Vacancy‐Rich Ternary Iron Phosphoselenide Multicavity Nanorods: A Highly Reversible and Fast Anode for Sodium‐Ion Batteries

Abstract The significance of exploring optimal electrode materials cannot be overstated, particularly in mitigating the critical issues posed by sluggish redox kinetics, significant volume variations, and severe structural collapse resulting from the insertion and extraction of sodium ions. These efforts are crucial for enhancing the longevity and rapid charging capabilities of sodium‐ion batteries (SIBs). Herein, a defect engineering strategy for the in situ encapsulation of single‐phase ternary iron phosphoselenide into porous carbon by robust chemical bonds with the formation of rod‐like multicavity nanohybrids (FePSe₃@C) is presented. The incorporation of Se atom not only modulates the electronic structure of the central metal Fe atom and enhances the intrinsic electrical conductivity, but also generates numerous additional reaction sites and accelerates the reaction kinetics of FePSe₃@C, as corroborated by theoretical calculations and kinetic analysis. Notably, the FePSe₃@C demonstrates an outstanding rate capability of 321.7 mAh g⁻¹ even at 20 A g⁻¹ and long cycling stability over 1000 cycles. The sodium‐ion full cell, pairing the FePSe₃@C anode with the Na₃V₂(PO₄)₃@C cathode, exhibits a remarkable energy density of 202 Wh kg⁻¹, demonstrating its practical applicability. This work provides a controllable defect and morphology engineering strategy to construct advanced materials with fast charge transfer for high‐power/energy SIBs.