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

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. (C) 2016 Elsevier Ltd. All rights reserved.