JPH07107888B2 - Electric double layer capacitor - Google Patents

Description

The present invention relates to an electric double layer capacitor.

(Prior Art) Electrolyte solutions used for electric double layer capacitors have conventionally been electrochemical such as perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid or trifluoromethanesulfonic acid alkali metal salts and tetraalkylammonium salts. It is known that a highly stable solute is dissolved in a polar organic solvent (Japanese Patent Application Laid-Open No. 49-49242).
-68254, JP-A-50-44463, JP-A-59-232409, etc.).

(Problems to be Solved by the Invention) However, electric double layer capacitors using these known solutes have a problem that sufficient performance cannot be obtained in terms of withstand voltage, capacitance value, long-term reliability and the like. there were.

An object of the present invention is to solve the above problems and provide an electric double layer capacitor excellent in withstand voltage, capacity and long-term reliability.

(Means for Solving the Problems) In order to solve the above problems, the present invention provides an electric double layer capacitor that uses an electric double layer formed at the interface between a polarizable electrode and the electrolytic solution. Solute is general formula (I)
(V) is a salt represented by any one of (V) to (V).

However, in the general formulas, R represents an alkyl group, an allyl (allyl) or aryl (aryl) group having from 6 to 15 carbon atoms having 1 to 15 carbon atoms, X is _{BF 4, PF 6, ClO 4} , AsF ₆ , Sb
It represents F ₆ , AlCl ₄ or RfSO ₃ (Rf is a fluoroalkyl group having 1 to 8 carbon atoms).

As the solute of the electrolytic solution used in the present invention, it is necessary to use the salts represented by the general formulas (I) to (V).

In these general formulas, R is an alkyl group having 1 to 15 carbon atoms, preferably 1 to 4 carbon atoms, an allyl group, or an aryl group having 6 to 15 carbon atoms, preferably 1 to 10 carbon atoms. Examples of preferable alkyl groups include methyl group, ethyl group, propyl group, butyl group, and the like, and examples of preferable aryl groups include phenyl group (C ₆ H ₅ —) and tolyl group (CH ₃ · C ₆ H ₄ −), naphthyl group (C ₁₀ H ₇ −) and the like. X is BF ₄ , PF ₆ , ClO ₄ , AsF ₆ , SbF ₆ , Al
Those having Cl ₄ or RfSO ₃ (RF is a fluoroalkyl group having 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms) are preferably used.

Preferred salts include, for example, 1-methylnorinium tetrafluoroborate 1-ethylpyridinium tetrafluoroborate Pyrylium tetrafluoroborate Diethyl piperidinium tetrafluoroborate Diethylpyrrolidinium tetrafluoroborate And so on.

As the concentration of such a solute (electrolyte) in the electrolytic solution,
0.1 to 3.0 M / is suitable, and 0.5 to 1.5 M / is particularly suitable. If this concentration is too low, the internal resistance increases and the loss (tan δ) increases. On the other hand, if it is too high, solutes may precipitate and the stability may decrease when the temperature becomes low. .

The solvent of the electrolytic solution used in the present invention is not particularly limited, propylene carbonate, butylene carbonate, β-butyrolactone, γ-butyrolactone,
Acetonitrile, dimethylformamide, 1,2-dimethoxyethane, sulfolane, nitromethane and the like are preferably used alone or in an appropriate mixture.

The material of the polarizable electrode used in the present invention is not particularly limited, but it is preferable to use activated carbon powder or activated carbon fiber which is electrochemically inactive to the electrolytic solution and has a large specific surface area.

In particular, polytetrafluoroethylene (PTF
Electrodes that are added with a binder such as E), roll-formed into a sheet, and more preferably uniaxially or biaxially stretched have excellent capacity per unit volume, strength and long-term reliability. Therefore, it is preferably used.

As the separator to be interposed between the pair of polarizable electrodes in the present invention, a normal separator made of polypropylene fiber non-woven fabric, glass fiber mixed paper non-woven fabric or the like can be used.

(Example) Next, an Example and a comparative example are concretely demonstrated based on drawing.

A unit cell (diameter 20 mm, thickness 2.0 mm) of a coin type electric double layer capacitor as shown in FIG. 1 was manufactured as follows, which is common to the examples of the present invention and the comparative example. First, 10 wt% of polytetrafluoroethylene was added to activated carbon powder (specific surface area of 2,000 m ² / g), and a sheet was formed by wet kneading. The sheet thus obtained was punched out into a disk shape and the polarizable electrodes 1 and 2 (diameter 15 mm,
The thickness of the polarizable electrodes 1 and 2 is 0.7 mm), and the polarizable electrodes 1 and 2 are faced to each other with a separator 3 made of polypropylene fiber non-woven fabric therebetween and housed in an outer container including a cap 4 made of stainless steel and a can 5 made of stainless steel. . Next, a predetermined electrolytic solution is injected into the unit cell to polarize the polarizable electrodes 1, 2.
After sufficiently impregnating the electrolytic solution into the separator 3 and the cap 4 via the polypropylene packing 6
And the end of the can 5 was caulked and sealed to be integrated.

Using the unit cell of the electric double layer capacitor manufactured as described above, each cell using various electrolytic solutions as shown in Table 1 at a concentration of 1.0 M / After measuring the initial capacitance and internal resistance, continue to apply a voltage of 2.8V to this cell at 70 ℃.
The capacity after storage for 1000 hours was measured, and the capacity deterioration rate (%) from the initial capacity was calculated. The results of these measurements are shown in Table 1 as Examples 1 to 13 and Comparative Examples 1 and 2.

The internal resistance was measured by the AC two-terminal method (frequency 1 KHz).

(Effects of the Invention) As described above, according to the present invention, an electric double layer capacitor having a high withstand voltage, a low capacity deterioration rate under high temperature conditions, and a high long-term reliability can be obtained.

[Brief description of drawings]

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

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-28815 (JP, A)

Claims (2)

[Claims] 1. An electric double layer capacitor utilizing an electric double layer formed at an interface between a polarizable electrode and an electrolytic solution,
An electric double layer capacitor, wherein the solute of the electrolytic solution is a salt represented by any one of the general formulas (I) to (V). However, in the above general formula, R represents an alkyl group having 1 to 15 carbon atoms, an allyl group, or an aryl group having 6 to 15 carbon atoms, and X represents BF ₄ , PF ₆ , ClO ₄ , AsF ₆ ,
SbF ₆ , AlCl ₄ or RfSO ₃ (Rf is a fluoroalkyl group having 1 to 8 carbon atoms) is shown. 2. The electric double layer capacitor according to claim 1, wherein the concentration of the solute is 0.1 to 3.0 M /.