JP5096906B2 - Electrolytic solution for electrochemical capacitor and electrochemical capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte for an electrochemical capacitor, capable of dramatically improving bulging of the electrochemical capacitor with the passage of time by controlling hydrolysis reaction of a solvent in the electrolyte. <P>SOLUTION: This electrolyte for the electrochemical capacitor contains an electrolyte (A) including an imidazolium cation (a1) and an anion (a2), carboxylic acid methyl ester (B), and a nonaqueous solvent (C) other than the carboxylic acid methyl ester (B), and the electrolyte containing 1-11 weight% of (B) to the total weight of (A), (B) and (C) is used. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

The present invention relates to an electrolytic solution for an electrochemical capacitor and an electrochemical capacitor using the same. More particularly, the present invention relates to an electrochemical capacitor that is suitable for memory backup of various electronic devices and for electric power of an electric vehicle that requires a large current.

As an electrolytic solution for electrolytic capacitors with little deterioration in performance over time, an electrolytic solution containing a quaternary ammonium salt or quaternary phosphonium salt containing a boron anion as a solute is known (for example, Patent Document 1).
Further, as an electrolytic solution for an electrochemical capacitor (such as an electric double layer capacitor) with little deterioration in performance over time, an electrolytic solution in which a high dielectric constant solvent such as propylene carbonate and a low dielectric constant solvent such as dimethyl carbonate are mixed is known. (For example, Patent Document 2).
Furthermore, an electrolytic solution whose electric conductivity is improved by mixing an aliphatic monocarboxylic acid ester is known (for example, Patent Documents 3 and 4).
In addition, a capacitor is known in which the pH change of the electrolytic solution is suppressed by a pH buffering agent, and the amount of gas generated due to solvent decomposition of the electrolytic solution in the capacitor is reduced (for example, Patent Document 5).

JP-A-1-194313 JP 2006-156728 A Japanese Patent Laid-Open No. 9-7898 JP-A-11-135374 JP 2006-261516 A

In the conventional non-aqueous electrolyte, water in the electrolyte is involved in the hydrolysis reaction of the solvent to generate gas, which may cause the capacitor to swell (capacitor deterioration in performance over time). Further, in a capacitor mixed with an aliphatic monocarboxylic acid ester, there is a problem that the aliphatic monocarboxylic acid ester may permeate from the sealing rubber to the outside of the capacitor. In addition, a capacitor in which the pH change of the electrolytic solution is suppressed by a pH buffering agent includes a large amount of the buffering agent, so that the adverse effect of the buffering agent itself is greatly affected, and the durability of the capacitor is reduced.
An object of the present invention is to provide an electrolytic solution for an electrochemical capacitor that can drastically improve the swelling of the electrochemical capacitor over time by controlling the hydrolysis reaction of the solvent in the electrolytic solution. .

The electrolyte solution for electrochemical capacitors of the present invention is characterized by an electrolyte (A) composed of an imidazolium cation (a1) and an anion (a2) represented by the general formula (1),
An electrolytic solution for an electrochemical capacitor containing a carboxylic acid methyl ester (B) represented by the general formula (2) and a nonaqueous solvent (C) other than the carboxylic acid methyl ester (B),
The non-aqueous solvent (C) consists of ether, amide, nitrile, carbonate, sulfoxide, sulfone or nitro compound, or
It consists of propylene carbonate as a main solvent and dimethyl carbonate or ethyl methyl carbonate as a sub solvent, the main solvent is 70 to 90% by weight, the sub solvent is 10 to 30% by weight,
The point is that 1 to 11% by weight of (B) is contained with respect to the total weight of (A), (B) and (C).

［式中、Ｒ^１〜Ｒ^５は水酸基を有していてもよい炭素数１〜５の１価炭化水素基又は水素原子である。］

[In formula, R < ¹ > -R < ⁵ > is a C1-C5 monovalent hydrocarbon group or hydrogen atom which may have a hydroxyl group. ]

［式中、Ｒ^６は炭素数１〜４の１価炭化水素基である。］

[Wherein, R ⁶ represents a monovalent hydrocarbon group having 1 to 4 carbon atoms. ]

The feature of the electrochemical capacitor or the electric double layer capacitor of the present invention is that the above-described electrolytic solution is used.

The electrolytic solution for electrochemical capacitors of the present invention can remarkably control the hydrolysis reaction of the solvent in the electrolytic solution.
Therefore, the electrochemical capacitor using the electrolytic solution of the present invention can dramatically improve the swelling of the capacitor over time.

Since the electrochemical capacitor or the electric double layer capacitor of the present invention uses the above electrolytic solution, the hydrolysis reaction of the solvent in the electrolytic solution is remarkably controlled, and the swelling of the electrochemical capacitor over time is drastically improved. can do.

Hereinafter, the present invention will be described in more detail.
In general, the moisture inside the electrochemical capacitor is considered to be contained in the member or the electrolyte at the time of manufacturing the capacitor, or the moisture in the environment that has entered the interior from the sealed portion or the like over time. And these water | moisture content is electrolyzed in the positive electrode vicinity, and electrolyte solution becomes acidic.
Further, the hydrolysis reaction of the solvent is promoted in an acidic environment. Propylene carbonate, which is the most widely used solvent for electrochemical capacitors, mainly generates carbon dioxide by the hydrolysis reaction, which is a major factor in gas generation in the capacitor. Further, gas generation occurs even when a solvent other than propylene carbonate is used.

In the electrolytic solution for an electrochemical capacitor of the present invention, the amount of gas generated in the capacitor can be greatly reduced by the action of the carboxylic acid methyl ester (B) represented by the general formula (2), and reliability is improved. It can be a high and highly durable capacitor.

This carboxylic acid methyl ester (B) is presumed to act as follows. Since the reaction rate between the water in the electrolyte and the carboxylic acid methyl ester (B) is extremely fast compared to other non-aqueous solvents (such as esters), the carboxylic acid methyl ester (B) is preferentially hydrolyzed. However, the generated carboxylic acid has low acidity and does not become an acid that corrodes the electrode.
Therefore, it is considered that the carboxylic acid methyl ester (B) has a function of efficiently trapping moisture existing from the time of manufacture and moisture entering with time.

In the general formula (1), among R ^{1 to} R ⁵ , the monovalent hydrocarbon group having 1 to 5 carbon atoms which may have a hydroxyl group includes methyl, ethyl, propyl, isopropyl, propenyl, isobutyl, 2 , 2-dimethylpropyl, 2-hydroxyethyl and the like.
Of R ^{1 to} R ⁵ , methyl, ethyl, propyl, isopropyl, propenyl and hydrogen atoms are preferable, and methyl, ethyl and hydrogen atoms are more preferable.

Preferred specific examples of the imidazolium cation (a1) represented by the general formula (1) include N, N′-dimethylimidazolium, N-ethyl-N′-methylimidazolium, N, N′-diethylimidazolium, 1,2,3-trimethylimidazolium, 1,3,4-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-ethyl-3,4-dimethylimidazolium, 1-ethyl-3, 5-dimethylimidazolium, 2-ethyl-1,3-dimethylimidazolium, 4-ethyl-1,3-dimethylimidazolium, 1,2-diethyl-3-methylimidazolium, 1,4-diethyl-3- Methylimidazolium, 1,5-diethyl-3-methylimidazolium, 1,3-diethyl-2-methylimidazolium, 1,3- Ethyl-4-methylimidazolium, 1,2,3-triethylimidazolium, 1,3,4-triethylimidazolium, 1,2,3,4-tetramethylimidazolium, 1-ethyl-2,3,4 -Trimethylimidazolium, 1-ethyl-2,3,5-trimethylimidazolium, 1-ethyl-3,4,5-trimethylimidazolium, 2-ethyl-1,3,4-trimethylimidazolium, 4-ethyl -1,2,3-trimethylimidazolium, 1,2-diethyl-3,4-dimethylimidazolium, 1,3-diethyl-2,4-dimethylimidazolium, 1,4-diethyl-2,3-dimethyl Imidazolium, 1,4-diethyl-2,5-dimethylimidazolium, 2,4-diethyl-1,3-dimethylimidazolium, 4,5-di Til-1,3-dimethylimidazolium, 1,2,3-triethyl-4-methylimidazolium, 1,2,4-triethyl-3-methylimidazolium, 1,2,5-triethyl-3-methylimidazolium 1,3,4-triethyl-2-methylimidazolium, 1,3,4-triethyl-5-methylimidazolium, 1,4,5-triethyl-3-methylimidazolium and 1,2,3 4,5-pentamethylimidazolium and the like can be mentioned. Of these, 1-ethyl-2,3-dimethylimidazolium, 1,2,3-trimethylimidazolium and 1,2,3,4-tetramethylimidazolium are more preferable from the viewpoint of molecular size and the like. Since these more preferable cations have a small molecular size, the viscosity of the electrolytic solution is low, and it is easy to prepare an electrolytic solution with higher conductivity. Also, when R ² is an alkyl group having 1 to 4 carbon atoms, electrochemical stability of the imidazolium cation is significantly improved, the durability of the capacitor is greatly improved.

Examples of the anion (a2) include BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (FSO ₂ ) ₂ ⁻ , F ⁻ , ClO ₄ ⁻ , AlF ₄ ⁻ , AlCl ₄ ⁻ , TaF ₆ ⁻ , NbF ₆ ⁻ , SiF ₆ ⁻ , CN ⁻ , CH ₃ BF ₃ ⁻ , F (HF) _n ⁻ (n represents an integer of 1 to 4), PCl ₆ ⁻ , BCl ₄ ⁻ , AsCl ₆ ⁻ , SbCl ₆ ⁻ , TaCl ₆ ⁻ , NbCl ₆ ⁻ , PBr ₆ ⁻ , BBr ₄ ⁻ , AsBr ₆ ⁻ , AlBr ₄ ⁻ , TaBr ₆ ⁻ , NbBr ₆ ⁻ , I ⁻ , Cl ⁻ , N (RfSO ₂ ) ₂ ⁻ , C (RfSO _{2) 3} ^-, RfSO ₃ ^- or RfCO ₂ ^- anion, and the like represented.

^{_{Incidentally, N (RfSO 2) 2 -}} , C (RfSO 2) 3 -, RfSO 3 - or RfCO ₂ ^- Rf contained in the anions represented by represents a fluoroalkyl group having 1 to 12 carbon atoms, trifluoromethyl Examples include methyl, pentafluoroethyl, heptafluoropropyl, and nonafluorobutyl. Of these, trifluoromethyl, pentafluoroethyl and heptafluoropropyl are preferable, trifluoromethyl and pentafluoroethyl are more preferable, and trifluoromethyl is particularly preferable.

Among these anions, from the viewpoint of electrochemical stability and the like, BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₂ ) ₂ ⁻ , C (RfSO ₂ ) ₃ ⁻ , RfSO ₃ ^- (Rf is a fluoroalkyl group having 1 to 12 carbon ^{_{atoms), N (FSO 2) 2}} -, F -, ClO 4 -, AlF 4 -, AlCl 4 -, TaF 6 -, NbF 6 -, SiF 6 -, CN ⁻ , CH ₃ BF ₃ ^— and F (HF) _n ⁻ (n represents a number of 1 to 4) are preferable, and BF ₄ ⁻ , PF ₆ ⁻ , N (FSO ₂ ) ₂ ^— and CH ₃ are more preferable. BF ₃ ⁻ , particularly preferably BF ₄ ^— and PF ₆ ^— .

Examples of the electrolyte (A) include 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate, 1,2,3-trimethylimidazole among salts composed of a combination of imidazolium cation (a1) and anion (a2). 1-ethyl-2,3-dimethylimidazolium hexafluorophosphate, 1,2,3-trimethylimidazolium hexafluorophosphate, and 1, tetrafluoroborate, 1,2,3,4-tetramethylimidazolium tetrafluoroborate 2,3,4-tetramethylimidazolium hexafluorophosphate is preferred.
In addition, electrolyte (A) may be used independently and 2 or more types of mixtures may be sufficient as it.

The content (% by weight) of the electrolyte (A) is preferably 9 to 35, more preferably 10 to 31 with respect to the total weight of the electrolyte (A), the carboxylic acid methyl ester (B) and the nonaqueous solvent (C). Especially preferably, it is 14-27.

The concentration (mol / L) of the electrolyte (A) is preferably 0.5 to 2.0, more preferably 0.6 to 1.8, particularly preferably 0.8 to 1, based on the capacity of the electrolytic solution. .5.

In the general formula (2), R ⁶ is a monovalent hydrocarbon group having 1 to 4 carbon atoms such as methyl, ethyl, vinyl, ethynyl (CH≡C—), propyl, isopropyl, propenyl, n-butyl, isobutyl, etc. Is mentioned. Of these, methyl, ethyl, propyl, isopropyl and propenyl are preferable, ethyl, propyl, isopropyl and propenyl are more preferable, and ethyl, propyl and isopropyl are particularly preferable.

Preferable specific examples of the carboxylic acid methyl ester (B) include methyl acetate, methyl propionate, methyl n-butyrate, methyl isobutyrate, methyl n-valerate, methyl isovalerate, methyl acrylate, methyl methacrylate, 3 , Methyl 3-dimethylacrylate, methyl propiolate (CH≡CCO ₂ CH ₃ ) and methyl crotonic acid.

Of these, methyl acetate, methyl propionate, methyl n-butyrate, methyl isobutyrate, methyl n-valerate and methyl isovalerate are preferred, and more preferred are methyl acetate and propionic acid from the viewpoint of electrolyte solubility and the like. Methyl, methyl butyrate and methyl isobutyrate, particularly preferably methyl propionate, methyl butyrate and methyl isobutyrate, most preferably methyl propionate.
In addition, carboxylic acid methyl ester (B) may be used independently and 2 or more types of mixtures may be sufficient as it.

The content (% by weight) of the carboxylic acid methyl ester (B) is preferably from 1 to 11, more preferably from the total weight of the electrolyte (A), the carboxylic acid methyl ester (B) and the non-aqueous solvent (C). It is 5-10, Most preferably, it is 6-9. Beyond this range, the carboxylic acid methyl ester (B) is not only easily transmitted from the sealing rubber of the capacitor to the outside of the capacitor, but also the flash point of the electrolyte tends to be lowered. On the other hand, when it is less than this range, it becomes difficult to exhibit a sufficient effect.

The non-aqueous solvent (C) is not particularly limited as long as it is a non-aqueous solvent other than the carboxylic acid methyl ester (B), and known ones can be used. Solubility and electrochemical stability of the electrolyte salt (A) Can be selected as appropriate.
Examples of the non-aqueous solvent (C) include the following.

Ether: C4-12 chain ether (diethyl ether, methyl isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.) And cyclic ethers having 4 to 12 carbon atoms {tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, 4-butyldioxolane and crown ether (1,4,7,10,13,16-hexaoxacyclooctadecane, etc.) And so on.

Amides: chain amides having 3 to 6 carbon atoms (N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, etc.) and cyclic having 4 to 6 carbon atoms Amides (such as pyrrolidinone, N-methylpyrrolidinone and N-vinylpyrrolidinone).

Nitrile: Nitriles having 2 to 5 carbon atoms (acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, 3-ethoxypropionitrile, acrylonitrile, etc.).

Carbonate: C3-C4 chain carbonate (dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, etc.) and C3-C4 cyclic carbonate (ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc.).

-Sulfoxide: Sulfoxide having 2 to 6 carbon atoms (such as dimethyl sulfoxide and dipropyl sulfoxide).

Sulfone: Sulfone having 4 to 6 carbon atoms (sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, etc.).

Nitro compounds: nitromethane, nitroethane, etc.

Other cyclic compounds: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and the like.

Of these, carbonate, sulfone and nitrile are preferable, and propylene carbonate, acetonitrile, sulfolane, dimethyl carbonate and ethyl methyl carbonate are more preferable.

These non-aqueous solvents (C) may be a mixture of two or more, but in the case of a mixture, it is preferably composed of a main solvent and a sub-solvent. Propylene carbonate is preferred as the main solvent. As the auxiliary solvent, dimethyl carbonate and ethyl methyl carbonate are preferable, and dimethyl carbonate is more preferable. Preferable examples of the mixture include propylene carbonate and dimethyl carbonate, propylene carbonate and ethyl methyl carbonate.

Here, the main solvent means a solvent containing 50 to 99% by weight, preferably 70 to 90% by weight, of the nonaqueous solvent. On the other hand, the sub-solvent means a solvent containing 1 to 50% by weight, preferably 10 to 30% by weight, of the non-aqueous solvent.

The content (% by weight) of the nonaqueous solvent (C) is preferably 55 to 90, more preferably 60, based on the total weight of the electrolyte (A), the carboxylic acid methyl ester (B) and the nonaqueous solvent (C). ˜85, particularly preferably 64˜80.

Combinations of carboxylic acid methyl ester (B) and non-aqueous solvent (C) include methyl acetate and propylene carbonate, methyl acetate and acetonitrile, methyl acetate and sulfolane, methyl acetate and dimethyl carbonate, methyl acetate and ethyl methyl carbonate, propionic acid Methyl and propylene carbonate, methyl propionate and acetonitrile, methyl propionate and sulfolane, methyl propionate and dimethyl carbonate, methyl propionate and ethyl methyl carbonate, methyl n-butyrate and propylene carbonate, methyl n-butyrate and acetonitrile, n-butyric acid Methyl and sulfolane, n-methyl butyrate and dimethyl carbonate, n-methyl butyrate and ethyl methyl carbonate, methyl isobutyrate and propylene carbonate, methyl isobutyrate and alcohol Tonitrile, methyl isobutyrate and sulfolane, methyl isobutyrate and dimethyl carbonate, methyl isobutyrate and ethyl methyl carbonate, methyl n-valerate and propylene carbonate, methyl n-valerate and acetonitrile, n-methyl methyl valerate and sulfolane, n- Methyl valerate and dimethyl carbonate, n-methyl valerate and ethyl methyl carbonate, methyl isovalerate and propylene carbonate, methyl isovalerate and acetonitrile, methyl isovalerate and sulfolane, methyl isovalerate and dimethyl carbonate, and isoyoshi Methyl herbate and ethyl methyl carbonate are preferable, and from the viewpoints of solubility and electrochemical stability of the electrolyte (A), methyl acetate and propylene carbonate, methyl acetate and acetonitrile, methyl acetate and sulfo are more preferable. Methyl propionate and propylene carbonate, methyl propionate and acetonitrile, methyl propionate and sulfolane, methyl n-butyrate and propylene carbonate, methyl n-butyrate and acetonitrile, methyl n-butyrate and sulfolane, methyl isobutyrate and propylene carbonate, Methyl isobutyrate and acetonitrile and methyl isobutyrate and sulfolane, particularly preferably methyl propionate and propylene carbonate.

When the non-aqueous solvent (C) is a mixture of two kinds of solvents, the combination of the carboxylic acid methyl ester (B) and the non-aqueous solvent (C) includes methyl acetate, propylene carbonate and dimethyl carbonate, and methyl acetate and propylene carbonate. And ethyl methyl carbonate, methyl propionate and propylene carbonate and dimethyl carbonate, methyl propionate and propylene carbonate and ethyl methyl carbonate, methyl n-butyrate and propylene carbonate and dimethyl carbonate, methyl n-butyrate and propylene carbonate and ethyl methyl carbonate, Methyl butyrate and propylene carbonate and dimethyl carbonate, methyl butyrate and propylene carbonate and ethyl methyl carbonate, methyl n-valerate and propylene carbonate and di Preferred are til carbonate, n-methyl valerate, propylene carbonate and ethyl methyl carbonate, methyl isovalerate, propylene carbonate and dimethyl carbonate, and methyl isovalerate, propylene carbonate and ethyl methyl carbonate, more preferably methyl acetate and propylene carbonate. And dimethyl carbonate, methyl propionate and propylene carbonate and dimethyl carbonate, methyl n-butyrate and propylene carbonate and dimethyl carbonate, and methyl isobutyrate and propylene carbonate and dimethyl carbonate, particularly preferably methyl propionate, propylene carbonate and dimethyl carbonate, n -Methyl butyrate and propylene carbonate and dimethyl carbonate, and methyl butyrate and Pyrene carbonate and dimethyl carbonate, and most preferably methyl propionate, propylene carbonate and dimethyl carbonate.

The water content (ppm) in the electrolytic solution for an electrochemical capacitor of the present invention is preferably 300 or less based on the capacity of the electrolytic solution from the viewpoint of electrochemical stability (suppression of performance deterioration with time). Preferably it is 100 or less, particularly preferably 50 or less, then preferably 30 or less, then preferably 25 or less, then preferably 22 or less, most preferably 20 or less.
The water content can be measured by the Karl Fischer method (JIS K0113-1997, coulometric titration method).

As a method of bringing the water content in the electrolytic solution into the above range, a method of using a sufficiently dried electrolyte (A), a carboxylic acid methyl ester (B) and a nonaqueous solvent (C) sufficiently dehydrated in advance. Etc.

Examples of the drying method include a method of drying by heating under reduced pressure (for example, drying at 2.6 kPa and 150 ° C.) to evaporate and remove a trace amount of water contained therein.

As the dehydration method, dehydration heating dehydration (for example, heat drying at 13.3 kPa, 150 ° C.) to evaporate and remove a trace amount of water contained therein, and a dehydrating agent {Molecular Sieve (Nacalai Tesque Co., Ltd.) And 3A 1/16, etc.) and activated alumina powder, etc.}.

In addition to these methods, the electrolytic solution can be dehydrated by heating under reduced pressure (for example, 13.3 kPa, heat-dried at 100 ° C.) to evaporate a trace amount of water. And a method using a dehydrating agent (such as molecular sieve and activated alumina powder).

These methods may be performed alone or in combination. Among these, a method of drying the electrolyte (A) by heating under reduced pressure and a method of drying by adding a dehydrating agent (preferably molecular sieve) to the electrolytic solution are preferable.

The contents (concentration, purity, etc.) of the electrolyte (A) and the nonaqueous solvent (C) can be quantified by high performance liquid chromatography (HPLC) or the like (for example, according to the conditions exemplified in the Examples). A calibration curve can be created using the electrolyte (A) fractionated by preparative HPLC.
The carboxylic acid methyl ester (B) can be obtained indirectly by subtracting the contents of the electrolyte and the non-aqueous solvent from the total amount of the electrolytic solution, and can be directly quantified by gas chromatography or the like.

When quantifying by gas chromatography, for example, it can be quantified under the following conditions.
Apparatus: GC-17A, Shimadzu Corporation column: Capillary column DBWAX (LENGTH30m, ID0.53mm, FILM1.5μm), J & W Scientific carrier gas: Helium flow rate: 0.8ml / min.
Column temperature: 60 ° C. to (heating rate 5 ° C./min.)
Injection temperature: 200 ° C
Detection temperature: 230 ° C

The electrolyte solution for electrochemical capacitors of the present invention may contain various additives in addition to the electrolyte (A), the carboxylic acid methyl ester (B), and the nonaqueous solvent (C). Additives include phosphoric acid compounds (phosphoric acid, phosphorous acid, phosphoric acid ester, phosphonic acid, etc.), boric acid compounds (boric acid, boric acid oxide, boric acid ester, boron, hydroxyl group and / or carboxyl group) A complex with a compound), nitrates (lithium nitrate, etc.), nitro compounds (nitrobenzoic acid, nitrophenol, nitrophenetole, nitroacetophenone, aromatic nitro compounds, etc.) and the like. When the additive is contained, the content thereof is preferably 0.5 to 10% by weight, more preferably 1 to 5 based on the weight of the electrolyte (A) from the viewpoint of conductivity.

The electrolytic solution for an electrochemical capacitor of the present invention can be easily obtained by uniformly mixing the electrolyte (A), the carboxylic acid methyl ester (B), the non-aqueous solvent (C), and additives as required.

The electrolytic solution of the present invention can be used for an electrochemical capacitor. In addition to the electrolytic solution, the electrochemical capacitor includes an electrode, a current collector, and a separator as a basic configuration, and optionally includes a case, a gasket, a sealing rubber, and the like. The electrolyte is impregnated into the electrode and the separator in a glove box or the like in an inert gas atmosphere {argon gas atmosphere (dew point-50 ° C), etc.}.

The electrolytic solution of the present invention is suitable for an electric double layer capacitor (one using a polarizable electrode such as activated carbon) as an electrochemical capacitor among electrochemical capacitors. The electrolytic solution for electrochemical capacitors of the present invention can also be used for aluminum electrolytic capacitors. The basic structure of an aluminum electrolytic capacitor is that an oxide film is formed by electrochemical treatment on the surface of the aluminum foil that becomes the electrode, and this is used as a dielectric, and the electrolytic solution is impregnated between the aluminum foil that becomes the other electrode. Electrolytic paper is sandwiched between them

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

Examples of the electric double layer capacitor of the present invention include a coin type, a wound type, a laminated type, and a square type.

Hereinafter, although an example and a comparative example explain the present invention, the present invention is not limited to these. Hereinafter, unless otherwise specified, “parts” means “parts by weight”.

<Production Example 1>
96 parts of 2,4-dimethylimidazole (manufactured by Kanto Chemical Co., Inc.), 144 parts of tetrahydrofuran and 56 parts of potassium hydroxide were charged into a stainless steel autoclave with a cooling capacitor and uniformly dissolved to obtain a mixed solution. When 71 parts of methyl chloride was gradually added dropwise to this mixed solution, a temperature increase was observed with the reaction. Therefore, the mixture was added dropwise over about 2 hours so as to maintain the temperature at 40 ° C. ± 5 ° C. Aging was performed at 40 ± 5 ° C. for about 2 hours to obtain a reaction product. The reaction product was distilled to obtain 50 parts of 1,2,4-trimethylimidazole.

After 110 parts of 1,2,4-trimethylimidazole, 135 parts of dimethyl carbonate and 192 parts of methanol were charged in a stainless steel autoclave with a cooling condenser and uniformly dissolved, the atmosphere was replaced with nitrogen, and the temperature was raised to 130 ° C. in a sealed state. Started. Although the pressure was initially about 441 kPa, it gradually increased due to the generation of carbon dioxide gas. Therefore, the pressure was adjusted to about 686 kPa or less by appropriately venting the gas from the top of the cooling condenser. After 60 hours, the reaction solution was cooled to 30 ° C., and the solvent was distilled away from a part of the reaction solution. As a result of ¹ H-NMR analysis, the 1,2,4-trimethylimidazole signal disappeared, It was found that 2,3,4-tetramethylimidazolium monomethyl carbonate was produced almost quantitatively.

To 428 parts of the obtained reaction solution, 205 parts of a 42% by weight aqueous borofluoric acid solution was gradually added dropwise at 25 ° C. over about 30 minutes with stirring. Along with the dropping, bubbles of carbon dioxide gas were generated. After completion of the dropping and the generation of bubbles was stopped, the entire solvent was distilled off at 2.6 kPa and 150 ° C. to obtain an electrolyte (A1) {208 parts of a white solid}. This electrolyte (A1) was analyzed by ¹ H-NMR, ¹⁹ F-NMR, ¹³ C-NMR and HPLC. As a result, 1,2,3,4-tetramethylimidazolium tetrafluoroborate 97 mol% and other impurities 3 mol% Met.

<Production Example 2>
Charge 82 parts of 2-methylimidazole (Cureazole 2MZ-P, manufactured by Shikoku Kasei Kogyo Co., Ltd., "Curazole" is a registered trademark of the company), 144 parts of tetrahydrofuran and 56 parts of potassium hydroxide into a stainless steel autoclave with a cooling condenser. The solution was uniformly dissolved to obtain a mixed solution. Next, the temperature of the mixed solution was raised to 70 ° C., and 71 parts of ethyl chloride was gradually added dropwise. As a result, a temperature increase was observed with the reaction. Therefore, it took about 2 hours to keep the temperature at 70 ° C. ± 5 ° C. After completion of the dropwise addition, the mixture was aged at 70 ± 5 ° C. for about 2 hours to obtain a reaction product. This reaction product was distilled to obtain 50 parts of 1-ethyl-2-methylimidazole.

110 parts of 1-ethyl-2-methylimidazole, 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave equipped with a cooling condenser and dissolved uniformly, then purged with nitrogen, heated to 130 ° C. in a sealed state, and reacted. Started. Although the pressure was initially about 441 kPa, it gradually increased due to the generation of carbon dioxide gas. Therefore, the pressure was adjusted to about 686 kPa or less by appropriately venting the gas from the top of the cooling condenser. After 60 hours, the reaction solution was cooled to 30 ° C., and the solvent was distilled off from a part of the reaction solution. As a result of ¹ H-NMR analysis, the 1-ethyl-2-methylimidazole signal disappeared, It was found that ethyl-2,3-dimethylimidazolium monomethyl carbonate was produced almost quantitatively.

To 428 parts of the obtained reaction solution, 205 parts of a 42% by weight aqueous borofluoric acid solution was gradually added dropwise at 25 ° C. over about 30 minutes with stirring. Along with the dropping, bubbles of carbon dioxide gas were generated. After completion of dropping and generation of bubbles was stopped, the entire solvent was distilled off at 2.6 kPa and 150 ° C. to obtain an electrolyte (A2) {208 parts of white solid}. As a result of ¹ H-NMR, ¹⁹ F-NMR, ¹³ C-NMR and HPLC analysis, this electrolyte (A2) was found to contain 98 mol% of 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate and 2 mol% of other impurities. there were.

<Production Example 3>
96 parts of 1,2-dimethylimidazole (Cureazole 1.2DMZ, manufactured by Shikoku Kasei Kogyo Co., Ltd.), 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave with a cooling condenser and dissolved uniformly, and then purged with nitrogen. The reaction was started by raising the temperature to 130 ° C. in a sealed state. Although the pressure was initially about 441 kPa, it gradually increased due to the generation of carbon dioxide gas. Therefore, the pressure was adjusted to about 686 kPa or less by appropriately venting the gas from the top of the cooling condenser. After 60 hours, the reaction solution was cooled to 30 ° C., and the solvent was distilled off from a part of the reaction solution. As a result of ¹ H-NMR analysis, the 1,2-dimethylimidazole signal disappeared, It was found that 3-trimethylimidazolium monomethyl carbonate was produced almost quantitatively.

To 415 parts of the resulting reaction solution, 205 parts of a 42% by weight borohydrofluoric acid aqueous solution was gradually added dropwise at 25 ° C. over about 30 minutes with stirring. Along with the dropping, bubbles of carbon dioxide gas were generated. After the completion of the dripping and the generation of bubbles ceased, the entire solvent was distilled off at 2.6 kPa and 150 ° C. to obtain an electrolyte (A3) {194 parts of white solid}. As a result of ¹ H-NMR, ¹⁹ F-NMR, ¹³ C-NMR and HPLC analysis, this electrolyte (A3) was 1,2,3-trimethylimidazolium tetrafluoroborate 98 mol% and other impurities 2 mol%. .

<Example 1>
After uniformly dissolving 19 parts of the electrolyte (A2), 9 parts of methyl acetate (B1) and 72 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 Part was added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain the electrolytic solution (1) of the present invention.
In addition, the water | moisture content of this electrolyte solution was 20 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Example 2>
After uniformly dissolving 19 parts of the electrolyte (A2), 9 parts of methyl propionate (B2) and 72 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (2) of the present invention. The water content of this electrolytic solution was 20 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Example 3>
After uniformly dissolving 19 parts of the electrolyte (A2), 9 parts of n-methyl butyrate (B3) and 72 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16 3 parts were added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain the electrolytic solution (3) of the present invention. The water content of this electrolytic solution was 22 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Example 4>
After uniformly dissolving 19 parts of the electrolyte (A2) obtained in Production Example 2, 9 parts of methyl isobutyrate (B4) and 72 parts of propylene carbonate (C1), a molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 degreeC for 60 hours, and it dried, and obtained the electrolyte solution (4) of this invention. The water content of this electrolytic solution was 20 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Example 5>
After uniformly dissolving 19 parts of the electrolyte salt (A2), 9 parts of methyl valerate (B5) and 72 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16 3 parts were added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain the electrolytic solution (5) of the present invention. The water content of this electrolytic solution was 21 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Example 6>
After uniformly dissolving 17 parts of the electrolyte (A1) obtained in Production Example 1, 1 part of methyl propionate (B2) and 82 parts of propylene carbonate (C1), molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (6) of the present invention. The water content of this electrolytic solution was 22 ppm. The concentration of the electrolyte (A1) in the electrolytic solution was 1.0 mol / L.

<Example 7>
After uniformly dissolving 20 parts of the electrolyte (A1), 9 parts of methyl propionate (B2) and 71 parts of propylene carbonate (C1) obtained in Production Example 1, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts were added, and it was left to stand at 25 degreeC for 60 hours, and it dried, and obtained the electrolyte solution (7) of this invention. The water content of this electrolytic solution was 20 ppm. Moreover, the density | concentration of the electrolyte (A1) in electrolyte solution was 1.1 mol / L.

<Example 8>
After uniformly dissolving 21 parts of the electrolyte (A1), 10 parts of methyl propionate (B2) and 69 parts of propylene carbonate (C1) obtained in Production Example 1, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 degreeC for 60 hours, and it dried, and obtained the electrolyte solution (8) of this invention. The water content of this electrolytic solution was 17 ppm. In addition, the concentration of the electrolyte (A1) in the electrolytic solution was 1.2 mol / L.

<Example 9>
After 27 parts of the electrolyte (A1), 8 parts of methyl isobutyrate (B4), 55 parts of propylene carbonate (C1) and 10 parts of ethyl methyl carbonate (C2) obtained in Production Example 1 were uniformly dissolved, molecular sieve (Nacalai Tesque) 3 parts manufactured by 3A 1/16) were added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (9) of the present invention. The water content of this electrolytic solution was 25 ppm. Moreover, the density | concentration of the electrolyte (A1) in electrolyte solution was 1.5 mol / L.

<Example 10>
After uniformly dissolving 21 parts of the electrolyte (A2), 6 parts of n-methyl butyrate (B3) and 73 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16 3 parts were added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain the electrolytic solution (10) of the present invention. The water content of this electrolytic solution was 22 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.2 mol / L.

<Example 11>
After uniformly dissolving 18 parts of the electrolyte (A2), 10 parts of methyl isobutyrate (B4) and 72 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (11) of the present invention. The water content of this electrolytic solution was 21 ppm. Moreover, the density | concentration of the electrolyte (A2) in electrolyte solution was 1.0 mol / L.

<Example 12>
After uniformly dissolving 18 parts of electrolyte (A2), 11 parts of methyl propionate (B2) and 71 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts were added, and it was left to stand at 25 degreeC for 60 hours, and it dried, and obtained the electrolyte solution (12) of this invention. The water content of this electrolytic solution was 25 ppm. Moreover, the density | concentration of the electrolyte (A2) in electrolyte solution was 1.0 mol / L.

<Example 13>
After uniformly dissolving 16 parts of the electrolyte (A2) obtained in Production Example 2, 1 part of methyl propionate (B2) and 83 parts of propylene carbonate (C1), a molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts were added, and it was left to dry at 25 degreeC for 60 hours, and obtained the electrolyte solution (13) of this invention. The water content of this electrolytic solution was 25 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.9 mol / L.

<Example 14>
After uniformly dissolving 23 parts of the electrolyte (A2), 9 parts of methyl propionate (B2) and 68 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts were added, and it was left to stand at 25 degreeC for 60 hours, and it dried, and obtained the electrolyte solution (14) of this invention. The water content of this electrolytic solution was 25 ppm. Moreover, the density | concentration of the electrolyte (A2) in electrolyte solution was 1.3 mol / L.

<Example 15>
After uniformly dissolving 15 parts of the electrolyte (A2), 7 parts of methyl propionate (B2), 63 parts of propylene carbonate (C1) and 15 parts of dimethyl carbonate (C3) obtained in Production Example 2, molecular sieve (Nacalai Tesque Co., Ltd.) 3 parts made by company, 3A 1/16) were added, left to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (15) of the present invention. The water content of this electrolytic solution was 27 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.8 mol / L.

<Example 16>
After 14 parts of the electrolyte (A3), 8 parts of n-methyl butyrate (B3), 54 parts of propylene carbonate (C1) and 24 parts of dimethyl carbonate (C3) obtained in Production Example 3 were uniformly dissolved, molecular sieve (Nacalai Tesque) 3 parts of 3A 1/16) manufactured by Co., Ltd. was added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain the electrolytic solution (16) of the present invention. The water content of this electrolytic solution was 19 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 0.8 mol / L.

<Example 17>
After uniformly dissolving 17 parts of the electrolyte (A3), 9 parts of methyl acetate (B1) and 75 parts of propylene carbonate (C1) obtained in Production Example 3, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 A portion was added, and the mixture was allowed to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (17) of the present invention. The water content of this electrolytic solution was 25 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 1.0 mol / L.

<Example 18>
After uniformly dissolving 20 parts of the electrolyte (A3), 9 parts of methyl propionate (B2) and 71 parts of propylene carbonate (C1) obtained in Production Example 3, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 ° C. for 60 hours and dried to obtain an electrolytic solution (18) of the present invention. The water content of this electrolytic solution was 22 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 1.2 mol / L.

<Comparative Example 1>
After uniformly dissolving 19 parts of the electrolyte (A2) and 81 parts of propylene carbonate (C1) obtained in Production Example 2, 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H1). The water content of this electrolytic solution was 27 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.1 mol / L.

<Comparative example 2>
After uniformly dissolving 17 parts of the electrolyte (A1) obtained in Production Example 1 and 83 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H2). The water content of this electrolytic solution was 24 ppm. The concentration of the electrolyte (A1) in the electrolytic solution was 1.0 mol / L.

<Comparative Example 3>
After uniformly dissolving 19 parts of the electrolyte (A1) obtained in Production Example 1 and 81 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque Co., Ltd., 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H3). The water content of this electrolytic solution was 18 ppm. Moreover, the density | concentration of the electrolyte (A1) in electrolyte solution was 1.1 mol / L.

<Comparative example 4>
After uniformly dissolving 21 parts of the electrolyte (A1) obtained in Production Example 1 and 79 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque Co., Ltd., 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H4). The water content of this electrolytic solution was 16 ppm. In addition, the concentration of the electrolyte (A1) in the electrolytic solution was 1.2 mol / L.

<Comparative Example 5>
After 27 parts of the electrolyte (A1), 61 parts of propylene carbonate (C1) and 12 parts of ethyl methyl carbonate (C2) obtained in Production Example 1 were uniformly dissolved, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) Three parts were added, and the mixture was left to stand at 25 ° C. for 60 hours and dried to obtain a comparative electrolytic solution (H5). The water content of this electrolytic solution was 13 ppm. Moreover, the density | concentration of the electrolyte (A1) in electrolyte solution was 1.5 mol / L.

<Comparative Example 6>
After uniformly dissolving 21 parts of the electrolyte (A2) and 79 parts of propylene carbonate (C1) obtained in Production Example 2, 3 parts of molecular sieve (manufactured by Nacalai Tesque Co., Ltd., 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H6). The water content of this electrolytic solution was 18 ppm. The concentration of the electrolyte (A2) in the electrolytic solution was 1.2 mol / L.

<Comparative Example 7>
After uniformly dissolving 17 parts of the electrolyte (A2) obtained in Production Example 2 and 83 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) was added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolytic solution (H7). The water content of this electrolytic solution was 18 ppm. Moreover, the density | concentration of the electrolyte (A2) in electrolyte solution was 1.0 mol / L.

<Comparative Example 8>
After uniformly dissolving 16 parts of the electrolyte (A2) and 84 parts of propylene carbonate (C1) obtained in Production Example 2, 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H8). The water content of this electrolytic solution was 13 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.9 mol / L.

<Comparative Example 9>
After uniformly dissolving 22 parts of the electrolyte (A2) and 78 parts of propylene carbonate (C1) obtained in Production Example 2, 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H9). The water content of this electrolytic solution was 18 ppm. Moreover, the density | concentration of the electrolyte (A2) in electrolyte solution was 1.3 mol / L.

<Comparative Example 10>
After 14 parts of the electrolyte (A2), 68 parts of propylene carbonate (C1) and 18 parts of dimethyl carbonate (C3) obtained in Production Example 2 were uniformly dissolved, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 Part was added and allowed to stand at 25 ° C. for 60 hours and dried to obtain a comparative electrolytic solution (H10). The water content of this electrolytic solution was 11 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.8 mol / L.

<Comparative Example 11>
After 13 parts of the electrolyte (A3), 60 parts of propylene carbonate (C1) and 27 parts of dimethyl carbonate (C3) obtained in Production Example 3 were uniformly dissolved, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 A comparative electrolytic solution (H11) was obtained by allowing the mixture to stand and drying at 25 ° C. for 60 hours. The water content of this electrolytic solution was 19 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 0.8 mol / L.

<Comparative Example 12>
After uniformly dissolving 16 parts of the electrolyte (A3) and 84 parts of propylene carbonate (C1) obtained in Production Example 3, 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolytic solution (H12). The water content of this electrolytic solution was 29 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 1.0 mol / L.

<Comparative Example 13>
After uniformly dissolving 19 parts of the electrolyte (A3) obtained in Production Example 3 and 81 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque Co., Ltd., 3A 1/16) were added at 25 ° C. It was allowed to stand for 60 hours and dried to obtain a comparative electrolyte (H13). The water content of this electrolytic solution was 28 ppm. Moreover, the density | concentration of the electrolyte (A3) in electrolyte solution was 1.2 mol / L.

<Comparative example 14>
After 14 parts of the electrolyte (A2), 13 parts of methyl propionate (B2) and 73 parts of propylene carbonate (C1) obtained in Production Example 2 were uniformly dissolved, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 parts was added, and it was left to stand at 25 ° C. for 60 hours and dried to obtain a comparative electrolytic solution (H14). The water content of this electrolytic solution was 29 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.8 mol / L.

<Comparative Example 15>
After uniformly dissolving 16 parts of the electrolyte (A2), 17 parts of methyl acetate (B1) and 67 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) 3 A comparative electrolytic solution (H15) was obtained by leaving the mixture at 25 ° C. for 60 hours and drying. The water content of this electrolytic solution was 28 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.9 mol / L.

<Comparative Example 16>
After uniformly dissolving 17 parts of triethylmethylammonium tetrafluoroborate, 9 parts of methyl propionate (B2) and 74 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) are added. Then, it was allowed to stand at 25 ° C. for 60 hours and dried to obtain a comparative electrolytic solution (H16). The water content of this electrolytic solution was 21 ppm. The concentration of the electrolyte (tetraethylammonium tetrafluoroborate) in the electrolytic solution was 1.0 mol / L.

<Comparative Example 17>
After uniformly dissolving 28 parts of triethylmethylammonium hexafluoroantimonate, 9 parts of methyl propionate (B2) and 63 parts of ethylene carbonate, 3 parts of molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) were added, and 25 It was allowed to stand at 60 ° C. for 60 hours and dried to obtain a comparative electrolyte (H17). The water content of this electrolytic solution was 26 ppm. The concentration of the electrolyte (triethylmethylammonium hexafluoroantimonate) in the electrolytic solution was 1.0 mol / L.

<Comparative Example 18>
After uniformly dissolving 16 parts of the electrolyte (A2), 50 parts of methyl propionate (B2) and 34 parts of propylene carbonate (C1) obtained in Production Example 2, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16) Three parts were added, and the mixture was left to stand at 25 ° C. for 60 hours and dried to obtain a comparative electrolytic solution (H18). The water content of this electrolytic solution was 28 ppm. Further, the concentration of the electrolyte (A2) in the electrolytic solution was 0.8 mol / L.

<Comparative Example 19>
After uniformly dissolving 17 parts of triethylmethylammonium tetrafluoroborate and 83 parts of propylene carbonate (C1), 3 parts of molecular sieve (manufactured by Nacalai Tesque Co., Ltd., 3A 1/16) are added and allowed to stand at 25 ° C. for 60 hours to dry As a result, a comparative electrolytic solution (H19) was obtained. The water content of this electrolytic solution was 24 ppm. In addition, the concentration of the electrolyte (triethylmethylammonium tetrafluoroborate) in the electrolytic solution was 1.0 mol / L.
In addition, as an electrode used for the winding type electric double layer capacitor for evaluation described later, a polarizable electrode described in JP-A-2006-261516 (81% by weight of alkali activated carbon, 9% by weight of potassium carbonate, Denka Black 5) Wt% and polytetrafluoroethylene 5 wt%).

^The measuring devices used for ¹ H-NMR, ¹⁹ F-NMR, and ¹³ C-NMR are as follows.
¹ H-NMR: AVANCE 300 (manufactured by Nippon Bruker Co., Ltd.), 300 MHz, deuterated dimethyl sulfoxide
¹⁹ F-NMR, ¹³ C-NMR: AL-300 (manufactured by JEOL Ltd.), 300 MHz, deuterated dimethyl sulfoxide

The content (concentration or purity) of the electrolyte (A) and the non-aqueous solvent (B) was determined by diluting the measurement sample (electrolyte or electrolyte) 500 times with a mobile phase, and then using a hydrophilic filter (Advantech) with a pore size of 0.20 μm. The solution was filtered through Toyo Co., Ltd., DISMIC-13JP, PTFF non-sterile) to prepare a measurement solution, which was quantified under the following conditions by high performance liquid chromatography (HPLC). A calibration curve for the electrolyte was prepared using the electrolyte (A) collected by preparative HPLC.

HPLC instrument: LC-10A, Shimadzu Corporation column: Develosil C30-MG (4.6 mmφ × 25 cm), Shiseido mobile phase: phosphoric acid concentration 10 mmol / l, sodium perchlorate concentration 100 mmol / l Aqueous solution flow rate: 0.8 ml / min
Detector: UV (210 nm)
Injection volume: 20 μl
Column temperature: 40 ° C

Using the electrolytic solutions (1) to (18) of the present invention and the comparative electrolytic solutions (H1) to (H19), a wound electric double layer capacitor {a cylindrical shape having a diameter of 1.5 cm and a height of 3 cm } Was evaluated, and the rate of change in equivalent series resistance was evaluated by the following method. Further, the sealing rubber surface of the sealing body was observed, and the swelling of the capacitor was measured. Moreover, the permeation | transmission amount of carboxylic acid methyl ester was evaluated from the weight retention of electrolyte solution. These results are shown in Table 1.
Note that the wound electric double layer capacitor is equivalent to the wound electric double layer capacitor described in paragraph 0070 of Japanese Patent Application Laid-Open No. 2006-319322 and FIG. The weight (E ₀ ) of the contained electrolytic solution is 4.9 to 5.1 g.

(1) Capacitor swelling After applying a voltage of 2.7 V to the electric double layer capacitor for 3000 hours in an atmosphere of 60 ° C., the height (H ₃₀₀₀ ) (mm) of the electric double layer capacitor is measured, The difference (mm) between the height (H ₃₀₀₀ ) and the height (H ₀ ) (mm) before voltage application was defined as the swelling of the capacitor. The smaller this value is, the smaller the deterioration in performance over time, which means that good charge / discharge characteristics can be maintained.

(2) Measure the equivalent series resistance (RE ₃₀₀₀ ) at 1 kHz after applying a voltage of 2.7 V to the electric double layer capacitor for 3000 hours in an atmosphere where the change rate of the equivalent series resistance is 60 ° C. The ratio (%) {(RE ₃₀₀₀ ) × 100 / (RE ₀ )} of the equivalent series resistance (RE ₃₀₀₀ ) to the equivalent series resistance (RE ₀ ) at 1 kHz before voltage application is the change in equivalent series resistance. Rate. The equivalent series resistance was measured at 25 ° C. using an impedance analyzer (SI1253, SI1286 manufactured by Solartron, UK). The smaller this value is, the smaller the deterioration in performance over time, which means that good charge / discharge characteristics can be maintained.

(3) After applying a voltage of 2.7 V to the electric double layer capacitor for 3000 hours in an atmosphere having a weight retention of 60 ° C. for the electrolyte, the weight (M ₃₀₀₀ ) of the electric double layer capacitor is measured and before applying the voltage. Was defined as M _0, and {(E ₀ − (M ₀ −M ₃₀₀₀ )) × 100 / E ₀ } was defined as the weight retention rate (%) of the electrolytic solution. It means that carboxylic acid methyl ester (B) has permeate | transmitted from the sealing rubber, so that this value is small.

MA: methyl acetate MP: methyl propionate MB: n-methyl butyrate MIB: methyl isobutyrate MV: n-methyl valerate PC: propylene carbonate DMC: dimethyl carbonate EMC: ethyl methyl carbonate SL: sulfolane AN: acetonitrile H1: triethylmethyl Ammonium tetrafluoroborate H2: triethylmethylammonium hexafluoroantimonate

As is clear from Table 1, the electric double layer capacitors using the electrolytic solutions obtained in Examples 1 to 18 were compared with the electric double layer capacitors using the electrolytic solutions obtained in Comparative Examples 1 to 19. The swelling was low, the equivalent series resistance change rate was suppressed, and the weight retention rate of the capacitor was high. The swelling of the capacitor is caused by gas generation, and the equivalent series resistance change rate is estimated to increase mainly due to gas generation.
When the electrolytic solution obtained in Comparative Example 14, 15 or 18 is used, an electric double layer capacitor containing a large amount of carboxylic acid methyl ester (B) is obtained, but the swelling of the capacitor and the equivalent series resistance change rate are suppressed. The weight retention rate of the electrolyte was small. This is probably because a large amount of carboxylic acid methyl ester permeates from the sealing rubber and leaks out of the capacitor.

Comparative Examples 16 and 17 are examples in which a tetraalkylammonium salt is used as the electrolyte. However, the swelling of the capacitor and the equivalent series resistance change rate are significantly inferior compared to the case of using the electrolytic solution of the present invention. It was.
The electrolytic solution obtained in Comparative Example 19 was the same as a polarizable electrode (81% by weight of alkali activated carbon, 9% by weight of potassium carbonate, 5% by weight of Denka black and 5% by weight of polytetrafluoroethylene). However, the swelling of the capacitor and the rate of change of the equivalent series resistance were significantly inferior to those using the electrolytic solution of the present invention.

As described above, the electrolytic solution of the present invention remarkably suppresses the swelling of the capacitor and the rate of change of the equivalent series resistance, dramatically improves the deterioration of performance of the electric double layer capacitor over time, and provides a highly reliable electric double layer capacitor. It is clear that can be configured.

  Since the electrolytic solution of the present invention is excellent in suppressing the swelling of the capacitor due to the gas generation of the electrochemical capacitor, the electrochemical capacitor prepared using this electrolytic solution is more time-dependent than the conventional electrochemical capacitor. Secondary battery such as power storage element used in combination with power source for memory backup of various electronic devices, various power source backup power source, solar cell, because there is very little performance degradation, high reliability and high durability. It can be applied to a power storage device that substitutes for, a power source for driving a motor that requires a large current, a power source for a power tool such as an electric tool, and a power source for a power source for an electric vehicle.

Claims (8)

An electrolyte (A) composed of an imidazolium cation (a1) and an anion (a2) represented by the general formula (1);
An electrolytic solution for an electrochemical capacitor containing a carboxylic acid methyl ester (B) represented by the general formula (2) and a nonaqueous solvent (C) other than the carboxylic acid methyl ester (B),
The non-aqueous solvent (C) consists of ether, amide, nitrile, carbonate, sulfoxide, sulfone or nitro compound, or
It consists of propylene carbonate as a main solvent and dimethyl carbonate or ethyl methyl carbonate as a sub solvent, the main solvent is 70 to 90% by weight, the sub solvent is 10 to 30% by weight,
1 to 11% by weight of (B) with respect to the total weight of (A), (B) and (C).

[In formula, R < ¹ > -R < ⁵ > is a C1-C5 monovalent hydrocarbon group or hydrogen atom which may have a hydroxyl group. ]

[Wherein, R ⁶ represents a monovalent hydrocarbon group having 1 to 4 carbon atoms. ] The electrolyte solution according to claim 1, wherein the carboxylic acid methyl ester (B) is at least one selected from the group consisting of methyl acetate, methyl propionate, methyl butyrate and methyl isobutyrate. In imidazolium cation (a1), electrolyte according to claim 1 or 2 R ¹ to R ³ is a monovalent hydrocarbon group of 1 to 5 carbon atoms which may have a hydroxyl group in the general formula (1) liquid. The anion (a2) is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₂ ) ₂ ⁻ , C (RfSO ₂ ) ₃ ⁻ , RfSO ₃ ⁻ (Rf is fluoro having 1 to 12 carbon atoms) alkyl _{^{group), N (FSO 2) 2}} -, F -, ClO 4 -, AlF 4 -, AlCl 4 -, TaF 6 -, NbF 6 -, SiF 6 -, CN -, CH 3 BF 3 - and F ( _{HF) n} ^- (n electrolyte according to any one of claims 1 to 3 is at least one selected from the group consisting of indicating a number of 1 to 4). Non-aqueous solvent (C) is propylene carbonate, the electrolyte according to any one of claims 1-4 carboxylic acid methyl ester (B) is methyl propionate. The electrolyte solution according to any one of claims 1 to 4 , wherein the non-aqueous solvent (C) is propylene carbonate and dimethyl carbonate, and the carboxylic acid methyl ester (B) is methyl propionate. An electrochemical capacitor using the electrolytic solution according to any one of claims 1 to 6 . An electric double layer capacitor using the electrolytic solution according to any one of claims 1 to 6 .