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 NaFe0.95Mn0.05PO4 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.