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 Fe 2 O 3 can transform to the cubic Fe 3 O 4 via a calcination treatment in a nitrogen atmosphere, and lithium-ion storage performances of Fe 3 O 4 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 Fe 3 O 4 provides lithium-ions with more transport channels for Li ions diffusion and storage without serious volume change, and thus the cubic Fe 3 O 4 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 Fe 2 O 3 . To further enhance the structural stability of electrodes, reduced graphene oxide is introduced. The Fe 3 O 4 /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 Fe 3 O 4 (417 and 300   mAh   g −1 ), Fe 2 O 3 (137.4 and 95   mAh   g −1 ) and Fe 2 O 3 /reduced graphene oxide (390.1 and 480   mAh   g −1 ). These results demonstrate that the structural phase transition and reduced graphene oxide of Fe 3 O 4 /reduced graphene oxide composites offer unique characteristics suitable for high-performance energy storage application.