Preparation of Si Composite Alloys as Anode Material for Lithium Batteries and their Lithiation/Delithiation Mechanism in the Charge/Discharge Processes

Abstract

We have prepared Si based composite alloy powders as anode material for lithium-ion batteries using mechanical alloying technique. Ag-Sn-Si powders with a size of several micrometers are composed of Si, Sn and Ag₃Sn alloy phases. The electrochemical experiments reveal that the Ag_36.4Sn₄₈ Si_15.6 electrode demonstrates better electrochemical performance than the others do in both reversible capacity and capacity retention. It can deliver an initial capacity of-800 Ah/kg and maintain a reversible capacity of approximately 180 Ah/kg even after 300 cycles. The structural changes of Ag_36.4Sn₄₈ Si_15.6 electrode during cycling were examined by X-ray diffraction analyses. The results reveal that the composite alloy consisting of Si, β-Sn and Ag₃Sn phases transforms mostly into that of ternary lithiated phase during Li insertion, and recovers to one involving Si, β-Sn, Ag₃Sn and residual Ag₂LiSn phases after Li extraction. In this type of lithiation/delithiation process, the alloy electrode suffers from a moderate volumetric variation, which is beneficial for the improvement of the cycle life. It has been found that this new Ag-Sn-Si composite material may be a promising candidate as anode material for Lithium Ion Batteries.