RAMAN-SPECTROSCOPY AND ELECTRON-MICROSCOPY OF HEAT-TREATED PETROLEUM COKES FOR LITHIUM-INTERCALATION ELECTRODES

Raman spectroscopy, coupled with high-resolution transmission electron microscopy (HRTEM) and x-ray diffraction analysis, were used to chara cterize the physical properties of carbonaceous materials obtained by heat-treatment of petroleum coke at 1800, 2100, and 2350 degrees C. Th e effects of heat-treatment and air milling process (to obtain an aver age particle size of 10 mu m) on the physical and microstructural prop erties of the carbon particles were examined. The Raman intensities of the D and G bands were used to estimate the crystallite size, L-a, an d x-ray diffraction was used to obtain L-c and the d(002) spacing of t he petroleum cokes. Heat-treatment of the petroleum coke at temperatur es above 2100 degrees C produces a L-a value of about 100 Angstrom, in terplanar distance, L-c, of >600 Angstrom, and d(002) spacing of 3.358 Angstrom, close to that of graphite. HRTEM showed that a distinct ord ering of the layer planes occurs with heat-treatment, and a perceptibl e difference in the surface morphology is evident with petroleum coke that is heat-treated at 2350 degrees C and then air milled. The electr ochemical results for lithium intercalation/deintercalation of the pet roleum cokes in 0.5 M LiN(CF3SO2)(2)/ethylene carbonate:dimethyl carbo nate electrolyte revealed that heat-treatment at 2350 degrees C improv es the reversible Li storage capacity of the petroleum coke, and that air milling after heat-treatment produces a petroleum coke with high r eversible capacity, equivalent to Li0.93C6.