Unique structured microspheres with multishells comprising graphitic carbon-coated Fe3O4 hollow nanopowders as anode materials for high-performance Li-ion batteries

Abstract

Multishell structured metal oxide microspheres with considerable structural stabilities during repeated cycling and higher volumetric capacities than those of hollow structured microspheres are popular as anode materials for lithium-ion batteries. However, the long-term cycling and rate performances of multishell metal oxide microspheres for lithium-ion storage require further improvement. Herein, novel and unique structured microspheres (Fe3O4-GC) with multishells comprising graphitic carbon (GC)-coated Fe3O4 hollow nanopowders are successfully synthesized. The reduction of pitch-infiltrated Fe2O3 yolk-shell microspheres yields metallic Fe yolk-shell microspheres filled with pitch-derived carbon. Oxidation yields yolk-shell Fe3O4-GC microspheres with multishells comprising hollow nanopowders coated with GC via the selective decomposition of amorphous carbon and oxidation of metallic Fe. Metallic Fe nanocrystals transform into hollow Fe3O4 nanopowders due to nanoscale Kirkendall diffusion. The primary hollow Fe3O4 nanopowders comprising yolk-shell microspheres and GC layer formed by pitch-derived carbon decrease the distance for lithium-ion diffusion and improve the electrical conductivity resulting in outstanding cycling and rate performances of Fe3O4-GC, respectively. The discharge capacity of Fe3O4-GC microspheres for the 1000(th) cycle at a current density of 2.0 A g(-1) is 1018 mA h g(-1), and the microspheres exhibit a high reversible capacity of 649 mA h g(-1) even at 20 A g(-1).