Abstract:
Crystallite carbons (CCs) with low BET specific surface area (<200 m2/g) have been prepared by KOH activation from preheated 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 tetrafluoroborate/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 doublelayer 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.