Synthesis And Electrochemical Properties Of Highly Graphitic Hollow Carbon Nano-spheres And Carbon-encapsulated Fe₃O₄Dendrites

The research contents in this paper can be divided into two parts:(1) Hollow carbon nanospheres (HCNSs) were prepared by a simple reaction between NiCl2·6H2O and CaC2at a low temperature of250℃in autoclaves. Characterizations by X-ray diffraction, Raman spectroscopy and electron microscopies demonstrate the formation of bulk quantities of HCNSs with a uniform size of about20nm and a high degree of graphitization in short distance. It is interesting to find out that the carbon nanospheres actually display polyhedral shapes, and the apexes are clearly visible on both outside and inner surfaces. Electrochemical measurement demonstrates that the HCNSs using as anode materials for lithium-ion battery exhibit a reversible capacity of302mAh g-1with high coulombic efficiency of97%after40cycles at a rate of C/10.(2) Six-armed Fe3O4dendrites with carbon coating were synthesized by a one-step reaction between (C5H5)2Fe and CO(NH2)2at550℃. Electron microscopy examinations indicate the formation of large numbers of Fe3O4dendrites with mutually vertical arms and uniform carbon shells. Electrochemical measurement demonstrates that the dendrites using as anode materials for lithium-ion battery exhibit an initial capacity of658mAh g-1and a reversible capacity of473mAh g-1after100cycles at a rate of C/10, as well as a high coulombic efficiency of97%after the forth cycle.