JP2002151361A - Nonaqueous electrolytic solution for electrochemical capacitor, and the electrochemical capacitor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution, which is less likely to be hydrolyzed in comparison with tetrafluoroborate salt actually used, and to provide an electrochemical capacitor using it. SOLUTION: The nonaqueous electrolytic solution for an electrochemical capacitor contains a quaternary onium salt represented formula (1): (1) Q+[(Rf)nRF6-n], wherein Q+ is onium ion; Rf is perfluoro alkyl; n is an integer 1-6. When n is 2 or larger, plural (Rf)s may be identical or different, and the plural (Rf)s can be bonded to one another and form an annular structure with phosphorus. The electrochemical capacitor uses such a nonaqueous electrolytic solution.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolytic solution for an electrochemical capacitor containing a phosphorus compound containing fluorine and an electrochemical capacitor using the electrolytic solution.
Electrochemical capacitors are useful for memory backup of various electronic devices and for powering electric vehicles that require a large current.

[0002]

2. Description of the Related Art In recent years, organic solvents such as propylene carbonate have been used.
Development of a non-aqueous electrolyte electrochemical capacitor using a non-aqueous electrolyte obtained by dissolving a quaternary ammonium salt, a quaternary phosphonium salt, or the like has been advanced. In addition to the electric double layer capacitor that stores electricity in the electric double layer generated at the interface between the polarizable electrode and the electrolyte, the electrochemical capacitor also uses the pseudo double capacitance of the non-polarizable electrode by redox with the electric double layer capacitance. There is a capacitor (redox capacitor) (BE Conway, J. Electroche
m. Soc. , 138, 1539 (1991)).

The polarizable electrodes of an electric double layer capacitor include:
Generally, a molded article or a coating film of activated carbon fibers or activated carbon particles is used. On the other hand, a metal oxide such as ruthenium oxide, iridium oxide, nickel oxide, or lead oxide, or a conductive polymer such as polypyrrole or polythiophene is used for the non-polarizable electrode of the pseudo capacitor. Electrolytes used in electrochemical capacitors include aqueous electrolytes such as aqueous sulfuric acid and potassium hydroxide, non-aqueous electrolytes in which quaternary ammonium salts and quaternary phosphonium salts are dissolved in an organic solvent such as propylene carbonate, and polyelectrolytes. ethylene oxide - is an alkali metal salt complexes and RbAg ₄ I solid electrolyte such as ₅ (宇恵Makoto, electrochemical, 66,904 (1998)).

[0004] An electrochemical capacitor using a non-aqueous electrolytic solution has an advantage that the withstand voltage can be increased, so that the energy density can be higher than that of an electrochemical capacitor using an aqueous electrolytic solution. It is used as a backup power supply for equipment and a drive power supply for portable equipment. In addition, electric vehicles, which have recently attracted attention,
For power applications such as hybrid vehicles and power storage, those using a non-aqueous electrolyte are suitable.

Various types of non-aqueous electrolytes for electrochemical capacitors satisfying such requirements have been proposed. A typical one is a quaternized fluorinated non-aqueous solvent such as propylene carbonate. Ammonium salts (Tanahashi et al., Electrochemistry, Vol. 56, p. 892, 1988) or quaternary phosphonium salts of borated (Hiratsuka et al., Electrochemistry, Vol. 59, 20)
9 (1991)).

[0006]

The non-aqueous electrolyte used for the electrochemical capacitor is manufactured so that its water content is as small as possible.
m of water. Also, when manufacturing an electrochemical capacitor using a non-aqueous electrolyte, moisture in the atmosphere may be mixed into the non-aqueous electrolyte. In some cases, the non-aqueous electrolyte used in the electrochemical capacitor contains water of several tens of ppm or more because it may be eluted into the electrolyte.

[0007] If moisture is present in the non-aqueous electrolyte used in the electrochemical capacitor, there is a problem that the dissolved electrolyte is hydrolyzed. For example, in the case of a quaternary ammonium borofluoride, the borofluoride anion after dissociation is hydrolyzed to generate hydrogen fluoride as in the following formula.

[0008]

BF ₄ ⁻ + nH ₂ O → BF _{4 −n} (OH) _n ⁻ + n
HF

[0009] Hydrogen fluoride is highly reactive and causes undesired reactions such as corrosion of the metal part of the electrochemical capacitor and decomposition of the non-aqueous electrolyte. When these reactions occur, various characteristics of the electrochemical capacitor, such as electric capacity, charge / discharge efficiency, withstand voltage, etc., decrease, and appearance defects such as expansion of the element due to gas generation occur. Accordingly, there is a need for a non-aqueous electrolyte that is less likely to undergo hydrolysis even in the presence of a trace amount of water. In recent years, as an electrolyte for a Li-ion battery, an electrolyte that is less likely to be hydrolyzed has been developed by using an electrolyte represented by the general formula (2).
(WO98 / 15562)

[0010]

Embedded image Li ⁺ [PF _a (CH _b F _c (CF ₃ ) _d ) _e ] (2) (a = 1 to 5, b = 0 or 1, c = 0 to 3, d = 0 to
3, e = 1-4)

However, this publication does not disclose any application of such an electrolytic solution to an electrochemical capacitor. As for an electrochemical capacitor, a non-aqueous electrolyte using an electrolyte satisfying such requirements has not been known so far. The present invention addresses this need.

[0012]

In view of such circumstances, the present inventors have synthesized and studied a quaternary onium salt having the same anionic species as the lithium salt represented by the formula (2). The inventors have found that the present invention has excellent properties, and have completed the present invention.

That is, the gist of the present invention is as follows. A non-aqueous electrolytic solution for an electrochemical capacitor, comprising a quaternary onium salt represented by the following general formula (1).

[0014]

Embedded image Q ⁺ [(R _f ) _n RF _6-n ] (1)

[0015] [in the formula, Q ⁺ represents an onium ion, R _f
Represents a perfluoroalkyl group, and n represents an integer of 1 to 6. When n is 2 or more, a plurality of R _f may be the same or different, and a plurality of R _f may be bonded to each other to form a ring structure together with phosphorus.

An electrochemical capacitor characterized by using the non-aqueous electrolyte described in item 2.1.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
(Non-Aqueous Electrolyte for Electrochemical Capacitor) The non-aqueous electrolyte of the present invention is characterized by containing a quaternary onium salt represented by the formula (1) as an electrolyte.

[0018]

Embedded image Q ⁺ [(R _f ) _n RF _6-n ] (1)

[0019] [in the formula, Q ⁺ represents an onium ion, R _f
Represents a perfluoroalkyl group, and n represents an integer of 1 to 6. When n is 2 or more, a plurality of R _f may be the same or different, and a plurality of R _f may be bonded to each other to form a ring structure together with phosphorus.

In the formula (1), examples of the onium ion of Q ⁺ include a quaternary ammonium ion and a quaternary phosphonium ion, and a quaternary ammonium ion is more preferable. Such quaternary ammonium ions include:
Specifically, for example, tetramethylammonium, ethyltrimethylammonium, diethyldimethylammonium, triethylmethylammonium, tetraethylammonium, trimethyl-n-propylammonium, trimethylisopropylammonium, trimethyl-n-
Butylammonium, trimethylisobutylammonium, trimethyl-t-butylammonium, trimethyl-n-hexylammonium, dimethyldi-n-propylammonium, dimethyldiisopropylammonium, dimethyl-n-propylisopropylammonium, methyltri-n-propylammonium, methyltriisopropyl Ammonium, methyldi-n-propylisopropylammonium, methyl-n-propyldiisopropylammonium, triethyl-n-propylammonium, triethylisopropylammonium, diethyldi-n-propylammonium, diethyldiisopropylammonium, diethyl-n-propylisopropylammonium, ethyltri- n-propylammonium, ethyltrii Propyl ammonium, ethyl di -n- propyl isopropyl ammonium, ethyl -
n-propyldiisopropylammonium, diethylmethyl-n-propylammonium, ethyldimethyl-n
-Propylammonium, ethylmethyldi-n-propylammonium, diethylmethylisopropylammonium, ethyldimethylisopropylammonium, ethylmethyldiisopropylammonium, ethylmethyl-
n-propylisopropylammonium, tetra-n-
Propyl ammonium, tetraisopropyl ammonium, n-propyl triisopropyl ammonium, di-
n-propyldiisopropylammonium, tri-n-
Tetraalkylammonium such as propylisopropylammonium; N, N-dimethylpyrrolidinium, N
Pyrrolidinium groups such as -ethyl-N-methylpyrrolidinium, N, N-diethylpyrrolidinium; N, N'-dimethylimidazolinium, N, N'-diethylimidazolinium, N-ethyl-N'- Methyl imidazolinium, 1,2,3-trimethyl imidazolinium, 1,
3,4-trimethylimidazolinium, 1,3-diethyl-2-methylimidazolinium, 1,3-diethyl-
Imidazolinium groups such as 4-methylimidazolinium, 1,2,3,4-tetramethylimidazolinium;
N, N'-dimethyltetrahydropyrimidinium, N,
N'-diethyltetrahydropyrimidinium, N-ethyl-N'-methyltetrahydropyrimidinium, 1,
2,3-trimethyltetrahydropyrimidinium, 1,
2,3-triethyltetrahydropyrimidinium, 1-
Ethyl-2,3-dimethyltetrahydropyrimidinium, 2-ethyl-1,3-dimethyltetrahydropyrimidinium, 1,2-diethyl-3-methyltetrahydropyrimidinium, 1,3-diethyl-2-methyltetrahydro Pyrimidinium, 5-methyl-1,5-diazabicyclo [4.3.0] nonene-5,8-methyl-1,8
Tetrahydropyrimidinium groups such as -diazabicyclo [5.4.0] undecene-7; N, N'-dimethylmorpholinium, N-ethyl-N-methylmorpholinium,
Morpholinium groups such as N, N-diethylmorpholinium; N, N-dimethylpiperidinium, N-ethyl-
Piperidinium groups such as N'-methylpiperidinium and N, N'-diethylpiperidinium; N-methylpyridinium, N-ethylpyridinium, Nn-propylpyridinium, N-isopropylpyridinium, Nn-butylpyridinium Pyridinium groups such as N, N'-dimethylimidazolium, N-ethyl-N-methylimidazolium, N, N'-diethylimidazolium, 1,2-
Diethyl-3-methylimidazolium, 1,3-diethyl-2-methylimidazolium, 1-methyl-3-n-
Propyl-2,4-dimethylimidazolium, 1,2-
Dimethyl-3-n-propylimidazolium, 1,2,2
Examples include various nitrogen-containing alicyclic or aromatic cyclic quaternary ammonium groups such as imidazolium groups such as 3,4,5-tetramethylimidazolium. The total number of carbon atoms of these quaternary ammoniums is preferably 4 to 12 in view of the solubility in a non-aqueous solvent and the electric conductivity of the obtained non-aqueous electrolyte.

The perfluoroalkyl group represented by R _f includes a trifluoromethyl group, a pentafluoroethyl group, a heptafluoropropyl group, a nonafluorobutyl group, an undecafluoropentyl group, a perfluorohexyl group, a perfluorooctyl group , A perfluorodecyl group, a perfluoroundecyl group, and a perfluoroalkyl group having 1 to 12 carbon atoms. Examples of a structure in which a plurality of R _f are mutually bonded include an octafluorotetramethylene group and a decafluoropentamethylene group. In the compound of the formula (1), the total number of carbon atoms in the fluorinated hydrocarbon group represented by R _f is preferably 18 or less. Examples of these compounds include trifluoromethylpentafluorophosphate, bis (trifluoromethyl) tetrafluorophosphate, tris (trifluoromethyl) trifluorophosphate, tetrakis (trifluoromethyl) difluorophosphate, pentakis (trifluoromethyl) fluoro Phosphate, hexakis (trifluoromethyl) phosphate, pentafluoroethylpentafluorophosphate, bis (pentafluoroethyl) tetrafluorophosphate, tris (pentafluoroethyl) trifluorophosphate, tetrakis (pentafluoroethyl) difluorophosphate, pentakis (pentafluoro Ethyl) fluorophosphate, hexakis (pentafluoroethyl) phosphate, heptaf Oropropyl pentafluorophosphate, bis (heptafluoropropyl) tetrafluorophosphate, tris (heptafluoropropyl) trifluorophosphate, tetrakis (heptafluoropropyl) difluorophosphate, pentakis (heptafluoropropyl) difluorophosphate, hexakis (heptafluoropropyl) Phosphate, nonafluorobutyl pentafluorophosphate,
Bis (nonafluorobutyl) tetrafluorophosphate, tris (nonafluorobutyl) trifluorophosphate, undecafluoropentylpentafluorophosphate, bis (undecafluoropentyl) tetrafluorophosphate, perfluorohexylpentafluorophosphate, bis (perfluoro Hexyl) tetrafluorophosphate, perfluorooctylpentafluorophosphate, perfluorodecylpentafluorophosphate, perfluoroundecylpentafluorophosphate, trifluoromethylpentafluoroethyltetrafluorophosphate, bis (trifluoromethyl) pentafluoroethyltrifluorophosphate , Tris (trifluoromethyl) pentafluoroethyldifluorophos Eto, tetrakis (trifluoromethyl) pentafluoroethyl fluorophosphate,
Hentakis (trifluoromethyl) pentafluoroethyl phosphate, trifluoromethyl bis (pentafluoroethyl) trifluorophosphate, trifluoromethyl tris (pentafluoroethyl) difluorophosphate, trifluoromethyltetrakis (pentafluoroethyl) fluorophosphate, trifluoro Methylpentakis (pentafluoroethyl) phosphate,
Bis (trifluoromethyl) bis (pentafluoroethyl) difluorophosphate, tris (trifluoromethyl) bis (pentafluoroethyl) fluorophosphate, tetrakis (trifluoromethyl) bis (pentafluoroethyl) phosphate, bis (trifluoromethyl) Tris (pentafluoroethyl) fluorophosphate, bis (trifluoromethyl) tetrakis (pentafluoroethyl) phosphate, tris (trifluoromethyl) tris (pentafluoroethyl) phosphate, perfluoro (P, P-tetramethylene) tetrafluorophosphate , Perfluoro [bis (P, P-tetramethylene)] difluorophosphate, perfluoro [tris (P, P-tetramethylene)] phosphate, perfluoro ( , P- pentamethylene) tetrafluoro phosphate, perfluoro [bis (P, P- pentamethylene)] difluoro phosphate, perfluoro [tris (P, P- tetramethylene)] phosphate and the like. In the present invention, _n of (R _f ) n is 1
It is preferable that the total number of carbon atoms in (R _f ) _n is 1 to 9.

In general, as the molecular weight of the compound of the formula (1) increases, the electric conductivity of an electrolytic solution using the compound as an electrolyte tends to decrease. Therefore, as the electrolyte, trifluoromethylpentafluorophosphate or bis (trifluoromethyl) tetrafluorophosphate, tris (trifluoromethyl) trifluorophosphate,
Pentafluoroethyl pentafluorophosphate or bis (pentafluoroethyl) tetrafluorophosphate, tris (pentafluoroethyl) trifluorophosphate, pentafluoroethyltrifluoromethyltetrafluorophosphate, pentafluoroethylbis (trifluoromethyl) trifluorophosphate,
Bis (pentafluoroethyl) trifluoromethyltrifluorophosphate, heptafluoropropylpentafluorophosphate, bis (heptafluoropropyl) tetrafluorophosphate, tris (heptafluoropropyl) trifluorophosphate, trifluoromethylheptafluoropropyltetrafluorophosphate, Trifluoromethylbis (heptafluoropropyl) trifluorophosphate, bis (trifluoromethyl) heptafluoropropyltrifluorophosphate, bis (trifluoromethyl) bis (heptafluoropropyl) difluorophosphate, tris (trifluoromethyl) bis (hepta) Fluoropropyl) fluorophosphate, pentafluoroethylheptafluoropropyltetrafur Lophosphate, bis (pentafluoroethyl) heptafluoropropyl trifluorophosphate, tris (pentafluoroethyl) heptafluoropropyl difluorophosphate, pentafluoroethyl bis (heptafluoropropyl) trifluorophosphate, pentafluoroethyltrifluoromethylheptafluoropropyl Trifluorophosphate,
Bis (pentafluoroethyl) trifluoromethylheptafluoropropyldifluorophosphate, bis (pentafluoroethyl) bis (trifluoromethyl) heptafluoropropylfluorophosphate, pentafluoroethylbis (trifluoromethyl) heptafluoropropyldifluorophosphate, pentafluoro C9 or less carbon atoms such as ethyltris (trifluoromethyl) heptafluoropropylfluorophosphate, pentafluoroethyltetrakis (trifluoromethyl) heptafluoropropylphosphate, and pentafluoroethyltrifluoromethylbis (heptafluoropropyl) difluorophosphate It is preferable to use a substance. In addition, two or more compounds of the formula (1) can be used in combination.

The compound of the formula (1) can be synthesized by applying a known method. For example, various tris (pentafluoroethyl) trifluorophosphates are available from N.I. Ignat'ev et al. , J. et al. Flu
orine. Chem. , 103, 57 (2000), by reacting phosphorous tris (pentafluoroethyl) difluoride synthesized by this method with various onium fluorides (Q ⁺ F ⁻ ). be able to. When the compound of the formula (1) is used as an electrolyte for an electrochemical capacitor, it is required that the compound of the formula (1) has extremely high purity. Purify to a desired purity and use it. The electrolyte is
Usually, the compound of the formula (1) is used by dissolving it in a solvent. However, when the compound of the formula (1) is liquid at room temperature, it may be used alone without using a solvent.

Examples of the solvent used include dimethyl carbonate,
Ethyl methyl carbonate, diethyl carbonate, diphenyl carbonate, methylphenyl carbonate, ethylene carbonate, propylene carbonate,
Carbonic esters such as 2,3-dimethyl ethylene carbonate, butylene carbonate, vinylene carbonate, and 2-vinyl ethylene carbonate;
Methyl formate, methyl acetate, methyl propionate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, methyl benzoate, ethyl benzoate, γ-butyrolactone, γ-
Carboxylic acid esters such as valerolactone and δ-valerolactone; ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, 1,4-dioxane, 1,3-dioxolan,
Tetrahydrofuran, 2-methyltetrahydrofuran,
Ethers such as 2,6-dimethyltetrahydrofuran and tetrahydropyran; nitriles such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile; N-methylformamide, N-ethyl Amides such as formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methylpyrrolidinone;
Dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, 2,4-
Sulfones such as dimethylsulfolane; sulfoxides such as dimethylsulfoxide, methylethylsulfoxide, diethylsulfoxide; dimethyl sulfate, diethyl sulfate;
Sulfuric esters such as ethylene sulfate and propylene sulfate; sulfites such as dimethyl sulfite, diethyl sulfite, ethylene sulfite and propylene sulfite; phosphate esters such as trimethyl phosphate, ethyl dimethyl phosphate, diethylmethyl phosphate and triethyl phosphate And 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,
4,5,6-tetrahydro-2 (1H) -pyrimidinone, 3-methyl-2-oxazolidinone, nitromethane and the like. When these solvents are used, two or more of them can be used in combination. Among these solvents, it is preferable to use a carbonate ester or a carboxylate ester or a solvent mainly composed of these, wherein 50% by weight or more is a carbonate ester or a carboxylate ester.

The non-aqueous electrolyte according to the present invention is obtained by dissolving the compound of the formula (1) in the above-mentioned solvent, or when the compound of the formula (1) is liquid at room temperature, the compound of the formula (1) is used alone. May be. In general, the higher the electric conductivity of the electrolytic solution, the better. Therefore, the concentration of the compound of the formula (1) in the electrolytic solution is preferably as high as possible within a range that does not precipitate due to a temperature change or the like. The concentration of these compounds in the electrolyte is usually 0.1 to ³ mol dm ^-3 , preferably 0.5 to 2 mol dm ^-3 . However, this does not apply when the salt is liquid at ordinary temperature and no solvent is used.

(Electrochemical Capacitor) The non-aqueous electrolyte electrochemical capacitor according to the present invention is manufactured according to a conventionally known method except that a non-aqueous electrolyte using the compound of the above formula (1) is used. Can be. As the polarized electrodes used as the positive electrode and the negative electrode, it is preferable to use carbon in terms of being inert to the electrolytic solution and having appropriate electric conductivity, and among them, activated carbon or carbon nanotube having a large electrode interface where electric charge is accumulated, It is preferable to use porous diamond or the like produced by the PVD method. Activated carbon usually has a specific surface area of 500 according to the BET method by nitrogen adsorption.
Activated carbon ~2500m ² / g, preferably larger capacitance per volume, preferably in particular to use those of 1000 to 2000 ² / g.

Activated carbon includes plant-based wood, sawdust, coconut shell, pulp waste liquor, fossil fuel-based coal, petroleum heavy oil, or thermally decomposed coal and petroleum pitch, petroleum coke, carbon aerogel, Tar pitch spun fiber, synthetic polymer, phenolic resin, furan resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyimide resin, polyamide resin, polyacene, ion exchange resin, liquid crystal polymer, plastic waste, waste tire, etc. After carbonizing a wide variety of raw materials, they are activated and manufactured. The activated carbon is activated by a gas activation method in which a carbonized raw material is brought into contact with steam, carbon dioxide, oxygen, or another oxidizing gas at a high temperature, or zinc chloride, phosphoric acid or phosphorus is added to a carbonized raw material. Evenly impregnate sodium acid, calcium chloride, potassium sulfide, potassium hydroxide, sodium hydroxide, potassium carbonate, sodium carbonate, sodium sulfate, potassium sulfate, calcium carbonate, boric acid, nitric acid, etc. in an inert gas atmosphere. There is a chemical activation method in which activated carbon is obtained by heating and dehydrating and oxidizing a chemical, and any of them can be used.

Prior to use, the activated carbon is subjected to a heat treatment at 500 to 2500 ° C., preferably 700 to 1500 ° C. in an inert atmosphere such as nitrogen or argon to remove unnecessary surface functional groups or to reduce the crystal structure. May be developed to improve conductivity. Various shapes such as crushing, granulation, granule, fiber, felt, fiber, sheet, etc. can be used as the shape of the activated carbon.However, in the case of granular, since the bulk density of the electrode can be improved and the internal resistance can be reduced, The average particle size is preferably 30 μm or less. An electrode is produced by mixing a conductive agent and a binder into such activated carbon and forming the mixture into a sheet. As the conductive agent, conductive carbon black such as acetylene black or Ketjen black, graphite, conductive carbon fiber, or the like is used. Further, metal fibers such as aluminum and nickel, conductive titanium oxide, and the like can also be used. Preferably, acetylene black or Ketjen black is used. These conductive materials are 5
It is preferable that the compounding amount be from 50 to 50% by weight, especially from 10 to 30% by weight.

As the binder, polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, polyimide, phenol resin, pitch and the like are used. The binder includes 0.5 to 30% by weight based on activated carbon,
In particular, it is preferable to mix them in an amount of 20 to 30% by weight. Note that, instead of using the conductive agent, an electrode can also be manufactured by forming a mixture of activated carbon and a binder into a sheet, heat-treating the sheet in an inert atmosphere, and sintering the sheet. Usually, a separator made of a material such as paper, polypropylene, polyethylene, or glass fiber is used as the separator. The shape of the manufactured electrochemical capacitor may be any shape such as a coin shape, a wound shape, a square shape, and an aluminum laminate type, and is not limited to these shapes.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the invention. The salts exemplified in Examples 1 to 3 and Comparative Examples 1 and 2 were converted into an aqueous solution having a concentration of 5 mmol dm ⁻³ , and the increase in F ⁻ ions due to hydrolysis was measured using ion chromatography. Table 1 shows the F ^- ion concentration after standing for two weeks. An electrolytic solution was prepared by the following method using the exemplified salt, and the following coin-type electrochemical capacitor (electric double layer capacitor) was prepared and evaluated using the electrolytic solution, and the capacity retention was calculated. Table 1 shows the results.

Preparation of Nonaqueous Electrolyte for Electric Double Layer Capacitor; Salts exemplified in Examples and Comparative Examples were dissolved in propylene carbonate so as to have a concentration of 1 mol dm ^-3 to prepare a nonaqueous electrolyte. An electrolytic solution was prepared by adding 0.5% by weight of water to the electrolytic solution.

Preparation of electrode for electric double layer capacitor; 80 parts by weight of coconut shell-based powdered activated carbon (specific surface area: 1700 m ² / g, average particle size: 10 μm, steam activated product), 10 parts by weight of acetylene black, and polytetrafluoroethylene After kneading the mixture of parts by weight, 50 kgf / cm ²
Pressure molding with a pressure of 0.5mm into a plate with a thickness of 0.5mm,
From this, a disk having a diameter of 10 mm was punched. This disk was kept at 300 ° C. for 3 hours in a vacuum of 0.1 Torr or less, and then allowed to cool in a nitrogen atmosphere.

Assembly of electric double layer capacitor: The two polarizable electrodes prepared above were impregnated with a non-aqueous electrolyte. The two electrodes were housed in a stainless steel case with a polyethylene separator interposed therebetween, and the case was caulked via a polypropylene gasket to produce a coin-type electric double layer capacitor.

Measurement of the capacity retention of the electric double layer capacitor: After applying a voltage of 3.0 V at 25 ° C. to the electric double layer capacitor prepared above, it was discharged at a constant current of 5 mA to obtain an initial capacitance. It was measured. Then, it is heated at 70 ° C. for 1 hour.
After holding for 000 hours, the capacitance was measured in the same manner, and the capacitance after 1000 hours with respect to the initial capacity was calculated as a capacity retention ratio.

[0035]

[Table 1]

[0036]

According to the present invention, a non-aqueous electrolyte which is less likely to be hydrolyzed than the currently used tetrafluoroborate can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Makoto Ue 8-3-1 Chuo, Ami-cho, Inashiki-gun, Ibaraki Pref. Mitsubishi Chemical Corporation Tsukuba Research Laboratory F-term (reference)

Claims (6)

[Claims] 1. A non-aqueous electrolytic solution for an electrochemical capacitor, comprising a quaternary onium salt represented by the following general formula (1). Embedded image Q ⁺ [(R _f ) _n RF _6-n ] (1) wherein Q ⁺ represents an onium ion, R _f represents a perfluoroalkyl group, and n is an integer of 1 to 6. Is shown. When n is 2 or more, a plurality of R _f may be the same or different, and a plurality of R _f may be bonded to each other to form a ring structure together with phosphorus. 2. n is an integer of 1 to 3, and (R _f ) _n
2. The non-aqueous electrolyte for an electrochemical capacitor according to claim 1, wherein the total number of carbon atoms is 1 to 9. 3. 3. The non-aqueous electrolyte for an electrochemical capacitor according to claim 1, wherein Q ⁺ is a quaternary ammonium ion having 4 to 12 carbon atoms. 4. The non-electrochemical capacitor according to claim 1, wherein an ester selected from the group consisting of carbonate and carboxylate is dissolved in a non-aqueous solvent occupying 50% by weight or more. Water electrolyte. 5. The non-aqueous electrolyte for an electrochemical capacitor according to claim 1, wherein the quaternary onium salt of the formula (1) is a liquid at room temperature and used alone. 6. An electrochemical capacitor using the non-aqueous electrolyte according to claim 1. Description: