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

Abstract In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe 1− x Co x Sn 2 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 57 Fe Mossbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe 1− x Co x Sn 2 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 CoSn 2 and FeSn 2 .