results of measuring the electric conductivity and the withstand voltage of the electrolytic solution were shown in Table 1.

[0030]

[Table 1]

Example 5. In Example 1, an electrolytic solution was prepared in the same manner as in Example 1 except that the addition amount of silica fine particles was changed as shown in Table 2, and the results of measuring the electric conductivity and the withstand voltage are shown in Table 2. .

[0032]

[Table 2]

Example 6. In Example 1, diphosphoric acid (2
-Ethylhexyl), diisodecyl phosphate having a purity of 95% was used, and the addition amount was changed as shown in Table 3. An electrolytic solution was prepared in the same manner as in Example 1 and its electrical conductivity and withstand voltage were measured. The results are shown in Table 3. In addition, Example 6-2
The electric conductivity and withstand voltage of the electrolytic solution after 110 hours at 110 ° C. were 4.6 ms / cm and 180 V, respectively.

[0034]

[Table 3]

Examples 7 and 8. An electrolytic solution was prepared in the same manner as in Example 1 except that dipartimyl phosphate having a purity of 97% or distearyl phosphate was used instead of di (2-ethylhexyl) phosphate in Example 1, and the conductivity and the withstand voltage were adjusted. The measurement results are shown in Table 4. Also, 110 ° C, 5
The withstand voltage after 00 hours is also shown.

[0036]

[Table 4]

Evaluation Examples as Capacitors Using the electrolytic solutions of Examples 1, 3, 6-2, 7, 8 and Comparative Example 1, 10 electrolytic capacitors each having a rated voltage of 100 V and 220 μF were prepared, and 110 A high temperature load test at ℃ was carried out. The occurrence rate of short circuit after 2000 hours is 0% in Examples 1, 3, 6-2, 7 and 8.
In Comparative Example 1, it was 50%.

[0038]

According to the present invention, it is possible to provide an electrolytic capacitor having a low impedance and a long life and a rated voltage of 50 V or more.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masayuki Takeda 8-3-1 Chuo, Ami-machi, Inashiki-gun, Ibaraki Mitsubishi Petrochemical Co., Ltd. Tsukuba Research Institute (72) Inventor Yutaka Yokoyama 1-chome, East Ome, Ome-shi, Tokyo No.167 No.1 within Nippon Chemi-Con Co., Ltd. (72) Inventor Kenji Tamami No. 1-1, Higashioume, Ome-shi, Tokyo No.167 No.1 within Nippon Chemi-Con Co., Ltd.

Claims (12)

[Claims] 1. Two saturated alkyl groups having 8 to 18 carbon atoms per 100 parts by weight of a solution containing a quaternary ammonium salt of benzoic acid as a main solute and a complex solvent containing gamma-butyrolactone and ethylene glycol as a main solvent. An electrolytic solution for an electrolytic capacitor, containing 1 to 8 parts by weight of a phosphoric acid dialkyl ester and 0.5 to 10 parts by weight of colloidal silica. 2. The electrolytic solution according to claim 1, wherein the quaternary ammonium is tetraalkylammonium. 3. The electrolytic solution according to claim 2, wherein the total number of carbon atoms in the alkyl group of tetraalkylammonium is 8 or less. 4. The electrolytic solution according to claim 1, wherein the concentration of the quaternary ammonium salt of benzoic acid in the solution is 15 to 25% by weight. 5. The weight ratio of ethylene glycol to gamma-butyrolactone in the composite solvent is 0.1 to 10.
The electrolytic solution according to claim 1, which is 0.4. 6. The electrolytic solution according to claim 1, wherein the amount of the phosphoric acid monoalkyl ester in the phosphoric acid dialkyl ester is 10% by weight or less. 7. The content of phosphoric acid dialkyl ester is 1 to
The electrolytic solution according to claim 1, which is 5 parts by weight. 8. The electrolytic solution according to claim 1, wherein the saturated alkyl group of the phosphoric acid dialkyl ester has 8 to 12 carbon atoms. 9. The electrolytic solution according to claim 1, wherein the silica is fine particles obtained by an ion exchange method, a peptization method or a sol-gel method. 10. The electrolytic solution according to claim 1, wherein the silica is fine particles having a particle size of 20 to 50 nm. 11. The electrolytic solution according to claim 1, wherein the content of silica is 2 to 8 parts by weight. 12. The electrolytic solution according to claim 1, wherein the water content in the electrolytic solution is 3% by weight or less.