Graphite Fluoride Prepared at Mild Temperature for High Energy/High Power Density Lithium Batteries

Abstract

Abstract We used a two-step fluorination of natural or synthetic graphites, the one at the ambient temperature in the presence of F2 + IF5 + HF and the second in the temperature range of 100 – 350°C in F2 atmosphere. This led to graphite fluorides characterized by the planarity of the carbon hexagons (sp2 hybridization), by the iono-covalent character of the C-F bondings and by the high F/C ratio, close to unity. These graphite fluorides were compared to conventional, highly covalent CFx (sp3 hybridization) in their electrochemical performances in lithium batteries, especially regarding the high rate discharge capability. We found a large advantage with the iono-covalent CFx that is they sustain a 5 C rate discharge where the covalent ones failed to discharge under 4 C. The difference is tentatively related to the internal structure and to the higher electrical conductivity of iono-covalent CFx.