Li Storage Behavior of C-Coated Si/SiOx Nanospheres As a High Capacity Anode Material for Lithium-Ion Battery

Si has gained much attention as anode materials for lithium-ion battery due to its high theoretical capacity (3,580 mAhg^-1) and low standard oxidation potential (0.4 V vs. Li/Li⁺). Despite these features, Si anode materials still have limits to commercial uses by poor cycle performance associated with their mechanical pulverization of Si due to severe volume change during alloying/dealloying with Li. To overcome this problem, various approaches have been suggested. In particular, the composites, which are composed of active Si and inactive buffer material, showed promising approaches for reducing the mechanical strain during cycles. On the other hand, nanostructuring of active materials would be helpful for further improvement of cycle performance. After heat treatment of Si/SiO_x precursor at 1200 °C under inert atmosphere, we obtained Si nanocrystals embedded SiO_x nanospheres with a size of 200 nm, in which about 10 nm sized Si nanocrystals are embedded in amorphous SiO_x matrix. In order to improve electrical conductivity of Si/SiO_x nanocomposites, carbon layer was coated on the surface of Si/SiO_x nanocomposites.

 The Si/SiO_x nanospheres and C-coated Si/SiO_x nanospheres were characterized by a field emission scanning electron microscope (FESEM), a high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) patterns, solid state ²⁹Si magnetic angle spinning nuclear magnetic resonance (MAS NMR) and X-ray photoelectron spectroscopy (XPS) analyses.

 The C-coated Si/SiO_x composites showed a reversible capacity of 950 mAh/g^-1 at current density of 200 mAg^-1 with stable cycle performance over 100 cycles and high rate capabilities. In this presentation, the electrochemical properties of the C-coated Si/SiO_x nanocomposites will be discussed in more detail.