Nanocrystalline Fe1−xCoxSn2 solid solutions prepared by reduction of salts in tetraethylene glycol

In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe1−xCoxSn2 solid solutions with x = 0.0, 0.25, 0.3, 0.5, 0.6 and 0.8 were prepared by chemical reduction in tetraethylene glycol. Precise control of the synthesis conditions allowed single-phase nanocrystalline materials to be prepared, with particle diameters of about 20 nm and cubic, nanorods, and U-shaped morphologies. The substitution of iron by cobalt induced a contraction of the unit cell volume. The hyperfine parameters of the 57Fe Mössbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe1−xCoxSn2 active materials delivered reversible capacities above 500 mAh g−1 that depended on the composition and cycling conditions. The intermediate compositions exhibit better electrochemical performance than the end compositions CoSn2 and FeSn2.

Research highlights▶ New nanoparticulate materials in the ternary system Fe1−xCoxSn2 are reported. ▶ The electrochemical behaviour of the intermediate nano-Fe1−xCoxSn2 compositions is better than the corresponding micro-CoSn2 and FeSn2. ▶ The samples that contain iron form LixSn phases during the discharge of the cell and exhibit capacities over 500 mAh g−1 during the first 30 cycles. ▶ The partial replacement of cobalt by iron could moderate the potential cost and toxicity of the materials in Li-ion batteries.