Abstract
A sputtering technique was adopted to synthesize Sn-Cu thin film electrodes. Island Sn particles were obtained on the copper foil. Cu 6 Sn 5 was spontaneously generated at the interface between Sn and Cu foil. To further improve the cycling stability, Cu source was introduced to increase the formation of Cu 6 Sn 5 and to serve as a buffer during cycling. Moreover, the phase and elemental ratio of Sn and Cu varied in the synthesized electrode by alternately adjusting sputtering time for Sn and Cu. The cell synthesized by sputtering Sn for 5 min and Cu for 9 s alternately exhibited the best cycling stability. The 1st charge capacity of cell was 635 mA hg -1 , and the 1st efficiency was even higher than 97%. The capacity remained higher than 500 mA hg -1 after 15 cycles. The phase transformation of cell was investigated through voltage profile, CV curve and in situ XRD analysis. The in situ XRD analysis confirmed that Cu 6 Sn 5 could react with lithium directly without the presence of Li 2 CuSn during cycling. The reaction mechanism of Cu 6 Sn 5 with lithium during cycling was demonstrated to be an alloying process, and the structure of Cu 6 Sn 5 was thus a low-temperature monoclinic phase. © 2010 Elsevier B.V. All rights reserved.