Hydrothermal synthesis and electrochemical properties of nano-sized Co–Sn alloy anodes for lithium ion batteries

Nano-sized Co–Sn alloys with a certain amount of Sn oxides used as potential anode materials for lithium ion batteries were synthesized by hydrothermal route. The effects of hydrothermal conditions and post annealing on the phase compositions and the electrochemical properties of synthesized powders were characterized by means of X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) with energy dispersive spectra (EDS) analysis and galvanostatic cycling tests. Prolonging the dwelling time at the same hydrothermal temperature can increase the content of Sn oxides, which will lead to a high initial irreversible capacity loss but a better cycling stability owing to the buffer effect of irreversible product Li2O. Heat-treatment can increase the crystallinity and cause the presence of a certain amount of inert CoSn component, which both have positive impact on the cycling stability of Co–Sn electrode. By comparison with the lithiation/delithiation processes of metal Sn, a two-step mechanism of CoSn2 alloy during cycling was confirmed.

Research highlights▶ Nano-sized Co–Sn alloys were synthesized by hydrothermal route. ▶ Li2O and CoSn can buffer the large volume change associated with lithiation of Sn. ▶ A two-step reaction mechanism of CoSn2 alloy during cycling was confirmed.