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

Abstract

Monodisperse Mn_xFe_3−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 Mn_0.6Fe_2.4O₄ octahedra possess the best rate cycling performance compared to that of Mn_0.3Fe_2.7O₄ 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.