JPH0256914A - Electric double-layer capacitor - Google Patents

Abstract

PURPOSE:To obtain an electric double-layer capacitor which is stable and shows little deterioration under a high temperature by employing material obtained by coupling cyclohexyl group or cyclopentyl group with quaternary ammonium salt or quaternary phosphonium salt or the like as electrolyte. CONSTITUTION:Material containing at least one of quaternary ammonium salt, quaternary phosphonium salt and tertiary sulfonium salt with which at least one cyclohexyl group or cyclopentyl group is coupled is employed as electrolyte. That is, by replacing at least one allyl group or alkyl group with cyclohexyl group or cyclopentyl group, the conductivity and thermal stability can be improved. With this constitution, the stability against a high temperature can be improved and the deterioration can be suppressed.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to an electric double layer capacitor.

(Prior art) Conventionally, as electrolytes used in electric double layer capacitors, acidic or alkaline aqueous solutions, non-aqueous solutions such as perchlorates, fluoroborates, and fluorophosphates of alkali metals or alkaline earth metals have been used. It is used. The former aqueous electrolyte has a higher withstand voltage than the latter non-aqueous electrolyte, and is therefore used in high-voltage capacitors.

(Problems to be Solved by the Invention) However, aqueous electrolytes are more unstable than non-aqueous solutions at high temperatures of 50°C or higher, resulting in gas generation, capacity reduction, increase in series resistance, etc. The disadvantage was that the increase in leakage current was more significant.

The purpose of the present invention is to improve the above-mentioned drawbacks and reduce deterioration at high temperatures. The present invention provides a layer capacitor.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides polarizable electrodes,
In an electric double layer capacitor in which a capacitor element comprising a separator and a current collector and impregnated with an electrolytic solution is housed in a case, the electrolyte is a quaternary ammonium salt bonded with one or more of at least one of a cyclohexyl group and a cyclopentyl group; The present invention provides an electric double layer capacitor characterized by containing at least one kind of quaternary phosphonium salt or tertiary sulfonium salt.

(Function) Quaternary ammonium salts, quaternary phosphonium salts, and tertiary sulfonium salts generally contain N and P, respectively.

It has a structure in which S is bonded to an aryl group or an alkyl group. However, an aryl group alone usually has low conductivity and tends to dissolve, and an alkyl group alone is thermally unstable. By replacing at least one of these aryl groups and alkyl groups with a cyclohexyl group or a cyclopentyl group, conductivity and thermal stability can be improved.

(Example) Hereinafter, the present invention will be explained based on examples.

As the polarizable electrode, a sheet formed by pressing electrochemically inactive activated carbon, activated carbon fiber, carbon black, etc. into an electrolytic solution, forming a sheet, and punching it out into a circular shape is used.

As the solvent for the electrolytic solution, propylene carbonate, γ-butyl lactone, acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane, etc., which are electrochemically stable well water solvents, are used. Among these, propylene carbonate, γ-butyl lactone, and acetonitrile are particularly preferred, and are used in a substantially anhydrous state.

For example, in the case of a quaternary ammonium salt, Fi or picric acid may be used as the electrolyte. Further, although an example is shown in which an ethyl group is bonded to a cyclohexyl group or a cyclopentyl group, an alkyl group such as a methyl group, a butyl group, a propyl group, an isobutyl group, etc. may be used instead of the ethyl group. Furthermore, the following is used as the quaternary ammonium salt of the pond. In this case, instead of tetrafluoroboric acid BF''4 as a negative ion, hexafluorophosphoric acid PFi
Hexafluoroarsenic acid AsFi, hexafluoroantimonic acid 5bF
i, aluminum tetrachloride AfiCIi, trifluoromethanesulfonic acid CFs SO3.

Thiocyanate SCN, TaRI hexafluorotantalate
R2\/N+ Biberidinium When a quaternary phosphonium salt is used, etc. are used as an electrolyte.

When a tertiary sulfonium salt is used, the following may be used, in which at least one of R, R1 to R7 is replaced with a cyclohexyl group or a cyclopentyl group, and the rest are an alkyl group or an aryl group.

etc. are used as electrolytes.

A nonwoven fabric such as polypropylene with a thickness of several tens of micrometers is used for the separator.

A stainless steel button-shaped case is used as the current collector, which also serves as the case.

Next, for the examples of the present invention and the comparative examples, a voltage of 2 V was applied in an atmosphere at a temperature of 70° C., and the leakage current after being left for 1000 hours was measured, and the results shown in the table were obtained.

In addition, the polarizable electrode has a specific surface area of 1450n? /+r, oil absorption 350mβ/100g, particle size 16mμm conductive carbon black and specific surface area 2000//g, particle size 20μ
After adding 1/2 m of activated carbon and kneading it with 1□vt% of tetrafluoroethylene, it was pressed to form a sheet with a thickness of 500 μm, and this was punched out to a size of 14φ in diameter. Also, the separator has a thickness of 100
A µm propylene nonwoven fabric is used. The electrolyte is prepared by dissolving the electrolyte shown in the table in IM and propylene carbonate.

Margin below.

As is clear from the table, 1 According to Examples 1 to 12 of the present invention,
Compared to Comparative Examples 1 to 4, the initial equivalent series resistance is approximately 4 to 6
It is 3% smaller, and the leakage current is ff40-71% lower. In particular, Example 1 in which trimethylcyclohexylammonium tetrafluoroborate was used as the solute had low equivalent series resistance and low leakage current, and had a remarkable effect.

Note that tetramethylammonium tetrafluoroborate hardly dissolves in propylene carbonate.

(Effects of the Invention) As described above, according to the present invention, since a substance in which a cyclohexyl group or a cyclohexyl group is bonded to a quaternary ammonium salt or a quaternary phosphonium salt is used as an electrolyte, it is stable at high temperatures. An electric double layer capacitor with little deterioration, equivalent series resistance, and leakage current can be obtained.

Patent applicant: Hitachi Capacitor Co., Ltd.

Claims (1)

[Claims] (1) In an electric double layer capacitor in which a capacitor element consisting of a polarizable electrode, a separator, and a current collector is impregnated with an electrolytic solution and housed in a case, one or more of at least one of a cyclohexyl group or a cyclopentyl group is bonded as an electrolyte. An electric double layer capacitor comprising at least one kind of quaternary ammonium salt, quaternary phosphonium salt, or tertiary sulfonium salt.