JPH0358526B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an electric double layer capacitor. (Prior Art) Conventionally, the electrolytes used in such electric double layer capacitors include perchloric acid, hexafluorophosphoric acid,
It is known that electrochemically stable solutes such as alkali metal salts and tetraalkylammonium salts of fluoroboric acid or trifluoromethanesulfonic acid are dissolved in polar organic solvents (Japanese Unexamined Patent Application Publication No. 1983-1972).
Publications such as No. 68254, No. 50-44463, No. 59-232409). (Problems to be Solved by the Invention) However, electric double layer capacitors using these known solutes have the problem that sufficient performance cannot be obtained in terms of internal resistance, capacitance value, long-term reliability, etc. It was hot. An object of the present invention is to solve the above-mentioned problems and provide an electric double layer capacitor with excellent internal resistance, capacitance value, and long-term reliability. (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte. The present invention provides an electric double layer capacitor characterized in that the solute is made of an asymmetric ammonium salt represented by the general formula (). However, in the general formula (), R ₁ , R ₂ ,
R ₃ and R ₄ each represent a hydrogen atom, an alkyl group having 1 to 15 carbon atoms, an allyl group, or an aryl group having 6 to 15 carbon atoms, and all of the above R ₁ to R ₄ are They are not the same group, and X is BF ₄ , PF ₆ , ClO ₄ , AsF ₆ , SbF ₆ ,
AlCl ₄ or R _f SO ₃ (R _f is a fluoroalkyl group having 1 to 8 carbon atoms). The solute of the electrolytic solution used in the present invention must be composed of an asymmetric ammonium salt represented by the above general formula (), and all of R ₁ to _{R 4 must not be the same group, and it is necessary that all of R 1 to R 4} are not the same group. In (), R ₁ to _{R 4} are hydrogen atoms (however, not all are H), and have 1 to 15 carbon atoms, preferably 1 to 4 carbon atoms.
an alkyl group, an allyl group ( _CH2 =CH- _CH2- ),
It is an aryl group having 6 to 15 carbon atoms, preferably 6 to 10 carbon atoms. Preferred alkyl groups include, for example, methyl, ethyl, propyl, and butyl groups, and preferred aryl groups include, for example, phenyl (C ₆ H ₅ -), tolyl (CH ₃ .C ₆ H ₄
−), naphthyl group (C ₁₀ H ₇ −), and the like. Examples of the combination of R ₁ to _{R 4} include, but are not limited to, methyltriethyl, dimethyldiethyl, ethyltrimethyl, diethyldibutyl, propyltributyl, and triphenylethyl. Among these, dimethyldiethyl, ethyltrimethyl,
Groups such as butyl triphenyl are particularly preferred in terms of solubility in solvents and availability. Furthermore, in the general formula (), as X,
Boric acid hexafluoride (BF ₄ ), phosphoric acid hexafluoride (PF ₆ ), perchloric acid (ClO ₄ ), arsenic acid hexafluoride (AsF ₆ ), antimonic acid hexafluoride (SbF ₆ ), tetrachloride Aluminic acid (AlCl ₄ ) or R _f SO ₃ (R _f is a fluoroalkyl group having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms) is suitable. The appropriate concentration of such a solute (electrolyte) in the electrolytic solution is 0.1 to 3.0M/, particularly 0.5 to 3.0M/.
It is preferable to set it to 1.5M/. If this concentration is too low, loss (tan δ) will increase due to an increase in internal resistance, while if it is too high, problems such as precipitation of solutes and decreased stability may occur when the temperature is lowered. The solvent for the electrolytic solution used in the present invention is not particularly limited, and includes, for example, propylene carbonate, butylene carbonate, β-butyrolactone, γ-butyrolactone, acetonitrile,
Dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane and the like are preferably used alone or in appropriate mixtures. Regarding the material of the polarizable electrode used in the present invention,
Although not particularly limited, it is preferable to use activated carbon powder or activated carbon fibers that are electrochemically inert to the electrolytic solution and have a large specific surface area. In particular, an electrode made by adding a binder such as polytetrafluoroethylene (PTFE) to activated carbon powder, roll-molding it into a sheet, and preferably stretching it uniaxially or biaxially, has a capacitance per unit volume. It is preferably used because it has excellent strength and long-term reliability. As the separator interposed between the pair of polarizable electrodes in the present invention, a normal separator made of polypropylene fiber nonwoven fabric, glass fiber mixed nonwoven fabric, etc. can be used. (Example) Next, Examples and Comparative Examples will be specifically described based on the drawings. A unit cell (diameter 20 mm, thickness 2.0 mm) of a coin type electric double layer capacitor as shown in FIG. 1, which is common to the examples and comparative examples of the present invention, was prepared in the following manner. First, 10% by weight of polytetrafluoroethylene was added to activated carbon powder (specific surface area: 2000 m ² /g) and formed into a sheet by wet kneading. The sheet thus obtained was punched out into a disk shape to form polarizable electrodes 1 and 2 (diameter 15 mm, thickness 0.7 mm), and these polarizable electrodes 1 and 2 were separated through a separator 3 made of a nonwoven polypropylene fiber fabric. Stainless steel caps 4 facing each other
and stored in an outer container consisting of a can 5 made of stainless steel. Next, a predetermined electrolytic solution is injected into the unit cell so that the polarizable electrodes 1 and 2 and the separator 3 are fully impregnated with this electrolytic solution, and then the ends of the cap 4 and can 5 are inserted through the polypropylene backing 6. The parts were caulked and sealed to integrate. For each cell using the unit cell of the electric double layer capacitor prepared as described above, and using various electrolytes with asymmetric ammonium salt as solute as shown in Table 1 at a concentration of 1.0M,
After measuring the initial capacitance and internal resistance when applying a voltage of 2.8V, the cell is subsequently
The capacity was measured after storage at 70°C for 1000 hours while applying a voltage of 100°C, and the capacity deterioration rate (%) from the initial capacity was calculated. The results of these measurements are shown in Table 1. Note that the internal resistance is calculated using the AC two-terminal method (frequency 1K).
Hz) and the results are shown in Table 1.

[Table] (Effects of the Invention) As explained above, according to the present invention, an electric double layer capacitor having a low internal resistance, a low rate of capacity deterioration under high temperature conditions, and excellent long-term reliability can be obtained.

[Brief explanation of drawings]

FIG. 1 is a partial sectional view showing one embodiment of an electric double layer capacitor according to the present invention. 1, 2...Polarizable electrode, 3...Separator, 4
... Cap, 5... Can, 6... Packing.

Claims (1)

[Claims] 1. In an electric double layer capacitor that utilizes an electric double layer formed at the interface between a polarizable electrode and an electrolyte, the solute of the electrolyte is an asymmetric ammonium salt represented by the general formula (). An electric double layer capacitor characterized by: However, in the general formula (), R ₁ , R ₂ ,
R ₃ and R ₄ are each a hydrogen atom (all are H
), or an alkyl group having 1 to 15 carbon atoms, an allyl group, or an allyl group having 6 carbon atoms.
~15 aryl groups, and the above R ₁ to _{R 4}
are not all the same group, and X is BF ₄ ,
_{PF6 , ClO4} , _AsF6 , _SbF6 , _AlCl4 , or _RfSO3
(R _f is a fluoroalkyl group having 1 to 8 carbon atoms). 2. The electric double layer capacitor according to claim 1, wherein the concentration of the solute is 0.1 to 3.0 M/.