Rationally designed nitrogen-doped yolk-shell Fe7Se8/Carbon nanoboxes with enhanced sodium storage in half/full cells

Development of efficient and robust electrode materials is significant for sodium-ion batteries (SIBs). Metallic selenides have been widely investigated as a promising anode material based on their relatively high theoretical capacity. However, rapid capacity fading and huge volume changes greatly hinder their practical application. Herein, for the first time, uniform yolk-shell Fe7Se8@C/N nanoboxes (Fe7Se8@C/N NBs) with the Fe7Se8 cores completely embedded by a thin and robust carbon shell are prepared using a strategy of facile etching method combined with selenization for advanced anode materials for SIBs. Benefiting from the unique structural merits, the Fe7Se8@C/N NBs electrodes for Na-ion half cells exhibit high Na-ion storage capacity (385.5 mAh g−1 at 0.1 A g−1) and superior rate performance (316.0 mAh g−1 at 5 A g−1) as well as impressive cyclability with no capacity decay over 1000 cycles. The sodium storage mechanism of Fe7Se8@C/N NBs electrode is systematically studied with the aid of ex-situ X-ray diffraction and transmission electron microscopy. Finally, the assembled full cells coupled with the lab-made high-voltage Na3V2(PO4)2O2F cathode and Fe7Se8@C/N NBs anode materials show superior energy-storage performance.