JP2010153560A - Electrolyte using quaternary ammonium salt electrolyte, and electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolyte which excels in performance at a low-temperature environment and having a high withstand voltage, and to provide an electrochemical element which can be used stably at low temperatures and excels in long-term stability. <P>SOLUTION: The electrolyte for electrochemical element includes the electrolyte (B) containing a compound (A) expressed by a general expression (1); at least one kind of sulfolane derivative (S) containing a nonaqueous mixed solvent (H) and the solvent (H) is selected from among a group including sulfolane, 3-methylsulfolane, and 2,4-dimethyl sulfolane; and a chain carbonate ester (C) represented by general expression (2). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to an electrolytic solution for an electrochemical device using a quaternary ammonium salt electrolyte.

An electrochemical element stores electrochemical energy inside the element. Specifically, the electrochemical element stores a battery for taking out chemical energy stored inside the element as electric energy, and a static electricity stored inside the element. A capacitor for taking out electric energy as electric energy to the outside, a dye-sensitized solar cell, and the like.
Conventionally, the electrolyte of the capacitor BF ₄ salt of tetraethyl ammonium, BF ₄ salt of triethyl methyl ammonium or 1-ethyl-3-BF ₄ salt of methyl imidazolium have been used as an electrolyte. Particularly in new application fields such as hybrid electric vehicles that are used under severe conditions and with large currents, there is a demand for electrochemical elements that can be used stably even at low temperatures and have excellent long-term stability. There is an urgent need to develop an electrolytic solution that can be used in a low temperature environment and has a high withstand voltage (wide potential window).
Under such circumstances, an electrolytic solution having a high withstand voltage has been developed by using a solvent having high decomposition resistance such as sulfolane (for example, Patent Documents 1 and 2).
JP 08-306591 A JP 2005-260031 A

However, when the non-aqueous electrolyte described in Patent Documents 1 and 2 is used, the withstand voltage is improved, but it cannot be used because electrolyte deposition or solidification of the electrolyte occurs in a low temperature environment of −30 ° C. or lower. In some cases, fatal defects may occur as electrolytes for electrochemical devices, such as a decrease in electrical conductivity due to a rapid increase in viscosity even without solidification.
That is, an object of the present invention is to provide an electrolytic solution having excellent performance in a low temperature environment and having a high withstand voltage, and an electrochemical device excellent in long-term stability that can be used stably even at low temperatures. It is.

As a result of intensive studies to solve the above problems, the present inventors have reached the present invention. That is, the present invention is an electrolyte solution containing an electrolyte (B) containing the compound (A) represented by the general formula (1) and a non-aqueous mixed solvent (H), which is a non-aqueous mixture. The solvent (H) is at least one sulfolane derivative (S) selected from the group consisting of sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane, and a chain carbonate ester represented by the general formula (2) ( An electrolytic solution for an electrochemical element comprising C);

［Ｒ^１はハロゲン原子、水酸基、ニトロ基、シアノ基及びエーテル結合を有する基からなる群より選ばれる少なくとも１種の基を有していてもよい炭素数１〜１０の１価炭化水素基である。Ｒ²はハロゲン原子、ニトロ基、シアノ基及びエーテル結合を有する基からなる群より選ばれる少なくとも１種の基を有していてもよい炭素数１〜１０の１価炭化水素基、水素原子、又はハロゲン原子である。Ｒ³〜Ｒ^１４は、炭素数１〜５のアルキル基、炭素数１〜５のフルオロアルキル基、水素原子、又はハロゲン原子である。Ｒ³〜Ｒ^１４は同じでも異なっていてもよい。ｈ、ｉ、ｊ、ｘ、ｙ及びｚは０〜６の整数であり、同じでも異なっていてもよい。ｈ＋ｘは０〜６の整数、ｉ＋ｙ及びｊ＋ｚは１〜６の整数である。Ｘ⁻は対アニオンを表し、該対アニオンの第一原理分子軌道計算によるＨＯＭＯエネルギーが、−０．６０〜−０．２０ａ.u.である。］

[R ¹ is a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have at least one group selected from the group consisting of a halogen atom, a hydroxyl group, a nitro group, a cyano group and a group having an ether bond. is there. R ² is a halogen atom, a nitro group, a cyano group and a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have at least one group selected from the group consisting of groups having an ether bond, a hydrogen atom, Or it is a halogen atom. R ^{3 to} R ¹⁴ are an alkyl group having 1 to 5 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, a hydrogen atom, or a halogen atom. R ^{3 to} R ¹⁴ may be the same or different. h, i, j, x, y, and z are integers of 0 to 6, and may be the same or different. h + x is an integer of 0-6, i + y and j + z are integers of 1-6. X ⁻ represents a counter anion, and the HOMO energy of the counter anion according to the first principle molecular orbital calculation is −0.60 to −0.20 a.u. ]

［Ｒ^１５とＲ^１６は炭素数１〜５のアルキル基であり、Ｒ^１５とＲ^１６は異なる基である。］
及び該電解液を用いた電気化学素子である。

[R ¹⁵ and R ¹⁶ are alkyl groups having 1 to 5 carbon atoms, and R ¹⁵ and R ¹⁶ are different groups. ]
And an electrochemical element using the electrolytic solution.

An electrochemical element using the electrolytic solution for an electrochemical element of the present invention can be used stably even at a low temperature with a high withstand voltage, and is excellent in long-term stability.

The present invention is described in detail below.
The compound (A) represented by the general formula (1) is a quaternary group consisting of a cation group having a specific ring structure in which the nitrogen at the cation center is sterically protected by an alkyl group, and an anion group having a high oxidation potential. Since it is an ammonium salt, it has a high LUMO value in the molecular orbital calculation and a high HOMO value of the anion group as compared with the electrolytes of the prior art, and is not easily subjected to redox. As a result, the difference between the oxidation potential and the reduction potential is large, electrochemically stable, and the withstand voltage of the electrolyte is very high.

In the cation species (a) of the compound (A) represented by the general formula (1), R ¹ is a halogen atom, a hydroxyl group, a nitro group, a cyano group, and a group having an ether bond (hereinafter referred to as a functional group Y). A monovalent hydrocarbon group having 1 to 10 carbon atoms which may have at least one group selected from the group consisting of a linear aliphatic hydrocarbon group and a branched aliphatic hydrocarbon. Groups, alicyclic hydrocarbon groups, aromatic hydrocarbon groups and the like. Specific examples of R ¹ are given below.

When the hydrocarbon group is a linear aliphatic hydrocarbon group: a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, an n-hexyl group, an n-decyl group, and a functional group Y Examples of the group include a hydroxymethyl group, a 1-hydroxyethyl group, a 2-hydroxyethyl group, a nitromethyl group, a nitroethyl group, a cyanomethyl group, a cyanoethyl group, a methoxymethyl group, and a methoxyethyl group.

When the hydrocarbon group is a branched aliphatic hydrocarbon group: iso-propyl group, 2-methylpropyl group, 2-butyl group, 2-pentyl group, 2-methylbutyl group, 3-methylbutyl group, 3-pentyl group, 2 -Methylbutyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 4-methylpentyl, 3-heptyl, 2-ethylbutyl, 3-methylpentyl, 3-hexyl, 2 A 2-hydroxy-iso-propyl group as the group having -ethylhexyl group, 1,2-dimethylbutyl, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group and 2-ethyloctyl group, and functional group Y 1-hydroxy-2-methylpropyl group, 2-amino-iso-propyl group, 2-nitro-iso-propyl group, 1-nitro-2-methyl group Propyl group, 2-cyano -iso- propyl group, 1-cyano-2-methylpropyl group, 2-methoxy -iso- propyl, and 1-methoxy-2-methylpropyl group and the like.

When the hydrocarbon group is a cyclic hydrocarbon group: a cyclohexyl group, a 1-methylcyclohexyl group, a 2-methylcyclohexyl group, a 3-methylcyclohexyl group, a 4-methylcyclohexyl group, and a group having a functional group Y are 1- Examples thereof include a hydroxycyclohexyl group, a 2-hydroxycyclohexyl group, a 3-hydroxycyclohexyl group, a 4-hydroxycyclohexyl group, a 1-methoxycyclohexyl group, a 2-methoxycyclohexyl group, a 3-methoxycyclohexyl group, and a 4-methoxycyclohexyl group.

When the hydrocarbon group is an aromatic hydrocarbon group: a phenyl group, a toluyl group, a benzyl group, and the like can be given.

The hydrocarbon group having a halogen atom is preferably a fluoroalkyl group, and the fluoroalkyl group is a group represented by C _n F _{2n + 1} (n is an integer of 10 or less), a trifluoromethyl group, a pentafluoroethyl group. And a heptafluoropropyl group.

Of these R ^1, a linear or branched aliphatic hydrocarbon group, an aliphatic hydrocarbon group having a group having an ether bond, and a fluoroalkyl group are preferable. More preferred are a methyl group, an ethyl group, a methoxyethyl group, a trifluoromethyl group and a pentafluoroethyl group. Particularly preferred are a methyl group, an ethyl group, a trifluoromethyl group and a pentafluoroethyl group. Highly preferred is a methyl group.

In General Formula (1), R ² is a monovalent group having 1 to 10 carbon atoms that may have at least one group selected from the group consisting of a halogen atom, a nitro group, a cyano group and a group having an ether bond. It is a hydrocarbon group, a hydrogen atom, or a halogen atom, and the same functional group as R ¹ , a hydrogen atom, a halogen atom, etc. are mentioned.
Of these R ^2, a hydrogen atom, a linear or branched aliphatic hydrocarbon group and a fluoroalkyl group are preferred. More preferred are a hydrogen atom, a methyl group, an ethyl group, a methoxyethyl group, a trifluoromethyl group and a pentafluoroethyl group. Particularly preferred are a hydrogen atom, a methyl group, an ethyl group, a trifluoromethyl group, and a pentafluoroethyl group. Very preferred is a hydrogen atom.

R ³ to R ¹⁴ in the general formula (1) is an alkyl group having 1 to 5 carbon atoms, fluoroalkyl group having 1 to 5 carbon atoms, a hydrogen atom or a halogen atom, an alkyl group having 1 to 5 carbon atoms Includes a linear aliphatic hydrocarbon group and a branched aliphatic hydrocarbon group. R ^{3 to} R ¹⁴ may be the same or different.

Specific examples of R ^{3 to} R ¹⁴ include methyl group, ethyl group, n-propyl group, n-butyl group, n-pentyl group, iso-propyl group, 2-methylpropyl group, 2-butyl group, 2- Pentyl group, 2-methylbutyl group, 3-methylbutyl group, 3-pentyl group, 2-methylbutyl group, trifluoromethyl group, pentafluoroethyl group, n-heptafluoropropyl group, hydrogen atom, fluorine atom, chlorine atom, bromine An atom, an iodine atom, etc. are mentioned. Among these, preferred are a methyl group, an ethyl group, an n-propyl group, a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl, a hydrogen atom, and a fluorine atom. More preferably, they are a methyl group, a trifluoromethyl group, a hydrogen atom, or a fluorine atom. Particularly preferred are a hydrogen atom and a fluorine atom. Very preferred is a hydrogen atom.

In the general formula (1), h, i, j, x, y, and z are integers of 0 to 6, and may be the same or different. h + x is an integer of 0-6, i + y and j + z are integers of 1-6. Preferably, i + y and j + z are integers of 2 or 3, and h + x is 2 or 1 or 0. More preferably, x, y and z are 0, i and j are integers of 2 or 3, and h is 2 or 1 or 0.
From the viewpoint of electrochemical stability, N-methyl-1-azabicyclo [2,2,2] octane-ium, N is preferable as the cation species (a) of the compound (A) represented by the general formula (1). -Ethyl-1-azabicyclo [2,2,2] octane-ium, N-methyl-1-azabicyclo [2,2,1] heptane-ium, N-ethyl-1-azabicyclo [2,2,1] heptane -Ium, N-trifluoromethyl-1-azabicyclo [2,2,2] octane-ium, N-trifluoromethyl-1-azabicyclo [2,2,1] heptane-ium and the like.

The tertiary amine used as a raw material of the compound (A) can be synthesized by a known method. In general,
(1) By heating a tribromoalkyl compound obtained by brominating a cyclic ether such as tetrahydrofuran or tetrahydropyran having a hydroxylalkyl group with hydrogen bromide to 130 to 150 ° C in methanol and ammonia in a sealed tube. , A method of detaching and cyclizing HBr,
(2) A dihalogenated primary amine compound obtained by reacting a hydrogen halide with a cyclic ether such as tetrahydrofuran or tetrahydropyran having an aminoalkyl group is added dropwise to a 0.1N aqueous sodium hydroxide solution to effect halogenation. A method of performing an intramolecular cyclization reaction by desorption of hydrogen,
(3) A cyclic secondary amine such as piperidine or pyrrolidine having a carboxyalkyl group is reduced with lithium aluminum hydride or the like, or an aromatic amine such as pyridine having a carboxyalkyl group is reduced with sodium and ethanol. A cyclic secondary amine having an alkyl group is obtained. Furthermore, by reacting a hydrohalic acid such as hydrogen bromide or hydroiodic acid, the hydroxyl group is substituted to obtain a halide. A method of synthesizing a tertiary amine by dropping the halogenated cyclic secondary amine compound into a 0.1N aqueous sodium hydroxide solution and carrying out an intramolecular cyclization reaction by elimination of the hydrogen halide;
(V. Prelog, Ann., 545, 229 (1940)).

Compound (A) is a known production method, for example, a method in which the tertiary amine compound is quaternized with a carbonate ester such as dialkyl carbonate, and the resulting carbonate salt is exchanged with a counter anion (X ⁻ ). (For example, Japanese Patent Laid-Open No. 61-239616). It can also be obtained by a method in which a tertiary amine is quaternized with an alkyl halide and the resulting halide salt is subjected to anion exchange.

The electrolyte (B) preferably contains 50 to 100% by weight, more preferably 70 to 100% by weight of the compound (A).
The electrolyte (B) may contain, in addition to the compound (A), another organic salt compound (D) different from the compound (A). Other organic salt compounds (D) include alkyl ammonium salts, amidinium salts (such as imidazolium salts), and the like. Specifically, for example, BF ₄ salt and PF ₆ salt of an alkyl ammonium, a BF ₄ salt and PF ₆ salts of imidazolium. For example, tetraethylammonium BF ₄ salt, triethylmethylammonium BF ₄ salt, 1,2,3-trimethylimidazolium BF ₄ salt and 1-ethyl-2,3-dimethylimidazolium BF ₄ salt, 1,2,3,4 Examples include tetramethylimidazolium BF ₄ salt. The amount of the other organic salt compound (D) is preferably 0 to 50% by weight, more preferably 5 to 25% by weight, based on the weight of the electrolyte (B).

The electrolyte (B) may contain various additives (E). As the additive (E), LiBF ₄ , LiPF ₆ , phosphoric acids and derivatives thereof (phosphoric acid, phosphorous acid, phosphoric esters, phosphonic acids, etc.), boric acids and derivatives thereof (boric acid, boric acid oxide, Boric acid esters, complexes of boron and compounds having a hydroxyl group and / or carboxyl group, etc., nitrates (lithium nitrate, etc.) and nitro compounds (nitrobenzoic acid, nitrophenol, nitrophenetole, nitroacetophenone, aromatic nitro compounds) Etc.). From the viewpoint of electrochemical stability and conductivity, the amount of additive (E) is preferably 50% by weight or less, more preferably 20% by weight or less, based on the weight of the electrolyte (B).

The anion component (counter anion X ⁻ ) of the compound (A) represented by the general formula (1) will be described. X ^-. Is, the HOMO energy (. Hereinafter abbreviated as HOMO energy) by the first principle molecular orbital calculation, in the range of -0.60~-0.20a.u, preferably -0.60～- Counter anion in the range of 0.25 a.u. Here, the HOMO (highest occupied molecular orbital) energy by first-principles molecular orbital calculation is a semi-empirical molecular orbital method by performing conformational analysis on the calculated anion by force field calculation. This value is calculated by the HartleyFock method with the basis function of 6-31G (d) after structural optimization by AM1. Gaussian 03 (manufactured by Gaussian) is used as the calculation program (Reference 1: “Exploration of Chemistry by Electronic Structure Theory (Second Edition), James B. Foresman, AElen Frisch, Kenzo Tazaki, Gaussian, Inc.)” .

Specific examples of the counter anion X ⁻ whose HOMO energy calculated by the above method is in the range of −0.60 to −0.20 a.u. include BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , PCl ₆ ⁻ , BCl ₄ ⁻ , AsCl ₆ ⁻ , SbCl ₆ ⁻ , TaCl ₆ ⁻ , NbCl ₆ ⁻ , PBr ₆ ⁻ , BBr ₄ ⁻ , AsBr ₆ ⁻ , AlBr ₄ ⁻ , TaBr ₆ ⁻ , NbBr ₆ ⁻ , SbF ₆ ⁻ , AlF ₄ ⁻ , ClO ₄ ⁻ , AlCl ₄ ⁻ , TaF ₆ ⁻ , NbF ₆ ⁻ , CN ⁻ , F (HF) _n ⁻ (wherein n represents a numerical value of 1 or more and 4 or less), N ( ^{_{RfSO 3) 2 -, C (}} RfSO 3) 3 -, RfSO 3 -, RfCO 2 - and the like.
^{_{N (RfSO 3) 2 -,}} C (RfSO 3) 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 pentafluoroethyl, heptafluoropropyl, and nonafluorobutyl. Of these, trifluoromethyl, pentafluoroethyl and heptafluoropropyl are preferable, trifluoromethyl and pentafluoroethyl are more preferable, and trifluoromethyl is particularly preferable.
Among the above counter anions, from the viewpoint of electrochemical stability, a counter anion having a small HOMO energy by first-principles molecular orbital calculation is preferable, and is represented by BF ₄ ⁻ , PF ₆ ^— or N (RfSO ₃ ) ₂ ^—. that counter anion, more preferably PF ₆ ^- or BF ₄ ^- represented by counter anion, particularly preferably BF ₄ ^- is a counter anion represented by.
The counter anion preferably has a small HOMO energy, but no compound having a value lower than −0.60 a.u. (hereinafter sometimes abbreviated as a.u.) is not known, and substantially. , PF6 @ - (HOMO energy ^{_{= -0.39), BF 4 - (}} HOMO energy ^{_{= -0.35), CF 3 SO 3}} - (HOMO energy = -0.27) is preferred. Conversely, a counter anion having a HOMO energy greater than −0.20 a.u. (small negative value) such as formic acid, acetic acid, benzoic acid (HOMO energy = −0.18), phthalic acid, succinic acid (HOMO) Carboxylic acid anions such as energy = −0.18), I ⁻ (HOMO energy = −0.16), Cl ⁻ (HOMO energy = −0.12), F ⁻ (HOMO energy = −0.08), etc. Inorganic anions are low in electrochemical stability of the electrolyte, and therefore, when used as an electrolytic solution, the withstand voltage is low, the long-term reliability is poor, and it is not useful as an electrochemical element.

Preferred examples of the compound (A) (cation component + anion component) include N-methyl-1-azabicyclo [2,2,2] octane-ium, N-ethyl-1-azabicyclo [2,2,2] octane -Ium, N-methyl-1-azabicyclo [2,2,1] heptane-ium, N-ethyl-1-azabicyclo [2,2,1] heptane-ium, N-trifluoromethyl-1-azabicyclo [2 , 2,2] octane-ium, BF _{4 of} N-trifluoromethyl-1-azabicyclo [2,2,1] heptane-ium cation species N-methyl-1-azabicyclo [2,2,2] octane-ium salts, cationic species N- ethyl-1-azabicyclo [2,2,2] octane - BF ₄ salt ium, cationic species N- methyl-1-azabicyclo [2,2,1] heptane - BF ₄ salt ium, Mosquito On species N- ethyl-1-azabicyclo [2,2,1] heptane - BF ₄ salt ium, cationic species N- trifluoromethyl-1-azabicyclo [2,2,2] octane - BF ₄ salt ium, BF ₄ salt of cationic species N-trifluoromethyl-1-azabicyclo [2,2,1] heptane-ium, PF ₆ salt of cationic species N-methyl-1-azabicyclo [2,2,2] octane-ium the cationic species N- ethyl-1-azabicyclo [2,2,2] octane - PF ₆ salt ium, cationic species N- methyl-1-azabicyclo [2,2,1] heptane - PF ₆ salt ium, cationic seed N- ethyl-1-azabicyclo [2,2,1] heptane - PF ₆ salt ium, cationic species N- trifluoromethyl-1-azabicyclo [2,2,2] octane - PF ₆ salt ium, cationic A PF ₆ salt of ium - N- trifluoromethyl-1-azabicyclo [2,2,1] heptane.
Among these, particularly preferred are BF ₄ salt of the cationic species N-methyl-1-azabicyclo [2,2,2] octane-ium, and the cationic species N-methyl-1 from the viewpoint of electrochemical stability. - azabicyclo [2,2,1] heptane - BF ₄ salt ium, cationic species N- trifluoromethyl-1-azabicyclo [2,2,2] octane - BF ₄ salt ium, cationic species N- trifluoroacetic methyl-1-azabicyclo [2,2,1] heptane - is BF ₄ salt ium.

The electrolytic solution for electrochemical elements (F) of the present invention comprises an electrolyte (B) and at least one sulfolane derivative (S) selected from the group consisting of sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane, It contains a solvent comprising a mixed solvent (H) with the chain carbonate ester (C) represented by the general formula (2).
Since the sulfolane derivative (S) has a high viscosity as a solvent for an electrolytic solution, it has a problem of low electrical conductivity and high internal resistance when an electrochemical element is produced. ) Can be used to lower the viscosity of the electrolytic solution. As a result, the conductivity of the electrolytic solution can be improved and the internal resistance of the electrochemical device can be reduced. Conventional quaternary ammonium electrolytes have problems such as insolubility in non-aqueous mixed solvent (H) or precipitation at low temperature, but compound (A) is soluble in non-aqueous mixed solvent (H). Therefore, the electrolyte is hardly deposited even at a low temperature, and the performance can be stably exhibited in a wide temperature range.

Examples of the chain carbonate (C) include those represented by the general formula (2). R ¹⁵ and R ¹⁶ in the general formula are alkyl groups having 1 to 10 carbon atoms, and R ¹⁵ and R ¹⁶ are different. Specific examples of the chain carbonate ester (C) include ethyl methyl carbonate, methyl isopropyl carbonate, ethyl isopropyl carbonate, 2,2,2-trifluoroethyl-methyl carbonate, and the like.

The electrolyte solution (F) for an electrochemical device of the present invention has a volume of the sulfolane derivative (S) of 76 to 95% by volume and a chain carbonate ester (C) with respect to the volume of the non-aqueous mixed solvent (H) at 25 ° C. The volume is preferably 5 to 24% by volume, more preferably (S) is 80 to 90% by volume, and (C) is 10 to 20% by volume. In this concentration range, an electrolyte having a very high withstand voltage can be obtained although the solubility at a low temperature is slightly reduced.

The non-aqueous mixed solvent (H) may contain a non-aqueous solvent (G) other than the chain carbonate ester (C). Preferred examples of the nonaqueous solvent (G) include the following (G1) to (G3).

Examples of the non-aqueous solvent (G1) include esters represented by the general formula (3).

R ¹⁷ and R ¹⁸ in the general formula (3) are aliphatic hydrocarbon groups having 1 to 10 carbon atoms, such as alkyl groups and cycloalkyl groups, and R ¹⁷ and R ¹⁸ may be the same or different. Also good. Alternatively, R ¹⁷ and R ¹⁸ may be bonded to each other to form a ring. Specific examples of the non-aqueous solvent (G1) include the following.
Carboxylic acid esters: methyl acetate, methyl propionate, etc.
Lactones: γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone, and the like.
Of these, methyl propionate and γ-butyrolactone are preferred.

Examples of the non-aqueous solvent (G2) include benzene derivatives having a molecular weight of 400 or less represented by the general formula (4).

The benzene derivative (G2) used in the present invention is represented by the above general formula (4) and has a molecular weight of 400 or less. The molecular weight of (G2) is preferably 300 or less, more preferably 92 to 200. When the molecular weight of (G2) exceeds 400, the viscosity of (G2) increases and is not suitable as a solvent, and (G2) less than 92 does not exist.
R ¹⁹ is a halogen atom (fluorine atom, chlorine atom, bromine atom) or an organic group (g) having 1 to 7 carbon atoms.
If the organic group (g) has 8 or more carbon atoms, the benzene derivative (G2) becomes a solid at room temperature, which is not suitable for an electrolyte solvent.
R ²⁰ and R ²¹ are a hydrogen atom, a halogen atom, or an organic group (g) having 1 to 7 carbon atoms. R ¹⁹ , R ²⁰ and R ²¹ may be the same or different. If the organic group (g) has 8 or more carbon atoms, the benzene derivative (G2) becomes a solid at room temperature, which is not suitable for an electrolyte solvent.

The organic group (g) of the benzene derivative (G2) is, for example, a nitrile group, an organosilyl group, a perfluoroalkyl group, or an ester bond, an ether bond, a carbonate bond, a sulfonyl bond, a fluorine atom, a chlorine atom, a bromine atom, A nitrile group, an alkyl group which may have an organosilyl group, etc., and having 1 to 7 carbon atoms. Among these, preferred are a nitrile group, an organosilyl group, a perfluoroalkyl group, or an alkyl group which may have an ester bond, an ether bond, a carbonic acid ester bond, a sulfonyl bond, or a nitrile group.
Examples of the alkyl group having an ester bond include —C (═O) OCH ₃ ,
_{-C (= O) OC 2 H} 5, -CH 2 OC (= O) CH 3, -CH 2 C (= O) OCH 3
Etc.
Examples of the alkyl group having an ether bond include a methoxy group, an ethoxy group, and a methoxymethyl group.
Examples of the alkyl group having a carbonate ester bond include —OC (═O) OCH ₃ ,
_{-OC (= O) OCH 2 CH} 3, etc. -CH 2 -OC (= O) OCH 3 and the like.
Examples of alkyl groups having a sulfonyl bond include
_{-S (= O) 2 -CH 3} , -S (= O) such as 2 _-CH 2 CH ₃ and the like.
Examples of the alkyl group having a nitrile group include —CH ₂ —CN.
Examples of the organosilyl group include —CH ₂ —Si (CH ₃ ) ₃ , —Si (CH ₃ ) _{3 and the} like.

Specific examples of the benzene derivative (G2) include the following.
Toluene, xylene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, 1,3,5 -Trichlorobenzene, 2-chlorotoluene, 3-chlorotoluene, 4-chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1-chloro-2-fluorobenzene, 1-chloro-2-fluorobenzene, bromobenzene, benzotrifluoride, 2-methylbenzotrifluoride, 4-chlorobenzotrifluoride, benzonitrile, phthalo Nitrile, 2-fluorobenzonitrile, 4-cyanobenzene Zotrifluoride, phenylacetonitrile, benzyl chloride, benzyl bromide, α-chloro-o-xylene, alkyl benzoate (eg, methyl benzoate, ethyl benzoate, etc.), dialkyl phthalate (eg, dimethyl phthalate, Ethyl methyl phthalate, diethyl phthalate, etc.), methyl o-toluate, methyl m-toluate, methyl p-toluate, dimethyl isophthalate, dimethyl terephthalate, methoxybenzene, methoxymethylbenzene, methylphenyl carbonate, methylphenyl Sulfone, trimethylphenylsilane, etc.
The benzene derivative (G2) is preferably a liquid at 25 ° C. or higher.
Further, the viscosity of the benzene derivative (G2) at 20 ° C. (viscosity measured with a Brookfield viscometer. For example, it can be measured with a TV-22 type viscometer manufactured by Toki Sangyo Co., Ltd.) is preferably 0. 0.1 mPa · s to 6 mPa · s, more preferably 0.2 mPa · s to 2 mPa · s.
Of the above, toluene, chlorobenzene, benzotrifluoride, and benzonitrile are preferable.

Examples of the non-aqueous solvent (G3) include nitrile derivatives represented by the general formula (5).

R ²² is an aliphatic hydrocarbon group having 1 to 2 carbon atoms which may have 1 to 2 cyano groups or an ether bond, and examples thereof include an alkyl group and a cycloalkyl group. Specific examples of the non-aqueous solvent (G3) include the following.
Nitriles: acetonitrile, propionitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile and the like. Of these, acetonitrile and propionitrile are preferred.

The non-aqueous mixed solvent (H) is a solvent selected from the group consisting of a sulfolane derivative (S), a chain carbonate ester (C), and an ester solvent (G1), a benzene derivative (G2), and a nitrile derivative (G3). And the three kinds of solvents are preferable because the capacity retention rate is high.

Examples of the non-aqueous solvent (G) include the following in addition to (G1) to (G3).
Ethers: chain ether [carbon number 2-6 (diethyl ether, methyl isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.); carbon number 7-12 (diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.)], cyclic ether [C2-C4 (tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, etc.); C5-C18 (4-butyldioxolane, crown ether, etc.)].
Amides: N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, N-methylpyrrolidone and the like.
Carbonic acid esters: ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, methyl ethyl carbonate, diethyl carbonate and the like.
Sulfoxides: dimethyl sulfoxide, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, etc.
・ Nitro compounds: Nitromethane, nitroethane, etc.
-Heterocyclic solvent: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.
Ketones: acetone, 2,5-hexanedione, cyclohexanone, etc.
-Phosphate esters: trimethyl phosphoric acid, triethyl phosphoric acid, tripropyl phosphoric acid and the like.

The water content in the electrolytic solution of the present invention is preferably 300 ppm or less, more preferably 100 ppm or less, particularly preferably 50 ppm or less based on the weight of the electrolytic solution from the viewpoint of electrochemical stability. Within this range, it is possible to suppress the deterioration in performance of the electrochemical capacitor over time.
The water content in the electrolytic solution can be measured by the Karl Fischer method (JIS K0113-1997, coulometric titration method).
Examples of the method for setting the water content in the electrolytic solution in the above range include a method using a sufficiently dried electrolyte (B) and a non-aqueous solvent sufficiently dehydrated in advance.
Examples of the drying method include heating and drying under reduced pressure (for example, heating at 150 ° C. under reduced pressure of 20 Torr), evaporating and removing a trace amount of water contained therein, recrystallization, and the like.
As the dehydration method, heat dehydration under reduced pressure (for example, heating at 100 Torr) to evaporate and remove a trace amount of water, molecular sieve (manufactured by Nacalai Tesque, 3A 1/16, etc.), activated alumina powder And a method using a dehydrating agent such as
In addition to these, the electrolytic solution is heated and dehydrated under reduced pressure (for example, heated at 100 ° C. under reduced pressure of 100 Torr) to evaporate and remove a trace amount of water, molecular sieve, activated alumina powder, etc. And a method of using a dehydrating agent. These methods may be performed alone or in combination. Of these, the method of highly purifying the electrolyte (B) by recrystallization and further heating and drying (B) under reduced pressure, and the method of adding molecular sieve to the non-aqueous solvent (C) or the electrolytic solution are preferable.

The electrolytic solution of the present invention can be used for electrochemical devices. An electrochemical element shows an electrochemical capacitor, a secondary battery, a dye-sensitized solar cell, etc. An electrochemical capacitor includes an electrode, a current collector, and a separator as basic components, and optionally includes a case, a gasket, and the like that are generally used for capacitors. The electrolytic solution is impregnated into the electrode and the separator, for example, in a glove box in an argon gas atmosphere (dew point −50 ° C.). 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.

As a basic structure of the electric double layer capacitor, a separator is sandwiched between two polarizable electrodes and impregnated with an electrolytic solution. The main component of the polarizable electrode is preferably a carbonaceous material such as activated carbon, graphite, and polyacene organic semiconductor because it is electrochemically inert to the electrolyte and has an appropriate electrical conductivity. Thus, at least one of the positive electrode and the negative electrode is a carbonaceous material. A porous carbon material (for example, activated carbon) having a specific surface area of 10 m ² / g or more determined by the BET method by the nitrogen adsorption method is more preferable because of the large electrode interface where charges are accumulated. 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 it has a specific surface area determined is 30~2,500m ² / g by the BET method, since the electrostatic capacity per volume is large, the specific surface area is particularly preferably activated carbon 300~2,300m ² / g.

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.

Examples of the electrochemical capacitor of the present invention include a coin type, a wound type, and a rectangular type. The electrolytic solution for electrochemical capacitors of the present invention can be applied to any electric double layer capacitor or any aluminum electrolytic capacitor.

EXAMPLES Next, specific examples of the present invention will be described, but the present invention is not limited thereto. Hereinafter, “parts” means “parts by weight” unless otherwise specified.
In the following examples, 1H-NMR, 19F-NMR and 13C-NMR were measured by the following methods.
Measurement conditions for 1H-NMR Instrument: AVANCE 300 (manufactured by Nippon Bruker Co., Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz.
Measurement conditions for 19F-NMR Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz
Measurement conditions for 13C-NMR Instrument: AL-300 (manufactured by JEOL Ltd.), solvent: deuterated dimethyl sulfoxide, frequency: 300 MHz

<Production Example 1>
Manufacture of electrolyte (A-1) and synthesis of iodide salt 1-Azabicyclo [2,2,2] octane (manufactured by Sigma-Aldrich Japan) 113 parts and 339 parts of acetone were charged into a glass beaker and uniformly dissolved. . While stirring the solution, 156 parts of methyl iodide was slowly added dropwise, and stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 255 parts of an iodide salt of the cation species (a-1) represented by the general formula (6).

-Preparation of AgBF ₄ solution A solution obtained by mixing 116 parts of silver oxide and 209 parts of 42 wt% aqueous borofluoric acid solution at 100 ° C under reduced pressure was dissolved in 550 parts of methanol, and dissolved in AgBF ₄ methanol. A solution was obtained.
-Preparation of BF ₄ salt 745 parts of the above AgBF ₄ solution was slowly added dropwise to a mixed solution of 253 parts of the iodide salt (a-1) and 253 parts of methanol, and then filtered to collect the filtrate. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 206 parts of white crystals. After adding 600 parts of methanol and dissolving at 30 ° C., it was cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried at 80 ° C. under reduced pressure to obtain 147 parts of electrolyte (A-1). As a result of analysis by 1H-NMR, 19F-NMR and 13C-NMR, the electrolyte (A-1) was a BF ₄ salt of a cationic species (a-1). From the integral value of 1H-NMR, the purity was 99%.

<Production Example 2>
Production of Electrolyte (A-2) Preparation of AgPF ₆ Solution In Example 1, 243 parts of 60% by weight HPF ₆ aqueous solution was mixed with 116 parts of silver oxide instead of 42% by weight borohydrofluoric acid aqueous solution, and the pressure was reduced at 100 ° C. after dehydration, added to and dissolved 550 parts of methanol to obtain a methanol solution of AgPF _6.
-Preparation of PF ₆ salt After gradually mixing 803 parts of the above AgPF ₆ solution with a mixed solution of 253 parts of the iodide salt of (a-1) and 255 parts of methanol, the filtrate was collected by filtration. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. After adding 600 parts of methanol to the obtained solid, it was cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 194 parts of electrolyte (A-2). As a result of analysis by 1H-NMR, 19F-NMR and 13C-NMR, the electrolyte (A-2) was a PF ₆ salt of the cation species (a-1). From the integral value of 1H-NMR, the purity was 99%.

<Production Example 3>
Production of Electrolyte (A-3) Preparation of AgCF ₃ SO ₃ Solution In Example 1, 250 parts of a 60 wt% CF ₃ SO ₃ H aqueous solution was mixed with 116 parts of silver oxide instead of the 42 wt% borohydrofluoric acid aqueous solution. After dehydration under reduced pressure, 550 parts of methanol was added and dissolved to obtain an AgCF ₃ SO ₃ methanol solution.
Preparation of CF ₃ SO ₃ salt After gradually mixing 807 parts of the above AgCF ₃ SO ₃ solution with 253 parts of iodide salt of cation species (a-1) and methanol, the filtrate was filtered and the filtrate was filtered. It was collected. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was removed at 80 ° C. under reduced pressure to obtain 265 parts of white crystals. After adding 600 parts of methanol to the obtained solid, it was cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and desolvated at 80 ° C. under reduced pressure to obtain 196 parts of electrolyte (A-3). As a result of analysis by 1H-NMR, 19F-NMR and 13C-NMR, the electrolyte (A-3) was a CF ₃ SO ₃ salt of the cation species (a-1). From the integral value of 1H-NMR, the purity was 99%.

<Production Example 4>
Production of electrolyte (A-4) Synthesis of 1-azabicyclo [2,2,1] heptane 110 parts of 4-pyridinemethanol (manufactured by Sigma-Aldrich Japan) and 1000 parts of ethanol are mixed, and 250 parts of sodium are gradually added. And refluxed for 6 hours. The solution was cooled and 250 parts of water was added. Ethanol was evaporated under reduced pressure, and 200 parts of diethyl ether was added to the residue for extraction. Desolvation under reduced pressure was performed at 30 ° C. to obtain a colorless viscous solution. To 114 parts of this solution, 250 parts of concentrated hydroiodic acid was gradually added dropwise and refluxed for another 3 hours. After adding 350 parts of 50% sodium hydroxide to this solution, it was heated at 50 ° C. for 3 hours. Thereafter, the mixture was cooled to 30 ° C., and 800 parts of diethyl ether was added to this solution for extraction. Sodium carbonate was added for dehydration, and diethyl ether was removed under reduced pressure at 10 ° C., followed by distillation. As a result of analyzing the fraction by 1H-NMR, it was found that the raw material disappeared and 1-azabicyclo [2,2,1] heptane was generated. The yield was 40%.
Synthesis of iodide salt 100 parts of 1-azabicyclo [2,2,1] heptane obtained and 300 parts of acetone were charged into a glass beaker and uniformly dissolved. While stirring the solution, 156 parts of methyl iodide was slowly added dropwise, and stirring was continued at 30 ° C. for 3 hours. The precipitated white solid was filtered and dried at 80 ° C. under reduced pressure to obtain 242 parts of an iodide salt of the cation species (a-2) represented by the general formula (7).

A methanol solution of AgBF ₄ was obtained in the same manner as in Production Example 1.
-Preparation of BF ₄ salt 745 parts of the above AgBF ₄ solution was slowly added dropwise to a mixed solution of 239 parts of the iodide salt of (a-2) and 239 parts of methanol, and then filtered to collect the filtrate. . An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 194 parts of white crystals. After adding 600 parts of methanol to the crystal and dissolving at 30 ° C., it was cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 138 parts of electrolyte (A-4). As a result of analysis by 1H-NMR, 19F-NMR and 13C-NMR, the electrolyte (A-4) was a BF ₄ salt of a cationic species (a-2). From the integral value of 1H-NMR, the purity was 99%.

<Production Example 5>
The electrolyte was mixed with prepared · AgPF ₆ solution prepared in Production Example 4 in 42% by weight of silver oxide 116 parts of HPF ₆ solution 243 parts of 60 wt% instead of fluoroboric acid aqueous solution (A-5), 100 ℃ vacuum after dehydration, added to and dissolved 550 parts of methanol to obtain a methanol solution of AgPF _6.

-Preparation of PF ₆ salt 803 parts of the above AgPF ₆ solution was gradually mixed with a mixed solution of 253 parts of the iodide salt (a-2) and 255 parts of methanol, and then filtered to collect the filtrate. An AgBF ₄ solution or an iodide salt solution was added little by little to the filtrate to finely adjust the silver ion content in the solution to 10 ppm or less and the iodine ion content to 5 ppm or less, and then filtered to collect the filtrate. The filtrate was desolvated at 80 ° C. under reduced pressure to obtain 262 parts of white crystals. After adding 600 parts of methanol to the obtained solid, it was cooled to −5 ° C. and allowed to stand for 12 hours for recrystallization. The precipitated crystals were filtered and dried under reduced pressure at 80 ° C. to obtain 194 parts of electrolyte (A-5). As a result of analysis by 1H-NMR, 19F-NMR and 13C-NMR, the electrolyte (A-5) was a PF ₆ salt of a cationic species (a-2). From the integral value of 1H-NMR, the purity was 99%.

<Production Example 6>
-Production of electrolyte (A-6) 100 parts of pyrrolidine (manufactured by Wako Pure Chemical Industries) and 97 parts of potassium carbonate were charged into a Teflon (registered trademark) -coated autoclave, and 1,4-dichlorobutane (manufactured by Wako Pure Chemical Industries) 179 Part was added and reacted at 90 ° C. for 8 hours. To this reaction solution, 294 parts of a 42 wt% aqueous borofluoric acid solution (manufactured by Stella Chemifa) was gradually added dropwise at 25 ° C. over about 30 minutes. After the completion of the dropping and the generation of bubbles was stopped, the whole solvent was distilled off at 20 Torr and 100 ° C. to obtain 195 parts of a solid. This solid was crystallized twice using ethanol (manufactured by Nacalai Tesque) and 2-propanol (manufactured by Nacalai Tesque), and an electrolyte salt of spiro- (1,1 ′)-bipyrrolidinium ion BF ₄ ⁻ (A- 6) 136 parts were obtained.

Electrolyte solvent dehydration All the electrolyte solvents used below were used after the following dehydration treatment.
After adding 3 parts of molecular sieve to 100 parts of the solvent to be used and drying it by leaving it at 25 ° C. for 60 hours, the molecular sieve was separated by filtration to obtain a dehydrated solvent.

<Example 1>
50 ml of dehydrated sulfolane, 50 ml of dehydrated ethyl methyl carbonate, and 20 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolyte solution. The water content of the electrolytic solution was 32 ppm.

<Example 2>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate, and 20 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 31 ppm.

<Example 3>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate and 25 g of electrolyte (A-2) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 26 ppm.

<Example 4>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate and 26 g of electrolyte (A-3) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolyte solution. The water content of the electrolytic solution was 19 ppm.

<Example 5>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate and 19 g of electrolyte (A-4) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 15 ppm.

<Example 6>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate and 24 g of electrolyte (A-5) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 15 ppm.

<Example 7>
50 ml of dehydrated sulfolane, 50 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated acetonitrile, and 30 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 37 ppm.

<Example 8>
76 ml of dehydrated sulfolane, 24 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated γ-butyrolactone, and 29 g of electrolyte (A-4) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 32 ppm.

<Example 9>
80 ml of dehydrated sulfolane, 20 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated chlorobenzene, and 30 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 22 ppm.

<Example 10>
80 ml of dehydrated sulfolane, 20 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated benzotrifluoride, and 30 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 25 ppm.

<Example 11>
80 ml of dehydrated sulfolane, 20 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated phenylacetonitrile, and 30 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 17 ppm.

<Example 12>
80 ml of dehydrated sulfolane, 20 ml of dehydrated ethyl methyl carbonate, 50 ml of dehydrated acetonitrile, and 30 g of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 34 ppm.

<Example 13>
40 ml of dehydrated sulfolane, 40 ml of dehydrated 3-methylsulfolane, 20 ml of dehydrated ethyl methyl carbonate, and 20 g of electrolyte (A-1) were uniformly mixed to obtain an electrolytic solution. The water content of the electrolytic solution was 19 ppm.

<Example 14>
60 ml of dehydrated sulfolane, 20 ml of dehydrated 2,4-dimethylsulfolane, 20 ml of dehydrated ethyl methyl carbonate, and 19 parts of electrolyte (A-4) were uniformly mixed to obtain an electrolytic solution. The water content of the electrolytic solution was 19 ppm.

<Comparative Example 1>
Dehydrated sulfolane (80 ml), dehydrated ethyl methyl carbonate (20 ml), and electrolyte (A-6) (20 g) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 32 ppm.

<Comparative example 2>
50 ml of dehydrated sulfolane, 50 ml of dehydrated ethyl methyl carbonate, and 20 g of tetraethylammonium BF ₄ (manufactured by Tokyo Chemical Industry Co., Ltd.) (A-7) as an electrolyte were uniformly mixed and dissolved at 25 ° C. to obtain an electrolyte solution. It was. The water content of the electrolytic solution was 32 ppm.

<Comparative Example 3>
50 ml of dehydrated sulfolane, 50 ml of dehydrated ethyl methyl carbonate, and 20 g of triethylmethyl ammonium BF ₄ (manufactured by Tokyo Chemical Industry Co., Ltd.) (A-8) as an electrolyte were uniformly mixed and dissolved at 25 ° C. Obtained. The water content of the electrolytic solution was 32 ppm.

<Comparative example 4>
100 parts of dehydrated sulfolane and 20 parts of electrolyte (A-1) were uniformly mixed to obtain an electrolytic solution. The water content of the electrolytic solution was 21 ppm.

<Comparative Example 5>
100 parts of dehydrated propylene carbonate and 20 parts of electrolyte (A-1) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 22 ppm.

<Comparative Example 6>
100 parts of dehydrated propylene carbonate and 25 parts of electrolyte (A-2) were uniformly mixed and dissolved at 25 ° C. to obtain an electrolytic solution. The water content of the electrolytic solution was 22 ppm.

In order to evaluate the characteristics of the electrolytic solution, the electrolytic solution was cooled from room temperature to −30 ° C. and allowed to stand for 3 hours, and the presence or absence of solidification of the electrolytic solution and precipitation of the electrolyte was visually confirmed.

Moreover, polarization measurement was performed using a glassy carbon electrode (manufactured by BAS, outer diameter 6 mm, inner diameter 1 mm) at a scanning potential speed of 5 mV / sec. The potential for Ag / Ag ⁺ reference electrode when a current of 10 μA / cm ² flows is an oxidation potential, and the potential for Ag / Ag ⁺ reference electrode when a current of −10 μA / cm ² flows is a reduction potential. The potential window was calculated from the difference in potential values. The potential window of the electrolytic solution indicates an electrochemically stable range of the electrolytic solution. An electrochemical element using an electrolytic solution having a wide potential window can be used in a wide voltage range. That is, it can be said that the withstand voltage is high.

The results are shown in Table 1. When the electrolyte was solidified by visual confirmation at −30 ° C., “solidification” was indicated, or “precipitation” was observed when precipitation was observed, and “no change” was indicated when solidification or precipitation was not observed.

As is clear from Table 1, the electrolytes of Examples 1 to 14 of the present invention have no solidification or precipitation at a low temperature of −30 ° C., and the potential window is as large as 6.9 V or more. It was shown that it can be used at a low temperature of 30 ° C. and has a high withstand voltage. Comparative Examples 1 to 3 cannot be used at low temperatures because electrolyte deposition occurs at low temperatures. Moreover, since the comparative example 4 is solidified at -30 degreeC, it cannot be used at low temperature.

Using the electrolytic solution of the present invention and the electrolytic solution of the comparative example, a three-electrode electric double layer capacitor (manufactured by Power System Co., Ltd., FIG. 1) was prepared. A charge / discharge cycle test was performed using this capacitor, and the capacitance, resistance, and leakage current were evaluated.

Powdered activated carbon (“MSP-20” manufactured by Kansai Thermal Chemical Co., Ltd.) was mixed with carbon black and polytetrafluoroethylene powder (PTFE). The weight ratio was 10: 1: 1.
The obtained mixture was kneaded for about 5 minutes in a mortar and rolled with a roll press to obtain an activated carbon sheet. The thickness of the activated carbon sheet was 400 μm. This activated carbon sheet was punched into a 20 mmφ disk shape to obtain an activated carbon electrode.

  A three-electrode electric double layer capacitor (manufactured by Power System Co., Ltd.) was assembled using the obtained activated carbon electrodes (positive electrode, negative electrode and reference electrode). These cells were dried in vacuum at 170 ° C. for 7 hours and cooled to 30 ° C. In a dry atmosphere, the electrolytes of <Examples 1 to 14> and <Comparative Examples 1 to 6> were injected into the cell, followed by vacuum impregnation to produce an electric double layer capacitor.

  Connect the charge / discharge test device (“CDT-5R2-4” manufactured by Power System Co., Ltd.) to the created electric double layer capacitor, perform constant current charging at 25 mA to the set voltage, and 25 mA 7200 seconds after the start of charging. A constant current discharge was performed at. This was carried out for 50 cycles at a set voltage of 3.3 V and 45 ° C., and the capacitance value and capacitance retention ratio (%) after the initial and 50 cycles of the cell, and the internal resistance and internal resistance after the initial and 50 cycles. The rate of increase (%) was measured and used as an indicator of long-term reliability. The test results are shown in Table 2.

As is clear from Table 2, the electric double layer capacitors using the electrolytic solutions of Examples 1 to 14 of the present invention are compared with the electric double layer capacitors using the electrolytic solutions of Comparative Examples 1 to 3, 5, and 6. Since the capacity retention after the cycle test is high and the internal resistance increase rate is low, it can be seen that the electrochemical capacitor using the electrolytic solution of the present invention has excellent long-term reliability. Comparative Example 4 has a high capacity retention rate and a low internal resistance increase rate as in Examples 1 to 14, but it can be used only for extremely limited applications because it solidifies at a low temperature.
The non-aqueous mixed solvent (H) is selected from the group consisting of a sulfolane derivative (S), a chain carbonate ester (C), and an ester solvent (G1), a benzene derivative (G2), and a nitrile derivative (G3). In the case of Examples 7 to 14 containing three kinds of solvents, the capacity retention rate is particularly high as shown in Table 2.
Therefore, it is clear that the long-term reliability of the electrochemical capacitor using the electrolytic solution of the present invention is drastically improved and a highly reliable electrochemical device can be constructed.

The quaternary ammonium salt electrolyte of the present invention can be used even in a low temperature environment and has a high withstand voltage. Therefore, by using the electrolytic solution of the present invention, an electrochemical element having excellent long-term stability that can be used stably even at low temperatures can be obtained. The electrochemical device of the present invention is applicable to electrochemical capacitors, secondary batteries, dye-sensitized solar cells and the like.

3 electrode type electric double layer capacitor

Claims (9)

An electrolyte solution containing an electrolyte (B) containing the compound (A) represented by the general formula (1) and a non-aqueous mixed solvent (H), wherein the non-aqueous mixed solvent (H) is And at least one sulfolane derivative (S) selected from the group consisting of sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane, and a chain carbonate ester (C) represented by the general formula (2). An electrolyte for an electrochemical element, characterized in that

[R ¹ is a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have at least one group selected from the group consisting of a halogen atom, a hydroxyl group, a nitro group, a cyano group and a group having an ether bond. is there. R ² is a halogen atom, a nitro group, a cyano group and a monovalent hydrocarbon group having 1 to 10 carbon atoms which may have at least one group selected from the group consisting of groups having an ether bond, a hydrogen atom, Or it is a halogen atom. R ^{3 to} R ¹⁴ are an alkyl group having 1 to 5 carbon atoms, a fluoroalkyl group having 1 to 5 carbon atoms, a hydrogen atom, or a halogen atom. R ^{3 to} R ¹⁴ may be the same or different. h, i, j, x, y, and z are integers of 0 to 6, and may be the same or different. h + x is an integer of 0-6, i + y and j + z are integers of 1-6. X ⁻ represents a counter anion, and the HOMO energy of the counter anion according to the first principle molecular orbital calculation is −0.60 to −0.20 a.u. ]

[R ¹⁵ and R ¹⁶ are alkyl groups having 1 to 5 carbon atoms, and R ¹⁵ and R ¹⁶ are different groups. ] The volume of the sulfolane derivative (S) is 76 to 95% by volume and the volume of the chain carbonate (C) is 5 to 24% by volume with respect to the volume of the non-aqueous mixed solvent (H) at 25 ° C. Electrolyte. In the general formula (1), the counter ion X ⁻ is BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , C (RfSO ₃ ) ₃ ⁻ and RfSO ₃ ⁻ (Rf). The electrolyte solution according to claim 1 or 2, which is at least one selected from the group consisting of a fluoroalkyl group having 1 to 12 carbon atoms. The electrolyte solution according to any one of claims 1 to 3, wherein the non-aqueous mixed solvent (H) further contains an ester solvent (G1) represented by the general formula (3).

[R ¹⁷ and R ¹⁸ are aliphatic hydrocarbon groups having 1 to 10 carbon atoms, and R ¹⁷ and R ¹⁸ may be the same or different. Alternatively, R ¹⁷ and R ¹⁸ may be bonded to each other to form a ring. ] The electrolyte solution according to any one of claims 1 to 4, wherein the non-aqueous mixed solvent (H) further contains a benzene derivative (G2) having a molecular weight of 400 or less represented by the general formula (4).

[Wherein, R ¹⁹ is a halogen atom or an organic group (g) having 1 to 7 carbon atoms, R ²⁰ and R ²¹ are a hydrogen atom, a halogen atom, or an organic group (g) having 1 to 7 carbon atoms. It is. R ¹⁹ , R ²⁰ and R ²¹ may be the same or different. ] The electrolyte solution according to any one of claims 1 to 5, wherein the non-aqueous mixed solvent (H) further contains a nitrile derivative (G3) represented by the general formula (5).

[R ²² is an aliphatic hydrocarbon group having 1 to 10 carbon atoms which may have 1 to 2 cyano groups or an ether bond. ] An electrochemical element using the electrolytic solution according to any one of claims 1 to 6. 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.

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