Multiroom-structured multicomponent metal selenide-graphitic carbon-carbon nanotube hybrid microspheres as efficient anode materials for sodium-ion batteries

Novel three-dimensional (3D) multiroom-structured multicomponent metal (NiFe) selenide-graphitic carbon (GC)-carbon nanotube (CNT) hybrid microspheres were prepared by spray pyrolysis and a subsequent selenization process. Phase segregation and the decomposition of dextrin resulted in multiroom-structured microspheres with uniformly distributed empty nanovoids in the spray pyrolysis process. Metal nanocrystals of iron and nickel components that formed as intermediate products during the selenization process transformed amorphous carbon into GC by acting as nanocatalysts. GC layers surrounding (NiFe)Se_x nanocrystals and CNTs uniformly skeletonized in multiroom-structured microspheres improved the electrical conductivity and structural stability. Due to the synergistic effect of the unique structure and conductivity of the carbon components, the multiroom-structured (NiFe)Se_x-GC-CNT hybrid microsphere showed excellent cycling and rate performance for sodium-ion storage. The discharge capacities of (NiFe)Se_x-GC, (NiFe)Se_x-CNT, and (NiFe)Se_x-GC-CNT for the 100^th cycle at a current density of 0.3 A g^-1 were 369, 284, and 455 mA h g^-1, respectively, and the respective capacity retentions measured from the second cycle were 74.1, 56.1, and 92.2%.