Electrochemical Behavior of surface-fluorinated natural graphite in propylene carbonate-containing solvent

Surface fluorination of natural-graphite samples with average particle sizes of 5, 10, and 15 mu m (abbreviated to NG5 mu m, NG10 mu m, and NG15 mu m) was performed by F-2 (3 x 10(4) Pa) at 200 and 300 degrees C for 2 min and electrochemical properties of surface-fluorinated natural-graphite samples were investigated in 1 mol/dm(3) 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 atom % for natural-graphite samples fluorinated at 200 and 300 S C, respectively, for three natural-graphite samples. The surface areas of NG10 mu m and NG15 mu m were only slightly increased by fluorination, while the increase in surface area was large in the case of NG5 mu m. However, the increase in surface disorder by fluorination was larger for NG10 mu m and NG15 mu m than for NG5 mu m. Electrochemical reduction of PC on NG10 mu m and NG15 mu m was highly reduced by surface fluorination, which led to a large increase in first coulombic efficiencies. The increase in first coulombic efficiencies for surface-fluorinated NG10 mu m and NG15 mu m is attributed to the increase in their surface disorder and probably actual electrode area by fluorination. (C) 2007 The Electrochemical Society.