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.