Electrochemical Study and Material Characterization of xSiO·(1-x)Sn30Co30C40 Composite Anode Material for Lithium-Ion Batteries

Abstract

A novel composite anode material, SiO·SnxCoyCz, has attracted much attention because of its good cycle life and high capacity. Seven compositions of xSiO·(1-x)Sn30Co30C40, 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, CoSn2 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% Sn30Co30C40 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% Sn30Co30C40. 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., Li1.2Ni0.15Co0.10Mn0.55O2 vs. 50 wt% SiO-50 wt% Sn30Co30C40 with solid lithium metallic powder coating) achieves 72% capacity retention in 200 cycles.