C₄F₈ plasma treatment as an effective route for improving rate performance of natural/synthetic graphite anodes in lithium ion batteries

Carbon-fluorine (C_mF_n) groups were selectively introduced on the surface of natural and synthetic graphites through plasma-fluorination using C₄F₈ vacuum plasma treatment. The type of carbon-fluorine bondings on the plasma-fluorinated graphite surface were selectively controlled by adjusting plasma processing time from 10 to 20 min. Systematic surface analyses revealed that the fluorine amount on the surface of plasma-fluorinated graphite was determined by the type of intrinsic structure and degree of graphitization of graphite. The electronegative semi-ionic carbon-fluorine groups on the graphite surface reduced the resistance related to lithium ion migration and charge transfer, leading to highest discharge capacity of 387 mA h/g at 1st cycle and discharge capacity of 293 mA h/g at high 10 C rate without deteriorating the 1st cycle Coulombic efficiency. This novel vacuum plasma treatment of introducing highly electronegative C_mF_n species on graphite can illuminate a new route of preparing superior lithium ion battery anode.