Interface engineering of Fe₃Se₄/FeSe heterostructure encapsulated in electrospun carbon nanofibers for fast and robust sodium storage

Looking for high-performance anode materials for the emerging sodium-ion batteries is an important topic for the research community. Even though iron selenides are promising candidates owning to their high theoretical capacities, they suffer from poor cycle life and inferior high-rate performance because of the conversion reaction during cycling and sluggish Na diffusion kinetics. In this work, we construct a Fe₃Se₄/FeSe heterostructure wrapped inside carbon nanofibers. When served as the anode material for sodium-ion batteries, the as-prepared sample presents a high capacity of 417.4 mAh g⁻¹ at 0.5 A g⁻¹ and a superior capacity retention of 89.1% after 1000 cycles at 5 A g⁻¹, outperforming the heterostructure-free counterpart of Fe₃Se₄@NCNF and many other FeSe-based anodes. Density Functional Theory calculation suggests that the Fe₃Se₄/FeSe interface would significantly improve the electronic conductivity, Na⁺ diffusion as well as structural stability of the electrode material.