JP5430464B2 - Electrolytic solution for electric double layer capacitor and electric double layer capacitor - Google Patents

Description

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

  An electric double layer capacitor is a capacitor using an electric double layer formed between an electrode and an electrolyte. In order to increase the stored energy of the capacitor, it is conceivable to increase the voltage applied to the capacitor. However, in an electric double layer capacitor using an electrolytic solution in which an electrolyte is dissolved in an organic solvent, a high voltage of about 3 V, for example, is used. When applied, there was a problem that durability and the like deteriorated.

  An ionic liquid is used as an electrolytic solution of the electric double layer capacitor. An ionic liquid is a salt that exhibits a liquid state near room temperature, and is known to have non-volatility, incombustibility, high thermal stability, high ionic conductivity, and electrolysis resistance. Also, since ionic liquids have better oxidation resistance than ordinary organic solvents, when ionic liquids are used as electrolytes for electric double layer capacitors, electrolytes in which electrolytes are dissolved in ordinary organic solvents are used. As compared with the above, it can be expected that the durability of the capacitor is improved under a high voltage application condition of about 3V.

  For example, Patent Document 1 discloses that an electrolyte containing a lithium salt, an ionic liquid, or an organic solvent is used as an electrolyte for a secondary power source, and examples of the organic solvent include sulfolane, ethylene carbonate, and tetraglyme. Is disclosed.

  Patent Document 2 discloses a non-aqueous electrolyte secondary battery, and discloses that a solvent such as ethylene carbonate or methyl glyme and at least one ionic liquid are used as an electrolytic solution of the battery. Yes.

Patent Document 3 discloses that the cathode material of the electrochemical cell structure includes an electrolyte containing an organic carbonate, glyme, or the like, or an ionic liquid.
Patent Document 4 discloses an electrolyte for an energy storage device containing a room temperature ionic liquid based on pyrrolidinium, and discloses that the electrolyte may contain polyvinyl pyrrolidone, polyethylene glycol, glyme and the like. ing.

  However, even in a capacitor using an ionic liquid as an electrolytic solution, durability under a high voltage application condition of about 3 V is still not sufficient, and further improvement is required.

Japanese Patent Laid-Open No. 2005-35352 Japanese Patent Laid-Open No. 2005-142047 Special table 2007-524204 gazette JP-T-2006-520997

  In view of the above situation, the present invention provides an electrolytic solution for an electric double layer capacitor having a high capacity retention rate and excellent durability even when charged by applying a high voltage of about 3 V, and An object is to provide a multilayer capacitor.

  Although the details of the cause of durability degradation when a high voltage is applied to an electric double layer capacitor using an ionic liquid are not clear, the ionic liquid has an extremely high viscosity compared to an electrolyte using an ordinary organic solvent. There is a demerit such as high, and therefore, impregnation into the electrode and escape of gas generated in the electrode worsened, which was considered to affect the deterioration. In addition, in the electric double layer capacitor, it is considered that the electrode pores are blocked by the electrolyte decomposition product as the durability deterioration progresses. For this reason, the high viscosity factor of the electrolyte promotes the deterioration further than before the deterioration. It was thought that it would be easy to make it.

  As a result of intensive studies in view of the above problems, the present inventors applied a high voltage of about 3 V for charging when an electrolytic solution in which glycol diether was added to an ionic liquid as an electrolytic solution for an electric double layer capacitor. Even in this case, it has been found that the capacity reduction of the electric double layer capacitor is suppressed and the durability is greatly improved. Details of this reason are not clear, but (1) the glycol diether is adsorbed on the surface of the electrode, so that the decomposition of the electrolytic solution is suppressed. Improve the impregnation of the ionic liquid, (3) By improving the impregnation of the electrolyte solution inside the electrode, it is possible that the gas generated by the decomposition of the electrolyte etc. will easily escape from the inside of the electrode. It is considered that the capacity reduction of the electric double layer capacitor is suppressed and the durability is improved. Further, when the amount of glycol diether added is 0.5 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of components other than the glycol diether in the electrolytic solution for electric double layer capacitor, the capacity is lowered and the durability is decreased. It has been found that the sex is remarkably improved. Furthermore, substitution of the glycol ether terminal with an alkyl group or a fluorinated alkyl group is preferable because the electrochemical stability is improved, and the same effect can be obtained even when a fluorinated glycol diether is used, and It has been found that fluorination improves the oxidation resistance of glycol diether itself, which is more advantageous for use at high voltages. The present inventors have further studied based on the above findings and have completed the present invention.

The present invention relates to the following inventions.
Item 1. Ionic liquid and the following formula (1)

(Wherein R ¹ and R ² are the same or different and each represents a linear or branched alkyl group or a fluorinated alkyl group having 1 to 4 carbon atoms, and R ^{3 to} R ¹⁰ are the same or different and represent hydrogen An atom, a fluorine atom, a methyl group or a methyl fluoride group, wherein m and n are each an integer of 0 or more, and m + n is 1 to 6. Electrolyte for electric double layer capacitor.
Item 2. The amount of the compound represented by the formula (1) is 0.5 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of components other than the compound in the electrolytic solution for electric double layer capacitors. Item 2. The electrolytic solution for an electric double layer capacitor according to item 1.
Item 3. The ionic liquid is represented by the following formula (2)

(Wherein R ¹¹ , R ¹² and R ¹³ are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms, and R ¹¹ and R ¹² may form a ring. R ¹⁴ represents an alkyl group having 1 or 2 carbon atoms, p represents 1 or 2, and X ⁻ represents a fluorine-containing anion. 3. The electrolytic solution for an electric double layer capacitor according to 1 or 2.
Item 4. The ionic liquid is represented by the following formula (3)

(Wherein, R ¹⁵ represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ¹⁶ represents a methyl group or an ethyl group, and Y ⁻ represents a fluorine-containing anion). Item 3. The electrolytic solution for an electric double layer capacitor according to Item 1 or 2, which is a quaternary ammonium salt.
Item 5. Item 5. An electric double layer capacitor using the electrolytic solution according to any one of Items 1 to 4.

  According to the present invention, even when charging is performed by applying a high voltage of about 3 V, it is possible to suppress a decrease in the capacity of the electric double layer capacitor and increase the capacity maintenance rate, and to achieve the electric double layer capacitor. The durability of can be improved.

FIG. 1 is a graph showing a change with time of the capacity retention rate of an electric double layer capacitor using the electrolytic solutions manufactured in Examples and Comparative Examples. FIG. 2 is a diagram showing a change with time of the capacity retention rate of the electric double layer capacitor using the electrolytic solutions manufactured in Examples and Comparative Examples. FIG. 3 is a front view showing a laminated electric double layer capacitor which is an example of the present invention. FIG. 4 is an internal configuration diagram showing a laminated electric double layer capacitor which is an example of the present invention.

  The electrolytic solution for an electric double layer capacitor of the present invention includes an ionic liquid and the following formula (1):

(Wherein R ¹ and R ² are the same or different and each represents a linear or branched alkyl group or a fluorinated alkyl group having 1 to 4 carbon atoms, and R ^{3 to} R ¹⁰ are the same or different and represent hydrogen An atom, a fluorine atom, a methyl group or a methyl fluoride group, wherein m and n are each an integer of 0 or more, and m + n is 1 to 6.
In the present invention, one type of compound represented by the formula (1) may be added, or two or more types may be added.

Examples of the linear or branched alkyl group having 1 to 4 carbon atoms in the above formula (1) include methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, sec-butyl group, and tert. -A butyl group is mentioned. Examples of the linear or branched alkyl group having 1 to 4 carbon atoms include a trifluoromethyl group, a pentafluoroethyl group, and a heptafluoropropyl group.
R ¹ and R ² are preferably the same or different and each represents a linear or branched alkyl group or a fluorinated alkyl group having 1 to 3 carbon atoms. Among these, a methyl group, an ethyl group, a methyl fluoride group, or an ethyl fluoride group is preferable. m + n is preferably 2-4.

  Specific examples of the compound represented by the above formula (1) include tetraethylene glycol dimethyl ether (methyl tetraglyme), triethylene glycol dimethyl ether (methyl triglyme), diethylene glycol diethyl ether (ethyl diglyme), diethylene glycol dimethyl. Examples thereof include glycol diethers such as butyl ether (butyl diglyme) diethylene glycol / dimethyl ether (methyl diglyme) and propylene glycol / dimethyl ether, and fluorinated part or all of the glycol diethers.

  Examples of the fluorinated part or all of the glycol diethers include perfluorotetraglyme, pentadecafluorotriethylene glycol dimethyl ether, 1,1,1,3,3,4,4,6, 6,7,7,9,9-tridecafluoro-2,5,8,11-tetraoxadodecane, 1,1,1,3,3,4,4,6,6-nonafluoro-2,5 8,11-tetraoxadodecane, 5,5,6,6,7,7,9,9-octafluoro-2,5,8,11-tetraoxadodecane, 7,7,9,9,10,10 , 12, 12, 13, 13, 15, 15-dodecafluoro-2,5,8,11,14,17,20-heptaoxahenicosan and the like.

  The amount of the compound represented by the above formula (1) is preferably about 0.5 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of components other than the compound in the electrolytic solution for electric double layer capacitors. . Within this range, even when charging is performed by applying a high voltage of about 3 V, an electrolytic solution for an electric double layer capacitor having an extremely high capacity retention rate and excellent durability can be obtained. More preferably, the addition amount of the compound represented by the formula (1) is about 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of components other than the compound in the electrolytic solution for electric double layer capacitor. The “component other than the compound in the electrolytic solution for electric double layer capacitor” means all components except the compound contained in the electrolytic solution for electric double layer capacitor of the present invention. It is a solvent to be blended.

  As the ionic liquid in the present invention, a quaternary ammonium salt or the like is preferable. The ionic liquid in the present invention is, for example, the following formula (2):

(Wherein R ¹¹ , R ¹² and R ¹³ are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms, and R ¹¹ and R ¹² may form a ring. R ¹⁴ represents an alkyl group having carbon 1 or 2. p represents 1 or 2. X ⁻ represents a fluorine-containing anion.), A quaternary ammonium salt represented by the following formula (3)

(Wherein, R ¹⁵ represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ¹⁶ represents a methyl group or an ethyl group, and Y ⁻ represents a fluorine-containing anion). Preferred are quaternary ammonium salts. An ionic liquid can also be used in combination of 2 or more types.

Examples of the linear or branched alkyl group having 1 to 4 carbon atoms represented by R ¹¹ , R ¹² and R ¹³ in the compound represented by the formula (2) include a methyl group, an ethyl group, an n-propyl group, an iso- A propyl group, n-butyl group, sec-butyl group, and tert-butyl group are mentioned. Of these, a methyl group or an ethyl group is preferable. Examples of the ring formed by R ¹¹ and R ¹² include an aziridine ring, an azetidine ring, a pyrrolidine ring, a piperidine ring, and a pyridinium ring.
Examples of the alkyl group having 1 or 2 carbon atoms represented by R ¹⁴ include a methyl group and an ethyl group.

The linear or branched alkyl group having 1 to 4 carbon atoms represented by R ¹⁵ in the compound represented by the formula (3) is the same as described above. R ¹⁵ is preferably a linear or branched alkyl group having 1 to 3 carbon atoms. Of these, a methyl group or an ethyl group is preferable.
R ¹⁶ is preferably a methyl group or an ethyl group.

  The fluorine-containing anion in the formulas (2) and (3) is not particularly limited as long as it is an anion containing a fluorine atom, and may be a fluorine-containing organic anion or a fluorine-containing inorganic anion. In the case of a fluorine-containing organic anion, the fluorine-containing anion preferably has 2 to 4 carbon atoms.

Specific examples of the fluorine-containing anion include, for example, CF ₃ CO ₂ ⁻ , CF ₃ SO ₃ ⁻ , N (FSO ₂ ) ₂ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , and N (CF ₃ CF ₂ SO ₂ ) _{2. ^{-, N (FSO 2) (}} CF 3 SO 2) -, N (CF 3 SO 2) (CF 3 CF 2 SO 2) -, C (CF 3 SO 2) 3 -, N (CF 3 SO 2) ( CF ₃ CO) ⁻ , CF ₃ BF ₃ ⁻ , C ₂ F ₅ BF ₃ ⁻ , (CF ₃ ) ₂ BF ₂ ⁻ , (CF ₃ ) (C ₂ F ₅ ) BF ₂ ⁻ , (C ₂ F ₅ ) ₂ BF ₂ ⁻ , (CF ₃ ) ₃ BF ⁻ , BF ₄ ⁻ , PF ₆ ^{− and the} like can be mentioned. Among them, ^{_{preferably, N (CF 3 SO 2)}} 2 -, CF 3 BF 3 -, C 2 F 5 BF 3 -, BF 4 - is.

  The quaternary ammonium salt represented by the formula (2) can be produced, for example, according to the method described in JP-A-2006-265132. The quaternary ammonium salt represented by the formula (3) can be produced by, for example, the method described in WO 2005/3108. In addition, these ionic liquids are commercially available, for example, from Kanto Chemical Co. under the trade name NNN-trimethyl-N-propylammonium bis (trifluoromethanesulfonyl) imide.

  The ionic liquid in the present invention is preferably composed of a quaternary ammonium cation and a fluorine-containing anion as represented by the formulas (2) and (3). Specific examples of the quaternary ammonium cation include, as the quaternary ammonium cation in the formula (2), N, N, N-trimethyl-N-methoxymethylammonium cation, N-ethyl-N, N-dimethyl-N- Methoxymethylammonium cation, N, N-diethyl-N-methyl-N-methoxymethylammonium cation, N, N, N-triethyl-N-methoxymethylammonium cation, N-propyl-N, N-dimethyl-N-methoxy Methylammonium cation, N-propyl-N, N-diethyl-N-methoxymethylammonium cation, N-butyl-N, N-dimethyl-N-methoxymethylammonium cation, N-butyl-N, N-diethyl-N- Methoxymethylammonium cation, N, N, N-trimethyl -N-methoxyethylammonium cation, N-ethyl-N, N-dimethyl-N-methoxyethylammonium cation, N, N-diethyl-N-methyl-N-methoxyethylammonium cation, N, N, N-triethyl- N-methoxyethylammonium cation, N-propyl-N, N-dimethyl-N-methoxyethylammonium cation, N-propyl-N-diethyl-N-methoxyethylammonium cation, N-butyl-N, N-dimethyl-N -Methoxyethylammonium cation, N-butyl-N, N-diethyl-N-methoxyethylammonium cation and the like.

  As quaternary ammonium cations in formula (3), N-methyl-N-methoxymethylpyrrolidinium cation, N-ethyl-N-methoxymethylpyrrolidinium cation, N-ethoxymethyl-N-methylpyrrolidinium cation N-ethyl-N-ethoxymethylpyrrolidinium cation, N-ethyl-N-methoxyethylpyrrolidinium cation, N-methyl-N-methoxyethylpyrrolidinium cation, N-ethoxyethyl-N-methylpyrrolidi Examples thereof include a nium cation and an N-ethyl-N-ethoxyethylpyrrolidinium cation.

  Among these, N-methyl-N-methoxymethylpyrrolidinium cation, N-ethyl-N-methoxymethylpyrrolidinium cation, N-ethoxymethyl-N-methylpyrrolidinium cation, N-methyl-N- Methoxyethylpyrrolidinium cation, N-ethyl-N-methoxyethylpyrrolidinium cation, N, N-diethyl-N-methyl-N-methoxyethylammonium cation, 1-ethyl-3-methylimidazolium cation, etc. It is done. More preferably, N-methyl-N-methoxymethylpyrrolidinium cation, N-ethyl-N-methoxymethylpyrrolidinium cation, N-ethoxymethyl-N-methylpyrrolidinium cation, N-methyl-N-methoxy And ethylpyrrolidinium cation.

  Of the salts comprising combinations of these cationic components and the above anionic components (fluorinated anions), N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, N-ethyl-N-methoxymethylpyrrolidi is particularly preferred. Ni-tetrafluoroborate, N-ethoxymethyl-N-methylpyrrolidinium tetrafluoroborate, N-methyl-N-methoxymethylpyrrolidinium bistrifluoromethanesulfonylimide (N-methoxymethyl-N-methylpyrrolidinium bistrifluoro) Methanesulfonylimide), N-ethyl-N-methoxymethylpyrrolidinium bistrifluoromethanesulfonylimide, N-ethoxymethyl-N-methylpyrrolidinium bistrifluoromethanesulfonylimide, N, N-die Ru-N-methyl-N-methoxyethylammonium tetrafluoroborate, N, N-diethyl-N-methyl-N-methoxyethylammonium bistrifluoromethanesulfonylimide, N-methyl-N-methoxyethylpyrrolidinium tetrafluoroborate N-methyl-N-methoxyethylpyrrolidinium bistrifluoromethanesulfonylimide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium trifluoromethanesulfonylimide. Among them, N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, N-ethyl-N-methoxymethylpyrrolidinium tetrafluoroborate, N-ethoxymethyl-N-methylpyrrolidinium tetrafluoroborate, N-methyl -N-methoxyethylpyrrolidinium tetrafluoroborate is preferred.

  The electrolytic solution of the present invention is usually produced by mixing an ionic liquid and a compound represented by the formula (1). The electrolytic solution of the present invention may contain components other than the ionic liquid and the compound represented by the formula (1) as long as the effects of the present invention are exhibited. Preferably, a solvent other than the ionic liquid and the compound represented by the formula (1) is substantially not contained. The term “substantially free” usually means about 5% by weight or less, preferably about 1% by weight or less in the electrolytic solution for electric double layer capacitor.

  The electrolytic solution of the present invention is suitable as an electrolytic solution for electric double layer capacitors. An electric double layer capacitor using the above electrolytic solution is also one aspect of the present invention. Hereinafter, the electric double layer capacitor of the present invention will be described.

  The shape of the electric double layer capacitor of the present invention is not particularly limited, and is a laminate type, a laminate type in which electrodes are stacked and accommodated in a can body, a wound type in which the electrodes are wound and stored, or an insulating gasket. And a so-called coin type made of a metal can electrically insulated by the above. Hereinafter, as an example, the structure of a laminated electric double layer capacitor will be described.

  3 and 4 are views showing a laminated electric double layer capacitor. The electrode 3 and the aluminum tab 1 are bonded to each other, are arranged to face each other via the separator 4, and are stored in the laminate 2. The electrode is composed of a polarizable electrode portion made of a carbon material such as activated carbon and a current collector portion. The laminate container body 2 is sealed by thermocompression bonding so that moisture and air from the outside of the container do not enter.

The polarizable electrode material is preferably a material having a large specific surface area and high electrical conductivity, and needs to be electrochemically stable with respect to the electrolyte within the range of applied voltage to be used. Examples of such a material include a carbon material, a metal oxide material, and a conductive polymer material. Considering the cost, it is preferable to use a carbon material as the polarizable electrode material.
As the carbon material, an activated carbon material is preferable. Specific examples include sawdust activated carbon, coconut shell activated carbon, pitch coke activated carbon, phenol resin activated carbon, polyacrylonitrile activated carbon, and cellulose activated carbon.

  Examples of the metal oxide material include ruthenium oxide, manganese oxide, and cobalt oxide. Examples of the conductive polymer material include a polyaniline film, a polypyrrole film, a polythiophene film, and a poly (3,4-ethylenedioxythiophene) film.

  For the electrode, the polarizable electrode material is kneaded with a binder such as PTFE, and the pressure-molded one is bound to a current collector such as an aluminum foil with an electric adhesive, or the polarizable electrode material is It can be obtained by mixing a binder together with a thickener such as CMC or an organic solvent such as pyrrolidone together with a binder, applying the paste to a current collector such as an aluminum foil, and then drying.

  The separator preferably has high electronic insulation, excellent wettability of the electrolyte, and high ion permeability, and needs to be electrochemically stable within the applied voltage range. The material of the separator is not particularly limited, but papermaking made of rayon, Manila hemp or the like; polyolefin-based porous film; polyethylene nonwoven fabric; polypropylene nonwoven fabric or the like is preferably used.

The electric double layer capacitor of the present invention can have an upper limit voltage (rated voltage) of about 2.7 V or more, and further about 3 V or more. The electric double layer capacitor of the present invention has a high capacity retention rate and excellent durability even when such a high voltage is applied.
The use of the electric double layer capacitor of the present invention is not particularly limited, and can be suitably used as, for example, a power storage device such as a hybrid vehicle, an uninterruptible power supply (UPS), solar power generation, wind power generation and the like.

  Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In this example, “%” means “% by weight” unless otherwise specified.

(Production of electrodes)
As a polarizable electrode, 80% by weight of activated carbon powder (pitch, coke activated carbon, steam activated, specific surface area 1400-1500 m ² / g), 10% by weight of acetylene black and 10% by weight of polytetrafluoroethylene powder are kneaded in a kneader. did. Thereafter, the sheet was rolled to produce a sheet having a thickness of 0.1 mm, and adhered to 0.03 mm etched aluminum with a conductive paste such as a carbon paste to obtain an electrode sheet. This sheet was punched with a mold and then dried at 220 ° C. under high vacuum to produce positive and negative electrodes.

(Production of electric double layer capacitor)
The element in which the positive electrode and the negative electrode were opposed to each other with a cellulose separator interposed between them was housed in an aluminum laminate outer case, and then an electrolytic solution was injected and sealed. The positive and negative terminals were taken out of the outer case from each electrode using an aluminum lead plate.

(Evaluation method)
In a constant temperature bath set at 25 ° C., 3.0 V constant voltage charging was performed for 24 hours, discharging to 0.0 V, and aging treatment was performed. In the long-term reliability test, a floating test was performed by applying a voltage of 3.0 V in a thermostat set to 60 ° C. The electrostatic capacity was obtained from the voltage gradient obtained by charging at a constant voltage of 3.0 V for 30 minutes in a thermostat set at 25 ° C. and discharging to a predetermined voltage at 2.0 mA / cm ² . .

  In the following examples, N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate used was synthesized according to the method described in WO2005 / 3108. The methyl tetraglyme used was made by Aldrich.

Example 1
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 0.1 part by weight of methyltetraglyme was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced by the above method using this electrolytic solution.

Example 2
0.5 parts by weight of methyltetraglyme was added to and mixed with 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate to obtain an electrolyte solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 3
1 part by weight of methyltetraglyme was added to and mixed with 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 4
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 5 parts by weight of methyltetraglyme was added and mixed to obtain an electrolyte solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 5
7 parts by weight of methyltetraglyme was added to and mixed with 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Comparative Example 1
An electric double layer capacitor was produced in the same manner as in Example 1 except that N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate was used as the electrolytic solution.

Comparative Example 2
To 26.3 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 73.7 parts by weight of propylene carbonate (PC) was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Reference example 1
10 parts by weight of methyltetraglyme was added to and mixed with 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Reference example 2
1 part by weight of methyltetraglyme was added to and mixed with 26.3 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate and 73.7 parts by weight of propylene carbonate to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Table 1 shows the compositions of the electrolyte solutions prepared in Examples 1 to 5 and Comparative Examples 1 to 2 and Reference Examples 1 to 2.
Further, using the electric double layer capacitor produced above, the change with time of the electrostatic capacity was measured by the above method. The results are shown in Table 2. Table 2 and FIG. 1 show changes with time in the capacitance retention rate (capacity retention rate (%)) when the capacitance at the start of discharge (at 0:00) is 100%. “Addition amount (parts by weight) of methyltetraglyme” in Table 1 is 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate shown in Table 1, or when propylene carbonate is used. Is the amount (parts by weight) of methyltetraglyme added to 100 parts by weight of the total of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate and propylene carbonate.

Example 6
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 1 part by weight of methyltriglyme was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 7
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 1 part by weight of ethyl diglyme was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 8
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 1 part by weight of propylene glycol dimethyl ether was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Example 9
With respect to 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 1 part by weight of perfluorotetraglyme was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Comparative Example 3
To 100 parts by weight of N-methyl-N-methoxymethylpyrrolidinium tetrafluoroborate, 1 part by weight of ethylene glycol was added and mixed to obtain an electrolytic solution. An electric double layer capacitor was produced in the same manner as in Example 1 except that this electrolytic solution was used.

Table 3 shows the compositions of the electrolytic solutions prepared in Examples 3 and 6 to 9 and Comparative Examples 1 and 3.
Further, using the electric double layer capacitor produced above, the change with time of the electrostatic capacity was measured by the above method. The results are shown in Table 4. Table 4 and FIG. 2 show changes with time in the capacitance retention rate (capacity retention rate (%)) when the capacitance at the start of discharge (0 o'clock) is 100%. “Addition amount of additive (parts by weight)” in Table 3 is the addition amount (parts by weight) of the additive with respect to 100 parts by weight of the ionic liquid shown in Table 3.

  As shown in Tables 2 and 4 and FIGS. 1 and 2, the electric double layer capacitor manufactured in each example was charged by applying a higher voltage of 3 V than the electric double layer capacitor of the comparative example. Even so, the capacitance retention rate was high and the durability was excellent.

  The present invention is useful in the field of electrochemical devices.

1 Aluminum tab 2 Laminate 3 Electrode 4 Separator

Claims (4)

Ionic liquid and the following formula (1)

(Wherein R ¹ and R ² are the same or different and each represents a linear or branched alkyl group or a fluorinated alkyl group having 1 to 4 carbon atoms, and R ^{3 to} R ¹⁰ are the same or different and represent hydrogen atom, a fluorine atom, are both .m and n represents a methyl group or a fluorinated methyl group and an integer of 0 or more, and m + n is an electric double layer containing a compound represented by 1 to 6.) In the electrolyte for capacitors ,
The amount of the compound represented by the formula (1) is 0.5 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of components other than the compound in the electrolytic solution for electric double layer capacitors. Electrolyte for electric double layer capacitor . The ionic liquid is represented by the following formula (2)

(Wherein R ¹¹ , R ¹² and R ¹³ are the same or different and each represents a linear or branched alkyl group having 1 to 4 carbon atoms, and R ¹¹ and R ¹² may form a ring. R ¹⁴ is, .p represents an alkyl group having a carbon 1 or 2, .X showing a 1 or 2 ^-. is characterized by a quaternary ammonium salt represented by showing a fluorine-containing anion) according Item 2. An electrolytic solution for an electric double layer capacitor according to Item 1 . The ionic liquid is represented by the following formula (3)

(Wherein, R ¹⁵ represents a linear or branched alkyl group having 1 to 4 carbon atoms, R ¹⁶ represents a methyl group or an ethyl group, and Y ⁻ represents a fluorine-containing anion). The electrolytic solution for an electric double layer capacitor according to claim 1 , wherein the electrolyte solution is a quaternary ammonium salt. The electric double layer capacitor using the electrolyte solution in any one of Claim 1 to 3 .

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