Enhanced lithium-ion storage performance by structural phase transition from two-dimensional rhombohedral Fe₂O₃ to cubic Fe₃O₄

Highlights: • The rhombohedral Fe₂O₃ transforms to the cubic Fe₃O₄ via a calcination treatment. • Phase structure of anodes has great influences on their electrochemical performances. • Fe₃O₄/reduced graphene oxide shows a high capacity of 825.3 mAh g⁻¹ at 50 mA g⁻¹. - Abstract: The electrochemical performance of a material varies with its structural phase transition. It is found that the rhombohedral Fe₂O₃ can transform to the cubic Fe₃O₄ via a calcination treatment in a nitrogen atmosphere, and lithium-ion storage performances of Fe₃O₄ get an obvious improvement due to its structural advantages. On the basis of data calculated by X-ray diffraction, the larger unit cell volume as well as the higher void fraction of cubic Fe₃O₄ provides lithium-ions with more transport channels for Li ions diffusion and storage without serious volume change, and thus the cubic Fe₃O₄ delivers an excellent reversible capacity of 921.1 mAh g⁻¹ after 15 cycles at the current density of 50 mA g⁻¹, which is much higher than 328.3 mAh g⁻¹ for the rhombohedral Fe₂O₃. To further enhance the structural stability of electrodes, reduced graphene oxide is introduced. The Fe₃O₄/reduced graphene oxide show an excellent specific capacity of 825.3 mAh g⁻¹ after 40 cycles and impressive rate performance of 600 mAh g⁻¹ at the current density of 400 mA g⁻¹, which are much higher than that of Fe₃O₄ (417 and 300 mAh g⁻¹), Fe₂O₃ (137.4 and 95 mAh g⁻¹) and Fe₂O₃/reduced graphene oxide (390.1 and 480 mAh g⁻¹). These results demonstrate that the structural phase transition and reduced graphene oxide of Fe₃O₄/reduced graphene oxide composites offer unique characteristics suitable for high-performance energy storage application.