Tuning fluorine and oxygen distribution in graphite oxifluorides for enhanced performances in primary lithium battery

Abstract

Fluorine Graphite Intercalation Compounds are one of the most common cathode used in primary lithium batteries, mainly for their high delivering potential. Nevertheless, to increase their capacities, fluorine can be partially substituted by oxygen. Oxifluorides offer then versatility to design cathode materials delivering the upmost performances. Combining the choice of the precursor (either graphite oxide or sub-fluorinated graphite fluoride) and two-step synthesis processes, which include Hummers' oxidation and direct fluorination, allow the tuning of the fluorine and oxygen atoms distribution. According to the sequence, i.e. fluorination/oxidation or oxidation/fluorination, several oxifluorides were then prepared. On one hand, direct fluorination using F2 gas resulted in homogeneous fluorine dispersion when precursor was graphite oxide. On the other hand, Hummers’ oxidation was modulated according to the temperature parameter. COH, COC, COOH, CF, CF2 and CF3 were identified through multinuclear solid-state MAS-NMR. Covalence and environment, especially in-plane organization of those chemical groups, were assessed. When oxifluorides are then used as cathode in primary lithium battery, the better performances are obtained for 3 phases compounds where fluorinated part insured high potential whereas oxygenated part allowed durability to be reached; carbonaceous region providing conductivity. A maximum of about 2400 Wh/kg of energy density is attempted.