A tin based anode material for a rechargeable battery comprises nanoparticles of composition SnMxOy wherein M is a further element selected from the group 5 consisting of Ni, Cu, In, Al, Ge, Pb, Bi, Sb, Fe, Co, Ga, with 0 <= x <= 0.5 and 0 <= y <= 2+2x. The nanoparticles form a substantially mono- disperse ensemble with an average size not exceeding 30 nm and a size deviation not exceeding 15%, the nanoparticles optionally being coated with a capping species. A method for preparing the tin based anode material is carried out in situ in a non-aqueous solvent and starts by reacting a tin salt and an organometallic amide reactant and oleylamine.