Electrochemical properties of SnO2 thin-film anodes improved by introduction of Cu intermediate and LiF coating layers

As anode materials for lithium microbatteries, SnO2 thin films were grown on Cu substrates with Cu intermediate and LiF coating layers by radio-frequency sputtering. While the room-temperature (RT)-grown Cu intermediate layers change from the amorphous to the polycrystalline after annealing at temperatures above 200 °C, the subsequent RT-grown SnO2 films are always polycrystalline. Investigations of surface morphologies indicated that the Cu intermediate layers annealed at 400 °C exhibit larger surface areas than others annealed at 200 °C and 600 °C, resulting in the better conduction property, larger capacity and better rate performance of the SnO2 thin-film anode. The reason for that is attributed to the increased electrical connections between the anodes and the current collectors as well as the enlarged spaces for volume changes. Further improvement of cycling stability was achieved by the 5-nm-thick LiF coating layers on the anode surfaces, which can benefit formation of more homogeneous and stable solid electrolyte interphase (SEI) films caused by the decomposition of electrolyte at the surface of Sn/Li2O composites.