Single-crystalline α-Fe2O3 nanohexahedron as outstanding anode material for lithium-ion batteries

In this paper, single-crystalline hexahedron hematite is successfully obtained by a simple hydrothermal approach with assistance of PVP as surfactant. SEM and XRD results show that the as-obtained alpha-Fe2O3 has a nanohexahedron shape with high uniformity and high crystallinity. The effects of a few factors influencing the morphology of alpha-Fe2O3, such as PVP amount, reaction temperature, etc., are investigated carefully. More importantly, time-dependent experiments are carried out to have in-depth insight into the formation of the single-crystalline alpha-Fe2O3 nanohexahedron. Based on the full characterization of as-obtained alpha-Fe2O3, it is concluded that PVP as surfactant plays an important role in the formation of the hexahedron shape of alpha-Fe2O3. Besides, the proposed formation mechanism of alpha-Fe2O3 nanohexahedron is that the shape of alpha-Fe2O3 evolves from the nuclei, needle-like shapes, and urchin-like aggregates to the hexahedron shape, driven by minimization of surface energy and Ostwald ripening. When used as an anode material for lithium-ion batteries, nanohexahedron alpha-Fe2O3 shows a high rate capability. Moreover, after 150 cycles, the storage capacity of alpha-Fe2O3 is still up to 680 mAh g(-1) and almost remains unchanged, suggesting high cyclability.