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

摘要

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 Ag_3Sn alloy phases. The electrochemical experiments reveal that the Ag_(36.4)Sn_(48)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 An/kg ever: after 300 cycles. The structural changes of Ag_(36.4)Sn_(48)Si_(15.6) electrode during cycling were examined by X-ray diffraction analyses. The results reveal that the composite alloy consisting of Si, beta-Sn and Ag_3Sn phases transforms mostly into that of ternary lithiated phase during Li Insertion, and recovers to one involving Si, beta-Sn, Ag_3Sn and residual Ag_2LiSn phases after Li extraction. In this type of lithiation/delitniation 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.