Effect of dual local structures of amorphous Fe–Si films on the performance of anode of lithium-ion batteries

Abstract

Amorphous silicon is a very promising anode material for lithium-ion batteries, but the poor cycle performance owing to volume expansion must be improved before application. In the present study, a series of amorphous FexSi100−x films with different local structures were prepared by magnetron sputtering system. The local structures of the films can be described using the cluster-plus-glue-atom model. For x = 5.3–14.0 at.%, the principal cluster is [Si–Si4], for x = 24.2–46.8 at.%, the principal cluster is [Fe–Si8Fe2], especially for x = 19.1 at.%, the film has both clusters. The films on copper foil substrates were tested as the anode electrode material of lithium-ion batteries. The results show that the cycling stability of the thin film electrode increases with increasing Fe content, but the specific capacity decreases. The impedance of the films also shows two completely different trends with the composition, which further confirms that these Fe–Si amorphous films have different local structures. Especially for the Fe19.1Si80.9 film, the charge transfer between the two electrolyte/electrode interfaces has the two smallest impedances, indicating that the film has the highest charge transfer efficiency.