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.

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A core-shell nanostructured composite material consisting of nano-Si as the core and SnO 2 as the shell is synthesized by a sol-gel method. The reaction mechanism between Li and a nano-Si/SnO 2 core-shell nanostructured electrode is investigated, the partial reversible reaction between Li and SnO 2 during the first cycle is identified, and the reactivity of the Si core is investigated by ex situ analyses. The nano-Si/ SnO 2 core-shell nanostructured electrode shows a reversible capacity of ca. 1000 mA h g À1 and good cycle retention close to 80% of the first charge capacity over 50 cycles. Experimental Sample preparationThe nano-Si/SnO 2 core-shell nanostructured material was prepared as follows. Commercial nano-Si particles (0.075 g, Aldrich, <100 nm) were put into distilled water (50 mL) with sonication for dispersion. Potassium stannate trihydrate (0.5 g,