JPH06275468A - Electric double-layer capacitor - Google Patents

Abstract

PURPOSE:To make the breakdown strength of a double-layer capacitor to be higher and improve its low-temperature characteristics by using an active carbon fiber for a polarization electrode and a solvent composed of at least sulfolane or sulfolane derivative for an electrolyte respectively. CONSTITUTION:Active carbon fibers are used as a material for a polarization electrode 3 and an aluminum-sprayed layer 2 is formed as a collector thereon by plasma spraying. The obtained electrode is punched out and dried in vacuum. Then a case made of stainless steel and the layer 2 as an electrode are welded. Although the stainless steel cases are formed as a case 6 on the positive side and a case 1 on the negative side respectively, both cases are similarily welded to the electrode. In addition, the electrode 3 is impregnated with electrolyte in which a 4 boric acid fluoride tetraethyl ammonium is dissolved in a sulfolane. Thus, the breakdown strength of an electric double-layer capacitor is made higher, and the number of capacitors to be coupled can be reduced.

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 capable of instantly charging and discharging a large amount of electricity.

[0002]

2. Description of the Related Art An electric double layer capacitor utilizes electric energy accumulated in an electric double layer formed at an interface between activated carbon and an electrolytic solution, and has a large capacity capable of instantaneously charging and discharging the electric capacity of farad order. It is a capacitor.

Conventionally, as a polarizable electrode of an electric double layer capacitor, powdered activated carbon is pressure-molded with a sulfuric acid aqueous solution or a fluorine-based binder, and powdered activated carbon and the binder are formed on an aluminum foil or net. It has been used such as those coated with an electrode, activated carbon fiber cloth with a metal sprayed layer formed on one side, and the like.

As the electrolytic solution, an aqueous solution electrolytic solution such as sulfuric acid or KOH, an organic solvent such as propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile or dimethylformamide in which an electrolyte such as tetraalkylammonium salt is dissolved. System electrolytes are known.

[0005]

However, in the above electric double layer capacitor, the withstand voltage per unit cell is about 2.5V even when the organic electrolyte is used. Therefore, when the electric double layer capacitor is mainly used for memory backup of a microcomputer or the like, a plurality of capacitors have been stacked in series to obtain a predetermined voltage. If the withstand voltage of the capacitor can be set to 3 V or more, the number of stacked capacitors can be reduced, and a recent low-voltage driven microcomputer can perform backup with a single cell.

However, the conventional electric double layer capacitor has three
When a voltage of V or more is applied, there is a problem that the outer case expands due to the pressure of the gas generated by the decomposition of the electrolytic solution, the internal resistance increases, and the electrolytic solution leaks.

The present invention solves the above problems, and an object of the present invention is to provide an electric double layer capacitor which does not generate a gas, has a low internal resistance, and does not leak even when a voltage of 3 V or more is applied. It is a thing.

[0008]

In order to solve the above problems, the electric double layer capacitor of the present invention uses activated carbon fiber as the polarizable electrode and a solvent containing at least sulfolane or a sulfolane derivative as the electrolytic solution. Is.

[0009]

In the electric double layer capacitor of the present invention, activated carbon fiber is used as the polarizable electrode material and sulfolane is used as the electrolytic solution. Since the activated carbon fiber is produced from a synthetic polymer as a raw material, the content of impurities is extremely small as compared with the conventional activated carbon produced from coconut husk or the like. Therefore, side reactions are unlikely to occur in the capacitor. Sulfolane is one of the most electrochemically stable solvents, and by combining it with activated carbon fiber having a low content of impurities, the storage stability, charge / discharge characteristics, and withstand voltage of the electric double layer capacitor can be improved.

2 and 3 show the stability of sulfolane and propylene carbonate as an electrolytic solution. 2 and 3 are current-potential curves of sulfolane and propylene carbonate measured using activated carbon fiber as a working electrode, Pt as a counter electrode, and Ag / Ag + as a reference electrode. As the electrolyte, tetraethylammonium tetrafluoroborate of 0.1.
A 65 mol / liter solution was used. The sulfolane shown in FIG. 2 has almost no change in the repetition characteristic of the current-potential characteristics, but the propylene carbonate shown in FIG. 3 has unstable current-potential repeating characteristics in the order of A → B → C → D → E and is unstable. It can be seen that it is.

[0011]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the electric double layer capacitor of this example.

Activated carbon fiber (specific surface area 2500 m ² / g) is used as the material of the polarizable electrode 3, and the aluminum sprayed layer 2 is formed on this as a current collector by plasma spraying. This electrode is punched out to a diameter of 13 mm and vacuum dried at 150 ° C. Next, the case made of stainless steel and the aluminum sprayed layer 2 of the electrode are welded. The stainless steel case has a positive case 6
There are two types, one is the negative electrode side case 1 and the other is the negative electrode side case 1. The electrodes are welded in the same manner. Next, the polarizable electrode is impregnated with an electrolytic solution prepared by dissolving 0.65 mol / liter tetraethylammonium tetrafluoroborate in sulfolane.

Although tetraethylammonium tetrafluoroborate was used as the electrolyte in this embodiment, the present invention is not particularly limited to this, and conventionally known substances such as tetraalkylammonium can be used. Tetrafluoroborate, hexafluorophosphate, perchlorate, 6
Fluoroarsenic acid salts, trifluoromethanesulfonic acid salts, etc. can be used. Further, the concentration of the electrolyte is not particularly limited to the above concentration.

Next, on the electrode 3 on the negative electrode side, a separator 4 made of a polypropylene porous film punched out to a diameter of 15 mm is laid, and a case 6 on the positive electrode side is laid on it. Then, the periphery of the positive electrode side case 6 was caulked by a press and sealed to produce a coin type electric double layer capacitor as shown in FIG.

Although a polypropylene porous film is used as the separator 4 in this embodiment, the separator 4 is not limited to this as long as it is non-electroconductive and ion-permeable.

As the initial characteristics of the electric double layer capacitor manufactured as described above, the electric capacity and the internal resistance were measured. Then, the capacitor was left for 1000 hours at 70 ° C. while applying a voltage of 3.0 V, and the capacity and internal resistance of the capacitor after 1000 hours were measured. Here, the electric capacity was calculated from a discharge curve obtained by discharging a capacitor charged at 3.0 V with a constant current. The internal resistance was measured with an LCR meter (frequency 1 kHz).

Comparative Example 1 With the same constitution as in Example 1, propylene carbonate in which 0.65 mol / l tetraethylammonium tetrafluoroborate was dissolved was used as an electrolytic solution. The comparison results are shown in (Table 1).

[0018]

[Table 1]

(Example 2) An electrode mixture containing powdered activated carbon made of phenolic resin as a raw material and a binder was prepared, and the mixture was made of an aluminum etching foil having a positive electrode 13 × 70 mm and a negative electrode 13 × 60 mm. It was applied on an electric body to form an activated carbon electrode. Each of the electrode foils was sandwiched and wound with a separator made of a polypropylene porous film. This was impregnated with the same electrolytic solution as in Example 1 and sealed in an aluminum case to produce a wound-type electric double layer capacitor. Then, the initial characteristics and the characteristics after 1000 hours were measured in the same manner as in Example 1.

(Comparative Example 2) With the same constitution as in Example 2, propylene carbonate in which 0.65 mol / liter tetraethylammonium tetrafluoroborate was dissolved was used as an electrolytic solution. The comparison results are shown in (Table 1).

(Embodiment 3) With the same constitution as in Embodiment 2, powdered activated carbon made from coconut husk was used. Then, the initial characteristics and the characteristics after 1000 hours were measured in the same manner as in Example 1.

(Comparative Example 3) With the same constitution as in Example 3, propylene carbonate in which 0.65 mol / liter of tetraethylammonium tetrafluoroborate was dissolved was used as an electrolytic solution. The comparison results are shown in (Table 1).

(Example 4) Activated carbon fibers (specific surface area 2
500 m ² / g), and an aluminum layer as a current collector is formed by plasma spraying. This electrode has a diameter of 1
It is punched out to 3 mm and vacuum dried at 150 ° C. Next, the stainless steel case and the aluminum layer of the electrode are welded. There are stainless steel cases on the positive electrode side and those on the negative electrode side, but the electrodes are welded in the same manner. Next, the electrode is impregnated with an electrolytic solution in which 0.65 mol / liter tetraethylammonium tetrafluoroborate is dissolved in 3-methylsulfolane.

In this embodiment, tetraethylammonium tetrafluoroborate was used as the electrolyte, but the present invention is not limited to this, and a conventionally known material such as tetraalkylammonium can be used. Fluoroborate, hexafluorophosphate, perchlorate, hexafluoroarsenate, trifluoromethanesulfonate and the like can be used. Further, the concentration of the electrolyte is not particularly limited to the above concentration.

Next, on the electrode on the negative electrode side, a separator made of a polypropylene porous film punched out to a diameter of 15 mm is placed, and a gasket is sandwiched on the separator, and the case on the positive electrode side is placed thereon. This was caulked by a press and sealed to prepare a coin type electric double layer capacitor as shown in FIG.

Although a polypropylene porous film is used as the separator in this embodiment, the separator is not limited to this as long as it is non-electroconductive and ion-permeable.

The internal resistance of the electric double layer capacitor produced as described above was measured at 25 ° C. and −10 ° C. by an LCR meter (frequency 1 KHz).

(Comparative Example 4) With the same structure as in Example 4, sulfolane was used as the solvent for the electrolytic solution. The comparison results are shown in (Table 2).

[0029]

[Table 2]

(Embodiment 5) With the same construction as in Embodiment 4, 3-ethylsulfolane was used as a solvent for the electrolytic solution. The results are shown in (Table 2).

(Embodiment 6) With the same construction as in Embodiment 4, 50% sulfolane and 5 propylene carbonate as an electrolytic solution are used.
0% mixed solvent was used. The results are shown in (Table 2).

As can be seen from Table 1, Examples 1 to 3
The initial characteristic of the capacitor is that the electric capacity is the same,
The internal resistance is nearly three times higher than that of the comparative example. In addition, the characteristics after applying a voltage of 3 V, which is higher than before, at 70 ° C. for 1000 hours and showing excellent pressure resistance with a smaller rate of change in both capacity and internal resistance than the comparative example, and for long-term use under high voltage application Can bear.

Further, as can be seen from (Table 2), the capacitors of Examples 4 to 6 show less increase in internal resistance at −10 ° C. and excellent characteristics at low temperature as compared with Comparative Example 4. Recognize.

[0034]

As is apparent from the above description, according to the present invention, the withstand voltage of the electric double layer capacitor is increased by using the activated carbon fiber as the polarizable electrode and forming the electrolytic solution with the sulfolane solvent. The number of capacitors to be connected can be reduced. Further, the low temperature characteristics of the capacitor can be improved by using sulfolane or a sulfolane derivative in the electrolytic solution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of an electric double layer capacitor according to an embodiment of the present invention.

FIG. 2 is a diagram showing a current-potential curve of sulfolane used in the electrolytic solution.

FIG. 3 is a diagram showing a current-potential curve of propylene carbonate used in a conventional electrolytic solution.

[Explanation of symbols]

 1 Negative electrode side case 2 Aluminum sprayed layer 3 Polarizing electrode 4 Separator 5 Gasket 6 Positive electrode side case

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiko Yoshida 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (6)

[Claims] 1. An electric double layer capacitor comprising a polarizable electrode and an electrolytic solution, wherein the polarizable electrode is mainly composed of activated carbon fibers, and the solvent of the electrolytic solution is mainly composed of sulfolane or a sulfolane derivative. Multilayer capacitor. 2. The electric double layer capacitor according to claim 1, wherein the activated carbon fiber used for the polarizable electrode is produced mainly from phenol fiber. 3. The electric double layer capacitor according to claim 1, wherein the carbon purity of the activated carbon fiber used for the polarizable electrode has a lower limit of 99%. 4. An electric double layer capacitor comprising a polarizable electrode and an electrolytic solution, wherein the solvent of the electrolytic solution is mainly composed of a sulfolane derivative having a melting point of 0 ° C. as an upper limit. 5. The electric double layer capacitor according to claim 4, wherein the sulfolane derivative contains an alkyl group. 6. An electrolytic solution containing a solvent containing at least sulfolane or a sulfolane derivative and at least one of propylene carbonate, butylene carbonate, γ-butyrolactone, 1,3-dioxolane, acetonitrile, dimethylformamide or 1,2-dimethoxyethane. The electric double layer capacitor according to claim 1 or 4, which is a mixed solvent with a solvent containing it.