JP2004221557A - Electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte that can control lowering of withstand voltage and volumetric lowering of a capacitor as well as an increase of internal resistance, and an electrochemical element using the same. <P>SOLUTION: This electrolyte is made of an electrolytic base (A), and its content in the electrolyte × 1 based on the weight of the electrolyte of carboxylic ammonium salt and/or carboxylic amine salt (al) is equal to or less than 1 wt%, and its content in the electrolyte × 2 based on the weight of the electrolyte of acid amide is equal to 1 wt%, and its content in the electrolyte × 3 based on the weight of the electrolyte of a cyclic amine compound (a3) is equal to or less than 3 weight %, and the sum of × 1 and × 2 and × 3 is equal to or more than 0.00001 wt% and equal to or less than 4 wt%. The electrolyte is useful as electrochemical element electrolyte for memory backups of various electronic devices, backup light sources for various light sources, capacitor devices such as a capacitor element, etc. used in combination with a solar cell, motor driving light sources requiring high current, e.g., for electric automobiles, electric-chemical capacitors used for a power tool light source for an electric power tool, etc., audio-visual systems, OA equipment, home appliances, onboard equipment electrolytic capacitors used for instruments/FA devices, etc., primary batteries, secondary batteries, sollar cells, fuel batteries, and so on. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to an electrolytic solution for an electrochemical element such as an electrochemical capacitor such as an electric double layer capacitor and a battery. More specifically, the present invention relates to an electrolytic solution for an electrochemical element having a high withstand voltage and a high energy density.

As a non-aqueous electrolyte for an electrochemical element, a solution in which a quaternary ammonium borofluoride or a quaternary phosphonium borofluoride is dissolved in a propylene carbonate solvent has been put to practical use.
When a quaternary ammonium salt or a quaternary phosphonium salt is used as an electrolyte for an electrochemical element, a strong alkali component generated on the surface of the cathode-side polarizable electrode or on the surface of the extraction lead connected to the cathode-side polarizable electrode. However, it is known that the use of a specific imidazolium salt in the electrolyte can suppress the generation of the strong alkali component. (For example, see Patent Document 1)

JP-A-11-054379 (page 3)

  However, when the above-mentioned imidazolium salt is used as the electrolyte of the electrolytic solution for an electrochemical element, there is a problem that the withstand voltage is low and not sufficient. The present invention has been made to solve this problem, and an object of the present invention is to provide an electrolytic solution for an electrochemical device having an improved withstand voltage.

The present inventors have conducted intensive studies in view of such circumstances, and as a result, the cause of this is that impurities in the electrolytic solution, particularly ammonium carboxylate and / or amine carboxylate (a1) derived from the electrolyte salt, and / or acid amide ( a2) and / or the cyclic amine compound (a3) and / or (a4) are contained. By reducing these, it is possible to suppress a decrease in withstand voltage, a decrease in capacitance of the capacitor, and an increase in internal resistance. The inventors have found that the present invention has been completed.
That is, the present invention
An electrolyte comprising the electrolyte salt (A), wherein the content of the ammonium carboxylate and / or amine carboxylate (a1) represented by the general formula (1) in the electrolyte is based on the weight of the electrolyte. x1 is 1% by weight or less, and
_{^{R 1 -CO 2 - · N +}} H 3 R 2 (1)
[In the formula, R ¹ may have one or more hydroxyl, amino, nitro, cyano, carboxyl, or formyl group, or may have one or more ether group in the main chain. A monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group) or a hydrogen atom; R ² is a monovalent hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom]
A content x2 of the acid amide (a2) represented by the general formula (2) in the electrolytic solution based on the weight of the electrolytic solution is 1% by weight or less, and
R ³ -CONHR ⁴ (2)
[Wherein, R ³ is the same as R ¹ above; R ⁴ is the same as R ² above]
The content x3 of the cyclic amine compound (a3) represented by the general formula (3) in the electrolytic solution based on the weight of the electrolytic solution is 3% by weight or less, and
[Wherein, R ⁵ , R ⁶ and R ⁷ may have one or more hydroxyl, amino, nitro, cyano, carboxyl, or formyl group, or have an amino group in the main chain. And / or a monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group), which may have one or more ether groups, or a hydrogen atom, X, Y and Z may have one or more hydroxyl, amino, nitro, cyano, carboxyl or formyl groups. Or a divalent hydrocarbon group having 1 to 10 carbon atoms which may be the same or different and may have one or more ether groups in the main chain]
An electrolytic solution characterized in that the sum of x1, x2, and x3 is 0.00001% by weight or more and 4% by weight or less; and an electrochemical element using the electrolytic solution.

  The electrolytic solution of the present invention has better electrochemical stability and higher withstand voltage than conventional electrolytic solutions. Further, the electric double layer capacitor using the electrolytic solution has a large residual voltage, is excellent in capacity retention, and has an effect of suppressing internal resistance.

Hereinafter, the present invention will be described in detail.
x1 is usually 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, and particularly preferably 0.01% by weight or less. If it exceeds 1% by weight, the withstand voltage may decrease or the capacity of the capacitor may decrease.
x2 is usually 1% by weight or less, preferably 0.5% by weight or less, more preferably 0.1% by weight or less, and particularly preferably 0.01% by weight or less. If it exceeds 1% by weight, the withstand voltage may decrease or the capacity of the capacitor may decrease.
x3 is usually at most 3% by weight, preferably at most 1.5% by weight, more preferably at most 0.3% by weight, particularly preferably at most 0.03% by weight. If it exceeds 3% by weight, the withstand voltage may decrease, or the capacity of the capacitor may decrease.
The sum of x1, x2 and x3 is usually 4% by weight or less, preferably 2% by weight or less, more preferably 0.4% by weight or less, particularly preferably 0.04% by weight or less, and usually 0.00001%. % By weight, preferably 0.0001% by weight or more, particularly preferably 0.001% by weight or more. If it exceeds 4% by weight, the withstand voltage may decrease, or the capacity of the capacitor may decrease.
x4 is preferably 5% by weight or less, more preferably 2% by weight or less, more preferably 0.5% by weight or less, particularly preferably 0.05% by weight or less from the viewpoint of the capacity of the capacitor.
The sum of x1, x2, x3 and x4 is preferably 8% by weight or less, more preferably 5% by weight or less, more preferably 0.8% by weight or less, particularly preferably 0.08% by weight from the viewpoint of the capacity of the capacitor. %, Preferably 0.00001% by weight or more, more preferably 0.0001% by weight or more, and particularly preferably 0.001% by weight or more.

  The electrolyte of the present invention comprises the electrolyte salt (A). (A) is a liquid having a fluidity of preferably 80 ° C. or lower, more preferably 50 ° C. or lower, particularly preferably 30 ° C. or lower. Further, in the electrolytic solution of the present invention, (A) is preferably further dissolved in a non-aqueous solvent (B).

  The electrolyte salt (A) is preferably an electrolyte salt obtained by further performing an anion exchange reaction on a quaternary ammonium salt (L1) produced by quaternizing imidazoles (L). Imidazoles (L) can be obtained by the reaction of an α-dicarbonyl compound, ammonia, aldehyde, and primary amine. In this reaction, ammonium carboxylate and / or amine carboxylate (a1) are produced as side reactions. It is also known that when a carboxylic acid ammonium salt and / or a carboxylic acid amine salt (a1) is heated, it is dehydrated to form an acid amide (a2). In addition, (a3) is generated by a condensation reaction between ammonia and an aldehyde. Further, the reaction of the quaternizing agent with (a2) produces (a4). Therefore, the imidazoles (L) produced by the reaction of the α-dicarbonyl compound, ammonia, aldehyde, and primary amine include (a1) and / or (a2) and / or (a3), and the imidazoles ( The electrolyte salt using L) contains (a1) and / or (a2) and / or (a3) and / or (a4) as impurities. For this reason, (a1) and / or (a2) and / or (a3) and / or (a4) are also contained in the electrolytic solution obtained by dissolving the electrolyte salt (A) as a solute in the nonaqueous solvent (B). Will be.

As a method for analyzing the contents of (a1), (a2), (a3) and (a4) defined in the present invention, a high performance liquid chromatograph (hereinafter abbreviated as HPLC) and a gas chromatograph (hereinafter abbreviated as GC) are used. it can.
HPLC measurement conditions were as follows. Equipment: model name (LC-10A), manufacturer (Shimadzu Corporation), column: CAPCELL PAC UG120C18 (4.6 mmφ × 25 cm) manufacturer (Shiseido Co., Ltd.), mobile phase: phosphoric acid with a concentration of 10 mmol / l and concentration of 100 mmol / L aqueous solution of sodium perchlorate, flow rate: 0.8 ml / min, detector: UV (210 nm), injection volume: 20 μl, column temperature: 40 ° C.
The measurement conditions for GC were as follows. Equipment: Model name (GC-17A), Maker (Shimadzu Corporation), Column: DB-5 (0.53 mmφ × 30 m) Maker (J & W Scientific), Injection volume: 1 μl, Detector: FID, Initial column temperature: 60 ° C., heating rate: 10 ° C./min, final column temperature 250 ° C., inlet temperature: 250 ° C., detector temperature: 250 ° C.

In the present invention, examples of the ammonium carboxylate and / or amine carboxylate (a1) include those represented by the general formula (1).
R ¹ may have at ^{least one} hydroxyl group, amino group, nitro group, cyano group, carboxyl group, or formyl group, or may have at least one ether group in the main chain. A monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group) or a hydrogen atom, and specifically, methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, 2-hydroxybutyl, Examples thereof include 1-aminoethyl, 1-nitroethyl, 2-cyanopropyl, 1-carboxypropyl, methoxyethyl, ethoxypropyl and the like.
R ² is a monovalent hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom. As a C1-C10 hydrocarbon group, a C1-C10 alkyl group and a C1-C10 hydrocarbon group containing an aromatic group are mentioned. Examples of the alkyl group having 1 to 10 carbon atoms include methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, lauryl, and stearyl. Examples of the aromatic group-containing hydrocarbon group having 1 to 10 carbon atoms include a phenyl group and a benzyl group. Among these, hydrocarbon groups or hydrogen atoms having 1 to 10 hydrocarbons are particularly preferred, and hydrocarbon groups or hydrogen atoms having 1 to 5 carbon atoms are more preferred.

Examples of (a1) include the following.
Ammonium formate, ammonium acetate, ammonium propionate, ammonium butyrate, ammonium isobutyrate, ammonium acrylate, ammonium methacrylate, methylamine formate, methylamine acetate, methylamine propionate, methylamine butyrate, methylamine butyrate, methylamine isobutyrate Salt, methylamine acrylate, methylamine methacrylate, ethylamine formate, ethylamine acetate, ethylamine propionate, ethylamine butyrate, ethylamine isobutyrate, ethylamine acrylate, ethylamine methacrylate, propylamine formate , Propylamine acetate, butylamine formate, butylamine acetate and the like.

Among these, ammonium formate, ammonium acetate, methylamine formate, methylamine acetate, ethylamine formate and ethylamine acetate are exemplified, and more particularly, ammonium formate, ethylamine formate and methylamine formate are exemplified.
One or more of these ammonium carboxylate salts may be used.

In the present invention, examples of the acid amide (a2) include those represented by the general formula (2). R ³ may have at least one hydroxyl group, amino group, nitro group, cyano group, carboxyl group, or formyl group, or may have at least one ether group in the main chain. A monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group) or a hydrogen atom, specifically, a methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, or 2-hydroxybutyl group , 1-aminoethyl group, 1-nitroethyl group, 2-cyanopropyl group, 1-carboxypropyl group, methoxyethyl group, ethoxypropyl group and the like.
R ⁴ is a monovalent hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom. As a C1-C10 hydrocarbon group, a C1-C10 alkyl group and a C1-C10 hydrocarbon group containing an aromatic group are mentioned. Examples of the alkyl group having 1 to 10 carbon atoms include methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, lauryl, and stearyl. Examples of the aromatic group-containing hydrocarbon group having 1 to 10 carbon atoms include a phenyl group and a benzyl group. Among these, hydrocarbon groups or hydrogen atoms having 1 to 10 hydrocarbons are particularly preferred, and hydrocarbon groups or hydrogen atoms having 1 to 5 carbon atoms are more preferred.

Examples of (a2) include the following examples.
Formamide, N-methylformamide, N-ethylformamide, acetamide, N-methylacetamide, N-ethylacetamide, propionamide, N-methylpropionamide, N-ethylpropionamide, butyramide, N-methylbutyramide, N- Ethylbutyroamide and the like.

Among these, formamide, N-methylformamide, N-ethylformamide, acetamido, N-methylacetamido, N-ethylacetamido, and more particularly, formamide, N-methylformamide, N-ethylformamide .
One or more of these acid amides may be used.

In the present invention, examples of the cyclic amine compound (a3) include those represented by the general formula (3).
R ⁵ , R ⁶ and R ⁷ may have at least one hydroxyl group, amino group, nitro group, cyano group, carboxyl group, or formyl group, or may have an amino group and / or an ether group in the main chain. A monovalent hydrocarbon group having 1 to 20 carbon atoms (including the number of carbon atoms of a functional group), a hydrogen atom, or a double bond bonded to each other, which may have one or more groups, May form a ring or a non-aromatic ring or a heterocyclic ring, specifically, methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, 1-hydroxymethyl, 2-hydroxybutyl, 1-aminoethyl, N , N-dimethyleneamino group, 1-nitroethyl group, 2-cyanopropyl group, 1-carboxypropyl group, methoxyethyl group, ethoxypropyl group, methylene group, ethylene group, vinylene group and the like. .
X, Y and Z may have at least one hydroxyl group, amino group, nitro group, cyano group, carboxyl group or formyl group, or have at least one ether group in the main chain. And a divalent hydrocarbon group having 1 to 20 carbon atoms which may be the same or different. Specifically, methylene, ethylene, trimethylene, propylene, propenylene, vinylene, 1-hydroxymethylene, 2-hydroxyethylene, 1-aminoethylene, N, N-dimethyleneamino, 1-nitro Examples include an ethylene group, a 2-cyanopropylene group, a 1-carboxypropylene group, a methoxyethylene group, and an ethoxypropylene group.
Among these, hydrocarbon groups having 1 to 10 hydrocarbons are particularly preferred, and hydrocarbon groups having 1 to 5 carbon atoms are more preferred.

Examples of (a3) include the following.
Cyclotrimethylenetriamine, trimethylcyclotrimethylenetriamine, triethylcyclotrimethylenetriamine, trimethylolcyclotrimethylenetriamine, hexamethylenetetramine, 3-methyl-1,3,5-triazabicyclo [3,2,1] octane, 3-ethyl-1,3,5-triazabicyclo [3,2,1] octane, 3-ethyl-1,3,5-triazabicyclo [3,2,1] octane, 3-methyl-1, 3,5-triazabicyclo [3,2,1] oct-6-ene, 3-ethyl-1,3,5-triazabicyclo [3,2,1] oct-6-ene, 3-methyl- 1,3,6-triazabicyclo [4,2,1] non-4-ene, 3-ethyl-1,3,6-triazabicyclo [4,2,1] non-4-ene, 3- Methyl 1,3,6-triazabicyclo [4,2,1] non-4,7-diene, 3-ethyl-1,3,6-triazabicyclo [4,2,1] non-4,7- Diene and so on.

Among them, particularly, cyclotrimethylenetriamine, triethylcyclotrimethylenetriamine, trimethylolcyclotrimethylenetriamine, hexamethylenetetramine, 3-methyl-1,3,5-triazabicyclo [3,2,1] octane, -Ethyl-1,3,5-triazabicyclo [3,2,1] octane, 3-methyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene, -Ethyl-1,3,6-triazabicyclo [4,2,1] non-4,7-diene, and more particularly, hexamethylenetetramine, 3-ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene.
One or more of these cyclic amine compounds may be used.

In the present invention, examples of the urethane compound (a4) include those represented by the general formula (4).
R ⁸ and R ⁹ may have at least one hydroxyl group, amino group, nitro group, cyano group, carboxyl group, or formyl group, or have at least one ether group in the main chain. A monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group) or a hydrogen atom, specifically, methyl, ethyl, isopropyl, hexyl, 2-ethylhexyl, Examples include hydroxybutyl, 1-aminoethyl, 1-nitroethyl, 2-cyanopropyl, 1-carboxypropyl, methoxyethyl, ethoxypropyl, and the like.

Examples of (a4) include the following.
Methyl carbamate, ethyl carbamate, propyl carbamate, butyl carbamate, N-methyl methyl carbamate, ethyl N-methyl carbamate, methyl N-ethyl carbamate, ethyl N-ethyl carbamate, methyl N-propyl carbamate, N -Methyl butylcarbamate, ethyl N-propylcarbamate, propylN-methylcarbamate, propylN-ethylcarbamate, butylN-methylcarbamate, butylN-ethylcarbamate, and the like.

Among these, methyl carbamate, ethyl carbamate, propyl carbamate, butyl carbamate, methyl N-methyl carbamate, ethyl N-methyl carbamate, methyl N-ethyl carbamate, ethyl N-ethyl carbamate, N-propyl Examples include methyl carbamate and methyl N-butylcarbamate, and more particularly, methyl carbamate, ethyl carbamate, methyl N-methylcarbamate, ethyl N-methylcarbamate, methyl N-ethylcarbamate, and ethyl N-ethylcarbamate. Is mentioned.
One or more of these urethane compounds may be used.

In the present invention, the electrolyte salt (A) has the general formula (4)
In imidazolium salt (A1) is preferably represented, counter anion X of (A1) ^{- _{The, PF 6 -, BF 4 -}} , F - 2.3HF, AsF 6 -, SbF 6 -, N (RfSO 3 _{^{) 2 -, C (RfSO 3}} ) 3 - and RfSO ₃ (Rf is preferably anion selected from the group consisting of fluoroalkyl group) having 1 to 12 carbon atoms.

Examples of the cation of the imidazolium salt (A1) used in the present invention include the following compounds (1) to (7).
(1) 1,3-substituted product 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-diethylimidazolium, 1-methyl-3-propylimidazolium, 1-butyl-3 -Methylimidazolium and the like.
(2) 1,2,3-position substituted 1,2,3-trimethylimidazolium, 1,3-dimethyl-2-ethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1,2,3 -Triethylimidazolium, 1,2-dimethyl-3-propylimidazolium and the like.
(3) 1,1,2-Substituted product 1,1-dimethyl-2-heptylimidazolium, 1,1-dimethyl-2-(-2′heptyl) imidazolium, 1,1-dimethyl-2-(− 3'heptyl) imidazolium, 1,1-dimethyl-2-(-4'heptyl) imidazolium, 1,1-dimethyl-2-dodecylimidazolium, 1,1-dimethylimidazolium, 1,1,2- Trimethylimidazolium and the like.
(4) 1,2,3,4-substituted 1,2,3,4-tetramethylimidazolium, 1,3,4-trimethyl-2-ethylimidazolium, 1,3-dimethyl-2,4- Diethylimidazolium, 1,2-dimethyl-3,4-diethylimidazolium, 1-methyl-2,3,4-triethylimidazolium, 1,2,3,4-tetraethylimidazolium and the like.
(5) 1,1,2,4-position substituted 1,1,2,4-tetramethylimidazolium and the like.
(6) 1,1,2,5-substituted product 1,1,2,5-tetramethylimidazolium and the like.
(7) 1,1,2,4,5-substituted 1,1,2,4,5-pentamethylimidazolium and the like.

  Of these, preferred are 1,3-substituted and 1,2,3-substituted, and more preferred are 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, Diethylimidazolium, 1,2,3-trimethylimidazolium, 1,3-dimethyl-2-ethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1,2,3-triethylimidazolium, 1- Butyl-3-methylimidazolium and 1,2-dimethyl-3-propylimidazolium, particularly preferably 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, and 1,3-diethylimidazolium It is.

The electrolytic solution of the present invention preferably comprises the above-mentioned imidazolium salt (A1), but may further comprise (A1) dissolved in a non-aqueous solvent (B).
When the electrolytic solution comprises only (A1), preferred (A1) is 1-ethyl-3-methylimidazolium BF ₄ salt, 1-ethyl-3-methylimidazolium F · 2.3HF salt, 1-ethyl 3-methylimidazolium N (CF ₃ SO _{3) 2} salt, 1-ethyl-3-methylimidazolium _{N (C 2 F 5 SO 3} ) 2 salt, 1-ethyl-3-methylimidazolium CF ₃ SO ₃ salt, 1-butyl-3-methylimidazolium BF ₄ salt, 1-butyl-3-methylimidazolium BF ₆ salt, 1-butyl-3-methylimidazolium CF ₃ SO ₃ salt, 1,2-dimethyl-3 -Propyl imidazolium N (CF ₃ SO ₃ ) ₂ salt, and 1,2-dimethyl-3-propyl imidazolium N (C ₂ F ₅ SO ₃ ) ₂ salt.

  As the non-aqueous solvent (B) used in the electrolytic solution of the present invention, a known non-aqueous solvent is used and is usually selected from the solubility and electrochemical stability of the electrolyte. The following are specific examples. Two or more of these can be used in combination.

Ethers: chain ethers [2 to 6 carbon atoms (diethyl ether, methyl isopropyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, etc.); 7 to 12 carbon atoms (diethylene glycol diethyl ether, triethylene glycol dimethyl ether, etc.)], cyclic ethers [C2-4 (tetrahydrofuran, 1,3-dioxolan, 1,4-dioxane, etc.); C5-C18 (4-butyldioxolan, crown ether, etc.)].
Amides: N, N-dimethylformamide, N, N-dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, N-methylpyrrolidone and the like.
-Carboxylic esters: methyl acetate, methyl propionate, and the like.
Lactones: γ-butyrolactone, α-acetyl-γ-butyrolactone, β-butyrolactone, γ-valerolactone, δ-valerolactone and the like.
-Nitriles: acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, acrylonitrile and the like.
-Carbonates: ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate and the like.
Sulfoxides: dimethylsulfoxide, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane and the like.
-Nitro compounds: nitromethane, nitroethane, etc.
-Heterocyclic solvents: N-methyl-2-oxazolidinone, 3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.

  Of these, preferred are carbonates and sulfoxides, and particularly preferred are ethylene carbonate, propylene carbonate and sulfolane.

  The content of (a1) and / or (a2) and / or (a3) and / or (a4) in the imidazoles (L) is preferably 5% by weight or less from the viewpoint of withstand voltage. It is preferably at most 1% by weight, particularly preferably at most 0.1% by weight. (A2) is preferably at most 5% by weight, more preferably at most 1% by weight, particularly preferably at most 0.1% by weight. (A3) is preferably at most 15% by weight, more preferably at most 3% by weight, particularly preferably at most 0.3% by weight. (A4) is preferably at most 25% by weight, more preferably at most 5% by weight, particularly preferably at most 0.5% by weight.

  The electrolyte salt (A) can be produced by reacting an imidazole (L) with a quaternizing agent (c) to produce a quaternary ammonium salt (L1) and then reacting with an acid. Typical production methods include a method of reacting an imidazole (L) with an alkyl halide to form a quaternary ammonium halide and reacting the quaternary ammonium halide with an acid. There is known a method of generating a quaternary ammonium salt and then reacting with an acid for decarboxylation.

Examples of the imidazoles (L) include, for example, the following.
1-methylimidazole, 1-ethylimidazole, 1-propylimidazole, 1-butylimidazole, 1-ethyl-2-methylimidazole, 1,2-dimethylimidazole, 1-methyl-2-ethylimidazole, 1,4-dimethyl Imidazole, 1,5-dimethylimidazole, 1,2,4-trimethylimidazole, 1,4-dimethyl-2-ethylimidazole, 1-methyl-2-propylimidazole, 1-ethyl-2-propylimidazole, 1-methyl -2-butylimidazole, 1-ethyl-2-butylimidazole, 1-propyl-2-butylimidazole, 1-butyl-2-propylimidazole and the like. Of these, preferred are 1-methylimidazole, 1-ethylimidazole, 1-ethyl-2-methylimidazole, 1,2-dimethylimidazole, 1-methyl-2-ethylimidazole, 1,4-dimethylimidazole, 1, 5-dimethylimidazole, particularly preferably 1-methylimidazole and 1-ethylimidazole.

Examples of the quaternizing agent (c) include the following compounds (1) to (7).
(1) Carbonate diester having 1 to 30 or more carbon atoms Dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl-i-propyl carbonate, di-n-propyl carbonate, di-i-propyl carbonate, di-n-butyl Carbonic acid, di-i-butyl carbonate, di-t-butyl carbonate, di-sec-butyl carbonate, dipentyl carbonate, dihexyl carbonate, diheptyl carbonate, dioctyl carbonate, dibenzyl carbonate, dinonyl carbonate, didecyl carbonate, diundecyl carbonate, didodecyl Carbonic acid and the like.
(2) Alkyl halide having 1 to 30 or more carbon atoms Methyl chloride, methyl bromide, methyl iodide, ethyl chloride, ethyl bromide, ethyl iodide, n-propyl chloride, isopropyl chloride, n-propyl bromide Isopropyl bromide, n-propyl iodide, isopropyl iodide and the like.
(3) Sulfuric acid diester having 1 to 30 or more carbon atoms Dimethyl sulfate, diethyl sulfate, di-n-propyl sulfate, diisopropyl sulfate and the like.
(4) Carboxylates having 1 to 30 or more carbon atoms Methyl formate, ethyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl acrylate, methyl methacrylate, methyl lactate, methyl oxalate, Methyl benzoate and the like.
(5) Nitrate ester having 1 to 30 or more carbon atoms Dimethyl nitrate, diethyl nitrate, di-n-propyl nitrate, diisopropyl nitrate and the like.
(6) Sulfonate having 1 to 30 or more carbon atoms Methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, methyl benzenesulfonate, ethyl benzenesulfonate, p-toluenesulfonic acid Methyl, ethyl p-toluenesulfonate and the like.
(7) Phosphonates having 1 to 30 or more carbon atoms Trimethyl phosphonate, triethyl phosphonate, tripropyl phosphonate, triphenyl phosphonate and the like.

  Of these, preferred are carbonic acid diesters having 1 to 30 or more carbon atoms, and alkyl halides having 1 to 30 or more carbon atoms, and more preferred are carbonic acid diesters having 1 to 30 or more carbon atoms. Yes, particularly preferred are dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, di-n-propyl carbonate and di-i-propyl carbonate. Two or more of these quaternizing agents may be used.

  The reaction molar ratio of (L) and (c) in the present invention is not particularly limited, but is preferably 1: (0.5 to 10), more preferably 1: (1 to 5), and particularly preferably 1: (1). 1-3). When (c) is 0.5 or more, the reaction yield is good, and when (c) is 10 or less, the selectivity of the reaction is good.

  The quaternization reaction in which (L) and (c) are reacted is preferably performed in the presence of a solvent for the purpose of adjusting viscosity, concentration, and the like. As the solvent, water or an organic solvent inert to the reaction is preferable. For example, those used in the reaction for obtaining (L1) can be mentioned, and more preferred are monoalcohol, monoether and nitrile. Two or more of these solvents may be used. The amount of the solvent to be used is generally about 0.5 to 5 times by weight, preferably about 1 to 3 times by weight, relative to the mass of (L1). The viscosity (25 ° C.) of the reaction solution obtained by dissolving (L1) in the above solvent is preferably 0.1 to 10,000 mPa · s, more preferably 0.1 to 500 mPa · s.

The quaternization reaction can be performed under an inert gas (eg, nitrogen) atmosphere at normal pressure or under pressure. Pressurization increases the reaction rate. The pressure is usually 1 × 10 ⁵ to 1 × 10 ⁷ Pa, preferably 1 × 10 ^{5 to} 7 × 10 ⁶ Pa, and more preferably 1 × 10 ^{5 to} 5 × 10 ⁶ Pa. The reaction can be carried out by a batch method or a continuous method, but the batch method is preferred because it has better operability. The reaction temperature is generally 0-300 ° C, preferably 20-250 ° C, and more preferably 50-200 ° C. The reaction rate is good at 0 ° C or higher, and the reaction yield of (L1) is good at 300 ° C or lower. The reaction time is generally 1 minute to 200 hours, preferably 30 minutes to 100 hours, more preferably 1 to 80 hours.

Examples of the quaternary ammonium salt (L1) include the following examples.
1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1,3-diethylimidazolium chloride, 1,2,3-trimethylimidazolium chloride, 1,3-dimethyl-2-ethyl chloride Imidazolium, 1-ethyl-2,3-dimethylimidazolium chloride, 1,2,3-triethylimidazolium chloride, 1,3-dimethylimidazolium bromide, 1-ethyl-3-methylimidazolium bromide, odor 1,3-diethylimidazolium bromide, 1,2,3-trimethylimidazolium bromide, 1,3-dimethyl-2-ethylimidazolium bromide, 1-ethyl-2,3-dimethylimidazolium bromide, odor 1,2,3-triethylimidazolium iodide, 1,3-dimethylimidazolium iodide, 1-ethyl-3-methylimidazolium iodide 1,3-diethylimidazolium iodide, 1,2,3-trimethylimidazolium iodide, 1,3-dimethyl-2-ethylimidazolium iodide, 1-ethyl-2,3-dimethylimidazolium iodide 1,2,3-triethylimidazolium iodide, 1,3-dimethylimidazolium monomethyl carbonate, 1-ethyl-3-methylimidazolium monomethyl carbonate, 1,3-diethylimidazolium monomethyl carbonate, 1, 2,3-trimethylimidazolium monomethyl carbonate, 1,3-dimethyl-2-ethylimidazolium monomethyl carbonate, 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate, 1,2,3-triethylimidazolium Monomethyl carbonate and the like. Of these, preferred are 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1,3-diethylimidazolium chloride, 1,3-dimethylimidazolium bromide, and 1-ethyl bromide. -3-methylimidazolium, 1,3-diethylimidazolium bromide, 1,3-dimethylimidazolium iodide, 1-ethyl-3-methylimidazolium iodide, 1,3-diethylimidazolium iodide, 1,3-dimethylimidazolium monomethyl carbonate, 1-ethyl-3-methylimidazolium monomethyl carbonate, 1,3-diethylimidazolium monoethyl carbonate, 1,2,3-trimethylimidazolium monomethyl carbonate, 1, 3-dimethyl-2-ethylimidazolium monomethyl carbonate, 1-ethyl-2,3-dimethyli Dazolium monomethyl carbonate and 1,2,3-triethylimidazolium monoethyl carbonate, particularly preferably 1,3-dimethylimidazolium chloride, 1-ethyl-3-methylimidazolium chloride, 1,3-chloride Diethyl imidazolium, 1,3-dimethyl imidazolium monomethyl carbonate, 1-ethyl-3-methyl imidazolium monomethyl carbonate, 1,3-diethyl imidazolium monoethyl carbonate, 1,2,3-trimethyl imidazolium monomethyl Carbonate, 1,3-dimethyl-2-ethylimidazolium monomethyl carbonate, 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate, 1,2,3-triethylimidazolium monoethyl carbonate, 1-butyl -3-methylimidazolium monomethyl carbonate, 1,2-dimethyl 3-propyl imidazolium monomethyl carbonate or the like.

  When (A) is dissolved in the non-aqueous solvent (B), the concentration of (A) in the electrolytic solution is preferably 0.1 mol / L or more from the viewpoint of the electric conductivity and the internal resistance of the electrolytic solution. Preferably, it is 0.5 mol / L or more, more preferably 5 mol / L or less, and even more preferably 4 mol / L or less, from the viewpoint of salt precipitation at low temperatures.

As a method for reducing the content of (a1) and / or (a2) and / or (a3) and / or (a4) to a very small amount as in the present invention, the method using imidazoles (L) or (L) is used. When producing the produced quaternary ammonium salt (L1) and electrolyte salt (A), a method and a method for suppressing by-products of (a1) and / or (a2) and / or (a3) and / or (a4) were produced. There is a way to remove it later.
(L) can be obtained by a reaction of an α-dicarbonyl compound, ammonia, an aldehyde, and a primary amine. Here, (L) As a method for suppressing by-products of (a1) and / or (a2) and / or (a3) and / or (a4) during production, a method using a raw material having a small impurity content may be used. The molar ratio of α-dicarbonyl compound: ammonia: aldehyde: primary amine, which is a kind of raw material, is approximately equivalent to 1: 0.8 to 1.2: 0.8 to 1.2: 0.8 to 1.2. , A method in which the reaction temperature is 20 to 70 ° C., a method in which an α-dicarbonyl compound, ammonia, an aldehyde, and a primary amine are reacted in one step, a reaction of an α-dicarbonyl compound and an aldehyde with a primary amine Then, there is a method of reacting ammonia and a method of reacting a mixed solution of ammonia and a primary amine in a mixed solution of an α-dicarbonyl compound and an aldehyde. Examples of the raw material having a low impurity content include an aldehyde having a carboxylic acid content of 0.2 g / L or less.
As a method for removing (a1) and / or (a2) and / or (a3) and / or (a4) after the production of (L), there is a method of purifying (L).
Examples of the purification method (L) include a method of removing by distillation, a method of removing by recrystallization, a method of extracting with a solvent, and a method of performing adsorption treatment with an adsorbent such as silica gel, activated carbon, activated alumina, or special molecular sieve. The method of distillation, the method of recrystallization, the method of extraction, and the method of adsorption treatment may be performed alone or in combination.

Similarly, as a method for suppressing the by-product of (a1) and / or (a2) and / or (a3) and / or (a4) during the production of the quaternary ammonium salt (L1), (a1) and (a2) There is a method using imidazoles (L) having a low content of (a3) and / or (a4). As a method for removing (a1) and / or (a2) and / or (a3) and / or (a4) after the production of the quaternary ammonium salt, there is a method of purifying the quaternary ammonium salt. Methods for purifying the quaternary ammonium salt include a method of removing by recrystallization, a method of extracting with a solvent, and a method of performing adsorption treatment with an adsorbent such as silica gel, activated carbon, activated alumina, and special molecular sieve. The method of recrystallization, the method of extraction, and the method of adsorption treatment may be performed alone or in combination.
As a method for suppressing the by-product of (a1) and / or (a2) and / or (a3) and / or (a4) during the production of the electrolyte salt (A), (a1) and / or (a2) And / or a method using a quaternary ammonium salt (L1) having a small content of (a3) and / or (a4). As a method for removing (a1) and / or (a2) and / or (a3) and / or (a4) after the production of the electrolyte salt, there is a method of purifying the electrolyte salt. As a method of purifying the electrolyte salt, there are a method of removing by recrystallization, a method of extracting with a solvent, and a method of performing adsorption treatment with an adsorbent such as silica gel, activated carbon, activated alumina, and special molecular sieve. The method of recrystallization, the method of extraction, and the method of adsorption treatment may be performed alone or in combination.

  The water content in the electrolytic solution of the present invention is preferably 3000 ppm or less from the viewpoint of electrochemical stability. It is more preferably at most 300 ppm, particularly preferably at most 100 ppm, most preferably at most 50 ppm.

  Examples of the electrochemical capacitor using the electrolytic solution of the present invention include an electric double layer capacitor and a redox capacitor. The electric double-layer capacitor described here is an electrochemical capacitor that utilizes a capacity developed by an electric double layer formed by a non-Faraday reaction between a polarizable electrode and an electrolytic solution, and a redox capacitor is an electric double-layer capacitor. In addition, the electrochemical capacitor utilizes a pseudo capacitance caused by an adsorption reaction or a redox reaction involving the transfer of electrons between an electrode and an ion.

  The electrochemical capacitor includes an electrode, a current collector, and a separator, and optionally includes a case generally used for the electrochemical capacitor, a gasket, and the like.At least one of the positive electrode and the negative electrode of the electrode mainly includes a carbonaceous material. It is a material such as a polarizable electrode. The electrolyte is impregnated into the electrode and the separator.

  Hereinafter, the present invention will be described with reference to Examples and Comparative Examples, but the present invention is not limited thereto. In Examples and Comparative Examples, parts indicate parts by weight.

  As a method for analyzing the contents of (a1), (a2), (a3) and (a4) specified in the present invention, HPLC and GC can be used as described above. In this analysis method, the contents of (a1), (a2), (a3) and (a4) were calculated using an internal standard. Using 4-dimethylaminopyridine as an internal standard substance for HPLC analysis and diethyl carbonate as an internal standard substance for GC analysis, the quantitative ratio of the internal standard substance to each of (a1), (a2), (a3) and (a4) was determined. A calibration curve was determined from the relationship with the peak area ratio, and (a1), (a2), (a3) and (a4) were quantified.

The method for measuring the withstand voltage of the electrolytic solution in the present invention will be described. The electrolytic solution was placed in a cell for withstanding voltage measurement, the potential was swept at 5 mV / sec with a potentiostat (manufactured by Solartron, Inc .: Model 1286), and the polarization was measured at 25 ° C. while stirring the electrolytic solution. Current density oxidation side, respectively oxidation potential the potential to be 1.0 mA / cm ² with a reducing side, the reduction potential, the potential range current density of 1.0 mA / cm ² or less, i.e., until the oxidation potential from reduction potential Is the withstand voltage of the electrolytic solution. In general, an electrolyte having a low reduction potential and a high oxidation potential is considered to have excellent electrochemical stability and a high withstand voltage of the electrolyte. A three-electrode cell using a glassy carbon electrode (manufactured by BAS; electrode area 0.008 cm ² ) as a working electrode, a platinum wire as a counter electrode, and a silver / silver ion electrode as a reference electrode is used for the cell for measuring the withstand voltage of the electrolyte. Was used.

A method for measuring the self-discharge characteristics, initial capacitance, capacitance change rate, and internal resistance of an electric double layer capacitor using an electrolytic solution according to the present invention will be described. The electrolytic solution was added to the opposing activated carbon electrode cells with the separator interposed therebetween to produce a coin-type electric double layer capacitor (size: 6.8 mm × 1.4 mm). A DC voltage of 2.3 V was applied to the coin-type electric double-layer capacitor at 25 ° C. for 6 hours at 25 ° C. using a constant voltage / constant current generator (R6741A manufactured by Advantest). The voltage between terminals of the coin-type electric double layer capacitor was measured. This measured value was defined as the residual voltage after self-discharge. The higher the residual voltage, the higher the withstand voltage, and the lower the residual voltage, the lower the withstand voltage.
Next, after charging by applying a voltage of 2.8 V at 25 ° C., the battery was discharged at a constant current of 1 mA to obtain an initial capacitance. The method of calculating the capacitance is C = i × Δt / ΔV from the relationship of Q = i × t = C × V, where Q is the discharge charge (C), i is the discharge current (A), and t is Is a discharge time (sec), C is a capacitance (F), and V is a voltage (V). The internal resistance was measured at a frequency of 1 KHz by an AC two-terminal method. As the durability evaluation, while applying a voltage of 2.8 V, holding at 70 ° C. for 1,000 hours, measuring a capacitance after discharging at a constant current of 1 mA, and calculating an initial value from the value. The capacitance change rate was obtained by dividing the subtracted value by the initial capacitance.

Hereinafter,% in Examples 1 to 6 and Comparative Examples 1 to 3 indicates% by weight.
Example 1
A mixture of 18 parts of glyoxal (40% aqueous solution) and 10 parts of formalin (37% aqueous solution) was charged into a reaction flask equipped with a stirrer, a thermometer, a dropping funnel, a reflux condenser, and a nitrogen gas inlet tube, and stirred. The solution was made homogeneous, and the temperature was raised to 40 ° C. while slightly flowing nitrogen gas. Thereafter, a mixture of 64 parts of ethylamine (70% aqueous solution) and 61 parts of ammonia (28% aqueous solution) was added dropwise from the dropping funnel over 4 hours and 35 minutes while maintaining the reaction temperature at 35 to 45 ° C. Next, 35 minutes after the dropping of the mixed solution of ethylamine and ammonia was started, a mixture of 127 parts of glyoxal (40% aqueous solution) and 71 parts of formalin (37% aqueous solution) was dropped from another dropping funnel over 4 hours. The mixed solution of ethylamine and ammonia was added dropwise over 4 hours and 35 minutes, and the dropping start time was shifted so that the addition of the mixed solution of glyoxal and formalin was completed simultaneously with the completion of the addition of the mixed solution of ethylamine and ammonia. After the completion of the dropping, the reaction was further performed at 40 ° C. for 1 hour. Next, the pressure was gradually reduced from the normal pressure to a pressure of 5.3 kPa at a temperature of 80 ° C., and dehydration was performed to obtain crude 1-ethylimidazole (L-0). Subsequently, (L-0) was purified by simple distillation under the conditions of a temperature of 100 ° C. and a reduced pressure of 0.7 kPa to obtain 1-ethylimidazole (L-1). The purity of the obtained (L-1) was 90% by GC analysis. Subsequently, HPLC and GC analyzes were performed to determine the contents of (a1), (a2), (a3), and (a4). Here, HPLC and GC analysis conditions were performed under the conditions described above. (A1) was quantified by HPLC, and (a2), (a3) and (a4) were quantified by GC. The total content of ammonium formate and ethylamine formate was 2.4%, the total content of formamide and N-ethylformamide was 2.5%, and hexamethylenetetramine, 3-ethyl-1,3,5- The total content of triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] non-4,7-diene was 3.5%. .
Next, 96 parts of the obtained (L-1), 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave equipped with a reflux condenser and uniformly dissolved. Next, the temperature was raised to 130 ° C. The reaction was performed at a pressure of about 0.8 MPa for 70 hours. NMR analysis of the reaction product (L1-1) revealed that 1-ethyl-3-methylimidazolium monomethyl carbonate was formed, and conversion to 1-ethyl-3-methylimidazolium monomethyl carbonate was performed. The rate was 99.5%. 423 parts (L1-1) (44% by weight of pure salt) of the (L1-1) were placed in a flask, and 209 parts of an aqueous borofluoric acid solution (42% by weight of pure content) were gradually added dropwise at room temperature over about 30 minutes with stirring. With the dropping, bubbles of carbon dioxide gas were generated. After the completion of the dropwise addition, after the generation of bubbles had subsided, the reaction solution was transferred to a rotary evaporator, and the solvent was completely distilled off. 198 parts of a colorless and transparent liquid (A-1) remained in the flask. As a result of NMR analysis of this liquid, the main component was 1-ethyl-3-methylimidazolium tetrafluoroborate. 198 g of the obtained (A-1) was uniformly dissolved in propylene carbonate in a total amount of 1 liter to prepare an electrolytic solution of the present invention. The obtained electrolyte was analyzed by HPLC and GC. Here, under the above-mentioned conditions, (a1) was quantified by HPLC, and (a2), (a3) and (a4) were quantified by GC. The content of (a1) ammonium formate was 0.4%, the total content of (a2) formamide and N-ethylformamide was 0.5%, and (a3) hexamethylenetetramine, 3-ethyl-1, The total content of 3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene is 2.0. %, And the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 4.0%. The total content of (a1), (a2), (a3) and (a4) was 6.9%.

Example 2
(L-0) obtained in Example 1 was purified by precision distillation under the conditions of a temperature of 100 ° C. and a reduced pressure of 0.7 kPa to obtain 1-ethylimidazole (L-2). The purity of the obtained (L-1) was 97% when analyzed by GC. Subsequently, HPLC and GC analysis were performed under the above-described conditions in the same manner as in Example 1, and the contents of (a1), (a2), (a3) and (a4) were measured. Here, (a1) was quantified by HPLC, and (a2), (a3) and (a4) were quantified by GC. The total content of ammonium formate and ethylamine formate is 0.5%, the total content of formamide and N-ethylformamide is 0.8%, and hexamethylenetetramine, 3-ethyl-1,3,5-triamine. The total content of zabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] non-4,7-diene was 1.0%. Next, 96 parts of (L-2), 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave with a reflux condenser, and the reaction was carried out in the same manner as in Example 1. NMR analysis of the reaction product (L1-2) revealed that 1-ethyl-3-methylimidazolium monomethyl carbonate was formed, and conversion to 1-ethyl-3-methylimidazolium monomethyl carbonate was performed. The rate was 99.5%. 423 parts (44% by weight of pure salt) of the obtained reaction mixture (L1-2) was placed in a flask, and 209 parts of an aqueous borofluoric acid solution (42% by weight of pure content) was stirred at room temperature for about 30 minutes at room temperature. After the dropwise addition, treatment was conducted in the same manner as in Example 1 to leave 198 parts of a colorless and transparent liquid (A-2). As a result of NMR analysis of this liquid, the main component was 1-ethyl-3-methylimidazolium tetrafluoroborate. 198 g of the obtained 1-ethyl-3-methylimidazolium tetrafluoroborate was uniformly dissolved in propylene carbonate in a total amount of 1 liter to prepare an electrolytic solution of the present invention. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) the total content of ammonium formate and ethyl ammonium formate is 0.05%; (a2) the total content of formamide and N-ethylformamide is 0.07% by weight; (a3) hexamethylenetetramine; 3-ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene The total content was 0.3% by weight, and the total content of (a4) methyl carbamate and N-ethyl methyl carbamate was 0.5%. The total content of (a1), (a2), (a3) and (a4) was 0.92%.

Example 3
After 421 parts of (L1-2) obtained in Example 2 were charged with 21 parts of activated carbon and the mixture was stirred at room temperature for 8 hours, the activated carbon was completely filtered with a dense filter paper 5C. 423 parts (purity 46% by weight) of the obtained filtrate are put in a flask, and 209 parts (hydrogen 42% by weight) of a borofluoric acid aqueous solution (L1-3) (L1-3) are gradually stirred at room temperature for about 30 minutes under stirring. Then, the mixture was treated in the same manner as in Example 1 to leave 198 parts of a colorless and transparent liquid (A-3). As a result of NMR analysis of this liquid, the main component was 1-ethyl-3-methylimidazolium tetrafluoroborate. 198 g of the obtained 1-ethyl-3-methylimidazolium tetrafluoroborate was uniformly dissolved in propylene carbonate in a total amount of 1 liter to prepare an electrolytic solution of the present invention. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) The total content of ammonium formate and ethyl formate is 0.01%, (a2) the total content of formamide and N-ethylformamide is 0.02%, and (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 0.1%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 0.2%. The total content of (a1), (a2), (a3) and (a4) was 0.33%.

Example 4
After adding 50 parts of activated carbon to 1000 parts of the electrolyte solution obtained in Example 2 and stirring the mixture at room temperature for 8 hours, the activated carbon was completely filtered off with a dense filter paper 5C. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) The total content of ammonium formate and ethylamine formate is 0.003%, (a2) the total content of formamide and N-ethylformamide is 0.007%, and (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 0.01%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 0.02%. The total content of (a1), (a2), (a3) and (a4) was 0.04%.

Example 5
198 g of (A-2) obtained in Example 2 was uniformly dissolved in acetonitrile to make the whole 1 liter, thereby preparing an electrolytic solution. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) The total content of ammonium formate and ethylamine formate is 0.05%, (a2) the total content of formamide and N-ethylformamide is 0.07%, and (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 0.3%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 0.5%. The total content of (a1), (a2), (a3) and (a4) was 0.92%.

Example 6
198 g of (A-2) obtained in Example 2 was uniformly dissolved in sulfolane to make the whole 1 liter to prepare an electrolytic solution. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) The contents of ammonium formate and ethylamine formate are 0.05%, the total content of (a2) formamide and N-ethylformamide is 0.07%, and (a3) hexamethylenetetramine, 3-ethyl The total content of -1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene is 0.3%, and the total content of (a4) methyl carbamate and N-ethyl methyl carbamate was 0.5%. The total content of (a1), (a2), (a3) and (a4) was 0.92%.

Example 7
In Example 1 of the present invention, instead of formalin, 6 parts of acetaldehyde (90% aqueous solution) was mixed with 18 parts of glyoxal (40% aqueous solution) and charged, and glyoxal (40% aqueous solution) was dropped from the dropping funnel as in Example 1. A mixture of 127 parts and 49 parts of acetaldehyde (90% aqueous solution) was dropped over 4 hours. Next, the pressure was gradually reduced from the normal pressure to a pressure of 5.3 kPa at a temperature of 80 ° C., and dehydration was performed to obtain crude 1-ethyl-2-methylimidazole (L-3). Subsequently, (L-3) was purified by precision distillation under the conditions of a temperature of 100 ° C. and a reduced pressure of 0.7 kPa to obtain 1-ethyl-2-methylimidazole (L-4). The purity of the obtained (L-4) was 80% by GC analysis. Subsequently, HPLC and GC analyzes were performed under the above-described conditions in the same manner as in Example 1, and the contents (a1), (a2), (a3) and (a4) were measured. Here, (a1) was quantified by HPLC, and (a2), (a3) and (a4) were quantified by GC. The total content of ammonium acetate and ethylamine salt is 0.8%, the total content of acetamide and N-ethylacetamide is 1.0%, and 2,4,6,8,9,10-hexamethyl-1 , 3,5,7-Tetraazatricyclo [3,3,1,1 (3,7)] decane, 3-ethyl-2,4,8-trimethyl-1,3,5-triazabicyclo [3 , 2,1] octane and 2,9-dimethyl-3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene had a total content of 1.5%. Was. Next, 110 parts of (L-4), 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave with a reflux condenser, and the reaction was carried out in the same manner as in Example 1. NMR analysis of the reaction product (L1-4) showed that 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate was formed, and 1-ethyl-2,3-dimethylimidazolium monomethyl carbonate was found to be formed. The conversion to salt was 99.5%. 435 parts (46% by weight of a pure salt) of the obtained reaction mixture (L1-4) is placed in a flask, and 209 parts of an aqueous borofluoric acid solution (42% by weight of a pure content) is stirred at room temperature for about 30 minutes. After the dropwise addition, the mixture was treated in the same manner as in Example 1 to leave 212 parts of a white solid (A-4). As a result of NMR analysis of this liquid, the main component was 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate. 212 g of the obtained 1-ethyl-2,3-dimethylimidazolium tetrafluoroborate was uniformly dissolved in propylene carbonate in its entirety to make the whole volume 1 liter, thereby preparing an electrolytic solution of the present invention. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) the total content of ammonium acetate salt and ethylamine acetate salt was 0.08%, (a2) the total content of acetamide and N-ethylacetamide was 0.1%, and (a3) 2,4,6 8,9,10-hexamethyl-1,3,5,7-tetraazatricyclo [3,3,1 (3,7)] decane, 3-ethyl-2,4,8-trimethyl-1, Of 3,5-triazabicyclo [3,2,1] octane and 2,9-dimethyl-3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene The total content was 0.45%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 0.5%. The total content of (a1), (a2), (a3) and (a4) was 1.13%.

Example 8
In Example 7 of the present invention, 78 parts of methylamine (40% aqueous solution) was charged instead of ethylamine, and the reaction was carried out in the same manner as in Example 7. Next, the pressure was gradually reduced from the normal pressure to a pressure of 5.3 kPa at a temperature of 80 ° C., and dehydration was performed to obtain crude 1,2-dimethylimidazole (L-5). Subsequently, (L-5) was purified by precision distillation at a temperature of 100 ° C. and a reduced pressure of 0.7 kPa to obtain 1,2-dimethylimidazole (L-6). The purity of the obtained (L-6) was 90% by GC analysis. Subsequently, HPLC and GC analyzes were performed under the above-described conditions in the same manner as in Example 1, and the contents (a1), (a2), (a3) and (a4) were measured. Here, (a1) was quantified by HPLC, and (a2), (a3) and (a4) were quantified by GC. The total content of ammonium acetate and methylamine acetate was 0.7%, the total content of acetamide and N-methylacetamide was 0.9%, and 2,4,6,8,9,10-hexamethyl- 1,3,5,7-tetraazatricyclo [3,3,1,1 (3,7)] decane, 2,3,4,8-tetramethyl-1,3,5-triazabicyclo [3 , 2,1] octane and 2,3,9-trimethyl-1,3,6-triazabicyclo [4,2,1] non-4,7-diene were 1.3% in total. Next, 96 parts of (L-6), 135 parts of dimethyl carbonate and 192 parts of methanol were charged into a stainless steel autoclave equipped with a reflux condenser, and the reaction was carried out in the same manner as in Example 1. NMR analysis of the reaction product (L1-5) showed that 1,2,3-trimethylimidazolium monomethyl carbonate was formed, and conversion to 1,2,3-trimethylimidazolium monomethyl carbonate was performed. The rate was 99.6%. 423 parts (44% by weight of pure salt) of the obtained reaction mixture (L1-5) was placed in a flask, and 209 parts of an aqueous borofluoric acid solution (42% by weight of pure content) was stirred at room temperature for about 30 minutes. After the dropwise addition, the mixture was treated in the same manner as in Example 1 to leave 198 parts of a white solid (A-4). As a result of NMR analysis of this liquid, the main component was 1,2,3-tridimethylimidazolium tetrafluoroborate. 198 g of the obtained 1,2,3-trimethylimidazolium tetrafluoroborate was uniformly dissolved in propylene carbonate in a total amount of 1 liter to prepare an electrolytic solution of the present invention. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) The total content of ammonium acetate and methylamine acetate was 0.07%, (a2) the total content of acetamide and N-methylacetamide was 0.09%, and (a3) 2,4,6 , 8,9,10-Hexamethyl-1,3,5,7-tetraazatricyclo [3,3,1 (3,7)] decane, 2,3,4,8-tetramethyl-1, Total content of 3,5-triazabicyclo [3,2,1] octane and 2,3,9-trimethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 0.43%, and the total content of (a4) methyl carbamate and N-methylmethyl carbamate was 0.45%. The total content of (a1), (a2), (a3) and (a4) was 1.04%.

Comparative Example 1
In Example 1, the charged amount of ethylamine (70% aqueous solution) was changed from 64 parts to 128 parts, and the other conditions were the same as in Example 1 to obtain an electrolyte salt (A-1 ′). (A-1 ′) 198 g of the total amount was uniformly dissolved in propylene carbonate to make the whole 1 liter to prepare an electrolytic solution. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) the total content of ammonium formate and ethylamine formate is 2.7%; (a2) the total content of formamide and N-ethylformamide is 2.8%; (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 4.0%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 8.0%. The total content of (a1), (a2), (a3) and (a4) was 17.5%.

Comparative Example 2
198 g of the salt (A-1 ′) was uniformly dissolved in acetonitrile to make the whole 1 liter, thereby preparing an electrolytic solution. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) the total content of ammonium formate and ethylamine formate is 2.7%; (a2) the total content of formamide and N-ethylformamide is 2.8%; (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 4.0%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 8.0%. The total content of (a1), (a2), (a3) and (a4) was 17.5%.

Comparative Example 3
198 g of the salt (A-1 ′) was uniformly dissolved in sulfolane, and the whole was adjusted to 1 liter to prepare an electrolytic solution. The obtained electrolyte was analyzed by HPLC and GC. Here, as in Example 1, (a1) was quantified by HPLC and (a2), (a3) and (a4) were quantified by GC under the above-mentioned conditions. (A1) the total content of ammonium formate and ethylamine formate is 2.7%; (a2) the total content of formamide and N-ethylformamide is 2.8%; (a3) hexamethylenetetramine, Total content of ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6-triazabicyclo [4,2,1] nona-4,7-diene Was 4.0%, and the total content of (a4) methyl carbamate and methyl N-ethylcarbamate was 8.0%. The total content of (a1), (a2), (a3) and (a4) was 17.5%.

The other impurity contents in the electrolyte solutions of Examples 1 to 8 and Comparative Examples 1 to 3 were all at the following levels. Moisture 50ppm or less, tertiary amines and tertiary amine salt 1 mmol / kg or less, BF ₄ ^- the hydrolyzate 100ppm or less, silicic hydrofluoric acid and silicates hydrogen fluoride salt is 1ppm or less, sulfuric acid and sulfate 1ppm or less , Hydrogen fluoride and fluoride salts 1 ppm or less, glycol 10 ppm or less, chlorhydrin 10 ppm or less, lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, zinc, lead ion content Are all 0.1 ppm or less.

  Table 1 shows the withstand voltage of the electrolytes of Examples 1 to 8 and Comparative Examples 1 to 3 and the measurement results of the initial capacitance, the capacitance change rate, the internal resistance, and the residual voltage of the electric double layer capacitor using the electrolytes. 1 is shown.

  As is clear from Table 1, ammonium carboxylate and / or amine carboxylate (a1) represented by the general formula (1) and / or acid amide represented by the general formula (2) in the electrolytic solution (A2) and / or the content of the cyclic amine compound (a3) represented by the general formula (3) and / or the urethane compound (a4) represented by the general formula (4) is based on the weight of the electrolytic solution. a1) is 1% by weight or less; (a2) is 1% by weight or less; (a3) is 3% by weight or less; and (a4) is 5% by weight or less. Showed a higher withstand voltage than the electrolytic solutions of Comparative Examples 1 to 3. Further, the electrochemical capacitor using the electrolytic solution had a lower internal resistance, a higher residual voltage, a higher initial capacitance, and an extremely low capacitance change rate as compared with the comparative example.

  Although the coin-type electric double-layer capacitors have been described in Examples 1 to 8 of the present invention, the present invention may be applied to an electrolytic solution of an electric double-layer capacitor having another structure such as a wound type or a laminated type. The same effects as in Examples 1 to 8 can be obtained.

The electrolytic solution of the present invention is used for memory backup of various electronic devices, backup power of various power supplies, power storage devices such as power storage elements used in combination with solar cells, and motors that require a large current such as electric vehicles. Electrochemical capacitors used for power supplies, power tools for power tools such as electric tools, etc., electrolytic capacitors used for AV equipment, OA equipment, home appliances, in-vehicle equipment, measurement / FA equipment, primary batteries, secondary batteries, solar batteries It is also useful as an electrolyte for electrochemical devices such as fuel cells, and also as a metal electrodeposition bath, an electrolytic reaction solvent, a reaction solvent, and a separation operation solvent.

Claims (10)

An electrolyte comprising the electrolyte salt (A), wherein the content of the ammonium carboxylate and / or amine carboxylate (a1) represented by the general formula (1) in the electrolyte is based on the weight of the electrolyte. x1 is 1% by weight or less, and
_{^{R 1 -CO 2 - · N +}} H 3 R 2 (1)
[In the formula, R ¹ may have one or more hydroxyl, amino, nitro, cyano, carboxyl, or formyl group, or may have one or more ether group in the main chain. A monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group) or a hydrogen atom; R ² is a monovalent hydrocarbon group having 1 to 10 carbon atoms or a hydrogen atom]
A content x2 of the acid amide (a2) represented by the general formula (2) in the electrolytic solution based on the weight of the electrolytic solution is 1% by weight or less, and
R ³ -CONHR ⁴ (2)
[Wherein, R ³ is the same as R ¹ above; R ⁴ is the same as R ² above]
The content x3 of the cyclic amine compound (a3) represented by the general formula (3) in the electrolytic solution based on the weight of the electrolytic solution is 3% by weight or less, and
[Wherein, R ⁵ , R ⁶ and R ⁷ may have one or more hydroxyl, amino, nitro, cyano, carboxyl, or formyl group, or have an amino group in the main chain. And / or a monovalent hydrocarbon group having 1 to 10 carbon atoms (including the carbon number of the functional group), which may have one or more ether groups, or a hydrogen atom, X, Y and Z may have one or more hydroxyl, amino, nitro, cyano, carboxyl or formyl groups. Or a divalent hydrocarbon group having 1 to 10 carbon atoms which may be the same or different and may have one or more ether groups in the main chain]
An electrolytic solution, wherein the sum of x1, x2 and x3 is 0.00001% by weight or more and 4% by weight or less. Further, the content x4 of the urethane compound (a4) represented by the general formula (4) in the electrolyte based on the weight of the electrolyte is 5% by weight or less, and
R ⁸ OOCHR ⁹ (4)
[Wherein, R ⁸ and R ⁹ may have one or more hydroxyl, amino, nitro, cyano, carboxyl, or formyl group, or have an amino group and / or The same or different monovalent hydrocarbon groups having 1 to 10 carbon atoms (including the number of carbon atoms of the functional group) or hydrogen atoms which may have one or more ether groups]
2. The electrolytic solution according to claim 1, wherein the sum of x1, x2, x3 and x4 is 0.00001% by weight or more and 8% by weight or less. 3. The electrolytic solution according to claim 1, wherein the electrolyte salt (A) is further dissolved in a non-aqueous solvent (B). The electrolyte solution according to any one of claims 1 to 3, wherein the electrolyte salt (A) is an imidazolium salt (A1) represented by the general formula (4).
[Wherein, R ⁸ and R ¹⁰ are the same or different and are a monovalent hydrocarbon group having 1 to 10 carbon atoms; R ⁹ , R ¹¹ and R ¹² are a hydroxyl group, an amino group, a nitro group, a cyano group, a carboxyl group, or A monovalent hydrocarbon group or hydrogen having 1 to 10 carbon atoms which may have one or more formyl groups or may have one or more ether groups in a main chain; atom; X ^- represents a counter anion Wherein wherein X ^{- _{PF 6 -, BF 4 -,}} F - · 2.3HF, AsF 6 -, SbF 6 -, N (RfSO 3) 2 -, C (RfSO 3) 3 - and RfSO ₃ ^- (Rf carbon The electrolytic solution according to any one of claims 1 to 4, which is an ion selected from the group consisting of (fluoroalkyl groups of Formulas 1 to 12). Based on the weight of the imidazoles (L), the content of (a1) is 5% by weight or less, the content of (a2) is 5% by weight or less, and the content of (a3) is 15% by weight or less. And an electrolyte salt obtained by further performing an anion exchange reaction on the quaternary ammonium salt (L1) produced using (L) in which the content of (a4) is 25% by weight or less, or The electrolyte according to any one of claims 1 to 5, wherein the electrolyte salt is dissolved in a non-aqueous solvent. (A1) is at least one selected from the group consisting of ammonium formate, methylamine formate and ethylamine formate, and (a2) is a group consisting of formamide, N-methylformamide and N-ethylformamide At least one selected from the group consisting of (a3) wherein hexamethylenetetramine, 3-ethyl-1,3,5-triazabicyclo [3,2,1] octane and 3-ethyl-1,3,6 -Triazabicyclo [4,2,1] nona-4,7-diene, wherein (a4) is methyl carbamate, ethyl carbamate, methyl N-methylcarbamate, A small number selected from the group consisting of ethyl N-methylcarbamate, methyl N-ethylcarbamate and ethyl N-ethylcarbamate. Kutomo which is a kind claims 1-6 electrolyte according to any one. The non-aqueous solvent (B) is at least one selected from the group consisting of propylene carbonate, ethylene carbonate, sulfolane, methylsulfolane, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. 7. The electrolytic solution according to any one of 7. An electrolytic solution for an electrochemical device, comprising the electrolytic solution according to claim 1. An electrochemical device comprising the electrolytic solution according to claim 1.