Dopant-induced shape evolution of polyhedral magnetite nanocrystals and their morphology/component-dependent high-rate electrochemical performance for lithium-ion batteries

Monodisperse MnxFe3−xO4 (x = 0, 0.3, 0.6) polyhedrons enclosed by {100}/{111} facets with different area ratios were synthesized through the thermolysis of Fe(acac)3 and Mn(acac)2 by effectively tuning the Mn/Fe ratio to mediate the adsorption properties of oleic acid (OA) on crystal surfaces after annealing treatment in N2, and studied as high rate (≥1 A g−1) anode materials for lithium ion batteries (LIBs). The electrochemical results show that Mn0.6Fe2.4O4 octahedra possess the best rate cycling performance compared to that of Mn0.3Fe2.7O4 cuboctahedra and Fe3O4 cubes, characterised by a 500th discharge capacity of 803.5 mA h g−1 at 1 A g−1 and a rate capability of 661.5 mA h g−1 when cycled at 4 A g−1, as a result of high electrochemical activity of {111} facets with the highest Fe atom surface density. The present results prove that the substitution of Fe by Mn in the spinel-type anode materials can result in better cycle stability and it would be helpful for the further understanding of Fe3O4 based anode materials and provide a simple and practical route to design high rate anode materials for lithium-ion batteries.