Improving the electrochemical properties of natural graphite spheres by coating with a pyrolytic carbon shell

Two kinds of modified natural graphite (MNG) spheres with a pyrolytic carbon shell on smooth or granular surface were obtained using fluidized bed chemical vapor deposition of acetylene by adjusting the reaction parameters. The core of the MNG has a highly ordered graphite structure and the shell has a disordered structure. Compared with natural graphite (NG) spheres, MNG with a core-shell structure shows improved first cycling efficiency and cyclability. Especially, the MNG spheres with a granular surface possess 84% retention of the first discharge capacity after 41cycles, owing to effective decrease of the contact resistance and increase of contact area between the MNG spheres.