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) ×10⁵Pa) in anhydrous liquid HF (aHF). The composition of the fluorinated graphite samples ranged from C_1.1F to C_1.9F containing small amounts of HF. IR absorption spectra revealed that stage 1 phase of C_xF contained several different phases with planar (sp²) and puckered (sp ³) 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 C_xF samples with less amounts of HF and HF₂^δ- had relatively flat discharge potentials and large discharge capacities. The discharge capacity reached 500-600mAh/g in 1mol/dm³ LiClO₄-propylene carbonate solution at 25°C. Chemical diffusion coefficients of Li ⁺ ion in the intermediate discharge products were (4.4-13) ×10^-12cm²/s from impedance measurement.