Improving the cyclability and rate capability of carbon nanofiber anodes through in-site generation of SiOx-rich overlayers

SiOx-rich overlayed carbon nanofibers (SiOx-CNFs) are facilely fabricated through the electrospinning of tetraethyl orthosilicate (TEOS) and polyacrylonitrile (PAN) solution and subsequent hydrolyzation and heat treatments. The SiOx-rich overlayer is apparently observed by high-resolution transmission electron microscopy (HR-TEM), which is also identified using X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). The SiOx-CNF electrode shows greatly improved cycle stability and rate capability, remaining 84.2% of its initial discharge capacity in contrast to only 61.4% for pure CNFs and exhibiting a reversible capacity of 288 mAh g−1 at 2 A g−1 compared with that (218 mAh g−1) of pure CNFs. This result is ascribed to the formation of a dense and stable SEI film and the highly improved ionic conductivity of SiOx-CNFs during the Li+ insertion/extraction processes. These results suggest that the introduction of SiOx-rich overlayer onto electrodes is an effective strategy to enhance the stability of SEI film and facilitate the surface Li-ion transfer of electrodes, and thus to improve their cycle stability and rate capability.