JPH08250378A - Nonaqueous electrolyte for electrochemical capacitor - Google Patents

Abstract

PURPOSE: To improve the conductivity of electrolyte by permitting the alkyl group bonded to the boron atom of a quaternary ammonium salt to have an asymmetrical structure. CONSTITUTION: Nonaqueous electrolyte is composed of a quaternary ammonium salt expressed by the formula I, where R<1> , R<2> , R<3> and R<4> are independent alkyl groups with 1-4 carbon atoms, and bipolar aprotic solvent. The dissolving quantity of the quaternary ammonium salt is 0.5-2.0mol concentration, and the bipolar aprotic solvent is selected from the following: ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone, δ- valerolactone, acetonitrile, 3-methoxy-propionitrile, trimethyl phosphate, sulfolane and 3-methylsulfolane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-electrochemical capacitor having a high electric conductivity which is used in an electrochemical capacitor used for memory backup of various electronic devices or for power of electric vehicles requiring a large current. It relates to an aqueous electrolytic solution.

[0002]

2. Description of the Related Art An electrochemical capacitor is not only a conventional electric double layer capacitor that uses only an electric double layer formed at the interface between a polarizable electrode and an electrolytic solution, but also an electric double layer capacitor and a pseudo-reduced electrode due to redox. Includes supercapacitors that incorporate capacity as a power storage element (BE Conwa
y, J. Electrochem. Soc. , 183
Vol., 1539, 1991). Ordinary electric double layer capacitors are produced by press-molding activated carbon particles, coating a mixture with a suitable binder on a collector metal,
Alternatively, it has a structure in which a plasma-sprayed aluminum on activated carbon fiber is used as a polarizable electrode, and these two polarizable electrodes are opposed to each other via an electrolytic solution and a separator and sealed in a case. On the other hand, it has been proposed to use an oxide such as nickel or ruthenium or a conductive polymer such as polypyrrole or polythiophene as an electrode for a supercapacitor using a pseudo capacitor (A. Rudge et al., Electrochim. Act).
a, 39, 273, 1994).

As an electrolytic solution used in these electrochemical capacitors, an aqueous electrolytic solution such as an aqueous solution of sulfuric acid or potassium hydroxide and a non-aqueous electrolytic solution obtained by dissolving a quaternary ammonium borofluoride salt in an organic solvent such as propylene carbonate are used. Liquid (Japanese Patent Publication No. 55-41015) is known. Since the aqueous electrolytic solution has a high electric conductivity, but the decomposition partial pressure is low, it is necessary to form a serial connection in order to obtain an element having a high withstand voltage, and there is a difficulty in downsizing. On the other hand, the non-aqueous electrolyte has an advantage that it can be downsized because of its high decomposition voltage, but its internal conductivity is high because of its low electrical conductivity,
It has a drawback that a large current cannot be taken out. An electric double layer capacitor utilizing an electric double layer formed at the interface between the polarizable electrode and the electrolytic solution is characterized in that the solute of the electrolytic solution is a salt represented by the general formula M · BR _4. An electric double layer capacitor has been proposed (Japanese Patent Laid-Open No. Sho 63-63).
-127518). (In the above general formula, M is tetraalkylammonium, tetraarylammonium, tetraalkylphosphonium or tetraarylphosphonium, B is boron, R is an alkyl group, an aryl group or an alkyl-substituted or perfluoroalkyl-substituted aryl group. However, a quaternary ammonium salt having an anion of boron in which an alkyl group is symmetrically bonded to the boron atom was used as a solute of the electrolytic solution. The electric conductivity of the electrolytic solution is not yet sufficient, and further development of an electrolytic solution having high electric conductivity is desired.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a non-aqueous electrolyte solution for electrochemical capacitors, which has a further improved electric conductivity.

[0005]

The present invention has the general formula (I)
Quaternary ammonium salt

[0006]

Embedded image

(Wherein R ¹ , R ² , R ³ and R ⁴ are
Each independently is an alkyl group having 1 to 4 carbon atoms. ) And a dipolar aprotic solvent, a non-aqueous electrolyte solution for an electrochemical capacitor is provided.

[0008]

[Function] By making the alkyl group bonded to the boron atom have an asymmetric structure, the mobility of the anion is improved by not significantly reducing the ion dissociation degree of the quaternary ammonium salt of the solute, The electric conductivity can be improved. (Outline of the Invention) Quaternary Ammonium Salt The quaternary ammonium salt represented by the general formula (I) is a salt in which an anion part in which an alkyl group is asymmetrically bonded to a boron atom and a cation part is a quaternary ammonium salt. Is. The quaternary ammonium in the cation moiety is a tetraalkylammonium salt in which the alkyl group has 1 to 4 carbon atoms, and specifically, tetramethylammonium,
Examples include tetraethylammonium, tetrapropylammonium, tetrabutylammonium, triethylmethylammonium, tripropylmethylammonium and tributylmethylammonium. Preferred among these are tetraethylammonium and triethylmethylammonium. These may be used alone or in combination of two or more.

Dipolar aprotic solvent The dipolar aprotic solvent used in the present invention includes carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, dimethyl carbonate, ethylmethyl carbonate and diethyl carbonate, and gamma. -Butyrolactone, gamma-valerolactone, delta-valerolactone and other lactone solvents, acetonitrile, 3-methoxypropionitrile and other nitrile solvents, trimethyl phosphate and other phosphate ester solvents, sulfolane, 3-methylsulfolane and other sulfur-containing solvents, etc. The single and mixed solvents having a wide potential window can be exemplified (Ue et al., J. E.
retrochem. Soc. , 141 volumes, 2989
P., 1994). Of these, preferred are propylene carbonate, gamma-butyrolactone or ethylene carbonate / dimethyl carbonate mixed solvent. Non-hydrogen Electrolyte Solution The charge solution of the present invention has a dissolution amount of the quaternary ammonium salt in the dipolar aprotic solvent of 0.5 to 2.0 molar concentration (mol / liter).

[0010]

[Examples] The present invention will be described below with reference to Examples and Comparative Examples.
Ming will be described more specifically. Example 1 0.65 mol in a propylene carbonate (PC) solvent
Concentration (C₂H_Five)_FourNB (C₂H_Five)₃CH₃Dissolve
Then, it was dehydrated by heating under reduced pressure to obtain an electrolytic solution. This electrolyte
Has an electric conductivity of 7.1 mS / cm at 25 ° C.
Was. Comparative Example 1 In Example 1, solute (C₂H_Five)_FourNB (C₂H
_Five)_FourThe electric conductivity of the electrolytic solution changed to
It was 6.3 mS / cm. Comparative Examples 2 and 3 In a propylene carbonate solvent,
(C₂H_Five)_FourNB (C _FourH₉)_FourOr (C
₂H_Five)_FourNB (C₆H_Five)_FourTrying to dissolve the electrolyte
Attempts were made to prepare them, but these solutes had poor solubility and left a precipitate.
It was unsuitable as a solute of electrolyte. Examples 2 to 4, Comparative Example 4 Same as Example 1 except that the solvent and solute are changed as shown in Table 1.
In this way, an electrolytic solution having the electric conductivity shown in the table was obtained.

[0011]

[Table 1]

[0012]

EFFECT OF THE INVENTION A non-aqueous electrolyte solution having improved electric conductivity was obtained.

Claims (3)

[Claims] 1. A quaternary ammonium salt represented by the general formula (I): (Wherein R ¹ , R ² , R ³ and R ⁴ are each independently an alkyl group having 1 to 4 carbon atoms) and a dipolar aprotic solvent. Aqueous electrolyte. 2. The amount of the quaternary ammonium salt represented by formula (I) dissolved in a dipolar aprotic solvent is 0.5 to 2.0.
The non-aqueous electrolyte solution according to claim 1, which has a molar concentration. 3. The dipolar aprotic solvent is ethylene carbonate, propylene carbonate, butylene carbonate, isobutylene carbonate, dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, gamma-butyrolactone, gamma-valerolactone, delta-valerolactone, acetonitrile. The nonaqueous electrolytic solution according to claim 1, which is selected from the group consisting of, 3-methoxypropionitrile, trimethylphosphate, sulfolane and 3-methylsulfolane.