Method for purification of indole derivative trimer, electrode active substance comprising the purified trimer, method for manufacturing the electrode active substance, and electrochemical cell using the same

Abstract

The present invention provides a method for easily removing metal impurities from an indole derivative trimer containing the metal impurities, which method involves mixing the indole derivative trimer containing the metal impurities with an imidazole compound in a solvent comprising water under heating, and filtering and separating the indole derivative trimer, from which the metal impurities have been removed, from the obtained mixture. Further, mixing a protonic acid allows the doping of the indole derivative trimer to be conducted simultaneously with the metal impurity removal, whereby the indole derivative trimer can be used as an electrode active substance of an electrochemical cell.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to a method for purification in which metal impurities are removed from a trimer of an indole derivative (hereinafter abbreviated as “indole derivative trimer”) containing the metal impurities, the indole derivative trimer being used for an electrode active substance of an electrochemical cell such as a secondary battery, an electric double layer capacitor, a redox capacitor or a capacitor. The present invention also relates to a method for manufacturing an electrode active substance in which doping to an indole derivative trimer and removal of transition metal impurities contained therein are simultaneously conducted. Further, the present invention relates to an electrode active substance comprising a high-purity indole derivative trimer manufactured thereby, and particularly to an electrochemical cell using the electrode active substance. [0003] 2. Related Art [0004] Indole compounds ...

AI Technical Summary

Benefits of technology

[0012] An object of the present invention is to provide a method for purification which can easily remove metal impurities from an indole derivative trimer containing the metal impurities. The present invention is also directed to provide a method for manufacturing an electrode active substance containing a high-purity indole derivative trimer in which method doping of an indole derivative trimer and removal of contained metal impurities can simultaneously be conducted.

[0013] Further, the present invention has an object to provide an electrochemical cell excellent in leak current characteristics in an electrochemical cell such as a secondary battery, an electric double layer capacitor, a redox capacitor or a capacitor by using the highly-purified indole derivative trimer in which the metal impurities have been sufficiently removed as an electrode active substance.

[0014] As a result of-extensive studies to solve the above problems, the present inventors have found that, by mixing an indole derivative trimer containing metal impurities with an imidazole compound to form metal complexes in a solvent comprising water under heating and filtering and separating a liquid component containing the metal complexes and an indole derivative trimer, from which the metal impurities have been removed, the metal impurities are simply and effectively removed from the indole derivative trimer. The inventions have further found that by using a protonic acid together, a simultaneous doping can be conducted, and achieved the present invention.

[0024] According to the present invention, it becomes possible to effectively and also simply removing metal impurities from an indole derivative trimer containing the metal impurities.

[0025] Further, use of an electrode active substance for which removal of metal impurities and doping can be simultaneously conducted by mixing a protonic acid, allows for providing an electrochemical cell excellent in leak current characteristics.

Problems solved by technology

But, it is difficult to manufacture the product in a large amount by the method, and a problem of being hardly applied as an industrially manufacturing method still remains.

However, since a metal compound such as ferric chloride or cupric chloride is used as an oxidizing agent, the obtained trimer inevitably has mingled metal and halogen compounds and the like derived from the oxidizing agent in the polymerization procedure.

When an indole derivative trimer containing particularly metal impurities as impurities is applied to an electrochemical cell as an electrode active substance, it causes the increase in leak current due to the side reaction of the impurities.

Although a method in which the metal impurities are eluted by treatment with a strong acid such as concentrated sulfuric acid or concentrated hydrochloric acid is generally known as the removing method of metal impurities, the treatment with these strong acids on an indole derivative trimer unfavorably causes a decrease in the performance as an electrode active substance.

For a carbonaceous material comprising a nano-scale carbon tube or a nano-scale carbon tube including a transition metal or its alloy in the space inside the tube and a transition metal impurity, which is a target to be treated in this method, there is a problem in that if the acid treatment is conducted, even the transition metal or its alloy included partially in the space inside the tube of the nano-scale carbon tube is eluted, and the nano-scale carbon tube including the transition metal or its alloy in the space inside the tube ends up being denatured; then, Patent Document 3 proposes a method which does not use an acid.

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