With the possible exhaust of fossil oil, effective utility of energy becomes an important issue, clean energy and rechargeable energy are thus highly developed. In which, rechargeable lithium-ion batteries attract much attention because of its extensive use such as portable electronic devices, powering hybrid electric vehicles (HEV) and zero-emission vehicles (ZEV). While, capacity and charging rate are needed to be highly improved for the utility in practice. Advancing battery with silicon anode thus becomes increasingly emphasized in the recent years because of the ultra-high theoretical capacity. But the dramatic volume expansion of silicon anode hinders its real utility. Lots of studies focus on this phenomenon and try to overcome this issue with specific design of nano-structure and so on. But one can’t get constant rule to stabilize silicon anode because the real mechanism of volume expansion has not been explored in detail. We thus intend to explore the structural evolution of silicon anode in detail by in-situ charging/discharging synchrotron x-ray techniques, to dig out the mechanism of volume expansion in silicon anode, in this study.

        Initially, hollow silicon spheres are synthesized by the reduction of SiO₂ surface and selective corrosion. After the measurements of CV, capacity and life time, in-situ charging/discharging synchrotron x-ray diffraction and absorption spectral analyses are used to probe structural variation in silicon anode. At the first cycle of lithiation, silicon structure gradually transforms from crystalline to amorphous and finally changes to Li₁₅Si₄ alloy phase. The created defects in silicon anode contribute to the structural disintegration and reconstruction as indicated by the x-ray line profile analysis. The change in local structure can also be evidenced by x-ray absorption near edge spectroscopy (XANES). Lithium ions cause Si-Si bond-breaking and result in the formation of identical short range ordering of Li₁₅Si₄.

        With the macro and micro analyses of structures, volume expansion of silicon anode with phase transformation has be expounded in detail. Results in this study could be the fundamental to design silicon anode with stable structure, facilitating the utility of Li-ion battery with ultra-high capacity in practice.