Facile formation of NiCo2O4 yolk-shell spheres for highly reversible sodium storage

Abstract Designing an anode material with high capacity and excellent cycling stability is a great challenge for sodium-ion batteries (SIBs) in energy storage systems. Traditional synthetic methods of transition metal oxides require intricate steps and lack of stable morphology. Herein, a novel synthetic method for the formation of yolk-shell structure is proposed and demonstrated by the NiCo 2 O 4 yolk-shell spheres (NCO-YS). When evaluated as an anode material for SIBs, the as-synthesized NCO-YS delivers the highly reversible specific capacities of 377 and 314 mA h/g after 50 and 100 cycles at the current density of 100 mA/g, while the NiCo 2 O 4 nanoparticle exhibits a moderate capacity of 157 mA h/g after 100 cycles The improved electrochemical performances of the NCO-YS can be originated from the complex hierarchical structure with high specific surface area, small primary building nanoparticles as well as its unique hollow structure between shell and core. The present approach provides an efficient strategy for building mixed metal oxide with yolk-shell structure to work as the alternative anode material for SIBs.