The reversible cyclability of Si based anodes is greatly improved by tuning the atomic ratio of Cu/Si and the thickness of films fabricated via magnetron sputtering. High electrochemical performance is achieved when the thin film made of 10% at.Cu-90% at.Si is used. 1100 mAhg(-1) specific capacity is delivered after the 100th cycles with 99.7% Coulombic efficiency. This remarkable performance is the result of the amorphous structure and enhanced physical and mechanical properties of the thin film. (C) 2014 The Electrochemical Society. All rights reserved.