Group 15 element-graphite composites synthesized by reduction of chlorides by KC8: Characterization and electrochemical lithiation

Group 15 element-graphite M/C composites were prepared by reduction of MClx chlorides (AsCl3, SbCl5, BiCl3) by KC8 in THF. Arsenic and antimony were both amorphous: antimony appeared as a film-like material, formed of aggregated nano-sized particles covering parts of the graphite surface; arsenic was present as large graphite supported particles. On the contrary, bismuth was present as crystalline metal nanoparticles distributed on the graphite surface. Amorphous As and Sb-graphite composites displayed stable reversible capacities of 310 and 420 mA h/g, respectively while that of crystalline Bi-graphite materials decreased regularly upon cycling. Although these practical capacities were lower than the expected theoretical ones corresponding to the formation of Li3M compounds, it appeared that, in the presence of graphite, amorphous solids exhibiting a (partly) covalent character like As and Sb gave better long life cycling properties than the crystalline and metallic bismuth. It was very likely that our one step synthesis could generate bonds between graphite and (partly) covalent solids reducing consequently the volume expansion effects occurring during cycling. On the contrary, metallic solids like bismuth that were not inclined to bond with graphite behave, upon cycling, as corresponding massive metals.