A comprehensive review on the electrochemical activation for non-aqueous carbon-based supercapacitors

Background: The electrical double layer capacitors (EDLCs) have been commercially available and useful in the daily lives. Nevertheless, conventional EDLCs have reached their limit in terms of cell capacitance and cell voltage. The resultant low energy density urges researchers to improve either the maximum cell voltage or the specific capacitance to obtain a high-energy-density supercapacitor. In a fixed voltage window, the electrochemical activation (EA) method has been demonstrated to effectively enhance the specific capacitance of certain carbons with small surface areas. Methods: Progress that has been made since the introduction of this EA method in 1998 will be systematically discussed. The choice of (1) carbon materials with different properties, (2) electrolytes composed of various salts/solvents, and (3) binders that have diverse chemical/mechanical properties, proves influential in determining the resultant capacitive performance after the EA process. Significant findings: Although the EA mechanism has been intensively investigated and described as the irreversible intercalation of ions into graphitic regions in initial charge-discharge steps, the interplay amongst carbon, electrolyte and binder has not been fully understood. Therefore, in this article, a few research topics have been recommended to inspire further research interest in order to improve the EA method for practical applications.