JP2012069931A - Electrolytic solution for electric double layer capacitor, and electric double layer capacitor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric double layer capacitor in which the rate of change in equivalent series resistance is low, low resistance is developed even under low temperatures, the ability of dissipating strong alkaline components generated on the surface of a cathode side polarizable electrode or the surface of a lead connected therewith can be enhanced, and degradation in the sealing performance of a sealing body can be prevented.SOLUTION: The electrolytic solution for an electric double layer capacitor is produced by dissolving a quaternary ammonium salt (A) represented by a specific chemical formula into an organic solvent (S), and contains tetramethyl ammonium tetrafluoroborate in the range of 0.3-10 wt% for the quaternary ammonium salt (A).

Description

  The present invention relates to an electrolytic solution for an electric double layer capacitor and an electric double layer capacitor using the same.

Conventionally, an electric double layer in the electrolyte of the capacitor tetraethylammonium tetrafluoroborate (hereinafter, described as TEA · BF ₄₎ salts (e.g., Patent Document 1) is mainly used as an electrolyte, ethyl trimethylammonium tetrafluoroborate ( Hereinafter, ETMA · BF ₄ ) salts (for example, Patent Document 2) have also been studied. In recent years, new applications such as hybrid electric vehicles, which are used for a long period of time from low temperature to high temperature and at high current, are spreading. In such fields, long-term durability, reliability and low temperature There is a need for an electric double layer capacitor that exhibits low resistance. For this reason, it is urgent to develop an electrolytic solution that is a member constituting the same, which is chemically stable, can be used for a long time, and develops a low resistance when discharging a large current at a low temperature. It has become.

JP-A-50-44463 JP2008-508736

When the tetraethylammonium salt described in Patent Document 1 is used, the sealing performance of the sealing body is improved by a strong alkali component generated on the surface of the cathode side polarizable electrode or the surface of the lead lead connected to the cathode side polarizable electrode. A decline is caused. The resistance at low temperature was high. Since the ethyltrimethylammonium salt described in Patent Document 2 has a small ionic diameter, it can improve resistance at low temperatures, but is not sufficient and has not yet been put into practical use.

The present invention solves the above-mentioned problems, can improve the ability to eliminate strong alkali components generated on the surface of the cathode-side polarizable electrode or on the surface of the lead lead connected to the cathode-side polarizable electrode, An object of the present invention is to provide an electric double layer capacitor that can prevent deterioration in body sealing performance, has a small rate of change in equivalent series resistance, and exhibits low resistance even at low temperatures.

［Ｒ_１〜Ｒ_４はメチル基またはエチル基であって、少なくとも１つは他と異なる。］ As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. That is, the present invention is an electrolytic solution for an electric double layer capacitor in which a quaternary ammonium salt (A) represented by the following general formula (1) is dissolved in an organic solvent (S). An electrolytic solution for an electric double layer capacitor containing tetramethylammonium tetrafluoroborate in a range of 0.3 to 10% by weight relative to (A), and an electric double capacitor using the electrolytic solution for an electric double layer capacitor.

_[R 1 to R ₄ is a methyl group or an ethyl group, at least one is different from others. ]

By using the electrolytic solution of the present invention, the electric double layer capacitor has a low equivalent series resistance at a low temperature, a small change rate of the equivalent series resistance, and a highly reliable electric double layer capacitor excellent in sealing performance of the sealing body. it can.

The present invention is described in detail below.
The electrolytic solution for an electric double layer capacitor of the present invention is described as a quaternary ammonium salt (A) represented by the above general formula (1) as an electrolyte, that is, diethyldimethylammonium tetrafluoroborate (hereinafter referred to as DEDMA · BF ₄ ). ), Ethyltrimethylammonium tetrafluoroborate (hereinafter sometimes referred to as ETMA · BF ₄ ), and triethylmethylammonium tetrafluoroborate (hereinafter sometimes referred to as TEMA · BF ₄ ). It contains at least one selected from more.
By adopting BF ₄ ⁻ (tetrafluoroborate) as the anion component of the quaternary ammonium salt (A), the equivalent series resistance change rate (−30 ° C.) and the equivalent series resistance (−30 ° C.) can be lowered. .
Since the quaternary ammonium salt (A) is more reactive with alkali than tetraethylammonium tetrafluoroborate, strong alkali is generated on the surface of the cathode-side polarizable electrode or on the surface of the lead lead connected to the cathode-side polarizable electrode. Although it has the ability to dissipate components, it was insufficient.

Molecular orbital calculation of quaternary ammonium salt (A) The anion radius calculated by the AM1 method was 0.23 nm, and the cation radius was 0.30 to 0.33 nm. In particular, the cation radius of the ETMA · BF ₄ salt was 0.30 nm. ETMA has the smallest cation radius among all the quaternary ammoniums dissolved in the organic solvent to such an extent that it can effectively exhibit performance as an electrolytic solution, but the cation radius is larger than the anion radius.
Quaternary ammonium salt (A) is smaller in size than other tetraethylammonium / BF ₄ salts, etc., which have a larger ionic diameter, but anion is more adsorbed on the activated carbon electrode when voltage is applied, and the anion absorbs the voltage. Many of the positive electrodes are applied (for example, when 2.8 V is applied, 1.5 V is applied to the positive electrode and 1.3 V is applied to the cathode). Therefore, the decomposition of anions occurred on the positive electrode side, and the deterioration was increased. The activated carbon electrode is composed of macropores of 25 nm or more, mesopores of 1 to 25 nm, and micropores of 0.2 to 1 nm. The macropores contribute to the diffusion of ions. Contributes to expression. If the cation size is large, the adsorption of cations to the micropores is limited.

The above problem can be solved by adding tetramethylammonium tetrafluoroborate in the range of 0.3 to 10% by weight with respect to the quaternary ammonium salt (A). Tetramethylammonium has an ionic radius of 0.28 nm and is easily adsorbed to the micropores of the activated carbon electrode, so that a voltage is applied almost evenly to the positive electrode and the cathode when a voltage is applied (for example, 1. 4V, 1.4V for the cathode).
The addition amount of tetramethylammonium tetrafluoroborate is preferably 0.6 to 5% by weight with respect to the quaternary ammonium salt (A), from the viewpoint of achieving both the equivalent series resistance at a low temperature and the change rate of the equivalent series resistance. Preferably it is 1-3 weight%.
Therefore, decomposition of the anion on the positive electrode side is suppressed. In addition, since the voltage is evenly applied to the cathode side, the reaction between the alkali generated by electrolysis and the cation of the quaternary ammonium salt (A) proceeds sufficiently, and the surface of the cathode side polarizable electrode or the cathode side polarizable electrode The ability to eliminate the strong alkali component generated on the surface of the lead lead connected to is sufficiently developed.
When the content of tetramethylammonium tetrafluoroborate is less than 0.3% by weight with respect to the quaternary ammonium salt (A), the effect is not manifested, and when the content exceeds 10% by weight, tetramethylammonium tetra Since the solubility of fluoroborate in an organic solvent is low, it precipitates and deteriorates the performance.

Specific examples of the organic solvent (S) include the following. Two or more of these can be used in combination.
Ethers: chain ether [carbon number 2-6 (diethyl ether, methyl isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.); carbon number 7-12 (diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.)], cyclic ether [C2-C4 (tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.); C5-C18 (4-butyldioxolane, crown ether, etc.)].
Amides: N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, N-methylpyrrolidone and the like.
-Chain esters: methyl acetate, methyl propionate, etc.
Lactones: γ-butyrolactone, α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone, and the like.
Nitriles: acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, acrylonitrile, benzonitrile and the like.
-Cyclic carbonates: propylene carbonate, ethylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, etc.-Chain carbonate esters: dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc.
Sulfones: ethylpropylsulfone, ethylisopropylsulfone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, and the like.
・ Nitro: Nitromethane, nitroethane, etc.
Benzenes: toluene, xylene, chlorobenzene, fluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and the like.
Heterocyclic class: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.
Ketones: acetone, 2,5 hexanedione, cyclohexane, etc.
-Phosphate esters: trimethyl phosphoric acid, triethyl phosphoric acid, tripropyl phosphoric acid and the like.

Of these, cyclic carbonates, chain carbonates, lactones, chain esters, nitriles, and sulfones are preferable, and propylene carbonate, dimethyl carbonate, ethylene carbonate, sulfolane, acetonitrile, And γ-butyrolactone.

The water content in the electrolytic solution of the present invention is preferably 300 ppm or less, more preferably 100 ppm or less, particularly preferably 50 ppm or less based on the weight of the electrolytic solution from the viewpoint of electrochemical stability. Within this range, it is possible to suppress the deterioration in performance of the electrochemical capacitor over time.
The water content in the electrolytic solution can be measured by the Karl Fischer method (JIS K0113-1997, coulometric titration method).
Examples of the method for setting the water content in the electrolytic solution in the above range include a method using a sufficiently dried electrolyte (A) and a non-aqueous solvent sufficiently dehydrated in advance.
Examples of the drying method include heating and drying under reduced pressure (for example, heating at 150 ° C. under reduced pressure of 20 Torr), evaporating and removing a trace amount of water contained therein, recrystallization, and the like.
As a dehydration method, heat dehydration under reduced pressure (for example, heating at 100 Torr) to evaporate and remove a trace amount of water, molecular sieve (manufactured by Nacalai Tesque, 3A
1/16, etc.) and a method using a dehydrating agent such as activated alumina powder.

In addition to these, the electrolytic solution is heated and dehydrated under reduced pressure (for example, heated at 100 ° C. under reduced pressure of 100 Torr) to evaporate and remove a trace amount of water, molecular sieve, activated alumina powder, etc. And a method of using a dehydrating agent. These methods may be performed alone or in combination.

As a basic structure of the electric double layer capacitor, a separator is sandwiched between two polarizable electrodes and impregnated with an electrolytic solution. The main component of the polarizable electrode is preferably a carbonaceous material such as activated carbon, graphite, or polyacene organic semiconductor because it is electrochemically inert to the electrolyte and has an appropriate electrical conductivity. Thus, at least one of the positive electrode and the negative electrode is a carbonaceous material. A porous carbon material (for example, activated carbon) having a specific surface area of 10 m ² / g or more determined by the BET method by the nitrogen adsorption method is more preferable because of the large electrode interface where charges are accumulated. The specific surface area of the porous carbon material is selected in consideration of the target capacitance per unit area (F / m ² ) and the decrease in bulk density associated with the increase in the specific surface area. preferably it has a specific surface area determined is 30~2,500m ² / g by the BET method, since the electrostatic capacity per volume is large, the specific surface area is particularly preferably activated carbon 300~2,300m ² / g.

Examples of the electric double layer capacitor of the present invention include a coin type, a wound type, and a rectangular type. The electrolytic solution for an electric double layer capacitor of the present invention can be applied to any electric double layer capacitor.

The electrolytic solution of the present invention can be prepared by a known method, and the concentration of the electrolyte (A) in the electrolytic solution is preferably 0.5 to 2.0 mol / L, and preferably 0.7 to 1.7 mol / L. Is more preferable, and 0.8 to 1.5 mol / L is most preferable. When the concentration of (A) is 0.5 mol / L or more, the conductivity of the electrolytic solution is sufficient, and when it is 2.0 mol / L or less, the low temperature characteristics are good and the economy is excellent.

Next, specific examples of the present invention will be described, but the present invention is not limited thereto. Hereinafter, “parts” means “parts by weight” unless otherwise specified.
In the following examples, ¹ H-NMR, ¹⁹ F-NMR, and ¹³ C-NMR were measured by the following methods.
Measurement conditions for ¹ H-NMR Instrument: AVANCE 300 (manufactured by Nippon Bruker Co., Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz.
¹⁹ F-NMR measurement conditions Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz
Measurement conditions for ¹³ C-NMR Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz
Moreover, the silver ion content was quantified by the turbidimetric method with an atomic absorption spectrophotometer (Shimadzu Corporation AA-6200).

In addition, the content of tetramethylammonium tetrafluoroborate in the quaternary ammonium salt (A) can be quantified by high performance liquid chromatography (HPLC).
HPLC measurement conditions are: column: packed with polymer-coated filler, mobile phase: phosphate buffer (pH 2-3), flow rate: 0.5 ml / min, detector: UV, temperature: 40 ° C. (For example, apparatus: model name (LC-10A), manufacturer (Shimadzu Corporation), column: Develosil C30-UG (4.6 mmφ × 25 cm) manufacturer (Nomura Chemical), mobile phase: phosphoric acid concentration 10 mmol / l, excess Sodium chlorate aqueous solution with a concentration of 100 mmol / l, flow rate: 0.8 ml / min, detector: UV (210 nm), injection volume: 20 μl, column temperature: 40 ° C. The calibration curve is quaternary ammonium salt (A) and It can be created using tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries.

<Production Example 1><Production of ETMA salt>
Synthesis of iodide salt 110 parts of N, N-dimethylethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 339 parts of acetone were charged into a glass beaker and uniformly dissolved. 234 parts of methyl iodide was slowly added dropwise while stirring the solution, and then stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 322 parts of ethyltrimethylammonium iodide salt.

Preparation of AgBF ₄ solution A solution obtained by mixing 174 parts of silver oxide and 314 parts of a 42% by weight aqueous solution of borohydrofluoric acid was dehydrated at 100 ° C. under reduced pressure, and 825 parts of methanol was added to dissolve it. AgBF ₄ methanol A solution was obtained.

-Preparation of BF ₄ salt 1117 parts of AgBF ₄ methanol solution was slowly added dropwise to the above mixed solution of 322 parts of ethyltrimethylammonium iodide salt and 353 parts of methanol, and then filtered to collect the filtrate. . The AgBF ₄ solution or mixed solution was added little by little to the collected filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate.
The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. Silver ions in the crystal were 10 ppm or less, and iodide ion content was 5 ppm or less. After adding 3000 parts of methanol to the crystal and dissolving at 60 ° C., the solution was cooled to −10 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 124 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, this white crystal was an ETMA · BF ₄ salt. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

<Production Example 2><< Production of DEDMA salt >>
Synthesis of iodide salt 131 parts of N, N-diethylmethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 339 parts of acetone were charged into a glass beaker and uniformly dissolved. 234 parts of methyl iodide was slowly added dropwise while stirring the solution, and then stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 330 parts of diethyldimethylammonium iodide salt.

Preparation of AgBF ₄ solution A solution obtained by mixing 174 parts of silver oxide and 314 parts of a 42% by weight aqueous solution of borohydrofluoric acid was dehydrated at 100 ° C. under reduced pressure, and 825 parts of methanol was added to dissolve it. AgBF ₄ methanol A solution was obtained.

-Preparation of BF ₄ salt 1117 parts of AgBF ₄ methanol solution were slowly added dropwise to the above mixed solution of 343 parts of diethyldimethylammonium iodide and 353 parts of methanol, and then filtered to collect the filtrate. . The AgBF ₄ solution or mixed solution was added little by little to the collected filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate.
The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. Silver ions in the crystal were 10 ppm or less, and iodide ion content was 5 ppm or less. After adding 3000 parts of methanol to the crystal and dissolving at 60 ° C., the solution was cooled to −10 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 117 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, the white crystals were DEDMA · BF ₄ salt. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

<Production Example 3><< Production of TEMA Salt >>
Synthesis of iodide salt 152 parts of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 339 parts of acetone were charged into a glass beaker and uniformly dissolved. 234 parts of methyl iodide was slowly added dropwise while stirring the solution, and then stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 317 parts of triethylmethylammonium iodide salt.

Preparation of AgBF ₄ solution A solution obtained by mixing 174 parts of silver oxide and 314 parts of a 42% by weight aqueous solution of borohydrofluoric acid was dehydrated at 100 ° C. under reduced pressure, and 825 parts of methanol was added to dissolve it. AgBF ₄ methanol A solution was obtained.

-Preparation of BF ₄ salt 1117 parts of AgBF ₄ methanol solution was slowly added dropwise to the above mixed solution of 364 parts of triethylmethylammonium iodide salt and 382 parts of methanol, and then filtered to collect the filtrate. . The AgBF ₄ solution or mixed solution was added little by little to the collected filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate.
The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. Silver ions in the crystal were 10 ppm or less, and iodide ion content was 5 ppm or less. After adding 3000 parts of methanol to the crystal and dissolving at 60 ° C., the solution was cooled to −10 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 127 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, the white crystals were TEMA · BF ₄ salt. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

<Production Example 4><< Production of TEA salt >>
Synthesis of iodide salt 102 parts of triethylamine (manufactured by Tokyo Chemical Industry Co., Ltd.) and 300 parts of acetone were charged into a glass beaker and dissolved uniformly. While stirring the solution, 171 parts of ethyl iodide was slowly added dropwise, and stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 257 parts of tetraethylammonium iodide salt.

-Preparation of AgBF ₄ solution A solution obtained by mixing 116 parts of silver oxide and 209 parts of 42 wt% aqueous borofluoric acid solution at 100 ° C under reduced pressure was dissolved in 550 parts of methanol, and dissolved in AgBF ₄ methanol. A solution was obtained.

-Preparation of BF ₄ salt 745 parts of the above AgBF ₄ solution was slowly added dropwise to a mixed solution of 257 parts of tetraethylmethylammonium iodide salt and 232 parts of methanol, and then filtered to collect the filtrate. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 186 parts of white crystals. 300 parts of methanol was added to the crystal and dissolved at 30 ° C., then cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 162 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, the white crystals were TEA · BF ₄ salt. ^From the integral value of ¹ H-NMR, the purity was 99%.

Example 1
172.06 parts of ETMA · BF ₄ salt of Production Example 1 and 0.52 part of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte The electrolyte solution 1 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 2
171.69 parts of ETMA · BF ₄ salt of Production Example 1 and 1.03 part of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte The electrolyte solution 2 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 3
170.96 parts of ETMA · BF ₄ salt of Production Example 1 and 1.71 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte The electrolyte solution 3 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 4
167.40 parts of ETMA · BF ₄ salt of Production Example 1 and 5.02 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte The electrolyte solution 4 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 5
163.99 parts of ETMA · BF ₄ salt of Production Example 1 and 8.20 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte) The electrolyte solution 5 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 6
156.03 parts of ETMA · BF ₄ salt of Production Example 1 and 15.60 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte) The electrolyte solution 6 of the present invention was obtained at a concentration of 1.0 mol / L).

Example 7
136.77 parts of ETMA · BF ₄ salt of Production Example 1 and 1.37 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte Concentration 0.8 mol / L), electrolyte solution 7 of the present invention was obtained.

Example 8
170.96 parts of ETMA · BF ₄ salt of Production Example 1 and 1.71 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated propylene carbonate to prepare a total of 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution 8 of the present invention was obtained.

Example 9
170.96 parts of ETMA · BF ₄ salt of Production Example 1 and 1.71 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated sulfolane to prepare a total of 1 liter (electrolyte concentration 1 0.0 mol / L), an electrolytic solution 9 of the present invention was obtained.

Example 10
189.0 parts of DEDMA · BF4 salt of Production Example 2 and 0.57 part of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to adjust the whole to 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution 10 of the present invention was obtained.

Example 11
189.00 parts of DEDMA · BF4 salt of Production Example 2 and 1.89 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to adjust the whole to 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution 11 of the present invention was obtained.

Example 12
203.000 parts of TEMA · BF4 salt of Production Example 3 and 0.61 part of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to adjust the whole to 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution 12 of the present invention was obtained.

Example 13
Dissolve 203.000 parts of TEMA · BF4 salt of Production Example 3 and 2.03 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. uniformly in dehydrated γ-butyrolactone and adjust the whole to 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution 13 of the present invention was obtained.

Comparative Example 1
172.8 parts of ETMA · BF ₄ salt of Production Example 1 was uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte concentration: 1.0 mol / L). Obtained.

Comparative Example 2
172.43 parts of ETMA · BF ₄ salt of Production Example 1 and 0.35 part of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte A concentration of 1.0 mol / L) and an electrolyte ratio of 2 of the present invention were obtained.

Comparative Example 3
148.81 parts of ETMA · BF ₄ salt of Production Example 1 and 22.32 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte A concentration of 1.0 mol / L) and an electrolyte ratio of 3 of the present invention were obtained.

Comparative Example 4
148.81 parts of ETMA · BF ₄ salt of Production Example 1 and 22.32 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated propylene carbonate to prepare a total of 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution ratio 4 of the present invention was obtained.

Comparative Example 5
148.81 parts of ETMA · BF ₄ salt of Production Example 1 and 22.32 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated sulfolane to prepare a total of 1 liter (electrolyte concentration 1 0.0 mol / L), an electrolytic solution ratio 5 of the present invention was obtained.

Comparative Example 6
175.00 parts of ETMA · BF ₄ salt of Production Example 1 and 21.00 parts of tetramethylammonium tetrafluoroborate manufactured by Wako Pure Chemical Industries, Ltd. were uniformly dissolved in dehydrated sulfolane to prepare a total of 1 liter (electrolyte concentration 1 0.0 mol / L), an electrolyte ratio 6 of the present invention was obtained.

Comparative Example 7
189.0 parts of DEDMA · BF4 salt of Production Example 2 and 28.4 parts of Wako Pure Chemical Industries Tetramethylammonium Tetrafluoroborate were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte concentration) 1.0 mol / L), an electrolytic solution ratio 7 of the present invention was obtained.

Comparative Example 8
203.0 parts of TEMA · BF4 salt of Production Example 3 and 30.5 parts of Wako Pure Chemical Industries Tetramethylammonium Tetrafluoroborate were uniformly dissolved in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte concentration) 1.0 mol / L), an electrolyte ratio 8 of the present invention was obtained.

Comparative Example 9
Uniformly dissolve 208.8 parts of TEA · BF ₄ salt of Production Example 2 in dehydrated γ-butyrolactone to prepare a total of 1 liter (electrolyte concentration: 1.0 mol / L). Obtained.

Using the electrolytic solutions 1 to 13 of the present invention and the comparative electrolytic solution ratios 1 to 9, a wound-type electric double layer capacitor (diameter 17 mm, height 40 mm) was produced, and an equivalent series was formed by the following method. The resistance, the rate of change of the equivalent series resistance, and the sealing rubber surface of the sealing body were observed. These results are shown in Table 1.

(1) Equivalent series resistance at 1 kHz equivalent series resistance was measured at −30 ° C. using an impedance analyzer (Solaron SI1253, SI1286).
(2) Rate of change of equivalent series resistance Equivalent series resistance (RE ₃₀₀₀ ) at 1 kHz of the electric double layer capacitor after applying a voltage of 2.8 V to the electric double layer capacitor at 85 ° C. for 3000 hours and 1 kHz before voltage application The ratio with respect to the equivalent series resistance (RE ₀ ) was calculated by the following formula, and this was taken as the rate of change of the equivalent series resistance. The equivalent series resistance was measured at −30 ° C. using an impedance analyzer (Solartron SI1253, SI1286). The withstand voltage is higher as the value of the change rate is smaller. That is, it means that performance deterioration with time is small, and good charge / discharge characteristics can be maintained.
(Equivalent Series Resistance Change Rate) (%) = [(RE ₃₀₀₀ ) / (RE ₀ )] × 100

(3) Sealing rubber surface of the sealing body The state of the sealing rubber surface constituting the sealing body of the electric double layer capacitor after applying a voltage of 2.8 V to the electric double layer capacitor at 85 ° C. for 3000 hours was confirmed.
The number of test of the sealing rubber surface of the sealing body is eight.

(4) Precipitation of electrolytic solution The electrolytic solution was sealed in a glass container and allowed to stand at −30 ° C. for 24 hours, and the presence or absence of precipitation was visually confirmed.

In Table 1, Examples 1 to 7 and Comparative Examples 1 to 3 and 6, Example 8 and Comparative Example 4, Example 9 and Comparative Example 5, and Examples 10 to 11 using the same solvent and the same kind of electrolyte Comparing Comparative Example 7 and Examples 12 to 13 with Comparative Example 8, it was found that the electric double layer capacitor of the example had a lower equivalent series resistance and a smaller change rate of the equivalent series resistance.
In Examples 1 to 13, it was found that the equivalent series resistance was lower than that of Comparative Example 9 using a tetraethylammonium tetrafluoroborate salt, and the change rate of the equivalent series resistance was small.
In Examples 1 to 13, no electrolyte solution was observed, and no abnormality such as liquid leakage due to deterioration of the sealing rubber was observed.

That is, by using the electrolytic solution of the present invention, a highly reliable electric double layer capacitor having a low equivalent series resistance of the electric double layer capacitor, a small change rate of the equivalent series resistance, and excellent sealing performance of the sealing body is constituted. Obviously you can.

The electric double layer capacitor produced using the electrolytic solution of the present invention is a power storage device that replaces secondary batteries such as power storage elements used in combination with memory backup for various electronic devices, various power backup power sources, and solar cells. As such, it can be applied to a power source for a power tool such as a motor driving power source and a power tool, in particular, a long-term durability, reliability, and a low-resistance hybrid vehicle and an electric vehicle power source that require low resistance.

Claims (4)

An electrolytic solution for an electric double layer capacitor in which a quaternary ammonium salt (A) represented by the following general formula (1) is dissolved in an organic solvent (S), and 0 for the quaternary ammonium salt (A) Electrolytic solution for electric double layer capacitor containing tetramethylammonium tetrafluoroborate in the range of 3 to 10% by weight.

_[R 1 to R ₄ is a methyl group or an ethyl group, at least one is different from others. ] The organic solvent (S) is at least one selected from the group consisting of cyclic carbonates, chain carbonates, lactones, chain esters, nitriles, and sulfones. Electrolytic solution for electric double layer capacitors. The electrolysis for electric double layer capacitor according to claim 1 or 2, wherein the organic solvent (S) is at least one selected from the group consisting of propylene carbonate, dimethyl carbonate, ethylene carbonate, sulfolane, acetonitrile, and γ-butyrolactone. liquid. The electric double layer capacitor using the electrolyte solution for electric double layer capacitors of any one of Claims 1-3.