JP2003324038A - Electrolyte for electrochemical capacitor and electrochemical capacitor using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide non-aqueous electrolyte which can inhibit a decrease of dielectric strength and a drop of a capacitor's capacity and an electrochemical capacitor. <P>SOLUTION: The electrolyte for the electrochemical capacitor, an electrolytic salt consisting of a strong-acid anion, and a strong-alkali cation are solved in a non-aqueous solvent, the equivalent ratio of anion/cation is 0.99-1.01. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrolytic solution for an electrochemical capacitor and an electrochemical capacitor using the electrolytic solution. More specifically, the present invention relates to an electrochemical capacitor having a high withstand voltage and a large energy density, which is used for memory backup of various electronic devices and for electric power of an electric vehicle or the like that requires a large current, and an electrolytic solution used therefor.

[0002]

2. Description of the Related Art An electrochemical capacitor using a non-aqueous electrolytic solution has an advantage that it can have a higher withstand voltage and hence a higher energy density than an electrochemical capacitor using an aqueous electrolytic solution. These are rapidly spreading as backup power sources for consumer electronic devices. Particularly, an electrochemical capacitor using a non-aqueous electrolytic solution is suitable for an electrochemical capacitor having an electrostatic capacity of 50 F or more, which has been attracting attention in recent years, for electric power system applications such as electric vehicles, hybrid vehicles, and electric power storage.

As a non-aqueous electrolytic solution for electrochemical capacitors, a quaternary ammonium borofluoride salt in a propylene carbonate solvent (Tanahashi et al., Electrochemistry, Vol. 56, p. 892).
(1988) or a quaternary phosphonium borofluoride salt (Hiratsuka et al., Electrochemistry, Vol. 59, p. 209, 1991) dissolved therein has been put to practical use.

[0004]

However, the electrochemical capacitor using such a non-aqueous electrolyte often has a problem that its withstand voltage is insufficient and its capacity decreases over time. An object of the present invention is to provide a non-aqueous electrolytic solution capable of suppressing a decrease in withstand voltage and a decrease in capacity of a capacitor, and an electrochemical capacitor using the same.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors in view of such circumstances, the cause is that the equivalent ratio of anions and cations in the electrolyte is not exactly equal. It has been found that by setting this ratio to 0.99 to 1.01, it is possible to suppress a decrease in withstand voltage and a decrease in capacitance of the capacitor, and have completed the present invention. It has not been known until now that such an equivalent ratio of anions and cations affects the performance of an electrochemical capacitor, particularly an electric double layer capacitor. That is, the present invention is an electrolytic solution for an electrochemical capacitor in which an electrolyte salt consisting of an anion of a strong acid and a cation of a strong base is dissolved in a non-aqueous solvent, and the equivalent ratio of the anion and the cation is 0.99 to 1 An electrolytic solution for an electrochemical capacitor of 0.01, an electrochemical capacitor using the electrolytic solution, and an electric double layer capacitor using the electrolytic solution.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
Anion of the electrolyte salt used in the electrolytic solution according to the present invention
Is a strong acid to H⁺Is an off anion and the electrolyte
Is a strong base OH⁻Is one or more than two
It is a cation. Here, a strong acid has a pKa of 3 or less,
It is preferably a 1 to 3 valent inorganic or organic acid
It A strong base has a pKa of 9 or more, preferably 10
The above-mentioned monovalent and trivalent inorganic and organic bases. Examples of strong acids
For example, HPF₆, HBF_Four, HAsF₆, H
SbF₆, HN (RfSO_Two)_Two, HC (RfSO_Two)
_Three, RfCOOH, RfSO _ThreeH (Rf has 1 to 1 carbon atoms
2 fluoroalkyl groups) and HClO_FourEtc.
It Examples of strong bases include, for example, quaternary ammonium.
Um hydroxide or quaternary phosphonium hydro
Examples thereof include oxides. Equivalent ratio of anion and cation
Is usually 0.99 to 1.01. Anions and cations
If the ratio of is less than 0.99 and exceeds 1.01, withstand voltage
Will decrease, and the capacitance of the capacitor will decrease. With anions
The equivalent ratio of cations is preferably 0.999 to 1.00.
1, and more preferably 0.9999 to 1.0001.
Is.

Of the anions and cations defined in the present invention
The equivalence ratio is measured by NMR. Normal ¹H-NMR measurement
Focusing on individual absorption derived from anions and cations,
The equivalent ratio can be calculated from the integral ratio of. However,
About PF₆ ⁻, BF _Four ⁻, AsF₆ ⁻, Sb
F₆ ⁻, N (RfSO_Two)_Two ⁻, C (RfS
O_Two)_Three ⁻, RfCOO⁻, And RfSO_Three ⁻And so on
In many cases, since hydrogen does not contain hydrogen,¹H-
NMR, and¹⁹F-NMR, hydrogen and fluorine in the molecule
Measurement with a compound containing
The cation¹From 1 H-NMR, the anion is
¹⁹Measurement can be performed using F-NMR.

In order to make the equivalent ratio of anions and cations close to such an extremely equal amount, for example, there is a method of preliminarily purifying, by recrystallization or the like, an electrolyte salt prepared to be approximately equal in calculated amount. Solvents used for recrystallization include alcohols such as methanol, ethanol, n-propanol and isopropanol; ketones such as acetone, methyl ethyl ketone, diethyl ketone and methyl isobutyl ketone; diethyl ether, ethyl-n-propyl ether and ethyl isopropyl. Examples thereof include ethers such as ether, di-n-propyl ether, diisopropyl ether, n-propyl isopropyl ether, dimethoxyethane, methoxyethoxyethane and diethoxyethane. These may be used alone or in combination of two or more. The amount of the solvent used for recrystallization depends on the type of the recrystallization solvent, but since sulfuric acid (salt) as an impurity is dissolved and the loss of the electrolyte salt is small, the weight ratio to the electrolyte salt is usually 0. It is preferably within the range of 0.5 to 10 times.

The electrolyte salt used in the present invention is preferably a quaternary ammonium salt or a quaternary phosphonium salt represented by the general formula (1). Q ⁺ X ⁻ (1) In the formula, Q ⁺ represents a quaternary ammonium ion or a quaternary phosphonium ion, and X ⁻ represents PF ₆ ⁻ , BF ₄ ⁻ , A.
sF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₂ ) ₂ ⁻ , C (R
fSO ₂ ) ₃ ⁻ , RfCOO ⁻ , and RfSO ₃ ⁻ (R
f represents a counter ion selected from the group consisting of C1-C12 fluoroalkyl groups). As a specific example of Rf,
Trifluoromethyl group, pentafluoroethyl group, n-
Examples thereof include perfluorobutyl group, t-perfluorobutyl group and perfluorooctyl group.

Preferably, the quaternary ammonium group represented by Q ⁺ is a carbon atom such as an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group containing an arbitrary tertiary amine (containing 1 to 3 nitrogen atoms). Number 1-20, preferably 1
What is quaternized with the hydrocarbon group of 5 is used. The hydrocarbon moiety forming the quaternary ammonium group has a hydroxyl group,
An amino group, a nitro group, a cyano group, a carboxyl group, an ether group, an aldehyde group or the like may be bonded. The following compounds are mentioned as main examples.

Tetraalkylammonium compound tetramethylammonium, ethyltrimethylammonium, triethylmethylammonium, tetraethylammonium, diethyldimethylammonium, methyltri-n-propylammonium, tri-n-butylmethylammonium, ethyltri-n-butylammonium, Tri-n-octylmethyl ammonium, ethyl tri-n-octyl ammonium, diethylmethyl-i-
Propyl ammonium etc. -Ethylenediammonium-based compound N, N, N, N ', N', N'-hexamethylethylenediammonium, N, N'-diethyl-N, N, N ',
N'-tetramethylethylene diammonium and the like. -Pyrrolidinium compounds N, N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N, N-diethylpyrrolidinium and the like. -Piperidinium compound N, N-dimethylpiperidinium, N-ethyl-N-methylpiperidinium, N, N-diethylpiperidinium, N-n-butyl-N-methylpiperidinium, N-
Ethyl-N-n-butylpiperidinium and the like. -Hexamethyleneiminium-based compound N, N-dimethylhexamethyleneiminium, N-ethyl-N-methylhexamethyleneiminium, N, N-diethylhexamethyleneiminium and the like. -Morpholinium compounds N, N-dimethylmorpholinium, N-ethyl-N-methylmorpholinium, N-butyl-N-methylmorpholinium, N-ethyl-N-butylmorpholinium and the like. -Piperazinium compound N, N, N ', N'-tetramethylpiperazinium, N
-Ethyl-N, N ', N'-trimethylpiperazinium, N, N'-diethyl-N, N'-dimethylpiperazinium, N, N, N'-triethyl-N'-methylpiperazinium, N, N, N ', N'-tetraethylpiperazinium and the like. -Tetrahydropyrimidinium compound 1,3-dimethyl-1,4,5,6-tetrahydropyrimidinium, 1,2,3-trimethyl-1,4,5,6
-Tetrahydropyrimidinium, 1,2,3,4-tetramethyl-1,4,5,6-tetrahydropyrimidinium, 1,2,3,5-tetramethyl-1,4,5,6-
Tetrahydropyrimidinium, 8-methyl-1,8-diazabicyclo [5.4.0] -7-undecenium, 5
-Methyl-1,5-diazabicyclo [4.3.0] -5
-Nonenium, 8-ethyl-1,8-diazabicyclo [5.4.0] -7-undecenium, 5-ethyl-
1,5-diazabicyclo [4.3.0] -5-nonenium and the like. -Pyridinium compound N-methylpyridinium, N-ethylpyridinium, N
-Methyl-4-dimethylaminopyridinium, N-ethyl-4-dimethylaminopyridinium and the like. -Picolinium-based compounds N-methylpicolinium, N-ethylpicolinium and the like.・ Imidazolinium compounds 1,2,3-trimethylimidazolinium, 1,2,
3,4-tetramethylimidazolinium, 1,3,4-
Trimethyl-2-ethylimidazolinium, 1,3-dimethyl-2,4-diethylimidazolinium, 1,2-
Dimethyl-3,4-diethylimidazolinium, 1-methyl-2,3,4-triethylimidazolinium, 1,
2,3,4-tetraethylimidazolinium, 1,3-
Dimethyl-2-ethylimidazolinium, 1-ethyl-
2,3-dimethylimidazolinium, 1,2,3-triethylimidazolinium, 1,1-dimethyl-2-heptylimidazolinium, 1,1-dimethyl-2- (2 '
-Heptyl) imidazolinium, 1,1-dimethyl-2
-(3'-heptyl) imidazolinium, 1,1-dimethyl-2- (4'-heptyl) imidazolinium, 1,
1-dimethyl-2-dodecylimidazolinium, 1,1
-Dimethylimidazolinium, 1,1,2-trimethylimidazolinium, 1,1,2,4-tetramethylimidazolinium, 1,1,2,5-tetramethylimidazolinium, 1,1,2 , 4,5-pentamethylimidazolinium and the like. -Imidazolium-based compound 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-diethylimidazolium, 1,2,3-trimethylimidazolium, 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, 1,3-dimethyl-
2-ethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1,2,3-triethylimidazolium, 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, 1,1,2,
4-tetramethylimidazolium, 1,1,2,5-tetramethylimidazolium, 1,1,2,4,5-pentamethylimidazolium and the like. -Quinolinium compounds N-methylquinolinium, N-ethylquinolinium and the like. -Bipyridinium compound N-methyl-2,2'-bipyridinium, N-ethyl-
2,2'-bipyridinium and the like. -A mixture of two or more of the above. Among the above, preferred are tetraalkylammonium compounds and imidazolium compounds.

The quaternary phosphonium group represented by Q ⁺ usually has 1 to 1 carbon atoms such as an alkyl group, a cycloalkyl group, an aryl group and an aralkyl group at the central phosphorus atom.
Those in which 20, preferably 1 to 5 hydrocarbon groups are bonded are used. Two or three of these hydrocarbon groups may be bonded to each other to form a ring. Further, these hydrocarbon groups include hydroxyl group, amino group, nitro group, cyano group,
A carboxyl group, an ether group, an aldehyde group or the like may be bonded. The following compounds are mentioned as main examples.

Tetramethylphosphonium, ethyltrimethylphosphonium, triethylmethylphosphonium, tetraethylphosphonium, diethyldimethylphosphonium, trimethyl-n-propylphosphonium, trimethylisopropylphosphonium, ethyldimethyl-n-propylphosphonium, ethyldimethylisopropylphosphonium, diethylmethyl-n -Propylphosphonium, diethylmethylisopropylphosphonium, dimethyldi-n-propylphosphonium, dimethyl-n-propylisopropylphosphonium, dimethyldiisopropylphosphonium, triethyl-n-propylphosphonium, n-butyltrimethylphosphonium, isobutyltrimethylphosphonium, t-butyltrimethylphosphonium , Triethyl Propyl phosphonium, Echirumechiruji -n- propyl phosphonium, ethyl methyl -n
-Propylisopropylphosphonium, ethylmethyldiisopropylphosphonium, n-butylethyldimethylphosphonium, isobutylethyldimethylphosphonium, t-butylethyldimethylphosphonium, diethyldi-n-propylphosphonium, diethyl-n-propylisopropylphosphonium, diethyldiisopropylphosphonium, methyltri- n-propylphosphonium, methyldi-n-propylisopropylphosphonium, methyl-n-propyldiisopropylphosphonium, n-butyltriethylphosphonium, isobutyltriethylphosphonium, t-butyltriethylphosphonium, di-n-butyldimethylphosphonium, diisobutyldimethylphosphonium, di -T-butyldimethylphosphonium, n-butylui Butyldimethyl phosphonium, n- butyl -t- butyl dimethyl phosphonium, isobutyl -t- butyl dimethyl phosphonium, tri -n
-Octylmethylphosphonium, ethyltri-n-octylphosphonium, etc., and mixtures of two or more of the above. Among the above, preferred are tetramethylphosphonium, ethyltrimethylphosphonium, triethylmethylphosphonium, tetraethylphosphonium and diethyldimethylphosphonium.

As the solvent used in the electrolytic solution of the present invention, a known solvent is used, and it is usually selected from the solubility of the electrolyte and the electrochemical stability. Specific examples include the following. It is also possible to use two or more of these together.

Ethers: chain ethers [C2-C2
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 [carbon number 2
~ 4 (tetrahydrofuran, 1,3-dioxolane,
1,4-dioxane etc.); C5-18 (4-butyldioxolane, crown ether etc.)]. -Amids: N, N-dimethylformamide, N, N-
Dimethylacetamide, N, N-dimethylpropionamide, hexamethylphosphorylamide, N-methylpyrrolidone and the like. -Carboxylic acid esters: methyl acetate, methyl propionate, etc.・ 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: dimethyl sulfoxide, sulfolane,
3-methylsulfolane, 2,4-dimethylsulfolane and the like. -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.

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

The concentration of the electrolyte salt in the electrolytic solution is preferably 0.1 mol / liter or more from the viewpoint of the electric conductivity and internal resistance of the electrolytic solution, and 4 mol / liter or less from the viewpoint of salt precipitation at low temperature. preferable. More preferably 0.5 to 3
Mol / liter.

The water content in the electrolytic solution is preferably 300 ppm or less, more preferably 1 from the viewpoint of electrochemical stability.
The amount is 00 ppm or less, particularly preferably 50 ppm or less. The water content can be measured by the Karl Fischer method.

The electrochemical capacitor according to the present invention uses the above-mentioned electrolytic solution according to the present invention. The electrochemical capacitor includes an electrode, a current collector, and a separator, and optionally includes a case, a gasket, and the like usually used for the capacitor, and at least one of the positive electrode and the negative electrode among the electrodes contains a carbonaceous substance as a main component. It is a substance such as a polarizable electrode. The electrode and the separator are impregnated with the electrolytic solution. Among electrochemical capacitors, one that uses activated carbon for its electrodes is called an electric double layer capacitor.

The main component of the polarizable electrode is the electric
It is chemically inert and has moderate electrical conductivity.
Therefore, a carbonaceous substance is preferable, and as described above,
At least one of the negative electrodes is a carbonaceous material. Accumulation of charge
BET by nitrogen adsorption method because of the large electrode interface
Specific surface area obtained by the method is 10 m^Two/ G or more porous charcoal
Elementary materials are more preferred. The specific surface area of the porous carbon material is
Target electrostatic capacity per unit area (F / m^Two)When,
It is selected in consideration of the decrease in bulk density due to the increase in specific surface area.
However, the specific surface area obtained by the BET method by the nitrogen adsorption method is
30-2500m ^Two/ G is preferable, per volume
The specific surface area is 300-23
00m^Two/ G of activated carbon is particularly preferred.

Raw materials for the activated carbon include wood, sawdust,
Plant materials such as coconut and pulp waste liquor; fossil fuel-based materials such as coal, petroleum heavy oil, or coal-based and petroleum-based pitch obtained by pyrolyzing them, petroleum coke, carbon aerogel, tar pitch, etc. Synthetic polymer substances such as phenolic resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, plastic waste; various kinds of waste tires and the like are used. After carbonizing these raw materials, they are activated by a gas activation method or a chemical activation method. The gas activation method is also called physical activation, and is a method of obtaining activated carbon by reacting a carbonized raw material with steam, carbon dioxide gas, oxygen, and other oxidizing gases at a high temperature. The chemical activation method is a method of uniformly impregnating a raw material with an activation chemical, heating the material in an inert atmosphere, and dehydrating and oxidizing the chemical to obtain activated carbon. Examples of the chemicals used include zinc chloride, phosphoric acid, sodium phosphate, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium sulfate, potassium sulfate, calcium carbonate and the like. Any of the above may be used as the method for producing the activated carbon used in the present invention.

Among these activated carbons, the activated carbon obtained by carbonizing coconut husks, coal or phenol resin in the gas activation method has a relatively high capacitance and is industrially mass produced. Since it is possible and inexpensive, it is suitable for the present invention. Also, in the chemical activation method,
Activated carbon obtained by chemical activation with potassium hydroxide is
Although the manufacturing cost is higher than that of steam activation, the electrostatic capacity tends to be large, which is preferable. The activated carbon after the activation treatment is heat-treated at a temperature of usually 500 to 2500 ° C., preferably 700 to 1500 ° C. under an inert atmosphere of nitrogen, argon, helium, xenon, etc. to remove unnecessary functional groups on the surface. , Develop the crystallinity of carbon,
Electronic conductivity may be increased.

The activated carbon has various shapes such as crushed shape, granular shape, granule, fiber, felt, woven fabric and sheet shape.
Either can be used in the present invention. In the case of a granular carbonaceous material, the bulk density of the electrode is improved and the internal resistance is reduced, so that the average particle diameter is preferably 30 μm or less.

The polarizable electrode mainly composed of the above-mentioned carbonaceous substance is usually composed of the carbonaceous substance, a conductive agent and a binder substance. The electrode can be formed by a conventionally known method. For example, it can be obtained by adding polytetrafluoroethylene to a mixture of a carbonaceous substance and acetylene black, mixing them, and press-molding them. Further, a carbonaceous substance and a binder substance such as pitch, tar, and phenol resin are mixed and molded, and then heat-treated in an inert atmosphere to obtain a sintered body. Alternatively, it is possible to sinter only the carbonaceous material to form a polarizable electrode without using a conductive agent or a binder. The shape of the electrode may be any of a thin coating film on the surface of the base material, a sheet-shaped or plate-shaped molded body, and a plate-shaped molded body made of a composite.

As the conductive agent used for the electrode, carbon black such as acetylene black and Ketjen black, carbon type conductive agent such as natural graphite, thermally expanded graphite and carbon fiber; metal oxide such as ruthenium oxide and titanium oxide. object;
In addition, metal fibers such as aluminum and nickel are preferable, and one kind or two or more kinds can be used. Acetylene black and Ketjen black are particularly preferable because the conductivity is effectively improved with a small amount.

The amount of the conductive agent blended in the electrode also varies depending on the type and shape of the carbonaceous substance. For example, when the carbonaceous substance is activated carbon, the amount blended with the activated carbon varies depending on the bulk density of the activated carbon. Holds the necessary capacitance for
And, in order to reduce the internal resistance, it is 5 to the activated carbon.
50% by weight is preferable, and 10 to 30% by weight is particularly preferable.

As the binder substance, polytetrafluoroethylene, polyvinylidene fluoride, fluoroolefin copolymer cross-linked polymer, polyvinyl alcohol, polyacrylic acid, carboxymethyl cellulose, polyimide, phenol resin, petroleum pitch and coal pitch are preferable. One kind or two or more kinds can be used.

The blending amount of the binder substance in the electrode body varies depending on the type and shape of the carbonaceous substance. For example, when the carbonaceous substance is activated carbon, it is preferably 0.5 to 30% by weight based on the activated carbon. -30 wt% is particularly preferred.

The current collector is not particularly limited as long as it is electrochemically and chemically resistant to corrosion, and examples of the positive electrode current collector include stainless steel, aluminum, titanium and tantalum. As the negative electrode current collector, stainless steel, aluminum, nickel, copper and the like are preferably used.

The separator is preferably made of a material having a small thickness and high electronic insulation and ion permeability, and is not particularly limited. For example, a nonwoven fabric such as polyethylene or polypropylene, or viscose rayon or natural cellulose is used. Papermaking and the like are preferably used.

Examples of the embodiment of the electrochemical capacitor of the present invention include coin type, wound type and prism type. The electrolytic solution for an electrochemical capacitor of the present invention can be applied to any of the electric double layer capacitors.

[0032]

EXAMPLES The present invention will be specifically described below with reference to examples, but the scope of the present invention is not limited to these examples. <Preparation of Electrolyte Solution><Comparative Example 1> Tetraethylammonium Hydroxide 1 The mol was dissolved in 500 ml of methanol, and 1 mol of borofluoric acid (42% aqueous solution) was gradually added dropwise to carry out the reaction. After the exotherm subsided, the solvent methanol and water were evaporated with an evaporator at a temperature of 60 to 80 ° C. and a pressure reduction degree of 2
It was distilled off at 0 mmHg, and tetraethylammonium tetrafluoroborate (hereinafter abbreviated as TEA.BF ₄ ).
Got The equivalent ratio of anion and cation of this electrolyte salt was analyzed by NMR, and as a result, anion / cation = 0.97.
Met. The electrolyte salt was dissolved in propylene carbonate (hereinafter abbreviated as PC) to a concentration of 1.0 mol / liter, and the water content was 20 pp with molecular sieves.
It was dehydrated to m to obtain an electrolytic solution.

<Example 1> TEA.BF ₄ 3 of Comparative Example 1
After completely dissolving 00 g in 600 mL of ethanol at a temperature of 60 ° C., the mixture was gradually cooled and then cooled to about 5 ° C. with ice water for recrystallization to obtain 200 g of an electrolyte. This operation was repeated 3 times to obtain 50 g of crystalline TEA.BF ₄ . As a result of analyzing the equivalent ratio of anion and cation of this crystal by NMR, it was anion / cation = 0.999. The electrolyte salt was dissolved in PC to a concentration of 1.0 mol / liter and dehydrated to a water content of 20 ppm with molecular sieves to obtain an electrolytic solution.

Comparative Example 2 1 mol of triethylmethylammonium hydroxide was dissolved in 500 ml of methanol, and 1 mol of borohydrofluoric acid (42% aqueous solution) was gradually added dropwise to the reaction. After the fever subsides,
The solvent methanol and water were evaporated at a temperature of 60-
Distilled off at 80 ° C. and a reduced pressure of 20 mmHg to give triethylmethylammonium tetrafluoroborate (hereinafter referred to as TEMA).
・ Abbreviated as BF ₄ . ) Got. The equivalent ratio of anion and cation of this electrolyte salt was analyzed by NMR, and the result was anion / cation = 0.97. The electrolyte salt was dissolved in PC to a concentration of 1.0 mol / liter and dehydrated to a water content of 20 ppm with molecular sieves to obtain an electrolytic solution.

Comparative Example 3 1 mol of triethylmethylammonium methyl carbonate was dissolved in 500 ml of methanol, and 1 mol of borohydrofluoric acid (42% aqueous solution) was gradually added dropwise to carry out the reaction. After the heat generation and the generation of carbon dioxide gas subsided, the solvents methanol and water were distilled off with an evaporator at a temperature of 60 to 80 ° C. and a pressure reduction degree of 20 mmHg.
EMA · BF ₄ was obtained. The equivalent ratio of anion to cation of this electrolyte salt was analyzed by NMR, and the result was anion / cation = 1.03. The concentration of the electrolyte salt in PC was 1.
It was dissolved at 0 mol / liter and dehydrated with molecular sieves to a water content of 20 ppm to obtain an electrolytic solution.

Example 2 TEMA · BF _{4 of} Comparative Example 2
After 300 g was completely dissolved in 600 mL of ethanol at a temperature of 60 ° C., the mixture was gradually cooled and then cooled to about 5 ° C. with ice water to recrystallize to obtain 200 g of an electrolyte. This operation was repeated 3 times to obtain 50 g of crystals TEMA.BF ₄ . As a result of analyzing the equivalent ratio of anion and cation of this crystal by NMR, it was anion / cation = 0.999. The electrolyte salt was dissolved in PC to a concentration of 1.0 mol / liter and dehydrated to a water content of 20 ppm with molecular sieves to obtain an electrolytic solution.

<Example 3> TEMA · BF _{4 of} Comparative Example 3
After 300 g was completely dissolved in 600 mL of ethanol at a temperature of 60 ° C., the mixture was gradually cooled and then cooled to about 5 ° C. with ice water to recrystallize to obtain 200 g of an electrolyte. This operation was repeated 3 times to obtain 50 g of crystals TEMA.BF ₄ . As a result of analyzing the equivalent ratio of anion and cation of this crystal by NMR, it was anion / cation = 1.000. The electrolyte salt was dissolved in PC to a concentration of 1.0 mol / liter and dehydrated to a water content of 20 ppm with molecular sieves to obtain an electrolytic solution.

Example 4 TEMA · B obtained in Example 2
A crystal of F ₄ was added to sulfolane (hereinafter abbreviated as SL) at a concentration of 1.
It was dissolved at 0 mol / liter and dehydrated with molecular sieves to a water content of 20 ppm to obtain an electrolytic solution.

<Example 5> TEMA.B obtained in Example 2
Γ-butyrolactone (hereinafter, abbreviated as GBL) as crystals of F ₄
To a concentration of 1.0 mol / liter, and the mixture was dehydrated with molecular sieves to a water content of 20 ppm to obtain an electrolytic solution.

Example 6 TEMA · B obtained in Example 2
Crystals of F ₄ were dissolved in acetonitrile (hereinafter abbreviated as AN) to a concentration of 1.0 mol / liter, and dehydrated with molecular sieves to a water content of 20 ppm to obtain an electrolytic solution.

Example 7 1.00 mol of 1-ethyl-3-methylimidazolium methyl carbonate was added to methanol 5
It was dissolved in 00 ml, and 1.000 mol of borofluoric acid (42% aqueous solution) was gradually added dropwise thereto to carry out a reaction. After the heat generation and the generation of carbon dioxide have subsided, the solvent methanol and water were evaporated using an evaporator at a temperature of 60 to 80 ° C and a degree of vacuum of
It was distilled off at 0 mmHg to give 1-ethyl-3-methylimidazolium tetrafluoroborate (hereinafter EMI.BF ₄
Abbreviated). The equivalent ratio of anion and cation of this electrolyte salt was analyzed by NMR, and as a result, anion / cation =
It was 1.000. The concentration of the electrolyte salt in PC is 1.0 m
It was dissolved so as to be ol / liter and dehydrated with molecular sieves to a water content of 20 ppm to obtain an electrolytic solution.

<Analytical Method of Equivalent Ratio of Anion and Cation>
An equivalent amount of 4-fluoroacetophenone (hereinafter abbreviated as 4FA) was added to the electrolyte salt to be analyzed and dissolved in heavy dimethyl sulfoxide to prepare a sample for NMR measurement. ¹ H-NMR and ¹⁹ F-NMR of this sample were measured,
The absorption intensity of the obtained spectrum was measured accurately, and the equivalent ratio of anion / cation was calculated according to the following formula. The integrated value of the absorption intensity in NMR needs to have a sufficient pulse delay time with respect to the relaxation time of the measurement nucleus in order to reduce an error. Usually, ¹ H-NMR requires 60 seconds or more, and ¹⁹ F-NMR requires 120 seconds or more. In order to further reduce the error, it is necessary to carry out a plurality of measurements and perform statistical processing such as taking an average. Anion / cation (equivalent ratio) = (strength of 1 fluorine of anion / 4 strength of 1 fluorine of FA) / (strength of 1 hydrogen of cation /
Strength of 1 hydrogen of 4FA)

A wound electric double layer capacitor (size: φ18 × L40, rating: 2.) using the electrolytic solutions of Examples 1 to 6 and the electrolytic solutions of Comparative Examples 1 to 3 and using activated carbon as a polarizable electrode. 3 V) was prepared, and the residual voltage was measured using this wound electric double layer capacitor. Table 1 shows the residual voltage after self-discharge.

<Measurement of Residual Voltage> The wound type electric double layer capacitor prepared above was charged at 2.3 V at room temperature for 24 hours and left at room temperature for 24 hours. Then, the terminal voltage of this wound electric double layer capacitor was measured. The terminal voltage obtained by this measurement was defined as the residual voltage. Generally, the lower the residual voltage is, the lower the withstand voltage is.

Using the wound electric double capacitor,
A high temperature load test at 70 ° C. and 2.5 V was performed, and the capacity retention rate after 1000 hours was measured. The results are shown in Table 1. <Capacity retention> A wound type electric double layer capacitor charged at 2.5 V at room temperature for 1 hour was charged with a constant current load device.
A constant current discharge was performed at 0 mA, and the capacity was calculated from the time during which the terminal voltage of the wound electric double layer capacitor changed from 1.5V to 1.0V. The capacity calculation method is Q = i ×
From the relationship of t = C × V, C = i × Δt / ΔV, and in this measurement, i = 0.5 (A), ΔV = 1.5−
It was set to 1.0 = 0.5 (V). Here, Q is the discharge charge amount (C), i is the discharge current (A), and t is the discharge time (se).
c) and C are capacitors (F) and V is voltage (V). When the initial capacity is C ₀ , 70 ° C., 2.5 V, and the capacity after 1000 hours is C ₁ , the capacity retention ratio = C ₁ / C ₀ × 10
It was calculated as 0 (%).

[0046]

[Table 1]

[0047]

EFFECTS OF THE INVENTION The electrolytic solution of the present invention has an equivalent ratio of anion to cation of 0.99 to 1.01, so that it contains few acids and bases as impurities and is excellent in withstand voltage and capacity retention. Due to such effects, the electrochemical capacitor using the electrolytic solution is used for memory backup of various electronic devices, backup power source of various power sources, secondary batteries such as power storage elements used in combination with solar cells. It is suitable as an alternative power storage device, a power source for driving a motor that requires a large current, a power source for a power tool such as an electric tool, and a power source for an electric vehicle.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshinori Takamukai             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd.

Claims (6)

[Claims] 1. An electrolytic solution for an electrochemical capacitor, comprising an electrolyte salt composed of an anion of a strong acid and a cation of a strong base dissolved in a non-aqueous solvent, wherein the equivalent ratio of the anion to the cation is 0.99 to 1. An electrolytic solution for an electrochemical capacitor, wherein the electrolytic solution is 0.01. 2. An electrolyte salt having a fourth structure represented by the general formula (1):
The electrolytic solution according to claim 1, which is a quaternary ammonium salt or a quaternary phosphonium salt. Q ⁺ X ⁻ (1) [In the formula, Q ⁺ represents a quaternary ammonium ion or a quaternary phosphonium ion, X ⁻ represents PF ₆ ⁻ , BF ₄ ⁻ ,
AsF ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₂ ) ₂ ⁻ , C
(RfSO ₂ ) ₃ ⁻ , RfCOO ⁻ , and RfSO ₃ ^−.
(Rf represents a counter alkyl group having 1 to 12 carbon atoms). ] 3. The non-aqueous solvent is propylene carbonate,
The electrolytic solution according to claim 1 or 2, which is at least one selected from the group consisting of ethylene carbonate, butylene carbonate, sulfolane, methylsulfolane, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate. 4. An electrochemical capacitor having a polarizable electrode impregnated with an electrolytic solution, which is used as the electrolytic solution.
3. Using the electrolytic solution for an electrochemical capacitor as described in 3 above,
Moreover, at least one of the positive electrode and the negative electrode is a polarizable electrode containing a carbonaceous substance as a main component. 5. The electrochemical capacitor according to claim 4, wherein the carbonaceous substance is activated carbon. 6. An electric double layer capacitor having a polarizable electrode impregnated with an electrolytic solution, which is used as the electrolytic solution.
An electric double layer capacitor comprising the electrolytic solution for an electrochemical capacitor according to any one of 3 to 3.