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

Maricite NaFePO 4 nanodots with minimized sizes (≈1.6 nm) uniformly embedded in porous N‐doped carbon nanofibers (designated as NaFePO 4 @C) are first prepared by electrospinning for maximized Na‐storage performance. The obtained flexible NaFePO 4 @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 NaFePO 4 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 (≈89% capacity retention over 6300 cycles) is achieved. Furthermore, the soft package Na‐ion full battery constructed by the NaFePO 4 @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 NaFePO 4 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.