JPH0888148A - Electrode of electric double layer capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE: To prevent nitrogen oxides from being adsorbed on the surface of an active carbon by a method wherein an electrode is formed into the active carbon oxidized electrochemically using a cyclic voltammetry method, in which the oxidation potential range of the active carbon is freely prescribed and it is free to change arbitrarily a potential scanning speed. CONSTITUTION: An active carbon fiber cloth is punched into a disc and that fiber cloth is dipped in a dilute sulfuric acid. This cloth is inserted in a holder 7 for a working pole 6 of a three-pole electrochemical cell 5, the cell 5 is connected with a cyclic voltammetry testing device and a current is made to flow through the testing device. Voltages between the pole 6 and paired poles 8 are controlled so as to change a potential difference between the pole 6 and a reference pole 9 at a constant speed. In short, a potential scanning is performed and an active carbon is electrochemically oxidized to manufacture an electrode. Thereby, nitrogen oxides are not adsorbed on the surface of the active carbon and even if the electrode is used for a long period of time, it is little deteriorated and a high-capacitance electric double layer capacitor can be obtained.

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 using an activated carbon as an electrode and an aqueous electrolyte.

[0002]

2. Description of the Related Art An electric double layer capacitor using an electric double layer generated at an interface between a solid and a liquid, which has a different operation principle from that of a capacitor using a dielectric material, can obtain a large electrostatic capacitance, and therefore a memory of an electronic device. A battery for electric vehicles is used as a back-up power source of the electric vehicle, and its use as an auxiliary power source for battery power has been proposed.

Various studies have been made on activated carbon used as an electrode of an electric double layer capacitor. For example, Japanese Patent Laid-Open No. 63-66373 discloses activated carbon which is oxidized by nitric acid. Application is shown.

In the above publication, attention is paid to the fact that the electric double layer capacity per unit volume of activated carbon is largely influenced by the functional groups on the surface of the activated carbon, and the functional groups are controlled to control the electric double layer per unit volume of the activated carbon. The purpose is to improve the capacity.Oxidizing the activated carbon with nitric acid, measuring the electric double layer capacity of the electric double layer capacitor using those activated carbons as electrodes, and measuring the electric double layer capacity with nitric acid It has been shown to increase.

[0005]

The electrode obtained by oxidizing the activated carbon shown in the above publication with nitric acid has a capacitance larger than that of the electrode using the untreated activated carbon as shown in the publication. However, it is difficult to control the degree of oxidation in nitric acid, and nitrogen oxides are adsorbed on the surface of activated carbon, and the adsorbed nitrogen oxides cannot be washed away. The nitrogen oxide adsorbed on the surface has a problem that it is desorbed and gasified in the process of being used as an electric double layer capacitor for a long period of time to deteriorate the performance of the electric double layer capacitor. Furthermore, since the washing water containing the oxidizing agent and the used oxidizing agent becomes waste liquid, it is necessary to perform the treatment.

The present invention solves the above problems of conventional activated carbon, and its purpose is to treat the surface of activated carbon for electrodes of electric double layer capacitors with an oxidizing agent as in the conventional case. Rather, a cyclic voltammetry method is used to provide an activated carbon electrode and a method for producing the same, in which nitrogen oxides are not adsorbed on the surface of the activated carbon and which is less deteriorated even after long-term use.

[0007]

In order to achieve the above object, according to the present invention, in an electrode of an electric double layer capacitor having activated carbon as an electrode, the electrode can freely define an oxidation potential range of the activated carbon. , An electrode of an electric double layer capacitor which is an activated carbon electrochemically oxidized by a cyclic voltammetry method capable of arbitrarily changing a potential scanning speed, and an electric double layer capacitor having an activated carbon and an electrolytic solution as electrodes In the method for producing an electrode, the method for producing an electrode is an electrochemical oxidation method using a cyclic voltammetry method capable of freely defining the oxidation potential range of the activated carbon and freely changing the potential scanning rate. A method of manufacturing an electrode of a double layer capacitor is provided.

[0008]

[Function] Since the activated carbon produced by electrochemical oxidation is used as the activated carbon for the electrode for improving the electrostatic capacity of the electric double layer capacitor, the electrode is not deteriorated even after long-term use and has a high electrostatic capacity. The electric double layer capacitor of is obtained.

[0009]

Next, embodiments of the present invention will be described in detail. A steam activated phenolic resin-based activated carbon fiber cloth was punched out into a disk shape with a diameter of 15 mm, which was then diluted with dilute sulfuric acid (1 NH
₂ SO ₄ ) for 10 hours. This is inserted into the holder 7 of the working electrode 6 of the three-electrode electrochemical cell 5 shown in FIG.
Glassy carbon was used as the counter electrode 8 and Ag / AgCl was used as the reference electrode 9. The triode type electrochemical cell 5 was connected to a known cyclic voltammetry experimental apparatus and energized. In the cyclic voltammetry experimental apparatus, a potentiostat having a potential sweeper is connected to the above-mentioned three-electrode electrochemical cell 5, and the above-mentioned action is performed so that the potential difference between the working electrode 6 and the reference electrode 9 is changed at a constant speed. This is a device capable of controlling the voltage between the pole 6 and the counter electrode 8, that is, performing potential scanning. The range of potentials for performing the potential scanning is called a potential scanning range. In the present embodiment, the reduction side is -0.2 (VvsAg / as the potential scanning range).
AgCl), + 0.8-1.0 (VvsAg /
AgCl) and the potential scanning speed is 1, 50, 100 (m
V / sec) and oxidation time (potential scanning time) were set to 4 levels in the range of 30 minutes to 40 hours to prepare an electrode.

The potential difference (E) between the working electrode 6 and the reference electrode 9 in the oxidation process and the current (i) between the working electrode 6 and the counter electrode 8
The waveform (cyclic voltammogram) of is shown in FIG.
In FIG. 4, the horizontal axis represents the potential difference (E), the vertical axis represents the current (i), and the cyclic voltammograms at the oxidation times of 0, 30 minutes, 1 hour, and 22 hours are shown in an overlapping manner. In the curve of FIG. 4, the curve indicated by a is a cyclic voltammogram when the oxidation time is 0, and the curves b, c, and d are cyclic time of 30 minutes, 1 hour, and 22 hours, respectively. It is a voltammogram. As can be seen from this figure, an increase in charging / discharging current is recognized as the oxidation time becomes longer (arrow direction in FIG. 4).

The electric double layer capacitor shown in FIG. 1 was manufactured using the electrodes manufactured as described above, and the charge / discharge electric quantity was measured by a known method. 1 in FIG. 1 is an electrode obtained by cutting an activated carbon fiber cloth into a diameter of 15 mm, 2 is a current collector, 3
Indicates a separator and 4 indicates an insulating gasket. Since the structure and operation of the electric double layer capacitor are well known, their explanation is omitted here. As described above, the charge / discharge quantity of electricity per unit weight of the electrode is obtained from the charge / discharge quantity of electricity measured by the well-known method, and the oxidation time is plotted along the horizontal axis and the charge / discharge quantity of electricity per unit weight of the electrode is plotted along the vertical axis. Plotted on. Figure 2
The potential scanning speed is 1, 50, 100 (mV / s
The relationship between the oxidation time and the amount of charge and discharge electricity per unit weight of the electrode in the case of ec) is shown. As can be seen from the figure, when the potential scanning speed is 1 mV / sec, the increase in the charge / discharge electricity quantity per unit weight of the electrode is most remarkable with respect to the oxidation time, and the electrode not subjected to the oxidation treatment after the oxidation for about 15 hours By comparison, about 1.5 times as much charge / discharge electricity per unit weight of the electrode was obtained. It was found that the increase in the amount of charge / discharge electricity per unit weight of the electrode was saturated when the oxidation time was about 20 hours. Potential scanning speed 50 mV /
Similarly, at sec and 100 mV / sec, the amount of charge / discharge electricity per unit weight of the electrode also increased, but it was found to be small. Although the present invention has been described above with reference to the above-described embodiments, various modifications and applications are possible within the scope of the gist of the present invention, and these modifications and applications are not excluded from the scope of the present invention.

[0012]

According to the present invention, an electrode of an electric double layer capacitor having activated carbon as an electrode is provided with a cyclic voltammetry method capable of freely defining the oxidation potential range of activated carbon and freely changing the potential scanning speed. Since it is electrochemically oxidized by using activated carbon, nitrogen oxides are not adsorbed on the activated carbon surface, so there is little deterioration even after long-term use, and an electric double layer capacitor with high capacitance can be obtained. Since no agent is used, the oxidizing agent and the washing water containing the oxidizing agent are not wasted, and the treatment can be made unnecessary.

[Brief description of drawings]

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

FIG. 2 is a graph showing the relationship between the capacitance and the oxidation time of the electric double layer capacitor of one example of the present invention.

FIG. 3 (A) is a photograph of a three-electrode electrochemical cell used for oxidizing an electrode of one embodiment of the present invention, and (B) is an enlarged view of a working electrode.

FIG. 4 is a cyclic voltammogram during electrode oxidation according to an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electrode 2 ... Current collector 3 ... Separator 4 ... Insulating gasket 5 ... Tripolar electrochemical cell 6 ... Working electrode 7 ... Holder 8 ... Counter electrode 9 ... Reference pole

Front Page Continuation (72) Inventor Toshiyuki Kadama 2-8-26 Nishi-Waseda, Shinjuku-ku, Tokyo Waseda University Institute for Materials Technology

Claims (2)

[Claims] 1. An electrode of an electric double layer capacitor having activated carbon as an electrode, wherein the electrode uses a cyclic voltammetry method capable of defining an oxidation potential range of the activated carbon and freely changing a potential scanning speed. An electrode of an electric double layer capacitor, which is an activated carbon that is electrochemically oxidized. 2. A method of manufacturing an electrode of an electric double layer capacitor using activated carbon as an electrode, wherein the method of manufacturing the electrode is capable of defining an oxidation potential range of the activated carbon and freely changing a potential scanning speed. A method of manufacturing an electrode of an electric double layer capacitor, which comprises electrochemically oxidizing the material using a cyclic voltammetry method.