Structures and Capacitance Characteristics of the Novel Crystallite Carbon for Supercapacitor

Crystallite carbons (CCs) with low BET specific surface area (<200 m2/g) have been prepared by KOH activation from preheated coal pitch based cokes. The pore structure, crystallite structure and surface chemistry of CCs were investigated by N2 adsorption, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The capacitance performance of CCs as electrode materials for supercapacitors in 1 mol/L tetraethylammonium tetrafluoroborate/propylene carbonate (Et4NBF4/PC) electrolyte was evaluated. Results reveal that CCs have a large amount of graphite-like crystallites and high graphitization degree. The value of d002 is in the range of 0.356 to 0.666 nm and the surface carbon contents are above 95%. When activating time is 6 h, the obtained CCs shows maximum mass capacitance of 139 F/g charging at 4.0 V. The energy storage behaviors are mainly composed of intercalation capacitance and electrochemical doublelayer capacitance. The intercalation capacitance initiated by "electrical activation" is the main part of the whole capacitance and the value is determined by graphitization degree of the electrode material.