JP2002334815A - Electric double-layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double-layer capacitor which is capable of preventing sealing material from deteriorating in sealing performance by enhancing the withstand voltage of the capacitor, so as to reduce the change in the internal resistance and a capacitance change, and to eliminate a strong alkaline component produced on the surface of a cathode-side polarizable electrode or the surface of an draw out lead connected to the cathode-side polarizable electrode. SOLUTION: An electric double layer capacitor is equipped with a pair of a polarizable electrodes, confronting each other through the intermediary of a separator and an electrolytic solution impregnating the polarizable electrodes, and the electrolytic solution contains electrolytes composed of a salt (A) of specific cation, an alkaline metal salt (B), and a quaternary ammonium slat and/or a quaternary phosphonium salt (C) which is added, as necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor used for various electronic devices and an electrolytic solution used for the same.

[0002]

2. Description of the Related Art When a quaternary ammonium salt or a quaternary phosphonium salt is used as an electrolyte for an electrolytic solution of an electric double layer capacitor, a lead-out lead connected to the surface of the cathode-side polarizable electrode or the cathode-side polarizable electrode is used. It is known that the strong alkali component generated on the surface causes a decrease in the sealing performance of the sealing body. However, it is known that the use of a specific imidazolium salt in the electrolyte can suppress the generation of the strong alkali component (Japanese Patent Application Laid-Open No. H11 (1999)). -054377).

[0003]

However, when (A) is used as an electrolyte, the withstand voltage is not higher than that of a quaternary ammonium salt or a quaternary phosphonium salt.
Since the voltage is as low as 3 V to 2.5 V, when a voltage is applied, there is a problem that the internal resistance change and the capacitance change of the electric double layer capacitor become large. The present invention solves the above-described problems, and can reduce internal resistance change and capacitance change, and is generated on the surface of the cathode-side polarizable electrode or the surface of the lead-out lead connected to the cathode-side polarizable electrode. It is an object of the present invention to provide an electric double layer capacitor capable of eliminating a strong alkali component and thereby preventing a decrease in sealing performance of a sealing body.

[0004]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above problems, and as a result, have reached the present invention.
That is, the electric double layer capacitor of the present invention has a pair of polarizable electrodes facing each other with a separator interposed therebetween, and the polarizable electrodes are impregnated with an electrolytic solution, and the electrolytic solution has the following general formula (I) and / or Or an electrolyte comprising a salt (A) comprising a cation represented by (II), an alkali metal salt (B), and a quaternary ammonium salt and / or a quaternary phosphonium salt (C) added as required. Electric double layer capacitor. General formula General formula (Wherein R ² has 1 carbon atom which may be substituted with a hydroxyl group)
To 20 hydrocarbon groups or hydrogen atoms; R ¹ , R ³ , R ⁴ , and R ⁵
Represents a hydroxyl group, an amino group, a nitro group, a cyano group,
A carboxyl group, which may have an ether group or an aldehyde group, represents a hydrocarbon group having 1 to 10 carbon atoms,
Part or all of R ¹ , R ² , R ³ , R ⁴ and R ⁵ may be mutually bonded to form a ring. )

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the above general formulas (I) and (II), R ² is a hydrocarbon group having 1 to 20 carbon atoms or a hydrogen atom which may be substituted by a hydroxyl group, for example, methyl, ethyl, isopropyl , Hexyl, 2-ethylhexyl,
Examples thereof include alkyl groups such as lauryl and stearyl, and hydroxyalkyl groups such as hydroxyethyl, 2-hydroxypropyl, 1-hydroxyhexyl and 1-hydroxylauryl. Preferably, it is a hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom. Particularly preferably, the carbon number is 1
To 5 hydrocarbon groups or hydrogen atoms. R ¹ , R ³ ,
R ⁴ and R ⁵ each represent a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group, an ether group, or a hydrocarbon group having 1 to 10 carbon atoms which may have an aldehyde group; May be partially or entirely bonded to each other to form a ring. For example, it may have a hydrocarbon group having 1 to 10 carbon atoms mentioned in the above R ² , and a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group, an aldehyde group at any of these positions, Further, the main chain may have an ether group (for example, methoxyethyl group, ethoxypropyl group, etc.). Preferably, it is an alkyl group having 1 to 5 carbon atoms and a ring-forming group, and more preferably, an alkyl group having 1 to 3 carbon atoms and a ring-forming group,
Particularly preferably, R ¹ and R ³ are alkyl groups having 1 to ³ carbon atoms, and R ⁴ and R ⁵ are ring-forming groups. As the ring-forming group, those represented by the following general formula (III) are particularly preferred.

General formula (Wherein R ² has 1 to 2 carbon atoms which may be substituted with a hydroxyl group.
0 hydrocarbon group or hydrogen atom: R ¹ and R ³ are each
A hydrocarbon group having 1 to 10 carbon atoms which may have an amino group, a cyano group, an ether group or an aldehyde group; R ⁶ is a carbon atom which may have an amino group, a cyano group, an ether group or an aldehyde group; It is a hydrocarbon group of formulas 1 to 9 or a hydrogen atom, and R ⁶ and R ³ may be mutually bonded to form a ring. )

In the above general formula (III), R ¹ ,
R ² and R ³ are the same as defined in the above general formulas (I) and (II), and R ⁶ is a hydrogen atom obtained by subtracting one carbon atom from R ⁵ or a hydrogen atom, a hydroxyl group, an amino group, A hydrocarbon group having 1 to 9 carbon atoms or a hydrogen atom which may have a nitro group, a cyano group, a carboxyl group, an ether group or an aldehyde group, and R ⁶ and R ³ are mutually bonded to form a ring It may be. For example, it may have a hydrocarbon group having 1 to 9 carbon atoms and the above functional group at any position thereof, and an ether group (for example, methoxyethyl group, ethoxypropyl group, etc.) in the main chain. May be included. It is preferably an alkyl group having 1 to 5 carbon atoms or a hydrogen atom, and particularly preferably an alkyl group having 1 to 3 carbon atoms or a hydrogen atom.

The cation component (a) constituting the salt (A) used in the present invention includes cations exemplified below. (I) imidazolium cation; 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1,2,3-trimethylimidazolium, 1,2,3,4 -Tetramethylimidazolium, 1-benzyl-3-methylimidazolium, 1,3-dimethyl-2-phenylimidazolium and the like; (ii) imidazolinium cation; 1,2,3-trimethylimidazolium, 1, 2,3,4-tetramethylimidazolinium, 1-ethyl-2,3-dimethylimidazolinium, 1,1,2-trimethylimidazolinium, 1,1,2,4-tetramethylimidazolinium, etc. (Iii) tetrahydropyrimidium cation and the like;
3-dimethyl-1,4,5,6-tetrahydropyrimidium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium, 1-methyl-1,8-diazabicyclo [5. 4.0] Undecene-7, 1-methyl-
1,5-diazabicyclo [4.3.0] nonene-5 and the like;

Of these, preferred are (i) imidazolium cation and (iii) tetrahydropyrimidinium cation, and more preferred are 1,3-
Dimethyl imidazolium, 1,3-diethyl imidazolium, 1-ethyl-3-methyl imidazolium, 1,
2,3-trimethylimidazolium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidium,
1-methyl-1,8-diazabicyclo [5.4.0] undecene-7 and 1-methyl-1,5-diazabicyclo [4.3.0] nonene-5, particularly preferably 1-ethyl -3-methylimidazolium.

As the anion component (b) of (A), a known anion used in an electric double layer capacitor can be used, for example, an anion obtained by removing a hydrogen atom from an acid as exemplified below. HClO ₄ , HBF ₄ , HPF ₆ ,
Strong inorganic acids such as HAsF ₆ and HSbF ₆ ; trifluoromethanesulfonic acid, pentafluoroethanesulfonic acid, heptafluoropropanesulfonic acid, trichloromethanesulfonic acid, pentachloropropanesulfonic acid, heptachlorobutanesulfonic acid, trifluoroacetic acid, and pentafluoropropion C1-C30 halogen-containing sulfonic acids such as acid, pentafluorobutanoic acid, trichloroacetic acid, pentachloropropionic acid, and heptachlorobutanoic acid; and C1-carbon atoms such as bis (trifluoromethylsulfonyl) imide
Halogen-containing sulfonylimides having 1 to 30 carbon atoms such as tris (trifluoromethylsulfonyl) methide;
Halogen-containing sulfonyl methide, etc., and anions used in ordinary electric double layer capacitors can be used. Of these, preferred are HClO ₄ , HB
Anion of F ₄ , HPF ₆ , HAsF ₆ , HSbF ₆ , bis (trifluoromethylsulfonyl) imide, and tris (trifluoromethylsulfonyl) methide obtained by removing a hydrogen atom from the acid, and particularly preferred are HBF ₄ and HPF ₆ Is an anion obtained by removing a hydrogen atom from.

Regarding the production method of (A) in the present invention,
As an example of the method of quaternizing the cationic component (a),
J. Am. Chem. Soc. , 69, 2269 (19
As described in 47), quaternization can be performed using a quaternizing agent and an alkyl halide. Further, as other quaternizing agents (a), dialkyl sulfates, sulfonates (U.S. Pat.
S. R. SU176290), dimethyl carbonate (USP2
635100), phosphate esters (Journal)
f. prakt. Chemie. Band 317, He
ft 5, 1975, 733) and an epoxy group-containing compound (US Pat. No. 2,127,476). When it is necessary to change the anion component to the anion constituting the quaternary salt (A) after quaternization in this way, for example, (a)
Is desired to be converted to an organic acid anion after quaternization with an alkyl halide, for example, after the quaternized halogen ion is once converted to a hydroxide ion and then reacted with the organic acid to obtain the desired organic acid. A quaternary salt having an anion can be produced.

The (A) thus obtained includes:
For example, those described in Table 1 can be mentioned.

[0013]

[Table 1]

Among them, preferred are salts of imidazolium cations and anions obtained by removing hydrogen atoms from strong inorganic acids, and particularly preferred are 1-ethyl-3-methylimidazolium and salts of HBF ₄ and HPF _6. Anion excluding hydrogen atoms.

In the present invention, specific examples of the alkali metal salt (B) are not particularly limited. For example, a salt comprising the above-mentioned anion component (b) and an alkali metal (lithium, sodium, potassium, etc.) cation is preferable. , More preferably, HClO ₄ , HBF ₄ , HPF ₆ , HAs
F ₆ , HSbF ₆ , bis (trifluoromethylsulfonyl) imide, tris (trifluoromethylsulfonyl)
A salt comprising an anion obtained by removing a hydrogen atom from an acid of a methide and a lithium cation, particularly preferred is HB
It is a salt comprising an anion obtained by removing a hydrogen atom from F ₄ and HPF ₆ and a lithium cation. The alkali metal salt (B)
For example, it can be produced by neutralizing a hydroxide of an alkali metal and an acid of the anion component and dehydrating the same.

The quaternary ammonium salt and / or quaternary phosphonium salt (C) optionally added in the present invention comprises the above-mentioned anion component (b) and a quaternary ammonium ion and / or quaternary phosphonium ion. And salts thereof. Specifically, the following are mentioned.

Specific examples of the quaternary ammonium ion include cations exemplified below. (I) aliphatic quaternary ammonium having an alkyl or alkenyl group having 4 to 30 or more carbon atoms; tetramethylammonium, ethyltrimethylammonium, diethyldimethylammonium, triethylmethylammonium, tetraethylammonium, trimethylpropylammonium, dimethyldiamine Contains alkenyl groups such as propylammonium, ethylmethyldipropylammonium, butyltrimethylammonium, dimethyldibutylammonium, tetraalkylammonium such as tetrabutylammonium, tetrahexylammonium and trimethyldecylammonium, trimethyloleylammonium, tetraarylammonium and vinyltrimethylammonium Ammonium;

(Ii) aromatic quaternary ammonium having 6 to 30 or more carbon atoms; trimethylphenylammonium, dimethylethylphenylammonium, triethylphenylammonium, etc .; (iii) 3 to 30 or more carbon atoms. Alicyclic quaternary ammonium; pyridinium such as N, N-dimethylpyrrolinium, N-ethyl-N-methylpyrrolidinium, N, N-diethylpyrrolidinium, N, N-dimethylmorpholinium, N- Ethyl-N-methylmorpholinium,
Morpholinium such as N, N-diethylmorpholinium,
Piperidinium such as N, N-dimethylpiperidinium and N, N-diethylpiperidinium;

Specific examples of the quaternary phosphonium ion include cations exemplified below. (I) an aliphatic quaternary phosphonium having an alkyl or alkenyl group having 1 to 30 or more carbon atoms; tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium, methyltriethylphosphonium,
Methyltributylphosphonium, dimethyldiethylphosphonium, trimethylethylphosphonium, trimethylpropylphosphonium, ethyltripropylphosphonium, ethyltributylphosphonium, diethyldibutylphosphonium, propyltributylphosphonium, dipropyldibutylphosphonium, tetraalkylphosphonium such as tripropylbutylphosphonium, trimethyloleyl Phosphonium, tetraarylphosphonium,
Alkenyl group-containing phosphonium such as vinyltrimethylphosphonium; (ii) aromatic quaternary phosphonium having 6 to 30 or more carbon atoms; triphenylmethylphosphonium, diphenyldimethylphosphonium, triphenylbenzylphosphonium and the like; (iii) carbon number 3 to 30, or more alicyclic quaternary phosphoniums; 1,1-dimethylphosphoranium, 1-
Methyl-1-ethylphosphoranium, phosphoranium such as 1,1-diethylphosphoranium, 1,1-dimethylphosphorinanium, 1-methyl-1-ethylphosphorinanium, 1,1-diethylphosphorinanium, 1,1-
A phosphorinanium such as pentamethylenephosphorinanium;

Among these, preferred are salts of aliphatic quaternary ammonium and aliphatic quaternary phosphonium with the above-mentioned anions, more preferably tetraalkylammonium, tetraalkylphosphonium and HClO ₄ , H
An anion obtained by removing a hydrogen atom from an acid of BF ₄ , HPF ₆ , HAsF ₆ , HSbF ₆ , bis (trifluoromethylsulfonyl) imide, or tris (trifluoromethylsulfonyl) methide, and particularly preferably tetramethylammonium, tetraethyl Ammonium, triethylmethylammonium, tetramethylphosphonium, tetraethylphosphonium, tetrabutylphosphonium and HB
It is a salt with an anion obtained by removing a hydrogen atom from F ₄ or HPF ₆ . These salts include, for example, quaternary ammonium and quaternary ammonium.
It can be produced by reacting a halide, hydroxide or the like of a secondary phosphonium with an acid of the above-mentioned anionic component.

The electrolytic solution used in the present invention comprises (A) and (B), but (C) may be added if necessary. The ratio of the (A), (B) and (C) is
The molar ratio is preferably from 50 to 99: 1 to 20: 0 to 49, and more preferably from 60 to 80:10 to 20: 0.
20. When the molar ratio of (A) is from 50 to 99, the effect of eliminating the strong alkali component generated on the surface of the cathode-side polarizable electrode or the surface of the extraction lead connected to the cathode-side polarizable electrode is improved. When the molar ratio of (B) is 1
When it is 20 to 20, the effect of improving the withstand voltage is good. When the molar ratio of (C) is 49 or less, the effect of improving the withstand voltage is improved.

The electrolyte may optionally contain a solvent and various additives. As the solvent, an aprotic solvent can be used. Specific examples of the aprotic solvent include:
Carbonate (propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc.), ester (cyclic carboxylic acid ester such as γ-butyrolactone, etc.), sulfolane (sulfolane, 3-methylsulfolane, 2,4- Dimethylsulfolane), nitrile (acetonitrile, etc.), and ether (tetrahydrofuran, etc.), or a mixture of two or more thereof. The amount of the solvent is preferably such that the total electrolyte concentration of the electrolytic solution is 0.3 to 2.5 mol / kg, more preferably 0.5 to 1.0 mol.
1 / kg. As additives, phosphoric acids and their derivatives (phosphoric acid, phosphorous acid, phosphoric acid esters,
Phosphonic acids, etc.), boric acids and their derivatives (boric acid,
Boric acid, boric acid esters, boron and hydroxyl groups and / or
Or a complex with a compound having a carboxyl group, etc., nitrates (such as lithium nitrate), and nitro compounds (such as nitrobenzoic acid, nitrophenol, nitrophenetol, nitroacetophenone, and aromatic nitro compounds). The amount of the additive is preferably 1% of the electrolyte from the viewpoint of conductivity.
It is at most 0% by weight, more preferably at most 5% by weight.

It is preferable that the water content of the electrolytic solution is small from the viewpoint of lowering the withstand voltage performance due to the electrolysis of water. Preferably, 3
000 ppm or less, more preferably 100 pp
m, particularly preferably 50 ppm or less.
The moisture measurement can be performed by the Karl Fischer method. The electrolytic solution is prepared by adding the components (A) and (B) and the component (C) as necessary in a container, and adding a solvent, an additive and the like as necessary. In order to dissolve the electrolyte salt uniformly, it is preferable to prepare it while stirring. During the preparation of the electrolytic solution, it is preferable to perform the operation in a dry atmosphere in order to prevent water from being mixed into the electrolytic solution, and to dehydrate the prepared electrolytic solution if the amount of water is outside the above range.

The electric double layer capacitor of the present invention comprises a capacitor element which is opposed to a pair of polarizable electrodes with a separator interposed therebetween, and the capacitor element is impregnated with the above-mentioned electrolytic solution. The polarizable electrode is immersed in the electrolytic solution and placed under vacuum for a predetermined time (about 1 to 2 hours) to impregnate the polarizable electrode with the electrolytic solution. The polarizable electrode is obtained by coating an electrode slurry on an aluminum foil or a copper foil. This electrode slurry is obtained by mixing activated carbon, graphite or a polyacene organic semiconductor with carbon black, acetylene black or ketjen black, and using PTFE as a binder. And CMC, etc.
It is moistened with pure water or alcohol. The electric double layer capacitor is used for, for example, a memory backup circuit of a device.

[0025]

The present invention will be further described with reference to the following examples and comparative examples.
However, the present invention is not limited to this.
No. The electrolytic solution and the electric double layer capacitor of the present invention
The measurement method used for evaluation is described below. Electric conductivity Measured using an electric conductivity meter (CM-40S made by Toa Denpa)
Put the electrolyte and stirrer piece in the cell and stir
At 30 ° C. Polarization measurement Electrochemical analyzer (ALS700 manufactured by BAS)
No, sweep speed 10mVs ^-1, Potential range -2.0V-
Perform at 2.0V and measure at 25 ° C while stirring the electrolyte.
Was. The measuring cell has glassy carbon as the working electrode,
Using platinum wire for counter electrode and silver / silver ion electrode for reference electrode
Was.

Equivalent Series Resistance (ESR) The equivalent series resistance of the electric double layer capacitor was measured at 1 kHz using an impedance analyzer (HP 4192A). Capacitance change rate Constant voltage / constant current generator (Advantest R6741)
A), calculated from the constant current discharge curve of an electric double layer capacitor prepared using the electrolytic solution (i = C × dV / d)
The capacitance was determined at t). From this capacitance, 70 ° C., 2.5 V with respect to the initial capacitance of the electric double layer capacitor
The change in capacitance after 500 hours from the application of the voltage was calculated, and the capacitance change rate was calculated.

[0027] Example 1 2L flask in propylene carbonate (hereinafter PC substantially) 1 kg 1-methyl-3-ethyl imidazolium tetrafluoroborate (hereinafter EMIBF ₄ approximately) 0.6
5 mol and 0.10 mol of LiBF ₄ were added, and at room temperature,
The mixture was stirred for 1 hour and uniformly dissolved to prepare an electrolytic solution (a). The water content was 49 ppm. In order to prevent water from being mixed into the electrolytic solution, all of the electrolytic solution was prepared in a glove box. The electric conductivity of the electrolyte (a) at 30 ° C. is 1
It was 2.9 mS / cm. Polarization measurement was performed using this electrolytic solution (a). Further, an electrolytic solution (a) was added to the activated carbon electrode cells opposed to each other with a separator interposed therebetween to prepare an electric double layer capacitor (rated voltage: 2.5 V-capacitance: 0.1 V).
2F, size: φ6.8 mm × 1.4 mm). A voltage of 2.5 V is applied to this electric double layer capacitor at 70 ° C.
The equivalent series resistance (ESR) and the rate of change in capacitance at 1 kHz after 500 hours were measured.

Examples 2 to 4 and Comparative Examples 1 to 4 In Examples 2 to 4 and Comparative Examples 1 to 4, electrolytes (b) to ( d)
And (i) to (ii) were prepared, and an electric double layer capacitor using these electrolytes was prepared. Table 3 shows (A) to (K) added to 1 kg of the solvent (propylene carbonate).
The number of moles of (C) is shown. Table 4 shows the results of measuring the conductivity of the electrolytes (a) to (d) and (a) to (d).

[0029]

[Table 2]

[0030]

[Table 3]

[0031]

[Table 4]

The electrolytic solution of Example 1 and Comparative Example 1 -2.
0 V to 2.0 V (vs. Ag / Ag ⁺) Polarization measurement result
The results are shown in FIG. 1 (Example 1) and FIG. 2 (Comparative Example 1). FIG.
At about 1.2 V to 2.0 V
But the peak is small in the electrolyte (a).
And shows that the electrochemical stability of the electrolyte (a) is high.
You.

Next, the electrolytes (a) to (d) and (a)
A voltage of 2.5 V is applied at 70 ° C. to the electric double-layer capacitor using (d) to (d), and the measurement results of ESR and capacitance change rate at 1 kHz after 500 hours are shown in (Table 5).

[0034]

[Table 5] As is clear from Table 5, the electric double layer capacitors using the electrolytes (a) to (d) (Examples 1 to 4) were the comparative electric double layers using the electrolytes (a) to (d). The ESR is smaller and the capacitance change rate is smaller than that of the capacitor, which indicates that the electric double layer capacitor using the electrolytic solution of the present invention has less deterioration.

[0035]

The electric double layer capacitor of the present invention has the following effects. (1) Since the withstand voltage is high, the change in the internal resistance and the change in the capacitance are small, and the deterioration of the electric double layer capacitor can be suppressed. (2) Strong alkali components generated on the surface of the cathode-side polarizable electrode or on the surface of the lead-out lead connected to the cathode-side polarizable electrode are eliminated, whereby a decrease in the sealing performance of the sealing body can be prevented.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing polarization measurement results of an electrolytic solution of Example 1.

FIG. 2 is a characteristic diagram showing polarization measurement results of the electrolytic solution of Comparative Example 1.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yoshinori Takamukai 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A battery comprising: a pair of polarizable electrodes opposed to each other via a separator, wherein the polarizable electrodes are impregnated with an electrolytic solution;
An electric double layer capacitor, wherein the electrolytic solution contains a salt (A) comprising a cation represented by the following general formula (I) and / or (II) and an alkali metal salt (B).
General formula General formula (Wherein R ² has 1 carbon atom which may be substituted with a hydroxyl group)
To 20 hydrocarbon groups or hydrogen atoms; R ¹ , R ³ , R ⁴ , and R ⁵
Represents a hydroxyl group, an amino group, a nitro group, a cyano group,
A carboxyl group, which may have an ether group or an aldehyde group, represents a hydrocarbon group having 1 to 10 carbon atoms,
Part or all of R ¹ , R ² , R ³ , R ⁴ and R ⁵ may be mutually bonded to form a ring. ) 2. The electric double layer capacitor according to claim 1, further comprising an electrolyte comprising (A), (B) and a quaternary ammonium salt and / or a quaternary phosphonium salt (C). . 3. The method (A), the method (B) and the method (C).
The electric double layer capacitor according to claim 1 or 2, wherein the molar ratio is 50 to 99: 1 to 20: 0 to 49 in molar ratio. 4. The electric double layer capacitor according to claim 1, wherein (A) is a salt comprising a cation represented by the general formula (III). General formula (Wherein R ² has 1 to 2 carbon atoms which may be substituted with a hydroxyl group.
0 hydrocarbon group or hydrogen atom: R ¹ and R ³ are each
A hydrocarbon group having 1 to 10 carbon atoms which may have an amino group, a cyano group, an ether group or an aldehyde group; R ⁶ is a carbon atom which may have an amino group, a cyano group, an ether group or an aldehyde group; It is a hydrocarbon group of formulas 1 to 9 or a hydrogen atom, and R ⁶ and R ³ may be mutually bonded to form a ring. ) 5. The electric double layer capacitor according to claim 1, wherein (A) is a 1-ethyl-3-methylimidazolium salt. 6. The method according to claim 1, wherein (B) is a lithium salt.
The electric double-layer capacitor according to any one of claims 1 to 5. 7. The electric double layer capacitor according to claim 1, wherein the electrolytic solution has a water content of 3000 ppm or less.