Electric double layer capacitor, activated carbon for electrode therefor and method for producing the same
A method for producing activated carbon for electrodes of electric double layer capacitors is disclosed which comprises an activation step wherein activated carbon is obtained by mixing an alkali metal hydroxide with a carbon raw material for the activated carbon and heating the mixture in an inert gas atmosphere, a deactivation removal step wherein the alkali metal in the activated carbon is deactivated and removed, and a heat treatment step wherein the activated carbon having gone through the deactivation removal step is heated in an inert gas atmosphere at a temperature higher than 400° C. but not higher than the heating temperature in the activation step. Also disclosed are activated carbon produced by such a method, activated carbon for electrodes of electric double layer capacitors wherein the alkali metal content is less than 100 mass ppm, activated carbon for electrodes of electric double layer capacitors having specific impedance characteristics, and activated carbon for electrodes of electric double layer capacitors having a specific amount of surface functional groups and a specific amount of surface carboxyl groups. In an electric double layer capacitor comprising a pair of electrodes and an electrolyte solution, at least one of the electrodes contains such an activated carbon.
1. A method for producing activated carbon for an electric double layer capacitor electrode characterized in that the method comprises:
an activation step of obtaining an activated carbon by mixing a raw carbon material for activated carbon with an alkali metal hydroxide, and heating the mixture in an inert gas atmosphere;
a deactivation and removal step of deactivating and removing alkali metal contained in the activated carbon; and
a heat treatment step of heating the activated carbon passed through the deactivation and removal step to a temperature higher than 400° C. and not higher than the heating temperature in the activation step, in an inert gas atmosphere.
2. The method according to claim 1 , wherein the alkali metal is deactivated in the deactivation and removal step by reacting the alkali metal with carbon dioxide gas at 200° C. or higher, and/or by washing the activated carbon with water.
3. The method according to claim 1 , wherein the alkali metal hydroxide is potassium hydroxide.
4. The method according to claim 1 , wherein the raw carbon material for activated carbon is graphitizable carbon.
5. The method according to claim 4 , wherein the graphitizable carbon is petroleum coke.
6. The method according to claim 4 , wherein the heating temperature in the activation step is set at a temperature higher than 600° C. and lower than 800° C.
7. The method according to claim 1 , further comprising a water washing step of washing the activated carbon passed through the heat treatment step with water.
8. Activated carbon for an electric double layer capacitor electrode, having an alkali metal content of less than 100 mass ppm, said activated carbon being produced by the method according to claim 7 .
9. Activated carbon for an electric double layer capacitor electrode produced by the method according to claim 1 .
10. The activated carbon for an electric double layer capacitor electrode according to claim 9 , wherein
the activated carbon have an alkali metal content of less than 100 mass ppm.
11. An electric double layer capacitor having a pair of electrodes and an electrolytic solution, characterized in that at least one of the pair of the electrodes includes the activated carbon according to claim 10 .
12. A method for producing activated carbon for an electric double layer capacitor electrode characterized in that the method comprises:
an activation step of obtaining an activated carbon by mixing a raw carbon material for activated carbon with an alkali metal hydroxide, and heating the mixture in an inert gas atmosphere;
a deactivation and removal step of deactivating and removing alkali metal contained in the activated carbon; and
a heat treatment step of heating the activated carbon passed through the deactivation and removal step to a temperature higher than 400° C. and lower than 750° C., in an inert gas atmosphere.
13. The method according to claim 12 , wherein the alkali metal is deactivated in the deactivation and removal step by reacting the alkali metal with carbon dioxide gas at 200° C. or higher, and/or by washing the activated carbon with water.
14. The method according to claim 12 , wherein the alkali metal hydroxide is potassium hydroxide.
15. The method according to claim 12 , wherein the raw carbon material for activated carbon is graphitizable carbon.
16. The method according to claim 15 , wherein the graphitizable carbon is petroleum coke.
17. The method according to claim 15 , wherein the heating temperature in the activation step is set at a temperature higher than 600° C. and lower than 800° C.
18. The method according to claim 12 , further comprising a water washing step of washing the activated carbon passed through the heat treatment step with water.
19. Activated carbon for an electric double layer capacitor electrode produced by the method according to claim 12 .
20. Activated carbon for an electric double layer capacitor electrode, having an alkali metal content of less than 100 mass ppm, said activated carbon being produced by the method according to claim 18 .
21. An electric double layer capacitor having a pair of electrodes and an electrolytic solution, characterized in that at least one of the pair of the electrodes includes the activated carbon according to claim 19 .