Approaching the Downsizing Limit of Maricite NaFePO4 toward High-Performance Cathode for Sodium-Ion Batteries

Maricite NaFePO4 nanodots with minimized sizes (approximate to 1.6 nm) uniformly embedded in porous N-doped carbon nanofibers (designated as NaFePO4@C) are first prepared by electrospinning for maximized Na-storage performance. The obtained flexible NaFePO4@C fiber membrane adherent on aluminum foil is directly used as binder-free cathode for sodium-ion batteries, revealing that the ultrasmall nanosize effect as well as a high-potential desodiation process can transform the generally perceived electrochemically inactive maricite NaFePO4 into a highly active amorphous phase; meanwhile, remarkable electrochemical performance in terms of high reversible capacity (145 mA h g(-1) at 0.2 C), high rate capability (61 mA h g(-1) at 50 C), and unprecedentedly high cyclic stability (approximate to 89% capacity retention over 6300 cycles) is achieved. Furthermore, the soft package Na-ion full battery constructed by the NaFePO4@C nanofibers cathode and the pure carbon nanofibers anode displays a promising energy density of 168.1 Wh kg(-1) and a notable capacity retention of 87% after 200 cycles. The distinctive 3D network structure of very fine NaFePO4 nanoparticles homogeneously encapsulated in interconnected porous N-doped carbon nanofibers, can effectively improve the active materials' utilization rate, facilitate the electrons/Na+ ions transport, and strengthen the electrode stability upon prolonged cycling, leading to the fascinating Na-storage performance.