Commercially available solid SiO is composed of amorphous Si with silicon suboxides of various valence states. Solid SiO is thermodynamically unstable at all temperatures, which would disproportionate to Si and SiO₂. Disproportionation of SiO at several temperatures was characterized with various analytical techniques, such as XRD, XPS, NMR and HRTEM methods, and it was found that the sample heat treated at 1000 °C contained well-developed Si nanocrystals uniformly dispersed within an amorphous SiO_x matrix. Using this sample, a nano-Si/SiO_x /graphite composite was obtained by a straightforward high-energy mechanical milling technique. The nano-Si/SiO_x /graphite composite was tested as an anode material for Li secondary batteries, and showed better electrochemical behaviors than those of pure SiO.

The silicon nanostructure is a promising candidate for an anode of Li-ion batteries due to its high theoretical capacity. In this work, we have demonstrated the scalable synthesis of Si nanosheets from natural sand by magnesiothermic reduction, and suggested a new formation mechanism for Si nanosheets. In the suggested mechanism, an Mg₂Si intermediate phase was formed at an early stage of the reduction process, which leads to the two-dimensional Si nanostructure. The synthesized Si nanosheets have a leaf-like sheet morphology ranging from several ten to several hundred nanometers, and show comparable electrochemical properties to the commercial Si nanopowder as an anode for lithium ion batteries. For the improved electrochemical performance, Si nanosheets are encapsulated with reduced graphene oxide (RGO), and the RGO-encapsulated Si nanosheet electrode exhibits high-reversible capacity and excellent rate capability.

SiO has been considered as one of the most promising anodes, the reaction mechanism of SiO with Li is still not well understood. High energy mechanical milling (HEMM) followed by etching of the SiO surface with NaOH solution was carried out in this study to enhance cycle performance. X-ray photoelectron spectroscopy (XPS) analyses showed the different compositions of the Si valence state before and after sputtering, and the atomic ratio of O/Si at the surface differed from that of the inside bulk SiO. Using high resolution transmission electron microscopy (HRTEM), the reaction mechanism of a SiO electrode was investigated. During the first discharge, Li₂Si₂O₅ and Li₆Si₂O₇ phases were identified as well as Li₄SiO₄ and Li rich amorphous binary Li_xSi phases. The surface etched SiO showed significantly better cyclability with the reversible capacity of 1260 mA h g⁻¹ over 50 cycles.