Chemical purification processes of the natural crystalline flake graphite for Li-ion Battery anodes

We investigated the effect of the acid species, the liquid-to-solid ratio, the reaction time, and temperature on the carbon content (CC) of natural crystalline flake graphite in Ethiopia. Specifically, after physical purification through a froth flotation, CC was observed to be 94.71 %. However, when the acid-alkali-acid, H2SO4/H2O2-NaOH−HCl, chemical purification process was employed in this study, CC was significantly improved to 99.68 % (or 99.72 % after additional HF leaching), based on both a loss-on-ignition test and thermogravimetric analysis. Here, the purified graphite powder exhibited a conductivity of 21.9 S/cm, placing it in the range of semiconductor materials. The hexagonal structure of graphite, when analyzed by X-ray diffraction, was independent of the purification process. However, according to the scanning electron microscopy image, the impurities in the graphite sample were removed effectively through the purification process. Finally, based on the overall material properties of this purified graphite, this natural flake graphite could be used for high tech applications such as Li-ion battery anodes.