Charge/discharge behavior of plasma-fluorinated natural graphites in propylene carbonate-containing solvent

Plasma-fluorination of natural graphite samples with average particle sizes of 5 μm, 10 μm and 15 μm (NG5μm, NG10μm and NG15μm) was performed using CF4 and charge/discharge characteristics of surface-fluorinated samples were investigated in 1 mol dm−3 LiClO4–ethylene carbonate (EC)/diethyl carbonate (DEC)/propylene carbonate (PC) (1:1:1, v/v/v). Fluorine contents obtained by elemental analysis were in the range of 0.3–0.6 at.% and surface fluorine concentrations determined by X-ray photoelectron microscopy (XPS) were 14.8–17.3 at.%. Plasma-fluorination increased surface disorder of natural graphite samples though reduced surface areas due to its surface etching effect. Electrochemical decomposition of PC was highly reduced on surface-fluorinated NG10μm and NG15μm with high disorder. First coulombic efficiencies of plasma-fluorinated NG10μm and NG15μm increased by 9.7 and 19.3% at 150 mA g−1, respectively.