JP2008091823A - Electrolyte for electric double layer capacitor and electric double layer capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for an electric double layer capacitor that has a superior impregnation property to an electrode and a separator, shows a low viscosity coefficient, high electric conductivity, and a wide potential window, and has excellent electrochemical stability, and to provide the electric double layer capacitor that uses the electrolyte, and has high capacity and low internal resistance in a wide temperature range, especially a low-temperature range, and shows excellent withstand voltage characteristics. <P>SOLUTION: An acetate derivative is added to the electrolyte for the electric double layer capacitor containing quaternary ammonium salt as the electrolyte in a solvent. The additive is added, thus obtaining the electrolyte that improves the impregnation property to the electrode of the electric double layer capacitor and the separator, shows the low viscosity coefficient and high electric conductivity, and has the wide potential window and high electrochemical stability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrolytic solution for an electric double layer capacitor and an electric double layer capacitor, and more specifically, an electric double layer in which impregnation into an activated carbon sheet electrode and a separator nonwoven fabric is improved and internal resistance is reduced by adding an additive. The present invention relates to an electrolytic solution for a capacitor and an electric double layer capacitor using the electrolytic solution.

  Electric double layer capacitors are safe, free from environmentally hazardous substances such as heavy metals, have excellent charge / discharge cycle life, and can charge and discharge large currents. Is being used for auxiliary power supplies.

  This electric double layer capacitor is required to reduce the internal resistance in order to improve the output density, and the electrolyte used for the electric double layer capacitor has electrochemical stability, high electrical conductivity, stability over time, etc. Characteristics are required. In addition, the electric double layer capacitor is assumed to be used under severe conditions, and the electrolyte can stably operate the electric double layer capacitor in a wide temperature range from low temperature to high temperature. Properties are also important.

  Conventional electrolytic solutions for electric double layer capacitors are often used in which a solid electrolyte made of an aliphatic quaternary ammonium salt is dissolved in an aprotic organic solvent such as propylene carbonate or γ-butyrolactone. Yes.

  The electrolytic solution is impregnated by being poured and immersed in a sheet-like activated carbon to be an electrode and a separator, and being subjected to reduced pressure or increased pressure, or repeated reduced pressure and increased pressure. Electric double layer capacitors such as reduced capacity, increased internal resistance, deteriorated current rate characteristics, etc., when electrolyte does not reach the pores inside the electrode sufficiently, or when an unimpregnated part such as the separator is not sufficiently wet occurs. It causes deterioration of the electrical characteristics of.

  On the other hand, if the pressure is excessively reduced in the impregnation step for the purpose of reducing the unimpregnated portion, the aprotic organic solvent such as propylene carbonate and γ-butyrolactone used in the electrolyte solution is evaporated and becomes a solute. The concentration of the aliphatic quaternary ammonium salt may change, and the electrical characteristics that can be originally expressed may be impaired.

  Therefore, there is a demand for an electrolyte solution that has superior impregnation into electrodes and separators and superior electrical characteristics than the conventionally known electrolyte solutions.

  For example, phosphazenes and their derivatives are listed as substances that have been proposed as additives for electrolytic solutions for electric double layer capacitors. (For example, see Patent Document 1 and Patent Document 2)

  However, the above phosphazene and its derivatives are mainly intended to impart flame retardancy to the electric double layer capacitor and to improve the characteristics at low temperature. Regarding the effect of improving the impregnation property and reducing the internal resistance of the electric double layer capacitor, It was insufficient.

  By adding an acetate derivative as an additive for an electrolyte solution such as a lithium ion battery in Patent Document 3, Patent Document 4, Patent Document 5, and Non-Patent Document 1, a conductive thin film is formed on the negative electrode, In addition, it is disclosed that the decomposition of the solvent and the electrolyte is suppressed, the withstand voltage is improved, the charge / discharge cycle characteristics are improved, and the overcharge is prevented.

  However, the charging / discharging mechanism and electrode reaction of the electric double layer capacitor are different from those of the lithium ion battery, and the effect of adding the additive to the electrolytic solution for the electric double layer capacitor is unknown.

  Patent Document 6 shows an example in which methyl acetate, which is an acetate derivative, is used as a solvent for an electrolytic solution for an electric double layer capacitor.

International Publication No. WO2002 / 021631 Pamphlet JP 2001-217152 A JP 2000-58112 A JP 2002-279959 A Japanese Patent Application No. 2005-347240 JP-A-10-125560 Nakamura Hiroyoshi, Kanno Kenichi, Yoshio Masayuki, Abe Koji, Yoshitake Hideya, Electrochemistry and Industrial Physical Chemistry 73, no. 9 (2005) P.I. 788-P. 790

  In view of the above problems, the present invention provides an electrolytic solution for an electric double layer capacitor that is excellent in impregnation into electrodes and separators, exhibits a low viscosity, high electrical conductivity, a wide potential window, and is excellent in electrochemical stability. And to provide an electric double layer capacitor having a high capacity and a low internal resistance in a wide temperature range, particularly in a low temperature range, and exhibiting an excellent withstand voltage characteristic.

  As a result of intensive investigations in view of the above problems, the inventors of the present invention added an acetate derivative to an electrolytic solution containing a quaternary ammonium salt as an electrolyte in a solvent. The electric double layer capacitor using the electrolytic solution can be improved in combination with the improvement of the impregnation property with the electrode and the separator. The inventors have found that the characteristics can be exhibited, and have completed the present invention.

  That is, according to the present invention, in an electrolytic solution for an electric double layer capacitor in which a quaternary ammonium salt and an additive are contained in a solvent, the additive is an acetate derivative represented by the following general formula (1). It is the electrolyte solution for electric double layer capacitors characterized.

In the formula (1), R ₁ represents an organic group, more preferably a hydrogen atom, a halogen atom, a chain alkyl group, a cyclic alkyl group, an alkoxy group, a benzylalkoxy group, a phenylalkoxy group, a phenyl group, or a benzyl group. Each of which can be bonded to a substituent may be substituted, and may be the same or different.

  The additive is an electrolytic solution for an electric double layer capacitor in which the additive is at least one acetate derivative selected from the group consisting of acetic anhydride, 2-methoxyethyl acetate, phenyl acetate, isopropyl acetate, and cyclohexyl acetate.

  The present invention also provides an electrolytic solution for an electric double layer capacitor, wherein the content of the additive is 0.01 to 10% by weight.

  The present invention also provides an electrolytic solution for an electric double layer capacitor, wherein the quaternary ammonium salt is a spiro compound represented by the following general formula (3).

In the above formula (3), m and n represent an integer of 3 to 7, and may be the same or different. X ⁻ represents an anion.

  Furthermore, the present invention is an electric double layer capacitor obtained by impregnating a polarizable electrode sandwiching a separator with the above electrolyte and sealing the container in a container.

  The electrolytic solution for an electric double layer capacitor of the present invention to which an acetate derivative is added exhibits a low viscosity, a high electrical conductivity, a wide potential window, and a high electrochemical stability.

  By adding the additive to the electric double layer capacitor, the viscosity of the electrolytic solution can be lowered, and the impregnation of the electrolytic solution into the activated carbon sheet electrode and the separator can be improved, and the accompanying internal resistance reduction effect can be obtained. .

  An electric double layer capacitor using the electrolytic solution of the present invention has a high capacity and a low internal resistance, and is particularly excellent in characteristics at a low temperature region. Further, the additive has a function of lowering the surface tension of the electrolytic solution, and when an electrolytic solution to which the additive is added is used, an effect of improving handling such as an impregnation rate at the time of manufacturing an electric double layer capacitor can be obtained.

  Hereinafter, the electrolytic solution for an electric double layer capacitor of the present invention will be described in detail.

  The additive added to the electrolytic solution for electric double layer capacitor of the present invention is an acetate derivative represented by the above general formula (1). By adding the additive to the electrolytic solution for an electric double layer capacitor containing a quaternary ammonium salt as an electrolyte in a solvent, the impregnation property of the electrode and separator of the electric double layer capacitor is improved, and low viscosity And an electrolyte with high electrical conductivity and a wide potential window and high electrochemical stability.

  An additive for an electric double layer capacitor according to the present invention, wherein the additive added to the electrolyte for an electric double layer capacitor is at least one acetate derivative represented by the following general formula (1): .

In the above formula (1), R ₁ represents an organic group, and each of which can be bonded to a substituent may be substituted.

  Preferred as the organic group are hydrogen atom, halogen atom, chain alkyl group, chain ether group, cyclic alkyl group, alkoxy group, benzylalkoxy group, phenylalkoxy group, phenyl group, benzyl group, amino group, epoxy group , Carboxyl group, epoxy group, hydroxyl group, styryl group, fluorine-containing alkyl group, and ester group.

R ₁ may be substituted as long as it can be bonded to a substituent, and may be the same or different. By adding an acetate derivative, the electrode-electrolyte interface becomes active and the compatibility between the electrode and the electrolyte is improved. As a result, it becomes possible to fill the pores of the electrode that could not be penetrated with the electrolytic solution, and the effect of increasing the capacitance of the capacitor and reducing the internal resistance can be obtained particularly at low temperatures.

  Moreover, it is preferable that content of the said acetate derivative is 0.01 to 10 weight%, More preferably, it is 0.1 to 1 weight%.

  The quaternary ammonium salt can be arbitrarily selected from conventionally known quaternary ammonium salts, and is not particularly limited. Specifically, the cation includes a quaternary ammonium cation such as tetraethylammonium ion or triethylmethylammonium ion, a quaternary imidazolium cation such as 1-ethyl-3-methylimidazolium ion or diethylimidazolium ion, propyl It is preferably selected from the group consisting of quaternary pyridinium cations such as pyridinium ions and isopropylpyridinium ions, and pyrrolidinium cations such as spiro- (1,1 ′)-bipyrrolidinium ions. In addition, 2 or more types of these cations may be mixed. The anion is not particularly limited, but an anion composed only of a nonmetallic element is preferable.

In the quaternary ammonium salt, the compound represented by the general formula (3) is excellent in solubility in a solvent, and is obtained from the viewpoint of the viscosity, electric conductivity and potential window of the electrolyte, and electrochemical stability. Can be used more suitably. (3) In the formula, m and n each represent a natural number of 3 to 7 which may be the same or different, and X ⁻ represents an anion.

  Specific examples of the compound represented by the general formula (3) include spiro- (1,1 ′)-bipyrrolidinium ion, spiro- (1,1 ′)-bipiperidinium ion, piperidine-1-spiro. -1′-pyrrolidinium ions and the like can be exemplified, and spiro- (1,1 ′)-bipyrrolidinium ions are particularly preferable.

Further, the anion is preferably an anion consisting of only a nonmetallic element, but is not limited thereto. Specific anions consisting only of the nonmetallic elements include BF ₄ ⁻ , PF ₆ ⁻ , CF ₃ SO ₃ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , N (C ₂ F ₅ SO ₂ ) ₂ ⁻ , It is preferably selected from the group consisting of N (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ) ⁻ , C (CF ₃ SO ₂ ) ₃ ^— and C (C ₂ F ₅ SO ₂ ) ₃ ^— . In addition, 2 or more types of these anions may be mixed.

  Examples of the solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like. Chain carbonates; chain esters such as methyl formate, methyl acetate, methyl butyrate; tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-di Ethers such as butoxyethane and methyldiglyme; nitriles such as acetonitrile and benzonitrile; dioxolane or derivatives thereof; ethylene sulfide, sulfolane, sultone or derivatives thereof; Examples thereof include, but are not limited to, fluorinated solvents such as lobenzene and (trifluoromethyl) ethyl carbonate, or a mixture of two or more thereof.

  The electrolytic solution for electric double layer capacitors of the present invention can be prepared by the following production method.

  That is, an electrolyte salt composed of a quaternary ammonium salt is added to the solvent at an arbitrary concentration, and after stirring to confirm that the salt is completely dissolved, the acetate derivative as an additive, preferably 0.01 To 10% by weight, more preferably 0.1 to 1% by weight. In the case of 0.01% by weight or less, the effect of lowering the surface tension due to the addition and the accompanying improvement in electrical conductivity and lowering the viscosity may not be exhibited. In the case of 10% by weight or more, the viscosity of the electrolyte The rate, electrical conductivity, and voltage holding characteristics may be extremely inferior, and the economy may be inferior. When the obtained electrolytic solution is dehydrated and the water content in the electrolytic solution is reduced to 100 ppm or less, preferably 20 ppm or less, the intended electrolytic solution for electric double layer capacitors is obtained.

  As for the density | concentration of the quaternary ammonium salt in the electrolyte solution of this invention, 0.5-3 mol / L is preferable with respect to the whole electrolyte solution. When the concentration of the quaternary ammonium salt is less than 0.5 mol / L, the electrical conductivity may be insufficient. When the concentration is more than 3 mol / L, the electrochemical stability is lowered and the economy is inferior. There is.

  An electric double layer capacitor can be produced using the electrolytic solution thus adjusted. The capacitor of the present invention can be produced by a general method for manufacturing a capacitor, that is, an electric double layer capacitor in which a polarizable electrode sandwiching a separator contains the additive of the present invention to be a driving electrolyte. It is carried out by impregnating with an electrolytic solution and sealing it in a container.

  As the polarizable electrode used for the capacitor electrode, porous carbon materials such as activated carbon powder and activated carbon fibers, noble metal oxide materials, conductive polymer materials, and the like are used, and porous carbon materials are preferable because they are inexpensive. Moreover, as a separator, the separator which consists of raw materials, such as polyethylene and a polypropylene-type nonwoven fabric, can be used.

  The shape of the electric double layer capacitor of the present invention is not particularly limited, and can be produced in a film shape, a coin shape, a cylindrical shape, a box shape or the like.

  FIG. 1 is a schematic cross-sectional view showing an example of a coin-type electric double layer capacitor of the above shapes, and showing an example of the configuration of the electric double layer capacitor of the present invention.

  In FIG. 1, it has a negative electrode part composed of a negative electrode cap 1, a negative electrode 2 and a current collector 3, and a positive electrode part composed of a current collector 3, a positive electrode 6 and a positive electrode case 7. Are arranged so as to face each other. The electrolytic solution 4 is impregnated and filled in electrodes, separators, and containers. The negative electrode cap 1 and the positive electrode case 7 are insulated and fitted by a gasket 8.

  The electric double layer capacitor of the present invention has an extremely high withstand voltage, and exhibits stable charge / discharge characteristics in a range including at least 2.8V to 3.2V.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited at all by the Example.

Example 1
Preparation of electrolytic solution for electric double layer capacitor Spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate is added to propylene carbonate to a concentration of 1.5 mol / L, and acetic anhydride (Wako Pure Chemical Industries, Ltd.) is added. Was added and dehydrated to obtain an electrolytic solution for an electric double layer capacitor having a moisture value of 100 ppm or less (hereinafter, this electrolytic solution and an electric double layer capacitor using the electrolytic solution were referred to as “Invention 1”). ”).

  Similarly, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate is added to propylene carbonate to a concentration of 1.5 mol / L, and 2-methoxyethyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) is added. An electrolytic solution for an electric double layer capacitor having 0 wt% added and dehydrated to a moisture value of 100 ppm or less was obtained (same as above, “Invention 2”).

  Similarly, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate is added to propylene carbonate to a concentration of 1.5 mol / L, and 1.0% by weight of phenyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) is added. An electrolytic solution for an electric double layer capacitor having a moisture value of 100 ppm or less was obtained by addition and dehydration (same as above, “Invention product 3”).

  Similarly, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate was added to propylene carbonate to a concentration of 1.5 mol / L, and isopropyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added at 1.0% by weight. An electrolytic solution for an electric double layer capacitor having a water value of 100 ppm or less was obtained by addition and dehydration (same as above, “Invention 4”).

  Similarly, spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate was added to propylene carbonate to a concentration of 1.5 mol / L, and cyclohexyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) was added at 1.0% by weight. An electrolytic solution for an electric double layer capacitor having a water value of 100 ppm or less was obtained by addition and dehydration (same as above, “Invention 5”).

  Similarly, tetraethylammonium tetrafluoroborate is added to propylene carbonate so as to have a concentration of 1.0 mol / L, 1.0 wt% of phenyl acetate (manufactured by Wako Pure Chemical Industries, Ltd.) is added, and dehydration is performed to reduce the moisture value to 100 ppm or less. An electrolytic solution for an electric double layer capacitor was obtained (same as above, referred to as “invention product 6”).

  For comparison, a propylene carbonate solution of 1.5 mol / L spiro- (1,1 ′)-bipyrrolidinium was prepared (same as above, “Comparative Product 1”). Further, a 1.0 mol / L tetraethylammonium propylene carbonate solution was prepared (same as above, “Comparative product 2”).

  Table 1 shows the physical properties of “acetic anhydride”, “2-methoxyethyl acetate”, “phenylacetate”, “isopropylacetate”, and “cyclohexylacetate” which are the acetate derivatives used this time.

Table 1 shows the results of measurement of the viscosity, electrical conductivity, and potential window of this electrolytic solution at 25 ° C. The potential window was measured by a redox decomposition voltage using a cyclic voltammogram. That is, a platinum wire (diameter 3 mm) as a working electrode, a platinum plate as a counter electrode, Ag / Ag ^{+ as} a reference electrode, a voltage until a current of 0.1 mA / cm ² flows at a sweep rate of 10 mV / s, and reductive decomposition is measured. The potential window was determined from the oxidative decomposition voltage value.

  As shown in Table 2, invention products 1-6, in which spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate is used as a quaternary ammonium salt and an acetate derivative is added as an additive, Compared with the comparative product 1 that does not use the material, the viscosity and electrical conductivity are excellent, and the potential window is comparable to the comparative product. Specifically, an effect of reducing the viscosity by about 11.9 to 21.4% and increasing the electric conductivity by about 1.3 to 8.8% was obtained. Further, it was confirmed that the more preferable additive was isopropyl acetate used in “Invention Product 4”.

  Further, the inventive product 7 in which tetraethylammonium tetrafluoroborate is used as a quaternary ammonium salt and an acetate derivative is added as an additive is also approximately 5.3% in viscosity as compared with the comparative product 2 in which no additive is used. The effect of reducing and increasing the conductivity by about 6.0% was obtained, and it was confirmed that the potential window also showed a decomposition voltage comparable to the comparative product.

Example 2
Production of Electric Double Layer Capacitor An electric double layer capacitor was produced using the electrolyte solution of Example 1 (Invention products 1 to 6 and Comparative products 1 and 2).

  The positive electrode and the negative electrode are active materials (activated carbon: Nippon Enviro Chemicals Co., Ltd., Shirahama KA), conductive materials (Ketjen Black: Lion Co., Ltd., ECP-600JD), and binder (PTFE: Mitsui DuPont Fluoro Chemical Co., Ltd.) 30-J). The weight composition ratio was active material: conductive material: binder = 80 parts: 10 parts: 10 parts. These mixtures were sufficiently kneaded while adding ethanol, and rolled to obtain an activated carbon sheet electrode having an average thickness of 0.85 mm. This activated carbon sheet electrode punched out with a φ15 punch is adhered to a case and cap (both made of SUS316) welded with a current collector (φ17 made of SUS316) with a conductive adhesive, respectively. A negative electrode part was obtained. Each of these electrodes was injected with the electrolyte solution of Example 1 and impregnated under reduced pressure at 0.060 MPa for 10 minutes, and then assembled by attaching a polypropylene gasket to the cap with a polypropylene non-woven fabric as a separator. The 2032 size coin type electric double layer capacitor was completed by fitting.

Evaluation of Electric Double Layer Capacitor Each electric double layer capacitor was subjected to a charge / discharge test at 20 ° C. Each capacitor is allowed to stand at a predetermined measurement temperature for 30 minutes or more, and after the capacitor reaches a predetermined temperature, 3.0 V is applied as a rated voltage for 30 minutes, and then a constant current discharge is performed at a discharge current of 2 mA. The capacitance was calculated from the time from 1V to 2V. Further, the lower limit value of discharge was set to 0.9V. The internal resistance was calculated from the IR drop when a constant current was discharged at a discharge current of 50 mA after applying 3.0 V as a rated voltage for 30 minutes as in the capacitance measurement. The leakage current was calculated by measuring the resistance voltage of a precision resistor with a rating of 1 kΩ connected in series in the circuit after applying 3.0 V as a rated voltage for 30 minutes, as in the capacitance measurement. These results are shown in Table 2 below.

  As shown in Table 3, invention products 1 to 6 using spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate as a quaternary ammonium salt and adding an acetate derivative as an additive are additives. Compared with the comparative product 1 that does not use A, the capacitance is excellent, the internal resistance is greatly reduced, and the leakage current is comparable to the comparative product. Specifically, the effect of increasing the capacitance by about 1.0 to 2.5% and reducing the internal resistance by about 8.8 to 13.2% was obtained. Further, it was confirmed that the preferred additive was “cyclohexyl acetate” used in “Invention Product 5”.

  In addition, the inventive product 6 in which tetraethylammonium tetrafluoroborate is used as the quaternary ammonium salt and phenyl acetate is added as an additive is also approximately 1. It was confirmed that an increase of 0% and an effect of increasing the internal resistance by about 4.1% were obtained, and the leakage current showed a decomposition voltage comparable to that of the comparative product.

  Next, the temperature characteristics of the electric double layer capacitor produced using the electrolyte solution of Example 1 (Invention products 1 to 7 and Comparative products 1 and 2) were measured. Each capacitor is allowed to stand at a predetermined measurement temperature for 30 minutes or more, and after the capacitor reaches a predetermined temperature, 3.0 V is applied as a rated voltage for 30 minutes, and then a constant current discharge is performed at a discharge current of 2 mA. The capacitance was calculated from the time from 1V to 2V. Further, the lower limit value of discharge was set to 0.9V. The internal resistance was calculated from the IR drop when a constant current was discharged at a discharge current of 50 mA after applying 3.0 V as a rated voltage for 30 minutes as in the capacitance measurement. The ambient temperature was tested in the direction of increasing the temperature from -40 ° C every 10 ° C. The measurement result of the temperature characteristic of the capacitance is shown in FIG. 2, and the measurement result of the temperature characteristic of the internal resistance is shown in FIG.

  The effect of the additive at −40 ° C. is shown in Table 4 below. When the comparative products 1 and 2 are set to 100, the percentages of the capacitance and internal resistance of each capacitor of the invention are shown. (Inventive products 1 to 6 are based on the comparative product 1, and the inventive product 7 is based on the comparative product 2.)

  Table 4 shows the results of measuring the temperature characteristics of the electrostatic capacity in FIG. 2 and the results of measuring the temperature characteristics of the internal resistance in FIG. Product 1 was compared.

  As shown in FIG. 2, FIG. 3 and Table 4, Invention 1 in which spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate is used as a quaternary ammonium salt and an acetate derivative is added as an additive ˜5 is excellent in electrostatic capacity development at −40 ° C. as compared with Comparative Product 1 in which no additive is used, and the internal resistance at −40 ° C. is greatly reduced. Specifically, the capacitance was increased by about 53.4 to 70.7%, and the internal resistance was reduced by about 14.5 to 34.1%. Moreover, as a more preferable additive, it was confirmed that it was “2-methoxyethyl acetate” used in “Invention 2”.

  In addition, the invention product 6 in which tetraethylammonium tetrafluoroborate is used as the quaternary ammonium salt and phenyl acetate is added as an additive is also similar to the comparative product 2 in which no additive is used. Compared with spiro- (1,1 ′)-bipyrrolidinium tetrafluoroborate, the capacitance increases by about 21.9%, and the internal resistance decreases by about 8.9%. It was confirmed that the effect to be obtained was obtained.

  When an acetate derivative, which is an additive for an electrolytic solution for an electric double layer capacitor according to the present invention, is used, as described above, the impregnation property when making an electric double layer capacitor is improved, and accordingly, the internal resistance can be lowered. Become. In particular, an electrolytic solution and a cell using a spiro compound as an electrolyte have various characteristics that are markedly superior to conventional ones.

The schematic sectional drawing which shows an example of a structure of the electrical double layer capacitor of this invention. FIG. 6 is a diagram showing temperature characteristics of capacitance in capacitor evaluation of Example 2. FIG. 10 is a diagram showing temperature characteristics of internal resistance in capacitor evaluation of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode cap 2 Negative electrode 3 Current collector 4 Electrolyte 5 Separator 6 Positive electrode 7 Positive electrode case 8 Gasket

Claims (5)

In an electrolytic solution for an electric double layer capacitor, wherein a quaternary ammonium salt and an additive are contained in a solvent, the additive is an acetate derivative represented by the following general formula (1). Electrolyte for multilayer capacitors.

(In the formula, R ₁ represents a hydrogen atom, a halogen atom, a chain alkyl group, a cyclic alkyl group, an alkoxy group, a benzylalkoxy group, a phenylalkoxy group, a phenyl group, or a benzyl group. May be the same or different.)   2. The electricity according to claim 1, wherein the additive is at least one acetate derivative selected from the group consisting of acetic anhydride, 2-methoxyethyl acetate, phenyl acetate, isopropyl acetate, and cyclohexyl acetate. Electrolyte for double layer capacitors.   The electrolytic solution for an electric double layer capacitor according to claim 1 or 2, wherein the content of the additive is 0.01 to 10% by weight. The electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 3, wherein the quaternary ammonium salt is a spiro compound salt represented by the following general formula (2).

(In the formula, m and n each represent an integer of 3 to 7, which may be the same or different. X ⁻ represents an anion.)   An electric double layer capacitor obtained by impregnating a polarizable electrode sandwiching a separator with the electrolytic solution for an electric double layer capacitor according to any one of claims 1 to 4, and sealing the same in a container.

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