Ultrafast and ultrastable FeSe₂embedded in nitrogen-doped carbon nanofibers anode for sodium-ion half/full batteries

Transition metal selenides are considered as promising anode materials for fast-charging sodium-ion batteries due to their high theoretical specific capacity. However, the low intrinsic conductivity, particle aggregation, and large volume expansion problems can severely inhibit the high-rate and long-cycle performance of the electrode. Herein, FeSe₂nanoparticles embedded in nitrogen-doped carbon nanofibers (FeSe₂@NCF) have been synthesized using the electrospinning and selenization process, which can alleviate the volume expansion and particle aggregation during the sodiation/desodiation and improve the electrical conductivity of the electrode. The FeSe₂@NCF electrode delivers the outstanding specific capacity of 222.3 mAh g^-1at a fast current density of 50 A g^-1and 262.1 mAh g^-1at 10 A g^-1with the 87.8% capacity retention after 5000 cycles. Furthermore, the Na-ion full cells assembled with pre-sodiated FeSe₂@NCF as anode and Na₃V₂(PO₄)₃/C as cathode exhibit the reversible specific capacity of 117.6 mAh g^-1at 5 A g^-1with the 84.3% capacity retention after 1000 cycles. This work provides a promising way for the conversion-based metal selenides for the applications as fast-charging sodium-ion battery anode.