JPH0629152A - Electric double layer capacitor - Google Patents

Abstract

PURPOSE:To prevent capacitance from being reduced and at the same time to improve a withstand voltage performance by suppressing generation of a gas while activated carbon is incorporated into an electric double-layer capacitor. CONSTITUTION:A constant potential is previously applied to a positive pole side activated carbon and a negative pole side activated carbon in an electrolyte before it is incorporated into a capacitor for eliminating a gas generated by oxidation or reduction reaction before use. The positive pole side activated carbon is immersed in an electrolyte 2 of 30wt.% dilute sulfuric acid liquid solution with what is obtained by performing thermocompression of an activated carbon electrode 3c to a steel plate 3a via a conductive sheet 3b as a work electrode 3, a platinum plate as an opposite pole 4, SCE(saturation calomel electrode) as a reference electrode 5 for forming a beaker cell and then +0.9V potential is applied to the reference electrode 5 by a potentiostat. For the activated carbon at the negative pole side, -0.25V potential is continuously applied to the reference electrode 5 in a same beaker cell.

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 which prevents deterioration of electrostatic capacity under a constant voltage load condition.

[0002]

2. Description of the Related Art An electric double layer capacitor comprises a polarizable electrode laminated inside and outside a frame-shaped gasket via a separator, and a conductive film disposed on the upper and lower surfaces of each polarizable electrode. It is composed of a metal current collector plate such as a copper plate which is on the upper and lower surfaces of the gasket and is connected to the conductive film.

As the polarizable electrode, an activated carbon sheet impregnated with dilute sulfuric acid as an electrolytic solution is used. Positive and negative electric charges taken in through each current collector plate at the time of charging are stored in each polarizable electrode, and at the time of discharging. Since the stored charges are gradually discharged to the outside through each current collector plate, the same usage pattern as a kind of secondary battery can be adopted.

The withstand voltage performance of this electric double layer capacitor is within the range before generation of oxygen and hydrogen gas by electrolysis of water, as shown in the potential-current characteristics of water shown in FIG. It can be used in the range of 4V to + 1.0V, and considering the reliability of the product, -0.2V to +
It is desirable to use in the range of 0.8V.

[0005]

However, when an activated carbon electrode is actually used, a temporary peak is generated from around +0.7 V on the anode side as shown by the broken line in the figure, and also around −0.1 V on the cathode side. Since a temporary peak occurs, the operating range is less than -0.1V to + 0.7V
Was limited to.

Further, the range of this peak, that is, −
When used in the range of 0.2V to + 0.8V, gas is generated inside, the electrolyte leaks or evaporates due to the internal pressure, and the weight decreases with the number of days of voltage application, and the capacitance also decreases accordingly. There was a tendency.

By the way, the activated carbon used for the polarizable electrode is conventionally used without pretreatment. However, since the bubbles inside the porous material are replaced with the electrolytic solution by impregnation with the electrolytic solution, the activated carbon is included. Gas generation due to bubbles is unlikely.

Therefore, the inventors of the present invention have found that the mechanism of gas generation is a region where a temporary peak occurs in the cyclic voltammogram, and an oxidizing reaction occurs in the causative substance on the positive electrode side inside the activated carbon to generate gas. It was presumed that gas was similarly generated by the reduction reaction on the negative electrode side.

The present invention has been made on the basis of the above assumptions. The purpose of the present invention is to activate activated carbon by applying an electric potential corresponding to the activated carbon in advance to remove the causative substance of the gas generation. An object of the present invention is to provide an electric double layer capacitor that suppresses the generation of gas in a state of being incorporated in the double layer capacitor, prevents the decrease in electrostatic capacitance due to this, and improves the withstand voltage performance.

[0010]

In order to achieve the above object, the present invention provides a polarizable electrode vertically stacked inside a gasket via a separator, and a conductive material disposed on the upper and lower opening surfaces of the gasket. In an electric double layer capacitor comprising a pair of upper and lower current collectors arranged on the upper and lower surfaces of the gasket via a film to seal the inside of the gasket, the activated carbon constituting the polarizable electrode is moved to the inside of the gasket. By applying a constant voltage in the electrolytic solution before assembling, the gas generated under the constant voltage load condition is removed beforehand.

In the actual removal process, a constant voltage on the positive electrode side is applied in the electrolytic solution to the activated carbon forming the positive electrode side polarizable electrode, and the active carbon forming the negative electrode side polarizable electrode is electrolyzed. A constant voltage on the negative electrode side is applied in the liquid to remove each generated gas.

Further, it is preferable to use an aqueous electrolytic solution as the electrolytic solution used for the removal treatment.

[0013]

[Function] Although the causative substance of gas generation in the above configuration has not been specified, the amount of gas generated by the potential applied to the activated carbon is finite, and when the pretreated activated carbon is incorporated into an electric double layer capacitor. Since the causative substance of gas generation has already been removed, there is no gas generation and the internal pressure does not increase.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below.
FIG. 1 is a side sectional view of an electric double layer capacitor according to the present invention, in which 10 is a gasket formed in a rectangular frame shape, and 12 is a gasket.
Reference numerals a and 12b denote positive and negative polarizable electrodes that are stacked one on top of the other in the gasket 10 with a separator 14 disposed in the middle therebetween, and 16 denotes polarizable electrodes 12a and 12b.
Is a conductive film laminated on the top and bottom openings of the gasket 10 so as to cover the basic cell.

A metal current collector plate 20 is disposed on the upper and lower surfaces of the gasket 10 with a frame-shaped hot melt film 18 interposed therebetween, and the inside of the gasket is hermetically sealed while being pressure-bonded to the surface of the conductive film 16. is doing.

In the above structure, the polarizable electrodes 12a,
No. 12b is an activated carbon sheet in which 30% by weight of dilute sulfuric acid is poured and impregnated.
The other constitutes a negative electrode, and accordingly, a polarity is displayed on the surface of the current collector plate 20 connected to each.

In the present invention, the polarizable electrode 12 described above is used.
Before the positive electrode side activated carbon sheet and the negative electrode side activated carbon sheet forming a and 12b are both incorporated into a capacitor, a constant potential is applied in advance in the electrolytic solution to remove the generated gas in advance.

More specifically, as illustrated in FIG.
The beaker 1 is filled with 30% by weight of dilute sulfuric acid as the electrolytic solution 2 (aqueous electrolytic solution), which is similar to the case of pouring into the polarizable electrode,
A copper plate 3a coated with a conductive sheet 3b and the activated carbon electrode 3c thermocompression bonded thereto were used as a working electrode 3, a platinum plate was used as a counter electrode 4, and a saturated calomel electrode (SCE) was used as a reference electrode 5 and immersed in an electrolytic solution 2. To form a beaker cell.

Then, a potential of 0.9 V is applied to the reference electrode 5 by a potentiostat with respect to the positive electrode side activated carbon sheet.

By applying this potential, gas is generated and the current value changes. This gas generation is finite,
By continuing to apply the potential until the current value becomes constant,
Gas generation is complete.

Although the composition of the gas has not been clarified so far, it is presumed that the causative substance undergoes an oxidation reaction on the surface of the activated carbon in the region where a temporary peak in FIG.

With respect to the activated carbon on the negative electrode side, a potential of -0.25 V is continuously applied to the reference electrode 5 in the same beaker cell until the current value becomes constant to generate gas. This gas is generated as a result of the reduction reaction of the causative substance on the surface of the activated carbon.

Next, the positive electrode side activated carbon sheet and the negative electrode side activated carbon sheet are removed from the electrodes, and the positive and negative electrode polarizable electrodes 12a and 12b are formed by combining them, and they can be incorporated into the electric double layer capacitor shown in FIG.

A constant voltage load of 1.0 V was applied to each of the electric double layer capacitor using the pretreated activated carbon and the conventional electric double layer capacitor using the non-pretreated activated carbon to determine whether or not liquid leakage occurred. When the change in capacitance was examined, the results shown in FIGS. 3 and 4 were obtained.

FIG. 3 shows the relationship between the number of days the voltage is applied and the weight. When 30 days have passed, the conventional one has about 30 times the initial load.
The amount was reduced to nearly%.
A decrease in capacitance of up to 0% is shown. This suggests that the internal pressure rises due to gas generation and the capacitance decreases due to leakage or evaporation of the electrolytic solution.

On the other hand, the weight of the electric double layer capacitor according to the present invention is hardly changed, the electrostatic capacity is kept constant, no gas is generated, and the capacity is lowered due to this. Suggests that there is no. Also,
Since the electric double layer capacitor according to the present invention does not generate gas at the peak time, in consideration of the flatness of the current, −
It has a withstand voltage performance in the range of 0.2V to + 0.8V, and can be improved by 0.2V compared to the conventional -0.1V to + 0.7V, and the range of use can be expanded.

In this embodiment, dilute sulfuric acid is used as the aqueous electrolytic solution, but the aqueous electrolytic solution is not limited to this, and potassium hydroxide, sodium hydroxide, hydrochloric acid or the like may be used. Good.

Further, in this embodiment, the activated carbon was pretreated by a laboratory method, but it goes without saying that it can be easily applied to an industrial method.

[0029]

As described in detail in the above embodiments, according to the electric double layer capacitor of the present invention, the amount of gas generated by the potential applied to the activated carbon is finite, and the activated carbon after pretreatment is electrically charged. When incorporated in a double-layer capacitor, the causative substance of gas generation is already removed and no gas is generated, so that the following effects can be obtained. It is possible to prevent leakage of liquid and deterioration of capacitance due to increase in internal pressure. The restriction on the voltage for preventing gas generation can be relaxed, and the range of voltage usage can be expanded as compared with the prior art.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram showing a voltage application device for pretreatment of activated carbon.

FIG. 3 is a graph showing the relationship between the number of voltage application days and the weight.

FIG. 4 is a graph showing the relationship between the number of voltage application days and the capacitance.

FIG. 5 is an example of a cyclic voltammogram of activated carbon.

[Explanation of symbols]

 1 Beaker 2 Electrolyte (Aqueous System) 3 Working Electrode 3a Copper Plate 3b Conductive Sheet 3c Activated Carbon Electrode 4 Counter Electrode (Platinum Plate) 5 Reference Electrode 10 Gasket 12a Polarizable Electrode (Active Carbon Electrode) 12b Polarized Electrode (Active Carbon Electrode) 14 Separator 16 Conductive film 20 Current collector

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuhiro Nakamura 5-36-11 Shinbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Tatsuya Yamazaki 5-36-11 Shinbashi, Minato-ku, Tokyo Fuji Electrochemical Co., Ltd.

Claims (3)

[Claims] 1. A gasket, which is arranged on the upper and lower surfaces of the gasket via a polarizable electrode which is vertically laminated inside a gasket via a separator, and a conductive film which is arranged on the upper and lower opening surfaces of the gasket. In an electric double layer capacitor comprising a pair of upper and lower collector plates that seal the inside of the, the activated carbon that constitutes the polarizable electrode is formed by applying a constant voltage in an electrolytic solution before being incorporated into the gasket. An electric double layer capacitor characterized in that a gas generated under a constant voltage load condition is previously removed. 2. A constant voltage on the positive electrode side is applied in the electrolytic solution to the activated carbon forming the polarizable electrode on the positive electrode side, and a constant voltage on the negative electrode side in the electrolytic solution is applied to the activated carbon forming the polarizable electrode on the negative electrode side. The electric double layer capacitor according to claim 1, wherein each of the generated gases is subjected to a removal treatment by being applied. 3. The electric double layer capacitor according to claim 1, wherein an aqueous electrolytic solution is used as the electrolytic solution.