Electrochemical Study and Material Characterization of xSiO-(1-x)Sn_(30)Co_(30)C_(40) Composite Anode Material for Lithium-Ion Batteries

摘要

A novel composite anode material, SiO-Sn_xCo_yC_z, has attracted much attention because of its good cycle life and high capacity. Seven compositions of xSiO-(1-x)Sn_(30)Co_(30)C_(40), where 0 ≤ x ≤ 1, were prepared by mechanical ball milling (SPEX). The milled materials were studied by X-ray diffraction (XRD), pair distribution function (PDF), and electrochemical testing. The XRD and PDF data show that CoSn is the main phase and is detected in all seven samples. As the amount of SiO increases, CoSn_2 is formed. Also with increasing SiO, the reversible specific capacity of the composite anode materials increases, but the cycle performance declines. The composition of 50 wt% SiO-50 wt% Sn_(30)Co_(30)C_(40) gives the best electrochemical performance, a reversible capacity of 633 mAh/g after 50 cycles. X-ray and neutron PDF techniques were used to probe the local structure of as-milled 50 wt% SiO-50 wt% Sn_(30)Co_(30)C_(40)- Ex-situ XRD and PDF study for samples taken at different cutoff voltages reveals a phase transformation during charge/discharge via an intercalation/conversion reaction. The full cell (i.e., Li_(1.2)Ni_(0.15)Co_(0.10)Mn_(0.55)O_2 vs. 50 wt% SiO-50 wt% Sn_(30)Co_(30)C_(40) with solid lithium metallic powder coating) achieves 72% capacity retention in 200 cycles.