Heteroatom Doping at Polyanionic Group Sites: Anion Confinement for High‐Performance Sodium‐Ion Battery Cathodes

ABSTRACT Sodium‐ion batteries (SIBs) have emerged as compelling candidates for next‐generation energy storage technologies owing to their abundant raw material reserves, low cost, and intrinsic safety. Among the cathode materials developed for SIBs, polyanion compounds have garnered significant attention due to their high operating potentials, cycling stability, and thermal safety. However, the strong covalent bonding within polyanionic groups and their steric hindrance lead to intrinsically low electronic conductivity and restricted energy density, which have impeded their commercialization. To overcome these bottlenecks, many modification strategies have been investigated, among which heteroatom doping into the polyanionic framework has been demonstrated to be effective. Given the lack of systematic understanding of heteroatom doping in polyanionic cathodes, this review provides a comprehensive and critical analysis of key modulation strategies, including site‐selective substitution, charge compensation, and synergistic multi‐element co‐doping. The fundamental mechanisms by which these dopants modulate crystal structure, electronic states, and ion transport kinetics are elucidated, and their intrinsic correlations with enhanced electrochemical performance are established. Finally, the remaining challenges and future research directions for anionic group engineering in polyanionic SIB cathodes are outlined to provide actionable guidance for rational heteroatom doping design and accelerate the development of electrode materials.