Fe7Se8 nanoparticles encapsulated by nitrogen-doped carbon with high sodium storage performance and evolving redox reactions

We demonstrate the availability of Fe7Se8 as anode for sodium-ion batteries (SIBs) for the first time. A Fe7Se8 nanocomposite encapsulated by nitrogen-doped carbon layers (Fe7Se8@NC) has been fabricated via a facile thermal method using Prussian Blue as precursor, and its sodium storage mechanisms and extraordinary activation process during cycling are revealed for comprehensive understanding of its reaction process. It shows that the sodium storage mechanisms of Fe7Se8 can be affected by the activation process, especially in the charge process. As SIB anode material, the Fe7Se8@NC exhibits an outstanding electrochemical performance with a reversible discharge capacity of 367 mAh g(-1) at 500 mA g(-1). Even at 2000 mA g(-1), the capacity can retain 251 mAh g(-1). Moreover, the Fe7Se8@ NC shows excellent cyclability, which maintains the capacity up to 339 mAh g(-1) at 1000 mA g(-1) after 1200 cycles. The results demonstrate that (FeSe8)-Se-7@NC is a promising anode material for SIBs.