JP2007281382A - Nonaqueous electrolyte for electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte by which internal resistance is effectively decreased without hardly causing capacity decrease of an electric double layer capacitor. <P>SOLUTION: In the nonaqueous electrolyte for electric double layer capacitor, an electrolytic solution containing a nonaqueous solvent and an electrolyte comprises an ammonium salt represented by a general formula (1) by 1 ppm-1 wt.% in proportion by weight as an additive agent. In the formula, R<SP>1</SP>is an alkyl group having carbon number 1-6, R<SP>2</SP>is an alkyl group having carbon number 1-6 or a hydrogen atom, and Y<SP>-</SP>is inorganic anion. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte for an electric double layer capacitor that reduces internal resistance. More specifically, the present invention relates to a non-aqueous electrolyte for an electric double layer capacitor that reduces internal resistance by adding a specific amount of an alkyl ammonium salt having a specific structure to a non-aqueous electrolyte composed of a non-aqueous solvent and an electrolyte.

  Conventionally, electric double layer capacitors have been mainly used as a backup power source for small electronic devices. However, in recent years, with the increase in capacity of electric double layer capacitors, application to electric vehicles, hybrid vehicles, large capacity power storage systems, etc. Is expected. These applications involve high-speed charging / discharging, and low internal resistance electric double layer capacitors are required. In addition, since electric double layer capacitors for electric vehicles and hybrid vehicles must be able to withstand the temperature rise due to heat radiation in cold regions and internal combustion engines, low internal resistance is maintained in a wide temperature range of about -20 to 70 ° C. I have to hit it.

  An electric double layer capacitor is an electricity storage device using electric energy stored in an electric double layer formed at the interface between a polarizable electrode and an electrolyte. In general, such an electric double layer capacitor is configured such that an activated carbon electrode having a high surface area impregnated with an electrolytic solution is opposed to each other with a porous separator for preventing a short circuit interposed therebetween. There are non-aqueous electrolytes and aqueous electrolytes, and the aqueous system has low withstand voltage due to water electrolysis. Since the energy stored in the capacitor is proportional to the square of the charging voltage, the non-aqueous electrolyte has a feature that the energy density can be increased as compared with the aqueous system.

  An electric double layer capacitor using a tetraalkylammonium salt as an electrolyte is conventionally known, and a nonaqueous electrolytic solution in which a tetraalkylammonium salt is dissolved in a nonaqueous solvent such as propylene carbonate has been put into practical use (for example, Patent Documents). 1 and non-patent document 1). Among the tetraalkylammonium salts, asymmetrical ammonium salts (for example, triethylmethylammonium) are particularly more advantageous in electric double layer capacitors than symmetrical ammonium salts such as tetraethylammonium in terms of internal resistance, capacitance, and long-term reliability. It has been reported that it is excellent (see, for example, Patent Document 2).

  In recent years, performance required for electric double layer capacitors, such as higher energy density and higher output density, has been increasing. In order to increase the energy density, a method of increasing the charging voltage or using an electrode having a large capacitance is used (for example, see Patent Document 5). However, when the charging voltage is increased or an electrode having a large electrostatic capacity is used, the internal resistance of the electric double layer capacitor generally increases and a large output density cannot be obtained. Under such circumstances, a technique for reducing the internal resistance of the electric double layer capacitor is strongly demanded.

As a method for reducing the internal resistance of an electric double layer capacitor, a method using an electrolytic solution having a high electrical conductivity is known (see, for example, Patent Document 6). This is a method using a low-viscosity solvent, and the low-viscosity solvent generally has a low boiling point and a low flash point, and a decrease in the boiling point of the electrolyte causes an increase in the amount of gas generated and causes the electric double layer capacitor cell to expand. May end up. In addition, there is a problem in terms of safety due to a decrease in the flash point of the electrolyte. Moreover, although the method of adding an additive to electrolyte solution and reducing internal resistance is also known (for example, refer patent document 7), the raw material of an additive is expensive, or a synthesis | combination is complicated in many cases.
JP-A 49-68254 Japanese Patent Publication No. 3-58526 Japanese Examined Patent Publication No. 7-116113 JP 2000-311839 A Japanese Patent Laid-Open No. 2002-93667 JP-A-7-74059 JP 2001-217157 A Ue, Electrochemistry, 66, 1988, 904

  An object of the present invention is to provide a non-aqueous electrolyte that reduces the internal resistance of an electric double layer capacitor.

（式中、Ｒ^１は炭素数１〜６のアルキル基であり，Ｒ^２は炭素数１〜６のアルキル基または水素原子を表す。Ｙ^―は無機のアニオンを表す。）
２. 前記一般式（１）で示されるアンモニウム塩を５ｐｐｍ〜２０００ｐｐｍの重量割合で含有する第１項記載の電気二重層キャパシタ用非水電解液。
３. 前記電解質のアニオン種と前記一般式（１）で示されるアンモニウム塩のアニオン種が同一である第１項または第２項記載の電気二重層キャパシタ用非水電解液。
４. 前記一般式（１）で示されるアンモニウム塩がモノアルキルアンモニウム・テトラフルオロボレートまたはジアルキルアンモニウム・テトラフルオロボレートである第１項〜第３項のいずれかに記載の電気二重層キャパシタ用非水電解液。
５. 前記一般式（１）で示されるアンモニウム塩がモノエチルアンモニウム・テトラフルオロボレートである第１項〜第４項のいずれかに記載の電気二重層キャパシタ用非水電解液。
６. 前記一般式（１）で示されるアンモニウム塩がジエチルアンモニウム・テトラフルオロボレートである第１項〜第４項のいずれかに記載の電気二重層キャパシタ用非水電解液。
７. 前記電解質がテトラアルキルアンモニウム・テトラフルオロボレートである第１項〜第６項のいずれかに記載の電気二重層キャパシタ用非水電解液。
８. 前記電解質がジエチルジメチルアンモニウム・テトラフルオロボレートである第１項〜第７項のいずれかに記載の電気二重層キャパシタ用非水電解液。
９. 第１項〜第８項のいずれかに記載の非水電解液を用いる電気二重層キャパシタ。 As a result of intensive studies on the non-aqueous electrolyte for electric double layer capacitors having the above-mentioned problems, the present inventors have found that a non-aqueous electrolyte containing a trace amount of a primary or secondary ammonium salt at a specific ratio is obtained. The present inventors have found that the internal resistance can be effectively reduced with almost no decrease in capacity. That is, the present invention is as follows.
1. An electrolytic solution composed of a nonaqueous solvent and an electrolyte contains an ammonium salt represented by the general formula (1) as an additive in a weight ratio of 1 ppm to 1 wt%. liquid.

(In the formula, R ¹ represents an alkyl group having 1 to 6 carbon atoms, R ² represents an alkyl group having 1 to 6 carbon atoms or a hydrogen atom. Y ⁻ represents an inorganic anion.)
2. The nonaqueous electrolytic solution for an electric double layer capacitor according to the first item, wherein the ammonium salt represented by the general formula (1) is contained at a weight ratio of 5 ppm to 2000 ppm.
3. The non-aqueous electrolyte for an electric double layer capacitor according to item 1 or 2, wherein the anion species of the electrolyte and the anion species of the ammonium salt represented by the general formula (1) are the same.
4. The non-water for an electric double layer capacitor according to any one of Items 1 to 3, wherein the ammonium salt represented by the general formula (1) is a monoalkylammonium tetrafluoroborate or a dialkylammonium tetrafluoroborate. Electrolytic solution.
5. The nonaqueous electrolytic solution for an electric double layer capacitor according to any one of Items 1 to 4, wherein the ammonium salt represented by the general formula (1) is monoethylammonium tetrafluoroborate.
6. The nonaqueous electrolytic solution for an electric double layer capacitor according to any one of Items 1 to 4, wherein the ammonium salt represented by the general formula (1) is diethylammonium tetrafluoroborate.
7. The nonaqueous electrolytic solution for an electric double layer capacitor according to any one of Items 1 to 6, wherein the electrolyte is tetraalkylammonium tetrafluoroborate.
8. The nonaqueous electrolytic solution for an electric double layer capacitor according to any one of Items 1 to 7, wherein the electrolyte is diethyldimethylammonium tetrafluoroborate.
9. An electric double layer capacitor using the non-aqueous electrolyte according to any one of Items 1 to 8.

  By adding a specific amount of an ammonium salt having a specific structure to the non-aqueous electrolyte, an electric double layer capacitor having a low internal resistance can be advantageously realized. Moreover, the fall of an electrostatic capacitance retention rate can be suppressed. Furthermore, the ammonium salt having a specific structure used as an additive in the present invention is inexpensive and can be easily synthesized.

  Hereinafter, embodiments of the present invention will be described in detail. The nonaqueous electrolytic solution of the present invention is usually produced by adding an ammonium salt represented by the general formula (1) in a specific weight ratio to a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent. Can do.

  The non-aqueous solvent used in the present invention is not particularly limited, but for example, cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and 1,3-dioxolan-2-one, chains such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Cyclic carbonates such as cyclic carbonate, γ-butyrolactone, γ-valerolactone, methyl acetate and methyl propionate, cyclic and chain ethers such as 2-methyltetrahydrofuran and 1,2-dimethoxyethane, acetonitrile, 3 Nitriles such as methoxypropionitrile, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, sulfur-containing compounds such as sulfolane, 3-methylsulfolane, dimethyl sulfoxide, ethylene sulfide Nitro compounds such as nitromethane and nitroethane, cyclic urethanes such as 3-methyl-2-oxazolidinone, and phosphorus-containing compounds such as trimethyl phosphate, preferably propylene carbonate, ethylene carbonate, γ-butyrolactone, acetonitrile and sulfolane. Yes, more preferably propylene carbonate. These nonaqueous solvents may be used alone or as a mixed solvent of two or more. Moreover, it can also be used by mixing with other additives, such as a dehydrating agent, a halogen removal agent, and a flame retardant.

  The electrolyte used for the non-aqueous electrolyte is not particularly limited, but examples of the cation include tetraethylammonium, triethylmethylammonium, diethyldimethylammonium, ethyltrimethylammonium, tetramethylammonium, and tetra-n-butylammonium. Tetraalkylammonium ion and tetraalkylphosphonium ion in which the nitrogen atom is replaced with a phosphorus atom, N, N-dimethylpiperidinium, N, N-ethylmethylpiperidinium, N, N-diethylpiperidinium, N, N- Dimethylpyrrolidinium, N, N-ethylmethylpyrrolidinium, N, N-diethylpyrrolidinium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-ethyl-2, 3- Dimethylimida Linium, 1,3-dimethyl-1,4,5,6-tetrahydropyrimidinium, 1,2,3-trimethyl-1,4,5,6-tetrahydropyrimidinium, 1-methyl-1,8- Quaternary amidinium ions such as diazabicyclo [5.4.0] undecene-7,1-methyl-1,5-diazabicyclo [4.3.0] nonene-5, and ions of compounds in which the nitrogen atom is replaced with a phosphorus atom , Trialkylsulfonium ions such as trimethylsulfonium and triethylsulfonium, alkali metal ions such as lithium, sodium and potassium, alkaline earth metal ions such as calcium and magnesium, and trivalent metal ions such as aluminum are particularly preferable. Is tetraalkylammonium. In the tetraalkylammonium, the alkyl group has 1 to 6 carbon atoms.

Examples of the anion of the electrolyte used for the non-aqueous electrolyte include fluoride ion (F ⁻ ), chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), iodide ion (I ⁻ ), perchlorate ion ( ClO ₄ ⁻ ), phosphate ion (PO ₄ ³⁻ ), cyanide ion (CN ⁻ ), thiocyanate ion (SCN ⁻ ), sulfide ion (S ₂ ⁻ ), nitrate ion (NO ₃ ⁻ ), nitrous acid Ions (NO ₂ ⁻ ), carbonate ions (CO ₃ ²⁻ ), borofluoride ions (BF ₄ ⁻ ), phosphor fluoride ions (PF ₆ ⁻ ), silicofluoride ions (SiF ₆ ⁻ ), trifluoromethanesulfonate ions (CF ₃ SO ₃ ⁻ ), bistrifluoromethanesulfonylimide ion ((CF ₃ SO ₂ ) N ⁻ ), toluenesulfonate ion (CH ₃ C ₆ H ₄₎ SO ₃ ⁻ ), fluorinated antimonate ion (SbF ₆ ⁻ ), fluorinated arsenate ion (AsF ₆ ⁻ ), fluorinated titanate ion (TiF ₆ ²⁻ ), etc., among which borofluoride ion (BF ₄ ⁻ ), Phosphor fluoride ion (PF ₆ ⁻ ), and bistrifluoromethanesulfonylimide ion ((CF ₃ SO ₂ ) N ⁻ ) are preferable, and borofluoride ion (BF ₄ ⁻ ) is particularly preferable.

  Particularly preferred as the electrolyte is tetraalkylammonium tetrafluoroborate. These electrolytes can be used alone or as a mixture of two or more.

  The concentration of the electrolyte in the nonaqueous electrolytic solution varies depending on the electrolyte used and the type of the nonaqueous solvent, but is preferably in the range of 0.1 to 5 mol / L, more preferably 0.5 to 3.5 mol / L. It is a range, Especially preferably, it is the range of 1-3 mol / L.

  Further, the electrolytic solution used in the present invention can also be used for a polymer gel electrolyte obtained by adding an electrolytic solution to a polymer such as polyacrylonitrile, polyethylene oxide, polyvinylidene fluoride, etc., and gelling.

In the ammonium salt represented by the general formula (1) used as an additive, R ¹ and R ² represent the same or different alkyl group having 1 to 6 carbon atoms or a hydrogen atom. However, at least one of R ¹ and R ² is an alkyl group. Y ^- is representative of an inorganic anion. Specific examples of the ammonium salt represented by the general formula (1) include alkyl ammonium, fluoride ion (F ⁻ ), chloride ion (Cl ⁻ ), bromide ion (Br ⁻ ), iodide ion (I ⁻ ), Perchlorate ion (ClO ₄ ⁻ ), phosphate ion (PO ₄ ³⁻ ), cyanide ion (CN ⁻ ), thiocyanate ion (SCN ⁻ ), sulfide ion (S ₂ ⁻ ), nitrate ion ( NO ₃ ⁻ ), nitrite ions (NO ₂ ⁻ ), carbonate ions (CO ₃ ²⁻ ), borofluoride ions (BF ₄ ⁻ ), phosphor fluoride ions (PF ₆ ⁻ ), silicofluoride ions (SiF ₆ ⁻ ), trifluoromethanesulfonate ion _(CF 3 SO ₃ ^-), bistrifluoromethanesulfonylimide ion _{((CF 3 SO 2) N} -), toluenesulfonyl Acid ion _{(CH 3 C 6 H 4 SO} 3 -), antimony fluoride ion (SbF ₆ ^-), fluoride arsenate ion (AsF ₆ ^-), a combination of a fluoride titanate ions _(TiF ^{6 2-)} Among them, it is particularly preferable to use an ammonium salt having the same anion species as the anion species of the electrolyte used as the nonaqueous electrolytic solution. These ammonium salts as additives can be used alone or in admixture of two or more.

  The ammonium salt represented by the general formula (1) can be easily synthesized. For example, in the case of diethylammonium tetrafluoroborate, an equimolar amount of diethylamine is added dropwise to a tetrafluoroboric acid aqueous solution at room temperature and then stirred for 2 hours, and unreacted components and moisture at 70 ° C. and 100 mmHg. Is distilled off, thoroughly washed with ethanol, and dried at 100 ° C. for 2 hours.

  The ammonium salt represented by the general formula (1) is usually added to the non-aqueous electrolyte, but a by-product generated during the synthesis of the electrolyte used in the non-aqueous electrolyte may be used as it is. For example, diethyldimethylammonium methyl carbonate is synthesized by quaternization reaction of diethylamine and dimethyl carbonate, and then diethyldimethyltetrafluoroborate is synthesized by anion exchange using an aqueous tetrafluoroboric acid solution. When an unreacted diethylamine is present in the anion exchange step, diethylammonium tetrafluoroborate is produced by reaction with tetrafluoroboric acid, and this is converted to an ammonium salt represented by the general formula (1). Can be used as

  The addition amount of the ammonium salt represented by the general formula (1) varies depending on the type of the ammonium salt, the solvent used in the non-aqueous electrolyte, the type of the electrolyte, the type of the electrode used, and the like. Is in the range of 1 ppm to 1 wt% with respect to the weight of the electrolyte. Preferably it is the range of 2 ppm-5000 ppm, More preferably, it is the range of 5 ppm-2000 ppm. Within the above range, there is an effect of reducing internal resistance, and the charge / discharge characteristics at high temperature are not deteriorated.

  In addition, when this ammonium salt does not melt | dissolve in electrolyte solution, it can also be introduce | transduced in an electric double layer capacitor cell only in a dissolved part or a dispersed state.

  The electric double layer capacitor in the present invention is composed of a positive electrode, a negative electrode and a non-aqueous electrolyte. The main component of the polarizable electrode used as the positive electrode and the negative electrode is preferably carbon, and carbon materials such as activated carbon, carbon nanotubes, and fullerenes can be used as the active material. In particular, activated carbon having a large specific surface area is preferable.

The specific surface area of the activated carbon cannot be generally specified depending on the type of activated carbon raw material used, the bulk density, etc., but the specific surface area determined by the BET method by the nitrogen adsorption method is preferably 100 to 2500 m ² / g. 500-2000 m ² / g activated carbon is preferred.

  The raw material and manufacturing method of activated carbon used in the present invention are not particularly limited. The activated carbon used in the present invention includes plant wood, coconut shell, fossil fuel coal, heavy petroleum oil, coal-based pitch and petroleum-based pitch obtained by pyrolyzing them, condensed polycyclic hydrocarbon, etc. in the presence of a catalyst. After carbonizing raw materials such as synthetic pitch, petroleum coke, carbon aerogel, pitch-spun fiber, phenol resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin obtained by polymerization in Activated and manufactured.

  Activation is a gas activation method in which a carbonized raw material is contacted with an oxidizing gas such as water vapor, carbon dioxide, oxygen, etc. at a high temperature, and the carbonized raw material is zinc chloride, calcium chloride, potassium sulfide, potassium hydroxide, Any chemical activation method in which activated carbon is obtained by impregnating sodium hydroxide, potassium carbonate, sodium carbonate or the like and heating in an inert gas atmosphere can be used. Further, if necessary, the activated carbon obtained by the activation treatment can be used after being heat-treated in an inert gas atmosphere such as nitrogen, argon, helium or xenon.

  A polarizable electrode is generally composed of activated carbon and a conductive aid such as acetylene black and a binder such as polytetrafluoroethylene, and these are kneaded, rolled, roll pressed into a sheet, or a collector such as aluminum. It is coated and manufactured. The mixing ratio of the activated carbon, the conductive assistant and the binder is preferably about 8 to 1 to 1 by weight.

  In addition, this invention can be used for any electric double layer capacitor such as a coin type, a wound type, a square type and the like.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.
The electrolyte and additive were both dehydrated in advance, and the electrodes, cells, etc. were sufficiently dried by vacuum drying and assembled in a glove box in a dry atmosphere. The internal resistance was determined from the voltage drop immediately after the start of discharge.

Example 1
(A) Preparation of electrolyte solution Electrolyte triethylmethylammonium tetrafluoroborate (TEMAB) was dissolved in propylene carbonate (PC) so that the electrolyte concentration was 1.8 mol / L, and 1.8 mol / L-TEMAB / PC was dissolved. Obtained. To 15.8 g of 42% -tetrafluoroboric acid aqueous solution, 5.3 g of ethylamine was slowly added dropwise with stirring under ice cooling. After stirring for 1 hour, unreacted raw materials and water were distilled off under reduced pressure to obtain 11.4 g of crude crystals. Finally, recrystallization was performed 3 times with 100 g of ethanol, and after drying at 80 ° C. overnight, 8.3 g of the additive ethylammonium tetrafluoroborate (C ₂ H ₅ ) NH ₃ .BF ₄ (ETHAB) was obtained. The ETHAB obtained as described above was dissolved in 1.8 mol / L-TEMAB / PC to prepare an electrolytic solution having an additive ETHAB concentration of 1000 ppm.
(B) Production of electric double layer capacitor cell After kneading a mixture of activated carbon powder (specific surface area 850 m ² / g measured by BET method by nitrogen adsorption method) 80%, acetylene black 10%, polytetrafluoroethylene 10% The pressure sheet was formed. The obtained sheet was punched into a disk shape to obtain an activated carbon electrode (diameter 16 mm, thickness 0.4 mm). The two electrodes were opposed to each other through a cellulose separator and housed in a stainless steel case. Thereafter, 1.0 g of the electrolytic solution obtained in the above (a) was impregnated and contained under reduced pressure to produce an electric double layer capacitor cell.
(C) Evaluation of internal resistance The electric double layer capacitor cell obtained in (b) above was charged to 2.7 V with a constant current of 5 mA at 25 ° C., then held for 60 minutes, and discharged to 0 V with a constant current of 5 mA. The internal resistance (unit Ω) was calculated. Thereafter, the battery was charged to 2.7 V with a constant current of 5 mA at 70 ° C., held for 5 hours, and then discharged to 0 V with a constant current of 5 mA, and the internal resistance was calculated. The measurement results are shown in Table 1.
(D) Evaluation of capacitance retention rate The electric double layer capacitor cell obtained in (b) above was charged to 2.7 V at a constant current of 5 mA at 25 ° C., then held for 60 minutes, and at a constant current of 5 mA. The cycle of discharging to 0 V was repeated 10 times, and the initial capacitance was determined from the discharge energy at the 10th cycle. Next, after charging to 2.7 V with a constant current of 5 mA at 70 ° C., holding for 5 hours and discharging to 0 V with a constant current of 5 mA was performed 50 times, and after 70 hours at 70 ° C. from the discharge energy of the 50th cycle. Was determined. A value obtained by dividing the capacitance after 70 hours at 70 ° C. by the initial capacitance was defined as a capacitance retention rate (unit%). The measurement results are shown in Table 1.

Example 2
The electrolytic solution was prepared, the electric double layer capacitor cell was prepared, and measured in the same manner as in Example 1 except that the additive ETHAB concentration was 10 ppm. The measurement results are shown in Table 1.

Example 3
To 15.8 g of 42% -tetrafluoroboric acid aqueous solution, 8.6 g of diethylamine was slowly added dropwise with stirring under ice cooling. After stirring for 1 hour, unreacted raw materials and water were distilled off under reduced pressure to obtain 14.4 g of crude crystals. Finally, recrystallization was performed 3 times with 100 g of ethanol, and after drying at 80 ° C. overnight, 10.5 g of the additive diethylammonium tetrafluoroborate (C ₂ H ₅ ) ₂ NH ₂ .BF ₄ (DEDHAB) was obtained. . DEDHAB obtained as described above was dissolved in 1.8 mol / L-TEMAB / PC to prepare an electrolytic solution having an additive DEDHAB concentration of 1000 ppm. An electric double layer capacitor cell was produced and measured in the same manner as in Example 1. The measurement results are shown in Table 1.

Example 4
The electrolytic solution was prepared, the electric double layer capacitor cell was prepared, and measured in the same manner as in Example 3 except that the additive DEDHAB concentration was 10 ppm. The measurement results are shown in Table 1.

Comparative Example 1
An electric double layer capacitor cell was prepared and measured in the same manner as in Example 1 except that 1.8 mol / L-TEMAB / PC containing no additive was used in the electrolytic solution. The measurement results are shown in Table 1.

Comparative Example 2
The electrolytic solution was prepared, the electric double layer capacitor cell was prepared, and measured in the same manner as in Example 3 except that the additive DEDHAB concentration was 2%. The measurement results are shown in Table 1.

  As is clear from Table 1, the electric double layer capacitor using the electrolytic solution to which an ammonium salt having a specific structure is added within a specific range has an internal resistance in a wide temperature range of 25 to 70 ° C. compared to the case where it is not added. It was low. Further, almost no decrease in the capacitance retention rate was observed within the specific addition range.

Claims (9)

A nonaqueous electrolytic solution for an electric double layer capacitor, wherein an electrolytic solution comprising a nonaqueous solvent and an electrolyte contains an ammonium salt represented by the general formula (1) in an amount of 1 ppm to 1 wt% as an additive.

(In the formula, R ¹ represents an alkyl group having 1 to 6 carbon atoms, R ² represents an alkyl group having 1 to 6 carbon atoms or a hydrogen atom. Y ⁻ represents an inorganic anion.)   The non-aqueous electrolyte for electric double layer capacitors according to claim 1, comprising an ammonium salt represented by the general formula (1) in a weight ratio of 5 ppm to 2000 ppm.   The non-aqueous electrolyte for an electric double layer capacitor according to claim 1 or 2, wherein the anion species of the electrolyte and the anion species of the ammonium salt represented by the general formula (1) are the same.   The nonaqueous electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 3, wherein the ammonium salt represented by the general formula (1) is monoalkylammonium tetrafluoroborate or dialkylammonium tetrafluoroborate.   The non-aqueous electrolyte for an electric double layer capacitor according to any one of claims 1 to 4, wherein the ammonium salt represented by the general formula (1) is monoethylammonium tetrafluoroborate.   The non-aqueous electrolyte for an electric double layer capacitor according to any one of claims 1 to 4, wherein the ammonium salt represented by the general formula (1) is diethylammonium tetrafluoroborate.   The non-aqueous electrolyte for an electric double layer capacitor according to any one of claims 1 to 6, wherein the electrolyte is tetraalkylammonium tetrafluoroborate.   The non-aqueous electrolyte for an electric double layer capacitor according to any one of claims 1 to 7, wherein the electrolyte is diethyldimethylammonium tetrafluoroborate. The electric double layer capacitor using the non-aqueous electrolyte in any one of Claims 1-8.