Electrochemical study and material characterization of xSiO·(1-x) Sn₃₀Co₃₀C₄₀ composite anode material for lithium-ion batteries

A novel composite anode material, SiOSn_xCo_yC _z, has attracted much attention because of its good cycle life and high capacity. Seven compositions of xSiO(1-x)Sn₃₀Co ₃₀C₄₀, 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., Li_1.2Ni_0.15Co _0.10Mn_0.55O2 vs. 50 wt% SiO-50 wt% Sn₃₀Co ₃₀C₄₀ with solid lithium metallic powder coating) achieves 72% capacity retention in 200 cycles.