Electrochemical behavior of surface-fluorinated graphite in propylene carbonate-containing solvent

Surface fluorination of natural graphite samples with average particle sizes of 5, 10 and 15 μm (NG5, NG10 and NG15 μm) was performed by F2 (3×104 Pa) at 200 and 300 °C for 2 min and charge/discharge behavior of surface-fluorinated samples was investigated in 1 mol/dm3 LiClO4-ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1 in volume). Surface fluorine concentrations were in the range of 11.1-15.3 and 17.7-20.5 at% for the samples fluorinated at 200 and 300 °C, respectively. Surface disorder and lattice defects were increased by fluorination. Electrochemical reduction of PC on NG10 and NG15 μm was highly reduced by surface fluorination, which led to large increase in first Coulombic efficiencies.