Anchoring Si nanoparticles to carbon nanofibers: an efficient procedure for improving Si performance in Li batteries

Abstract

Carbon fibers obtained by pyrolysis of tailored resorcinol/formaldehyde polymer particles were used to anchor Si nanoparticles at their surface. The carbonization process, carried out at 1000 °C under nitrogen, induced strong interactions between Si particles and the carbon matrix through a thick amorphous silicon oxide layer as revealed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Therefore, the actual composition of the composites was Si/SiO_x/C (fibers). Component contents were determined from thermogravimetric measurements (TG) made under oxygen. The composites delivered specific capacities as high as 2500 mA h g_Si⁻¹ at rather high current densities (500 mA g_si⁻¹) and exhibited good capacity retention on cycling. By contrast, a mixture of pristine Si nanoparticles and carbon nanofibers performed considerably worse, their capacity fading abruptly with cycling. The improved performance of composites is ascribed to a combination of the properties of the amorphous SiO_x layer, and the texture and morphological properties of carbon, increasing the electrode conductivity and buffering Si expansion and shrinkage during Li insertion and deinsertion.