JP2003173936A - Electrolyte solution for electrochemical capacitor and electrochemical capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte solution which has a high withstand voltage and is excellent in long-term reliability and an electrochemical capacitor using the same. <P>SOLUTION: Electrolytic salt is dissolved into a non-aqueous solvent for the formation of an electrolyte solution for an electrochemical capacitor, and the content of metal ion in the electrolyte solution amounts to 500 ppm or less. <P>COPYRIGHT: (C)2003,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 requiring 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 applications such as electric vehicles, hybrid vehicles, and electric power storage.

As a non-aqueous electrolytic solution for electrochemical capacitors, a quaternary ammonium borofluoride (see Non-Patent Document 1) or a quaternary phosphonium borofluoride salt (see Non-Patent Document 2) is dissolved in a propylene carbonate solvent. Have been put to practical use.

[0004]

[Non-Patent Document 1] Tanahashi et al., "Electrochemistry", 1988.
Year 56, p. 892

[Non-Patent Document 2] Hiratsuka et al., "Electrochemistry", 1991.
Year, Volume 59, p. 209

[0005]

However, an electrochemical capacitor using such a non-aqueous electrolyte often has an insufficient withstand voltage and lacks reliability. An object of the present invention is to provide a non-aqueous solvent excellent in withstand voltage and long-term reliability, and an electrochemical capacitor using the same.

[0006]

The inventors of the present invention have made extensive studies in view of such circumstances, and as a result, the cause is that the electrolyte solution contains impurities, particularly metal ions derived from the electrolyte salt. It has been found that the short circuit between the electrodes of the capacitor can be suppressed and the long-term reliability can be improved by reducing the ions, and the present invention has been completed. It has not been known so far that such impurities affect the performance of the electrochemical capacitor, particularly the electric double layer capacitor. That is, the first aspect of the present invention is an electrochemical capacitor electrolytic solution obtained by dissolving an electrolyte salt in a non-aqueous solvent, wherein the content of metal ions in the electrolytic solution is 500 ppm or less. The electrolytic solution, the electrochemical capacitor using the electrolytic solution, and the electric double layer capacitor using the electrolytic solution.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The metal ions of the electrolytic solution according to the present invention include lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper,
Ions of zinc and lead are included.

The total content of metal ions in the electrolytic solution according to the present invention must be 500 ppm or less. 500ppm
When the amount of the metal ion exceeds 100, the leakage current increases due to the redox reaction of the metal ion (in the case where the capacitor is used for a long period of time, the metal is deposited and the electrode is short-circuited). The total content of metal ions in the electrolyte is
Preferably 100 ppm or less, more preferably 10 p
pm or less, more preferably 2 ppm or less, particularly preferably 1 ppm or less, very preferably 0.1 ppm or less,
Most preferably, it is 0.01 ppm or less. Content is by weight. In the present invention, the iron ion content in the electrolytic solution is preferably 200 ppm or less in order to achieve more excellent withstand voltage and long-term reliability.
More preferably 50 ppm or less, still more preferably 5 p
pm or less, particularly preferably 1 ppm or less, very preferably 0.06 ppm or less, most preferably 0.0
It is below 05 ppm. The metal ions in the electrolyte salt used in the electrolytic solution of the present invention are mixed in from the cation raw material component, the anion raw material component and the manufacturing process of the electrolyte.

As a method for quantifying the metal ions in the electrolytic solution according to the present invention, a quantification method such as an atomic absorption analysis method and an ICP (high frequency inductively coupled plasma emission spectroscopy) method can be used.

In order to produce an electrolytic solution in which the total content of metal ions is reduced to such a minute amount, for example, there is a method in which an electrolyte salt to be used is purified in advance by recrystallization and solvent extraction. Solvents used for recrystallization and solvent extraction 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. , Ethyl isopropyl ether, di-n-
Examples thereof include ethers such as 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 solvent used for purification depends on the type of solvent used, but it dissolves metal ions that are impurities, and since loss of the electrolyte salt is small, it is usually 0.5 to 10 times the amount of the electrolyte salt. The range of is preferable.

As the electrolyte salt, the following general formula (2)
Examples include the quaternary ammonium salt or the quaternary phosphonium salt represented by (3) or (4). ^{Q m + X n- (2)} Q m + (X -) n (3) (Q +) m X n- (4) formula, ^{Q m +} is a quaternary ammonium group or a 4 m-valent
Represents a primary phosphonium group, and X ⁿ⁻ represents an n-valent perfluoroalkanesulfonate ion, an n-valent perfluoroalkanecarboxylate ion, PF ₆ ⁻ , BF ₄ ⁻ , As.
F ₆ ⁻ , SbF ₆ ⁻ , N (RfSO ₃ ) ₂ ⁻ , and C
(RfSO ₃ ) ₃ ⁻ (Rf represents a fluoroalkyl group having 1 to 12 carbon atoms) or the like represents an anion produced using hydrogen fluoride as a raw material. m and n represent the integer of 1-3.

The electrolyte salt used in the present invention has the general formula
Quaternary ammonium salt represented by (1) or quaternary ammonium salt
It is preferably a sulphonium salt. Q⁺X⁻    (1) (In the formula, Q⁺Is a quaternary ammonium group or quaternary phosphine
Represents a phonium group, X⁻Is PF₆ ⁻, BF_Four ⁻, AsF
₆ ⁻, N (RfSO_Three)_Two ⁻, C (RfSO_Three) _Three ⁻Oh
And RfSO_Three ⁻(Rf is a fluorocarbon having 1 to 12 carbon atoms.
Represents a counter ion selected from the group consisting of: )

As the quaternary ammonium group represented by Q ⁺ , any tertiary amine can be used as an alkyl group (having 1 to 2 carbon atoms).
0), a cycloalkyl group (having 6 to 20 carbon atoms), an aryl group (having 6 to 20 carbon atoms), an aralkyl group (having 7 to 2 carbon atoms).
0) and the like, preferably those quaternized with an alkyl group having 1 to 5 carbon atoms are used. 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 to the hydrocarbon moiety forming the quaternary ammonium group. The following compounds are mentioned as main examples.

Tetraalkylammonium compounds 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. ・ Ethylene diammonium compounds N, N, N, N ', N', N'-hexamethylethylene diammonium, N, N'-diethyl-N, N, N ',
N'-Tetramethylethylenediammonium / pyrrolidinium-based compound N, N-dimethylpyrrolidinium, N-ethyl-N-methylpyrrolidinium, N, N-diethylpyrrolidinium / piperidinium-based compound N, N- Dimethylpiperidinium, N-ethyl-N-methylpiperidinium, N, N-diethylpiperidinium, N-n-butyl-N-methylpiperidinium, N-
Ethyl-N-n-butylpiperidinium, etc., hexamethyleneiminium-based compound N, N-dimethylhexamethyleneiminium, N-ethyl-N-methylhexamethylminiminium, N, N-diethylhexamethyleneiminium, etc. -Morpholinium compounds N, N-dimethylmorpholinium, N-ethyl-N-methylmorpholinium, N-butyl-N-methylmorpholinium, N-ethyl-N-butylmorpholinium, etc.-Piperazinium compounds 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, etc.-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, etc.-Picolinium compound N-methylpicolinium, N-ethylpicolinium, etc.-Imidazolinium compound 1,2,3-trimethylimidazolium Nium, 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, etc./Imidazolium-based compounds 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1,3-diethylimidazolium, 1,2,3-trimethylimidazolium Rium, 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, etc.-Quinolinium compounds N-methylquinolinium, N-ethylquino Norinium, etc.-Bipyridinium compounds N-methyl-2,2'-bipyridinium, N-ethyl-
It represents an ion such as 2,2′-bipyridinium. )

As the quaternary phosphonium group represented by Q ⁺ , an alkyl group (having 1 to 20 carbon atoms), a cycloalkyl group (having 6 to 20 carbon atoms), an aryl group (carbon Number 6 to 20), aralkyl group (carbon number 7)
~ 20) and the like, preferably those having an alkyl group having 1 to 5 carbon atoms bonded thereto. Two or three of these hydrocarbon groups may be bonded to each other to form a ring.
Further, 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 to these hydrocarbon groups. 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, diethyldiisopropylisopropylphosphonium, methyltri -N-propylphosphonium, methyldi-n-propylisopropylphosphonium, methyl-n-propyldiisopropylphosphonium, n-butyltriethylphosphonium, isobutyltriethylphosphonium, t-butyltriethylphosphonium, di-n-butyldimethylphosphonium, diisobutyldimethylphosphonium, Di-t-butyldimethylphosphonium, - butyl isobutyl dimethyl phosphonium, n- butyl -t- butyl dimethyl phosphonium, isobutyl -t- butyl dimethyl phosphonium, tri -n- octyl methyl phosphonium, ethyltri -n
-Octylphosphonium and the like.

As the solvent used in the electrolytic solution of the present invention, known solvents are used, and they are 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 ether [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. ); Carbon number 5-18 (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 solvents: N-methyl-2-oxazolidinone,
3,5-dimethyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylpyrrolidinone and the like.

Among 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, more preferably 0.5 mol / liter or more from the viewpoint of the electric conductivity and internal resistance of the electrolyte solution, and at low temperature. 4 mol / from the viewpoint of salt precipitation at the time
It is preferably 1 liter or less, more preferably 3 mol / liter or less.

The water content in the electrolytic solution is preferably 300 ppm or less, more preferably 100 ppm or less, and particularly preferably 50 ppm or less, from the viewpoint of electrochemical stability.

The electrochemical capacitor according to the present invention uses the above-mentioned electrolytic solution according to the present invention as an electrolytic solution. The electrochemical capacitor includes an electrode, a current collector,
In addition to the separator, a case and a gasket that are usually used for capacitors are optionally provided, and at least one of the positive electrode and the negative electrode among the electrodes is a polarizable electrode containing a carbonaceous substance as a main component. The electrode and the separator are impregnated with the electrolytic solution.

The main component of the polarizable electrode is preferably a carbonaceous substance because it is electrochemically inactive to the electrolytic solution and has a suitable electric conductivity. At least one is a carbonaceous material. Because of the large electrode interface where charges accumulate, BET by nitrogen adsorption method
A porous carbon material having a specific surface area of 10 m ² / g or more determined by the method is more preferable. The specific surface area of the porous carbon material is the target electrostatic capacity per unit area (F / m ² ).
And is selected in consideration of the decrease in bulk density due to the increase in the specific surface area, but the specific surface area obtained by the BET method by the nitrogen adsorption method is preferably from 30 to 2,500 m ² / g, and the static volume per volume is Due to its large capacitance, the specific surface area is 300
Especially preferred is ˜2,300 m ² / g of activated carbon.

Raw materials for activated carbon include wood, sawdust,
Plant material such as coconut and pulp waste liquid; coal, petroleum heavy oil, or fossil fuel material such as coal and petroleum pitch, petroleum coke, carbon aerogel, tar pitch obtained by pyrolyzing them Synthetic polymer substances such as phenol 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, in which the carbonized raw material is steamed at high temperature,
In this method, activated carbon is obtained by reacting with carbon dioxide gas, oxygen, or other oxidizing gas. In the chemical activation method, the raw material is uniformly impregnated with the activation chemical and heated in an inert atmosphere,
It is a method of obtaining activated carbon by dehydration and oxidation reaction of chemicals. 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 from carbonized coconut husks, coal or phenol resin in the gas activation method has a relatively high electrostatic capacity and is industrially mass produced. Since it is possible and inexpensive, it is suitable for the present invention. In addition, in the chemical activation method, activated carbon obtained by chemical activation using potassium hydroxide has a higher manufacturing cost than steam activation, but is preferable because it tends to have a large capacitance. Activated carbon after activation, nitrogen, argon, helium, xenon,
In an inert atmosphere such as, usually 500 ~ 2,500 ℃,
By heat treatment preferably at 700 to 1,500 ° C., unnecessary functional groups on the surface may be removed, the crystallinity of carbon may be developed, and the electron conductivity may be increased.

The activated carbon may have various shapes such as a crushed shape, a granular shape, a granule, a fiber, a felt, a woven fabric and a sheet shape, and any of them 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 carbonaceous material is usually composed of the carbonaceous material, a conductive material and a binder material. 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 in the electrode, carbon black such as acetylene black and Ketjen black, carbon type conductive agent such as natural graphite, thermally expanded graphite, carbon fiber; metal oxide such as ruthenium oxide and titanium oxide. And 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 blending amount of the conductive agent in the electrode also depends on the type and shape of the carbonaceous material. For example, when the carbonaceous material is activated carbon, the blending amount with respect to the activated carbon varies depending on the bulk density of the activated carbon. In order to maintain the necessary electrostatic capacity and to reduce the internal resistance, 5 to 50% by weight is preferable, and 10 to 30% by weight is particularly preferable with respect to the activated carbon.

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. These metals usually do not dissolve in the electrolytic solution, but caution is required because dissolution occurs when the water content in the electrolytic solution becomes high.

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 prismatic type. The electrolytic solution for an electrochemical capacitor of the present invention can be applied to any electric double layer capacitor.

[0035]

The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited to these examples.

Example 1 200 g of ethylmethyl imidazolium tetrafluoroborate (hereinafter EMI.BF ₄ ) was added to isopropanol 9
It was put into 00 ml, heated to 80 ° C., stirred and subjected to solvent extraction. The mixture was left standing while hot and then cooled to 0 ° C. to obtain a free substance in the lower layer. This was dried under reduced pressure and purified EMI / BF
Got ₄ . The obtained EMI.BF ₄ was dissolved in preliminarily dehydrated propylene carbonate to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 2 200 g of tetraethylammonium hexafluorophosphate (hereinafter referred to as TEA.PF ₆ ) was added to 900 ml of methanol, and the mixture was heated to 60 ° C. to be dissolved and then filtered while hot. The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered.
This was washed with ethanol at -25 ° C and then dried under reduced pressure to obtain purified TEA · PF ₆ . Pre-dehydrated propylene carbonate, the obtained TEA · PF
₆ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 3 Triethylmethyl ammonium tetrafluoroborate
(Hereinafter TEMA / BF_Four) 200 g of methanol 900
Add to ml and heat to 60 ° C to dissolve and then heat
Filtered. The filtrate was cooled to 0 ° C, and the precipitated crystals were filtered.
did. After washing this with ethanol at -25 ° C,
Pressure dried and purified TEMA · BF_FourGot Araka
The obtained TE was added to the dehydrated propylene carbonate.
MA ・ BF _FourSo that the concentration becomes 1.5 mol / liter
To prepare an electrolytic solution.

Example ₄ 200 g of EMI.BF _{4 was} added to 900 ml of isopropanol.
And heated to 80 ° C. and stirred for solvent extraction. The mixture was left standing while hot and then cooled to 0 ° C. to obtain a free substance in the lower layer. This was dried under reduced pressure to obtain a purified EMI.BF ₄ . The previously obtained dehydrated acetonitrile was added to the obtained E
MI.BF ₄ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 5 Tetraethylammonium bis (trifluoromethanesulfonyl) imide salt (hereinafter TEA.N (CF ₃ SO ₂ ))
₂ ) Pour 200 g into 900 ml of methanol, 60 ° C
After heating to dissolve it, it was filtered while hot. The filtrate is 0 ℃
And the precipitated crystals were filtered. This is -25
After washing with ethanol at ℃, it was dried under reduced pressure to obtain purified TEA · N (CF ₃ SO ₂ ) ₂ . The resulting TEA.N (CF ₃ S
O ₂ ) ₂ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 6 200 g of TEMA · BF ₄ was put into 900 ml of methanol, heated at 60 ° C. to dissolve it, and then filtered while hot. The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered.
This was washed with ethanol at -25 ° C and then dried under reduced pressure to obtain purified TEMA · BF ₄ . The obtained TEMA · BF ₄ was dissolved in previously dehydrated acetonitrile so that the concentration became 1.5 mol / liter to prepare an electrolytic solution.

Example 7 200 g of EMI.BF _{4 was} added to 900 ml of isopropanol.
And heated to 80 ° C. and stirred for solvent extraction. The mixture was left standing while hot and then cooled to 0 ° C. to obtain a free substance in the lower layer. This was dried under reduced pressure to obtain a purified EMI.BF ₄ . The EMI obtained from the previously dehydrated sulfolane
BF ₄ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 8 200 g of TEMA · BF ₄ was put into 900 ml of methanol, heated to 60 ° C. to dissolve it, and then filtered while hot. The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered.
This was washed with ethanol at -25 ° C and then dried under reduced pressure to obtain purified TEMA · BF ₄ . The obtained TEMA · BF ₄ was dissolved in previously dehydrated sulfolane to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 9 200 g of triethylmethylammonium hexafluorophosphate (hereinafter TEMA.PF ₆ ) was added to 900 parts of methanol.
The mixture was poured into ml, heated to 60 ° C. to dissolve it, and then filtered while hot. The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered. This was washed with ethanol at -25 ° C and then dried under reduced pressure to obtain purified TEMA · PF ₆ . The TEM obtained from the previously dehydrated gamma-butyrolactone
A.PF ₆ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 10 Ethylmethyl imidazolium bis (trifluoromethane
Sulfonyl) imide salt (hereinafter EMI · N (CF_ThreeS
O_Two)_Two) 200 g in 900 ml isopropanol
It was charged, heated to 80 ° C., stirred and subjected to solvent extraction. heat
After leaving still for a while, it was cooled to 0 ° C. to obtain a free substance in the lower layer. This
It is dried under reduced pressure and purified to produce EMI.N (CF _ThreeS
O_Two)_TwoGot Pre-dehydrated gamma butyrolac
Tons of obtained EMIN (CF_ThreeSO_Two)_TwoThe concentration
To 1.5 mol / l to dissolve the electrolyte
Created.

Example 11 200 g of tetraethylammonium tetrafluoroborate (hereinafter TEA.BF ₄ ) was added to 900 ml of methanol, and the mixture was heated at 60 ° C. to dissolve it and then filtered while hot. The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered.
This was washed with ethanol at -25 ° C and then dried under reduced pressure to obtain purified TEA · BF ₄ . TEA.BF ₄ obtained by pre-dehydrating gamma-butyrolactone
Was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 12 200 g of EMI.BF _{4 was} added to 900 ml of isopropanol.
And heated to 80 ° C. and stirred for solvent extraction. The mixture was left standing while hot and then cooled to 0 ° C. to obtain a free substance in the lower layer. EMI · BF ₄ obtained by drying this under reduced pressure was subjected to the same solvent extraction once more to obtain purified EM.
I-BF ₄ was obtained. To the previously dehydrated sulfolane,
The obtained EMI · BF ₄ was dissolved to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 13 200 g of TEA.PF ₆ was put into 900 ml of methanol, heated at 60 ° C. to dissolve it, and then filtered while hot.
The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered. This was washed with ethanol at −25 ° C. and then dried under reduced pressure, and the same recrystallization was further performed on TEA · PF ₆ obtained.
This was repeated to obtain purified TEA.PF ₆ . The previously obtained dehydrated propylene carbonate was added to the TEA obtained.
- a PF ₆ concentration creates a dissolved electrolyte such that 1.5 mol / l.

Example 14 EMI ・ N (CF_ThreeSO_Two)_Two200 g of isopropano
In 900 ml, heat to 80 ° C and stir to dissolve
Agent extraction was performed. After standing still under heat, cool to 0 ° C, and lower layer
A free product was obtained. EMI obtained by drying this under reduced pressure
N (CF_ThreeSO_Two)_TwoFor similar solvent extraction
Purified EMIN (CF _ThreeSO_Two)_Two
Got To dehydrated gamma-butyrolactone in advance,
Obtained EMIN (CF_ThreeSO_Two)_TwoThe concentration is 1.5
Dissolve it so that it becomes mol / liter and make an electrolyte.
It was

Example 15 200 g of EMI.BF _{4 was} added to 900 ml of isopropanol.
And heated to 80 ° C. and stirred for solvent extraction. The mixture was left standing while hot and then cooled to 0 ° C. to obtain a free substance in the lower layer. EMI · BF ₄ obtained by drying this under reduced pressure was subjected to the same solvent extraction twice more to obtain purified EM.
I-BF ₄ was obtained. The obtained EMI.BF ₄ was dissolved in preliminarily dehydrated propylene carbonate to a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Example 16 TEMA ・ BF_FourPour 200 g into 900 ml of methanol
Put it in, heat it to 60 ℃ to dissolve it, then filter while hot
It was The filtrate was cooled to 0 ° C., and the precipitated crystals were filtered.
This was washed with ethanol at -25 ° C and then dried under reduced pressure.
Obtained TEMA ・ BF_FourA similar recrystallization against
Purified TEMA BF _FourGot
Obtained TEM in pre-dehydrated acetonitrile
A ・ BF_FourSo that the concentration becomes 1.5 mol / liter
An electrolyte was prepared by dissolving.

Comparative Example 1 EMIN (CF ₃ SO ₂ ) ₂ which had not been purified was dissolved in propylene carbonate which had been dehydrated in advance so as to have a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Comparative Example 2 An electrolytic solution was prepared by dissolving unpurified EMI.BF ₄ in preliminarily dehydrated acetonitrile to a concentration of 1.5 mol / liter.

Comparative Example 3 EMI.BF ₄ which had not been purified was dissolved in preliminarily dehydrated sulfolane so as to have a concentration of 1.5 mol / liter to prepare an electrolytic solution.

Comparative Example 4 Preliminarily dehydrated gamma-butyrolactone was mixed with unpurified ethylmethylimidazolium hexafluorophosphate (hereinafter referred to as EMI · PF ₆ ) at a concentration of 1.5 mol / mol.
An electrolytic solution was prepared by dissolving the solution so that it became liter.

Iron ions and metal ions (the total of lithium, sodium, magnesium, potassium, calcium, chromium, manganese, iron, cobalt, nickel, copper, zinc and lead ions) in the electrolytic solution were determined by atomic absorption spectrometry. It was quantified (unit: ppm), and the results are shown in Table 1.

Furthermore, by using the electrolytic solutions of Examples 1 to 16 and the electrolytic solutions of Comparative Examples 1 to 4 shown in Table 1, a wound type electric double layer capacitor (size: φ18 × L40, rating: 2.3).
V) was prepared and the self-discharge characteristics were measured using this wound electric double layer capacitor. Table 1 shows the residual voltage after self-discharge.

Next, a method of measuring the self-discharge characteristic and the leakage current will be described. The wound electric double layer capacitor charged at 2.3 V at room temperature for 24 hours was allowed to stand at room temperature for 24 hours, and then the terminal voltage of this wound electric double layer capacitor was measured. The terminal voltage after 24 hours obtained by this measurement was defined as the residual voltage. The leakage current is 50V when a voltage of 2.7V is applied to the wound electric double layer capacitor in an environment of 25 ° C.
The current value after the lapse of 0 hours was defined as the leakage current.

[0059]

[Table 1]

Although the wound type electric double layer capacitors have been described in the first to sixteenth embodiments of the present invention,
Even when applied to an electrolytic solution of an electric double layer capacitor having another structure such as a coin type or a laminated type, the same effects as those of Examples 1 to 16 of the present invention can be obtained.

[0061]

The electrolytic solution of the present invention is excellent in withstand voltage and reliability because it contains few metal ions as impurities.
An electrochemical capacitor using this requires a large current as a power storage device to replace a secondary battery such as a memory backup for various electronic devices, a backup power source for various power sources, and a power storage element used in combination with a solar cell. It is suitable as a power source for driving a motor, a power source for power tools such as electric tools, and a power source for electric vehicles.

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

Claims (7)

[Claims] 1. An electrolytic solution for an electrochemical capacitor, wherein an electrolyte salt is dissolved in a non-aqueous solvent, and a metal ion content in the electrolytic solution is 500 ppm or less. 2. The electrolytic solution for an electrochemical capacitor according to claim 1, wherein the iron ion content in the electrolytic solution is 200 p.
An electrolytic solution for an electrochemical capacitor, which is at most pm. 3. The electrolyte for an electrochemical capacitor according to claim 1, wherein the electrolyte is a quaternary ammonium salt and / or a quaternary phosphonium salt represented by the general formula (1). . Q ⁺ X ⁻ (1) [In the formula, Q ⁺ represents a quaternary ammonium group and / or a quaternary phosphonium group, and X ⁻ represents PF ₆ ⁻ , B.
F ₄ ⁻ , ClO ₄ ⁻ , AsF ₆ ⁻ , SbF ₆ ⁻ , N (R
^{_{fSO 3) 2 -, C (}} RfSO 3) 3 - and RfSO
₃ ⁻ (Rf represents a fluoroalkyl group having 1 to 12 carbon atoms) represents a counter ion selected from the group consisting of. ] 4. The non-aqueous solvent is propylene carbonate,
Ethylene carbonate, butylene carbonate, sulfolane, 3-methylsulfolane, dimethyl carbonate,
The electrolytic solution for an electrochemical capacitor according to claim 1, wherein at least a main component selected from the group consisting of ethylmethyl carbonate and diethyl carbonate is used. 5. An electrochemical capacitor having a polarizable electrode impregnated with an electrolytic solution, wherein the electrolytic solution is used as an electrolytic solution.
4. Using the electrolytic solution for an electrochemical capacitor as described in 4 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. 6. The electrochemical capacitor according to claim 5, wherein the carbonaceous substance is activated carbon. 7. An electric double layer capacitor having a polarizable electrode impregnated with an electrolytic solution, wherein the electrolytic solution is used as the electrolytic solution.
4. An electric double layer capacitor comprising the electrolytic solution for an electrochemical capacitor according to any one of 4 to 4.