Na-ion Storage Performances of FeSex and Fe2O3 Hollow Nanoparticles-Decorated Reduced Graphene Oxide Balls prepared by Nanoscale Kirkendall Diffusion Process

Uniquely structured FeSe(x)-reduced graphene oxide (rGO) composite powders, in which hollow FeSe(x) nanoparticles are uniformly distributed throughout the rGO matrix, were prepared by spray pyrolysis applying the nanoscale Kirkendall diffusion process. Iron oxide-rGO composite powders were transformed into FeSe(x)-rGO composite powders by a two-step post-treatment process. Metallic Fe nanocrystals formed during the first-step post-treatment process were transformed into hollow FeSe(x) nanoparticles during the selenization process. The FeSe(x)-rGO composite powders had mixed crystal structures of FeSe and FeSe2 phases. A rGO content of 33% was estimated from the TG analysis of the FeSe(x)-rGO composite powders. The FeSe(x)-rGO composite powders had superior sodium-ion storage properties compared to those of the Fe2O3-rGO composite powders with similar morphological characteristics. The discharge capacities of the FeSe(x)- and Fe2O3-rGO composite powders for the 200(th) cycle at a constant current density of 0.3 A g(-1) were 434 and 174 mA h g(-1), respectively. The FeSe(x)-rGO composite powders had a high discharge capacity of 311 mA h g(-1) for the 1000(th) cycle at a high current density of 1 A g(-1).