Design of double-shelled NiS-FeS@NC hollow nanocubes for high-performance sodium-ion batteries

Mixed metal sulfides (MMSs) are highly noticeable as prospective materials for sodium storage due to their prominent electrochemical reversibility and excellent redox activity. Nevertheless, the fast capacity decay and poor rate capability hinder their application in sodium-ion batteries (SIBs). In this work, a facile template method, using Prussian blue analogue as the precursor, was employed to fabricate the double-shelled hollow structure with nitrogen (N)-doped carbon layer coated on the outer shell of NiS-FeS hollow nanocubes (NiS-FeS@NC). Specifically, the NiS-FeS@NC composite provides a glorious reversible capacity (395.8 mAh g−1 after 200 cycles at 1.0 A g−1) and superior rate capability (322.2 mAh g−1 at 5.0 A g−1) when employed as electrode material for SIBs. In addition, the designed NiS-FeS@NC= |Na3V2(PO4)2 @C full battery can maintain an excellent reversible capacity (68.7 mAh g−1 after 200 cycles at 1.0 A g−1) as well as robust cycling stability. The improvement of the sodium storage performance can be mainly attributed to the synergistic coupling of the N-doped carbon coating layer and the hollow nanostructure, which can effectively maintain the integrity of the nanocube structure and accelerate the transportation of electrons/ions, thus contributing to improving the electrochemical sodium storage performance. Importantly, the unique modification strategy reported in this paper, combining with the mechanism and kinetics revealing, is expected to provide insights for facilitating high-performance electrodes for SIBs.