Spherical silicon/graphite/carbon composites as anode material for lithium-ion batteries

A spherical nanostructured Si/graphite/carbon composite is synthesized by pelletizing a mixture of nano-Si/graphite/petroleum pitch powders, followed by heat treatment at 1000 °C under an argon atmosphere. The structure of the composite sphere is examined by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDAX). The resultant composite sphere consists of nanosized silicon and flaked graphite embedded in a carbon matrix pyrolyzed from petroleum pitch, in which the flaked graphite sheets are concentrically distributed in a parallel orientation. The composite material exhibits good electrochemical properties, a high reversible specific capacity of ~700 mAh g−1, a high coulombic efficiency of 86% on the first cycle, and a stable capacity retention. The enhanced electrochemical performance is attributed to the structural stability of the composite sphere during the charging–discharging process.