Constructing Heterotransition Metal Ligand Field Clusters with a Compact Spatial Structure for Maintaining Unimpeded Sodium-Ion Migration

Revealing the mechanism of Mn doping in polyanionic NaFePO₄ materials advances our fundamental understanding of electrochemical reactions. Herein, we propose the concept of heterotransition metal ligand field clusters (H-TMLFC) as a framework to investigate the structural evolution of transition metal (TM) ligand fields at the microscopic level. The introduced [MnO₆] octahedra exhibit a distinctive half-filled frontier orbital configuration, thereby strengthening σ-bonding interactions and modulating the charge distribution between adjacent [FeO₆] units. The redistribution of charge density around the edge-sharing oxygen atoms in [FeO₆]-[MnO₆] pairs enhances Fe-O covalency and mitigates Fe/Na antisite defects. As a result, H-TMLFC-derived NaFe_0.95Mn_0.05PO₄ achieves an exceptional capacity of 148.9 mAh·g^-1 (96.7% of the theoretical capacity) and exhibits superior long-term cycling stability. This work introduces a novel approach for designing high-performance sodium-ion batteries through TM doping, offering atomic-scale insights into the optimization of polyanionic cathode materials.