JP2013179204A - Electrolyte for electric double layer capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for electric double layer capacitor exhibiting high heat resistance and durability while having leakage resistance, and not causing solidification over a wide temperature range.SOLUTION: The electrolyte for electric double layer capacitor is produced by dissolving ethyl trimethyl ammonium tetrafluoroborate and/or diethyl dimethyl ammonium tetrafluoroborate into a solvent mixture (S) containing sulfolane (SL) and chain sulfone (S1) of 2-6C. Weight mixture ratio of the sulfolane (SL) and chain sulfone (S1) is preferably 60:40-95:5, and the chain sulfone (S1) is preferably dimethyl sulfone or ethyl methyl sulfone.

Description

The present invention relates to an electrolytic solution for an electric double layer capacitor.

Conventionally, as an electrolytic solution for an electric double layer capacitor, a quaternary ammonium salt typified by tetraethylammonium tetrafluoroborate (hereinafter abbreviated as TEA · BF ₄ ) is dissolved in propylene carbonate (hereinafter abbreviated as PC). Is generally used (Patent Document 1).

However, since such a non-aqueous electrolyte may not have a sufficient withstand voltage, the electrochemical capacitor using this electrolyte may have a significant performance deterioration over time.
In order to solve this problem, it has been proposed to use sulfolane (hereinafter abbreviated as SL) as a solvent (Patent Document 2). Although the withstand voltage is improved by using SL, since the freezing point of SL is 28 ° C., there is a drawback that the electrolyte is solidified in a low temperature region.
Further, it has been proposed to use a mixed solvent in which a carbonate having a low viscosity is mixed with SL. However, since the withstand voltage of carbonate is inferior to that of SL, the withstand voltage and heat resistance of the electrolytic solution are insufficient ( Patent Document 3).

In order to improve the problem of coagulation in the low temperature region, it has been proposed to use a mixed solvent containing SL and chain sulfone with spiro quaternary ammonium salt as an electrolyte. (Patent Document 4).
Furthermore, a capacitor using an electrolytic solution containing a spiro-type quaternary ammonium salt has a drawback that the sealing body is deteriorated by alkali because it does not have the ability to capture strong alkali generated by voltage application.

JP 2000-114105 A JP-A-06-275468 JP 08-306591 A JP2008-171902

The problem to be solved by the present invention is to provide an electrolytic solution for an electric double layer capacitor that exhibits high heat resistance and durability, has liquid leakage resistance, and does not cause solidification in a wide temperature range.

As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. That is, according to the present invention, ethyl trimethylammonium tetrafluoroborate (hereinafter abbreviated as ETMA · BF ₄ ) and / or diethyldimethylammonium tetrafluoroborate (hereinafter abbreviated as DEDMA · BF ₄ ) is synthesized with sulfolane (SL) and carbon number. An electrolytic solution for an electric double layer capacitor, which is dissolved in a mixed solvent (S) containing 2 to 6 chain sulfone (S1).

  The electrolytic solution for electric double layer capacitor of the present invention exhibits high heat resistance and durability, has leakage resistance, and does not solidify in a wide temperature range.

The present invention is an electrolytic solution obtained by dissolving DEDMA · BF ₄ and / or ETMA · BF ₄ in a mixed solvent (S) containing SL and a chain sulfone (S1).

As the type of the chain sulfone (S1), a chain sulfone having 2 to 6 carbon atoms is preferable from the viewpoint of the freezing point, and a chain sulfone having 2 to 3 carbon atoms is more preferable.
Preferred examples of S1 include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-propyl ethyl sulfone, isopropyl ethyl sulfone, di n-propyl sulfone, diisopropyl sulfone, and mixtures thereof. Etc. Among these, dimethyl sulfone (hereinafter referred to as DMS) and ethyl methyl sulfone (hereinafter referred to as EMS) are more preferable.

The weight mixing ratio of sulfolane (SL) and chain sulfone (S1) in the mixed solvent (S) is preferably 60:40 to 95: 5, more preferably 70:30 to 90:10, from the viewpoint of the freezing point. More preferably, it is 80: 20-90: 10.

The mixed solvent (S) may contain a solvent (T) other than (SL) and (S1).
Specific examples of the solvent (T) include the following.
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.
・ Nitro compounds: Nitromethane, nitroethane, etc.
Aromatic compounds: toluene, xylene, chlorobenzene, fluorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene and the like.
Heterocyclic compounds: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.
Ketones: acetone, 2,5-hexanedione, cyclohexanone, etc.
-Phosphate esters: trimethyl phosphoric acid, triethyl phosphoric acid, tripropyl phosphoric acid and the like.

The content of the solvent (T) is preferably 50% or less, more preferably 20% or less, based on the total weight of the solvent.

The concentration of DEDMA · BF ₄ or ETMA · BF ₄ contained in the electrolytic solution is 0.5 to 2.5 mol / L, preferably 0.8 mol / L to 2.0 mol / L. The concentration of the mixture of DEDMA · BF ₄ and ETMA · BF ₄ is similar.
If it is 0.5 mol / L or more, the conductivity is sufficient, and if it is 2.5 mol / L or less, the low-temperature characteristics do not deteriorate.

Examples of combinations of DEDMA • BF ₄ or ETMA • BF ₄ and mixed solvent (S) include DEDMA • BF ₄ / SL / EMS, DEDMA • BF ₄ / SL / DMS, DEDMA • BF ₄ / SL / EMS / DMS , ETMA / BF ₄ / SL / EMS, ETMA / BF ₄ / SL / DMS, ETMA / BF ₄ / SL / EMS / DMS, DEDMA / BF ₄ / ETMA / BF ₄ / SL / EMS, DEDMA / BF ₄ / ETMA · _BF 4 _/ SL _/ DMS, such as _{DEDMA · BF 4 / ETMA · BF} 4 / SL / EMS / DMS , and the like.
Among them, an electrolytic solution in which DEDMA · BF ₄ is dissolved in a mixed solvent in which the weight mixing ratio of SL and DMS or EMS is 80:20 to 90:10 is particularly preferable.

The water content (ppm) of the non-aqueous solvent in the electrolytic solution is preferably 300 or less, more preferably 100 or less, particularly preferably 50 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 electric double layer 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 of using a sufficiently dried electrolyte salt (A) and a non-aqueous solvent sufficiently dehydrated in advance.
Examples of the drying method include a method of heating and drying under reduced pressure (for example, heating at 150 ° C. under a reduced pressure of 2.7 kPa) to evaporate and remove a trace amount of water contained therein.
As a dehydration method, heat dehydration under reduced pressure (for example, heating at 13.5 kPa) to evaporate and remove a trace amount of water contained therein, a method using a dehydrating agent such as molecular sieve or activated alumina powder Etc. Of these, the method of drying (A) by heating under reduced pressure and the method of adding molecular sieve to the electrolyte are preferred.

  The electrolytic solution of the present invention can be used for an electric double layer capacitor. The electric double layer capacitor includes an electrode, a current collector, and a separator as basic components, and optionally includes a case that is usually used for a capacitor, a sealing body that seals an opening of the case, a gasket, and the like.

  As sealing bodies for electric double layer capacitors, butyl rubber containing isoprene and isobutylene is generally used. Among them, butyl rubber to which alkylphenol formalin resin is added as a vulcanizing agent and peroxide as a vulcanizing agent are used. Added butyl rubber is preferred.

The electrolytic solution for electric double layer capacitor of the present invention can be applied to coin type, wound type and square type, and is particularly suitable for small surface mount type electric double layer capacitor for backup use such as cellular phone. Yes.
The electrolytic solution for an electric double layer capacitor of the present invention can also be applied to a surface mount type electric double layer capacitor having a peak temperature of 260 ° C. in the reflow soldering process.

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.

<Production Example 1><< Production of DEDMA · BF ₄ >>
Synthesis of iodide salt 131 parts of diethyl methylamine (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 344 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 945 parts of AgBF ₄ methanol solution was slowly added dropwise to the above mixed solution of 344 parts of diethyldimethylammonium iodide and 294 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 289 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 255 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 2><< Manufacture of ETMA · BF ₄ >>
Synthesis of iodide salt 110 parts of 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%.

<Comparative Production Example 3><Production of Spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate (hereinafter abbreviated as SBP · BF ₄ ) >>
100 parts of pyrrolidine and 97 parts of potassium carbonate were charged into an autoclave coated with Teflon (registered trademark), 198 parts of 1,5-dichloropentane was added, and the reaction was performed at 90 ° C. for 8 hours. To this reaction solution, 294 parts of a 42% by weight aqueous borohydrofluoric acid solution was added dropwise at 25 ° C. over about 30 minutes. After the completion of the dropping and the generation of bubbles was stopped, the entire solvent was distilled off at 20 Torr and 100 ° C. to obtain 200 parts of a solid. This solid was crystallized twice using ethanol and 2-propanol to obtain 155 parts of white crystals. As a result of analysis by ¹ H-NMR, ¹⁹ F-NMR and ¹³ C-NMR, the white crystals were SBP · BF ₄ .

<Comparative Production Example 4><< Production of 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate (EDMI · BF ₄ ) >>
A reaction flask equipped with a stirrer, thermometer, dropping funnel, reflux condenser, and nitrogen gas introducing agent was charged with a mixture of 31 parts ethylamine (70% aqueous solution) and 32 parts ammonia (28% aqueous solution) while stirring. Dissolved uniformly. While maintaining the temperature at 45 ° C. or lower, a mixed solution of 69 parts of glyoxal (40% aqueous solution) and 71 parts of acetaldehyde (30% aqueous solution) was dropped from the dropping funnel. Whether or not the mixture of glioxal and acetaldehyde was an enemy was carried out over 5 hours, and the reaction was carried out at 40 ° C. for 1 hour after completion of the dropwise addition. Next, dehydration was performed by gradually reducing the pressure from normal pressure to 5.0 kPa at a temperature of 80 ° C., followed by rough purification by simple distillation under the conditions of a temperature of 105 ° C. and a pressure of 1.0 kPa. Got. In a stainless steel autoclave with a reflux condenser, 100 parts of 1-ethyl-2-methylimidazole, 135 parts of dimethyl carbonate and 192 parts of methanol were charged and uniformly dissolved. Next, the temperature was raised to 130 ° C. The reaction was performed at a pressure of 0.8 kPa for 80 hours. 1H-NMR analysis of the reaction product revealed that 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate was produced. 427 parts of the resulting reaction mixture was placed in a flask, and 207 parts of a borohydrofluoric acid aqueous solution (purity 42% by weight) was gradually added dropwise over about 30 minutes at room temperature with stirring. Carbon dioxide gas was generated during the dropping. After generation | occurrence | production of foam | bubble settled, the reaction liquid was moved to the rotary evaporator and the whole quantity of solvent was removed. In the flask, 82 parts of a tan transparent liquid remained. The obtained yellowish brown transparent liquid was crystallized using methanol and isopropanol to obtain a white solid. When this solid was analyzed by 1H-NMR, it was 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate. ^From the integral value of ¹ H-NMR, the purity was 99 mol%.

<< Comparative Production Example 5 >><< Production of Tetraethylammonium Tetrafluoroborate (TEA · BF ₄ ) >>
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 tetraethylammonium iodide salt and 232 parts of methanol, followed by filtration, and the filtrate was collected. 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, this white crystal was TEA · BF ₄ . ^From the integral value of ¹ H-NMR, the purity was 99%.

<Comparative Production Example 6><< Manufacture of triethylmethylammonium tetrafluoroborate (TEMA.BF ₄ ) >>
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 364 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 borofluoric acid solution was dehydrated at 100 ° C. under reduced pressure to add 825 parts of methanol to dissolve, and dissolve AgBF ₄ methanol. A solution was obtained.

-Preparation of BF ₄ salt 1129 parts of the above AgBF ₄ solution was slowly added dropwise to a mixed solution of 364 parts of triethylmethylammonium iodide salt and 351 parts of methanol, followed by filtration, and the filtrate was collected. 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 295 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 152 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 . ^From the integral value of ¹ H-NMR, the purity was 99%.

Example 1 Preparation of Electrolyte Solution (A-1) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were dehydrated and 54.4 parts SL Sumitomo Seika Co., Ltd. and EMS 23. Sumitomo Seika Co., Ltd. It melt | dissolved uniformly in the mixture which consists of 3 parts, and obtained the electrolyte solution A-1 of this invention.

Example 2 Preparation of Electrolyte (A-2) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were dehydrated, 54.4 parts of SL manufactured by Sumitomo Seika Co., Ltd., and EMS 15. of EMS manufactured by Sumitomo Seika Co., Ltd. It was uniformly dissolved in a mixture consisting of 5 parts and 7.8 parts of DMS manufactured by Sumitomo Seika Co., Ltd. to obtain an electrolytic solution A-2 of the present invention.

Example 3 Preparation of Electrolyte Solution (A-3) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were dehydrated and 66.0 parts of SL manufactured by Sumitomo Seika Co., Ltd. and DMS 11 of Sumitomo Seika Co., Ltd. produced. It melt | dissolved uniformly in the mixture which consists of 7 parts, and obtained the electrolyte solution A-3 of this invention.

Example 4 Preparation of Electrolyte Solution (A-4) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were dehydrated and 69.9 parts of SLMS manufactured by Sumitomo Seika Co., Ltd. and DMS7. It melt | dissolved uniformly in the mixture which consists of 8 parts, and obtained the electrolyte solution A-4 of this invention.

Example 5 Preparation of Electrolyte Solution (A-5) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were dehydrated and 73.8 parts of SL made by Sumitomo Seika Co., Ltd. and DMS 3. produced by Sumitomo Seika Co., Ltd. It melt | dissolved uniformly in the mixture which consists of 88 parts, and obtained the electrolyte solution A-5 of this invention.

Example 6 Preparation of Electrolytic Solution (A-6) 20.7 parts of ETMA · BF ₄ salt of Production Example 2 were dehydrated and 55.5 parts of SL Sumitomo Seika Co., Ltd. and EMS 23. Sumitomo Seika Co., Ltd. It uniformly melt | dissolved in the mixture which consists of 8 parts, and obtained the electrolyte solution A-6 of this invention.

Example 7 Preparation of Electrolyte Solution (A-7) 20.7 parts of ETMA · BF ₄ salt of Production Example 2 were dehydrated and 63.5 parts of SL made by Sumitomo Seika Co., Ltd. and EMS15. It uniformly melt | dissolved in the mixture which consists of 9 parts, and obtained the electrolyte solution A-7 of this invention.

Example 8 Preparation of Electrolyte Solution (A-8) 120.7 parts of ETMA · BF ₄ salt of Production Example 2 were dehydrated and SL71.4 parts made by Sumitomo Seika Co., Ltd. and DMS7 made by Sumitomo Seika Co., Ltd. were used. It uniformly melt | dissolved in the mixture which consists of 9 parts, and obtained the electrolyte solution A-8 of this invention.

Comparative Example 1 Preparation of Comparative Electrolyte (B-1) 22.3 parts of DEDMA · BF ₄ salt of Production Example 1 were uniformly dissolved in 77.7 parts of SL made by Sumitomo Seika Co., Ltd., and Comparative Electrolyte B -1 was obtained.

Comparative Example 2 Preparation of Comparative Electrolytic Solution (B-2) 20.7 parts of ETMA · BF ₄ salt from Production Example 2 were uniformly dissolved in 79.3 parts of Sumitomo Seika Co., Ltd. SL and Comparative Electrolytic Solution B -2 was obtained.

Comparative Example 3 Preparation of Comparative Electrolyte (B-3) Sumitomo Seika Co., Ltd. SL63.7 parts and Sumitomo Seika Co., Ltd. DMS11 which dehydrated 25.0 parts of EDMI · BF ₄ salt of Comparative Production Example 4 .. 3 parts uniformly dissolved to obtain a comparative electrolytic solution B-3.

Comparative Example 4 Preparation of Comparative Electrolyte (B-4) Sumitomo Seika Co., Ltd. SL63.2 parts obtained by dehydrating 25.6 parts of TEA · BF ₄ salt of Comparative Production Example 5 and Sumitomo Seika Co., Ltd. DMS11 Dissolve uniformly in 2 parts to obtain a comparative electrolytic solution B-4.

Comparative Example 5 Preparation of Comparative Electrolytic Solution (B-5) Sumitomo Seika Co., Ltd. SL64.6 parts dehydrated TEMA · BF ₄ salt 24.0 parts of Comparative Production Example 6 and Sumitomo Seika Co., Ltd. DMS11 .4 parts was uniformly dissolved to obtain a comparative electrolytic solution B-5.

Comparative Example 6 Preparation of Comparative Electrolyte (B-6) Sumitomo Seika Co., Ltd. SL61.3 parts and Sumitomo Seika Co., Ltd. DMS15 dehydrated 23.4 parts of SBP · BF ₄ salt of Comparative Production Example 3 Dissolve uniformly in 3 parts to obtain an electrolytic solution B-6 of the present invention.

Comparative Example 7 Preparation of Comparative Electrolyte (B-7) Sumitomo Seika Co., Ltd. SL61.3 parts and Sumitomo Seika Co., Ltd. EMS15 which dehydrated 23.4 parts of SBP · BF ₄ salt of Comparative Production Example 3 Dissolve uniformly in 3 parts to obtain an electrolytic solution B-7 of the present invention.

Comparative Example 8 Preparation of Comparative Electrolyte (B-8) Sumitomo Seika Co., Ltd. SL65.1 parts and Sumitomo Seika Co., Ltd. DMS11 from which 23.4 parts of SBP · BF ₄ salt of Comparative Production Example 3 were dehydrated Dissolve uniformly in 5 parts to obtain an electrolytic solution B-8 of the present invention.

The compositions of the electrolytic solutions (A-1) to (A-8) of the present invention and comparative electrolytic solutions (B-1) to (B-8) are shown in Table 1. Further, the freezing point of the electrolytic solution was measured by the following method, and the results are shown in Table 1.

Using the same electrolyte, a wound type electric double layer capacitor (diameter 17 mm, height 40 mm) and a surface mount type electric double layer capacitor (diameter 3.8 mm, height 1.5 mm) were prepared. The equivalent series resistance and the rate of change of the equivalent series resistance were measured by the following method.
In addition, the sealing rubber of the electric double layer capacitor created above was used as two kinds of butyl rubber using alkylphenol formalin resin and peroxide as vulcanizing agents, and the sealing rubber surface of the sealing body was observed for each. . These results are shown in Tables 2 and 3.

Equivalent series resistance change rate Equivalent series resistance (RE ₃₀₀₀ ) at 1 kHz of the electric double layer capacitor after applying a voltage of 2.8 V at 85 ° C. for 3000 hours to the electric double layer capacitor and equivalent at 1 kHz before applying the voltage The ratio with the series resistance (RE ₀ ) was calculated by the following formula, and this was used as the rate of change of the equivalent series resistance. The equivalent series resistance was measured at 0 ° C. using an impedance analyzer (Solaron SI1253, SI1286). The smaller the value of the rate of change, the better the heat resistance and the higher the withstand voltage. 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
Also, the smaller the equivalent series resistance, the better the capacitor characteristics.

-State of the sealing rubber surface of the sealing body The liquid leakage 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 1000 hours was observed.
The number of test of the sealing rubber surface of the sealing body is eight.

-The freezing point electrolyte was placed in a temperature-controllable glass container, the temperature was lowered from room temperature at a rate of 1 ° C / min, and the temperature at which precipitation occurred was defined as the freezing point.

From the measurement results of Tables 1 and 2, the electrolytic solution for electric double layer capacitors of the present invention exhibits high heat resistance and durability because of the small change rate of the equivalent series resistance, and the appearance of the sealing rubber surface is abnormal. From this, it was found that it has liquid leakage resistance and has a low freezing point, so that solidification does not occur in a wide temperature range.
On the other hand, the change rate of the equivalent series resistance of the electric double layer capacitors of Comparative Examples 9 to 11 and 17 to 19 using the electrolytic solutions of Comparative Examples 1 to 3 is large, and the heat resistance and durability are low. Moreover, the electric double layer capacitors of Comparative Examples 12 to 16 and 20 to 24 using the electrolytic solutions of Comparative Examples 4 to 8 have liquid leakage and have no leakage resistance.
That is, by using the electrolytic solution of the present invention, it is clear that a highly reliable electric double layer capacitor having high durability, excellent sealing performance of the sealing body, and not solidifying in a wide temperature range can be configured.

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, particularly a hybrid vehicle and a power source for an electric vehicle that require long-term durability and reliability.

Claims (3)

Ethyltrimethylammonium tetrafluoroborate and / or diethyldimethylammonium tetrafluoroborate is dissolved in a mixed solvent (S) containing sulfolane (SL) and a chain sulfone (S1) having 2 to 6 carbon atoms. An electrolytic solution for electric double layer capacitors. 2. The electrolytic solution according to claim 1, wherein a weight mixing ratio of the sulfolane (SL) and the chain sulfone (S1) is 60:40 to 95: 5. The electrolytic solution according to claim 1 or 2, wherein the chain sulfone (S1) is dimethyl sulfone and / or ethyl methyl sulfone.