Microstructural Evolution of Electrochemically Cycled Si-Doped SnO2–Lithium Thin-Film Battery

SnO2 and Si-doped SnO2 thin-film electrodes were deposited on a Mo/Si substrate with an e-beam evaporator at room temperature. In the voltage range of 0.1–0.8 V, a reversible capacity of 400 mAh/g was attained after 200 cycles with the Si doping whereas the pure SnO2 exhibited a much faster capacity fade. Transmission electron microscopy (TEM) revealed that Si has segregated to form a Sn–Si solid solution after the first discharge. After subsequent cycling, the tin particles in the Si-doped film were observed to break up in contrast to the particle growth observed in the pure film. TEM study indicated that Si in the tin particles forms a stable amorphous layer whereas in the pure SnO2, recrystallization of the amorphous material is believed to occur. TEM study showed that there were important differences in the microstructure, which could be responsible for the improvement of the Si addition on the cycling performance.