Fluorination of fullerene C60 and electrochemical properties of C60Fx

Fluorinated fullerene polycrystalline powders C60Fx have been obtained by direct fluorination of C60 at 100°C. Electrochemical behaviors of C60 and C60Fx were investigated by the cyclic voltammetry and galvanostatic discharges on Li/1M LiClO4PC/C60 and C60F4 cells. The electronic structure changes of C60 upon fluorination were also investigated by XANES and UPS. Three stepwise reversible reduction peaks (2.50, 2.15 and 1.85 V), and an irreversible reduction peak (2.8–3.2 V) corresponding to CF reduction were observed on the cyclic voltammograms. The fluorination of C60 renders the open circuit voltage (OCV) higher by 1 V (OCV = 4 V vs. Li reference electrode), and the reversible reduction potentials nobler by 0.15 V. These electrode behaviors reflect the changes in the C60 electronic structure through fluorination.