Co‐Manipulation of Ultrafine Nanostructure and Uniform Carbon Layer Activates Maricite‐Structured NaFePO4 as a High‐Performance Cathode for Sodium‐Ion Batteries

Sodium iron phosphate (NaFePO 4 ) has attracted significant attention because of its high theoretical capacity (155 mA h g −1 ), remarkable structural stability, and abundant elemental composition. However, the electrochemical reversibility of maricite NaFePO 4 is generally considered inactive. Herein, a nanoengineering strategy to activate the electrochemical activity of maricite NaFePO 4 is presented. This approach involves the construction of ultrasmall maricite NaFePO 4 nanoparticles encapsulated within an ultrathin carbon layer (denoted as m‐NFP@C), which greatly improves the electrochemical properties of the material. Notably, the optimized m‐NFP@C nanoparticles exhibit an impressive reversible capacity of 101.4 mA h g −1 after 100 cycles at a current density of 20 mA g −1 , demonstrating a remarkable capacity retention of 90.5%. Furthermore, when coupled with the bismuth–carbon microfoam‐like compound (Bi@NC‐MF) anode, the fabricated sodium‐ion full cell exhibits exceptional cycling stability with a capacity retention of 90.6% over 250 cycles. The remarkable electrochemical performance of this material can be attributed to its excellent structural stability, ultrafine nanostructure, and uniform carbon coating, which effectively shorten the Na + diffusion pathways, prevent the aggregation and fragmentation of nanoparticles, and enhance electronic conductivity. This work is anticipated to open up a new route for activating maricite NaFePO 4 and advancing the development of polyanion‐type electrode materials.