Superior Electrochemical Properties of Composite Microspheres Consisting of Hollow Fe₂O₃ Nanospheres and Graphitic Carbon

Several micron-sized composite microspheres comprising hollow metal oxide nanospheres and in situ-formed graphitic carbon (GC) can be efficiently applied as anode materials for lithium-ion batteries. Herein, unique porous structured microspheres consisting of hollow Fe₂O₃ nanospheres and GC layers are prepared by spray drying. Fe nanocrystals are formed by carbothermal reduction. They are responsible for the transformation of the dextrin-derived amorphous carbon (AC) into well-developed GC layers, while the excess amount of dextrin remains as AC. The key point is the selective elimination of the AC without burning, which is achieved by a low-rate airflow during the oxidation process. Finally, porous- and hierarchical-structured Fe₂O₃-GC composite microspheres are obtained via Kirkendall diffusion. Because of their superior structural stability and excellent electrical conductivity, the porous-structured Fe₂O₃-GC microspheres show excellent lithium-ion storage performances. The discharge capacity of Fe₂O₃-GC-350 for the 1000th cycle at 3 A g^-1 is 760 mA h g^-1, and their capacity retention calculated from the second cycle is 92%.