Enhanced specific capacitance of modified needle cokes by controlling oxidation treatment

The electric double-layer performance of needle cokes can be affected by the morphology of structures. Hence, we introduce modified needle cokes by using simple oxidation treatment. The degree of graphitization with high specific capacitance is controlled by acid and heat treatment. The active sites of cokes are increased with increasing oxidation time. Dilute nitric acid (HNO3) and sodium chlorate (NaClO3) are used for the activation of cokes. In this case, the interlayer distance is dramatically increased from 3.5 to 8.9 A. The specific capacitances are 33 F g-1 and 30 F ml-1, respectively, on a two-electrode system with a potential range of 0-2.5 V. The behaviors of double-layer capacitance are demonstrated by the charge-discharge process and the morphologies of modified needle cokes are analyzed by XRD, FE-SEM, BET and elemental analysis.