New Ag-Sn alloy anode materials for lithium-ion batteries

The Ag-Sn alloys prepared by mechanical alloying technique have been studied as negative electrode materials for lithium-ion batteries. With optimized compositions and structure morphologies, both Ag52Sn48 and Ag46Sn54 composite electrodes exhibit an initial capacity of #~800 mAh/g and maintain a reversible capacity of above 350 mAh/g for more than 50 cycles. Even after 300 cycles, the former still keeps a reversible capacity of approximately 200 mAh/g. Typically, the structural changes of Ag52Sn48 electrode accompanied by Li insertion/extraction processes were examined by means of X-ray diffraction analyses. The results reveal that the composite alloy consisting of *b-Sn and Ag3Sn phases transforms mostly into that of ternary lithiated phase during Li insertion and recovers to one involving *b-Sn, Ag3Sn, and residual Ag2LiSn phases after Li extraction. It is considered that the composite structure containing the ternary lithiated phase, which is formed during the first cycle, is beneficial for the improvement of the cycle life of the Ag-Sn alloy electrode, although the residual lithiated product possibly leads to an increase of the irreversible loss.