Electrochemical Properties of Surface-Fluorinated Vapor Grown Carbon Fiber for Lithium Ion Battery

Surface fluorination of graphitized vapor grown carbon fiber (VGCF) has been performed with F 2 , F 2 -O 2 , NF 3 or ClF 3 under mild conditions. Charge/discharge characteristics were investigated in 1 mol/l LiClO 4 -ethylene carbonate (EC)/diethyl carbonate (DEC) and EC/DEC/ propylene carbonate (PC) solutions. The main effect of surface fluorination was increase in charge capacities. The increase in charge capacities was larger for VGCF fluorinated with ClF 3 or NF 3 than F 2 or F 2 -O 2 . The reason is that the fluorination reactions of graphite with ClF 3 and NF 3 are radical reactions having surface etching effect, effectively breaking cylindrically rolled graphene layers of VGCF.