Subunits controlled synthesis of alpha-Fe2O3 multi-shelled core-shell microspheres and their effects on lithium/sodium ion battery performances

Two kinds of Fe2O3 core-shell microspheres were synthesized. The Fe2O3 sample obtained using ethanol (E-Fe2O3) contains a shell and a core assembled by nanoparticles with a diameter of similar to 150 nm and the surface is fairly smooth. Fe2O3 with optimized subunits was produced using water (W-Fe2O3). The core is assembled by smaller nanoparticles of similar to 50 nm. The thicker shell and exterior surface possess porous nanorods. These peculiar subunits endow W-Fe2O3 with a higher specific surface area, more pore volume and larger nanopores. W-Fe2O3 displayed 733.1 mA h g(-1) at 6000 mA g(-1), which is more than two times that of E-Fe2O3 (306.5 mA h g(-1)). Encouragingly, W-Fe2O3 also expressed relatively promising sodium ion battery performances. The significantly different performances between E-Fe2O3 and W-Fe2O3 can be almost entirely attributed to their distinctive subunits. The study demonstrated that enhanced lithium/sodium ion storage properties can be achieved by adjusting the subunits.