Influence of cointercalated HF on the electrochemical behavior of highly fluorinated graphite

Highly fluorinated graphite was prepared at room temperature using high oxidation state transition metal complex fluoride (K2PdF6, K2MnF6, K2NiF6 or KAgF4) and elemental fluorine under pressure ((5.9–11.8) ×105 Pa) in anhydrous liquid HF (aHF). The composition of the fluorinated graphite samples ranged from C1.1F to C1.9F containing small amounts of HF. IR absorption spectra revealed that stage 1 phase of CxF contained several different phases with planar (sp2) and puckered (sp3) graphene layers. Electrochemical discharge of the fluorinated graphite showed that profile of discharge potential and discharge capacity varied depending on the amount of cointercalated HF. The CxF samples with less amounts of HF and HF2δ− had relatively flat discharge potentials and large discharge capacities. The discharge capacity reached 500–600 mAh/g in 1 mol/dm3 LiClO4–propylene carbonate solution at 25 °C. Chemical diffusion coefficients of Li+ ion in the intermediate discharge products were (4.4–13) ×10−12 cm2/s from impedance measurement.