Electrochemical oxidation of graphite in aqueous hydrofluoric acid solution at high current densities

•Electrochemical oxidation of graphite was performed at high current densities in 47% HF aqueous solution.•Covalent CF bonding formed above 2.4 V vs Pb/PbF2.•Stage 1 type oxygenated fluorine–graphite intercalation compound with an interlayer spacing of 0.55 nm was obtained.•This material showed a high capacity of 550 mAh/g as a cathode of lithium primary battery.

Electrochemical oxidation of graphite was performed at high current densities in 47% HF aqueous solution. Cyclic voltammetry indicated that covalent CF bonding formed above 2.4 V vs Pb/PbF2. The sample obtained at higher current densities than 200 mA cm−2 was stage 1 type material with an interlayer spacing of 0.55 nm and it contained a considerable amount of oxygen, together with the covalently bonded fluorine. The discharge profile of this sample as a cathode of lithium primary battery was similar to that of C2.5F prepared under F2 gas atmosphere and the capacity reached 550 mAh g−1. This strongly indicated that not only fluorine but also oxygen in this sample was utilized.

Graphical abstractA new phase of oxygenated stage 1 covalent type CxF with an interlayer spacing of 0.55 nm was obtained at the potential plateau higher than 3.5 V vs Pb/PbF2 by the constant current oxidation of graphite in 47% HF aqueous solution.Figure optionsDownload full-size imageDownload as PowerPoint slide