Process for producing activated carbon for electrode of electric double-layer capacitor

Abstract

To produce activated carbon for an electrode of an electric double-layer capacitor, the following steps are carried out sequentially: a step of subjecting a massive mesophase pitch to a pulverizing treatment to provide a pulverized powder; a step of subjecting the pulverized powder to an infusibilizing treatment under conditions of a temperature in a range of 300° C. (inclusive) to 450° C. (inclusive) in the atmospheric air current, a step of subjecting the pulverized powder to a carbonizing treatment under conditions of a temperature in a range of 600° C. (inclusive) to 900° C. (inclusive) in an inert gas current to provide a carbonized powder, a step of subjecting the carbonized powder to an alkali activating treatment under conditions of a temperature in a range of 500° C. (inclusive) to 1,000° C. (inclusive) in an inert gas atmosphere, followed by the post treatments, thereby producing alkali-activated carbon, and a step of subjecting the alkali-activated carbon to a pulverizing treatment. If an electrode is produced using the activated carbon, the electrode density can be increased.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a process for producing activated carbon for an electrode of an electric double-layer capacitor. BACKGROUND ART [0002] Such a conventionally known type of activated carbon for an electrode includes alkali-activated carbon, which is a carbonized powder made using a graphitizable carbon powder, e.g., mesophase pitch as a starting material, aiming at the increase of the electrostatic capacity. [0003] This alkali-activated carbon is produced by a process comprising a step of producing a fibrous material by spinning using mesophase pitch, a step of subjecting the fibrous material to an infusibilizing treatment and then to a carbonizing treatment, a step of subjecting the carbonized material to an alkali activating treatment and then to a pulverizing treatment, or to a pulverizing treatment and then to an alkali activating treatment. [0004] The alkali-activated carbon made in the conventional process, however, suffers from the...

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Benefits of technology

[0009] The alkali-activated carbon produced by the above-described process comprises fine massive particles, because the powder resulting from the pulverization of the massive mesophase pitch is used as a starting material. Therefore, fine massive particles in an electrode made using the alkali-activated carbon present a structure near the closest filled structure and hence, the electrode density can be enhanced largely.

[0011] It is another object of the present invention to provide a producing process of the above-described type, capable of producing activated carbon for an electrode, which has a pore diameter facilitating the diffusion of a liquid electrolyte and ions, and an electrostatic capacity density as hitherto.

[0013] If the above-described means is employed, the metal compound is decomposed and gasified in the carbonizing treatment to produce a gas, and fine pores are formed by the gas. In the activating treatment, the fine pores serves as a source, and the metal serves as an assistant or a catalyst to promote the formation of the pores. Therefore, the diameter of the pores in the activated carbon for the electrode is enlarged. In addition, the conductivity of the activated carbon itself for the electrode is enhanced by the incorporation of the metal. Thus, the internal resistance of an electric double-layer capacitor produced can be reduced. On the other hand, if the enlargement of the pore diameter is to this extent, the electrostatic capacity density of the activated carbon for the electrode is not varied and hence, the activated carbon has the electrostatic capacity density as hitherto.

[0014] It is a further object of the present invention to provide a producing process of the above-described type capable of producing activated carbon for an electrode, wherein when a polarizing electrode is produced from the activated carbon, the amount of polarizing electrode expanded during charging can be decreased.

[0016] It can be considered that NaOH in the mixed activating agent exhibits a function to decrease the diameters of pores in the activated carbon and reduce the distance between carbon crystallites to strengthen the cross-linking of —C—O—C— (therefore, reduce the decomposition of the crosslinkage). Thus, it is possible to reduce the amount of polarizing electrode expanded during charging, as compared with a case where only KOH is employed.

[0018] If the oxygen-adding treatment as described above is carried out, when a polarizing electrode is formed using the activated carbon produced through the subsequent carbonizing and activating treatments, the amount of polarizing electrode expanded during charging can be reduced.

Problems solved by technology

If the temperature in the infusibilizing treatment is lower than 300° C., the infusibilization is insufficient and for this reason, the pulverized powder is molten in the subsequent carbonizing treatment.

On the other hand, if the temperature in the infusibilizing treatment exceeds 450° C., the oxidization advances excessively and hence, the temperature exceeding 450° C. is not preferred.

On the other hand, if the temperature in the carbonizing treatment exceeds 900° C., the activation of the carbonized powder is very hard to advance.

Further, if the temperature in the alkali activating treatment is lower than 500° C., the activation is hard to advance.

On the other hand, if the temperature in the alkali activating treatment exceeds 1,000° C., the activation advances excessively, resulting in a decreased density of the resulting alkali-activated carbon and a reduced yield of the alkali-activated carbon.

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