Controlling Surface Oxides in Si/C Nanocomposite Anodes for High-Performance Li-Ion Batteries

Si/C composites represent one promising class of anode materials for next-generation lithium-ion batteries. To achieve high performances of Si-based anodes, it is critical to control the surface oxide of Si particles, so as to harness the chemomechanical confinement effect of surface oxide on the large volume changes of Si particles during lithiation/delithiation. Here a systematic study of Si@SiOx/C nanocomposite electrodes consisting of Si nanoparticles covered by a thin layer of surface oxide with a tunable thickness in the range of 1-10 nm is reported. It is shown that the oxidation temperature and time not only control the thickness of the surface oxide, but also change the structure and valence state of Si in the surface oxide. These factors can have a strong influence on the lithiation/delithiation behavior of Si nanoparticles, leading to different electrochemical performances. By combining experimental and modeling studies, an optimal thickness of about 5 nm for the surface oxide layer of Si nanoparticles is identified, which enables a combination of high capacity and long cycle stability of the Si@SiOx/C nanocomposite anodes. This work provides an in-depth understanding of the effects of surface oxide on the Si/C nanocomposite electrodes. Insights gained are important for the design of high-performance Si/C composite electrodes.