Surface-Structure Change and Charge/Discharge Behavior of Petroleum Cokes Surface-Modified by Thermally Activated ClF3 and NF3

Heat-treatment of oxygen-containing petroleum coke (PC) at a high temperature (∼2800°C) gave rise to closure of edge planes by carbon-carbon bond formation. To change the surface structure, surface modification of PC and those heat-treated at 1860, 2300, and 2800°C (PC1860, PC2300, and PC2800) has been performed by ClF 3 and NF 2 at 200-500°C. No surface fluorine was detected except in one sample treated by NF 3 , while small amounts of surface chlorine were found in all samples treated by ClF 3 . Small amounts of nitrogen were detected in two samples treated by NF 3 . Brunauer-Emmett-Teller surface areas and total mesopore volumes were reduced by surface modification. Transmission electron microscopic observation revealed that closed-edge planes of graphitized PC were destroyed and opened by surface modification with ClF 2 and NF 3 . Removal of closed-edge planes increased first-charge capacities of many PC samples heat-treated at 1860-2800°C by ∼63 mAh/g (∼29.6%) at 150 mA/g.