JPH07101661B2 - Electric double layer capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric double layer capacitor.

[0002]

2. Description of the Related Art Conventional electrolytic solutions for electric double layer capacitors include perchloric acid, hexafluorophosphoric acid, tetrafluoroboric acid,
Alternatively, an electrolyte solution in which a solute such as a tetraalkylammonium salt of trifluoromethanesulfonic acid, an ammonium salt, or an alkali metal salt is dissolved in an organic solvent such as propylene carbonate, γ-butyrolactone, acetonitrile, or dimethylformamide is known ( JP-A-48-
50255, JP-A-49-68254, JP-A-59-2
32409).

However, when these known solvents are used, the withstand voltage of the obtained capacitor is not sufficient, and when the capacitor is exposed to high temperature with a voltage applied, the rated capacity of the capacitor decreases. There was a problem of being lost.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above problems in the prior art, and has a high withstand voltage, little capacity deterioration at high temperatures, and an excellent electric double layer at low temperatures. It is intended to provide a capacitor.

[0005]

That is, the present invention provides an electric double layer capacitor utilizing an electric double layer formed at the interface between a polarizable electrode made of activated carbon and the electrolytic solution, wherein the electrolytic solution is sulfolane. Another object of the present invention is to provide an electric double layer capacitor, which is a solution in which a solute is dissolved in a mixed solvent composed of and a derivative thereof.

In the present invention, the sulfolane derivative mixed and used as a solvent for the electrolyte is preferably 3
-Methylsulfolane and 2,4-dimethylsulfolane are exemplified.

In the present invention, a mixed solvent in which sulfolane and its derivative are mixed is used. In this case, sulfolane alone has a high freezing point of 28.5 ° C., but has a large dielectric constant, while 3-methylsulfolane or 2,
Sulfolane derivatives such as 4-dimethylsulfolane have a low freezing point and good physical properties at low temperatures. Then, these mixed solvents have both properties, that is, a low temperature property and a large dielectric constant.

The amount of the derivative mixed in the mixed solvent prepared by mixing sulfolane with the derivative is preferably 20 to 70% by weight, particularly 30 to 60% by weight, so that sufficient low temperature characteristics and internal resistance can be obtained. Preferred for imparting.

Of course, other known solvents such as propylene carbonate, γ-butyrolactone and acetonitrile can be added to the above-mentioned sulfolane and its derivatives to improve its characteristics.

In the present invention, the type of solute in the electrolytic solution is not particularly limited, and various conventionally known or well known solutes can be adopted. Preferred examples include tetrafluoroborate salts such as alkali metal, alkaline earth metal, ammonium or tetraalkylammonium which are electrochemically stable solutes, hexafluorophosphate salts, perchlorate salts, and hexachlorine salts. Fluoroarsenate, tetrachloroaluminate, or trifluoroalkane (preferably methane) sulfonate is used.

Among them, tetraalkylammonium tetrafluoroborate or hexafluorophosphate is a preferable solute in view of solubility in a solvent, electric conductivity, and electrochemical stability.

In the present invention, these solutes in the electrolytic solution are dissolved at a concentration of preferably 0.1 to 3 mol, particularly 0.5 to 1.5 mol.

[0013]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples and Comparative Examples. In the following examples and comparative examples, the test device was assembled as follows.

First, a cathode-side activated carbon fiber (specific surface area: 2000 m ^{2 /} g, 3.14 cm) impregnated with an electrolytic solution to be tested in a cylindrical bottomed container made of nickel having threads on its inner surface.
² , 0.4 mm thickness), a polypropylene nonwoven fabric separator (4.9 cm ² , 0.4 mm thickness), and anode side activated carbon fiber (3.14 cm ² , 2 mm thickness) are sequentially stacked.

At this time, the activated carbon fibers are arranged so as to be completely opposed to each other with the separator interposed therebetween. Next, a polytetrafluoroethylene ring having threads on both inner and outer surfaces is screwed into this container to fix the positions of the activated carbon fiber and the separator.

Then, a platinum net current collector with a platinum lead wire (2
(00 mesh) at the tip is screwed into a threaded polytetrafluoroethylene rod into the opening of the ring, and the conduction between the platinum lead wire and the nickel container is confirmed by the LCR meter AC two-terminal method to complete the setting. . The platinum lead wire is drawn to the outside through a hole provided at the center of the rod.

Using the test apparatus assembled as described above, capacitors used by sufficiently impregnating the anode and cathode electrodes made of activated carbon fibers with various electrolytic solutions containing solutes and solvents shown in Table 1 were used. The characteristics were evaluated.

The evaluation items are the decomposition voltage of the electrolytic solution, which is an index of the withstand voltage, and the capacity retention rate after high temperature storage, which were measured by the following procedures.

As for the decomposition voltage, after setting the test capacitor, a DC voltage was applied and the leakage current was measured 10 minutes later,
The voltage at which the leakage current rises rapidly when the applied voltage is gradually increased was taken as the decomposition voltage.

The capacity retention rate (I ₀ ) after high temperature storage was measured as follows. First, after setting the test capacitor, constant voltage charging is performed at 2.8 V for 1 hour. afterwards,
After constant current discharge at 1mA, measure the time until the terminal voltage reaches 1.0V at the time of discharge, and from that value, measure the initial capacity (F ₀ )
Was calculated.

Next, the test cell was stored in a constant temperature bath at 85 ° C. for 1000 hours while applying a voltage of 2.8 V, and the capacity (F) after storage was measured by the same method as described above.
The capacity retention rate after high temperature storage, I ₀ = F / F ₀ × 100 was calculated. Table 1 shows the test results obtained by changing the type of the electrolytic solution.

Examples 5 to 9 in Table 1 are examples of the present invention, and others are comparative examples. In Table 1, SN is sulfolane, MSN is 3-methylsulfolane, DMSN is 2,4-dimethylsulfolane, PC is propylene carbonate, and
BL represents γ-butyrolactone, DMF represents dimethylformamide, TEA represents tetraethylammonium, and TBA represents tetrabutylammonium.

[0023]

[Table 1]

[0024]

The electric double layer capacitor according to the present invention is
It is superior to conventional ones in terms of withstand voltage and capacity deterioration at high temperatures, and its low temperature characteristics are good, so its industrial value is extremely large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-61-214417 (JP, A) JP-B-55-41015 (JP, B2) O.K. Popovych, R.P. P. T. TOMKINS "NONAQUEOUS SOLUTION CHEMISTRY" (1981) JOHN WILEY & SONS. INC (US), P.I. 406-418

Claims (3)

[Claims] 1. An electric double layer capacitor using an electric double layer formed at an interface between a polarizable electrode made of activated carbon and an electrolytic solution, wherein the electrolytic solution dissolves a solute in a mixed solvent made of sulfolane and its derivative. An electric double layer capacitor, which is a prepared solution. 2. The electric double layer capacitor according to claim 1, wherein the derivative of sulfolane is 3-methylsulfolane or 2,4-dimethylsulfolane. 3. The electric double layer capacitor according to claim 1, wherein the mixed amount of the sulfolane derivative in the mixed solvent is 20 to 70% by weight.