JPH0774059A - Electrical double-layer capacitor - Google Patents

Abstract

PURPOSE:To improve the characteristics of an electrical double-layer capacitor at a low temperature by using a liquid solution consisting sulfolane or its derivative or an admixture for reducing the freezing point. CONSTITUTION:Activated carbon fiber is used with polarization electrodes 1 and 3 as materials, an aluminum layer is formed on it as pyroelectrics 2 and 4, it is punched in a circle, and then the positive electrode side and negative electrode side of the aluminum layer are welded to a sealing plate 7. Then, sulfolane and a solvent medium where diethyl carbonate is mixed as an admixture for reducing the freezing point are dipped into the electrode as an electrolyte. Then, a separator 5 is overlapped on the electrode at the negative electrode side, a case 6 at the positive electrode side is overlapped on it while holding a gasket 8, and the edge part of the case 6 is caulked by a press for sealing, thus manufacturing a coin-type electrical double-layer capacitor and hence improving low-temperature characteristics.

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, and more particularly to improvement of its electrolytic solution.

[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 a polarizable electrode made of activated carbon and an electrolytic solution, and has an electric capacity of farad order. It is a large-capacity capacitor that can be charged and discharged instantly. Conventionally, as polarizable electrodes for electric double layer capacitors, powdered activated carbon pressure-molded with an aqueous sulfuric acid solution or a fluororesin binder, or an electrode made of powdered activated carbon and a binder on an aluminum foil or net. Materials coated with materials, activated carbon fiber cloth with a metal sprayed layer formed on one side, and the like have been used. Further, as the electrolytic solution, sulfuric acid or KOH
Known are aqueous solution electrolytes such as, and organic electrolytes obtained by dissolving an electrolyte such as a tetraalkylammonium salt in an organic solvent such as propylene carbonate, butylene carbonate, γ-butyrolactone, acetonitrile, and dimethylformamide.

[0003]

An electric double layer capacitor using an aqueous electrolytic solution has a withstand voltage per unit cell regulated to 1.23 V, which is the theoretical decomposition voltage of water.
It is impossible to further improve the withstand voltage per unit cell. On the other hand, when an organic electrolytic solution is used, the withstand voltage can be improved as compared with the aqueous electrolytic solution, but at present, the withstand voltage per unit cell is about 2.5V.
Therefore, when using it for memory backup of microcomputer etc. which is the main application of electric double layer capacitor,
To obtain a predetermined voltage, a plurality of capacitors have been stacked in series and used. 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.

When a voltage of 3 V or more is applied to the conventional electric double layer capacitor, the decomposition of the electrolytic solution causes the generation of gas, which expands the outer case and increases the internal resistance, or the electrolytic solution leaks. Although there were problems, it was possible to reduce these problems by using sulfolane or its derivative as the solvent of the electrolytic solution. However, since sulfolane has a relatively high melting point of 28.5 ° C,
There is a problem that the capacitor characteristics deteriorate at low temperature. Therefore, an object of the present invention is to improve the characteristics of an electric double layer capacitor at low temperature by lowering the freezing point of an electrolytic solution using sulfolane or its derivative as a solvent.

[0005]

In order to solve the above-mentioned problems, the present invention uses a solvent consisting of sulfolane or a derivative thereof and an additive for lowering the freezing point thereof in an electrolytic solution. As the additive, diethyl carbonate,
Dimethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, 1,2-diethoxyethane,
One or more selected from the group consisting of 1,3-dioxolane, 4,4-dimethyl-1,3-dioxane, diethyl ether and ethylene glycol is used.

Further, as the derivative of sulfolane, 3-
Examples include methylsulfolane and 2,4-dimethylsulfolane. The mixing ratio of sulfolane or a derivative thereof and the additive is preferably 1: 1 to 4: 1 by volume.

[0007]

With the above structure, the freezing point of the electrolytic solution can be lowered to about 0 ° C. to −10 ° C., and the electric conductivity at low temperature can be increased. As a result, the characteristics of the electric double layer capacitor at low temperatures can be improved.

[0008]

EXAMPLES Specific examples of the present invention will be described below. [Example 1] Activated carbon fibers (specific surface area 2500 m ² / g) were used as the material of the polarizable electrode, and an aluminum layer as a current collector was formed thereon by plasma spraying. This electrode is punched out into a disk having a diameter of 13 mm and vacuum dried at 150 ° C. The aluminum layers of these electrodes are welded to the stainless steel case on the positive electrode side and to the stainless steel sealing plate on the negative electrode side, respectively. Next, a solvent was prepared by mixing sulfolane and diethyl carbonate at a volume ratio of 75% and 25%, and 0.65 mol / l tetraethylammonium tetrafluoroborate was dissolved in the solvent to prepare an electrolytic solution. Impregnate the electrodes.

Next, a separator made of a polypropylene porous film punched out into a disk having a diameter of 15 mm was placed on the negative electrode, and a positive electrode case was placed on top of that with a gasket interposed therebetween. Then, the end of the case is crimped by a press and sealed to produce a coin type electric double layer capacitor as shown in FIG. In FIG. 1, 1 and 3 are polarizable electrodes, 2 and 4 are current collector aluminum layers, 5 is a separator, 6 is a case, 7 is a sealing plate, and 8 is a gasket.

[Embodiment 2] With the same structure as in Embodiment 1, sulfolane and diethyl carbonate are used as electrolytes in a volume ratio of 50% and 5%.
A solvent prepared by dissolving 0.4 mol / l tetraethylammonium tetrafluoroborate in a solvent mixed at a ratio of 0% is used. [Embodiment 3] With the same configuration as that of Embodiment 1, sulfolane and 1,2-dimethoxyethane are used as electrolytes in a volume ratio of 75% and 2
A solvent prepared by dissolving 0.65 mol / l tetraethylammonium tetrafluoroborate in a solvent mixed at a ratio of 5% is used.

Example 4 An electrode mixture containing powdered activated carbon (specific surface area 2000 m ² / g) made of phenolic resin as a raw material, acetylene black and methyl cellulose as a binder was prepared. Size 13 x 70 mm
The negative electrode is coated on a collector made of aluminum etching foil having a size of 13 × 60 mm to form an activated carbon electrode. These polarizable electrodes are spirally wound through a separator made of a polypropylene porous film to form a capacitor element. Next, a solvent was prepared by mixing sulfolane and diethyl carbonate in a volume ratio of 75% and 25%, and 0.65 mol / l of tetraethylammonium tetrafluoroborate was dissolved in the solvent to prepare an electrolytic solution. Impregnate the capacitor element.

Next, this capacitor element is inserted into an aluminum case and the case opening is sealed with a synthetic resin sealing plate to produce a wound type electric double layer capacitor as shown in FIG. . In FIG. 2, 11 is a polarizable electrode on the positive electrode side, 12 is a polarizable electrode on the negative electrode side, 13 is a separator,
Reference numeral 14 is a case, 15 is a sealing plate, and the sealing plate 15 has a positive electrode terminal 1 connected to the polarizable electrodes 11 and 12, respectively.
6 and the negative electrode terminal 17 are provided.

[Embodiment 5] With the same constitution as in Embodiment 4, powdery activated carbon (specific surface area 1800 m ² / g) made from coconut husk is used as the activated carbon. [Embodiment 6] With the same configuration as in Embodiment 4, 0.4 mol / l tetraethylammonium tetrafluoroborate was added to a solvent in which sulfolane and diethyl carbonate were mixed at a volume ratio of 50% and 50% as an electrolytic solution. It is used by dissolving.

[Comparative Example 1] The same composition as in Example 1 was used, but an electrolytic solution prepared by dissolving 0.65 mol / l tetraethylammonium tetrafluoroborate in sulfolane was used. [Comparative Example 2] The same composition as in Example 4 was used, but an electrolyte prepared by dissolving 0.65 mol / l tetraethylammonium tetrafluoroborate in sulfolane was used.

The capacitance and internal resistance of each of the various electric double layer capacitors produced as described above were measured at 25 ° C. and −10 ° C. Here, the capacity was calculated from a discharge curve at that time when a capacitor charged at 3.0 V was discharged at a constant current. The internal resistance was measured at a frequency of 1 kHz by an LCR meter. The results are shown in Table 1.

[0016]

[Table 1]

Next, an electric double layer capacitor similar to that of Example 1 was prepared by using an electrolytic solution prepared by dissolving tetraethylammonium tetrafluoroborate in various mixed solvents mainly containing sulfolane, and the same conditions as above were applied to 25 ° C. And the capacity and internal resistance were measured at -10 ° C. Table 2 shows the solvent mixed with sulfolane, the mixing ratio thereof, and the concentration of the electrolyte,
Table 3 shows the measurement results of capacitance and internal resistance.

[0018]

[Table 2]

[0019]

[Table 3]

In the above example, tetraethylammonium tetrafluoroborate was used as the electrolyte, but it is not particularly limited to this, and those known in the art,
For example, tetrafluoroborate such as tetraalkylammonium, hexafluorophosphate, perchlorate, hexafluoroarsenate, trifluoromethanesulfonate and the like can be used. Also, the concentration of the electrolyte is not limited to the above example.

[0021]

As is clear from the above description, according to the present invention, the low temperature characteristics of an electric double layer capacitor having a high withstand voltage using an electrolytic solution containing an electrochemically stable sulfolane or a derivative thereof as a solvent, Can be improved.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an electric double layer capacitor of one embodiment of the present invention.

FIG. 2 is a cross-sectional perspective view of an essential part showing an electric double layer capacitor of another embodiment of the present invention.

[Explanation of symbols]

 1, 3 minute polarity electrode 2, 4 current collector 5 separator 6 case 7 sealing plate 8 gasket

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

Claims (2)

[Claims] 1. An electric machine comprising a polarizable electrode made of activated carbon and an electrolytic solution, wherein the solvent of the electrolytic solution is made of sulfolane or a derivative thereof and an additive for lowering the freezing point of sulfolane or the derivative thereof. Double layer capacitor. 2. The additive is diethyl carbonate, dimethyl carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,2-dimethoxyethane, 1,2-ethoxymethoxyethane, 1,2-diethoxyethane, 1,3- The electric double layer capacitor according to claim 1, which is selected from the group consisting of dioxolane, 4,4-dimethyl-1,3 dioxane, diethyl ether and ethylene glycol.