Preparation of a carbon nanofiber/natural graphite composite and an evaluation of its electrochemical properties as an anode material for a Li-ion battery

A carbon nanofiber (CNF)/natural graphite (NG) composite was prepared to improve the rate capability of as-received NG to be used as the anode material in a Li-ion battery. Optimum control over both the amount and shape of the CNFs to enable their growth on NG remarkably improved the cycle performance and rate capability of the as-received NG. The first-cycle discharge capacity of the CNF/NG composite was 95% of that of the as-received NG. The amount of grown CNFs was controlled to be less than 15% of the as-received NG. CNF growth on the surface edges of NG in an ivy leaf shape proved to be most effective in improving the rate capability by controlling the extent of volumetric expansion and shrinkage occurring in the charge and discharge processes. Schematic structural models of the as-received NG and CNF/NG composite were proposed to account for the volumetric stability of the electrode in repeated charge-discharge processes. The improved rate capability is ascribed to the thin solid electrolyte interphase and reduced volumetric change of the anode in the charge/discharge processes, both of which are achieved by growing ivy-like CNFs over the graphite surface.