Fabrication of carbon microcapsules containing silicon nanoparticles for anode in lithium ion battery

Carbon microcapsules containing silicon (Si) nanoparticles (NPs) were prepared from silicon-embedded polymer microspheres. The precursors, polymeric microspheres containing silicon nanoparticles were fabricated by a facile emulsion polymerization with surfactants, sodium dodecyl sulfate and dodecyltrimethylammonium bromide. The effects of monomer, surfactant concentration, and ionic character of surfactant on the formation of microspheres were demonstrated. The successful fabrication of polystyrene/polydivinylbenzene microspheres with Si NPs was confirmed by scanning electron microscopy. Subsequent thermal treatment produced carbon microcapsules having Si NPs. Volume shrinkage of polymer spheres during carbonization step resulting in the formation of internal free spaces in carbon microcapsules is the critical process in this experiment, which can accommodate volume changes of Si NPs during Li ion charge/discharge processes. The successful encapsulation of Si NPs with exterior carbon shell was clearly shown by transmission electron microscopy and X-ray diffraction. The change in size distribution and structure of polymer and carbon microspheres was also revealed. The cyclic performances of these Si@C microcapsules were measured with lithium battery half cell tests.