Surface structure and electrochemical characteristics of plasma-fluorinated petroleum cokes for lithium ion battery

Plasma-fluorination of petroleum coke and those heat-treated at 1860, 2300 and 2800 degrees C (abbreviated to PC, PC 1860, PC2300 and PC2800) was conducted for 15, 30 and 60 min using CF4 gas at 90 degrees C. Fluorine contents obtained by elemental analysis were negligible except PC fluorinated for 60 min (0.7 at.%). Fluorine concentration on the surface decreased with increasing heat-treatment temperature of petroleum coke, i.e. from PC to PC2800 when plasma-fluorination was made for 30 and 60 min. Transmission electron microscopic observation revealed that the closed edges of PC2800 were destroyed and opened by plasma-treatment. Plasma-fluorination increased surface disorder of heat-treated petroleum cokes, however, slightly reduced surface areas. These surface structure changes increased first coulombic efficiencies of PC2300 and PC2800 by 6-8 and 8-10% at both 60 and 150 mA g(-1), respectively. (C) 2007 Elsevier B.V. All rights reserved.