JP3440515B2 - Electrode for electric double layer capacitor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode for an electric double layer capacitor. The electric double layer capacitor is also called an electric double layer capacitor, and has recently been receiving attention as a backup power supply, an auxiliary power supply, and the like. In particular, an electric double layer capacitor using activated carbon as a polarizable electrode has excellent performance, and the demand is growing rapidly along with the development of the electronics field. Recently, in addition to conventional small-sized products such as memory backup power supplies, large-capacity products used for auxiliary power supplies such as motors have been developed. [0002] The principle of an electric double layer capacitor has been known for a long time, but it has been relatively recently that practical use has begun. This is considered to be related to the start of using activated carbon having a high specific surface area for the polarizable electrode. The amount of electricity of the electric double layer capacitor is mainly determined by the surface area of the polarizable electrode on which the electric double layer is formed, the electric double layer capacitance per unit area, the resistance of the electrode, and the like. In practical terms, it is also important to increase the density of the electrodes themselves in order to increase the amount of electricity per unit volume and reduce the capacitor volume. In other words, the main points of the electric double layer capacitor are the performance of the activated carbon used for the electrode and the method of manufacturing the electrode. However, in general, when activation for increasing the surface area is promoted for the purpose of improving the performance of activated carbon, the density of activated carbon decreases due to the increase in pores, and the amount of electricity per unit volume decreases. In addition, since the activated carbon performance that controls the amount of electricity has not been sufficiently elucidated, it is not an exaggeration to say that there is no activated carbon that can be practically used particularly for large-capacity capacitors. [0004] In order to produce activated carbon for use in a large-capacity capacitor, the density decreases even if the activation is excessively promoted and the specific surface area is increased by an existing method. It is difficult because the amount of electricity per unit decreases. Therefore, an object of the present invention is to increase the specific surface area of activated carbon by a method other than changing the activation degree, and to obtain an electrode having a large amount of capacitor electricity per volume. The present inventors have investigated the relationship between the amount of electricity of a large-capacity electric double layer capacitor and the performance of activated carbon used for a polarizable electrode. It has been found that when an electrode is made of activated carbon having a specific surface area, the quantity of electricity can be greatly improved, and the present invention has been completed. [0006] That is, the gist of the present invention is characterized in that a carbonaceous material obtained by steam activation of a carbonaceous raw material is activated by an alkali metal hydroxide, and the obtained granules are formed by pulverization. The electrode for an electric double layer capacitor. The carbonaceous raw material to be steam-activated in the present invention is not particularly limited as long as pores are formed by the steam activation treatment. For example, coal, palm, sawdust, resin, coal coke, coal tar,
Any of carbonaceous materials such as petroleum pitch, carbon fiber and carbon black may be used, and at least one of them can be used. Preferably, coal, coconut, sawdust, or resin carbonized at 300 ° C. or more is desirable. After these carbon materials have been activated by the steam, they may be subjected to post-heat treatment as they are or further. Further, the conditions for activating with an alkali metal hydroxide such as KOH, NaOH or the like cannot be unequivocally determined because they differ depending on the water vapor activating substance to be used. , Preferably 5
50 ° C to 800 ° C. The amount of the activator used is 1 to 25 times the weight of the steam activator as KOH, preferably 2 to 25 times.
Six times the amount is desirable. The form of the alkali metal hydroxide is not particularly limited as long as it can activate carbonaceous substance substantially uniformly. For example, when the alkali metal hydroxide is used as an aqueous solution, uniform activation can be performed at a relatively low temperature. Can be. The specific surface area is calculated from the amount of nitrogen adsorbed at the temperature of liquid nitrogen. The larger the specific surface area, the better, unless the electrode density is reduced. That is,
The specific surface area of steam activation was preferably 300~2500m ² / g, which carbonaceous obtained by activating with the alkali metal hydroxide is preferably has a specific surface area of more than 500m ² / g. After alkali activation, if necessary, contact with water or an acid solution to demineralize. The activated matter is demineralized because if the product after the reaction of the alkali metal hydroxide is in activated carbon, it becomes foreign matter and may be undesirable. In addition, the reason why the activator is deashed and then pulverized is used because it is difficult to increase the density when the particle diameter is large during electrode molding, or the density of the compact does not increase, and the amount of capacitor electricity per volume is large. It is because it does not become. It is preferable to use a powder that is substantially ground to 0.2 mm or less. [0010] As a method of forming the carbonaceous material, a generally known method can be applied. That is,
Add a substance known as a binder such as polytetrafluoroethylene resin, phenolic resin, polyvinyl alcohol, cellulose, etc. in an amount of 1% to several%, mix well, put it in a mold, press-mold, or if necessary It is also possible to apply heat during pressure molding. Further, at the time of forming the electrode, conductive carbon black or another conductive substance may be added to lower the resistance of the electrode. This is because the internal resistance of the polarizable electrode is reduced and the volume of the electrode is used effectively. The present invention will be described in more detail with reference to the following Examples, which, however, are not intended to limit the scope of the present invention. Example 1 10 g of activated carbon powder having a specific surface area of 1255 m ² / g obtained by steam activation of a bituminous carbon carbide at 1000 ° C.
Was immersed in an aqueous solution in which 55 g of potassium hydroxide was dissolved. Thereafter, the powder was placed in a laboratory-scale rotary kiln, heated to 650 ° C. in a nitrogen atmosphere, and then cooled to room temperature. After washing with water 5 times, put in a dryer for 1
Dried at 15 ° C. The obtained carbonaceous material was pulverized to 200 μm or less, and the specific surface area of the powder determined from the nitrogen adsorption amount was:
It was 1584 m ² / g. 0.02 g of ethylene tetrafluoride powder was added to 1 g of the obtained sample, mixed well, and then, using a hydraulic press manufactured by JASCO, diameter 20 mm, thickness 1.5
mm to obtain a disk-shaped electrode. A polyethylene separator made by Mitsubishi Kasei Co., Ltd. is inserted between the two electrodes created by this method, and the whole is sandwiched between two platinum plates used for the current collector. Was sandwiched between two Teflon plates having a thickness of 5 mm and four bolt holes from the outermost side so as to make good contact. The capacitor electrode part thus obtained was immersed in 30% by weight sulfuric acid in a beaker to remove air bubbles adhering to the electrode, thereby producing an electric double layer capacitor. Using a charge / discharge device manufactured by Hokuto Denko and an X-T recorder manufactured by Senno Seisakusho, a constant current charge / discharge cycle test of about 860 mA was repeated 10 times at −20 ° C. to measure the electrostatic capacity. The average value of the quantity of electricity obtained from the discharge curve by a conventional method was used as the quantity of electricity of the prepared capacitor. Table 1 shows the quantity of electricity under the above measurement conditions. Example 2 An experiment was performed in the same manner as in Example 1 except that the specific surface area of the carbonaceous material obtained by steam activation of the bituminous carbon was 970 m ² / g. went. Table 1 shows the specific surface area and the amount of electricity of the obtained activated carbon. Comparative Example 1 In Example 1, activated carbon obtained by immersing 10 g of the bituminous carbon powder in an aqueous solution in which 30 g of potassium hydroxide was dissolved without activating steam and activating with an alkali hydroxide was used. An experiment was carried out in the same manner as in Example 1 except that the sample was put again in the rotary kiln shown in (1) and fired at 900 ° C. in a nitrogen atmosphere, but the amount of electricity was measured under each measurement condition. Table 1 shows the specific surface area and the amount of electricity of the obtained activated carbon. Comparative Example 2 Specific surface area of 16 obtained by steam activation of bituminous carbon carbide
The quantity of electricity of the pulverized activated carbon powder having 80 m ² / g under each measurement condition was measured in the same manner as in Example 1.
Table 1 shows the amount of electricity of the obtained activated carbon. Comparative Example 3 In Example 1, 55 g of 10 g of bituminous carbon powder was used.
Activated carbon obtained by immersion in an aqueous solution in which potassium hydroxide was dissolved and activation treatment with an alkali hydroxide were put again in the rotary kiln shown in Example 1, and steam activated at 900 ° C. under a nitrogen atmosphere. The experiment was performed in the same manner as in Example 1 except that the amount was measured. Table 1 shows the specific surface area and the amount of electricity of the obtained activated carbon. [Table 1] As described above, according to the present invention, it is possible to provide an electric double layer capacitor having a larger amount of electricity than conventional ones. As a result, applications can be expanded to fields requiring a large discharge current, such as an auxiliary power supply for a motor, and the value in industrial use is extremely large.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-217804 (JP, A) JP-A-5-258996 (JP, A) JP-A-5-139712 (JP, A) JP-A-60-1985 255608 (JP, A) JP-A-59-172230 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01G 9/058

Claims (1)

(57) [Claims 1] An electric double layer formed by activating a carbonaceous raw material with steam, further activating it with an alkali metal hydroxide, and then pulverizing the obtained granular material. Electrode for condenser.