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 (abbreviated to , , and ) was performed by at 200 and for and electrochemical properties of surface-fluorinated natural-graphite samples were investigated in –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 for natural-graphite samples fluorinated at 200 and 300°C, respectively, for three natural-graphite samples. The surface areas of and were only slightly increased by fluorination, while the increase in surface area was large in the case of . However, the increase in surface disorder by fluorination was larger for and than for . Electrochemical reduction of PC on and 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 and is attributed to the increase in their surface disorder and probably actual electrode area by fluorination.